title: Inhibition by dizocilpine (MK-801) of striatal dopamine release induced by MPTP and MPP+: possible action at the dopamine transporter.
abstract: 1. The NMDA-type glutamate receptor antagonist, dizocilpine (MK-801) can protect against neurotoxicity associated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its principal metabolite, the 1-methyl-4-phenylpyridinium ion (MPP+). It has been suggested that these neurotoxic effects may be mediated by release of excitatory amino acids, but possible alternative mechanisms have been little investigated. 2. MPTP and MPP+ (0.1-1000 microM) were tested in superfused rat striatal synaptosomes preloaded with [3H]-dopamine. Both MPTP (10 microM and higher) and MPP+ (1 microM and higher) evoked an immediate and concentration-dependent release of [3H]-dopamine. The maximal effect exceeded that achievable with nicotine. For subsequent experiments, submaximal concentrations of MPTP (50 microM) and MPP+ (10 microM) were tested. 3. MK-801 (0.1-100 microM) inhibited responses to MPTP (50 microM) and MPP+ (10 microM) in a concentration-dependent manner. However, further tests of NMDA-type glutamate receptor involvement proved negative. Responses to MPTP or MPP+ were unaffected by the omission of Mg2+ or Ca2+ and were not reduced by the NMDA receptor antagonists, AP-7 (200 microM) and kynurenic acid (300 microM). In this assay, N-methyl-D-aspartate (even in the absence of Mg2+ and with added glycine and strychnine) did not evoked [3H]-dopamine release. 4. In crude membrane preparations of rat cerebral cortex, MPTP and MPP+ inhibited high-affinity [3H]-nicotine binding to nicotinic cholinoceptors (IC50 1.8 microM and 26 microM, respectively). 5. [3H]-dopamine release evoked by nicotine (1 microM) was blocked by the nicotinic antagonists,mecamylamine and chlorisondamine, and by MK-801 (all at 100 micro M); K+-evoked release was not affected. Release evoked by MPTP and MPP+ was significantly attenuated by MK-801 but not by mecamylamine or chlorisondamine.6. At a high concentration (1O I1M), the selective dopamine uptake inhibitor, nomifensine, completely blocked [3HJ-dopamine release evoked by amphetamine 0.3 microM and MPP+ 10 flM, attenuated responses to MPTP 50 AM and did not affect responses to 12 mM K+. MK-801 100 microM evinced a similar profile but was less effective.7. MK-801 inhibited [3H]-dopamine uptake in striatal synaptosomes with an IC5o of 115 M.8. It is concluded that high concentrations of MK-801 inhibit the acute dopamine release evoked by MPTP and MPP+ in synaptosomes. This antagonism may occur, at least in part, through inhibition of the cell membrane dopamine transporter. MPTP and MPP+ also appear to interact with brain nicotinic cholinoceptors but the functional consequences of this interaction are not yet clear.
authors.affiliation: Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada.
authors.forename: P B
authors.initials: PB
authors.lastname: Clarke
authors.forename: M
authors.initials: M
authors.lastname: Reuben
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015655:1-Methyl-4-phenylpyridinium / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003913:Dextroamphetamine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000494:pharmacology; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D009538:Nicotine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018492:Dopamine Antagonists; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D016291:Dizocilpine Maleate; D009538:Nicotine; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D015655:1-Methyl-4-phenylpyridinium; D003913:Dextroamphetamine; D004298:Dopamine