PHARMACOLOGICAL MODULATION OF SOCIAL TRANSMISSION OF POSITIVE AFFECT THROUGH 50-KHZ ULTRASONIC VOCALISATIONS IN RATS

Rats are a highly social species that form complex group structures and rely on a rich repertoire of communicative signals, including ultrasonic vocalizations (USV), to coordinate and regulate their social interactions. These vocalizations are typically categorized as 22-kHz calls reflecting negative affect and 50-kHz calls associated with positive affect. Several drugs of abuse have been demonstrated to elicit 50-kHz USV in rats, with psychostimulants, most notably d-amphetamine (AMPH), increasing the emission of 50-kHz USV at moderate doses. Drug-induced 50-kHz USV are strongly influenced by multiple contextual factors, including procedural factors, environmental cues, social conditions, and substance-specific administration parameters. Although most research on 50-kHz calls has focused on the sender’s vocal emissions, playback studies indicate that these calls elicit approach behaviors in receivers. However, the extent to which 50-kHz USV influence receivers’ emotional states remains underexplored. In contrast to the limited understanding of positive affect transmission, 22-kHz calls associated with negative affect have been shown to support emotional contagion. This study investigates the transmission of positive affect through 50-kHz USV in rats, examining social interactions within both male and female dyads. Specifically, we assessed the behavioral and vocal responses of drug-naïve rats interacting with AMPH-treated conspecifics administered varying doses (1, 2.5 and 5 mg/kg). Preliminary observations indicate that AMPH dose-dependently increased both 50-kHz USV emission and locomotor activity in individually tested rats. Moreover, different AMPH doses elicited distinct behavioral profiles across locomotion, 50-kHz USV emission, and play behavior, reflecting dose-dependent modulation of social interaction dynamics within the sender-receiver communication loop.