METABOLIC INHIBITION POTENTIATES AMPA-INDUCED CA2+ FLUXES AND NEUROTOXICITY IN RAT CEREBELLAR GRANULE CELLS

The effects of partial metabolic inhibition (induced by 2 h exposure t o low concentrations of cyanide (NaCN)) on the glutamate receptor agon ist pha-amino-3-hydroxy-5-methyl-3-isoxazolepropionate (AMPA)-induced excitotoxicity and elevation of free cytoplasmic Ca2+ levels ([Ca2+](i )) were studied in glucose-deprived primary cultures of cerebellar gra nule cells. Go-application of AMPA plus NaCN caused a marked increase of cell death, with morphological features of both necrotic and apopto tic cell death as estimated by the capacity of cultured cerebellar gra nule cells to metabolize (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetraz olium bromide into formazan (MTT method), and by measuring the amount of DNA fragmentation in neurons using an ELISA test for histone-bound DNA fragments, respectively. Cell morphology was assessed by confocal microscopy of propidium iodide-stained cultures. No toxic effects were observed when AMPA or a low concentration of NaCN (0.1-0.3 mM; in the presence of NMDA receptor antagonist MK-8011 10 mu M) were applied al one. The neurotoxic actions induced by AMPA plus NaCN were preceded an d accompanied by a significant elevation of [Ca2+](i), as well as by d epletion of neuronal ATP stores. The marked enhancement in the functio nal responsiveness of AMPA receptors in energetically compromised neur ons suggests that at least under certain conditions AMPA receptors may play an important role in excitotoxic processes which might be of rel evance for the slowly developing neuronal death seen in several neurod egenerative diseases. (C) 1998 Elsevier Science B.V.