TYROSINE-HYDROXYLASE NEURONS IN THE MALE HAMSTER CHEMOSENSORY PATHWAYCONTAIN ANDROGEN RECEPTORS AND ARE INFLUENCED BY GONADAL-HORMONES

Chemosensory and hormonal signals, both of which are essential for mat ing in the male Syrian hamster, are relayed through a distinct forebra in circuit. Immunocytochemistry for tyrosine hydroxylase, a catecholam ine biosynthetic enzyme, previously revealed immunoreactive neurons in the anterior and posterior medial amygdaloid nucleus, one of the nucl ei within this pathway. In addition, dopamine-immunoreactive neurons w ere located in the posterior, but not the anterior, medial amygdala. I n the present study, tyrosine hydroxylase-immunostained neurons were a lso observed in other areas of the chemosensory pathway, including the posteromedial bed nucleus of the stria terminalis and the posterior, lateral part of the medial preoptic area, while dopamine immunostainin g was only seen in the posteromedial bed nucleus of the stria terminal is. The colocalization of tyrosine hydroxylase and androgen receptors was examined in these four tyrosine hydroxylase cell groups by a doubl e immunoperoxidase technique. The percentage of tyrosine hydroxylase-i mmunolabeled neurons that were also androgen receptor-immunoreactive w as highest in the posterior medial amygdaloid nucleus (74%) and the be d nucleus of the stria terminalis (79%). Fewer tyrosine hydroxylase-im munostained neurons in the anterior medial amygdala (33%) and the medi al preoptic area (4%) contained androgen receptors. Surprisingly, cast ration resulted in a significant decrease in the number of tyrosine hy droxylase-immunoreactive neurons only in the anterior medial amygdaloi d nucleus, and this effect was transient. Six weeks after castration, the anterior medial amygdala contained 61% fewer tyrosine hydroxylase- immunolabeled neurons, but 12 weeks after gonadectomy, immunostaining returned to intact values. The number of immunostained neurons in test osterone-replaced, castrated hamsters was not significantly different from that of intact or castrated animals at any time. The results of t his study indicate that a substantial number of tyrosine hydroxylase-i mmunostained neurons in the chemosensory pathway are influenced by and rogens; the majority of these neurons in the posterior medial amygdala and the posteromedial bed nucleus of the stria terminalis produce and rogen receptors, and tyrosine hydroxylase immunoreactivity is altered by castration in the anterior medial amygdala.