Partial regeneration of the above-elbow amputated rat forelimb. I. Innate responses.

Although a number of recent studies describe the facilitation of limb regeneration by electrical and other forms of stimulation, little is known of innate regenerative capacity in the mammalian limb. The present report describes spontaneous regenerative responses following subtotal forelimb amputation in the young white rat. In one group of animals the forelimb was amputated through the lower humerus and the skin sutured closed. In a second group, adjacent muscle tissue still attached to bone at its origin(s) was interposed between the cut surface of the humerus and the skin. Among animals of the first group (skin closure only) bone growth and limb regenerative responses were generally not observed. Animals of the second group displayed significant elaborations of cartilage and bone at the limb terminus. The appearance and subsequent modification of these tissues suggest that some capacity for limb regeneration exists innately in the young rat and can be more readily evoked than has been recognized heretofore. It is concluded that extant and forthcoming reports of electrically stimulated skeletal tissue growth, repair and regeneration among eutherial mammals should be examined to determine whether reported responses to stimulation represent advances beyond what might be expected from innate replacement processes alone.