DISTRIBUTION AND NEUROCHEMICAL PHENOTYPES OF CAUDAL MEDULLARY NEURONSACTIVATED TO EXPRESS CFOS FOLLOWING PERIPHERAL ADMINISTRATION OF CHOLECYSTOKININ

Immunocytochemical localization of the protein product of the proto-on cogene c-fos allows anatomical identification of physiologically activ ated neurons. The present study examined the subnuclear distribution o f cFos protein in the rat caudal medulla following peripheral administ ration of cholecystokinin octapeptide, which reduces feeding and gastr ic motility by a vagally mediated mechanism. To begin phenotypic chara cterization of neurons activated to express cFos following cholecystok inin treatment, double-labeling techniques were used to identify vagal motor neurons and neurons immunoreactive for tyrosine hydroxylase, ne uropeptide Y, and neurotensin. Activated cells were most prevalent in the subnucleus medialis of the nucleus of the solitary tract, less pre valent in the subnucleus commissuralis, and virtually absent in the su bnuclei centralis and gelatinosus. Many activated cells occupied the c audal area postrema; some of these were catecholaminergic. In contrast , activated cells were sparse within the medial rostral area postrema. Other activated cells occupied the dorso- and ventrolateral medulla a nd the midline raphe nuclei. Retrograde labeling of vagal motor neuron s confirmed that very few were activated. Those that were activated oc cupied the caudal dorsal motor nucleus. In the dorsomedial medulla, 51 % of catecholaminergic neurons and 39% of neurons positive for neurope ptide Y were activated, but no neurotensin-positive neurons were activ ated. In the ventrolateral medulla, 25% of catecholaminergic neurons a nd 27% of neuropeptide Y-positive neurons were activated. By character izing the subnuclear distribution and chemical phenotypes of neurons a ctivated by exogenous cholecystokinin, these data contribute to elucid ation of the neural circuits mediating the behavioral, physiological, and neuroendocrine effects produced by this peptide. (C) 1993 Wiley-Li ss, Inc.