The neural organization of the chemosensory pathway that mediates male sexual behavior in Syrian hamsters

Previous research described sex differences in pheromonal stimulation of the chemosensory pathway that mediates copulatory behavior in Syrian hamsters. The goal of the studies described herein is to further characterize this pathway in males and females in an attempt to identify functional sex differences in this pathway.; The projections of the medial nucleus of the amygdala (Me) to the bed nucleus of the stria terminalis (BST) and the medial preoptic area (MPOA) in females do not underlie sex differences in behavior and physiology in response to pheromones. Within the MPOA, a small nuclear group—the magnocellular subdivision of the medial preoptic nucleus (MPN mag) has been shown to play a critical role in the regulation of male mating behavior in the hamster. There are extensive connections between the MPN mag and chemosensory and brainstem motor areas supporting the hypothesis that the MPN mag regulates male mating behavior by relaying pheromonal information to brainstem areas that control motor output.; The MPN mag maintains bi-directional connections with the periaquaductal gray (PAG), a brainstem area implicated in female reproduction, and that the connection is sexually dimorphic. A small proportion of pheromonally stimulated cells in the MPN mag projects to the PAG. These findings support the idea that the PAG may influence the function of the MPN mag. Other MPN mag targets in the brainstem that maintain uni-directional connections with the MPN mag express Fos following exposure to pheromones. These areas regulate copulation in other species and may play more critical roles in hamster mating behavior as well.; We have mapped the distribution of estrogen receptor alpha in adult male hamster from the forebrain to the brainstem to show that the MPN mag maintains bi-directional connections with most ERα-containing groups. These results indicate that the MPN mag may influence the function of a large steroid responsive neural network that regulates behavior.; Taken together, these results support the hypothesis that the MPN mag regulates male mating behavior by relaying chemosensory and hormonal signals to brainstem areas that control motor output.