The evaluation of role of NMDA receptor and spinal microglia on age dependent differences of neuropathic pain in SNL model in male rats

Background: Induced neuropathic pain following nerve injury has behavioral signs such as allodynia and hyperalgesia. There are reports about the age dependent differences in severity and incidence and even therapeutic response of this pain. In this study, we have tried to evaluate behavioral differences of this pain in an induced neuropathic model in different ages, according to important role of N-methyl, D-aspartate (NMDA) receptor and spinal microglia on induction and maintenance of pain. Material and methods: Male rats were grouped in young (5-6 week) and mature (10-11 week). Under general anesthesia, the spinal nerve ligation (SNL) surgery was operated on right leg. The effect of different doses of dextromethorphan (NMDA blocker) and minocycline (microglia inhibitor) on 5 th day after surgery was evaluated and compared in two age-groups. Results: In this study, both Minocycline and dextromethorphan diminished neuropathic pain in a dose dependent manner in these two ages. Minocycline in contrast to dextromethorphan was more effective in young rats. The co-administration of ineffective doses of minocycline and dextromethorphan could be effective. Conclusion: Microglia and NMDA receptor function in neuropathic pain is different in different ages and the role of microglia is more evident. On the other hand the inhibition of both microglia and NMDA receptor can be considered for lowering neuropathic pain.