INTRODUCTION: Ultrasonic vocalizations (USV) of adult rats are thought to be means of social communication and are divided into two categories, 55 kHz and 22 kHz, signaling, respectively, appetitive and aversive states. These states are also known for changes in the heart rate (HR). The autonomous system has a role in both USV shaping and HR response. A common signaling pathway via the vagus nerve connects the laryngeal muscles and the heart. This causes an overlap in HR parameters and many behavioral reactions (the polivagal theory). AIM(S): The aim of this study was to investigate USV emissions and HR changes in rats evoked by USV presentation. METHOD(S): Ten weeks old Wistar male rats were housed in pairs or separately for 4 weeks. Telemetry transmitters for HR acquisition were implanted in the peritoneum with the detector placed in the aorta. Rats were exposed to five 10‑s sets of sounds (counterbalanced): 55-kHz, 22-kHz USV (both natural, collected from other animals), 55-kHz, 22-kHz tones, 22-kHz uninterrupted tone (all three artificial, software‑generated) separated with 5 min silence intervals. HR and USV emitted were registered. RESULTS: Rats of both groups responded with USV mostly and more often to 55-kHz tones and vocalizations than during presentation of 22-kHz sounds. The responses were, almost exclusively, within 55 kHz range. In general, single-housed rats vocalized more often than pair-housed ones but the effect was not strong. Also, HR changes were more pronounced following presentation of natural USV. During 55-kHz USV presentation, there was an elevation of HR in single-housed animals, while in pair-housed animals, this elevation was preceded by a transient HR drop. During 22-kHz USV presentation, a decrease in HR in both groups was observed, although it was more clear in paired-housed rats. CONCLUSIONS: Social context may have an impact on HR levels and USV emissions in response to ultrasounds presentations. However, it does not seem to influence the distinction between artificial and natural USV. FINANCIAL SUPPORT: The work was supported by National Science Centre, Poland, grant no. 2015/19/B/ NZ4/03393.
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