CORTICOTROPIN-RELEASING FACTOR MODULATION OF THE ULTRASONIC VOCALIZATION RATE OF ISOLATED RAT PUPS

The effect of corticotropin-releasing factor (CRF) on ultrasonic vocal izations (USVs) and other behaviors of isolated rat pups was examined at 5/6-, 9/10-, and 13/14-days. The hypothesis tested was that central CRF affects USV rate biphasically: as endogenous CRF increases from l ow basal levels it initiates USV production, but at higher levels CRF diminishes USV production. As predicted, the largest doses of CRF (0.1 and 1 mu g) and of its antagonist alpha-helical CRF(9-41) (aH-CRF; 20 mu g) administered intracerebroventricularly (ICV) reduced USV rate c ompared to saline treatment during a 2-min isolation at ambient temper ature in pups of all ages. Other behaviors were either unaffected or i ncreased by drug treatment. Effects were not attributable to sedation or to a change in core temperature. Peripheral administration of 1 mu g CRF or 20 mu g aH-CRF had no effect. When isolation occurred in a he ated chamber containing soiled bedding from the home cage to minimize baseline USV rate, ICV-CRF (0.001, 0.01, 0.1, or 1 mu g) did not enhan ce the rate. The quieting ability of aH-CRF is evidence that central e ndogenous CRF enhances the rate of ongoing USVs during brief isolation ; the quieting ability of CRF suggests that this peptide may also be r esponsible for the reduction in USV rate that normally occurs during m ore protracted isolation. However, CRF alone is not sufficient to indu ce vocalizing in quiet pups.