EVIDENCE FOR THE COLOCALIZATION OF ESTROGEN RECEPTOR-BETA MESSENGER-RNA AND ESTROGEN RECEPTOR-ALPHA IMMUNOREACTIVITY IN NEURONS OF THE RAT FOREBRAIN

Estrogen receptor beta (ER beta) mRNA is expressed in several rat brai n regions where ER alpha is abundant. In vitro studies have shown that ER alpha and ER beta can heterodimerize and that the activity of this complex may be different than an ER alpha or ER beta homodimer comple x. The purpose of the present study was to ascertain if ER alpha and E R beta are co-expressed by certain neuronal populations using a double label in situ hybridization/immunocytochemistry method. The results r evealed that neurons in the bed nucleus of the stria terminalis, media l amygdala and preoptic area contain both ERs, with the vast majority of the neurons being double labeled. In other brain regions including the arcuate nucleus, cortical amygdaloid nuclei and ventromedial nucle us, only a few double-labeled cells were detected, while neurons in th e paraventricular nucleus, supraoptic nucleus, and cerebral cortex exp ressed only ER beta mRNA. The results of these double label experiment s provide the first evidence that ER alpha and ER beta coexist in neur ons under in vivo conditions and suggest that estrogens may differenti ally modulate the activity of certain neuronal populations depending o n whether the cells expresses ER alpha, ER beta or both ERs.