Inter-sexual variation in social interactions and distribution of estrogen receptor alpha in the brain of mandarin voles Microtus mandarinus

To explore the effects of estrogen receptor alpha (ERα) on social behaviors of mandarin voles (Microtus mandarinus), same-sex social interaction tests in mandarin voles were conducted and the distribution of ERα immunoreactivity(IR) cells were examined in the brains of male and female mandarin voles by immunocytochemistry. The results showed that female mandarin voles displayed significantly less affiliation and more defense (P<0.01) and more aggressive behaviors (P<0.05) than males. The ERα-IR cells were mainly localized in arcuate hypothalamic nucleus (ARC), medial amygdaloid nucleus (MeA), central amygdaloid nucleus (Ce), medial prioptic area (MPOA), ventromedial hypothalamic nucleus (VMH) and bed nucleus of the stria terminalis (BST). The distribution of ERα-IR cells varied between the sexes with females expressing significantly more ERα-IR in the BST, MPOA, MeA and Ce (P<0.01) and males expressed more ERα-IR in the ARC (P<0.05). There was no significant inter-sexual difference in ERα-IR cell densities in VMH (P>0.05). These findings suggest that there is significant difference in aggression, affiliation and defense as well as distribution of ERα-IR cells between males and females for mandarin voles. Sexual differences in social interactions and distribution of ERα-IR cells are consistent with the characteristics of a monogamous rodent. The inter-sexual variation in the distribution of ERα-IR cells may be one of the important neural mechanisms underlying monogamous social and reproductive behaviors [Acta Zoologica Sinica 54（6）：1020–1028, 2008].