title: Stimulation of NMDA and AMPA glutamate receptors elicits distinct concentration dynamics of nitric oxide in rat hippocampal slices.
abstract: Nitric oxide ((*)NO) is an intercellular messenger implicated in memory formation and neurodegeneration in the hippocampus. Owing to its physical and chemical properties, the concentration dynamics of (*)NO is a critical issue in determining its bioactivity as a signaling molecule. Its production is closely related to glutamate N-methyl-D-aspartate (NMDA) receptors, following a rise in intracellular calcium levels. However, that dependent on alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors remains elusive and controversial, despite reports describing a role for these receptors in other brain regions, largely because of lack of quantitative and dynamic measurements of (*)NO. Using a (*)NO-selective microsensor inserted in the diffusional spread of (*)NO in the CA1 region of rat hippocampal slices, we measured its real-time endogenous production, following activation of ionotropic glutamate receptors and under tissue physiological oxygen tension. Both NMDA and AMPA stimulation resulted in a concentration-dependent (*)NO production but encompassing distinct kinetics for lag phases and slower rates of (*)NO production were observed for AMPA stimulation. Robustness of the results was achieved instrumentally and pharmacologically, by means of nitric oxide synthase (NOS) inhibitors and antagonists of NMDA (D-(-)-2-amino-5-phosphonopentanoic acid, AP5) and AMPA (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide, NBQX) receptors. When using glutamate as a stimulus, (*)NO production was of lower magnitude in the presence of AP5 plus NBQX than with AP5 alone, suggesting that even when NMDA receptors are inhibited Ca(2+) rises to levels to induce a peak of (*)NO from the background. Whereas extracellular Ca(2+) was required for the (*)NO signals, Philanthotoxin-4,3,3 (PhTX-4,3,3) a toxin used to target Ca(2+)-permeable AMPA receptors, attenuated (*)NO production. These observations are interpreted on basis of a distinct coupling between the glutamate receptors and neuronal NOS. A role for Ca(2+)-permeable AMPA receptors in the Ca(2+) activation of neuronal NOS is suggested.
authors.affiliation: Center for Neurosciences and Cell Biology, University of Coimbra, 3000 Coimbra, Portugal.
authors.forename: J G
authors.initials: JG
authors.lastname: Frade
authors.forename: R M
authors.initials: RM
authors.lastname: Barbosa
authors.forename: J
authors.initials: J
authors.lastname: Laranjinha
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D011073:Polyamines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D011073:Polyamines; D011810:Quinoxalines; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D009569:Nitric Oxide; D018698:Glutamic Acid; D015763:2-Amino-5-phosphonovalerate; C034092:delta-philanthotoxin; D019001:Nitric Oxide Synthase; D002118:Calcium