Gravity stress elevates the nociceptive threshold level with immunohistochemical changes in the rat brain

Young Wistar male rats were exposed to 2G hypergravity by continuous centri fugation for 15 minutes. The nociceptive threshold was measured by using th e von Frey type filament on the rat skin surfaces after hypergravity exposu re. Following the hypergravity exposure, rats were sacrificed with anesthes ia, then perfused and fixed for immunohistochemical examination. The 2G hyp ergravity elevated the nociceptive threshold up to 2-fold and induced analg esic effects on rats that remained for 2 hours after termination of centrif ugation. Expression of Fos-immunoreactive proteins was prominently induced by 2G hypergravity in the arcuate nucleus and the paraventricular nucleus o f the hypothalamus. The 15-minute flash exposure to 2G hypergravity induced pain suppression in rats, which might be attributed to change of neuronal activity in rat hypothalamus. (C) 2001 Elsevier Science Ltd. All rights res erved.