White Muscle Fibres Research Articles

Effect of Dietary Digestible Protein Levels on Muscle Growth and Oxidative Stress in Amazonian Pintado (Pseudoplatystoma reticulatum × Leiarius marmoratus).

This study aimed to evaluate the effects of dietary digestible protein levels on the growth dynamics and oxidative stress status of white muscle fibers in Amazonian Pintado (Pseudoplatystoma reticulatum × Leiarius marmoratus). Four hundred and fifty-five juveniles of Amazonian Pintado were fed diets containing varying digestible protein levels (225, 250, 275, 300, 325, 350, or 375 g kg-1) for 75 days. At the end of the experiment, the fish were fasted for 24 h, anesthetized, and euthanized to obtain muscle samples. The linear and quadratic effects of dietary digestible protein levels on white muscle fiber diameter, metabolite concentrations, and oxidative stress were assessed. The results revealed that increasing dietary digestible protein levels linearly raised the concentrations of free amino acids and total proteins in muscle tissue but also led to elevated levels of TBARS, indicating increased oxidative stress. Notably, the average area of muscle fibers with a cell area greater than 1133 µm2 decreased, reflecting restricted muscle hypertrophy, whereas glycogen and glucose levels also declined. These findings suggest that although high dietary digestible protein enhances protein and free amino acid concentrations in muscle tissue, it may compromise muscle hypertrophy and increase oxidative damage in Amazonian Pintado, underscoring the complexity of optimizing diet formulation.

Mitochondrial function in skeletal muscle contributes to reproductive endothermy in tegu lizards (Salvator merianae).

In cyclic climate variations, including seasonal changes, many animals regulate their energy demands to overcome critical transitory moments, restricting their high-demand activities to phases of resource abundance, enabling rapid growth and reproduction. Tegu lizards (Salvator merianae) are ectotherms with a robust annual cycle, being active during summer, hibernating during winter, and presenting a remarkable endothermy during reproduction in spring. Here, we evaluated whether changes in mitochondrial respiratory physiology in skeletal muscle could serve as a mechanism for the increased thermogenesis observed during the tegu's reproductive endothermy. We performed high-resolution respirometry and calorimetry in permeabilized red and white muscle fibers, sampled during summer (activity) and spring (high activity and reproduction), in association with citrate synthase measurements. During spring, the muscle fibers exhibited increased oxidative phosphorylation. They also enhanced uncoupled respiration and heat production via adenine nucleotide translocase (ANT), but not via uncoupling proteins (UCP). Citrate synthase activity was higher during the spring, suggesting greater mitochondrial density compared to the summer. These findings were consistent across both sexes and muscle types (red and white). The current results highlight potential cellular thermogenic mechanisms in an ectothermic reptile that contribute to transient endothermy. Our study indicates that the unique feature of transitioning to endothermy through nonshivering thermogenesis during the reproductive phase may be facilitated by higher mitochondrial density, function, and uncoupling within the skeletal muscle. This knowledge contributes significant elements to the broader picture of models for the evolution of endothermy, particularly in relation to the enhancement of aerobic capacity.

Effect of Cage and Floor Housing Systems on Muscle Fiber Characteristics, Carcass Characteristics, and Meat Quality of Slow-Growing Meat-Type Chickens

This study compared floor (FS) with cage systems (CS) for slow-growing meat-type chickens in terms of muscle fiber characteristics, carcass characteristics, and meat quality. Following the design of a factorial arrangement of 2 housing systems × 2 genders, 180 male and 180 female Beijing You chickens of 8 weeks old were allocated to FS and CS. At the end of 17 weeks, five males and five females from each replicate were selected for measurement. No difference was observed in body, carcass, or eviscerated weight (p > 0.05). FS birds showed higher muscle yield and lower abdominal fat composition (p < 0.05). Inosine-5′-monophosphate (IMP) content was not affected by housing system or gender (p > 0.05). On the contrary, intramuscular fat (IMF) content was affected by both in a way that CS birds and females had higher IMF content (p < 0.05). FS birds had a higher percentage of white muscle fibers (p < 0.05). In conclusion, carcass characteristics, meat quality, and muscle fiber type of slowing-growing broilers are influenced: rearing on the floor may improve muscle development and reduce fat deposition without impairing marketing weight and rearing in cages may improve IMF content.

Long-Term Effects of a Short Juvenile Feeding Period with Diets Enriched with the Microalgae Nannochloropsis gaditana on the Subsequent Body and Muscle Growth of Gilthead Seabream, Sparus aurata L.

Currently, microalgae are used in fish diets, but their long-term growth effect is unknown. In this experiment, juvenile seabream specimens were fed with microalgae-enriched diets for three months, and then transferred to a microalgae-free diet for 10 months to assess long-term effects up to commercial size (≈27 cm and ≈300 g). The juvenile diets contained Nannochloropsis gaditana at 2.5 or 5% inclusion levels, either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups). The body length and weight were measured in 75 fish group-1 at commercial stage. The size, number, and fibrillar density of white muscle fibers and the white muscle transverse area were measured in nine fish group-1 at commercial stage. The results showed the highest body weight in H5 at commercial stage. The white muscle transverse area and the white fibres hyperplasia and density also showed the highest values in H5, followed by H2.5. In contrast, the highest hypertrophy was observed in C and R2.5, being associated with the lowest muscle growth in both groups. These results showed a microalgae concentration-dependent effect in hydrolyzed diets as well as an advantageous effect of the hydrolyzed versus raw diets on the long-term growth of Sparus aurata.

Non-Invasive estimation of muscle fiber type using ultra Sonography

Introduction: The aim of this study was to estimate the muscle fiber type i.e., fast/white muscle fibers and slow/red muscle fibers) on the basis of selected muscle architectural parameters i.e., Pen-nation angle, Muscle thickness and Fascicle Length of Rectus Femoris and Vastus Lateralis using ultrasound image analysis. Materials and Methods: In this work of investigation, a total sample comprised of 30 highly trained male athletes of Lakshmibai National Institute of Physical Education Gwalior, Madhya Pradesh was considered as sample for present investigation. Purposive sampling technique was employed for selecting sample, out of which 15 were marathon runners and 15 were 100-meter sprinters. The selected subjects’ age ranged between 19 to 25 years. Muscle architectural parameters such as Pen-nation angle, Fascicle length, and Muscle thickness were measured using a B-Mode ultrasonography method (Model-WIPRO GE VOLUSON E 6). Results: The developed estimate model explains 54.6% to 72.8% of the variation in muscle fiber type. Thus, the logistic regression equation developed was: - Log p/(1-p) = 10.955 - 3.278 (VL_FL) + 1.267 (VL_PA). Conclusion: The wald statistics obtained from the logistic model revealed that decreasing the vastus lateralis pen nation angle by one unit increases the likelihood of having white muscle fiber by 2.54 times, while increasing the Vastus Lateralis Fascicle Length by one unit increases the likelihood of having white muscle fiber by 0.62 times. In order to determine muscle fiber type on the basis of muscle architectural parameters Vastus lateralis pen-nation angle and fascicle length were the most discriminating variables among selected fiber types.

Generation of fast growth Nile tilapia (Oreochromis niloticus) by myostatin gene mutation

Tilapia is the second most prolific species grown in aquaculture after carp, and is widely grown in >100 countries. Myostatin (MSTN) has been proved to be a negative regulator of skeletal muscle growth. Mutation of MSTN gene resulted in significant increase in both body size and muscle mass in vertebrates, mostly with a species-specific effect. To generate a new strain in Nile tilapia (Oreochromis niloticus) with fast growth traits, the molecular characterization, gene expression and functional studies of mstn gene were extensively investigated. Phylogenetic and synteny analyses indicated that mstnb, but not mstna, might be the orthologous gene of mammalian MSTN gene. Expression pattern analyzed by qRT-PCR demonstrated that mstnb is abundant in muscle, while mstna is dominantly expressed in the brain. Fluorescence in situ hybridization (FISH) analysis also demonstrated that mstnb is exclusively expressed in the basement membrane of white skeletal muscle fibers, further suggesting the possible role of mstnb gene in tilapia muscle growth. To verify the roles of mstnb in skeletal muscle growth, we obtain the mstnb−/− mutant using CRISPR/Cas9 gene editing technology. Compared with the wild type (WT) fish, the mstnb−/− mutants showed a typical double-muscle phenotype with increased muscle mass, sticking out between head and dorsal fin, from 5 months after hatching (mah). Morphological observation revealed an excessive proliferation of white muscle fibers at 7 mah. The average body weights (21.67 ± 8.26 g), body heights (4.46 ± 0.65 cm) and body widths (2.36 ± 0.53 cm) of the mstnb−/− fish were 49.45%, 32.74% and 37.21% higher than those of the mstnb+/+ fish (body weight, 14.50 ± 8.60 g; body height, 3.36 ± 0.45 cm; body width, 1.72 ± 0.18 cm) at 5 mah. The results showed that the growth performance parameters of the mstnb−/− fish, including weight gain rate (1.99 times), condition factor (1.77 times) and specific growth rate (1.23 times), were significantly higher than the mstnb+/+ fish under laboratory conditions at 5 mah. In addition, the parameters of WGR, CF, SGR and FE were significantly increased in mstnb−/− Nile tilapia than those of mstnb+/+ Nile tilapia and GIFT tilapia for a 90-day feeding trial under the wild natural environment. Interestingly, sexually dimorphic effects on muscle growth have been found with an increase of growth performance of skeletal muscle in mstn−/− XY fish, but not mstn−/− XX fish at 7 mah. Taken together, this study, for the first time, proved that mstn gene mutation might promote the generation of new fast-growing male strain of Nile tilapia.

Induced sustained swimming modifies the external morphology, increasing the oxygen-carrying capacity and plasma lactate levels of juvenile gilthead seabream (Sparus aurata) without changing fish performance or skeletal muscle characteristics

Some species of fish can be induced to swim under optimal conditions aiming to improve their growth performance and welfare. This study was undertaken to investigate the effects of induced sustained swimming on the growth performance, metabolic parameters [standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS), and excess post-exercise oxygen consumption (EPOC)], external morphology, skeletal muscle fiber characteristics and distribution of juvenile gilthead seabream (Sparus aurata), as well as immune and metabolic markers. Fish with a body mass of 26.89 ± 0.26 g and a total length of 12.27 ± 0.04 cm were induced to swim continuously at 1.1 body lengths s−1 (S group) or maintained under minimal water flow with fish displaying spontaneous swimming activity (C group) for 13 weeks. The water current in the S group was maintained at a similar level and by the end of the trial; the swimming speed was 0.8 body lengths s−1. Long-term induced swimming activity had no significant effect on the growth rate, feed efficiency, or red and white muscle cross-sectional area, fiber diameter, and density. However, swimming significantly changed the body shape of gilthead seabream, with the S group having shallower bodies, more pronounced nuchal humps, flatter abdomens, and larger caudal fins compared with the C group. SMR, MMR, AAS, and EPOC were similar in both experimental groups. Hematocrit and plasma lactate levels were significantly higher in the S group, whereas plasma glucose, protease, and anti-protease activities were not different between both groups. Despite the lack of changes in growth performance, feed efficiency, skeletal muscle morphological traits, and metabolic rates, induced swimming changed the body shape of seabream, and increased the oxygen-carrying capacity and plasma lactate levels.

A Comparative Study of White Muscle and Red Muscle Fiber Architectural Parameters

The primary objective of this research was to compare red muscle fiber and white muscle fiber muscle architectural parameters of vastus lateralis (VL). The study sample consisted of 70 recreationally active male students from Gwalior, Madhya Pradesh. One repetition maximum Dr. Hatfield test was used to determine muscle fiber type. Thirty (N1 = 15 red muscle fiber group and N2 = 15 red muscle fiber group) out of 70 samples were retained in study for further evaluation. Muscle architectural parameters (VL, pennation angle [PA], fascicle length [FA], and muscle thickness [MT]) were measured using B-mode ultrasonography. Independent sample t-test was employed to determine a significant difference between selected white muscle fibers group and selected red muscle fibers on the basis of selected muscle architectural parameters. The vastus lateralis muscle showed differences in its PA, FA, and MT between different muscle fiber groups. The PA of red muscle fiber group was greater than white muscle fiber group, whereas the FA and MT of white muscle fiber group were greater than red muscle fiber group. In conclusion, architectural parameters studies carried on specific sports group will be helpful in future, and muscle architectural parameters may be considered as a new approach for muscle fiber type classification in the future.

Study Proportions and Chemical Composition of red and white muscles of Tilapia Zillii and Acanthopagrus latus

The present study deals with two types of teleost; Tilapia zillii (Cichlidae), and Acanthopagrus latus (Sparidae), to study some aspects with relation to the fish activity such as the proportion of red and white muscle fibers, and estimation of the chemical content (protein, lipid, moisture, ash) in different regions of fish studied. The results showed that the red muscles less than the white muscles in (R1, R2) in studied fish, The red muscles ranged between (5.01–10.5%) and (4.67–9.64%) in T. zillii and A. latus respectively, while the proportion of white muscles were ranged between (94.98–88.49%) and (95.32–90.35%) in T. zillii and A. latus respectively beside to increasing of red muscles towards of the posterior region (caudal peduncle), therefore these fish are put in the intermediate activity. The results which related to chemical content in muscles including (protein, lipid, moisture, ash) in (R1, R2) from fish body, showed that the proportion of protein were ranged (17.97–19.05%) and (16.89–17.46%) in T. zillii and A. latus respectively, while the proportion of lipid were ranged between (1.54–2.08%) and (3.08–3.13%) in fish studied, therefore T. zillii put in non-lipid fishes or flesh fishes, while A. latus put in intermediate lipid fishes.

Effects of ploidy and nutritional conditions on muscle morphology, proliferation and myogenic proteins expression in Rhamdia quelen larvae

Although Rhamdia quelen is a promising species for farming in South America, many aspects of its development and optimal conditions of culture remain unknown. In this sense, we explore muscle development and some proteins related to myogenic process in diploid and triploid larvae submitted to fasting-refeeding. Regarding muscle morphology, within diploid groups, fasted larvae (FD) showed a significant decrease in white muscle fiber area compared with control (CD) and refed (RD-1) groups. Then, when food was provided, area values restored nearly to control. Based on these results, it is probable that temporary muscle fiber atrophy takes place in fasted diploid fish. Conversely, no significant morphological changes were observed among triploid groups. When the effects of ploidy on somatic growth were assessed, FD and RT-1 groups registered a significantly higher percentage of fibers with an area smaller than 500 μm2 compared with fasted triploid larvae (FT) and RD-1 groups, respectively. Additionally, immunolocalization of the proliferating cell nuclear antigen (PCNA) decreased during starvation in fish of both ploidies and only recovered to normal after refeeding in triploid fish. An increase in PCNA related to ploidy was detected in CD and RD-1 compared with their triploid counterparts. In relation to myogenic proteins, Myog showed a significant increase expression in diploid larvae during starvation. Mstn was not affected by ploidy or alimentary variations. Our results show that diploid fish are more affected by short-term starvation than triploid fish, which could be indicative of differential physiological responses of diploid and triploid larvae to alimentary changes in culture. This might be relevant to optimize conditions of culture for both diploid and triploid fish.

Analysis of Biomechanical Parameters of Muscle Soleus Contraction and Blood Biochemical Parameters in Rat with Chronic Glyphosate Intoxication and Therapeutic Use of C60 Fullerene.

The widespread use of glyphosate as a herbicide in agriculture can lead to the presence of its residues and metabolites in food for human consumption and thus pose a threat to human health. It has been found that glyphosate reduces energy metabolism in the brain, its amount increases in white muscle fibers. At the same time, the effect of chronic use of glyphosate on the dynamic properties of skeletal muscles remains practically unexplored. The selected biomechanical parameters (the integrated power of muscle contraction, the time of reaching the muscle contraction force its maximum value and the reduction of the force response by 50% and 25% of the initial values during stimulation) of muscle soleus contraction in rats, as well as blood biochemical parameters (the levels of creatinine, creatine phosphokinase, lactate, lactate dehydrogenase, thiobarbituric acid reactive substances, hydrogen peroxide, reduced glutathione and catalase) were analyzed after chronic glyphosate intoxication (oral administration at a dose of 10 μg/kg of animal weight) for 30 days. Water-soluble C60 fullerene, as a poweful antioxidant, was used as a therapeutic nanoagent throughout the entire period of intoxication with the above herbicide (oral administration at doses of 0.5 or 1 mg/kg). The data obtained show that the introduction of C60 fullerene at a dose of 0.5 mg/kg reduces the degree of pathological changes by 40–45%. Increasing the dose of C60 fullerene to 1 mg/kg increases the therapeutic effect by 55–65%, normalizing the studied biomechanical and biochemical parameters. Thus, C60 fullerenes can be effective nanotherapeutics in the treatment of glyphosate-based herbicide poisoning.

Rules of nature’s Formula Run: Muscle mechanics during late stance is the key to explaining maximum running speed

The maximum running speed of legged animals is one evident factor for evolutionary selection—for predators and prey. Therefore, it has been studied across the entire size range of animals, from the smallest mites to the largest elephants, and even beyond to extinct dinosaurs. A recent analysis of the relation between animal mass (size) and maximum running speed showed that there seems to be an optimal range of body masses in which the highest terrestrial running speeds occur. However, the conclusion drawn from that analysis—namely, that maximum speed is limited by the fatigue of white muscle fibres in the acceleration of the body mass to some theoretically possible maximum speed—was based on coarse reasoning on metabolic grounds, which neglected important biomechanical factors and basic muscle-metabolic parameters. Here, we propose a generic biomechanical model to investigate the allometry of the maximum speed of legged running. The model incorporates biomechanically important concepts: the ground reaction force being counteracted by air drag, the leg with its gearing of both a muscle into a leg length change and the muscle into the ground reaction force, as well as the maximum muscle contraction velocity, which includes muscle–tendon dynamics, and the muscle inertia—with all of them scaling with body mass. Put together, these concepts’ characteristics and their interactions provide a mechanistic explanation for the allometry of maximum legged running speed. This accompanies the offering of an explanation for the empirically found, overall maximum in speed: In animals bigger than a cheetah or pronghorn, the time that any leg-extending muscle needs to settle, starting from being isometric at about midstance, at the concentric contraction speed required for running at highest speeds becomes too long to be attainable within the time period of a leg moving from midstance to lift-off. Based on our biomechanical model, we, thus, suggest considering the overall speed maximum to indicate muscle inertia being functionally significant in animal locomotion. Furthermore, the model renders possible insights into biological design principles such as differences in the leg concept between cats and spiders, and the relevance of multi-leg (mammals: four, insects: six, spiders: eight) body designs and emerging gaits. Moreover, we expose a completely new consideration regarding the muscles’ metabolic energy consumption, both during acceleration to maximum speed and in steady-state locomotion.

Exercise duration and cohort affect variability and longevity of the response to exercise training in California Yellowtail (Seriola dorsalis)

Five cohorts of cultured California Yellowtail (Seriola dorsalis) were used in exercise training experiments to assess the duration of exercise necessary to induce a positive growth and fitness response, quantify the variability and replicability of this response between cohorts, and track the longevity (persistence) of exercise-induced benefits following removal from the exercise stimulus. Custom-designed raceways were used to continuously exercise juvenile yellowtail at their optimal swimming speed for two, three, or four weeks following which several fitness metrics including measures of somatic growth, white muscle fiber area, metabolic rate, and feed conversion were tracked for up to 20 weeks post exercise in comparison to non-exercised controls. Within a cohort, the longest duration of exercise (4 weeks) generally had the largest and longest-lasting impact on growth, followed by the 3-week, and then the 2-week exercise regimes. However, all exercise treatments showed substantial variability in the magnitude and longevity of the response between cohorts. For example, the positive growth response (increase in mass above that of controls) of the 4-week swimming group ranged from 9.8% to 37.8% between cohorts. This variability in the exercise response between cohorts is similar in magnitude to that associated with other experimentally manipulated variables in the exercise regimes of previous studies, and thus highlights the need for additional species-specific experiments to quantify replicability of positive exercise results. In addition, the longevity of exercise-induced benefits was highly variable between cohorts and generally not retained for prolonged periods post exercise. Most notably, the exercise-induced growth response which may result from muscle hypertrophy (increase in white muscle fiber size) during exercise, subsided within weeks. Taken together, these results indicate that exercise can play an important role in the growth and fitness of S. dorsalis and other species, however the duration of the exercise, as well as the timing of exercise in the rearing process likely have important implications for optimizing exercise training for aquaculture enhancement.

Potential mechanism of different gelation properties of white and red muscle fibre from crocodile (Crocodylus siamensis) meat: Study of myofibrillar protein

The present study was performed to investigate the effects of myofibrillar proteins (MPs) extracted from crocodile (tail, legs, torso) on gel formation mechanism and gel characteristics. The results showed that protein compositions and ratios were different in the three body parts. The tail MPs had a higher surface hydrophobicity than the legs and torso MPs, while the leg MPs had more reactive sulfhydryl groups than the tail and torso MPs (P < 0.05). According to the Raman spectroscopy results, before heating, the leg MPs' β-sheet content was significantly higher than that of tail MPs (P < 0.05). Heating significantly reduced the contents of α-helices in the legs and torso, and there were significant differences in β-sheet content between the legs and tail (P < 0.05). Moreover, with increasing myosin content, a denser microstructure of the tail gel was observed by scanning electron microscopy, leading to its gel strength and water-holding capacity being significantly higher than those of other parts. The tail MPs revealed a higher storage modulus (G′) and spin–spin relaxation time (T21) than those in the other two parts. In conclusion, the tail of crocodile (white muscle) has stronger protein gelation properties than other parts (red muscle), which is conducive to producing gel products.

Probiotic additive affects muscle growth of Nile tilapia (Oreochromis niloticus)

This study aimed to evaluate the probiotic additive on tilapia growth by establishing growth curves, as well as assessing the morphology of the muscular and ventral subcutaneous adipose tissues, carcass characteristics and gene expression that controls growth. Fingerlings of 5 g were grown in a recirculating aquaculture system consisting of 15 water tanks (0.25 m3) at 80 fish/m3. Fish were fed three times daily with the same feed, using additive with Bacillus subtilis, Bifidobacterium bifidum, Enterococcus faecium, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus lactis, Lactobacillus plantarum and Pediococcus acidilactici (1.0 × 109 CFU/g). They were assessed levels of 0.1% and 0.2% of additive probiotic homogenized in 2% soy oil and sprinkled over the feed. Exponential models were fit to compare growth rates, weighing samples at days 0, 30, 60 and 90 of cultivation. The probiotic mixture used in this study as feed additive may be diffused in aquaculture in order to increase productivity, as demonstrated by feed conversion rate, final weight and growth (13%–37% for 0.1% and 0.2% of additive level respectively). Growth stimulation occurred by white muscle fibre hypertrophy, accompanied by inhibition of MyoD and myostatin, gene expression and increase in the number of intestinal villi, ensuring greater absorption and utilization of nutrients provided in the diet.

366 The Ham Halo condition: Characterization and a possible approach for mitigation

Abstract The Halo condition is a meat quality defect characterized by very pale lean tissue on the superficial portion of fresh ham muscles. This tissue does not allow proper cured color development and has been the subject of customer complaints for ham processors. Surveys of raw materials revealed an issue affecting many suppliers and genetic lines. Further investigation indicated that the condition was most prominent in the distal portion of the biceps femoris muscle and was present in pigs of all ages and stages of production. Halo-affected tissue had much higher proportion of white muscle fibers. Consequently, Halo-affected tissue exhibited much lower myoglobin concentration, as well as much greater lightness, and much lower redness values, compared to normal tissue in the deeper portion of the muscle. These differences are consistent with increased expression of genes coding for white muscle fiber specific proteins in the Halo-affected tissue relative to tissue from the Inside portion of the biceps femoris muscle. Virtually all muscles evaluated have exhibited some degree of the Halo condition, but significant variation exists in the size of the affected portion of the muscle as well as the severity of the condition. Sire has a substantial impact on variation in Halo condition severity. Thus, genetic selection should help mitigate the condition. We will provide an overview of efforts to characterize the Halo condition and discuss genetic selection as a means to mitigate the condition.

Dietary Selenium Promotes Somatic Growth of Rainbow Trout (Oncorhynchus mykiss) by Accelerating the Hypertrophic Growth of White Muscle.

As a nutritionally essential trace element, selenium (Se) is crucial for fish growth. However, the underlying mechanisms remain unclear. Fish somatic growth relies on the white muscle growth. This study aimed to explore the effects and underlying mechanisms of Se on fish white muscle growth using a juvenile rainbow trout (Oncorhynchus mykiss) model. Fish were fed a basal diet unsupplemented or supplemented with selenium yeast at nutritional dietary Se levels (2 and 4mg/kg Se, respectively) for 30days. Results showed that dietary Se supplementation significantly enhanced trout somatic growth. Histological and molecular analysis of trout white muscle tissues at the vent level showed that dietary Se supplementation elevated the total cross-sectional area of white muscle, mean diameter of white muscle fibers, protein content, nuclei number, and DNA content of individual muscle fiber, and suppressed the activities of calpain system and ubiquitin-proteasome pathway. Overall, this study demonstrated that dietary Se within the nutritional range inhibits calpain- and ubiquitin-mediated protein degradation and promotes the fusion of myoblasts into the existed muscle fibers to promote the hypertrophic growth of white muscle, thereby accelerating the somatic growth of rainbow trout. Our results provide a mechanistic insight into the regulatory role of Se in fish growth.

Variable impacts of L-arginine or L-NAME during early life on molecular and cellular markers of muscle growth mechanisms in rainbow trout

Two experiments were conducted to test if manipulations of the Arginine-Nitric oxide pathway during the early life of rainbow trout would act on its early myogenic process. In experiment 1, trout embryos were immersed at 72° days post-fertilization (°dpf) or 104°dpf in water alone (control treatment, C) or containing 2 mM/L L-Arg (treatment A) or 1 mM/L of L-NAME, a NOS inhibitor (treatment N). We observed the beginning of expression of myf5 and fmhc genes at 72°dpf and 96°dpf, respectively. “A” treatment doubled the free Arg content of eggs but did not affect either the pattern of expression of myf5 and fmhc, nor white muscle cross-sectional area and number of white muscle fibres at hatching, nor embryo survival and fry growth. “N” treatment also did not affect these markers. In experiment 2, trout fry were fed from first feeding onwards and during 20 days either a control diet (C) or the same diet supplemented with L-NAME (0.1 g/100 g diet, N-diet). In C-fed fry, distribution of a single meal after overnight fasting induced changes in pcna, myod1, myog, fmhc, inos, nnos and ctsd gene expressions. N-feeding decreased fry growth but did not change their growth trajectory or survival. Twenty days of N-feeding led, compared to C-feeding, to changes in kinetics of transcription of pcna, myod1, myog, fmhc, inos, nnos, ctsd genes and to decreased white muscle cross-sectional area, total number of white muscle fibres, and number of large muscle fibres. L-NAME feeding thus decreased fry muscle growth by altering both hyperplasia and hypertrophy.

Early Exposure to THC Alters M-Cell Development in Zebrafish Embryos.

Cannabis is one of the most commonly used illicit recreational drugs that is often taken for medicinal purposes. The psychoactive ingredient in cannabis is Δ9-Tetrahydrocannabinol (Δ9-THC, hereafter referred to as THC), which is an agonist at the endocannabinoid receptors CB1R and CB2R. Here, we exposed zebrafish embryos to THC during the gastrulation phase to determine the long-term effects during development. We specifically focused on reticulospinal neurons known as the Mauthner cells (M-cell) that are involved in escape response movements. The M- cells are born during gastrulation, thus allowing us to examine neuronal morphology of neurons born during the time of exposure. After the exposure, embryos were allowed to develop normally and were examined at two days post-fertilization for M-cell morphology and escape responses. THC treated embryos exhibited subtle alterations in M-cell axon diameter and small changes in escape response dynamics to touch. Because escape responses were altered, we also examined muscle fiber development. The fluorescent labelling of red and white muscle fibers showed that while muscles were largely intact, the fibers were slightly disorganized with subtle but significant changes in the pattern of expression of nicotinic acetylcholine receptors. However, there were no overt changes in the expression of nicotinic receptor subunit mRNA ascertained by qPCR. Embryos were allowed to further develop until 5 dpf, when they were examined for overall levels of movement. Animals exposed to THC during gastrulation exhibited reduced activity compared with vehicle controls. Together, these findings indicate that zebrafish exposed to THC during the gastrula phase exhibit small changes in neuronal and muscle morphology that may impact behavior and locomotion.

Dietary DHA affects muscle fiber development by activating AMPK/Sirt1 pathway in blunt snout bream (Megalobrama amblycephala)

This study was conducted to evaluate the effect of DHA on muscle development mechanism of blunt snout bream by a feeding trial and a primary hepatocyte culture. Fish (average weight 26.40 ± 0.11 g) were randomly fed three diets: a deficient DHA diet (0% DHA, DD), a control diet (0.1% DHA, DC) and a high level of DHA diet (0.8% DHA, DH) for 8 weeks. Results were indicated that the weight gain rate (WGR) of fish feed with DC diets was significantly higher than the DD and DH diets (P < .05). The texture (hardness, gumminess and chewiness), fibers density, the proportion of small-sized fiber (< 20 μm) and sarcomere lengths in the white muscle were significantly increased in the DH group than DD and DC groups (P < .05). The gene expression of Myog and Mrf4 were significantly increased (P < .05), and the gene expression of MSTNa and MSTNb were significantly decreased in the fish fed DH diets than DD and DC diets (P < .05). These results suggested that DHA increased the flesh quality and promoted the white muscle hyperplasia and muscle fiber development. In addition, the gene expression of AMPKα2 and Sirt1 in the DC and DH group was significantly higher than the DD group (P < .05). The protein level of AMPK, phosphor-AMPK and AMPK/phosphor-AMPK were significantly increased in DC and DH group (P < .05). In vitro, the isolated primary hepatocytes from blunt snout bream were incubated with 0, 100 and 400 μM DHA for 24 h. The results showed that 400 μM DHA was significantly up-regulate the gene expression of AMPKα2 and Sirt1, and increased the protein level of AMPK, phosphor-AMPK, AMPK/phosphor-AMPK and Sirt1 (P < .05). In summary, DHA promoted the white muscle hyperplasia and muscle fiber development, which may be in association with the activation of AMPK/Sirt1 pathway.