Repeated cocaine exposure induces sensitization of ultrasonic vocalization in rats.

Ultrasonic vocalization at 55kHz (55kHz-USVs) by rodents has been proposed to be a behavioral manifestation of affectively positive incentive motivation. To examine the extent to which 55kHz-USV emissions correlate with cocaine-induced locomotor activity, we measured cocaine-induced 55kHz-USVs and their relationship to cocaine-induced locomotor sensitization in rats. We demonstrate that similar to locomotor responses, 55kHz-USVs are also sensitized by exposure to cocaine. Furthermore, we show that the magnitude of cocaine-induced 55kHz-USV sensitization is positively correlated with that of locomotor sensitization. Moreover, we demonstrate that rats selectively bred for high rates of 55kHz-USVs exhibit higher levels of cocaine-induced 55kHz-USV sensitization than animals selectively bred for low levels of 55kHz USVs. These results suggest that the neural circuits underlying 55kHz-USV, which may directly reflect affective experience/motivation, can be sensitized by cocaine in a way that resembles locomotor sensitization.