Enzyme-histochemical studies on the nonsecretory neurons of the rat supraoptic nucleus with the application of karyometry and electronmicroscopy

An electrophysiological analysis of the hippocampal projections to the neurosecretory cells of the supraoptic nucleus of the hypothalamus and the neurons of the perinuclear zone of rats

Impulse activity of antidromically identified neurosecretory cells, orthodromically activated neurons, and neurons not responding to this stimulation was recorded in the supraoptic area of the hypothalamus under conditions of the stimulation of the hypophyseal stalk. The reactions of all groups of cells to the stimulation of the ventral hippocampus were investigated; the number of responding cells came to 14, 59, and 46%, respectively. Short-latency excitatory reactions predominated substantially. It is conjectured that the influences of the hippocampus are most significant for the neurons of the perinuclear zone as compared with the neurosecretory cells of the supraoptic nucleus. Particular aspects of the morphofunctional organization of the supraoptic area are discussed, taking into account both the convergence of afferent inputs from the neurosecretory cells and the hippocampus on the orthodromically activated neurons and the features of the organization of the hippocampal projections to various groups of cells of the perinuclear zone of the supraoptic nucleus.

4-aminobutyrate: 2-oxoglutarate transaminase-containing neurons in the perinuclear zone of the rat supraoptic nucleus

A pharmaco-histochemical method for demonstrating the enzyme 4-aminobutyrate: 2-oxoglutarate transaminase was applied to the sections of the rat supraoptic nucleus region. The reactions of GABAergic interneurons and their relationship to neurosecretory neurons were studied. Medium-sized neurons heavily stained for transaminase were detected in the perinuclear zone just dorsal to the supraoptic nucleus. Neurons within the supraoptic nucleus were not stained. However, the perikarya of some neurosecretory neurons in the dorsal region of the supraoptic nucleus, as well as in discrete groups scattered throughout the nucleus; were surrounded by the granular reaction products. The results strongly suggest that these strongly positive neurons in the perinuclear zone send axons to the supraoptic nucleus, where they richly divide into many branches, which synapse on the perikarya of some vasopressin and oxytocin cells.