Effects of increasing doses of apomorphine during stereotaxic neurosurgery in Parkinson's disease: clinical score and internal globus pallidus activity

We analysed the firing activity of internal globus pallidus cells in two Parkinson's disease patients undergoing stereotaxic surgery. Both patients showed an advanced rigid-akinetic syndrome with disabling levodopa induced dyskinesias. Apomorphine, intraoperatively administered at doses (1-2mg) inducing a short but clear clinical improvement without involuntary movements, reduced the pallidal discharge rate by >50% in both patients. An higher apomorphine dose (2.5mg), tested in one hemisphere, blocked the firing activity with a time course independent from the occurrence of dyskinesias. These finding suggest that the reduction of internal pallidus excitability is one of the mechanisms underlying the efficacy of dopaminergic therapy, but also that changes in other basal ganglia stations are likely to be involved in dyskinesias.