Cerebrospinal fluid from amyotrophic lateral sclerosis patients preferentially elevates intracellular calcium and toxicity in motor neurons via AMPA/kainate receptor

Several lines of evidence in the literature purport the contribution of glutamate mediated excitotoxicity in the etiology of amyotrophic lateral sclerosis (ALS) but the cellular mechanisms responsible for selective loss of motor neurons are still obscure. Elevation of intracellular Ca2+ is considered as the early event in glutamate mediated cell injury. We have studied the changes in [Ca2+]i and cytotoxicity in motor neurons and other spinal neurons in culture upon exposure to cerebrospinal fluid (CSF) from ALS patients. CSFs from 20 ALS patients and 20 disease control patients were examined. Eighteen out of twenty (90%) ALS-CSF samples induced a transient but pronounced elevation of [Ca2+]i in neurons, whereas only 1/20 (5%) sample from disease control patients induced a marginal elevation of [Ca2+]i. Strikingly the [Ca2+]i rise was 2-3-fold higher and longer lasting in motor neurons in comparison to the other spinal neurons. Exposure of cells to ALS-CSF drastically decreased the survival rate of motor neurons to 32.26 ± 2.06% whereas a moderate decrease was observed in case of other spinal neurons (67.90 ± 2.04%). In cultures treated with disease control CSF, a small decrease was observed in the survival rate with 80.14 ± 2.00% and 90.07 ± 1.37% survival of motor neuron and other spinal neurons respectively. The AMPA/kainate receptor antagonist NBQX rendered significant protection against the ALS-CSF induced Ca2+ influx and neurotoxicity while the NMDA receptor antagonist APV showed a mild effect. Our data demonstrate that the exposure of spinal cord neurons to ALS-CSF differentially elevates [Ca2+]i and neurotoxicity in motor neurons by activation of glutamate receptors, the AMPA/kainate receptor playing the major role.