[Reconstruction of the spinal cord and its motor connections using embryonal nervous tissue transplantation and peripheral nerve autotransplantation. A study in the adult rat].

Our research group is studying, in the adult rat, the conditions of an anatomical and functional reconstruction of the spinal cord and of its motor connections, following a spinal lesion that is either small (focal) or large (depletive). In this attempt to repair the damaged neuronal circuitry, we use, alone on in combination, two transplantation techniques, namely that of embryonic neural tissue, to replace the lost neurons, and that of long segments of autologous peripheral nerves to stimulate and guide either the axonal regrowth from injured host spinal neurons or the axogenesis of transplanted embryonic neurons. The common denominator to the whole experimentation is the setting up of a "nerve bridge" (peroneal nerve autograft) joining the injured cervical spinal cord an aneural region of a nearby denervated skeletal muscle. In a first experimental model (focal lesion), in which only a peripheral nerve autograft is used, it can be observed that local injured (or uninjured?) motoneurons have the actual capacity to extend axons throughout the nerve bridge and, thus, to reach the muscle and reform functional and stable, mainly ectopic, neuromuscular connections. In a second experimental model (depletion lesion) a cavity is made, by suction, in the cervical spinal cord, thus causing a damage which resembles, in some respects, certain types of neurodegenerative spinal lesions. This cavity is filled with different kinds of embryonic neural transplants. The surviving transplanted neurons differentiate axonal projections, some of them extending into the peripheral nerve bridge. Studies aimed at determining the capacities of motor endplate formation by the axons that have grown from these neurons of substitution throughout the nerve bridge, as well as the possibilities of reafferentiation of the transplanted tissues by regenerating host "central" nerve fibres, are in progress.