Abstract
In this study the growth of neural transplants was analyzed in relation to the age of the host animals and the site of transplantation. The influence of these two host parameters on the growth of neural transplants with high growth potential (tissue from 15βdayβold embryos) and low growth potential (tissue from 18βdayβold embryos) was investigated. Neocortical neural tissues of constant volume, obtained from 15β and 18βdayβold embryos, were tranplanted into the forebrain or cerebellum of 5β, 10β, 20β, 25β, 30β, 35β and 180βdayβold host animals and analyzed, quantitatively as well as qualitatively, 90 days after transplantation. The transplants grew larger in volume in the cerebellum than in the forebrain region of the hosts of all ages. In both sites, tissue from 15βdayβold embryos yielded larger transplants than tissue from 18βdayβold embryos. Transplants from 15βdayβold embryos grew most extensively in 5βdayβold host animals (33βfold in the cerebellum, and 23βfold in the forebrain region.) In older host animals it grew less extensively, and without much variation in size that could be attributed to the age of host animals. Tissue from 18βdayβold embryos grew little, regardless of site of transplantation or age of host. Apparently the age of the host animals and the site of transplantation had greater influence on the growth of the neural transplants with high growth potential than on those with low growth potential. Histologically, the neural transplants in all cases contained normalβlooking and fully differentiated neurons and were anatomically integrated with the host brain.