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

Regenerated host axons form synapses with neurons derived from neural stem cells transplanted into peripheral nerves

It is reported that neural stem cells (NSC) can arrest denervated muscle atrophy and promote nerve regeneration when transplanted into injured peripheral nerves, and that regenerated host axons can form synapses with transplanted and differentiated NSC. In this study, F344 rat nerve segments and F344 rat NSC were transplanted into host green fluorescence protein (GFP) transgenic F344 rats. This allowed transplanted F344 rat tissue to be used as a nonluminous background for the clear visualization of regenerated host GFP axons. Regenerated host axons grew into the transplanted F344 nerve segment 2 weeks after nerve anastomosis. Immunohistochemical staining and confocal microscope analysis revealed that regenerated host axons formed synapses with NSC-derived neurons. The findings confirmed that regenerated peripheral axons form synapses with neurons in peripheral nerves, possibly forming the basis for clinical application in peripheral nerve injury.

Neurotrophic factors improve muscle reinnervation from embryonic neurons

Motoneurons die in diseases like amyotrophic lateral sclerosis and after spinal cord trauma, inducing muscle denervation. We tested whether transplantation of embryonic cells with neurotrophic factors into peripheral nerve of adult rats improves muscle reinnervation and motor unit function more than cells alone. One week after sciatic nerve section, embryonic ventral spinal cord cells were transplanted into the tibial nerve with or without glial cell line-derived neurotrophic factor, hepatocyte growth factor, and insulin-like growth factor-1. These cells represented the only neuron source for muscle reinnervation. Ten weeks after transplantation, all medial gastrocnemius muscles contracted in response to electrical stimulation of cell transplants with factors. Only 80% of muscles responded with cells alone. Factors and cells resulted in survival of more motoneurons and reinnervation of more muscle fibers for a given axon (motor unit) number. Greater reinnervation from embryonic cells may enhance muscle excitation by patterned electrical stimulation.

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.

Restoration of neurological functions by neuroprosthetic technologies: future prospects and trends towards micro-, nano-, and biohybrid systems

Today applications of neural prostheses that successfully help patients to increase their activities of daily living and participate in social life again are quite simple implants that yield definite tissue response and are well recognized as foreign body. Latest developments in genetic engineering, nanotechnologies and materials sciences have paved the way to new scenarios towards highly complex systems to interface the human nervous system. Combinations of neural cells with microimplants promise stable biohybrid interfaces. Nanotechnology opens the door to macromolecular landscapes on implants that mimic the biologic topology and surface interaction of biologic cells. Computer sciences dream of technical cognitive systems that act and react due to knowledge-based conclusion mechanisms to a changing or adaptive environment. Different sciences start to interact and discuss the synergies when methods and paradigms from biology, computer sciences and engineering, neurosciences, psychology will be combined. They envision the era of "converging technologies" to completely change the understanding of science and postulate a new vision of humans. In this chapter, these research lines will be discussed on some examples as well as the societal implications and ethical questions that arise from these new opportunities.

A critical review of interfaces with the peripheral nervous system for the control of neuroprostheses and hybrid bionic systems

Considerable scientific and technological efforts have been devoted to develop neuroprostheses and hybrid bionic systems that link the human nervous system with electronic or robotic prostheses, with the main aim of restoring motor and sensory functions in disabled patients. A number of neuroprostheses use interfaces with peripheral nerves or muscles for neuromuscular stimulation and signal recording. Herein, we provide a critical overview of the peripheral interfaces available and trace their use from research to clinical application in controlling artificial and robotic prostheses. The first section reviews the different types of non-invasive and invasive electrodes, which include surface and muscular electrodes that can record EMG signals from and stimulate the underlying or implanted muscles. Extraneural electrodes, such as cuff and epineurial electrodes, provide simultaneous interface with many axons in the nerve, whereas intrafascicular, penetrating, and regenerative electrodes may contact small groups of axons within a nerve fascicle. Biological, technological, and material science issues are also reviewed relative to the problems of electrode design and tissue injury. The last section reviews different strategies for the use of information recorded from peripheral interfaces and the current state of control neuroprostheses and hybrid bionic systems.

Stem cell transplantation and other novel techniques for promoting recovery from spinal cord injury

A number of potential approaches aim to optimize functional recovery after spinal cord injury. They include minimizing the progression of secondary injury, manipulating the neuroinhibitory environment of the spinal cord, replacing lost tissue with transplanted cells or peripheral nerve grafts, remyelinating denuded axons, and maximizing the intrinsic regenerative potential of endogenous progenitor cells. We review the application of stem cell transplantation to the spinal cord, emphasizing the use of embryonic stem cells for remyelinating damaged axons. We speculate that harnessing the potential of endogenously born stem cells already present in the spinal cord represents an important therapeutic target. We also discuss the potential application of peripheral nervous system reconstruction to recovery from spinal cord injury. The principles of peripheral nerve regeneration and concepts of nerve grafting are reviewed. Particular attention is given to peripheral nerve allotransplantation for repairing extensively injured tissue when autologous donor nerve material is scarce. The potential role of nerve transfers for reconstructing the injured spinal cord, particularly the cauda equina and lumbosacral plexus, are also described.

Functional motor neurons differentiating from mouse multipotent spinal cord precursor cells in culture and after transplantation into transected sciatic nerve

OBJECT

One of the current challenges in neurobiology is to ensure that neural precursor cells differentiate into specific neuron types, so that they can be used for transplantation purposes in patients with neuron loss. The goal of this study was to determine if spinal cord precursor cells could differentiate into motor neurons both in culture and following transplantation into a transected sciatic nerve.

METHODS

In cultures with trophic factors, neurons differentiate from embryonic precursor cells and express motor neuronal markers such as choline acetyltransferase (ChAT), Islet-1, and REG2. Reverse transcription-polymerase chain reaction analysis has also demonstrated the expression of Islet-1 in differentiated cultures. A coculture preparation of neurospheres and skeletal myocytes was used to show the formation of neuromuscular connections between precursor cell-derived neurons and myocytes both immunohistochemically and electrophysiologically. Following various survival intervals, precursor cells transplanted distal to a transection of the sciatic nerve differentiated into neurons expressing the motor neuron markers ChAT and the alpha1 1.2 (class C, L-type) voltage-sensitive Ca++ channel subunit. These cells extended axons into the muscle, where they formed cholinergic terminals.

CONCLUSIONS

These results demonstrate that motor neurons can differentiate from spinal cord neural precursor cells grown in culture as well as following transplantation into a transected peripheral nerve.

A biohybrid system to interface peripheral nerves after traumatic lesions: design of a high channel sieve electrode

Peripheral nerve lesions lead to nerve degeneration and flaccid paralysis. The first objective in functional rehabilitation of these diseases should be the preservation of the neuro-muscular junction by biological means and following functional electrical stimulation (FES) may restore some function of the paralyzed limb. The combination of biological cells and technical microdevices to biohybrid systems might become a new approach in neural prosthetics research to preserve skeletal muscle function. In this paper, a microdevice for a biohybrid system to interface peripheral nerves after traumatic lesions is presented. The development of the microprobe design and the fabrication technology is described and first experimental results are given and afterwards discussed. The technical microprobe is designed in a way that meets the most important technical requirements: adaptation to the distal nerve stump, suitability to combine the microstructure with a containment for cells, and integrated microelectrodes as information transducers for cell stimulation and monitoring. Micromachining technologies were applied to fabricate a polyimide-based sieve-like microprobe with 19 substrate-integrated ring electrodes and a distributed counter electrode. Monolithic integration of fixation flaps and a three-dimensional shaping technology led to a device that might be adapted to nerve stumps with neurosurgical sutures in the epineurium. First experimental results of the durability of the shaping technology and electrochemical electrode properties were investigated. The three-dimensional shape remained quite stable after sterilization in an autoclave and chronic implantation. Electrode impedance was below 200 kOmega at 1 kHz which ought to permit recording of signals from nerves sprouting through the sieve holes.

Immunohistochemical characterization of axonal sprouting and reactive tissue changes after long-term implantation of a polyimide sieve electrode to the transected adult rat sciatic nerve

The development of artificial microstructures suited for interfacing of peripheral nerves is not only relevant for basic neurophysiological research but also for future prosthetic approaches. Aim of the present study was to provide a detailed analysis of axonal sprouting and reactive tissue changes after implantation of a flexible sieve electrode to the proximal stump of the adult rat sciatic nerve. We report here that massive neurite growth after implantation, steadily increasing over a period of 11 months, was observed. Parallel to this increase was the expression of myelin markers like Po, whereas non-myelin-forming Schwann cells did not change. Compared to five weeks post-implantation. where both Schwann-cell phenotypes were intermingled with each other, non-myelin-forming Schwann cells occupied a peripheral position in each microfascicle after 11 months. After an initial increase, hematogenous macrophages were down-regulated in number but maintained close contact with the implant. However, at no time were signs of its degradation observed. It is concluded that the introduced flexible polyimide electrode is suitable for contacting peripheral nerves since it permits substantial neurite growth and offers excellent long-term stability.

Towards micro electrode implants: in vitro guidance of rat spinal cord neurites through polyimide sieves by Schwann cells

Our goal is to develop biohybrid neural microprobe implants with sieve electrodes for external stimulation of co-implanted neurons whose axons penetrate through the holes of electrodes and innervate host targets such as denervated muscle fibers. For evaluation of implants, potential scar formation was imitated in fibroblast-spinal cord co-cultures. In vitro neurite extension through flexible 10-microm thick polyimide sieves was inhibited by co-cultured fibroblasts. In contrast, the neurite penetration of sieves could be greatly stimulated by oriented exposure to Schwann cells. To our knowledge this is the first direct proof that Schwann cells display a guidance effect on spinal cord neurons in vitro. The results pave the way for novel biohybrid neuro-implants and provide means to circumvent the obstacle of inhibitory scar formation.

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.