Neural transplantation: autoradiographic analysis of histogenesis in neocortical transplants.

Neurohistogenesis in neocortical transplants obtained from 15-, 16-, 17-, 18-, 19-, 20- and 21-day-old embryos, was studied employing [3H]thymidine autoradiography. The neural tissues were transplanted in the midvermis of cerebellum of the host animals. Following transplantation the host animals in different groups were injected with the radiochemical at 6 hr, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 day intervals, to label the neurons forming on different days in the developing transplants. Analysis of autoradiograms showed that all the neocortical transplants did undergo histogenesis in the host cerebellum, and that it was similar to that seen in a normally developing neocortex. Transplants from the 15-day embryos showed histogenesis lasting for 9 days, and at the other extreme transplants from the 21-day embryos showed histogenesis lasting only for 1 day. Histogenesis in other transplants fell between these two extremes in a graded fashion in relation to the age of the donor embryos. The magnitude of histogenesis in transplants from different donor embryos was closely related to the final size of the transplants. Transplants from 15-day embryos were the largest in size, and they were followed by those from 16-, 17-, 18-, 19-, 20- and 21-day donor embryos in a graded fashion. All transplants were intraparenchymal, and histologically appeared normal. They contained fully differentiated neurons, and were anatomically integrated with the host cerebellum without any glial scar tissue or necrotic tissue intervening between them.