NITRIC-OXIDE SYNTHASE INHIBITOR BLOCKS SPINAL SENSITIZATION INDUCED BY FORMALIN INJECTION INTO THE RAT PAW

This study evaluated the role of nitric oxide (NO) in spinal cord noci ceptive transmission during peripheral inflammation evoked by formalin injection into the rat paw, using N(omega)-nitro-L-arginine (N-Arg), an NO synthase inhibitor. Male rats were prepared with intrathecal (IT ) catheters. To quantify the formalin response, the instances of ''fli nching behavior'' were counted at 5-min intervals for 60 min. IT N-Arg depressed the flinching behavior in a dose-dependent manner when N-Ar g was administered 10 min before the formalin injection. This N-Arg ef fect was reversed with L-arginine but not D-arginine. We conclude that NO plays an important role in nociceptive transmission in the spinal cord during the formalin test.