Skilled forelimb use in the rat: amelioration of functional deficits resulting from neonatal damage to the frontal cortex by neonatal transplantation of fetal cortical tissue.

Limb preference and dexterity of right and left forelimbs were studied in a food reaching task in normal rats (control group), in rats that sustained a neonatal lesion of the left frontal cortex (lesion group) and in animals that received a transplant obtained from the frontal cortex of 16-day-old embryos immediately after the lesion (graft group). In addition, an anatomical study of host-transplant interconnections was performed in several transplanted animals. The results indicate that the lesion slightly increased the preference for the limb ipsilateral to the lesion and transplantation of fetal cortical tissue did not restore the preference for the contralateral limb. Furthermore, lesion of the motor cortex induced a deficit in the dexterity of limb use in the food-reaching task. This motor deficit was more pronounced when the limb contralateral to the lesion was used. Transplantation of embryonic cortical tissue led to a reduction of the motor deficit. Compared to the lesion group, the graft group had a higher success rate and a lower percentage of motor abnormalities, whichever forelimb was used, ipsi- or contralateral to the transplant. Nevertheless, larger improvement was noted with contralateral forelimb usage. Functional recovery was not complete since the control group still performed significantly better than the graft group, although almost complete sparing in skilled reaching was noted when the limb ipsilateral to the transplant was used. Analysis of host-transplant interconnections indicates that the transplants sent fibers to the host spinal cord, caudate-putamen, thalamus and homotopic contralateral cortex and received projections from the host thalamus and contralateral cortex. It is therefore suggested that neonatal transplantation of fetal cortical tissue promotes functional recovery from damage to the motor cortex occurring at birth.