Muscle atrophy and neuromuscular impairment are consequences of spinal cord injury (SCI) that impede quality of life and functional recovery. PURPOSE: To examine time course changes in muscle fiber type distribution, fiber cross-sectional area (fCSA), and other histologic characteristics of muscle pathology occurring in rats in response to moderate-severe contusion SCI. METHODS: Twenty-four 4-month old male Sprague-Dawley rats received SHAM surgery or T9 laminectomy plus moderate-severe (250 kilodyne) contusion SCI by a computer-guided impactor. Body weight and Basso-Beattie-Bresnahan (BBB) hindlimb locomotor rating scores were measured weekly. Animals were euthanized and soleus were harvested at 2-weeks, 1-month, 2-months, or 3-months post-surgery. Soleus fiber-type distribution, fCSA, and muscle-nerve bundle morphology were assessed by immunofluorescent staining, imaged using an epifluorescent microscope, and quantified with semi-automatic muscle analysis using segmentation of histology (SMASH). RESULTS: At 1-week post-surgery, SCI animals exhibited near-complete hindlimb paralysis (indicated by BBB scores <3), with minimal improvement in voluntary hindlimb locomotor function thereafter. Body weight, soleus mass, and median fCSA were significantly lower in SCI vs SHAM animals (p<0.01 at all timepoints). A slow-to-fast fiber-type shift was observed in SCI animals, with a progressive ~20% decrease in the number of type I fibers, ~8% increase in type IIa fibers, and ~5% increase in hybrid type I/IIa fibers at each consecutive timepoint, along with the emergence of unstained type IIx/b muscle fibers (~30% of total) at 3-months. In addition, muscle fiber splitting was present in SCI animals at 2-months, as well as reduced neurofilament staining in SCI muscle-nerve bundles. Furthermore, evidence of growth related remodeling occurred in SHAM muscles from increased centrally nucleated fibers across timepoints but not in SCI. CONCLUSION: Deterioration in motor ability accompanying SCI produced muscle atrophy and progressive impairments in muscle oxidative capacity that may have resulted from repetitive denervation-reinnervation cycles. These factors may have contributed to muscle pathology resulting in limited capacity for muscle growth and remodeling.
Sublesional bone loss occurs rapidly following spinal cord injury (SCI) and contributes to a 20-100 fold greater bone fracture risk. PURPOSE: To determine the time course of bone strength deficits at different femoral test sites in a rodent contusion SCI model. METHODS: Sixty 16-week old male Sprague-Dawley rats received SHAM surgery or T9 laminectomy plus severe (250 kilodyne) contusion SCI using a computer-guided impactor and were euthanized 1-, 2-, or 3-months (m) post-surgery. Hindlimb locomotion was assessed weekly using the BBB locomotor scale and bone strength was assessed ex vivo at the distal femur, femoral midshaft, and femoral neck. SCI vs SHAM comparisons were made at each time point using independent t-tests. RESULTS: SCI animals exhibited persistent hindlimb locomotor deficits [BBB score < 6 (0-21 scale), p < 0.01 vs SHAMs at all time points], characterized by an inability to support the hindlimbs in stance or to perform hindlimb weight supported stepping. Bone strength deficits were observed at all testing sites after SCI in a somewhat variable pattern. At the distal femur, maximal breaking load (N) was 19% lower at 1-m (p < 0.05), 10% lower at 2-m (p < 0.05), and 16% lower at 3-m (p < 0.01) in SCI vs SHAM animals using a cantilever bending test. In addition, displacement at max load was 29% lower at 1-m (p < 0.05) and 22% lower at 3-m (p < 0.05). At the femoral neck, maximal breaking load was 22% lower at 1-m in SCI vs SHAM (p < 0.05), but was not different at 2-m or 3-m post-surgery. At the femoral midshaft, maximal breaking load was not different at 1-m post-surgery, but was 11% lower at 2-m (p < 0.05), and 23% lower at 3-m (p < 0.05) in SCI vs SHAMs, using a 3-point breaking test. No other differences in displacement or stiffness were observed among groups. CONCLUSION: In our SCI model, femoral skeletal integrity is compromised 1-m post-injury, with strength deficits dependent upon the skeletal site and the tests that were utilized. The distal femur cantilever test yielded less variability and typifies a common site of fracture in humans after SCI, suggesting this test is clinically-relevant. Interventions focused on preventing bone loss after SCI should initiate therapy soon after the injury occurs to ensure maintenance of skeletal integrity. Supported by VA RR&D SPiRE 1I21RX001373-01 to JFY.
The purpose of this study was to compare the total testosterone (TT), bioavailable testosterone (BT), growth hormone (GH), lactate, and ratings of perceived exertion (RPE) responses between a single bout of traditional (TRAD) and eccentric-enhanced resistance exercise (ECC+) of matched training volumes.Twenty-two previously untrained males (21.9+/-0.8 yr) completed one familiarization and one baseline 1RM testing bout, for the bench press and squat exercises, and then two exercise bouts. During exercise bout 1, all subjects completed a TRAD protocol (four sets of six reps at 52.5% 1RM), and the subsequent exercise bout consisted of either a TRAD or an ECC+ protocol (three sets of six reps at 40% 1RM concentric and 100% 1RM eccentric) for the bench press and squat exercises. Blood samples acquired at rest, immediately after (T1), and 15, 30, 45, and 60 min after exercise were assessed for serum TT, BT, GH, and blood lactate concentrations.Resting and postexercise TT, BT, and GH were not significantly different between groups. Postexercise TT was not elevated during either bout or in either group, whereas BT increased 15-16% at T1 in both groups during bout 2. Postexercise GH concentrations were elevated 500-7000% above baseline after both protocols. Postexercise lactate accumulation and RPE were greater with ECC+ than TRAD.TRAD and ECC+ show similar neuroendocrine and differing metabolic responses during the early phase of resistance exercise in untrained, college-age men.
We tested the hypothesis that chronic testosterone treatment would promote a cardioprotective phenotype against ischemia/reperfusion (I/R) injury. For this study, 3-month-old F344 male rats underwent sham-surgery, orchiectomy (ORX), or ORX plus 21 days testosterone treatment (1.0 mg testosterone/day). At sacrifice, cardiac performance was assessed in a working heart model of I/R (25 min of global ischemia and 45 min of reperfusion). ORX reduced serum testosterone by approximately 98% and testosterone administration elevated serum testosterone to a concentration of 4.6-fold over that of Sham-operated controls (p<0.05). ORX did not significantly impair recovery of cardiac performance following I/R, but did increase cardiac release of lactate dehydrogenase (LDH) during pre- and post-ischemia (p<0.05). Testosterone administration prevented the ORX-induced increase in LDH during both pre- and post-ischemia and increased post-ischemic recovery of aortic flow, cardiac output, cardiac work, left ventricular developed pressure, and contractility (p<0.05) during reperfusion. Testosterone administration also increased left ventricular expression of catalase, but did not affect the expression of manganese superoxide dismutase, glutathione peroxidase, or sarcolemmal K (ATP) channel protein Kir6.2. Neither circulating nor cardiac concentrations of estradiol were altered by either treatment. We conclude that administration of high-dose testosterone confers cardioprotection through yet to be identified androgen-dependent mechanism(s).
Influence of 5α‐reductase and/or aromatase enzymes on androgen‐induced skeletal muscle maintenance in older adults is not fully elucidated. Our purpose was to determine the androgen‐induced alterations in adult rodent skeletal muscle fiber cross sectional area (fCSA), satellite cell content, and myostatin (Mstn) signaling by comparing the effects of testosterone (TEST) versus trenbolone (TREN, a non‐5α‐reducible, non‐aromatizable synthetic TEST analogue) in 10 month old Fisher 344 rats (n=41) randomly assigned to receive Sham surgery, orchiectomy (ORX), ORX+TEST (7.0 mg/week), or ORX+TREN (1.0 mg/week). After 29 days animals were euthanized and the levator ani/bulbocavernosus (LABC) muscle complex was weighed and preserved for analyses. LABC muscle fCSA after ORX was 37% lower than SHAM and ~50% lower than ORX+TEST and ORX+TREN (p<0.01). LABC fCSA was 28% higher in ORX+TEST compared to SHAM (p=0.012). ORX+TEST and ORX+TREN increased satellite cell numbers compared to SHAM and ORX (p<0.05), with no differences between conditions for myonuclear number per muscle fiber (p=0.948). Mstn protein was increased roughly 3‐fold in the ORX+TEST and ORX+TREN groups versus Sham and ORX groups (p<0.01). Mstn mRNA, was lower in ORX, ORX+TEST and ORX+TREN compared to SHAM (p<0.05). Muscle fCSA was highly positively correlated with muscle satellite cell number (r = 0.730, p < 0.001). Mature Mstn protein was positively correlated with muscle satellite cell number (r = 0.430, p = 0.008). TEST and TREN increased muscle fCSA and satellite cell number without increasing myonuclei number, and increased Mstn protein levels. Mstn protein and Muscle fCSA were associated with increased muscle satellite cell number. TEST and TREN appear to up‐regulate Mstn protein levels to prevent uncontrolled muscle growth in older animals. In addition, the similar effects of TEST and TREN observed in the current study suggest the action of 5α‐reductase and/or aromatase enzymes are inconsequential for the androgenic maintenance of skeletal muscle in older adult males. Support or Funding Information LABC analyses were performed at Auburn University and reagents for this study were purchased by discretionary laboratory funds from M.D.R. This study was also supported in part by work supported from the Office of Research and Development, Rehabilitation Research and Development (RR&D) Service, Department of Veterans Affairs Merit Award to S.E.B., Veteran's Health Administration Advanced Geriatrics Fellowship to D.T.B., and RR&D CDA‐2 to J.F.Y.
Diminished bone perfusion develops in response to disuse and has been proposed as a mechanism underlying bone loss. Bone blood flow (BF) has not been investigated within the unique context of severe contusion spinal cord injury (SCI), a condition that produces neurogenic bone loss that is precipitated by disuse and other physiological consequences of central nervous system injury. Herein, 4-mo-old male Sprague-Dawley rats received T9 laminectomy (SHAM) or laminectomy with severe contusion SCI (n = 20/group). Time course assessments of hindlimb bone microstructure and bone perfusion were performed in vivo at 1- and 2-wk postsurgery via microcomputed tomography (microCT) and intracardiac microsphere infusion, respectively, and bone turnover indices were determined via histomorphometry. Both groups exhibited cancellous bone loss beginning in the initial postsurgical week, with cancellous and cortical bone deficits progressing only in SCI thereafter. Trabecular bone deterioration coincided with uncoupled bone turnover after SCI, as indicated by signs of ongoing osteoclast-mediated bone resorption and a near-complete absence of osteoblasts and cancellous bone formation. Bone BF was not different between groups at 1 wk, when both groups displayed bone loss. In comparison, femur and tibia perfusion was 30%-40% lower in SCI versus SHAM at 2 wk, with the most pronounced regional BF deficits occurring at the distal femur. Significant associations existed between distal femur BF and cancellous and cortical bone loss indices. Our data provide the first direct evidence indicating that bone BF deficits develop in response to SCI and temporally coincide with suppressed bone formation and with cancellous and cortical bone deterioration.NEW & NOTEWORTHY We provide the first direct evidence indicating femur and tibia blood flow (BF) deficits exist in conscious (awake) rats after severe contusion spinal cord injury (SCI), with the distal femur displaying the largest BF deficits. Reduced bone perfusion temporally coincided with unopposed bone resorption, as indicated by ongoing osteoclast-mediated bone resorption and a near absence of surface-level bone formation indices, which resulted in severe cancellous and cortical microstructural deterioration after SCI.
Spinal cord injury (SCI) produces paralysis and a unique form of neurogenic disuse osteoporosis that dramatically increases fracture risk at the distal femur and proximal tibia. This bone loss is driven by heightened bone resorption and near-absent bone formation during the acute post-SCI recovery phase and by a more traditional high-turnover osteopenia that emerges more chronically, which is likely influenced by the continual neural impairment and musculoskeletal unloading. These observations have stimulated interest in specialized exercise or activity-based physical therapy (ABPT) modalities (e.g., neuromuscular or functional electrical stimulation cycling, rowing, or resistance training, as well as other standing, walking, or partial weight-bearing interventions) that reload the paralyzed limbs and promote muscle recovery and use-dependent neuroplasticity. However, only sparse and relatively inconsistent evidence supports the ability of these physical rehabilitation regimens to influence bone metabolism or to increase bone mineral density (BMD) at the most fracture-prone sites in persons with severe SCI. This review discusses the pathophysiology and cellular/molecular mechanisms that influence bone loss after SCI, describes studies evaluating bone turnover and BMD responses to ABPTs during acute versus chronic SCI, identifies factors that may impact the bone responses to ABPT, and provides recommendations to optimize ABPTs for bone recovery.
