EFFERENT PROJECTIONS OF THE SUPRACHIASMATIC NUCLEUS IN THE GOLDEN-HAMSTER (MESOCRICETUS-AURATUS)

The efferent projections of the suprachiasmatic nucleus (SCN) in the g olden hamster have been examined by using the anterograde tracer Phase olus vulgaris leucoagglutinin (Pha-L). SCN projections were further lo calized through a combination of restricted SCN-lesions and immunocyto chemistry for three well-known peptidergic transmitters contained in S CN neurons, viz. vasopressin (VP), vasoactive intestinal peptide (VIP) , and gastrin-releasing peptide (GRP). Thus, major terminal fields of SCN-derived VP were detected in the medial preoptic nucleus, the anter ior part of the paraventricular nucleus of the thalamus (PVA), the med ial parvicellular part of the paraventricular nucleus of the hypothala mus (PVN), and the medial part of the dorsomedial nucleus of the hypot halamus (DMH). VIP-containing projections from the SCN were discovered in the PVA, anterior and dorsal parvicellular divisions of the PVN, s ubparaventricular area, and medial DMH. Efferent fibers from the SCN c ontaining GRP were restricted to the subparaventricular area, medial D MH, and supraoptic nucleus. In addition, Pha-L tracing indicated the e xistence of SCN projections which could not be ascribed to one of the presently investigated peptides. Furthermore, a pronounced innervation of the contralateral SCN was observed, of which the neurotransmitter remains to be established. The results of the present study indicate t hat the different neuronal populations in the SCN, as characterized by their transmitter content, also show a clear diversity in their prefe rential target areas.