Axons regenerated through silicone tube splices. I. Conduction properties.

Changes in conduction properties of axons regenerating across a 10-mm gap bridged by a silicone cuff were investigated from compound action potential responses. Compound action potentials were detected as early as 6 weeks after surgery, and were small and slowly conducted at maximum velocities of about 3 m/s. With longer regeneration time, the potentials increased in size, velocity, and complexity. Conduction velocities increased rapidly at first than slowly and asymptotically approached rates that were approximately 40% below normal after 10 months. One component of the compound action potential, the refractory period, decreased from 5 ms to near normal value after only 3 months. The time constant of excitation changed more rapidly, and after 2 months approximated values near those for controls. The properties of axons regenerated across an epineural suture with no gaps. The database for the time course of events established here will be useful in guiding studies using the silicone cuff technique as an in situ experimental chamber for studies of regeneration and remyelination.