Ultrasonic Vocalizations in Rat Sexual Behavior

Abstract

Ultrasonic vocalizations are very conspicuous during rat mating activity. Two types of calls are produced by both sexes. The first, brief complex calls with the main frequency centered about 50 kHz, occur primarily in conjunction with solicitation and mounting activity. The second type of call is the long, 22 kHz whistle which is emitted mainly by the male during the postejaculatory refractory period, but also by both male and female at other times during the copulatory sequence. The occurrence of ultrasonic vocalizations is correlated with sexual motivation of rats. Males emit more 50 kHz calls before successful mating tests than before tests in which they fail to ejaculate. Furthermore, more vocalizations are emitted by the pair prior to intromissions than prior to mounts without intromission. Just before ejaculation there is a large increase in the rate of calling and, at times, transition by the male to calling at 22 kHz. This latter event may represent physiological dearousal by the male. Following ejaculation, the male characteristically emits 22 kHz vocalizations and exhibits a sleep-like EEG pattern. The function of the postejaculatory vocalization may be to enforce separation between the mating pair, while at the same lime maintaining contact between the partners. Fifty kHz calls, on the other hand, prime and facilitate sexual responsiveness of the female. Tape recorded vocalizations of mating rats facilitate solicitation behavior of estrous females in the presence of castrated males, and such females also show a preference for these sounds in a “Y” maze. Deafening of females does not affect their normal pacing of copulatory contacts, but it drastically reduces their solicitation behavior. The studies summarized in this paper lead us to conclude that ultrasonic vocalizations play a major role in the integration of reproductive activity in the Norway rat, Rattus norvegicus .