MEAL-INDUCED C-FOS EXPRESSION IN BRAIN-STEM IS NOT DEPENDENT ON CHOLECYSTOKININ RELEASE

Sprague-Dawley rats injected with a ''physiological'' dose of cholecys tokinin octapeptide (CCK-8; 6 mug/kg ip) expressed c-fos immunoreactiv ity in the nucleus of the tractus solitarius (NTS) and the area postre ma (AP) of the brain stem. Injection of the CCK-A antagonist L-364,718 30 min before CCK-8 injection eliminated c-fos expression in these re gions. These findings support the hypothesis that CCK-8 induced c-fos expression is mediated by CCK-A receptors. We then tested whether a me al (Isocal) could activate c-fos, and, if so, whether this response co uld be eliminated by L-364,718. Ingestion of Isocal induced c-fos immu noreactivity in the NTS and AP. Meal-induced c-fos expression was not blocked by the CCK-A antagonist L-364,718. These findings demonstrate for the first time that a purely physiological nonnoxious stimulus, a meal, induces c-fos in the rat brain stem and indicate that feeding in duces c-fos expression by a pathway that is largely, if not entirely, independent of CCK release.