HYPOXIA AND ELECTRICAL-STIMULATION OF THE CAROTID-SINUS NERVE INDUCE FOS-LIKE IMMUNOREACTIVITY WITHIN CATECHOLAMINERGIC AND SEROTONINERGIC NEURONS OF THE RAT BRAIN-STEM

A complete understanding of the neural mechanisms responsible for the chemoreceptor and baroreceptor reflexes requires precise knowledge of the locations and chemical phenotypes of higher-order neurons within t hese reflex pathways. In the present study, the protein product (Fos) of the c-fos protooncogene was used as a metabolic marker to trace cen tral neural pathways following activation of carotid sinus nerve affer ent fibers. In addition, immunohistochemical double-labeling technique s were used to define the chemical phenotypes of activated neurons. Bo th electrical stimulation of the carotid sinus nerve and physiological stimulation of the carotid bodies by hypoxia induced Fos-like immunor eactivity in catecholaminergic neurons containing tyrosine hydroxylase or phenylethanolamine-N-methyltransferase in the ventrolateral medull a oblongata and, to a lesser degree, in the dorsal vagal complex. Tyro sine hydroxylase/Fos colocalization was also observed in the locus coe ruleus and the Ag noradrenergic cell group in pens. Many serotoninergi c neurons in nucleus raphe pallidus, nucleus raphe magnus, and along t he ventral medullary surface contained Foe-like immunoreactivity. In p ens and midbrain, Fos-like immunoreactivity was observed in the latera l parabrachial and Kolliker-Fuse nuclei, the inferior colliculus, the cuneiform nucleus, and in the vicinity of the Edinger-Westphal nucleus , but no catecholaminergic or serotoninergic colocalization was observ ed in these regions, Although Fos-labeled cells were observed within a nd lateral to the dorsal raphe nucleus, few were catecholaminergic or serotoninergic. This study further defines a potential central neuroan atomical substrate for the chemoreceptor and/or baroreceptor reflexes. (C) 1994 Wiley-Liss, Inc.