[Sources of cortical, hypothalamic and spinal serotoninergic projections: topical organization in the dorsal Raphe...

Distribution of primuline, fast blue, fluoro-gold and nuclear yellow-labelled monoamine-containing cells in periventricular gray and dorsolateral tegmentum (including locus coeruleus) was studied in the rat after injection of these fluorochromes into the frontal cortex, hypothalamus and spinal cord. Combination of monoamine fluorescence method and retrograde cell-labelling was used. Two big groups of serotonin-positive cells projecting into the upper thoracic spinal segments were found in dorsomedial zone of the dorsal raphe. Part of these units also had divergent axon projections to the frontal cortex. Such cellular arrangement allows a supposition that analgetic effects of dorsal raphe stimulation can be partially based on the direct participation of this structure in the descending control at the spinal level. Neurones, sources of cortical projections are intermingled with the cells projecting to the hypothalamus but some topical differentiation can be distinguished. Neurotransmitter and neuroregulatory roles of separate cortical and hypothalamic projections of serotonin-containing neurons of the dorsal raphe cells is discussed.