ORGANIZATION OF PROJECTIONS FROM THE VENTROMEDIAL NUCLEUS OF THE HYPOTHALAMUS - A PHASEOLUS-VULGARIS-LEUKOAGGLUTININ STUDY IN THE RAT

The organization of projections from the four parts of the ventromedia l nucleus (VMH) and a ventrolaterally adjacent region tentatively iden tified as the tuberal nucleus (TU) have been analyzed with small injec tions of the anterograde axonal tracer Phaseolus vulgaris-leucoaggluti nin (PHA-L). Extrinsic and intranuclear projections of each part of th e VMH display clear quantitative differences, whereas the overall patt erns of outputs are qualitatively similar. Overall, the VMH establishe s massive intrahypothalamic terminal fields in other parts of the medi al zone, tending to avoid the periventricular and lateral zones. The v entrolateral VMH is more closely related to other parts of the hypotha lamus that also express gonadal steroid hormone receptors, including t he medial preoptic, tuberal, and ventral premamillary nuclei, whereas other parts of the VMH are more closely related to the anterior hypoth alamic and dorsal premammillary nuclei. All parts of the VMH project t o the zona incerta (including the A13 region) and parts of the midline thalamus, including the paraventricular and parataenial nuclei and nu cleus reuniens. The densest inputs to the septum are to the bed nuclei of the stria terminalis, where the ventrolateral and central VMH inne rvate the anteroventral and anterodorsal areas and transverse and inte rfascicular nuclei, whereas the anterior and dorsomedial VMH innervate the latter two. The central, lateral, and medial amygdalar nuclei rec eive substantial inputs from various parts of the VMH. Other regions o f the telencephalon, including the nucleus accumbens and the piriform- amygdaloid, infralimbic, prelimbic, anterior cingulate, agranular insu lar, piriform, perirhinal, entorhinal, and postpiriform transition are as, also receive sparse inputs. All parts of the VMH send a massive, t opographically organized projection to the periaqueductal gray. Other brainstem terminal fields include the superior colliculus, peripeduncu lar area, locus coeruleus, Barrington's nucleus, parabrachial nucleus, nucleus of the solitary tract, and the mesencephalic, pontine, gigant ocellular, paragigantocellular, and parvicellular reticular nuclei. Th e projections of the TU are similar to, and a subset of, those from th e VMH and are thus not nearly as widespread as those from adjacent par ts of the lateral hypothalamic area. Because of these similarities, th e TU may eventually come to be viewed most appropriately as the latera l component of the VMH itself. The functional implications of the pres ent findings are discussed in view of evidence that the VMH plays a ro le in the expression of ingestive, affective, and copulatory behaviors . (C) 1994 Wiley-Liss, Inc.