Recently, we demonstrated that transplantation of the frontal cortex lesion with fetal cortical tissue can promote functional recovery of skilled forelimb use when rats were obliged to use the impaired limb (Riolobos et al. 2001). The present experiment was undertaken to investigate the mechanisms of this neurotransplantation-induced recovery using different types of donor materials.

Before surgery, rats were trained in a paw-reaching for food-task. All animals were anaesthetised in all stages of the subsequent procedure (Equithesin, 20 mg kg^-1 I.P.). At the end of the experiments all animals were killed humanely. The experimental animals were unilaterally lesioned by aspiration in the sensorimotor cortex of the contralateral hemisphere to the preferred paw in the paw reaching for food task. After lesion, animals were retested in the paw reaching task to evaluate the deficit induced by the lesion. Only animals with an unequivocal impairment of the forelimb were subjected to transplantation. Four weeks later, fetal frontal cortex was placed in the lesion cavities in one group of rats; in a second group fetal striatal primordium was employed as donor tissue and adult sciatic nerve tissue in a third group. These groups were compared to a group of non-lesion rats considered as controls. Four months later, animals with homotopic or heterotopic transplants showed amelioration of the deficits caused by the lesion when animals were forced to reach with the lesion paw. By contrast, sciatic nerve transplants failed to produce any significant recovery in the reaching-for-food task. Morphological studies showed that the transplant-induced recovery was independent of the number of surviving neurons. However, it was conditioned by the size of the lesion, the transplant location as well as the nature and degree of the transplant connectivity with the host brain.

This work was supported by the following grants: FIS-FOH3 and DGICYT-PBI 2000-11900.