Involvement of nitric oxide in long-term potentiation of spinal nociceptive responses in rats

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Abstract
Nitric oxide plays an important role in spinal nociception. The present study explored the effects of nitric oxide on the spinal long-term potentiation associated with nociception. (1) Nitric oxide synthase inhibitor L-NAME (1 mM, 20 μl) and the nitric oxide scavenger hemoglobin (2 mg/ml, 20 μl) strikingly blocked the induction of tetanic sciatic stimulation-induced spinal long-term potentiation of C-fiber-evoked field potentials. L-arginine, a substrate of nitric oxide synthase, completely reversed L-NAME-induced inhibition. However, D-NAME (1 mM, 20 μl), an inactive form of L-NAME, had little effect on the spinal LTP. (2) The same tetanic sciatic stimulation induced long-term thermal hyperalgesia, which was blocked by pre-application of L-NAME. These results suggest the involvement of nitric oxide in the spinal long-term potentiation of C-fiber-evoked field potentials and related behavior changes.