Getting to compliance in forced exercise in rodents: a critical standard to evaluate exercise impact in aging-related disorders and disease

A Formalized Method to Acclimate Dogs to Voluntary Treadmill Locomotion at Various Speeds and Inclines

Simple Summary

The land treadmill provides a range of behavioral and physical training benefits for dogs. Walking and trotting on the treadmill, however, is unfamiliar to many dogs and requires acclimation. This study developed and conducted a voluntary treadmill acclimation protocol on eight working dogs in training or working dogs performing detection research. The acclimation protocol was successfully completed for seven out of eight dogs. An acclimation assessment protocol was developed to measure a previously exposed dog’s degree of acclimation. This protocol was successfully used in two previously exposed dogs. A muscle soreness protocol was created to evaluate the soreness developed during the acclimation protocol. These protocols offer an option to acclimate dogs to the treadmill and determine the degree of acclimation for previously exposed dogs for research and training purposes.

Abstract

The land treadmill is a multipurpose tool with a unique set of behavioral and physical benefits for training and assessing active dogs. Habituation to voluntary treadmill locomotion is crucial for training a dog or accurately assessing a dog’s fitness on a treadmill. Therefore, a treadmill acclimation program was developed and evaluated with working dogs in training or working dogs performing detection research. Seven of eight naive dogs became acclimated to the treadmill using the protocol developed. Two previously experienced dogs successfully conducted an acclimation assessment to test for habituation to the treadmill. A muscle soreness protocol was created to evaluate the soreness developed during the acclimation program. This detailed protocol was successful in acclimating dogs to the treadmill at various safe speeds and inclines.

Low-Intensity Exercise Routine for a Long Period of Time Prevents Osteosarcopenic Obesity in Sedentary Old Female Rats, by Decreasing Inflammation and Oxidative Stress and Increasing GDF-11

The loss of skeletal muscle mass and strength is known as sarcopenia; it is characterized as a progressive and generalized muscle disorder associated with aging. This deterioration can seriously compromise the elderly's health and reduce their quality of life. In addition to age, there are other factors that induce muscle mass loss, among which are sedentary lifestyle, chronic diseases, inflammation, and obesity. In recent years, a new clinical condition has been observed in older adults that affects their physical capacities and quality of life, which is known as osteosarcopenic obesity (OSO). Osteoporosis, sarcopenia, and obesity coexist in this condition. Physical exercise and nutritional management are the most widely used interventions for the treatment and prevention of sarcopenia. However, in older adults, physical exercise and protein intake do not have the same outcomes observed in younger people. Here, we used a low-intensity exercise routine for a long period of time (LIERLT) in order to delay the OSO appearance related to sedentarism and aging in female Wistar rats. The LIERLT routine consisted of walking at 15 m/min for 30 min, five days a week for 20 months. To evaluate the effects of the LIERLT routine, body composition was determined using DXA-scan, additionally, biochemical parameters, inflammatory profile, oxidative protein damage, redox state, and serum concentration of GDF-11 at different ages were evaluated (4, 8, 12, 18, 22, and 24 months). Our results show that the LIERLT routine delays OSO phenotype in old 24-month-old rats, in a mechanism involving the decrease in the inflammatory state and oxidative stress. GDF-11 was evaluated as a protein related to muscle repair and regeneration; interestingly, rats that perform the LIERLT increased their GDF-11 levels.

Cardiovascular Metrics Associated With Prevention of Aging-Related Parkinsonian Signs Following Exercise Intervention in Sedentary Older Rats

Preservation of motor capabilities is vital to maintaining independent daily living throughout a person's lifespan and may mitigate aging-related parkinsonism, a progressive and prevalent motor impairment. Physically active lifestyles can mitigate aging-related motor impairment. However, the metrics of physical activity necessary for mitigating parkinsonian signs are not established. Consistent moderate intensity (~10 m/min) treadmill exercise can reverse aging-related parkinsonian signs by 20 weeks in a 2-week on, 2-week off, regimen in previously sedentary advanced middle-aged rats. In this study, we initiated treadmill exercise in sedentary 18-month-old male rats to address two questions: (1) if a rest period not longer than 1-week off exercise, with 15 exercise sessions per month, could attenuate parkinsonian signs within 2 months after exercise initiation, and the associated impact on heart rate (HR) and mean arterial pressure (MAP) and (2) if continuation of this regimen, up to 20 weeks, will be associated with continual prevention of parkinsonian signs. The intensity and frequency of treadmill exercise attenuated aging-related parkinsonian signs by 8 weeks and were maintained till 23 months old. The exercise regimen increased HR by 25% above baseline and gradually reduced pre-intervention MAP. Together, these studies indicate that a practicable frequency and intensity of exercise reduces parkinsonian sign severity commensurate with a modest increase in HR after exercise. These cardiovascular changes provide a baseline of metrics, easily measured in humans, for predictive validity that practicable exercise intensity and schedule can be initiated in previously sedentary older adults to delay the onset of aging-related parkinsonian signs.

Complex Movement Control in a Rat Model of Parkinsonian Falls: Bidirectional Control by Striatal Cholinergic Interneurons

Older persons and, more severely, persons with Parkinson's disease (PD) exhibit gait dysfunction, postural instability and a propensity for falls. These dopamine (DA) replacement-resistant symptoms are associated with losses of basal forebrain and striatal cholinergic neurons, suggesting that falls reflect disruption of the corticostriatal transfer of movement-related cues and their striatal integration with movement sequencing. To advance a rodent model of the complex movement deficits of Parkinsonian fallers, here we first demonstrated that male and female rats with dual cortical cholinergic and striatal DA losses (DL rats) exhibit cued turning deficits, modeling the turning deficits seen in these patients. As striatal cholinergic interneurons (ChIs) are positioned to integrate movement cues with gait, and as ChI loss has been associated with falls in PD, we next used this task, as well as a previously established task used to reveal heightened fall rates in DL rats, to broadly test the role of ChIs. Chemogenetic inhibition of ChIs in otherwise intact male and female rats caused cued turning deficits and elevated fall rates. Spontaneous turning was unaffected. Furthermore, chemogenetic stimulation of ChIs in DL rats reduced fall rates and restored cued turning performance. Stimulation of ChIs was relatively more effective in rats with viral transfection spaces situated lateral to the DA depletion areas in the dorsomedial striatum. These results indicate that striatal ChIs are essential for the control of complex movements, and they suggest a therapeutic potential of stimulation of ChIs to restore gait and balance, and to prevent falls in PD.SIGNIFICANCE STATEMENT In persons with Parkinson's disease, gait dysfunction and the associated risk for falls do not benefit from dopamine replacement therapy and often result in long-term hospitalization and nursing home placement. Here, we first validated a new task to demonstrate impairments in cued turning behavior in rodents modeling the cholinergic-dopaminergic losses observed in Parkinsonian fallers. We then demonstrated the essential role of striatal cholinergic interneurons for turning behavior as well as for traversing dynamic surfaces and avoiding falls. Stimulation of these interneurons in the rat model rescued turning performance and reduced fall rates. Our findings indicate the feasibility of investigating the neuronal circuitry underling complex movement control in rodents, and that striatal cholinergic interneurons are an essential node of such circuitry.

A three-criteria performance score for rats exercising on a running treadmill

In this study, we propose a novel three-criteria performance score to semiquantitatively classify the running style, the degree of involvement and compliance and the validity of electric shock count for rats exercising on a treadmill. Each score criterion has several style-marks that are based on the observational registry of male Sprague-Dawley rats running for 4-7 weeks. Each mark was given a score value that was averaged throughout a session-registry and resulting in a session score for each criterion, ranging from "0" score for a hypothetical "worst runner", to score "1" for a hypothetical "perfect runner" rat. We found significant differences throughout a training program, thus providing evidence of sufficient sensitivity of this score to reflect the individual evolution of performance improvement in exercise capacity due to training. We hypothesize that this score could be correlated with other physiological or metabolic parameters, thus refining research results and further helping researchers to reduce the number of experimental subjects.

Aging-related limit of exercise efficacy on motor decline

Identifying lifestyle strategies and allied neurobiological mechanisms that reduce aging-related motor impairment is imperative, given the accelerating number of retirees and increased life expectancy. A physically active lifestyle prior to old age can reduce risk of debilitating motor decline. However, if exercise is initiated after motor decline has begun in the lifespan, it is unknown if aging itself may impose a limit on exercise efficacy to decelerate further aging-related motor decline. In Brown-Norway/Fischer 344 F1 hybrid (BNF) rats, locomotor activity begins to decrease in middle age (12-18 months). One mechanism of aging-related motor decline may be decreased expression of GDNF family receptor, GFRα-1, which is decreased in substantia nigra (SN) between 12 and 30 months old. Moderate exercise, beginning at 18 months old, increases nigral GFRα-1 and tyrosine hydroxylase (TH) expression within 2 months. In aged rats, replenishing aging-related loss of GFRα-1 in SN increases TH in SN alone and locomotor activity. A moderate exercise regimen was initiated in sedentary male BNF rats in a longitudinal study to evaluate if exercise could attenuate aging-related motor decline when initiated at two different ages in the latter half of the lifespan (18 or 24 months old). Motor decline was reversed in the 18-, but not 24-month-old, cohort. However, exercise efficacy in the 18-month-old group was reduced as the rats reached 27 months old. GFRα-1 expression was not increased in either cohort. These studies suggest exercise can decelerate motor decline when begun in the latter half of the lifespan, but its efficacy may be limited by age of initiation. Decreased plasticity of GFRα-1 expression following exercise may limit its efficacy to reverse motor decline.

Regulation of Skeletal Muscle Plasticity by Protein Arginine Methyltransferases and Their Potential Roles in Neuromuscular Disorders

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins, thereby mediating a diverse set of intracellular functions that are indispensable for survival. Indeed, full-body knockouts of specific PRMTs are lethal and PRMT dysregulation has been implicated in the most prevalent chronic disorders, such as cancers and cardiovascular disease (CVD). PRMTs are now emerging as important mediators of skeletal muscle phenotype and plasticity. Since their first description in muscle in 2002, a number of studies employing wide varieties of experimental models support the hypothesis that PRMTs regulate multiple aspects of skeletal muscle biology, including development and regeneration, glucose metabolism, as well as oxidative metabolism. Furthermore, investigations in non-muscle cell types strongly suggest that proteins, such as peroxisome proliferator-activated receptor-γ coactivator-1α, E2F transcription factor 1, receptor interacting protein 140, and the tumor suppressor protein p53, are putative downstream targets of PRMTs that regulate muscle phenotype determination and remodeling. Recent studies demonstrating that PRMT function is dysregulated in Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA), and amyotrophic lateral sclerosis (ALS) suggests that altering PRMT expression and/or activity may have therapeutic value for neuromuscular disorders (NMDs). This review summarizes our understanding of PRMT biology in skeletal muscle, and identifies uncharted areas that warrant further investigation in this rapidly expanding field of research.

Exercise-Mediated Increase in Nigral Tyrosine Hydroxylase Is Accompanied by Increased Nigral GFR-α1 and EAAC1 Expression in Aging Rats

Exercise may alleviate locomotor impairment in Parkinson's disease (PD) or aging. Identifying molecular responses immediately engaged by exercise in the nigrostriatal pathway and allied tissue may reveal critical targets associated with its long-term benefits. In aging, there is loss of tyrosine hydroxylase (TH) and the glial cell line-derived neurotrophic factor (GDNF) receptor, GFR-α1, in the substantia nigra (SN). Exercise can increase GDNF expression, but its effect on GFR-α1 expression is unknown. Infusion of GDNF into striatum or GFR-α1 in SN, respectively, can increase locomotor activity and TH function in SN but not striatum in aged rats. GDNF may also increase glutamate transporter expression, which attenuates TH loss in PD models. We utilized a footshock-free treadmill exercise regimen to determine the immediate impact of short-term exercise on GFR-α1 expression, dopamine regulation, glutamate transporter expression, and glutamate uptake in 18 month old male Brown-Norway/Fischer 344 F1 hybrid rats. GFR-α1 and TH expression significantly increased in SN but not striatum. This exercise regimen did not affect glutamate uptake or glutamate transporter expression in striatum. However, EAAC1 expression increased in SN. These results indicate that nigral GFR-α1 and EAAC1 expression increased in conjunction with increased nigral TH expression following short-term exercise.

Preclinical mouse models for assessing axial compression of long bones during exercise

The aim of this laboratory method is to describe two approaches for the investigation of bone responses to mechanical loading in mice in vivo. The first is running exercise, because it is easily translatable clinically, and the second is axial compression of the tibia, because it is precisely controllable. The effects of running exercise, and in general physical activity, on bone tissue have been shown to be both direct through mechanical loading (ground impact and muscle tension) and indirect through metabolic changes. Therefore, running exercise has been considered the most convenient preclinical model for demonstrating the general idea that exercise is good for bone health, either early in age for increasing peak bone mass or later in age by slowing down bone loss. However, numerous combinations of protocols have been reported, which makes it difficult to formulate a simple take-home message. This laboratory method also provides a detailed description of in vivo direct mechanical axial compression of the mouse tibia. The effects of mechanical loading depend on the force (strain), frequency, waveform and duration of application, and they range from bone anabolism with low bone remodeling, inducing lamellar bone accumulation, to bone catabolism with high bone remodeling, leading to microdamage, woven bone formation and bone loss. Direct in vivo loading models are extensively used to study mechanotransduction pathways, and contribute by this way to the development of new bone anabolism treatments. Although it is particularly difficult to assemble an internationally adopted protocol description, which would give reproducible bone responses, here we have attempted to provide a comprehensive guide for best practice in performing running exercise and direct in vivo mechanical loading in the laboratory.