Response of ERα-IR and ERβ-IR cells in the forebrain of female rats to mating stimuli

Sexual behavior in female rats depends on the action of estradiol on estrogen receptors (ERs) found in particular brain regions. While hormonal regulation of female sexual behavior requires ERα, the possible functions of ERβ remain to be clarified. Mating stimulation has several behavioral and physiological consequences and induces Fos expression in many brain areas involved in the regulation of reproductive behavior and physiology. In addition, some cells in which mating induces Fos expression coexpress ERα. To determine whether cells in which Fos is induced by a particular mating stimulus coexpress ERα, ERβ, or both, we used a triple-label immunofluorescent technique to visualize ERα-, ERβ-, and mating-induced Fos-immunoreactivity (Fos-ir) in neurons in which mating stimulation reliably increases Fos expression. Ovariectomized, hormone-primed rats were either unmated, received 15 mounts, or received 15 intromissions. In the rostral medial preoptic area, Fos-ir was induced by mounts alone primarily in cells coexpressing ERα-ir, while Fos-ir was induced by intromissions mainly in cells coexpressing both ERα-ir and ERβ-ir (ERα/ERβ-ir). In the dorsal part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions in cells coexpressing ERα-ir and ERα/ERβ-ir. However, in the ventral part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions primarily in cells coexpressing only ERβ-ir. These data suggest that qualitatively different sexual stimuli may be integrated through distinct ER-containing circuits in the rostral medial preoptic area and posterodorsal medial amygdala. The diversity in coexpression of type of ER in cells in different brain areas after various mating stimuli suggests a role for both ERα and ERβ in the integration of hormonal information and information related to mating stimuli.