Characterization of glutamate toxicity in cultured rat cerebellar granule neurons at reduced temperature.
We have defined conditions whereby glutamate becomes toxic to isolated cerebellar granule neurons in a physiologic salt solution (pH 7.4). In the presence of a physiologic Mg++ concentration, acute glutamate excitotoxicity manifests only when the temperature was reduced from 37 degrees C to 22 degrees C. In contrast to glutamate, N-methyl-D-aspartate (NMDA) was nontoxic at either temperature at concentrations as high as 1 mM. Glycine strongly potentiated both the potency and efficacy of glutamate but revealed only a modest NMDA response. The non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxalinedione (CNQX), potently protected against glutamate challenge, although the contribution of antagonism at strychnine-insensitive glycine sites could not be excluded. To further characterize the non-NMDA receptor contribution to the excitotoxic response, the promiscuity of glutamate interaction with ionotropic receptors was simulated by exposing neurons to NMDA in the presence of non-NMDA receptor agonists. NMDA toxicity was potentiated four- to sevenfold when non-NMDA receptors were coactivated by a subtoxic concentration of AMPA, kainate, or domoate. These results suggest that non-NMDA receptor activation participates in the mechanism of acute glutamate toxicity by producing neuronal depolarization (via sodium influx), which in turn promotes the release of the voltage-dependent magnesium blockade of NMDA receptor ion channels.
Berman
F W
FW
College of Pharmacy and Toxicology Program, Oregon State University, Corvallis 97331, USA.
Murray
T F
TF
D000818:Animals; D002452:Cell Count; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects*; D003080:Cold Temperature / Q000009:adverse effects*; D004357:Drug Synergism; D018698:Glutamic Acid / Q000633:toxicity*; D005998:Glycine / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000187:drug effects / Q000378:metabolism; D016202:N-Methylaspartate / Q000633:toxicity; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism
D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D007770:L-Lactate Dehydrogenase; D005998:Glycine