CONTRIBUTION OF THE EXTERNAL GLOBUS PALLIDUS IN BASAL GANGLIA CIRCUIT OSCILLATORY ACTIVITY IN BEHAVING RODENT MODEL OF PARKINSON'S DISEASE

Excessive synchrony in beta frequency range (15-35 Hz) has been found in the motor cortex (MCx) and basal ganglia (BG) of Parkinson's disease (PD) patients, and has been hypothesized to be responsible for motor impairments in PD. The mechanisms underlying the abnormal brain patterns are not fully understood. A major goal of the study was to identify a role of the external globus pallidus (GPe), the key element of the BG, in the emergence and transition of synchronized beta activity in basal ganglia-thalamocortical circuits after loss of dopamine (DA) in rat model of PD. Analysis of local field potentials (LFPs) from MCx and BG nuclei during locomotion showed the emergence of abnormal beta-oscillations (30-36 Hz) in all examined regions from DA-depleted hemisphere, but not in control animals. LFP power and coherence of oscillations were the highest in the MCx and SNr, while that in the dStr and GPe and their coherence with the MCx and SNr were significantly lower. In addition to the beta band LFPs, a narrow 50-56 Hz gamma activity emerged exclusively in the dStr and GPe in DA-depleted hemisphere, but very rare in control group when rats resist walking. Robust coherent beta and gamma activity in the DA-depleted hemispheres was significantly reduces by the treatment with levodopa, with parallel improvements in locomotion.