[Post-traumatic reconnection of the cervical spinal cord with skeletal striated muscles. Study in adult rats and marmosets]. / Reconnexion post-traumatique de la moelle épinière cervicale avec la musculature striée squelettique. Etude chez le rat et le marmouset adultes.

In an attempt at repairing the injured spinal cord of adult mammals (rat, dog and marmoset) and its damaged muscular connections, we are currently using: 1) peripheral nerve autografts (PNG), containing Schwann cells, to trigger and direct axonal regrowth from host and/or transplanted motoneurons towards denervated muscular targets; 2) foetal spinal cord transplants to replace lost neurons. In adult rats and marmosets, a PNG bridge was used to joint the injured cervical spinal cord to a denervated skeletal muscle (longissimus atlantis [rat] or biceps brachii [rat and marmoset]). The spinal lesion was obtained by the implantation procedure of the PNG. After a post-operative delay ranging from 2 to 22 months, the animals were checked electrophysiologically for functional muscular reconnection and processed for a morphological study including retrograde axonal tracing (HRP, Fast Blue, True Blue), histochemistry (AChE, ATPase), immunocytochemistry (ChAT) and EM. It was thus demonstrated that host motoneurons of the cervical enlargement could extend axons all the way through the PNG bridge as: a) in anaesthetized animals, contraction of the reconnected muscle could be obtained by electrical stimulation of the grafted nerve; b) the retrograde axonal tracing studies indicated that a great number of host cervical neurons extended axons into the PNG bridge up to the muscle; c) many of them were assumed to be motoneurons (double labelling with True Blue and an antibody against ChAT); and even alpha-motoneurons (type C axosomatic synapses in HRP labelled neurons seen in EM in the rat); d) numerous ectopic endplates were seen around the intramuscular tip of the PNG. In larger (cavitation) spinal lesions (rat), foetal motoneurons contained in E14 spinal cord transplants could similarly grow axons through PNG bridges up to the reconnected muscle. Taking all these data into account, it can be concluded that neural transplants are interesting tools for evaluating both the plasticity and the repair capacities of the mammalian spinal cord and of its muscular connections.

Motoneurons of the injured spinal cord of the adult dog can grow lengthy axons into an autologous peripheral nerve graft. A retrograde axonal tracing study.

To our knowledge, the capacity of injured spinal neurons to regenerate axons into peripheral nerve autografts has not yet been documented with axonal tracing methods in large adult mammals such as dogs. In the present study, one end of an autologous peripheral nerve graft (PNG), 10-15 cm long, was introduced dorsally into the lumbar (L4) spinal cord of six adult beagle dogs, thus producing a small focal lesion. The other end of the PNG was driven outside the spinal cord, then crushed and tied to nearby peripheral tissue with non-absorbable suture. Clinical examination of the operated animals was performed throughout the postoperative period. In five animals (out of six), the neurological deficit induced by the grafting procedure disappeared within five days. Four months after surgery, application of horse radish peroxidase (HRP) to the transected peripheral tip of the PNG led to the retrograde axonal labelling of about 30 lumbar neurons. The labelled cells, which had extended lengthy (up to 10 cm) axons into the PNGs, were mainly located in the vicinity of the intraspinal tip of the grafted nerve. Upon specific criteria, most of them were characterized as motoneurons. As the surgical procedure probably left the original stem axon of these neurons uninjured, it is suggested that axonal production from the labelled motoneurons might have arisen either from collateral axonal sprouts or even directly from the neuronal soma.