Electrophysiological studies on plasticity of cerebellothalamic neurons in rats following neonatal hemicerebellectomy.

Changes in the cerebello-thalamo-cerebral projection following hemicerebellectomy were investigated in 16 rats by laminar field potential analysis of cerebello-cerebral responses in the cerebral cortex and by unitary recording of antidromic responses of cerebellar nuclear neurons to stimulation of the thalamus. In contrast to the occurrence of an exclusively contralateral cerebello-cerebral response in intact rats, a significant bilateral cerebello-cerebral response could be evoked in all 8 rats hemicerebellectomized before 6 days of age (early hemicerebellectomy). On the other hand, in all 5 rats operated on at 8 to 15 days of age (late hemicerebellectomy) and in the 3 rats operated on in adulthood, the cerebello-cerebral response was evoked only contralaterally just as in intact rats. Unitary recordings of antidromic responses of cerebellar nuclear neurons revealed that bilateral or ipsilateral cerebellothalamic projection neurons were remarkably more numerous in early hemicerebellectomized rats than in controls (P less than 0.001). Such neurons were less frequently found in late hemicerebellectomized rats, but they were still more numerous than in controls (P less than 0.005). Absence of the ipsilateral cerebello-cerebral response in late hemicerebellectomized rats indicates that even though bilateral or ipsilateral cerebellothalamic projection neurons may exist in these rats more numerously than in intact rats, they may not be sufficient in number or in efficiency to mediate a detectably response.