TRIHEXYPHENIDYL POTENTIATION OF L-DOPA - REDUCED EFFECTIVENESS 3 YEARS LATER IN MPTP-INDUCED CHRONIC HEMIPARKINSONIAN MONKEYS

The effects of a combination of trihexyphenidyl and L-DOPA methyl este r given i.m. were studied 3-5 years after MPTP induced hemiparkinsonis m in five female adult Macaca nemistrina monkeys. Three years later, t hese studies were repeated to determine if the drug combination was eq ually effective. Although the combination of trihexyphenidyl and L-DOP A produced potentiation in both studies, 3 years later it was quantita tively less. This was due primarily to the reduced effectiveness of L- DOPA methyl ester in II dose of 12.5 mg/kg i.m. Even though the combin ation was less effective ire subsequent years, the animals continued t o show the same clinical signs of hemiparkinsonism. Reduced effectiven ess of the drug combination does not appear to be due to a lessening o f MPTP-induced hemiparkinsonism, but rather to the reduced effectivene ss of L-DOPA (C) 1998 Academic Press.