The number of nerve fibers in the limb of the mouse and its relation to regenerative capacity

Abstract

In regeneration of the salamander limb the nerve must satisfy a quantitative threshold below which regeneration does not occur. The present work explores the reason for the inability of the mammalian limb to regenerate by analyzing the number of nerve fibers available in the wound of the amputated limb. The number expressed per unit area of amputation wound is only 16% of that of the newt, Triturus, a regenerating form. It is known that when the number of fibers in the newt's limb is reduced to about a third or less of the normal number, regrowth docs not occur. The results are discussed against the background of published unsuccessful attempts to induce regrowth in the mammal. Finally, the results affirm findings published previously of a n evolutionary trend in the vertebrate series of decline in quantity of peripheral innervation which attended elaboration of central nervous mechanisms.

Response of amputated rat limbs to fetal nerve tissue implants and direct current

“…The greater the number or caliber of nerves per unit amputation area, the larger the amount of trophic agent delivered. He and Rzehek found, for instance (15), that in the mammal (mouse) the limb contains only 16% of the number of nerves per unit area of amputated limb as that found in the newt. These nerves are also thinner.…”

Prospects for human digit regeneration

“…Calculation of the number of nerve fibers per unit area in this lizard gave a value that was about half that obtained for the salamander (Zika and Singer, 1965). Equivalent calculations for mammalian limbs indicated that the corresponding value here was half again that of the lizard (Rzehak and Singer, 1966). T h e implication seems to be that there is a relationship between the degree of peripheral innervation and the ability to regenerate.…”

The threshold quantity of nerve required to induce limb regeneration in the chick embryo

“…The threshold was calculated to be about one third to one half the normal nerve supply. It has been shown by Rzehak and Singer [1966] that the mouse, which does not regenerate amputated limbs, has only 16% as many nerve fibers per unit area as the regenerating urodele. The nerve deficit in limbs is smaller in the lizard, a form that can be stimulated to regenerate by deviating additional nerves from the opposite limb to the amputated side [Singer, 1961;Kudokotsev, 19621.…”