ESTROGEN RECEPTOR-IMMUNOREACTIVE FOREBRAIN NEURONS PROJECT TO THE VENTROLATERAL HYPOTHALAMUS IN FEMALE GUINEA-PIGS

In rodents, the facilitation of sexual receptivity by estradiol and pr ogesterone is suspected to be mediated by a network of neurons contain ing estrogen and progestin receptors. In female guinea pigs, this netw ork would include estrogen receptor-immunoreactive (ER-ir) neurons loc ated within the rostro-ventral ventrolateral hypothalamus (r-vVLH). Th is hypothesis predicts that a proportion of the neurons projecting to the r-vVLH contains estrogen receptors. This prediction was tested thr ough retrograde tracing combined with immunocytochemistry for estrogen receptors. Retrogradely labelled neurons were particularly abundant w ithin the medial preoptic nucleus (MPN), bed nucleus of the stria term inalis (BST), anterior hypothalamus, amygdala, and lateral parabrachia l nucleus. As predicted by the hypothesis, retrogradely labelled neuro ns were mostly observed in estrogen receptor-rich areas. Retrogradely labelled neurons also containing estrogen receptor-immunoreactivity (E R-IR) were primarily found within the MPN, BST, and amygdala. However, a majority of retrogradely labelled neurons did not contain ER-IR. As the preoptic area and the r-vVLH are both responsive to estradiol in the facilitation of sexual receptivity by progesterone, these data are consistent with the hypothesis tested. However, our data also suggest that the network of neurons controlling sexual receptivity may includ e elements not directly sensitive to estradiol. Finally, the location of retrogradely labelled neurons is discussed with respect to the stim uli provided to the r-vVLH in the context of sexual receptivity facili tated by estradiol and progesterone. (C) 1993 Wiley-Liss, Inc.