Paw and limb use in skilled and spontaneous reaching after pyramidal tract, red nucleus and combined lesions in the rat: behavioral and anatomical dissociations

The pyramidal tract and red nucleus send prominent projections to the spinal cord and are thought to co-operate in producing skilled movements. In the present study, skilled reaching for food located on a shelf and spontaneous grasping, handling and eating pieces of pasta were video-recorded and analyzed in control rats, rats with unilateral ibotenic acid lesions of the red nucleus (RN), unilateral pyramidal tract lesions (PT) and combined lesions. The behavioral results suggest that skilled movements are organized as action patterns, easily recognizable and distinctive for each task. In both skilled and spontaneous reaching, PT lesions reduced success more than RN lesions, suggesting a greater role for the PT in guiding limb movements. Both lesions impaired rotatory movements including limb aiming, pronation and supination. RN lesions additionally abolished the arpeggio movement by which the paw is oriented for searching and grasping. Combined lesions were additive as rats lost both rotatory movements and arpeggio. Nevertheless, even after combined lesions, the rats were able to advance the limb, grasp food and withdraw the limb. The sparing following combined lesions suggests that other neural systems as well as compensatory adjustments assist the impaired limb. The results are discussed in relation to the possible distinctive contributions of the rubrospinal and corticospinal tract to the action patterns that comprise skilled movements in rats. (C) 1998 Elsevier Science B.V. All rights reserved.