DISTRIBUTION OF BOMBESIN-LIKE IMMUNOREACTIVITY IN THE NUCLEUS OF THE SOLITARY TRACT AND DORSAL MOTOR NUCLEUS OF THE RAT AND HUMAN - COLOCALIZATION WITH TYROSINE-HYDROXYLASE

Bombesin is a peptide neurotransmitter/neuromodulator with important a utonomic and behavioral effects that are mediated, at least in part, b y bombesin-containing neurons and nerve terminals in the nucleus of th e solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV) . The distribution of bombesin-like immunoreactive nerve terminals/fib ers and cell bodies in relation to a viscerotopically relevant subnucl ear map of this region was studied by using an immunoperoxidase techni que. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gela tinous, central, and rostral commissural subnuclei and the periventric ular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissu ral and dorsal subnuclei had light bombesin fiber/terminal staining, a s did the intermediate, interstitial, ventral, and ventrolateral subnu clei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal c ommissural. intermediate, interstitial, ventral, and ventrolateral sub nuclei. Bombesin-like immunoreactive neurons were found in numerous ot her areas of the brain, including the ventrolateral medulla, the parab rachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreact ive neurons were labeled in a number of subnuclei, with clusters of ne urons labeled in the dorsal and ventrolateral subnuclei. Double immuno fluorescence studies in rat demonstrated that bombesin colocalizes wit h tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other l ocation in the brain. In conclusion, the distribution of bombesin in t he NTS adheres to a viscerotopically relevant map. This is the anatomi cal substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic si milarities between human and rat suggest that bombesin has similar fun ctions in the visceral neuraxis of these two species. Bombesin coexist s with catecholamines in neurons in the dorsal subnucleus, which likel y mediate, in part, the cardiovascular effects of bombesin. (C) 1996 W iley-Liss, Inc.