The sites of origin of serotoninergic afferent fibers in the trigeminal motor, facial, and hypoglossal nuclei in the rat.

The sites of origin of serotoninergic afferents in the trigeminal motor (Vm), facial (VII), and hypoglossal nuclei (XII) were studied in the rat by fluorescent retrograde labeling with Fluoro-Gold, in combination with immunofluorescence histochemistry for serotonin (5-HT). The results indicated: (1) The nucleus raphe magnus, nucleus raphe pallidus, and nucleus raphe obscurus contained 5-HT neurons projecting to the Vm, VII or XII. (2) The nucleus raphe dorsalis sends 5-HT fibres to the Vm and VII, but not to the XII. (3) The gigantocellular reticular nucleus pars alpha contained 5-HT neurons projecting to the VII.