Effect of levodopa chronic administration on behavioral changes and fos expression in basal ganglia in rat model of PD.

To study behavioral character and changes of neuronal activity in the basal ganglia of rat model of levodopa-induced dyskinesia, unilateral 6-hydroxydopamine lesioned rat model of Parkinson disease (PD) was treated with levodopa/benserazide twice daily for 4 weeks and the behavior observed on the 1st, 3rd, 4th, 7th, 9th, 10th, 14th, 21st and 28th day. The animals were sacrificed and immunohistochemical technique was used to measure the changes of Fos expression in the caudate putamen (CPU), globus pallidus (GP) and sensorimotor area of cerebral cortex 2 h after the last treatment. The results showed that pulsatile treatment with a subthreshold dose of levodopa gradually induced abnormal involuntary movement (AIM), including stereotypy (limb dyskinesia, axial dystonia and masticatory dyskinesia) towards the side contralateral to the dopamine-denervated striatum and increased contraversive rotation. The motor pattern of each subtype was highly stereotypic across individual rats, and the proportion of each subtype was not consistent among individual rats. Fos positive nuclei in the CPU and GP were increased by levodopa acute administration, and more remarkably in the CPU, but not in the cerebral cortex. After repeated levodopa treatment. Fos positive nuclei were reduced remarkably in the CPU, but were increased in the GP and cerebral cortex. It was concluded that the neural mechanisms underlying levodopa induced AIM in rat model of PD was very similar to those seen in levodopa-induced dyskinesia (LID) in PD patients and MPTP-lesioned monkeys, and increased striatopallidal neuronal activity might be involved in occurrence of LID.