title: Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis.
abstract: Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.
authors.affiliation: Department of Experimental Medicine, University of Genova, Genova, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Milanese
authors.forename: Simona
authors.initials: S
authors.lastname: Zappettini
authors.forename: Franco
authors.initials: F
authors.lastname: Onofri
authors.forename: Laura
authors.initials: L
authors.lastname: Musazzi
authors.forename: Daniela
authors.initials: D
authors.lastname: Tardito
authors.forename: Tiziana
authors.initials: T
authors.lastname: Bonifacino
authors.forename: Mirko
authors.initials: M
authors.lastname: Messa
authors.forename: Giorgio
authors.initials: G
authors.lastname: Racagni
authors.forename: Cesare
authors.initials: C
authors.lastname: Usai
authors.forename: Fabio
authors.initials: F
authors.lastname: Benfenati
authors.forename: Maurizio
authors.initials: M
authors.lastname: Popoli
authors.forename: Giambattista
authors.initials: G
authors.lastname: Bonanno
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000704:Analysis of Variance; D000818:Animals; D017849:Animals, Inbred Strains; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D018377:Neurotransmitter Agents / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D013116:Spinal Cord / Q000473:pathology / Q000648:ultrastructure; D013482:Superoxide Dismutase / Q000235:genetics; D016704:Synapsins / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D014316:Tritium / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D018377:Neurotransmitter Agents; D016704:Synapsins; D014316:Tritium; D018698:Glutamic Acid; D015759:Ionomycin; D011189:Potassium Chloride; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2