Red nucleus lesions impair overground locomotion in rats: a kinetic analysis

The red nucleus is a prominent brainstem nucleus in mammals which is though t to be involved in production of skilled limb movements. The presence of t he red nucleus and associated rubrospinal tract in animals that do not prod uce skilled limb movements, however, suggests that these structures might a lso be involved in control of more general limb actions, such as those occu rring during locomotion. The present study investigates this question by me asuring the three-dimensional ground reaction forces produced by locomoting rats with unilateral excitotoxic lesions of the red nucleus. Twenty-four t o 48 h after the lesion, rats moved with an asymmetric gait during which ab normal braking and propulsive forces were produced during the dual contact time of the forelimb contralateral to the lesion and the ipsilateral hindli mb. Rats did not recover normal symmetrical locomotion within the 55-day du ration of the study. The persistent asymmetry produced by red nucleus ablat ion provides the first unequivocal demonstration that the red nucleus plays a role in ongoing overground locomotion in the rat. Species differences in phylogeny and connectivity of the red nucleus are discussed, as well as th e possibility that there is a general compensatory response to unilateral C NS injury in the rat.