Chronic levodopa therapy does not improve skilled reach accuracy or reach range on a pasta matrix reaching task in 6-OHDA dopamine-depleted (hemi-Parkinson analogue) rats

L-dopa therapy reverses some but not all of the motor deficits in human Par kinson patients. Although a number rat analogues of human Parkinson's disea se have been developed for evaluating the efficacy of drug therapies, it is not known whether L-dopa has a similar selective action on the motor sympt oms in the rat models. To examine the effectiveness of L-dopa in reversing the motor deficits in rats, we administered 6-OHDA unilaterally to produce hemi-Parkinson rats, which were then trained to reach for food using either their impaired (contralateral to the lesion) limb or their good (ipsilater al to the lesion) limb. To assess the skill, accuracy and range of limb mov ement, rats reached for pasta from a horizontal array of 260 vertically ori entated pieces of pasta. The number and location of pasta pieces taken from this matrix was calculated and the qualitative aspects of the reaching mov ements were rated. The quantitative data on pasta sticks retrieved indicate d that forelimb extension and movement radius around the shoulder joint was reduced by 6-OHDA treatment and did not improve after chronic L-dopa treat ment. The qualitative analysis showed that grasping patterns, paw movements and body movements impaired by the lesion were also not improved by L-dopa treatment. These findings are the first in the rat to suggest that whereas L-dopa has a general activating effect on the rat's whole-body movements, as displayed in contralateral rotation, its effectiveness does not extend t o skilled forelimb movements. The results are discussed in relationship to the idea that the restoration of some skilled movements may require normal synaptic function.