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 α‐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. © 2008 Wiley‐Liss, Inc.