Comparative histology, histochemistry and innervation of the striated muscle fibers of the peroneus longus muscle

The morphology of the peroneus longus muscle was compared in three Galliformes and five Passeriformes in relation to partial behavioral characteristics. In the quail two fibre types are found, while the muscle of the other species is composed of three fibre types. The frequencies of these fibres are different, especially between Galliformes and Passeriformes. The peroneus longus muscle in the quail is innervated only from the phasic system. The other species show phasic and tonic innervation. There is a correlation between the muscle fibre calibre and the extent of the synaptic gutter.     

Histochemistry, immunocytochemistry, and biometry of muscle fibers and their innervation of the peroneus longus muscle]

The morphology of the peroneus longus muscle of the Chinese quail was studied in relation to partial behavorial characteristics. On the basis of the actomyosin ATPase reaction after alkaline and acid preincubation, three fiber types are revealed. The indirect immunofluorescence, using specific antibodies against 'slow' myosin from the human vastus lateralis muscle, provokes a strong reaction on the small fiber type. The characteristics of the innervation revealed by the cholinesterase activity, concentrated in the synaptic gutters and the direct study of the nerve fibres, show focal, mono-axonal 'en plaques' endings, typical of the phasic motor system.     

Fusimotor innervation in the cat

The motor innervation of cat spindles was examined in hindlimb muscles using a variety of techniques employed in light and electron microscopy. Observations were made on teased, silver preparations of 267 spindles sampled from the peroneal, flexor hallucis longus, and soleus muscles, hereafter referred to as the PER/FHL/SOL series. The γ innervation. Trail endings are almost invariably present, and innervate both bag and chain muscle fibres. Trail fibres accounted for 64.6 to 74.8% of the total fusimotor supply to samples of spindle poles in the PER/FHL/SOL series, the mean number of fibres per pole varying from 2.7 to 5.0 in the different muscles, and the mean number of ramifications (areas of synaptic contact) per fibre being 3.7. By contrast, the p?innervation of a spindle pole generally consists of a single fibre supplying only one plate. In the above samples p(2) fibres accounted for 4.1 to 28.0% of the total fusimotor supply, and the mean number of fibres per pole varied from 0.3 to 1.2 in the different muscles. Ninety per cent of p(2) plates innervate bag fibres. The α innervation. The structure of p?plates as seen in both light and electron microscopy compares very closely with that of extrafusal plates. After nerve section p?plates degenerate at the same time as extrafusal plates, being the first of the three types of fusimotor ending to disappear. The frequency of the p?innervation is similar to that of the p?innervation. In the same samples of PER/FHL/SOL spindle poles as above p? fibres accounted for 6.0 to 28.8% of the total fusimotor supply, the mean number of fibres per pole varying from 0.25 to 2.1 in the different muscles. The majority of p? fibres enter a pole to terminate in one plate only. Seventy-five per cent of the plates innervate bag fibres. The three types of fusimotor ending are thus not selectively distributed to the two types of intrafusal muscle fibre. All three types of fusimotor fibre may branch within the spindle so as to innervate both bag and chain fibres. Bag fibres receive both types of plate ending as well as trail endings. Most chain fibres receive trail endings only; the rest receive either a p?or a p?plate innervation in addition, 25% of the p?and 10% of the p?innervation being distributed to chain fibres. The significance of this nonselective innervation is interpreted as indicating that the type of contraction elicited by stimulating a fusimotor fibre depends upon the type of ending initiating it rather than upon the type of muscle fibre executing it. Reasons are given for concluding that the dynamic response is controlled via the p?and p?plates, and that the static response is controlled by the trail endings. The participation of the α fibres in mammalian fusimotor innervation, previously regarded as a vestigial feature, proved to be widespread in the muscles studied and more prevalent in fast muscles (FHL, peroneus digiti quinti) than slow (soleus). A low frequency of p?innervation is offset by a high frequency of p?(as in peroneus longus), and vice versa (as in FHL). It is unlikely that collaterals from slow α fibres innervating type B muscle fibres are wholly responsible for the high frequency of the p?innervation in FHL, and it is suggested that collaterals may also be derived from fast α fibres innervating type C muscle fibres. The possibility of there being some motor fibres of α conduction velocity and with an exclusively fusimotor distribution is also taken into account.     

Histology, immunocytology, histochemistry and muscle fiber innervation of the pectoralis major and supracoracoideus muscles of Excalfactoria chinensis chinensis (L.)]

The morphology of the pectoralis major muscle and its antagonist, the supracoracoideus muscle, of the Chinese quail was studied in comparison with the Japanese quail, in relation to behavioral characteristics. The actomyosin ATPase reaction after alkaline and acid preincubation reveals two fibre types. The indirect immunofluorescence, using specific antibodies against 'slow' (twitch) myosin from the human vastus lateralis muscle, provokes a weak reaction. All fibres observed show focal, monoaxonal 'en plaques' endings, typical of the phasic motor system. For the two quail species, the muscle structure seems adequate in relation to the movement characteristics, meaning muscle activity of migratories, flying long distances.     

Quantitative investigation of the neuromuscular junction of rat skeletal muscle fibres after double innervation

Summary In normal (untreated) rats the mean length ratio of postsynaptic to presynaptic membrane was 2.7±0.8 for neuromuscular junctions of slow-twitch soleus muscle fibres and 4.2±1.0 for neuromuscular junctions of fast-twitch extensor digitorum longus muscle fibres; this difference was significant (P<0.001). After experimental double innervation by fast and slow muscle nerves for four months, the ratio was (1) 2.9±0.8 for the original slow-twitch fibre end-plate and 2.8±0.8 for the newly established one, both not significantly different from that of the normal slow-twitch fibres; and (2) 2.2±0.5 for the original fast-twitch fibre end-plate and 2.2±0.7 for the newly established one, both significantly smaller than that of the normal fast-twitch fibres (P<0.001). This means that the double innervated slow-twitch muscle fibres retained their original neuromuscular junction type, whereas the doubly-innervated fast-twitch muscle fibres underwent a dramatic transformation of their neuromuscular junction from the fast-muscle to the slow-muscle type. In both doubly innervated fibres, the ultrastructural characteristics of neuromuscular junctions, whether altered or not, were identical at both end-plate regions.     

Calcitonin gene-related peptide expression at endplates of different fibre types in muscles in rat hind limbs

Calcitonin gene-related peptide (CGRP) occurs only in some motoneurons. In this study, the presence of CGRP in motor endplates in relation to muscle fibre types was examined in slow (soleus muscle) and fast [tibialis anterior (TA) and extensor digitorum longus (EDL)] leg muscles of the rat. CGRP was detected by use of immunohistochemical methods, and staining for the mitochondrial-bound enzyme NADH-TR was used for demonstration of fibre types. The fibres showing low NADH-TR activity were interpreted as representing IIB fibres. All such fibres located in the superficial portion of TA were innervated by endplates displaying CGRP-like immunoreactivity (LI), whereas in the deep portion of TA some of these fibres lacked CGRP-LI at their endplates. Thirty per cent of the IIB fibres in EDL showed CGRP-LI at the endplates. All fibres in TA and EDL displaying high NADH-TR activity and interpreted as type-IIA fibres, lacked CGRP-LI in their motor innervation. One third of the fibres with intermediate NADH-TR activity in TA exhibited CGRP-LI at their endplates, whereas in EDL only few such fibres displayed CGRP-LI in the endplate formation. These fibres are likely to belong to type-IIX or type-I motor units. CGRP-LI was very rarely detected at the endplates in the soleus muscle. These observations show that distinct differences exist between the slow muscle, soleus, and the fast muscles, TA and EDL, but that there are also differences between the different types of fibres in TA and EDL with respect to presence of CGRP-LI at the endplates. As CGRP-LI was frequently detected at endplates of IIB fibres, it is likely that CGRP has a particular role related to the differentiation and maintenance of these fibres.     

Effects of Latrodectus spider venoms on sensory and motor nerve terminals of muscle spindles

The effects of the venoms of the spiders Latrodectus mactans tredecimguttatus (black widow) and Latrodectus mactans hasselti (red back) on sensory nerve terminals in muscle spindles were studied in the mouse. A sublethal dose of venom was injected into tibialis anterior and extensor digitorum longus muscles of one leg. After survival from 30 minutes to 6 weeks muscles were examined in serial paraffin sections impregnated with silver or by electron microscopy. Sensory endings became swollen, some within 30 minutes, while over the next few hours there was progressive degeneration of annulospiral endings. By 24 hours every spindle identified by light or electron microscopy was devoid of sensory terminals. Degenerated nerve endings were taken up into the sarcoplasm of intrafusal muscle fibres. Regeneration of sensory axons began within 24 hours, new incomplete spirals were formed by 5 days and by 1 week annulospiral endings were almost all normal in appearance. Intrafusal motor terminals underwent similar acute degenerative and regenerative changes. These experiments show that intrafusal sensory and motor terminals are equally affected by Latrodectus venoms. Sensory nerve fibres possess a capacity for regeneration equal to that of motor fibres and reinnervate intrafusal muscle fibres close to their original sites of innervation.     

Organization of skeletal muscle in the urodele Triturus cristatus: muscle fibre types and motor units

Four muscle fibre types are described in the biceps and extensor digitorum communis muscles of the newt forelimb. The histological criteria forming the basis for the distinctions include differential staining with p-phenylenediamine and succinate dehydrogenase histochemistry and electron microscopy. In addition, three distinctive motor unit types are described for the biceps muscle. These are fast units, slow units and intermediate units. The structure of muscle fibre and the physiological characteristics of muscle fibres belonging to each motor unit, have been correlated by using iontophoretic passage of Lucifer yellow into muscle fibres belonging to physiologically characterized motor units and their subsequent histological identification by the succinate dehydrogenase reaction. The three motor unit types correspond to slow muscle fibres, intermediate muscle fibres and two classes of fast muscle fibres.     

Studies on the distribution of calcitonin gene-related peptide-like and substance P-like immunoreactivities in rat hind limb muscles

Summary The tibialis anterior, extensor digitorum longus and soleus muscles in the rat were examined with respect to the presence of calcitonin gene-related peptide-like as well as substance P-like immunoreactivity. In some of the motor endplates in these muscles, identified by staining for acetylcholinesterase activity, calcitonin gene-related peptide-like immunoreactivity was detected, but in others it was not. Calcitonin gene-related peptide-like immunoreactivity was found to coexist with substance-P-like immunoreactivity in nerve fibres located outside and inside the capsule of the muscle spindles, as well as in nerve fibres located in nerve fascicles. These fibres presumably represent sensory nerve fibres. Calcitonin gene-related peptide-like immunoreactivity, but not substance P-like immunoreactivity, was also detected, in cap-like structures located on the surface of the intrafusal muscle fibres in the polar regions of the spindles, structures which are likely to correspond to motor plate endings. The observations suggest that calcitonin gene-related peptide is heterogeneously present in the endplates of rat hind limb muscles, and gives for the first time immunohistochemical evidence for the presence of calcitonin gene-related peptide and substance P in the innervation of muscle spindles.     

A study of the peripheral innervation and muscle fibre types of Ictalurus nebulosus (Lesueur) and Ictalurus punctatus (Rafinesque)

The innervation pattern and fibre types of the axial musculature of two closely related catfish species with differing lifestyles, Ictalurus nebulosus (Lesueur) and I. punctatus (Rafinesque) were investigated. Both fish displayed the multiple innervation pattern in the red muscle. However, the white muscle of I. nebulosus demonstrated terminal innervation while I. puncrurus displayed multiply innervated white muscle fibres. Fibre typing utilizing histochemical techniques for glyco-gen, lipid, succinic dehydrogenase and glucose-6-phosphate dehydrogenase revealed the typical teleostean distribution of red, intermediate and white muscle fibres in both fish. Staining was greatest in the red muscle fibres and least in the white muscle fibres. The white muscle fibres of I. punctatus stained slightly more for lipid than the white fibres of I. nebulosus which may be correlated with a greater aerobic capacity related to lifestyle and possibly innervation.     

Dual motor innervation in the axial musculature of fishes

A systematic survey of motor innervation in the myotomal muscle fibres in several groups of fishes was conducted to observe the extent of dual innervation, a phenomenon found within those myotomal muscle fibres with terminal innervation. It is concluded that the dually innervated myotomal muscle fibre is a primitive vertebrate feature. Furthermore, it is suggested that this particular form of polyneuronal innervation is retained in the course of neural evolution within the homogeneous white myotomal muscle fibre region in these fish groups in order to insure synchrony of firing during sudden, rapid locomotion. The findings are examined in light of current ideas regarding the direct adrenergic innervation in addition to cholinergic innervation of striated muscle fibres.     

The fine structure of the guinea-pig muscle spindle

Summary Nuclear bag and nuclear chain intrafusal fibres are present in guinea-pig muscle spindles. Unlike muscle spindles in other species two types of nuclear chain fibre seem to be present. The electron microscopical appearance of one type of nuclear chain fibre is similar to that of nuclear bag fibres.It is suggested that under tension the nuclei of small nuclear bag fibres become sufficiently displaced to form nuclear chain-like fibres. The frequent occurrence of fibres which combine some of the properties of both nuclear bag and nuclear chain fibres indicates the possible occurrence of a third type of intrafusal fibre.The sensory innervation of guinea-pig muscle spindles is similar to that of the cat and the rat. Three types of motor nerve ending which could be classified according to the complexity of their subneural apparatus were seen.     

Myosin heavy chain isoform composition in striated muscle after denervation and self-reinnervation

The total content of myosin heavy chains (MHC) and their isoform pattern were studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (extensor digitorum longus) muscles of adult rat during atrophy after denervation and recovery after self-reinnervation. The pattern of fibre types, in terms of ultrastructure, was studied in parallel. After denervation, total MHC content decreased sooner in the slow-twitch muscle than in the fast-twitch. The ratio of MHC-1 and the MHC-2B isoforms to the MHC-2A isoform decreased in the slow and the fast denervated muscles, respectively. After reinnervation of the slow muscle, the normal pattern of MHC recovered within 10 days and the type 1 isoform increased above the normal. In the reinnervated fast muscle, the 2B/2A isoform ratio continued to decrease. Traces of the embryonic MHC isoform, identified by immunochemistry, were found in both denervated and reinnervated slow and fast muscles. A shift in fibre types was similar to that found in the MHC isoforms. Within 2 months of recovery a tendency to normalization was observed. The results show that (a) MHC-2B isoform and the morphological characteristics of the 2B-type muscle fibres are susceptible to lack of innervation, similar to those of type 1, (b) during muscle recovery induced by reinnervation the MHC isoforms and muscle fibres shift transiently to type 1 in the soleus and to type 2A in the extensor digitorum longus muscles, and (c) the embryonic isoform of MHC may appear in the adult skeletal muscles if innervation is disturbed.     

Immunohistochemical differences in myosin composition among intrafusal muscle fibres

Summary Mammalian intrafusal fibre types (nuclear chain, nuclear bag₁ and nuclear bag₂ fibres) are known to differ in their ultrastructure, intensity of the myofibrillar histochemical ATP-ase reaction, type of innervation and time course of contraction. The present study concerns the myosin composition of these intrafusal fibre types in the soleus muscle (mouse) and the extensor digitorum longus muscle (rat). We used an immunohistochemical method with three myosin antisera raised in rabbits: anti chicken pectoral myosin, anti chicken heart myosin (1) and anti chicken heart myosin (2) (=anti chicken heart myosin (1) adsorbed with muscle powder from soleus muscle of guinea pig). The results showed that three intrafusal fibre types differed in their myosin composition. A comparison of intrafusal fibre types with extrafusal fibre types for the histochemical myofibrillar ATP-ase reactivity and the reactivity with myosin antisera showed a resemblance of nuclear chain fibres with extrafusal type II fibres and a difference between nuclear bag₁ and nuclear bag₂ fibres and all other fibre types.     

Form and classification of motor endings in mammalian muscle spindles

The presynaptic features of 234 motor endings supplied to cat hindlimb muscle spindles have been studied in teased, silver preparations, and the postsynaptic features of a further 27 endings have been studied in serial, 1 micron thick, transverse sections. In the presynaptic study motor endings received by the three types of intrafusal muscle fibre were compared with the endings supplied to spindles by the various functional categories of motor axon. Three forms of motor ending were found that had significantly different presynaptic features. These forms correspond closely to those previously identified in the literature as p1 (beta), p2 (dynamic gamma) and trail (static gamma). The results of the postsynaptic study showed that the degree of indentation of the intrafusal muscle fibres by motor axon terminals increases with greater distance from the primary ending, irrespective of muscle-fibre type. We conclude that the postsynaptic form of intrafusal motor endings is determined by distance from primary ending and muscle-fibre type. It is not determined by type of motor axon, and cannot be correlated with presynaptic form so as to produce a unified classification of intrafusal motor endings.     

Dynamic mechanism of visual accommodation in teleosts: structure of the lens muscle and its nerve control

The accommodatory system was examined in two teleosts (mackerel and bass). The fine structure and innervation of the lens muscle is presented to characterize the muscle organization. The neural pathway involved in the dynamic accommodation was examined by analysing the fibre spectrum of the ciliary nerve, and the nerve that controls the lens-muscle activity was studied by means of electrical stimulation. The lens muscle is composed of smooth-muscle cells, which contain numerous mitochondria. Many synaptic endings are also found on the muscle cells; these synaptic endings contain many agranular vesicles. From the results of the fibre analysis, it was found that the nerve that controls the lens muscle contains less than 100 myelinated nerve fibres in both fish: the electrical stimulation experiments demonstrate that the muscle is controlled by oculomotor (parasympathetic) nerve fibres. Ultrastructural features of the lens muscle and its nerve control resemble those of the mammalian ciliary muscle. The teleostean lens muscle is classified as a multi-unit smooth muscle.     

Intrafusal fibre types in rat limb muscle spindles: morphological and histochemical characteristics.

Morphological, histochemical and ultrastructural characteristics of intrafusal fibre types were studied in rat muscle spindles. The existence of three intrafusal fibre types, namely the typical bag, the intermediate bag and the chain fibres was confirmed. Intrafusal fibres differ in diameter, length and number of nuclei in the equatorial zone. Histochemically, typical bag fibres exhibit both alkali- and acid-stable ATPase activity and low SDH activity. Intermediate bag fibres possess low alkali-stable ATPase activity; after acid-preincubation, however, they have low activity only in the juxtaequatorial region, whereas in the polar zones they exhibit high acid-stable ATPase activity. The SDH activity varies from moderate to high. The chain fibres exhibit high alkali-stable and low acid-stable ATPase and high SDH activity in the extensor digitorum longus muscle, whereas in the soleus muscle the acid-stable ATPase activity varies from a low one to a high one, either among individual chain fibres in one spindle, and/or repeatedly along the fibre length. Since there are regional differences in morphological characteristics and in staining properties of intrafusal fibres, a reliable identification of intrafusal fibre types can only be achieved by an analysis of serial sections.     

Afferent proprioreceptive fibers in the rat and their distribution in the dorsal roots

The distribution in the dorsal roots of proprioceptive afferent fibres from tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of the rat and the physiological characteristics of the related nervous endings have been investigated. Axons of proprioceptive endings from TA and EDL were found mainly in L4, only a few in L5. Afferent proprioceptive fibres from posterior superficial crural muscles (gastrocnemius, soleus, plantaris) pass mainly through root L5; axons of extrafusal motor units are distributed in a similar way. Sensory endings in TA and EDL were examined, after identification, by means of their static threshold to passive stretch. Almost all steady-state responses to passive stretch, within the physiological extension range, came from muscle spindles. 1-2 to 20 g loads were necessary to obtain steady-state discharges from these receptors. Spindle endings were classified as primary or secondary by measuring the conduction velocity of the afferent fibres, and according to the features of their passive behaviour. Threshold difference cannot be regarded as a fundamental characteristic, because of the considerable overlapping of the values obtained from the two types of endings. Conduction velocities of 50 to 80 m/sec for primary and of 20 to 40 m/sec for secondary afferent fibres were observed. Afferent fibres conducting at intermediate velocity often behave like primary ones. As a rule, tendon organs showed a higher static threshold to passive stretch; the loads employed only rarely elicited a steady-state response. As for these receptors, which usually showed marked adaptation characteristics, passive force is a less effective stimulus than active contraction. The conduction velocity range of afferent fibres from tendon organs is the same as that of primary afferents. The results are discussed.     

Myosin-ATPase fibre typing of chemically skinned muscle fibres

Summary The efficacy of myosin (M)-ATPase fibre typing to differentiate fibre types in chemically (EGTA) skinned muscle fibres was investigated. Cryosections or single fibres from isolated bundles of chemically skinned rat extensor digitorum longus (EDL) and soleus (SOL) muscles were stained for M-ATPase activity. The results indicate that two major fibre types (type I and II, Brooke & Kaiser, 1970) can be indentified, as well as subgrouping of the type II fibres into types IIa and IIb. Thus, chemically skinning muscle fibres appears to have no detrimental effects on subsequent M-ATPase fibre typing.     

Structure and distribution of fibre types in the external eye muscles of the rat

Rat extraocular muscles are composed of two layers differing in muscle fibre diameter. In both layers multiply innervated fibres are found besides focally innervated ones. Significant differences in internal structure thus demand further subtyping. The global layer (predominantly larger fibres) contains 10" 'clear' fibres (multiple innervation, medium size) and a spectrum of focally innervated fibres, from small 'dark' fibres (30%, abundant mitochondria) over 'intermediate' fibres (30%) to large 'pale' fibres (30 %, few mitochondria). The orbital layer (exclusively small fibres) contains 80% focally innervated 'dark' fibres and 20% extremely small 'clear' fibres with multiple innervation. An ultrastructural characterization of the fibre types is given and possible functional implications are discussed.