STUDYING RAT SOCIAL BEHAVIOR IN A SEMINATURAL ENVIRONMENT: EXPLORING THE EFFECTS OF PLAYBACK OF SOCIO-AFFECTIVE ULTRASONIC VOCALIZATIONS

Rats are highly social animals that live in large colonies and communicate extensively through ultrasonic vocalizations (USV). Juvenile and adult rats emit two main types: 22-kHz alarm calls and 50-kHz pro-social calls. Although 22-kHz USV are generally associated with negative affect and 50-kHz USV with positive affect, most supporting evidence comes from laboratory studies with simple setups involving one or two animals, which restrict the expression of natural social behaviors. Ethologically oriented research in seminatural environments, such as the visible burrow system, has demonstrated that 22-kHz USV are context-dependent and socially modulated by factors such as escape routes and the presence of conspecifics. However, the effects of 50-kHz USV on receivers in socially and environmentally complex settings remain largely unexplored. Here, we examined how playback of socio-affective 22-kHz and 50-kHz USV affects groups of rats housed in a seminatural environment. The LiveRatTracker was integrated with a visible burrow system to enable five days of continuous monitoring in same-sex juvenile male and female rats. Intermittent playback of 22-kHz USV, 50-kHz USV, and background noise (control) was conducted. Playback of 50-kHz USV increased locomotor activity, typically directed toward the sound source, supporting their role as social contact calls. No clear induction of social play behaviors, such as wrestling or pinning, was observed. Playback of 22-kHz USV did not increase locomotor activity. These findings demonstrate distinct behavioral responses to 22-kHz and 50-kHz USV in a seminatural setting and highlight a promising approach for investigating socio-affective dysfunctions in rat models of mental disorders.