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 often emit
long-duration (~22-kHz) ultrasonic vocalizations (USVs) in response to
predator detection, unlike shorter (~50-kHz) USVs associated with positive
states. These vocalizations can also trigger defensive behaviors in other
rats. We studied the impact of a predator-associated stimulus (cat fur)
and the context in which it was experienced on ~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 gram) 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,
but not in the context alone. 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 influenced by
social context, highlighting an altruistic communicative function.