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Psychobiology of Sexual Behavior in the Guinea Pig
Abstract
This chapter discusses the psychobiology of the sexual behavior in the guinea pig. When a female guinea pig is placed with a male, he begins to follow and circle her almost immediately, usually sniffing at the anogenital region. This behavior is called “nuzzling.” Within a few seconds he may mount her, usually posteriorly, but often elsewhere. Frequently, the mounting is accompanied by pelvic thrusts without intromission, but more commonly it is followed by intromission with or without pelvic thrusts. The duration of the pelvic thrusts varies, depending partly on the male and partly on the responsiveness of the female. Following ejaculation, both animals roll back on their haunches and lick the genitalia. The male can be seen to drag his butt along the floor of the cage somewhat like a dog infested with intestinal worms does. Unless the female with which copulation has occurred is replaced by another female ejaculation usually marks the end of any strong interest in the female. A behavior that is displayed by many males is a “nondirected hyper-excitability.” The frequency of this behavior is increased following castration of sexually experienced adult males and its frequency is much greater in intact males reared alone in which the organization of normal patterns has not been perfected.
... Reports in the literature also give a wide range for male age at maturity. Young (1969) mentions that males show most ...
... Thus, they mature about as early as house mice despite a much larger body mass (500 vs. 25 g, respectively, for fully grown females). This also applies to the domestic relative of the wild cavy , the guinea-pig Cavia aperea f. porcellus, for which a mean age at maturity (first vaginal opening) of 50-68 days was reported (Young, 1969). Given that body mass predicts age at maturity quite well in mammals (Millar, 1977;Wooton, 1987), this observation comes as a surprise. ...
... Rood & Weir (1970) which might have produced strong female-female inhibitory effects as reported for mice in the literature (Vandenbergh, Drickamer & Colby, 1972;Drickamer, 1982a). Young (1969) also found age at first oestrus in domestic guinea-pigs to be much later than in our experiments, namely at 56-68 days. However, in contrast to Rood & Weir (1970), he found that females that were oestrous for the first time achieved the same pregnancy rates as multiparous females. ...
Age at maturity, a particularly important parameter in the life history of small mammals, contributes greatly to fitness. Social influences on age at maturity have been demonstrated for altricial rodents, in particular, mice. Nothing is known about such effects in precocial small mammals. Wild cavies Cavia aperea are born in a highly precocial state and mature early in life, briefly after weaning. We investigated whether the wild cavy C. aperea and the domestic guinea-pig Cavia aperea f. porcellus reach maturity earlier in the presence of adults of the opposite sex. Juvenile females kept in pairs without males showed first vaginal opening (=oestrus) when 59 days old in cavies and at about 40 days in the guinea-pig. However, in the company of adult males, cavy females kept in pairs reached maturity when about 30 days old, and guinea-pig females when 26 days old. Most cavy females experienced successful pregnancy following first vaginal opening. In cavies, female mass at birth and at first oestrus was not correlated with age at first oestrus. In guinea-pigs, birth mass predicted age at maturity only when a male was present. The growth rate from birth to first oestrus related to age at first oestrus. In the wild cavy, the presence of a male appeared to influence maturation more between days 25 and 30 than earlier in life. Male C. aperea matured and had fully descended testes when about 65–70 days old. All male cavies produced abundant motile sperm from day 75. First successful copulations occurred at about the same age. Surprisingly, the priming effect of the presence of an adult male on female maturation proved stronger in these highly precocial caviomorphs than in altricial rodents investigated so far.
... Estimates of the age of puberty in male guinea pigs have varied greatly over the years (Young, 1969). In agreement with the results of others (e.g., Sachser & Prove, 1988;Webster & Young, 1951) and our own observations at the time (Hennessy et al., 1995(Hennessy et al., ,1996, we referred to 35-55-day-old males as "juveniles" in earlier articles. ...
... However, in recent preliminary observations, we found that two female guinea pigs, each exposed to only a single male of about this age (38 and 40 days of age) subsequently became pregnant. Forty days is the youngest age in the range at which guinea pigs have been estimated to reach puberty on the basis of the ability to ejaculate (Young, 1969). Although variability is again common, both active spermatazoa (Avery, 1925) and sharply elevated circulating plasma testosterone levels (Rigaudiere et al., 1976) have been observed by 40 days of age. ...
... Yet, in our preliminary observations, males that had been housed continuously with their mothers impregnated unfamiliar females and, therefore, were clearly directing their mounts appropriately. During development, guinea pig males exhibit misdirected mounting before appropriately directed mounting is observed (Young, 1969). It may be that rehousing for 24 hr without the mothers was not a sufficient amount of time to completely eliminate the suppression of mother-directed sexual behavior and that the more established components of behavior emerged before those that had been more recently acquired. ...
Periadolescent male guinea pigs (Cavia porcellus) housed continuously with their mother displayed little or no sexual behavior when they were tested with her in a novel environment. However, if males were rehoused without their mother for 24 hr before testing, they frequently directed courtship and sexual behavior toward her. This effect occurred whether the mother was isolated or not during the rehousing period. In addition, rehousing without the mother produced a significant rise in the plasma testosterone levels of the males. It appears that continuous housing with the mother inhibits sexual and courtship behavior directed toward her, as well as gonadal activity, in periadolescent male guinea pigs. These effects may serve to prevent inbreeding.
... In order to detect any systematic changes correlated with endogenous hormone variations, it is necessary to align the data relative to the underlying endocrine events associated with ovulation. Lordotic behavior, spontaneous rupture of the vaginal membrane, and vaginal cytology are closely correlated indicators of ovulation (Kelly & Papanicolaou, 1927;Quinn, 1969;Young, 1969) all of which indicate a cycle duration of 16-17 days (Ford & Young, 1953). ...
... Furthermore, the results show that water intake and body weight are similarly depressed during that portion of the ovarian cycle. Estradiol is known to be a necessary hormonal factor in inducing ovu- lation, behavioral estrus, and vaginal membrane rupture (Young, 1969). In addition, estradiol depresses food intake of ovariectomized guinea pigs, whereas progesterone does not (Czaja & Goy, 1975). ...
Conducted 6 experiments to examine the effects of estradiol on ingestive behaviors of guinea pigs. Estradiol treatment was found to reduce water intake independently of its actions on food intake and body weight. In the 1st experiment, minimum intake and body weight of 17 intact female guinea pigs coincided with rupture of the vaginal membrane, the estimated time of ovulation. In Exp II, injections of 3 |mg of estradiol benzoate (EB)/day to 7 ovariectomized females significantly depressed food intake, water intake, and body weight, compared with 7 Ss that received oil injections. Reducing food rations to 30% below ad lib levels in Exp III by itself had no significant effect on drinking in ovariectomized Ss. In Exp IV, therefore, ovariectomized females were first placed on a food ration 30% below ad lib levels and then injected daily with either 3 |mg of EB or oil. Compared with oil injections, these EB injections significantly reduced water intake, while food intake did not decline significantly. Findings indicate that estradiol operates through different mechanisms to affect water intake and food intake. (40 ref)
... This form is hydrolyzed in vivo to the physiologically active 17-estradiol. Progesterone is injected only in an unmodified form (80). Testosterone is usually administered as testosterone or testosterone propionate (81). ...
... In much of the early work in behavioral endocrinology, estradiol benzoate was the most effective form of estrogen found to induce sexual receptivity in females when followed by progesterone (80), so this became standard in the field of hormonal regulation of feminine sexual behaviors. It is likely that this form was chosen over free 17-estradiol or estrone because it is generally effective in lower doses than either of these free, unesterified estrogens. ...
This chapter provides a conceptual and methodological overview of relevant issues in sex differences/sexual differentiation research, and provides guidance to investigators studying the role of sex and/or gonadal steroids in a variety of physiological or behavioral functions in experimental animals and man. Topics discussed include the difference between sex and gender, testing organizational effects of gonadal steroids, testing activational effects of gonadal hormones, conditions that can affect the endocrinology of the estrous cycle, and testing sex-specific effects of sex chromosome genes.
... Much of what we know about the hormonal regulation of female copulatory behavior comes from the pioneering work of W.C. Young and his collaborators. A superb review describing in detail much of the early behavioral work in this field is available (Young, 1969). Ovariectomy abolishes the appearance of sexual behavior by eliminating the cyclic release of sex steroid hormones (Boling and Blandau, 1939;Dempsey et al., 1936). ...
... The period of sexual receptivity for each species is rather tightly regulated. For example, in estrous-cycling guinea pigs, as after estradiol and progesterone treatments, heat lasts about eight hours (Young, 1969) Likewise, rats remain sexually receptive for approximately 14 hours (Blandau et al., 1941), but in ovariectomized rats, the duration is very dependent on hormonal treatment. It has been suggested that this timing of sexual receptivity is referable to the regulation of occupied PRs in particular neurons (Blaustein and Olster, 1989). ...
Feminine sexual behavior has been used extensively as a model system for understanding the mechanisms by which hormonal and neural signals interact at the cellular level to modulate behavior. Synthesis of much of the early behavioral and neuroendocrine work on this system with new cellular and molecular findings suggests that a fruitful direction to pursue is to examine how behavioral, hormonal, and sensory factors inter-act to modulate changes in the suite of female sexual behaviors. The neuronal integration of hormonal and neural mechanisms is a major contributor to the control of this behavior. This review offers a revised, theoret-ical framework with which to approach the study of feminine sexual behavior. Although some of the defi-ciencies in our knowledge of how the hormonal and mating stimuli are integrated in the brain will be dis-cussed, so too will results of experiments showing the substantial progress made in understanding mecha-nisms of steroid hormone action, as well as integra-tion of neural input with steroid hormone receptor processes. Collectively these studies are beginning to demonstrate the ways that hormonal and afferent, neu-ronal sensory inputs are orchestrated to alter brain and behavior.
... Early descriptive studies (Avery 1925;Louttit 1927Louttit , 1929 were enlarged by W. C. Young and his associates at the University of Kansas whose improved analytical and experimental techniques provided data (inter alia) on sexual patterns and cycles, the genetics of sexual behaviour, and effects of sex hormones on behaviour. Much of this work is summarized in a recent review paper (Young 1969). In these studies observations were ordinarily made on a male and oestrous female placed together in a laboratory cage. ...
... In the following work I initially name and describe the principal behaviour patterns found in the Caviinae. Many names of the behaviour patterns have been taken from the rodent literature (primarily from Grant & Mackintosh 1963;Eisenberg 1963;Young 1969) but some are my own. Observations on ecology and social behaviour, including quantitative data on the principal social behaviour patterns, are then discussed separately for each genus. ...
... In rats, the lordosis rating, a rating on a 0–3 scale reflecting the intensity of the response, is often used as well (Hardy and Debold, 1971; Hardy and DeBold, 1972). In guinea pigs and hamsters, species with a sustained and obvious lordosis posture, lordosis duration is typically used, often in response to manual palpation (Young, 1969; Noble, 1973) (often with a soft brush in hamsters). Although it took many decades and a multitude of experiments to fully understand the basic hormonal underpinnings of feminine sexual behavior in rats and guinea pigs, it is clear that during the estrous cycle, the sequential secretion of estradiol and progesterone from the ovaries results in a period of sexual behavior that is linked to the time of ovulation (Collins et al., 1938; Boling and Blandau, 1939; Powers, 1970; Barfield and Lisk, 1974) (>Figure 3-1 ). ...
... The period of sexual receptivity typical for each species is rather tightly regulated. For example, in estrous‐cycling guinea pigs, as after estradiol and progesterone treatments, sexual receptivity lasts about 8 h (Young, 1969). Similarly, rats remain sexually receptive for approximately 14 h (Blandau et al., 1941), but in ovariectomized rats, the duration is very dependent on hormonal treatment and the manner in which heat duration is defined (Pfaus et al., 2000). ...
... Ovarian steroid hormones, estradiol (E 2 ) and progesterone (P) regulate cellular functions in the central nervous system resulting in alterations in reproductive physiology and behaviors in various species (Young, 1969; Pfaff, 1980; Blaustein and Olster, 1989; Meisel et al., 1990; Pfaff et al., 1994; Blaustein and Mani, 2007; Mani and Portillo, 2010). In addition to reproduction, P plays a role on other biological functions including aggression, maternal behavior, learning and memory, mood, and sexual differentiation (Fraile et al., 1987; Meisel et al., 1990; Flood et al., 1992; Vallee et al., 1997; Wagner et al., 1998; Numan et al., 1999; Bloch et al., 2000; Wagner, 2006; Dreher et al., 2007 ). ...
... While P-initiated mechanisms contributing to these physiological effects are actively being investigated, a wide body of literature exists on P action in reproductive behavior in female rodents. Reproductive behavior can be manipulated in a predictable fashion by sequential treatment of E 2 and P to an ovariectomized female rodent (Young, 1969; Pfaff, 1980; Feder, 1984). This behavior can be measured with a high degree of validity and reliability, and has remained the model of choice for investigations of mechanisms of P action in the brain. ...
Steroid hormone, progesterone, modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and behavior. These neuronal effects are mediated primarily by intracellular progestin receptors (PRs) in the steroid-sensitive neurons, resulting in transcription-dependent genomic actions (classical mechanism). In addition to progesterone, intracellular PRs can also be activated in a “ligand-independent” manner by neurotransmitters, peptide growth factors, cyclic nucleotides, and neurosteroids. Recent studies indicate that rapid, non-classical progesterone actions involving cytoplasmic kinase signaling and/or extranuclear PRs can result in both transcription-independent and transcription-dependent actions. Cross-talk between extranuclear and classical intracellular signaling pathways promotes progesterone-dependent behavior in mammals. This review focuses on the mechanisms by which progesterone-initiated signaling mechanisms converge with PRs in the brain to modulate reproductive behavior in female rodents.
... The major findings of these studies are that prenatal stress leads to significant but sex-dependent changes in behavioural and neurodevelopmental outcomes in the guinea pig at an age equivalent to childhood in humans (pre-puberty) (Young, 1969). The changes in behaviour following prenatal stress suggest marked hyperactivity in male offspring and, to a lesser extent, anxiety-like behaviour in female offspring. ...
Background
Chronic psychosocial stress during pregnancy and/or after birth, and the associated elevation in cortisol, is linked with the onset of behavioural disorders in childhood. Previously, prenatal stress has been shown to reduce neurosteroid pathways in the fetus and the levels of the neurosteroid and GABAA receptor agonist, allopregnanolone. In late gestation, elevated levels of GABAergic activity increases inhibitory tone and protects against excessive excitation. These levels of allopregnanolone may also contribute to promoting myelination, thus stress-induced suppression of protective neurosteroid levels may disrupt neurodevelopmental processes and can result in reduced myelination. The objective of this study was to examine whether prenatal and postnatal stress reduces levels of inhibitory pathways to result in behavioural, myelin, and GABAergic/glutamatergic pathway deficits in the hippocampus at a postnatal time point in the guinea pig equivalent to childhood in humans.
Methods
Pregnant guinea pig dams were exposed to prenatal stress (PRE) with strobe light exposure for 2 h/day on gestational age (GA) 50, 55, 60 and 65 (term is ∼GA70), with postnatal stress (POST) caused by maternal separation for 2 h/day from postnatal day (PND) 1–7), or a double-hit of both stressors (PRE + POST). Control dams and offspring groups (CON) were handled at the same time each day without causing stress. Behavioural outcomes were assessed using open field and elevated plus maze testing on PND27. After euthanasia on PND30, plasma samples were collected for steroid quantification of cortisol, allopregnanolone and progesterone by ELISA. Hippocampal samples were collected to assess markers of oligodendrocyte development and mature cells by myelin basic protein (MBP) immunostaining and GABAergic and glutamatergic pathway component gene expression by real time PCR.
Results
Male guinea pig offspring exposed to prenatal stress exhibited hyperactive-like behaviour at childhood equivalence, while female offspring displayed anxious-like behaviour, to a lesser extent. In both sexes, MBP immunostaining was significantly decreased in the hippocampal region following prenatal stress, despite normal levels of MBP mRNA, which suggests a disruption to the MBP protein translation pathway. Many components of the GABAergic and glutamatergic pathways were disrupted following prenatal stress, notably GABAA receptor subunits, GABA production and uptake, glutamate ionotropic and metabotropic receptor subunits and glutamate transport. Following prenatal + postnatal stress, many of the behavioural and neurodevelopmental deficits were improved compared to the prenatal stress only group.
Conclusion
We conclude that prenatal stress disrupts GABAergic and glutamatergic pathways that may contribute to reduced myelination and subsequent behavioural deficits in the offspring. The deficits seen following prenatal stress are ameliorated when paired with subsequent postnatal stress, which highlights the early postnatal period as an important treatment window.
... It was domesticated about 3000-6000 years ago (Hu¨ckinghaus 1961;Ku¨nzl and Sachser 1999;Stahnke and Hendrichs 1988;Weir 1974). It had been commonly used as laboratory animals in biological and biomedical research for a long time (Avery 1925;Kaiser et al. 2003;Sachser 1986Sachser , 1998Young 1937Young , 1969. Guinea pigs are popular pets worldwide for many decades (MHller-Haye, 1981). ...
The present study was carried out to elucidate the grooming behavior under clean and dust environmental condition in domestic American guinea pig (Cavia porcellus). The domestic guinea pig was allowed to provide all necessary food items and water prior to the initiation of experiment in order to minimize physiological stress and the present study was carried out in residential place at Homagama during the period of December 2015 to January 2016. The guinea pig was placed for 1 hour in the clean environment and allowed another 1 hour in dust environment. Wood shavings were applied to the cage in order to make cage as dust environment. Then number of grooming and time taken for each grooming in seconds in each environment were recorded. As this manner recordings were taken for 10 days. Data were analyzed statistically using Microsoft Excel 2013 for Chi-Square test. Results revealed that the Grooming behaviour of Guinea pig was significantly high in dust environment in comparing with the clean environment (χ 2 test; p<0.001).
... The timing of the duration of the period of sexual receptivity is referable to the regulation of activated PRs in particular neurons (Blaustein and Olster, 1989). The period of sexual receptivity for each species is rather tightly regulated, with heat in guinea pigs lasting about 8 h (Young, 1969), and heat in rats lasting approximately 14 h (Blandau et al., 1941). Injection of a behaviorally effective dose of progesterone in estrogen-primed guinea pigs and rats (Blaustein and Feder, 1980;McGinnis et al., 1981;Rainbow et al., 1982) or the preovulatory secretion of progesterone during the estrous cycle of rats (Rainbow et al., 1982) causes the rapid binding to PRs, including those in the hypothalamus and preoptic area. ...
... The duration of sexual receptivity for each species is tightly regulated, lasting about 8 h in guinea pigs 360 and about 14 h in rats. 361 The timing of the duration of sexual receptivity is referable at least in part to the regulation of activated PRs in particular neurons. ...
This chapter reviews the current state of knowledge concerning the neurobiology of female sexual behavior, including sexual arousal, appetitive desire, pacing of sexual stimulation, the receptive postures that allow vaginal penetration to occur, and the inhibitory or refractory states induced by sexual stimulation, sexual nonreward, and/or the steroid hormone milieu. Data from a variety of species, including humans, is discussed at several levels of analysis that link neuroendocrinology, neuropharmacology, and molecular biology. The context in which sexual behavior occurs, especially during an animal's first sexual experiences, is considered in terms of culture and experimental conditioning, processes that alter neuronal responses, and ultimately behavior in the presence of external sexual incentive cues that predict sexual pleasure or nonreward. New vistas for further research are discussed.
... The guinea pig is one of the oldest domestic animals of South America and was already domesticated about 3,000-6,000 years ago (Hückinghaus 1961;Künzl and Sachser 1999;Stahnke and Hendrichs 1988;Weir 1974). Nowadays it is one of the most commonly used laboratory animals and pets throughout the world and has been subject to biological and biomedical research for many decades (Avery 1925;Kaiser et al. 2003;Sachser 1986Sachser , 1998Young 1937Young , 1969. Surprisingly, until today little knowledge has existed about the behavior of the wild cavy (Cavia aperea), the feral ancestor of the domestic guinea pig, in its natural habitat, and a sound investigation of the social organization is still lacking. ...
This study aims to elucidate the social system of the wild cavy (Cavia aperea), the feral ancestor of the domestic guinea pig, whose behavior under natural conditions is almost unstudied. Therefore, a population of C. aperea was investigated for a 6-month period in its natural habitat in southeastern Brazil. The animals' space use was examined via radiotelemetry, social interactions were recorded using direct observations, and genetic relationships were analyzed via DNA fingerprinting. Additionally, the distribution of plant cover, food resources, and predation risk was recorded to investigate the impact of different ecological factors on evolution of the social system. In the study period, a low population density was detected and a strong predation pressure existed, which resulted in a high mortality rate of C. aperea. Spatial distribution of wild cavies was strongly associated with areas of dense ground vegetation. Within these areas, small groups consisting of 1 male and 1-2 females occupied stable home ranges that overlapped only slightly with home ranges of adjacent groups. Social interactions were restricted mainly to individuals of the same group, and initial analyses of paternity indicate that the females' offspring were sired by the respective group male. The social system and spatial organization of C. aperea are regarded as adaptations to high predation pressure because in dense vegetation small group size reduces the risk of detection by predators. Moreover, habitat use, social interactions, and paternity point to a single-male system in this low-density population of wild cavies.
... The timing of the duration of the period of sexual receptivity is referable to the regulation of activated PRs in particular neurons (Blaustein and Olster, 1989 ). The period of sexual receptivity for each species is rather tightly regulated, with heat in guinea pigs lasting about 8 h (Young, 1969), and heat in rats lasting approximately 14 h (Blandau et al., 1941). Injection of a behaviorally effective dose of progesterone in estrogen-primed guinea pigs and rats (Blaustein and Feder, 1980; McGinnis et al., 1981; Rainbow et al., 1982) or the preovulatory secretion of progesterone during the estrous cycle of rats (Rainbow et al., 1982) causes the rapid binding to PRs, including those in the hypothalamus and preoptic area. ...
but met an untimely death between publication of the first and second edition. Although Mary could not contribute directly to this chapter, her contributions to the first edition, as well as to the field, were incalculable. Our review in the first edition of this volume was a true team effort with each author bringing a unique perspective to this problem. Mary spent most of her scientific career doing integrative studies aimed at understanding the neuroendocrine underpinnings and outcomes of sexual behaviors from a wide variety of perspectives. Many of the ideas in this chapter are the result of her research and her thinking. Mary is missed by her friends, trainees, and colleagues, but she will live on through her many scientific contributions and fond memories.
... All were in vaginal estrous at the onset of the experiment to control for phase-specific behavior and stress responses (Birke 1981;Viau & Meaney 1991). Estrous was defined after visual inspection of the anogenital region (Stockard & Papanicolaou 1917;Young 1969). To familiarize the animals to the experimenter they were exposed to a handling pre-treatment during isolation (Igarashi & Takeshita 1995). ...
Numerous studies have demonstrated interactions between oxytocin (OT) secretion, adrenal activity, an animal's social environment, and stress responses. In the present study, we hypothesized that partner preference and pair bonding cause increased peripheral OT, which down-regulates the adrenal and behavioral response in stress. In addition, we tested whether these interactions depended on sex, the social environment of the individual, or the type of stressor. Experiments were carried out on guinea-pigs held in sexual-pairs or stressed by isolation. Among the paired individuals choice tests were carried out to document partner preference. Female preference for a male was expressed by spatial cohesion. Stress responses to abiotic stimuli were examined and compared between isolated and cohabited animals with or without preference. Results show that OT of cohabited animals was significantly higher than during isolation. OT levels were further increased in males preferred by females. Cortisol (CORT) levels were elevated in isolated animals. There were no significant differences between pairs with and without female preference. Behaviorally, partner preferences were expressed by high amounts of tactile contact. The stress-induced behavioral immobility response after exposure to a noise stressor was significantly reduced in preferred males and to a lesser extent in their female partners. Only females with preferences showed an endocrine stress response. Their levels of OT increased. There was no consistent post-stressor release of CORT. The data indicate that the social environment of an individual, here expressed as preference or isolation, influences peripheral OT secretion. Behavioral stress responses were similarly affected by social factors without a clear involvement of peripheral CORT or OT.
... PGMRC1 is thought to activate P450 proteins functioning as a component of multi-protein Pbinding complex [223]. The mPRs, initially discovered in teleost ovaries, are G-protein coupled receptors (GPCRs) that belong to the seven-transmembrane progesterone adiponectin Q receptor (PAQR) family and comprise of at least three subtypes, α, β and γ. mPRs identified in the seatrout are localized to the plasma membrane, bind P with high affinity (Kd~5 nM), and have been shown to be involved in P-mediated induction of meiotic maturation [278,279] and sperm motility [260]. mPRα receptors down-regulate adenylyl cyclase activity [257] by direct coupling to G proteins and activating pertussis-sensitive inhibitory proteins (G i/o ). ...
The steroid hormone, progesterone (P), modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and reproductive behavior in female mammals. A wide body of evidence indicates that these neural effects of P are predominantly mediated via their intracellular progestin receptors (PRs) functioning as "ligand-dependent" transcription factors in the steroid-sensitive neurons regulating genes and genomic networks. In addition to P, intracellular PRs can be activated by neurotransmitters, growth factors and cyclic nucleotides in a ligand-independent manner via crosstalk and convergence of pathways. Furthermore, recent studies indicate that rapid signaling events associated with membrane PRs and/or extra-nuclear, cytoplasmic PRs converge with classical PR activated pathways in neuroendocrine regulation of female reproductive behavior. The molecular mechanisms, by which multiple signaling pathways converge on PRs to modulate PR-dependent female reproductive behavior, are discussed in this review.
... W.C. Young and his colleagues outlined the principles of gonadal steroid actions on sexual differentiation of the brain (reviewed by Young, 1961 and1969;Young et al., 1964). They used the term activational for the reversible effects by which gonadal hormones stimulate sexual behaviors in adult animals, and organizational for the permanent effects that testosterone (T) exerts in perinatal life in decreasing adult sensitivity to ovarian hormones (Phoenix et al., 1959) and increasing adult sensitivity to T (Grady et al., 1965). ...
In the fifty years since the organizational hypothesis was proposed, many sex differences have been found in behavior as well as structure of the brain that depend on the organizational effects of gonadal hormones early in development. Remarkably, in most cases we do not understand how the two are related. This paper makes the case that overstating the magnitude or constancy of sex differences in behavior and too narrowly interpreting the functional consequences of structural differences are significant roadblocks in resolving this issue.
William C. Young was a major founder of the discipline of behavioral endocrinology. His impact derived from theoretical writing, voluminous important empirical research, and the many scientists he trained and inspired. He was instrumental in establishing that effects of androgens secreted pre-– and/or postnatally organize structures that mediate mating behavior in several mammalian species. His academic descendants are major contributors to modern behavioral neuroendocrinology.KeywordsGuinea pigAndrogensOrganizational hypothesisSex behavior
Childhood psychological trauma appears to sensitize stress‐related neuroinflammatory systems to increase later vulnerability for depression and other stress‐related mental disorders. Isolation of guinea pig pups from the maternal attachment figure for 3 h in threatening surroundings leads to a sensitization of inflammatory‐mediated, depressive‐like behavior and fever during later isolations. A previous study found the non‐selective COX inhibitor naproxen administered before the initial isolation moderated depressive‐like behavior and its sensitization. Here, we examined effects of naproxen given following early isolation. Male and female guinea pig pups surgically implanted with telemetry devices to measure core temperature were isolated for 3 h on 2 consecutive days near weaning (first isolation Day 20–24). Several days later, they began 4 consecutive days of injection with either saline vehicle or 10 or 20 mg/kg naproxen prior to a third isolation in early adolescence, that is, 10 days after their first isolation. Across the first two isolations, depressive‐like behavior and fever sensitized. Both doses of naproxen attenuated depressive‐like behavior during the third isolation. Fever was unaffected. Results suggest prostaglandin mediation of sensitization of depressive‐like behavioral, but not febrile, responses to subsequent isolation. Findings also support further study of anti‐inflammatory treatments to mitigate lasting consequences of early‐attachment disruption.
Estradiol injections reproduced part of the testosterone effect on masculine sex behavior in both 11 castrated male and 11 ovariectomized female Sprague-Dawley rats. Testosterone injections alone were not effective in stimulating feminine sex behavior, but testosterone + progesterone reproduced part of the estradiol effect on feminine behavior in female rats. The male or female Ss showing the most vigorous masculine behavior under 1 effective hormone condition also tended to respond most vigorously under other hormone conditions. Those Ss showing the most feminine behavior under 1 hormone condition also tended to do so under other hormone conditions. However, there was no significant relationship between an individual S's levels of masculine and feminine behavior either among the males or among the female rats. (29 ref.)
The desire to understand female sexual behavior and reproduction dates back several centuries. One of the first medical texts to discuss causes for women's reproductive health, like problems with fertility, contraception, and pregnancy and propose treatments was found in Egypt in 1889 and dated to at least 1800 BCE. While rudimentary understanding of female sexual arousal, desire, pleasure, and inhibition has been present in art and prose and date back to Ancient Greece, the more formal study of female sexual behavior began in the late 1800s with Darwin. In the last 80 years, research on female sexual behavior has become more sophisticated and has made tremendous progress.
Female sexual behaviors can be subdivided into three functional components, which are useful in studying neuroendocrine regulation of female sexual responsiveness: copulatory, paracopulatory, and progestative behaviors. Besides influencing these behaviors, the fluctuating ovarian hormones influence sexual motivation in virtually all species. In addition, sexual behavior and reproductive physiology are both influenced by external factors, typically received from the male. The interactions between hormones and the social environment influence short- and long-term modulation of sexual behaviors and reproductive physiology as well as the cellular mechanisms underlying these interactions.
Experiments initiated by W.C. Young and collaborators in the early 1930s (reviewed by Young 1961, 1969) have dominated the work on control of feminine mating behavior by ovarian hormones. The conceptual developments of this group still guide research in the field as well as in related fields, e.g., the hormonal control of body weight regulation (Wade 1976). In initial attempts to identify the endocrine factors controlling the induction of sexual receptivity in the guinea pig, it was found that growth of the Graafian follicle was accelerated in the hours preceding the onset of sexual behavior (Myers et al. 1936). Knowing that exogenous administration of luteinizing hormone (LH) induces rapid growth of the preovulatory follicle (Foster and Hisaw 1935), Dempsey et al. (1936) found that administration of LH to cyclic guinea pigs induced sexual receptivity if given at a stage of the estrous cycle when the ovaries contained ripe follicles; but not if given early in the cycle or if given to ovariectomized animals pretreated with estrogen. It was shown that the LH acted on the well-developed ovarian follicles, stimulating the production of a factor which in turn induced the behavior. The follicular factor was identified as progesterone. Thus, the hormonal factors controlling the display of sexual behavior during the guinea pig estrous cycle were shown to be estrogen and progesterone, and it was shown that progesterone acted on a background of estrogen priming, i.e., after a period of estrogen conditioning.
Female sexual behavior has been an active area of investigation for over 75 years. Sexual behaviors can be subdivided into three functional components, which are useful in studying neuroendocrine regulation of female sexual responsiveness: copulatory, paracopulatory, and progestative behaviors. Besides influencing these behaviors, the fluctuating ovarian hormones influence sexual motivation in virtually all species. In addition, sexual behavior and reproductive physiology are both influenced by external factors, typically received from the male. The interactions between hormones and the social environment influence short- and long-term modulation of sexual behaviors and reproductive physiology as well as the cellular mechanisms underlying these interactions.
This chapter summarizes the progress made in understanding how hormones, the central nervous system, and the periphery interact to regulate male sexual behavior, focusing on how that understanding developed, and where it is incomplete. It summarizes recent research on the neural mechanisms by which males integrate hormonal and sensory inputs to produce adaptive behavioral and physiological responses, not only in the context of mating, but also in other contexts. It describes the copulatory behaviors of species commonly studied in the laboratory, the paradigms and measures used to study them, and the conceptual contexts in which the research takes place. It also reviews the behavioral effects of gonadal steroids, and systemically or intraventricularly administered drugs. It summarizes the information about the functions of the brain areas implicated in the control of male sexual behavior, including effects of lesions and stimulation, local hormonal and pharmacological manipulations, and measures of neural activity. Further, it describes the interconnections among the neural structures that mediate sexual behavior.
The introduction, about 20 years ago, of sensitive and specific assay methods has permitted the measurement of plasma androgens, estrogens, and progestins in the systemic circulation in representatives of all vertebrate classes. The present survey deals with such measurements in adult mammals. The survey begins with a review of the systemic levels of plasma androgens in males of various mammalian orders. The second section considers estrogen and progestin levels in adult, nonpregnant females. The third section deals with the value of plasma hormone measurements in neurobiological research.
In the previous chapter, several experimental manipulations designed to demonstrate that the secretions of the hypothalamus, the anterior pituitary, and the ovary can have stimulatory and inhibitory effects on one another were discussed. These experimental approaches were basically analytic. They served to dissect the effects of a particular hormone on one tissue from its effects on another tissue. From this analytic approach, an appreciation was gained of the range of potential reactions to hormonal stimuli of individual components of the hypothalamo-hypophyseal-ovarian axis. However, the analytic approach does not indicate which of the potential reactions are actually utilized during the course of normal reproductive cycles. Nor does the analytic method deal with the question of how the various stimulatory and inhibitory actions of hormones become linked together to form a repeatable endocrine pattern with a consistent periodicity. To resolve these problems, one must adopt a more synthetic outlook.
This chapter discusses the facility design, environment, and basic husbandry recommendations for the guinea pig. Although general laboratory animal facility design and principles for rats, mice, and hamsters have applicability to the guinea pig, characteristics and behavior unique to this species have fostered implementation of new and/or adjunct husbandry practices to improve the care and use of this laboratory animal. In addition to the natural behavior and physiology of the species, the nature of the research activity performed considers planning, design, or modifications of guinea pig holding rooms. Quarantine facilities, breeding colonies, conventional and infectious disease research have different requirements for housing. The Guinea pigs are generally docile and seldom bite; however, they are easily frightened and will try to avoid capture or being held. This chapter further explains the housing condition required for guinea pigs, which includes the right ventilation, illumination, temperature, humidity, sanitation, noise conditions, and space requirements. Ventilation for laboratory animals should balance air quality, animal comfort, and energy efficiency to provide cage environments that will optimize animal welfare and research results. Furthermore, the chapter reviews the nutritional diseases and record keeping of guinea pigs. For the identification of the animals, cage cards are used and the cards should include the strain of guinea pigs, sex, number, principal investigator, and research protocol identification.
It has been known since the 1930s that the occurrence of sexual receptivity during the guinea pig oestrous cycle is regulated by the actions of oestradiol and progesterone (Young 1969). Work on the subcellular mechanisms of oestradiol action on sexual behaviour has steadily progressed through the years (McEwen et al. 1979). In the past 5 years substantial progress has also been made on the subcellular mechanisms of the interactions between oestradiol and progesterone on this behaviour. In this chapter we will focus on our work characterizing the cellular bases of the following three interactions between oestradiol and progesterone in the regulation of the expression of the lordosis posture in female guinea pigs:
1.
Progesterone facilitates the expression of lordosis in oestrogen-primed guinea pigs. Although oestradiol alone can induce sexual behaviour in oestrogen-primed, ovariectomized guinea pigs, a progesterone injection results in a shorter latency to heat and a more consistent heat duration. Treatment with progesterone also allows a lower priming dose of oestradiol to be used (Dempsey et al. 1936).
2.
Progesterone causes a period of refractoriness to further stimulation of lordosis by progesterone. This refractoriness has been referred to by a variety of terms depending upon the authors’ emphasis. It has been called the biphasic effect of progesterone, because progesterone first facilitates and then causes a failure to respond to progesterone (Zucker 1966). It has been called a refractory period because during this period guinea pigs are refractory to a progesterone injection (Morin 1977). It has also been called sequential inhibition to emphasize the fact that progesterone treatment follows oestradiol treatment (Powers and Moreines 1976). Finally, based on behavioural and biochemical experiments, we now view this influence of progesterone as desensitization to further stimulation by progesterone (Blaustein 1982a,b).
3.
Oestradiol and progesterone interact to determine the duration of the period of sexual behaviour. Although there has been a question of the relative importance of each hormone in this regulation (Wallen and Thornton 1979), both hormones influence the duration of the period of sexual receptivity (Collins et al. 1938, Morin and Feder 1973).
This chapter provides a survey of psychopharmacological studies of male and female sexual behavior, primarily conducted on rodent species. Because the expression of these behaviors normally requires the presence of gonadal hormones, this chapter attempts to integrate behavioral studies with studies on the effects of these hormones on neurotransmitter metabolism. The bulk of the literature in these fields focuses on norepinephrine (NE), dopamine (DA), serotonin (5-HT) and acetylcholine (ACh), all of which are involved in neuroendocrine regulation and in a variety of behaviors other than mating. For this reason, we also have attempted to place the neuropharmacology of reproductive behavior within a broader context. The other chapters in Part IV of this volume present closely related material.
Progesterone is the most biologically active progestin, which modulates neuroendocrine functions in the central nervous system to coordinate physiology and reproduction in female mammals. Progesterone action in the brain is primarily mediated via their intracellular nuclear receptors, progestin receptors (PRs) functioning as ligand-dependent transcription factors, in steroid-sensitive regions to regulate genes and genomic networks. PRs exist as two distinct isoforms, PR-A and PR-B. Recent studies suggest that in addition to progesterone, intracellular PRs can be activated in a ligand-independent manner by neurotransmitters, growth factors, and cyclic neucleotides via crosstalk and convergence of pathways. Nonclassical rapid signaling events associated with membrane PRs and/or cytoplasmic PRs also converge with classical PR activation to regulate PR gene expression in neuroendocrine regulation of reproductive behavior. The molecular mechanisms underlying PR-dependent transcriptional activation require the sequential recruitment of various coregulators. Coregulators are versatile regulatory proteins, influencing transcriptional initiation, elongation, splicing, and translation. Differential coregulator interactions could regulate the crosstalk between different signaling pathways to modulate biological processes.
Although it originally was believed that neuronal steroid hormone receptors require binding to cognate ligand for activation, more recent evidence suggests that the receptors can be activated indirectly by other compounds, such as neurotransmitters and growth factors, acting through their own membrane receptors and specific intracellular signaling pathways. For example, as is the case with facilitation of sexual behavior by progesterone, facilitation of sexual behavior by D1/D5 dopamine receptor agonists is blocked by disruption of progestin receptors. Therefore, some dopamine agonists facilitate sexual behavior at least in part by a progestin receptor-dependent mechanism, as does progesterone. This “ligand-independent activation” of neuronal progestin receptors is not limited to dopamine agonists; a variety of other compounds, as well as mating stimulation, facilitate sexual receptivity by a progestin receptor-dependent process. Steroid hormone receptors also can be regulated by afferent input in another way. Various neurotransmitters upregulate or downregulate steroid hormone receptors in some neurons. This, in turn, presumably confers greater or decreased sensitivity to the particular factors that can activate the particular steroid receptor in those particular neurons. Therefore, steroid hormones are but one class of factors that can regulate and activate steroid hormone receptors. Some additional factors that activate steroid hormone receptors have been identified, as have some factors that can regulate concentrations of receptors. Relatively little is known at this time about the range of neurotransmitters, humoral factors, and intracellular signaling pathways that are involved.
FOLLOWING TERMINATION OF ESTROGEN-PROGESTERONE-INDUCED RECEPTIVITY, SPAYED GUINEA PIGS WERE REFRACTORY TO FURTHER HORMONAL STIMULATION. REFRACTORINESS DID NOT OCCUR FOLLOWING ESTRUS WHEN ESTROUS BEHAVIOR WAS INDUCED WITH ESTROGEN ALONE, SUGGESTING THAT REFRACTORINESS IS ATTRIBUTABLE TO THE ACTIONS OF PROGESTERONE. UNDER MOST CONDITIONS PROGESTERONE EXERTED A BIPHASIC ACTION, 1ST FACILITATING AND THEN INHIBITING RECEPTIVITY. FOR AT LEAST 1 MEASURE OF RECEPTIVITY THESE ACTIONS OF PROGESTERONE APPEARED TO BE ALL-OR-NONE IN NATURE. A PRINCIPAL METABOLITE OF PROGESTERONE, 20 ALPHA-OH PROGESTERONE, FACILITATED RECEPTIVITY WITHOUT SUBSEQUENTLY DEPRESSING SEXUAL RESPONSIVENESS. THIS SUGGESTS A POSSIBLE DISSOCIATION OF FACILITATORY AND INHIBITORY MECHANISMS OF RECEPTIVITY FOR THIS SPECIES.
This chapter discusses the major molecular, behavioral, and population features of the t complex as an illustration of the relevance of data gathered at one level of analysis for interpretations at other levels. Behavior may be a major factor in determining the frequency of t haplotypes in wild mice. Genes within the t complex appear to have important effects on mating preference, parental investment, and aggressive behavior. There are probably two ways in which behavior regulates gene frequency. First, it seems likely that there is selection for t haplotypes because possession of a t mutation enhances male aggressive behavior. In all other respects, however, possession of a t haplotypes appears to lower fitness and mice appear to be capable of behaviorally altering the transmission of these otherwise deleterious genes to their progeny. Genes within the t complex have a large number of pleiotropic consequences for behavior. Understanding the behavioral consequences of t complex genotype can elucidate, in turn, the process controlling the frequency of these genes in natural populations.
Evolutionary theory suggests that offspring sex should be adjusted to environmental conditions in order to maximize future reproductive success. In several animal taxa environmental factors indeed affect the secondary sex ratio. In humans, changes in the sex ratio at birth have been associated with population stressors like war, environmental disasters or economic strife during pregnancy. Here we compared litter sex ratios of female guinea pigs, exposed experimentally to a stable and an unstable social environment. In the latter group composition was changed every three days. Under unstable social conditions the sex ratio was significantly more biased towards daughters than in the stable social situation. This finding was consistent among four independent experiments, conducted independently from each other. Life expectancy can be dramatically reduced under conditions of social instability. Hence mothers in such conditions should bias their investment towards the sex that reaches sexual maturity first, which is the female sex in this species. Thus, to shift the offspring sex ratio towards more daughters under conditions of social instability may represent a maternal strategy to maximize future reproductive success.
French child-rearing beliefs share features of both individualist and collectivist cultural orientations and have appeared contradictory within this individualism–collectivism framework in previous research. For this study, 32 Parisian mothers of infants and young children were interviewed regarding four possible sources of variation in their relationships with their children: interpersonal distance, communicative accommodation, desirable and undesirable early behaviors, and long-term goals and values. Five themes are identified and a cultural model of Parisian parenting is elaborated, demonstrating how beliefs, practices, and goals are connected in mothers' minds. This study demonstrates that individualism and collectivism are orthogonal, multifaceted orientations, each containing dimensions, such as autonomy as separateness and group affiliation and belonging, that can coexist both harmoniously and in dynamic tension within individuals and within cultures.
We review information on copulation behaviour and sperm competition in mammals using data primarily from the literature. Female mammals of many species regularly copulate with more than one male during each oestrous period. Such multi-male copulations are reported more often in social, compared with solitary species. In addition, the mates of males of polygynous species experience multi-male copulations as often as the mates of males or monogamous species. Male mammals attempt to increase their certainty of paternity through a number of reproductive tactics. Copulation frequency is higher in specks with multi-male copulations compared with other species. Consortships, which can br regarded as a form of mate guarding, are often absent from species in which more than one male copulates with each female during her oestrous period. Most solitary burrow-living small mammal species copulate in the open, whereas social species often copulate inside their burrows. Insurance copulations may occur in many species since high copulation rates occur in four circumstances: (i) when mates are reunited, (ii) when a new male takes over a female, (iii) when a strange male steals a copulation, and (iv) when an audience of males is present.
Some aspects of the experimental study of hormonally controlled sexually dimorphic behavior patterns are discussed, using results derived from research on rat and guinea pig sexual behavior as the model. The traditional concept that sex differences in behavior are due to differences in hormone sensitivity may be only partially correct and it is suggested that the sexes differ primarily in the extent to which their behavior is influenced by diurnal rhythm mechanisms.
Nine adult male rhesus monkeys were given eight 10-min tests of sexual behavior with eight ovariectomized female rhesus pretreated with estradiol benzoate. Males differed significantly in the number of tests during which they ejaculated, and females differed in the frequency with which specific males ejaculated when tested with them. With phylogenetic increase in neocortex, pair compatibility may be as important as hormonal stimulation in regulating male sexual performance. If this is correct, the problem of understanding the determinants of primate sexual behavior becomes more formidable.
Why are Mammalian Pinealocytes Equipped with Processes?Intercellular Communication of PinealocytesInnervation of PinealocytesConclusions
ReferencesDiscussionReferences
Object of the study was the variability of social behavior and organization in female guinea pigs as a function of the presence of a male. Four groups of 8 females were observed. Two of these groups were without a male, the other two had a sexually experienced, sterilized male. All females were about 20 d old at the beginning of the study. In the groups without a male the females formed clear and stable dominance relationships resulting in a linear rank order. The frequency of agonistic behavior was higher compared to the other groups. Some of these females displayed male-like courtship behavior. Among the females in the groups with a male only the alpha and omega positions were stable, while the dominance relations between the other females remained unstable. These females directed about 40–50 % of their contact behavior towards the male. In relation to the presence or absence of a male the females differed in their social orientation: those who lived with a male were strongly orientated towards it, those living without a male were strongly oriented towards each other. The hypothesis is put forward, that the females in the two situations differed in their motivational states. For the females living with a male this animal was a stable point of social reference, while for the females living without a male their stable dominance structure — with more agonistic behavior — was the most important stabilizing factor.
The ideal animal model would contribute no confounding variables in experimental science. Variables affect experimental design resulting in increased animal use or repeated studies. We demonstrated a simple refinement which may reduce the number of animals used experimentally while simultaneously improving animal welfare. The objective of this study was to determine if the presence of a hut was an impact on physiological stress levels, as determined by faecal cortisol concentration, during a routine four-day acclimatization period of newly received male Hartley-Outbred guineapigs. We hypothesized that those animals provided with huts would have decreased physiological stress compared with animals not provided with huts. We examined this effect within both paired and single-housed animals. A between-subjects one-way analysis of variance revealed that pair-housed animals with a hut had significantly lower faecal cortisol concentration than pair-housed animals without a hut and the presence and absence of a hut had no significant impact on faecal cortisol concentration in single-housed animals. These findings show that presence of a hut is beneficial in reducing physiological stress when pair housing male guineapigs and does not appear to have an impact when single housing male guineapigs. In addition, we have shown that faecal cortisol, and therefore physiological stress, is still increasing on study day 4 suggesting a longer acclimatization period is necessary. A simple refinement in housing environment and acclimatization time can both reduce the number of animals used experimentally and improve animal welfare.
Previous work from our laboratory showed that pretreatment with the antiestrogen enclomiphene (ENC) or with subthreshold doses of estradiol benzoate (EB) facilitates the action of subsequent EB plus progesterone injections on lordosis behavior in ovariectomized guinea pigs. The present study was performed in order to explore possible neurochemical correlates of this phenomenon. We found that facilitative behavioral actions of ENC or subthreshold EB pretreatment were correlated with significant increases in KCl extractable nuclear receptor for progestin (NRP) in hypothalamus-preoptic area-septum (HPS) samples (ENC pretreatment group= 54.8 ± 10.6, behaviorally subthresholdEB pretreatment group= 70.5 ± 11.2, vs contraol group given only oil vehicle17.6 ± 4.8fmol [3H]R5020 bound/mgDNA in the nuclear pellet. On the other hand, females given an injection of EB 11 h prior to progesterone but not given pretreatment with ENC or behaviorally subthreshold EB failed to show significant increases in HPS-NRP concentration compared to the uninjected control group (28.6 ± 3.3vs17.6 ± 4.88, respectively). These data suggest that: (1) ENC has some degree of estrogenic activity in brain; and (2) ENC or behaviorally subthreshold EB pretreatment facilitates subsequent EB plus progesterone action by increasing the induction of cytoplasmic progestin receptor and/or altering NRP levels in the HPS.
These experiments were designed to determine whether drug-induced changes in NA transmission affect lordosis behavior of female guinea pigs by altering steroid action within hypothalamic target cells. In the first experiment, we examined the effects of the dopamine-β-hydroxylase inhibitor, U-14,624, on cytoplasmic progestin receptors (measured using a one-point [3H]R5020 binding assay) in hypothalamus (HYPO), preoptic area (POA), cerebral cortex (CORT) and midbrain (MB) of estradiol benzoate (EB)-primed females. At 12 h after U-14,624 administration, specific binding of [3H]R5020 was 36% less in cytosol from HYPO (binding in POA, CORT, and MB was not affected by U-14,624) in drug-treated than in non-drug-treated controls. To determine whether this reduction in [3H]R5020 binding was due to competition of U-14,624 with [3H]R5020 for progestin receptors, we examined the effects of U-14,624 on [3H]R5020 binding in vitro. U-14,624 had no effects on [3H]R5020 binding under these conditions. By using a range of [3H]R5020 concentrations to assay cytoplasmic progestin receptors, we found that the reduction in [3H]R5020 binding on hypothalamic cytosol after U-14,624 treatment was due to a lower concentration of progestin receptors rather than to a lower progestin receptor affinity for [3H]R5020. Several lines of evidence indicate that the lower (compared to non-drug-treated females) concentration of these receptors was attributable to a reduction in NA transmission. First, U-14,624 caused a significant reduction in regional brain NE content. Second, activation of α-adrenergic receptors with clonidine completely reversed the effects of U-14,624 on cytoplasmic progestin receptors, although clonidine had no effect on progestin receptors when administered alone. Third, blockade of α-adrenergic receptors by i.p. injection of phenoxybenzamine (Pb) resulted in a relative reduction of specific [3H]R5020 binding in hypothalamic (but not POA, CORT or MB) cytosol of EB-primed females. There was a 3–4 h delay between the blockade of α-receptors by Pb (determined using a [3H]WB4101 binding assay) and a significant effect on the concentration of progestin receptors in cytoplasm of HYPO. The effects of Pb on hypothalamic progestin receptors did not appear to be due to a peripheral action of the drug. When administered intraventricularly, Pb caused a relative reduction in specific [3H]R5020 binding in hypothalamic (but not POA, CORT or MB) cytosol of EB-primed females. The lower concentration of progestin receptors in HYPO after drug treatment also did not appear to be attributable to the release of adrenal progesterone. The concentrations of progesterone in plasma at 0.5, 2, 4, and 12 h after Pb and at 12 h after U-14,624 administration were not different from control values. Furthermore, the concentration of cytoplasmic progestin receptors was lower only in HYPO after Pb and U-14,624 treatment, whereas injection of 100 μg progesterone caused a reduction in the concentration of these receptors in all brain areas examined. The lower concentration of cytoplasmic progestin receptors in HYPO after drug treatment might be attributable to a drug-induced interference with the EB-induced increase in the concentration of these receptors. This hypothesis is supported by the finding that Pb has no effect on hypothalamic progestin receptors in the absence of EB priming. Thus, changes in NA transmission might alter EB action in HYPO in addition to altering target cell sensitivity (through effects on progestin receptor concentration) to progestins.On the basis of these results we propose that the modulation of target tissue responsiveness to steroids is an important mechanism by which neurotransmitters affect steroid-dependent processes. The operation of such a mechanism would provide a rapid means by which environmental, behavioral and emotional events could modulate steroid-dependent behaviors and anterior pituitary function.
The new steroidal progestin receptor antagonist, RU 38486, was used to determine if progesterone-facilitation of sexual behavior in female guinea pigs requires interaction of the hormone with neural progestin receptors. Five milligrams but not 0.5 mg RU 38486 inhibits the expression of sexual behavior in ovariectomized, estrogen-primed guinea pigs treated with 0.1 mg progesterone. This inhibition can be overcome by administration of a large dose of progesterone, suggesting that the drug-effect is specific to the progestin receptor system. RU 38486 binds, in vitro, to progestin receptors and decreases the availability of hypothalamic progestin receptors in estrogen-treated guinea pigs. These studies provide strong evidence that progesterone interaction with intracellular neural progestin receptors mediates the facilitation of sexual behavior by progesterone in female guinea pigs.
Treatment with the dopamine beta-hydroxylase (DBH) inhibitor U-14,624 (50, 100, or 150 mg/kg) blocked the induction of lordosis behavior be estradiol benzoate (EB) and progesterone (P) in ovariectomized guinea pigs. After treatment with U-14,624 (100 mg/kg), norepinephrine (NE) content of medial basal hypothalamus, preoptic area and cortex was reduced (by 55%) and dopamine (DA) content of medial basal hypothalamus was increased (by 155%) during the period when females treated with EB and P normally display lordosis. Treatment with the NE receptor stimulator clonidine (1.0 mg/kg) restored lordosis behavior in females treated with EB, P, and U-14,624 (100 mg/kg), but the putative DA and serotonin (5-HT) receptor blockers pimozide (1.0 mg/kg) and methysergide (20.0 mg/kg) were ineffective in this respect. Thus, inhibition of lordosis after treatment with U-14,624 appeared to be attributable primarily to a reduction in NE neurotransmission, rather than to increase in DA or 5-HT activity. Because clonidine induced lordosis in females treated with EB, P, and U-14,624, it seemed unlikely that the facilitatory effects of clonidine on lordosis were mediated by activation of presynaptic alpha-adrenergic receptors (i.e. inhibitory NE autoreceptors) rather than by postsynaptic alpha-receptors. In addition, pretreatment with the postsynaptic alpha-adrenergic antagonist phenoxybenzamine (20.0 mg/kg) blocked the facilitation of lordosis by clonidine (1.0 mg/kg) in females primed with EB alone and with EB plus P. Thus, the facilitatory effects of clonidine on lordosis appear to be mediated by activation of postsynaptic alpha-adrenergic (i.e. NE) receptors. The results of this study provide further evidence that NE neurotransmission facilitates the expression of female sexual behavior in guinea pigs.
Male and female guinea pigs received radiofrequency lesions in the medial preoptic area (MPOA). Animals were gonadectomized, treated with estrogen and progesterone, and tested for the occurrence of the lordosis response to manual stimulation. Females with MPOA lesions exhibited enhanced lordosis behavior, shorter latencies to heat, longer duration of heat and longer maximum lordosis duration than sham control females. In males with MPOA lesions, the lordosis response could be elicited by manual stimulation, in contrast to no response in the sham control males. Furthermore, MPOA-lesioned males were insensitive to the inhibitory effects of progesterone on lordosis behavior, while MPOA-lesioned females were as sensitive as sham controls to the inhibitory effects of progesterone. The results suggest that a neural mechanism resides within the MPOA which inhibits the occurrence of lordosis behavior in both male and female guinea pigs and which is not involved in a sexual dimorphism in responsiveness to progesterone.
Progesterone was measured by radioimmunoassay in the plasma of Day 10 pregnant rats and in the plasma of ovariectomized rats injected with doses of progesterone that result in a decrease in sexual receptivity. Doses of progesterone (1–2.5 mg) that result in behavioral refractoriness to further progesterone treatment result in lower plasma levels of progesterone than those measured on the tenth day of pregnancy, a time of naturally-occurring behavioral inhibition. These data re-assert the possibility that endogenous progesterone produced during pregnancy in the rat is at least partially responsible for the decrease in female sexual behavior seen during pregnancy in this species.
Correlations between energy output as measured by resting O^B2) consumption and increased sexual excitability of male guinea pigs are reported. "It may be postulated that the physiological change provides the basis for measurable concomitant changes in an animal's rate of sexual response." 15 references.
An attempt was made to induce sexual precocity in male guinea pigs by prenatal and postnatal injections of testosterone propionate. Experimental groups were: (a) oil injected controls, (b) injected daily postnatally with testosterone propionate, (c) treated by injecting mothers from the 10th day of pregnancy until parturition with testosterone propionate, (d) both pre- and postnatally treated. 3 or 4 mating tests were given each week to 27 Ss starting 9-12 days after birth and to 9 Ss starting 20 days after birth. Postnatally treated Ss exhibited intromission and ejaculation 3-6 days earlier and mounting approximately 15 days earlier than oil injected controls. Prenatal administration of testosterone propionate alone did not advance the appearance of sexual responses. Less sexual precocity was produced than is reported for androgen-treated rats. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Inbred strains showed lower degrees of sexual behavior and were less variable than the males from heterogeneous strains. It is suggested that the character of mating behavior may have a genetic basis. (PsycINFO Database Record (c) 2006 APA, all rights reserved).
The sexual behavior of male and female guinea pigs from mothers receiving testosterone propionate during most of pregnancy was studied after the attainment of adulthood. As a part of the investigation, the responsiveness of the females to estradiol benzoate and progesterone and to testosterone propionate was determined.
The larger quantities of testosterone propionate produced hermaphrodites having external genitalia indistinguishable macroscopicalty from those of newborn males. Gonadectomized animals of this type were used for tests of their responsiveness to estradiol benzoate and progesterone and to testosterone propionate. The capacity to display lordosis following administration of estrogen and progesterone was greatly reduced. Male-like mounting behavior, on the other hand, was displayed by many of these animals even when lordosis could not be elicited. Suppression of the capacity for displaying lordosis was achieved with a quantity of androgen less than that required for masculinization of the external genitalia.
The hermaphrodites receiving testosterone propionate as adults displayed an amount of mounting behavior which approached that displayed by the castrated injected males receiving the same hormone.
The data are uniform in demonstrating that an androgen administered prenatally has an organizing action on the tissues mediating mating behavior in the sense of producing a responsiveness to exogenous hormones which differs from that of normal adult females.
No structural abnormalities were apparent in the male siblings and their behavior was essentially normal.
The results are believed to justify the conclusion that the prenatal period is a time when fetal morphogenic substances have an organizing or “differentiating” action on the neural tissues mediating mating behavior. During adulthood the hormones are activational.
Attention is directed to the parallel nature of the relationship, on the one hand, between androgens and the differentiation of the genital tracts, and on the other, between androgens and the organization of the neural tissues destined to mediate mating behavior in the adult.
Sunz?nary.-The normal rate of O2 consumption of 10 mature male guinea pigs was compared with that produced during the first several days in the novel situation and by sexual satiation and frustration. A higher than normal rate of OL' consumption recorclcd on the first day was followed by a lower than normal rate on the second and third days. Neither sexual satiation derived from ejacalation nor frustration produced by interrupting the copulatory pattern after the first intromission was found to modify significantly the normal rate of merabolism. In an attempt to explain these results, several hypotheses were suggestecl based on either the tendency of the guinea pig to crouch when frightened or the nature of the stimuli in the chamber of the metabolism apparatus. The concept of drive as used by many psychologists hns incli~ded reference to an energizing or activating function that can be altered by various antecedent environmental conditions ~nd measured by changes in overt behavior. The energizing property of drives has also been attributed to or correlated with various physiological processes. Malmo, who recently argued for the necessity of using physiological measures to estimate drive level, remarked that one might ". . . expect deprivation of food, water, sexual gratification, and the like, in raising the general drive state, co increase levels of physiological activity" (1958, p. 236). Similarly, Riss and Goy (1957) made the ass~lmption that the energizing capacity of drive should be a function of degree of metabolic activity and reported a positive correlation between mnle guinea pig sexual drive and rate of O2 consumption. The purpose of the present study was to relate O2 consumption in guinea pigs to various experimental conditions which might be presiuned to influence drive level. In particular, rate of O2 utilization was measured after the animals experienced three different experimental conditions: a novel situation, sexual gratification, and frustratios.
The influence of sexual experience gained prior to castration, on the degree of retention of sexual behavior after removal of the testes was investigated in an experiment involving 15 male cats raised from weaning in the laboratory. During a series of 20-minute tests, nine males were permitted between 11 and 81 intromissions per animal (Group I). Six males were permitted only minimal sexual experience (Group II). Four of these cats were tested until the first mount was performed, at which time they were gently separated from the female. The other two males were not permitted any sexual behavior. After castration the males of both groups were tested weekly until sexual behavior had ceased to appear, or in the case of
Using females from the highly inbred strains 2 and 13 and from a genetically heterogeneous stock (strain T), five measures of sexual behavior were investigated tfor the consistency with which they are displayed by each strain when equal and different quantities of α-estradiol benzoate are followed by a constant amount of progesterone. The five measures were 1) latency of estrus, 2) duration of estrus, 3) duration of the maximum lordosis, 4) frequency of male-like mounting, and 5) per cent of animals brought into heat by the treatment. From strain to strain there are consistent differences in the five measures. Strain 2 females show the shortest latencies, the longest duration of estrus, the least male-like mounting behavior, and the highest responsiveness to the estrogen. Their maximum lordosis which is intermediate in length is exhibited during the third hour of heat. Strain T females are characterized by long latencies, relatively short heat periods, and are intermediate with respect to mounting behavior and their responsiveness to α-estradiol benzoate. Their mean maximum lordosis is shortest and is exhibited during the first hour of heat. Strain 13 females display a latency and duration of heat similar to those which characterize the strain T females, but more male-like mounting than the other animals. They are least responsive to the estrogen. The mean maximum lordosis which is longest in this strain appears during the second hour of heat. The sexual vigor of strains 2 and 13 is greater than that of the strain T females. This order is opposite that in males from the same strains. The relatively vigorous sexual behavior of the inbred females is postulated to be of value for the perpetuation of these strains. Latency varied inversely and duration of heat directly with increases in the amount of α-estradiol benzoate, although with respect to the length of time that vigorous lordoses were elicited, above-threshold quantities were without effect on the response. Duration of lordosis and the frequency of mounting were not effected by changes in the amount of hormone. In general, therefore, the principle established for the male, that supra-liminal quantities of gonadal hormone do not alter the characteristic pattern of the behavior, can be extended to the female. The distinction between responsiveness to the hormone and vigor of the reaction is discussed.
Thirteen male kittens were castrated at the age of 4 months. When tested in adulthood with oestrous females they performed very little sexual behaviour. Only one of these males mounted the female, but stepping, thrusting and intromission were absent. When the above tests were completed, 11 of the males were treated with testosterone propionate by injection and pellet implantation. Six males (Group I) were permitted sexual experiences during the period of hormone administration. Of these, four showed the complete sexual pattern after relatively large doses of androgen. The other two never approached the female even after receiving over 3 gr. of hormone.
In 1935, Young, Dempsey and Myers (1) reported studies of the copulatory response in the normal adult female guinea-pig which can be elicited at the time of heat by stroking the animal in the dorso-lumbar region. Later Dempsey, Hertz and Young (2) demonstrated the synergistic action of estrogen followed by progesterone in inducing this behavior in the spayed female guinea-pig. Simultaneous injections had no effect and it became apparent that the estrogen must act for a period of time before the reaction can be completed by progesterone. The time of action of the estrogen prior to the injection of progesterone is called the conditioning² period; the interval between the administration of progesterone and first copulatory response is the latent period.
It seemed important to analyze quantatively the factors of the estrogenprogesterone reaction by determining, a), the conditioning period after which the greatest number of animals is brought into heat, b), the length of time an animal remains conditioned following a single injection of estrogen, c), the length of the latent period and heat, d), the effect of different estrogens, e), the effect of different quantities of estrogen and progesterone. The value of such an analysis lies in its contribution to an understanding of the physiology of the conditioning process by supplying information on the time factors involved in the absorption, inactivation and excretion of the hormones responsible for heat. The analysis also furnishes a method for the accurate bio-assay of estrogens and progesterone.
IN A PREVIOUS PUBLICATION (1) we reported that diethylstilbestrol, the synthetic estrogen discovered by Dodds and his coworkers (2), when followed by the subcutaneous administration of progestin, would induce sexual receptivity in spayed guinea pigs. The results obtained both by injection and percutaneous administration of this synthetic estrogen were comparable with those obtained when equal doses of estrone were used. Since then we have extended this work to include the percutaneous administration of progestin, as well as the estrogen, the thought being that perhaps in this way we could obtain some information of the effectiveness of progestin by this route of administration.
Since the first report of Zondek (3) in 1938, on the cutaneous application of follicular hormone,as well as progestin, several papers have appeared dealing with this mode of administration for estrogens and male hormones (4–7) but as far as the authors are aware, no other reports on progestin have appeared. Zondek (3, 5) r e ported that alcohol was a better medium for the application of the sex hormones than oil.
Broad relationships exist between the gonadal hormones and behavior.
This study reports selective effects on the mating pattern of the female rat of partial destruction of the hypothalamus. Independent
neural control of the ovarian cycle and of the mating response are demonstrated. Both depressed and augmented female sexual
activity are reported.
Somewhat after the fashion of Stone, Avery, Stockard, Draper, Tressider, Loeb, and Ishii, the investigator observed closely the behavior of both the male and female, when the latter was in heat and when the latter was not, when thrown together. A watch was held and the behavior was recorded for each full minute up to as many as 13 minutes. The observations are more detailed than those of previous observers, and are correlated with the lapse of time. Seven tables and ten references to the literature. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
"Four male rats received 1.0 mgm. of testosterone propionate daily from 14 days of age until the complete copulatory response appeared. Two litter-mate males were given control injections of sesame oil. Four females were injected with 100 R.U. of estrogen at intervals from 14 to 27 days. The sexual behavior of males and females was measured in a series of copulation tests. Both control males and all estrogen-injected females showed certain elements of the masculine copulatory pattern at 16 to 22 days of age, but did not display the complete mating response. Testosterone-treated males first exhibited complete copulation at 21 to 29 days (average 24.5 days). Two injected males displayed the ejaculation pattern at 27 and 29 days. All females showed sexual receptivity, indicated by lordosis, and this behavior appeared 21 to 25 days of age." The author advances a possible hypothesis that prepuberal rats of both sexes possess innately organized neuromuscular mechanisms capable of mediating the masculine copulatory pattern, and that the reactions appear at about the same age in each sex. At puberty, testicular androgens stimulate an expansion of the male's behavior to complete copulation and ejaculation, while the female's masculine responses remain relatively unchanged. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
All of the animals were born in the laboratory, each litter in a separate cage. "The data for three experiments, viz., males and females (1) separated until thirty days of age, and then put together for five minutes each day, (2) put together five minutes each day from the age of ten days, and (3) put together twenty-five minutes each day from the age of ten days, seem to indicate that physical maturation is of more importance in the development of the reproductive behavior in the guinea pig than experience gained from association with animals of the opposite sex." (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The same animals were observed continuously day and night during five to eleven reproductive cycles one year and three to four the next. Reported data concern the age of first heat, average length of heat period, consistency of duration per period, receptivity to mating, ovulation without heat, split estrus, and the lack of correlation between frequency of mounting and length of heat period. Bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
2 out of 4 castrated male and 3 out of 4 castrated female guinea pigs which were given copulation tests during testosterone propionate injections and control injections of oil exhibited increased copulatory activity while getting the hormone. Testosterone propionate also increased other sexually motivated activities of castrated animals. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The authors observed the behavior of 165 female guinea pigs continuously throughout 449 reproductive cycles and 623 oestrous periods. They found the average duration of the reproductive cycle to be 16 days, 6 hours, with a coefficient of variability of 6.1%. Oestrus, defined as the period of sexual receptivity, had an average length of 8.21 ± 0.07 hours. Most animals manifested very little difference from one cycle to the next, whereas the difference was greater from animal to animal. Oestrus was essentially nocturnal, the mean points ranging from 11:52 p.m. to 1:32 a.m., depending upon the season. The length of the period was not, however, related to the time of day it began. Procestrum was characterized by readily identifiable behavior which usually began as long as two days before the onset of oestrus. "It consists of an increase in activity, a pursuit of other animals and numerous successful attempts at mounting which are accompanied by all the motions of copulation." It was found that the beginning of oestrus and its entire duration could be detected readily from external signs. The copulatory reflex was the most depndable index. Bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
15 adult male animals castrated prepubertally were divided into two groups. The animals of group B served as controls when those in group A received injections. After a long period of hormone withdrawal, group A served as control for group B, then injected. Criteria of the influence of the hormone were: (1) frequency of mounting; (2) total copulation time with a receptive female within a period of 10 minutes; (3) frequency of contacts involving nudging, licking, etc.; and (4) attempts to mount non-receptive females in a 3-minute period. By every criterion, animals receiving injections of testosterone propionate exhibited more sexual activity than did controls injected with oil. Withdrawal of the hormone decreased sexual activity. These observations hold not only for averages but, with a single exception, for individual animals. Bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Much as Stone had done with respect to the white rat, Avery has described how both male and female guinea pigs act in pursuing, being caught, licking and being licked, fondling and being fondled, mounting and being mounted, intromission of the penis, palpation, and the like, characteristic of copulation. He also gives the age at which sexual activity begins in each, and the duration of the oestrus in the female. The male apparently discovers the receptivity of the female by a trial-and-error method, usually after having tried mounted or having tried to mount. Male guinea pigs, reared in isolation or with one another, may contain homosexualists in their number. A bibliography of 21 references is given. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The injection of 100 microg of estradiol benzoate into female rats 96 hours after birth abolished sexual receptivity in adulthood, even with estrogen and progesterone replacement after ovariectomy. The administration of testosterone propionate to these animals in adulthood elicited the full pattern of male sexual behavior. The same dose of estrogen given to male rats 96 hours after birth produced adults which were unable to achieve intromission, although they mounted as frequently as normal animals. Testosterone replacement after castration in adulthood reproduced this abnormal behavior.
An Hoden von menschlichen Feten (Scheitel-Fersenlnge 20–42 cm) wurden die Fettfrbung mit Sudanschwarz B, der Cholesterinnachweis und die Reaktion auf Ketongruppen (NAHD) ausgefhrt. Alle Reaktionen fielen in den Zwischenzellen am strksten, in den Sertolizellen schwcher aus. Alle brigen Gewebsbestandteile des Hodens verhielten sich negativ.Die vorgelegten Ergebnisse machen wahrscheinlich, da in den Zwischenzellen des fetalen menschlichen Hodens Wirkstoffe vom Charakter der Ketosteroide gebildet und gespeichert werden. Die zum Teil feste Bindung der Ketosteroide an zytoplasmatische Strukturen spricht dafr, da die Wirkstoffe nur in sehr geringem Mae an die Blutbahn abgegeben werden. Ein gewisses Quantum ist jedoch fr die normale Entwicklung der mnnlichen Genitalorgane whrend der Fetalzeit notwendig.
Cover-title. Typewritten in part. Pages 303-329 reprinted from the American journal of anatomy, vol. 64, no. 2, March 1939. This constitutes the thesis except for data summarized in fig. 2. Thesis (Ph. D.)--Brown University, 1939. "Literature cited": p. 318-320.
Estrus behaviour in ovariectomised rats is normally activated by progesterone after pretreatment with estrogen. It has now been found that progesterone but not estrogen can be replaced by the amine depletors reserpine and tetrabenazine.
The effect of reserpine lasted several weeks.
ACTH can only partly replace progesterone and the reserpine effect is obtained even after adrenalectomy. This indicates that reserpine does not act by inducing steroid release from the adrenals.
The results give further evidence of monoamine dependent central nervous pathways mediating heat inhibition.
The current studies have demonstrated that the single injection of 100 µg estradiol benzoate to 5-day-old female rats results in permanent sterility. When adult, these rats exhibit anovulatory vaginal cycles in which the stage of vaginal cornification predominates; they mate, but not in correlation with the vaginal cycle. Ovulation is not induced by mating or by progesterone injections, and only infrequently following electrical stimulation of the hypothalamus. By varying the amount of estrogen administered it was found that 5 µg is the minimal dosage capable of inducing this sterility syndrome. These and other data suggest that the female pattern of cyclic release of gonadotrophins differentiates in the absence of significant estrogen titers.
THYROPARATHYROIDECTOMY of the young rat has been found to result in a general dwarfing (Hammett, 1929; Salmon, 1936, 1938). Following thyroidectomy (Scow and Simpson, 1945), rats developed slowly; differentiation was possible in the absence of the thyroid, but growth proceeded at a slower rate, with retarded opening of the eyes, late eruption of the teeth, and delayed pubescence. Thiouracil or thiourea treatment of young rats (Hughes, 1944; Williams, Weinglass, Bissell, and Peters, 1944; Leathern, 1945, 1946; Barker, 1949) resulted in dwarfing or growth retardation. No significant effect was observed on the relative weights of the pituitary, gonads, kidneys, spleen, liver, or adrenals. Propylthiouracil treatment of young rats (Goddard, 1948) also resulted in growth retardation with no effect on general health, sexual maturation, hematology, or behavior. In all the cases cited above, where goitrogenic drugs were used to induce a hypothyroid state, the thyroid glands showed a large increase in weight.
Many investigators have directed attention to the close relationship between the reactivity of tissues, sometimes referred to as sensitivity or responsiveness, and the degree of response to hormonal stimulation. The literature in which the subject is discussed has never been reviewed completely, but a few references will indicate something of the extent to which differences in reactivity influence endocrine function. Smith and Engle (1927) reported that the response of immature rats and mice to pituitary transplants increased with age; that in older animals fewer transplants were required to produce precocious sexual maturity. Bradbury (1944) and McCormack and Elden (1945) found an inherent seasonal variation in the sensitivity of the rabbit to pituitary extracts. Albright, Burnett, Smith, and Parson (1942) presented evidence that in certain clinical cases of idiopathic hypoparathyroidism the disturbance was not a lack of hormone, rather a resistance to it. Selye and Albert (1942) described a differential...
The sexual activity of the male guinea pig can be stimulated during the first hour after ejaculation by the replacement of the first female by a second female. The stimulation, although definite and statistically significant, generally falls far short of that shown in response to the introduction of the first female.
Dividing male guinea pigs into high, medium and low sexual drive groups on the basis of pre-castration behavior, the sexual behavior following castration and consequent to varying size doses of testosterone was observed. Decrease in sexual behavior following castration showed no differences between the various drive level groups. Response to androgen therapy reflected the pre-castration behavior patterns. Dosages higher than that which restored pre-castration sexual pattern did not further effect behavior. 16 references.