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This article is part of a Special Issue "Puberty and Adolescence". Puberty is a critical period for brain maturation that is highly dependent on gonadal sex hormones. Modifications in the gonadal steroid environment, via the use of anabolic androgenic steroids (AAS), have been shown to affect brain development and behavior. Studies in both humans and animal models indicate that AAS exposure during adolescence alters normal brain remodeling, including structural changes and neurotransmitter function. The most commonly reported behavioral effect is an increase in aggression. Evidence has been presented to identify factors that influence the effect of AAS on the expression of aggression. The chemical composition of the AAS plays a major role in determining whether aggression is displayed, with testosterone being the most effective. The hormonal context, the environmental context, physical provocation and the perceived threat during the social encounter have all been found to influence the expression of aggression and sexual behavior. All of these factors point toward an altered behavioral state that includes an increased readiness to respond to a social encounter with heightened vigilance and enhanced motivation. This AAS-induced state may be defined as emboldenment. The evidence suggests that the use of AAS during this critical period of development may increase the risk for maladaptive behaviors along with neurological disorders., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Androgens are intricately involved in reproductive and aggressive behaviors, but the role of the androgen receptor in mediating these behaviors is less defined. Further, activity of the hypothalamic-pituitary-gonadal axis and hypothalamic-pituitary-adrenal axis can influence each other at the level of the androgen receptor. Knowledge of the mechanisms for androgens' effects on behaviors through the androgen receptor will guide future studies in elucidating male reproductive and aggressive behavior repertoires., (Copyright © 2012 S. Karger AG, Basel.)

During puberty, humans develop a later chronotype, exhibiting a phase-delayed daily rest/activity rhythm. The purpose of this study was to determine: 1) whether similar changes in chronotype occur during puberty in a laboratory rodent species, 2) whether these changes are due to pubertal hormones affecting the circadian timekeeping system. We tracked the phasing and distribution of wheel-running activity rhythms during post-weaning development in rats that were gonadectomized before puberty or left intact. We found that intact peripubertal rats had activity rhythms that were phase-delayed relative to adults. Young rats also exhibited a bimodal nocturnal activity distribution. As puberty progressed, bimodality diminished and late-night activity phase-advanced until it consolidated with early-night activity. By late puberty, intact rats showed a strong, unimodal rhythm that peaked at the beginning of the night. These pubertal changes in circadian phase were more pronounced in males than females. Increases in gonadal hormones during puberty partially accounted for these changes, as rats that were gonadectomized before puberty demonstrated smaller phase changes than intact rats and maintained ultradian rhythms into adulthood. We investigated the role of photic entrainment by comparing circadian development under constant and entrained conditions. We found that the period (τ) of free-running rhythms developed sex differences during puberty. These changes in τ did not account for pubertal changes in entrained circadian phase, as the consolidation of activity at the beginning of the subjective night persisted under constant conditions in both sexes. We conclude that the circadian system continues to develop in a hormone-sensitive manner during puberty., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Early abuse and anabolic androgenic steroids (AAS) both increase aggression. We assessed the behavioral and neurochemical consequences of AAS, alone or in combination with social subjugation (SS), an animal model of child abuse. On P26, gonadally intact male rats began SS consisting of daily pairings with an adult male for 2 weeks followed by daily injections of the AAS, testosterone on P40. As adults, males were tested for sexual and aggressive behaviors towards females in various hormonal conditions and inter-male aggression in a neutral setting using home or opponent bedding. Neurotransmitter levels were assessed using HPLC. Results showed that AAS males displayed significantly more mounts toward sexually receptive, vaginally obstructed females (OBS) and displayed significantly more threats towards ovariectomized females. SS males mounted OBS females significantly less and were not aggressive toward females. The role of olfactory cues in a neutral setting did not affect aggression regardless of treatment. AAS significantly increased brainstem DOPAC and NE. SS decreased 5HIAA, DA, DOPAC, and NE in brainstem. 5HIAA was significantly increased in the prefrontal cortex of all experimental groups. We conclude that AAS and SS differentially affect behavior towards females as well as neurotransmitter levels., (Published by Elsevier Inc.)

Anabolic androgenic steroid (AAS) use increased dramatically among adolescent males. This review focuses on studies using animal models of AAS exposure during adolescence which is a hormonally sensitive developmental period. AAS exposure during this critical period has wide-ranging consequences, including increased dendritic spine density, altered brain serotonin levels and escalated aggression in response to physical provocation. Human data suggest that AAS induces indiscriminate and unprovoked aggression often described as "'roid rage". However, animal studies indicate that the behavioral impact of AAS is modulated by experiential and social contingencies, a perceived provocation, and the chemical composition of the AAS. The AAS, testosterone increases aggression in juvenile and adult male rats when physically provoked. In contrast, stanzolol, inhibits aggression in both juvenile and adult male rats, even when physically provoked. Nandrolone has minimal effects on aggression, unless preceded by attack training. Exposure to AAS during adolescence may have a host of unintended bio-behavioral consequences. Yet, the perception of harmlessness surrounds AAS use. The perception of harmlessness is promoted by the availability of AAS especially through internet pharmacies. The perception of acceptability is reflected in current cultural ethics that no longer condemn cheating to obtain personal achievement or success. A prevailing conviction is that although AAS are illegal they are not really bad. Reduction of the availability of AAS to adolescents requires ardent legislative and legal intervention. The problem of acceptability can be addressed by educating adolescents about the short-term and long-term effects of AAS on brain and behavior, to increase awareness of the potential consequences of AAS use that apply directly to them., (Published by Elsevier Inc.)

The behavioral and neurochemical impact of low serotonin (5-HT) was examined in gonadally intact male rats exposed to an anabolic androgenic steroid (AAS) during puberty. Low 5-HT was induced beginning on postnatal day 26 using parachlorophylalanine (PCPA). Injections of the AAS, testosterone (TP), began on day 40. The rats were tested in both non-social (locomotor activity and nose poke for food) and social (low-threat and high-threat) contexts. PCPA and TP+PCPA significantly decreased locomotor activity. PCPA alone significantly increased nose poke latency compared to controls. Freezing in the PCPA group was significantly elevated compared to TP and TP+PCPA groups, but not compared to controls. AAS did not affect non-social behaviors. Thus, low serotonin may increase freezing in a non-social context. Following provocation, PCPA and TP+PCPA significantly increased aggression toward smaller non-threatening opponents, suggesting that males with low 5-HT are more aggressive in a low-threat context when provoked. In the resident-pair intruder test, TP significantly increased aggression whereas PCPA did not, suggesting that in a high-threat context, aggression is primarily mediated by AAS. TP+PCPA males were also significantly more aggressive in the high-threat context suggesting that exposure to AAS may override freezing behavior induced by low serotonin. Both PCPA and TP+PCPA significantly and substantially depleted 5-HT and 5-HIAA in all brain regions examined. AAS significantly decreased 5-HIAA levels in the hypothalamus and increased 5-HT levels in the frontal cortex. Following withdrawal from TP+PCPA, most behavioral and neurochemical measures returned to control levels. These data suggest that low serotonin may be a contributing factor in the increased aggression displayed by adolescents who abuse AAS.

Abused children are more prone to abuse drugs, such as anabolic androgenic steroids (AAS), as teenagers and display violence as adults. AAS use has been linked with elevated aggression. Thus, exposure to child abuse and AAS may potentiate aggression. A social subjugation paradigm was used as an animal model of childhood abuse to determine whether prior subjugation increases AAS-induced aggression in male rats. Prepubertal gonadally intact male rats were exposed to social subjugation, a novel cage experience, or remained undisturbed in their home cages. Experimental males were socially subjugated by being placed in the home cage of an adult male. At puberty, both subjugated and nonsubjugated rats were injected with either the AAS testosterone or vehicle. AAS treatment continued for 5 weeks. Aggression was measured during the last week of AAS exposure. AAS was then discontinued. Aggression was again tested 12 weeks after AAS withdrawal. Aggression was tested under three conditions: (i) physical provocation of the experimental male; (ii) provocation of the intruder male; and (iii) without provocation. Both AAS-treated males and socially subjugated males displayed significantly more aggression than did controls. Elevated aggression by subjugated males was still present 17 weeks after social subjugation. AAS males also showed increased aggression 12 weeks after AAS withdrawal. However, exposure to both social subjugation and AAS had no long-term effects on aggression. The results of the present study indicate that social subjugation may have lasting consequences on the expression of adaptive social behaviours.

Human studies show that the number of teenagers abusing anabolic androgenic steroids (AAS) is increasing. During adolescence, brain development is altered by androgen exposure, which suggests that AAS may potentially alter central nervous system (CNS) development. The goal of the present study was to determine whether pubertal AAS exposure increased dendritic spine densities on neurons within the medial amygdala and the dorsal hippocampus. Pubertal gonadally intact male rats received the AAS testosterone propionate (5 mg/kg) or vehicle for 5 days/week for 4 weeks. To determine the long-term implications of pubertal AAS use, another set of males received the same AAS treatment and was then withdrawn from AAS exposure for 4 weeks. Results showed that pubertal AAS exposure significantly increased spine densities on neurons in the anterior medial amygdala, posterodorsal medial amygdala, and the cornu ammonis region 1 (CA1) of the hippocampus compared with gonadally intact control males. Spine densities returned to control levels within the anterior medial amygdala and the posterodorsal medial amygdala 4 weeks after withdrawal. However, spine densities remained significantly elevated after AAS withdrawal in the CA1 region of the hippocampus, suggesting that pubertal AAS exposure may have a long-lasting impact on CA1 hippocampal neuroanatomy. Since pubertal AAS exposure increased spine densities and most excitatory synapses in the CNS occur on dendritic spines, AAS may increase neuronal excitation. It is proposed that this increase in excitation may underlie the behavioral responses seen in pubertal AAS-treated male rats.

In humans, anabolic androgenic steroid (AAS) use has been associated with hyperactivity and disruption of circadian rhythmicity. We used an animal model to determine the impact of AAS on the development and expression of circadian function. Beginning on day 68 gonadally intact male rats received testosterone, nandrolone, or stanozolol via constant release pellets for 60 days; gonadally intact controls received vehicle pellets. Wheel running was recorded in a 12:12 LD cycle and constant dim red light (RR) before and after AAS implants. Post-AAS implant, circadian activity phase, period and mean level of wheel running wheel activity were compared to baseline measures. Post-AAS phase response to a light pulse at circadian time 15 h was also tested. To determine if AAS differentially affects steroid receptor coactivator (SRC) expression we measured SRC-1 and SRC-2 protein in brain. Running wheel activity was significantly elevated by testosterone, significantly depressed by nandrolone, and unaffected by stanozolol. None of the AAS altered measures of circadian rhythmicity or phase response. While SRC-1 was unaffected by AAS exposure, SRC-2 was decreased by testosterone in the hypothalamus. Activity levels, phase of peak activity and circadian period all changed over the course of development from puberty to adulthood. Development of activity was clearly modified by AAS exposure as testosterone significantly elevated activity levels and nandrolone significantly suppressed activity relative to controls. Thus, AAS exposure differentially affects both the magnitude and direction of developmental changes in activity levels depending in part on the chemical composition of the AAS.

The goal of this study was to assess the interactive effects of chronic anabolic androgenic steroid (AAS) exposure and brain serotonin (5-hydroxytryptamine, 5-HT) depletion on behavior of pubertal male rats. Serotonin was depleted beginning on postnatal day 26 with parachlorophenylalanine (PCPA 100 mg/kg, every other day); controls received saline. At puberty (P40), half the PCPA-treated rats and half the saline-treated rats began treatment with testosterone (T, 5 mg/kg, 5 days/week). Behavioral measures included locomotion, irritability, copulation, partner preference, and aggression. Animals were tested for aggression in their home cage, both with and without physical provocation (mild tail pinch). Brain levels of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), were determined using HPLC. PCPA significantly and substantially depleted 5-HT and 5-HIAA in all brain regions examined. Chronic T treatment significantly decreased 5-HT and 5-HIAA in certain brain areas, but to a much lesser extent than PCPA. Chronic exposure to PCPA alone significantly decreased locomotor activity and increased irritability but had no effect on sexual behavior, partner preference, or aggression. T alone had no effect on locomotion, irritability, or sexual behavior but increased partner preference and aggression. The most striking effect of combining T+PCPA was a significant increase in attack frequency as well as a significant decrease in the latency to attack, particularly following physical provocation. Based on these data, it can be speculated that pubertal AAS users with low central 5-HT may be especially prone to exhibit aggressive behavior.

Previous results showed that male rats pubertally exposed to anabolic androgenic steroids (AAS) displayed aggression towards females in response to physical provocation. This experiment examined two factors that may modulate AAS-induced behavior towards females: olfactory cues and frustration. Gonadally intact males began one of three AAS treatments at puberty (D40): testosterone propionate (T), stanozolol (S), T+S, or vehicle control. To test for the relevance of olfactory cues in the elicitation of behavior toward females, a hidden neighbor paradigm was used. The proximal stimulus was an ovariectomized (OVX) female, estrogen plus progesterone (E+P) female, or an E+P female with tape-obstructed vagina (OBS). Distal olfactory cues from a hidden neighbor were delivered from a separate cage connected to the testing arena. The vaginally obstructed, sexually receptive female (OBS) was used to determine the effects of frustration on behavior by AAS males. Both sexual and aggressive behaviors were measured. The presence of distal olfactory cues had no effect on either sexual or aggressive behavior. In the presence of E+P and OBS females, all males displayed sex behaviors, not aggression. However, AAS males displayed significantly more aggression towards proximal OVX females than controls. AAS males mounted OBS females significantly more than controls, indicating a persistence of once rewarded behavior. These results suggest (1) proximal cues of the conspecific female are more salient than distal olfactory cues in determining behavior and (2) AAS males display frustration-induced persistence in response to vaginally obstructed receptive females.

Human studies suggest that anabolic androgenic steroid (AAS) users are aggressive towards women. This study used a rat model to evaluate whether AAS potentiated aggression towards females and the conditions under which this occurs. Gonadally intact pubertal male rats received one of the following AAS treatments (5 mg/kg s.c. 5 days/week for nine weeks): testosterone (T), stanozolol (S), testosterone + stanozolol (T + S), or vehicle control. Each rat was tested with 3 conspecific stimuli: ovariectomized females (OVX), estrogen only females (E), and estrogen + progesterone females (E + P). The response to physical provocation was tested under three conditions: without physical provocation, provocation of the experimental male, and provocation of the conspecific female. Provocation was a mild tail pinch. Both aggressive and sexual behaviors were measured during each test. In the absence of physical provocation, AAS males were not aggressive towards females. However, provocation significantly increased aggression in males treated with testosterone but only towards OVX females. In the presence of E or E + P females, all animals displayed sex behavior, not aggression. Thus, factors such as the nature of the AAS and the hormonal status of the females are important in determining whether male rats will be aggressive towards females. However, the most salient factor determining aggression towards females is the presence of provocation in combination with high levels of testosterone.

Anabolic androgenic steroid (AAS) abuse is increasing in teenagers. We examined the effects of stacked AAS in adolescent male rats. Stacking, in which multiple AAS are taken simultaneously, is commonly employed by humans. Beginning at puberty gonadally intact male rats received testosterone, nandrolone, or stanozolol. Additional groups received stacked AAS: testosterone + stanozolol, nandrolone + stanozolol, or nandrolone + testosterone. Injections continued during tests for sexual behavior, vocalizations, scent marking, partner preference, aggression and fertility. Body and reproductive tissue weights were taken. Sexual and aggressive behaviors were increased by testosterone yet inhibited by stanozolol; nandrolone had no effect. Stacking testosterone with stanozolol prevented the inhibitory effects of stanozolol. Body weight was decreased by testosterone and all stacked AAS. Cell nuclear androgen receptor binding in brain was significantly increased in nandrolone males and decreased in stanozolol males; testosterone males were slightly higher than controls. Androgen receptors in stacked groups were intermediate between individual AAS suggesting that stanozolol competed with other AAS for androgen receptors despite its low affinity. The results indicate that stacking AAS influences the effects of individual AAS on behavioral and endocrine measures, and levels of androgen receptor occupation are not directly correlated with AAS effects on behavior.

Electrolytic microlesions aimed at the dorsomedial portion of the ventromedial nucleus (VMN) of the hypothalamus were generated, and effects on copulation, 50-kHz vocalizations, scent marking, and sexual motivation were measured. Male rats were tested before and after lesions, after castration, and after testosterone replacement. Three control groups were used: One received sham surgery, another received no surgery or testosterone replacement, and a 3rd received lesions primarily outside the VMN. VMN lesions produced impairments in testosterone's ability to restore ultrasonic vocalizations and scent marking, assessed with 2 different test methods. Copulation, sexual motivation, and weight gain were largely unaffected, although some differences were observed in copulatory efficiency. The authors conclude that the integrity of the VMN is important for full expression of sociosexual behaviors in male rats.

The use of anabolic androgenic steroids (AASs) has escalated in teenagers and is associated with increased violence. Adolescent exposure to chronic high levels of AASs is of particular concern because puberty is a hormonally sensitive period during which neural circuitry for adult male patterns of behavior develop. Thus, teenage AAS use may have long-term repercussions on the potential for displaying aggression and violence. Animal models have contributed valuable information on the effects of AAS use. For example, studies in rodents confirmed that exposure to the AASs testosterone and nandrolone, but not stanozolol, does indeed increase aggression. A side effect of AAS use reported in humans is "'roid rage," characterized by indiscriminate and unprovoked aggression. Results of animal studies demonstrated that pubertal rats receiving AASs respond appropriately to social cues as they are more aggressive toward intact males than are castrates. Also, testosterone-treated males recognize appropriate environmental cues as they are most aggressive in their home cage. Thus, adolescent AAS exposure increases aggressive behaviors, but does not induce indiscriminate aggression. To assess whether AAS exposure increases aggression after provocation, rats were tested following a mild tail-pinch. In adolescent males, provocation increased aggression after withdrawal from testosterone, nandrolone, and stanozolol, an effect which persisted for many weeks. The data suggest that AASs sensitize animals to their surroundings and lower the threshold to respond to provocation with aggression. Thus, in humans, pubertal AAS exposure may not cause violent behaviors, but may increase the likelihood that aggressive acts will result in violence. This may persist into adulthood.

The current study examined acute and long-term effects of anabolic-androgenic steroid (AAS) exposure during puberty on copulation, vocalizations, scent marking, and intermale aggression, both with and without tail pinch, in intact male rats. Animals received 5 mg/kg of testosterone, nandrolone, stanozolol, or vehicle, beginning at puberty. After 5 weeks, behavior tests were performed while continuing AAS injections. AAS treatment was then discontinued. Behaviors were tested during 3-5 weeks, 9-11 weeks, and 15-17 weeks of withdrawal. During AAS administration, stanozolol males showed significant reductions in all behaviors compared with controls, except aggression with tail pinch. Nandrolone treatment significantly reduced vocalizations and scent marking, and testosterone had no significant effect on behavior. During withdrawal, behaviors in stanozolol males recovered to control levels at variable rates: aggression at 4 weeks; mounts, vocalizations, and scent marking at 9 weeks; and ejaculations at 15 weeks of withdrawal. Stanozolol males showed significantly higher levels of tail pinch-induced aggression during every withdrawal test. Nandrolone-treated males scent-marked at control levels by 9 weeks withdrawal but displayed significantly fewer vocalizations and significantly more tail pinch-induced aggression than controls for the entire study. Testosterone-treated males scent-marked significantly below controls at 3 weeks withdrawal and showed significantly more tail pinch-induced aggression at 5 weeks withdrawal. All three AAS significantly increased tail pinch-induced aggression compared with corresponding nontail pinch tests, even at study endpoint. These results suggest that alterations in androgen-dependent behaviors by pubertal AAS exposure can persist long after drug exposure, and some effects may even be permanent.

Previously, our laboratory has shown that androgen receptors in the medial preoptic area (MPOA) and ventromedial nucleus (VMN) are necessary for copulation in male rats. The present study examined whether these receptors are required for other sociosexual behaviors. In Experiment 1, different regions of the VMN were implanted with the antiandrogen hydroxyflutamide (OHF). We found that implants located in anterodorsal portions of the VMN were more effective at inhibiting the restoration of copulation than implants in the posteroventral VMN. In Experiment 2, a second set of male rats was pretested for copulation and other sociosexual behaviors and was castrated. Experimental animals then received Silastic capsules filled with testosterone (T) plus intracranial (IC) implants filled with OHF to selectively block androgen receptors in either the MPOA or VMN. We found that androgen receptor blockade in the MPOA inhibited the restoration of copulation but had no effect on other sociosexual behaviors. OHF directed at the VMN inhibited the restoration of copulation and 50-kHz vocalizations but had no effect on scent marking. Two tests were used to assay sexual motivation: partner preference and conditioned place preference (CPP). Both methods revealed impairments in sexual motivation in the VMN group but not in animals receiving OHF in the MPOA. Taken together, these data suggest that androgen receptors in the MPOA are essential for copulatory performance, while androgen receptors in the VMN are important for copulation, sexual motivation, and androgen-dependent vocalizations.

Adolescence in human males is a hormonally sensitive period when many adult behaviors develop, including sexual and aggressive behaviors. Using a rat model, the authors examined the effects of three anabolic-androgenic steroids (AAS) during puberty: testosterone, nandrolone, and stanozolol. Copulation, vocalizations, scent-marking, and aggression were tested following AAS exposure. Relative to gonadally intact controls, rats injected with testosterone showed a significant increase in scent-marking and aggression in the opponent's home cage. Nandrolone had no effect. Stanozolol significantly inhibited all behaviors. Results suggest that depending on the chemical structure of the steroid, AAS exposure during puberty affects several androgen-dependent behaviors. Because adolescence in humans is a period of hormonal change, abuse of AAS, particularly stanozolol, during this time may disrupt the establishment of normal adult behavior patterns., ((c) 2003 APA, all rights reserved)

Male and female rats emit ultrasonic vocalizations in reproductive encounters. While estrous bedding has been used to elicit vocalizations of males, the number of responses is variable. We report a reliable method to assess vocalizations using exposure to a stimulus animal. The stimulus rat is placed behind a wire barrier for 5 min, then removed. Vocalizations are then recorded for 5 min. Experiment 1 validated this method and it was used for subsequent experiments. In Experiment 2, male rats were castrated and tested for the restoration of vocalizations. In one group, males were allowed to copulate freely; in the other, females had vaginal masks to prevent ejaculation, but not mounting. Vocalizations were restored only in males allowed to ejaculate. In Experiment 3, we measured vocalizations in sexually nai;ve and sexually experienced males following exposure to either castrated (CAS) males, testosterone (T)-treated males, ovariectomized (OVX) females, or OVX females receiving estrogen plus progesterone (E+P). Males vocalized most after exposure to E+P females, whether they were sexually experienced or naive. However, the rate of vocalizations was significantly higher after exposure to E+P females when the males were sexually experienced. In Experiment 4, we measured vocalizations in females following exposure to CAS males, T-treated males, OVX females, or E+P females. Females vocalized most after exposure to T-treated males. Our results show that (1) sexual experience facilitates vocalizations in male rats, (2) vocalizations are highest after exposure to hormonally receptive conspecifics, and (3) ultrasonic signaling is a sensitive index for assessing the hormonal disposition of conspecifics.

The present study tested whether testosterone propionate (TP) implanted in the ventromedial nucleus (VMN) of the hypothalamus could initiate performance, motivational, or sociosexual components of sexual behavior in castrated male rats. Twenty-seven intact male Long Evans rats were pretested for copulation, partner preference, and 50-kHz vocalization and were subsequently castrated. Approximately 3 weeks after castration, males were retested to confirm that these behaviors had declined, and groups were assigned. Groups 1 and 2 were implanted with bilateral stainless steel cannulae directed at the VMN that were either filled with TP (TVMN group) or remained empty (Blank group). A third group (TSC) was implanted subcutaneously with two 10-mm Silastic capsules filled with testosterone. Restoration of behavior was measured for 2 weeks after implants. We found that copulation and 50-kHz vocalization were not restored by TP in the VMN alone. However, partner preference returned to preoperative levels in both the TVMN and TSC groups, indicating that TP in the VMN was sufficient to restore sexual motivation. Following behavioral testing, prostate glands and seminal vesicles were weighed and confirmed that TP did not leak into the periphery in the TVMN group. Immunostaining for androgen receptors also verified that TP spread was confined to the immediate area surrounding the cannula tip. These results suggest that androgen activation at the VMN is sufficient to induce the motivational components of male sexual behavior, whereas activation of other brain sites is required for copulation and ultrasonic vocalization., (Copyright 2003 Elsevier Science (USA))

We examined whether androgen receptors in the medial preoptic area (MPOA) and lateral septum (LS) are required for the expression of copulation and sexual motivation. Castrated males received testosterone-filled silastic capsules to restore behavior, and were implanted with the antiandrogen hydroxyflutamide (OHF) or blank cannulae. One group was implanted in either the anteroventral MPOA or LS (ANT group). Another group was implanted in the posterodorsal MPOA or LS (POST group). Copulation was tested on days 2, 6, 10, and 14 of OHF exposure; partner preference, a measure of sexual motivation, was tested on day 15. The results showed that sexual behavior was significantly suppressed by OHF in the MPOA of the ANT group, but not the POST group. However, sexual motivation was significantly reduced by OHF in the MPOA of the POST group, but not the ANT group. In the LS, OHF had no effect on sexual behavior and partner preference regardless of implant site. The data suggest site specificity within the MPOA for androgen receptor activation of male reproductive behaviors., (Copyright 2002 Elsevier Science Inc.)

In gonadally intact male rats, chronic exposure to high levels of testosterone propionate (TP) increases aggression, nandrolone (ND) has little effect and stanozolol (ST) suppresses aggression. The present experiment tested whether the effects of TP, ND and ST on aggression and reproductive tissues are reversed following anabolic androgenic steroid (AAS) withdrawal. Gonadally intact males received TP, ND, ST or vehicle for 12 weeks. Injections were then discontinued. Aggression was tested 3 weeks (short term) and 12 weeks (long term) after withdrawal of AAS treatment, with either a gonadally intact or a castrated opponent in three different environments (home, opponent's and neutral cage). After short-term withdrawal, some parameters of aggression were significantly above control levels in TP males. There were no significant differences between ND or ST males and controls, though ST males showed the lowest levels of aggression. No significant differences between any of the groups were found after long-term withdrawal. Eighteen weeks after AAS withdrawal, serum testosterone (T) and LH levels were comparable to controls in all groups. Testes weights were at control levels in ST males, but significantly higher than controls in TP and ND males. Seminal vesicle weights were significantly elevated in TP males, but similar to controls in both ND and ST males. None of the prostate weights were significantly different from controls. These results suggest that aggression gradually returns to normal following withdrawal from AAS. Some, if not all, hormone levels and tissue weights return to normal, suggesting possible long-lasting effects of chronic AAS exposure.

Anabolic androgenic steroids (AAS) have been linked to indiscriminant and unprovoked aggression and violence. We employed a brief tail pinch to examine the effects of different AAS on intermale aggression in gonadally intact male rats in response to a mild physical provocation. Animals received 5 mg/kg testosterone propionate (TP), nandrolone (ND), or stanozolol (ST) 5 days/week. Controls received vehicle injections. After 12 weeks, rats were tested for aggression while treatments continued. Animals were paired with either gonadally intact or castrated opponents and were tested in the subject rat's home cage, the opponents's home cage, and a neutral cage. Aggression was tested during tail pinch of the subject rat and during tail pinch of the opponent rat. In TP-treated males, tail pinch significantly enhanced aggression in all social and environmental conditions compared to intact controls. TP treatment also significantly enhanced aggression when the opponents were tail pinched. Tail pinch did not increase aggression in ND-treated males, and aggression was significantly lower than controls in ST-treated males. As expected, cell nuclear androgen receptor binding was significantly elevated by the high dose of TP. Our results show that while AAS alone does not induce the indiscriminate and unprovoked aggression characteristic of 'roid rage, TP heightens the animals sensitivity to

This study examined the effects of anabolic androgenic steroids (AAS) on aggression under different social and environmental conditions. Three AAS were tested in gonadally intact male rats: testosterone propionate (TP), nandrolone (ND), and stanozolol (ST). Doses of 5 mg/kg were given 5 times/week, with gonadally intact controls receiving vehicle only (propylene glycol). Animals received six weekly tests under each condition in a counterbalanced order. Results show that the three AAS differed in their ability to elicit aggression. Males receiving TP were more aggressive than controls, ND males were similar to controls, and ST males were less aggressive than controls. In the social and environmental provocation tests TP-treated males were more aggressive than other groups, but were able to discriminate between intact and castrated opponents and between their home cage and a neutral cage. In the environmental provocation test, TP males were also more aggressive against opponents when tested in the opponent's home cage. It is suggested that chronic exposure to high levels of TP does not eliminate the ability to discriminate between social or environmental cues, as might be expected if it induces a " 'roid rage." However, TP does increase the likelihood that the animal will respond with aggression/dominance in a provoking situation. All three AAS variably affected serum testosterone and LH levels, as well as testes, seminal vesicle, and prostate weights. No effect on body weight was observed., (Copyright 2001 Academic Press.)

This study compared AR proteins in four cranial nerve motor nuclei among male and female rats that were intact, gonadectomized, or gonadectomized and given TP by immunohistochemistry. AR-immunoreactive (ir) neurons were found, in descending order of abundance, in the nucleus ambiguus, hypoglossal nucleus, and the facial and trigeminal motor nuclei of both males and females of intact and gonadectomized plus TP rats. Virtually every neuron of the nucleus ambiguus was AR-ir. In contrast, AR-ir neurons were either restricted to a specific area of the hypoglossal nucleus, or randomly distributed in the facial and trigeminal motor nuclei. The predominant AR-ir site shifted from cell nuclei to the cytoplasm, depending upon the presence or absence of ligand. Sex differences in the amount and staining intensity of AR-ir neurons were discernable in all four motor nuclei of intact rats, and these differences were maintained in gonadectomized plus TP rats, with the exception of the nucleus ambiguus. The immunostaining results were complemented by results from AR binding studies. Cytosolic AR binding values for the hypoglossal and facial motor nuclei of females were only approximately 50% of those of males despite the absence of a sex difference in neuron number. These results indicate that intrinsic sex differences in AR levels and androgenic regulation of AR exist in cranial nerve motor nuclei, and that there are differences in the abundance and distribution pattern of AR responsive neurons in cranial nerve motor nuclei. These results are consistent with the idea that sex differences in AR could account for sex differences observed in nerve regeneration and neuron loss following cranial nerve injury., (Copyright 2000 John Wiley & Sons, Inc.)

This work tested the hypothesis that gonadal steroid receptor activation was necessary for the restoration of several sociosexual behaviors (such as copulatory behavior, partner preference, 50-kHz vocalizations, and scent marking) in testosterone-treated gonadectomized male rats. Gonadal steroid receptors were blocked by systemic administration of the antiandrogen hydroxyflutamide, the antiestrogen RU 58668, or both antagonists simultaneously in a restoration paradigm. Inhibiting androgen receptors with hydroxyflutamide blocked the restoration of male copulatory behavior, partner preference (time spent with a sexually receptive female over a nonreceptive female), 50-kHz ultrasonic vocalizations, and scent marking. On the other hand, we did not find that blocking estrogen receptors with RU 58668 inhibited the restoration of copulatory behavior or partner preference in testosterone-treated gonadectomized male rats, even though the level of brain nuclear estrogen receptor occupation was significantly reduced to the level found in gonadectomized males. However, the restoration of scent marking and 50-kHz vocalizations were impaired by RU 58668. Blocking both nuclear androgen and estrogen receptors with the two antagonists simultaneously did not have a greater inhibitory effect than treatment with each antagonist alone. Therefore, the activation of nuclear estrogen receptors is necessary for the restoration of some, but not all, sociosexual behaviors, which are also androgen receptor-dependent. Besides nuclear estrogen receptors, there are additional, but unknown, targets of estradiol that play a role in mediating copulatory behavior in adult male rats. Moreover, the signals from multiple gonadal steroid signaling pathways converge in the regulation of some sociosexual behaviors in adult male rats., (Copyright 1998 Academic Press.)

The purpose of this study was to determine if injections of the 11 beta-substituted steroidal antioestrogen, RU 58668, would block two measures of oestrogen receptor action in ovariectomized adult female rats. Using an in vitro nuclear exchange assay, it was found that RU 58668 reduced cell nuclear [3H]-oestradiol binding in brain tissue 24 h after it was injected. However, pituitary cell nuclear [3H]-oestradiol binding was significantly reduced just 2 h after the antioestrogen was injected. Our results demonstrate that RU 58668 can reach the brain following a subcutaneous injection, but that it needs more time to reach the brain than it does to reach the pituitary. Since the levels of hypothalamic and pituitary progestin receptors are known to be regulated by oestradiol, cytosolic [3H]-R5020 binding was used as an in vitro assay of endogenous oestrogen receptor action. RU 58668 blocked induction by oestradiol of cytosolic [3H]-R5020 binding in both the brain and pituitary 48 h after it was injected. In the absence of oestradiol, RU 58668 did not stimulate cell nuclear [3H]-oestradiol binding or cytosolic [3H]-R5020 binding in either brain or pituitary. In conclusion, injections of RU 58668 blocked two measures of oestrogen receptor action in the brain and pituitary without showing oestrogenic activity itself.

This study assessed the effects of high doses of anabolic-androgenic steroids (AAS) and their withdrawal on male reproductive behavior and reproductive tissues during development. Prepubertal, peripubertal, and adult male Long Evans rats were divided into 4 groups: 1) Testosterone propionate for 16 weeks (TP), 2) TP for 3 weeks and withdrawn for 13 weeks (TPWL), 3) TP for 16 weeks and withdrawn for 3 weeks (TPWS), 4) propylene glycol (control vehicle) for 16 weeks (PG). As determined by sexual performance and sexual preference tests, administration of high doses of AAS to the peripubertal animals enhanced sexual performance and sexual motivation. There was no significant effect on sexual behavior of the prepubertal animals. High doses of anabolic-androgenic steroids depleted Leydig cell number in the prepubertal and adult rats, but had no effect on the Leydig cell number of the peripubertal animals. After long-term withdrawal from AAS no significant effects on sexual behavior were found. The depletion of Leydig cells that occurred in the prepubertal animals after withdrawal was reversible, while the depletion of the Leydig cells of the adult animals did not return to the control level suggesting a long lasting alteration.

This study assessed the role of aromatization in the expression of male reproductive behavior by testing the effects of the aromatase inhibitor, fadrozole, on the restoration of male sexual behavior and partner preference in testosterone-treated gonadectomized rats. We measured nuclear estrogen receptor occupation to determine whether fadrozole blocked brain aromatase. In addition, nuclear androgen receptor assays were used to verify that fadrozole does not block androgen receptors. Mini-osmotic pumps fitted to brain infusion cannulas were used to deliver fadrozole (20 micrograms/day) into the right lateral ventricle. The majority of animals receiving fadrozole treatment with two, 10 mm testosterone filled Silastic capsules (T/F group) failed to display any sexual behavior 7 and 13 days following implant surgery. In contrast, animals receiving fadrozole treatment which were implanted with two, 10 mm testosterone capsules and one, 5 mm 1% estradiol capsule (T/F/E group) copulated normally, indicating that fadrozole's inhibition of male sex behavior was specifically due to blocking aromatase activity. Moreover, the animals which received only one, 5 mm 1% estradiol capsule (E group) also failed to exhibit male sexual behavior. Partner preference for either a sexually receptive female or a non-receptive female was measured in a three chambered apparatus for an index of sexual motivation. Repeated measures contrasts on the group x test interaction indicated that the T/F group was not significantly different from the T group. In addition, the E group did not show a preference for the receptive females and was significantly different from the T group. Fadrozole treatment resulted in a 59% decrease in brain nuclear estrogen receptor occupation relative to the T group. Fadrozole had no significant effect on brain nuclear androgen receptor occupation. Our results lend support to the hypothesis that both androgen receptor activation and aromatization are necessary for the restoration of male sexual behavior in rats. However, we found that estradiol is neither necessary nor sufficient for the restoration of partner preference.

Castrated male rats received testosterone (T) via silastic capsules and bilateral implants of either anisomycin (ANI) in a cocoa butter/beeswax mixture or cocoa butter/beeswax alone as a control. Cannulae were placed directly into the medial preoptic area (MPOA) to determine if protein synthesis in this brain region is required for the expression of male sexual behavior. In the first experiment, using a restoration paradigm, it was found that a 25% mixture of ANI prevented restoration of male sexual behavior, whereas 4% ANI was only partially effective. In a second experiment, the ability of 25% ANI to suppress male sexual behavior in a maintenance paradigm was tested and found to be completely ineffective. In a third experiment, a 50% ANI dose was used and this dose significantly suppressed male sexual behavior by the fourth week. Sexual behavior returned following ANI discontinuation. Males receiving 50% ANI were also tested for sexual motivation (measured in a place preference test), as well as for scent marking and vocalizations. ANI implanted into the MPOA did not affect sexual motivation, as males in both ANI and control groups spent more time with a sexually receptive female than with a nonreceptive female. ANI in the MPOA did not affect scent marking, but significantly decreased ultrasonic vocalizations. These results suggest that, in rats, protein synthesis in the MPOA is required for the expression of male sexual behavior and vocalizations, but not for sexual preference or scent marking.

Inhibition of masculine copulatory behavior was previously demonstrated following systemic injections of hydroxyflutamide (OHF). In the present study, we examined the localization of the effects of this androgen receptor blocker by direct intracranial implantation of OHF into the medial preoptic area (MPOA), ventromedial nucleus of hypothalamus (VMN), medial amygdala (AME), and lateral septum (SEPT). Animals were implanted intracranially with crystalline OHF or cholesterol, and at the same time received two 10-mm testosterone-filled Silastic capsules SC. Tests for restoration of copulatory behavior were initiated 3 days later, and conducted twice weekly for 2 weeks. Implants of OHF into the MPOA were effective in preventing restoration of male sexual behavior. However, the most effective site was the VMN. Implants of OHF into the AME were only partially effective in stimulating male sexual behavior, whereas implants into the SEPT had no effect. The OHF was discontinued and 1 week later males were retested for sexual behavior. The majority of these animals ejaculated, indicating, that the effects of OHF are reversible. The result of this study demonstrate that the functional integrity of androgen receptors in some, but not all, androgen-concentrating brain loci is necessary for the expression of the complete pattern of male sexual behavior. These data lend support to the view that androgen receptor populations in specific brain loci differentially express proteins involved in mediating the masculine copulatory response.

Olfactory bulbectomy (OBX) in SWR outbred male mice lengthened the free-running period and delayed the phase of a circadian rhythm for wheel-running activity. OBX also increased mean levels of activity. Two weeks of daily intraperitoneal injections of Fluoxetine (8 mg/kg), a serotonin re-uptake inhibitor, reversed the effects of bulbectomy on the mean level of activity and significantly shortened the free-running period of the activity rhythm. The phase of the activity rhythm was not significantly affected by the Fluoxetine treatment. These results are consistent with a hyposerotonergic mediation of the effects of OBX on circadian period and activity level.

The purpose of this experiment was to determine if there are sex differences in cytosolic androgen receptors (AR) in individual brain nuclei. Bilateral 500 mu diameter samples from 300 mu thick frozen brain sections were micropunched from males and females 2-3 weeks following gonadectomy. Tissue samples were taken from 12 brain nuclei: lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus, anterior hypothalamic area, arcuate nucleus, corticomedial nucleus of the amygdala, lateral preoptic area, parietal cortex, medial nucleus of the amygdala, dorsomedial nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, and dorsal hippocampus. Cytosolic ARs were found in brain regions involved in the neuromodulation of androgen dependent responses. These data suggest that behavioral differences in male reproductive responses may be the sexually dimorphic distribution of androgen receptor containing neurons.

RU 58668 is a steroidal antiestrogen believed to be devoid of any partial agonist activity. Most of the work with RU 58668 has focused on its potential as an antineoplastic agent in the treatment of breast cancer, but it has not been tested for its effects on the brain and behavior. Other antiestrogens are problematic because most are either partial agonists or do not cross the blood-brain barrier. The purpose of this study was to test if RU 58668 blocks two classic estrogen-dependent behaviors: female sexual behavior and feeding behavior. We used a repeated measures design to examine if RU 58668 reversibly blocked female sexual behavior. RU 58668 significantly reduced both the level of sexual receptivity and the level of proceptivity in a reversible manner. Changes in body and food weight were also measured. Our results show that RU 58668 blocked estrogen's suppressive effects on feeding behavior and body weight. Therefore, RU 58668 is the first antiestrogen that blocks estradiol's effects on female sexual behavior while also inhibiting estradiol's effects on feeding behavior and body weight.

Sensory and motor events are important for mating, and several cranial nerve nuclei mediating these events contain androgen receptors (AR). Since mating behavior declines with age, we tested whether AR binding is decreased in cranial nerve nuclei of old male rats. Cytosol and cell nuclear androgen receptor (AR) binding was assessed in the cochlear, hypoglossal and facial nuclei in young (4 months) and old (20 months) male Fischer 344 rats. For comparison with other neural and non-neural tissue, AR binding in combined hypothalamus, preoptic area and amygdala (HPA), and muscle tissue from tongue and masseter were examined. Cytosol AR binding was significantly decreased in all three cranial nerve nuclei of old males. No age-related changes were observed in HPA or muscle. Cell nuclear AR binding was unaffected by age in all of the tissues analyzed. Neuron numbers in motor nuclei of the hypoglossal, facial and trigeminal nerves were compared between young and old rats. A significant decrease in neuron number was found only in the hypoglossal nucleus of old rats, indicating that neuronal loss is not a factor in the reduction of AR's in cranial nerve nuclei. It is suggested that the loss of AR's in cranial nerve nuclei of old rats contributes to the decline in male copulatory behavior by reducing responsiveness to sensory and motor cues.

To determine if chronic exposure to high doses of anabolic androgenic steroids (AAS) increase aggression and sexual activity in gonadally intact rats, we administered SC injections of testosterone propionate (TP: 1 mg) or propylene glycol (PG: as a vehicle control) three times per week for 10 consecutive weeks. Weekly tests for male copulation were conducted by pairing each male with a sexually receptive female in a glass arena and recording various parameters of copulation. Chronic treatment with TP did not alter any parameter of male copulation including ejaculation and post ejaculatory interval. Sexually experienced males were tested once per week for intermale aggression in a neutral environment. For aggression tests, each experimental animal was placed into an arena with an opponent male for 15 min. The opponent, a gonadally intact male, was used only for the purpose of the aggression test. Frequencies of dominance, submissive, threat, and fight postures, as well as approaches were scored for each animal. TP-treated males did not differ in body weight from PG-treated males, suggesting that the increased aggression was not due to increased body mass. The results of this study show that chronic exposure to the anabolic androgenic steroid, testosterone, potentiates male aggressive response patterns but does not alter male sexual behavior or body weight.

LY163502, a selective D2 receptor agonist, has been reported to stimulate sexual behavior in both copulating and noncopulating male rats. Three experiments were conducted to further characterize the role of dopamine on male sexual behavior. In the first experiment, quinelorane (LY163502) was directly infused into the medial preoptic area (MPOA) of castrated males either alone or in combination with subphysiological levels of testosterone (T) exposure. The results showed that male sexual behavior was not affected by infusion of LY163502 alone, subphysiological T levels alone, or the combination of LY163502 and subphysiological T levels. For the second experiment, all animals received physiological levels of T and MPOA infusions of LY163502 or saline. The results showed an earlier restoration of male sexual behavior in the LY163502 group when compared to the T-only group. In the third study, noncopulating, gonadally intact males received SC injections of either LY163502 or saline 30 min prior to copulatory testing. The results showed that LY163502 induced a significant decrease in mount and intromission latencies after 14 days of drug exposure. From these results, we conclude a) that D2 receptors play a role in the facilitation of male sexual behavior and b) that the action of dopamine at D2 receptors requires the presence of T.

The effects of olfactory bulb removal (OBX) and chronic psychosocial stress on serum glucocorticoids and sexual behavior were assessed in female rats primed with a subthreshold level of estradiol (E2). Ovariectomized females underwent either OBX or sham surgery. Half of the OBX and half of the sham animals were exposed to chronic psychosocial stress (crowding, strobe light, and intermittent noise) for one-half h per day for 27 days. On day 22, three blood samples were collected from each animal for serum corticosterone analysis; 1) before, 2) during, and 3) after acute stress (one-half h restraint). On day 28, females were exposed to either 4 or 24 h of E2. On day 29, all females received 500 micrograms progesterone (P) 4 h prior to sexual behavior testing. Sexual receptivity was measured using the lordosis quotient (LQ = [number of lordotic responses/10 mounts] x 100). Sexual proceptivity (dart and ear wiggling sequences) and rejection (number of nonlordotic responses to mount attempts) were measured throughout a 10-min test period. Results showed that chronic psychosocial stress dramatically increased sexual receptivity and proceptivity while decreasing sexual rejection in female rats primed with a subthreshold level of E2. Chronic psychosocial stress also elevated serum glucocorticoids and significantly exacerbated the glucocorticoid response to acute stress. OBX, while increasing sexual receptivity and decreasing sexual rejection, had no effect on serum glucocorticoids. These findings support the hypothesis that OBX potentiates female sexual behavior directly through an increase in neural sensitivity to E2. In contrast, the enhancing effect of chronic psychosocial stress on female sexual behavior may result from alterations of the hypothalamo-pituitary-adrenal system.

For further characterization of the olfactory bulb's role in the medication of chronobiological phenomena, we examined basal cyclic- 3',5'-adenosine monophosphate (cAMP) levels in the suprachiasmatic nuclei (SCN) and lateral hippocampus (LHIP) following bilateral olfactory bulbectomy (OBX) to assess the effects of olfactory bulb removal on the biological clock. Two groups of adult Long-Evans rats underwent OBX or sham control surgery (SHAM). Eight weeks postoperative, the animals were decapitated at the time of maximal cAMP accumulation (circadian time 9-11 h), brains were removed, frozen in liquid nitrogen, and sectioned on a cryostat. Individual brain nuclei (SCN and LHIP) were microdissected using the Palkovits punch technique and analyzed by scintillation proximity assay for cAMP. We report a 83.6% increase in basal cAMP levels in the SCN following OBX (OBX = 63.7 pmol cAMP/mg protein, SHAM = 34.7 pmol cAMP/mg protein, p less than 0.01). No significant differences in LHIP cAMP levels were found. This specific increase in SCN cAMP, at the time of maximum cAMP accumulation, may give insight into the biochemical basis for altered activity levels following OBX.

The purpose of the present experiment was to assess the effect of olfactory bulbectomy and ovarian hormones on female sexual motivation. Ovariectomized female rats underwent either bilateral bulbectomy or sham surgery. Females received one of four subthreshold hormone treatments: 0% estradiol (E2) plus 500 micrograms progesterone (P), 100% E2 alone, 10% E2 plus 500 micrograms P, or 100% E2 plus 500 micrograms P. Sexual motivation (as indicated by a female's preference for a sexually active male over a castrated male) and proceptivity (dart and ear wiggling sequences) were measured in a three compartment partner preference apparatus. Sexual receptivity (lordosis) was measured separately in a glass arena with a sexually active male. Results showed that olfactory bulb removal facilitates sexual receptivity and proceptivity in females exposed to 10% or 100% E2 in combination with 500 micrograms P. In contrast, sexual motivation was only demonstrated by olfactory bulbectomized females which received 100% E2 in combination with 500 micrograms P. These findings support the hypothesis that olfactory bulbectomy induces a behavioral hypersensitivity to estrogen, and suggest that sexual motivation is an estrogen-mediated response which requires a higher level of estrogen stimulation than sexual receptivity and proceptivity.

Ablation of mouse olfactory bulbs lengthened the circadian period of wheel-running activity by 43 min and delayed the onset of entrained activity by 108 min. A transient increase in activity during the light phase of the 12:12 h light-dark photoperiod also occurred following surgery. These disruptions suggest that olfactory systems can modulate mammalian circadian rhythms.

We characterized the temporal dynamics of brain and pituitary cell nuclear androgen receptor binding and serum androgen and gonadotropin levels associated with the implantation and removal of testosterone (T)-filled Silastic capsules into performed s.c. flank pouches of castrated, awake male rats. These capsules produced serum T levels in the physiologic range. The number of cell nuclear androgen + receptor complexes, as measured in an exchange assay using [3H]R1881, increased 15-fold at 0.5 h after capsule insertion in the HPAS (combined hypothalamus, preoptic area, amygdala and septum) and anterior pituitary gland, but then showed a second progressive rise within the next 8 h. This pattern suggests that T exerts an initial action in the tissues to alter the affinity and/or number of available androgen receptors. There was a lag time of 2-4 h to the first indication of negative feedback suppression of LH secretion. Serum LH levels declined only slightly at 4 h after capsule insertion but continued to fall thereafter, reaching undetectable values by 24 h. In contrast, serum FSH levels declined only slightly after 24 h of T exposure. After removal of the T capsules, serum T levels declined to castrate values within 2 h at which time the level of androgen + receptor complexes had fallen to 60% in the brain and pituitary. Serum LH and FSH concentrations were unchanged at 2 h after capsule removal, but rose significantly within the next 2 h. The data indicate that the occupation of androgen receptors rapidly changes in response to variations in circulating T in a fashion that implicates their involvement in the expression of this steroid's negative feedback actions on gonadotropin secretion.

Nuclear and cytosolic androgen receptors in the limbic brain were measured in neonatal male and female rat pups. There were no sex differences in cytosolic receptor concentrations during the neonatal period in any of the regions studied (hypothalamus, amygdala, preoptic area and septum). Receptor concentrations in all 4 regions increase gradually over the first 10 days of life, with no change in the affinity for 5-alpha-dihydrotestosterone. Nuclear receptor levels in intact pups, measured using an exchange assay, are highest between days 4 and 8 of life. In general, nuclear receptor levels are higher in males than in females; however, this sex difference is most consistently seen in the amygdala. These results are discussed in relation to sex differences in circulating testosterone levels and with respect to the contribution of androgens to the sexual differentiation of behavior.

The purpose of this study was 2-fold: 1) to use gonadal steroid hormone exposures in the physiological range to assess the relative roles of testosterone (T), estradiol (E2), and dihydrotestosterone (DHT) in the expression of male sexual behavior, and 2) to determine whether androgen receptor (AR) or estrogen receptor (E2R) occupation is increased after exposure to these various gonadal steroid hormones. Sexually experienced, castrated male rats implanted sc with Silastic capsules containing T, 10% E2, DHT, 10% E2 plus DHT, or blanks provided hormone levels in the physiological range. Copulatory behavior was measured on days 2-4, 5-7, 10-12, and 14-16 of steroid treatment. Although T, E2, and E2 plus DHT treatments all activated mounting, only T was effective in restoring ejaculation in 100% of the males. DHT alone had no effect on any aspect of male sexual behavior. Brains of males given these various hormone treatments were assayed for both cell nuclear AR and cell nuclear E2R binding in the hypothalamus, preoptic area, amygdala, and septum. Results indicate that when hormone levels in the physiological range were employed, T and DHT bind primarily to AR, whereas E2 binds to E2R. In a second experiment, 0.5% E2 plus DHT was found to yield AR and E2R levels comparable to those in rats receiving T capsules. Male rats bearing these capsules showed virtually no sexual behavior, demonstrating that elevation of AR and E2R levels comparable to those generated by T is not sufficient to induce male sexual behavior. We then measured intact AR and E2R levels and determined that in intact males E2R levels were higher than in T-treated males. These E2R levels could be replicated using 1.0% E2. Males exposed to 1.0% E2 plus DHT failed to display male sexual behavior. These data suggest that 1) relatively high and prolonged levels of E2R occupation are required for estrogen activation of male sexual behavior, 2) high levels of AR occupation induced by DHT are not sufficient to activate male sexual behavior, and 3) in intact male rats T, acting via androgen receptors, plays a primary role in mediating the expression of masculine sexual behavior.

This study was designed to assess the temporal relationship between the appearance and retention of cell nuclear progestin receptors in hypothalamus and the facilitation and decline of feminine sexual behavior following an i.v. injection of progesterone (P). Nuclear translocation of progestin receptors preceded the earliest appearance of behavior. The behavioral effects of P outlasted the nuclear progestin receptor elevation by several hours. Our results are consistent with the idea that P-induced effects on feminine sexual behavior involve genomic activation.

Glucocorticoid hormones alter functional cardiac responses in the rat heart. In the neonatal rat heart, glucocorticoid treatment on post-natal day 2 alters heart function for up to 3 weeks post-injection, which suggests that cardiac glucocorticoid receptors mediate cardiac function in neonates. However, glucocorticoid receptors have not been identified in neonatal rat heart. Glucocorticoid receptor binding was measured in neonatal rat heart cytosol extract using [3H] dexamethasone as ligand, and characterized by competition assays and Scatchard analysis. Saturable, specific, high affinity glucocorticoid receptor binding was found in the cytosol of the neonatal rat heart. We then examined the effects of a single, post-natal day 2 injection of hydrocortisone acetate on glucocorticoid receptor binding in 12 to 14-day-old rat heart. While this injection paradigm results in altered cardiac function in 12-day-old rat hearts, cytosol glucocorticoid receptor binding in 12 to 14-day-old heart was not altered by treatment on post-natal day 2 with hydrocortisone acetate. It is postulated that exposure to elevated glucocorticoid levels on neonatal day 2 may alter cardiac function by producing permanent organizational effects on cardiac tissue.