The efficacy of deep brain stimulation (DBS) in the subthalamic nucleus (STN) in Parkinson's disease (PD) has focused attention on the role of STN firing patterns in PD symptomatology. Oscillatory activity in the beta frequency range is of special interest as local field potential (LFP) recordings in the STN in bradyki-netic PD patients during DBS electrode placement show prominent activity in this frequency range. As increased synchronization between the globus pallidus pars externus (GP) and STN has been implicated in the emergence of oscillatory activity in the STN, the effect of dopamine loss and increased dopamine stimulation on beta range activity in paired GP-STN single unit and LFP recordings was examined in intact or nigrostriatally lesioned, locally anesthetized, and immobilized rats. Spike-triggered waveform averages (STWAs) show that GP spiking becomes significantly more synchronized with STN LFP oscillations in the beta range after dopamine cell lesion. Coherences between GP spiking and STN LFP and between STN spiking and STN LFP are increased after dopamine cell lesion. A desynchronizing effect of increased dopamine receptor stimulation with apomorphine on GP-STN relationships in both intact and lesioned rats is observed. Results support a role for increased synchronization between STN and GP in the emergence of beta range activity in the STN and a greater impact of GP on STN activity after decreased dopamine receptor stimulation.
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