Afferent connections of the caudal raphe pallidus nucleus in rats: a studyusing the fluorescent retrograde tracers fluorogold and true-blue

Afferent connections to the caudal region of the nucleus raphe pallidus (RP a) in rats were studied using fluorogold and true-blue as tracers. Due to i ts ability to produce limited injection sites, true-blue proved to be more appropriate than fluorogold for studying long distance connections in a nar row structure such as the RPa. Fluorescent, retrogradely-labeled perikarya were found in the preoptic area (median, medial and lateral nuclei), hypoth alamus (anterior. dorsal, lateral and posterior areas, and the peri- and pa raventricular nuclei), zona incerta, central gray (dorsal, ventral and vent ro-lateral), reticular formation of the brainstem, trigeminal spinal nuclei and in the spinal cord (laminae V-X at thoracic, lumbar and sacral levels) . This connection pattern suggests the involvement of the RPa in autonomic, somatic and endocrine functions.