The role of pretraining on skilled forelimb use in an animal model of Huntington's disease.

After a unilateral striatal lesion, animals have generally been seen to have a bilateral impairment in paw reaching, with the contralateral paw being more affected. However, most studies to date have not used a pretraining paradigm to assess maximal capacity for paw reaching, to compare with any lesion-induced loss. This study compared animals that were pretrained with naive animals in their ability to paw reach after a striatal lesion, to address the role of the striatum in either acquisition or execution of this motor task. All lesioned animals showed a significant decrease in reaching ability with their contralateral paw compared with the ipsilateral paw. Pretrained lesioned animals showed a clear lesion deficit with the contralateral paw immediately after lesion, and no impairment whatsoever with the ipsilateral paw. Naive lesioned animals showed delayed acquisition of the task with both paws, possibly due to postural deficits, and a lasting deficit on the contralateral side. The variability of performance between animals was higher in the naive lesioned group. These results suggest that animals should be pretrained on the staircase task prior to lesion to enable maximum sensitivity in detecting both loss and recovery of function of skilled forelimb use.