Pharmacological protection against the toxicity of [formula omitted] in immature rat cerebellar slices

Abstract

In order to delineate the pharmacological characteristics of the toxicity of N-methyl-D-aspartate (NMDA), slices of cerebellum from 7-day old rats were incubated with NMDA, together with various putative protective agents. These comprised three different groups: (i) a competitive receptor antagonist (kynurenic acid), (ii) direct (cobalt ions, flunarizine) and indirect (taurine) calcium entry blockers, (iii) cyclo-oxygenase inhibitors (indomethacin and acetylsalicylic acid) and a blocker of calcium-activated, neutral proteases (leupeptin). When the slices were incubated for 30 min in medium containing 100 μM NMDA, postmigratory granule cell nuclei were rounded and swollen. After 90 min of recovery in normal medium, the nuclei were pyknotic and the cells were irreversibly injured. As expected, these changes were completely blocked by kynurenate, indicating that NMDA receptors mediate the cell death. Cobalt ions abolished the acute toxicity of NMDA, but after recovery, some granule cell nuclei were swollen. This effect could be attributed to the toxicity of cobalt ions and not to delayed toxicity of NMDA. The other inhibitors of the uptake of calcium, flunarizine and taurine, did neither affect acute nor persistent toxicity of NMDA. These results support the previous finding that the toxicity of NMDA is calcium-dependent and that organic calcium channel blockers are ineffective against NMDA-induced uptake of calcium. Leupeptin had no effect on the toxicity of NMDA, suggesting that calcium-activated proteolysis was not the crucial event in excitotoxic necrosis. Indomethacin, but not acetylsalicylic acid, prevented neuronal degeneration provoked by NMDA, but only in very large concentrations (⩾ 100 μM). This finding opens the possibility that synthesis of prostaglandins is responsible for the deleterious actions of a raised intracellular level of calcium. However, as the other cyclo-oxygenase inhibitor (acetylsalicylic acid) did not exert a similar effect, the significance of the result awaits further investigation.