Ultrasonic cries from infant rats stimulate prolactin release in lactating mothers

Lactating female rats, separated from their litters for 6 hr, showed a dramatic elevation in plasma prolactin following a 15-min playback of ultrasonic vocalizations recorded from 7-day-old pups. Virgin females exhibited a smaller but still significant prolactin response to recorded pup calls. Control recordings of either background noise or adult ultrasonic vocalizations (22–26 kHz) had no effect on prolactin secretion even in lactating females. These results demonstrate that infant vocalizations can act as a stimulus for prolactin release and suggest that such communications may play a role in the maintenance of normal lactation.