REGENERATION OF RAT SCIATIC-NERVES IN SILICONE TUBES - CHARACTERIZATION OF THE RESPONSE TO LOW-INTENSITY D.C. STIMULATION

Endogenous d.c. electric fields have been postulated to play a role in normal development and repair functions of a variety of living system s. The corollary hypothesis, that exogenous electric fields can after development and repair mechanisms, has led to the use of d.c. electric fields as a means to enhance mammalian peripheral nerve regeneration. This study investigates the response of transected rat sciatic nerves within silicone tubes to low intensity d.c. stimulation. In 40 rats, the right sciatic nerves were transected and sutured into silicone tub es, leaving a 5.0 mm gap between the stumps. The nerves were either tr eated with 10 mu A d.c., with the cathode at the midpoint of the tube and the anode distant, or received no exogenous current. Three weeks l ater, transverse sections from the center of the tissue bridging the t wo segments were analysed by sampling approximately 12% of the cross s ectional area, using x 1000 magnification on the light microscope. All non-stimulated (control) nerves showed regeneration of myelinated axo ns at the center of the bridge, while only 35% of the nerves stimulate d with 10 mu A had such a response. Of the nerves with regeneration of myelinated axons at the center of the tube, the control nerves had si gnificantly more myelinated axons (P = 0.0028) than treated nerves. St imulated nerves showed bizarre regeneration responses, including forma tion of multiloculated cysts and neuroma-like formations. In control n erves there was a gradual tapering of axon number from proximal to dis tal in the regeneration bridge, while in the stimulated nerves there w as a sharp decrease in the number of axons proximal to the cathode. We hypothesize that this effect is due to the accumulation of electrolys is products at the cathode, which inhibit regeneration through this re gion. Regeneration of transected rat sciatic nerves is not enhanced by electric currents applied in this manner. Previous work interpreted t he increased number of axonal cross-sections in the tube as an increas e in the absolute number of regenerating fibers. Our data suggest that the increased number of axonal cross-sections is due to neuroma forma tion, probably in response to the accumulation of electrolysis product s at the cathode. This work brings into question claims of an enhancem ent of peripheral nerve regeneration by applied electric fields.