Neuromuscular organization of avian flight muscle: Morphology and contractile properties of motor units in the pectoralis (pars thoracicus) of pigeon (Columba livia)

We used acid digestion and glycogen depletion to determine fascicle organization, fiber morphology, and physiological and anatomical features of individual motor units of an in-series muscle, the pectoralis (pars thoracicus) of the pigeon (Columba livia). Most fascicles are attached at one end to connective tissue. Average fiber length in the four regions examined range from 42% to 66% of average fascicle length. More than 65% of fibers are blunt at one end of a fascicle and taper intrafascicularly. Fibers with blunt–blunt endings range from 13% to 31% of the population in different regions; taper–taper fibers range from 2% to 17%. Pigeon pectoralis fibers are distinguished histochemically into fast-twitch glycolytic (FG) and fast-twitch oxidative-glycolytic (FOG) populations. Three units composed of FG fibers (FG units) contract more quickly than three units composed of FOG fibers (FOG units) (range 31–37 vs 47–62 msec), produce more tetanic force (0.11–0.32 vs 0.02–0.05 N) and are more fatigable (<18% initial force vs >50% after repeated stimulation). Most motor units are confined to one of the four muscle regions. Territory of two FOG units is <30% of parent fascicle length. Territories of other units spanned parent fascicles; most fibers in these units do not extend the full fascicle length. Compared to FG units, FOG units have lower maximum innervation ratios and density indices (ratio of depleted/total FOG fibers in territory 8–14% vs 58–76% for FG units). These differences support the hypothesis that FG units are organized to produce substantial force and power for takeoff, landing and other ballistic movements whereas FOG units are suited for sustained flight when power requirements are reduced. Implications of findings for understanding the control of in-series muscles and the use of connective tissue elastic elements during wing movements are discussed. J.Morphol. 236:179–208, 1998. © 1998 Wiley-Liss, Inc.     

Effects of anabolic steroids and high intensity exercise on rat skeletal muscle fibres and capillarization. A morphometric study.

The effects were investigated of high intensity short duration exercise and anabolic steroid treatment on the medial gastrocnemius muscle of female rats. Twelve rats were divided equally into four groups, exercise with and without steroid administration and sedentary with and without steroid administration. Animals were made to swim for 5 weeks, 6 days.week-1. Muscle fibres were classified as slow-twitch (ST), fast-twitch oxidative glycolytic (FOG) and fast-twitch glycolytic (FG). Muscle fibre size was measured as the equivalent circle diameter. Exercise (P less than 0.001) and steroid (P less than 0.05) treatments alone, significantly elevated FOG and decreased FG fibre proportions. Overall proportions of fast-twitch and ST muscle fibres did not vary with any of the treatments. Significant differences in the proportion of muscle fibres were found to exist between different areas within the gastrocnemius muscle (P less than 0.05). Exercise and steroid treatments alone did not alter muscle fibre diameters. Combined exercise and steroid treatments did significantly increase ST fibre diameters (P less than 0.05). Exercise only treatment resulted in significant increases in the number of capillaries surrounding ST fibre (P less than 0.05) and FOG fibre (P less than 0.01) types. In conclusion the main finding of this study indicated that anabolic steroids in conjunction with high intensity swimming instigated ST fibre hypertrophy. Exercise and steroid only treatments significantly elevated FOG fibre proportions while FG fibre proportions diminished. Exercise only treatment resulted in significant increases in the number of capillaries surrounding both ST and FOG fibre types.     

Loss of thick filaments from fast-twitch glucolytic muscle fibers of the pigeon pectoralis after chronic administration of dantrolene sodium.

Adult pigeons received dantrolene sodium, a skeletal muscle relaxant which blocks the release of calcium during excitation-contraction coupling, for 12 to 16 weeks. The pectoralis muscles of these birds were analyzed for changes occurring in the various fiber types of the muscle. Both histochemistry (ATPase and SDH activity) and electron microscopy (mitochondrial and lipid volume percentages) differentiated two fiber types. The two fiber-types consisted of fast-twitch glycolytic fibers (FG) and fast-twitch oxidative-glycolytic (FOG) fibers. After dantrolene treatment some FG fibers showed little or no ATPase activity. Dantrolene treatment also produced a disappearance of thick filaments in some FG fibers. We infer that the fibers without thick filaments are the ones lacking ATPase activity. The FOG fibers were nearly normal. Since drug-fed birds lose weight, a few birds were starved to determine whether the filament loss was related solely to the bird's loss in weight. No fibers in starved birds showed reduced ATPase activity or loss of thick filaments. In fibers that showed thick filament disappearance, the I-bands remained organized and intact, suggesting that the I-band maintains its integrity without interaction with the thick filaments. Changes in activity patterns may cause loss of thick filaments by inhibiting either their synthesis or assembly.     

Fiber type homogeneity of the flight musculature in small birds

Studies of medium- and large-bodied avian species have suggested that variation in flight muscle composition is related to differences in flight behavior. For example, slow-twitch or tonic fibers are generally found only in the flight muscles of non-volant or soaring/gliding birds. However, we know comparatively little about fiber composition of the muscles of the smallest birds. Here we describe the fiber composition of muscles from the wings, shoulders, and legs of two small avian species, which also display very high wingbeat frequencies: Anna's hummingbirds (Calypte anna) and zebra finches (Taeniopygia guttata). All flight muscles examined in both species contained exclusively fast oxidative glycolytic (FOG) fibers. These unique results suggest that fast oxidative fibers are both necessary and sufficient for the full range of flight behaviors in these small-bodied birds. Like all other studied birds, the zebra finch gastrocnemius, a tarsometatarsal extensor, contained a mixture of FOG (27.1%), slow oxidative (SO, 12.7%), and fast glycolytic (FG, 60.2%) fibers. By contrast, the hummingbird gastrocnemius lacked FG fibers (85.5% FOG, 14.5% SO), which may reflect the reduced role of the hindlimb during take-off. We further hypothesize that thermogenic requirements constrain fiber type heterogeneity in these small endothermic vertebrates.     

Chromosome studies in four species of Ratitae (Aves)

Chromosomes were studied in female specimens of the ostrich, Struthio camelus L., cassowary, Casuarius casuarius (L.), emu, Dromiceius novaehollandiae (Lath.) and rhea, Rhea americana L. by means of blood and feather pulp culture techniques. Male karyotypes were also studied in the emu and rhea. The diploid chromosome number was most likely 80 in the ostrich and rhea and 82 in the emu, while the exact number could not be determined in the cassowary. Karyotypes of the 4 species were strikingly similar and apparently interchangeable with one another with slight modifications of the centromeric position in one or two pairs of macrochromosomes. No heteromorphic macrochromosomal pair was found either in female specimens or in male ones of the ratite species so far examined, except for a female rhea. This specimen was found to possess an acrocentric chromosome which was evidently a member of nos. 4–6, but considerably smaller than any other chromosome of the group. ³H-thymidine autoradiography provided no more information than the straightforward morphological analysis with regard to the differentiation of the sex-chromosomes.Contributions from the Chromosome Research Unit, Hokkaido University. Dedicated to Emeritus Professor Sajiro Makino on the occasion of his retirement, in honor of his 40 years' service with the University. Supported by a grant from the Scientific Research Fund of the Ministry of Education (No. 584099).     

Comparative morphology,morphometry and distribution pattern of the trigeminal nerve branches supplying the bill tip in the ostrich (Struthio camelus) and emu (Dromaius novaehollandiae)

The subdivisions of the trigeminal nerve (N. ophthalmicus R. medialis and N. intramandibularis) innervating the upper and lower bill tip, respectively, were well developed in both the ostrich and emu and displayed extensive branching. Transmission electron microscopy revealed that both nerves displayed features typical of a mixed, peripheral nerve. Nerve fibre size in the ostrich and emu was larger than that reported in domestic poultry. There were a significantly higher number of myelinated nerve fibres in the N. ophthalmicus R. medialis in the emu by comparison with the same nerve in the ostrich, or by comparison with the N. intramandibularis of either species. As myelinated nerve fibres supply Herbst corpuscles, and these structures have been demonstrated in this region in these two species, this may indicate that the upper bill of the emu is more sensitive to vibrational stimuli than the upper bill of the ostrich or the lower bill of both species. The large size of the nerve fibres, the high nerve fibre count and the particular distribution of the nerves in the bill tip support the existence of a well‐developed sensory area in this region of the ostrich and emu.     

Catalase-positive microperoxisomes in rat soleus and extensor digitorum longus muscle fiber types

The size, distribution, and content of catalase-reactive microperoxisomes were studied cytochemically in slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), and fast-twitch glycolytic (FG) fibers of soleus and extensor digitorum longus (EDL) rat muscles. Fiber types were classified on the basis of mitochondrial content and distribution, Z-band widths, and myofibril size and shape. Microperoxisomes were generally located between myofibrils at the I-bands. The absence of crystalloid inclusions prevented positive identification of microperoxisomes in nonreacted and aminotriazole-inhibited muscles. EDL and soleus SO fibers possessed the largest microperoxisomes, whereas FOG and FG fibers of the EDL contained small- to medium-sized microperoxisomes. Comparing either microperoxisome number per muscle fiber area or microperoxisome area per fiber area revealed significant differences between fiber types with this ranking: soleus SO greater than EDL SO greater than EDL FOG greater than EDL FG. The present observations demonstrate that the content of catalase-positive microperoxisomes is greatest in the oxidative muscle fiber types. These cytochemical findings account for the higher catalase activity in homogenates of soleus muscles as compared to that of EDL muscles, because the soleus contains more oxidative fibers than EDL.     

Fiber composition and capillarity in growing guinea pigs acclimated to cold and cold plus hypoxia

The central portion of the medial head of the gastrocnemius of control (normoxic and normothermic), hypoxia-, cold-, and cold plus hypoxia-acclimated guinea pigs was analyzed for capillary supply and fiber composition to elucidate changes in capillarity induced by environmental stresses. The muscle was cut at midbelly, frozen, sectioned, and stained for myosin ATPase. Fiber cross-sectional areas; percentages of slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG), and fast-twitch glycolytic (FG) fibers; and numbers of capillaries around each fiber type were measured. Growth rates of all four guinea pig groups were similar. Capillarity was not affected by acclimation to hypoxia. Cold and cold plus hypoxia acclimation led to increased numbers of capillaries around the fiber in all three fiber types. In addition, significant increases in the percentage of FOG fibers and concomitant decreases in the percentage of FG fibers compared to controls were found in cold and in cold plus hypoxia indicating that a transformation of fiber type from FG to FOG had occurred. The increase in FOGs at the expense of the FGs did not occur in the guinea pigs grown in a hypoxic environment. The increased total capillarity in those muscles studied was the result of more capillaries around all fiber types and was not due to simple transformation of fibers.     

Comparative analysis of fiber-type composition in the iliofibularis muscle of phrynosomatid lizards (Squamata).

The lizard family Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. This family exhibits great variation in ecology, behavior, and general body plan. Previous studies also show that this family exhibits great diversity in locomotor performance abilities; as measured on a high-speed treadmill, sand lizards are exceptionally fast sprinters, members of the Sceloporus group are intermediate, and horned lizards are slowest. These differences are paralleled by differences in relative hindlimb span. To determine if muscle fiber-type composition also varies among the three subclades, we examined the iliofibularis (IF), a hindlimb muscle used in lizard locomotion, in 11 species of phrynosomatid lizards. Using histochemical assays for myosin ATPase, an indicator of fast-twitch capacity, and succinic dehydrogenase, denoting oxidative capacity, we classified fiber types into three categories based on existing nomenclature: fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG), and slow-twitch oxidative (SO). Sand lizards have a high proportion of FG fibers (64-70%) and a low proportion of FOG fibers (25-33%), horned lizards are the converse (FG fibers 25-31%, FOG fibers 56-66%), and members of the Sceloporus group are intermediate for both FG (41-48%) and FOG (42-45%) content. Hence, across all 11 species %FOG and %FG are strongly negatively correlated. Analysis with phylogenetically independent contrasts indicate that this negative relationship is entirely attributable to the divergence between sand and horned lizards. The %SO also varies among the three subclades. Results from conventional nested ANCOVA (with log body mass as a covariate) indicate that the log mean cross-sectional area of individual muscle fibers differs among species and is positively correlated with body mass across species, but does not differ significantly among subclades. The log cross-sectional area of the IF varies among species, but does not vary among subclades. Conversely, the total thigh muscle cross-sectional area does not vary among species, but does vary among subclades; horned lizards have slimmer thighs. Muscle fiber-type composition appears to form part of a coadapted suite of traits, along with relative limb and muscle sizes, that affect the locomotor abilities of phrynosomatid lizards.     

Ultrastructural localization of lectin receptors on the bone-marrow sinusoidal endothelium of the rat

The purpose of this study was to estimate the absolute and relative masses of the three types of skeletal muscle fibers in the total hindlimb of the male Sprague-Dawley rat (Rattus norvegicus). For six rats, total body mass was recorded and the following weights taken from dissection of one hindlimb: 32 individual major muscles or muscle parts, remaining skeletal musculature (small hip muscles and intrinsic foot muscles), bone, inguinal fat pad, and skin. The fibers from the 32 muscles or muscle parts (which constituted 98% of the hindlimb skeletal muscle mass) were classified from histochemistry as fast-twitch oxidative glycolytic (FOG), fast-twitch glycolytic (FG), or slow-twitch oxidative (SO), and their populations were determined. Fiber cross-sectional areas from the same muscles were measured with a digitizer. Mass of each of the fiber types within muscles and in the total hindlimb was then calculated from fiber-type population, fiber-type area, and muscle-mass data. Skeletal muscle made up 71% of the total hindlimb mass. Of this, 76% was occupied by FG fibers, 19% by FOG fibers, and 5% by SO fibers. Thus, the FG fiber type is clearly the predominant fiber type in the rat hindlimb in terms of muscle mass. Fiber-type mass data are compared with physiological (blood flow) and biochemical (succinate dehydrogenase activities) data for the muscles taken from previous studies, and it is demonstrated that these functional properties are closely related to the proportions of muscle mass composed of the various fiber types.     

Ultrastructural and cytological changes in the muscle fibers of the pectoralis of the giant Canada goose (Branta canadensis maxima) in disuse atrophy during molt

Summary Adult male Branta canadensis maxima were collected from a nonmigratory feral population during their premolt, molt and postmolt phases. Lean dry weight of the pectoralis muscle decreased significantly (p0.0001) during molt, as a result of disuse atrophy. Histochemical analysis revealed that the region of the pectoralis muscle sampled consisted of Red (fast-twitch oxidative-glycolytic) and White (fast-twitch glycolytic) muscle fiber types, in an approximate ratio of 9 to 1. There was no significant (p= 0.1238) difference in the relative percentages of the two fiber types during the three periods of study. There was, however, a significant decrease in mean cross-sectional area of both Red (p0.0194) and White (p0.0001) fibers during molt. Red and White fiber areas were strongly correlated with each other during molt (r ²=0.76, p=0.0010) and postmolt (r ²=0.70, p=0.0052), but not during premolt (r ²=0.02, p=0.7626). The latter finding may be related to fiber-type specific hypertrophy in premolt breeding males. Analysis of ultrastructure revealed that there was a significant (p=0.0003) decrease in the mean myofibrillar crosssectional area, and a significant increase in both the density (p=0.0227) and total number (p=0.0058) of myofibrils within the muscle fibers of the molting birds. These results indicate that the myofibrils split longitudinally during moltassociated disuse atrophy. A significant (p=0.0375) reduction in the amount of non-myofibrillar material (mitochondria) was also observed in the periphery of the muscle fibers of the molting birds. The changes observed during disuse atrophy are neither as pathological nor as extreme as those induced by experimental models of avian muscle atrophy.     

Neuromuscular organization of avian flight muscle: architecture of single muscle fibres in muscle units of the pectoralis (pars thoracicus) of pigeon (Columba livia)

The M. pectoralis (pars thoracicus) of pigeons (Columba livia) is comprised of short muscle fibres that do not extend from muscle origin to insertion but overlap ''in-series''. Individual pectoralis motor units are limited in territory to a portion of muscle length and are comprised of either fast twitch, oxidative and glycolytic fibres (FOG) or fast twitch and glycolytic fibres (FG). FOG fibres make up 88 to 90% of the total muscle population and have a mean diameter one-half of that of the relatively large FG fibres. Here we report on the organization of individual fibres identified in six muscle units depleted of glycogen, three comprised of FOG fibres and three comprised of FG fibres. For each motor unit, fibre counts revealed unequal numbers of depleted fibres in different unit cross-sections. We traced individual fibres in one unit comprised of FOG fibres and a second comprised of FG fibres. Six fibres from a FOG unit (total length 15.45 mm) ranged from 10.11 to 11.82 mm in length and averaged (± s.d.) 10.74 ± 0.79 mm. All originated bluntly (en mass) from a fascicle near the proximal end of the muscle unit and all terminated intramuscularly. Five of these ended in a taper and one ended bluntly. Fibres coursed on average for 70% of the muscle unit length. Six fibres from a FG unit (total length 34.76 mm) ranged from 8.97 to 18.38 mm in length and averaged 15.32 ± 3.75 mm. All originated bluntly and terminated intramuscularly; one of these ended in a taper and five ended bluntly. Fibres coursed on average for 44% of the muscle unit length. Because fibres of individual muscle units do not extend the whole muscle unit territory, the effective cross-sectional area changes along the motor unit length. These non-uniformities in the distribution of fibres within a muscle unit emphasize that the functional interactions within and between motor units are complex.     

Histochemical localization of lactate dehydrogenase isoenzymes in human skeletal muscle fibers.

Lactate dehydrogenase (LDH) activity was histochemically localized in fibers of the vastus lateralis muscle of men and for comparative purpose in the soleus and plantaris muscleo of rats. Human muscle fibers were identified as fast twitch (FT) or slow twitch (ST) from the histochemical stain for myofibrillar adenosine triphosphatase activity. Rat skeletal muscle fibers were classified as fast-twitch-oxidative-glycolytic (FOG), fast-twitch-glycolytic (FG), or slow-twitch-oxidative (SO) on the basis of NADH-diaphorase and myofibrillar adenosine triphosphatase activities. Heart-type (H) LDH was identified by inhibition of the muscle-type (M) isozyme with 4 M urea. Total LDH as estimated histochemically was highest in the human FT and rat FG fibers. This was predominantly the M-LDH isozyme. ST fibers of human and SO fibers of rat skeletal muscle had the least total LDH but the most H-LDH activity. The FOG fibers of rat muscle contained a total LDH activity intermediate to that of the FG and SO fibers and a combination of H- and M-LDH. There were no fibers in the human muscle samples studied that had LDH activities similar to the FOG fibers of rat muscle.     

Histochemical and biochemical properties of flight muscle fibers in the little brown bat,Myotis lucifugus

Summary The purpose of this investigation was (1) to determine the fiber composition of pectoralis muscle of the little brown bat,Myotis lucifugus; (2) to compare the fiber composition of this muscle with two of the animal's accessory flight muscles; and (3) to study the effect of hibernation on pectoralis muscle fiber composition. Bat skeletal muscle fibers were also compared with those of white laboratory rats (Rattus norvegicus). Bat pectoralis muscles possessed exceptionally high oxidative capacities as indicated by their succinate dehydrogenase activities, but relatively low glycolytic potentials (phosphofructokinase activities). Muscle histochemistry demonstrated that fiber composition of bat pectorlis muscle was homogeneous; all fibers possessed high aerobic and low glycolytic potentials, and high myofibrillar ATPase activities indicating fast contractile properties. In contrast, accessory flight muscles possessed three distinguishable fiber types. During hibernation there was a significant decline in oxidative potential, no change in glycolytic potential, and no alteration in basic fiber composition of bat pectoralis muscle. The findings of this study suggest that pectoralis muscles ofM. lucifugus may approach the ultimate adaptation of a mammalian locomotory muscle for aerobic generation of muscular power.Abbreviations FG fast-twich glycolytic - FOG fast-twitch-oxydative-glycolytic - -GPDH -glycerophosphate dehydrogenase - LDH lactate dehydrogenase - NADH-D reduced nicotinamide adenine dinucleotide diaphorase - PFK phosphofructokinase - SDH succinate dehydrogenase - SO slowtwich-oxidative     

Molecular characterization of goose- and chicken-type lysozymes in emu (Dromaius novaehollandiae): evidence for extremely low lysozyme levels in emu egg white

Lysozyme (LZ), a bacteriolytic enzyme, is found in the egg white of many avian eggs and plays an important role in host defense; however, LZ activity in emu (Dromaius novaehollandiae) egg white is exceptionally undetectable. We cloned and characterized emu goose-type LZ (LZG) and chicken-type LZ (LZC) genes. RT-PCR analysis revealed very low LZG gene expression levels and absence of LZC gene expression in the emu oviduct. Sequencing of full-length LZG and LZC cDNAs indicated that their amino acid sequences show high similarities to ostrich LZG and LZC, respectively, with conserved catalytic residues for enzymatic activities. Whereas recombinant emu LZG prepared using Pichia pastoris exhibited similar enzyme activity as ostrich LZG, recombinant emu LZC exhibited significantly higher lytic activity than chicken LZC. We concluded that emus have functional genes for both LZG and LZC like many other avians, and the LZG gene is expressed in oviduct probably as in other ratite, however, its expression levels in egg white were low to be detected.     

Histochemical studies on the amphibian opercularis muscle (Amphibia)

Summary Histochemical studies of the opercularis muscle of the bullfrog (Rana catesbeiana) and the tiger salamander (Ambystoma tigrinum) provide evidence that the opercularis muscle of anurans is a specialized, tonic portion of the levator scapulae superior muscle. Staining results for myosin adenosine triphosphatase (ATPase) and succinate dehydrogenase (SDH), combined with measurements of muscle fiber diameters, demonstrate that the opercularis/levator scapulae superior muscle mass of both the tiger salamander and bullfrog consists of an anterior tonic portion, a middle fast oxidative-glycolytic (FOG) twitch portion, and a posterior fast-glycolytic (FG) twitch portion. In R. catesbeiana the tonic fibers represent 57.3% of the fiber total and (because they have relatively narrow diameters) about 29% of the cross-sectional area of the muscle mass, and form that part of the muscle (=opercularis muscle) that inserts on the operculum. In Ambystoma the tonic fibers represent only 8.8% of the fiber total and represent about 4% of the cross-sectional area. In the tiger salamander, the entire levator scapulae superior muscle inserts on the operculum and therefore represents the opercularis muscle. The bullfrog differs from the tiger salamander, therefore, in that the anterior tonic part of the opercularis/levator scapulae superior complex is greatly enlarged and the insertion on the operculum is limited to these tonic fibers. No evidence of a columellar muscle was found in R. catesbeiana. Previous reports of one in this species and in other anurans may be based on the tripartite nature of the opercularis/levator scapulae superior muscle mass. The middle FOG portion of the muscle may have been considered a muscle distinct from the anterior tonic portion (=opercularis muscle) and the posterior FG portion.     

Distribution and morphology of motoneurons innervating different muscle fiber types in an amphibian muscle complex

The distribution and morphology of motoneurons innervating specific types of muscle fibers in the levator scapulae superior (LSS) muscle complex of the bullfrog (Rana catesbeiana) and tiger salamander (Ambystoma tigrinum) were studied by retrograde labelling with cholera toxin-conjugated horseradish peroxidase (CT-HRP). The LSS muscle complex in both of these amphibians has a segregated pattern of muscle-fiber types (tonic; fast oxidative-glycolytic twitch [FOG]; fast glycolytic twitch [FG]) along an anteroposterior axis. The entire motor pool was labelled by injection of CT-HRP into the whole LSS muscle complex. The motoneurons innervating specific fiber types were labelled by injection of CT-HRP into certain muscle regions. The organization of the motoneuron pool of the LSS complex of both species was arranged in two columns—one ventrolateral and one medial. In bullfrogs, the ventrolateral column contains motoneurons innervating FG and tonic fiber types and the medial column contains motoneurons innervating FOG fiber types. In tiger salamanders, the ventrolateral column contains motoneurons innervating FG fiber types and the medial column contains motoneurons innervating FOG and tonic fiber types. The different motoneuron types also have different soma sizes and patterns of dendritic arborization. In both species, FG motoneurons are the largest, whereas FOG motoneurons are intermediate in size and tonic motoneurons are the smallest. In bullfrogs, the main dendrites of FG motoneurons extend into the dorsolateral and the ventrolateral gray matter of the spinal cord, whereas the dendrites of FOG motoneurons extend into the ventral and medial cord. In the tiger salamander, dendrites of FG motoneurons extend into the ventrolateral spinal cord and dendrites of the FOG motoneurons extend more generally into the ventral cord. Dendrites of tonic motoneurons in both amphibians were small and short, and difficult to observe. These results establish that motoneurons innervating different types of muscle fibers in the LSS muscle complex are segregated spatially and display consistent morphological differences. © 1993 Wiley-Liss, Inc.     

Comparative histochemical study of prosimian primate hindlimb muscles. I. Muscle fiber types

The profiles of fiber types in hindlimb muscles from the tree shrew (Tupaia glis), lesser bushbaby (Galago senegalensis), and the slow loris (Nycticebus coucang) were determined using histochemical techniques. Fibers were classified as fast-twitch oxidative-glycolytic (FOG), fast-twitch glycolytic (FG), slow-twitch oxidative (SO), or fast-twitch oxidative (FO), according to reactions for alkaline-stable ATPase, acid-stable ATPase, alpha-glucan phosphorylase, reduced nicotinamide adenine dinucleotide diaphorase, succinate dehydrogenase, mitochondrial alpha-glycerophosphate dehydrogenase (MaGPDH), and beta-hydroxybutyric dehydrogenase, as well as glycogen staining by the periodic acid-Schiff technique. Prolonged dissection of numerous muscles was carried out on hindlimbs submersed in cold Tyrode's solution; such treatment had no qualitative effect on enzyme staining reactions, but it is not a suitable procedure if one wishes to stain for glycogen. Fast-twitch oxidative (FO) fibers are alkaline-stable ATPase-positive and possess low MalphaGPDH enzyme activity. These fibers have not been reported previously in any hindlimb muscles. No muscles of any species studies were homogeneous with respect to fiber type. Slow loris muscles lacked FG fibers. The majority of the muscles of the slow loris contained numerous SO fibers. The relationship between enzyme activities and locomotor pattern is discussed.     

The relationship of voluntary running to fibre type composition, fibre area and capillary supply in rat soleus and plantaris muscles

Twenty 4-week-old Wistar rats exercised voluntarily in running wheels each day for 45 days. Fibre type composition, fibre cross-sectional area and the number of capillaries around a fibre of the slow-twitch soleus and fast-twitch plantaris muscles were examined and compared with animals which had no access to running wheels. The exercise group had a higher percentage of fast-twitch oxidative glycolytic (FOG) fibres and a lower percentage of fast-twitch glycolytic (FG) fibres in the deep portion of the plantaris muscle. The area of FOG fibres in the surface portion of the plantaris muscle was also greater in the exercise group. In the exercised animals, there was a positive relationship between the running distance and the area of FOG fibres in both the deep and surface portions of the plantaris muscle. In addition, the running distance correlated positively with the percentage of FOG fibres and negatively with that of FG fibres in the deep portion of the plantaris muscle. There were no relationships between the running distance and fibre type composition, or fibre area and capillary supply in the soleus muscle. These results suggested that the increase in the percentage and area of FOG fibres in the fast-twitch muscle was closely related to voluntary running.     

The relationship of pork longissimus muscle pH to mitochondrial respiratory activities,meat quality and muscle structure

The way the pH falls post-slaughter has an impact on meat quality. Pork longissimus muscles (n=48) were sorted in fast- (FG) (n=15) and normal glycolysing (NG) (n=33) muscles according to the post-slaughter pH 45 min values (FG<6.0; NG>6.0). FG muscles (5.84±0.04) compared with NG muscles (6.27±0.04) were accompanied with higher temperature, electrical conductivity, lightness and yellowness, and reduced grill loss and shear force values (P<0.05), but there were no pH-dependent changes of the drip loss and redness results. FG muscles had higher (P<0.05) percentages of fast-twitch glycolytic and lower proportions of fast-twitch oxidative and slow-twitch oxidative (P<0.05) muscle fibres. The study confirms the relationship of pH value to meat quality and muscle fibre characteristics also showing that pH values have no impact on intrinsic mitochondrial respiratory function.