Background and aims: Rats emit ultrasonic vocalizations (USVs) in the range of 22-kHz and 50-kHz to communicate the presence of positive or negative emotional states, respectively. USVs may be influenced by several factors, including the social context. Likewise, pain behavior can be modulated by the social context, as can be transferred to conspecifics. Herein we investigated if acute pain was related to changes in calls’ emission and how different social contexts affected the nociceptive behavior and USVs. Methods: Male and female Wistar rats were used (authorization CEUA # 1151). Formalin (2.5%) was injected into the upper lip followed by recording of USVs and facial grooming for 30 min. The effect of morphine (2.5 mg/kg) was assessed in both parameters. The same protocol was repeated in different social contexts: 1) exposure to cagemates , 2) non-cagemates and 3) female rats. Results: Formalin induced facial grooming and aversive calls, which were both reduced by morphine. Exposure of formalin-injected rats to familiar cagemates had no effect on the demonstrator’s behavior, but the observer showed emotional contagion of pain. Non-cagemates interaction decreased the nociceptive behavior of the demonstrator, but failed to influence the observer’s behavior. Females’ presence reduced the nociceptive behavior and the emission of aversive calls by the demonstrator. Conclusions: USV analysis may represent and additional measure in pain studies. We suggest that emotional contagion of pain depends on familiarity and analgesia may be a result of social interaction with a stranger or with a female. Acknowledgements: CAPES.

ULTRASONIC VOCALIZATION ANALYSIS FOR THE STUDY OF THE AFFECTIVE COMPONENT OF ACUTE OROFACIAL PAIN AND EMOTIONAL CONTAGION OF PAIN IN RATS