Partial recovery of skilled forelimb reaching after transplantation of fetal cortical tissue in adult rats with motor cortex lesion - anatomical and functional aspects.

We have studied the effect of transplantation of embryonic frontal cortex on the motor deficit resulting from motor cortex lesion in the adult rat. Twenty-four 2-month-old rats were first trained in a food reaching task with right and left forelimbs. Then, at 4 months of age, the subjects were divided into two equal groups. In the lesion group, the animals sustained a lesion of the left motor cortex, whereas in the graft group the animals received a fetal cell suspension of embryonic (E16) frontal cortical tissue three days after the lesion. Postoperative reaching ability was assessed every week during eight weeks and then every two months until the age of one year. The results indicate that the deficit resulting from the lesion is bilateral but mainly affects the limb contralateral to the lesion. During the first 3 weeks of postoperative testing, both groups displayed comparable evolution of performance with contralateral forelimb, characterized by an initial large drop followed by progressive recovery. But, whereas in the lesion group performance did not increase after the fourth postoperative week, in the graft group the reaching scores further improved, without recovering, however, preoperative levels. This improvement was still observed eight months after transplantation. However, no improvement appeared using the limb ipsilateral to the transplant. An anatomical study of the volumes of transplant and/or lesion revealed that the importance of the recovery or deficit varied as a function of the sizes of the transplant and/or lesion within the rostral part of the motor cortex, approximately corresponding to the rostral forelimb area of Neafsey et al. [37]. It is therefore suggested that in adult rats, some components of the motor deficit resulting from a lesion of the motor cortex can be partially reduced by transplantation of homotopic embryonic cortex.