NEURONAL PROJECTIONS FROM THE MESENCEPHALIC RAPHE NUCLEAR-COMPLEX TO THE SUPRACHIASMATIC NUCLEUS AND THE DEEP PINEAL-GLAND OF THE GOLDEN-HAMSTER (MESOCRICETUS-AURATUS)

Neuronal projections from the mesencephalic raphe system to the suprac hiasmatic nucleus and the pineal complex were mapped in this study of the golden hamster, by use of the anterograde tracer Phaseolus vulgari s-leucoagglutinin and the retrograde tracer cholera toxin subunit B. F rom the median raphe nucleus, a rostral projection ascended in the ven tral part of the mesencephalon to continue in the medial forebrain bun dle of the forebrain. Nerve fibres from this bundle innervated the ven tral and medial parts of the suprachiasmatic nucleus. At the level of the interpeduncular nucleus of the mesencephalon, fibres of the ventra l bundle bent dorsally to reach the epithalamic area and to continue i n the forebrain in a periventricular position. Some of these fibres in nervated the dorsal tip of the suprachiasmatic nucleus. The dorsal rap he nucleus was the origin of a nerve fibre bundle, located in the peri aqueductal gray of the mesencephalon, innervating the deep pineal glan d and pineal stalk. Injection of cholera toxin B into the suprachiasma tic nucleus labelled cells in the median raphe. Combination of the ret rograde tracing from the suprachiasmatic nucleus and serotonin transmi tter immunohistochemistry showed that some of the cholera toxin B-immu noreactive nerve cells also contained serotonin. Thus, this study of t he golden hamster shows a serotonergic projection from the median raph e nucleus to the suprachiasmatic nucleus and a projection from the dor sal raphe nucleus to the deep pineal gland supporting physiological in dications of an influence of serotonin on the photoreceptive circadian system of the brain. J. Comp. Neurol. 399:73-93, 1998. (C) 1998 Wiley -Liss, Inc.