Pallidal neuronal discharge in Parkinson's disease following intraputamenal fetal mesencephalic allograft.

Abstract

Human intrastriatal fetal allografts survive over long periods of time in the brains of Parkinson's disease (PD) patients and integrate into host circuitry. However, some grafted patients with a prior history of levodopa-induced dyskinesias have developed off-medication dyskinesias and dystonias following allografting whose mechanism remains poorly understood. The authors present single-unit discharge characteristics in the external and internal globus pallidus (GPe and GPi) in an awake patient with PD undergoing microelectrode-guided surgery for pallidal deep brain stimulation, 10 years following bilateral intraputamenal fetal mesencephalic allografting in an NIH-funded protocol. Pallidal single-unit activity at 'rest' and during active movement was evaluated and compared with data sets from 13 PD patients in the 'off-medication' state and from one non-dyskinetic PD patient in the 'on-medication' state. Analysis of firing rate, bursting discharge and oscillatory activity showed that the graft corrected some, but not all, of the abnormalities associated with the off-medication state. Additionally, in the transplanted patient, voluntary hand movement produced a marked reduction in pallidal discharge rate at multiple GPi recording sites, which was not observed during active movement in other patients. These findings are consistent with a persistent effect of transplanted dopamine cells on basal ganglia outflow and suggest a mechanism for the graft-induced dystonic phenotype.