Gonadal steroids regulate behavioral responses to pheromones by actions on a subdivision of the medial preoptic nucleus.

Mating behavior in male hamsters is initiated by pheromones, detected by two chemosensory systems which converge on the medial nucleus of the amygdala and the bed nucleus of the stria terminalis. Neurons in these areas project to the medial preoptic nucleus. All three of these areas contain androgen receptors. Using Fos as a marker of stimulation we have found that pheromones stimulate neurons in all three areas in intact males but fail to stimulate the magnocellular division of the medial preoptic nucleus of castrates. As this area plays a critical role in the regulation of male mating behavior our results suggest that steroids regulate mating by maintaining the responsiveness of the magnocellular division of the medial preoptic nucleus to pheromones.