Ultrasonic vocalization in juvenile and adult male rats: A comparison among stocks.

Ultrasonic vocalizations (USV) are widely studied in mice and rats, and in case of rats, the bulk of empirical evidence is based on outbred rats, which in most studies belong to either Long Evans, Sprague-Dawley or Wistar stocks. It is known that these stocks can differ in terms of specific brain variables and also behaviorally, but there is only few evidence so far showing whether these stocks behave in similar or substantially different ways in paradigms which are often used to study USV. Therefore, we have started a larger series of comparative studies, where we analyzed different classes of USV in rats from these three stocks spanning from pups to adults. Here, we report our findings in juvenile and adult male Long Evans, Sprague-Dawley and Wistar rats, which we tested as juveniles for appetitive 50-kHz calls during a so-called cage test or when being tickled by an experimenter, and later as adults for 22-kHz calls in a fear conditioning paradigm. In general, all three stocks showed the expected USV responses, indicating that they are all feasible for this kind of research. In detail, however, there were various quantitative differences between stocks both, in terms of specific USV features (like call rates, call durations etc.) as well as visible behavior, like spontaneous locomotor activity and shock-induced immobility. These findings are discussed in the context of the relevant, but somewhat equivocal literature on these stocks, including factors which might contribute to such variability, like breeding, housing, or details of the given test.