Estrogen receptor alpha distribution and expression in the social neural network of monogamous and polygynous Peromyscus

Abstract

In microtine and dwarf hamsters low levels of estrogen receptor alpha (ER?) in the bed nucleus of the stria terminalis (BST) and medial amygdala (MeA) play a critical role in the expression of social monogamy in males, which is characterized by high levels of affiliation and low levels of aggression. In contrast, monogamous Peromyscus males display high levels of aggression and affiliative behavior with high levels of testosterone and aromatase activity. Suggesting the hypothesis that in Peromyscus ER? expression will be positively correlated with high levels of male prosocial behavior and aggression. ER? expression was compared within the social neural network, including the posterior medial BST, MeA posterodorsal, medial preoptic area (MPOA), ventromedial hypothalamus (VMH), and arcuate nucleus in two monogamous species, P. californicus and P. polionotus, and two polygynous species, P. leucopus and P. maniculatus. The results supported the prediction, with male P. polionotus and P. californicus expressing higher levels of ER? in the BST than their polygynous counter parts, and ER? expression was sexually dimorphic in the polygynous species, with females expressing significantly more than males in the BST in both polygynous species and in the MeA in P. leucopus. Peromyscus ER? expression also differed from rats, mice and microtines as in neither the MPOA nor the VMH was ER? sexually dimorphic. The results supported the hypothesis that higher levels of ER? are associated with monogamy in Peromyscus and that differential expression of ER? occurs in the same regions of the brains regardless of whether high or low expression is associated with social monogamy. Also discussed are possible mechanisms regulating this differential relationship.