Peripherally administered CRH suppresses the vocalizations of isolated guinea pig pups

In Experiment 1, an SC injection of 14 micrograms CRH greatly suppressed the vocalizing of isolated guinea pig pups 1 h later and produced highly elevated plasma cortisol levels. In Experiment 2, SC injection of 18 international units of ACTH produced similar cortisol elevations, but had a negligible effect on vocalizations. In Experiment 3, the minimum effective dose of CRH for suppressing vocalizations was found to be about 7 micrograms. This dose also suppressed locomotor activity and produced cortisol elevations that were as great as those produced by the 14 micrograms dose. In Experiment 4, suppression of vocalizations by CRH was not reversed by 1 or 5 mg/kg body weight of naloxone. Rectal temperature was unaffected by CRH or naloxone. Thus, peripheral administration of CRH has a suppressive effect on the vocalizations of isolated guinea pig pups. The effect is accompanied by a reduction in locomotor activity and does not appear to be mediated by ACTH, cortisol, beta-endorphin, or an altered body temperature response to the isolation procedure. These results are consistent with the hypothesis that increased secretion of CRH contributes to the waning of the vocalizations of guinea pig pups during prolonged isolation.