Ultrasonic vocalization of laboratory rats in response to handling and touch

The goal of the study was to investigate the ultrasonic vocalization induced in freely behaving, naive rats by gentle touch with a human hand. Thirty-nine rats were tested in an unfamiliar experimental cage with repeatable hand touch. Vocalization appeared with an average latency of 4.6 +/- 5.0 s (SD). The nape of the neck was the most effective area, and after a couple of stimuli applied, 66.7% of rats emitted 21-32 kHz ultrasonic vocalization. It consisted of multiple series of long calls, about 70% of which exceeded 300 ms. The responses quickly habituated from session to session to extinction. Significantly more rats housed in single cages vocalized ultrasonically than animals housed in community cages. The long latencies of the vocalization, their appearance in multiple series to a single touch, and quick habituation to the stimuli indicate that 22 kHz ultrasonic vocalization of rats reflects a distress caused by a potential danger to the animal and it does not necessarily reflect physical discomfort or pain. This vocalization may, therefore, play an adaptive role in increasing chances of survival by conveying information about potential threats to other conspecifics.