title: Changes in acoustic startle reflex in rats induced by playback of 22-kHz calls.
abstract: In aversive or dangerous situations, adult rats emit long characteristic ultrasonic calls, often termed "22-kHz calls," which have been suggested to play a role of alarm calls. Although the playback experiment is one of the most effective ways to investigate the alarming properties of 22-kHz calls, clear behavioral evidence showing the anxiogenic effects of these playback stimuli has not been directly obtained to date. In this study, we investigated whether playback of 22-kHz calls or synthesized sine tones could change the acoustic startle reflex (ASR), enhancement of which is widely considered to be a reliable index of anxiety-related negative affective states in rats. Playback of 22-kHz calls significantly enhanced the ASR in rats. Enhancement effects caused by playback of 22-kHz calls from young rats were relatively weak compared to those after calls from adult rats. Playback of synthesized 25-kHz sine tones enhanced ASR in subjects, but not synthesized 60-kHz tones. Further, shortening the individual call duration of synthesized 25-kHz sine tones also enhanced the ASR. Accordingly, it is suggested that 22-kHz calls induce anxiety by socially communicated alarming signals in rats. The results also demonstrated that call frequency, i.e., of 22kHz, appears important for ultrasonic alarm-signal communication in rats.
authors.affiliation: Center for Animal Research and Education, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. Electronic address: ahina@aichi-med-u.ac.jp.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Inagaki
authors.affiliation: Multidisciplinary Pain Center, Aichi Medical University, Yazakokarimata, Nagakute, Aichi 480-1195, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ushida
mesh_terms: D000161:Acoustic Stimulation; D000375:Aging / Q000502:physiology*; D000818:Animals; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013216:Reflex, Startle / Q000502:physiology*; D014465:Ultrasonics; D014828:Vocalization, Animal / Q000502:physiology*
keywords: Alarm call; Anxiety; Social communication; Stress response; Ultrasonic vocalization