Firing patterns and correlations of spontaneous discharge of pallidal neurons in the normal and the tremulous 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine vervet model of parkinsonism

To investigate the role of the basal ganglia in parkinsonian tremor, we rec orded hand tremor and simultaneous activity of several neurons in the exter nal and internal segments of the globus pallidus (GPe and GPi) in two verve t monkeys, before and after systemic treatment with 1-methyl-4-phenyl-1,2,3 ,6-tetrahydropyridine (MPTP) and development of parkinsonism with tremor of 5 and 11 Hz. In healthy monkeys, only 11% (20/174) of the GPe cells and 3% (1/29) of the GPi cells displayed significant 3-19 Hz oscillations. After MPTP treatment , 39% (107/271) of the GPe cells and 43% (26/61) of the GPi cells developed significant oscillations. Oscillation frequencies of single cells after MP TP treatment were bimodally distributed around 7 and 13 Hz. For 10% of the oscillatory cells that were recorded during tremor periods, there was a sig nificant tendency for the tremor and neuronal oscillations to appear simult aneously. Cross-correlation analysis revealed a very low level of correlated activity between pallidal neurons in the normal state; 95.6% (477/499) of the pairs were not correlated, and oscillatory cross-correlograms were found in only 1% (5/499) of the pairs. After MPTP treatment, the correlations increased dramatically, and 40% (432/1080) of the cross-correlograms had significant oscillations, centered around 13-14 Hz. Phase shifts of the cross-correlogr ams of GPe pairs, but not of GPi, were clustered around 0 degrees. The results illustrate that MPTP treatment changes the pattern of activity and synchronization in the GPe and GPi. These changes are related to the sy mptoms of Parkinson's disease and especially to the parkinsonian tremor.