Ultrastructural analysis of the noradrenergic innervation of rat supraoptic nucleus

The noradrenergic innervation of the rat supraoptic nucleus (SON) was examined by high resolution radioautography after animals had been intracerebrally injected with [3H]noradrenaline (NA). In the medial portion of the SON, noradrenergic varicosities were scattered throughout this nucleus, but were preferentially concentrated in its ventral subdivision. 25.5% of these NA varicosities displayed typical synaptic contacts, with either the somatic or proximal dendritic portions of neurosecretory neurons (9.2%) or with small dendritic processes of such neurons (16.3%). The possibility is discussed that at least some of the dendritic NA synapses detected in the ventral subdivision of the SON, which preferentially contains vasopressinergic perikarya, may affect the neurosecretory neurons located in the dorsal part of this nucleus, which preferentially contains oxytocinergic perikarya.