Electrophysiological and clinical desensitization to apomorphine administration in parkinsonian patients undergoing stereotaxic neurosurgery

A decreased motor response after repeated doses of apomorphine is observed in severely affected Parkinson's disease patients. We simultaneously studied clinical symptoms and internal pallidus single unit activity in three parkinsonian patients underlying stereotaxic neurosurgery for deep brain stimulation. In each patient, two closely spaced doses of intraoperatory apomorphine were administered, while recording the same extracellular unit. The reduced clinical effect of the second administration was correlated to a lessened inhibition of the pallidal single unit recorded throughout the double administration. Our data support the proposition that fast postsynaptic desensitization to dopamine agonists may take place in the basal ganglia nuclei and play a role in the physiopathology of levodopa long-term treatment syndrome.