CHOLECYSTOKININ ACTIVATES CATECHOLAMINERGIC NEURONS IN THE CAUDAL MEDULLA THAT INNERVATE THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS INRATS

Stimulation of gastric vagal afferents by systemic administration of c holecystokinin octapeptide (CCK) inhibits gastric motility, reduces fo od intake, and stimulates pituitary secretion of oxytocin and adrenoco rticotropic hormone in rats. To characterize further the central neura l circuits responsible for these effects, the present study used tripl e-labeling immunocytochemical methods to determine whether or not exog enous CCK activates cFos expression in catecholaminergic neurons in th e caudal medulla that project to the paraventricular nucleus of the hy pothalamus (PVN). To identify these neurons, the retrograde tracer flu orogold (FG) was iontophoresed into the PVN of anesthetized rats under stereotaxic guidance. After 2 weeks, rats were injected with CCK (100 mu g/kg, i.p.) and then anesthetized and killed 1 hour later by perfu sion fixation. Medullary sections were processed for triple immunocyto chemical localization of cFos, retrogradely transported FG, and tyrosi ne hydroxylase (TH). In rats with FG injections centered in the PVN (n = 10), approximately 70% of the FG-labeled neurons in the caudal nucl eus of the solitary tract (NST) and ventrolateral medulla (VLM) expres sed cFos, Of these activated PVN-projecting neurons, approximately 78% in the NST and 89% in the VLM were catecholaminergic (TH positive). T hese results indicate that PVN-projecting catecholaminergic neurons wi thin the caudal medulla are activated by peripheral administration of CCK, further implicating these ascending catecholaminergic pathways in the neuroendocrine, physiological, and behavioral effects produced by gastric vagal stimulation. (C) 1995 Wiley-Liss, Inc.