The projections of the dorsomedial hypothalamic nucleus in the rat.

The dorsomedial hypothalamic nucleus (DMH) output pathways are revealed by using autoradiographic tracing of tritium labeled Leucine and by the recently introduced Phaseolus vulgaris leuco-agglutinin immunocytochemical method. Terminal labeling appears in the dorsal motor nucleus of the vagus, nucleus ambiguus and in the parvocellular reticular formation at the lower medullary level. Mesencephalic labeling is found in the periaqueductal gray at the level of the oculomotor nucleus. In the hypothalamus labeled terminal boutons are identified in the lateral and ventromedial hypothalamic nuclei but also in the parvocellular paraventricular nucleus. Furthermore, the circumventricular organs are found to receive a dense DMH input, particularly the organum vasculosum of the lamina terminalis and the subfornical organ. These findings are discussed in relation to the dorsomedial nucleus involvement in the control of feeding and pancreatic hormone release. It appears that the DMH participates in this control via descending pathways to the preganglionic pancreas innervating neurons but also via a neuroendocrine route. The latter connection is indicated by terminal labeling in the parvocellular paraventricular nucleus in the area that contains the corticotropin-releasing factor positive cells.