Prenatal and Postnatal Exposures to 1-Methyl-4-phenyl-1,2,3,6-tetra Hydropyridine (MPTP) Impaired Mouse Midbrain Dopamine System and May Produce a Predisposing and Inducing Model for Parkinson’s Disease

Abstract

Dopamine cell bodies in the substantia nigra of the midbrain and with their terminals projecting to the neostriatum form the nigrostriatum and these dopamine neurons degenerate in Parkinson’s disease (PD). Based on metabolic and func- tional specialization of the cell bodies versus the axon terminals, the level and disposition of dopamine, its metabolites and enzymes are different in both regions and are likely to be affected differently in PD. We examined changes in the midbrain dopamine system following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to test the hypothesis that a predisposing/sensitization stage and a inducing/precipitating stage underlie PD. Pregnant mice were treated with a low dose of MPTP during gestation days 8 - 12 to model the predisposing/sensitization stage, by interrupting the fetal mid- brain dopamine system during its neurogenesis. For the inducing/precipitating stage, the 12-weeks offspring were ad- ministered MPTP. The prenatal-MPTP offspring appear normal, but midbrain dopamine, 3,4-di-hydroxy-phenyl-acetic- acid, 3-methoxytyramine, tyrosine-hydroxylase and L-aromatic-amino-acid-decarboxylase, were reduced by 49.6%, 48%, 54%, 20.9% and 25%. Postnatal-MPTP of 10, 20, 30 mg/kg administered to the prenatal-PBS vs prenatal-MPTP offspring reduced midbrain dopamine by 43.6%, 47.2%, 70.3% vs 85.4%, 89.1%, 95.2%; tyrosine-hydroxylase by 30%, 63%, 81% vs 30.7%, 70.4%, 91.4%; L-aromatic-amino-acid-decarboxylase by 0%, 2%, 40% vs 32%, 40%, 58%. The prenatal-MPTP may render the DA system sensitive by causing sub-threshold reduction of DA, its metabolites and en- zymes, enabling postnatal-MPTP to reduce dopamine above the 70% - 80% PD-inducing threshold. Thus, the study may produce a prenatal predisposing/sensitization and postnatal inducing/precipitation model of PD. It also indicates that some cases of PD may have a fetal basis, in which sub-threshold nigrostriatal impairments occur early in life and PD-symptoms are induced during aging by further insults to the dopaminergic system that would not cause PD symptoms in normal indi-viduals.