Estrogen receptors in the medial amygdala inhibit the expression of male prosocial behavior

Abstract

Studies using estrogen receptor α (ERα) knock-out mice indicate that ERα masculinizes male behavior. Recent studies of ERα and male prosocial behavior have shown an inverse relationship between ERα expression in regions of the brain that regulate social behavior, including the medial amygdala (MeA), and the expression of male prosocial behavior. These studies have lead to the hypothesis that low levels of ERα are necessary to "permit" the expression of high levels of male prosocial behavior. To test this, viral vectors were used to enhance ERα in male prairie voles (Microtus ochrogaster), which display high levels of prosocial behavior and low levels of MeA ERα. Adult male prairie voles were transfected with ERα in the MeA (MeA-ERα) or the caudate-putamen (ERα control) or luciferase (MeA-site-specific control), and 3 weeks later tested for spontaneous alloparental behavior and partner preference. Enhancing ERα in the MeA altered/reduced male prosocial behavior. Only one-third of MeA-ERα males, compared with all control males, were alloparental. MeA-ERα males also displayed a significant preference for a novel female. This is a critical finding because the manipulations of neuropeptides, oxytocin and vasopressin, can inhibit the formation of a partner preference, but do not lead to the formation of a preference for a novel female. The results support the hypothesis that low levels of ERα are necessary for high levels of male prosocial behavior, and provide the first direct evidence that site-specific ERα expression plays a critical role in the expression of male prosocial behavior. Copyright © 2008 Society for Neuroscience.