THE DIETARY EXCITOTOXINS BETA-N-METHYLAMINO-L-ALANINE AND BETA-N-OXALYLAMINO-L-ALANINE INDUCE NECROTIC-LIKE AND APOPTOTIC-LIKE DEATH OF RATCEREBELLAR GRANULE CELLS

The neurotoxic properties of the dietary excitotoxins beta-N-methylami no-L-alanine and beta-N-oxalylamino-L-alanine have been studied in rat cerebellar granule cells and compared with those of glutamate. Glutam ate caused dose-dependent death of cerebellar granule cells after a 30 -min exposure when viability was assessed 24 h later. beta-N-Methylami no-L-alanine and beta-N-oxalylamino-L-alanine, however, were toxic onl y after 24 or 48 h of exposure. The neurotoxic effects of beta-N-methy lamino-L-alanine were blocked by D(-)2-amino-5-phosphonopentanoic acid , and those of beta-N-oxalylamino-Lalanine were blocked by kynurenic a cid, which demonstrated that these excitotoxins caused cerebellar gran ule cell death through the activation of glutamate receptors. The feat ures of this death were examined morphologically (fluorescent dyes, el ectron microscopy) and biochemically (conventional agarose gel electro phoresis, effect of aurintricarboxylic acid). Characteristics of apopt osis were identified by transferring cerebellar granule cells from a h igh K+ (30 mM)- to a low K+ (10 mM)-containing medium. In cerebellar g ranule cells exposed to beta-N-methylamino-L-alanine or beta-N-oxalyla mino-L-alanine (3 mM), hallmarks of necrotic-and apoptotic-like death were observed at various time points over a 72-h period. Therefore, in cerebellar granule cells, beta-N-methylamino-L-alanine and beta-N-oxa lylamino-L-alanine induce death over 12-72 h of exposure via a mechani sm that involves both necrotic-and apoptotic-like cell death.