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Electrical currents near regenerating newt limbs were measured with a recently developed vibrating probe.Steady currents with local surface densities of 10 to 100 MA/cm2 or more leave the end of the stump during the first 5-10 days after amputation and are balanced by currents with densities of only 1-3 jA/cm2 that enter the intact skin around the stump. They are immediately dependent upn the entry of sodium ions into this skin and are therefore inferred to be skin-driven. The outward currents are comparable in direction, density, duration, and position to artificially imposed currents previously found sufficient to induce significant regeneration of amputated adult frog limbs. This comparison suggests that the endogenous stump currents play some causal role in initiating regeneration. We have recently demonstrated that anuran limb regeneration can be initiated by driving a small steady current through the stump. The effective stimulus is truly electrical (i.e., the effect is not mediated by electrode products). Current must be pulled out of the stump to induce regeneration, whereas inward current actually induces degeneration (1). Many other stimuli are known to induce a measure of regeneration in adult anurans (2, 3). The critical question is whether a comparable electrical component is part of a natural control system. As a first step in answering this question, we ask whether normally regenerating amphibian stumps generate comparable currents after amputation.An old and nearly forgotten paper of Monroy's indicates that endogenous currents do, indeed, leave the regenerating amphibian stump surface (4). Monroy used a relatively low-resistance galvanometer to make these measurements. Hence, as will be discussed below, it is possible to estimate the size of these currents. Two subsequent studies have yielded somewhat contradictory results (5-7). However, both Becker and the Roses used instruments with very high resistance, so the resistance between the points of measurement was essentially the resistance along the skin surface. Because this was not measured, the size of the currents responsible for the measured voltages cannot be inferred.We have therefore reinvestigated the stump currents in amputated and regenerating newt limbs, using the recently developed ultrasensitive vibrating probe (8). With it, one can directly measure the pattern of current densities entering or leaving a biological source immersed in its natural aqueous medium. Furthermore, the probe is placed at a sufficient distance from the animal as to practically avoid disturbing it. The probe is vibrated between two external points and registers the minute voltage difference generated by any current that may travel between these two points. The only accessory measurement needed to infer the current density is the resistivity of the medium. Use of the vibrating probe allows one to measure exThe costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertis...

The strength of the electric fields in the vicinity of 1.5 mm circular lesions in the bovine cornea has been found to influence the rate of re-epithelization. A decrease in the field strength by submersion of the lesions or by treating the lesions with the Na+-channel blocker, benzamil, significantly retarded healing. An increase in the field strength of lesions treated with Na+-depleted Hanks' solution, by the addition of direct current, increased epithelization. Epithelization was fastest in wounds with field strengths raised to - 80 mV/mm, more than twice the normal field strength present in wounds maintained in Hanks' solution alone. Epithelization decreased, however, when the field strengths were increased to -120 mV/mm. A similar pattern was also observed when the field's polarity was reversed. By manipulating and monitoring the field strengths, we have been able to show for the first time that increased wound field strengths enhance corneal wound epithelization, and that field strengths with reversed polarity also enhance this epithelization.

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We have applied 0.2 pamps of current to the forelimb stump of Rana adults for several weeks. The stimulator was designed to avoid introduction of any physiologically active electrode products into the tissue. Current was applied to the dorsal postaxial region of the stump. Cathodal (i.e., distally negative) current initiated partial regeneration; anodal (i.e., distally positive) current initiated extensive destruction of the limb; while implantation of sham stimulators (delivering no current) yielded limbs showing just a healing response. Regeneration was indicated by organized extension of the severed radio-ulna, newly formed muscle, ligament, and isolated cartilage rods that were partially segmented. Moreover, extraordinarily large amounts of nerve developed in the regenerated tissue. We conclude that the cathodally initiated regeneration was mediated by small electrical fields within the stump and not by electrode products. However, a n electrode product (Ag' ion) cannot be completely excluded as a possible mediator of anodal destruction.