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1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication of mice is a standard model of Parkinson's disease (PD). However, it does not reproduce functionally PD. Given the occurrence of PD during aging, symptoms might only be detected in MPTP-intoxicated mice after aging. To address this, mice injected with MPTP at 2.5 months were followed up to a maximum age of 21 months. There was no loss of dopamine cells with aging in control mice; moreover, the initial post-MPTP intoxication decrease in dopamine cell was no longer significant at 21 months. With aging, striatal dopamine level remained constant, but concentrations of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were markedly reduced in both groups. There was also a late impairment of fine motor skills. After MPTP intoxication, hyperactivity was immediately detected and it became greater than in control mice from 14 months of age; fine motor skills were also more impaired; both these symptoms were correlated with striatal dopamine, DOPAC and HVA concentrations. In bothgroups, neither motor symptoms nor dopamine changes worsened with age. These findings do not support the notion that PD develops with age in mice after MPTP intoxication and that the motor deficits seen are because of an aging process., (© 2012 The Authors. Journal of Neurochemistry © 2012 International Society for Neurochemistry.)

Epidemiological studies have found a negative association between cigarette smoking and Parkinson's disease (PD). In order to analyze the putative neuroprotective effect of cigarette smoke and nicotine, one of its major constituents, we examined their effects in an animal model of PD provoked by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. Two groups of mice were chronically exposed to cigarette smoke (a low exposure subgroup and a high exposure subgroup; 5 exposures per day at 2-h intervals), two other groups received nicotine treatment (two doses tested 0.2 and 2 mg/kg, 5 injections i.p. per day at 2-h intervals) and one group placebo. On day 8 after the beginning of the treatment, 4 injections of MPTP hydrochloride (15 mg/kg, i.p., at 2-h intervals) or saline were administered to these animals. Nicotine and cotinine plasmatic concentration was quantified by the HPLC method, and degeneration of the nigrostriatal system was assessed by tyrosine hydroxylase (TH) immunohistochemistry. The loss of dopaminergic neurons induced by MPTP in the substantia nigra was significantly less severe in the chronic nicotine treatment groups (at 0.2 and 2 mg/kg) and the low exposure to cigarette smoke group than in the high exposure to cigarette smoke subgroup and the placebo treated subgroup. In contrast, no preservation of TH immunostaining of nerve terminals was observed in the striatum in any group. This suggests that nicotine and low exposure to cigarette smoke may have a neuroprotective effect on the dopaminergic nigrostriatal system by an as yet unknown mechanism.