Spinal cord implantation of avulsed ventral roots in primates; correlationbetween restored motor function and morphology

Functional restitution following spinal cord implantation of avulsed ventra l roots was assessed electromyographically and correlated with the morpholo gy of the regenerated neural structures in primates. The C5-C8 Ventral root s were avulsed from the spinal cord in seven Macaca fascicularis monkeys. I n three animals the roots were immediately reimplanted into the ventrolater al part of the spinal cord. In two monkeys the avulsed roots were reimplant ed with a delay of 2 months and in two control animals the roots were not r eimplanted. There was substantial recovery of function after both immediate and delayed spinal cord implantation of the avulsed ventral roots. The pop ulation of neurons that had regenerated was larger than on the control side , indicating a rescue of cells after an immediate root implantation. Differ ent functional types of neurons had been attracted to regrow axons to the i mplanted root as judged by their position in the ventral horn. Thus, neuron s normally supplying antagonistic muscles, such as the triceps muscle, part icipated in the innervation of the biceps muscle. Functionally this deficie nt directional specificity was correlated to both spasticity and co-contrac tions among agonistic and antagonistic muscles. Occasional electromyographi c signs of function occurred also in control animals where the avulsed root s had not been implanted. This recovery was found to depend on regrowth fro m the sire of avulsion, within the pie mater among the leptomeningeal cells and to the avulsed roots. The acceptable functional dexterity regained due to corrective surgery is discussed in terms of neurotrophism and plasticit y.