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

Studies of histogenetic and neurodegenerative processes in the nervous system using heterotopic neurotransplantation

The aim of the present article is to summarize our own experimental and published data on neurotransplantation into ectopic sites such as peripheral nerves (mainly) and the anterior chamber of the eye in rats. The review addresses questions touching on the following problems: the histogenesis and survival of nervous tissue after transplantation, the interaction between transplanted tissues with recipient tissues, assessment of long-term living transplants, simultaneous transplantation of different embryonic rudiments, transplantation of spinal cord ganglia, and the effects of trophic factors on the development of transplants. New data on stem cell transplantation into peripheral nerves are discussed.

Regeneration of a transected peripheral nerve by transplantation of spinal cord encapsulated in a vein

The objective was to investigate the regeneration of a transected peripheral nerve after transplantation of fragmented embryonic (E14-15) spinal cord cells which were encapsulated within a vein cavity. After 3 months transplantation, axonal regeneration was observed by staining with HE and antibody to neurofilament subtypes in six of 10 rats. In all six animals compound muscle action potentials to electrical stimulation could be recorded and indicated incomplete reinnervation of the fibular and tibial nerve, respectively. A chronic inflammation process around the transplant and a negative result of staining neurofilaments within the vein cavity and the transected nerve were found in animals lacking electrophysiological response to stimulation.

Reinnervation of denervated muscle by transplantation of fetal spinal cord to transected sciatic nerve in the rat

When motor neurons in the spinal cord are destroyed, regeneration of motor axons and muscle reinnervation cannot be expected. We attempted reinnervation of the denervated muscle, i.e. motor unit reconstruction, using transplantation of the fetal spinal cord to the peripheral nerve. The sciatic nerve of an adult rat was resected for 20 mm, and a cavity was prepared using an autologous femoral vein at the distal stump of the nerve. The fetal spinal cord was then transplanted into the venous cavity. After 3-6 months, no voluntary muscle contraction was observed due to the absence of communication with the central nervous system. However, reinnervation of the muscles via the sciatic nerve by the transplanted spinal neurons was demonstrated electrophysiologically and histochemically. This suggested that a motor unit can be reconstructed by fetal spinal cord transplantation even if the original motor neurons in the spinal cord are not available.

Regeneration of axons from the adult rat optic nerve: influence of fetal brain grafts, laminin, and artificial basement membrane

After transection of the optic nerve of adult rats, most of the axons in the proximal stump die and the surviving ones are unable to regenerate into the distal optic nerve. Since the fetal brain has an inherent capacity to regenerate axons, we investigated whether fetal (E16) target regions of optic axons (thalamus and tectum) transplanted to the completely transected optic nerve of adult rats would promote axon regeneration. In control operated rats, axon growth beyond the site of transection was restricted to a few fibers that grew irregularly within the connective tissue scar. By contrast, in grafted animals directed outgrowth of optic axons toward the transplant started at 6 days postoperation (p.o.) and reached its maximum 15 days p.o. and later, when numerous single optic fibers and small axon fascicles had grown toward and into the graft, where they formed arborizations and terminal varicosities. Regenerating optic axons were further advanced than GFAP-positive strands of astroglia that emanated from the proximal optic nerve stump. Laminin immunoreactivity appeared at 6 days p.o. in the zone of reactive astroglia in the terminal part of the optic nerve stump. Later it showed a distribution complementary to the pattern of GFAP immunoreactivity, which it seemd to circumscribe. There was no unequivocal codistribution of laminin immunoreactivity with regenerating axons. In further experiments, target regions from different ontogenetic stages (E14 to neonate and adult) and nontarget regions (E16, cerebral cortex or spinal cord) were grafted to the optic nerve stump. With the exception of the adult grafts, all transplants had effects on axon regeneration comparable to those of E16 target regions. In order to test the effects of extracellular matrix molecules on axon regeneration, a basement membrane gel reconstituted from individual components of the Engelbreth-Holm-Sarcoma (EHS) sarcoma was implanted between proximal and distal optic nerve stumps. No axons were induced to regenerate by this matrix. Likewise, laminin adsorbed to nitrocellulose paper and implanted at the lesion site did not stimulate axon growth from the proximal optic nerve stump. These results indicate that fetal brain is able to induce and direct regrowth of axons from the optic nerve toward the graft across a substrate that is not composed of astroglia or basement membrane components like laminin. The directed growth of axons in the absence of a preformed substrate implies a chemotactic growth response along a concentration gradient mediated by neurotropic molecules released from the graft.

Regeneration of adult dorsal root axons into transplants of embryonic spinal cord

Transplants of the embryonic rat spinal cord survive and differentiate in the spinal cords of adult and newborn host rats. Very little is known about the extent to which these homotopic transplants can provide an environment for regeneration of adult host axons that normally terminate in the spinal cord. We have used horseradish peroxidase injury filling and transganglionic transport methods to determine whether transected dorsal roots regenerate into fetal spinal cord tissue grafted into the spinal cords of adult rats. Additional transplants were examined for the presence of calcitonin gene-related peptide-like immunoreactivity, which in the normal dorsal horn is derived exclusively from primary afferent axons. Host animals had one side of the L4-5 spinal cord resected and replaced by a transplant of E14 or E15 spinal cord. Adjacent dorsal roots were sectioned and juxtaposed to the graft. The dorsal roots and their projections into the transplants were then labeled 2-9 months later. The tracing methods that used transport or diffusion of horseradish peroxidase demonstrated that severed host dorsal root axons had regenerated and grown into the transplants. In addition, some donor and host neurons had extended their axons into the periphery to at least the midthigh level as indicated by retrograde labeling following application of tracer to the sciatic nerve. Primary afferent axons immunoreactive for calcitonin gene-related peptide were among those that regenerated into transplants, and the projections shown by this immunocytochemical method exceeded those demonstrated by the horseradish peroxidase tracing techniques. Growth of the host dorsal roots into transplants indicates that fetal spinal cord tissue permits regeneration of adult axotomized neurons that would otherwise be aborted at the dorsal root/spinal cord junction. This transplantation model should therefore prove useful in studying the enhancement and specificity of the regrowth of axons that normally terminate in the spinal cord.

Viability of mature superior cervical ganglia transplants in peripheral nerve of adult rat

Allografts of mature rat superior cervical ganglia (SCG) survived for up to 120 days following transplantation to regenerating and degenerating peripheral nerves of adult rats. Transplants contained the constituents of normal superior cervical ganglia and there was evidence of outgrowth of catecholamine containing fibers from the transplants. However, fibers did not attain the length necessary to enter peripheral muscles and no muscle response could be elicited by electrical stimulation of the implanted nerve where the transplanted mature SCG was the only source of nerve fibers.

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.