Functional switch between motor tracts in the presence of the mAb IN-1 in the adult rat

Fine finger and hand movements in humans, monkeys, and rats are under the d irect control of the corticospinal tract (CST). CST lesions lead to severe, long-term deficits of precision movements. We transected completely both C STs in adult rats and treated the animals for 2 weeks with an antibody that neutralized the central nervous system neurite growth inhibitory protein N ogo-A (mAb IN-1). Anatomical studies of the rubrospinal tracts showed that the number of collaterals innervating the cervical spinal cord doubled in t he mAb IN-1- but not in the control antibody-treated animals. Precision mov ements of the forelimb and fingers were severely impaired in the controls, but almost completely recovered in the mAb IN-1-treated rats. Low threshold microstimulation of the motor cortex induced a rapid forelimb electromyogr aphy response that was mediated by the red nucleus in the mAb IN-1 animals but not in the controls, These findings demonstrate an unexpectedly high ca pacity of the adult central nervous system motor system to sprout and reorg anize in a targeted and functionally meaningful way.