Augmentation of basal forebrain cell populations with fetal tissue transplants.

Grafted fetal basal forebrain, previously labeled by intraperitoneal injection of gestating female rats with tritiated thymidine, was transplanted into the same area (homotopically) of host animals of various ages. Some animals were serially sacrificed up to 60 days after surgery, while others remained intact for the entire 60-day period prior to sacrifice. Transplants were highly (92%) successful. Early (2-10 days) grafted tissue was mainly composed of a gradient of heavily labeled differentiating cell profiles, strikingly similar to primitive subependymal cells reported elsewhere, which proceeded to mature thereafter. Evidence of cell turnover and tissue continuity at the host-graft interface was also obtained during this time. While many cells bearing label were found at the original implantation site in autoradiograms of all experimental animals, some were found in host tissue as early as 5 days following surgery. At later ages, greater numbers of labeled cells were found at considerable distances into host tissue in apparently specific locations. The lateral ventricle overlying the graft site was occupied by donor-derived tissue in 40% of all experimental animals. Islands of apparent germinal matrix persisted throughout the duration of the experiment. Results obtained in these experiments with transplanted tissue accord well with previous studies of neural genesis in intact animals. They further suggest that cell populations of specific nuclei of the host basal forebrain may be selectively augmented by observing critical embryogenetic time constraints when harvesting fetal donor tissue.