The effect of anabolic-androgenic steroids on aromatase activity and androgen receptor binding in the rat preoptic area

Androgen receptor deficiency is associated with reduced aromatase expression in the ventromedial hypothalamus of male cichlids

Social behaviors are regulated by sex steroid hormones, such as androgens and estrogens. However, the specific molecular and neural processes modulated by steroid hormones to generate social behaviors remain to be elucidated. We investigated whether some actions of androgen signaling in the control of social behavior may occur through the regulation of estradiol synthesis in the highly social cichlid fish, Astatotilapia burtoni. Specifically, we examined the expression of cyp19a1, a brain-specific aromatase, in the brains of male A. burtoni lacking a functional ARα gene (ar1), which was recently found to be necessary for aggression in this species. We found that cyp19a1 expression is higher in wild-type males compared to ar1 mutant males in the anterior tuberal nucleus (ATn), the putative fish homolog of the mammalian ventromedial hypothalamus, a brain region that is critical for aggression across taxa. Using in situ hybridization chain reaction, we determined that cyp19a1+ cells coexpress ar1 throughout the brain, including in the ATn. We speculate that ARα may modulate cyp19a1 expression in the ATn to govern aggression in A. burtoni. These studies provide novel insights into the hormonal mechanisms of social behavior in teleosts and lay a foundation for future functional studies.

ADHD symptoms and use of anabolic androgenic steroids among male weightlifters

Use of anabolic androgenic steroids (AAS) is associated with adverse health effects. The factors that predispose to AAS use among athletes are poorly understood, but attention deficit/hyperactivity disorder (ADHD), which is known to occur among athletes more often than in the general population, is associated with risk behaviors, including substance abuse. We aimed to see if AAS use in male weightlifters was associated with ADHD symptoms, and test the link between ADHD symptoms and cognitive performance. Hundred and forty male weightlifters, 72 AAS users and 68 weightlifting controls (WLC), completed the Achenbach system of empirically based assessment (ASEBA) for ADHD symptoms and underwent cognitive examination. Self-reported ADHD symptom scores were significantly higher among AAS users compared to WLC, and scores in the range indicating clinically important ADHD was significantly more common in the AAS-using group. Age of onset of AAS use correlated inversely with ADHD scale score (r = - 0.35; p = 0.003). ADHD score correlated inversely with cognitive scores for working memory (r = - 0.25, p < 0.001), processing speed (r = - 0.24, p < 0.001), verbal learning and memory (r = - 0.19, p = 0.03), and problem solving (r = - 0.20, p = 0.02). AAS use among weightlifters is associated with ADHD symptoms and corresponding lower cognitive performance. Recognising a relationship between ADHD symptoms and AAS use may guide drug prevention strategies in sports.

Anabolic steroids and their effects of on neuronal density in cortical areas and hippocampus of mice

Anabolic substances have been increasingly used by bodybuilders and athletes with the goal of improving performance and aesthetics. However, this practice has caused some concern to physicians and researchers because of unknowledge of consequences that the indiscriminate and illicit use of these substances can cause. Thus, this study analyzed the effects of two commercially available anabolic steroids (AS), Winstrol Depot® (Stanozolol) and Deposteron® (Testosterone Cypionate), in the neuronal density of limbic, motor and sensory regions on the cerebral cortex and in CA1, CA2, CA3 regions of the hippocampus. A total of 60 Swiss mice were used (30 males and 30 females), separated into three groups: control and two experimental groups, which received the AAS. From each brain, homotypic and semi-serial samples were taken in frontal sections from areas established for the study. The results showed that females treated with testosterone cypionate presented a reduction in all regions tested and the ones treated with Stanozolol showed a decrease in some hippocampal areas. Regarding male animals, stanozolol led to a decrease in neuron number in one hippocampal region. These data allow us to conclude that supra-physiological doses of steroids used in this study, can cause considerable damage to nervous tissue with ultrastructural and consequently behavioral impairment. These changes could interfere with the loss of physical yield and performance of athletes and non-athletes and may cause irreparable damage to individuals making irresponsible use of anabolic steroids.

Pubertal anabolic androgenic steroid exposure in male rats affects levels of gonadal steroids, mating frequency, and pregnancy outcome

Background Testosterone, nandrolone, and stanozolol are among the highly consumed anabolic androgenic steroids (AASs). Although the desired effects of AAS are being achieved by the abusers, unfortunately, this leads to numerous physical and physiological side effects. The present study was designed to investigate and determine whether early pubertal exposure to AAS treatment had detrimental effects on blood testosterone and estradiol concentrations, mating behavior, and pregnancy outcome during the pubertal period in male rats. Materials Early pubertal rats (PND41) were given two doses (2.5 mg/kg and 5 mg/kg) each of testosterone, nandrolone, and stanozolol subcutaneously for 6 weeks. Upon completion, three rats with the highest weight were chosen from each group for mating with the females, in a ratio of one male to two females for 10 days. After 10 days, all male rats were sacrificed to obtain the testes for weight recording, and blood samples were collected for testosterone and estradiol quantitation. Pregnant females were housed separately until birth, and the number of offsprings produced was counted. Results The results clearly show a reduction in reproductive hormonal and behavioral parameters between testosterone and nandrolone, and testosterone and stanozolol. Stanozolol administration exhibited suppressing effects in all parameters including testicular weight deterioration, serum testosterone and estradiol reduction, low mating preferences, and declined pregnancy outcome. Conclusions AAS exposure during the onset of puberty results in reproductive detrimental effects, which are postulated to affect the pregnancy rate.

Nandrolone administration abolishes hippocampal fEPSP-PS potentiation and passive avoidance learning of adolescent male rats

Despite the chronic effects of nandrolone decanoate (ND), the acute effects of ND on passive avoidance learning (PAL) and memory and its mechanism have not been investigated. This research examines the acute effect of ND on PAL, CA1 synaptic plasticity, testosterone and corticosterone serum levels, and the role of androgenic receptors (ARs). Adolescent male rats were treated with ND, 30 min before training and retention and after training test. AR antagonist was applied 15 min before ND. Hippocampal slices were perfused by ND. ND administration had an inverted U-shape effect on acquisition of PAL and on testosterone and corticosterone serum levels. The consolidation was only affected by high dose of ND. ND significantly decreased the retention of PAL across all doses. The magnitude of field excitatory postsynaptic potential long term potentiation was lower than that of control slices. In addition, an attenuation of field excitatory postsynaptic potential population spike coupling was also observed. Nilutamide could nullify the ND impairment effect. We concluded although a single dose of ND could affect all stages of PAL, its effects were more potent on retrieval, possibly arising from the acute effect of ND on the alterations of CA1 synaptic plasticity. In addition, ND may induce its effects directly through ARs and indirectly through plasma testosterone and corticosterone.

The binding properties of metandienone and human serum albumin by comparing with other five similar compounds

Metandienone (MET) is an exogenous anabolic androgenic steroid. The interaction between MET and human serum albumin (HSA) was investigated by molecular modeling and different optical techniques. There was no possibility of energy transfer, and the fluorescence quenching of HSA induced by MET was mainly due to the complex formation. The differences of binding ability between MET and compounds 1-5 were significantly caused by space steric hindrance. The single crystallographic data of two steroids (compounds 4 and 5) were obtained in the methanol at the first time. In addition, the binding ability was slightly affected by -OH, -CH₃ , and -COCH₃ . The results of displacement experiment demonstrated that the MET binding site was mainly located in site 1 of HSA. H-bonding and van der Waals forces were significant in the MET-HSA binding. MET played an insignificant role on the local conformation change in HSA.

The impact of nandrolone decanoate on the central nervous system

Nandrolone is included in the class II of anabolic androgenic steroids (AAS) which is composed of 19-nor-testosterone-derivates. In general, AAS is a broad and rapidly increasing group of synthetic androgens used both clinically and illicitly. AAS in general and nandrolone decanoate (ND) in particular have been associated with several behavioral disorders. The purpose of this review is to summarize the literature concerning studies dealing with ND exposure on animal models, mostly rats that mimic human abuse systems (i.e. supraphysiological doses). We have focused in particular on researches that have investigated how ND alters the function and expression of neuronal signaling molecules that underlie behavior, anxiety, aggression, learning and memory, reproductive behaviors, locomotion and reward.

The effect of the anabolic steroid, nandrolone, in conditioned place preference and D1 dopamine receptor expression in adolescent and adult mice

Adolescents and adults engage in anabolic-androgenic steroid (AAS) misuse seeking their anabolic effects, even though later on, many could develop neuropsychological dependence. Previously, we have shown that nandrolone induces conditioned place preference (CPP) in adult male mice. However, whether nandrolone induces CPP during adolescence remains unknown. In this study, the CPP test was used to determine the rewarding properties of nandrolone (7.5 mg/kg) in adolescent mice. In addition, since D1 dopamine receptors (D1DR) are critical for reward-related processes, the effect of nandrolone on the expression of D1DR in the nucleus accumbens (NAc) was investigated by Western blot analysis. Similar to our previous results, nandrolone induced CPP in adults. However, in adolescents, nandrolone failed to produce place preference. At the molecular level, nandrolone decreased D1DR expression in the NAc only in adult mice. Our data suggest that nandrolone may not be rewarding in adolescents at least during short-term use. The lack of nandrolone rewarding effects in adolescents may be due, in part to differences in D1DR expression during development.

Neurotoxicity by synthetic androgen steroids: oxidative stress, apoptosis, and neuropathology: A review

Anabolic-androgenic steroids (AAS) are synthetic substances derived from testosterone that are largely employed due to their trophic effect on muscle tissue of athletes at all levels. Since a great number of organs and systems are a target of AAS, their adverse effects are primarily on the following systems: reproductive, hepatic, musculoskeletal, endocrine, renal, immunological, infectious, cardiovascular, cerebrovascular, and hematological. Neuropsychiatric and behavioral effects as a result of AAS abuse are well known and described in the literature. Mounting evidence exists suggesting that in addition to psychiatric and behavioral effects, non-medical use of AAS carries neurodegenerative potential. Although, the nature of this association remains largely unexplored, recent animal studies have shown the recurrence of this AAS effect, ranging from neurotrophin unbalance to increased neuronal susceptibility to apoptotic stimuli. Experimental and animal studies strongly suggest that apoptotic mechanisms are at least in part involved in AAS-induced neurotoxicity. Furthermore, a great body of evidence is emerging suggesting that increased susceptibility to cellular oxidative stress could play a pivotal role in the pathogenesis of many neurodegenerative disorders and cognitive impairment. As in other drug-evoked encephalopathies, the key mechanisms involved in AAS - induced neuropathology could represent a target for future neuroprotective strategies. Progress in the understanding of these mechanisms will provide important insights into the complex pathophysiology of AAS-induced neurodegeneration, and will pave the way for forthcoming studies. Supplementary to abandoning the drug abuse that represents the first step in reducing the possibility of irreversible brain damage in AAS abusers, neuroprotective strategies have to be developed and implemented in future.

Anabolic androgenic steroid abuse: multiple mechanisms of regulation of GABAergic synapses in neuroendocrine control regions of the rodent forebrain

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone originally developed for clinical purposes but are now predominantly taken at suprapharmacological levels as drugs of abuse. To date, almost 100 different AAS compounds that vary in metabolic fate and physiological effects have been designed and synthesised. Although they are administered for their ability to enhance muscle mass and performance, untoward side effects of AAS use include changes in reproductive and sexual behaviours. Specifically, AAS, depending on the type of compound administered, can delay or advance pubertal onset, lead to irregular oestrous cyclicity, diminish male and female sexual behaviours, and accelerate reproductive senescence. Numerous brains regions and neurotransmitter signalling systems are involved in the generation of these behaviours, and are potential targets for both chronic and acute actions of the AAS. However, critical to all of these behaviours is neurotransmission mediated by GABA(A) receptors within a nexus of interconnected forebrain regions that includes the medial preoptic area, the anteroventral periventricular nucleus and the arcuate nucleus of the hypothalamus. We review how exposure to AAS alters GABAergic transmission and neural activity within these forebrain regions, taking advantage of in vitro systems and both wild-type and genetically altered mouse strains, aiming to better understand how these synthetic steroids affect the neural systems that underlie the regulation of reproduction and the expression of sexual behaviours.

The Buzz about anabolic androgenic steroids: electrophysiological effects in excitable tissues

Anabolic androgenic steroids (AAS) comprise a large and growing class of synthetic androgens used clinically to promote tissue-building in individuals suffering from genetic disorders, injuries, and diseases. Despite these beneficial therapeutic applications, the predominant use of AAS is illicit: these steroids are self-administered to promote athletic performance and body image. Hand in hand with the desired anabolic actions of the AAS are untoward effects on the brain and behavior. While the signaling routes by which the AAS impose both beneficial and harmful actions may be quite diverse, key endpoints are likely to include ligand-gated and voltage-dependent ion channels that govern the activity of electrically excitable tissues. Here, we review the known effects of AAS on molecular targets that play critical roles in controlling electrical activity, with a specific focus on the effects of AAS on neurotransmission mediated by GABA(A) receptors in the central nervous system.

PET of aromatase in gastric parietal cells using 11C-vorozole

Aromatase is a rate-limiting enzyme for estrogen biosynthesis and has been implicated in pathophysiological states of various diseases via estrogen production. This enzyme is known to be widely distributed in extragonadal and gonadal tissues including the stomach. In contrast to circulating estrogen, the functional role of gastric aromatase/estrogen has not been elucidated in detail, because there is no efficient methodology to investigate spatiotemporal changes of gastric aromatase/estrogen in vivo. Recently, (S)-(11)C-6-[(4-chlorophenyl)(1H-1,2,4-triazole-1-yl)methyl]-1-methyl-1H-benzotriazole ((11)C-labeled vorozole), based on a potent nonsteroidal aromatase inhibitor, has been developed as a tracer to investigate aromatase distribution in living animals and humans using a noninvasive PET technique. In the present study, we investigated gastric aromatase expression by means of PET with (11)C-vorozole.

METHODS

After bolus injection of (11)C-vorozole into the tail vein, emission scans were obtained for 90 min on male and female rats under isoflurane anesthesia. Displacement studies with unlabeled vorozole and autoradiographic analysis were conducted for demonstration of specific binding. Immunohistochemistry was performed to confirm aromatase expression.

RESULTS

PET scans revealed that (11)C-vorozole highly accumulated in the stomach and adrenal glands. Displacement studies and autoradiography demonstrated that aromatase was expressed in the stomach but that the accumulation of (11)C-vorozole in the adrenal glands might be through nonspecific binding. Immunohistochemical analysis revealed that aromatase is expressed in gastric parietal cells but not in adrenal glands. Moreover, the accumulation of (11)C-vorozole in the stomach was significantly increased in fatigued rats.

CONCLUSION

These results suggest that the (11)C-vorozole PET technique is a useful tool for evaluation of gastric aromatase dynamics in vivo, which may provide important information for understanding the molecular mechanisms of gastric aromatase/estrogen-related pathophysiological processes and for the development of new drugs.

Impact of anabolic androgenic steroids on adolescent males

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.

The aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) reduces disinhibitory behavior in intact adult male rats treated with a high dose of testosterone

Anabolic androgenic steroids and high testosterone doses have been reported to induce impulsive behavior in man and behavioral disinhibition in rats. The purpose of the present study was to investigate whether aromatization of testosterone to estradiol is of importance for the behavioral disinhibiting effect of a high testosterone dose in adult male rats. Testosterone administered via five testosterone-filled silastic capsules implanted subcutaneously (s.c.) to non-castrated, group-housed rats for six days induced behavioral disinhibition in a modified Vogel's drinking conflict model and yielded supraphysiological serum levels of testosterone and increased accessory sex organ weights. Moreover, concurrent administration of the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD; 60 mg/kg/day s.c.) decreased behavioral disinhibition in testosterone-treated rats (without affecting accessory sex organ weights) while behavior was not significantly affected in sham-treated animals. Since some reports indicate that ATD, in addition to inhibit aromatase, also may affect the binding of testosterone to the androgen receptor, the effect of the non-steroidal androgen receptor antagonist flutamide was investigated. Flutamide treatment did not affect disinhibited behavior in testosterone-treated rats. However, in sham-treated animals, flutamide (50mg/kg/day) produced behavioral disinhibition. These results suggest that estradiol is of importance in the mechanisms underlying behavioral disinhibition in non-castrated rats treated with a high testosterone dose. Speculatively, aromatization may be involved in pro-impulsive effects of high testosterone doses in humans.

Integrating statistical predictions and experimental verifications for enhancing protein-chemical interaction predictions in virtual screening

Predictions of interactions between target proteins and potential leads are of great benefit in the drug discovery process. We present a comprehensively applicable statistical prediction method for interactions between any proteins and chemical compounds, which requires only protein sequence data and chemical structure data and utilizes the statistical learning method of support vector machines. In order to realize reasonable comprehensive predictions which can involve many false positives, we propose two approaches for reduction of false positives: (i) efficient use of multiple statistical prediction models in the framework of two-layer SVM and (ii) reasonable design of the negative data to construct statistical prediction models. In two-layer SVM, outputs produced by the first-layer SVM models, which are constructed with different negative samples and reflect different aspects of classifications, are utilized as inputs to the second-layer SVM. In order to design negative data which produce fewer false positive predictions, we iteratively construct SVM models or classification boundaries from positive and tentative negative samples and select additional negative sample candidates according to pre-determined rules. Moreover, in order to fully utilize the advantages of statistical learning methods, we propose a strategy to effectively feedback experimental results to computational predictions with consideration of biological effects of interest. We show the usefulness of our approach in predicting potential ligands binding to human androgen receptors from more than 19 million chemical compounds and verifying these predictions by in vitro binding. Moreover, we utilize this experimental validation as feedback to enhance subsequent computational predictions, and experimentally validate these predictions again. This efficient procedure of the iteration of the in silico prediction and in vitro or in vivo experimental verifications with the sufficient feedback enabled us to identify novel ligand candidates which were distant from known ligands in the chemical space.

The anabolic steroids testosterone propionate and nandrolone, but not 17alpha-methyltestosterone, induce conditioned place preference in adult mice

Anabolic androgenic steroids (AAS) are often misused by adolescents and athletes. Their effects vary according to chemical structure and metabolism, route of administration, and AAS regimen. In this study, adult C57Bl/6 male mice were systemically exposed to testosterone propionate (TP), nandrolone or 17alpha-methyltestosterone (17alpha-meT), type I, type II and type III AAS, respectively, in order to determine the hedonic or aversive properties of each drug. For this purpose, the conditioned place preference (CPP) test was employed at three different AAS doses (0.075, 0.75 and 7.5 mg/kg). Other behavioral domains monitored were light-dark transitions (side changes) and general activity. TP shifted place preference at all doses tested, and nandrolone shifted place preference at 0.75 and 7.5 mg/kg, but not at 0.075 mg/kg, the lower dose tested. Conversely, mice receiving 17alpha-meT did not show alteration in the preference score. The lower dose of nandrolone did modify exploratory-based anxiety showing a decrease in light-dark transitions if compared to vehicle-treated animals, while mice treated with TP or 17alpha-meT were not affected. Our data suggest that when studying hedonic and rewarding properties of synthetic androgens, distinction has to be made based on type of AAS and metabolism.

Neurosteroid biosynthesis regulates sexually dimorphic fear and aggressive behavior in mice

The neurosteroid allopregnanolone is a potent positive allosteric modulator of GABA action at GABA(A) receptors. Allopregnanolone is synthesized in the brain from progesterone by the sequential action of 5alpha-reductase type I (5alpha-RI) and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD). 5alpha-RI and 3alpha-HSD are co-expressed in cortical, hippocampal, and olfactory bulb glutamatergic neurons and in output neurons of the amygdala, thalamus, cerebellum, and striatum. Neither 5alpha-RI nor 3alpha-HSD mRNAs is expressed in glial cells or in cortical or hippocampal GABAergic interneurons. It is likely that allopregnanolone synthesized in principal output neurons locally modulates GABA(A) receptor function by reaching GABA(A) receptor intracellular sites through lateral membrane diffusion. This review will focus on the behavioral effects of allopregnanolone on mouse models that are related to a sexually dimorphic regulation of brain allopregnanolone biosynthesis. Animal models of psychiatric disorders, including socially isolated male mice or mice that receive a long-term treatment with anabolic androgenic steroids (AAS), show abnormal behaviors such as altered fear responses and aggression. In these animal models, the cortico-limbic mRNA expression of 5alpha-RI is regulated in a sexually dimorphic manner. Hence, in selected glutamatergic pyramidal neurons of the cortex, CA3, and basolateral amygdala and in granular cells of the dentate gyrus, mRNA expression of 5alpha-RI is decreased, which results in a downregulation of allopregnanolone content. In contrast, 5alpha-RI mRNA expression fails to change in the striatum medium spiny neurons and in the reticular thalamic nucleus neurons, which are GABAergic.By manipulating allopregnanolone levels in glutamatergic cortico-limbic neurons in opposite directions to improve [using the potent selective brain steroidogenic stimulant (SBSS) S-norfluoxetine] or induce (using the potent 5alpha-RI inhibitor SKF 105,111) behavioral deficits, respectively, we have established the fundamental role of cortico-limbic allopregnanolone levels in the sexually dimorphic regulation of aggression and fear. By selectively targeting allopregnanolone downregulation in glutamatergic cortico-limbic neurons, i.e., by improving the response of GABA(A) receptors to GABA, new therapeutics would offer appropriate and safe management of psychiatric conditions, including impulsive aggression, irritability, irrational fear, anxiety, posttraumatic stress disorders, and depression.

Influence of anabolic steroid on anxiety levels in sedentary male rats

The aim of this study was to evaluate the influence of nandrolone decanoate on anxiety levels in rats. Male Wistar rats were treated with nandrolone decanoate (5mg/kg, two times per week, i.m.) or vehicle (propylene glycol--0.2 ml/kg, two times per week, IM) for 6 weeks. Control rats were subject only to procedures related to their routine husbandry. By the end of 6 weeks, all groups (24-29 rats/group) were submitted to the elevated plus maze test in order to evaluate their anxiety level. Some of these animals (12-14/group) were treated with diazepam (1 mg/kg i.p.) 30 min before the elevated plus maze test. Nandrolone decanoate significantly decreased the percentage of time spent in the open arms (1.46+/-0.49%) compared with control (3.80+/-0.97%) and vehicle (3.96+/-0.85%) groups, with no difference between control and vehicle treatments. The percentage of open arm entries was also reduced in the group treated with nandrolone decanoate in comparison with the vehicle and control. No changes in the number of closed arm entries were detected. Diazepam abolished the effects of nandrolone decanoate on the percentage of time in, and entries into the open arms. The present study showed that chronic treatment with a high dose of nandrolone decanoate increased the anxiety level in male rats.

Effects of anabolic androgenic steroids on the development and expression of running wheel activity and circadian rhythms in 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.

Nanomolar concentrations of anabolic-androgenic steroids amplify excitotoxic neuronal death in mixed mouse cortical cultures

The use of anabolic-androgenic steroids (AASs) in the world of sport has raised a major concern for the serious, sometimes life-threatening, side effects associated with these drugs. Most of the CNS effects are of psychiatric origin, and whether or not AASs are toxic to neurons is yet unknown. We compared the effect of testosterone with that of the AASs, 19-nortestosterone (nandrolone), stanozolol, and gestrinone, on excitotoxic neuronal death induced by N-methyl-d-aspartate (NMDA) in primary cultures of mouse cortical cells. In the most relevant experiments, steroids were applied to the cultures once daily during the 4 days preceding the NMDA pulse. Under these conditions, testosterone amplified excitotoxic neuronal death only at very high concentrations (10 muM), whereas it was protective at concentrations of 10 nM and inactive at intermediate concentrations. Low concentrations of testosterone became neurotoxic in the presence of the aromatase inhibitors, i.e. anastrozole and aminoglutethimide, suggesting that the intrinsic toxicity of testosterone was counterbalanced by its aromatization into 17beta-estradiol. As opposed to testosterone, nortestosterone, stanozolol and gestrinone amplified NMDA toxicity at nanomolar concentrations; their action was insensitive to aromatase inhibitors, but was abrogated by the androgen receptor antagonist, flutamide. None of the AASs were toxic in the absence of NMDA. These data suggest that AASs increase neuronal vulnerability to an excitotoxic insult and may therefore facilitate neuronal death associated with acute or chronic CNS disorders.

Increase in [11C]vorozole binding to aromatase in the hypothalamus in rats treated with anabolic androgenic steroids

In the present study, we investigated the alteration of aromatase expression in the brain by anabolic androgenic steroid treatment in male rats. The rats were given nandrolone decanoate (15 mg/kg/day) for 14 days, and the brains were used for autoradiography with [C]vorozole, which has been developed as a positron emission tomography tracer for aromatase by our group. The results indicated a significant increase of [C]vorozole binding by anabolic androgenic steroids in the bed nucleus of the stria terminalis and preoptic area. In contrast, no significant change of [C]vorozole binding was observed in the medial amygdala. Our results suggest that aromatase is significantly upregulated in the bed nucleus of the stria terminalis and preoptic area by anabolic androgenic steroids and also suggest that androgens regulate aromatase differently in these structures compared with the medial amygdala.

Preliminary investigation of changes in the sexually dimorphic nucleus of the rat medial preoptic area following prenatal exposure to fenitrothion

In vitro, the organophosphate insecticide fenitrothion is a potent competitive androgen receptor antagonist, whereas in vivo it affects the development of the male rat reproductive system. The purpose of this pilot study was to determine whether prenatal exposure to fenitrothion affects development of the rat sexually dimorphic nucleus of the medial preoptic area (SDN-POA). Pregnant rats (n = 5-6 litters/group) were orally dosed with corn oil (vehicle) or fenitrothion (20 or 25 mg kg(-1) day(-1)) from gestation day (GD) 12-21. Offspring were euthanized after reaching sexual maturity (females 60-65 days old and males 96-105 days old) and the SDN-POA volumes determined for two rats/sex/litter. Tremors, increased lacrimation and decreased body weight gain were observed in dams from both fenitrothion exposure groups. Reproductive effects in male offspring, including reduced anogenital distance on postnatal day (PND) 1 and increased retention of areolae (PND 13) were observed following fenitrothion exposure at these dose levels. These effects did not persist into adulthood. There was a dose-related increase in the SDN-POA volume in males and a dose-related decrease in SDN-POA volume in females exposed to fenitrothion. These SDN-POA volume changes contrast with those seen with flutamide, another potent anti-androgen, and suggest that fenitrothion may have mixed endocrine effects on the developing brain.

Sex- and age-specific effects of anabolic androgenic steroids on reproductive behaviors and on GABAergic transmission in neuroendocrine control regions

Illicit use of anabolic androgenic steroids (AAS) has become a prevalent health concern not only among male professional athletes, but, disturbingly, among a growing number of women and adolescent girls. Despite the increasing use of AAS among women and adolescents, few studies have focused on the effects of these steroids in females, and female adolescent subjects are particularly underrepresented. Among the hallmarks of AAS abuse are changes in reproductive behaviors. Here, we discuss work from our laboratories on the actions of AAS on the onset of puberty and sexual behaviors in female rodents, AAS interactions and sex- and age-specific effects of these steroids on neural transmission mediated by gamma-aminobutyric acid receptors within forebrain neuroendocrine control regions that may underlie AAS-induced changes in these behaviors.

Imaging of aromatase distribution in rat and rhesus monkey brains with [11C]vorozole

Aromatase is an enzyme that converts androgens to estrogens and may play a role in mood and mental status. The aim of this study was to demonstrate that brain aromatase distribution could be evaluated with a novel positron emission tomography (PET) tracer [(11)C]vorozole. Vorozole is a nonsteroidal aromatase inhibitor that reversibly binds to the heme domain of aromatase. In vitro experiments in rat brain, using frozen section autoradiography, illustrated specific binding in the medial amygdala (MA), the bed nucleus of stria terminalis (BST) and the preoptic area (POA) of male rat brain. Specific binding in female rat brain was found in the MA and the BST; however, the signals were lower than those of males. The K(d) of [(11)C]vorozole binding to aromatase in MA was determined to be 0.60+/-0.06 nM by Scatchard plot analysis using homogenates. An in vivo PET study in female rhesus monkey brain demonstrated the uptake of [(11)C]vorozole in the amygdala, where the uptake was blocked by the presence of excess amounts of unlabeled vorozole. Thus, this tracer has a high affinity for brain aromatase and could have a potential for in vivo aromatase imaging. This technique might enable the investigation of human brain aromatase in healthy and diseased persons.

Stacking anabolic androgenic steroids (AAS) during puberty in rats: A neuroendocrine and behavioral assessment

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.

Anabolic androgenic steroids and forebrain GABAergic transmission

Anabolic androgenic steroids are synthetic derivatives of testosterone designed for therapeutic purposes, but now taken predominantly as drugs of abuse. The most common behavioral effects associated with anabolic androgenic steroid use are changes in anxiety, aggression and reproductive behaviors, including the onset of puberty and sexual receptivity. GABAergic circuits in the forebrain underlie these behaviors and are regulated by gonadal steroids. Work from our laboratories has shown that the expression and function of GABA(A) receptors in the rat and mouse forebrain varies between the sexes and across the estrous cycle. We have also shown that there are significant changes in GABA(A) receptor expression that occur with the progression through puberty to adulthood. Because GABAergic systems are both steroid-sensitive and critical for the expression of behaviors altered with anabolic androgenic steroid use, forebrain GABA(A) receptors are an attractive candidate to assess how molecular actions of anabolic androgenic steroids may be translated to known behavioral outcomes. Our studies demonstrate that anabolic androgenic steroids elicit both acute modulation of GABA(A) receptor-mediated currents, as well as chronic regulation of GABA(A) receptor expression and forebrain GABAergic transmission. Because anabolic androgenic steroid use has now become prevalent not only among adolescent boys, but in an increasing number of adolescent girls, we have also been particularly interested in determining age- and sex-specific effects of anabolic androgenic steroids. Our data show that the effects of chronic anabolic androgenic steroid exposure can be greater for adolescent than adult animals and are more marked in females than in males. These data have particularly important implications with respect to studies we have done demonstrating that chronic anabolic androgenic steroid exposure alters the onset of puberty, estrous cyclicity and sexual receptivity.

The effect of sub-chronic nandrolone decanoate treatment on dopaminergic and serotonergic neuronal systems in the brains of rats

Anabolic-androgenic steroids (AASs) are widely abused by adolescents, although persistent AAS use can cause several adverse physical and mental effects, including drug dependence. The first aim of the present study was to study the action of nandrolone decanoate on dopaminergic and serotonergic activities in the brains of rats. In order to evaluate the anabolic or toxic effects of the dosing regimens used, selected peripheral effects were monitored as well. Male Wistar rats were treated for 2 weeks. Injections containing nandrolone (5 and 20 mg/kg, i.m.) or vehicle were given once daily, 5 days a week. The levels of dopamine (DA), 5-hydroxytryptamine (5-HT) and their metabolites were assayed from dissected brain regions 3 days after the last injection. Blood was collected for chemical assays before, after 1 week treatment and at decapitation. Both doses of nandrolone significantly increased the levels of 3,4-dihydroxyphenylacetic acid (DOPAC), a metabolite of DA in the cerebral cortex, and the higher dose of nandrolone increased the concentrations of 5-HT in the cerebral cortex compared with the vehicle. In addition, after nandrolone treatment, the levels of hemoglobin and erythrocytes increased, and reticulocyte levels decreased. The results suggest that nandrolone at supraphysiological doses, high enough to induce erythropoiesis, induces changes in the dopaminergic and serotonergic neuronal system in the brains of rats. These phenomena may account to some of the observed central stimulatory properties that have been reported following AAS abuse.

Modulation of affect after chronic exposure to the anabolic steroid 17alpha-methyltestosterone in adult mice

A battery of behavioral tasks in C57BL/6J mice was used to assess changes in affective components of behavior after systemic exposure to the anabolic-androgenic steroid (AAS) 17alpha-methyltestosterone (7.5 mg/kg). Gonadal weight in both sexes was reduced after 16 days of AAS exposure. Changes in discrete components of social behaviors were observed. No changes were recorded in the elevated plus-maze, the light-dark transition, and defensive behavior tests on exposure to 17alpha-methyltestosterone. When compared with controls, AAS-exposed females received a greater number of shocks, and AAS-exposed males displayed a shorter recovery time to consume water after a negative reinforcer in the modified Vogel conflict test. Results show that systemic exposure to a single AAS modified social behaviors, whereas minimal effects on anxiety-related behaviors were observed according to sex.

Nandrolone decanoate has long-term effects on dominance in a competitive situation in male rats

The aim of the present study was to examine possible long-term effects of the anabolic androgenic steroid (AAS), nandrolone decanoate (ND), on dominance in a provoking and competitive situation in sexually matured male rats. The experimental group (n=10) received daily injections of ND [15 mg/kg in a volume of 1 ml/kg subcutaneous (s.c.) injection for 14 days]. During the corresponding period, the controls (n=10) were given daily injections of an oil vehicle (1 ml/kg s.c.). All animals were tested in a competitive situation at four occasions after the end of the treatment period (week 5, 8, 11 and 14). Water-deprived pairs of rats, consisting of one ND-treated rat and one control, had to compete for access to water. The results showed that the ND-treated rats approached the water spout significantly more often compared to the controls. During the competition tests, the ND-treated rats spent more time drinking, an effect that was prominent for 11 weeks after the end of the treatment period. The ND-treated rats also displayed more frequently piloerection than the controls. The results indicate that ND has long-term effect on dominance in a provoking and competitive situation.

Neurotropic action of androgens: principles, mechanisms and novel targets

The importance of androgen signaling is well recognized for numerous aspects of central nervous system (CNS) function, ranging from sex-specific organization of neuroendocrine and behavioral circuits to adaptive capacity, resistance and repair. Nonetheless, concepts for the therapeutic use of androgens in neurological and mental disorders are far from being established. This review outlines some critical issues which interfere with decisions on the suitability of androgens as therapeutic agents for CNS conditions. Among these, sex-specific organization of neural substrates and resulting differential responsiveness to endogenous gonadal steroids, convergence of steroid hormone actions on common molecular targets, co-presence of different sex steroid receptors in target neuronal populations, and in situ biotransformation of natural androgens apparently pose the principal obstacles for the characterization of specific neurotropic effects of androgens. Additional important, albeit less explored aspects consist in insufficient knowledge about molecular targets in the CNS which are under exclusive or predominant androgen control. Own experimental data illustrate the variability of pharmacological effects of natural and synthetic androgens on CNS functions of adaptive relevance, such as sexual behavior, anxiety and endocrine responsiveness to stress. Finally, we present results from an analysis of the consequences of aging for the rat brain transcriptome and examination of the influence of androgens on differentially expressed genes with presumable significance in neuropathology.

Long-term effects of pubertal anabolic-androgenic steroid exposure on reproductive and aggressive behaviors in male rats

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.

Behavioral and physiological responses to anabolic-androgenic steroids

Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone originally designed for therapeutic uses to provide enhanced anabolic potency with negligible androgenic effects. Although AAS continue to be used clinically today, the medical benefits of low therapeutic doses of AAS stand in sharp contrast to the potential health risks associated with the excessive doses self-administered not only by elite athletes and body builders, but by a growing number of recreational users, including adolescent boys and girls. The deleterious effects of AAS on peripheral organs and the incidence of altered behaviors in AAS abusers have been well documented in a number of excellent current reviews for clinical populations. However, a comparable synthesis of nonclinical studies has not been made. Our purpose in this review is to summarize the literature for animal models of the effects of supraphysiological doses of AAS (e.g. those that mimic human abuse regimes) on behaviors and on the neural circuitry for these behaviors. In particular, we have focused on studies in rodents that have examined how AAS alter aggression, sexual behaviors, anxiety, reward, learning, and locomotion and how AAS alter the expression and function of neurotransmitter systems and other signaling molecules that underlie these behaviors.

Effects of pubertal anabolic-androgenic steroid (AAS) administration on reproductive and aggressive behaviors in male rats

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.

Repeated anabolic-androgenic steroid treatment during adolescence increases vasopressin V(1A) receptor binding in Syrian hamsters: correlation with offensive aggression

Repeated anabolic-androgenic steroid treatment during adolescence increases hypothalamic vasopressin and facilitates offensive aggression in male Syrian hamsters (Mesocricetus auratus). The current study investigated whether anabolic-androgenic steroid exposure during this developmental period influenced vasopressin V(1A) receptor binding activity in the hypothalamus and several other brain areas implicated in aggressive behavior in hamsters. To test this, adolescent male hamsters were administered anabolic steroids or sesame oil throughout adolescence, tested for offensive aggression, and examined for differences in vasopressin V(1A) receptor binding using in situ autoradiography. When compared with control animals, aggressive, adolescent anabolic steroid-treated hamsters showed significant increases (20-200%) in the intensity of vasopressin V(1A) receptor labeling in several aggression areas, including the ventrolateral hypothalamus, bed nucleus of the stria terminalis, and lateral septum. However, no significant differences in vasopressin V(1A) receptor labeling were found in other brain regions implicated in aggressive responding, most notably the lateral zone from the medial preoptic area to anterior hypothalamus and the corticomedial amygdala. These data suggest that adolescent anabolic steroid exposure may facilitate offensive aggression by increasing vasopressin V(1A) receptor binding in several key areas of the hamster brain.

Physical provocation potentiates aggression in male rats receiving anabolic androgenic steroids

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

17alpha-methyl testosterone is a competitive inhibitor of aromatase activity in Jar choriocarcinoma cells and macrophage-like THP-1 cells in culture

17alpha-methyl testosterone is a synthetic androgen with affinity for the androgen receptor. 17alpha-methyl testosterone is used widely as a component of hormone replacement therapy. Previous reports have indicated that contrary to testosterone, 17alpha-methyl testosterone is not aromatized. However, 17alpha-methyl testosterone still could affect local estrogen formation by regulating aromatase expression or by inhibiting aromatase action. Both possibilities have important clinical implications. To evaluate the effect of 17alpha-methyl testosterone on the expression and activity of aromatase, we tested the choriocarcinoma Jar cell line, a cell line that express high levels of P450 aromatase, and the macrophage-like THP-1 cells, which express aromatase only after undergoing differentiation. We found that in both cell lines, 17alpha-methyl testosterone inhibits aromatase activity in a dose-related manner. The curve of inhibition parallels that of letrozole and gives complete inhibition at 10(-4) M 17alpha-methyl testosterone, determined by the tritium release assay. 17alpha-methyl testosterone does not have detectable effects on aromatase RNA and protein expression by Jar cells. Undifferentiated THP-1 cells had no aromatase activity and showed no effect of 17alpha-methyl testosterone, but differentiated THP-1 (macrophage-like) cells had a similar inhibition of aromatase activity by 17alpha-methyl testosterone to that seen in Jar cells. The Lineweaver-Burke plot shows 17alpha-methyl testosterone to be a competitive aromatase inhibitor. Our results show for the first time that 17alpha-methyl testosterone acts as an aromatase inhibitor. These findings are relevant for understanding the effects of 17alpha-methyl testosterone as a component of hormone replacement therapy. 17alpha-methyl testosterone may, as a functional androgen and orally active steroidal inhibitor of endogenous estrogen production, also offer special possibilities for the prevention/treatment of hormone-sensitive cancers.

Effect of particle size on the prolonged action of subcutaneous danazol in male and female rats

OBJECTIVE

To investigate the effects of two different particle sizes of danazol in male and female rats.

DESIGN

Prospective, vehicle-controlled study.

SETTING

Undergraduate college research facility and medical research laboratory.

ANIMALS

18 castrated male rats and 18 cycling female rats.

INTERVENTION(S)

Preparations of danazol with particle sizes of 2.05 microm or 5.2 microm were administered as a single subcutaneous injection of 400 mg/kg to castrated male rats or estrus-cycling females.

MAIN OUTCOME MEASURE(S)

Serum LH level in males and estrous cycle length in females.

RESULT(S)

In males, both preparations significantly (P<. 001) suppressed serum LH by day 5 of treatment. Gonadotropin levels remained low throughout the 35-day study in rats that received the larger-particle danazol, whereas LH levels began to increase after 25 days in rats that received smaller-particle danazol. In females, the normal 4- to 5-day estrous cycle interval was prolonged to 38.7 days (P<.001) in those that received the larger-particle danazol and 25.5 days in those that received the smaller-particle danazol.

CONCLUSION(S)

The results demonstrate the prolonged effectiveness of a single subcutaneous dose of danazol and indicate that one might be able to predict the effective duration of activity by changing the particle size of the danazol administered.

Inhibition of estrogen-induced sexual receptivity by androgens: role of the androgen receptor

Both naturally occurring and synthetic androgens have been shown to inhibit estrogen-induced sexual receptivity when administered to ovariectomized (OVX) rats. The mechanisms by which androgens exert these effects, however, remain unclear. Experiments were conducted to determine the role of the androgen receptor in the inhibition of estrogen-induced sexual receptivity in OVX rats by using flutamide, an androgen receptor antagonist. In each experiment, OVX Long-Evans rats received 6 consecutive days of estradiol benzoate (EB; 2.0 microg/day) followed by 15 days of EB concurrent with flutamide (10. 0 mg/kg; twice daily) or the vehicle and one of the following androgens or the vehicle: dihydrotestosterone propionate (7.5 mg/kg), 3alpha-androstanediol (3.75 mg/kg), 17alpha-methyltestosterone (7.5 mg/kg), stanozolol (7.5 mg/kg), or nandrolone decanoate (7.5 mg/kg). On Day 15, all female rats received progesterone (P; 1.0 mg/rat) 4 h before testing. Tests for sexual receptivity were conducted on Days 3, 6, 14, and 15 of androgen/flutamide treatment. Each androgen inhibited sexual receptivity as expected, and concurrent treatment with flutamide reversed the inhibitory effects of all androgens on sexual receptivity on all test days. High levels of sexual receptivity were displayed in response to P on Day 15, regardless of experimental treatment. These results suggest that naturally occurring and synthetic androgens act at the androgen receptor to inhibit estrogen-induced sexual receptivity in OVX rats.