EXCITOTOXIC CELL-DEATH AND DELAYED RESCUE IN HUMAN NEURONS DERIVED FROM NT2 CELLS

The excitotoxic response of NT2-N cells, a clonal line of human terato carcinoma cells that are terminally differentiated into neuron-like ce lls, was examined using several endpoints. A 15 min exposure to glutam ate produced a dose-dependent toxicity with a maximal cell loss of 80- 90% in 6 week old cells. The rapidly triggered excitotoxicity induced by glutamate was blocked by NMDA selective antagonists, was calcium de pendent and pH sensitive and could be mimicked by NMDA but not by non- NMDA agonists, AMPA, kainate or quisqualate. The non-NMDA agonists how ever caused toxicity on prolonged exposure. The NMDA receptor modulato rs glycine and spermidine enhanced glutamate-mediated toxicity whereas ifenprodil potently and completely inhibited toxicity suggesting that the toxic response is mediated by the NR1/NB2(B) combination of NMDA subunits. These cells can be rescued from death up to 1 hr after remov al of glutamate by NMDA receptor blockade, removal of extracellular Ca 2+ or lowering of pH. The extent of rescue is directly related to the time elapsed before intervention. Blockade of NMDA receptor activity f or 1 hr immediately after removal of glutamate is both necessary and s ufficient for complete rescue. Glutamate-mediated toxicity was not pre vented by nitric oxide synthase inhibitors nor was nitric oxide syntha se detected in NT2-N cells indicating that nitric oxide is not require d for glutamate-mediated excitotoxicity. In summary, NT2-N cells exhib it a robust excitotoxic response and represent a novel model system in which to study the molecular basis of excitotoxic cell death.