Peptidergic neurons in the nucleus raphe magnus and the nucleus gigantocellularis: their distributions, interrelationships, and projections to the spinal cord.
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This chapter discusses the identification, distribution, and connectivity of several species of peptidergic neurons within the nucleus raphe magnus (NRM) and the nucleus gigantocellularis (NGC). The anatomical organization of the neurotransmitters in these two nuclei is described. The neurotransmitters are not homogeneously distributed throughout these two cell groups and are segregated into subpopulations. While the neurotransmitter identities of several of these inputs are known, including the catecholamines, enkephalin (ENK) and neurotensin, many inputs to these cell groups are not yet identified. Future work designed to unravel the anatomical complexities of these nuclei to understand the circuitry involved in the descending control of nociception must focus on a small number of the neurotransmitter elements within the NRM/ NGC region and must analyze all potential transmitter interactions in terms of their coded afferents and efferent projections, the intrinsic neurons and the receptor organization. Only then can these two critical links in the rostral medulla in the descending control of nociception is understood. 1988, Elsevier Science Publishers, B.V. All rights reserved.