Some sex differences in the brain may be latent differences, in which the same functional endpoint is achieved through distinct underlying mechanisms in males versus females. Here we report a latent sex difference in molecular regulation of excitatory synapses in the hippocampus. The steroid 17β-estradiol is known to acutely potentiate glutamatergic synaptic transmission in both sexes. We find that this occurs through a combination of increased presynaptic glutamate release probability and increased postsynaptic sensitivity to glutamate in both sexes, but that distinct estrogen receptor subtypes underlie each aspect of potentiation in each sex. These results indicate that therapeutics targeting a specific estrogen receptor subtype or its downstream signaling would likely affect synaptic transmission differently in the hippocampus of each sex.

Estradiol (E2) acutely potentiates glutamatergic synaptic transmission in the hippocampus of both male and female rats. Here, we investigated whether E2-induced synaptic potentiation occurs via presynaptic and/or postsynaptic mechanisms and which estrogen receptors (ERs) mediate E2's effects in each sex. Whole-cell voltage-clamp recordings of mEPSCs in CA1 pyramidal neurons showed that E2 increases both mEPSC frequency and amplitude within minutes, but often in different cells. This indicated that both presynaptic and postsynaptic mechanisms are involved, but that they occur largely at different synapses. Two-photon (2p) glutamate uncaging at individual dendritic spines showed that E2 increases the amplitude of uncaging-evoked EPSCs (2pEPSCs) and calcium transients (2pCaTs) at a subset of spines on a dendrite, demonstrating synapse specificity of E2's postsynaptic effects. All of these results were essentially the same in males and females. However, additional experiments using ER-selective agonists indicated sex differences in the mechanisms underlying E2-induced potentiation. In males, an ER␤ agonist mimicked the postsynaptic effects of E2 to increase mEPSC, 2pEPSC, and 2pCaT amplitude, whereas in females, these effects were mimicked by an agonist of G protein-coupled ER-1. The presynaptic effect of E2, increased mEPSC frequency, was mimicked by an ER␣ agonist in males, whereas in females, an ER␤ agonist increased mEPSC frequency. Thus, E2 acutely potentiates glutamatergic synapses similarly in both sexes, but distinct ER subtypes mediate the presynaptic and postsynaptic aspects of potentiation in each sex. This indicates a latent sex difference in which different molecular mechanisms converge to the same functional endpoint in males versus females.

SummaryIn the past several decades, the therapeutic use of anabolic androgenic steroids (AAS) has been overshadowed by illicit use of these drugs by elite athletes and a growing number of adolescents to enhance performance and body image. As with adults, AAS use by adolescents is associated with a range of behavioral effects, including increased anxiety and altered responses to stress. It has been suggested that adolescents, especially adolescent females, may be particularly susceptible to the effects of these steroids, but few experiments in animal models have been performed to test this assertion. Here we show that chronic exposure of adolescent female mice to a mixture of three commonly abused AAS (testosterone cypionate, nandrolone decanoate and methandrostenolone; 7.5 mg/kg/day for 5 days) significantly enhanced anxiety-like behavior as assessed by the acoustic startle response (ASR), but did not augment the fear-potentiated startle response (FPS) or alter sensorimotor gating as assessed by prepulse inhibition of the acoustic startle response (PPI). AAS treatment also significantly increased the levels of corticotropin releasing factor (CRF) mRNA and somalassociated CRF immunoreactivity in the central amygdala (CeA), as well as neuropil-associated immunoreactivity in the dorsal aspect of the anterolateral division of the bed nucleus of the stria terminalis (dBnST). AAS treatment did not alter CRF receptor 1 or 2 mRNA in either the CeA or the dBnST; CRF immunoreactivity in the ventral BNST, the paraventricular nucleus (PVN) or the median eminence (ME); or peripheral levels of corticosterone. These results suggest that chronic AAS treatment of adolescent female mice may enhance generalized anxiety, but not sensorimotor gating or learned fear, via a mechanism that involves increased CRF-mediated signaling from CeA neurons projecting to the dBnST.

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Anabolic androgenic steroids (AAS) are illicitly administered to enhance athletic performance and body image. Although conferring positive actions on performance, steroid abuse is associated with changes in anxiety and aggression. AAS users are often keenly invested in understanding the biological actions of these drugs. Thus, mechanistic information on AAS actions is important not only for the biomedical community, but also for steroid users. Here we review findings from animal studies on the impact of AAS exposure on neural systems that are crucial for the production of anxiety and aggression, and compare the effects of the different classes of AAS and their potential signaling mechanisms, as well as context-, age- and sex-dependent aspects of their actions.

Increased anxiety is commonly observed in individuals who illicitly administer anabolic androgenic steroids (AAS). Behavioral effects of steroid abuse have become an increasing concern in adults and adolescents of both sexes. The dorsolateral bed nucleus of the stria terminalis (dlBnST) has a critical role in the expression of diffuse anxiety and is a key site of action for the anxiogenic neuromodulator, corticotropin releasing factor (CRF). Here we demonstrate that chronic, but not acute, exposure of female mice during adolescence to AAS augments anxiety-like behaviors; effects that were blocked by central infusion of the CRF receptor type 1 antagonist, antalarmin. AAS treatment selectively increased action potential (AP) firing in neurons of the central amygdala (CeA) that project to the dlBnST, increased the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in dlBnST target neurons, and decreased both c-FOS immunoreactivity (IR) and AP frequency in these postsynaptic cells. Acute application of antalarmin abrogated the enhancement of GABAergic inhibition induced by chronic AAS exposure whereas application of CRF to brain slices of naïve mice mimicked the actions of this treatment. These results, in concert with previous data demonstrating that chronic AAS treatment results in enhanced levels of CRF mRNA in the CeA and increased CRF-IR in the dlBnST neuropil, are consistent with a mechanism in which the enhanced anxiety elicited by chronic AAS exposure involves augmented inhibitory activity of CeA afferents to the dlBnST and CRF-dependent enhancement of GABAergic inhibition in this brain region.

Summary Disruption of reproductive function is a hallmark of abuse of anabolic androgenic steroids (AAS) in female subjects. To understand the central actions of AAS, patch clamp recordings were made in estrous, diestrous and AAS-treated mice from gonadotropin releasing hormone (GnRH) neurons, neurons in the medial preoptic area (mPOA) and neurons in the anteroventroperiventricular nucleus (AVPV); regions known to provide GABAergic and kisspeptin inputs to the GnRH cells. Action potential (AP) frequency was significantly higher in GnRH neurons of estrous mice than in AAS-treated or diestrous animals. No significant differences in AAS-treated, estrous or diestrous mice were evident in the amplitude or kinetics of spontaneous postsynaptic currents (sPCSs), miniature PSCs or tonic currents mediated by GABAA receptors or in GABAA receptor subunit expression in GnRH neurons. In contrast, the frequency of GABAA receptor-mediated sPSCs in GnRH neurons showed an inverse correlation with AP frequency across the three hormonal states. Surprisingly, AP activity in the medial preoptic area (mPOA), a likely source of GABAergic afferents to GnRH cells, did not vary in concert with the sPSCs in the GnRH neurons. Furthermore, pharmacological blockade of GABAA receptors did not alter the pattern in which there was lower AP frequency in GnRH neurons of AAS-treated and diestrous versus estrous mice. These data suggest that AAS do not impose their effects either directly on GnRH neurons or on putative GABAergic afferents in the mPOA. AP activity recorded from neurons in kisspeptin-rich regions of the anteroventroperiventricular nucleus (AVPV) and the expression of kisspeptin mRNA and peptide did vary coordinately with AP activity in GnRH neurons. Our data demonstrate that AAS treatment imposes a “diestrous-like” pattern of activity in GnRH neurons and suggest that this effect may arise from suppression of presynaptic kisspeptin-mediated excitatory drive arising from the AVPV. The actions of AAS on neuroendocrine regulatory circuits may contribute the disruption of reproductive function observed in steroid abuse.

Anabolic androgenic steroids (AAS) are taken by both sexes to enhance athletic performance and body image, nearly always in conjunction with an exercise regime. Although taken to improve physical attributes, chronic AAS use can promote negative behavior, including anxiety. Few studies have directly compared the impact of AAS use in males versus females or assessed the interaction of exercise and AAS. We show that AAS increase anxiety-like behaviors in female but not male mice and that voluntary exercise accentuates these sex-specific differences. We also show that levels of the anxiogenic peptide corticotrophin releasing factor (CRF) are significantly greater in males, but that AAS selectively increase CRF levels in females, thus abrogating this sex-specific difference. Exercise did not ameliorate AAS-induced anxiety or alter CRF levels in females. Exercise was anxiolytic in males, but this behavioral outcome did not correlate with CRF levels. Brain-derived neurotrophic factor (BDNF) has also been implicated in the expression of anxiety. As with CRF, levels of hippocampal BDNF mRNA were significantly greater in males than females. AAS and exercise were without effect on BDNF mRNA in females. In males, anxiolytic effects of exercise correlated with increased BDNF mRNA, however AAS-induced changes in BDNF mRNA and anxiety did not. In sum, we find that AAS elicit sex-specific differences in anxiety and that voluntary exercise accentuates these differences. In addition, our data suggest that these behavioral outcomes may reflect convergent actions of AAS and exercise on a sexually differentiated CRF signaling system within the extended amygdala.