Social context increases ultrasonic vocalizations during restraint in adult mice

Adult mice emit many ultrasonic vocalizations (USVs) during social interaction tasks, but only a few studies have yet reported USVs in stressed adult mice. Our aim was to study which experimental conditions favor USV emission during behaviors associated with different emotional states. As USVs likely mediate social communication, we hypothesized that temporary social isolation followed by exposure to a novel social congener would promote USV emission. USVs were recorded in three different behavioral paradigms: restraint, free moving in a new environment, and during a social interaction task. We compared USV emission, with or without the presence of a social congener, in animals socially isolated during different periods (0, 6 or 21 days). Social isolation decreased the number of USVs during free moving, whereas it increased during restraint. During the social interaction task, animals produced high-frequency USVs (median: 72.6 kHz, 25-75% range: 67.6-78.2 kHz), especially when the social partner was active and social motivation was high. During restraint, presence of a social congener increased the call rate of low-frequency USVs (median: 52.4 kHz, 25-75% range: 44.8-56.5 kHz). USV frequency followed two unimodal distributions that distinguished low-frequency USVs (≤ 60 kHz) mainly emitted during free-moving (90.9% of total USVs) and restraint (93.1%) conditions, from high-frequency USVs (> 60 kHz) mainly emitted during the social interaction task (85.1% of total USVs). The present study confirms that USV call rate and frequency depend on behavioral states, and provides evidence that the presence of a congener promotes ultrasonic vocalizations in restrained adult mice.