Hemicerebellectomy and motor behaviour in rats. I. Development of motor function after neonatal lesion

This study was undertaken to determine the effect of a neonatal hemicerebellectomy (HCb) on the motor development of rats and to determine whether various aspects of motor behaviour were affected to a similar degree. Postnatal development of postural reflexes, locomotion and dynamic postural adjustments was examined during the first four months of life in normal and in neonatal HCbed rats. The results indicate that classes of motor responses are controlled by cerebellar networks to clearly different extents. Emergence of quadruped stance, placing reactions and swimming development were unaffected by neonatal cerebellar lesion. Righting reflexes, cliff avoidance and geotaxic reactions, pivoting and crawling all showed a delayed development although the subsequent recovery was almost complete. The complex postural adjustments required in crossing a narrow path or in suspending on a wire remained permanently impaired. Finally, some behaviours developed normally and only subsequently became defective. This "growing into a deficit" was displayed by the progressively reduced hindlimb grasping and the development of a vestibular drop response with a directional bias. An impressive finding was the shifting of postural asymmetries from the lesion side to the contralateral one occurring around the third postnatal week. These data providing a description of the effect of HCb on motor development are interpreted as indicating a progressive involvement of the archi- and neo-cerebellar structures in the motor function of the rat.