Anti-stress effect of hypothalamic oxytocin -Importance of somatosensory stimulation and social buffering

Abstract

A growing body of evidence suggests that stress stimuli, both acute and chronic, promote different physiological mechanisms and neuroendocrine responses. Oxytocin (OXT) is mainly synthesized in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. Central OXT has an anxiolytic effect and attenuates the hypothalamic–pituitary–adrenal (HPA) axis in response to stress. Anti-stress effect of OXT has been explained by its inhibitory effect on corticotropin releasing factor (CRF) expression at the PVN via GABA_A receptors. Repeated experience with the same stressor produces habituation, or diminution of behavioral responses and HPA axis responses. Up-regulated OXT expression in the PVN is involved in mediating habituation in response to chronic homotypic stress in rats. In contrast to chronic homotypic stress, no habituation is observed when rats are singly housed and received different types of stressors for 7 days (chronic heterotypic stress). Increased CRF expression and reduced OXT expression at the PVN are observed following chronic heterotypic stress in singly housed rats. Thus, it is conceivable that stress responses to chronic heterotypic stress would be diminished if endogenous OXT expression is upregulated.

Various manual therapies such as massage, acupuncture and transcutaneous electrical nerve stimulation (TENS) involve the stimulation of somatosensory neurons. OXT system is activated by manual therapies. TENS increases OXT expression and decreases CRF expression at the PVN following chronic heterotypic stress in singly housed rats. OXT has been implicated in a number of social behaviors, including maternal care, affiliation and social attachment. Social attachment is known to stimulate OXT release in the hypothalamus in rats. A recent study demonstrates an increased OXT expression following chronic heterotypic stress when rats are pair-housed. Somatosensory stimulation is a promising treatment for stress-associated diseases. A social interaction is also important to adapt to our daily life stress.