The regeneration of a limb muscle in the axolotl from minced fragments.

In over 50 cases the puho-ischio-tibialis muscle in mature axolotls was removed, minced and the minced fragments replaced into the site from which the muscle was removed. In 13 control animals the same muscle was removed but nothing was replaced. Regenerates were studied at postaperational intervals of up to 150 days. Both grossly and histologically the regeneration of muscles from minced fragments in the axolotl follows a course very similar to that observed in frogs and rats. There is an initial period of destruction of the sarcoplasm of the minced muscle fragments. This is characterized by intense phagocytic activity. Following this, a population of myoblasts is established and the differentiation of mature muscle fibers ensues. The regeneration of muscles from minced fragments is compared with the formation of muscles in regenerating limbs. Following mincing, new muscle fibers develop rapidly and without the mediation of a blastema. Following limb amputation, a blastema 1s established before any differentiation of muscle occurs in the regenerate. This occurs more slowly than the differentiation of muscle fibers following mincing. The implications of these differences are discussed. '68) have demonstrated that completely removed muscles in higher vertebrates (frogs, chickens and rats) can be reconstituted from re-implanted minced muscle fragments by a regenerative process his-tologically similar to that which occurs after many types of minor trauma. This type of regeneration is often referred to as tissue regeneration and consists of the appearance of a population of myoblastic cells, their fusion into multinucleated strap-like elements called sarcoblasts or myo-tubes and the differentiation of the elements of the contractile apparatus within these regenerating fibers. Such muscle re-generation proceeds without the early appearance of a blastema, but neither the cellular origin of the myoblastic cells nor the factors which control the differentiation and ultimate morphogenesis of minced muscle regenerates are known.