Binge Ethanol-Induced Brain Damage in Rats: Effect of Inhibitors of Nitric Oxide Synthase

Testing the possible role of endogenous nitric oxide (NO) in the neurotoxicity of ethanol, we examined how two different NO synthase (NOS) inhibitors affected the extent of cerebrocortical and olfactory neuronal damage in a modified "binge intoxication" rat model (Collins et al., Alcohol Clin. Exp. Res. 20:284–292, 1996). Male rats intragastrically fed ethanol (6.5 to 12 g/kg/day) in nutrient solution three times daily for 4 days also received N^G-nitro-L-arginine methyl ester by chronic intracerebroventricular infusion or 7-nitro-indazole by daily intraperitoneal injection; control rats were given nutrient solution only and/or vehicles. Blood ethanol levels did not differ among the ethanol-treated groups. The amount of ethanol-dependent neuronal degeneration in the entorhinal cortex, dentate gyrus, and olfactory bulb glomeruli—visualized with the de Olmos cupric silver stain and quantitatively assessed in the binge-intoxicated rats—was either unchanged or significantly increased by the NOS inhibitors. Although the efficacies of the inhibitors cannot be directly compared because various NOS forms were probably inhibited to differing extents, the results do not support the idea that endogenous NO is a neurotoxic mediator of ethanol's effects. Rather, NO may have a modest neuroprotectant role in this model of early brain damage induced by ethanol. In addition, the NOS that is localized histochemically as NADPH diaphorase was present primarily in regions and/or cells not damaged by binge ethanol treatment. Assuming that NADPH diaphorase represents most of the NO forming enzyme(s), this suggests a transcellular mechanism for NO. A further observation was that hippocampal CA pyramidal neuron degeneration was extensive in rats infused centrally with N^G-nitro-L-arginine methyl ester.