MEDULLARY C-FOS ACTIVATION IN RATS AFTER INGESTION OF A SATIATING MEAL

The distribution and chemical phenotypes of hindbrain neurons that are activated in rats after food ingestion were examined. Rats were anest hetized and perfused with fixative 30 min after the end of l-h meals o f an unrestricted or rationed amount of food, or after no meal. Brain sections were processed for localization of the immediate-early gene p roduct c-Fos, a marker of stimulus-induced neural activation. Hindbrai n c-Fos expression was low in rats that ate a rationed meal or no meal . Conversely, c-Fos was prominent in the medial nucleus of the solitar y tract (NST) and area postrema in rats that ate to satiety. There was a significant positive correlation between postmortem weight of gastr ic contents and the proportion of NST catecholaminergic neurons expres sing c-Fos. Cells in the ventrolateral medulla (VLM) were not activate d in rats after food ingestion, in contrast with previous findings tha t stimulation of gastric vagal afferents with anorexigenic doses of ch olecystokinin activates c-Fos expression in both NST and VLM catechola minergic cells. These findings indicate that anatomically distinct sub sets of hindbrain catecholaminergic neurons are activated in rats afte r food ingestion and that activation of these cells is quantitatively related to the magnitude of feeding-induced gastric distension.