κ-opioid receptor as a key mediator in the regulation of appetitive 50-kHz ultrasonic vocalizations.

Rationale Acute administration of high doses of morphine reduced 50-kHz ultrasonic vocalizations (USVs). Although morphine meets the classical criteria for inducing 50-kHz USVs (it causes place preference and induces dopamine release in nucleus accumbens), it also inhibits appetitive vocalizations.