Initial growth of transplanted E11 fetal cortex and spinal cord in adult rat spinal cord.

Fetal CNS (cortex and spinal cord) transplants survive and grow in the spinal cord of adult rats. The present experiments study the initial stages (10 days) to determine the developmental pattern of early (E11) fetal cortex and spinal cord transplants implanted into the T6 spinal cord of adult rats (n = 50). Controls were age-matched fetuses or pups from the donor females and surgical and vehicle controls (n = 20). E11 fetal cortex (0.5 X 1.0 mm pieces of neuroepithelium) or spinal cord (1.0 mm) were dissected from caesarean delivered fetuses from time pregnant Sprague-Dawley rats. The fetal tissue was pressure-injected between the dorsal horn and dorsal column of the host. Hosts were prepared for light and electron microscopy 1, 3, 7 and 10 days postimplantation (DPI). At 1 DPI, ovoid, ventriculated multiple neuroepithelia formed in an implantation-induced cyst in the host spinal cord. The inner layer of cells lining the ventricle of the ovoid neuroepithelia was actively dividing. The nuclei of the cells differentiated as they reached the surface of the neuroepithelium. This pattern was repeated at 3-10 DPI. At 7-10 DPI, differentiated neurons and neuroglia surrounded actively dividing neuroepithelia. These cells comprised the bulk of the transplant in the cyst. Transplanted mesenchymal cells formed pockets of cartilage in the implanted spinal cord. Although transplanted CNS consisted of only neuroepithelial cells, they differentiated into neurons that were typical for cortex or spinal cord. These data indicate that the transplanted E11 fetal tissue formed neuroepithelia which established the pattern of growth for these transplants.