The hypothalamus of the human adult: chiasmatic region.

The human hypothalamus can be divided into a chiasmatic region, a tuberal region, and a mamillary region. The chiasmatic region comprises the magnocellular neurosecretory nuclei, several nuclei that are mainly formed of small nerve cells, and an ill-defined nerve cell assembly referred to as the chiasmatic gray. Small to medium-sized bipolar nerve cells predominate in the chiasmatic gray. With the use of Nissl preparations counterstained for demonstration of lipofuscin pigment, four types of neurons have been distinguished. Type I cells contain coarse and intensely stained lipofuscin granules. Type II cells are characterized by dense accumulations of small granules. Type III neurons harbour only a fine scattering of dust-like granules while type IV neurons are devoid of pigment. Pigmentoarchitectonic analysis of the chiasmatic region reveals the presence of eight nuclei embedded in or partially surrounded by the chiasmatic gray. The intermediate nucleus is a small compact accumulation of non-pigmented nerve cells located at the level of the optic chiasm half way between the paraventricular nucleus and the supraoptic nucleus. The periventricular nucleus and the uncinate nucleus are mainly formed of small pigment-laden type I and type II cells and appear as an anterior, respectively lateral extension of the paraventricular nucleus. Besides non-specific small cells, three neuronal types can be distinguished in the paraventricular nucleus on account of characteristic differences in their pigmentation. The supraoptic nucleus is formed of only two types of nerve cells. The cuneiform nucleus extends from the supraoptic nucleus to the ependymal lining of the third ventricle separating the suprachiasmatic nucleus from the retrochiasmatic nucleus. The suprachiasmatic nucleus contains the smallest neurons of the region. Cells of this nucleus are devoid of lipofuscin pigment. The retrochiasmatic nucleus is formed of a heterogeneous population of small and unusually large nerve cells. Numerous melanin-containing nerve cells and accumulations of nerve cells belonging to the lateral tuberal nucleus can be encountered within the boundaries of this nucleus as well. The technique and the data presented provide a basis for investigations of the aged and the diseased human brain.