Tenotomy of the avian anterior latissimus dorsi muscle. I. Effect of age on fiber-type transformation and regeneration from the stump in chicks.

The chick's anterior latissimus dorsi muscle (ALD) was tenotomized at its origin at either 1 day or 4 weeks of age, and investigated histochemically and ultrastructurally at intervals thereafter to determine whether muscle fiber-type transformation from a slow to a twitch type is greater in young birds than older birds. No transformation of fiber type occurred in either procedure, but a new muscular connection regenerated between the scar tissue at the end of the original tenotomized stump and the former origin. This regenerated muscle had a mosaic pattern of fiber types, as demonstrated by myofibrillar ATPase activity, and contained predominantly fast fibers, as contrasted with controls or the tenotomized portion, which contained predominantly slow tonic muscle fibers. The regenerated portion contained muscle spindles. The original portion of the tenotomized muscle was indistinguishable from the control muscle. These responses of the chick ALD to tenotomy are quite different from those in the pigeon, which are reported in the following study.