Protective effect of riluzole on excitatory amino acid-mediated neurotoxicity in motoneuron-enriched cultures

Excitatory amino acid-mediated neurotoxicity was investigated in motoneuron-enriched cultures from fetal rats at 12-14 days of gestation. The cultures were mainly composed of differentiated motoneurons identified by choline acetyl transferase and calcitonin gene-related peptide (CGRP) immunoreactivity. Addition of glutamate (600 microM) to the conditioned medium induced no acute neuronal swelling. However, it was followed by a widespread neuronal degeneration over the next 24 h, accounting for 77% of the total cell number. Glutamate toxicity was dose dependent, with an EC50 around 300 microM. Treatment for 24 h with the agonists, N-methyl-D-aspartate (NMDA, 100 microM), kainate (500 microM) or RS-alpha-amino-3-hydroxy-5-methyl-4-isoxalopropionate (AMPA, 10 microM), also induced a significant cell loss. Riluzole (2 amino 6-trifluoromethoxybenzothiazole), a compound known to interfere with glutamatergic transmission pre- and postsynaptically, significantly reduced glutamate and NMDA neurotoxicity in a dose-dependent manner. These results suggest that a prolonged activation of one or more subtypes of ionotropic excitatory amino acid receptors can lead to motoneuron degeneration in vitro, and provide direct experimental evidence supporting the neuroprotective effect of riluzole in cultured motoneurons.