The lack of an effect of applied d.c. electric fields on peripheral nerve regeneration in the guinea pig.

This study was undertaken to provide evidence of enhanced regeneration of mammalian peripheral nerves in response to applied d.c. electric fields. Peroneal nerves of adult guinea-pigs were crushed or transected and anastomosed. Constant current d.c. stimulators (20 microA) were implanted in the flank with platinum/iridium electrodes routed to the ankles. Animals with crush lesions were tested for toe spreading ability from the 14th to the 23rd day following the lesion. Animals with transection lesions were allowed to recover for 40 days and isometric force measurements of toe abduction and foot flexion were made. Both myelinated and unmyelinated fiber densities were determined. There proved to be no difference between legs treated with an anode, a cathode, or a sham electrode as evaluated by: the time to return of the toe spreading reflex, the isometric force of either twitches or tonic contractions, the latency between stimulation and contraction, or the number or density of either myelinated or unmyelinated fibers. These negative results are at variance with other studies that have reported beneficial effects of d.c. electric fields on peripheral nerve regeneration. The stimulation and analysis techniques used in this study were well within the variety of protocols that have yielded reports of highly significant positive effects with smaller numbers of animals than used in this study. The conclusion is that either there is a subtle but highly specific and critical difference between the present protocol and others, or the other studies need to be reevaluated. In either case, it seems that the ability of applied d.c. fields to enhance peripheral nerve regeneration in vivo remains open to question.