Long-term social isolation increases visceral pain in rats.

Long-term social isolation can alter the sensitivity to somatic pain, however, its impact on visceral pain sensitivity remains unknown. The purpose of this study is to investigate the effect of long-term social isolation on visceral pain sensitivity in rats. 4-week social isolation rearing significantly increased CRD-induced AWR score and decreased pain threshold as compared to group rearing. There was no significant difference in the number of spontaneous visceral pain behaviors between group and isolation rearing rats. The number of fecal bolus produced by isolation rearing rats was comparable to that produced by group rearing rats. Consistent with 4-week isolation, CRD-induced AWR score in 8-week isolation rearing rats was higher than that in group rearing rats. While, pain threshold was lower in 8-week isolation rearing rats than in group rearing rats. There was no significant difference in the number of spontaneous visceral pain behaviors and fecal bolus between 8-week isolation and group rearing rats. There results indicated that long-term social isolation induces visceral hypersensitivity in rats, but this effect is unrelated to an increase in stress levels.