CNS plasticity after hemicerebellectomy in the young rat. Quantitative relations between aberrant and normal cerebello-rubral projections.

The double labelling technique has been applied to study the quantitative relations between aberrant and normal cerebello-rubral projections in rats hemicerebellectomized on the 2nd, 5th, 10th, 20th or 30th day after birth, respectively. In the group of rats lesioned on the 2nd day about 30% of cells in the lateral nucleus and 20% in the interpositus nuclei are labelled retrogradely by the fluorescent tracer injected in the aberrant ipsilateral projection area. These values decreased in the groups of rats operated on the 5th or 10th day and reached values of about 1-2% in rats lesioned on the 20th or 30th day. These values have been also found in control rats. Both in experimental rats and in control rats less than 0.5% of cells are double labelled from both projection areas. This implies that the aberrant cerebello-rubral fibres stem from separate parent cells and are not collaterals from normally projecting fibres.