N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) affects locomotor activity without producing a nigrostriatal lesion in the rat

Drug addicts abusing heroin substitutes contaminated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and perhaps those who work with this substance, may develop symptoms similar to those seen in Parkinson's disease [7, 12, 13]. We describe the results of a study in which rats were given daily injections of MPTP for two weeks. A progressive suppression of activity was seen, but the subjects rapidly recovered when treatment ceased. The animals were then injected with D-amphetamine or apomorphine; the former drug enhanced activity, to levels seen in control (non-MPTP treated) subjects. Apomorphine had no effect, either on control or MPTP-treated subjects. The effects of acute (0, 2.5, 5.0 and 10.0 mg per rat) administration of MPTP were also studied. The two lower doses significantly decreased activity, but the highest dose did not. Histological examination showed that 2 weeks' treatment with MPTP did not produce neuronal degeneration in the pars compacta of the substantia nigra (SN). In these animals, there were no changes in levels of dopamine, 5-hydroxytryptamine, or their metabolites in either the SN or the caudate nucleus. MPTP had no effect on the levels of neurotensin, somatostatin and substance P in several brain areas. It is concluded that MPTP has reliable effects on locomotor activity in rats without producing measurable histological or neurochemical changes in the nigrostriatal dopaminergic system.