Tenotomy of the avian anterior latissimus dorsi muscle. II. Can regeneration from the stump occur in the pigeon?

Myosin heavy-chain composition in striated muscle after tenotomy

The myosin heavy-chain (MHC) isoform pattern was studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles of adult rats during atrophy after tenotomy and recovery after tendon regeneration. The tenotomized slow muscle atrophied more than the tenotomized fast muscle. During the 12 days after tenotomy the total MHC content decreased by about 85% in the slow muscle, and only by about 35% in the fast muscle. In the slow muscle the ratio of MHC-1 to MHC-2A(2S) remained almost unchanged, showing that similar diminution of both isoforms occurs. In the fast muscle the MHC-2A/MHC-2B ratio decreased, showing the loss of MHC-2A mainly. After tendon regeneration, the slow muscle recovered earlier than the fast muscle. Full recovery of the muscles was not observed until up to 4 months later. The embryonic MHC, which seems to be expressed in denervated adult muscle fibres, was not detected by immunoblotting in the tenotomized muscles during either atrophy or recovery after tendon regeneration. The influence of tenotomy and denervation on expression of the MHC isoforms is compared. The results show that: (a) MHC-1 and MHC-2A(2S) are very sensitive to tenotomy, whereas MHC-2B is much less sensitive; (b) expression of the embryonic MHC in adult muscle seems to be inhibited by the intact neuromuscular junction.

Myosin isozyme expression in response to stretch-induced hypertrophy in the Japanese quail

When skeletal muscle is subjected to stretch it undergoes a rapid increase in muscle mass. However, the effect of stretch on the native myosin isozyme content of muscle has received attention only recently. Using the Japanese quail to investigate stretch-induced hypertrophy, we demonstrated an increase in the expression of fast myosin in the predominantly slow anterior latissimus dorsi muscle (ALD). The fast myosin content of the control quail ALD is not sufficient to be quantified on native myosin pyrophosphate gels. After 33 days of stretch, the fast myosin content (N = 10) averaged 16 +/- 11% in the stretched muscles and reached a maximum of 40%. Mean hypertrophy in the stretched muscle, as indicated by muscle weight, was 247 +/- 91% (range, 168-378%). Fast myosin was consistently expressed in muscles with hypertrophy greater than 250%. Muscle fiber size from the stretched muscles contained a greater number of fibers with small cross-sectional areas than was observed in controls. These results indicate that substantial remodeling occurs in the stretched ALD muscle of the Japanese quail.

Quantitative ultrastructure of histochemically identified avian skeletal muscle fiber types

A cryostat retrieval method and combined adenosine triphosphatase (ATPase) and acetylcholinesterase (AChase) method were used to study the ultrastructure and innervation of histochemically identified skeletal muscle fibers in different pigeon muscles. The Z-line structure and volume percentage sarcotubular system were analyzed from different muscles selected for their composition by fiber type. Histochemically, three main fiber types were investigated: slow tonic fibers with a moderate ATPase activity after preincubation at acid or alkaline pH; fast-twitch fibers that had high activity after alkaline treatment and low activity after acid preincubation; and a type considered to be slow-twitch that had low activity after alkaline, and high after acid preincubation. Both the slow tonic and slow-twitch fibers had multiple, en grappe innervation, while the fast-twitch fibers had robust, single end plates. The Z-line of the fast-twitch and slow-twitch fibers had a regular square lattice pattern, in contrast to the granular, nonlattice structure of the slow tonic Z-line. The volume percentage sarcotubular system of the slow-twitch fibers was intermediate between and significantly different from that of the fast-twitch and slow tonic fibers. These correlative analyses suggest that the avian muscles contain not only the fast-twitch and slow tonic fibers previously known, but also a slow-twitch fiber that appears to be intermediate between the tonic and the mammalian slow-twitch fiber type. Based on the abundance of the sarcotubular system, this fiber type appears to be fast-contracting and -relaxing, in spite of being multiply innervated.

Ultrastructural and cytological changes in the muscle fibers of the pectoralis of the giant Canada goose (Branta canadensis maxima) in disuse atrophy during molt

Adult male Branta canadensis maxima were collected from a nonmigratory feral population during their premolt, molt and postmolt phases. Lean dry weight of the pectoralis muscle decreased significantly (p less than or equal to 0.0001) during molt, as a result of disuse atrophy. Histochemical analysis revealed that the region of the pectoralis muscle sampled consisted of Red (fast-twitch oxidative-glycolytic) and White (fast-twitch glycolytic) muscle fiber types, in an approximate ratio of 9 to 1. There was no significant (p = 0.1238) difference in the relative percentages of the two fiber types during the three periods of study. There was, however, a significant decrease in mean cross-sectional area of both Red (p less than or equal to 0.0194) and White (p less than or equal to 0.0001) fibers during molt. Red and White fiber areas were strongly correlated with each other during molt (r2 = 0.76, p = 0.0010) and postmolt (r2 = 0.70, p = 0.0052), but not during premolt (r2 = 0.02, p = 0.7626). The latter finding may be related to fiber-type specific hypertrophy in premolt breeding males. Analysis of ultrastructure revealed that there was a significant (p = 0.0003) decrease in the mean myofibrillar cross-sectional area, and a significant increase in both the density (p = 0.0227) and total number (p = 0.0058) of myofibrils within the muscle fibers of the molting birds. These results indicate that the myofibrils split longitudinally during molt-associated disuse atrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Network and lamellar structures in the tail muscle fibers of the metamorphosing anuran tadpole

Networks of regularly arranged tubular units and lamellar structures were observed in the degenerating tail muscle fibers of spontaneously metamorphosing anuran tadpoles. These networks appeared to be similar to those previously found in the skeletal muscle of other animals under abnormal conditions. They stained clearly with ruthenium red (RR) and a continuity with the transverse tubular system (T tubules) of triads was clearly observed. The diameter of the tubular unit, 20-25 nm, was almost equal to that of the T tubules of the intact tail muscle fibers, indicating the network structures were probably formed by T tubules connecting together. In the early stages of metamorphosis, networks in the tetragonal configuration were observed within the end region of the muscle fibers. At the climax of metamorphosis, well-developed networks in which the tubular units were arranged in a hexagonal pattern were seen in various regions of the fibers. Other observed lamellar structures may originate from lateral elements of the triads. The formation of the network structure is discussed.

Heterogeneity of the chicken ALD muscle: evidence for a minor, twitch fiber type

Examination of the anterior latissimus dorsi muscle of the chicken using histochemical, immunofluorescent, and ultrastructural techniques revealed the presence of a minor muscle fiber type which was similar but not identical to the fast-twitch fibers of the posterior latissimus dorsi muscle. Heterogeneity of muscle fiber type appeared within the 1st week after hatching.

Skeletal muscle-smooth muscle interaction: an unusual myoelastic system

The serratus superficialis metapatagialis (SSM) of pigeons is a skeletal muscle with unusual properties. It lies between the ribs and the trailing edge of the wing, where it is attached to the skin by a system of smooth muscles having elastic tendons. Wing movements during flight induce marked changes in this muscle's length. The SSM inserts onto the deep fascia, and at its termination the skeletal muscle contains large numbers of microtubules. Many myofibrils attach to leptomeric organelles, which then attach to the terminal end of the skeletal muscle fiber. The deep fascia next connects to the dermis of the skin by bundles of smooth muscles that have elastic tendons at both ends. This system allows large movements of the muscle while preventing its fibers from overstretching. The movements and presumed forces acting at this muscle make the presence of sensory receptors such as muscle spindles unlikely. Spindles are absent in this muscle.

Patterns of avian muscle fiber type regeneration. Evidence for a myotrophic influence

Serratus superficialis metapatagialis (SSM) and posterior biventer cervicis (BVC) muscles were free-grafted into the site of the slow tonic anterior latissimus dorsi (ALD) of adult pigeons. Grafts were prepared for histochemical examination at 1, 3, 7, 12 and 15 days; at monthly intervals from 1 to 4 months; and at various intervals up until 23 months after surgery. Few original muscle fibers survived the trauma of grafting and contributed to the regenerated muscle. The arrangement of fast and slow fibers and the percentage of slow fibers were recorded for each graft at least one month of age. Young grafts of the SSM (one to four months of age) regenerated a segregated pattern of fast and slow fibers that resembled control SSM muscles, whereas early grafts of the BVC regenerated a mosaic arrangement characteristic of normal BVC muscles. The percentages of slow fibers in both SSM and BVC grafts up to 4 months after surgery did not significantly differ from control muscles. Both SSM and BVC grafts older than 4 months of age had a significantly higher percentage of slow fibers than control muscles. These data indicate that the donor muscle influences the pattern of fiber types that is originally manifested and this pattern is maintained relatively intact for 4 months. Eventually the nerve at the host site modifies this pattern, and the fibers of the graft assume the histochemical characteristics of the muscle removed from the host site. In addition, the time required for histochemical stabilization of muscle fibers of avian heterotopic autografts is longer than that for whole muscle grafts in rats or avian minced muscle preparations, and is comparable to tenotomized avian muscle.

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.