Effect of Acute Brief Social Isolation on Visceral Pain.

Objective: The sensitivity of somatic pain could be affected by social isolation; however, few studies have examined the impact of social isolation on visceral pain. In the present study, the effect of acute brief social isolation on visceral pain response was investigated. Methods: Adult male rats were either reared individually or grouped for 2 hours or 24 hours. Colorectal distention (CRD)-induced abdominal withdrawal reflex (AWR) score and pain threshold were used to assess visceral pain sensitivity. The amount of fecal bolus was used to determine the stress level. Results: Acute brief isolation rearing for 2 hours significantly increased AWR score and reduced visceral pain threshold in rats when compared to group rearing. Similarly, acute isolation for 24 hours resulted in visceral hypersensitivity, as indicated by an increase in the AWR score and a decrease in the visceral pain threshold. Furthermore, the amount of fecal bolus in acute isolation rearing (2 or 24 hours) rats was considerably higher than in the control group rearing rats. Conclusion: Acute short-term social isolation enhances visceral pain sensitivity, which could be related to an increase in stress levels.