Capillarity and fibre types in locomotory muscles of wild mallard ducks (Anas platyrhynchos)

Post-activation muscle potentiation and its relevance to cyclical behaviours

Muscle can experience post-activation potentiation (PAP), a temporary increase in force and rate of force development, when contractions are closely timed; therefore, cyclical behaviours are likely affected by PAP, as succeeding contraction cycles can lead to potentiation over several subsequent cycles. Here, we examined PAP during in situ cyclical contractions of the mallard lateral gastrocnemius (LG). Surface swimming, a cyclical behaviour, was mimicked with work-loops using in vivo LG length change and stimulation parameters. Tests were performed at mallards' preferred cycle frequency as well as at lower and higher frequencies. Like muscles from mammals, anurans and arthropods, the mallard LG exhibited PAP with increases in peak force, average force rate and net work. Staircase potentiation occurred over two or more work-loop cycles, resulting in gradual increases in PAP. The number of cycles needed to reach maximum work varied with cycle frequency, requiring more cycles at higher cycle frequencies. PAP occurred under in vivo-like stimulation parameters, suggesting a potentially important role of PAP in animal locomotion, especially in cyclical behaviours.

Seasonal muscle ultrastructure plasticity and resistance of muscle structural changes during temperature increases in resident black-capped chickadees and rock pigeons

Resident birds in temperate zones respond to seasonally fluctuating temperatures by adjusting their physiology, such as changes in basal metabolic rate or peak metabolic rate during cold exposure, or altering their organ sizes, so as to match the thermogenic requirements of their current environment. Climate change is predicted to cause increases in the frequency of heat and cold wave events, which could increase the likelihood that birds will face an environmental mismatch. Here, we examined seasonality and the effects of acute and chronic heat shock to 33°C and subsequent recovery from heat shock on the ultrastructure of the superficial pectoralis muscle fiber diameter, myonuclear domain (MND) and capillary density in two temperate bird species of differing body mass, the black-capped chickadee (Poecile atricapillus) and the rock pigeon (Columba livia). We found that muscle fiber ultrastructure did not change with heat treatment. However, in black-capped chickadees, there was a significant increase in fiber diameter in spring phenotype birds compared with summer phenotype birds. In rock pigeons, we saw no differences in fiber diameter across seasons. Capillary density did not change as a function of fiber diameter in black-capped chickadees, but did change seasonally, as did MND. Across seasons, as fiber diameter decreased, capillary density increased in the pectoralis muscle of rock pigeons. For both species in this study, we found that as fiber diameter increased, so did MND. Our findings imply that these two temperate birds employ different muscular growth strategies that may be metabolically beneficial to each.

Muscle fiber structure in an aging long-lived seabird, the black-legged kittiwake (Rissa tridactyla)

Many long-lived animals do not appear to show classic signs of aging, perhaps because they show negligible senescence until dying from "catastrophic" mortality. Muscle senescence is seldom examined in wild animals, yet decline in muscle function is one of the first signs of aging in many lab animals and humans. Seabirds are an excellent study system for physiological implications of aging because they are long-lived animals that actively forage and reproduce in the wild. Here, we examined linkages between pectoralis muscle fiber structure and age in black-legged kittiwakes (Rissa tridactyla). Pectoralis muscle is the largest organ complex in birds, and responsible for flight and shivering. We obtained and fixed biopsies from wild black-legged kittiwakes of known age. We then measured muscle fiber diameter, myonuclear domain and capillaries per fiber area among birds of differing ages. All muscle parameters were independent of age. Number of nuclei per mm of fiber showed a positive correlation with muscle fiber cross-sectional area, and myonuclear domain increased with muscle fiber diameter. Thus, as muscle fibers increased in size, they may not have recruited satellite cells, increasing the protein turnover load per nuclei. We conclude that senescence in a long-lived bird with an active lifestyle, does not entail mammalian-like changes in muscle structure.

The anatomy and histochemistry of flight hindlimb posture in birds. II. The flexed hindlimb posture of perching birds

During flight, birds employ one of two hindlimb postures. Perching birds utilize a flexed posture with their folded legs tucked beneath the body, whereas shorebirds and raptors use an extended posture with straightened legs trailing behind the body. Maintenance of either posture during flight requires the hindlimbs to hold their position for prolonged periods. Slow contracting fibers are known for their fatigue-resistant properties and are often found in high percentages in muscles utilized for postural actions. Given the similar actions required of the hip and knee flexors used during flight, we hypothesized that the equivalent postural muscles of perching birds (flexed posture) would contain similar percentages of slow fibers as shorebirds (extended posture). We investigated the anatomy and fiber type composition of seven hindlimb muscles in yellow-headed and red-winged blackbirds and revealed that they possess a smaller percentage of slow fibers than we found previously in the same muscles of American avocets and black-necked stilts. The comparably smaller body size of yellow-headed and red-winged blackbirds could mitigate the need for more slow fibers. In addition, the biomechanical placement of the weight force in the flexed posture may require less muscle force for postural support during flight and, therefore, fewer slow fibers.

Expression profile of IGF-I-calcineurin-NFATc3-dependent pathway genes in skeletal muscle during early development between duck breeds differing in growth rates

The insulin-like growth factor I (IGF-I)-calcineurin (CaN)-NFATc signaling pathways have been implicated in the regulation of myocyte hypertrophy and fiber-type specificity. In the present study, the expression of the CnAα, NFATc3, and IGF-I genes was quantified by RT-PCR for the first time in the breast muscle (BM) and leg muscle (LM) on days 13, 17, 21, 25, and 27 of embryonic development, as well as at 7 days posthatching (PH), in Gaoyou and Jinding ducks, which differ in their muscle growth rates. Consistent expression patterns of CnAα, NFATc3, and IGF-I were found in the same anatomical location at different development stages in both duck breeds, showing significant differences in an age-specific fashion. However, the three genes were differentially expressed in the two different anatomical locations (BM and LM). CnAα, NFATc3, and IGF-I messenger RNA (mRNA) could be detected as early as embryonic day 13 (ED13), and the highest level appeared at this stage in both BM and LM. Significant positive relationships were observed in the expression of the studied genes in the BM and LM of both duck breeds. Also, the expression of these three genes showed a positive relationship with the percentage of type IIb fibers and a negative relationship with the percentage of type I fibers and type IIa fibers. Our data indicate differential expression and coordinated developmental regulation of the selected genes involved in the IGF-I-calcineurin-NFATc3 pathway in duck skeletal muscle during embryonic and early PH growth and development; these data also indicate that this signaling pathway might play a role in the regulation of myofiber type transition.

Anatomy and histochemistry of hindlimb flight posture in birds. I. The extended hindlimb posture of shorebirds

Birds utilize one of two hindlimb postures during flight: an extended posture (with the hip and knee joints flexed, while the ankle joint is extended caudally) or a flexed posture (with the hip, knee, and ankle joints flexed beneath the body). American Avocets (Recurvirostra americana) and Black-necked Stilts (Himantopus mexicanus) extend their legs caudally during flight and support them for extended periods. Slow tonic and slow twitch muscle fibers are typically found in muscles functioning in postural support due to the fatigue resistance of these fibers. We hypothesized that a set of small muscles composed of high percentages of slow fibers and thus dedicated to postural support would function in securing the legs in the extended posture during flight. This study examined the anatomy and histochemical profile of eleven hindlimb muscles to gain insight into their functional roles during flight. Contrary to our hypothesis, all muscles possessed both fast twitch and slow twitch or slow tonic fibers. We believe this finding is due to the versatility of dynamic and postural functions the leg muscles must facilitate, including standing, walking, running, swimming, and hindlimb support during flight. Whether birds use an extended or flexed hindlimb flight posture may be related to the aerodynamic effect of leg position or may reflect evolutionary history.

Morphofunctional responses to anaemia in rat skeletal muscle

Adult male Sprague-Dawley rats were randomly assigned to two groups: control and anaemic. Anaemia was induced by periodical blood withdrawal. Extensor digitorum longus and soleus muscles were excised under pentobarbital sodium total anaesthesia and processed for transmission electron microscopy, histochemical and biochemical analyses. Mitochondrial volume was determined by transmission electron microscopy in three different regions of each muscle fibre: pericapillary, sarcolemmal and sarcoplasmatic. Muscle samples sections were also stained with histochemical methods (SDH and m-ATPase) to reveal the oxidative capacity and shortening velocity of each muscle fibre. Determinations of fibre and capillary densities and fibre type composition were made from micrographs of different fixed fields selected in the equatorial region of each rat muscle. Determination of metabolites (ATP, inorganic phosphate, creatine, creatine phosphate and lactate) was done using established enzymatic methods and spectrophotometric detection. Significant differences in mitochondrial volumes were found between pericapillary, sarcolemmal and sarcoplasmic regions when data from animal groups were tested independently. Moreover, it was verified that anaemic rats had significantly lower values than control animals in all the sampled regions of both muscles. These changes were associated with a significantly higher proportion of fast fibres in anaemic rat soleus muscles (slow oxidative group = 63.8%; fast glycolytic group = 8.2%; fast oxidative glycolytic group = 27.4%) than in the controls (slow oxidative group = 79.0%; fast glycolytic group = 3.9%; fast oxidative glycolytic group = 17.1%). No significant changes were detected in the extensor digitorum longus muscle. A significant increase was found in metabolite concentration in both the extensor digitorum longus and soleus muscles of the anaemic animals as compared to the control group. In conclusion, hypoxaemic hypoxia causes a reduction in mitochondrial volumes of pericapillary, sarcolemmal, and sarcoplasmic regions. However, a common proportional pattern of the zonal distribution of mitochondria was maintained within the fibres. A significant increment was found in the concentration of some metabolites and in the proportion of fast fibres in the more oxidative soleus muscle in contrast to the predominantly anaerobic extensor digitorum longus.

Force-velocity properties of two avian hindlimb muscles

Recent work has provided measurements of power output in avian skeletal muscles during running and flying, but little is known about the contractile properties of avian skeletal muscle. We used an in situ preparation to characterize the force-velocity properties of two hind limb muscles, the lateral gastrocnemius (LG) and peroneus longus (PL), in Wild Turkeys (Meleagris gallopavo). A servomotor measured shortening velocity for at least six different loads over the plateau region of the length-tension curve. The Hill equation was fit to the data to determine maximum shortening velocity and peak instantaneous power. Maximum unloaded shortening velocity was 13.0+/-1.6 L s(-1) for the LG muscle and 14.8+/-1.0 L s(-1) for the PL muscle (mean+/-S.E.M.). These velocities are within the range of values published for reptilian and mammalian muscles. Values recorded for maximum isometric force per cross-sectional area, 271+/-28 kPa for the LG and 257+/-30.5 kPa for the PL, and peak instantaneous power output, 341.7+/-36.4 W kg(-1) for the LG and 319.4+/-42.5 W kg(-1) for the PL, were also within the range of published values for vertebrate muscle. The force-velocity properties of turkey LG and PL muscle do not reveal any extreme differences in the mechanical potential between avian and other vertebrate muscle.

Anatomy and histochemistry of spread-wing posture in birds. 3. Immunohistochemistry of flight muscles and the ?shoulder lock? in albatrosses

As a postural behavior, gliding and soaring flight in birds requires less energy than flapping flight. Slow tonic and slow twitch muscle fibers are specialized for sustained contraction with high fatigue resistance and are typically found in muscles associated with posture. Albatrosses are the elite of avian gliders; as such, we wanted to learn how their musculoskeletal system enables them to maintain spread-wing posture for prolonged gliding bouts. We used dissection and immunohistochemistry to evaluate muscle function for gliding flight in Laysan and Black-footed albatrosses. Albatrosses possess a locking mechanism at the shoulder composed of a tendinous sheet that extends from origin to insertion throughout the length of the deep layer of the pectoralis muscle. This fascial "strut" passively maintains horizontal wing orientation during gliding and soaring flight. A number of muscles, which likely facilitate gliding posture, are composed exclusively of slow fibers. These include Mm. coracobrachialis cranialis, extensor metacarpi radialis dorsalis, and deep pectoralis. In addition, a number of other muscles, including triceps scapularis, triceps humeralis, supracoracoideus, and extensor metacarpi radialis ventralis, were found to have populations of slow fibers. We believe that this extensive suite of uniformly slow muscles is associated with sustained gliding and is unique to birds that glide and soar for extended periods. These findings suggest that albatrosses utilize a combination of slow muscle fibers and a rigid limiting tendon for maintaining a prolonged, gliding posture.

Effect of selection for improved body weight and composition on muscle and meat characteristics in Muscovy duck

1. For 25 years, the Muscovy duck has been selected for greater body weight at slaughter age, higher meat yield and lower fat content. The aim of this study was to analyse the effects of such selection on the biochemical and technological characteristics of duck meat. 2. A line which has been maintained without any selection since 1975 (control line) and a heavy line now commercialised (selected line) were reared under the same conditions. We compared growth performances, dressing and dissection yields and biochemical and technological characteristics of duck meat at 8, 10 and 12 weeks of age. 3. Our results showed that an indirect effect of selection was to increase the duck growth rate. At a given age, muscle weights and yields as well as carcase fat content were higher for selected ducks. In the selected line, muscle fibres were larger and the collagen content in muscles lower. 4. The Sartorius muscle in ducks from the selected line exhibited a higher percentage in numbers of white type IIb fibres to the detriment of red type IIa fibres. Its glycolytic enzyme activity was higher and its oxidative enzyme activity lower. 5. In breast muscle, selection decreased the rate of post-mortem decline in pH value, increased protein and mineral contents and decreased moisture. It did not affect fibre type, colour, haem pigment and lipid contents, collagen solubility or drip loss. 6. In conclusion, the effects of Muscovy duck selection on meat quality were relatively moderate.

Effects of age and sex on the structural, chemical and technological characteristics of mule duck meat

1. The aim of the study was to analyse the effect of age and sex on the chemical, structural and technological characteristics of mule duck meat. 2. Ten males and 10 females were weighed and slaughtered at 8, 10, 11, 12 and 13 weeks of age. Weight, pH value, colour, tenderness and juice loss of breast muscle were determined. 3. The activities of 3 enzymes (citrate synthase, beta-hydroxyacyl CoA dehydrogenase, lactate dehydrogenase) which indicate muscular metabolic activity were assayed. 4. Chemical composition (moisture, lipids, proteins, minerals, lipid and phospholipid classes, fatty acid composition) of breast muscle was analysed. 5. Fibre type, fibre type percentage and cross-sectional areas were determined using histochemistry and an image analysis system. 6. For growth performance and muscular structure, the ideal slaughter age of mule ducks is 10 weeks of age. Chemical and technological analysis indicated that muscular maturity in Pectoralis major was reached at 11 weeks of age, but, at this age, breast lipid content is high. Moreover, after 10 weeks of age, food costs rapidly increased. 7. Lastly, sexual dimorphism for body weight is minor. In this study, at any given age, no significant differences between males and females were shown. Thus, it is possible to rear both sexes together and to slaughter them at the same age.

Descriptive and functional morphometry of skeletal muscle fibres in wild birds

The fibre types of four forelimb and two hind-limb muscles involved in locomotion were morphometrically analyzed in three species of wild birds: the mallard (Anas platyrhynchos), common coot (Fulica atra), and yellow-legged gull (Larus cachinnans). Fibre cross-sectional area and perimeter, maximal diffusion distance, and number of capillaries per fibre were measured and the functional implications and physiological demands of the muscles of each species were inferred. In general, all morphometric values were lower in oxidative fibres than in anaerobic fibres, indicating that the supply of oxygen and metabolites available to aerobically working muscles is enhanced. The lower level of activity required during gliding as opposed to flapping flight, and the need to maintain the wings in an outstretched position, presumably by means of isometric contractions, may explain the greater size of the oxidative fibres of the pectoralis and scapulotriceps muscles of the gull. In contrast, the high oxidative demand imposed on mallards and coots by sustained flapping flight is met by small oxidative fibres, possibly at the expense of a reduction in the ability of each fibre to generate force. Anaerobic fibres of the gastrocnemius muscle had greater cross-sectional areas in the mallard and coot than in the gull. This is interpreted as an adaptive response to force generation during burst locomotion, which is usually performed by both mallards and coots, in sharp contrast to the buoyant swimming and postural activities undertaken by gull's legs. The fast oxidative fibres of the gastrocnemius muscle were, in general, larger than those of the iliotibialis muscle in the three species, which matches the different mechanical and functional roles of these muscles during swimming.

Posthatching myofiber development in the M. pectoralis of White Pekin Ducks

BACKGROUND

A posthatching transformation of fast-twitch oxidative-glycolytic (FTO) to fast-twitch glycolytic (FTG) fibers in the breast muscle in domestic chickens and turkeys is well documented. There is, however, no information on the situation in Anseriformes having a M. pectoralis with a mixed fiber composition in adults. Differences in the growth of the different fiber types were reported for some muscles in ducks as well as in other birds. They are examined in the main flight muscle using growth curve analysis, until now mostly applied to the analysis of overall growth.

METHODS

Biopsies were taken longitudinally from the M. pectoralis, Pars thoracica, of 40 White Pekin Ducks at 11 different ages from hatching through day 146. The samples were processed for a combination of nicotinamide adenine dinucleotide tetrazolium reductase and myosin adenosine triphosphatase after acid preincubation at pH 4.1. Mean fiber diameter was determined for the different fiber types in relation to age. The Janoschek growth curve was fitted to these values.

RESULTS

FTG fibers were first detected at 20 days of age. Thereafter, the fiber composition hardly changed. When distinguishable by enzyme histochemistry, FTG fibers were already larger in diameter than FTO. There were only gradual differences in the growth pattern. FTG fibers, however, showed much higher absolute, percentage, and relative growth rates. The radial growth of myofibers is slow when compared to other one-dimensional measurements.

CONCLUSIONS

Fiber transformation seems to take place within a short age period. However, further studies are necessary to discriminate effects resulting from sample depth. FTG fibers are presumably recruited from those FTO fibers that show higher growth rates. Growth curve analysis, more frequently used in gross morphological studies, provides an analytical tool for evaluating growth processes of cells and tissues as well. Fiber size differences are mainly due to a higher growth rate in FTG fibers, whereas the growth patterns show only minor differences.

Anatomy and histochemistry of spread-wing posture in birds. 2. Gliding flight in the California gull, Larus californicus: a paradox of fast fibers and posture

Gliding flight is a postural activity which requires the wings to be held in a horizontal position to support the weight of the body. Postural behaviors typically utilize isometric contractions in which no change in length takes place. Due to longer actin-myosin interactions, slow contracting muscle fibers represent an economical means for this type of contraction. In specialized soaring birds, such as vultures and pelicans, a deep layer of the pectoralis muscle, composed entirely of slow fibers, is believed to perform this function. Muscles involved in gliding posture were examined in California gulls (Larus californicus) and tested for the presence of slow fibers using myosin ATPase histochemistry and antibodies. Surprisingly small numbers of slow fibers were found in the M. extensor metacarpi radialis, M. coracobrachialis cranialis, and M. coracobrachialis caudalis, which function in wrist extension, wing protraction, and body support, respectively. The low number of slow fibers in these muscles and the absence of slow fibers in muscles associated with wing extension and primary body support suggest that gulls do not require slow fibers for their postural behaviors. Gulls also lack the deep belly to the pectoralis found in other gliding birds. Since bird muscle is highly oxidative, we hypothesize that fast muscle fibers may function to maintain wing position during gliding flight in California gulls.