The Immune-Pineal Axis Stress as a Modulator of Pineal Gland Function

摘要

tal light/dark cycle. The environmental light detected by the retina adjusts the centralclock in the suprachiasmatic nuclei, which innervate the pineal gland through a polysy-naptic pathway. During the night, this gland produces and releases the nocturnal hor-mone melatonin, which circulates throughout the whole body and adjusts several bodilyfunctions according to the existence and duration of darkness. We have previously shownthat during the time frame of an inflammatory response, pro-inflammatory cytokines,such as tumor necrosis factor-a, inhibit while anti-inflammatory mediators, such asglucocorticoids, enhance the synthesis of melatonin, interfering in the daily adjustmentof the light/dark cycle. Therefore, injury disconnects the organism from environmentalcycling, while recovery restores the light/dark information to the whole organism. Here,we extend these observations by evaluating the effect of a mild restraint stress, whichdid not induce macroscopic gastric lesions. After 2 h of restraint, there was an increase incirculating corticosterone, indicating activation of the hypothalamus-pituitary-adrenal(HPA) axis. In parallel, an increase in melatonin production was observed. Taking intoaccount the data obtained with models of inflammation and stress, we reinforce thehypothesis that the activity of the pineal gland is modulated by the state of the immunesystem and the HPA axis, implicating the darkness hormone melatonin as a modulatorof defense responses.