Conspecific presence facilitates 22-kHz ultrasonic calls in male rats exposed to cat odor.

Rats (Rattus norvegicus) exhibit defensive behaviors such as hiding, freezing, and fleeing when confronted with predators. They also may emit long-duration, flat frequency (~ 22-kHz), ultrasonic vocalizations (USVs) in response to predator detection. These are in contrast to the shorter, higher frequency (~ 50-kHz), frequency modulated USVs often associated with positive affective states. Long duration ~ 22-kHz vocalizations can trigger defensive behaviors in other rats. Here, we studied the impact of a predator-associated stimulus (cat fur) and the context in which it was experienced on these ~ 22-kHz and ~ 50-kHz USVs in laboratory rats, along with how the presence of conspecifics (none, one, or two familiar rats) influenced these vocalizations. Group-housed rats were habituated to a testing arena with a hide box alone or in pairs or trios. The next day, they were exposed to cat fur (1 g) in the arena, and defensive behaviors and USVs were recorded. Subsequently, the rats returned to the arena without cat fur to assess contextual fear. Cat fur prompted significant hiding and ~ 22-kHz USVs, especially in social groups. However, ~ 22-kHz USVs were not elicited by the context alone in any social grouping. Cat fur also suppressed ~ 50-kHz USVs, with recovery faster in trios, indicating a social buffering effect. These findings suggest that predator cues induce ~ 22-kHz USVs that are influenced by social context, perhaps indicating an altruistic communicative function.