Distribution of Neurons Innervating the Supraoptic Nucleus of the Rat with Special Reference to Neighbouring Relay Neurons Using HRP and Golgi Methods

Abstract

Detailed histochemical studies have been performed on the distribution of the nuclei innervating the supraoptic nucleus (SO) in the whole brain after horseradish peroxidase (HRP) injections through fine glass micropipettes (2-8μm tip diameter) into the SO of 39 Wistar rats. The chromatogenic reaction was carried out according to Mesulam's No.8 procedure (1976). In the 3 cases, where injected HRP was most exactly restricted to the SO, HRP-labeling was limited to some small neurons located just dorsal to the SO. The other successful HRP injections into the SO resulted in labeling rather few neurons which are sparsely distributed in various regions of the brain. The following conclusions were drawn from the analysis of these successful cases. The rapid Golgi method was used to check the morphology and possible functions of these small neurons revealed in the 3 cases.
Every nuclei of the subthalamus and posthypothalamus innervate the SO whereas probably very few neurons of the hypothalamic arcuate and ventromedial nuclei send axons to it. The afferent monoaminergic fibers arise largely from the B7 and B8, and to a lessor extent from the A6 and A10 cell groups. There is a high possibility that the mesencephalic central gray directly innervates the SO. The septum, diagonal band nucleus and amygdala send very few projections, whereas the olfactory tubercle and pyriform cortex may not. It remains unanswered whether the hippocampus projects to it or not. Small non-secretory neurons in and around the SO may be important relay neurons to large neurosecretory ones.