title: Endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the development of nigro-striatal damage induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice.
abstract: We combined the use of knock-out mice and subtype-selective antagonists [2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-(2-phenylethenyl)-pyridine (SIB1893)] to examine whether endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the pathophysiology of nigro-striatal damage in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. High doses of MPTP (four injections of 20 mg/kg, i.p., every 2 hr) induced a high mortality rate and a nearly total degeneration of the nigro-striatal pathway in wild-type mice. mGlu5 knock-out mice were less sensitive to MPTP toxicity, as shown by a higher survival and a milder nigro-striatal damage. Protection against MPTP (80 mg/kg) toxicity was also observed after MPEP injections (four injections of 5 mg/kg, i.p., 30 min before each MPTP injection). MPEP treatment did not further increase neuroprotection against 80 mg/kg of MPTP in mGlu5 knock-out mice, indicating that the drug acted by inhibiting mGlu5 receptors. In wild-type mice, MPEP was also neuroprotective when challenged against lower doses of MPTP (either 30 mg/kg, single injection, or four of 10 mg/kg injections). The action of MPEP was mimicked by SIB1893 but not by the mGlu1 receptor antagonist 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester. MPEP did not change the kinetics of 1-methyl-4-phenylpyridinium ion formation in the striatum of mice injected with MPTP. We conclude that mGlu5 receptors act as amplifiers of MPTP toxicity and that mGlu5 receptor antagonists may limit the extent of nigro-striatal damage in experimental models of parkinsonism.
authors.affiliation: Istituto Neurologico Mediterraneo Neuromed, 86077 Pozzilli, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Battaglia
authors.forename: Carla L
authors.initials: CL
authors.lastname: Busceti
authors.forename: Gemma
authors.initials: G
authors.lastname: Molinaro
authors.forename: Francesca
authors.initials: F
authors.lastname: Biagioni
authors.forename: Marianna
authors.initials: M
authors.lastname: Storto
authors.forename: Francesco
authors.initials: F
authors.lastname: Fornai
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Nicoletti
authors.forename: Valeria
authors.initials: V
authors.lastname: Bruno
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000378:metabolism; D015655:1-Methyl-4-phenylpyridinium / Q000378:metabolism / Q000493:pharmacokinetics; D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006719:Homovanillic Acid / Q000378:metabolism; D020267:MPTP Poisoning / Q000139:chemically induced / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D018345:Mice, Knockout; D018696:Neuroprotective Agents / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013378:Substantia Nigra / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015996:Survival Rate; D013574:Synaptosomes / Q000378:metabolism
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018696:Neuroprotective Agents; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C120148:SIB 1893; D015102:3,4-Dihydroxyphenylacetic Acid; C121465:6-methyl-2-(phenylethynyl)pyridine; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D015655:1-Methyl-4-phenylpyridinium; D004298:Dopamine; D006719:Homovanillic Acid