gms | German Medical Science

Objective: This study investigates the neuronal firing characteristics and oscillatory activities of the striatum and entopeduncular nucleus (EPN) in the 6-OHDA rat model of Parkinson's disease (PD) with and without L-DOPA-induced dyskinesia (LID). The nigrostriatal loss of dopamine leads to hypokinesia together with excessive oscillatory beta band activity within the basal ganglia-cortical loop, while enhanced theta band activity is related to LID.

Method: Twelve 6-OHDA lesioned hemiparkinsonian (HP) rats, eight of which were rendered dyskinetic by repeated injection of L-DOPA (HP-LID) were used. Single unit activity and local field potentials were measured in urethane (1.2 g/kg, i.p) anesthesia in the dorsolateral striatum and the EPN by platinum-tungsten microelectrodes “off” and after L-DOPA injection “on”. Motorcortex activity was measured by an electrocorticogram.

Results: Firing activity in the striatum and EPN was similar in HP-LID and HP rats. Injection of L-DOPA decreased the firing rate in both groups in the EPN, without affecting the striatal firing rate. Striatal oscillatory activity in the theta band (4-8 Hz) was higher in HP-LID rats in both, “on” and “off” state as compared to HP rats. In the EPN theta activity did not differ between groups, but decreased in the “on” state in both groups. In both regions the beta activity (12-30 Hz) was higher in HP rats as compared to HP-LID rats in the “off” state, L-DOPA injection, however, reduced beta activity to a larger extent in HP-LID rats as compared to HP rats.

Conclusions: The findings of this study indicate that LID is associated with increased theta oscillatory activity in the strito-cortical loop of basal ganglia.