Ultrasonic vocalizations of defeated male rats.

Abstract

The resident-intruder aggression paradigm was used to investigate the conditionability of 20-25 kHz vocalizations of defeated male rats [Rattus norvegicus] (territorial intruders). Of intruding males, 90% consistently emitted ultrasounds in the presence of an inaccessible aggressive male with which they had received repeated defeat experiences (4-12 attacks). Intruders tested 1 wk after initial conditioning emitted 20-25 kHz calls of comparable latency and number in the presence of familiar and unfamiliar aggressors. Defeated animals emitted few or no ultrasonic calls in response to male or female castrates, imobilized aggressive males, anosmic males or the soiled bedding material of an aggressor''s home cage. Vocalizations by aggressors (45-70 kHz) were not required to stimulate production of 20-25 kHz signals of defeated animals. Though olfactory cues alone were not sufficient to elicit ultrasonic vocalizations, they may be an important part of the stimulus complex capable of consistent elicitation. Rats may be uniquely prepared to emit 20-25 kHz calls in response to a limited subset of conspecific cues experienced during aggressive contact.