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Chronic exposure to low doses of MPTP. I. Cognitive deficits in motor asymptomatic monkeys
J S Schneider1, C J Kovelowski
1Department of Neurology, Hahnemann University School of Medicine, Philadelphia, PA 19102.
Abstract:
Cognitive deficits which may occur following chronic low-dose exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were studied in monkeys who remained motor asymptomatic for parkinsonism throughout the study. The tasks used to assess cognitive functioning are those which have proved in the past to be sensitive to disruption of frontal cortical and or striatal integrity (delayed response and delayed alternation) or sensitive to inferior temporal lobe dysfunction (visual pattern discrimination). Since Parkinson's disease patients have been described as exhibiting frontal signs, we were interested to examine whether MPTP-treated monkeys might exhibit deficits on frontally-mediated tasks, without the confound of motor disturbances. We found that macaque nemistrina monkeys exposed to cumulative doses of 14.94-75.42 mg of MPTP over periods ranging from 5 to 13 months never developed parkinsonian motor signs. However, all 4 animals examined showed significant post-MPTP deficits in delayed response and delayed alternation performance, while visual pattern discrimination performance remained intact. These animals also developed other behavioral problems including irritability and decreased attentiveness. These results show that MPTP can cause specific cognitive deficits independent of the motor deficits which can be produced by this toxin.
Insights
Chronic low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure caused cognitive deficits in monkeys. These deficits occurred without motor symptoms, indicating MPTP
Area of Science:
- Neuroscience
- Toxicology
- Primate Behavior
Background:
- Chronic low-dose exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can induce neurological deficits.
- Parkinson's disease is associated with cognitive impairments, particularly those mediated by frontal cortical and striatal pathways.
- Investigating MPTP's effects in the absence of motor symptoms is crucial for understanding toxin-induced cognitive dysfunction.
Purpose of the Study:
- To investigate cognitive deficits following chronic low-dose MPTP exposure in motor-asymptomatic monkeys.
- To determine if MPTP selectively impairs cognitive functions mediated by frontal cortical and striatal areas.
- To differentiate cognitive effects from motor symptoms in MPTP neurotoxicity.
Main Methods:
- Macaque nemistrina monkeys were exposed to cumulative doses of MPTP (14.94-75.42 mg) over 5-13 months.
- Cognitive functions were assessed using delayed response, delayed alternation, and visual pattern discrimination tasks.
- Behavioral observations monitored for motor symptoms, irritability, and attentiveness.
Main Results:
- MPTP-treated monkeys did not develop parkinsonian motor signs.
- All MPTP-exposed animals exhibited significant deficits in delayed response and delayed alternation tasks.
- Visual pattern discrimination performance remained intact, suggesting specific cognitive impairments.
Conclusions:
- MPTP can induce specific cognitive deficits independent of motor impairments.
- Frontal cortical and striatal functions are particularly vulnerable to chronic low-dose MPTP exposure.
- These findings provide a model for studying toxin-induced cognitive dysfunction in the absence of motor deficits.