Domoic acid neurotoxicity in cultured cerebellar granule neurons is controlled preferentially by the NMDA receptor Ca²⁺ influx pathway

We have monitored real-time alterations in [Ca²⁺]_i in fluo-3-loaded cerebellar granule neurons exposed to domoate, and ascertained the influence of pharmacological blockers of various Ca²⁺ entry pathways on intracellular Ca²⁺ accumulation, excitatory amino acid (EAA) release and neuronal death. Domoate produced a rapid and concentration-dependent increase in [Ca²⁺]_i, the magnitude of which correlated closely with the severity of neuron loss. The increase in [Ca²⁺]_i was derived from activation of NMDA receptors, L-type voltage-sensitive calcium channels (VSCC) and the reversed mode of operation of the Na⁺/Ca²⁺ exchanger. When the level of neuroprotection conferred by pharmacological manipulation of these calcium entry pathways was regressed with the corresponding reductions in [Ca²⁺]_i load, it was observed that neuronal vulnerability is controlled preferentially by NMDA receptors. This observation is consistent with our previous study of brevetoxin-induced autocrine excitotoxicity and with the source specificity hypothesis of others [J. Neurochem. 71 (1998) 2349], which suggests that elevation of [Ca²⁺]_i in the vicinity of the NMDA receptor ion channel activates processes leading to neuronal death.