Testosterone, acting via estrogenic and androgenic pathways, is the major endocrine mechanism promoting sexual differentiation of the mammalian nervous system and behavior, but we have an incomplete knowledge of which cells and tissues mediate these effects. To distinguish between neural and nonneural actions of androgens in sexual differentiation of brain and behavior, we generated a loxP-based transgenic mouse, which overexpresses androgen receptors (ARs) when activated by Cre. We used this transgene to overexpress AR globally in all tissues using a cytomegalovirus (CMV)-Cre driver (CMV-AR), and we used a Nestin-Cre driver to overexpress AR only in neural tissue (Nes-AR). We then examined whether neural or global AR overexpression can affect socio-sexual behaviors using a resident-intruder paradigm. We found that both neural and global AR overexpression resulted in decreased aggressive behaviors and increased thrusting during mounting of intruders, consistent with a neural site of action. Global, but not neural, AR overexpression in males led to an increase in same-sex anogenital investigation. Together, these results suggest novel roles for nonneural AR in sexual differentiation of mice, and indicate that excess AR can lead to a paradoxical reduction of male-typical behavior.

Memory formation is a protracted process that initially involves the hippocampus and becomes increasingly dependent on the cortex over time, but the mechanisms of this transfer are unclear. We recently showed that hippocampal depletion of the histone variant H2A.Z enhances both recent and remote memories, but the use of virally mediated depletion reduced H2A.Z levels throughout testing, making its temporally specific function unclear. Given the lack of drugs that target histone variants, we tested existing drugs for efficacy against H2A.Z based on their targeting of known H2A.Z regulators. The Tip60 (part of H2A.Z deposition complex) inhibitor Nu9056 reduced H2A.Z binding, whereas the histone deacetylase (HDAC) inhibitor Trichostatin-A increased H2A.Z acetylation without influencing total H2A.Z in cultured hippocampal neurons. Tip60 (but not HDAC) inhibition 23 h after learning enhanced remote (tested at 7 d) and not recent (tested at 24 h) contextual fear memory in mice. In contrast, Tip60 inhibition 30 d after learning impaired recall of remote memory after 1 h, but protected the memory from further decline 24 h later. These data provide the first evidence of a delayed postlearning role for histone variants in supporting memory transfer during systems consolidation.

Polyglutamine (polyQ) expansion of the androgen receptor (AR) causes Kennedy's disease/spinobulbar muscular atrophy (KD/SBMA) through poorly defined cellular mechanisms. Although KD/SBMA has been thought of as a motor neuron disease, recent evidence indicates a key role for skeletal muscle. To resolve which early aspects of the disease can be caused by neurogenic or myogenic mechanisms, we made use of the tet-On and Cre-loxP genetic systems to selectively and acutely express polyQ AR in either motor neurons (NeuroAR) or myocytes (MyoAR) of transgenic mice. After 4 weeks of transgene induction in adulthood, deficits in gross motor function were seen in NeuroAR mice, but not MyoAR mice. Conversely, reduced size of fast glycolytic fibers and alterations in expression of candidate genes were observed only in MyoAR mice. Both NeuroAR and MyoAR mice exhibited reduced oxidative capacity in skeletal muscles, as well as a shift in fast fibers from oxidative to glycolytic. Markers of oxidative stress were increased in the muscle of NeuroAR mice and were reduced in motor neurons of both NeuroAR and MyoAR mice. Despite secondary pathology in skeletal muscle and behavioral deficits, no pathological signs were observed in motor neurons of NeuroAR mice, possibly due to relatively low levels of polyQ AR expression. These results indicate that polyQ AR in motor neurons can produce secondary pathology in muscle. Results also support both neurogenic and myogenic contributions of polyQ AR to several acute aspects of pathology and provide further evidence for disordered cellular respiration in KD/SBMA skeletal muscle.

Emerging evidence suggests that histone variants are novel epigenetic regulators of memory, whereby histone H2A.Z suppresses fear memory. However, it is not clear if altered fear memory can also modify risk for PTSD, and whether these effects differ in males and females. Using conditionalinducible H2A.Z knockout (cKO) mice, we showed that H2A.Z binding is higher in females and that H2A.Z cKO enhanced fear memory only in males. However, H2A.Z cKO improved memory on the non-aversive object-in-place task in both sexes, suggesting that H2A.Z suppresses non-stressful memory irrespective of sex. Given that risk for fear-related disorders, such as PTSD, is biased toward females, we examined whether H2A.Z cKO also has sex-specific effects on fear sensitization in the stress-enhanced fear learning (SEFL) model of PTSD, as well as associated changes in pain sensitivity. We found that H2A.Z cKO reduced stress-induced sensitization of fear learning and pain responses preferentially in female mice, indicating that the effects of H2A.Z depend on sex and the type of task, and are influenced by history of stress. These data suggest that H2A.Z may be a sex-specific epigenetic risk factor for PTSD susceptibility, with implications for developing sex-specific therapeutic interventions. The capacity to remember fear-related cues is an important survival-promoting adaptation, but it can become maladaptive in some psychiatric conditions, such as post-traumatic stress disorder (PTSD). PTSD develops in response to a traumatic experience and is characterised by intrusive memories of the trauma and sensitization to fear, which presents as enhanced formation of new memories for relatively mild fearful stimuli 1-7. PTSD disproportionately affects women, who have twice the risk of developing the disorder 8 , and who are more prone to developing new fear memories compared to men with PTSD 9-11. In rodents, fear sensitization is modeled with stress-enhanced fear learning (SEFL), a paradigm in which exposure to a strong stressor (used to model traumatic experience) results in strengthened acquisition of fear memory compared to mice without prior stress exposure 10. This sensitization effect is observable within 24 h after stress, is long lasting, and is associated with a range of PTSD-like symptoms, including increased anxiety and impaired fear extinction 10. Some evidence suggests that PTSD may also sensitize patients to various forms of painful stimuli. Rates of chronic pain are higher among patients with PTSD compared to the general population, pain onset begins after PTSD symptoms emerge, and intensity of pain positively correlates with the severity of PTSD 12. Although sex differences in pain sensitivity in PTSD patients have not been widely studied, sex differences in pain sensitivity in the general population are widely reported, with women exhibiting higher prevalence of chronic pain and lower pain thresholds compared to men 13-15. One recent study in rodents showed that exposure to a single prolonged

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic neuromuscular system in which the masculinisation of cell number is assumed to depend on the action of perinatal androgen in non-neural targets, whereas the masculinisation of cell size is assumed to depend primarily on the action of adult androgen on SNB cells themselves. To test these hypotheses, we characterised the SNB of Cre/loxP transgenic mice that overexpress androgen receptor (AR) throughout the body (CMV-AR) or in neural tissue only (Nestin-AR). Additionally, we examined the effects of androgen manipulation in male mutants and wild-type (WT) controls. We reproduced the expected sex differences in both motoneurone number and size, as well as the expected adult androgen dependence of SNB size. We found effects of genotype such that both Nestin-AR and CMV-AR have more SNB motoneurones than WT littermates and also that CMV-AR females have larger SNB motoneurones than Nes-AR or WT females. These results raise the possibility that AR can act in neurones and/or glia to rescue SNB motoneurones, as well as on non-neural AR to increase SNB cell size.