The role of 50 kHz ultrasonic vocalizations as play signals was examined, in this thesis by investigating the effects of devocalization on playful interactions in both juveniles and adults. In both studies, the animals played either with a devocalized or an intact partner. In juveniles, it was shown that 50 kHz calls are not essential for playful interactions to remain playful. However, in adults, it appears that the tactical use of 50 kHz calls is necessary to keep playful interactions from becoming aggressive in some contexts. Thus, 50 kHz calls appear to be functioning simply as an expression of affect in juveniles, whereas once sexually mature, the tactical use of ultrasonic vocalizations in male rats becomes more essential in navigating some social situations.NSERC AIS
