Dopamine activates masculine sexual behavior independent of the estrogen receptor alpha

Estrogen receptor alpha (ER alpha) is believed to be a critical part of the regulatory processes involved in normal reproduction and sexual behavior. However, in this study we show the ER alpha is not required for display of masculine sexual behavior. Male and female, ER alpha knock-out (ER alpha KO ) and wild-type mice were gonadectomized and implanted with testosterone. S exual behavior and social preferences were tested after injection of the do pamine agonist, apomorphine (APO), or vehicle. All wild-type mice showed no rmal masculine behavior, including mounts and pelvic thrusts in females, an d ejaculation in males. In agreement with past reports, ER alpha KO mice, g iven vehicle, failed to show mating behavior. Yet, ER alpha KO males given APO showed masculine copulatory behavior and chemoinvestigatory behavior di rected at females. ER alpha KO females, treated with APO, mounted and thrus ted when tested with receptive females. HPLC revealed that wild-type and ER alpha KO mice had equivalent catecholamine content in brain regions associ ated with masculine sexual behavior. These data show that the ER alpha is n ot essential during development or adulthood for the expression of masculin e sexual behavior in mice. Moreover, dopamine can activate sexual behavior via a mechanism that either acts on an ER other than ER alpha or via an est rogen-independent pathway.