Fetal neocortical transplants grafted into cortical lesion cavities made in newborn rats receive multiple host afferents. A retrograde fluorescent tracer analysis

Several reports have demonstrated efferent projections from fetal neocortical transplants placed in the cerebral cortex of newborn rats. Fewer studies have examined transplant afferents, and these have primarily used techniques based on the axonal transport of horseradish peroxidase. In the present study, we extend these initial findings on transplant afferent connections by using retrogradely transported fluorescent dyes to demonstrate a topographic and more extensive pattern of cortical transplant afferents than has been previously reported. Fetal neocortical tissue was grafted into frontal cortical lesion cavities made by aspiration in newborn rats. At 1.5-10 months later, the fluorescent dyes Fast blue and Diamidino yellow were injected into the transplants. Subsequent histological analysis demonstrated numerous retrogradely labeled fluorescent neurons within the host thalamus and cerebral cortex as well as several other areas of the host brain. The neurons were primarily single-labeled and generally found in areas that normally project to the ablated area of the cortex. The topographic distribution of retrograde labeling in several animals with non-overlapping dye injections confined to the transplants suggests that the host projections were distributed selectively within the grafts. These results support and extend previous studies suggesting the use of fetal neocortical tissue in repair of the neonatally damaged central nervous system.