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Evaluating the role of inhibiting the biosynthesis of estrogens in the sex-specific antidepressant-like effects of ketamine in rats
Preprints and early-stage research may not have been peer reviewed yet.
Abstract
Ketamine has been recently approved to treat resistant depression; however preclinical studies showed sex differences in its efficacy. Sex steroids, such as estrogen and testosterone, both in the periphery and locally in the brain, are regarded as important modulators of these sex differences. Therefore, the present study evaluated the role of inhibiting estrogen biosynthesis with letrozole, an aromatase inhibitor that catalyzes the conversion of androgen into estrogen, in the differential antidepressant-like-response induced by ketamine with sex. We performed several consecutive studies in adult Sprague-Dawley rats to evaluate potential sex differences in the antidepressant-like effects of ketamine (5 mg/kg, 7 days, i.p.), letrozole (1 mg/kg, 8 days, i.p.) and their combination (letrozole pre-treatment 3 h before ketamine). Acute and repeated antidepressant-like responses were ascertained in a series of behavioral tests (forced-swim, novelty-suppressed feeding, two-bottle choice for sucrose preference). The main results proved clear sex differences in the antidepressant-like response induced by ketamine, which was observed following a repeated paradigm in adult male rats, but rendered inefficacious in female rats. Moreover, decreasing estrogen production with letrozole induced on itself an antidepressant-like response in female rats, while also improved ketamine’s response in male rats (i.e., quicker response, only after a single dose). Interestingly, both the antidepressant-like effects induced by ketamine in male rats or letrozole in female rats persisted over time up to 65 days post-treatment, suggesting long-term sex-directed benefits for these drugs. The present results demonstrated a sex-specific role for inhibiting estrogen biosynthesis in the antidepressant-like response induced by ketamine in male rats. Moreover, letrozole presented itself as a potential antidepressant for females with persistent effects over time. Clearly, estrogen production is key in modulating, in a sex-specific manner, affective-like responses and thus deserve further studies.
Background:
We recently showed sex differences in the antidepressant-like potential of electroconvulsive seizures (ECS) in adolescent rats; while it worked for male rats it rendered inefficacious in females. Since sex steroids might be important modulators of these sex disparities, we evaluated the role of estrogens in the differential response induced by adolescent ECS. Moreover, given the literature suggesting certain cognitive sequelae from ECS exposure, we aimed at evaluating its long-term safety profile in adulthood.
Methods:
Adolescent Sprague-Dawley rats were pretreated with letrozole (1 mg/kg/day) or vehicle (1 ml/kg/day) for 8 days (i.p.), and treated during the last 5 days (3-h later) with ECS (95 mA, 0.6 s, 100 Hz) or SHAM. Antidepressant-like responses were measured in the forced swim-test, and long-term cognitive performance was assessed in the Barnes maze.
Results:
During adolescence, while ECS only exerted an antidepressant-like response in male rats, its combination with letrozole permitted ECS to also induce efficacy in females. Moreover, adolescent ECS treatment improved cognitive performance in adulthood, although exclusively in male rats.
Conclusions:
Adolescent ECS demonstrated an antidepressant-like potential together with certain long-term beneficial cognitive effects but exclusively in male rats. For females, efficacy was restricted to a situation in which the biosynthesis of estrogens was reduced. Therefore, estrogens and/or testosterone levels play a crucial role in the sex-disparities induced by ECS in Sprague-Dawley rats. Based on this study, and on the literature supporting its safety, ECS should be encouraged to use in cases of treatment-resistant depression during adolescence, while adhering to sex-specific considerations.
Background
The preclinical antidepressant-like characterization of desipramine relied almost exclusively in male rodents, with only a few contradictory reports done in females. Given that most experiments assessed a single dose and/or timepoint of analysis after-treatment, this study evaluated potential sex-differences in the length of the antidepressant-like response induced by different doses of desipramine as well as the molecular underpinnings driving the different responses by sex.
Methods
Male and female Sprague–Dawley rats were treated (i.p.) with 3 pulses of desipramine (5, 10 or 20 mg/kg) or vehicle (0.9% NaCl) within 24 h. The antidepressant-like effects were evaluated in the forced-swim test 1-h, 1- and 3-day post-treatment. The rate of cell proliferation and the regulation of key neuroplasticity markers (FADD, Cdk5, p35, p25) involved in antidepressant-like responses in the hippocampus were evaluated 1-h, 1-day and 5-day post-treatment.
Results
Desipramine induced similar antidepressant-like effects in male and female rats (effective doses of 10 and 20 mg/kg, with effects that lasted up to 1-day post-treatment), without altering the rate of cell proliferation. However, some sex-differences emerged when evaluating neuroplasticity markers in the hippocampus, while no changes were observed for female rats, desipramine regulated FADD, Cdk-5 and p25 in males in a way that suggested neuroprotective actions.
Conclusions
Our findings imply that while desipramine induced similar antidepressant-like responses for male and female rats, some differences emerged in the regulation of certain neuroplasticity markers, suggesting that distinctive molecular mechanisms might be participating in the therapeutic response of desipramine for both sexes.
Adult neurogenesis in the hippocampus is modulated by steroid hormones, including androgens, in male rodents. In this review, we summarize research showing that chronic exposure to androgens, such as testosterone and dihydrotestosterone, enhances the survival of new neurons in the dentate gyrus of male, but not female, rodents, via the androgen receptor. However, the neurogenesis promoting the effect of androgens in the dentate gyrus may be limited to younger adulthood as it is not evident in middle-aged male rodents. Although direct exposure to androgens in adult or middle age does not significantly influence neurogenesis in female rodents, the aromatase inhibitor letrozole enhances neurogenesis in the hippocampus of middle-aged female mice. Unlike other androgens, androgenic anabolic steroids reduce neurogenesis in the hippocampus of male rodents. Collectively, the research indicates that the ability of androgens to enhance hippocampal neurogenesis in adult rodents is dependent on dose, androgen type, sex, duration, and age. We discuss these findings and how androgens may be influencing neuroprotection, via neurogenesis in the hippocampus, in the context of health and disease.
Major depressive disorder (MDD) is a common psychiatric illness that manifests in sex-influenced ways. Men and women may experience depression differently and also respond to various antidepressant treatments in sex-influenced ways. Ketamine, which is now being used as a rapid-acting antidepressant, is likely the same. To date, the majority of studies investigating treatment outcomes in MDD do not disaggregate the findings in males and females, and this is also true for ketamine. This review aims to highlight that gap by exploring pre-clinical data-at a behavioral, molecular, and structural level-and recent clinical trials. Sex hormones, particularly estrogen and progesterone, influence the response at all levels examined, and sex is therefore a critical factor to examine when looking at ketamine response. Taken together, the data show females are more sensitive to ketamine than males, and it might be possible to monitor the phase of the menstrual cycle to mitigate some risks associated with the use of ketamine for females with MDD. Based on the studies reviewed in this article, we suggest that ketamine should be administered adhering to sex-specific considerations.
RationaleCannabidiol is a non-psychoactive phytocannabinoid with great therapeutic potential in diverse psychiatric disorders; however, its antidepressant potential has been mainly ascertained in adult rats.Objectives
To compare the antidepressant-like response induced by cannabidiol in adolescent and adult rats and the possible parallel modulation of hippocampal neurogenesis.Methods
Male Sprague-Dawley rats were repeatedly treated with cannabidiol (3, 10, and 30 mg/kg) or vehicle (1 mL/kg) during adolescence (postnatal days, PND 27-33) or adulthood (PND 141-147) and exposed to 3 consecutive tests (forced swim, open field, two-bottle choice) that quantified behavioral despair, anxiety, and sucrose intake respectively.ResultsCannabidiol induced differential effects depending on the age and dose administered, with a decreased sensitivity observed in adolescent rats: (1) cannabidiol (30 mg/kg) decreased body weight only in adult rats; (2) cannabidiol ameliorated behavioral despair in adolescent and adult rats, but with a different dose sensitivity (10 vs. 30 mg/kg), and with a different extent (2 vs. 21 days post-treatment); (3) cannabidiol did not modulate anxiety-like behavior at any dose tested in adolescent or adult rats; and (4) cannabidiol increased sucrose intake in adult rats.Conclusions
Our findings support the notion that cannabidiol exerts antidepressant- and anorexigenic-like effects in adult rats and demonstrate a decreased potential when administered in adolescent rats. Moreover, since cannabidiol did not modulate hippocampal neurogenesis (cell proliferation and early neuronal survival) in adolescent or adult rats, the results revealed potential antidepressant-like effects induced by cannabidiol without the need of regulating hippocampal neurogenesis.
This article updates the guidance published in 2015 for authors submitting papers to British Journal of Pharmacology (Curtis et al., 2015) and is intended to provide the rubric for peer review. Thus, it is directed towards authors, reviewers and editors. Explanations for many of the requirements were outlined previously and are not restated here. The new guidelines are intended to replace those published previously. The guidelines have been simplified for ease of understanding by authors, to make it more straightforward for peer reviewers to check compliance and to facilitate the curation of the journal's efforts to improve standards.
In June 2015, the National Institutes of Health (NIH) released a Guide notice (NOT-OD-15-102) that highlighted the expectation of the NIH that the possible role of sex as a biologic variable be factored into research design, analyses, and reporting of vertebrate animal and human studies. Anticipating these guidelines, the NIH Office of Research on Women's Health, in October 2014, convened key stakeholders to discuss methods and techniques for integrating sex as a biologic variable in preclinical research. The workshop focused on practical methods, experimental design, and approaches to statistical analyses in the use of both male and female animals, cells, and tissues in preclinical research. Workshop participants also considered gender as a modifier of biology. This article builds on the workshop and is meant as a guide to preclinical investigators as they consider methods and techniques for inclusion of both sexes in preclinical research and is not intended to prescribe exhaustive/specific approaches for compliance with the new NIH policy.-Miller, L. R., Marks, C., Becker, J. B., Hurn, P. D., Chen, W.-J., Woodruff, T., McCarthy, M. M., Sohrabji, F., Schiebinger, L., Wetherington, C. L., Makris, S., Arnold, A. P., Einstein, G., Miller, V. M., Sandberg, K., Maier, S., Cornelison, T. L., Clayton, J. A. Considering sex as a biological variable in preclinical research.
We recently reported a greater sensitivity of female rats to rapid antidepressant-like effects of ketamine compared to male rats, and that ovarian-derived estradiol (E2) and progesterone (P4) are essential for this response. However, to what extent testosterone may also contribute, and whether duration of response to ketamine is modulated in a sex- and hormone-dependent manner remains unclear. To explore this, we systematically investigated the influence of testosterone, estradiol and progesterone on initiation and maintenance of hedonic response to low-dose ketamine (2.5 mg/kg) in intact and gonadectomized male and female rats. Ketamine induced a sustained increase in sucrose preference of female, but not male, rats in an E2P4-dependent manner. Whereas testosterone failed to alter male treatment response, concurrent administration of P4 alone in intact males enhanced hedonic response low-dose ketamine. Treatment responsiveness in female rats only was associated with greater hippocampal BDNF levels, but not activation of key downstream signaling effectors. We provide novel evidence supporting activational roles for ovarian-, but not testicular-, derived hormones in mediating hedonic sensitivity to low-dose ketamine in female and male rats, respectively. Organizational differences may, in part, account for the persistence of sex differences following gonadectomy and selective involvement of BDNF in treatment response.
The ARRIVE guidelines have been implemented in BJP for 4 years with the aim of increasing transparency in reporting experiments involving animals. BJP has assessed our success in implementing them and concluded that we could do better. This editorial discusses the issues and explains how we are changing our requirements for authors to report their findings in experiments involving animals. This is one of a series of editorials discussing updates to the BJP Instructions to Authors LINKED EDITORIALS: This Editorial is part of a series. To view the other Editorials in this series, visit: http://onlinelibrary.wiley.com/doi/10.1111/bph.12956/abstract; and http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1476-5381.
© 2015 The British Pharmacological Society.
Women are twice as likely to develop depression as men. Moreover, the symptoms they experience also show sex differences: women tend to develop depression at an earlier age and show more severe symptoms than men. Likewise, the response to antidepressant pharmacotherapy appears to have sex differences. These differences can partially be explained by differences in pharmacokinetic properties (i.e., absorption, distribution, metabolism, and excretion) of drugs in males and females. More recent research has shown that sex hormones may influence all these previously named pharmacokinetic processes. As concentrations of sex hormones vary throughout the female lifespan, these hormonal variations can have effects on therapeutic responses to antidepressants as well as the occurrence of adverse events. The purpose of this paper is therefore to review the literature reporting on the effects of female sex hormones on the pharmacokinetics of antidepressants and to discuss and evaluate the implications of changes in levels of sex hormones throughout life for the treatment of depression.
Aromatase inhibitors block the conversion of androgens to oestrogens and are used for the treatment of hormone-responsive breast cancer in menopause and recently also in premenopausal women. We investigate whether decreased oestrogen synthesis following aromatase inhibition leads to a depressive-like behavioural response in cycling female rats. Using the forced swim test (FST) we estimate the response of acute (three injections in 24 h) and sustained (7 d) letrozole and fluoxetine administration. Acute aromatase inhibition decreases immobility duration in the FST, indicating its antidepressant potential. Instead, sustained aromatase inhibition did not show such antidepressant potential. Testosterone elevation associates with the decreased depressive behaviour in the FST following acute letrozole treatment, but interestingly progesterone explains the increased swimming behaviour. Present findings may have potential implications for women treated with aromatase inhibitors, especially before menopause, as well as for the role of gonadal hormones in the expression of depressive symptoms and antidepressant response.
The forced swim test (FST) is one of the most commonly used animal models for assessing antidepressant-like behavior. This protocol details using the FST in rats, which takes place over 48 h and is followed by the video analysis of the behavior. The swim test involves the scoring of active (swimming and climbing) or passive (immobility) behavior when rodents are forced to swim in a cylinder from which there is no escape. There are two versions that are used, namely the traditional and modified FSTs, which differ in their experimental setup. For both versions, a pretest of 15 min (although a number of laboratories have used a 10-min pretest with success) is included, as this accentuates the different behaviors in the 5-min swim test following drug treatment. Reduction in passive behavior is interpreted as an antidepressant-like effect of the manipulation, provided it does not increase general locomotor activity, which could provide a false positive result in the FST.
Introduction:
Sex differences have been identified in antidepressant treatment; however, it remains unclear to what extent pharmacokinetics contributes to these differences. As current antidepressant pharmacotherapy is less than optimal, understanding the role of sex in pharmacokinetics may substantially contribute to a gender-based optimized treatment.
Areas covered:
An unrestricted PubMed literature search on antidepressant pharmacokinetics and sex was performed. Sex differences in absorption, distribution, metabolism and elimination of antidepressants, as well as the interaction of sex with age, genetic polymorphisms and gonadal hormones are discussed. We also provide an overview of how each antidepressant presents a particular sex-differentiated pharmacokinetic profile. Most antidepressants present to some extent pharmacokinetic sex differences, which often are further accentuated by gonadal hormones. In most cases, women, particularly elderly women, are expected to have higher exposure to antidepressants when dosed in a similar way as men.
Expert opinion:
Although the available pharmacokinetic evidence indicates that women should receive lower doses of antidepressants and men should receive higher doses, current guidelines do not recommend dose adjustment, because these sex differences are considered to be clinically insignificant. Unless we understand the link between pharmacokinetics and pharmacodynamics of antidepressants, it will be difficult to determine whether sex differences are of clinical importance or not. Thus, further systematic and particularly focused research is needed on sex differences in pharmacokinetics.
Existing therapies for major depression have a lag of onset of action of several weeks, resulting in considerable morbidity. Exploring pharmacological strategies that have rapid onset of antidepressant effects within a few days and that are sustained would have an enormous impact on patient care. Converging lines of evidence suggest the role of the glutamatergic system in the pathophysiology and treatment of mood disorders.
To determine whether a rapid antidepressant effect can be achieved with an antagonist at the N-methyl-D-aspartate receptor in subjects with major depression.
A randomized, placebo-controlled, double-blind crossover study from November 2004 to September 2005.
Mood Disorders Research Unit at the National Institute of Mental Health. Patients Eighteen subjects with DSM-IV major depression (treatment resistant).
After a 2-week drug-free period, subjects were given an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 test days, a week apart. Subjects were rated at baseline and at 40, 80, 110, and 230 minutes and 1, 2, 3, and 7 days postinfusion. Main Outcome Measure Changes in scores on the primary efficacy measure, the 21-item Hamilton Depression Rating Scale.
Subjects receiving ketamine showed significant improvement in depression compared with subjects receiving placebo within 110 minutes after injection, which remained significant throughout the following week. The effect size for the drug difference was very large (d = 1.46 [95% confidence interval, 0.91-2.01]) after 24 hours and moderate to large (d = 0.68 [95% confidence interval, 0.13-1.23]) after 1 week. Of the 17 subjects treated with ketamine, 71% met response and 29% met remission criteria the day following ketamine infusion. Thirty-five percent of subjects maintained response for at least 1 week.
Robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist; onset occurred within 2 hours postinfusion and continued to remain significant for 1 week.
Anhedonia is a core symptom of major depression. Deficits in reward function, which underlie anhedonia, can be readily assessed in animals. Therefore, anhedonia may serve as an endophenotype for understanding the neural circuitry and molecular pathways underlying depression.
Surprisingly, there is scant knowledge regarding alterations in brain reward function after olfactory bulbectomy (OB), an animal model which results in a behavioural syndrome responsive to chronic antidepressant treatment. Therefore, the present studies aimed to assess reward function after bulbectomy.
The present study utilized sucrose preference, cocaine-induced hyperlocomotion and intra-cranial self-stimulation (ICSS) responding to examine reward processes in the OB model.
Bulbectomized animals showed a marked preference (>90%) for 0.8% sucrose solution compared with water; similar to the preference exhibited by sham controls. Importantly, there were pronounced deficits in brain reward function, as assessed using ICSS, which lasted 8 days before returning to baseline levels. Furthermore, bulbectomized animals were hyper-responsive to the locomotor stimulating properties of an acute and a repeated cocaine regimen. However, no difference in ICSS facilitation was observed in response to an acute cocaine injection.
Taken together, these results suggest that bulbectomized rats display alterations in brain reward function, but these changes are not long-lasting and thus, not amenable to investigating the effects of pharmacological interventions. However, given that OB animals are hypersensitive to drugs of abuse, bulbectomy may be an appropriate inducing factor for the development of animal models of co-morbid depression and drug dependence.
In male rats, the antidepressant-like effect of fluoxetine (FLX) and desipramine (DMI) in the forced swimming test (FST) is reduced by orchidectomy and partially restored by testosterone (T). It is unknown if this modulation of T is produced by its estrogenic metabolites. The objectives of this study were to evaluate if the aromatase inhibitor, formestane, interferes with the antidepressant-like effect of DMI and FLX in intact male rats, and to analyze if 17beta-estradiol (E2) modifies the FST and interacts with the antidepressants in orchidectomized (Orx) males. Intact males received DMI (1.25-5.0 mg/kg) and FLX (2.5-10 mg/kg) alone or in combination with formestane (17.5 mg/kg). Orx rats received E2 (5, 10, 20 and 40 microg/rat) or the combination of E2 [at sub-threshold (5 microg/rat) and optimal (10 microg/rat) doses] plus sub-effective doses of DMI (2.5 mg/kg) or FLX (10 mg/kg). Serum testosterone and estradiol levels were measured in intact-control and -formestane treated animals as well as in castrated males replaced with various doses of E2. Formestane in intact males lacked of an action in the FST, but cancelled the antidepressant-like effect of DMI and FLX. E2 at the supra-physiological doses of 10 and 20 microg/rat produced antidepressant-like effects. E2 at 5 microg/rat (that re-established the levels of this hormone to physiological levels) and at 10 microg/rat restored the antidepressant-like action of DMI and FLX in Orx rats. It was concluded that estrogens participate in the antidepressant-like effect of DMI and FLX in the FST.
The neurotrophic hypothesis of depression proposes that reduced levels of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) contribute to neuronal atrophy or loss in the prefrontal cortex (PFC) and hippocampus and impaired hippocampal adult neurogenesis, which are associated with depressive symptoms. Chronic, but acute, treatment with typical monoaminergic antidepressants can at least partially reverse these deficits, in part via induction of BDNF and/or VEGF expression, consistent with their delayed onset of action. Ketamine, an N-methyl-d-aspartate receptor antagonist, exerts rapid and sustained antidepressant effects. Rodent studies have revealed that ketamine rapidly increases BDNF and VEGF release and/or expression in the PFC and hippocampus, which in turn increases the number and function of spine synapses in the PFC and hippocampal neurogenesis. Ketamine also induces the persistent release of insulin-like growth factor 1 (IGF-1) in the PFC of male mice. These neurotrophic effects of ketamine are associated with its rapid and sustained antidepressant effects. In this review, we first provide an overview of the neurotrophic hypothesis of depression and then discuss the role of BDNF, VEGF, IGF-1, and other growth factors (IGF-2 and transforming growth factor-β1) in the antidepressant effects of ketamine and its enantiomers.
Recent meta-analyses have demonstrated that data from female rodents, tested without regard for estrous stage, is no more variable than male data across a range of traits. Nonetheless, widespread use of male-only samples persists in preclinical studies of anxiety disorders, despite this condition being twice more prevalent amongst women relative to men. We conducted a meta-analysis of over 4900 data points obtained from 263 articles assessing behavioural measures of fear and anxiety in rodents. We found no evidence for greater female variability on any measure. Overall, males had greater variability than unstaged females, which was predominantly driven by studies of learned fear. Compared to unstaged females, staged, but not ovariectomised, females showed reduced variability. Experiments using individual housing and rats were associated with greater variability relative to those using group housing and mice; these effects were not moderated by sex. These results illustrate that the estrous cycle does not inflate variability in females beyond that of males, despite being a female-specific modulator of fear and anxiety behaviour.
Replicated clinical trials have demonstrated rapid and robust antidepressant effects with ketamine in treatment resistant mood disorders. Sex (biological) and gender differences in therapeutic effects for any new intervention is an important consideration, however, the differential efficacy, safety and tolerability of ketamine in males versus females remains underexplored. The objective of the present systematic review is to identify and qualitatively synthesize all published clinical studies relevant to the sex differential effects of ketamine for mood disorders. A systematic search of PubMed, Medline, and PsycInfo from inception until January 20, 2021, yielded 27 reports including 1715 patients (742 males and 973 females) that met inclusion criteria. Results from the vast majority of studies (88.8%) do not support significant sex differences in antidepressant response, tolerability or safety of ketamine. Nine (33.3%) of the reports included a bioanalytical component in the analysis and only one reported on sex differences. Evidence from the present review does not support clinically or statistically significant sex differences in therapeutic effects with ketamine. Nevertheless, future studies should continue to consider sex and biological sex differences in study design and data analytic plans.
Background
Further studies are needed to better understand the effects of potential novel antidepressants, such as cannabidiol, for the treatment of psychiatric disorders during adolescence. In this context, we evaluated in a rodent model of early-life stress (a single 24-h episode of maternal deprivation, PND 9), the antidepressant-like effects of adolescent cannabidiol alone and/or in combination with adolescent cocaine exposure (given the described beneficial effects of cannabidiol on reducing cocaine effects).Methods
Maternally deprived Sprague-Dawley male rats were treated in adolescence with cannabidiol (with or without concomitant cocaine) and exposed to a battery of behavioral tests (forced-swim, novelty-suppressed feeding, open field, sucrose preference) across time. Putative enduring molecular correlates (CB receptors, BDNF) were evaluated in the hippocampus by western blot.ResultsCannabidiol exerted antidepressant- and anxiolytic-like effects in rats exposed to early-life stress. Cocaine did not alter affective-like behavior during adolescence in rats exposed to early-life stress; however, a depressive- and anxiogenic-like phenotype emerged during adulthood, and cannabidiol exerted some behavioral improvements, along with the growing literature supporting its beneficial role for reducing cocaine intake and/or reinstatement in rodents. Finally, cannabidiol did not modulate hippocampal CB receptors or BDNF proteins, and although the data raised interesting questions about the possible role of CB1 receptors on modulating the long-term effects of cocaine, future research is needed to expand these findings.Conclusion
Cannabidiol showed a promising therapeutic response in terms of ameliorating affect in a rat model of early-life stress during adolescence and up to adulthood.
Various antidepressants are commonly used to treat depression and anxiety disorders, and sex differences have been identified in their efficacy and side effects. Steroids, such as estrogens and testosterone, both in the periphery and locally in the brain, are regarded as important modulators of these sex differences. This review presents published data from preclinical and clinical studies that measure testosterone and estrogen level changes during and/or after acute or chronic administration of different antidepressants. The majority of studies show an interaction between sex hormones and antidepressants on sexual function and behavior, or in depressive symptom alleviation. However, most of the studies omit to investigate antidepressants’ effects on circulating levels of gonadal hormones. From data reviewed herein, it is evident that most antidepressants can influence testosterone and estrogen levels. Still, the evidence is conflicting with some studies showing an increase, others decrease or no effect. Most studies are conducted in male animals or humans, underscoring the importance of considering sex as an important variable in such investigations, especially as depression and anxiety disorders are more common in women than men. Therefore, research is needed to elucidate the extent to which antidepressants can influence both peripheral and brain levels of testosterone and estrogens, in males and females, and whether this impacts the effectiveness or side effects of antidepressants.
The American Society for Pharmacology and Experimental Therapeutics has revised the Instructions to Authors for Drug Metabolism and Disposition, Journal of Pharmacology and Experimental Therapeutics, and Molecular Pharmacology These revisions relate to data analysis (including statistical analysis) and reporting but do not tell investigators how to design and perform their experiments. Their overall focus is on greater granularity in the description of what has been done and found. Key recommendations include the need to differentiate between preplanned, hypothesis-testing, and exploratory experiments or studies; explanations of whether key elements of study design, such as sample size and choice of specific statistical tests, had been specified before any data were obtained or adapted thereafter; and explanations of whether any outliers (data points or entire experiments) were eliminated and when the rules for doing so had been defined. Variability should be described by S.D. or interquartile range, and precision should be described by confidence intervals; S.E. should not be used. P values should be used sparingly; in most cases, reporting differences or ratios (effect sizes) with their confidence intervals will be preferred. Depiction of data in figures should provide as much granularity as possible, e.g., by replacing bar graphs with scatter plots wherever feasible and violin or box-and-whisker plots when not. This editorial explains the revisions and the underlying scientific rationale. We believe that these revised guidelines will lead to a less biased and more transparent reporting of research findings.
Letrozole, a third-generation aromatase inhibitor, prevents the production of estrogens in the final step in conversion from androgens. Due to its efficacy at suppressing estrogens, letrozole has recently taken favor as a first-line adjuvant treatment for hormone-responsive breast cancer in middle-aged women. Though patient response to letrozole has generally been positive, there is conflicting evidence surrounding its effects on the development of depression. It is possible that the potential adverse effects of letrozole on mood are a result of the impact of hormonal fluctuations on neurogenesis in the hippocampus. Thus, to clarify the effects of letrozole on the hippocampus and behavior, we examined how chronic administration affects hippocampal neurogenesis and depressive-like behavior in middle-aged, intact female mice. Mice were given either letrozole (1 mg/kg) or vehicle by injection (i.p.) daily for 3 weeks. Depressive-like behavior was assessed during the last 3 days of treatment using the forced swim test, tail suspension test, and sucrose preference test. The production of new neurons was quantified using the immature neuronal marker doublecortin (DCX), and cell proliferation was quantified using the endogenous marker Ki67. We found that letrozole increased DCX and Ki67 expression and maturation in the dentate gyrus, but had no significant effect on depressive-like behavior. Our findings suggest that a reduction in estrogens in middle-aged females increases hippocampal neurogenesis without any adverse impact on depressive-like behavior; as such, this furthers our understanding of how estrogens modulate neurogenesis, and to the rationale for the utilization of letrozole in the clinical management of breast cancer.
Sex differences have been observed across many psychiatric diseases, especially mood disorders. For major depression, the most prevalent psychiatric disorder, females show a roughly two-fold greater risk as compared to males. Depression is sexually dimorphic with males and females exhibiting differences in clinical presentation, course, and response to antidepressant treatment. In this review, we first discuss sex differences observed in depressed patients, as well as animal models that reveal potential underlying mechanisms. We then discuss antidepressant treatments including their proposed mechanism of action and sex differences observed in treatment response. We include possible mechanisms underlying these sex differences with particular focus on synaptic transmission.
Clinical studies have demonstrated that a single sub-anesthetic dose of the dissociative anesthetic ketamine induces rapid and sustained antidepressant actions. Although this finding has been met with enthusiasm, ketamine’s widespread use is limited by its abuse potential and dissociative properties. Recent preclinical research has focused on unraveling the molecular mechanisms underlying the antidepressant actions of ketamine in an effort to develop novel pharmacotherapies, which will mimic ketamine’s antidepressant actions but lack its undesirable effects. Here we review hypotheses for the mechanism of action of ketamine as an antidepressant, including synaptic or GluN2B-selective extra-synaptic N-methyl-D-aspartate receptor (NMDAR) inhibition, inhibition of NMDARs localized on GABAergic interneurons, inhibition of NMDAR-dependent burst firing of lateral habenula neurons, and the role of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor activation. We also discuss links between ketamine’s antidepressant actions and downstream mechanisms regulating synaptic plasticity, including brain-derived neurotrophic factor (BDNF), eukaryotic elongation factor 2 (eEF2), mechanistic target of rapamycin (mTOR) and glycogen synthase kinase-3 (GSK-3). Mechanisms that do not involve direct inhibition of the NMDAR, including a role for ketamine’s (R)-ketamine enantiomer and hydroxynorketamine (HNK) metabolites, specifically (2R,6R)-HNK, are also discussed. Proposed mechanisms of ketamine’s action are not mutually exclusive and may act in a complementary manner to exert acute changes in synaptic plasticity, leading to sustained strengthening of excitatory synapses, which are necessary for antidepressant behavioral actions. Understanding the molecular mechanisms underpinning ketamine’s antidepressant actions will be invaluable for the identification of targets, which will drive the development of novel, effective, next-generation pharmacotherapies for the treatment of depression.
Rationale:
Low-dose ketamine is a rapid-acting antidepressant, to which female rodents are more sensitive as compared to males. However, the mechanism mediating this sex difference in ketamine sensitivity remains elusive.
Objectives:
We sought to determine whether male and female mice differ in their behavioral sensitivity to low doses of ketamine, and uncover how ovarian hormones influence females' ketamine sensitivity. We also aimed to uncover some of the molecular mechanism(s) in mood-related brain regions that mediate sex differences in ketamine antidepressant effects.
Methods:
Male and female mice (freely-cycling, diestrus 1 [D1], proestrus [Pro], or D1 treated with an estrogen receptor (ER) α, ERβ, or progesterone receptor (PR) agonist) received ketamine (0, 1.5, or 3 mg/kg intraperitoneally) and were tested in the forced swim test (FST) 30 min later. Ketamine's influence over synaptic plasticity markers in the prefrontal cortex (PFC) and hippocampus (HPC) of males, D1, and Pro females was quantified by Western blot 1 h post-treatment.
Results:
Males, freely-cycling females, D1 and Pro females exhibited antidepressant-like responses to 3 mg/kg ketamine. Pro females were the only group where ketamine exhibited an antidepressant effect at 1.5 mg/g. D1 females treated with an agonist for ERα and ERβ exhibited an antidepressant-like response to 1.5 mg/kg ketamine. Ketamine (3 mg/kg) increased synaptic plasticity-related proteins in the PFC and HPC of males, D1, and Pro females. Yet, Pro females exhibited an increase in p-Akt and p-CaMKIIα in response to 1.5 and 3 mg/kg ketamine.
Conclusion:
Our results indicate that females' enhanced sensitivity to ketamine during Pro is likely mediated through estradiol acting on ERα and ERβ, leading to greater activation of synaptic plasticity-related kinases within the PFC and HPC.
Aromatase inhibitors, which are widely used for the treatment of estrogen-dependent cancers, have been associated with psychiatric side effects ranging from mania to depression. In the present study, we investigated sex differences in the behavioral and neurochemical effects of aromatase inhibition on male and female, sham-operated or gonadectomized adult rats. Three weeks after surgery, rats received chronic treatment with the aromatase inhibitor letrozole or vehicle and were then subjected to the open field test, which assesses general activity. Half of the subjects were subsequently exposed to the stressful procedure of the forced swim test (FST), which is also a test of antidepressant activity. Aromatase activity was analyzed in the hypothalamus and testosterone and corticosterone were assayed in the blood serum of all rats. The hippocampus and prefrontal cortex (PFC) were analyzed for monoamine (noradrenaline, dopamine and serotonin), as well as amino acid (GABA, glutamate, glycine, taurine, alanine and histidine) levels. The observed decrease in hypothalamic aromatase activity confirmed the efficacy of letrozole treatment in both sexes. Moreover, letrozole enhanced testosterone levels in sham-operated females. In the open field test, females were overall more active and explorative than males and gonadectomy eliminated this sex difference. In the FST, females exhibited overall higher immobility than males and gonadectomy further enhanced this passive behavior in both sexes. However, sustained aromatase inhibition had no effect on open field and FST behaviors. Head shakes during FST, which were fewer in females than in males, were reduced by castration in males and by letrozole treatment in ovariectomized females, suggesting a role of testosterone and extra-gonadal estrogens in the expression of this behavior. Sustained aromatase inhibition also decreased noradrenaline and the dopaminergic turnover rates [DOPAC/DA, HVA/DA] in the hippocampus and PFC of male and female rats, irrespectively of gonadectomy. Moreover, letrozole treatment enhanced the serotonergic turnover [5HIAA/5HT] rate in the hippocampus of males and females, irrespectively of gonadectomy. Amino acid levels were not influenced by letrozole, but sex differences were demonstrated with higher levels in the PFC of females vs. males. Present findings suggest that the neuropsychiatric effects of aromatase inhibition can be attributed to the inhibition of extragonadal estrogen synthesis, presumably in the brain, and could be further associated with serotonergic and catecholaminergic changes in brain regions involved in mood and cognition. Importantly, present data could be linked with the neurobiology of affective side-effects in post-menopausal women receiving aromatase inhibitors.
Background:
Not including female rats or mice in neuroscience research has been justified due to the variable nature of female data caused by hormonal fluctuations associated with the female reproductive cycle. In this study, we investigated whether female rats are more variable than male rats in scientific reports of neuroscience-related traits.
Methods:
PubMed and Web of Science were searched for the period from August 1, 2010, to July 31, 2014, for articles that included both male and female rats and that measured diverse aspects of brain function. Only empirical articles using both male and female gonad-intact adult rats, written in English, and including the number of subjects (or a range) were included. This resulted in 311 articles for analysis. Data were extracted from digital images from article PDFs and from manuscript tables and text. The mean and standard deviation (SD) were determined for each data point and their quotient provided a coefficient of variation (CV) as a measure of trait-specific variability for each sex. Additionally, the results were coded for the type of research being measured (behavior, electrophysiology, histology, neurochemistry, and non-brain measures) and for the strain of rat. Over 6000 data points were extracted for both males and females. Subsets of the data were coded for whether male and female mean values differed significantly and whether animals were grouped or individually housed.
Results:
Across all traits, there were no sex differences in trait variability, as indicated by the CV, and there were no sex differences in any of the four neuroscience categories, even in instances in which mean values for males and females were significantly different. Female rats were not more variable at any stage of the estrous cycle than male rats. There were no sex differences in the effect of housing conditions on CV. On one of four measures of non-brain function, females were more variable than males.
Conclusions:
We conclude that even when female rats are used in neuroscience experiments without regard to the estrous cycle stage, their data are not more variable than those of male rats. This is true for behavioral, electrophysiological, neurochemical, and histological measures. Thus, when designing neuroscience experiments to include both male and female rats, power analyses based on variance in male measures are sufficient to yield accurate numbers for females as well, even when the estrous cycle is not taken into consideration.
Background:
The mechanistic underpinnings of sex differences in occurrence of depression and efficacy of antidepressant treatments are poorly understood. We examined the effects of isolation stress (IS) and the fast-acting antidepressant ketamine on anhedonia and depression-like behavior, spine density, and synaptic proteins in male and female rats.
Methods:
We used a chronic social IS paradigm to test the effects of ketamine (0, 2.5 mg/kg, and 5 mg/kg) on behavior and levels of synaptic proteins synapsin-1, postsynaptic density protein 95, and glutamate receptor 1 in male rats and female rats in diestrus. Medial prefrontal cortex spine density was also examined in male rats and female rats that received ketamine during either the diestrus or the proestrus phase of their estrous cycle.
Results:
Male rats showed anhedonia and depression-like behavior after 8 weeks of IS, concomitant with decreases in spine density and levels of synapsin-1, postsynaptic density protein 95, and glutamate receptor 1 in the medial prefrontal cortex; these changes were reversed by a single injection of ketamine (5 mg/kg). After 11 weeks of IS, female rats showed depression-like behavior but no signs of anhedonia. Although both doses of ketamine rescued depression-like behavior in female rats, the decline observed in synaptic proteins and spine density in IS and in diestrus female rats could not be reversed by ketamine. Spine density was higher in female rats during proestrus than in diestrus.
Conclusions:
Our findings implicate a role for synaptic proteins synapsin-1, postsynaptic density protein 95, and glutamate receptor 1 and medial prefrontal cortex spine density in the antidepressant effects of ketamine in male rats subjected to IS but not in female rats subjected to IS, suggesting dissimilar underlying mechanisms for efficacy of ketamine in the two sexes.
The current meta-analysis examines the effects of ketamine infusion on depressive symptoms over time in major depressive disorder (MDD) and bipolar disorder (BD).
Following a systematic review of the literature, data were extracted from 21 studies (n = 437 receiving ketamine) and analysed at four post-infusion time points (4 h, 24 h, 7 days and 12-14 days). The moderating effects of several factors were assessed including: repeat/single infusion, diagnosis, open-label/participant-blind infusion, pre-post/placebo-controlled design and the sex of patients.
Effect sizes were significantly larger for repeat than single infusion at 4 h, 24 h and 7 days. For single infusion studies, effect sizes were large and significant at 4 h, 24 h and 7 days. The percentage of males was a predictor of antidepressant response at 7 days. Effect sizes for open-label and participant-blind infusions were not significantly different at any time point.
Single ketamine infusions elicit a significant antidepressant effect from 4 h to 7 days; the small number of studies at 12-14 days post infusion failed to reach significance. Results suggest a discrepancy in peak response time depending upon primary diagnosis - 24 h for MDD and 7 days for BD. The majority of published studies have used pre-post comparison; further placebo-controlled studies would help to clarify the effect of ketamine over time. Copyright © 2015 John Wiley & Sons, Ltd.
Copyright © 2015 John Wiley & Sons, Ltd.
During the past decade, one of the most striking discoveries in the treatment of major depression was the clinical finding that a single infusion of a sub-anesthetic dose of the N-methyl-d-aspartate receptor antagonist ketamine produces a rapid (i.e. within a few hours) and long-lasting (i.e. up to two weeks) antidepressant effect in both treatment-resistant depressed patients and in animal models of depression. Notably, converging clinical and preclinical evidence support that responsiveness to antidepressant drugs is sex-differentiated. Strikingly, research regarding the antidepressant-like effects of ketamine has focused almost exclusively on the male sex. Herein we report that female C57BL/6J stress-naïve mice are more sensitive to the rapid and the sustained antidepressant-like effects of ketamine in the forced swim test (FST). In particular, female mice responded to lower doses of ketamine (i.e. 3 mg/kg at 30 min and 5 mg/kg at 24 h post-injection), doses that were not effective in their male counterparts. Moreover, tissue levels of the excitatory amino acids glutamate and aspartate, as well as serotonergic activity, were affected in a sex-dependent manner in the prefrontal cortex and the hippocampus, at the same time-points. Most importantly, a single injection of ketamine (10 mg/kg) induced sex-dependent behavioral effects in mice subjected to the chronic mild stress (CMS) model of depression. Intriguingly, female mice were more reactive to the earlier effects of ketamine, as assessed in the open field and the FST (at 30 min and 24 h post-treatment, respectively) but the antidepressant potential of the drug proved to be longer lasting in males, as assessed in the splash test and the FST (days 5 and 7 post-treatment, respectively). Taken together, present data revealed that ketamine treatment induces sex-dependent rapid and sustained neurochemical and behavioral antidepressant-like effects in stress-naïve and CMS-exposed C57BL/6J mice.
There may be a role of age-related decline in androgen production and/or its metabolism for late-onset depression disorders of men and women. Thus, the anti-depressant-like effects of testosterone (T) and its metabolites are of interest. Given that these androgens have disparate mechanisms of action, it is important to begin to characterize and compare their effects in an aged animal model. We hypothesized that there would be sex differences in depression behavior of aged mice and that androgens would reduce depression-like behaviors in the forced swim test. To investigate this, male and female mice (approximately 24 months old) were subcutaneously administered T, or one of its 5alpha-reduced metabolites (dihydrotesterone-DHT, 5alpha-androstane,17beta-diol-3alpha-diol), or aromatized metabolite (estradiol--E(2)), or oil vehicle. Mice were administered androgens (1 mg/kg) 1 h before being tested in the forced swim test, an animal model of depression. We found that males spent more time immobile, and less time swimming, than females. Administration of T, DHT, or 3alpha-diol similarly reduced time spent immobile, and increased time spent struggling, of male and female mice. E(2), compared to vehicle administration, decreased time spent immobile of males and females, but increased time spent swimming of females and time spent struggling of male mice. Together, these data suggest that T and its 5alpha-reduced and aromatized metabolites have anti-depressant-like effects in aged male and female mice.
A growing body of evidence has pointed to the blockade of the N-methyl-d-aspartate (NMDA) receptor signaling as a potential therapeutic target for the treatment of major depression. The present study was aimed to evaluate behavioural and molecular effects of the chronic treatment with ketamine and imipramine in rats. To this aim, rats were 14 days treated once a day with ketamine (5, 10 and 15 mg/kg) and imipramine (10, 20 and 30 mg/kg) and then subjected to the forced swimming and open-field tests. Ketamine and imipramine, at the all doses tested, reduced immobility time, and increased both climbing and swimming time of rats compared to the saline group, without affecting spontaneous locomotor activity. Brain-derived neurotrophic factor (BDNF) hippocampal levels were assessed in imipramine- and ketamine-treated rats by ELISA sandwich assay. Chronic administration of both drugs, ketamine and imipramine, did not modify BDNF protein levels in the rat hippocampus. In conclusion, our findings demonstrate for the first time that chronic administration of acute inactive doses of ketamine (5 mg/kg) becomes active after chronic treatment, while no signs of tolerance to the behavioural effects of ketamine were observed after chronic administration of acute active doses (10 and 15 mg/kg). Finally, these findings further support the hypothesis that NMDA receptor could be a new pharmacological target for the treatment of mood disorders.
We have examined the anxiolytic activity of acute and chronic antidepressant treatment in an animal model of anxiety involving novelty-suppressed feeding. Rats were food deprived for 48 h, placed into a novel environment containing food, and the latency to begin eating was recorded. Chronic (21 days), but not acute injections of desipramine (DMI; 10 mg/kg) and amitriptyline (AMI; 10 mg/kg) significantly reduced the latency to begin eating compared to controls, but the percentage decrease was not as great as that seen with either acute or chronic treatment with diazepam (2 mg/kg) or adinazolam (20 mg/kg). A time course study indicated that at least 2 weeks of treatment was necessary to observe a significant anxiolytic effect of antidepressants. The anxiolytic effect of the antidepressants was specific to the novel environment, as 2 weeks of treatment with either diazepam or DMI did not influence the latency to begin eating in the home cage. Finally, a single dose of the central benzodiazepine receptor antagonist, Ro15-1788 (20 mg/kg), given 15 min prior to testing, did not block the anxiolytic effects of chronic DMI, while it completely eliminated the effect of chronic diazepam treatment. These data suggest that antidepressants acquire anxiolytic properties following chronic administration and that this effect appears to be independent of the benzodiazepine receptor system.
It is well established that depressive disorders are more prevalent in women; however gender differences in the pharmacological response to antidepressants are not a consistent finding in all reports. It is considered that this discrepancy can be explained by the fact that in most clinical trials drug use for comparative purposes is not completely different. In this study gender differences in antidepressant response with citalopram (CTP), a selective serotonin reuptake inhibitor and reboxetine (RBX), a selective noradrenaline reuptake inhibitor were evaluated in a group of young men and premenopausal women.
Eighty-six depressed patients 18 to 40 years old participated in an 8-week double-blind clinical trial. Subjects were divided in four groups according to sex and treatment assignation: females treated with CTP (n = 25) or RBX (n = 23), and males treated with CTP (n = 19) or RBX (n = 19). Response was determined using HDRS and BDI.
ANOVA analysis considering change in HDRS scores from baseline to last evaluation found a significant interaction between gender and type of treatment. Females treated with CTP showed a significantly greater response than females treated with RBX, while in men no differences were observed for both drugs.
Replication using larger sample size and longer treatment periods is required.
These results support previous findings which show that premenopausal women respond better than men to serotonergic antidepressants. They also support that a plausible interaction between gonadal hormones and serotonin may explain gender differences in antidepressant response.
Ketamine is a non-competitive antagonist to the phencyclidine site of N-methyl-d-aspartate (NMDA) receptor. Clinical findings point to a rapid onset of action for ketamine on the treatment of major depression. Considering that classic antidepressants may take long-lasting time to exhibit their main therapeutic effects, the present study aims to compare the behavioral effects and the BDNF hippocampus levels of acute administration of ketamine and imipramine in rats. To this aim, rats were acutely treated with ketamine (5, 10 and 15 mg/kg) and imipramine (10, 20 and 30 mg/kg) and animal behavioral was assessed in the forced swimming and open-field tests. Afterwards, BDNF protein hippocampal levels were assessed in imipramine- and ketamine-treated rats by ELISA-sandwich assay. We observed that ketamine at the doses of 10 and 15 mg/kg, and imipramine at 20 and 30 mg/kg reduced immobility time compared to saline group, without affecting locomotor activity. Interesting enough, acute administration of ketamine at the higher dose, but not imipramine, increased BDNF protein levels in the rat hippocampus. In conclusion, our findings suggest that the increase of hippocampal BDNF protein levels induced by ketamine might be necessary to produce a rapid onset of antidepressant action.