Hemicerebellectomy and motor behaviour in rats. II. Effects of cerebellar lesion performed at different developmental stages.

Rats with a right hemicerebellectomy (HCb) performed in adulthood or at weaning were compared behaviourally to rats with a similar lesion performed on the first postnatal day. The age at which animals received cerebellar lesions made a significant difference with respect to the behavioural outcome in adulthood. Posture, locomotion and motor behaviour were analysed by a battery of sensorimotor tests. Behavioural measurements showed a clear relationship between age at surgery and behavioural effects; rats with neonatal cerebellar lesions showed a slight extensor hypotonia contralateral to the lesion side and efficient locomotor activity, while the adult operated group exhibited a severe extensor hypotonia ipsilateral to the lesion side and hampered locomotion characterized by a wide base and ataxia. Weanling operated rats displayed a symptomatology similar to that observed in adult operates, although less severe. In the postural dynamic adjustments which the sensorimotor tests required, the youngest operated animals obtained higher scores in comparison to the other two experimental groups, except for the lack of hindlimb usage in the suspension on a wire test. These results, which show the importance of the age-at-lesion factor for the recovery of motor function after HCb in the rat, are discussed in the light of the widespread anatomical reorganization already demonstrated following neonatal HCb in rats.