Social Modulation and Communication of Pain in the Laboratory Mouse

Pain sensitivity is importantly affected by a number of factors, and may best be evaluated using a biopsychosocial framework. Although such a framework has been applied to the study and treatment of pain in humans, the concept of pain as a multidimensional experience in rodent models has been given considerably less attention. There is evidence, however, that pain is significantly modulated by a variety of psychosocial factors; therefore, identifying such factors is important, especially considering the extensive use of rodent subjects in pain research. A previous study performed in our laboratory described a within-cage order-of-testing effect that suggested the social communication of pain amongst mice, a finding that inspired the research described in this dissertation. Using novel experimental paradigms, the research presented describes the effects of the immediate social environment on pain sensitivity in the laboratory mouse, as well as the converse, the effect of pain on social interactions among mice. Social conditions in pain experiments vary with respect to familiarity (i.e., cagemate versus stranger), sex, and pain state of the conspecific and such factors appear to significantly modulate both pain sensitivity and social behaviour. Here I present social modulation of pain as evidence for empathy in mice, such that mice observing a cagemate in pain exhibit significant hypersensitivity to a noxious stimulus; such modulation is dependent on visual cues. I also show that varying perceived social threat by permitting or limiting full physical contact in stranger male dyads significantly modulates pain behaviour resulting in testosterone-dependent stress-induced analgesia or hyperalgesia, respectively.