The present study was designed to evaluate dopaminergic neuronal loss in the substantia nigra pars compact (SNpc) with immunohistochemical staining. C57BL/6 mice were intraperitoneally injected four times with 15 mg/kg 1methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), at 2 h intervals on 10 and 21 days, and 6, 12, 24 and 48 weeks of age. Animals were sacrificed 48 hours after the last injection. No change in the number of tyrosine hydroxylase (TH)positive neurons was observed in 10-and

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... old mice after MPTP treatment compared with their corresponding controls. In contrast, MPTP produced a loss of 20.3% of TH-positive neurons in 6 week-old mice, and further decreases with advancing age, i.e., 35.8%, 39.9% and 56.2% TH-positive neuronal loss at 12, 24 and 48 weeks of age, respectively. These results provide evidence of age-related susceptibility of C57BL/6 mice to MPTP using TH immunohistochemistry. However, we failed to observe apoptosis of neurons in SNpc of mice of all ages after a subacute protocol of MPTP treatment (30 mg/kg/day × 5days). (J Toxicol Pathol 2004; 17: 239-244)