Structure and function of fetal cortex implanted into degenerating peripheral nerve of adult rat.

The growth, differentiation and function of E11 fetal cortex was studied over 4 months after implantation into the degenerating nerve to the biceps femoris muscle of 70 rats. At 7 days postimplantation (DPI) the implant formed a neuroepithelium which contained mainly undifferentiated cells within a reconstituted perineurium. At 14-21 DPI the neurons contained differentiated, mature nuclei, poorly developed Nissl bodies and normal cytoplasmic organelles. Neuroglia were also observed with typical nuclei and a dense cytoplasmic ground. At 30 days the implants reached their greatest degree of differentiation. Neurons had mature nuclei and cytoplasmic organelles. There were few axosomatic synapses or neuronal cell processes. Neuroglia were prominent with many cell processes. The neuropil contained myelinated and unmyelinated nerve fibers, dendrites and many axodendritic synapses. At 40-50 DPI the neurons and neuronal cell processes were degenerating. At 60-120 DPI the implant contained only neuroglia. Stimulation of only the implant resulted in biceps femoris muscle contraction in 5 animals at 30 DPI and one animal at 40, 45 and 50 days. Injection of 10 microliter of WGA-HRP into the biceps femoris muscle resulted in at least 20 neurons in 3 30-day implants that contained HRP reaction product. These data show that fetal cortical neurons can assume functions different from normal, functionally reinnervate adult muscle and can differentiate and form an ectopic nervous system for at least 30-days after implantation into a degenerating adult host peripheral nerve.