EXOGENOUS CHOLECYSTOKININ ACTIVATES CFOS EXPRESSION IN MEDULLARY BUT NOT HYPOTHALAMIC NEURONS IN NEONATAL RATS

The central distribution of neurons activated to express cFos immunore activity in response to peripheral administration of cholecystokinin o ctapeptide (CCK) was examined in 2-day-old rats. Similar to previous r esults in adult rats, neurons in specific subregions of the area postr ema and nucleus of the solitary tract (NST) expressed cFos after CCK t reatment. However, in marked contrast to results in adult rats, CCK tr eatment in neonates did not stimulate cFos expression in hypothalamic neurons or in other forebrain areas, and did not increase plasma oxyto cin levels. These results suggest that vagal sensory activation of int rinsic brainstem circuits may be sufficient for the known inhibitory e ffects of exogenous CCK on gastric motility and feeding in neonatal ra ts. The prominent forebrain activation produced by CCK administration in adult rats likely reflects later maturation of direct and relayed a scending neural projections from the NST.