Evidence that endogenous corticotropin-releasing factor suppresses behavioral responses of guinea pig pups to brief isolation in novel surroundings.

Guinea pig pups were injected subcutaneously with a corticotropin-releasing factor antagonist (CRF12-41) or saline vehicle and then placed into a novel cage for 30 or 60 min. Isolated 20- to 26-day-old pups vocalized more and exhibited more locomotor activity when given 15 to 150 micrograms of CRF12-41 than when given saline. The presence of the mother in the test cage prevented the antagonist from affecting behavior. The influence of the antagonist during isolation was not limited to guinea pigs near weaning age: CRF12-41 increased levels of vocalizing in isolated, 4- to 6-day-old pups, though no changes were seen in locomotor activity. Results support the hypothesis that endogenous corticotropin-releasing factor, perhaps acting at a peripheral binding site, suppresses the active behavioral response characteristic of pups during the early phase of isolation in novel surroundings.