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Apparent unilateral visual neglect in MPTP-hemiparkinsonian monkeys is due to delayed initiation of motion
K S Bankiewicz1, E H Oldfield, R J Plunkett
1Surgical Neurology Branch, NINDS, National Institutes of Health, Bethesda, MD 20892.
Abstract:
Monkeys made hemiparkinsonian by infusion of a solution of MPTP into one carotid artery appeared to ignore food presented from the contralateral side. Initial observations suggested neglect of visual stimuli presented as fruit treats by automated delivery system in the half-field contralateral to MPTP treatment. Further studies in which fruit treats were left in the 'neglected' visual field indicated that this apparent neglect, unlike neglect attending cortical lesions, was rather a marked delay in initiating movements (unilateral hypokinesia). These observations may explain apparent subcortical neglect and are consistent with the known role of nigrostriatal dopaminergic neurones in movement regulation. This is a useful animal model in which difficulties in initiation of movement (hypokinesia). a cardinal symptom of Parkinson's disease, can be studied separately from other deficits in motor performance.
Insights
Monkeys with MPTP-induced hemiparkinsonism showed delayed movement initiation, not visual neglect, in the visual field opposite the lesion. This highlights a useful model for studying Parkinson's disease hypokinesia.
Area of Science:
- Neuroscience
- Primate Models
- Movement Disorders
Background:
- Parkinson's disease is characterized by hypokinesia, a difficulty in initiating movement.
- The nigrostriatal dopaminergic pathway plays a crucial role in regulating movement.
- MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is a neurotoxin used to create animal models of Parkinson's disease.
Purpose of the Study:
- To investigate the nature of apparent visual neglect in MPTP-treated monkeys.
- To determine if the observed deficit is true neglect or a motor initiation problem.
- To establish the utility of this model for studying Parkinson's disease hypokinesia.
Main Methods:
- Induction of hemiparkinsonism in monkeys via unilateral carotid artery infusion of MPTP.
- Observation of monkey behavior in response to visually presented food treats.
- Analysis of movement initiation latency in response to stimuli in different visual fields.
Main Results:
- MPTP-treated monkeys exhibited a marked delay in initiating movements towards food in the contralateral visual field.
- This delay, termed unilateral hypokinesia, was distinct from neglect seen in cortical lesions.
- The findings suggest a subcortical origin for the observed motor deficit.
Conclusions:
- Apparent subcortical neglect in MPTP-treated monkeys is primarily a deficit in movement initiation (hypokinesia).
- This primate model effectively isolates hypokinesia, a key symptom of Parkinson's disease.
- The study reinforces the role of nigrostriatal dopaminergic neurons in movement regulation.