Loss of TRPC2 function in mice alters sex differences in brain regions regulating social behaviors.

The transient receptor potential cation channel 2 (TRPC2) conveys pheromonal information from the vomeronasal organ (VNO) to the brain. Both male and female mice lacking this gene show altered sex-typical behavior as adults. We asked whether TRPC2, highly expressed in the VNO, normally participates in the development of VNO-recipient brain regions controlling mounting and aggression, two behaviors affected by TRPC2 loss. We now report significant effects of TRPC2 loss in both the posterodorsal aspect of the medial amygdala (MePD) and ventromedial nucleus of the hypothalamus (VMH) of male and female mice. In the MePD, a sex difference in neuron number was eliminated by the TRPC2 knockout (KO), but the effect was complex, with fewer neurons in the right MePD of females, and fewer neurons in the left MePD of males. In contrast, MePD astrocytes were unaffected by the KO. In the ventrolateral (vl) aspect of the VMH, KO females were like wildtype (WT) females, but TRPC2 loss had a dramatic effect in males, with fewer neurons than WT males and a smaller VMHvl overall. We also discovered a glial sex difference in VMHvl of WTs, with females having more astrocytes than males. Interestingly, TRPC2 loss increased astrocyte number in males in this region. We conclude that TRPC2 normally participates in the sexual differentiation of the mouse MePD and VMHvl. These changes in two key VNO-recipient regions may underlie the effects of the TRPC2 KO on behavior.

Down, But Not Out: Partial Elimination of Androgen Receptors in the Male Mouse Brain Does Not Affect Androgenic Regulation of Anxiety or HPA Activity.

We previously found that androgen receptor (AR) activity mediates two effects of T in adult male mice: reduction of anxiety-like behaviors and dampening of the hypothalamic-pituitary-adrenal response to stress. To determine whether brain ARs mediate these effects, we used the Cre/loxP technology seeking to disable AR throughout the central nervous system (CNS). Female mice carrying the floxed AR allele (ARlox) were crossed with males carrying cre recombinase transgene controlled by the nestin promoter (NesCre), producing cre in developing neurons and glia. Among male offspring, four genotypes resulted: males carrying ARlox and NesCre (NesARko), and three control groups (wild types, NesCre, and ARlox). Reporter mice indicated ubiquitous Cre expression throughout the CNS. Nevertheless, AR immunocytochemistry in NesARko mice revealed efficient knockout (KO) of AR in some brain regions (hippocampus and medial prefrontal cortex [mPFC]), but not others. Substantial AR protein was seen in the amygdala and hypothalamus among other regions, whereas negligible AR remained in others like the bed nucleus of the stria terminalis and dorsal periaqueductal gray. This selective KO allowed for testing the role of AR in hippocampus and mPFC. Males were castrated and implanted with T at postnatal day 60 before testing on postnatal day 90-100. In contrast with males with global KO of AR, T still modulated anxiety-related behavior and hypothalamic-pituitary-adrenal activity in NesARko males. These results leave open the possibility that AR acting in the CNS mediates these effects of T, but demonstrate that AR is not required in the hippocampus or mPFC for T's anxiolytic effects.

Androgen effects on hippocampal CA1 spine synapse numbers are retained in Tfm male rats with defective androgen receptors.

The effects of estradiol benzoate (EB), dihydrotestosterone (DHT), or the antiandrogen hydroxyflutamide on CA1 pyramidal cell dendritic spine synapses were investigated in adult male rats. To elucidate the contribution of the androgen receptor to the hormone-induced increase in hippocampal CA1 synapses, wild-type males were compared with males expressing the Tfm mutation, which results in synthesis of defective androgen receptors. Orchidectomized rats were treated with EB (10 microg/rat.d), DHT (500 mug/rat.d), hydroxyflutamide (5 mg/rat.d), or the sesame oil vehicle sc daily for 2 d and examined using quantitative electron microscopic stereological techniques, 48 h after the second injection. In wild-type males, DHT and hydroxyflutamide both induced increases in the number of spine synapses in the CA1 stratum radiatum, whereas EB had no effect. DHT almost doubled the number of synaptic contacts observed, whereas hydroxyflutamide increased synapse density by approximately 50%, compared with the vehicle-injected controls. Surprisingly, in Tfm males, the effects of EB, DHT, and hydroxyflutamide were all indistinguishable from those observed in wild-type animals. These observations demonstrate that Tfm male rats resemble normal males in having no detectable hippocampal synaptic response to a dose of EB that is highly effective in females. Despite the reduction in androgen sensitivity as a result of the Tfm mutation, hippocampal synaptic responses to both DHT and a mixed androgen agonist/antagonist (hydroxyflutamide) remain intact in Tfm males. These data are consistent with previous results suggesting that androgen effects on hippocampal spine synapses may involve novel androgen response mechanisms.