Abstract
Increased activity of glutamate N-methyl-d-aspartate (NMDA) receptors is the dominant mechanism by which nitric oxide (NO·) is generated. By using a selective direct-current amperometry method, we characterized real time NO· release in vivo in response to chemical stimulation of NMDA receptors in the rat striatum. The application of NMDA caused the appearance of a sharp and transient oxidation signal. Concentration-response studies (10–500 μM) indicated an EC50 of 48 μM. The NMDA-induced amperometric signal was suppressed by focal application of the nitric-oxide synthase inhibitor l-nitro-arginine methyl ester (l-NAME, 100 μM) or d-(-)-2-amino-5-phosphonopentanoic acid (AP-5, 100 μM) or by systemic injection of dizocilpine (1 mg/kg i.p.), drugs that, when given alone, had no effect on baseline oxidation current. Repeated injections of NMDA at short intervals (∼80 s) resulted in a progressive reduction of the amperometric signal with a decay half-life of 1.36 min. Sixty min after the last NMDA application the amperometric response was restored to initial levels. Finally, the coapplication of glycine (50 or 100 μM), which, when given alone had no effect, potentiated the NMDA-induced response. Thus, NMDA receptor-mediated activation of striatal NO· system shuts off quickly and undergoes rapid desensitization, suggesting a feedback inhibition of NMDA receptor function. To the extent of NO· release can represent a correlate of NMDA receptor activity, its amperometric detection could be useful to assess in vivo the state of excitatory transmission under physiological, pharmacological, or pathological conditions.
Footnotes
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This work was supported by Grant 9805108207 from Ministero dell'Istruzione, dell'Università e della Ricerca (to Z.L.R.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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DOI: 10.1124/jpet.103.061069.
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ABBREVIATIONS: NO·, nitrogen monoxide; NMDA, N-methyl-d-aspartate; NOS, nitric-oxide synthase; mCFE, carbon fiber microelectrode; PBS, phosphate-buffered saline; aCSF, artificial cerebrospinal fluid; AP-5, d-(-)-2-amino-5-phosphonopentanoic acid; l-NAME, Nω-nitro-l-arginine methyl ester; ANOVA, analysis of variance.
- Received October 7, 2003.
- Accepted December 31, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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