Transplantation of fetal rat cortex into regenerating nerve to the biceps femoris of adult rat.

Morphological aspects of the implantation of 11-day-old fetal (E11) rat cortex into regenerating peripheral nerves of adult rats were analyzed during the first 3 weeks after transplantation. On day 11 of gestation, donor fetuses were removed from one uterine horn of pregnant Sprague-Dawley rats and pieces of cortex (1.0 X 0.5 mm) were dissected from them for transplantation. Fetuses and normally delivered pups from the other uterine horn were used as age-matched controls. In 45 adult male Sprague-Dawley rat hosts (200 to 300 g), the epineurium of the nerve to the biceps femoris muscle was crushed and incised, the perineurium minced, and E11 donor cortex was injected into the nerve. At 1 to 7 days postimplantation (DPI), undifferentiated neuroepithelial cells were dispersed or in oval neuroepithelial-like structures throughout the regenerating nerve. At 7 to 14 DPI, neurons and neuroglia were differentiating and interspersed among fascicles of regenerating host axons. At 14 to 21 DPI, aggregates of differentiated neurons surrounded by neuropil containing a rich synaptic bed were interspersed with regenerated host peripheral axons. Fetal cortical implants survived, increased in size, and differentiated throughout the postoperative period, matching their timed controls.