Inflammatory pain induces neuronal alterations in NO and JNK dependent manners

Background: Dark neurons are generated in vivo as an acute or delayed consequence of several pathological situations and lesions. The present study was designed to evaluate whether inflammatory pain induces formation of dark neurons in the dorsal horn of rat spinal cord. Since NO and JNK pathway are involved in the mechanisms of pain generation and degenerative neuronal alteration, their roles were also considered.Methods: Histological procedures were employed for detection of dark neurons following induction of inflammatory pain.Results: On the fifth day; following daily injections of 5% formalin, numbers of dark neurons increased significantly. Acute and chronic administration of 1% or 2.5% formalin did not induce any remarkable neuronal alteration in the dorsal horn of lumbar spinal cord. Daily intrathecal administration of quercetin (inhibitor of JNK pathway) 100μg/rat, or PTIO (NO scavenger) 30μg/rat before injection of 5% formalin, led to a reliable reduction of formation of dark neurons.Conclusion: Results indicate that induction of inflammatory pain for longer periods may result in a serious central disorder, and administration of neutralizers or inhibitors of NO and JNK may exert neuroprotective effects.