Parkinsonism produced by tetrahydroisoquinoline (TIQ) or the analogues

The effect of chronic administration of a probable endogenous dopaminergic neurotoxin, tetrahydroisoquinoline, has been examined on squirrel monkeys. Chronically administered TIQ produced motor symptoms similar to parkinsonism in squirrel monkeys even 7 days after discontinuation of TIQ and the symptoms were alleviated remarkably by L-DOPA treatment. Biochemical analysis of the brains of TIQ-treated monkeys revealed significant decrease in dopamine (DA) and total biopterin (BP) concentrations, and tyrosine hydroxylase (TH) activity in the substantia nigra. Morphological changes of the substantia nigra of mice were also analyzed. The effect of long-term administration of N-methyl-TIQ, N-methyl-TIQ+, and N-methyl-norsalsolinol on aged monkeys was described.