Enhancement of human motor cortex inhibition by the dopamine receptor agonist pergolide: evidence from transcranial magnetic stimulation.

Focal transcranial magnetic stimulation was used to evaluate the effect a single oral dose (0.125 mg) of the dopamine agonist pergolide on the excitability of the motor cortex in five healthy subjects. Resting and active motor thresholds of the abductor digiti minimi muscle were unaffected. The mean duration of the cortical silent period was significantly lengthened by up to 22 ms. The cortico-cortical inhibition as studied by a paired conditioning-test stimulation (interstimulus intervals of 1-5 ms) was enhanced significantly while the cortico-cortical facilitation at longer intervals (6-15 ms) showed only an insignificant trend towards less facilitation. All effects peaked at 3 h after drug intake and were reversible after 24 h. Peripheral motor excitability as tested by the duration of the peripheral silent period and the size of the maximum M wave remained unchanged. The present data support the view that pergolide is capable of enhancing motor cortex inhibition which is known to be deficient in idiopathic Parkinson's disease.