Red nucleus lesions do not affect limb preference or use, but exacerbate the effects of motor cortex lesions on grasping in the rat.

The corticospinal and rubrospinal systems are thought to collaborate in the production of skilled forelimb movements in primates. This study examined whether this relation holds in rodents. Limb preference and limb skill were assessed in a reaching-for-food task in rats with ibotenic acid lesions of the red nucleus or combined red nucleus lesions and aspirative motor cortex lesions. Major findings were: (1) Unilateral red nucleus lesions did not influence subsequent development of limb preference in naive rats. (2) Unilateral red nucleus lesions in pretrained rats failed to affect the incidence of reaching (total reaches) and reaching success (hit percent) by either the contralateral or ipsilateral limb. (3) Whereas motor cortex lesions impaired subsequent use of the contralateral limb, additional red nucleus lesions did not change total reaches or hit percent, but did produce moderate qualitative changes in limb accuracy and paw opening during grasping. The results demonstrate that in the rat, the red nucleus is not essential for the ballistic component of reaching but may contribute to fine motor control.