Behavioural responses of laboratory rats to playback of 22 kHz ultrasonic calls.

It has been demonstrated that cholinergic stimulation of the anterior hypothalamic-preoptic region induces 22 kHz ultrasonic vocalization in rats. Acoustic features of the cholinergically induced vocalization did not differ from those of 22 kHz calls emitted in natural situations and, therefore, could have a behavioural significance for other conspecifics. The 22 kHz calls induced by intracerebral injection of carbachol were played back to rats and their responses were compared with responses to playback of 22 kHz calls induced by tactile stimuli and to those with background noise. Animal responses were measured by an accelerometric sensor as an average ergometric activity. The average activity count was not changed during presentation of acoustic stimuli, however, striking differences were found in animal responses immediately after discontinuation of the sound. Activity of the rats consistently and significantly decreased after presentation of 22 kHz calls induced by tactile stimuli or by injection of carbachol. Animal responses to calls induced by carbachol were indistinguishable from responses to calls induced by tactile stimuli. No significant changes in the general activity of the animals were observed after presentation of the background noise or during the sessions without stimuli. The results demonstrate that carbachol-induced ultrasonic calls have behavioural significance for other conspecifics and could serve as an alarm call in a similar way to naturally produced 22 kHz vocalization.