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A Rowlerson

Publications and source records attributed to A Rowlerson.

At least 19 recordsLinked to original sources
PubMed2006

Long-term culture of muscle explants from Sparus aurata.

Although there are mammalian myoblast cell lines, no fish myoblast cell line has been developed so far. The aim of this study was to develop a culture system of muscle explants for fish, as explants provide an approximation of the in vivo conditions for cell proliferation and differentiation, and enable a close comparison with events in muscle regenerating in vivo. Here we describe the main features of a long-term in vitro culture system for muscle explants from Sparus aurata fry. At the time of sampling, the original fibres were damaged and subsequently degenerated as shown by the loss of parvalbumin (PV) and presence of apoptotic nuclei. This mechanical damage provoked a myogenic response by activation of myogenic precursor cells. After a few days, new mononucleate cells aligned with the original fibres were seen in the explants, some with proliferating cell nuclear antigen (PCNA-) and Myf-5-positive nuclei, indicating proliferation and their myogenic fate. By 1 week, multinucleate cells with desmin immunoreactivity but PCNA- and Myf5-negative nuclei were present, equivalent to differentiated, postmitotic myotubes. Some of these myotubes were also immunoreactive for PV and insulin-like growth factors (IGFs). By 11 days, many of the myotubes were also immunoreactive for myostatin (MSTN). By 23 days, many of the myotubes had increased in diameter, were packed with myofibrils, and were strongly PV-positive and immunoreactive for MSTN, IGF-I and IGF-I receptor. This study shows that a proliferative process occurs in the explants despite the death of the original muscle fibres, and new muscle fibres expressing growth regulators are formed by regeneration from myogenic precursors present in the explants at the time of sampling.

Animals↗
PubMed1998

Skeletal fiber types and spindle distribution in limb and jaw muscles of the adult and neonatal opossum, Monodelphis domestica.

The South American opossum, Monodelphis domestica, is very immature at birth, and we wished to assess its potential for studies of jaw muscle development. Given the lack of prior information about any Monodelphis fiber types or spindles, our study aimed to identify for the first time fiber types in both adult and neonatal muscles and the location of spindles in the jaw muscles. Fiber types were identified in frozen sections of adult and 6-day-old jaw and limb muscles by using myosin ATPase and metabolic enzyme histochemistry and by immunostaining for myosin isoforms. The distribution of fiber types and muscle spindles throughout the jaw-closer muscles was identified by immunostaining of sections of methacarnoy-fixed, wax-embedded heads. Most muscles contained one slow (type I) and two fast fiber types (equivalent to types IIA and IIX), which were similar to those in eutherian muscle, and an additional (non-IIB) fast type. In jaw-closer muscles, the main extrafusal fiber type was IIM (characteristic of these muscles in some eutherians), and almost all spindles were concentrated in four restricted areas: one in masseter and three in temporalis. Six-day neonatal muscles were very immature, but future spindle-rich areas were revealed by immunostaining and corresponded in position to the adult areas. Extrafusal and spindle fiber types in Monodelphis share many similarities with eutherian mammalian muscle. This finding, along with the immaturity of myosin isoform expression observed 6 days postnatally, indicates that Monodelphis could provide a valuable model for studying early developmental events in the jaw-closer muscles and their spindles.

Animals↗
PubMed1997

Regeneration of skeletal muscle in two teleost fish: Sparus aurata and Brachydanio rerio.

Regeneration of skeletal muscle was studied in the sea bream Sparus aurata, in which extensive post-larval muscle hyperplasia contributes to its large adult size, and in the zebrafish Brachydanio rerio, which shows little post-larval hyperplasia and reaches only a small adult size. Small mechanical lesions of body wall muscle were made under general anaesthesia, and the progress of subsequent regeneration was assessed at various intervals by histology and electron microscopy (for general morphology), by immunostaining for desmin and myosin isoforms (to identify the phenotype of new fibres), and by 5'-bromo-2'-deoxyuridine (BrdU) incorporation (to identify proliferating cells). Despite the difference in normal growth-related hyperplasia in these fish, a vigorous regeneration occurred in both species, giving rise to new fibres with an initial myosin composition that differed from that in mature fast-white fibres. However, species differences in myosin expression in these fibres suggest that they may have derived from different myoblast populations. In sea bream, myosin expression in regenerating fibres resembled that seen in new fibres produced in post-larval white muscle, whereas in the zebrafish it resembled that of the primitive monolayer fibres formed during embryonic development. Subsequently, most regenerating fibres gradually transformed into the mature fast-white phenotype in both species.

Animals↗
PubMed1996

Motor units of juvenile rat lumbrical muscles and fibre type compositions of the glycogen-depleted component.

1. Fourth deep lumbrical muscles were dissected out, with their nerve supply, from juvenile rats aged 8-15 days (a period corresponding to maximal rate of decline of polyneuronal innervation), and aged 28, 29 and 30 days (when developmental synapse elimination is complete). Preparations were superfused with rat Ringer solution at 25 degrees C. 2. Isometric twitches and tetani were recorded from the whole muscles and from a single motor unit in the muscle. Unit isolation was by partial section of the sural or lateral plantar nerves. The axon of a single unit occurred naturally in the sural nerve in some cases. 3. Fibres in single units were depleted of glycogen by repetitive stimulation, and studied histologically in frozen midbelly sections of the muscle, stained for glycogen with periodic acid-Schiff's reagent (PAS). Most fibre counts were based on transmittance measurements made with an image analysis system. Contralateral muscles were unstimulated and acted as controls. 4. Motor unit sizes were estimated from tetanic tensions and from muscle fibre cross-sectional area measurements. Comparison of the two methods indicated that in most units glycogen depletion was not complete. This effect was maximal at 8 and 10 days postnatally. It is suggested that this is due to weak neuromuscular transmission at synapses in the process of natural elimination during development. 5. Other sections (serial and semi-serial) were immunostained with a polyclonal antibody raised against slow myosin. Fibres staining for the antibody (slow; S-fibres) contribute about 12-9% of muscle fibres depending on age. In some muscles, fibre types were determined by myosin ATPase staining following alkali pre-incubation. Fast fibres (F-fibres) contained no slow myosin. 6. Some units had no S-fibres (i.e. they were homogeneous), and many units had a small proportion of S-fibres, though less than in the whole muscle (i.e. they were heterogeneous but composition was biased in favour of F-fibres). 7. One unit from a 10-day-old rat contained more S- than F-fibres. Many of the F-fibres were small. It is proposed that this was a developing IIC/IIA unit, a type known to occur in adults. 8. It is concluded that mismatched connections in developing motor units possibly become weak early (by 8 days postnatally) in the process of synapse elimination (which is complete by 20 days postnatally), but that the time course of actual withdrawal cannot be followed by the technique of glycogen depletion.

Animals↗
PubMed1996

Muscle spindles in the jaw-closer muscles of the domestic cat.

The objectives of this study were to identify the exact location of spindles in jaw-closer muscles of the cat, to count the total number of spindles and to compare their distribution with the distribution of slow extrafusal fibres. The jaw-closer muscle group with all the skeletal attachments intact was fixed in a modified Carnoy solution, decalcified and processed through to wax. Complete series of sections were cut transverse, sagittal and perpendicular to the anterior temporalis muscle. At regular intervals, serial sections were stained by the Weigert-van Gieson method or immunostained for myosin isoforms. Spindle counts were made only from muscle areas where fibres were cut in transverse section, and the spindles were followed individually. The extrafusal fibres were identified by indirect immunoperoxidase staining with antibodies specific for the slow (type I) and fast (type IIM) isoforms of myosin found in jaw-closer muscles. The mean numbers and locations of spindles found were 13 in medial pterygoid (close to inferior border), 123 (one count only) in the deep anterior portion of the temporalis muscle (between the coronoid process of the mandible and the cranium), 50.5 in a small deep zone of superficial masseter anterior to the temporomandibular joint, and 50 in zygomaticomandibularis (the deepest portion of masseter). Most of the spindles were simple spindles. Spindle complexes (4 or more spindle units fused in parallel) were rare and were found only in zygomaticomandibularis and in masseter. Most parts of the jaw-closer muscles had no spindles and contained only fast fibres. Cosegregation of muscle spindles with slow fibres was found in most parts of this muscle group, but the distribution of spindles was more restricted than that of slow fibres.

Animals↗
PubMed1995

Differentiation and growth of muscle in the fish Sparus aurata (L): I. Myosin expression and organization of fibre types in lateral muscle from hatching to adult.

Post-hatching development of lateral muscle in a teleost fish, Sparus aurata (L) was examined. At hatching only two fibre types were present, several layers of mitochondria-poor, myofibril-rich deep muscle fibres surrounded the notochord and were covered by a superficial monolayer of mitochondria-rich, myofibril-poor A third ultrastructurally distinct fibre type first appeared as one or two fibres located just under the lateral line at 6 days post-hatching. This type, which gradually increased in number during larval life, contained a slow isoform of myosin, identified by mATPase staining and immunostaining with myosin isoform-specific antibodies. Deep muscle fibres--the presumptive fast-white type--contained a fast myosin, and superficial monolayer fibres an isoform similar but not identical to that in adult pink muscle fibres. The only fibres present during larval life which showed a clear change in myosin expression were the superficial monolayer fibres, which gradually transformed into the slow type post-larvally. Pink muscle fibres first appeared near the end of larval life. Both slow and pink muscle fibres remained concentrated around the horizontal septum under the lateral line during larval life, expanding outwards towards the apices of the myotomes only after metamorphosis. Between 60 and 90 days very small diameter fibres with a distinct mATPase profile appeared scattered throughout the deep, fast-white muscle layer, giving it a 'mosaic' appearance, which persisted into adult life. A marked expansion in the slow muscle layer began at the same time, partly by transformation of superficial monolayer fibres, but mainly by addition of new fibres both on the deep surface of the superficial monolayer and close to the lateral line. The order of appearance of these fibre types, their myosin composition, and the significance of the superficial monolayer layer are discussed and compared to muscle fibre type development in higher vertebrates.

Aging↗
PubMed1995

Differentiation and growth of muscle in the fish Sparus aurata (L): II. Hyperplastic and hypertrophic growth of lateral muscle from hatching to adult.

Post-hatching growth of lateral muscle in a teleost fish, Sparus aurata (L) was studied morphometrically to identify and quantify muscle fibre hyperplasia and hypertrophy, and by in vivo nuclear labelling with 5-bromo-deoxyuridine to identify areas of myoblast proliferation. Muscle fibre types were identified principally by myosin ATPase histochemistry and immunostaining, and labelled nuclei were identified at light and electronmicroscope level by immunostaining with a specific monoclonal antibody. Hyperplastic growth was slow at hatching, but then increased to a maximum at the mid-point of larval life. Larval hyperplastic growth occurred by apposition of new fibres along proliferation zones, principally just under the lateral line and in the apical regions of the myotome, but also just under the superficial monolayer at intermediate positions. The first of these zones gave rise to slow and pink muscle fibres, in a process which continued through into postlarval life. The other zones added new fibres to the fast-white muscle layer in a process which was exhausted by the end of larval life. Post-larvally, between 60 and 90 days posthatching, a new hyperplastic process started in the fast-white muscle as nuclei proliferated and new muscle fibres were formed throughout the whole layer. This process resulted in a several-fold increase in the number of fast-white fibres over a few weeks, and then waned to very low levels in juveniles. Hyperplasia by apposition continued for some time postlarvally on the deep surface of the superficial monolayer, but at this stage gave rise to slow fibres only. Hypertrophic growth occurred at all ages, but was the dominant mechanism of muscle growth only in the juvenile and adult stages. Mechanisms giving rise to these different growth processes in fish muscle are discussed, and compared with muscle development in higher vertebrates.

Aging↗
PubMed1995

Natural involution of muscle in the proximal sesamoidean ligament in sheep.

In sheep, the muscle component of the proximal sesamoidean ligament, which is well developed at birth, undergoes a progressive involution postnatally. The development of muscle fibres in the proximal sesamoidean ligament was compared with masseter and semimembranosus muscles from before birth into adult life, using histochemical, immunohistochemical and biochemical methods. Neonatal myosin (a marker for developmental immaturity) disappeared earlier, and the adult pattern of myosin expression and fibre type composition was reached earlier in the proximal sesamoid ligament than masseter and semimembranosus. Proximal sesamoid ligament muscle fibres therefore complete normal development, but with a faster time course than the other muscles. Invasion of fibrous connective tissue between muscle fibres of the proximal sesamoidean ligament adjoining the tendinous component (one feature of the involution) was found to begin perinatally, eventually resulting in a marked fibrosis and atrophy of peripheral fibres. Regeneration of muscle fibres was absent or abortive, even near areas of fibre necrosis.

Animals↗
PubMed1993

Muscle growth and myosin isoform transitions during development of a small teleost fish, Poecilia reticulata (Peters) (Atheriniformes, Poeciliidae): a histochemical, immunohistochemical, ultrastructural and morphometric study.

The myosin composition of lateral muscle in Poecilia reticulata from birth to adult was studied by ATPase histochemistry and immunostaining with myosin isoform-specific antibodies. At birth the muscle consists of two layers containing developmental isoforms of myosin. In deep layer fibres the developmental myosin is replaced by the adult fast-white isoform soon after birth. In the epaxial and hypaxial monolayer fibres the myosin composition present at birth (J1) is replaced within 3 days by another (J2). In some fibres, this J2 composition is retained in the adult, but in others it is slowly replaced by the adult slow-red muscle isoform. Close to the lateral line, all monolayer fibres are already in transition between the J2 myosin and the adult slow-red form at birth, and rapidly complete the transition to slow-red form. These fibres, together with others generated de novo in an underlying hyperplastic zone, form the red muscle layer of the adult. The pink muscle develops during the first month after birth, and by 31 days it consists of an outer, middle and inner layer. A few middle layer fibres are already present at birth, while the outer layer fibres first appear 3 days after birth. The thin inner layer is probably a transitional form between the middle pink and adult white types, and appears at about 31 days. A morphometric analysis showed that growth of the white muscle occurs principally by hypertrophy. Even at the magnification level of the electron microscope, no satellite cells or myoblasts which could give rise to new fibres were found in the white muscle, except in the far epaxial and hypaxial regions and only in the first 10 days. A zone of hyperplastic growth was also found lying just under the superficial monolayer close to the lateral line, and this presumably contributes fibres to the red and pink muscle layers.

Animals↗
PubMed1992

Tertiary myotubes in postnatal growing pig muscle detected by their myosin isoform composition.

The postnatal development of skeletal muscles was studied in growing pigs from 8 to 210 d of age. Indirect immunoperoxidase staining of frozen sections of porcine semimembranosus muscle and longissimus muscle revealed a distinct population of small fibers (tertiary myotubes) that were stained specifically by an antibody (anti-NE) selective for the developmental (embryonic and neonatal) isoforms of muscle myosin. At 8 d of age the other larger fibers were already anti-NE negative and differentiated into Types I and II. A gradual decrease in the number of anti-NE positive fibers together with a gradual increase in area of the remaining positive fibers was observed throughout the pigs' growth. These results may indicate that hyperplastic growth does not cease at birth. Possible mechanisms to explain the origin of these tertiary myotubes containing developmental isoforms of myosin are suggested.

Adenosine Triphosphatases↗
PubMed1991

Organization of motor units in the axolotl: a continuously growing animal.

The characteristics of motor units in the iliotibialis posterior muscle of the axolotl hindlimb are described. Tension recording and intracellular electrophysiological methods demonstrate that the physiological properties of the population of motor units are continuously distributed rather than grouped into a series of discrete types. Overlap between motor units occurs and this is positively correlated with motor unit size but negatively correlated with differences in time to peak tension. Immunocytochemical staining with antimyosin antibodies combined with histochemical demonstration of actomyosin ATPase activity revealed at least four types of muscle fibre which were distributed asymmetrically within iliotibialis posterior. The results are discussed in terms of the continuous growth of the muscle and the interactions between muscle and nerve in the formation of the axolotl motor system.

Ambystoma↗
PubMed1991

Motor units of the fourth deep lumbrical muscle of the adult rat: isometric contractions and fibre type compositions.

1. Isometric twitch and tetanic tensions were recorded from whole muscles and single motor units in fourth deep lumbrical muscles isolated from young adult (60 days) rats. Muscles were superfused with oxygenated Ringer solution at 25 degrees C except where stated otherwise. 2. It was confirmed that the muscle is supplied most commonly by eleven motor axons, nine via the lateral plantar nerve (LPN), and two via the sural nerve (SN). Motor units whose axons were isolated from either LPN or SN were studied. There was no difference in mean motor unit size. 3. In their unfused tetani most units showed 'sag' and some 'no sag', with no segregation between LPN and SN. 'No sag' units were always small (unit tetanic tension less than 8% whole-muscle tetanic tension), tended to be relatively slowly contracting and relaxing during an isometric twitch, and tended to have relatively low twitch:tetanus ratios. Units showing sag ranged from large to small. 4. In some motor units muscle fibres were depleted of their glycogen by repetitive stimulation at 30 degrees C in glucose-free Ringer solution, and the muscle and its unstimulated control frozen and sectioned. Neighbouring sections were stained for glycogen and for binding of two myosin-specific antibodies, one specific for slow myosin and the other for type IIA myosin. Myosin ATPase and succinic dehydrogenase histochemistry were also carried out in some muscles. 5. Serial reconstructions showed that all or virtually all extrafusal fibres in the muscle were present in a midbelly section, and that the myosin type of individual fibres did not change significantly along their length. Spindle profiles were seen frequently and in two muscles eight and twelve spindles were identified. 6. Of twenty-six motor units examined twenty contained almost exclusively muscle fibres of the recently described type IIX. All these units showed sag in their isometric tetani. 7. Six units each contained 50% or more of slow myosin-containing fibres (IIC and a few type I). The remaining fibres in these units were IIA. All these units were therefore of mixed fibre composition, and are discussed as IIC/IIA units. In whole muscles slow-myosin-containing fibres were generally distributed evenly (non-randomly) throughout the muscle cross-section. 8. Whole muscles contained on average 970 fibres (S.D. +/- 70) of which 82 (+/- 9) were slow-myosin-containing. A few muscles from older rats (3-24 months) contained very few such fibres.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Neonatal myosin in bovine and pig tensor tympani muscle fibres.

In previous studies of middle ear muscles, the classification of fibre types by histochemical methods was particularly difficult in the bovine and porcine tensor tympani muscle, suggesting the presence of immature fibres. We therefore reexamined the tensor tympani from pigs and cattle of various ages immunohistochemically, using a panel of antimyosin antibodies, including one (anti-NE) specific for neonatal and embryonic myosins. Fibres positive to anti-NE were found in tensor tympani in both species in all ages examined; only a few of these fibres reacted exclusively with this antibody; some also contained slow myosin and the majority also contained adult fast (type IIA) myosin. Furthermore, although the remaining fibres included some of the classical types I and IIA, the majority of them showed a mismatch between their histochemical and immunohistochemical profiles. The morphological appearance of the muscle, the widespread presence of neonatal myosin (often together with another myosin in the same fibre) and the persistence of this composition from birth to adulthood, could be explained by an incomplete development of the muscle fibres, resulting in a 'muscle' much better suited to the role of a ligament.

Aging↗
PubMed1990

Hyperplastic and hypertrophic growth of lateral muscle in Dicentrarchus labrax (L.). An ultrastructural and morphometric study.

In this EM study of lateral muscle in Dicentrarchus labrax, we observed that during the larval period, growth of the presumptive red and white muscle layers occurs both by hypertrophy (as fibres already present at hatching complete their maturation) and by production of new fibres in germinal zones specific to the two muscle layers. In the first half of larval life the presumptive white muscle increases in thickness by the addition, superficially, of new fibres derived from a germinal zone of presumptive myoblasts lying beneath the red muscle layer. In the second half of larval life new fibres produced in this same zone form the intermediate (or pink) muscle layer. Dorsoventrally the myotome grows throughout larval life, largely by addition of new fibres from germinal zones at the hypo- and epi-axial extremities. Towards the end of larval life all these germinal zones are becoming exhausted, but another source of fibres arises as satellite cells, associated with large-diameter presumptive white muscle fibres, are activated to produce new fibres. The addition of small, new fibres gives the white muscle its mosaic appearance. Morphometric analysis of fibre diameters in the white muscle confirms that whereas these hyperplastic processes are important during the larval and juvenile periods, when growth is very rapid, they have ceased by the time the adult stage is attained. By contrast, fibre hypertrophy continues through into adult life. The presumptive red muscle consists initially of a monolayer of fibres present only near the lateral line, and during larval life it grows hypo- and epi-axially by addition of fibres derived from myoblasts already present in these areas at hatching. Lying superficially to the presumptive red muscle monolayer there is a near-continuous layer of external cells with a "flattened" profile. During the second half of larval life, differentiation of these external cells into myoblasts provides the source of new fibres which are added to the red muscle layer. This process, which occurs initially in the region around the lateral line and later spreads outwards, is responsible for the increase in thickness of the red muscle.

Animals↗
PubMed1988

Muscle-spindle distribution in relation to the fibre-type composition of masseter in mammals.

The various parts of the masseter muscle complex (pars superficialis, pars profunda, zygomaticomandibularis, maxillomandibularis) in the rat, guinea-pig, rabbit, cat and macaque monkey were examined to discover whether they showed any relationship between the distribution of muscle spindles and extrafusal fibre types. Intrafusal (spindle) and extrafusal fibre types in masseter were compared with those in limb muscles and were identified by a combination of standard histochemical methods and indirect immunoperoxidase staining with antibodies specific for the various isoforms of myosin characteristic of fibre types in mammalian muscle. In general, the fibre-type properties of intrafusal fibres in masseter resembled those in limb muscle spindles, but the extrafusal fibre-type composition was unlike that in most limb muscles. In the rat masseter, most of the spindles were clustered together in a few very restricted areas. Extensive fusion of the external capsules of adjacent spindles, resulting in the formation of giant spindles, was seen in the cat and monkey masseter; this was sometimes accompanied by the enclosure of extrafusal fibres within the fused spindles. Common to all species, but strongest of all in the rat, was a close association between the distributions of muscle spindles and extrafusal Type I (slow twitch) fibres within the masseter complex. Muscle spindles and Type I fibres were either absent or rarest in the superficial part of masseter, but were most common in the deep layer (pars profunda) or zygomaticomandibularis. The functional significance of these observations is discussed.

Animals↗
PubMed1987

Fibre types in extraocular muscles: a new myosin isoform in the fast fibres.

We report on the existence of a myosin heavy chain (MHC) isoform with unique structural properties in extraocular (EO) muscles. Differences in MHC composition are apparent using a polyclonal antibody prepared against myosin isolated from bovine EO muscle myosin. In enzyme immunoassays and western blotting experiments, this anti-EO myosin antibody reacted specifically with the heavy chains of EO muscle myosin and not with the heavy chains of other myosins. The distribution of this new MHC isoform in the globe rotating muscles from different mammalian species was analysed using a panel of specific anti-myosin antibodies and comparing the histochemical myosin ATPase profile of muscle fibres with their isomyosin content. Most fibres which display a type 2 ATPase reaction pattern were selectively labelled by anti-EO antibodies. A few type 2 fibres were found to react with both anti-EO and anti-2A myosin antibodies and others, located almost exclusively in the orbital layers, reacted with anti-foetals as well as anti-EO antibodies. The presence of a distinct form of myosin in EO muscle fibres is probably related to the particular functional characteristics of these muscles, which are known to be exceptionally fast-contracting but display a very low tension output.

Animals↗
PubMed1987

The non-selective innervation of muscle fibres and mixed composition of motor units in a muscle of neonatal rat.

1. Motor-unit size was measured by tension recording in neonatal (3-5 day) rat skeletal muscle (fourth deep lumbrical muscle). Each unit was then depleted of glycogen and its fibres studied in mid-belly frozen sections, by staining for glycogen (periodic acid-Schiff reagent and antibody labelling for slow myosin. The contralateral muscle acted as control, and further controls for the method are described. 2. All the motor units contained both slow-myosin-containing (S; antibody-positive) and slow-myosin-free (F; antibody-negative) fibres. 3. The proportion of each unit that was made up of S fibres was compared with the whole muscle. Of the twelve units studied seven were not selectively innervated, four may have been selectively innervated in favour of F fibres, and one was selectively innervated in favour of S fibres. The last unit was much smaller than the others. 4. Fibre cross-sectional areas were measured in units and in the whole muscles. Mean cross-sectional areas for individual F fibres in all the motor units were smaller than in the corresponding whole muscles (ratio 0.71), implying that small fibres have higher levels of polyneuronal innervation than larger ones (each small fibre occurring in more overlapping units than each larger fibre). There was no such difference in S fibres (ratio 0.96). 5. Motor-unit sizes (as a percentage of whole muscle) were smaller when obtained from summed fibre cross-sectional areas than from fibre counts (this follows from 4, above). Comparisons with unit sizes from tension recording are discussed. 6. Controls show that there is little, if any, non-specific fatigue of muscle fibres that are not part of the unit subjected to glycogen depletion. 7. Evidence is given that muscle fibre conduction block occurs during the depletion regime, leading to less glycogen depletion towards the ends of the muscle fibres than in the end-plate zone.

Animals↗