Affiliative behavior attenuates stress responses of GI tract via up-regulating hypothalamic oxytocin expression

Hypothalamic oxytocin (OXT) has stress-attenuating effects. Social interaction in a positive environment continuously activates OXT release system. We have recently shown that pair housing restores delayed gastric emptying following chronic heterotypic stress, via up-regulation of OXT mRNA expression in rats. We tested the hypothesis that affiliative behavior attenuates stress responses via upregulating OXT expression. Adult male SD rats were divided into two groups: the rat with a stressed partner (RSP) and the rat with a non-stressed partner (RNSP). RSPs were pair housed with a partner that received different types of stress for 7 consecutive days (chronic heterotypic stress). RNSPs were pair housed with a partner who did not receive any stress. After each stress loading, the rats were returned to their home cages and the behaviors of RSPs and RNSPs toward their partners were videotaped. After the study completion, RSPs and RNSPs were loaded with acute restraint stress. Then, gastric emptying and colonic transit were measured. Corticotropin releasing factor (CRF) and OXT expression in the paraventricular nucleus (PVN) were evaluated by real time RT-PCR and immunohistochemistry. The time of affiliative behaviors toward their partners was increased in RSPs, compared to that of RNSPs. Delayed gastric emptying and accelerated colonic transit induced by acute restraint stress were significantly attenuated in RSPs, compared to RNSPs. CRF expression was reduced, while OXT expression was increased in RSPs in response to acute stress, compared to controls. It is suggested that affiliative behaviors may upregulate hypothalamic OXT expression, which in turn attenuates stress responses.