ORGANIZATION OF INPUTS TO THE DORSOMEDIAL NUCLEUS OF THE HYPOTHALAMUS- A REEXAMINATION WITH FLUOROGOLD AND PHAL IN THE RAT

Possible inputs to the DMH were studied first using the fluorescent re trograde tracer Fluorogold, and identified cell groups were then injec ted with the anterograde tracer PHAL to examine the distribution of la beled axons in and around the DMH. From this work, we conclude that th e majority of inputs to the DMH arise in the hypothalamus, although th ere are a few significant projections from the telencephalon and brain stem. With few exceptions, each major nucleus and area of the hypothal amus provides inputs to the DMH. Telencephalic inputs arise mainly in the ventral subiculum, infralimbic area of the prefrontal cortex, late ral septal nucleus, and bed nuclei of the stria terminalis. The majori ty of brainstem inputs arise in the periaqueductal gray, parabrachial nucleus, and ventrolateral medulla. In addition, it now seems clear th at inputs to the DMH use only a few discrete pathways. Descending inpu ts course through a periventricular pathway through the hypothalamic p eriventricular zone, a medial pathway that follows the medial corticoh ypothalamic tract, and a lateral pathway traveling through medial part s of the medial forebrain bundle. Ascending inputs arrive through a mi dbrain periventricular pathway that travels adjacent to the cerebral a queduct in the periaqueductal gray, and through a brainstem lateral pa thway that travels through central and ventral midbrain tegmental fiel ds and enters the hypothalamus, and then the DMH from more lateral par ts of the medial forebrain bundle. The results are discussed in relati on to evidence for involvement of the DMH in ingestive behavior, and d iurnal and stress-induced corticosterone secretion. (C) 1998 Elsevier Science B.V. All rights reserved.