Effect of deep brain stimulation on levodopa-induced dyskinesias and striatal oscillatory local field potentials in a rat model of Parkinson's disease.

Background: In Parkinson's disease (PD) dyskinesias appear after long-term dopaminergic treatment. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the globus pallidus internus (GPi) is a well-established treatment option for both PD symptoms and complications of medication.

Objective: To elucidate physiological mechanisms of the effect of DBS on levodopa-induced dyskinesias (LID) we investigated both DBS in the GPi and the centromedian-parafascicular complex (CM-Pf), which are part of an internal basal ganglia loop connecting with the dorsolateral striatum. In particular, we focused on changes of oscillatory activity in the dorsolateral striatum, which also presents the entrance region of the basal ganglia (BG).

Methods: 6-Hydroxydopamine (6-OHDA) hemiparkinsonian (HP) rats and 6-OHDA lesioned HP rats with LID (HP-LID) were used to compare the effect of DBS in the entopeduncular nucleus (EPN, the equivalent to the human GPi) and the thalamic parafascicular nucleus (Pf, the equivalent of the human CM-Pf) on dyskinesias and neuronal oscillatory activity of selected frequency bands in the dorsolateral striatum on and off levodopa.

Results: In HP-LID rats the relative beta and gamma power was lower, while relative theta power was higher as compared to HP rats. Chronic DBS of either the EPN or the Pf improved dyskinesia scores in HP-LID rats, and no differences in oscillatory activity were observed between groups.

Conclusions: Stimulation of the Pf has a specific impact on dyskinesias, which is similar to that found after EPN stimulation, and which is accompanied by changes of oscillatory activity.