Comparison between cholinergically and naturally induced ultrasonic vocalization in the rat.

Ultrasonic vocalization in rats accompanying stressful situations or induced by direct brain stimulation may be used as a measure of emotionality and as a potential response model for testing anti-anxiety agents. The aim of the present study was to compare physical features of pharmacologically-induced ultrasonic vocalization with naturally triggered vocalization. Ultrasonic calls induced by hand touch, footshock, or by direct intracerebral injection of carbachol in adult rats were compared. Ultrasonic calls obtained in all these situations were described as '22 kHz' vocalization. Average frequencies of vocalization were 24.1 +/- 0.78 kHz, 26.0 +/- 2.64 kHz and 25.0 +/- 1.87 (SD) kHz for handled, footshocked and carbachol injected rats, respectively, and they did not differ significantly from each other. Histograms of single call duration showed similar distribution patterns for all groups with a predominance of long calls, although carbachol-induced calls were shorter than calls induced by touch or footshock. Histograms for inter-call intervals showed one major peak at 100-150 ms for all groups. Sonograms and power spectra showed similar characteristics both for calls induced by intracerebral carbachol and by hand touch or footshock. The results indicate that physical features of ultrasonic vocalization induced by intracerebral carbachol are comparable with those for naturally induced vocalization and fall into the category of '22 kHz' calls.