The magnocellular medial preoptic nucleus I. Sources of afferent input.

The magnocellular medial preoptic nucleus plays a crucial role in the regulation of male sexual behavior in Syrian hamsters. Histological and behavioral studies suggest that the magnocellular medial preoptic nucleus regulates male mating behavior by integrating chemosensory and hormonal signals. The present study is the first to systematically identify the afferent connections of the magnocellular medial preoptic nucleus by tracing the uptake of cholera toxin B from deposits in the magnocellular medial preoptic nucleus of adult male Syrian hamsters. Our findings indicate that the magnocellular medial preoptic nucleus receives 1) chemosensory input from areas in the main and accessory olfactory pathways including the posterior medial bed nucleus of the stria terminalis, anterior medial, anterior cortical and posterior cortical nuclei of the amygdala; 2) input from steroid responsive structures such as the posterior medial nucleus of the amygdala, bed nucleus of the stria terminalis, lateral septum, anteroventral periventricular nucleus, medial preoptic nucleus, ventromedial nucleus of the hypothalamus and arcuate nucleus; 3) input from structures in the brainstem such as the subparafascicular thalamic nucleus, peripeduncular nucleus and the premamillary nucleus in the hypothalamus that carry sensory information from the genitalia. The major afferent input to the magnocellular medial preoptic nucleus was confirmed by injecting anterograde tracer biotinylated dextran amine into the anterior medical nucleus of the amygdala, the posterodorsal part of the medial nucleus of the amygdala, the posteromedial part of the bed nucleus of the stria terminalis and the posterointermediate part of the bed nucleus of the stria terminalis. Our results support the hypothesis that the magnocellular medial preoptic nucleus is part of the chemosensory pathway that receives chemosensory and hormonal input to regulate mating behavior and suggest that the magnocellular medial preoptic nucleus may utilize information from the genitalia to regulate male mating behavior.