Levels of Endogenous Adenosine in Rat Striatum. I. Regulation by Ionotropic Glutamate Receptors, Nitric Oxide and Free Radicals1
- Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Manitoba, R3E 0T6, Canada
Abstract
Glutamate release after ischemia, hypoxia and seizure activity plays an important role in stimulating adenosine production and release. We characterized the ionotropic glutamate receptor subtype that regulates adenosine levels in vivo and investigated the role of nitric oxide and free radicals in mediating N-methyl-d-aspartate (NMDA)-induced increases in adenosine levels. Rats received unilateral intrastriatal injections and were sacrificed 15 min postinjection by high-energy focused microwave irradiation (10 kW, 1.25 s). Adenosine levels were measured by high-performance liquid chromatography in ipsilateral and contralateral striata. NMDA and kainic acid dose-dependently increased levels of adenosine whereas (±)-α-amino-3-hydroxy-5-methyl-4-isoxazol proprionic acid had no effect. The NMDA- and kainic acid-induced increases were blocked by dizocilpine, and the kainic acid response was decreased by 6-cyano-7-nitroquinoxaline-2,3-dione. The effects of NMDA and kainic acid on levels of adenosine were not additive. Intrastriatall-arginine decreased, and the nitric oxide synthase inhibitor, NG-nitro-l-arginine methyl ester, increased basal adenosine levels. Coadministration of NMDA withl-arginine or NG-nitro-l-arginine methyl ester did not significantly affect NMDA-induced increases in levels of adenosine. N-Tert-butyl-phenylnitrone, a free radical scavenger, reversed l-arginine-induced decreases and NMDA-induced increases in levels of adenosine. Together, these results indicate that NMDA-type ionotropic receptors play an important role in regulating in vivo levels of adenosine in rat striatum and that free radicals, but not nitric oxide, apparently are involved in NMDA-induced increases in levels of adenosine. Conversely, nitric oxide, but not free radicals, apparently exert tonic control over basal levels of endogenous adenosine.
Footnotes
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Send reprint requests to: Dr. J. D. Geiger, Department of Pharmacology and Therapeutics, University of Manitoba, 753 McDermot Avenue, Winnipeg, Manitoba, R3E 0T6 Canada.
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↵1 These studies were supported by a grant from the Medical Research Council of Canada (to J.D.G.).
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↵2 Recipient of a Medical Research Council of Canada Studentship. Current address: Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599.
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↵3 Recipient of a National Science and Engineering Council Studentship award.
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↵4 Recipient of a Medical Research Council of Canada Scientist award.
- Abbreviations:
- AMPA
- (±)-α-amino-3-hydroxy-5-methyl-4-isoxazol proprionic acid
- CNQX
- 6-cyano-7-nitroquinoxaline-2,3-dione
- l-NAME
- NG-nitro-l-arginine methyl ester
- NMDA
- N-methyl-d-aspartate
- NO
- nitric oxide
- NOS
- nitric oxide synthase
- PBN
- N-tert-butyl-phenylnitrone
- HPLC
- high-performance liquid chromatography
- HEPES
- N-2-hydroxyethylpiperaine-N′-ethanesulfonic acid
- EDTA
- ethylenediaminetetraacetic acid
- CNS
- central nervous system
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- Received August 28, 1997.
- Accepted January 23, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
