Differential effectiveness of low-intensity exercise in young and old rats

Transcutaneous and Direct Electrical Stimulation of Mouse Sciatic Nerve Accelerates Functional Recovery After Nerve Transection and Immediate Repair

BACKGROUND

Electrical stimulation can accelerate peripheral nerve regeneration after injury and repair. Clinically, direct electrical stimulation (DES) may involve longer operating times, increasing risks of perioperative complications. Transcutaneous electrical stimulation (TCES) is a noninvasive alternative. In this study, we investigate how transcutaneous and DES compare for accelerating functional nerve recovery in a mouse sciatic nerve model.

METHODS

Twenty-eight mice were divided into sham (n = 4), axotomy (n = 8), DES (n = 8), and TCES (n = 8) groups. After sciatic nerve transection and repair, the proximal nerve was subjected to DES or TCES at 20 Hz for 1 hour. Sciatic functional index was measured before the injury, and at weeks 1, 2, 4, 6, 8, 10, and 12 by walking-track analysis. Electrophysiological measures were taken at week 12.

RESULTS

Kinematic studies showed significant improvement from the 8th week to the 12th week for both electrical stimulation groups compared with the axotomy group (P < 0.05), with no difference between the electrical stimulation groups. At the 12th week, both DES and TCES groups had significantly faster average conduction velocity than the axotomy group.

CONCLUSIONS

Functional recovery was significantly better from 8 weeks onward in mice receiving either DES or TCES stimulation when compared with axotomy and repair alone. Transcutaneous electrical stimulation is a minimally invasive alternative treatment for accelerating functional recovery after peripheral nerve injury.

Resistance Exercise and Whey Protein Supplementation Reduce Mechanical Allodynia and Spinal Microglia Activation After Acute Muscle Trauma in Rats

Muscle injury caused by direct trauma to the skeletal muscle is among the main musculoskeletal disorders. Non-pharmacological treatments have been effective in controlling muscle injury–induced pain; however, there are just a few studies in the literature investigating this response. Thus, the present study aimed to evaluate the effect of a resistance exercise training protocol combined or not with whey protein supplementation on mechanical allodynia induced by muscle injury. In addition, we also investigated the involvement of spinal glial cells in this process. For this purpose, male Wistar rats underwent a muscle injury model induced by direct trauma to the gastrocnemius muscle. Mechanical allodynia was measured by a digital von Frey algesimeter test. To evaluate the effect of exercise and/or supplementation on mechanical allodynia, the animals practiced exercises three times a week for 14 days and received supplementation daily for 14 days, respectively. Moreover, the effect of both the participation of spinal glial cells in the muscle injury and the resistance exercise training and/or whey protein supplementation on these cells was also investigated by the Western blot assay. The results demonstrated that resistance exercise training and whey protein supplementation, combined or alone, reduced mechanical allodynia. These treatments also reduced the number of interstitial cells and pro-inflammatory cytokine IL-6 levels in the injured muscle. It was also found that spinal microglia and astrocytes are involved in muscle injury, and that resistance exercise training combined with whey protein supplementation inhibits spinal microglia activation. The results suggest that both resistance exercise training and whey protein supplementation may be effective non-pharmacological treatments to control pain in the muscle after injury induced by acute trauma.

Effects of loaded voluntary wheel exercise on performance and muscle hypertrophy in young and old male C57Bl/6J mice

This study compared the capacity of young and old male C57Bl/6J mice to exercise with increasing resistance over 10 weeks, and its impact on muscle mass. Young mice (aged 15-25 weeks) were subjected to low (LR) and high (HR) resistance exercise, whereas only LR was used for old mice (107-117 weeks). Weekly patterns of voluntary wheel activity, food consumption and body weights were measured. Running patterns changed over time and with age, with two peaks of activity detected for young, but only one for old mice: speed and distance run was also less for old mice. The mass for six limb muscles was measured at the end of the experiment. The most pronounced increase in mass in response to exercise was for the soleus in young and old mice, and also quadriceps and gastrocnemius in young mice. Soleus and quadriceps muscles were analyzed histologically for myofiber number and size. A striking feature was the many small myofibers in response to exercise in young (but not old) soleus, whereas these were not present after exercise in young or old quadriceps. Overall, there was a striking difference in response to exercise between muscles and this was influenced by age.

A rehabilitation exercise program induces severe bone mineral deficits in estrogen-deficient rats after extended disuse

OBJECTIVE

Both estrogen and mechanical loading regulate bone maintenance. However, mechanical overload seems less effective in enhancing bone mineral density (BMD) in estrogen-deficient women. The aim of this study was to determine whether estradiol (E2) influences early-phase bone adaptations to reambulation (REAMB) and/or rehabilitation exercises after hindlimb unloading (HLU) of ovariectomized rats.

METHODS

Eighty-one 5-month-old female Sprague-Dawley rats were randomized into the following groups: (1) intact controls, (2) ovariectomy (OVX), (3) OVX + E2, (4) OVX + 4 weeks of HLU, (5) OVX + E2 + HLU, (6) OVX + HLU + 2 weeks of quadrupedal REAMB, (7) OVX + E2 + HLU + REAMB, (8) OVX + HLU + REAMB + supplemental climbing, jumping, and balance exercises (EX), or (9) OVX + E2 + HLU + REAMB + EX. Serial dual-energy x-ray absorptiometry scans were performed to track total body bone characteristics throughout the study, and peripheral quantitative computerized tomography was used to determine distal femoral metaphyseal bone mineral characteristics.

RESULTS

Total body BMD increased by 4% to 8% in all animals receiving supplemental E2, whereas BMD did not change in animals without E2. OVX reduced trabecular BMD at the femoral metaphysis, and HLU exacerbated this loss while also reducing cortical BMD. E2 protected against OVX + HLU-induced bone loss at the femoral metaphysis. Conversely, REAMB did not alter BMD, regardless of estrogen status. In the absence of E2, REAMB + EX resulted in severe bone loss after OVX + HLU, with trabecular BMD and cortical BMD measurements that were 91% and 7% below those of controls, respectively (P ≤ 0.001). However, in the presence of E2, REAMB + EX did not negatively influence bone mineral characteristics.

CONCLUSIONS

E2 protects against bone loss resulting from combined OVX + HLU of rodents. In the absence of estrogen, exercise induces disadvantageous early-phase bone adaptations after extended disuse.

Effects of early-stage aging on locomotor dynamics and hindlimb muscle force production in the rat

Attenuation of locomotor function is common in many species of animals as they age. Dysfunctions may emerge from a constellation of age-related impairments, including increased joint stiffness, reduced ability to repair muscle tissue, and decreasing fine motor control capabilities. Any or all of these factors may contribute to gait abnormalities and substantially limit an animal's speed and mobility. In this study we examined the effects of aging on whole-animal locomotor performance and hindlimb muscle mechanics in young adult rats aged 6–8 months and ‘early aged’ 24-month-old rats (Rattus norvegicus, Fischer 344 × Brown Norway crosses). Analyses of gaits and kinematics demonstrated that aged rats moved significantly more slowly, sustained longer hindlimb support durations, moved with a greater proportion of asymmetrical gaits, were more plantigrade, and moved with a more kyphotic spinal posture than the young rats. Additionally, the external mechanical energy profiles of the aged animals were variable across trials, whereas the younger rats moved predominantly with bouncing mechanics. In situ analyses of the ankle extensor/plantar flexor muscle group (soleus, plantaris, and medial and lateral gastrocnemii) revealed reduced maximum force generation with aging, despite minimal changes in muscle mass. The weakened muscles were implicated in the degradation of hindfoot posture, as well as variability in center-of-mass mechanics. These results demonstrate that the early stages of aging have consequences for whole-body performance, even before age-related loss of muscle mass begins.

Regional stiffening with aging in tibialis anterior tendons of mice occurs independent of changes in collagen fibril morphology

The incidence of tendon degeneration and rupture increases with advancing age. The mechanisms underlying this increased risk remain unknown but may arise because of age-related changes in tendon mechanical properties and structure. Our purpose was to determine the effect of aging on tendon mechanical properties and collagen fibril morphology. Regional mechanical properties and collagen fibril characteristics were determined along the length of tibialis anterior (TA) tendons from adult (8- to 12-mo-old) and old (28- to 30-mo-old) mice. Tangent modulus of all regions along the tendons increased in old age, but the increase was substantially greater in the proximal region adjacent to the muscle than in the rest of the tendon. Overall end-to-end modulus increased with old age at maximum tendon strain (799 ± 157 vs. 1,419 ± 91 MPa) and at physiologically relevant strain (377 ± 137 vs. 798 ± 104 MPa). Despite the dramatic changes in tendon mechanical properties from adulthood to old age, collagen fibril morphology and packing fraction remained relatively constant in all tendon regions examined. Since tendon properties are influenced by their external loading environment, we also examined the effect of aging on TA muscle contractile properties. Maximum isometric force did not differ between the age groups. We conclude that TA tendons stiffen in a region-dependent manner throughout the life span, but the changes in mechanical properties are not accompanied by corresponding changes in collagen fibril morphology or force-generating capacity of the TA muscle.

A rehabilitation exercise program to remediate skeletal muscle atrophy in an estrogen-deficient organism may be ineffective

To determine rehabilitation exercise program effects under hormone deficient (ovariectomy or OVX) and hormone supplemented [OVX + 17-beta estradiol (E2)] conditions. Mature female rats (n = 123) were assigned to OVX or OVX + E2-supplemented groups. OVX and OVX + E2 groups were allocated to one of four conditions: (1) control, (2) hindlimb unweighted (HLU) for 4 weeks to induce muscle atrophy, (3) cage Recovery for 2 weeks after HLU, and (4) Recovery with 2 weeks of rehabilitation exercise program after 4 weeks of HLU. Atrophy following HLU was comparable for OVX and OVX + E2-supplemented rats and was significant in all muscles examined (soleus, tibialis anterior, plantaris, gastrocnemius, quadriceps). Also significant with HLU was the decline in muscle force (P < 0.05) in soleus, plantaris, gastrocnemius and tibialis anterior (quadriceps not tested). There were trends toward return of muscle mass in Recovery OVX and Recovery OVX + E2 groups but only the E2 supplemented OVX rats had return of muscle mass (4/5 muscles studied) with exercise. Peak tetanic tension (Po) returned to control values in the E2 supplemented Exercise rats but not in the unsupplemented Exercise group. For example, gastrocnemius Po for OVX HLU, OVX Recovery and OVX-Exercise groups was 82%*, 82%* and 76%* of control. Gastrocnemius Po for E2 supplemented HLU, Recovery and Exercise groups was 72%*, 95% and 106% of control (*P < 0.05 compared to control). H&E cross-sections from OVX-Exercise rats showed central nuclei. In conclusion, a rehabilitation exercise program to remediate acute atrophy in females appears more effective if E2 is present.

The act of voluntary wheel running reverses dietary hyperphagia and increases leptin signaling in ventral tegmental area of aged obese rats

To test the hypothesis that exercise increases central leptin signaling, and thus reduces dietary weight gain in an aged obese model, we assessed the effects of voluntary wheel running (WR) in 23-month-old F344×BN rats fed a 60% high-fat (HF) diet for 3 months. After 2 months on the HF diet, half of the rats were provided access to running wheels for 2 weeks while the other half remained sedentary. Following the removal of the wheels, physical performance was evaluated, and 4 weeks later leptin signaling was assessed in hypothalamus and VTA after an acute bout of WR. Introduction of a HF diet led to prolonged hyperphagia (63.9 ± 7.8 kcal/day on chow diet vs. 88.1 ± 8.2 kcal/day on high-fat diet (when food intake stabilized), p < 0.001). As little as 9 (ranging to 135) wheel revolutions per day significantly reduced caloric consumption of HF food (46.8 ± 11.2 kcal/day) to a level below that on chow diet (63.9 ± 7.8 kcal/day, p < 0.001). After 2 weeks of WR, body weight was significantly reduced (7.9 ± 2.1% compared with prerunning weight, p < 0.001), and physical performance (latency to fall from an incline plane) was significantly improved (p = 0.04). WR significantly increased both basal (p = 0.04) and leptin-stimulated (p = 0.001) STAT3 phosphorylation in the ventral tegmental area (VTA), but not in the hypothalamus. Thus, in aged dietary obese rats, the act but not the extent of voluntary WR is highly effective in reversing HF consumption, decreasing body weight, and improving physical performance. It appears to trigger a response that substitutes for the reward of highly palatable food that may be mediated by increased leptin signaling in the VTA.

Protective effects of preconditioned local somatothermal stimulation on neuromuscular plasticity against ischemia--reperfusion injury in rats

The aim of this study was to investigate whether preconditioned local somatotheral stimulation (LSTS) protects the muscle and nerve against ischemia-reperfusion (I/R) injuries. Male rats were randomly assigned to normal, preconditioned LSTS only, and I/R-injured groups with or without LSTS preconditioning. I/R injuries of the lower limb were induced by rubber band wrapping, followed by measurements of gait function and nerve conduction, muscle pathology, serum enzymatic activity, and the expression of heat-shock protein 70 (HSP-70) in the gastrocnemius muscles. No significant change of neuromuscular function was found between LSTS (-) and LSTS (+) groups on the first day after I/R injury. In contrast, gait stride length, compound motor action potential, and serum creatine phosphokinase MM isoenzyme were significantly improved on the eighth day after one or two doses of preconditioned LSTS and subsequent I/R injury. Western blot analysis disclosed no significant change of HSP-70 expression in the muscle of I/R injured limbs between LSTS (-) and LSTS (+) groups. We conclude that preconditioned LSTS is a safe modality that improves the neuromuscular plasticity against I/R injured limbs, which provides a new strategy for I/R injury in clinical applications, such as intraoperative use of tourniquets.

Effect of aging on tongue protrusion forces in rats

The purpose of this study was to ascertain the effect of aging on muscle contractile properties associated with tongue protrusion in a rat model. Fischer 344/Brown Norway hybrid rats, ten young (9 months old) and ten old (32 months old), were used to measure protrusive contractile properties. Results showed a significant reduction in tetanic forces in the old animals. The following measures of muscle contraction were not different between age groups: mean twitch contraction force, twitch contraction time, twitch contraction half-decay time, and a calculated measure of fatigability. In conclusion, aging influenced protrusive tongue muscle contractions in a rat model such that tetanic forces were reduced. The reduction of tetanus force may parallel findings in human subjects relative to isometric tongue force generation and may be associated with age-related disorders of swallowing.

Prehabilitation and rehabilitation for attenuating hindlimb unweighting effects on skeletal muscle and gait in adult and old rats

OBJECTIVE

To compare the effectiveness of no exercise with prehabilitation (exercise before hindlimb unweighting [HLU]) versus rehabilitation (exercise given after HLU) on gait function and skeletal muscle mass and force.

DESIGN

Randomized controlled trial.

SETTING

Animal laboratory.

ANIMALS

Male-specific, pathogen-free Fisher344/Brown Norway rats (N=149). Groups consisted of adult and old controls, HLU, prehabilitation, rehabilitation, natural cage recovery (reloading), and exercise without HLU.

INTERVENTIONS

Ten days of general conditioning exercise were given to 6-month-old adult and 30-month-old old rats before or after a week of HLU.

MAIN OUTCOME MEASURES

Gait stride length and width; soleus, plantaris, extensor digitorum longus, and peroneus longus mass and peak contractile force; whole gastrocnemius mass; and total protein concentration for the soleus and gastrocnemius.

RESULTS

Muscle mass (approximately 30%) and force (24%-36%) declined with age in all muscles studied. In adult rats declines in muscle mass occurred with HLU in the soleus, plantaris, and gastrocnemius. Prehabilitation did not prevent the loss of muscle mass in adult rats. Rehabilitation and natural recovery effectively restored soleus and gastrocnemius muscle mass in adult rats but not soleus peak force. Old rats had a significant 23% HLU effect only on gastrocnemius mass (control, 1670+/-129 mg; HLU, 1274+/-184 mg). Prehabilitation did not prevent the decline in gastrocnemius mass. Rehabilitation in old rats restored gastrocnemius mass to within 13% of control levels. Prehabilitation was effective for preventing and rehabilitation was effective for restoring soleus contractile force in old rats (control, 114+/-9 mg; HLU, 67+/-22 mg; prehabilitation, 106+/-31 mg; rehabilitation, 120+/-26 mg) compared with recovery without exercise (86+/-29 g). A significant reduction in stride length was observed with aging (136+/-18 mm vs 98+/-10 mm), which decreased further with HLU (78+/-14 mm). Prehabilitation attenuated HLU-related reductions in stride length, and rehabilitation was effective for stride length restoration in old rats.

CONCLUSIONS

Exercise, particularly rehabilitation, was more effective for old than young rats. Prehabilitation and rehabilitation diminished some of the detrimental effects of HLU on skeletal muscle mass and force and gait function in old rats.

[Skeletal muscle histomorphometric study of rats in anestrus]

Castration, as well as the menopause, represents endocrine suppression that prevails the hypoestrogenism and their larger consequence on the skeletal muscle is to provoke sarcopenia.

OBJECTIVE

To study the morphometric alteration of striated muscle of castrated female rats.

METHODS

Twenty six female rats Wistar , distributed in two sub-groups, A and B, submitted initially to weigh-in place, vaginal cytology, ovariectomy, and biopsy of the muscle rectus femoris on the back paws, A group on right paw, and B on the left. Elapsed 20 days it was collected vaginal cytology to prove the anestrus status. After 70 days the animals went through weigh-in place, and new muscle biopsy, A group in left paw and B in right paw. The morphometric study was accomplished with the aids of a graduated lens, with reticules of 100 mm2, it was counted the myofibrils with six readings in the vertical and five in the horizontal in each sheet, being obtained a multiple number that applied on a specific formula to calculate the coefficient of muscular density.

RESULTS

In A the muscular density varied from 60.0 to 52.33, (p<0.05%), with variation of 14.12%, and in B from 73.5 to 54.0, (p<0.05%), with variation of 26.53%.

CONCLUSION

The castration provoked sarcopenia in the striated muscle and reduction of myofibrils number.

The Effects of Aging and Treadmill Running on Soleus and Gastrocnemius Muscle Morphology in the Senescence-Accelerated Mouse (SAMP1)

We investigated the effects of aging on the soleus and gastrocnemius muscles in male SAMP1 (senescence-accelerated mouse prone 1). Body mass, muscle wet weight, fiber size, and the percent of type II fibers declined from 50 weeks of age. Voluntary motor behavior also significantly declined with age. Furthermore, we examined the effects of high (twice daily) and low (once daily) frequency treadmill running, for 6 weeks at 5 days per week, beginning when the mice were 50 weeks old. Muscle fiber size for the high frequency running significantly increased. Pathological fiber alterations in these mice were increased by running, especially by high frequency running. This suggests that age-related muscle morphological changes in SAMP1 occurs from 50 weeks of age, and that the decline in voluntary motor behavior is an important factor in aging muscle atrophy. In addition, high frequency running is more beneficial for aged muscle hypertrophy. This model is useful for studying the acceleration of the aging process in skeletal muscle of the SAM.