Ultrasonic vocalization in female rats: A comparison among three outbred stocks from pups to adults

Long Evans (LE), Sprague-Dawley (SD) and Wistar (WU) are outbred rat stocks, which differ in terms of brain, physiology, pharmacological reactivity and behavior. Extending our previous work with males from these stocks, we here report the analysis of ultrasonic vocalizations (USV) in females. Identical to our previous studies, we tested them as pups for 40-kHz calls during short-term isolation, as juveniles for appetitive 50-kHz calls during a cage test or when being tickled, and finally as adults for 22-kHz calls in a fear conditioning paradigm. Stock differences were obtained in all four tests, albeit with different patterns: As pups, WU rats emitted more calls and spent more time calling than SD or LE rats. Furthermore, LE rats emitted calls with shorter durations, whereas SD emitted calls with lower peak frequencies and less frequency modulation. Furthermore, stock differences in call sub-types were detected. In the cage test, 50-kHz calls were most frequent in WU and rather few in LE rats. Call durations were longer in WU rats. When being tickled, SD females emitted calls with shorter durations and lower peak frequencies. Also, frequency modulation and call amplitude was higher in LE. Finally, the fear-conditioning test led to partly unexpected results, since many females, especially WU, did not emit 22-kHz calls even during the conditioning phase, but all stocks showed the expected behavioral immobility and responded with audible calls to the aversive shocks. These results are discussed with respect to factors of testing, development, gender, and stock.