Quantitative Graft Integration of Fetal Hippocampal Transplants Labeled with 5′ Bromodeoxyuridine into Normal Adult Hippocampus

Quantitative studies of neural graft development require: (1) a cell label which is both preferential for neurons and can be measured in terms of specific labeling; (2) a serial reconstruction method for identifying labeled cells in a three-dimensional pattern in the host; and (3) measurements of cell dispersion which indicate the specificity of cell movement in the host. We have used 5' bromodeoxyuridine (BrdU) as a nuclear marker of transplanted fetal hippocampal cells, performing daily injections into the donor to label the majority of cells in the hippocampus between Gestation Days 15 and 19. After harvesting, the BrdU-labeled hippocampal cell suspensions were either cultured or grafted into normal adult hippocampus. The labeling index of these fetal hippocampal cells was calculated to be 90% in both smears of cell suspensions and 48-h cultures and these were predominantly (77%) neurons by immunostains. Quantitative studies of potential toxicity of the BrdU in culture also revealed no differences in neurite development or survival, compared to unlabeled cells. The survival and migration of grafted cells were quantitatively evaluated by three-dimensional serial reconstruction of host brain sections. Absolute graft cell survival (cells recovered/cells injected) varied according to location: grafts in close proximity to the ventricle and white matter tracts (corpus callosum or fimbria) showed improved survival (20 and 25%, respectively) compared to grafts localized entirely within the (normal) hippocampus (only 9% survival). Although the grafts expanded considerably from the initial injection site, the graft cell dispersion appeared nonspecific. Thus, this format of quantitative graft assessment indicates that under normal (nonlesioned) host conditions the location of the grafts critically influenced graft development and there was minimal specific migration of grafted cells into cell body regions.