Gepirone and 1-(2-pyrimidinyl)-piperazine-induced reduction of aversively evoked ultrasonic vocalisation in the rat.

Ultrasonic (22 kHz) vocalisation in response to a mildly aversive foot shock was measured in the dark compartment of a light-dark box both immediately and 24 h after the shock. Gepirone (1 and 5 mg/kg, IP) produced a reduction in the duration of vocalisation at both times. Although a metabolic inhibitor, proadifen (40 mg/kg) did not reduce this effect of gepirone, the gepirone hepatic metabolite, 1-(2-pyrimidinyl)-piperazine (1-PP, 1 mg/kg), was also active in the test. Performance of a 24 h step-through passive avoidance task was impaired by gepirone only at a dose, 5 mg/kg, which also reduced spontaneous locomotor and rearing activity in the apparatus. It would appear that mild foot shock-evoked ultrasonic vocalisation may provide a more sensitive indicator of the effect of gepirone and related drugs on the affective response of rats to aversive stimulation.