Sm. Hanson et Me. Mcginnis, REGENERATION OF RAT SCIATIC-NERVES IN SILICONE TUBES - CHARACTERIZATION OF THE RESPONSE TO LOW-INTENSITY D.C. STIMULATION, Neuroscience, 58(2), 1994, pp. 411-421
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.