Effects of age and nerve-repair grafts on reinnervation and fiber type distribution of rat medial gastrocnemius muscles

Abstract

Aging is associated with a decline in skeletal muscle function. Previous research suggests that this decline in skeletal muscle function may, in part, be explained by an age-associated decline in the ability of skeletal muscle to reinnervate and/or age-associated changes in fiber types and distribution during reinnervation. This study used a nerve-repair graft model to investigate age-associated changes in the ability to reinnervate via expression of neural cell adhesion molecule (NCAM), a marker of denervated and recently reinnervated muscle fibers and changes in fiber type and Type I fiber grouping in medial gastrocnemius (MG) muscles of 6-, 12-and 24-month-old male Fischer 344 rats. Age had no effect on total MG muscle fiber number. Aging and nerve-repair grafting led to an increase in percent Type I and a decrease in percent Type IIB fibers. Aging and nerve-repair grafting led to an increase in NCAM positive fibers and an increase in the percentage of enclosed Type I muscle fibers, which was greatest in the 24 month nerve-repair grafted group. Thus, we conclude that diminished contractile function of aged and/or nerve-repair grafted MG muscle may be explained, in part, by an increase in the percentage of denervated fibers.

Automated rodent in situ muscle contraction assay and myofiber organization analysis in sarcopenia animal models

“…In this study, several histological features of muscle aging, including fiber degeneration and disorganization, were observed. All aged rats showed an increased proportion of type I over type II fibers, which is in agreement with the literature (30). However, the organization/distribution of type I fibers in relation to type II fibers appeared to be different among aged rats.…”

“…In the unsuccessful cohorts, a higher percentage of type I fibers is clustered together in aged rats (Fig. 7, A, C, and E) (30).…”

“…A85 has the most-abundant type I fibers. observations are related to the fact that these muscles are predominantly composed of fast-fatigable fibers (ϳ75%), which are affected more significantly by aging than fatigue-resistant fibers (2,10,30,51). On the other hand, body composition parameters were poor predictors of muscle function (58).…”

“…Sarcopenia is frequently associated with a significant loss of type II fibers (1,30,31), structural changes that affect "muscle quality", including motor unit remodeling (39), altered muscular architecture (21,42), type I fiber grouping (35), reduced type II fiber size (34,36), changes of major histocompatibility complex expression pattern (28,49), and changes in extracellular matrix composition. To characterize myofiber remodeling, ATPase activity-based muscle histology enables differential staining of subtypes of myofibers (23,48).…”

Engineered Skeletal Muscle Units for Repair of Volumetric Muscle Loss in the Tibialis Anterior Muscle of a Rat

“…34 Past studies in our lab have also demonstrated that reinnervation of the rat medial gastrocnemius muscle after denervation is an extensive process that may require over 3 months before maximum recovery is achieved. 35 Thus, despite the promising innervation and neuromuscular junction formation observed in our SMUs, it is likely that their neuromuscular interfaces had not yet fully matured after only 28 days in vivo. We hypothesize that given greater time to recover, the developing muscle fibers within our SMUs will increase their size and strength toward that of native muscle fibers.…”