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The evolution of nigrostriatal neurochemical changes in the MPTP-treated squirrel monkey
I Irwin1, L E DeLanney, L S Forno
1Veteran's Administration Medical Center, Palo Alto, CA 94304.
Abstract:
The MPTP-treated monkey has become an important model for the study of Parkinson's disease. However, studies on the acute evolution of the neurotoxic effects of MPTP in primates are lacking. In the present study, 17 squirrel monkeys were given a single subcutaneous injection of MPTP (2.5 mg/kg). The behavioral effects and the concentrations of dopamine (DA), dihydroxyphenylacetic acid and homovanillic acid were determined in caudate, putamen and substantia nigra 1, 3, 5 (n = 3/time point) and 10 days (n = 6) after drug administration. Two animals were studied neuropathologically 8 and 9 days after MPTP. Profound parkinsonism was evident in all animals after 1 day and neuropathological examination revealed severe nerve cell destruction in the substantia nigra. Surprisingly, although 50-75% reductions in nigral DA were observed 1 and 3 days after MPTP, caudate DA was not reduced and putaminal DA was increased at these time points. The temporal sequence of these events differs markedly from that which occurs in the MPTP-treated mouse and suggests that, in the monkey, nigral cell bodies may represent an important initial site of MPTP-induced damage. Five and 10 days after MPTP, nigral DA depletions remained greater than 60% of control and striatal DA was reduced 50-85%. At these time points, the putamen was always more affected than the caudate. This interregional pattern of striatal DA deficits is similar to that seen in idiopathic Parkinson's disease.
Insights
The MPTP primate model shows acute Parkinson's disease effects, with initial substantia nigra damage preceding striatal dopamine loss. This differs from mice, highlighting nigral cell bodies as the primary MPTP target in primates.
Area of Science:
- Neuroscience
- Toxicology
- Primate Models
Background:
- Parkinson's disease research heavily utilizes the MPTP-treated monkey model.
- Limited studies exist on the acute neurotoxic effects of MPTP in primates.
Purpose of the Study:
- To investigate the acute time course of MPTP-induced neurotoxicity in squirrel monkeys.
- To compare the temporal progression of MPTP effects in primates versus rodents.
Main Methods:
- 17 squirrel monkeys received a single MPTP injection (2.5 mg/kg).
- Behavioral, biochemical (dopamine levels), and neuropathological assessments were performed at multiple time points (1-10 days).
Main Results:
- Profound parkinsonism and substantia nigra cell destruction observed within 1 day.
- Initial nigral dopamine reduction (50-75%) at 1-3 days, with no caudate reduction and putaminal increase.
- Later striatal dopamine deficits (50-85%) by 5-10 days, with putamen more affected than caudate.
- Temporal pattern differs significantly from MPTP-treated mice.
Conclusions:
- Substantia nigra neurons are the primary initial site of MPTP toxicity in primates.
- The observed striatal dopamine deficit pattern resembles idiopathic Parkinson's disease.
- This study refines the MPTP primate model for Parkinson's disease research.