Beneficial effects of social attachment to overcome daily stress.

Accumulation of daily life stress (chronic stress) often causes functional gastrointestinal diseases. Central oxytocin plays an important role in attenuating stress responses and regulating positive social interactions. Adult male rats were either paired or singly housed 1 week prior to the stress loading. Solid gastric emptying was measured after 7 consecutive days of chronic heterotypic stress. To study whether endogenous oxytocin is involved in restoring the delayed gastric emptying after paired housing, an oxytocin antagonist was injected intracerebroventricularly (icv) before the gastric emptying study. CRF and oxytocin mRNA expression in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) was evaluated by real time RT-PCR. In singly housed rats, chronic heterotypic stress significantly delayed gastric emptying (35.1+/-2.8%, n=6, P<or=0.01), compared to that of non-stressed rats (53.2+/-1.3%, n=6). Delayed gastric emptying observed in singly housed rats induced by chronic heterotypic stress was significantly improved by paired housing (54.8+/-3.5%, n=8, P<0.05). Central-administration of oxytocin antagonist attenuated the restored gastric emptying in paired housed rats (33.2+/-4.1%, n=6) following chronic heterotypic stress. Increased CRF mRNA expression at the PVN and SON observed in singly housed rats was significantly reduced in paired housed rats following chronic heterotypic stress. In contrast, oxytocin mRNA expression at the PVN and SON was significantly increased in paired housed rats. Social attachment restores delayed gastric emptying following chronic heterotypic stress, via down-regulating CRF expression and up-regulating oxytocin mRNA expression. Our study may provide the scientific benefit of social attachment in our daily life.