Hindlimb Immobilization Research Articles

Hindlimb Immobilization in a Wheelchair Alters Functional Recovery Following Contusive Spinal Cord Injury in the Adult Rat

Background. Locomotor training of rats with thoracic contusion spinal cord injuries can induce task-specific changes in stepping but rarely results in improved overground locomotion, possibly due to a ceiling effect. Thus, the authors hypothesize that incompletely injured rats maximally retrain themselves while moving about in their cages over the first few weeks postinjury. Objective. To test the hypothesis using hindlimb immobilization after mild thoracic contusion spinal cord injury in adult female rats. A passive stretch protocol was included as an independent treatment. Methods. Wheelchairs were used to hold the hindlimbs stationary in an extended position leaving the forelimbs free. The wheelchairs were used for 15 to 18 hours per day, 5 days per week for 8 weeks, beginning at 4 days postinjury. A 20-minute passive hindlimb stretch therapy was applied to half of the animals. Results. Hindlimb locomotor function of the wheelchair group was not different from controls at 1 week postinjury but declined significantly over the next 4 weeks. Passive stretch had no influence on wheelchair animals but limited functional recovery of normally housed animals, preventing them from regaining forelimb–hindlimb coordination. Following 8 weeks of wheelchair immobilization and stretch therapy, only the wheelchair group displayed an improvement in function when returned to normal housing but retained significant deficits in stepping and coordination out to 16 weeks. Conclusion. Hindlimb immobilization and passive stretch may hinder or conceal the normal course of functional recovery of spinal cord injured rats. These observations have implications for the management of acute clinical spinal cord injuries.

Deptor Knockdown Enhances mTOR Activity and Protein Synthesis in Myocytes and Ameliorates Disuse Muscle Atrophy

Deptor is an mTOR binding protein that affects cell metabolism. We hypothesized that knockdown (KD) of Deptor in C2C12 myocytes will increase protein synthesis via stimulating mTOR-S6K1 signaling. Deptor KD was achieved using lentiviral particles containing short hairpin (sh)RNA targeting the mouse Deptor mRNA sequence, and control cells were transfected with a scrambled control shRNA. KD reduced Deptor mRNA and protein content by 90%, which increased phosphorylation of mTOR kinase substrates, 4E-BP1 and S6K1, and concomitantly increased protein synthesis. Deptor KD myoblasts were both larger in diameter and exhibited an increased mean cell volume. Deptor KD increased the percentage of cells in the S phase, coincident with an increased phosphorylation (S807/S811) of retinoblastoma protein (pRb) that is critical for the G(1) to S phase transition. Deptor KD did not appear to alter basal apoptosis or autophagy, as evidenced by the lack of change for cleaved caspase-3 and light chain (LC)3B, respectively. Deptor KD increased proliferation rate and enhanced myotube formation. Finally, in vivo Deptor KD (~50% reduction) by electroporation into gastrocnemius of C57/BL6 mice did not alter weight or protein synthesis in control muscle. However, Deptor KD prevented atrophy produced by 3 d of hindlimb immobilization, at least in part by increasing protein synthesis. Thus, our data support the hypothesis that Deptor is an important regulator of protein metabolism in myocytes and demonstrate that decreasing Deptor expression in vivo is sufficient to ameliorate muscle atrophy.

Curcumin treatment prevents increased proteasome and apoptosome activities in rat skeletal muscle during reloading and improves subsequent recovery

Immobilization is characterized by activation of the ubiquitin (Ub)–proteasome-dependent proteolytic system (UPS) and of the mitochondrial apoptotic pathway. Increased oxidative stress and inflammatory response occur in immobilized skeletal muscles. Curcumin exhibits antioxidant and anti-inflammatory properties, blocked proteasome activation in intact animals, and may favor skeletal muscle regeneration. We therefore measured the effects of curcumin on immobilization-induced muscle atrophy and subsequent recovery. Rats were subjected to hindlimb immobilization for 8 days (I8) and allowed to recover for 10 days (R10). Fifty percent of the rats were injected daily with either curcumin or vehicle. Proteolytic and apoptotic pathways were studied in gastrocnemius muscles. Curcumin treatment prevented the enhanced proteasome chymotrypsin-like activity and the trend toward increased caspase-9-associated apoptosome activity at I8 in immobilized muscles. By contrast, the increase of these two activities was blunted by curcumin at R10. Curcumin did not reduce muscle atrophy at I8 but improved muscle recovery at R10 and the cross-sectional area of muscle fibers of immobilized muscles. Curcumin reduced the increased protein levels of Smac/DIABLO induced by immobilization and enhanced the elevation of X-linked inhibitory apoptotic protein levels at R10. Ub-conjugate levels and caspase-3 activity increased at I8 and were normalized at R10 without being affected by curcumin treatment. Altogether, the data show that curcumin treatment improved recovery during reloading. The effect of curcumin during the atrophic phase on proteasome activities may facilitate the initiation of muscle recovery after reloading. These data also suggest that this compound may favor the initial steps of muscle regeneration.

Evidence That The Overexpression Of The Inducible Heat Shock Protein 70 In Mouse Improves Recovery Of Skeletal Muscle From Atrophy

This work aimed to investigate the effect of the overexpression of the inducible heat shock protein 70 (HSP70i) in mouse on skeletal muscle atrophy and subsequent recovery. Wild type (WT) and HSP70i-overexpressing transgenic mice were subjected to hindlimb immobilization for 7 days or for immobilization (7 days) and subsequent recovery (7 days). The muscle weight and the myofiber cross sectional area of extensor digitorum longus (EDL) from atrophied HSP70i mice were unaltered; however they were increased in atrophied + recovered HSP70i mice when compared to those from WT mice. The maximal tetanic contraction of EDL muscle was decreased in atrophied WT mice but not in atrophied HSP70i mice. EDL muscles from all groups of HSP70i mice subjected to a fatigue protocol showed an increased force production when compared to those from WT mice. The preliminary results suggest that HSP70i improves skeletal muscle recovery from atrophy. Financial support: FAPESP (2009/53528-7).

Disuse atrophy induced by rat hindlimb immobilization leads to resistance of skeletal muscle protein synthesis to a meal‐feeding stimulus

Anabolic resistance is a term coined from results of studies performed in human subjects whereby protein synthesis in skeletal muscle under disuse atrophy conditions responds less robustly to an amino acid induced stimulus than does active muscle. The objective of the studies described here was to develop an experimental model in rodents of anabolic resistance and to employ the model to gain an understanding of the molecular mechanisms responsible for the defective nutrient-induced stimulation of skeletal muscle protein synthesis. One hindlimb of a meal-trained male Sprague-Dawley rat was immobilized with a cast while an uncasted hindlimb served as a control. Seven days later, at various times post-feeding and following administration of a flooding dose of [3H]phenylalanine, gastrocnemius, soleus, and plantaris muscles from each hindlimb were collected for measurement of protein synthesis and analysis of biomarkers of the mTORC1 signaling pathway. Immobilization resulted in an approximate 50% reduction in the feeding-induced stimulation of protein synthesis as well as a delay in onset and attenuation of activation of the mTORC1 signaling pathway. Overall, the results validate the suitability of this experimental model for studies aimed at identification of molecular targets for intervention to prevent or reverse the loss of muscle mass under disuse atrophy conditions. (Supported by NIH grant DK-15658)

Animal models for bone and joint disease. Animal models of immobilization and unloading

Animal models of immobilization and unloading mimic the situation of lack of mechanical stimulation on the limb. Immobilization or unloading of the hindlimb for one or two weeks rapidly reduces tibial trabecular bone volume by approximately 50% of the baseline level. We should pay attention on the fact that the subsequent results after immobilization or unloading significantly depend on the strains of the mice. Here, we describe the practical technique for preparing animal models and the obtained results concerning the mechanism of bone loss and articular degeneration due to immobilization or unloading.

Effects of Different Types of Dietary Fat on Muscle Atrophy According to Muscle Fiber Types and PPARδ Expression in Hindlimb-Immobilized Rats

This study investigated how dietary fat affects muscle atrophy and lipid metabolism in various muscles during hindlimb immobilization in rats. Twenty-four male Sprague?Dawley rats had their left hindlimb immobilized and were divided into four groups by dietary fat content and composition. The contralateral hindlimb (control) was compared with the immobilized limb in all dietary groups. Rats (n = 6/group) were fed a 4% corn oil diet (CO), 2.6% corn oil + 1.4% fish oil diet (FO), 30% corn oil diet (HCO), or a 30% beef tallow diet (HBT)after their hind limbs were immobilized for 10 days. Data were collected for the gastrocnemius, plantaris and soleus muscles. Muscle atrophy was induced significantly after 10 days of hindlimb immobilization, resulting in significantly decreased muscle mass and total muscle protein content. The protein levels of peroxisome proliferator activated receptor (PPAR) in the plantaris, gastrocnemius, and soleus increased following hindlimb immobilization irrespective of dietary fat intake. Interestingly, the PPAR mRNA level in the plantaris decreased significantly in all groups and that in the FO group was lower than that in the other groups. The soleus PPAR mRNA level decreased significantly following hindlimb immobilization in the FO group only. Muscle carnitine palmitoyl transferase 1 (mCPT1) mRNA level was not affected by hindlimb immobilization. However, the mCPT1 mRNA level in the FO group was significantly lower in the plantaris but higher in the soleus than that in the other groups. The pyruvate dehydrogenase kinase 4 (PDK4) mRNA level in the plantaris decreased significantly, whereas that in the soleus increased significantly following hindlimb immobilization. The plantaris, but not soleus, PDK4 mRNA level was significantly higher in the FO group than that in the CO group. The increased PPAR protein level following hindlimb immobilization may have suppressed triglyceride accumulation in muscles and different types of dietary fat may have differentially affected muscle atrophy according to muscle type. Our results suggest that -3 polyunsaturated fatty acids may suppress muscle atrophy and lipid accumulation by positively affecting the expression level and activity of PPAR and PPAR-related enzymes, which are supposed to play an important role in muscle lipid metabolism.

The effects of β-adrenergic stimulation and exercise on NR4A3 protein expression in rat skeletal muscle

β-Adrenergic stimulation and exercise up-regulate the mRNA expression of nuclear receptor NR4A3, which is involved in the regulation of glucose and fatty acid utilization genes in skeletal muscle. The objective of our study was to examine the effects of β-adrenergic stimulation and exercise on the expression of NR4A3 protein in rat skeletal muscle. A single subcutaneous injection of clenbuterol, which is a β2-adrenergic receptor (β2-AR) agonist, increased NR4A3 mRNA and protein expression in the fast-twitch glycolytic triceps muscle. On the other hand, an acute 3-h session of either treadmill running or swimming did not increase the NR4A3 protein level in the exercised muscle, although both treadmill running and swimming increased NR4A3 mRNA. Finally, loss of postural contractile activity because of hindlimb immobilization reduced NR4A3 mRNA and protein in the slow-twitch oxidative soleus muscle. These results suggest that: β-adrenergic stimulation up-regulates not only NR4A3 mRNA but also NR4A3 protein in fast-twitch glycolytic muscle; exercise may increase NR4A3 mRNA but not NR4A3 protein in skeletal muscle; and local postural contractile activity plays a crucial role in maintaining NR4A3 protein expression level in postural muscle.

Mitochondrial ROS Production Is Required For Disuse Muscle Atrophy

PURPOSE: Hind-limb immobilization (e.g. casting) in rodents results in significant atrophy in both the soleus and plantaris muscles. In this regard, oxidative stress has been proposed to play a major role in muscle fiber atrophy during periods of prolonged skeletal muscle inactivity. These experiments tested the hypothesis that hind-limb immobilization leads to increased mitochondrial ROS emission and mitochondrial bioenergetic dysfunction. We also hypothesized that the mitochondrial-targeted antioxidant SS31 can prevent immobilization-induced mitochondrial dysfunction and rescue the inactivity-induced loss of mass in the soleus and plantaris muscles. METHODS: C57/B16 mice were randomly assigned to one of three experimental groups: 1) ambulatory controls; 2) 14-days of hind-limb immobilization; and 4) 14-days of hind-limb immobilization and treated with the mitochondrial antioxidant, SS-31. At the completion of the experiments, the soleus, and plantaris weights were recorded and mitochondria function was determined by measuring state 3 and state 4 respiration rates. In addition, the levels of oxidatively modified muscle proteins were determined by 4-HNE. RESULTS: Compared to control, 14 days of hind-limb immobilization resulted in significant atrophy in both the soleus and plantaris muscles. Treatment with SS31 rescued this immobilization-induced decrease in the soleus and plantaris muscle weights. Further, hind-limb immobilization resulted in mitochondrial uncoupling and oxidative stress in both the soleus and plantaris muscles, but treatment of animals with SS31 prevented the inactivity-induced mitochondrial dysfunction and attenuated the increase in oxidative stress in both muscles. CONCLUSION: Collectively, these results support the hypothesis that mitochondrial ROS emission contributes to immobilization-induced skeletal muscle atrophy and that mitochondrial-targeted antioxidants prevent disuse-induced oxidative damage and atrophy in locomotor skeletal muscles. Supported by NIH R01 HL087839 awarded to SKP

Physiological loading of joints prevents cartilage degradation through CITED2

Both overuse and disuse of joints up-regulate matrix metalloproteinases (MMPs) in articular cartilage and cause tissue degradation; however, moderate (physiological) loading maintains cartilage integrity. Here, we test whether CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2), a mechanosensitive transcriptional coregulator, mediates this chondroprotective effect of moderate mechanical loading. In vivo, hind-limb immobilization of Sprague-Dawley rats up-regulates MMP-1 and causes rapid, histologically detectable articular cartilage degradation. One hour of daily passive joint motion prevents these changes and up-regulates articular cartilage CITED2. In vitro, moderate (2.5 MPa, 1 Hz) intermittent hydrostatic pressure (IHP) treatment suppresses basal MMP-1 expression and up-regulates CITED2 in human chondrocytes, whereas high IHP (10 MPa) down-regulates CITED2 and increases MMP-1. Competitive binding and transcription assays demonstrate that CITED2 suppresses MMP-1 expression by competing with MMP transactivator, Ets-1 for its coactivator p300. Furthermore, CITED2 up-regulation in vitro requires the p38δ isoform, which is specifically phosphorylated by moderate IHP. Together, these studies identify a novel regulatory pathway involving CITED2 and p38δ, which may be critical for the maintenance of articular cartilage integrity under normal physical activity levels.

Dietary fish oil alleviates soleus atrophy during immobilization in association with Akt signaling to p70s6k and E3 ubiquitin ligases in rats

Reduced muscle activity leads to impaired insulin signaling, which leads to loss of contractile proteins and muscle mass via the Akt pathway. Dietary fish oil rich in long chain n-3 polyunsaturated fatty acids has been shown to prevent insulin signaling resistance in skeletal muscle. This study was conducted to elucidate the protective effect of dietary fish oil on disuse-induced perturbations in insulin signaling and soleus muscle atrophy. To accomplish this, rats were fed a corn-oil- (control) or fish-oil-based diet for 2 weeks, and then subjected to hindlimb immobilization while still receiving the same diets. After 10 days of immobilization, the soleus muscle mass and myosin heavy chain level had markedly decreased; however, these losses were significantly suppressed in rats fed dietary fish oil, compared with the control group. Dietary fish oil nearly completely attenuated the disturbances in activation of the Akt and p70 S6 kinase proteins, as well as the gene expression of muscle-specific E3 ubiquitin ligases (muscle atrophy F-box and muscle RING finger 1). However, insulin receptor substrate 1 associated with the p85 subunit of phosphoinositide 3-kinase was not altered during immobilization. Dietary fish oil also inhibited alterations in the gene expression of cyclooxygenase-2 and inducible nitric oxide synthase, with no additional observation of oxidative stress. Collectively, these findings indicate that dietary fish oil prior to and during immobilization may alleviate the immobilization-induced soleus muscle atrophy, at least in part, via the Akt pathway through E3 ubiquitin ligases and p70s6k.

Effect of prior treatment with resveratrol on density and structure of rat long bones under tail-suspension

Physical inactivity during space flight or prolonged bed rest causes rapid and marked loss of bone mass in humans. Resveratrol, a red wine polyphenol that is currently under study for its therapeutic antioxidant properties, has been shown to significantly modulate biomarkers of bone metabolism, i.e., to promote osteoblast differentiation and to prevent bone loss induced by estrogen deficiency. However, there is no direct evidence supporting its inhibitory effect toward bone loss during physical inactivity. In the present study, effects of resveratrol on bone mineral density (BMD), bone mineral content, and bone structure were examined in the femora and tibiae of tail-suspended and unsuspended rats using X-ray micro-computed tomography (micro-CT). Rats were treated with 400mg/kg/day of resveratrol for 45days and half of them were suspended during the last 2weeks of treatment. Suspension caused a decrease in tibial and femoral BMD and deterioration of trabecular and cortical bone. Bone deterioration during suspension was paralleled by increased bone marrow area, which could be caused by an increase in stromal cells with osteoclastogenic potential or in adipocytes. Resveratrol had a preventive effect against bone loss induced by hindlimb immobilization. In particular, trabecular bone in the proximal tibial metaphysis was totally preserved in rats treated with resveratrol before tail-suspension.

Involvements of Akt and phospholipase D‐mediated phosphatidic acid in the regulation of mTOR signaling during immobilization and remobilization of rat skeletal muscle

Skeletal muscle activity is known to determine its mass by regulating protein synthesis through Akt‐mTOR‐p70s6k signaling. It has been revealed that mTOR and its downstream signaling is also activated by phosphatidic acid (PA) in mechanically stimulated skeletal muscle. This study was conducted to investigate, during altered skeletal muscle usage, how phospholipase D (PLD)‐mediated phosphatidic acid (PA) level is modulated, and that is involved in Akt signaling to p70s6k. Eleven‐weeks‐old male rats were subjected to unilateral hindlimb immobilization (Im) for 10 days and allowed to recover by remobilization (Rm) for 3 or 13 days. Non‐immobilized muscles were served as an internal control. Immobilized gastrocnemius was significantly atrophied (muscle mass loss), but during Rm its mass had been gradually recovered. Deactivated Akt signaling to p70s6k induced by Im was also recruited by Rm. Specifically changes in activation of p70s6k were more dramatic than that of Akt during Im and Rm periods. The level of PA was reduced during Im with impaired activity of PLD. However, Rm increased the activity of PLD and level of PA, and even greater than control muscle at the 3 day. These results suggest that mTOR signaling during inactive or active skeletal muscle use may be regulated by PLD‐mediated PA level as well as Akt activation. Supported by the Korea Research Foundation (KRF‐2008‐C00071).

Matrix metalloproteinase-3 in articular cartilage is upregulated by joint immobilization and suppressed by passive joint motion

Both underloading and overloading of joints can lead to articular cartilage degradation, a process mediated in part by matrix metalloproteinases (MMPs). Here we examine the effects of reduced loading of rat hindlimbs on articular cartilage expression of MMP-3, which not only digests matrix components but also activates other proteolytic enzymes. We show that hindlimb immobilization resulted in elevated MMP-3 mRNA expression at 6 h that was sustained throughout the 21 day immobilization period. MMP-3 upregulation was higher in the medial condyle than the lateral, and was greatest in the superficial cartilage zone, followed by middle and deep zones. These areas also showed decreases in safranin O staining, consistent with reduced cartilage proteoglycan content, as early as 7 days after immobilization. One hour of daily moderate mechanical loading, applied as passive joint motion, reduced the MMP-3 and ADAMTS-5 increases that resulted from immobilization, and also prevented changes in safranin O staining. Intra-articular injections of an MMP-3 inhibitor, N-isobutyl-N-(4-methoxyphenylsulfonyl)-glycylhydroxamic acid (NNGH), dampened the catabolic effects of a 7 day immobilization period, indicating a likely requirement for MMP-3 in the regulation of proteoglycan levels through ADAMTS-5. These results suggest that biomechanical forces have the potential to combat cartilage destruction and can be critical in developing effective therapeutic strategies.

Leucine attenuates skeletal muscle wasting via inhibition of ubiquitin ligases

The aim of this study was to assess the effect of leucine supplementation on elements of the ubiquitin-proteasome system (UPS) in rat skeletal muscle during immobilization. This effect was evaluated by submitting the animals to a leucine supplementation protocol during hindlimb immobilization, after which different parameters were determined, including: muscle mass; cross-sectional area (CSA); gene expression of E3 ligases/deubiquitinating enzymes; content of ubiquitinated proteins; and rate of protein synthesis. Our results show that leucine supplementation attenuates soleus muscle mass loss driven by immobilization. In addition, the marked decrease in the CSA in soleus muscle type I fibers, but not type II fibers, induced by immobilization was minimized by leucine feeding. Interestingly, leucine supplementation severely minimized the early transient increase in E3 ligase [muscle ring finger 1 (MuRF1) and muscle atrophy F-box (MAFbx)/atrogin-1] gene expression observed during immobilization. The reduced peak of E3 ligase gene expression was paralleled by a decreased content of ubiquitinated proteins during leucine feeding. The protein synthesis rate decreased by immobilization and was not affected by leucine supplementation. Our results strongly suggest that leucine supplementation attenuates muscle wasting induced by immobilization via minimizing gene expression of E3 ligases, which consequently could downregulate UPS-driven protein degradation. It is notable that leucine supplementation does not restore decreased protein synthesis driven by immobilization.

The Effect of Amino Acid Infusion on Anesthesia-Induced Hypothermia in Muscle Atrophy Model Rats

An infusion of amino acids stimulates heat production in skeletal muscle and then attenuates the anesthesia-induced hypothermia. However, in a clinical setting, some patients have atrophic skeletal muscle caused by various factors. The present study was therefore conducted to investigate the effect of amino acids on the anesthesia-induced hypothermia in the state of muscle atrophy. As the muscle atrophy model, Sprague-Dawley rats were subjected to hindlimb immobilization for 2 wk. Normal rats and atrophy model rats were randomly assigned to one of the two treatment groups: saline or amino acids (n=8 for each group). Test solutions were administered intravenously to the rats under sevoflurane anesthesia for 180 min, and the rectal temperature was measured. Plasma samples were collected for measurement of insulin, blood glucose, and free amino acids. The rectal temperature was significantly higher in the normal-amino acid group than in the muscle atrophy-amino acid group from 75 to 180 min. The plasma insulin level was significantly higher in the rats given amino acids than in the rats given saline in both normal and model groups. In the rats given amino acids, plasma total free amino acid concentration was higher in the model group than in the normal group. These results indicate that skeletal muscle plays an important role in changes in body temperature during anesthesia and the effect of amino acids on anesthesia-induced hypothermia decreases in the muscle atrophy state. In addition, intravenous amino acids administration during anesthesia induces an increase in the plasma insulin level.

Succinylcholine-induced Hyperkalemia and Beyond

The mechanism of succinylcholine-induced hyperkalemia was studied in three lesions affecting canine gastrocnemius muscle. Dogs were treated for 1 month before study: 10 with normal activity, 5 with unilateral sciatic nerve section, active on 3 legs, 5 with unilateral cast immobilization of a hind limb and pelvis, active on 3 legs, and 7 inactive with T6 section of the spinal cord. Succinylcholine responses were determined during thiopental―ha lothane (mean expired halothane 1.0 ± 0.2%) endotracheal anesthesia with arterial carbon dioxide tension of 38—42 mmHg, arterial oxygen tension of 100—120 mmHg, and muscle and body temperatures maintained at 37° ± 0.2°C. The investigators isolated and collected the venous drainage of gastrocnemius muscle and measured its total blood flow. Muscle potassium release and oxygen consumption were calculated as blood flow x (arterial content — venous content). Succinylcholine-induced gastrocnemius potassium release was greatest after both sciatic and cord section; oxygen consumption was increased in parallel. Disuse atrophy of one leg slightly increased both values but was insufficient to produce systemic hyperkalemia. Reuptake of potassium followed succinylcholine-induced release. Given before succinylcholine, modest doses of gallamine slightly modified the release of potassium, and total paralysis by gallamine blocked it.

POINT: IGF IS THE MAJOR PHYSIOLOGICAL REGULATOR OF MUSCLE MASS

The insulin-like growth factors (IGFs)-I and -II are homologous peptides that are structurally related to insulin. However, IGFs retain the C-peptide, enabling binding to their main signaling receptor, the IGF type 1 receptor (IGF1R). IGF-II, however, can also bind to and signal via the A isoform of

Ros‐mediated activation of NF‐κB and Foxo during muscle disuse

We examined reactive oxygen species as upstream activators of nuclear factor kappaB; (NF-kappaB) and forkhead box O (Foxo) in skeletal muscle during disuse atrophy. Catalase, an enzyme that degrades H2O2, was overexpressed in soleus muscles via plasmid injection prior to 7 days of hindlimb immobilization. The increased catalase activity abolished immobilization-induced transactivation of both NF-kappaB and Foxo and attenuated the loss of muscle mass. Thus, H2O2 may be an important initiator of these signaling pathways that lead to muscle atrophy.

Different effects of anoxia and hind-limb immobilization on sensorimotor development and cell numbers in the somatosensory cortex in rats

Cerebral palsy (CP) is a group of movement and posture disorders attributed to insults in the developing brain. In rats, CP-like motor deficits can be induced by early hind-limb sensorimotor restriction (SR; from postnatal days P2 to P28), associated or otherwise with perinatal anoxia (PA; on P0 and P1). In this study, we address the question of whether PA, early SR or a combination of both produces alterations to sensorimotor development. Developmental milestones (surface righting, cliff aversion, stability on an inclined surface, proprioceptive placing, auditory startle, eye opening) were assessed daily from P3 to P14. Motor skills (horizontal ladder and beam walking) were evaluated weekly (from P31 to P52). In addition, on P52, the thickness of the somatosensory (S1) and cerebellar cortices, and corpus callosum were measured, and the neuronal and glial cell numbers in S1 were counted. SR (with or without PA) significantly delayed the stability on an inclined surface and hastened the appearance of the placing reflex and impaired motor skills. No significant differences were found in the thickness measurements between the groups. Quantitative histology of S1 showed that PA, either alone or associated with SR, increased the number of glial cells, while SR alone reduced neuronal cell numbers. Finally, the combination of PA and SR increased the size of neuronal somata. We conclude that SR impairs the achievement of developmental milestones and motor skills. Moreover, both SR and PA induce histological alterations in the S1 cortex, which may contribute to sensorimotor deficits.