Karina Kouzaki

Effect of Intermittent Low-Frequency Electrical Stimulation on the Rat Gastrocnemius Muscle

Low-frequency neuromuscular electrical stimulation (NMES) has been used as an endurance exercise model. This study aimed to test whether low-frequency NMES increases the phosphorylation of anabolic signaling molecules and induces skeletal muscle hypertrophy, as seen with high-frequency NMES. Using Sprague-Dawley rats, 1 bout of exercise (with dissection done immediately (Post0) and 3 h (Post3) after exercise) and another 6 sessions of training were performed. All experimental groups consisted of high- and low-frequency stimulation (HFS: 100 Hz; LFS: 10 Hz). Periodic acid-Schiff (PAS) staining was conducted to investigate type II fiber activation, and western blot analysis (WB) was conducted to examine whether NMES leads to anabolic intracellular signaling. At first, we examined the acute effect of exercise. PAS staining revealed that glycogen depletion occurred in both type I and type II fibers. WB results demonstrated that p70S6K phosphorylation was significantly increased by HFS, but there was no significant difference with LFS. In contrast, ERK 1/2 phosphorylation was increased by LFS at Post0. In the 6-session training, the wet weight and myofibrillar protein were significantly increased by both HFS and LFS. In conclusion, LFS has a similar anabolic effect for skeletal muscle hypertrophy as HFS, but the mediating signaling pathway might differ.

Eccentric contractions of gastrocnemius muscle-induced nerve damage in rats

We examined the effects of gastrocnemius eccentric contractions (ECs) on the sciatic nerve in rats. Methods: Rats were divided randomly into the following 3 groups: control, 180EC (ECs with 180°/s angular velocity), and 30EC (ECs with 30°/s angular velocity). Twenty ECs were induced by electrical stimulation of the gastrocnemius. On days 3, 7, and 10 after the ECs, nerve conduction velocity (NCV) was measured, and sciatic nerve branches were harvested for analysis. Results: A significant decrease in NCV was observed between the control and day‐7 180EC. Significant reduction in the levels of myelin sheath protein zero (p0) between day 7 and day 3 180EC and a significant increase of macrophage‐related protein and tyrosine kinase receptor C were observed between day 7 180EC and day 7 30EC. Conclusions: ECs with fast angular velocities induce functional and structural damage in innervating nerve. Muscle Nerve 50: 87–94, 2014

Repeated bouts of fast eccentric contraction produce sciatic nerve damage in rats

Introduction: We evaluated sciatic nerve impairment after eccentric contractions (ECs) in rat triceps surae. Methods: Wistar rats were randomly assigned to different joint angular velocity: 180°/s (FAST), 30°/s (SLOW), or nontreated control (CNT). FAST and SLOW groups were subjected to multiple (1–4) bouts of 20 (5 reps, 4 sets) ECs. Nerve conduction velocity (NCV) and isometric tetanic ankle torque were measured 24 h after each ECs bout. We also assessed nerve morphology. Results: After 4 ECs bouts, NCVs and isometric torque in the FAST group were significantly lower than those in the CNT (NCV: 42%, torque: 66%; P < 0.05). After 4 bouts, average nerve diameter was significantly smaller in the FAST group [2.39 ± 0.20 μm vs. 2.69 ± 0.20 μm (CNT) and 2.93 ± 0.24 μm (SLOW); P < 0.05] than that in other two groups. Conclusions: Chronic ECs with high angular velocity induce serious nerve damage. Muscle Nerve 54: 936–942, 2016

Cervical Intervertebral Disc Degeneration and Low Cervical Extension Independently Associated With a History of Stinger Syndrome

Background: Stinger syndrome frequently occurs in athletes who compete in collision sports. Sharp pain and impairment of neck motion are major symptoms. Cervical intervertebral disc degeneration (CIDD) is also frequently observed in those who compete in collision sports. Purpose/Hypothesis: To investigate whether CIDD and neck functionality are related to a history of stinger syndrome. The hypothesis was that a significant relationship exists between CIDD and neck motion and a history of stinger syndrome in Japanese collegiate football players. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 49 male Japanese collegiate football players (mean age, 20.0 ± 1.1 years; mean athletic experience, 3.8 ± 2.3 years; mean height, 172.3 ± 4.8 cm; mean weight, 83.1 ± 12.2 kg) were subdivided into athletes with stinger syndrome (stinger group) and those without (control group). Stinger syndrome was confirmed based on a questionnaire and interview. CIDD was assessed by using T2-weighted magnetic resonance imaging. Range of motion (ROM) and isometric muscle strength were measured for neck function testing. Results: Thirty-nine percent (19/49) of athletes had at least 1 episode of stinger syndrome. The prevalence of CIDD was significantly higher in the stinger group (68%) than in the control group (30%) (P < .01). A statistically significant difference in cervical extension ROM was found between the stinger group (50.9° ± 11.1°) and the control group (60.2° ± 11.4°) (P < .01). Logistic regression analysis showed that CIDD and low cervical extension were independently associated with a history of stinger syndrome. Conclusion: Study results suggest that stinger syndrome is associated with CIDD and low cervical extension in collegiate football players.

Dietary apple polyphenols increase skeletal muscle capillaries in Wistar rats

Dietary apple polyphenols (AP) have been shown to exhibit beneficial effects on muscle endurance. Fast‐to‐slow change in the composition of myosin heavy chains was known as one of the molecular mechanisms. Here, we examined the effects of dietary AP on the capillaries and mitochondria in the rat skeletal muscle to elucidate the mechanisms underlying muscular endurance enhancement. Twenty‐four Wistar male rats were divided into three groups, namely, the control group, 0.5% AP group, and 5% AP group (n = 8 in each group). After a feeding period of 4 weeks, rats were dissected, gastrocnemius muscles were removed, and the density of capillaries and levels of mitochondrial proteins were analyzed. Capillary density of the gastrocnemius increased to 17.8% in rats fed with 5% AP as compared to the control rats. No significant change was observed in the mitochondrial content and dynamics (fusion/fission) of regulatory proteins. To investigate the mechanisms underlying the increase in the capillary density, positive (vascular endothelial cell growth factor, VEGF) and negative (thrombosponsin‐1, TSP‐1) factors of angiogenesis were analyzed. TSP‐1 expression significantly decreased in rats fed with 0.5% AP and 5% AP by approximately 25% and 40%, respectively, as compared with the control rats. There were no significant differences in VEGF expression. Thus, dietary AP may increase the muscle capillary density by decreasing TSP‐1 expression. We concluded that the increase in the capillary density and the fast‐to‐slow change in myosin heavy chains by AP feeding are the main causes for muscle endurance enhancement in Wistar rats.

Local cyclical compression modulates macrophage function in situ and alleviates immobilization-induced muscle atrophy

Physical inactivity gives rise to numerous diseases and organismal dysfunctions, particularly those related to aging. Musculoskeletal disorders including muscle atrophy, which can result from a sedentary lifestyle, aggravate locomotive malfunction and evoke a vicious circle leading to severe functional disruptions of vital organs such as the brain and cardiovascular system. Although the significance of physical activity is evident, molecular mechanisms behind its beneficial effects are poorly understood. Here, we show that massage-like mechanical interventions modulate immobilization-induced pro-inflammatory responses of macrophages in situ and alleviate muscle atrophy. Local cyclical compression (LCC) on mouse calves, which generates intramuscular pressure waves with amplitude of 50 mmHg, partially restores the myofiber thickness and contracting forces of calf muscles that are decreased by hindlimb immobilization. LCC tempers the increase in the number of cells expressing pro-inflammatory proteins, tumor necrosis factor-α and monocyte chemoattractant protein-1 (MCP-1), including macrophages in situ The reversing effect of LCC on immobilization-induced thinning of myofibers is almost completely nullified when macrophages recruited from circulating blood are depleted by administration of clodronate liposomes. Furthermore, application of pulsatile fluid shear stress, but not hydrostatic pressure, reduces the expression of MCP-1 in macrophages in vitro Together with the LCC-induced movement of intramuscular interstitial fluid detected by µCT analysis, these results suggest that mechanical modulation of macrophage function is involved in physical inactivity-induced muscle atrophy and inflammation. Our findings uncover the implication of mechanosensory function of macrophages in disuse muscle atrophy, thereby opening a new path to develop a novel therapeutic strategy utilizing mechanical interventions.

Sciatic Nerve Conductivity is Impaired by Hamstring Strain Injuries

The aim of this study was to assess sciatic nerve conductivity in athletes with a history of hamstring strain injuries. Twenty-seven athletes with a history of hamstring strain injuries were included in the injured group. The control group consisted of 16 uninjured participants. We measured the proximal and distal latencies and calculated the sciatic nerve conduction velocity to evaluate neuronal conductivity. The results were expressed as median values and interquartile ranges. Both proximal latency and distal latency of the injured limb in the injured group were significantly longer than those of the uninjured limb (p<0.05). The nerve conduction velocity of the injured limb in the injured group was significantly lower than that of the uninjured limb (p<0.05). There were no significant side-to-side differences in the control group. Sciatic nerve conductivity impairments may exist in athletes with a history of hamstring strain injuries.