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Chronic social isolation and chronic variable stress during early development induce later elevated ethanol intake in adult C57BL/6J mice
Abstract
Experience with stress situations during early development can have long-lasting effects on stress- and anxiety-related behaviors. Importantly, this can also favor drug self-administration. These studies examined the effects of chronic social isolation and/or variable stress experiences during early development on subsequent voluntary ethanol intake in adult male and female C57BL/6J mice. The experiments were conducted to evaluate the effect of chronic isolation between weaning and adulthood (Experiment 1), chronic isolation during adulthood (Experiment 2), and chronic variable stress (CVS) alone or in combination with chronic social isolation between weaning and adulthood (Experiment 3) on subsequent voluntary ethanol intake. Mice were born in our facility and were separated into two housing conditions: isolate housed (one mouse/cage) or group housed (four mice/cage) according to sex. Separate groups were isolated for 40 days starting either at time of weaning postnatal day 21 (PD 21) (early isolation, Experiments 1 and 3) or at adulthood (PD 60: late isolation, Experiment 2). The effects of housing condition on subsequent ethanol intake were assessed starting at around PD 65 in Experiments 1 and 3 or PD 105 days in Experiment 2. In Experiment 3, starting at PD 32, isolate-housed and group-housed mice were either subjected to CVS or left undisturbed. CVS groups experienced random presentations of mild stressors for 14 days, including exposure to an unfamiliar open field, restraint, physical shaking, and forced swim, among others. All mice were tested for ethanol intake for 14 days using a two-bottle choice (ethanol 15% vol/vol vs. water) for a 2-h limited access procedure. Early social isolation resulted in greater ethanol intake compared with the corresponding group-housed mice (Experiment 1). In contrast, social isolation during adulthood (late isolation) did not increase subsequent ethanol intake compared with the corresponding group-housed mice (Experiment 2). For mice that did not experience CVS, early social isolation resulted in greater ethanol intake compared with group-housed mice (Experiment 3). CVS subsequently resulted in a significant increase in ethanol intake in group-housed mice, but CVS failed to further increase ethanol intake in mice that experienced chronic social isolation early in life (Experiment 3). Overall, female mice consumed more ethanol than males, whether isolated (early or late) or group housed. These results indicate that early but not late social isolation can subsequently influence ethanol consumption in C57BL/6J mice. Thus, the developmental timing of chronic social isolation appears to be an important factor in defining later effects on ethanol self-administration behavior. In addition, experience with CVS early in life results in elevated ethanol intake later in adulthood. Taken together, these results emphasize the important role of early stress experiences that modulate later voluntary ethanol intake during adulthood.
... Post-weaning social isolation has been used to model adolescent stress in rats and mice and to investigate the relationship between adolescent stress and alcohol intake. Social isolation beginning at weaning (PND 21) led to increased drinking in adult mice (Lopez et al., 2011;Lopez and Laber, 2015) and rats (Hall et al., 1998). In contrast, adulthood social isolation for the same length of time did not influence levels of alcohol intake (Lopez et al., 2011). ...
... Social isolation beginning at weaning (PND 21) led to increased drinking in adult mice (Lopez et al., 2011;Lopez and Laber, 2015) and rats (Hall et al., 1998). In contrast, adulthood social isolation for the same length of time did not influence levels of alcohol intake (Lopez et al., 2011). Drinking levels following adolescent social isolation were similar to those following chronic variable stress (Lopez et al., 2011). ...
... In contrast, adulthood social isolation for the same length of time did not influence levels of alcohol intake (Lopez et al., 2011). Drinking levels following adolescent social isolation were similar to those following chronic variable stress (Lopez et al., 2011). Housing in an enriched environment could reduce alcohol drinking levels in mice following adolescent social isolation to drinking levels of grouphoused mice (Lopez and Laber, 2015). ...
Human adolescence is a period of development characterized by wide ranging emotions and behavioral risk taking, including binge drinking ( Konrad et al., 2013 ). These behavioral manifestations of adolescence are complemented by growth in the neuroarchitecture of the brain, including synaptic pruning ( Spear, 2013 ) and increases in overall white matter volume ( Perrin et al., 2008 ). During this period of profound physiological maturation, the adolescent brain has a unique vulnerability to negative perturbations. Alcohol consumption and stress exposure, both of which are heightened during adolescence, can individually and synergistically alter these neurodevelopmental trajectories in positive and negative ways (conferring both resiliency and susceptibility) and influence already changing neurotransmitter systems and circuits. Importantly, the literature is rapidly changing and evolving in our understanding of basal sex differences in the brain, as well as the interaction between biological sex and life experiences. The animal literature provides the distinctive opportunity to explore sex-specific stress- and alcohol- induced changes in neurocircuits on a relatively rapid time scale. In addition, animal models allow for the investigation of individual neurons and signaling molecules otherwise inaccessible in the human brain. Here, we review the human and rodent literature with a focus on cortical development, neurotransmitters, peptides, and steroids, to characterize the field’s current understanding of the interaction between adolescence, biological sex, and exposure to stress and alcohol.
... Beneficial and adverse social experiences during adolescence influence anxiety-like (Weiss et al., 2004;Voikar et al., 2005;Koike et al., 2009;McCool and Chappell, 2009;Makinodan et al., 2012;Chappell et al., 2013;Yorgason et al., 2013;Skelly et al., 2015;Lander et al., 2017) and depressive-like behavior (Koike et al., 2009;Amiri et al., 2015), as well as cognition in adulthood (Koike et al., 2009;Zhang et al., 2016;Cao et al., 2017;Lander et al., 2017;Pais et al., 2019). Social isolation can be particularly disruptive at this time as it alters proper neural development and function (Arain et al., 2013;Butler et al., 2016) and increases risk for alcohol use (Lopez et al., 2011;Sanna et al., 2011). Thus, the age at which an individual is deprived of social interactions is critical for ongoing brain and behavioral development. ...
... Using a variety of voluntary drinking models, adolescent social isolation without a history of adolescent drinking leads to increased drinking in adulthood in 2BC (Chappell et al., 2013;Butler et al., 2014a;Lesscher et al., 2015;Skelly et al., 2015), DID (Sanna et al., 2011), and operant responding models (Deehan et al., 2007;McCool and Chappell, 2009). In the few studies that have directly investigated drinking behavior in single versus group housed rodents, social isolation usually increases ethanol consumption behaviors in rats (Schenk et al., 1990;Wolffgramm, 1990;Chappell et al., 2013;Skelly et al., 2015) and mice (Advani et al., 2007;Lopez et al., 2011;Sanna et al., 2011). These effects appear to be limited to adolescence, as increased ethanol preference does not occur in isolated adult rodents (Schenk et al., 1990;Lopez et al., 2011;Chappell et al., 2013), suggesting that early timing of social isolation is crucial to produce significant changes in the sensitivity to ethanol in adulthood (Tables 1-3). ...
... In the few studies that have directly investigated drinking behavior in single versus group housed rodents, social isolation usually increases ethanol consumption behaviors in rats (Schenk et al., 1990;Wolffgramm, 1990;Chappell et al., 2013;Skelly et al., 2015) and mice (Advani et al., 2007;Lopez et al., 2011;Sanna et al., 2011). These effects appear to be limited to adolescence, as increased ethanol preference does not occur in isolated adult rodents (Schenk et al., 1990;Lopez et al., 2011;Chappell et al., 2013), suggesting that early timing of social isolation is crucial to produce significant changes in the sensitivity to ethanol in adulthood (Tables 1-3). Not all studies have found similar effects of social housing on ethanol drinking. ...
Adolescence is a critical developmental period characterized by enhanced social interactions, ongoing development of the frontal cortex and maturation of synaptic connections throughout the brain. Adolescents spend more time interacting with peers than any other age group and display heightened reward sensitivity, impulsivity and diminished inhibitory self-control, which contribute to increased risky behaviors, including the initiation and progression of alcohol use. Compared to adults, adolescents are less susceptible to the negative effects of ethanol, but are more susceptible to the negative effects of stress, particularly social stress. Juvenile exposure to social isolation or binge ethanol disrupts synaptic connections, dendritic spine morphology, and myelin remodeling in the frontal cortex. These structural effects may underlie the behavioral and cognitive deficits seen later in life, including social and memory deficits, increased anxiety-like behavior and risk for alcohol use disorders (AUD). Although the alcohol and social stress fields are actively investigating the mechanisms through which these effects occur, significant gaps in our understanding exist, particularly in the intersection of the two fields. This review will highlight the areas of convergence and divergence in the fields of adolescent social stress and ethanol exposure. We will focus on how ethanol exposure or social isolation stress can impact the development of the frontal cortex and lead to lasting behavioral changes in adulthood. We call attention to the need for more mechanistic studies and the inclusion of the evaluation of sex differences in these molecular, structural, and behavioral responses.
... Of note, in this and other cited studies, animals are single housed for varying periods of time prior to and during the drinking sessions. Single housing in adolescence can be particularly detrimental to proper neurodevelopment and function (Arain et al., 2013;Butler, Karkhanis, Jones, & Weiner, 2016) and increases risk for alcohol use and abuse (Lopez, Doremus-Fitzwater, & Becker, 2011;Sanna et al., 2011). Adolescents are particularly vulnerable to social isolation stress as compared to adults and thus single housing is frequently used to model post-traumatic stress (Gilpin & Weiner, 2017;Skelly, Chappell, Carter, & Weiner, 2015), depression, and anxiety (Amiri et al., 2015;Koike et al., 2009). ...
... In the few studies that have directly investigated drinking behavior in single-vs. group-housed rodents, social isolation usually increases ethanol consumption in rats (Chappell, Carter, McCool, & Weiner, 2013;Schenk, Gorman, & Amit, 1990;Skelly et al., 2015;Wolffgramm, 1990) and mice (Advani, Hensler, & Koek, 2007;Lopez et al., 2011;Sanna et al., 2011). These effects appear to be limited to adolescents, as increased ethanol preference does not usually occur in isolated adult rodents (Chappell et al., 2013;Lopez et al., 2011;Schenk et al., 1990), suggesting that early exposure to social isolation may interact with developmental processes and contribute to ethanol sensitivity later in adult life. ...
... group-housed rodents, social isolation usually increases ethanol consumption in rats (Chappell, Carter, McCool, & Weiner, 2013;Schenk, Gorman, & Amit, 1990;Skelly et al., 2015;Wolffgramm, 1990) and mice (Advani, Hensler, & Koek, 2007;Lopez et al., 2011;Sanna et al., 2011). These effects appear to be limited to adolescents, as increased ethanol preference does not usually occur in isolated adult rodents (Chappell et al., 2013;Lopez et al., 2011;Schenk et al., 1990), suggesting that early exposure to social isolation may interact with developmental processes and contribute to ethanol sensitivity later in adult life. The social behavior circuits may be uniquely altered by ethanol's actions in adolescence; however, this is not addressed in the current study. ...
Alcohol is the most widely used and abused drug among youth in the United States. Teens aged 12-20 years old drink almost 11% of all alcohol consumed in the United States and typically these teens are consuming alcohol in the form of binge drinking. Particularly concerning is that the risk of developing an alcohol use disorder over their lifetime increases the younger one begins to drink. Here we investigated the impact of ethanol drinking in early adolescence on adult ethanol intake using C57BL/6J and DBA/2J mice. We modeled low-dose binge drinking in adolescent mice using a modified Drinking in the Dark (DID) model where the total ethanol intake during adolescence was similar between the strains to specifically ask if low-dose ethanol exposure in the high-alcohol preferring C57BL/6J strain will also lead to increased ethanol intake in adulthood. Our results show that low-dose ethanol drinking in early adolescence dramatically increases adult intake, but only in the alcohol-preferring C57BL/6J strain. Early adolescent ethanol exposure had no effect on ethanol intake in the alcohol-non-preferring DBA/2J mice. These data add to the growing evidence that low-dose ethanol exposures, below the pharmacologically relevant dose, can also contribute to increased drinking in adulthood, but the effect may be influenced by genetic background.
... Like humans, adolescent mice demonstrate a potentiated response to stress (Romeo et al., 2006). Although there are some reports that chronic isolation beginning in adolescence increases depressiveand anxiety-like behaviors and drug self-administration in mice (Lopez et al., 2011;Amiri et al., 2015), these results are variable and may be strain and sex-dependent (Arakawa, 2018;Mumtaz et al., 2018;Walker et al., 2019). C57BL/6J mice are commonly used in studies of alcohol self-administration (Rhodes et al., 2005;Melendez et al., 2006;Lyons et al., 2008;Yoneyama et al., 2008;Hwa et al., 2011;Mulligan et al., 2011) and as such are regularly singly housed for long periods. ...
... C57BL/6J mice are commonly used in studies of alcohol self-administration (Rhodes et al., 2005;Melendez et al., 2006;Lyons et al., 2008;Yoneyama et al., 2008;Hwa et al., 2011;Mulligan et al., 2011) and as such are regularly singly housed for long periods. However, the lasting behavioral effects of social isolation (either in adolescence or adulthood) on escalated alcohol self-administration and anxiety-like behaviors in this strain have been variable (Lopez et al., 2011;Lopez and Laber, 2015;Huang et al., 2017;Caruso et al., 2018). ...
... Adolescent isolation has been demonstrated to increase alcohol self-administration in male rats and both male and female mice (Lopez et al., 2011;Butler et al., 2014bButler et al., , 2016Lopez and Laber, 2015;Skelly et al., 2015). Here, we evaluated adolescent social isolation on binge alcohol drinking using a modified DID paradigm and found no effects on 20%, 30%, and quinine-adulterated 20% ethanol consumption or preference, nor on a rewarding 1% sucrose solution, in either sex (Figure 3). ...
Chronic stress during the developmental period of adolescence increases susceptibility to many neuropsychiatric diseases in adulthood, including anxiety, affective, and alcohol/substance use disorders. Preclinical rodent models of adolescent stress have produced varying results that are species, strain, sex, and laboratory-dependent. However, adolescent social isolation is a potent stressor in humans that has been reliably modeled in male rats, increasing adult anxiety-like and alcohol drinking behaviors, among others. In this study, we examined the generalizability and sex-dependence of this model in C57BL/6J mice, the most commonly used rodent strain in neuroscience research. We also performed a parallel study using social isolation in adulthood to understand the impact of adult social isolation on basal behavioral phenotypes. We found that 6 weeks of social isolation with minimal handling in adolescence through early adulthood [postnatal day (PD) 28–70] produced a hypersocial phenotype in both male and female mice and an anxiolytic phenotype in the elevated plus-maze in female mice. However, it had no effects in other assays for avoidance behavior or on fear conditioning, alcohol drinking, reward or aversion sensitivity, or novel object exploration in either sex. In contrast, 6 weeks of social isolation in adulthood beginning at PD77 produced an anxiogenic phenotype in the light/dark box but had no effects on any other assays. Altogether, our results suggest that: (1) adolescence is a critical period for social stress in C57BL/6J mice, producing aberrant social behavior in a sex-independent manner; and (2) chronic individual housing in adulthood does not alter basal behavioral phenotypes that may confound interpretation of behavior following other laboratory manipulations.
... Housing in isolation post weaning in male rats causes increased drinking compared to pair housed (Hall et al., 1998) or group housed rats (Schenk et al., 1990;McCool and Chappell, 2009) when provided a choice between water and ethanol. In a two-bottle choice paradigm, female rats enriched post weaning also drink less compared to group housed rats (de Carvalho et al., 2010) and female mice group housed from weaning also drink less ethanol compared to isolated (Lopez et al., 2011). Thus, environmental enrichment produces a resilient phenotype in both male and female mice and rats to ethanol regardless of ethanol exposure paradigm, while isolation housing produces a susceptible phenotype for ethanol. ...
... Lopez et al. also found that male and female mice reared in isolation from weaning drank significantly more ethanol in a two bottle choice paradigm compared to group housed mice but male mice isolated in adulthood did not show increased ethanol intake (2011). Additionally, female mice overall consumed more ethanol compared to males and female mice isolated in adulthood rather than immediately post weaning, showed a small but statistically significant decrease in ethanol intake (Lopez et al., 2011). Environmental enrichment in adult female mice during abstinence from ethanol drinking is able to reduce depressive-like behavior compared to isolated animals (Pang et al., 2013). ...
... These results also suggest that the adolescent period may be particularly sensitive to alcohol exposure compared to other drugs of abuse, since environmental enrichment in adulthood can reduce drug taking and seeking behaviors for many other drugs of abuse, but not alcohol (Schenk et al., 1990;Solinas et al., 2008;Thiel et al., 2010;Lopez et al., 2011;Ranaldi et al., 2011;Chauvet et al., 2012;Sikora et al., 2018). Additionally, environmental enrichment during adolescence increases dendritic arborization (Renner and Rosenzweig, 1987) and increases survival of hippocampal progenitor cells, but fetal alcohol exposure completely blocks this increased survival of progenitor cells in male and female mice (Choi et al., 2005). ...
... At a behavioral level, social isolation has been seen to promote anxiety-and depression-like symptoms in rodents (Amiri et al., 2015;Beery and Kaufer, 2015;Lukkes et al., 2009;Lupien et al., 2009). Additionally, previous research has shown that isolation, particularly during early development, can foster increases in EtOH consumption and preference in mice and rats (Advani et al., 2007;Ju arez and V azquez-Cort es, 2003;L opez et al, 2011;Sanna et al., 2011). Less is known, however, about the impact of social isolation in later stages of development and/or whether it can affect EtOH intake using DID procedures. ...
... CRF-1 KO mice also showed reductions in EtOH intake at 20% but not 10% EtOH (Pastor et al., 2011). Prior evidence also indicates that age and sex critically modulate the effects of stress, including isolation-induced stress, on EtOH drinking (Advani et al., 2007;Caruso et al., 2018;L opez et al., 2011). In adolescent rats, isolation has been shown to induced increases in EtOH intake in males, but not females (Butler et al., 2014;McCool and Chappell, 2009). ...
... In adolescent rats, isolation has been shown to induced increases in EtOH intake in males, but not females (Butler et al., 2014;McCool and Chappell, 2009). In mice, whereas postweaning isolation produced increases in EtOH intake in male and female B6 (Advani et al., 2007;L opez et al., 2011), isolation during adulthood has been found to induce sex-dependent effects. L opez and colleagues (2011) found that~7 weeks of isolation in B6 only affected females with a slight, but significant decrease in EtOH consumption compared to social females. ...
Background:
Binge alcohol drinking has been characterized as a key feature of alcoholism. The Drinking-in-the-Dark (DID) preclinical model, a procedure that promotes high levels of ethanol (EtOH) intake in short periods of time, has been extensively used to investigate neuropharmacological and genetic determinants of binge-like EtOH consumption. Using DID methodology, alcohol-preferring strains of mice such as C57BL/6J (B6) mice consume enough EtOH to achieve blood concentrations (≥ 1.0 mg/ml) associated with behavioral intoxication (i.e., motor incoordination). DID procedures typically involve the use of socially isolated animals (single-housed prior to and during the experiment). Previous research indicates that stress associated with social isolation can induce anxiety-like behavior and promote increases in EtOH intake. The present study investigates the role of housing conditions in anxiety-like behavior and binge-like EtOH intake using a DID procedure.
Methods:
Male and female B6 mice were isolated or pair-housed for a period of 6 weeks prior to evaluation of anxiety-like (elevated plus maze, light and dark box, open field) and drinking (water, 10% sucrose, 10-30% EtOH) behavior. In order to measure intake, a variation of the standard DID procedure using a removable, transparent and perforated plastic barrier strip (designed to temporarily divide the cage in two) was introduced. This allowed for individual intake records (2-h test) of isolated and socially-housed animals.
Results:
Increased anxiety-like behavior and reduced sucrose consumption were found in isolated mice. The effects of housing conditions on EtOH intake were sex- and concentration-dependent. In male mice, isolation increased 20% and 30% EtOH intake. In females, however, an increased intake of EtOH (30%) was found in socialized animals. No effects of housing or sex were found at EtOH 10%.
Conclusions:
Together with previous literature, the present study suggests that social isolation can promote anxiety-associated behavior and produce sex-dependent changes in binge-like EtOH consumption.
... Additionally, early life stress has been shown to increase later ethanol intake (Butler, Karkhanis, Jones, & Weiner, 2016;Lopez, Doremus-Fitzwater, & Becker, 2011). ...
... Herein, we employ chronic variable stress (CVS), a non-habituating chronic stress paradigm (Herman, 2013), to examine the long-term effects of adolescent stress on adult changes in VTA neurophysiology and the associated ethanol self-administration. We selected chronic variable and unpredictable stress exposure because it models chronic stress in rats, where it has been shown to modulate the response to drugs of abuse, including alcohol (Lopez et al., 2011). We sought to examine long-term stress-induced changes in behavior and neurophysiology isolated from the proximal effects of stress, such as immediate fear and behavioral freezing. ...
... Adolescence demarks a period of critical neural development, during which the individuals are at increased vulnerability to long-term consequences of stress (Spear, 2000). Our finding, that adolescent, but not adult, stress resulted in a long-term increase in ethanol self-administration is in agreement with prior work examining the effects of adolescent social isolation stress (Butler et al., 2016;Lopez et al., 2011;Schenk, Gorman, & Amit, 1990;Skelly, Chappell, Carter, & Weiner, 2015). Similarly, age-dependent stress effects have been observed in neurobiological and stress function (Cotella et al., 2019;Yorgason, Espana, Konstantopoulos, Weiner, & Jones, 2013). ...
Alcohol use disorders (AUDs) continue to be a significant public health problem. Early life stress and adversity have long-lasting effects on a wide range of behaviors, including responses to drugs of abuse. Epidemiological evidence indicates that exposure to early life stress contributes to alcohol use disorders and, while it is known that stress and alcohol both act on overlapping mesolimbic circuitry, the cellular mechanisms underlying the relationship between stress and alcohol intake are not well understood. Previous work has demonstrated that acute stress increases ethanol intake mediated by changes in GABA signaling within the ventral tegmental area (VTA). Here we investigated if adolescent stress exposure might elicit long-term, persistent increases in ethanol self-administration associated with altered VTA GABA signaling. To this end, we exposed adolescent postnatal day (PND) 28 male rats to 14 days of chronic variable stress (CVS) and then examined operant ethanol self-administration begun at least 30 days later. We found that adolescent stress exposure resulted in significantly increased ethanol self-administration in adulthood. In contrast, adult (PND 82) male rats exposed to the same CVS protocol did not display increased ethanol self-administration that was begun 30 days later. Furthermore, we found that adolescent stress exposure resulted in enhancement of ethanol-induced GABA signaling onto VTA dopamine neurons and impairments in VTA GABA chloride homeostasis. The results indicate that adolescence is a period vulnerable to stress, which produces long-term changes in VTA GABA signaling associated with increased ethanol self-administration behavior.
... No que se refere ao consumo prejudicial de álcool, alguns estudos experimentais (FERRIS, 2003;SACHARCZUK et al., 2008;LOPEZ et al., 2011;DELIS et al., 2013;PATTERSON-BUCKENDAHL et al., 2014) revelam que fatores ambientais influenciam, em grande medida, seu consumo e o consequente desenvolvimento de um uso nocivo à saúde, bem como, a dependência química. ...
... Dois estudos experimentais (LOPEZ et al., 2011;FERRIS, 2003) verificaram os efeitos do estresse no consumo de álcool, a longo prazo. Tais trabalhos atribuíram à experiência de situações estressantes durante o desenvolvimento infantil os comportamentos de estresse e ansiedade na vida adulta e que, por sua vez, podem ter favorecido o consumo de substâncias psicoativas. ...
... Cabe ressaltar, bem como trazem as pesquisas (LOPEZ et al., 2011;FERRIS, 2003) que diversos fatores estão envolvidos na dependência de álcool: início do consumo, frequência, quantidade consumida e resposta ao álcool e que, portanto, ainda não é claro se os fatores genéticos ocupam maior importância no início do consumo de álcool. Até o momento entende-se que os fatores ambientais explicam ...
... No que se refere ao consumo prejudicial de álcool, alguns estudos experimentais (FERRIS, 2003;SACHARCZUK et al., 2008;LOPEZ et al., 2011;DELIS et al., 2013;PATTERSON-BUCKENDAHL et al., 2014) revelam que fatores ambientais influenciam, em grande medida, seu consumo e o consequente desenvolvimento de um uso nocivo à saúde, bem como, a dependência química. ...
... Dois estudos experimentais (LOPEZ et al., 2011;FERRIS, 2003) verificaram os efeitos do estresse no consumo de álcool, a longo prazo. Tais trabalhos atribuíram à experiência de situações estressantes durante o desenvolvimento infantil os comportamentos de estresse e ansiedade na vida adulta e que, por sua vez, podem ter favorecido o consumo de substâncias psicoativas. ...
... Cabe ressaltar, bem como trazem as pesquisas (LOPEZ et al., 2011;FERRIS, 2003) que diversos fatores estão envolvidos na dependência de álcool: início do consumo, frequência, quantidade consumida e resposta ao álcool e que, portanto, ainda não é claro se os fatores genéticos ocupam maior importância no início do consumo de álcool. Até o momento entende-se que os fatores ambientais explicam ...
... No que se refere ao consumo prejudicial de álcool, alguns estudos experimentais (FERRIS, 2003;SACHARCZUK et al., 2008;LOPEZ et al., 2011;DELIS et al., 2013;PATTERSON-BUCKENDAHL et al., 2014) revelam que fatores ambientais influenciam, em grande medida, seu consumo e o consequente desenvolvimento de um uso nocivo à saúde, bem como, a dependência química. ...
... Dois estudos experimentais (LOPEZ et al., 2011;FERRIS, 2003) verificaram os efeitos do estresse no consumo de álcool, a longo prazo. Tais trabalhos atribuíram à experiência de situações estressantes durante o desenvolvimento infantil os comportamentos de estresse e ansiedade na vida adulta e que, por sua vez, podem ter favorecido o consumo de substâncias psicoativas. ...
... Cabe ressaltar, bem como trazem as pesquisas (LOPEZ et al., 2011;FERRIS, 2003) que diversos fatores estão envolvidos na dependência de álcool: início do consumo, frequência, quantidade consumida e resposta ao álcool e que, portanto, ainda não é claro se os fatores genéticos ocupam maior importância no início do consumo de álcool. Até o momento entende-se que os fatores ambientais explicam ...
... No que se refere ao consumo prejudicial de álcool, alguns estudos experimentais (FERRIS, 2003;SACHARCZUK et al., 2008;LOPEZ et al., 2011;DELIS et al., 2013;PATTERSON-BUCKENDAHL et al., 2014) revelam que fatores ambientais influenciam, em grande medida, seu consumo e o consequente desenvolvimento de um uso nocivo à saúde, bem como, a dependência química. ...
... Dois estudos experimentais (LOPEZ et al., 2011;FERRIS, 2003) verificaram os efeitos do estresse no consumo de álcool, a longo prazo. Tais trabalhos atribuíram à experiência de situações estressantes durante o desenvolvimento infantil os comportamentos de estresse e ansiedade na vida adulta e que, por sua vez, podem ter favorecido o consumo de substâncias psicoativas. ...
... Cabe ressaltar, bem como trazem as pesquisas (LOPEZ et al., 2011;FERRIS, 2003) que diversos fatores estão envolvidos na dependência de álcool: início do consumo, frequência, quantidade consumida e resposta ao álcool e que, portanto, ainda não é claro se os fatores genéticos ocupam maior importância no início do consumo de álcool. Até o momento entende-se que os fatores ambientais explicam ...
... For example, social isolation or binge ethanol can reduce myelin content in the frontal cortex (De Bellis et al., 2005;Medina et al., 2008;Makinodan et al., 2012;Vargas et al., 2014;Montesinos et al., 2015;Vetreno et al., 2016;Wolstenholme et al., 2017;Pfefferbaum et al., 2018;Hinton et al., 2019;Tavares et al., 2019;El Marroun et al., 2021), disrupt dopamine signaling in the nucleus accumbens (NAc) (Yorgason et al., 2013(Yorgason et al., , 2016Karkhanis et al., 2014;Zhang et al., 2021) and prefrontal cortex (PFC) (Trantham-Davidson et al., 2014, and disrupt proper functioning of the hypothalamic-pituitary-adrenal (HPA) axis (Butler et al., 2014;Varlinskaya et al., 2015Varlinskaya et al., , 2017Hinton et al., 2019). Behaviorally, these early life experiences can lead to memory deficits (Bianchi et al., 2006;Pascual et al., 2007;Koike et al., 2009;McLean et al., 2010;Vargas et al., 2014;Montesinos et al., 2015;Vetreno and Crews, 2015;Vetreno et al., 2016;Marco et al., 2017;Wolstenholme et al., 2017;Pais et al., 2019;Pascual et al., 2021;Bent et al., 2022), changes in social behavior Spear, 2002, 2004;Kercmar et al., 2011;Makinodan et al., 2012;Varlinskaya et al., 2014;Lander et al., 2017;Varlinskaya et al., 2017;Medendorp et al., 2018;Liu et al., 2019;Rivera-Irizarry et al., 2020;Zhang et al., 2021), anxiety-like behavior (Weiss et al., 2004;Võikar et al., 2005;Koike et al., 2009;McCool and Chappell, 2009;Chappell et al., 2013;Yorgason et al., 2013;Gass et al., 2014;Karkhanis et al., 2014;Lopez and Laber, 2015;Pandey et al., 2015;Skelly et al., 2015;Montesinos et al., 2016;Sakharkar et al., 2016;Vetreno et al., 2016;Lander et al., 2017;Lee et al., 2017Lee et al., , 2018Szumlinski et al., 2019;Rivera-Irizarry et al., 2020), and increased drinking in adulthood (Deehan et al., 2007;McCool and Chappell, 2009;Moore et al., 2010;Strong et al., 2010;Lopez et al., 2011;Metten et al., 2011;Sanna et al., 2011;Chappell et al., 2013;Butler et al., 2014;Lesscher et al., 2015Lesscher et al., , 2021Skelly et al., 2015;Montesinos et al., 2016;Carrara-Nascimento PF et al., 2017;Lee et al., 2017;Younis et al., 2019;Wolstenholme et al., 2020). ...
... Drinking in proximity to another mouse, but not in the same physical space, did not affect ethanol intake in males or females. Social isolation tends to lead to increased ethanol intake in adolescent rats (Schenk et al., 1990;Wolffgramm, 1990;Chappell et al., 2013;Skelly et al., 2015) and mice (Advani et al., 2007;Lopez et al., 2011;Sanna et al., 2011) as compared to group housing. A few studies have used a semi-permeable partition cages in adult rats and mice (Wolffgramm, 1990;Tomie et al., 2015), but ethanol intake did not always differ between group housed and single housed rodents (Palm and Nylander, 2014). ...
Introduction
Adolescence is a critical period in cognitive and emotional development, characterized by high levels of social interaction and increases in risk-taking behavior including binge drinking. Adolescent exposure to social stress and binge ethanol have individually been associated with the development of social, emotional, and cognitive deficits, as well as increased risk for alcohol use disorder. Disruption of cortical development by early life social stress and/or binge drinking may partly underlie these enduring emotional, cognitive, and behavioral effects. The study goal is to implement a novel neighbor housing environment to identify the effects of adolescent neighbor housing and/or binge ethanol drinking on (1) a battery of emotional and cognitive tasks (2) adult ethanol drinking behavior, and (3) the nucleus accumbens and prefrontal cortex transcriptome.
Methods
Adolescent male and female C57BL/6J mice were single or neighbor housed with or without access to intermittent ethanol. One cohort underwent behavioral testing during adulthood to determine social preference, expression of anxiety-like behavior, cognitive performance, and patterns of ethanol intake. The second cohort was sacrificed in late adolescence and brain tissue was used for transcriptomics analysis.
Results
As adults, single housed mice displayed decreased social interaction, deficits in the novel object recognition task, and increased anxiety-like behavior, relative to neighbor-housed mice. There was no effect of housing condition on adolescent or adult ethanol consumption. Adolescent ethanol exposure did not alter adult ethanol intake. Transcriptomics analysis revealed that adolescent housing condition and ethanol exposure resulted in differential expression of genes related to synaptic plasticity in the nucleus accumbens and genes related to methylation, the extracellular matrix and inflammation in the prefrontal cortex.
Discussion
The behavioral results indicate that social interaction during adolescence via the neighbor housing model may protect against emotional, social, and cognitive deficits. In addition, the transcriptomics results suggest that these behavioral alterations may be mediated in part by dysregulation of transcription in the frontal cortex or the nucleus accumbens.
... Progressive Ratio Testing: Following FR4 testing, mice were tested in an exponential progressive ratio test, (single 45 min session) where the number of lever presses required to earn a single ethanol reward exponentially increased over the session according to the formula (rounded to the nearest integer) = [5e (R*0.2) ]-5, where R is equal to the number of rewards already earned plus 1 (i.e., next reinforcer). Thus, the number of responses required to earn a single reward followed the order 1, 2, 4, 6,9,12,15,20,25,32,40, 50, 62…and so on. The total number of rewards each animal was willing to work for under this schedule was recorded as the "break point. ...
... Finally, and perhaps most importantly, mice were singly housed for the entirety of the home cage binge study while they remained group housed for the present operant self-administration studies. Social isolation is well known to have effects on mood, affect, motivation, and alcohol drinking behavior [14,25,26], and thus the stress of this housing condition could have influenced the manner in which BNST 5HT2c knockdown affected alcohol consumption in Drinking in the Dark, particularly with regard to its initially aversive qualities. Overall, these results suggest that BNST 5HT2c does not mediate alcohol consumption behavior in males, but in part mediates aversive responses to alcohol in females only when the alcohol is made sufficiently aversive. ...
The serotonin 5HT 2c receptor has been widely implicated in the pathophysiology of alcohol use disorder (AUD), particularly alcohol seeking and the affective consequences of chronic alcohol consumption. However, little is known about the brain sites in which 5HT 2c exerts its effects on specific alcohol-related behaviors, especially in females. Here, we investigated the effects of site-specific manipulation of the 5HT 2c receptor system in the BNST on operant alcohol self-administration behaviors in adult mice of both sexes, including the acquisition and maintenance of fixed-ratio responding, motivation for alcohol (progressive ratio), and quinine-adulterated responding for alcohol on a fixed-ratio schedule (punished alcohol seeking). Knockdown of 5HT 2c in the BNST did not affect the acquisition or maintenance of operant alcohol self-administration, nor did it affect progressive ratio responding for alcohol. This manipulation had only a subtle effect on responding for quinine alcohol selectively in females. On the other hand, chemogenetic inhibition of BNST 5HT 2c -containing neurons (BNST 5HT2c ) increased operant alcohol self-administration behavior in both sexes on day 2, but not day 9, of testing. It also increased operant responding for 1000 μM quinine-adulterated alcohol selectively in males. Importantly, chemogenetic inhibition of BNST 5HT2c did not alter operant sucrose responding or motivation for sucrose in either sex. We then performed cell-type specific anterograde tracing, which revealed that BNST 5HT2c project to similar regions in males and females, many of which have been previously implicated in AUD. We next used chemogenetics and quantification of the immediate early gene cFos to characterize the functional influence of BNST 5HT2c inhibition on vlPAG activity. We show that chemogenetic inhibition of BNST5HT2c reduces vlPAG cFos in both sexes, but that this reduction is more robust in males. Together these findings suggest that BNST 5HT2c neurons, and to a small extent the BNST 5HT 2c receptor, serve to promote aversive responses to alcohol consumption, potentially through sex-dependent disinhibition of vlPAG neurons.
... The Chronic variable stress (CVS) model used was a modified version of chronic variable stress procedure used in previous experiments [10]. Different stressors with different duration were applied one by one every day. ...
The corticotropin-releasing factor neuropeptides (CRH and UCN-1,2,3), as well as spexin, contribute to the control of energy balance and
limit food intake in mammals. However, the role of these neuropeptides in chronic variable stress remains unknown. The effect of chronic
varied stress on circulating corticosterone levels and urocortin expression levels in the brains of experimental rats was studied in this study.
Rats were subjected with 28 days long term stress protocol, end of stress protocol experimental and control animal organs isolated, brain
urocorcortin-1,2,3 expression by RT-PCR and serum corticosterone by ELISA method. UCN levels in the brain were altered in rats subjected
to prolonged varied stress. Furthermore, corticosterone levels were elevated as a result of the same urocortin expression pattern, indicating
that urocortin expression is controlled by glucocorticoids via a glucocorticoid-responsive element (GRE). Thus, data shows that
hypothalamus-pituitary-adrenal (HPA) axis, also known as the LHPA axis, and limbic system are both stimulated by stress, which is
reflected in the form of elevated corticosterone levels, according to the genes UCN1, 2, and 3.
... The Chronic variable stress (CVS) model used was a modified version of chronic variable stress procedure used in previous experiments [10]. Different stressors with different duration were applied one by one every day. ...
The corticotropin-releasing factor neuropeptides (CRH and UCN-1,2,3), as well as spexin, contribute to the control of energy balance and
limit food intake in mammals. However, the role of these neuropeptides in chronic variable stress remains unknown. The effect of chronic
varied stress on circulating corticosterone levels and urocortin expression levels in the brains of experimental rats was studied in this study.
Rats were subjected with 28 days long term stress protocol, end of stress protocol experimental and control animal organs isolated, brain
urocorcortin-1,2,3 expression by RT-PCR and serum corticosterone by ELISA method. UCN levels in the brain were altered in rats subjected
to prolonged varied stress. Furthermore, corticosterone levels were elevated as a result of the same urocortin expression pattern, indicating
that urocortin expression is controlled by glucocorticoids via a glucocorticoid-responsive element (GRE). Thus, data shows that
hypothalamus-pituitary-adrenal (HPA) axis, also known as the LHPA axis, and limbic system are both stimulated by stress, which is
reflected in the form of elevated corticosterone levels, according to the genes UCN1, 2, and 3.
... The Chronic variable stress (CVS) model used was a modified version of chronic variable stress procedure used in previous experiments [10]. Different stressors with different duration were applied one by one every day. ...
The corticotropin-releasing factor neuropeptides (CRH and UCN-1,2,3), as well as spexin, contribute to the control of energy balance and limit food intake in mammals. However, the role of these neuropeptides in chronic variable stress remains unknown. The effect of chronic varied stress on circulating corticosterone levels and urocortin expression levels in the brains of experimental rats was studied in this study. Rats were subjected with 28 days long term stress protocol, end of stress protocol experimental and control animal organs isolated, brain urocorcortin-1,2,3 expression by RT-PCR and serum corticosterone by ELISA method. UCN levels in the brain were altered in rats subjected to prolonged varied stress. Furthermore, corticosterone levels were elevated as a result of the same urocortin expression pattern, indicating that urocortin expression is controlled by glucocorticoids via a glucocorticoid-responsive element (GRE). Thus, data shows that hypothalamus-pituitary-adrenal (HPA) axis, also known as the LHPA axis, and limbic system are both stimulated by stress, which is reflected in the form of elevated corticosterone levels, according to the genes UCN1, 2, and 3.
... Within the last 15 years there has been a shift to social housing with enrichment as the standard to improve the welfare of rodents [48,49], but in many of these older studies rats were singly housed. Further, rats are often single-housed during 2BC in order to precisely measure intake, although single housing can increase corticosterone levels [50] and increase rates of alcohol drinking and drug self-administration [51][52][53][54][55][56][57]. Environmental enrichment (EE) in the home cage of single-housed rodents allows them to experience a range of natural behaviors while removing enrichment and/or housing the rats in isolation conditions can increase the incidence of stereotypic and perseverative behaviors [58], as well as impair normal brain development and function (reviewed in [59][60][61]). ...
During adolescence, the brain is highly susceptible to alcohol-induced damage and subsequent neuroimmune responses, effects which may enhance development of an alcohol use disorder (AUD). Neuroimmune reactions are implicated in adolescent alcohol exposure escalating adulthood drinking. Therefore, we investigated whether intermittent alcohol exposure in male, adolescent rats (AIE) escalated adult drinking via two-bottle choice (2BC). We also examined the influence of housing environment across three groups: standard (group-housed with enrichment during 2BC), impoverished (group-housed without enrichment during 2BC), or isolation (single-housed without bedding or enrichment throughout). In the standard group immediately after AIE/saline and after 2BC, we also examined the expression of microglial marker, Iba1, reactive astrocyte marker, vimentin, and neuronal cell death dye, FluoroJade B (FJB). We did not observe an escalation of adulthood drinking following AIE, regardless of housing condition. Further, only a modest neuroimmune response occurred after AIE in the standard group: no significant microglial reactivity or neuronal cell death was apparent using this model, although some astrocyte reactivity was detected in adolescence following AIE that resolved by adulthood. These data suggest that the lack of neuroimmune response in adolescence in this model may underlie the lack of escalation of alcohol drinking, which could not be modified through isolation stress.
... Evidence shows that stress induced by social isolation can trigger somatic responses typical of chronic stress, such as destabilization of the hypothalamic-pituitary-adrenal axis (Serra et al. 2005; Ros-Simó and Valverde 2012), causing hyper-reactivity to new stressors (Chida et al. 2005(Chida et al. , 2007Lopez et al. 2011). Changes in weight, which have been linked to chronic stress (Rygula et al. 2005;Torres and Nowson 2007), have been proposed as a qualitative stress marker. ...
Chronic social stress is a significant risk factor for several neuropsychiatric disorders, mainly major depressive disorder (MDD). In this way, patients with clinical depression may display many symptoms, including disrupted social behavior and anxiety. However, like many other psychiatric diseases, MDD has a very complex etiology and pathophysiology. Because social isolation is one of the multiple depression-inducing factors in humans, this study aims to understand better the link between social stress and MDD using an animal model based on social isolation after weaning, which is known to produce social stress in mice. We focused on cellular composition and white matter integrity to establish possible links with the abnormal social behavior that rodents isolated after weaning displayed in the three-chamber social approach and recognition tests. We used the isotropic fractionator method to assess brain cellularity, which allows us to robustly estimate the number of oligodendrocytes and neurons in dissected brain regions. In addition, diffusion tensor imaging (DTI) was employed to analyze white matter microstructure. Results have shown that post-weaning social isolation impairs social recognition and reduces the number of neurons and oligodendrocytes in important brain regions involved in social behavior, such as the anterior neocortex and the olfactory bulb. Despite the limitations of animal models of psychological traits, evidence suggests that behavioral impairments observed in patients might have similar biological underpinnings.
... In Drosophila, social isolation has been found to decrease synapse number in PDF neurons and reduce alcohol sensitivity [67,68]. Studies using rodent models have shown that social isolation increases alcohol preferences [141][142][143][144]. Therefore, we used a group-housed sleep deprivation method that significantly increased homeostatic sleep pressures in both male and females, as seen by increased sleep in the 36 h following the period of sleep deprivation. ...
Alcohol abuse is a significant public health problem. While considerable research has shown that alcohol use affects sleep, little is known about the role of sleep deprivation in alcohol toxicity. We investigated sleep as a factor modulating alcohol toxicity using Drosophila melanogaster, a model for studies of sleep, alcohol, and aging. Following 24 h of sleep deprivation using a paradigm that similarly affects males and females and induces rebound sleep, flies were given binge-like alcohol exposures. Sleep deprivation increased mortality, with no sex-dependent differences. Sleep deprivation also abolished functional tolerance measured at 24 h after the initial alcohol exposure, although there was no effect on alcohol absorbance or clearance. We investigated the effect of chronic sleep deprivation using mutants with decreased sleep, insomniac and insulin-like peptide 2, finding increased alcohol mortality. Furthermore, we investigated whether pharmacologically inducing sleep prior to alcohol exposure using the GABAA-receptor agonist 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP) mitigated the effects of alcohol toxicity on middle-aged flies, flies with environmentally disrupted circadian clocks, and flies with short sleep. Pharmacologically increasing sleep prior to alcohol exposure decreased alcohol-induced mortality. Thus, sleep prior to binge-like alcohol exposure affects alcohol-induced mortality, even in vulnerable groups such as aging flies and those with circadian dysfunction.
... Social isolation during adolescence can increase alcohol consumption later in life compared to group-housed adolescent mice. 48 It is possible that adolescent PME males are more sensitive to social isolation and this heightened stress response is what produces their increased alcohol consumption. We have modelled treatment of OUD with methadone as epidemiological data indicate this represents a frequent clinical scenario. ...
As the opioid crisis has continued to grow, so has the number of infants exposed to opioids during the prenatal period. A growing concern is that prenatal exposure to opioids may induce persistent neurological changes that increase the propensity for future addictions. Although alcohol represents the most likely addictive substance that the growing population of prenatal opioid exposed will encounter as they mature, no studies to date have examined the effect of prenatal opioid exposure on future sensitivity to alcohol reward. Using a recently developed mouse model of prenatal methadone exposure (PME), we investigated the rewarding properties of alcohol and alcohol consumption in male and female adolescent PME and prenatal saline exposed (PSE) control animals. Conditioned place preference to alcohol was disrupted in PME offspring in a sex-dependent manner with PME males exhibiting resistance to the rewarding properties of alcohol. Repeated injections of alcohol revealed enhanced sensitivity to the locomotor-stimulating effects of alcohol specific to PME females. PME males consumed significantly more alcohol over 4 weeks of alcohol access relative to PSE males and exhibited increased resistance to quinine-adulterated alcohol. Further, a novel machine learning model was developed to employ measured differences in alcohol consumption and drinking microstructure to reliably predict prenatal exposure. These findings indicate that PME alters the sensitivity to alcohol reward in adolescent mice in a sex-specific manner and suggests prenatal opioid exposure may induce persistent effects on reward neurocircuitry that can reprogram offspring behavioural response to alcohol later in life.
... In addition, social isolation is known to induce profound behavioral and neurobiological alterations (Mumtaz et al., 2018). Besides inducing anxiety and depressive-like behaviors in rodents (Amiri et al., 2015), several studies pointed that isolation induces an increase in ethanol consumption in mice and rats (Advani et al., 2007;Evans et al., 2020;Juárez and Vázquez-Cortés, 2003;Lopez et al., 2011;Sanna et al., 2011). ...
Large preclinical evidence shows that exposure to social defeat (SD) increases vulnerability to drug abuse, increasing the consumption of ethanol. However, not all subjects are equally affected by the changes induced by stress. Previous reports have evidenced that the resilient phenotype to depressive-like behaviors after SD is associated with the resistant phenotype to cocaine-increased rewarding effects and the smaller neuroinflammatory response. The aim of the present study was to further clarify whether the resilient profile to depressive-like behavior also predicts a protection against the increase in ethanol intake induced by SD. The neuroinflammatory profile was studied after the end of the oral ethanol self-administration (SA) procedure, measuring levels of the pro-inflammatory cytokine IL-6 and the chemokine CX3CL1 or fractalkine in the striatum and prefrontal cortex. Previous studies have shown that environmental enrichment (EE) is an effective mechanism to dimish the detrimental effects of social stress. In a second study, we aimed to evaluate if EE housing before exposure to SD could potentiate resilience. Our results showed that mice with a phenotype susceptible to SD-induced depressive-like behaviors showed increased ethanol consumption and increased neuroinflammatory signaling. In contrast, despite the lack of effect on depressive-like behaviors, defeated mice previously housed under EE conditions did not show an increase in ethanol SA or an increase in immune response. To sum up, the resilient phenotype to SD develops at different levels, such as depressive-like behaviors, ethanol consumption and the neuroinflammatory response. Our results also point to the protective role of EE in potentiating resilience to SD effects.
... Since mice are social animals, group housing during laboratory experiments is also important to promote animal behavior that comes as close as possible to their natural state. In addition, studies have shown that isolation of mice causes stress and lasting damage [3][4][5]. As a consequence, for biomedical research, a more natural setting might even strengthen translational research with regard to understanding how certain treatments affect mice without constraints imposed by barren housing conditions. ...
Despite tremendous efforts at standardization, the results of scientific studies can vary greatly, especially when considering animal research. It is important to emphasize that consistent different personality-like traits emerge and accumulate over time in laboratory mice despite genetic and environmental standardization. To understand to what extent variability can unfold over time, we conducted a long-term study using inbred mice living in an exceptionally complex environment comprising an area of 4.6 m2 spread over five levels. In this semi-naturalistic environment (SNE) the activity and spatial distribution of 20 female C57Bl/6J was recorded by radio-frequency identification (RFID). All individuals were monitored from an age of 11 months to 22 months and their individual pattern of spatial movement in time is described as roaming entropy. Overall, we detected an increase of diversification in roaming behavior over time with stabilizing activity patterns at the individual level. However, spontaneous behavior of the animals as well as physiological parameters did not correlate with cumulative roaming entropy. Moreover, the amount of variability did not exceed the literature data derived from mice living in restricted conventional laboratory conditions. We conclude that even taking quantum leaps towards improving animal welfare does not inevitably mean a setback in terms of data quality.
... The effects of social isolation in behavior and cognition have been extensively studied mainly in vertebrates (Blanchard et al. 2001;Cacioppo and Hawkley 2009;Gluck and Harlow 1971;Lopez et al. 2011;Makinodan et al. 2016;Medendorp et al. 2018;Shams et al. 2015). However, less is known about the effects in invertebrate models. ...
Cognitive abilities of an animal can be influenced by distinct social experiences. However, the extent of this modulation has not been addressed in different learning scenarios: are all tasks similarly affected by social experiences? In the present study, we analyzed the effect of social dominance in aversive and appetitive memory processes in the crab Neohelice granulata. In addition, we studied the influence of social isolation on memory ability. Social dominance experiments consisted of an agonistic phase immediately followed by a memory phase. During the agonistic phase, matched pairs of male crabs were staged in 10-min encounters and the dominant or subordinate condition of each member of the dyad was determined. During the memory phase, crabs were trained to acquire aversive or appetitive memory and tested 24 h later. Results showed that the agonistic encounter can modulate long-term memory according to the dominance condition in such a way that memory retention of subordinates results higher than their respective dominant. Remarkably, this result was found for both aversive and appetitive memory tasks. In addition, we found that isolated animals showed no memory retention when compared with animals that remained grouped. Altogether this work emphasizes the importance of social context as a modulator of cognitive abilities.
... Increased synaptic activity in the dopaminergic dorsal raphe neurons is observed in adult mice submitted to social contact after an isolation period, suggesting their role in detecting the disparity between the current and desired social environments (Matthews et al., 2016). Interestingly, social isolation during early development predisposes rodents to increased consumption of alcohol and other drugs as adults (Lopez et al., 2011). ...
Social behavior represents a beneficial interaction between conspecifics that is critical for maintaining health and wellbeing. Dysfunctional or poor social interaction are associated with increased risk of physical (e.g., vascular) and psychiatric disorders (e.g., anxiety, depression and substance abuse). Although the impact of negative and positive social interactions is well-studied, their underlying mechanisms remain poorly understood. Zebrafish have well-characterized social behavior phenotypes, high genetic homology with humans, relative experimental simplicity and the potential for high-throughput screens. Here, we discuss the use of zebrafish as a candidate model organism for studying the mechanisms underlying social interactions, as well as potential impacts of social isolation on human health and wellbeing. Overall, the growing utility of zebrafish models may improve our understanding of how the presence and absence of social interactions can differently modulate molecular and physiological biomarkers, as well as other behaviors.
... The mechanisms by which ELS affects an individual's susceptibility to these psychopathological outcomes are not fully understood, and rodent models have been used to address this. Adolescent social isolation (ASI) in rodents has been shown to induce enduring increases in anxietylike behaviors and ethanol self-administration (Chappell, Carter, McCool, & Weiner, 2013;Lopez, Doremus-Fitzwater, & Becker, 2011;Yorgason, Espana, Konstantopoulos, Weiner, & Jones, 2013). Studies focused on the mesolimbic circuitry have identified areas in which neurobiological adaptations may be induced by ASI (Butler, Karkhanis, Jones, & Weiner, 2016), including the ventral tegmental area (Fabricius et al., 2010;Koob & Volkow, 2010;Whitaker, Degoulet, & Morikawa, 2013), the nucleus accumbens (Karkhanis, Rose, Weiner, & Jones, 2016;Yorgason et al., 2013Yorgason et al., , 2016, and the basolateral amygdala (Karkhanis, Alexander, McCool, Weiner, & Jones, 2015;Rau, Chappell, Butler, Ariwodola, & Weiner, 2015). ...
Early life stress is known to impact vulnerability to psychopathological disorders in adulthood, including anxiety and alcohol use disorder (AUD), but the mechanisms underlying susceptibility to these outcomes are not fully understood. In the current study, we used adolescent social isolation (ASI) to determine if Heterogeneous Stock (HS) rats, an outbred model used for fine genetic-mapping, could be used to study the genetics contributing to ASI-induced anxiety- and AUD-like behavior. We isolated or group-housed (AGH) 64 male HS rats at 4 weeks of age. After 5 weeks in these housing conditions, multiple anxiety and coping/despair-like behaviors were measured. All rats were then individually housed and assessed for voluntary ethanol self-administration. At euthanasia, synaptoneurosomes were isolated from a subset of brains to examine the expression of two proteins associated with alcohol drinking-related behaviors, GluA1 and SK2, in the dorsal (dHC) and ventral hippocampus (vHC). We found that ASI increased hyperactivity in the open field test relative to AGH, with no changes in other anxiety-like behaviors. Surprisingly, ASI rats demonstrated decreased immobility and increased climbing in the forced swim test relative to AGH. In contrast to prior studies by us and others, we found no difference in self-administration of 20% ethanol, with decreased ethanol self-administration in ASI relative to AGH rats at higher ethanol concentrations. Furthermore, while ASI in Long-Evans rats resulted in decreased SK2 expression in vHC synaptosomes, no differences were seen in vHC synaptosomes for SK2 or GluA1 in HS rats. These results demonstrate that HS rats are protected against many of the negative effects previously seen in response to ASI, namely anxiety-like behavior and increased ethanol self-administration. The current work suggests that a lack of change in SK2 and GluA1 expression levels in the vHC may play a role in conferring this protection.
... However, most existing preclinical models of alcohol drinking escalation induced by early-life adversity yield sub-intoxicating blood ethanol concentrations (BECs) and do not discriminate between patterns of moderate/controlled vs. excessive/compulsive alcohol drinking. Moreover, limited research has been conducted in C57BL/6J mice, in which a wealth of genetic tools is available for mechanistic investigation (Advani et al., 2007;Lopez et al., 2011;Moriya et al., 2015). This limitation is all the more critical given that maternal separation, an early-life adversity procedure that elicits long-lasting emotional-like disturbances, stress hyperreactivity and alcohol drinking escalation in rats, does not trigger similar changes in mice (Holmes et al., 2005;Millstein and Holmes, 2007;Tan et al., 2017). ...
Childhood adversity increases vulnerability to alcohol use disorders and preclinical models are needed to investigate the underlying neurobiological mechanisms. The present study modeled early-life adversity by rearing male and female C57BL/6J mouse pups in a limited bedding and nesting (LBN) environment, which induces erratic maternal care. As adults, mice were given limited access to two-bottle choice (2BC) alcohol drinking, combined or not with chronic intermittent ethanol (CIE) vapor inhalation to induce alcohol dependence. We tested the hypothesis that LBN rearing might exacerbate or facilitate the emergence of the motivational and affective effects of CIE. Consistent with our hypothesis, although LBN-reared males consumed the same baseline levels of alcohol as controls, they escalated their ethanol intake at an earlier stage of CIE exposure, i.e., after 4 rounds vs. 5 rounds for controls. In contrast, females were insensitive to both LBN rearing and CIE exposure. Males were further subjected to a behavioral test battery. Withdrawal from CIE-2BC increased digging activity and lowered mechanical nociceptive thresholds regardless of early-life conditions. On the other hand, LBN-reared CIE-2BC males showed reduced open arm exploration in the elevated plus maze and increased immobility in the tail suspension test compared to alcohol-naïve counterparts, while no group differences were detected among control-reared males. Finally, LBN rearing and alcohol exposure did not affect grooming in response to a sucrose spray (splash test), novel object recognition, or corticosterone levels. In summary, the LBN experience accelerates the transition from moderate to excessive alcohol drinking and produces additional indices of affective dysfunction during alcohol withdrawal in C57BL/6J male mice.
... The mice were placed in the box for 5 min, and software was used to analyze the total travel distance, number of rearings, number of grooming episodes, and number of defecations. The test was conducted with reference to the analysis method and experimental device described in Matsuo et al. [40] and Lopez et al. [41] with minor modifications. ...
This study applied high-pressure processing (HPP) technology to enrich the gamma aminobutyric acid (GABA) content in vegetable soybeans and evaluated its antidepressant efficacy on mice, with depression induced by the unpredictable chronic mild stress (UCMS) model. The optimal conditions for HPP, storage time, and storage temperature, as well as antidepressant-like effects of vegetable soybeans, were evaluated and discussed. HPP could effectively and significantly increase GABA content in soybean, with optimum conditions at 200 MPa. The GABA content in the whole vegetable soybean was 436.05 mg/100 g. In mice animal tests, the tail suspension test (TST) showed that the immobility time of the GABA group was significantly shorter than that of the control group. The total travel distance in the open field test (OFT) showed that depressed mice fed with the GABA feed exhibited exploratory behavior. The GABA group showed a significantly higher degree of sucrose preference than the control group. Both results indicate that the GABA feed could effectively alleviate depressive symptomatology. Regarding biochemical parameters, the fecal and serum corticosterone (CORT) levels in the control group increased to 104.86 pg/mg after the onset of depression. In contrast, the fecal CORT level in the GABA group was significantly reduced to 23.98 pg/mg and was comparable to that in the control group (33.38 pg/mg). Reduced serum CORT level in the GABA group suggests an improvement in depressive symptomatology. The serotonin concentration was maintained in the GABA group after the induction of depression, suggesting its preventive activity. The HPP GABA-enriched soybeans exerted modulatory effects on the behaviors of depressed mice and displayed a potential for commercialization.
... Similar models, involving varied schedules of repeated stress have also been performed: these include chronic variable stress (Lopez, Doremus-Fitzwater, & Becker, 2011;McGuire, Herman, Horn, Sallee, & Sah, 2010;Rompala, Simons, Kihle, & Homanics, 2018) and intermittent unpredictable stress (Peay et al., 2020;Sequeira-Cordero, Salas-Bastos, Fornaguera, & Brenes, 2019). These models capitalize on mercurial stressor application, in order to simulate a context in which the stressor may appear at any time. ...
Alcohol use disorder (AUD) and (PTSD) frequently co-occur and individuals suffering from this dual diagnosis often exhibit increased symptom severity and poorer treatment outcomes than those with only one of these diseases. Although there have been significant advances in our understanding of the neurobiological mechanisms underlying each of these disorders, the neural underpinnings of the comorbid condition remain poorly understood. This chapter summarizes recent epidemiological findings on comorbid AUD and PTSD, with a focus on vulnerable populations, the temporal relationship between these disorders, and the clinical consequences associated with the dual diagnosis. We then review animal models of the comorbid condition and emerging human and non-human animal research that is beginning to identify maladaptive neural changes common to both disorders, primarily involving functional changes in brain reward and stress networks. We end by proposing a neural framework, based on the emerging field of affective valence encoding, that may better explain the epidemiological and neural findings on AUD and PTSD.
... This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. Lopez, Doremus-Fitzwater, & Becker, 2011;Tambour, Brown, & Crabbe, 2008) or where there was no sex difference reported Juárez and Barrios De Tomasi, 1999). ...
Early postnatal experiences are important for shaping the development of the stress response and may contribute to the later emergence of alcohol use disorders. We have previously found that early life sleep disruption impairs social development and alters GABA neurons in the brain of adult prairie voles, a socially monogamous rodent that displays natural ethanol preference in the laboratory. However, it is unclear whether these effects on social behavior are due, in part, to overall anhedonia and/or altered behavioral response to stress. To address this question, litters containing prairie vole pups were sleep disrupted by gentle cage agitation for 7 consecutive days from postnatal days (P) 14 to 21 (early life sleep disruption, or ELSD group) or allowed to sleep undisturbed (Control). Adult voles underwent a 2-bottle choice ethanol drinking procedure integrated with a single session of footshocks. Ethanol intake after footshock was measured as well as c-Fos immunoreactivity in the lateral and central amygdala. ELSD animals showed increased ethanol consumption and increased neural activity in these amygdala regions after footshock compared to control animals. There were no differences in baseline ethanol drinking prior to exposure to a stressor. These results suggest that early life sleep disruption in prairie voles does not produce anhedonia but can have long-lasting effects on stress reactivity. In addition to shaping species-typical social behavior, early life sleep may be important in the development of stress induced ethanol consumption and the activation of limbic pathways associated with stress. (PsycInfo Database Record (c) 2020 APA, all rights reserved).
... In other words, the anxiolytic effects of alcohol could be underlying the exacerbated intake of the drug of MS adolescents. The present finding is consistent with previous studies in mice (Lopez et al. 2011) and rats (Fernández et al. 2016) whereas an anxiogenic state during adolescence enhances subsequent alcohol consumption. ...
RationaleSocial attachment plays an important role in offspring development. Different parenting experiences during lactation may shape offspring behavior and later alcohol use.Objectives
We tested the hypothesis that differential rearing conditions (single mother, SM or biparental, BP) in the non-monogamous C57BL/6J mice may affect (1) parental behavior during lactation, (2) adolescent behavior, and (3) adolescent initiation of alcohol drinking.Methods
Mice were reared in SM or BP (cohabitation of father-mother since copulation) condition until weaning (postnatal day, PND, 21). Litters from both conditions were filmed during PNDs 6, 9, and 12 and an ethogram was made taking into account nest-, pup-, or self-directed behaviors. At PNDs, 28–29 adolescent animals were evaluated in a modified version of the concentric square field for measurement of behavioral patterns. Other groups of adolescents were tested in a 4-h daily, two-bottle choice alcohol consumption test (10% alcohol vs. water) during 3 weeks (4 days per week).ResultsSingle mothers spent less time in the nest, left unattended the nest more times, displayed more self-directed and less pup-directed behaviors than BP parents. SM-reared adolescents displayed more anxiogenic-like and less risk-associated behaviors than BP counterparts. The alcohol consumption test indicated a strong effect of rearing condition. Since the fifth day of test, SM adolescents consumed more quantities of alcohol than BP adolescents.Conclusions
During single-mother parenting, pups are left unattended more often, and during adolescence, these organisms exhibited increased anxiety responses. This behavioral phenotype may act as a risk factor for alcohol initiation during adolescence.
... Interestingly, in most studies, alcohol intake is tested in conditions of isolation, a stressful situation for rats that could facilitate the observation of differential effects of alcohol consumption. Prolonged isolation housing during early development has also been shown to induce augmented alcohol intake in rodents (Lopez et al., 2011;Kutcher et al., 2016). Additionally, in one study it was found that this heightened alcohol intake was facilitated in adolescent males exposed to alcohol during gestation and the first week of lactation (Fernández et al., 2019). ...
Prenatal alcohol exposure has been found to be an important factor determining later consumption of this drug. In humans, despite the considerable diversity of variables that might influence alcohol consumption, longitudinal studies show that maternal alcohol intake during gestation is one of the best predictors of later alcohol use from adolescence to young adulthood. Experimental studies with animals also provide abundant evidence of the effects of prenatal alcohol exposure on later alcohol intake. In addition to increased consumption, other effects include enhanced palatability and attractiveness of alcohol flavor as well as sensitization to its sensory and reinforcing effects. Most of these outcomes have been obtained after exposing rats to binge-like administrations of moderate alcohol doses during the last gestational period when the fetus is already capable of detecting flavors in the amniotic fluid and learning associations with aversive or appetitive consequences. On this basis, it has been proposed that one of the mechanisms underlying the increased acceptance of alcohol after its prenatal exposure is the acquisition (by the fetus) of appetitive learning via an association between the sensory properties of alcohol and its reinforcing pharmacological effects. It also appears that this prenatal appetitive learning is mediated by the activation of the opioid system, with fetal brain acetaldehyde playing an important role, possibly as the main chemical responsible for its activation. Here, we review and analyze together the results of all animal studies testing these hypotheses through experimental manipulation of the behavioral and neurochemical elements of the assumed prenatal association. Understanding the mechanisms by which prenatal alcohol exposure favors the early initiation of alcohol consumption, along with its role in the causal pathway to alcohol disorders, may allow us to find strategies to mitigate the behavioral effects of this early experience with the drug. We propose that prenatal alcohol exposure is regarded as a case of involuntary early onset of alcohol use when designing prevention policies. This is particularly important, given the notion that the sooner alcohol intake begins, the greater the possibility of a continued history of alcohol consumption that may lead to the development of alcohol use disorders.
... However, social isolation has also been shown to increase general anxietylike behaviors such as a novelty-induced avoidance, decreased environmental exploration, and reduced time spent in vulnerable positions (e.g., open portions of a plus maze; Barnes et al., 2017;Huang et al., 2017;Caruso et al., 2018). Further, socially isolated mice have been shown to display higher locomotor activity, longer rates of immobility in tail suspension tests, increased adipose mass, and increased voluntary ethanol consumption later in life (Lopez et al., 2011;Sun et al., 2014;Lopez and Laber, 2015;Ieraci et al., 2016). The DA system is significantly impacted by this paradigm, such that following social isolation, mice have demonstrated increased DA-receptor 2 mRNA and protein levels in the NAc, suggestive of excessive dopaminergic activity in mesolimbic areas that are key to motivation and reward salience (Li et al., 2017). ...
Social anxiety disorder (SAD) is a common and serious psychiatric condition that typically emerges during adolescence and persists into adulthood if left untreated. Prevailing interventions focus on modulating threat and arousal systems but produce only modest rates of remission. This gap in efficacy suggests that most mainstream treatment concepts do not sufficiently target core processes involved in the onset and maintenance of SAD. This idea has further driven the development of new theoretical models that target dopamine (DA)-driven reward circuitry and motivational deficits that appear to be systematically altered in SAD. Most of the available data linking systemic alterations in DA neurobiology to SAD in humans, although abundant, remains at the level of correlational evidence. Accordingly, the purpose of this brief review is to critically evaluate the relevance of experimental work in rodent models that link details of DA function to symptoms of social anxiety. We conclude that, despite certain systematic limitations inherent in animal models, these approaches provide useful insights into human biomarkers of social anxiety including that (1) adolescence may serve as a critical period for the convergence of neurobiological and environmental factors that modify future expectations about social reward through experience dependent changes in DA-ergic circuitry, (2) females may show unique susceptibility to social anxiety symptoms when encountering relational instability that influences DA-related neural processes, and (3) separate from fear and arousal systems, the functional neurobiology of central DA systems contribute uniquely to susceptibility and maintenance of anhedonic factors relevant to human models of SAD.
... social isolation stress, chronic variable stress) can increase adult ethanol intake (e.g. [103][104][105][106][107], see also reviews: [108,109]). Elevated ethanol intake in other neurodevelopmental models may be linked to molecular changes such as decreased firing of dopaminergic VTA neurons in an LPS model [103], and may be related to altered anxiety-like states, as ethanol consumption in two-bottle free choice can be reduced by administration of anxiolytic adrenergic drugs [105]. ...
Schizophrenia is a severe psychiatric disorder which is worsened substantially by substance abuse/addiction. Substance abuse affects nearly 50% of individuals with schizophrenia, extends across several drug classes (e.g. nicotine, cannabinoids, ethanol, psychostimulants) and worsens overall functioning of patients. Prominent theories explaining schizophrenia and addiction comorbidity include the primary addiction hypothesis (i.e. schizophrenia susceptibility primes drug reward circuits, increasing drug addiction risk following drug exposure), the two-hit hypothesis (i.e. drug abuse and other genetic and/or environmental risk factors contribute to schizophrenia development) and the self-medication hypothesis (i.e. drug use alleviates schizophrenia symptoms). Animal models can be used to evaluate the utility and validity of these theories. Since this literature was last reviewed by Ng and colleagues in 2013 [Neurosci Biobehav Rev, 37(5)], significant advances have been made to our understanding of schizophrenia and substance abuse comorbidity. Here we review advances in the field since 2013, focussing on two key questions: 1) Does schizophrenia susceptibility increase susceptibility to drug addiction (assessing the primary addiction hypothesis), and 2) Do abused drugs exacerbate or ameliorate schizophrenia symptoms (assessing the two-hit hypothesis and the self-medication hypothesis). We addressed these questions using data from several schizophrenia preclinical models (e.g. genetic, lesion, neurodevelopmental, pharmacological) across drug classes (e.g. nicotine, cannabinoids, ethanol, psychostimulants). We conclude that addiction-like behaviour is present in several preclinical schizophrenia models, and drugs of abuse can exacerbate but also ameliorate schizophrenia-relevant behaviours. These behavioural changes are associated with altered receptor system function (e.g. dopaminergic, glutamatergic, GABAergic) critically implicated in schizophrenia and addiction pathology.
... For example, repeated social defeat induced social avoidance in both adolescent and adult mice, but only mice that were socially defeated during early adolescence displayed enduring problems with cognitive flexibility [13]. Chronic social isolation and/or chronic variable stress in adolescence, but not adulthood, increased ethanol drinking in adulthood [16]. Thus, the role of experience is critical to the developing neurocircuitry of the adolescent brain and can have lasting affects into adulthood in mice. ...
Adolescence is characterized by high levels of playful social interaction, cognitive development, and increased risk-taking behavior. Juvenile exposure to social isolation or social stress can reduce myelin content in the frontal cortex, alter neuronal excitability, and disrupt hypothalamic pituitary adrenal (HPA) axis function. As compared to group housed animals, social isolation increases anxiety-like phenotypes and reduces social and cognitive performance in adulthood. We designed a neighbor housing environment to alleviate issues related to social isolation that still allowed individual homecages. Neighbor housing consists of four standard mouse cages fused together with semi-permeable ports that allow visual, olfactory, and limited social contact between mice. Adolescent C57BL/6J males and females were group housed (4/cage), single housed (1/cage), or neighbor housed (4/complex). As adults, mice were tested for social, anxiety-like, and cognitive behaviors. Living in this neighbor environment reduced anxiety-like behavior in the social interaction task and in the light-dark task. It also rescued cognitive deficits from single housing in the novel object recognition task. These data suggest that neighbor housing may partially ameliorate the social anxiety and cognitive deficits induced by social isolation. These neighbor cage environments may serve as a conduit by which researchers can house mice in individual cages while still enabling limited social interactions to better model typical adolescent development.
... Ce sujet est d'autant plus intéressant qu'il a été démontré que cette période sensible, où l'occurrence d'événements de vie stressants (isolation sociale chronique, appauvrissement de l'environnement, manque de stimulation) menait à des expressions chroniques de stress, d'anxiété et parfois de symptômes dépressifs. Ces événements indésirables peuvent influencer à leur tour l'initiation et le développement de comportements toxicomanogènes pendant l'âge adulte(Kaufman et al. 2007 ;Lopez & Becker, 2011 ;Koob et al. 2014 ;Lopez & Laber, 2015). Cependant, des conditions environnementales sociales et physiques enrichies et adaptées à l'animal favorisent les comportements sociaux adaptés, diminuent les réactions anxiogènes anormales, les symptômes dépressifs, etc. Les influences du stress, de l'anxiété ou de la dépression durant l'enfance et l'adolescence sur l'addiction à l'âge adulte sont également largement étudiées chez l'homme(Spear, 2000 ;Keynes et al., 2012 ;Watt, Weber, Davies, & Forster, 2017).Étant donné le manque de littérature scientifique abordant les questions liées à l'influence de l'enrichissement environnemental sur la sensibilisation à l'éthanol chez le rongeur (voirRueda et al., 2012 ;Araujo et al., 2005), ce mémoire devrait apporter des éléments de réflexions nouveaux concernant les futures études sur les processus d'addiction et d'alcoolo-dépendance.4.1 L'enrichissement physique préalable influence-t-il l'activité locomotrice basale et la réactivité locomotrice aigüe à l'éthanol ?Les résultats que nous obtenons en phase d'habituation à l'environnement (figure 13) ne montrent aucun effet de la condition d'hébergement (EE vs. SC) sur l'activité locomotrice basale. ...
Mémoire présenté en vue de l'obtention du diplôme de master en psychologie à finalité spécialisée en neuroscience cognitive et comportementale Théo van Ingelgom Service de neuroscience comportementale et psychopharmacologie expérimentale Mémoire présenté en vue de l'obtention du diplôme de master en psychologie à finalité spécialisée en neuroscience cognitive et comportementale Théo van Ingelgom
... One important limitation in our voluntary ethanol consumption protocol is the individual housing necessary for fluid intake measurement. In adolescents, social isolation increases alcohol intake and preference (Butler, Karkhanis, Jones, & Weiner, 2016) while it is not effective when animals are isolated during the adulthood (Lopez, Doremus-Fitzwater, & Becker, 2011). This could contribute to a ceiling effect in adolescents' alcohol consumption, which could be a factor that masked the effects of MS in this variable. ...
Maternal separation (MS) is an animal model widely used to evaluate the influence of early-life stress exposure on ethanol consumption and dependence. The goal of this study was to evaluate the effects of brief and prolonged MS on the pattern of consumption and ethanol conditioned place preference (CPP) in male and female rats during adolescence and adulthood. Wistar rat pups were separated daily from their dams for 15 or 180 minutes during the 2 to 10 postnatal days (PND). In adolescence, half of the litter from each group was evaluated in the ethanol consumption test using the three-bottle test choice paradigm. In addition, using biased procedure, ethanol-conditioned place preference was also evaluated. In adulthood, the other half of the litter was evaluated on the same tests. Our results showed that there are differences in consumption pattern and in alcohol reinforcement between males and females, adolescents and adults. While prolonged MS had no effect on total ethanol consumption in adolescents of both sexes, it induced CPP in these animals. In turn, in adults, previous exposure to prolonged MS increased ethanol consumption without altering ethanol-CPP.
• Lay summary
• Giving the importance of the mother-children (dam-pups when talking about rodents) relationship to proper brain development, the separation of pups from their dam is broadly used as an animal model to study the impact of early-life stress exposure. Here, we used a protocol of brief or prolonged maternal separation to study the impact of early-life stress exposure in the alcohol consumption and conditioned place preference in rats, and how age and sex influence it. We showed that, overall, the prolonged maternal separation increased alcohol consumption in both males and females, but only when animals were tested during the adulthood. In the other hand, prolonged maternal separation increased ethanol conditioned place preference in adolescent rats, both male and female.
... The Socially Isolated Mouse Model of PTSD emotional behavioral deficits, such as aggression, sensory gating and fear deficits Koike et al., 2009;Gan et al., 2014;Kumari et al., 2016;. Home-cage elevated alcohol consumption and preference that lasted even 1 month during adulthood was primarily observed in male socially isolated mice (Advani et al., 2007;Lopez et al., 2011;Talani et al., 2014). ...
Post-traumatic stress disorder (PTSD) is a debilitating undertreated condition that affects 8%-13% of the general population and 20%-30% of military personnel. Currently, there are no specific medications that reduce PTSD symptoms or biomarkers that facilitate diagnosis, inform treatment selection or allow monitoring drug efficacy. PTSD animal models rely on stress-induced behavioral deficits that only partially reproduce PTSD neurobiology. PTSD heterogeneity, including comorbidity and symptoms overlap with other mental disorders, makes this attempt even more complicated. Allopregnanolone, a neurosteroid that positively, potently and allosterically modulates GABA A receptors and, by this mechanism, regulates emotional behaviors, is mainly synthesized in brain corticolimbic glutamatergic neurons. In PTSD patients, allopregnanolone down-regulation correlates with increased PTSD re-experiencing and comorbid depressive symptoms, CAPS-IV scores and Simms dysphoria cluster scores. In PTSD rodent models, including the socially isolated mouse, decrease in corticolimbic allopregnanolone biosynthesis is associated with enhanced contextual fear memory and impaired fear extinction. Allopregnanolone, its analogs or agents that stimulate its synthesis offer treatment approaches for facilitating fear extinction and, in general, for neuropsychopathologies characterized by a neurosteroid biosynthesis downregulation. The socially isolated mouse model reproduces several other deficits previously observed in PTSD patients, including altered GABA A receptor subunit subtypes and lack of benzodiazepines pharmacological efficacy. Transdiagnostic behavioral features, including expression of anxiety-like behavior, increased aggression, a behavioral component to reproduce behavioral traits of suicidal behavior in humans, as well as alcohol consumption are heightened in socially isolated rodents. Potentials for assessing novel biomarkers to predict, diagnose, and treat PTSD more efficiently are discussed in view of developing a precision medicine for improved PTSD pharmacological treatments.
Aims:
This study examined how adolescent social isolation affects adult binge-like alcohol drinking and stress-axis function, via basal levels of circulating corticosterone (CORT), in male and female mice with a genetic predisposition toward high alcohol preference (HAP).
Methods:
Male and female HAP2 mice were randomly assigned to a group-housed or social isolation (ISO) group. Social isolation began at postnatal Days 40-42 and lasted for 21 days prior to assessment of binge-like alcohol drinking using a 4-day drinking-in-the-dark (DID) procedure. Blood samples to assess basal CORT were taken 6 days after social isolation ended and 24 h before DID started, and again 60 h after DID ended, during the light portion of the light cycle.
Results:
Adolescent social isolation increased adult binge-like alcohol drinking in male but not female mice. All groups showed significantly lower CORT after DID compared to before DID. Pearson bivariate correlation coefficients between the first 2 h of grams-per-kilogram alcohol intake on Day 4 and CORT levels indicated a significant positive correlation in ISO males only after DID and negative correlations in ISO females before and after DID.
Conclusions:
These findings demonstrate that adolescent social isolation increased binge-like alcohol drinking in male but not female adult HAP2 mice. Stress-axis adaptations in male HAP2 mice may be associated with the social-isolation-induced increase in binge-like alcohol drinking.
The serotonin 5HT2c receptor has been widely implicated in the pathophysiology of alcohol use disorder (AUD), particularly alcohol seeking and the affective consequences of chronic alcohol consumption. However, little is known about the brain sites in which 5HT2c exerts its effects on specific alcohol-related behaviors, especially in females. Here, we investigated the effects of site-specific manipulation of the 5HT2c receptor system in the BNST on operant alcohol self-administration behaviors in adult mice of both sexes, including the acquisition and maintenance of fixed-ratio responding, motivation for alcohol (progressive ratio), and quinine-adulterated responding for alcohol on a fixed-ratio schedule (punished alcohol seeking). Knockdown of 5HT2c in the BNST did not affect the acquisition or maintenance of operant alcohol self-administration, nor did it affect progressive ratio responding for alcohol. This manipulation had only a subtle effect on responding for quinine alcohol selectively in females. On the other hand, chemogenetic inhibition of BNST 5HT2c-containing neurons (BNST5HT2c) increased operant alcohol self-administration behavior in both sexes on day 2, but not day 9, of testing. It also increased operant responding for 1000 μM quinine-adulterated alcohol selectively in males. Importantly, chemogenetic inhibition of BNST5HT2c did not alter operant sucrose responding or motivation for sucrose in either sex. We then performed cell-type specific anterograde tracing, which revealed that BNST5HT2c project to similar regions in males and females, many of which have been previously implicated in AUD. We next used chemogenetics and quantification of the immediate early gene cFos to characterize the functional influence of BNST5HT2c inhibition on vlPAG activity. We show that chemogenetic inhibition of BNST5HT2c reduces vlPAG cFos in both sexes, but that this reduction is more robust in males. Together these findings suggest that BNST5HT2c neurons, and to a small extent the BNST 5HT2c receptor, serve to promote aversive responses to alcohol consumption, potentially through sex-dependent disinhibition of vlPAG neurons.
Alcohol use disorder (AUD) is a debilitating psychiatric disorder characterized by drinking despite negative social and biological consequences. AUDs make up 71% of substance use disorders, with relapse rates as high as 80%. Current treatments stem from data conducted largely in males and fail to target the psychological distress motivating drinking in stress-vulnerable and at-risk populations. Here we employed a rat model and hypothesized that early life stress would reveal sex differences in ethanol intake and drinking despite negative consequences in adulthood. Rats were group housed or isolated postweaning to evaluate sex and stress effects on ethanol consumption in homecage drinking, self-administration (SA), and punishment-SA (drinking despite negative consequences) in adulthood. Stressed rats showed elevated homecage ethanol intake, an effect more pronounced in females. During SA, males were more sensitive to stress-induced elevations of drinking over time, but females drank more overall. Stressed rats, regardless of sex, responded more for ethanol than their non-stressed counterparts. Stressed females showed greater resistance to punishment-suppressed SA than stressed males, indicating a more stress-resistant drinking phenotype. Results support our hypothesis that adolescent social isolation stress enhances adult ethanol intake in a sex- and model-dependent manner with females being especially sensitive to early life stress-induced elevations in ethanol intake and punished SA in adulthood. Our findings echo the clinical literature which indicates that stress-vulnerable populations are more likely to 'self-medicate' with substances. Elucidating a potential mechanism that underlies why vulnerable populations 'self-medicate' with alcohol can lead towards developing catered pharmacotherapeutics that could reduce punishment-resistant drinking and relapse.
There is an urgent need to develop more effective treatments for stress-related illnesses, which include depression, post-traumatic stress disorder, and anxiety. We view animal models as playing an essential role in this effort, but to date, such approaches have generally not succeeded in developing therapeutics with new mechanisms of action. This is partly due to the complexity of the brain and its disorders, but also to inherent difficulties in modeling human disorders in rodents and to the incorrect use of animal models: namely, trying to recapitulate a human syndrome in a rodent which is likely not possible as opposed to using animals to understand underlying mechanisms and evaluating potential therapeutic paths. Recent transcriptomic research has established the ability of several different chronic stress procedures in rodents to recapitulate large portions of the molecular pathology seen in postmortem brain tissue of individuals with depression. These findings provide crucial validation for the clear relevance of rodent stress models to better understand the pathophysiology of human stress disorders and help guide therapeutic discovery. In this review, we first discuss the current limitations of preclinical chronic stress models as well as traditional behavioral phenotyping approaches. We then explore opportunities to dramatically enhance the translational use of rodent stress models through the application of new experimental technologies. The goal of this review is to promote the synthesis of these novel approaches in rodents with human cell-based approaches and ultimately with early-phase proof-of-concept studies in humans to develop more effective treatments for human stress disorders.
Stress is known to contribute to mental illness and alcohol use disorders, which are highly prevalent and lead to considerable disability. These stress-related disorders are characterized by significant sex differences, which remain poorly understood. Preclinical research comparing the effects of stress in males and females has the potential to provide new insights into the neurobiology of these conditions. The current study compared the effects of chronic and sub-chronic exposure to variable environmental stressors on binge-like alcohol consumption using the drinking-in-the-dark model in male and female c57BL6 mice. The results reveal that chronic, but not sub-chronic, exposure to variable stress increases alcohol intake in both sexes. Stress-induced alterations in gene expression were also compared in the nucleus accumbens, a brain region widely known to play a key role in stress susceptibility and reward processing. Real-time PCR data indicate that chronic, but not sub-chronic, environmental stress leads to downregulation of adenosine 2A (A2A) receptor mRNA. By contrast, sub-chronic stress increased CREB expression, while chronic stress did not. Several sex differences in the effects of stress on gene expression were also noted. Our results demonstrate that reductions in A2A receptor mRNA in the nucleus accumbens are associated with the increased binge drinking of chronically stressed animals, but future work will be required to determine the functional importance of this gene expression change. Continuing to define the molecular alterations associated with stress-induced increases in alcohol intake has the potential to provide insights into the development and progression of stress-related disorders.
Initiating alcohol use in adolescence significantly increases the likelihood of developing adult alcohol use disorder (AUD). However, it has been difficult to replicate adolescent alcohol exposure leading to increased adult alcohol intake across differing preclinical models. In the present study, differentially housed male rats (group vs. single cages) were used to determine the effects of voluntary intermittent exposure of saccharin-sweetened ethanol (EtOH) during adolescence on adult intake of unsweetened 20% EtOH. Adolescent male rats were assigned to group or isolated housing conditions and underwent an intermittent 2-bottle choice in adolescence (water only or water vs. 0.2% saccharin/20% EtOH), and again in adulthood (water vs. 20% EtOH). Intermittent 2-bottle choice sessions lasted for 24 h, and occurred three days per week, for 5 weeks. Rats were moved from group or isolated housing to single housing cages for 2-bottle choice tests and returned to their original housing condition on off days. During adolescence, rats raised in isolated housing conditions consumed significantly more sweetened EtOH than rats raised in group housing conditions, an effect that was enhanced across repeated exposures. In adulthood, rats raised in isolated housing conditions and exposed to sweetened EtOH during adolescence also consumed significantly higher levels of unsweetened 20% EtOH compared to group housed rats. The effect that was most pronounced over the first 5 re-exposure sessions. Housing conditions alone had little effect on adult EtOH intake. These preclinical results suggest that social isolation stress, combined with adolescent EtOH exposure, may play a key role in adult AUD risk.
Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.
Background
Ethanol use during adolescence is a significant health problem, yet the pharmacological treatments to reduce adolescent binge drinking are scarce. The present study assessed, in male and female adolescent Wistar rats, if the sigma-1 receptor (S1-R) antagonists S1RA or BD-1063 disrupted ethanol drinking.
Methods
Three times a week, for two weeks, the rats received the S1-R antagonists. Thirty min later they were exposed, for 2 h, to a bottle of 8% or 10% v/v ethanol. A 24 h, two-bottle, ethanol intake test was conducted after termination of these procedures. A subset of these rats was tested for recognition memory via the novel object recognition test.
Results
The rats given 64 mg/kg S1RA drank, in each binge session, significantly less than vehicle counterparts. Male rats given 4 or 16 mg/kg S1RA drank significantly less than those given 0 mg/kg in session 3 or in session 1 and 2, respectively; whereas female rats given 4 or 16 mg/kg drank significantly less than females given 0 mg/kg in session 2-5 or in sessions 2-6, respectively. Administration of 32 mg/kg, but not of 2 or 8 mg/kg, BD-1063 suppressed, across sessions, ethanol drinking. S1-R antagonism reduced absolute ethanol drinking at the two-bottle choice post-test. Recognition memory was not affected by the ethanol exposure.
Conclusions
The results indicate that S1-R antagonists may be promising targets to prevent increases in ethanol intake at adolescence. The persistent effect of S1-R antagonism in free-choice drinking suggests that modulation of the S1-R is altering plastic effects associated with ethanol exposure.
Background:
Trauma related psychiatric disorders, such as posttraumatic stress disorder (PTSD), and alcohol use disorder (AUD) are highly comorbid illnesses that separately present an opposing, sex-specific pattern, with increased prevalence of PTSD in females and increased prevalence of AUD diagnoses in males. Likewise, PTSD is a risk factor in the development of AUD, with conflicting data on the impact of sex in the comorbid development of both disorders. Because the likelihood of experiencing more than one traumatic event is high, we aim to utilize chronic repeated predatory stress (CRPS) to query the extent to which sex interacts with CRPS to influence alcohol consumption, or cessation of consumption.
Methods:
Male (n = 16) and female (n = 15) C57BL/6 J mice underwent CRPS or daily handling for two weeks during adolescence (P35-P49) and two weeks during adulthood (P65-P79). Following the conclusion of two rounds of repeated stress, behavior was assessed in the open field. Mice subsequently underwent a two-bottle choice intermittent ethanol access (IEA) assessment (P90-131) with the options of 20% ethanol or water. After establishing drinking behavior, increasing concentrations of quinine were added to the ethanol to assess the drinking response to adulteration of the alcohol.
Results:
CRPS increased fecal corticosterone concentrations and anxiety-like behaviors in the open field in both male and female mice as compared to control mice that had not been exposed to CRPS. Consistent with previous reports, we observed a sex difference in alcohol consumption such that females consumed more ethanol per gram of body mass than males. In addition, CRPS reduced alcohol aversion in male mice such that higher concentrations of quinine were necessary to reduce alcohol intake as compared to control mice. CRPS did not alter alcohol-related behaviors in female mice.
Conclusion:
Collectively, we demonstrate that repeated CRPS can induce anxiety-like behavior in both sexes but selectively influences the response to ethanol adulteration in males.
Binge eating disorder (BED) is characterized, in part, by recurrent episodes of eating large quantities of food in a short period of time. Repetitive binge episodes are a common pattern of consumption during the early stages of substance abuse, and it has been proposed that binge patterns of consumption might favor the transition to BED and “food addiction”. Therefore, it is of paramount importance to provide new behavioral strategies that protect vulnerable binge-prone individuals from transitioning to BED and food addiction. Recently, we showed protective and therapeutic benefits of environmental enrichment (EE) on binge-like intake of ethanol in C57BL/6J mice, in agreement with previous evidence showing EE modulation of drug intake, drug relapse and drug reward. In the present study, adolescent mice reared under EE conditions were evaluated for binge-like consumption of sucrose during adulthood in a long-term drinking in the dark (DID) procedure that effectively models binge consumption in humans. Additionally, we tested binge-like intake in adults reared under standard conditions (SE) with long-term exposure to sucrose DID and the effects on sucrose DID of switching from SE to EE conditions. We report here, for the first time, that early EE exposure protects mice from binge-like excessive sucrose intake during adulthood. Ongoing binge-like high sucrose intake in SE-reared mice was also significantly reduced when switched to EE conditions. The present observations suggest that EE exposure might be a promising tool for preventing repetitive binge-like sucrose consumption from transitioning to BED and food addiction.
Background:
Exposure to stress during adolescence is known to be a risk factor for alcohol-use and anxiety disorders. This study examined the effects of footshock stress during adolescence on subsequent alcohol drinking in male and female mice selectively bred for high-alcohol preference (HAP1 lines). Acoustic startle responses and prepulse inhibition (PPI) were also assessed in the absence of, and immediately following, subsequent footshock stress exposures to determine whether a prior history of footshock stress during adolescence would produce enduring effects on anxiety-related behavior and sensorimotor gating.
Methods:
Alcohol-naïve, adolescent (male, n = 27; female, n = 23) and adult (male, n = 30; female, n = 30) HAP1 mice were randomly assigned to a stress or no stress group. The study consisted of 5 phases: (1) 10 consecutive days of exposure to a 30-minute footshock session, (2) 1 startle test, (3) one 30-minute footshock session immediately followed by 1 startle test, (4) 30 days of free-choice alcohol consumption, and (5) one 30-minute footshock session immediately followed by 1 startle test.
Results:
Footshock stress exposure during adolescence, but not adulthood, robustly increased alcohol drinking behavior in both male and female HAP1 mice. Before alcohol drinking, females in both the adolescent and adult stress groups showed greater startle in phases 2 and 3; whereas males in the adolescent stress group showed greater startle only in phase 3. After alcohol drinking, in phase 5, enhanced startle was no longer apparent in any stress group. Males in the adult stress group showed reduced startle in phases 2 and 5. PPI was generally unchanged, except that males in the adolescent stress group showed increased PPI in phase 3 and females in the adolescent stress group showed decreased PPI in phase 5.
Conclusions:
Adolescent HAP1 mice appear to be more vulnerable to the effects of footshock stress than adult mice, as manifested by increased alcohol drinking and anxiety-related behavior in adulthood. These results in mice suggest that stress exposure during adolescence may increase the risk for developing an alcohol-use and/or anxiety disorder in individuals with a genetic predisposition toward high alcohol consumption.
Chronic stress produces numerous adaptations within the hypothalamic-pituitary-adrenal (HPA) axis that persist well after cessation of chronic stress. We previously demonstrated profound attenuation of HPA axis responses to novel environment 4-7 days following chronic stress. The present study tests the hypothesis that this HPA axis hyporesponsivity is associated with reductions in stress-evoked c-fos mRNA expression, a marker of neuronal activation, in discrete brain regions. Adult male Sprague-Dawley rats underwent 1 week of chronic variable stress (CVS), with unhandled rats serving as controls. Independent groups of control and CVS rats were exposed to novel environment at 16 h, 4 days, 7 days, or 30 days after CVS. Marked reductions of c-fos mRNA expression in the CVS group persisted for at least 30 days within the paraventricular nucleus of the hypothalamus, and for at least 1 week in rostroventrolateral septum and lateral hypothalamus. Lower levels of c-fos mRNA expression were observed at 16 h recovery in the ventrolateral medial preoptic area, basolateral amygdala, anterior cingulate cortex, and prelimbic cortex. The results demonstrate long-term alterations in neuronal activation within neurocircuits critical for regulation of physiological and psychological responses to stressors.
This study examined the relationship between voluntary ethanol consumption and ethanol concentrations measured in the nucleus accumbens of ethanol dependent and nondependent C57BL/6J mice.
Mice were offered ethanol in a two-bottle choice; limited access paradigm and consummatory behavior was monitored with lickometers. After baseline intake stabilized, mice received chronic intermittent ethanol (EtOH group) or air (CTL group) exposure by inhalation (16 h/day for 4 days) and then resumed drinking. Brain ethanol levels during voluntary drinking were measured by microdialysis procedures and compared to brain ethanol concentrations produced during chronic intermittent ethanol vapor exposure.
Voluntary ethanol consumption progressively increased over repeated cycles of chronic intermittent ethanol exposure but remained unchanged in CTL mice. Analysis of lick patterns indicated EtOH mice consumed ethanol at a faster rate compared to CTL mice. The greater and faster rate of ethanol intake in EtOH mice produced higher peak brain ethanol concentrations compared to CTL mice, and these levels were similar to levels produced during chronic intermittent ethanol exposure.
These results show that in this model of dependence and relapse drinking, dependent mice exhibit enhanced voluntary ethanol consumption relative to nondependent controls, which consequently produces blood and brain ethanol concentrations similar to those experienced during chronic intermittent ethanol exposure.
In rodents, prolonged maternal separation has been used as a model of developmentally early environmental stress to influence adult drug intake.
The aim of the present study was to evaluate the long-term effects of prolonged maternal separation on alcohol consumption using two different self-administration procedures in mice: operant alcohol self-administration vs. three-bottle choice.
From postnatal day (PND) 1 to 14, pups were separated from the dam (maternal separation, MS) daily for 180 min or were left undisturbed, only handled during cage cleaning (animal facility rearing, AFR). On PND 60, they were assigned to one of two experimental manipulations: either a three-bottle choice or operant oral alcohol self-administration. In the three-bottle choice procedure, mice were given access to 6% or 10% alcohol or 0.05% saccharin solution for 2 h/day for 10 days. In the second experiment, mice were reinforced for nose poking by delivery of oral alcohol (6% or 10% in saccharin) or 0.05% saccharin solutions during daily 30-min sessions. Following the acquisition phase, "break points" were determined. Later, mice were allowed 1 h access to the reinforcing solution with no dosage limitation.
In the three-bottle choice procedure, MS mice showed higher alcohol intake than AFR at the 10% alcohol concentration. In the operant alcohol self-administration, MS mice achieved higher alcohol intake than AFR at the concentrations 6% and 10% during the 1-h session.
The results demonstrate the long-term consequences of MS on alcohol intake in male mice, suggesting early life stress as a risk factor for alcohol consumption and abuse.
Isolated C57BL/10 mice fed liquid diet as their only nutritional supply consumed 44% more diet than did grouped-housed mice. A similar increase due to isolation of 36% for C57BL/10 mice and 89% for DBA/1 mice was demonstrated when the sucrose in the liquid diet was replaced by an equicaloric (6% v/v) amount of ethanol. The ethanol-drinking isolated mice suffered a higher mortality rate than the grouped mice. When isolated mice were given a restricted amount of ethanol diet to match the consumption of the grouped mice, their death rate still remained higher. It was concluded that isolation increased the sensitivity to ethanol effects. The observed changes in the sensitivity to ethanol effects may have been mediated by the known isolation-induced changes in the levels of brain amines and corticosterone. Generally, DBA/1 mice were more susceptible to chronic ethanol than C57BL/10, and the young more susceptible than the adults.
Studies investigating the influence of chronic ethanol treatment on the beta-endorphin content and the proopiomelanocortin (POMC) gene expression in the rat pituitary revealed contradictory results. Because of this we decided to start a more complex study to investigate the effects of isolation stress, chronic ethanol treatment and voluntary ethanol consumption on the POMC mRNA level in the rat pituitary. The immediately prepared total RNA from rat pituitaries was used in hybridization experiments (Northern- and Dot-blots). The results suggest a correlation between the POMC gene expression and the different fashions of 'living conditions' tested. So the POMC gene expression in long-term alcohol-treated animals was decreased supporting the theory of beta-endorphin deficiency in alcoholism. More interestingly, data obtained from the group of voluntary ethanol consumption suggest an inverse correlation between total ethanol ingestion and POMC gene expression. This indicates the importance of the method of ethanol administration. Consistent with a decreased POMC gene expression in the pituitary during chronic ethanol treatment are previous studies showing a decrease in the plasma beta-endorphin content in such situations. Surprisingly, in the present study the plasma beta-endorphin levels measured by radioimmunoassay were only slightly decreased in chronically ethanol-treated rats. This may be due to dysregulatory effects of ethanol on post-translational processing, degradation and/or release of beta-endorphin.
The effects of immobilization stress, isolation stress and administration of Hoe-427 on free-choice consumption of ethanol by Lewis and Sprague-Dawley rats were studied. The animals were offered two-bottle choice consumption of 0.2% saccharin and 10% ethanol/0.2% saccharin, then exposed to 4 days of immobilization stress or isolation stress on an irregular, unpredictable schedule or 4 days of i.p. doses of Hoe-427 at 1800 hours. Both stresses resulted in significant decreases in ethanol consumption during the stress period. Hoe-427 produced a significant decrease in ethanol consumption, in a dose-dependent manner. Saccharin consumption was not significantly affected by any of the treatments. The ability to correlate the Lewis and Sprague-Dawley rat response further aids in supporting the role of the adrenocorticotropic peptide in the development of ethanol consumption.
This study was based on the findings of a high comorbidity among anxiety and depression as well as with alcohol abuse.
To evaluate first exposure alcohol preference in a rodent model of moderate neonatal maternal separation.
Rat pups were exposed to either normal animal facility rearing (AFR) or 15 min (HMS15) or 180 min (HMS180) of maternal separation from postnatal days 2-14. The adult (>60 days) male Long Evans progeny was tested for pituitary-adrenal axis responsiveness to airpuff startle, anxiety-like behavior in the elevated plus maze, and alcohol preference using a two-bottle, free-choice test.
In response to home cage airpuff startle, HMS180 rats displayed an elevation in the integrated adrenocorticotropic hormone and corticosterone responses. In addition, HMS180 rats spent less time in the open arms and more time in the closed arms in the elevated plus maze. HMS180 rats drank significantly less of a water-sucrose solution and significantly more of an ethanol-sucrose solution than AFR or HMS15 rats. No rearing group differences were observed in total fluid intake. The integrated corticosterone response to airpuff startle was highly correlated with ethanol consumption and there was a negative correlation between percentage of time spent in the open arms of the elevated plus maze and ethanol consumption. Treatment with the selective serotonin reuptake inhibitor paroxetine for 21 days eliminated differences in the elevated plus maze and HPA axis responsiveness, and significantly reduced the amount of ethanol consumed by the HMS180 rats, without affecting these parameters in the HMS15 rats.
These observations suggest that this maternal separation paradigm is a good model to study the effects of early adverse experience on the development of alcohol preference and anxiety.
There is substantial evidence that early life events influence brain development and subsequent adult behaviour and play an important role in the causation of certain psychiatric disorders including schizophrenia and depression. The underlying mechanism of the effects of these early environmental factors is still not understood. It is a challenge to attempt to model early environmental factors in animals to gain understanding of the basic mechanisms that underlie the long-term effects. This paper reviews the effects of rearing rats from weaning in social isolation and reports some recent results indicating hippocampal dysfunction. Isolation rearing in rats from weaning produces a range of persistent behavioural changes in the young adult, including hyperactivity in response to novelty and amphetamine and altered responses to conditioning. These are associated with alterations in the central aminergic neurotransmitter functions in the mesolimbic areas and other brain regions. Isolation-reared rats have enhanced presynaptic dopamine (DA) and 5-HT function in the nucleus accimbens (NAC) associated with decreased presynaptic 5-HT function in the frontal cortex and hippocampus. Isolation-reared rats have reduced presynaptic noradrenergic function in the hippocampus, but have enhanced presynaptic DA function in the amygdala. These neurochemical imbalances may contribute to the exaggerated response of the isolated rat to a novel stimulus or to stimuli predictive of danger, and isolation-induced behavioural changes. These changes have neuroanatomical correlates; changes which seem to parallel to a certain degree those seen in human schizophrenia. A greater understanding of the processes that underlie these changes should improve our knowledge of how environmental events may alter brain development and function, and play a role in the development of neuropsychiatric disorders.
Food-deprived C57BL/6 (C57) mice of either sex responded for oral ethanol rewards delivered on ratio schedules of reinforcement, thus extending to female C57 mice effects previously reported only for male members of the strain. Lever responding for ethanol reward was influenced by thirst motivation (post- vs. preprandial tests), time of access to ethanol reward, ethanol concentration, and reinforcement schedule. A particularly high response output for 12% ethanol delivered on a PR2 schedule (e.g., ∼ 1400/15 min test session) indicates its efficacy as a reinforcer for C57 mice. Estimated consumption of ethanol differed from lever responding when reward access time was relatively long (10 s) and response demand of the reinforcement schedule was low, but paralleled lever responding when reward access time was restricted (3 s) and response demands were greater. Gender influenced lever responding for ethanol reward and its consumption, the difference depending upon reward access time and reinforcement schedule. When the response demands were low and the reward access time long, females tended to respond more than males for ethanol reward; with greater response demands and shorter reward access time, males tended to respond more. In conjunction with our companion report, the present study helps define the behavioral conditions under which ethanol is rewarding for C57 mice and establish the conditions under which ethanol reward differs for male and female mice.
Both sexes of C57BL/6 (C57) mice consumed substantial quantities of ethanol without food or water deprivation whether access was continuous or limited. Food deprivation increased the amount of ethanol consumed, and the amount consumed depended upon when the animals were tested with reference to their daily food allotment. Ethanol consumption was greater if the mice were tested postprandially, high thirst motivation, rather than preprandially (∼10 vs. ∼4.5 g/kg/30 min). Preference for ethanol over water, however, was greater when mice were under low thirst motivation (i.e., tested preprandially or with water available during the test). Compared to males, female mice consumed more of a high-ethanol concentration solution (10%) when access was continuous or limited to the first hour of the dark (active) phase of the circadian cycle. Also, in contrast to males, female mice exhibited increased ethanol consumption across days of drinking experience. Finally, although ethanol consumption under the food deprivation conditions of this experiment did not differ according to sex, females had higher blood ethanol concentrations than male C57 mice, a finding not previously reported for rodents but common to humans.
Isolating an animal refers to the situation where the animal is physically fully demarcated from conspecifics without physical, visual, olfactory and auditory contact. Animals housed in separate cages in the same room are, although deprived of physical and visual contact, still in olfactory and auditory contact, and thus not totally isolated. During the fifties and sixties several studies claimed to show physiological and behavioural differences between individually and group housed rats and mice. The so-called ‘Isolation Syndrome’ characterised by changes in corticosterone levels, metabolism, growth, and behaviour was introduced, rather as a model for psychoneurosis than through any concern for animal welfare. Today, it is often stated as common knowledge in laboratory animal science textbooks that individual housing as well as isolation of rats and mice has an effect on physiology and behaviour. It is, however, unclear whether this effect actually impairs animal welfare.
The aim of this paper is to analyse studies on individual housing of mice and rats to evaluate whether there is documented proof that individual housing affects welfare, and, alternatively whether it is possible to house these animals individually without negative impact on welfare, eg by providing special housing improvements.
A range of studies have shown that individual housing or isolation has effects on corticosterone, the open field behaviour, barbiturate sleeping time and the metabolism of different pharmaceuticals in the animals. However, this review of 37 studies in rats and 17 studies in mice showed divergence in test results difficult to explain, as many studies lacked basal information about the study, eg information on genetic strains and housing conditions, such as bedding, enrichment and cage sizes. Furthermore, test and control groups most frequently differed in cage sizes and stocking densities, and behavioural tests differed in ways which may very well explain the differences in results. Overall, there seemed to be an effect of individual housing, although it may be small, and it seems reasonable to assume that, through making small changes in the procedures and housing environments, the effects can be minimised or even eliminated. More well-controlled and standardised studies are needed to give more specific answers to the questions this issue poses.
Models for early stress and voluntary drinking were used to determine the contribution of early stress to increased intake of alcoholic beverages during puberty and adulthood. Newborn litters of Long Evans rats were: (1) stressed by daily separation from the mother for 15 midday on days 1 to 7 of life [“handled” (H)]; or (2) left untouched with the mother on days 1 to 7 of life [“nonhandled” (NH)]. All animals were weaned on day 22, separated by sex (M and F), and caged individually with an assignment of 10 animals per sex per treatment group (H and NH). From 25 to 85 days of age, all animals were given free access to beer containing 5% ethanol (v/v), water, and regular laboratory food. Beer, food, and water intake was measured daily at the same time each day, and animals were weighed weekly. HM had greater ethanol intake and preference for ethanol during the peripu-bertal period (days 32 to 45), compared with all other groups. There were no differences in ethanol intake between NHF and NHM. HM had greater ethanol preference than HF on 22 of the 60 drinking days. HF consumed the same amount of water as the males and significantly greater amounts of water than NHF on 28 of the 60 drinking days. HM had greater ethanol preference than NHM on 8 of the 60 drinking days. From day 75 to day 85, HF had greater ethanol intake than HM, and NHF had greater ethanol intake than NHM. There were no differences in body weights of HF and NHF throughout the study. Growth of HM lagged behind NHM into adulthood. Early stress of males was linked to increased ethanol intake during the peripubertal and adult periods and stunted body growth into adulthood. Early stress of females was linked to polydipsia (water) throughout development and continuing into adulthood, and to increased alcohol intake in adulthood.
The effects of exposure to four environmental rearing conditions on subsequent voluntary ethanol intake and response to immobilization stress were examined. Male weanling rats were reared in an enriched environment, with a female partner, with a male partner, or individually, for 90 days. At 111 days of age, voluntary consumption of ethanol in increasing concentrations (3 to 9%, v/v) was assessed. Following the ethanol-exposure period, rats were randomly divided into stressed and nonstressed groups and exposed to 3 h of immobilization. Results indicated that the enriched animals consumed greater amounts of ethanol as compared to all other groups, suggesting that the enriched environment and not handling, housing conditions, or the presence of another male or female is responsible for the observed increase in ethanol drinking behavior. Ulcer data indicated that among environmentally enriched rats, ethanol attenuated stress ulcer development relative to their non-ethanol-exposed but stressed controls. In nonstressed enriched rats, ethanol alone exacerbated stomach damage. We suggest that environmental rearing conditions markedly influence the complex interaction between ethanol intake and the response to stress.
The present research studied the influence of an early chronic variable stress (CVS) paradigm — an animal model of depression — on behavioral responses to subsequent environmental challenges suggested to model anhedonia and emotional reactions such as anxiety and fear. In order to explore a potential involvement of an endogenous opiate mechanism — presumably activated during CVS exposure — in the development of such behavioral reactions, in all experiments rats were administered naltrexone (NAL, 2 mg/kg, i.p.) or vehicle (VH) prior to each daily stressor of the CVS procedure. Animals were exposed to CVS and 1 week later tested for sucrose preference (1%) in a free choice paradigm after the presentation or not of a 90-min restraint period. Only CVS treated animals that were later exposed to restraint showed a reduction of sucrose preference, this reduction was absent when CVS rats were pretreated previously with NAL. Moreover, CVS rats were one week later tested on the elevated plus maze (EPM) and in their conditioned and unconditioned freezing response to a single shock session. Early chronic stress resulted in an anxiogenic behavior in the EPM and in an enhanced conditioned and unconditioned freezing which were all abolished by NAL pretreatment. These behavioral findings suggest that the potential activation of an endogenous opiate mechanism during CVS participates in the development of anhedonia and exaggerated emotional reactions in response to subsequent stressful experiences.
Chronic stress precipitates pronounced enhancement of central stress excitability, marked by sensitization of hypothalamic-pituitary-adrenocortical (HPA) axis responses and increased adrenocorticotropic hormone (ACTH) secretagogue biosynthesis in the paraventricular nucleus of the hypothalamus (PVN). Chronic stress-induced enhancement of HPA axis excitability predicts increased excitatory and/or decreased inhibitory innervation of the parvocellular PVN. We tested this hypothesis by evaluating chronic variable stress (CVS)-induced changes in total (synaptophysin), glutamatergic (VGluT2), GABAergic (GAD65), and noradrenergic (DBH) terminal immunoreactivity on PVN parvocellular neurons using immunofluorescence confocal microscopy. CVS increased the total PVN bouton immunoreactivity as well as the number of glutamatergic and noradrenergic immunoreactive boutons in apposition to both the corticotropin-releasing hormone (CRH)-immunoreactive cell bodies and dendrites within the parvocellular PVN. However, the number of GABAergic-immunoreactive boutons in the PVN was unchanged. CVS did not alter CRH median eminence immunoreactivity, indicating that CVS does not enhance CRH storage within the median eminence. Taken together, the data are consistent with a role for both glutamate and norepinephrine in chronic stress enhancement of HPA axis excitability. These changes could lead to an enhanced capacity for excitation in these neurons, contributing to chronic stress-induced hyperreactivity of stress effector systems in the brain.
The hypothalamo-pituitary-adrenocortical (HPA) axis is responsible for initiation of glucocorticoid stress responses in all vertebrate animals. Activation of the axis is regulated by diverse afferent input to the hypothalamic paraventricular nucleus (PVN). This review discusses brain mechanisms subserving generation and inhibition of stress responses focusing on the contribution of the limbic system and highlighting recent conceptual advances regarding organization of stress response pathways in the brain. First, control of HPA axis responses to psychogenic stimuli is exerted by a complex neurocircuitry that involves oligosynaptic networks between limbic forebrain structures and the PVN. Second, individual stress-modulatory structures can have a heterogeneous impact on HPA axis responses, based on anatomical micro-organization and/or stimulus properties. Finally, HPA axis hyperactivity pursuant to chronic stress involves a substantial functional and perhaps anatomical reorganization of central stress-integrative circuits. Overall, the data suggest that individual brain regions do not merely function as monolithic activators or inhibitors of the HPA axis and that network approaches need be taken to fully understand the nature of the neuroendocrine stress response.
Background:
Postweaning social isolation in rats produces profound and long-lasting cognitive and behavioral deficits in adult animals. Importantly, this housing manipulation alters sensitivity to a number of drugs of abuse including ethanol. However, most studies with ethanol have utilized continuous or limited home-cage access to examine interactions between juvenile social experience and drinking. More recently, social isolation was shown to increased ethanol responding in a "dipper" model of self-administration (Deehan et al., 2007). In the current study, we utilize a "sipper" operant self-administration model to distinguish the effects of isolation rearing on ethanol seeking- and drinking-related behaviors.
Methods:
Postweaning juvenile male Long-Evans rats were placed into 2 housing groups for 6 weeks: one group consisted of individually housed animals; the second group was housed 4 animals per cage. Following the isolation period, anxiety-like behavior was assessed to confirm the efficacy of the isolation procedure. In some animals, ethanol drinking in the home cage was assessed using a continuous access, 2-bottle choice paradigm. All animals were then individually housed and trained to lever-press for a sipper tube containing either an ethanol solution or a sucrose solution.
Results:
Postweaning social isolation increased the expression of anxiety-like behavior in the elevated plus maze but not the light-dark box. Ethanol consumption was also increased during continuous home-cage access with the 2-bottle choice paradigm. During operant self-administration, isolation housing increased the response rate and increased ethanol consumption but did not alter responding for or consumption of sucrose. The housing manipulation did not change the total number of lever responses during extinction sessions. Paired-pulse inhibition deficits that are characteristic of juvenile isolation remained intact after prolonged experience with sucrose self-administration.
Discussion:
The effects of postweaning social isolation on ethanol drinking in the home cage are also manifest during operant self-administration. Importantly, these alterations in adult operant self-administration are ethanol-specific.
A challenging question that continues unanswered in the field of addiction is why some individuals are more vulnerable to substance use disorders than others. Numerous risk factors for alcohol and other drugs of abuse, including exposure to various forms of stress, have been identified in clinical studies. However, the neurobiological mechanisms that underlie this relationship remain unclear. Critical neurotransmitters, hormones and neurobiological sites have been recognized, which may provide the substrates that convey individual differences in vulnerability to addiction. With the advent of more sophisticated measures of brain function in humans, such as functional imaging technology, the mechanisms and neural pathways involved in the interactions between drugs of abuse, the mesocorticolimbic dopamine system and stress systems are beginning to be characterized.
This review provides a neuroadaptive perspective regarding the role of the hormonal and brain stress systems in drug addiction with a focus on the changes that occur during the transition from occasional drug use to drug dependence. We also review factors that contribute to different levels of hormonal/brain stress activation, which has implications for understanding individual vulnerability to drug dependence. Ultimately, these efforts may improve our chances of designing treatment strategies that target addiction at the core of the disorder.
The impact of ostensibly aversive social stresses on triggering, amplifying and prolonging intensely rewarding drug taking is an apparent contradiction in need of resolution. Social stress encompasses various types of significant life events ranging from maternal separation stress, brief episodes of social confrontations in adolescence and adulthood, to continuous subordination stress, each with its own behavioral and physiological profile. The neural circuit comprising the VTA-accumbens-PFC-amygdala is activated by brief episodes of social stress, which is critical for the DA-mediated behavioral sensitization and increased stimulant consumption. A second neural circuit comprising the raphe-PFC-hippocampus is activated by continuous subordination stress and other types of uncontrollable stress. In terms of the development of therapeutics, brief maternal separation stress has proven useful in characterizing compounds acting on subtypes of GABA, glutamate, serotonin and opioid receptors with anxiolytic potential. While large increases in alcohol and cocaine intake during adulthood have been seen after prolonged maternal separation experiences during the first two weeks of rodent life, these effects may be modulated by additional yet to be identified factors. Brief episodes of defeat stress can engender behavioral sensitization that is relevant to escalated and prolonged self-administration of stimulants and possibly opioids, whereas continuous subordination stress leads to anhedonia-like effects. Understanding the intracellular cascade of events for the transition from episodic to continuous social stress in infancy and adulthood may provide insight into the modulation of basic reward processes that are critical for addictive and affective disorders.
Relationships between social deprivation, dominance, and voluntary intake of ethanol (ETOH) and diazepam (D) were studied in male adult Wistar rats. Social behavior was registered by tetradic encounters in the open field prior to the rats' drug experiences. Social deprivation was induced by individual housing (LI) and contact caging (C). Nondeprived rats were housed in groups of four individuals (G) each. Social deprivation facilitated ETOH intake: LI rats consumed 30% more ETOH than G. Increase of deprivation by change of housing condition additionally raised ETOH consumption. ETOH experiences did not affect subsequent D choice. However, rats with a high ETOH consumption also preferred D. Individual drug disposition correlated with social dominance (in G: to social activity). Even in individual isolation dominant rats took less drugs than subordinate ones, but these rats raised their ETOH consumption when the housing conditions were changed. After nine months of voluntary ETOH intake and subsequently nine months without access to ETOH the rats showed signs of "behavioral dependence." Compared to naive animals they took twice as much ETOH and even after adulterating ETOH by quinine a high preference was perpetuated. During this state modifying social factors were no longer effective.
To study the effects of different kinds of social deprivation on voluntary ethanol (ETOH) intake male Wistar rats were housed by (a) individual caging, (b) "contact" caging (partial social deprivation), and (c) group caging (four individuals per cage). In the latter condition the individuals were separated once a week from each other for 24 h. The rats simultaneously received water 5%, 10% and 20% ETOH for a period of 14 weeks. Additional control animals received water. Isolated individuals drank significantly more alcohol than group-housed or contact-caged rats. After a few days they preferred the 20% solution. Circadian measures revealed a discontinuous intake of high doses (greater than 0.5 g/kg/h) during short time periods. Contact-caged rats consumed much less ETOH, but both the preference for 20% ETOH and the circadian course of intake were similar to those occurring after isolation. ETOH intake of group-housed individuals was low. These individuals preferred the 5% solution and continuously consumed small ETOH doses. During the period of short-term isolation they drank even more ETOH than long-term isolated individuals. In contrast to the latter, the enhancement of intake decreased after some weeks. It is suggested that the differences between the housing groups not only reflect different degrees of isolation stress, but may also be explained by a contribution of different reinforcing or aversive psychotropic effects of ETOH. Reduction of isolation stress is probably most important in the situation of short term separation, whereas dose-dependent reinforcement via social stimulation or sedation may affect the drug taking behavior under the other social conditions.
Studies of the influence of housing conditions on ethanol self-administration have been inconsistent, with findings that isolation housing increases, decreases or produces no effects on ethanol intake. One possible explanation for these discrepant findings is that the effects of housing are dependent on the age at which the manipulation is performed. In the present experiment rats were housed from weaning or from age 65 days in either an isolated or grouped condition. After 12 weeks, they were tested for the voluntary oral self-administration of ethanol. Although all rats consumed comparable quantities of ethanol when lower concentrations were available, the rats isolated from weaning consumed significantly greater amounts of more concentrated ethanol than their group-housed counterparts. In contrast, there was no difference in ethanol consumption between isolated and grouped rats when they were differentially housed at maturity. These data suggest that an important determinant of ethanol intake in rats is related to environmental factors and that the influence of these factors is age-dependent.
1. Previous studies conducted in our laboratory demonstrated that rats given a choice between a 0.1% saccharin solution or 10% ethanol/0.1% saccharin solution and repeatedly exposed on an unpredictable basis to stressful stimuli, consumed increasing quantities of the ethanol solution following cessation of stressor presentation as compared to nonstressed control rats. 2. Stressful stimuli potently activate the hypothalamic-pituitary-adrenocortical (HPA) axis, thus a systematic investigation of the HPA axis and its involvement in post-stress induced ethanol consummatory behavior was undertaken. 3. Exposure to repetitive unpredictable stressful stimuli did not induce the free-choice consumption of ethanol in either hypophysectomized rats or chronic dexamethasone treated rats. 4. Adrenalectomized rats exposed to chronic unpredictable stressful stimuli consumed increased quantities of ethanol following cessation of stressful stimuli in both a quantitative and qualitative manner which mirrored that of intact animals. 5. Repeated intravenous administration of exogenous adrenocorticotropin (ACTH1-39) on an unpredictable basis also induced ethanol consuming behavior, following the discontinuation of its administration. 6. These results suggest that elimination of the pituitary or pharmacological antagonism of stress-induced HPA activation will prevent post-stress induced ethanol consummatory behavior. 7. Conversely, activation of a functional hypothalamic-pituitary system or repeated administration of exogenous ACTH1-39 will initiate ethanol consumption in rats. 8. Thus, hormones secreted from the pituitary, namely ACTH, appear to play a crucial role in the post-stress induced initiation of ethanol consuming behavior in rats.
As a result of selective breeding, NC900 mice exhibit isolation-induced attacks in a social interaction test, whereas NC100 mice do not attack but freeze instead. Administration of the D1 receptor agonist dihydrexidine was previously shown to reduce aggression in NC900 mice and nonagonistic approaches in NC100 mice. This resulted from induction of a marked social reactivity in both selected lines. Because isolation rearing also induces social reactivity, the present experiment was designed to test the hypothesis that D1 dopamine receptors mediate isolation-induced social reactivity. Isolation was expected to potentiate the effects of a D1 agonist and to increase D1 dopamine receptor density. Thus, isolated and group-reared mice were administered dihydrexidine, and their social behavior was compared to vehicle-injected controls. Dihydrexidine induced higher levels of reactivity among isolated than among group-reared animals, especially in NC900 mice. In independent experiments, increased densities of D1 dopamine receptors in the striatum of isolated animals were found, with no change in affinity. These studies suggest an important role for the D1 dopamine receptor as a mediator of isolation-induced social reactivity.
Adult male rats were exposed to a chronic variable stress treatment, an animal model of depression, with or without concurrent daily administration of desipramine. Animals given chronic and variable stress were submitted daily to a different stressor following an injection of either saline or desipramine (5 mg/kg, i.p.), whereas control animals were unmanipulated except for the injection process. One day after the last event of the chronic procedure, control and stressed animals were administered saline or morphine (0.75 or 1.5 mg/kg, i.p.) and their locomotion assessed for 90 min. In an additional experiment, 24 h after the last stressor, stressed and control rats were challenged with either saline or one of two higher doses (behaviorally suppressant) of morphine (5 and 10 mg/kg, i.p.). A significantly greater increase in locomotor activity following a low dose (1.5 mg/kg) of morphine was observed in chronically stressed rats as compared to control rats. This potentiated locomotor response to morphine in stressed rats was prevented by desipramine pretreatment. The chronic and variable stress treatment did not modify the sedative response to the high doses of morphine. These data support the suggestion that a chronic and variable stress procedure results in sensitization to the stimulant effect of opioid stimulation, and that pretreatment with the antidepressant agent desipramine blocks the development of this sensitization.
In this critical review the authors evaluate the literature regarding the relationship between lifelong DSM-III-R anxiety disorders and alcohol dependence. Many alcohol-dependent individuals demonstrate severe anxiety symptoms in the context of acute or protracted abstinence syndromes, but it is unclear whether these anxiety conditions are independent psychiatric disorders or temporary syndromes likely to disappear on their own.
Reports since 1975 describing the relationship between alcoholism and anxiety disorders were reviewed to determine whether 1) lifelong anxiety disorders are unusually prevalent among alcohol-dependent individuals, 2) children of alcoholics are more likely to develop anxiety disorders than comparison populations, 3) anxiety syndromes are likely to disappear with abstinence, 4) the rate of alcohol dependence among subjects with lifelong anxiety disorders is higher than normal, 5) there is familial crossover between alcohol dependence and anxiety disorders, and 6) alcoholism is often preceded by anxiety disorders in groups from the general population studied prospectively.
The interaction between alcohol use and anxiety disorders is complex. The available data, while imperfect, do not prove a close relationship between life-long anxiety disorders and alcohol dependence. Further, prospective studies of children of alcoholics and individuals from the general population do not indicate a high rate of anxiety disorders preceding alcohol dependence.
The high rates of comorbidity in some studies likely reflect a mixture of true anxiety disorders among alcoholics at a rate equal to or slightly higher than that for the general population, along with temporary, but at times severe, substance-induced anxiety syndromes.
The present study investigated the influence of early weaning and separation from mother and littermates on voluntary ethanol intake and general activity during prepuberal age, and adult age corticosterone levels. On day 16 after birth the male offspring of a litter were divided in three groups, each subjected to a different rearing condition: 1)early weaned and isolated from its littermates; 2) early weaned but growing up together with two littermates; 3) staying with mother and two littermates. On day 25 the animals were tested for general activity including assessment of fearfulness. From day 30 all animals were given a free choice between water and ethanol solution. The ethanol concentration was increased by 2% during each of the following weeks until 10% was reached during the 5th week. Ten days later, after cessation of alcohol testing, blood samples were taken from the tail for assessment of plasma levels corticosterone. The isolated, early weaning pups displayed higher activity levels than both normally reared pups and group-living, early weaning pups. The quotient peripheral locomotion/total locomotion was lower for the isolated pups compared with the other groups, suggesting less fearfulness in the early weaned, isolated pups. For 2%, 4%, and 6% ethanol solutions the normal-reared rats consumed more ethanol and displayed higher ethanol preference than either of the early weaned groups of animals. No group differences were observed either at 8% or 10% ethanol solutions. Levels of plasma corticosterone in adult age in the early weaned rats were slightly reduced, not reaching statistical significance, compared to the normally weaned animals.
These experiments examined the hypothesis that isolation-rearing and strain influence hedonic mechanisms. In experiment 1, voluntary consumption of ethanol and water was monitored in the home cage of Fawn Hooded (FH) and Wistar rats. FH rats were found to consume more ethanol at low concentrations than Wistar rats, independent of rearing condition, and isolation-reared rats were found to consume more of high ethanol concentrations, independent of strain. In experiment 2, isolation-reared rats were found to consume more sucrose, independent of concentration, than socially reared rats. In experiment 3, Fawn Hooded rats were found to be more sensitive to low concentration solutions of saccharin, and to consume less of the high concentration solutions, while isolation-rearing was found to enhance consumption of high concentrations. Thus, hedonic processes are independently modulated by strain and rearing conditions, although the effects of isolation-rearing appear to be exacerbated in Fawn Hooded rats.
Voluntary ethanol (EtOH) consumption is increased by isolation-rearing in several rat strains. The following experiments examined the effects of isolation-rearing on basal and ethanol-stimulated behavior in Fawn Hooded rats, an alcohol-preferring rat strain, compared to Wistar rats. Locomotor activity and anxiety were examined under both conditions. Basal locomotor activity was higher in isolated subjects of both strains in low light conditions, but under bright light conditions, this difference was only observed in Wistar rats. Locomotor stimulant effects of EtOH were only observed in isolation-reared rats. In the elevated plus maze, Fawn Hooded rats were more anxious than Wistar rats under low light conditions, but under bright light conditions, Wistar socials were less anxious than all of the other groups. Administration of 1.5 mg/kg EtOH produced an anxiolytic response in the elevated plus maze under bright light conditions in Fawn Hooded rats, but to a lesser degree Wistar rats, particularly Wistar isolates. In conclusion, although both strain and isolation-rearing had effects on locomotion and anxiety as well as the stimulatory and anxiolytic effects of EtOH, these effects appeared to be independent.
Food-deprived C57BL/6 (C57) mice of either sex responded for oral ethanol rewards delivered on ratio schedules of reinforcement, thus extending to female C57 mice effects previously reported only for male members of the strain. Lever responding for ethanol reward was influenced by thirst motivation (post- vs. preprandial tests), time of access to ethanol reward, ethanol concentration, and reinforcement schedule. A particularly high response output for 12% ethanol delivered on a PR2 schedule (e.g., approximately 1400/15 min test session) indicates its efficacy as a reinforcer for C57 mice. Estimated consumption of ethanol differed from lever responding when reward access time was relatively long (10 s) and response demand of the reinforcement schedule was low, but paralleled lever responding when reward access time was restricted (3 s) and response demands were greater. Gender influenced lever responding for ethanol reward and its consumption, the difference depending upon reward access time and reinforcement schedule. When the response demands were low and the reward access time long, females tended to respond more than males for ethanol reward; with greater response demands and shorter reward access time, males tended to respond more. In conjunction with our companion report, the present study helps define the behavioral conditions under which ethanol is rewarding for C57 mice and establish the conditions under which ethanol reward differs for male and female mice.
Both sexes of C57BL/6 (C57) mice consumed substantial quantities of ethanol without food or water deprivation whether access was continuous or limited. Food deprivation increased the amount of ethanol consumed, and the amount consumed depended upon when the animals were tested with reference to their daily food allotment. Ethanol consumption was greater if the mice were tested postprandially, high thirst motivation, rather than preprandially (approximately 10 vs. approximately 4.5 g/kg/30 min). Preference for ethanol over water, however, was greater when mice were under low thirst motivation (i.e., tested preprandially or with water available during the test). Compared to males, female mice consumed more of a high-ethanol concentration solution (10%) when access was continuous or limited to the first hour of the dark (active) phase of the circadian cycle. Also, in contrast to males, female mice exhibited increased ethanol consumption across days of drinking experience. Finally, although ethanol consumption under the food deprivation conditions of this experiment did not differ according to sex, females had higher blood ethanol concentrations than male C57 mice, a finding not previously reported for rodents but common to humans.
To successfully negotiate the developmental transition between youth and adulthood, adolescents must maneuver this often stressful period while acquiring skills necessary for independence. Certain behavioral features, including age-related increases in social behavior and risk-taking/novelty-seeking, are common among adolescents of diverse mammalian species and may aid in this process. Reduced positive incentive values from stimuli may lead adolescents to pursue new appetitive reinforcers through drug use and other risk-taking behaviors, with their relative insensitivity to drugs supporting comparatively greater per occasion use. Pubertal increases in gonadal hormones are a hallmark of adolescence, although there is little evidence for a simple association of these hormones with behavioral change during adolescence. Prominent developmental transformations are seen in prefrontal cortex and limbic brain regions of adolescents across a variety of species, alterations that include an apparent shift in the balance between mesocortical and mesolimbic dopamine systems. Developmental changes in these stressor-sensitive regions, which are critical for attributing incentive salience to drugs and other stimuli, likely contribute to the unique characteristics of adolescence.
Dopamine dysfunction in the nucleus accumbens is thought to underlie the altered propensity of isolation-reared rats to self-administer psychomotor stimulants.
To identify specific changes in monoamine and glutamate function in the nucleus accumbens and c-fos induction in the amygdala and striatum which may be correlated with altered cocaine self-administration in isolates.
In three separate studies, group-reared and isolation-reared rats were trained to self-administer cocaine (0.083. 0.25 or 1.5 mg/kg per IV infusion; FR1), intracerebral microdialysis was used to measure cocaine-induced changes in extracellular levels of dopamine, serotonin and glutamate in the nucleus accumbens and the expression of the immediate-early gene c-fos was quantified using quantitative immunocytochemistry of its protein product Fos in several amygdala and striatal brain regions following cocaine administration.
Isolation-reared rats showed an enhanced sensitivity to self-administer the lowest dose of cocaine but showed retarded acquisition at the highest dose. Isolation rearing produced no effect on basal levels of dopamine, serotonin or glutamate in the nucleus accumbens but potentiated the increase in dopamine efflux, though not serotonin efflux, induced by cocaine. Cocaine increased FOS expression in most amygdala and striatal brain regions examined that were relatively greater in isolation-reared rats in core and shell regions of the nucleus accumbens, medial and lateral regions of the dorsal striatum as well as the central nucleus of the amygdala.
These data are consistent with the hypothesis that isolation rearing produces enduring changes in the sensitivity of dopamine-mediated functions in amygdala-striatal circuitry that may be directly related to the altered reinforcing properties of cocaine and other psychomotor stimulants.
The present research studied the influence of an early chronic variable stress (CVS) paradigm - an animal model of depression - on behavioral responses to subsequent environmental challenges suggested to model anhedonia and emotional reactions such as anxiety and fear. In order to explore a potential involvement of an endogenous opiate mechanism - presumably activated during CVS exposure - in the development of such behavioral reactions, in all experiments rats were administered naltrexone (NAL, 2 mg/kg, i.p.) or vehicle (VH) prior to each daily stressor of the CVS procedure. Animals were exposed to CVS and 1 week later tested for sucrose preference (1%) in a free choice paradigm after the presentation or not of a 90-min restraint period. Only CVS treated animals that were later exposed to restraint showed a reduction of sucrose preference, this reduction was absent when CVS rats were pretreated previously with NAL. Moreover, CVS rats were one week later tested on the elevated plus maze (EPM) and in their conditioned and unconditioned freezing response to a single shock session. Early chronic stress resulted in an anxiogenic behavior in the EPM and in an enhanced conditioned and unconditioned freezing which were all abolished by NAL pretreatment. These behavioral findings suggest that the potential activation of an endogenous opiate mechanism during CVS participates in the development of anhedonia and exaggerated emotional reactions in response to subsequent stressful experiences.
Semi-quantitative hybridization histochemical analyses were undertaken to determine expression levels of mRNA transcripts encoding the beta1-3 subunits of the GABA(A)receptor within the rat hypothalamic paraventricular nucleus (PVN) and hippocampal formation following exposure to a chronic non-habituating stress protocol. After delivery of a battery of stressors on a randomized schedule over a 3-week period, expression levels of the beta1 subunit of the GABA(A) receptor were found to be decreased in the medial parvocellular PVN (mpPVN) by 48.3% relative to control animals. Levels of beta2 mRNA following chronic stress were also found to be decreased in the mpPVN (29.8%), but increased in hippocampal subfields CA(1) and CA(3) (33.9 and 23.2%, respectively) and increased (24%) in the dentate gyrus. The results suggest that GABA(A) receptor subunit composition may be altered at a key regulatory site, and may have important implications for studies aimed at understanding GABAergic inhibitory influences upon the hypothalamic-pituitary-adrenocortical (HPA) axis. Hypophysiotropic CRH neurons serve as the origin of the final common pathway for glucocorticoid secretion in response to stressful stimuli, and GABAergic afferents have been implicated in afferent control of these neurons. Regulation of GABA(A) receptors at these sites may alter the efficacy of a major inhibitory influence upon the stress axis, and thereby modulate stress-induced glucocorticoid secretion.
Previous work has shown that environmental enrichment alters amphetamine-induced locomotor activity and conditioned place preference.
The present study examined the effect of environmental enrichment on amphetamine self-administration.
Female and male rats were raised from 21 days of age in one of three different conditions: an enriched condition (EC) containing novel objects and social partners, a social condition (SC) containing social partners only, or an isolated conditioned (IC) without objects or social partners. Beginning at 51 days of age, rats were then tested for operant responding for a sucrose reinforcer using an incremental fixed ratio (FR) requirement across four sessions. Rats were then implanted with a chronic indwelling intravenous catheter and were allowed to self-administer amphetamine (0.03 or 0.1 mg/kg per infusion) for five FR1 sessions, followed by a progressive ratio (PR) session.
EC rats initially showed an increase in sucrose-reinforced responding relative to IC rats and this environment-induced difference was greater in females than in males. However, in both sexes, the environment-induced difference in sucrose-reinforced responding dissipated completely across repeated sessions. With amphetamine self-administration, both EC and SC rats earned fewer infusions than IC rats across repeated FRI sessions using the low dose of amphetamine (0.03 mg/kg per infusion), but not using the higher dose of amphetamine (0.1 mg/kg per infusion). EC rats also earned fewer self-infusions of the low amphetamine dose on the PR session relative to IC rats. The effects of environmental enrichment on amphetamine self-administration were similar in both females and males.
These results suggest that environmental enrichment may serve as a protective factor for reducing amphetamine self-administration.
It has long been believed that stress and drug abuse are related. Studies using animal models have repeatedly demonstrated that stressed animals more readily self-administer alcohol or other drugs. Similarly, human patients consistently report in clinical interviews that stress is one reason for taking drugs. There are also studies that document neurophysiological, neuroanatomical, neurochemical, and physiological changes to animals and humans who are stressed. Many of these changes occur within biological systems that are also affected by psychoactive drugs. Early response to stress also modifies neurodevelopment in permanent ways, and these neuroadaptations occur within the same neuronal systems which comprise the drug-reward circuit. But absent are studies in humans that link early stress and modifications of neurodevelopment with increased vulnerability to drug abuse. This article provides a glimpse of research relating stress to alteration of brain functions and to drug abuse, and points to the work of others in this volume for more details. We hope this attempt to understand how early stress affects the developing brain and increases vulnerability to drug abuse will lead to a new program of research in this emerging area.
In humans, chronic intermittent and uncontrollable stress during adolescence is viewed as a key factor for vulnerability to drug abuse and development of psychopathologies later in life. Less is known about the long-term effects of chronic stress in animals during the juvenile period. Although there is evidence of cross sensitization during prenatal period and adulthood between chronic stress and amphetamine-induced behavioral sensitization in the rat, no studies have been conducted on cross sensitization between chronic variable stress in adolescence and behavioral sensitization to amphetamine. To address this question, at the onset of adolescence (28 days) male rats were subjected to 28 days of intermittent non-habituating social stress (isolation, novel environment, crowding, litter-shifting, subordination), or physical stress (restraint, swim, cold, ether, noise), or were handled as controls. Twenty-four hours after the last stressor or handling, all groups were exposed to a novel environment for 1 h, after which they underwent a regimen of behavioral sensitization to amphetamine. Our results showed that socially stressed rats have low locomotor activity in the novel environment, when compared to the control and physical groups who were identical in the same test. Even though socially stressed rats had lower locomotor activity in response to amphetamine injections, there were no significant differences during the training phase between the three groups at this dose of amphetamine. However, when tested for behavioral sensitization to amphetamine control and physically stressed rats showed a robust sensitization, socially stressed rats were significantly inhibited. We conclude that our chronic variable social stress protocol during adolescence inhibits behavioral sensitization to amphetamine during adulthood.
Corticotropin releasing factor is a neuropeptide associated with the integration of physiological and behavioural responses to stress. More recently, corticotropin releasing factor has been implicated in the actions of abused drugs, including ethanol. Moreover, previous studies have demonstrated that the non-selective corticotropin releasing factor receptor antagonist, alpha-helical corticotropin releasing factor(9-41), can diminish some of the behavioural effects associated with ethanol withdrawal, whilst the selective corticotropin releasing factor(1) receptor antagonist CP-154,526 has been beneficial in decreasing stress-induced relapse into alcohol-seeking behaviour. However, as yet the ability of selective corticotropin releasing factor compounds to modulate volitional ethanol consumption has not been investigated. For these reasons the present study aims to examine the effects of antalarmin, a selective, centrally acting corticotropin releasing factor(1) receptor antagonist, on both the initiation and maintenance of ethanol consumption in isolation-reared Fawn-Hooded rats. Here we demonstrate that whilst both antalarmin and diazepam can decrease the acquisition of an ethanol-preferring phenotype by Fawn-Hooded rats, only antalarmin can alter established, volitional ethanol consumption. This ability of antalarmin to reduce established ethanol consumption is apparently unrelated to changes in ingestive behaviour, or a generalised anxiolytic action. For these reasons, such drugs may provide a new therapeutic approach for the treatment of alcoholism; however, this requires further investigation.
There is substantial evidence that early life events influence brain development and subsequent adult behavior and play an important role in the causation of certain psychiatric disorders including schizophrenia and depression. The underlying mechanism of the effects of these early environmental factors is still not understood. It is a challenge to attempt to model early environmental factors in animals to gain understanding of the basic mechanisms that underlie the long-term effects. This paper reviews the effects of rearing rats from weaning in social isolation and reports some recent results indicating hippocampal dysfunction. Isolation rearing in rats from weaning produces a range of persistent behavioral changes in the young adult, including hyperactivity in response to novelty and amphetamine and altered responses to conditioning. These are associated with alterations in the central aminergic neurotransmitter functions in the mesolimbic areas and other brain regions. Isolation-reared rats have enhanced presynaptic dopamine (DA) and 5-HT function in the nucleus accumbens (NAC) associated with decreased presynaptic 5-HT function in the frontal cortex and hippocampus. Isolation-reared rats have reduced presynaptic noradrenergic function in the hippocampus, but have enhanced presynaptic DA function in the amygdala. These neurochemical imbalances may contribute to the exaggerated response of the isolated rat to a novel stimulus or to stimuli predictive of danger, and isolation-induced behavioral changes. These changes have neuroanatomical correlates, changes which seem to parallel to a certain degree those seen in human schizophrenia. A greater understanding of the processes that underlie these changes should improve our knowledge of how environmental events may alter brain development and function, and play a role in the development of neuropsychiatric disorders.
We investigated whether age of drinking onset and/or the housing condition in experimental animals affected alcohol drinking behavior to extrapolate the experimental findings to alcohol drinking patterns of aged people. At the time of the experiments, all 1-, 4-, 10- and the 16-month-old rats were divided into two groups, isolated and aggregated groups, and then maintained in the same housing conditions for six months. The amounts of voluntary alcohol consumption (g/kg/day) of all rats were investigated by two-bottle methods at 7, 10, 16 and 22 months old. No significant difference in alcohol drinking behavior was shown in the 7- and 10-month-old rats. A decrease in voluntary alcohol consumption was shown in the 16-month-old rats of the aggregated groups. In the 22-month old rats, a significant suppression of voluntary alcohol consumption was found in the aggregated groups compared with the isolated group. The results demonstrate that an important determinant of EtOH intake is related to environmental factors. It was suggested that alcohol drinking behavior strongly depends on the housing conditions and the age of onset of alcohol drinking.
We assessed the effects of alcohol exposure in social and isolation housing before puberty on the alcohol consumption later in adulthood. From 25 to 35 days of age, Wistar male rats were exposed to either (a) continuous isolation; (b) continuous social housing; (c) continuous isolation, but placed in social housing during 12 hr every other day; or (d) continuous social housing, but placed in isolation during 12 hr every other day (SOIS group). All males were exposed to 8% ethanol as the only available liquid 12 hr/day every other day in this prepubescent period and to continuous free-choice access to 8% ethanol or water in both social and isolation housing when adulthood was reached. Alcohol consumption before puberty was higher in the group permanently housed in isolation. Both voluntary alcohol intake and preference for alcohol in adulthood also were higher during the isolation than in the social condition in all groups, except in the SOIS group. Alcohol consumption was higher in the SOIS group than in the other groups only during social condition in adulthood. Food intake decreased during the social interaction of the groups that changed their condition from isolated to social or from social to isolated. Results support that (a) isolation facilitates alcohol consumption, and (b) rearing characteristics associated to alcohol intake at an early age can play an important role in later alcohol intake.
Individual differences in the response to stressful stimuli have been documented in humans and in a variety of animal species. Recently, we demonstrated that social stress induced a state of glucocorticoid (GC) resistance in mouse splenocytes, however this response was highly variable among cage mates. Since these studies were conducted using inbred mice (C57BL/6), it was suggested that environmental factors were the source of this variability. The following study examined possible factors that may have contributed to the development of individual differences in the susceptibility of mice to social stress. First, the effect of rearing conditions was studied by comparing the development of GC resistance in mice reared in isolation or in groups. In addition, the effect of previous social experiences was studied in mice that were re-housed to facilitate the formation of new social hierarchies in the cages. The results indicated that isolation altered the behavior of the mice during the social stress, but did not affect the development of GC resistance in response to the stress. Re-housing and the resulting loss of social status increased the susceptibility of mice to the development of GC resistance following social stress. Together, these findings indicate that environmental factors, such as previous social experiences, may alter the susceptibility to the effects of future social stress in inbred mice.
Development of procedures yielding substantial blood alcohol concentrations during voluntary access to an alcohol solution in mice is necessary to further characterize genetic and neurobiologic mechanisms underlying alcohol self-administration. Although, in experimental situations, some populations of mice readily drink an alcohol solution, results from previous studies have not typically revealed high blood alcohol concentrations after voluntary access, probably because of the high alcohol metabolism rate in mice. Toward development of a murine drinking model, 36 selectively bred high-alcohol-preferring mice of both sexes were subjected to a 30-min scheduled-access procedure by using saccharin fading to gradually introduce an alcohol solution. Mice had ad libitum access to food and water 24 h a day. The alcohol solution was available 1 h after the start of the dark part of the cycle for 30 min per day, 5 days per week. After complete removal of saccharin from the drinking tubes, mice consistently drank 1.4 g/kg of a 10% [volume/volume (vol./vol.)] alcohol solution in 30 min. Analysis of tail blood samples, taken immediately after the end of the 30-min access period, indicated blood alcohol concentrations were tightly correlated with alcohol intakes (range, 6-130 mg/dl; average, nearly 60 mg/dl). A concentration-response function of 10%, 12%, 15%, 18%, and 21% (vol./vol.) alcohol solutions indicated an inverted U-shaped relation between alcohol intake and alcohol concentration, with peak intake of greater than 1.75 g/kg per 30 min when a 15% alcohol solution was available. No sex differences were seen. These findings indicate the utility of this procedure in obtaining pharmacologically relevant blood alcohol concentrations after voluntary oral self-administration of an alcohol solution in mice.
Social isolation can induce psychological behavior changes. It is interesting to know whether there is sex difference in responding to social isolation or not. The present study compared the behavior difference between male and female mice isolated for 1-4 months. The results showed that the isolated male mice had higher accounts of locomotor activity than the isolated female and group-housed ones. Both isolated male and female mice spent shorter time in the dark box than the group-housed mice in the light/dark test, and isolated male mice spent less time in the closed arms than isolated female and group-housed mice when isolated for 2, 3 and 4 months in the elevated plus-maze test. These results suggest that isolation induce an anxiolytic-like effect. The immobile time in the forced swimming test was shortened in male mice isolated for 1 and 2 months. Both isolated male and female mice showed shorter time in pentobarbital-induced loss of righting reflex and less body weight gain. These results demonstrated that there was a sex difference in psychological behavior changes in mice undergoing social isolation and the male mice were more easily affected by isolation.
The present study investigated the effects of post-weaning social isolation (SI) on behavioural and neuroendocrine reactivity to stress of male and female rats. Innate aspects of fear and anxiety were assessed in the open field and elevated plus maze tests. Spontaneous startle reflex and conditioned fear response were further investigated. The neuroendocrine response of isolates was examined by measuring basal and stress release of ACTH and corticosterone and by evaluating the mRNA expression of mineralocorticoid (MR) and glucocorticoid (GR) receptors using in situ hybridization. Locomotor activity in the open field was not modified by chronic SI. In males, but not females, SI produced an anxiogenic profile in the elevated plus maze. Male isolates showed a trend towards increased startle reflex amplitude relative to socially-reared controls. Moreover, SI in males produced alterations of the HPA axis functioning as reflected by higher basal levels of ACTH, and enhanced release of ACTH and corticosterone following stress. In contrast, startle response or HPA axis functioning were not altered in female isolates. Social isolates from both genders showed reduced contextual fear-conditioning. Finally, the mRNA expression of MR and GR was not modified by SI. The results of the present study suggest that chronic SI increases emotional reactivity to stress and produces a hyperfunction of the HPA axis in adult rats, particularly in males.
Research examining brain development during adolescence is escalating rapidly along multiple dimensions, as illustrated by the remarkable diversity of trans-disciplinary work shown in this symposium. Ontogenetic transitions characteristics of adolescence are common among mammalian species. Although no other species demonstrates the full complexity of brain and behavioral function seen in human adolescents, adolescence appears to be a highly conserved developmental stage, its characteristics sculpted to meet common evolutionary pressures that include the avoidance of inbreeding at this time of sexual emergence. Numerous similarities are found between human adolescents and adolescents of other species in terms of developmental history and genetic constraints, as well as neurobehavioral and physiological characteristics. These similarities provide face and construct validity to support use of animal models as tools for the study of adolescence and the unique opportunities and vulnerabilities afforded by this developmental transition.
Animal studies on the effects of chronic variable stress during the peripubertal-juvenile period on hippocampal structure and function are lacking. Twenty-eight-day-old Sprague-Dawley rats were subjected to random, variable physical or social stress regimens for 4 weeks. Hippocampal volume was found to continue to grow in all lamina examined during the transition into young adulthood. Our variable physical stress paradigm led to inhibition of this growth in the CA1 pyramidal cell layer (PCL) and in the dentate gyrus-granular cell layer (DG-GCL), which reached full arrest in the CA3-PCL. Volume deficits were first observed after chronic stress exposure when 3 weeks, but not 24 h, of recovery had elapsed. Moreover, these volume deficits were associated with impairments in the Morris water-maze navigation, sustained down-regulation in the basal hippocampal glucocorticoid receptor gene expression, and deficits in the shutdown of acute stress-induced corticosterone secretion. Volume changes both due to normal maturation and after chronic stress exposure were independent of neuron number. Thus, a peripubertal-juvenile chronic stress paradigm that leads to significant alterations in the limbic-hypothalamic-pituitary-adrenal axis can produce robust effects in hippocampal structure and cognitive ability, lasting into adulthood.