Fig. 2.8. The electrical mechanism producing regeneration of the salamander limb. After the
epithelium alone grows over the end of the amputation stump, and the nerve fibers that were cut
regrow, these two tissues grow together at the end of the stump. The nerve fibers attach themselves to
the epithelial cells, producing a neuro-epidermal junction. This strucrure is then responsible for
producing the specific electrical current that causes the cells left in the stump to dedifferentiate. If the
neuro-epidermal junction fails to form for any reason, regeneration will not occur.
In an attempt to evaluate this concept we attempted to surgically produce such neuroepidermal
junctions in animals that normally lacked regenerative ability (46). Hind limb amputations were done
in a series of adult rats. Experimental animals had the sciatic nerve surgically inserted into the
epidermis, while control animals had the nerve similarly mobilized but not inserted into the epidermis.
The skin was sewn closed over the amputation stump and representative animals were sacrificed and
the area examined daily. We found that, by the third postoperative day, the sciatic nerve in the
experimental animals had grown laterally into the epidermis where it made junctions with the
epidermal cells similar to the NEJ of the salamander. In the same group, blastemas appeared by the
fifth day and regeneration of the major part of the hind limb ensued. No junctions were formed in the
control group and neither blastemas nor regenerative growth occurred. Of most interest, however, were
electrical measurements that were made daily on all animals. The control group demonstrated a series
of potential changes identical to those of the nonregenerating frog or normal rat, while in the
experimental group the changes paralleled those of the normal regenerating salamander, with a
negative potential appearing concurrent with the formation of the junction between the nerve and the
epidermis. It would now appear fairly certain that the specific sequence of changes in electrical
potential that produce regenerative growth are themselves produced by the neuro-epidermal junction
and not by either the nerves or the epidermis alone.
Intrinsic electromagnetic energy inherent in the nervous system of the body is therefore the
factor that exerts the major controlling influence over growth processes in general. The nerves, acting
in concert with some electrical factor of the epidermis, produce the specific sequence of electrical
potential changes that cause limb regenerative growth. In animals not normally capable of regeneration
this specific sequence of electrical changes is absent. However, it can be simulated by artificial means,
resulting in blastema formation and major regenerative growth even in mammals.
The two effects of the intrinsic DC system previously described-biasing the activity level of the
neurones and the stimulation of growth processes-obviously require exquisite sensitivity of certain cells
to extremely low levels of current. In the case of the neurone, the cellular response is an alteration
presumably in the properties of the membrane, rendering it more or less active in generating action
potentials. In the case of growth stimulation, however, the cellular response is much more complex. In
regenerative growth, for example, the blastema is formed by the dedifferentiation of mature specialized
ELECTROMAGNETISM & LIFE - 36