SOD1 and amyotrophic lateral sclerosis: However, Glu transport defects do not seem to be the only origin of excessive extracellular Glu, since it has been shown that the spontaneous release of Glu and that induced by depolarization [25], by group I metabotropic Glu receptors (mGluRs) [26] or GABA and glycine hetero-transporter [27,28,29] activation, is abnormal in the mouse model of human ALS expressing a high copy number of mutant human superoxide dismutase 1 (SOD1) with a Gly93Ala substitution (SOD1G93A) [30].