Effects of hyperbaric oxygen on pain-related behaviors and nitric oxide synthase in a rat model of neuropathic pain.

BACKGROUND: Neuropathic pain is complex, and a satisfactory therapeutic method of treatment has yet to be developed; therefore, finding a new and effective therapeutic method is an important issue in the field of neuropathic pain. OBJECTIVE: To determine the effects of hyperbaric oxygen (HBO) on pain-related behaviours and nitric oxide synthase (NOS) expression in a rat model of neuropathic pain. METHODS: Forty male Sprague Dawley rats were randomly divided into five groups (eight rats per group) including control, sham operation, sciatic nerve with chronic constriction injury (CCI), HBO pretreatment (pre-HBO) and HBO post-treatment (post-HBO) groups. Pain-related behaviours and NOS expression in the spinal cord were compared among the five groups. RESULTS: Compared with the CCI group, the mechanical withdrawal threshold was significantly increased and thermal withdrawal latency was significantly extended in the pre-HBO and post-HBO groups (all P<0.05). After CCI, expression of spinal neuronal NOS and inducible NOS were increased. Expression of spinal neuronal NOS and inducible NOS were significantly decreased in the pre-HBO and post-HBO groups compared with the CCI group (all P<0.05). Spinal eNOS expression changed very little. DISCUSSION: HBO has been used as an effective and noninvasive method for the treatment of spinal cord injuries and high-altitude sickness, and in immunosuppression and stem-cell research; however, it has yet to be applied to the treatment of neuropathic pain. The present study indicated that HBO effectively increased mechanical withdrawal threshold and thermal withdrawal latency, demonstrating that HBO has therapeutic effects on neuropathic pain. CONCLUSION: HBO inhibits pain in rats with CCI through the regulation of spinal NOS expression.