Glutamate release induced by activation of glycine and GABA transporters in spinal cord is enhanced in a mouse model of amyotrophic lateral sclerosis.
Amyotrophic lateral sclerosis is a progressive and fatal neurodegenerative disease, involving both upper and lower motor neurons, the cause of which is obscure, although glutamate (GLU)-induced excitotoxicity has been suggested to play a major role. We studied the release of [3H]d-aspartate ([3H]d-ASP) and endogenous glutamate evoked by glycine (GLY) or GABA from spinal cord synaptosomes in mice expressing a mutant form of human SOD1 with a Gly93Ala substitution ([SOD1-G93A(+)]), a transgenic model of amyotrophic lateral sclerosis, in mice expressing the non-mutated form of human SOD1 [SOD1+], and in non-transgenic littermates [SOD1(-)/G93A(-)]. In parallel experiments, we also studied the release of [3H]GABA evoked by GLY and that of [3H]GLY evoked by GABA. Mutant mice were killed at advanced phase of pathology or during the pre-symptomatic period. In SOD1(-)/G93A(-) or SOD1(+) mice GLY evoked [3H]d-ASP and [3H]GABA release, while GABA caused [3H]d-ASP, but not [3H]GLY, release. The GLY-evoked release of [3H]d-ASP, but not that of [3H]GABA, and the GABA-evoked [3H]d-ASP release, but not that of [3H]GLY, were more pronounced in SOD1-G93A(+) than in SOD1(+) or SOD1(-)/G93A(-) mice. Furthermore, the excessive potentiation of [3H]d-ASP by GLY or GABA was already present in asymptomatic 30-40 day-old SOD1-G93A(+) mice. The releases of endogenous glutamate and GABA also were enhanced by GLY and the GLY-evoked release of endogenous glutamate, but not of endogenous GABA, was higher in SOD1-G93A(+) than in control animals. Potentiation of the spontaneous amino acid release is likely to be mediated by activation of a GLY or a GABA transporter, since the effect of GLY was counteracted by the GLY transporter blocker glycyldodecylamide but not by the GLY receptor antagonists strychnine and 5,7-dichlorokynurenate while the effect of GABA was diminished by the GABA transporter blocker SKF89976-A but not by the GABA receptor antagonists SR9531 and CGP52432. It is concluded that the glutamate release machinery seems excessively functional in SOD1-G93A(+) animals.
Raiteri
Luca
L
Department of Experimental Medicine, Pharmacology and Toxicology Section, University of Genoa, 16148 Genoa, Italy.
Zappettini
Simona
S
Stigliani
Sara
S
Paluzzi
Silvio
S
Raiteri
Maurizio
M
Bonanno
Giambattista
G
D000465:Algorithms; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D013116:Spinal Cord / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics; D000072105:Superoxide Dismutase-1; D013574:Synaptosomes / Q000378:metabolism
D018076:DNA, Complementary; D050485:GABA Plasma Membrane Transport Proteins; D050487:Glycine Plasma Membrane Transport Proteins; C000606290:SOD1 protein, human; D018698:Glutamic Acid; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1