Apomorphine induces changes in GPi spontaneous outflow in patients with Parkinson's disease.

To determine the effect of a single dose of apomorphine on internal globus pallidus (GPi) neuronal discharge in patients with Parkinson's disease (PD). Nine PD patients who underwent microelectrode-guided posteroventral pallidotomy (PVP) were studied. After identification of a single GPi unit discharge with sufficient spike S/N ratio to allow reliable thresholding, basal recording was followed by a single 3-mg subcutaneous injection. One-minute samples were recorded 10', 30', and 60' after apomorphine. In four patients, recording was lost after 5-10 minutes. In two, changes were observed at peak-of-dose but recording was then lost, whereas three completed recording and returned to baseline, all five showing significant reduction in GPi firing rate (mean +/- standard deviation for basal and post-apomorphine were 143+/-55.6 and 52+/-19.2, respectively; p <0.002). In patients with PD, apomorphine induces changes in GPi spontaneous discharge and modifies firing rates resembling recordings in normal primates. These findings show that clinical improvement as well as induction of dyskinesias following DA administration could be mediated by reduction of GPi outflow.