Skeletal muscle effects of two different 10-week exercise regimens, voluntary wheel running, and forced treadmill running, in mice: A pilot study

Exercise performance in well-trained male mice is promoted by intermittent hyperoxia via improving metabolic properties and capillary profiles

Although training under intermittent hyperoxia has been shown to improve exercise performance, its effect on well-trained mice remains undetermined. Voluntary run for 7 weeks increased maximal work values by 7.4-fold (Bayes factor, BF ≥ 30). Subsequently, mice underwent 4 weeks of treadmill training with (INT) or without (ET) intermittent hyperoxia (30% O2). INT training significantly increased maximal exercise capacity compared to ET (BF ≥ 30). INT group exhibited significantly higher levels of cytochrome-c-oxidase (COX) in soleus muscle (SOL, BF ≥ 3.0). Additionally, INT enhanced 3-hydroxyacyl-CoA-dehydrogenase (HAD) levels in white gastrocnemius (Gw) and plantaris (PL) muscles compared to ET (BF ≥ 3.0). Pyruvate dehydrogenase complex (PDHc) levels were significantly higher in the INT group compared to the ET group in red gastrocnemius and left ventricle (BF ≥ 30). Capillary-to-fiber ratio (C/F) was significantly higher in the INT group than in the ET group in SOL and PL muscles (BF ≥ 3.0). COX, PDHc, capillary density (CD), and catalase protein values in SOL, HAD, and C/F levels in Gw and PL, as well as CD values in Gw showed a significant positive correlation with maximal work values using data from ET and INT groups (p < 0.05). These findings suggest that training under intermittent hyperoxia promotes endurance performance probably by improving metabolic enzyme levels and capillary profiles in well-trained mice.

Brief early-life motor training induces behavioral changes and alters neuromuscular development in mice

In this study, we aimed to determine the impact of an increase in motor activity during the highly plastic period of development of the motor spinal cord and hindlimb muscles in newborn mice. A swim training regimen, consisting of two sessions per day for two days, was conducted in 1 and 2-day-old (P1, P2) pups. P3-trained pups showed a faster acquisition of a four-limb swimming pattern, accompanied by dysregulated gene expression in the lateral motor column, alterations in the intrinsic membrane properties of motoneurons (MNs) and synaptic plasticity, as well as increased axonal myelination in motor regions of the spinal cord. Network-level changes were also observed, as synaptic events in MNs and spinal noradrenaline and serotonin contents were modified by training. At the muscular level, slight changes in neuromuscular junction morphology and myosin subtype expression in hindlimb muscles were observed in trained animals. Furthermore, the temporal sequence of acquiring the adult-like swimming pattern and postural development in trained pups showed differences persisting until almost the second postnatal week. A very short motor training performed just after birth is thus able to induce functional adaptation in the developing neuromuscular system that could persist several days. This highlights the vulnerability of the neuromuscular apparatus during development and the need to evaluate carefully the impact of any given sensorimotor procedure when considering its application to improve motor development or in rehabilitation strategies.

Environmental enrichment for neuropathic pain via modulation of neuroinflammation

Neuropathic pain causes tremendous biological and psychological suffering to patients worldwide. Environmental enrichment (EE) is a promising non-pharmacological strategy with high cost-effectiveness to reduce neuropathic pain and support rehabilitation therapy. Three researchers reviewed previous studies to determine the efficacy of EE for neuropathic pain to research how EE improves neuropathic pain through neuroinflammation. For this review, Embase, PubMed, and Cochran were searched. Three authors did study selection and data extraction. Out of 74 papers, 7 studies met the inclusion criteria. In the chronic constriction injury rats with acute or chronic detrimental stimulation, the change of pain behavior was influenced by environmental settings like start time, and cage size. Besides, physical EE has a larger effect than socially EE in inflammatory pain. These articles suggest employing various EE to regulate the release of pain-causing substances and changes in ion channels in the peripheral and central nerves to improve neuropathic pain behavior and depression and anxiety conditions. The existing proof provides important knowledge for upcoming preclinical investigations and the practical use of EE in clinical pain treatment. This analysis aids in the advancement of improved approaches for managing chronic pain, with a focus on internal mechanisms for controlling pain.

Effects of voluntary and forced physical exercise on the retinal health of aging Wistar rats

Aging is accompanied by an increased prevalence of degenerative conditions, including those affecting ocular health, which significantly impact quality of life and increase the burden on healthcare systems. Among these, retinal aging is of particular concern due to its direct link to vision impairment, a leading cause of disability in the elderly. Vision loss in the aging population is associated with heightened risks of cognitive decline, social isolation, and morbidity. This study addresses the critical gap in our understanding of modifiable lifestyle factors, such as physical exercise, that may mitigate retinal aging and its related pathologies. We investigated the effects of different exercise regimens-voluntary (recreational-type) and forced (high-intensity)-on the retinal health of aging Wistar rats (18-month-old), serving as a model for studying the translational potential of exercise interventions in humans. Male Wistar rats were divided into four groups: a young control (3-month-old) for baseline comparison, an aged sedentary control, an aged group engaging in voluntary exercise via a running wheel in their cage, and an aged group subjected to forced exercise on a treadmill for six sessions of 20 min each per week. After a 6-month experimental period, we assessed retinal function via electroretinography (ERG), measured retinal thickness histologically, and analyzed protein expression changes relevant to oxidative stress, inflammation, and anti-aging mechanisms. Our findings reveal that voluntary exercise positively impacts retinal function and morphology, reducing oxidative stress and inflammation markers while enhancing anti-aging protein expression. In contrast, forced exercise showed diminished benefits. These insights underscore the importance of exercise intensity and preference in preserving retinal health during aging. The study highlights the potential of recreational physical activity as a non-invasive strategy to counteract retinal aging, advocating for further research into exercise regimens as preventative therapies for age-related ocular degenerations.

Effects of sclerostin injection on soleus and extensor digitorum longus muscle tissue in male mice

Sclerostin, a potent inhibitor of the Wnt signaling pathway, plays a critical role in bone homeostasis. Evidence suggests that sclerostin may also be involved in crosstalk between other tissues, including muscle. This pilot study attempted to examine the effects of sclerostin on soleus and extensor digitorum longus (EDL) muscle tissue from male mice that were given continuous recombinant sclerostin injections for 4 weeks. A total of 48 10-week-old male C57BL/6J mice were assigned to be sedentary or perform 1 h treadmill running per day for 4 weeks and administered subcutaneous injections of either saline or recombinant sclerostin 5 days/week. Sclerostin injection led to a reduction in the soleus myosin heavy chain (MHC) I, MHC I/IIA, MHC IIA/X, and MHC IIB cross-sectional area (p < 0.05) with no exercise effects on these reductions. In contrast, there were no effects of sclerostin injections or exercise on the fast-twitch EDL muscle in terms of size, MHC protein, or markers of Wnt signaling. These findings provide preliminary evidence of sclerostin's endocrine role in muscle via decreases in myofiber cross-sectional area, which seems to be independent of fiber type but muscle type-specific. More studies, however, are needed to confirm these preliminary results.

Targeting Hub Genes Involved in Muscle Injury Induced by Jumping Load Based on Transcriptomics

The purpose of this study was to find hub genes that may play key roles in skeletal muscle injury induced by jumping load. Twelve female Sprague Dawley rats were divided into the normal control (NC) group and the jumping-induced muscle injury (JI) group. After 6 weeks of jumping, transmission electron microscopy, hematoxylin-eosin staining, transcriptomics sequencing and genes analysis, interaction network prediction of multiple proteins, real-time PCR detection, and Western blotting were performed on gastrocnemius muscles from NC and JI groups. As compared with NC rats, excessive jumping can result in notable structural damage and inflammatory infiltration in JI rats. A total of 112 differentially expressed genes were confirmed in NC rats versus JI rats, with 59 genes upregulated and 53 genes downregulated. Using the online String database, four hub genes in the transcriptional regulatory network were targeted, including FOS, EGR1, ATF3, and NR4A3. All expression levels of FOS, EGR1, ATF3, and NR4A3 mRNAs were decreased in JI rats compared with NC rats (p < 0.05 or p < 0.01). All expression levels of c-Fos, EGR1, ATF3, and NOR1 proteins were upregulated in JI rats (p < 0.01, p < 0.05, p > 0.05, and p < 0.01, respectively). Collectively, these findings indicate that FOS, EGR1, ATF3, and NR4A3 genes may be functionally important in jumping-induced muscle injury.

Sow-Offspring Diets Supplemented with Probiotics and Synbiotics Are Associated with Offspring's Growth Performance and Meat Quality

Probiotics and synbiotics supplementation have been shown to play potential roles in animal production. The present study aimed to evaluate the effects of dietary probiotics and synbiotics supplementation to sows during gestation and lactation and to offspring pigs (sow-offspring) on offspring pigs' growth performance and meat quality. Sixty-four healthy Bama mini-pigs were selected and randomly allocated into four groups after mating: the control, antibiotics, probiotics, and synbiotics groups. After weaning, two offspring pigs per litter were selected, and four offspring pigs from two litters were merged into one pen. The offspring pigs were fed a basal diet and the same feed additive according to their corresponding sows, representing the control group (Con group), sow-offspring antibiotics group (S-OA group), sow-offspring probiotics group (S-OP group), and sow-offspring synbiotics group (S-OS group). Eight pigs per group were euthanized and sampled at 65, 95, and 125 d old for further analyses. Our findings showed that probiotics supplementation in sow-offspring diets promoted growth and feed intake of offspring pigs during 95-125 d old. Moreover, sow-offspring diets supplemented with probiotics and synbiotics altered meat quality (meat color, pH_45min, pH_24h, drip loss, cooking yield, and shear force), plasma UN and AMM levels, and gene expressions associated with muscle-fiber types (MyHCI, MyHCIIa, MyHCIIx, and MyHCIIb) and muscle growth and development (Myf5, Myf6, MyoD, and MyoG). This study provides a theoretical basis for the maternal-offspring integration regulation of meat quality by dietary probiotics and synbiotics supplementation.

LSD1 defines the fiber type-selective responsiveness to environmental stress in skeletal muscle

Skeletal muscle exhibits remarkable plasticity in response to environmental cues, with stress-dependent effects on the fast-twitch and slow-twitch fibers. Although stress-induced gene expression underlies environmental adaptation, it is unclear how transcriptional and epigenetic factors regulate fiber type-specific responses in the muscle. Here, we show that flavin-dependent lysine-specific demethylase-1 (LSD1) differentially controls responses to glucocorticoid and exercise in postnatal skeletal muscle. Using skeletal muscle-specific LSD1-knockout mice and in vitro approaches, we found that LSD1 loss exacerbated glucocorticoid-induced atrophy in the fast fiber-dominant muscles, with reduced nuclear retention of Foxk1, an anti-autophagic transcription factor. Furthermore, LSD1 depletion enhanced endurance exercise-induced hypertrophy in the slow fiber-dominant muscles, by induced expression of ERRγ, a transcription factor that promotes oxidative metabolism genes. Thus, LSD1 serves as an 'epigenetic barrier' that optimizes fiber type-specific responses and muscle mass under the stress conditions. Our results uncover that LSD1 modulators provide emerging therapeutic and preventive strategies against stress-induced myopathies such as sarcopenia, cachexia, and disuse atrophy.

Effect of Feeding System on Muscle Fiber Composition, Antioxidant Capacity, and Nutritional and Organoleptic Traits of Goat Meat

The objective of this study was to evaluate the effect of feeding system on muscle fiber composition, antioxidant capacity, and nutritional and organoleptic traits of goat meat. Goats that grazed on flatland (whole area with about 0% inclination, FG group) and mountain range (whole area with about 40% inclination, MG group) were selected for the analysis. The results showed that grazing on flatland increased oxidized-twitch fiber percentage, the expression of the MyHC IIa gene (p < 0.001), the activity of glutathione peroxidase (GSH-Px) (p < 0.05), total antioxidant capacity (T-AOC) (p = 0.001), and radical scavenging ability (RSA) (p < 0.05); meanwhile, the MyHC IIb gene expression (p < 0.01) and malondialdehyde (MDA) content (p = 0.001) were decreased. Feeding system affected nutritional and organoleptic traits of goat meat, and grazing on flatland increased protein content, total content of monounsaturated fatty acid (MUFA), polyunsaturated fatty acid (PUFA), pH45min, a* value, and variety of volatile flavor compounds but decreased the content of saturated fatty acid (SFA), shear force, and b* value. In addition, the key flavor substances were screened using relative odor activity value (ROAV), including hexanal, heptanal, (E)-2-octenal, octanal, nonanal, decanal, (E)-2-nonenal, and 1-octen-3-ol. Among them, 1-octen-3-ol and (E)-2-nonenal were the most contributing flavor compounds in the FG and MG groups, respectively, providing distinctive odor to goat meat.

Bored at home?—A systematic review on the effect of environmental enrichment on the welfare of laboratory rats and mice

Boredom is an emotional state that occurs when an individual has nothing to do, is not interested in the surrounding, and feels dreary and in a monotony. While this condition is usually defined for humans, it may very well describe the lives of many laboratory animals housed in small, barren cages. To make the cages less monotonous, environmental enrichment is often proposed. Although housing in a stimulating environment is still used predominantly as a luxury good and for treatment in preclinical research, enrichment is increasingly recognized to improve animal welfare. To gain insight into how stimulating environments influence the welfare of laboratory rodents, we conducted a systematic review of studies that analyzed the effect of enriched environment on behavioral parameters of animal well–being. Remarkably, a considerable number of these parameters can be associated with symptoms of boredom. Our findings show that a stimulating living environment is essential for the development of natural behavior and animal welfare of laboratory rats and mice alike, regardless of age and sex. Conversely, confinement and under-stimulation has potentially detrimental effects on the mental and physical health of laboratory rodents. We show that boredom in experimental animals is measurable and does not have to be accepted as inevitable.