Halothane minimum alveolar anesthetic concentration and neuronal nitric oxide synthase activity of the dorsal horn and the locus ceruleus in rats

There is some evidence of a relationship between nitric oxide and pain cont rol pathways. However, it is still controversial whether nitric oxide synth ase (NOS) inhibitors affect minimum alveolar anesthetic concentration (MAC) . We examined the effects of 7-nitro indazole (7-NI), a selective neuronal NOS (nNOS) inhibitor, on halothane MAC. With nicotinamide adenine dinucleot ide phosphate diaphorase histochemistry, we also investigated the nNOS acti vity of the dorsal horn and the locus ceruleus in 26 Sprague-Dawley rats. 7 -NI (100, 500, 1000 mg/kg intraperitoneally) reduced halothane MAC to 0.34% +/- 0.12%, 0.1% +/- 0.03%, and 0.05% +/- 0.12%, dose dependently (P < 0.01 ). 7-NI also reduced the number of nicotinamide adenine dinucleotide phosph ate diaphorase-positive cells by 20% to 65% (P < 0.05 or 0.01) and the stai ning intensity of the axons in the locus ceruleus and lumbar and thoracic s pinal cord as compared with the control group. 7-NI reduced the MAC observe d with halothane anesthesia, which was accompanied by nNOS activity suppres sion in the spinal cord and the locus ceruleus. Our results support the hyp othesis that the nitric oxide signaling pathway is related to MAC. Implicat ions: We examined the effects of a selective neuronal nitric oxide synthase inhibitor, 7-nitro indazole, on halothane minimum alveolar anesthetic conc entration and measured the nitric oxide synthase activity in the spinal cor d and the locus ceruleus of Sprague-Dawley rats using nicotinamide adenine dinucleotide phosphate diaphorase staining method. 7-Nitro indazole decreas ed both the minimum alveolar anesthetic concentration and neuronal nitric o xide synthase activity.