The effects of reserpine on motor activity and pallidal discharge in monkeys: implications for the genesis of akinesia.

1. A reversible disturbance of basal ganglia function was produced in monkeys by the intramuscular administration of reserpine.2. Pallidal discharge was then compared with that recorded in the same animals during movement performance and following passive manipulation of the limbs.3. Akinesia, loss of postural support of the trunk, head and neck and absent postural reflexes were the predominant motor abnormalities produced by reserpine administration.4. Occasionally, postural tremor and catatonia were apparent. Rigidity and resting tremor were absent.5. Recordings made in the pallidum during the presence of akinesia revealed a marked reduction in natural neuronal discharge.6. Some pallidal neurones that remained active were driven in an uncharacteristic manner by peripherally generated afferent inputs from wide territories and by a variety of peripheral stimuli.7. The findings suggest the hypothesis that the akinesia in these animals was due to the diminished pallidal activity, and that pallidal discharge is normally a prerequisite for the performance of spontaneous motor activity. Pallidal neuronal firing may provide a background excitability to motor regions involved in the maintenance and elaboration of natural motor activity.