MICE EMIT UNIQUE HIGH FREQUENCY VOCALIZATIONS ABOVE 100 KHZ IN RESPONSE TO BEING TICKLED

Social play is a widespread behaviour among juvenile mammals and is important for the development of social skills. One form of social play is tickling, which comprises unpredictable elements of social touch in a safe environment, leading to involuntary laughter-like vocalizations. Tickling animals in the lab resembles relatively naturalistic and freely moving social behaviour while the tickling bouts can be controlled by the experimenter. Rats which are being tickled by an experimenter emit ultrasonic vocalizations (USVs) at 50 kHz, typical for a positive affective state. However, extending such research to mice would open up a greater number of genetic tools to investigate the neuronal mechanisms of social play. Here we show for the first time that wildtype C57Bl6 mice elicit unique vocalizations in response to being tickled. Furthermore, these tickling-induced USVs are in the ultrahigh frequency range of 100 – 150 kHz and differ from the vocalizations made in a subsequent free interaction test between two mice. Fmr1-knockout mice, modelling the neurodevelopmental disorder Fragile-X, also respond to being tickled. We are currently looking into their specific vocalization frequency and repertoire. In preference tests, all mice prefer tickling over access to the hut from their home cage, suggesting that mice are not aversive to tickling, but prefer solitary motor play over tickling. Our results first of all challenge existing views on the sociability and play behaviour of mice, and secondly open up opportunities to use mouse-specific tools to investigate neuronal mechanisms of social play during controlled yet more naturalistic social behaviour.