WESTPORT, CT (Reuters Health) Jan 04 - Researchers in France and Morocco have found that in a small primate, injured spinal cord axons will migrate into and reinnervate skeletal muscle after insertion of a peripheral nerve graft.
Peripheral nerve grafts have already been shown to promote regeneration of injured spinal cord axons towards a peripheral target, but only in small adult mammals such as rats, according to Dr. Jean-Claude Horvat from Rene Descartes University in Paris, and colleagues.
To see if this approach would also work in a small primate, the researchers transected and crushed the musculocutaneous nerve innervating the biceps brachii muscle in adult marmosets. They then grafted a peripheral nerve from the same animal between the spinal cord and the denervated muscle. Control animals had the graft directly sutured to the transected musculocutaneous nerve.
Within 2 to 4 months after surgery, the graft remained firmly attached to both the spinal cord and the biceps brachii muscle in 8 out of the 10 surviving animals. Stimulation of the graft led to partial or whole muscle contraction, the researchers report in the December 15th issue of the Journal of Neuroscience Research.
Axonal tracing studies showed that a mean of 314 spinal neurons, mostly near the grafting site, grew and extended axons into the peripheral nerve graft, compared with only 45 spinal neurons in the control group. Many of these spinal neurons also grew into the biceps brachii muscle and formed functional motor endplates. In addition, many of these neurons expressed choline acetyl-transferase, which the authors said marked them as motor neurons.
However, they noted that reinnervation of the muscle did not restore muscle mass to normal, at least within the time frame of the study. The mass of the reinnervated muscle remained significantly lower than that of the opposite biceps brachii muscle on the same animal. They did find that the reinnervated muscle had three types of muscle fibers and topographic distribution similar to that in normal muscle.
"Our experimentation clearly indicates that motoneurons of the injured spinal cord of a small-sized primate can re-establish a motor function by extending new axons all the way through a peripheral nerve bridge connected to a denervated skeletal muscle," Dr. Horvat and colleagues conclude. Based on similar experiments conducted in rats and dogs, they suggest that "the size of the animal is a parameter that has to be duly taken into consideration in the study of post-traumatic spinal cord repair."
J Neurosci Res 2000;62:821-829.
2000 Reuters Ltd.