Startle-inducing acoustic stimuli evoke ultrasonic vocalization in the rat

The present study demonstrates that acoustic stimuli which induce a startle response (ASR) also evoke ultrasonic vocalization in the rat. Sound recordings were done on three consecutive days of testing during sessions of 20 acoustic stimuli each and on the following day for three minutes following 5 acoustic stimuli (nonstimulus condition). Startle-inducing stimuli evoked continuous ultrasonic calling which was maintained throughout testing. Immediately following each acoustic stimulus, however, vocalization was interrupted by a period of silence (gap). The mean duration of sounds was reduced and the interpulse interval tended to increase during acoustic stimulation as compared to the nonstimulus condition. It is concluded that startle-eliciting stimuli induce a state of fear in the rat and that the acoustic-startle-elicited ultrasonic vocalization may provide a novel model in the study of anxiety.