Halothane and isoflurane dose-dependently inhibit the cyclic GMP increase caused by N-methyl-D-aspartate in rat cerebellum: novel localization and quantitation by in vitro autoradiography.

Using a novel technique combining immunohistochemistry and in vitro quantitative autoradiography, we were able simultaneously to localize and quantitate cyclic guanosine 3',5'-monophosphate (cGMP)-immunoreactive binding in adult rat cerebellum. The cGMP-immunoreactive binding was predominantly detected in the molecular layer of the cerebellum under both basal and N-methyl-D-aspartate-stimulated conditions. N-Methyl-D-aspartate significantly increased the cGMP binding density in the molecular layer. This increased cGMP level was dose-dependently and significantly inhibited by the inhalational anesthetics halothane and isoflurane. This increased cGMP level was also significantly inhibited by L-NG-nitroarginine methyl ester, an inhibitor of nitric oxide synthases. L-Arginine, the substrate of nitric oxide synthase, reversed the inhibition by L-NG-nitroarginine methyl ester on the cGMP increase. This novel combination of immunohistochemistry and quantitative autoradiography may be used to localize and quantitate simultaneously cGMP or other substances in animal tissues. Our data also confirm that nitric oxide is involved in the stimulation of cGMP formation by N-methyl-D-aspartate. Halothane and isoflurane inhibit the nitric oxide-guanylyl cyclase signaling pathway activated by the excitatory amino acid N-methyl-D-aspartate in the brain, which may be a component of the mechanisms by which these two inhalational anesthetics produce their anesthetic effects.