Modulation of social behavior and dominance status by chronic pain in mice.

The potential influence of pain on social behavior in laboratory animals has rarely been evaluated. Using a new assay of social behavior, the tube co-occupancy test (TCOT), we assess propinquity-the tendency to maintain close physical proximity-in mice exposed to pain using subcutaneous zymosan or spared nerve injury as noxious stimuli. Our previous experience with the TCOT showed that outbred mouse sibling dyads show higher levels of tube co-occupancy than stranger dyads. We find here that long-lasting pain from spared nerve injury given to both mice in the dyad abolishes this effect of familiarity, such that strangers also display high levels of propinquity. We performed a separate experiment to assess the effect on dominance behavior of nerve injury to one or both mice of a dyad in which relative dominance status had been previously established via the confrontation tube test. We find that neuropathic pain given only to the dominant mouse reverses the relationship in male but not female mice, such that the previously subordinate mouse becomes dominant. These observations bolster the scant but growing evidence that pain can robustly affect social behavior in animals.