MATING ACTIVATES ANDROGEN RECEPTOR-CONTAINING NEURONS IN CHEMOSENSORY PATHWAYS OF THE MALE SYRIAN-HAMSTER BRAIN

Fos-immunoreactivity is induced during mating in the male Syrian hamster in limbic areas that relay chemosensory information and contain receptors for gonadal steroid hormones. The induction of Fos is an index of neuronal activation. After mating, c-fos expression is greatest in subnuclei of the medial amygdaloid nucleus (Me), bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). The present study determined if individual neurons in these activated subnuclei contain androgen receptors. We aim to understand how essential chemosensory and hormonal signals are integrated to control copulation Adult male hamsters (n = 6) were allowed to mate with a sexually receptive female for 30 min. They were perfused 1 h later with 4% paraformaldehyde and 40 mum frozen sections were processed for immunocytochemistry using antisera against Fos (Cambridge Research Biochemicals) and the androgen receptor (G.S. Prins). The brains of three non-mated males were also processed for Fos immunocytochemistry. Mating significantly increased the number of Fos-immunoreactive neurons within subnuclei of Me, BNST, and MPOA relative to non-mated males (P < 0.05). These nuclei contained abundant androgen receptors. In the corticomedial amygdala, 20-40% of Fos-immunoreactive neurons in mated hamsters expressed androgen receptors. Although few androgen receptors are found in the anteromedial and postero-intermediate subdivisions of the BNST, these areas exhibited 26% and 47% co-localization, respectively. In posteromedial BNST, which contains large numbers of steroid receptor-containing neurons, androgen receptors were identified in 48% of Fos-immunoreactive neurons. In the MPOA, 54% of Fos-immunoreactive neurons expressed the androgen receptor throughout the rostrocaudal extent of the medial preoptic nucleus (MPN). The largest percentage of co-localized Fos neurons (70%) was found in the magnocellular subdivision of MPN. These results provide the first direct evidence that androgen receptor, neurons are activated by mating behavior, suggesting that such neurons may be incorporated in the neural circuitry underlying copulation. Further, they show that mating selectively and differentially activates androgen receptor cells.