The organization of the ventromedial hypothalamic nucleus.

Abstract

Summary (1) The ventromedial hypothalamic (HVM) nucleus has been studied in mature mouse and rat brains with the rapid Golgi method. (2) HVM dendrites are long and generally unramified and bear a number of spinous processes. They extend beyond the nucleus into adjacent hypothalamic regions. (3) Completely encircling the nucleus is a capsule formed partly by HVM afferents. Buried in this capsule are neurons whose dendrites curve along the periphery of the nucleus to form a dendritic grid. (4) Three general axonal patterns can be recognized. One type is characterized by having numerous collaterals that ramify extensively in HVM. Another variety has few collaterals. The third variety has no collaterals. (5) The numerous intranuclear collaterals with their boutons en passant synaptically interconnect individual HVM units. (6) Most of the axons are beaded. None of the axonal systems studied has been found to be confined to HVM. They project to (1) lateral hypothalamus, especially ventral to the plane of the fornix, (2) anterior hypothalamus, (3) towards the zona incerta, perhaps into dorsolateral hypothalamus, (4) caudally, with the medial forebrain bundle, and (5) into the periventricular fiber system.