Rain Projections from the Medullary Dorsal Reticular Ucleus: an Anterograde and Retrograde Tracing Study N the Rat

bstract—In the last 15 years a role has been ascribed for the edullary dorsal reticular nucleus as a supraspinal pain modlating area. The medullary dorsal reticular nucleus is reciproally connected with the spinal dorsal horn, is populated mainly y nociceptive neurons and regulates spinal nociceptive proessing. Here we analyze the distribution of brain projections rom the medullary dorsal reticular nucleus using the iontohoretic administration of the anterograde tracer biotinylatedextran amine and the retrograde tracer cholera toxin subunit B. Fibers and terminal boutons labeled from the medullary doral reticular nucleus were located predominately in the braintem, although extending also to the forebrain. In the medulla blongata, anterograde labeling was observed in the orofacial otor nuclei, inferior olive, caudal ventrolateral medulla, rostral entromedial medulla, nucleus tractus solitarius and most of he reticular formation. Labeling at the pons-cerebellum level as present in the locus coeruleus, A5 and A7 noradrenergic ell groups, parabrachial and deep cerebellar nuclei, whereas in he mesencephalon it was located in the periaqueductal gray atter, deep mesencephalic, oculomotor and anterior pretectal uclei, and substantia nigra. In the diencephalon, fibers and erminal boutons were found mainly in the parafascicular, venromedial, and posterior thalamic nuclei and in the arcuate, ateral, posterior, periand paraventricular hypothalamic areas. elencephalic labeling was consistent but less intense and conentrated in the septal nuclei, globus pallidus and amygdala. The well-known role of the medullary dorsal reticular nuleus in nociception and its pattern of brain projections in rats uggests that the nucleus is possibly implicated in the moduation of: (i) the ascending nociceptive transmission involved in he motivational-affective dimension of pain; (ii) the endogeous supraspinal pain control system centered in the periaqueuctal gray matter–rostral ventromedial medulla–spinal cord ircuitry; (iii) the motor reactions associated with pain. © 2006 ublished by Elsevier Ltd on behalf of IBRO.