Morphological study of noradrenaline innervation in the caudal raphe nuclei with special reference to fine structure.

Previous histofluorescence studies have demonstrated that the caudal raphe nuclei (CRa) of the rat, particularly the ventral portion (VCRa), contains a very high density of noradrenaline (NA) terminals and in the present study we attempted to elucidate the origins and free structure of the NA terminals in this region. The majority of NA terminals found in the VCRa originated from A1 and A3 NA neurons and disclosed that a small number of very strongly fluorescent fibers located along the blood vessels arise from the superior cervical ganglion (SGC). Electron microscopic analysis after potassium permanganate fixation demonstrated that the NA terminals originated from A1 and A3 NA neurons are connected with neuronal elements, while NA fibers from the SGC were identified among the vascular elements. Axodendritic contacts were found to be predominant among the synapselike contacts of NA terminals in this area.