Non-motile sensory cilia and neuromuscular junctions in a ctenophore independent effector organ

1965 ◽  
Vol 162 (988) ◽  
pp. 333-350 ◽  
Keyword(s):  
Neuromuscular Junctions ◽  
Ciliated Cell ◽  
Sensory Nerve ◽  
Spatial Summation ◽  
Muscle Cells ◽  
Sensory Cells ◽  
Muscle Fibres ◽  
Water Displacement ◽  
Single Finger ◽  
Effector Organ

Non-motile cilia of the (9 + 2) pattern, having a specialized onion-like root structure, act as sensitive receptors of water displacement and thereby detect vibrations of small objects in the water nearby. These receptors are situated on sensory nerve cells on finger-like processes up to 1 cm long, on the surface of the ctenophore Leucothea ( = Eucharis) multicornis . In response to vibration a single finger can shoot outwards as an independent effector by an extension of its mesogloeal hydrostatic skeleton, acted on by circular and transverse muscle fibres which run mainly through the mesogloea. A copepod which may be hit is immobilized, presumably by a poisonous secretion. Retraction is brought about by longitudinal ectodermal fibres. The neuromuscular junctions have presynaptic vesicles of 30 to 50 nm diameter, a cleft of 15 to 20 nm wide, and occur at discrete points far from each other on the muscle cells, suggesting that excitation is propagated along the muscle fibres. No direct connexion has been traced between a sensory ciliated cell and a muscle fibre, but sensory cells connect with nerve net neurons and these form synapses with each other and with muscle cells. There are numerous nerve fibres in the epithelium and synapses with vesicles on one side of a cleft 12 to 15 nm wide occur between them sufficiently closely for spatial summation to be possible. The separate co-ordination of movements of extension, retraction and bending requires that certain types of sensory cells be connected specifically, if in directly, with muscle fibres of a particular directionality. This provides a primitive example of specificity of connexions which must imply two overlapping nerve nets.

The innervation of the ampulla of the tube foot in the starfish Astropecten irregularis

1967 ◽  
Vol 168 (1010) ◽  
pp. 91-99 ◽  
Keyword(s):  
Methylene Blue ◽  
Electron Microscope ◽  
Neuromuscular Junctions ◽  
Muscle Cells ◽  
Central Core ◽  
Muscle Fibres ◽  
Nerve Fibres ◽  
Clear Cytoplasm ◽  
Tube Feet

In the ampullae of the starfish Astropecten irregularis extensions stretch from the main soma of the muscle cells down the seams of the ampullae into bulbs of tissue in the tube feet. Their terminations range from 0.2 to 4.0 μm in diameter. Here axons in tracts from the radial cord form synapses upon the extensions of the muscle cells. In sections examined with the electron microscope the extensions are distinguished from nerves by their central core of myofilaments, surrounded by clear cytoplasm. The junctions between the extensions of the muscle cells and the nerve fibres show no peculiarities of the membrane and are recognized as synapses only by their vesicles. No nerve fibres or neuromuscular junctions can be identified in the ampulla, and structures described from material vitally stained with methylene blue must be reinterpreted. The fibres which run along the seam of the ampullae, formerly described as axons, are extensions of muscle cells, to which they can be traced. The muscle fibres of the ampullae have large fluid-filled spaces around the myofilaments and it is proposed that some stain selectively and give rise to the structures originally described as ribbon axons.

scholarly journals Prion Infection of Skeletal Muscle Cells and Papillae in the Tongue

2004 ◽  
Vol 78 (13) ◽  
pp. 6792-6798 ◽  
Author(s):  
Ellyn R. Mulcahy ◽  
Jason C. Bartz ◽  
Anthony E. Kincaid ◽  
Richard A. Bessen
Keyword(s):  
Skeletal Muscle ◽  
Sensory Nerve ◽  
Meat Products ◽  
Muscle Cells ◽  
Nerve Fibers ◽  
Skeletal Muscle Cells ◽  
Lingual Papillae ◽  
Intracerebral Inoculation ◽  
Axon Terminals ◽  
Prion Infection

ABSTRACT The presence of the prion agent in skeletal muscle is thought to be due to the infection of nerve fibers located within the muscle. We report here that the pathological isoform of the prion protein, PrPSc, accumulates within skeletal muscle cells, in addition to axons, in the tongue of hamsters following intralingual and intracerebral inoculation of the HY strain of the transmissible mink encephalopathy agent. Localization of PrPSc to the neuromuscular junction suggests that this synapse is a site for prion agent spread between motor axon terminals and muscle cells. Following intracerebral inoculation, the majority of PrPSc in the tongue was found in the lamina propria, where it was associated with sensory nerve fibers in the core of the lingual papillae. PrPSc staining was also identified in the stratified squamous epithelium of the lingual mucosa. These findings indicate that prion infection of skeletal muscle cells and the epithelial layer in the tongue can be established following the spread of the prion agent from nerve terminals and/or axons that innervate the tongue. Our data suggest that ingestion of meat products containing prion-infected tongue could result in human exposure to the prion agent, while sloughing of prion-infected epithelial cells at the mucosal surface of the tongue could be a mechanism for prion agent shedding and subsequent prion transmission in animals.

scholarly journals Association of beta-cytoplasmic actin with high concentrations of acetylcholine receptor (AChR) in normal and anti-AChR-treated primary rat muscle cultures.

1984 ◽  
Vol 32 (9) ◽  
pp. 973-981 ◽  
Author(s):  
B W Lubit
Keyword(s):  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Morphological Changes ◽  
Muscle Cells ◽  
High Concentration ◽  
Rat Muscle ◽  
Cytoplasmic Actin ◽  
High Concentrations

Previous immunocytochemical studies in which an antibody specific for mammalian cytoplasmic actin was used showed that a high concentration of cytoplasmic actin exists at neuromuscular junctions of rat muscle fibers such that the distribution of actin corresponded exactly to that of the acetylcholine receptors. Although clusters of acetylcholine receptors also are present in noninnervated rat and chick muscle cells grown in vitro, neither the mechanism for the formation and maintenance of these clusters nor the relationship of these clusters to the high density of acetylcholine receptors at the neuromuscular junction in vivo are known. In the present study, a relationship between beta-cytoplasmic actin and acetylcholine receptors in vitro has been demonstrated immunocytochemically using an antibody specific for the beta-form of cytoplasmic actin. Networks of cytoplasmic actin-containing filaments were found in discrete regions of the myotube membrane that also contained high concentrations of acetylcholine receptors; such high concentrations of acetylcholine receptors have been described in regions of membrane-substrate contact. Moreover, when primary rat myotubes were exposed to human myasthenic serum, gross morphological changes, accompanied by an apparent rearrangement of the cytoplasmic actin-containing cytoskeleton, were produced. Although whether the distribution of cytoplasmic actin-containing structures was influenced by the organization of acetylcholine receptor or vice versa cannot be determined from these studies, these findings suggest that in primary rat muscle cells grown in vitro, acetylcholine receptors and beta-cytoplasmic actin-containing structures may be somehow connected.

scholarly journals Post-synaptic morphology of mouse neuromuscular junctions is linked to muscle fibre type

2020 ◽  
Author(s):  
Aleksandra M. Mech ◽  
Anna-Leigh Brown ◽  
Giampietro Schiavo ◽  
James N. Sleigh
Keyword(s):  
Motor Neuron ◽  
Muscle Fibre ◽  
Fibre Type ◽  
Neuromuscular Junctions ◽  
Fibre Diameter ◽  
Neuromuscular Diseases ◽  
Neuronal Morphology ◽  
Muscle Fibre Type ◽  
Muscle Membrane ◽  
Muscle Fibres

AbstractThe neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, ultimately facilitating the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, whether muscle fibre type impacts NMJ morphology and growth, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31-32) timepoints. Post-synaptic AChR morphology was found to be more variable between muscles than that of the motor neuron terminal and there were greater differences in the developing NMJ than at the mature synapse. Post-synaptic architecture, but not neuronal morphology or post-natal synapse growth, correlates with fibre type and is largely independent of muscle fibre diameter. Counter to previous observations, this study indicates that smaller NMJs tend to innervate muscles with higher proportions of fast twitch fibres and that NMJ growth rate is not conserved across all muscles. Furthermore, healthy pre- and post-synaptic NMJ morphological parameters were collected for five anatomically and functionally distinct mouse muscles, generating reference data that will be useful for the future assessment of neuromuscular disease models.Graphical Abstract

scholarly journals Myomirnas Role in Als Suggest a Crosstalk between Muscle and Motor Neuron

2018 ◽  
Author(s):  
Valentina Pegoraro ◽  
Antonio Merico ◽  
Corrado Angelini
Keyword(s):  
Skeletal Muscle ◽  
Motor Neuron ◽  
Aerobic Exercise ◽  
Muscle Atrophy ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Neurodegenerative Disorder ◽  
Disease Process ◽  
Muscle Fibres ◽  
Wide Range

Amyotrophic lateral sclerosis (ALS) is a rare, progressive, neurodegenerative disorder caused by degeneration of upper and lower motor neurons. The disease process leads from lower motor neuron involvement to progressive muscle atrophy, weakness, fasciculations for the upper motor neuron involvement to spasticity. Muscle atrophy in ALS is caused by a dysregulation in the molecular network controlling fast and slow muscle fibres. Denervation and reinnervation processes in skeletal muscle occur in the course of ALS and are modulated by rehabilitation. MicroRNAs (miRNAs) are small non-coding RNAs that modulate a wide range of biological functions under various pathophysiological conditions. MiRNAs can be secreted by various cell types and they are markedly stable in body fluids. MiR-1, miR-133 a, miR-133b, and miR-206 are called “myomiRs” and are considered markers of myogenesis during muscle regeneration and neuromuscular junction stabilization or sprouting. We observed a positive effect of a standard aerobic exercise rehabilitative protocol conducted for six weeks in 18 ALS patients during hospitalization in our center. We correlated clinical scales with molecular data on myomiRs. After six weeks of moderate aerobic exercise, myomiRNAs were down-regulated, suggesting an active proliferation of satellite cells in muscle and increased neuromuscular junctions. Our data suggest that circulating miRNAs modulate during skeletal muscle recovery in response to physical rehabilitation in ALS.

Reflex Control of Abdominal Flexor Muscles in the Crayfish

1965 ◽  
Vol 43 (2) ◽  
pp. 229-246
Author(s):  
DONALD KENNEDY ◽  
KIMIHISA TAKEDA
Keyword(s):  
Neuromuscular Junctions ◽  
Reciprocal Relationship ◽  
Muscle Fibres ◽  
Reflex Inhibition ◽  
Motor Axons ◽  
Efferent Nerve ◽  
Temporal Properties ◽  
Presynaptic Mechanisms ◽  
Flexor Muscles ◽  
Central Inhibition

1. Fibres from the tonic, superficial abdominal flexor muscles in the crayfish receive a complex, highly polyneuronal innervation from among five motor axons and one inhibitor. All efferent nerve fibres show some degree of ‘spontaneous’ activity. 2. The muscle fibres therefore exhibit a constant flux of membrane potential, and hence of tension, in intact preparations. Depolarization is the result of facilitation and/or summation of junctional potentials of various amplitudes, and in some fibres of superimposed electrogenic responses. Neighbouring fibres tend to show similar innervation patterns, more distant ones dissimilar ones. 3. No useful distinction may be made between ‘fast’ and ‘slow’ motor axons. A given axon may produce junctional potentials of very different amplitudes (and some what different rise-times) in neighbouring muscle fibres while another exhibits a precisely reciprocal relationship. The largest axon produces facilitating junctional potentials in all the muscle fibres it innervates, but others may exhibit facilitation in one muscle fibre and antifacilitation in another. 4. Most muscle fibres are innervated by two or three excitatory axons; fibres with single, quadruple or quintuple motor innervation are relatively rare. There is a pronounced tendency for fibres with a rich excitatory innervation to receive the inhibitor as well. The innervation is not shared equally among motor axons: one serves over 90% of the muscle fibres, and two others 20% or less. Statistical analysis of the combinations of motor axons serving muscle fibres reveals that these are apparently random, with all variations from randomness accountable on the grounds of broad regional differences in distribution. 5. The motor axons are selectively activated by specific reflex inputs. Since muscle fibres receive, on the average, only a restricted sample of the available motor supply, it follows that they participate differentially in different reflex actions. Evidence is presented that the firing pattern of motor nerves is appropriate for the temporal properties of their neuromuscular junctions. 6. Reflex inhibition is accomplished by central inhibition of all excitatory motor outflow, accompanied by reciprocal firing in the inhibitor axon. This and the fact that less than half the muscle fibres receive inhibitory innervation demonstrate that, in contrast to the one other crustacean system analysed, reflex inhibition is primarily a central event. Peripheral inhibition in the slow flexor system must serve mainly as a device to achieve repolarization and thus terminate contractions. Such action necessarily depends upon post-synaptic rather than presynaptic mechanisms.

Acetylcholine Receptors of Cultured Muscle Cells Demonstrated with Ferritin-α-Bungarotoxin Conjugates

1974 ◽  
Vol 16 (2) ◽  
pp. 473-479
Author(s):  
B. T. HOURANI ◽  
B. F. TORAIN ◽  
M. P. HENKART ◽  
R. L. CARTER ◽  
V. T. MARCHESI ◽  
...  
Keyword(s):  
Binding Sites ◽  
Acetylcholine Receptors ◽  
Surface Membrane ◽  
Freeze Fracture ◽  
Muscle Cells ◽  
Muscle Fibres ◽  
Toxin Binding ◽  
Thin Section Electron Microscopy ◽  
Section Electron ◽  
Small Clusters

α-Bungarotoxin-ferritin conjugates were used to visualize by freeze-fracture and thin-section electron microscopy toxin-binding sites, presumably acetylcholine (ACh) receptors, in membranes of muscle cells grown in tissue culture. Toxin conjugated to ferritin by a glutaraldehyde reaction and purified by column chromatography in a buffer of high ionic strength remains active in blocking the effect of iontophoretically applied ACh. The potency of the conjugates was decreased 5-10 times compared to native α-bungarotoxin. Toxin-ferritin conjugates were identified in small clusters which were not uniformly distributed over the surface membrane. Binding was inhibited by preincubation in D-tubocurare or unconjugated toxin. The relation of the clusters to the non-uniform distribution of ACh sensitivity and α-bungarotoxin binding on cultured muscle fibres is discussed.

Occurrence, composition and function of intracellular calcium phosphate granules in the musculature of nephtyid polychaetes (Annelida)

1986 ◽  
Vol 66 (2) ◽  
pp. 343-365 ◽  
Author(s):  
G. W. Bryan ◽  
P. E. Gibbs
Keyword(s):  
Calcium Phosphate ◽  
Intracellular Calcium ◽  
Muscle Cells ◽  
Muscle Fibres ◽  
Natural Occurrence ◽  
Animal Kingdom ◽  
Wide Range ◽  
And Function ◽  
Different Tissues

INTRODUCTIONIntracellular calcium granules rich in phosphorus are found throughout the animal kingdom and occur in a wide range of different tissues (Simkiss, 1976; Mason & Nott, 1981). However, few examples of the natural occurrence of such granules in muscle cells have been recorded and thus the discovery of abundant granules composed of calcium phosphate within the muscle fibres of the polychaete Nephtys, described by Gibbs & Bryan (1984), is of considerable interest, particularly regarding the formation and function of these unusual sarcoplasmic inclusions.

A survey of the new findings presented and the discussions arising during sessions I, II and lII

1973 ◽  
Vol 265 (867) ◽  
pp. 157-165 ◽  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Smooth Muscles ◽  
Muscle Cells ◽  
Muscle Physiology ◽  
Muscle Fibres ◽  
New Findings ◽  
Separate Identity ◽  
Skeletal Muscle Fibres ◽  
Passive Electrical Properties

One of the earliest studies on the physiology of smooth muscle was that reported by Engelmann over 100 years ago. In setting the stage for this discussion on new developments in smooth muscle physiology, Professor Bozler recalled Engelmann’s description of the ureter as a ‘giant hollow muscle fibre’. Recent work on the passive electrical properties of smooth muscle has shown that Engelmann’s concept of the syncytial behaviour of smooth muscle is true for a great many smooth muscles - perhaps for all vertebrate smooth muscles. When smooth muscle cells come into contact they interact with each other so as to form a tissue. In this sense, a community of smooth muscle cells is analogous with the liver, epithelial tissues and the heart. One can contrast this ‘collective’ behaviour of smooth muscle cells with the separate identity maintained by most nerve cells and skeletal muscle fibres.

Erster Nachweis von freien Cilien im Mitteldarm von Arthropoden / Discovery of Cilia in the Mid-Gut of Arthopoda

1978 ◽  
Vol 33 (7-8) ◽  
pp. 598-599 ◽  
Author(s):  
Norbert Rieder ◽  
Friedrich Schlecht
Keyword(s):  
Muscle Cells ◽  
Sensory Cells

Abstract Cells bearing two cilia are found in the mid-gut of the Phyllopod Leptestheria dahalacensis. These cells seem to be sensory cells. They may be in contact with the muscle cells of the mid-gut.

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