Viability, growth, and maturation of fetal brain and spinal cord in the sciatic nerve of adult rat.

The feasibility for growth, maturation, and differentiation of fetal nervous system implanted into adult mammalian peripheral nervous system was studied. Thirty-five adult rats had the epineurium of the sciatic nerve crushed, perineurium minced, and fetal rat cortex or spinal cord implanted. Rats were utilized 7, 14, and 21 days, and 1, 2, 3, and 4 months later. A 1-mm cube of cortex or a 1-mm segment of spinal cord of 11-, 12-, or 15-day gestation fetuses was placed into the epineurium. Age-matched controls (7 DPI (days postimplantation) control for E15 implant was a 1-day pup, 21 days' gestation) were utilized for comparison (two per time group). Five animals had sciatic crush and perineurial mince only, and the gait and toe-spreading response were observed over 4 months. All implanted animals walked normally at 30 days. All implants were successful and survived the duration of the experiment. Cortical implants produced prominent bulges in the epineurium (21 days-4 months). Maximal neuronal and neurolgial cell division was observed at 7-21 days, decreased at 30 days, and stopped by 60 days. Most implanted cortical neurons had mature nuclei and immature dendritic patterns (apolar), and rarely had mature dendritic patterns. Neuroglia were abundant. The younger the cortical implant, the larger the cell mass produced (E11 greater than E15). The spinal cord implants survived, were viable, contained mainly neuroglia, and grew minimally. Host Schwann cells and nerve fibers were found in and around the implants. These data show that adult peripheral nervous system can act as an environment for growth and viability of fetal CNS implants.