Intrahippocampal administration of an androgen receptor antagonist, flutamide, can increase anxiety-like behavior in intact and DHT-replaced male rats

Chronic administration of androgens with actions at estrogen receptor beta have anti-anxiety and cognitive-enhancing effects in male rats

Androgen levels decline with aging. Some androgens may exert anti-anxiety and cognitive-enhancing effects; however, determining which androgens have anxiolytic-like and/or mnemonic effects is of interest given the different mechanisms that may underlie some of their effects. For example, the 5 alpha-reduced metabolite of testosterone (T), dihydrotesterone, can be further converted to 5 alpha-androstane,17beta-diol-3 alpha-diol (3 alpha-diol) and 5 alpha-androstane,17beta-diol-3beta-diol (3beta-diol), both of which bind with high affinity to the beta isomer of the intracellular estrogen receptor beta (ER beta). However, androsterone, another metabolite of T, does not bind well to ER beta. To investigate the effects of T metabolites, male rats were subjected to gonadectomy then implanted with silastic capsules of 3 alpha-diol, 3beta-diol, androsterone, or oil control. After recovery, the rats were tested in elevated plus maze (EPM), light/dark transition (LD), and Morris water maze (MWM). 3 alpha-diol both decreased anxiety-like behavior in the EPM and LD, and increased cognition in MWM, while 3beta-diol improved cognition in MWM, but had no effects on anxiety behavior, compared to vehicle or androsterone. These data suggest that the actions of 3 alpha-diol and 3beta-diol at ER beta may be responsible for some of testosterone's anti-anxiety and cognitive-enhancing effects.

Examining the intersection of sex and stress in modelling neuropsychiatric disorders

Sex-biased neuropsychiatric disorders, including major depressive disorder and schizophrenia, are the major cause of disability in the developed world. Elevated stress sensitivity has been proposed as a key underlying factor in disease onset. Sex differences in stress sensitivity are associated with corticotrophin-releasing factor (CRF) and serotonin neurotransmission, which are important central regulators of mood and coping responses. To elucidate the underlying neurobiology of stress-related disease predisposition, it is critical to develop appropriate animal models of stress pathway dysregulation. Furthermore, the inclusion of sex difference comparisons in stress responsive behaviours, physiology and central stress pathway maturation in these models is essential. Recent studies by our laboratory and others have begun to investigate the intersection of stress and sex where the development of mouse models of stress pathway dysregulation via prenatal stress experience or early-life manipulations has provided insight into points of developmental vulnerability. In addition, examination of the maturation of these pathways, including the functional importance of the organisational and activational effects of gonadal hormones on stress responsivity, is essential for determination of when sex differences in stress sensitivity may begin. In such studies, we have detected distinct sex differences in stress coping strategies where activational effects of testosterone produced females that displayed male-like strategies in tests of passive coping, but were similar to females in tests of active coping. In a second model of elevated stress sensitivity, male mice experiencing prenatal stress early in gestation showed feminised physiological and behavioural stress responses, and were highly sensitive to a low dose of selective serotonin reuptake inhibitors. Analyses of expression and epigenetic patterns revealed changes in CRF and glucocorticoid receptor genes in these mice. Mechanistically, stress early in pregnancy produced a significant sex-dependent effect on placental gene expression that was supportive of altered foetal transport of key growth factors and nutrients. These mouse models examining alterations and hormonal effects on development of stress pathways provide necessary insight into how specific stress responses can be reprogrammed early in development resulting in sex differences in stress sensitivity and neuropsychiatric disease vulnerability.

Organizational and activational effects of testosterone on masculinization of female physiological and behavioral stress responses

The prevalence of affective disorders is two times greater in women than in men. The onset of anxiety and depression occurs at different ages that may correspond to key developmental periods when the brain is more vulnerable to hormonal and exogenous influences. Because stressful life events can precipitate disease onset, the development of greater stress sensitivity in females may contribute to their increased vulnerability. Gonadal hormone exposure in males during early development and again from puberty onward plays a prominent role in sexually dimorphic brain formation, possibly contributing to sex differences in stress responsivity. Therefore, organizational effects of testosterone propionate (TP) administered postnatally and activational effects of TP administered beginning at puberty on adult female physiological and behavioral stress responses were examined in mice. Although the activational effects of TP in females ameliorated the sex difference in the hypothalamic-pituitary-adrenal axis stress response, there was no effect of postnatal TP. Similarly, higher immobile time in intact females in the tail suspension test was blunted by activational TP in the absence of postnatal TP. However, in the marble-burying test of anxiety-like behaviors, organizational and activational TP independently resulted in increased burying behaviors. These results show that TP administration has distinct effects on reducing physiological and behavioral stress responsivity in rodent models and suggest that sex differences in these responses may partially result from the absence of testosterone in females.

Nandrolone abuse decreases anxiety and impairs memory in rats via central androgenic receptors

Anabolic androgenic steroids (AASs) affect areas of the central nervous system, which are involved in emotional and cognitive responses such as sexuality, anxiety, and memory. In the present study we imitated the abuse of AASs by administering high doses of the AAS nandrolone decanoate (ND) to rats. Thereafter rats were exposed to an elevated plus-maze and an olfactory social memory test to evaluate their anxiety-like and cognitive behaviour. To reveal whether these emotional and cognitive changes evoked by ND were caused via direct activation of androgenic receptors (ARs) in the brain, the AR antagonist flutamide (FL) was administered intracerebroventricularly (i.c.v.). Male rats were randomly divided in four groups, one group received 15 mg/kg ND subcutaneously, once daily for 6 wk (ND group). In the second group, in addition to ND, a daily dose of 5 microg FL was injected i.c.v. also for 6 wk (ND+FL group). The third group of rats received only FL and in the control group the vehicle was injected. The ND group clearly spent more time investigating the open arms in the maze test and recognizing the juvenile during the olfactory social memory test in comparison to the control group. In the ND+FL group rats showed similar emotional behaviour and cognitive ability to that of the control group. Injection of FL alone did not affect either anxiety or memory. These results indicate that repeated, high-dose administration of ND decreases anxiety and impairs memory in rats via direct activation of central ARs.

Androgens with activity at estrogen receptor beta have anxiolytic and cognitive-enhancing effects in male rats and mice

Testosterone (T) and its metabolites may underlie some beneficial effects for anxiety and cognition, but the mechanisms for these effects are unclear. T is reduced to dihydrotestosterone (DHT), which can be converted to 5alpha-androstane,3alpha,17beta-diol (3alpha-diol) and/or 5alpha-androstane-3beta,17beta-diol (3beta-diol). Additionally, T can be converted to androstenedione, and then to androsterone. These metabolites bind with varying affinity to androgen receptors (ARs; T and DHT), estrogen receptors (ERbeta; 3alpha-diol, 3beta-diol), or GABA(A)/benzodiazepine receptors (GBRs; 3alpha-diol, androsterone). Three experiments were performed to investigate the hypothesis that reduced anxiety-like and enhanced cognitive performance may be due in part to actions of T metabolites at ERbeta. Experiment 1: Gonadectomized (GDX) wildtype and ERbeta knockout mice (betaERKO) were subcutaneously (SC) administered 3alpha-diol, 3beta-diol, androsterone, or oil vehicle at weekly intervals, and tested in anxiety tasks (open field, elevated plus maze, light-dark transition) or for cognitive performance in the object recognition task. Experiment 2: GDX rats were administered SC 3alpha-diol, 3beta-diol, androsterone, or oil vehicle, and tested in the same tasks. Experiment 3: GDX rats were androsterone- or vehicle-primed and administered an antagonist of ARs (flutamide), ERs (tamoxifen), or GBRs (flumazenil), or vehicle and then tested in the elevated plus maze. Both rats and wildtype mice, but not betaERKO mice, consistently had reduced anxiety and improved performance in the object recognition task. Androsterone was only effective at reducing anxiety-like behavior in the elevated plus maze and this effect was modestly reduced by flumazenil administration. Thus, actions at ERbeta may be required for T's anxiety-reducing and cognitive-enhancing effects.

Androgen administration to aged male mice increases anti-anxiety behavior and enhances cognitive performance

Although androgen secretion is reduced with aging, and may underlie decrements in cognitive and affective performance, the effects and mechanisms of androgens to mediate these behaviors are not well understood. Testosterone (T), the primary male androgen, is aromatized to estrogen (E(2)), and reduced to dihydrotestosterone (DHT), which is converted to 5alpha-androstane, 3alpha, 17beta-diol (3alpha-diol). To ascertain whether actions of the neuroactive metabolite of T, 3alpha-diol, mediates cognitive and affective behaviors, intact, aged male C57/B6 mice (24 month old) as well as young, intact and gonadectomized (GDX; 12 week old) mice were administered s.c. T, 3alpha-diol, E(2), or sesame oil vehicle (1 mg/kg; n=4-5/group) at weekly intervals and 1 h later mice were tested in the activity box, roto-rod, open field, elevated plus maze, zero maze, mirror maze, dark-light transition, forced swim, or Vogel tasks. Mice were trained in the inhibitory avoidance or conditioned contextual fear and were administered hormones following training and then were tested. After the last test occasion, tissues were collected for evaluation of hormone levels and effects on gamma-aminobutyric acid (GABA)-stimulated chloride flux. T, 3alpha-diol, or E(2) increased anti-anxiety and antidepressant behavior of aged, intact mice in the open field, light-dark transition, mirror maze, and forced swim tasks. T or 3alpha-diol, but not E(2), enhanced anti-anxiety behavior in the elevated plus maze, zero maze, and the Vogel task, and increased motor behavior in the activity monitor, latency to fall in the Roto-rod task, and cognitive performance in the hippocampally-mediated, but not the amygdala-mediated, portion of the conditioned fear task and in the inhibitory avoidance task. Anti-anxiety and enhanced cognitive performance was associated with regimen that increased plasma and hippocampal 3alpha-diol levels and GABA-stimulated chloride flux. Similar patterns were seen among young, adult GDX but not in intact mice. Thus, 3alpha-diol can enhance affective and cognitive behavior of male mice.

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.

Sexual experience of male rats influences anxiety-like behavior and androgen levels

There is a wide body of literature to suggest that sexual experience may influence androgen secretion in various species, in turn, androgens may also influence anxiety. We hypothesized that sexual experience may alter anxiety behavior and secretion of endogenous androgens. Experiment 1: anxiety behavior of rats with a history of sexual experience was compared to that of sexually-inexperienced, naïve male rats. Sexually-experienced rats showed less anxiety-like behavior in the open field and elevated plus maze, and exhibited increased plasma and hippocampal testosterone (T) levels. Experiment 2: the effects of recent sexual experience on anxiety behavior of sexually-experienced male rats, sexually-responsive but inexperienced male rats, and sexually-unresponsive, inexperienced male rats exposed to a receptive female immediately prior to testing was examined. Recent sexual experience significantly decreased anxiety-like behavior in the open field, elevated plus maze, and the elevated zero maze tasks, and tended to decrease anxiety-like behavior in the light-dark task. Rats with recent sexual experience exhibited increased plasma and hippocampal T levels. Experiment 3: to examine the effect of recent sexual experience, anxiety behavior of rats with a history of sexual experience that received sexual experience with a stimulus female immediately prior to testing was compared to that of rats with a history of sexual experience that did not receive sexual experience immediately prior to behavioral testing. Experienced rats that were exposed to a female prior to testing showed decreased anxiety-like behavior in the open field, elevated plus maze, and light-dark transition tasks, and showed increased plasma and hypothalamic, T and 3alpha-diol, and increased hippocampal T. Thus, sexual experience is associated with lower levels of anxiety-like behavior and higher levels of androgen secretion.

Androgens’ performance-enhancing effects in the inhibitory avoidance and water maze tasks may involve actions at intracellular androgen receptors in the dorsal hippocampus

Androgens can have performance-enhancing effects in some cognitive tasks, but the mechanism of these effects has not been established. Experiments examined whether androgens' actions to bind to intracellular androgen receptors (ARs) in the hippocampus are necessary to enhance cognitive performance in the inhibitory avoidance and water maze tasks. If androgens' binding at ARs are essential, then blocking them through intrahippocampal administration of flutamide, an AR receptor antagonist, should attenuate androgens' performance-enhancing effects in the inhibitory avoidance and water maze tasks. In Experiments 1 and 2, flutamide was administered through intrahippocampal inserts to intact male rats immediately pre- and post-training in the inhibitory avoidance and water maze tasks. Both pre- and post-training administration of flutamide to the dorsal hippocampus, but not missed sites, produced significantly poorer performance in the inhibitory avoidance and water maze tasks, without influencing control measures such as flinch/jump threshold or swim speed. In Experiment 3, flutamide administration to the hippocampus was delayed two hours following training in the inhibitory avoidance and water maze tasks. There was no significant effect of delayed administration of flutamide on performance in either of these tasks. Together, these findings suggest that blocking ARs in the dorsal hippocampus with flutamide administration immediately pre- or post-training can produce decrements in cognitive performance, which implies that androgens' performance-enhancing effects may occur, in part, through binding at intracellular androgen receptors in the dorsal hippocampus.