AFFERENT-PROJECTIONS TO THE RAT NUCLEI RAPHE MAGNUS, RAPHE PALLIDUS AND RETICULARIS GIGANTOCELLULARIS PARS-ALPHA DEMONSTRATED BY IONTOPHORETIC APPLICATION OF CHOLERATOXIN (SUBUNIT-B)

The aim of the present study was to identify the specific afferent pro jections to the rostral and caudal nucleus raphe magnus, the gigantoce llular reticular nucleus pars alpha and the rostral nucleus raphe pall idus. For this purpose, small iontophoretic injections of the sensitiv e retrograde tracer choleratoxin (subunit b) were made in each of thes e structures. In agreement with previous retrograde studies, after all injection sites, a substantial to large number of labeled neurons wer e observed in the dorsal hypothalamic area and dorsolateral and ventro lateral parts of the periaqueductal gray, and a small to moderate numb er were found in the lateral preoptic area, bed nucleus of the stria t erminalis, paraventricular hypothalamic nucleus, central nucleus of th e amygdala, lateral hypothalamic area, parafascicular area, parabrachi al nuclei, subcoeruleus area and parvocellular reticular nucleus. In a ddition, depending on the nucleus injected, we observed a variable num ber of retrogradely labeled cells in other regions. After injections i n the rostral nucleus raphe magnus, a large number of labeled cells we re seen in the prelimbic.