Endogenous cholecystokinin reduces vocalization in isolated 10-day-old rats.

Devazepide, the cholecystokinin (CCK) A receptor blocker, markedly and specifically affected the behavior of 10-day-old rats isolated from their mother and siblings. Whereas intraoral infusions of milk or fat, which cause CCK release, calmed infants, that is, reduced levels of ultrasonic vocalization, devazepide fully blocked this reduction. Devazepide did not affect calming caused by sucrose infusions, which do not release CCK. Moreover, devazepide did not reduce the elevated pain limen caused by milk or fat infusions. These data parallel earlier findings obtained with administration of exogenous CCK and implicate endogenous CCK in the maintenance of infant steady state and calm. The possibility that CCK contributes to the normal development of mother-infant affectional systems is discussed.