Skilled reaching deficits in unilateral dopamine-depleted rats: impairments in movement and posture and compensatory adjustments.

Rats receiving unilateral dopamine (DA) depletions have bilateral deficits in using the forelimbs for skilled reaching. These impairments were investigated using end-point, video, and kinematic measures. Control rats and groups of rats with > 98% unilateral depletions (confirmed by tissue, apomorphine, and amphetamine assay), produced by 6-hydroxydopamine (6-OHDA) injected into the nigrostriatal bundle, were tested for 100 d on two reaching tasks. One depleted group used the contralateral-to-lesion (bad), and the other the ipsilateral-to-lesion (good), limb. Rats using their bad limb made few successful reaches and had dysfunctions in aiming, pronating, and supinating, and in using the digits to grasp and release food. Rats using the good limb were initially impaired, but improved, and could make these movements. Neither depleted group was able to use their bad limbs to assist actively the postural changes required for reaching. Thus, they did not use the diagonal supporting pattern (the nonreaching forelimb and diagonal hind limb) from which control rats initiated reaching. The group using their bad limb initiated reaching from a base of support distributed on the ipsilateral-to-lesion limbs, while the group using their good limb initiated reaching from a base of support centered on the ipsilateral rear limb. The impairments in making voluntary movements and postural adjustments with the bad limbs and the behavioral changes introduced by the compensatory dependency on good limbs account for the bilateral deficits in skilled movements. The results show that DA is required for skilled movements and postural adjustments and demonstrate that behavioral compensation can contribute to recovery.