Cytological observations on the ventromedial hypothalamic nucleus.

Two sorts of neurons are recognized in Golgi impregnations of the rat ventromedial hypothalamic nucleus (HVM). The two cell types, category I and II neurons, are differentiated on the basis of their somatic, dendritic, and axonal characteristics. Category I neurons form most of the neuronal population and are located throughout HVM. The small number of category II neurons that have been studied occur in lateral HVM. Two varieties of neuronal profile, "common" and "uncommon cells", are seen in thin sections of HVM. The "uncommon cells", in comparison with the "common ones", appear to have a larger soma, a more electron-dense cytoplasmic matrix, an abundance of Nissl bodies, and a population of dense-cored vesicles (100--130 nm in diameter). Some of the somata and proximal dendrites of "common", but not "uncommon" cells, are wrapped in multiple layers of astrocytic processes. Although the correlation is tentative, it is argued that category I neurons correspond to "common cells" and category II, to "uncommon cells". One possible implication of this correspondence is discussed regarding neuronal alteration in response to change in the endocrinological environment of the brain.