title: Nitric oxide regulates excitatory amino acid release in a biphasic manner in freely moving rats.
abstract: The effect of altering hippocampal nitric oxide levels on basal and N-methyl-D-aspartate (NMDA) receptor-evoked release of glutamate and aspartate has been studied in freely moving rats. NMDA increased extracellular glutamate and aspartate in a concentration-dependent manner. The nitric oxide synthase inhibitor L-nitro-arginine-methyl ester (L-NAME; 100 microM) increased basal glutamate and aspartate release, and also enhanced release of these amino acids evoked by NMDA (100 microM) compared with the same concentration of NMDA infused alone. L-NAME at 200 microM increased basal dialysate glutamate, but not aspartate, to a lesser extent than the 100 microM concentration of the drug, and the NMDA-induced release of glutamate and aspartate was decreased. L-NAME at 1.0 mM did not significantly alter basal extracellular glutamate but significantly decreased dialysate aspartate, while abolishing the NMDA-evoked release of both amino acids. The actions of L-NAME were not mimicked by its much less active isomer D-nitro-arginine-methyl ester. The nitric oxide donor drug S-nitroso-N-penicillamine decreased dialysate glutamate and aspartate at a 500 microM concentration but increased the extracellular level of both amino acids when infused at 1.0 mM and 2.0 mM concentrations. These data suggest that nitric oxide may mediate both excitatory and inhibitory functions, according to the level of nitric oxide production in vivo.
authors.affiliation: Department of pharmacology, School of Pharmacy, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Segieth
authors.forename: S J
authors.initials: SJ
authors.lastname: Getting
authors.forename: C S
authors.initials: CS
authors.lastname: Biggs
authors.forename: P S
authors.initials: PS
authors.lastname: Whitton
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001224:Aspartic Acid / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018846:Excitatory Amino Acids / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology; D008297:Male; D017551:Microdialysis; D009043:Motor Activity / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D026423:S-Nitroso-N-Acetylpenicillamine; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D018846:Excitatory Amino Acids; D014665:Vasodilator Agents; D001224:Aspartic Acid; D009569:Nitric Oxide; D018698:Glutamic Acid; D016202:N-Methylaspartate; D026423:S-Nitroso-N-Acetylpenicillamine; D001120:Arginine; D019001:Nitric Oxide Synthase; D010396:Penicillamine; D019331:NG-Nitroarginine Methyl Ester