Survival of fetal neocortical grafts implanted in brain infarcts of adult rats: the influence of postlesion time and age of donor tissue.

We have previously found that fetal cortex taken from 16- to 18-day-old donors survives grafting to the infarcted cortex 5-7 days after middle cerebral artery occlusion. The present study was undertaken to examine the effect on graft survival of varying the age of the fetal donor tissue and the time between vessel occlusion and graft implantation. First, a cell suspension of neocortical tissue was grafted from fetuses aged 15, 17, or 20 gestational days to the infarcted cortex of hypertensive rats which had undergone arterial occlusion 5-7 days earlier. There were no significant differences in the mean size or general morphology assessed in Nissl- and acetylcholinesterase-stained sections between the groups. Second, neocortical tissue was grafted from fetuses aged 15 gestational days to the infarcted cortex at different times following arterial occlusion. When surgery was delayed until 5-7 days, 3 weeks, or 8 weeks postocclusion, graft survival was significantly better than when implanted 1 day postocclusion. Implantation after 3 weeks yielded grafts that also were significantly larger than those in rats grafted 5-7 days after cortical infarction. The results indicate that there is no crucial upper donor age limit for dissociated fetal neocortical grafts in terms of graft survival and volume. Furthermore, a delay between lesion and transplantation is desirable in this stroke model. The host brain environment seems to be most hospitable around 3 weeks after arterial occlusion.