Region-Specific Responses of Adductor Longus Muscle to Gravitational Load-Dependent Activity in Wistar Hannover Rats

Abstract

Response of adductor longus (AL) muscle to gravitational unloading and reloading was studied. Male Wistar Hannover rats (5-wk old) were hindlimb-unloaded for 16 days with or without 16-day ambulation recovery. The electromyogram (EMG) activity in AL decreased after acute unloading, but that in the rostral region was even elevated during continuous unloading. The EMG levels in the caudal region gradually increased up to 6th day, but decreased again. Approximately 97% of fibers in the caudal region were pure type I at the beginning of experiment. Mean percentage of type I fibers in the rostral region was 61% and that of type I+II and II fiber was 14 and 25%, respectively. The percent type I fibers decreased and de novo appearance of type I+II was noted after unloading. But the fiber phenotype in caudal, not rostral and middle, region was normalized after 16-day ambulation. Pronounced atrophy after unloading and re-growth following ambulation was noted in type I fibers of the caudal region. Sarcomere length in the caudal region was passively shortened during unloading, but that in the rostral region was unchanged or even stretched slightly. Growth-associated increase of myonuclear number seen in the caudal region of control rats was inhibited by unloading. Number of mitotic active satellite cells decreased after unloading only in the caudal region. It was indicated that the responses of fiber properties in AL to unloading and reloading were closely related to the region-specific neural and mechanical activities, being the caudal region more responsive.

Recovery of muscle weakness and physical function in a patient with severe ICU‐acquired weakness following pulmonary embolism: A case report

“…Because there is a possibility that decreasing muscle mass may precede the muscle strength, the disuse muscle atrophy proceeds to the muscle strength. It is important that the muscle strength is induced muscle contractions commanded from the motor area of the cerebral cortex to muscle via complex nerves after sensory receptors stimulated from EM, such as anti‐gravity posture 11. In this case, we tried to produce her active muscle contractions by sitting and standing with assistance due to EM.…”

Macrophage deficiency in osteopetrotic (op/op) mice inhibits activation of satellite cells and prevents hypertrophy in single soleus fibers

“…It was also reported that gravitational unloading downregulates the satellite cell mitotic activity (11,(35)(36)(37)49). Furthermore, atrophy and regrowth of muscle fibers in soleus (59) and adductor longus (41) of Wistar Hannover rats were closely related to the number of satellite cells, which is also positively correlated with the distribution of myonuclei. Unloading-related decrease or loss of satellite cells was noted in the central region of soleus fibers (59) and the caudal region of adductor longus (41), in which the sarcomere length was shortened in response to passive plantarflexion of ankle joints.…”

“…Furthermore, atrophy and regrowth of muscle fibers in soleus (59) and adductor longus (41) of Wistar Hannover rats were closely related to the number of satellite cells, which is also positively correlated with the distribution of myonuclei. Unloading-related decrease or loss of satellite cells was noted in the central region of soleus fibers (59) and the caudal region of adductor longus (41), in which the sarcomere length was shortened in response to passive plantarflexion of ankle joints. Such decrease of satellite cell distribution was increased to the control level following stretching of muscle fibers during reloading in the cage.…”

“…Muscle fiber atrophy and the shift toward a faster myosin heavy chain profile are reversed in response to muscle reloading (41,45,46,59). The muscular response to reloading appears to be closely related to intramuscular stimuli that are activated by mechanical loading (20,21,41,47,59) and/or muscle activation with reloading (1,12,20,22,41).Macrophage colony-stimulating factor (M-CSF, CSF-1) is a cytokine that influences hematopoietic stem cells to differentiate into macrophages and other cell types (54). Deficiency of macrophages has been well-reported in osteopetrotic (op/op) mutant mice with inactivating mutation of M-CSF gene, which results in the absence of certain macrophage and in osteopetrosis, following a lack of osteoclasts (60, 63).…”

“…For example, chronic unloading of muscles by bedrest in humans (45,46,64) and hind limb suspension and actual spaceflight in animals (6, 40 -42, 47, 59) result in muscle fiber atrophy and a shift toward a faster myosin heavy chain profile, particularly in antigravity muscles composed predominantly of slow-twitch fibers, such as the soleus (6,42,(45)(46)(47) and adductor longus (41,59). Muscle fiber atrophy and the shift toward a faster myosin heavy chain profile are reversed in response to muscle reloading (41,45,46,59). The muscular response to reloading appears to be closely related to intramuscular stimuli that are activated by mechanical loading (20,21,41,47,59) and/or muscle activation with reloading (1,12,20,22,41).…”