Effects of static interventions on disuse atrophy of the rat soleus muscle at different sites along its longitudinal axis

Division of loading time in reloading the disused atrophic soleus muscle induces proximal muscle injury

[Purpose] This study aimed to compare the effects of loading time division in reloading atrophied muscles in different muscle long-axis regions. [Materials and Methods] We divided 8-week-old male Wistar rats into control (CON), 14-day hindlimb suspension (HS), 7-day hindlimb suspension followed by 60-min reloading for 7 consecutive days (WO), and 7-day hindlimb suspension followed by 60-min reloading on two separate occasions for 7 days (WT) groups. After the experimental period, muscle fibre cross-sectional area and necrotic fibre/central nuclei fibre ratio were measured in the soleus muscle's proximal, middle, and distal regions. [Results] The necrotic fibre/central nuclei fibre ratio was higher in the WT group than in the other groups in the proximal region. Proximal muscle fibre cross-sectional area was higher in the CON group than in the other groups. In the middle region, only HS group had muscle fibre cross-sectional area lower than the CON group. Similarly, muscle fibre cross-sectional area of the HS group was lower than the CON and WT groups in the distal region. [Conclusion] When reloading atrophied muscles, dividing the loading time can inhibit atrophy in the distal region but induce muscle injury in the proximal region.

Morphological changes of lower leg muscles according to ankle joint position during sitting evaluated by gravity mri in young females

[Purpose] This study aimed to clarify whether the morphological changes of the lower leg muscle occur equally in the longitudinal direction of the muscle according to changes in ankle joint position during sitting. [Participants and Methods] The participants were 15 healthy young females whose dominant lower legs were analyzed. The participants sat with the lower leg vertical to the floor with a neutral, dorsiflexed, or plantarflexed ankle position. Images were obtained from the fibular head from 290 mm distal using gravity magnetic resonance imaging. The muscle cross-sectional areas of the soleus, medial and lateral heads of the gastrocnemius, and anterior tibialis were measured. [Results] The muscle cross-sectional area of the soleus at the 1/4 proximal muscle belly in the plantarflexed position was greater than those in the other positions. The 1/4 distal part in the plantarflexed position was smaller than those in the other positions. The muscle cross-sectional area of the gastrocnemius at the 1/4 distal part in the plantarflexed position was smaller than that in the dorsiflexed position. In contrast, the muscle cross-sectional area of the tibialis anterior at the 1/4 proximal part in the dorsiflexed position was greater than those in the other positions, while that at the 1/4 distal part in the dorsiflexed position was smaller than that in the plantarflexed position. [Conclusion] In the sitting position, the morphological changes of the lower leg muscle according to changes in ankle joint position are not uniform in the longitudinal muscle direction.

Experimental Periodontitis in the Potentialization of the Effects of Immobilism in the Skeletal Striated Muscle

This study aims to evaluate if ligature-induced periodontitis can potentiates the deleterious effects of immobilization in the skeletal striated muscle, contributing to the development of muscle atrophy due to disuse. Forty Wistar rats were divided into four groups: (1) Control Group (CG), (2) Periodontal Disease (PDG), (3) Immobilized (IG), and (4) Immobilized with Periodontal Disease (IPDG). Periodontal disease was induced for 30 days, with ligature method, and the immobilization was performed with cast bandage for 15 days. Prior to euthanasia, nociceptive threshold and muscular grasping force were evaluated. Afterwards, the soleus muscle was dissected and processed for sarcomere counting and morphological/morphometric analysis. For data analysis, was used the one-way ANOVA and post-test Tukey (p < 0.05). The IG and IPDG presented lower muscle weight, lower muscular grip strength, and less number of sarcomeres compared to CG. The PDG showed reduction of muscle strength and nociceptive threshold after 15 days of periodontal disease and increased connective tissue compared to CG. The IPDG presented lower muscle length and nociceptive threshold. The IG presented reduction in cross-sectional area and smaller diameter, increase in the number of nuclei and a nucleus/fiber ratio, decrease in the number of capillaries and capillary/fiber ratio, with increase in connective tissue. The IPDG had increased nucleus/fiber ratio, decreased capillaries, and increased connective tissue when compared to the IG. The IPDG presented greater muscle tissue degeneration and increased inflammatory cells compared to the other groups. Ligature-induced periodontitis potentiated the deleterious effects of immobilization of the skeletal striated muscle.

Alteration of cathepsin-D expression in atrophied muscles and apoptotic myofibers by hindlimb unloading in a low-temperature environment

[Purpose] The purpose of this study was to elucidate the cathepsin-D involvement in signaling pathways for the survival and apoptosis of myofibers in rats with hindlimb-unloading in a low-temperature environment. [Subjects and Methods] Wistar rats were divided into two groups: a control group and a group that underwent hindlimb unloading in a low-temperature environment to induce muscle apoptosis. Cathepsin-D localization in the soleus and extensor digitorum longus muscles, along with the expression of cathepsin-D in apoptotic myofibers, was examined. Expression of the active and inactive forms of cathepsin-D was also analyzed. [Results] Cathepsin-D was mainly expressed in type I myofibers and was observed to have punctate patterns in the control group. In the hindlimb unloading in a low-temperature environment group, the type I myofiber composition ratio decreased, and caspase-3 activation and TUNEL-positive apoptotic myofibers were observed. In caspase-3-activated myofibers, cathepsin-D overexpression and leakage of it into the cytoplasm were observed. In the hindlimb unloading in a low-temperature environment group, the amount of inactive cathepsin-D decreased, whereas that of the active form increased. [Conclusion] Cathepsin-D was deduced to be indicative of a myofiber-type classification and a factor related to myofiber type maintenance. In addition, cathepsin-D leakage into the cytoplasm was appeared to be involved in caspase-3 activation in the hindlimb unloading in a low-temperature environment group.