Dorsal raphe nucleus efferents: Termination in peptidergic fields

Abstract

This study was performed to identify the efferents of the dorsal raphe nucleus (DRN), particularly in regard to nociception. Phaseolus vulgaris leucoagglutinin (PHA-L) was microiontophoresed into the DRN and visualized immunocytochemically; PHA-L-immunoreactive (-IR) fibers and terminals were identified in the forebrain, hypothalamus, midline and intralaminar thalamus, habenula, periaqueductal gray, locus coeruleus, parabrachial nucleus, medullary raphe and reticular nuclei, and nucleus tractus solitarius. Dual immunocytochemistry was used to identify corticotropin-releasing factor, neurotensin, and enkephalin neurons in DRN terminal fields, in some cases in close proximity to PHA-L-IR terminals. Terminal fields were identified in regions that influence nociception, and the neuroactive substances identified in these terminal fields may play modulatory roles in nociception.