The role of excitatory amino acid transmission in cyanide-induced neuronal injury
Abstract
The objective of the present studies was to examine the role of excitatory amino acid transmission in cyanide-mediated neuronal injury. Initially, the effect of cyanide on endogenous glutamate release from mouse cortical, cerebellar and hippocampal slices was studied. Incubation of slices with cyanide over a 30 min period resulted in extracellular accumulation of glutamate which was decreased in the absence of calcium in the incubation media. When glutamate release was continuously monitored by fluorometry, cyanide initiated a rapid release of glutamate which was independent of extracellular calcium. Next cyanide-induced alterations of cytosolic free calcium levels and cytotoxicity were examined in primary cultures of rat hippocampus. Cytosolic free calcium ( (Ca$\sp{2+}\rbrack\sb{\rm i}$) levels were measured in hippocampal neurons using the fluorescent probe, fura-2. A concentration-dependent rise in (Ca$\sp{2+}\rbrack\sb{\rm i}$ occurred rapidly following exposure of cells to 0.5-10 mM cyanide. Ca$\sp{2+}$ elevation produced by cyanide was blocked by removal of Ca$\sp{2+}$ from the external medium or by pretreatment with the N-methyl- scD-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonovalerate (APV). Cyanide enhanced the NMDA-induced increase in (Ca$\sp{2+}\rbrack\sb{\rm i}$ and NMDA-activated current in the presence but not in the absence of extracellular Mg$\sp{2+}$. Cyanide produced a concentration-dependent cytotoxicity in hippocampal cultures following 18 hrs of incubation. This was not blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an antagonist of non-NMDA receptors, but completely blocked by APV and simultaneous exposure to CNQX and APV did not offer added protection. Cyanide-induced cytotoxicity was potentiated by glyburide. Finally, cyanide did not alter the binding of labelled ((+)-11-dihydro-5H-dibenzo (a,d) cyclohepten, 5,10-imine maleate) (MK-801) to rat brain membranes. These results suggest that excitotoxicity produced by the activation of NMDA receptors may be a key event by which cyanide induces neuronal injury in hippocampal cultures.
Degree
Ph.D.
Advisors
Isom, Purdue University.
Subject Area
Pharmacology|Toxicology|Neurology
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