Inhibition of ultrasonic distress vocalizations in rat pups by chlordiazepoxide and diazepam

Wistar rat pups emit ultrasonic distress cries when placed on a cold plate or when held by the tail. More sounds were induced by tail holding than by placing on the cold plate, but in both cases the number emitted was relatively constant from 7 to 13 days of age. Chlordiazepoxide and diazepam inhibited the sounds, and their activity was only associated with sedation and muscle relaxation at higher doses. The muscle relaxant mephenesin had little effect. Prazosin induced sedation and hypothermia and inhibited sounds induced by tail holding more than those on the cold plate. Clonidine induced hypothermia and weak sedation and increased sound emission weakly for the tail holding response but markedly for responses on the plate. This separation of responses may result from potentiation of responses on the plate by drug‐induced hypothermia. Although sedative effects result in decreased ultrasounds, the benzodiazepines continue to reduce sounds at doses showing little or no sedation. It is suggested that the benzodiazepines may reduce the sound via their anxiolytic action.