Wake-promoting actions of median nerve stimulation in TBI-induced coma: An investigation of orexin-A and orexin receptor 1 in the hypothalamic region

A coma is a serious complication, which can occur following traumatic brain injury (TBI), for which no effective treatment has been established. Previous studies have suggested that neural electrical stimulation, including median nerve stimulation (MNS), may be an effective method for treating patients in a coma, and orexin-A, an excitatory hypothalamic neuropeptide, may be involved in wakefulness. However, the exact mechanisms underlying this involvement remain to be elucidated. The present study aimed to examine the arousal-promoting role of MNS in rats in a TBI-induced coma and to investigate the potential mechanisms involved. A total of 90 rats were divided into three groups, comprising a control group, sham-stimulated (TBI) group and a stimulated (TBI + MNS) group. MNS was performed on the animals, which were in a TBI-induced comatose state. Changes in the behavior of the rats were observed following MNS. Subsequently, hypothalamic tissues were extracted from the rats 6, 12 and 24 h following TBI or MNS, respectively. The expression levels of orexin-A and orexin receptor-1 (OX1R) in the hypothalamus were examined using immunohistochemistry, western blotting and an enzyme-linked immunosorbent assay. The results demonstrated that 21 rats subjected to TBI-induced coma exhibited a restored righting reflex and response to pain stimuli following MNS. In addition, ignificant differences in the expression levels of orexin-A and OXIR were observed among the three groups and among the time-points. Orexin-A and OX1R were upregulated following MNS. The rats in the stimulated group reacted to the MNS and exhibited a re-awakening response. The results of the present study indicated that MNS may be a therapeutic option for TBI-induced coma. The mechanism may be associated with increasing expression levels of the excitatory hypothalamic neuropeptide, orexin-A, and its receptor, OX1R, in the hypothalamic region.