Effects of 1‐Methyl‐4‐Phenyl‐ 1,2,3,6‐Tetrahydropyridine and 1 ‐Methyl‐4‐Phenylpyridinium Ion on ATP Levels of Mouse Brain Synaptosomes

Abstract

Mouse brain synaptosomes, essentially devoid of mitochondrial contamination, were used as a model to study the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its toxic metabolite 1-methyl-4-phenylpyridinium ion (MPP⁺) on the levels of ATP of neuronal terminals. Similar to known inhibitors of ATP synthesis, both MPTP and MPP⁺ caused a dramatic depletion of synaptosomal ATP. This depletion was dose dependent and occurred as a relatively early biochemical event in the absence of any apparent damage to synaptosomal membranes. MPP⁺ was more effective than its parent compound in decreasing ATP; it induced a significant loss at concentrations (10–100 γM) similar to those it reaches in the brain in vivo. MPTP-induced ATP depletion was completely prevented by the monoamine oxidase B inhibitor deprenyl, which, on the contrary, was ineffective against MPP⁺. As expected in view of the heterogeneous population of nerve terminals present in our synaptosomal preparations, the catecholamine uptake blocker mazindol did not significantly affect the ATP loss caused by both compounds. Data indicate that (1) administration of MPTP may cause a depletion of ATP within neuronal terminals resulting from the generation of MPP⁺, and (2) exposure to the levels of MPP⁺ reached in vivo may cause biochemical changes that are nonselective for dopaminergic terminals.