Ca2+-Independent Excitotoxic Neurodegeneration in Isolated Retina, an Intact Neural Net: A Role for Cl− and Inhibitory Transmitters
- Departments of 1Ophthalmology and Visual Sciences (Q.C., P.D.L., C.R.), 2Psychiatry (Q.C., J.W.O., T.A.), and 3Anatomy and Neurobiology (P.D.L., C.R.), Washington University School of Medicine, St. Louis, Missouri 63110
Abstract
Rapidly triggered excitotoxic cell death is widely thought to be due to excessive influx of extracellular Ca2+, primarily through the N-methyl-d-aspartate subtype of glutamate receptor. By devising conditions that permit the maintenance of isolated retina in the absence of Ca2+, it has become technically feasible to test the dependence of excitotoxic neurodegeneration in this intact neural system on extracellular Ca2+. Using biochemical, Ca2+ imaging, and electrophysiological techniques, we found that (1) rapidly triggered excitotoxic cell death in this system occurs independently of both extracellular Ca2+ and increases in intracellular Ca2+; (2) this cell death is highly dependent on extracellular Cl−; and (3) lethal Cl− entry occurs by multiple paths, but a significant fraction occurs through pathologically activated γ-aminobutyric acid and glycine receptors. These results emphasize the importance of Ca2+-independent mechanisms and the role that local transmitter circuitry plays in excitotoxic cell death.
Footnotes
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Send reprint requests to: Carmelo Romano, Ph.D., Department of Ophthalmology & Visual Sciences, Campus Box 8096, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110. E-mail: romano{at}am.seer.wustl.edu
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This work was supported by Grants EY08089, EY08922, EY09370, EY02687, and DA07261 and an unrestricted grant from Research to Prevent Blindness, Inc.
- Abbreviations:
- NMDA
- N-methyl-d-aspartate
- GABA
- γ-aminobutyric acid
- KA
- kainic acid
- EGTA
- ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- AMPA
- α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
- DIDS
- 4,4′-diisothiocyanatostilbene-2,2′-disulfonate
- LDH
- lactate dehydrogenase
- BSS
- balanced salt solution
- BAPTA
- 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid
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- Received August 4, 1997.
- Accepted November 26, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
