A cholecystokinin receptor antagonist blocks milk-induced but not maternal-contact-induced decrease of ultrasonic vocalization in rat pups

The role of cholecystokinin (CCK) in reducing separation-induced ultrasonic vocalization (USV) was examined by peripheral administration of the selective CCK<SUBA> receptor antagonist devazepide to 10-11-day-old rats. Pups placed alone-for 2min emitted a mean of 55.1 USV/min. When placed on a paper towel wet with warm, sweet milk, USV rate decreased to 23.2/min for the following 8 min. Devazepide (150-600 μg/kg IP) prevented this USV reduction, but did not increase feeding. In contrast, USV reduction produced by contact with the anesthetized dam was not affected by devazepide. Similarly, the opiate antagonist naltrexone (0.5 and 1.0mg/kg) has been shown to block morphine-induced USV decrease in pups away from the dam, but was ineffective when USV reduction was induced by the presence of the dam (Blass et al., 1990; Carden and Hofer, 1990). The current findings suggest that CCK's role is specific, in that it mediates milk- but not daminduced quieting of USV. The results, however, are not incompatible with the possibility that CCK and opioids are part of multiple, redundant pathways that mediate the quieting of USV by the dam. (C) 2000 John Wiley and Sons, Inc.