Behavioral, ultrasonic, and cardiovascular responses of male wistar rats in different social and emotional contexts after ultrasonic playback

Rats are social animals that use ultrasonic vocalizations (USV) to communicate. USV are usually divided into 50 kHz calls which accompany appetitive states, and 22 kHz vocalizations which are usually associated with aversive states. Both kinds of states are known to affect animals’ heart rate (HR). Also, the polyvagal theory claims that both cardiovascular parameters and USV emission is affected by the autonomous system, as they share a common signaling pathway. The aim of the study was to evaluate the changes in behavior, HR, and USV emission after playback of ultrasounds. Male Wistar rats were housed in pairs or separately for 4 weeks, and some of the animals underwent fear conditioning. Animals were implanted with DSI telemetry transmitters for acquisition of cardiovascular parameters. After recovery, rats were subjected to ultrasounds playback consisting of initial 10 min of static silence and five sets of 10 s sounds (50 or 22 kHz), either natural, collected from animals, or artificial tones, separated by 5 min silence intervals. Video, audio, and cardiovascular parameters were collected. Surprisingly, presentation of both 50 and 22 kHz sounds induced approach behavior. Both single- and pair-housed animals responded with a larger number of USV to both natural and artificial 50 kHz sounds playback rather than to 22 kHz sounds. The emitted USV were, almost exclusively, within the 50 kHz range. Animal HR levels decreased gradually during the experimental session. Single‑housed animals had, in general, higher HR than paired rats. There was an impact of every kind of ultrasonic presentation on HR levels; in general, 50 kHz ultrasonic playback caused a sudden increase in HR, whereas 22 kHz presentations evoked a HR drop. Surprisingly, USV and artificial tones had similar effects on HR and USV responses. Social context did not appear to alter rats’ USV emission. The results following fear conditioning are being analyzed. Also, in a separate set of experiments, rats ultrasonic responses were analyzed following presentation of a defined number of pre‑recorded USV.