Change in phase synchronization of local field potentials in anesthetized rats after chronic dopamine depletion

In order to investigate temporal characteristics of oscillatory neural activity and the effect of chronic dopamine depletion on it, local field potentials were measured in anesthetized rats without or with a 6-OHDA lesion at either the ventral tegmental area or the substantia nigra compacta, using a pair of electrodes that were separated by 120 microm. Coupling of neural activity in this mesoscopic scale was measured by a synchronization index that quantified the distribution of differences in instantaneous phase between the two potentials recorded. Phase synchrony was significantly stronger at deep basal ganglia sites, more so than at cortical sites, over a gamma range (30-120 Hz) in normal rats. After chronic dopamine depletion, this synchrony was no longer observable, especially after a substantia nigra lesion, while there was an increase in phase synchrony in the cortex at a lower frequency band (10 Hz). These findings are consistent with previously reported findings that the effect of dopaminergic innervation on oscillatory neural activity varies from synchronizing to desynchronizing, depending on the structure innervated and the frequency of the oscillation.