[Morphological and immunohistochemical investigation of serotonergic neurons in the dorsal raphe nucleus of Wistar rats].

The serotonergic neurons of the nucleus raphe dorsalis (NRD) of the adult male Wistar rat were characterized morphologically using Nissl and Golgi-Kopsch techniques, fluorescence histochemistry as well as a peroxidase-antiperoxidase (PAP) immunocytochemical method employing specific antibodies to serotonin. 1. The numerous serotonin-positive neurons within (and around) the NRD exhibit--in agreement with data of the literature--characteristic heterogeneous distribution patterns both in rostro-caudal direction and also dorsoventral particularly in the mesencephalic part, the zone of the largest extension of the nucleus. Several groups with high cell concentration could be divided. The neurons differ in their immunoreactivity. 2. Based on different criteria, especially the number and arrangement of dendrites as well as the cell shape, three types of serotonergic neurons could be identified: multipolar, fusiform (bipolar) and small ovoid ones. A parallel analysis in Golgi-stained material offers the possibility for more detailed studies and further characterization. 3. With respect to functional interpretations some morphological peculiarities seem to be remarkable, e.g. the close relation between several neurons, the tight dendritic contact to many blood vessels or the formation of a dense serotonin-positive fiber plexus along the floor of the aqueductus and fourth ventricle. Studies, following stereotactic application of the neurotoxin 5.7-dihydroxytryptamine into the NRD, show furthermore that the majority of serotonergic neurons--independently of the cell type--reveals signs of cell degeneration. The findings presented confirm previous studies and should provide also further insights into the morphology of the 5-HT neurons of rat NRD as well as for the explanation of functional aspects.