Ultrasonic vocalisations facilitate sexual behaviour of female rats.

Nature Vol. 272 9 March 1978 approximately 1 pg per week and of volatile heterocyclic nitrosamines 3 pg per week. We thank the National Cancer Institute for the loan of a Thermal Energy Analyser under contract NOI CP 65795. T. A. Gouou K. S. WEBB R. F. COLEMAN Laboratory of the Government Chemist, Stamford Street, London SE1, UK Received 14 November 1977; accepted 24 January 1978. Gough, T. A., McPhail, M. F., Webb, K. S., Wood, B. J. & Coleman, R. F. J. Sci. F4 Agric. 28, 345-351 (1977). . Goodhead, K. & Gough, T. A. H! Cormet. Toxicol. 13, 307-312 (1975). . Gough, T. A. & Webb, K. S. J. Chromat. 79, 57-63 (1973). . T. A., Goodhcad, K. & Walters, C. L. J. Sci. Fd Agrie. 27, 181-185 ). . Household Food Consumption and Experidi/urefor 1973 (HMSO, London, 1974) 1. Magee, P. N. & Barnes, .l.M. Br. J. Cancer 10, 114-122 (1956). 2. Warthesen, J. 1., Scanlan, R. A., Bills, D. D. & Libbey, L. M. J. Agric. Fd Chem. 23, 898-902 (1975). 3. Mirvlsh, S. S. J. mun. Cancer Inst. 44, 633-639 (1970). 4. Smith, P. A. S. & Loeppky, R. N. J. Am. chem. Soc. 89, 1147-1157 (1967). 5. F;((1)(;lE(5ll&#39;,9;h2/)., Pensabene, .1. W. Doerr, R. C. & Wasserman, A. E. Nature 236, 6. Coloe, P. J. & Hayward, N. J. J. med. Microbiol. 9, 211-223 (1976). 7. Scanlan, R. A. CRC Critical Reviews in Food Technology 5, 357-402 (1975). 8. Fine. D. H., Rufeh, F., Lieb, D. & Rounbehler, D. P. Analyl. Chem. 47, 9 1188-1190 (1975). 10 .—-—._. wN_. Ultrasonic vocalisations facilitate sexual behaviour of female rats ULTRASONIC vocalisations commonly occur during social inter- actions among rodents. During mating, adult male and female rats (Rattus norvegicus) emit brief 50-60 kl-lz ultrasonic callsl; however, the function of these vocalisations is not known. In this study, we demonstrate that these mating calls have a precise function for communication. Speciﬁcally, 50-kHz vocalisations elicit sexual activity in female rats. Female rats exhibit a series of solicitation patterns during sexual behaviour, including orientation, darting and ear wiggling. These movements excite the male and enhance the likelihood of mounting, thereby facilitating copulation“. (Beach has emphasised the importance of solicitation by the female during mating and has suggested the term ‘proceptivity’ to include the female’s behaviour in the initiation and main- tenance of copulation.) Although the presence of an intact male is usually a prerequisite for solicitation behaviour, the speciﬁc sensory cues which elicit it are not known. Isolated oestrous female rats exposed to ultrasonic vocalisations from a male exhibited a shorter latency to, and higher rate of darting when subsequently placed in a mating situation? Although the auditory cues primed oestrous females to dis- play increased solicitation behaviour when later confronted with an intact male, there was no indication that these ultra- sonic vocalisations had a direct function for communication in the induction of these behaviour patterns. The objective of the present report was to determine if ultrasonic mating calls of rats have a direct function for communication during copulation. Sixteen ovariectomised Long—Evans female rats served as subjects. Fifteen experienced males and 15 experienced female rats were used for transmitting vocal signals. Seven long-term castrated males were used as stimulus animals. The animals were maintained on a l2:l2h light—dark cycle (lights off at 0930). Ultrasonic vocalisations were electronically transmitted from a transmitting cage to a receiving cage. Both were glass- walled aquaria (52gl26gl29 cm high). The transmitting cage contained a central divider of wire mesh screen and was covered by a 10-Cm thick sheet of polyfoam. The polyfoam was covered by corrugated cardboard within which a hole was made to hold a 0.64-cm Bruel and Kjaer microphone (model 4136). The microphone was placed directly over the male’s section of the cage. Vocalisations wers picked up using the microphone, and ampliﬁed, ﬁltered and relayed by a transducer driver 163 ampliﬁer to an electrostatic condenser microphone head con- nected for use as a speaker. The speaker was angled above the receiving cage. The speaker input was monitored on an oscilloscope and a Holgate ultrasonic receiver (bat detector) recorded vocalisations in the receiving cage. The transmitting cage and receiving cage were placed at diagonal corners of a 3 X 3 in room. Illumination was provided by red light above the receiving cage. Female rats received subcutaneous injections of 50 pg oestradiol benzoate 54 h and 500 ug progesterone 6 h before the tests to induce behavioural oestrus. Testing was carried out during hours 4-8 of the 12-h dark period. Experimental females were placed in the empty receiving cage for a 2—min acclimation period. A castrated male was then introduced into the receiving cage and the stimulus treatments were begun simultaneously. Females were tested for 10 min in the receiving cage with one of the following treatments: (1) transmitted vocalisations from oestrous female and intact male previously given three intromissions (vocalisa- tions, Voc); (2) transmitted sounds from empty cage (control, C); (3) transmitted sound from empty cage to receiving cage containing intact male urine (urine, U). (Urine from intact males was obtained on the test day by placing a male and oestrous female on opposite sides of a wire-mesh divider. The male typically urinated and his urine was collected on gauze squares. The urine-covered gauze was placed in a small wire box on the cage wall which enabled the female to smell the urine but prevented any gustatory contact.); (4) trans- mitted vocalisations from oestrous female and intact male to receiving cage containing intact male urine (urine+voca1isa- tion, U .LVoc). Each female received each treatment at 1-week intervals in a counterbalanced fashion. Darting and lordosis by the female in the receiving cage were manually scored on a pushbutton-activated Rustrak event recorder, as was the occurrence of transmitted vocalisations at 50 and 22 kHz. Darting and lordosis latencies and frequencies were calculated from the strip-chart record. As shown in Table 1, females exposed to both treatments with vocalisation showed signiﬁcantly more darting behaviour than those in the non-vocalisation treatments (two-way analysis of variance: P l 0.01). Similarly, both vocalisation treatments resulted in signiﬁcantly shorter latencies to darting compared with control or urine alone treatments (two-way analysis of variance: P l0.0l). Table 1 also demonstrates that signiﬁ- cantly higher lordosis frequently occurred during the two treatments involving vocalisations compared with non-vocal- isation treatments (Friedman analysis of variance: P l 0.001). No differences were found between the Voc and Voc—l~ U groups. It is important to note here that lordosis was usually exhibited in response to minimal contact stimulation by the castrated males. Castrated males were never observed to mount the females, and often during the vocalisation treatments a slight ano-genital sniff or nudge would be an adequate stimulus to elicit a lordosis posture. On occasion, lordoses were exhibited without any physical contact from the male. It was generally observed that vocalisations occurred in an episodic fashion during the 10-min test period. The sexual responses of the female seemed to follow the fluctuations in vocalisation very closely. When transmitted vocalisations slowed or ceased, there was a decrease in the rate of solicita- tion; accordingly, when vocalisations were re-initiated, darting and lordosis were markedly increased in frequency. In some tests, males in the transmitting cage exhibited a transition from 50- to 22-kHz vocalisations. It was casually observed that at these times the females in the receiving cages immedi- ately increased their rate of darting. A point-biserial correla- tion“ showed that there were signiﬁcantly more darts in tests with (median, 78; n = 8) than in those without (median, 21.5; n = 24) 22-kHz vocalisations (P l 0.001). The results of this experiment demonstrate that ultrasonic vocalisations are a sufﬁcient cue to increase darting by a female rat in the presence of a castrated male rat. This comple- © Macmillan Journals Ltd 1978