Fine structure of identified muscle fibers and their neuromuscular synapses in the limb closer muscle of the crab Eriphia spinifrons

1993 ◽  
Vol 271 (1) ◽  
pp. 23-31 ◽  
Author(s):  
A. T. Read ◽  
C. K. Govind
Keyword(s):  
Fine Structure ◽  
Muscle Fibers ◽  
Neuromuscular Synapses

ULTRASTRUCTURAL FEATURES OF CRAYFISH PHASIC AND TONIC MUSCLE FIBERS

1967 ◽  
Vol 45 (5) ◽  
pp. 601-606 ◽  
Author(s):  
S. S. Jahromi ◽  
H. L. Atwood
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Transverse Section ◽  
Muscle Fibers ◽  
Orconectes Virilis ◽  
Neuromuscular Synapses ◽  
Thick Filaments ◽  
Tonic Muscle ◽  
Extensor Muscles

Phasic and tonic muscle fibers from the abdominal extensor muscles of the crayfish, Procambarus clarki and Orconectes virilis, were examined for differences in fine structure with the electron microscope. The myofibrils of the two types of fiber were similar in size as seen in transverse section, unlike those in vertebrate twitch and tonus fibers. The ratio of thin to thick filaments was about 5:1 in tonic fibers and 3:1 in phasic fibers. Neuromuscular synapses in tonic fibers were enclosed by arms of noncontractile sarcoplasm, whereas the synapses seen in phasic fibers lacked this feature.

Activity-dependent induction of functional secretory properties at cultured neuromuscular synapses of Helisoma

1996 ◽  
Vol 76 (4) ◽  
pp. 2635-2643 ◽  
Author(s):  
J. C. Poyer ◽  
M. J. Zoran
Keyword(s):  
Cell Culture ◽  
Critical Role ◽  
Muscle Fibers ◽  
Pond Snail ◽  
Culture Dish ◽  
Neuromuscular Synapses ◽  
Neuronal Processes ◽  
Activity Dependent

1. The role of activity-dependent mechanisms in target-mediated induction of secretory properties was investigated at regenerating neuromuscular synapses of the American pond snail, Helisoma trivolvis, in cell culture. 2. Identified motoneurons were isolated into cell culture conditions that promoted neurite outgrowth. Buccal neurons 19 (B19) were cultured alone for 2 days, at which time dissociated muscle fibers were manipulated into contact with newly formed neurites. 3. Immediately before the plating of muscle fibers, the sodium channel blocker, tetrodotoxin (TTX), or the acetylcholine receptor antagonist, d-tubocurarine chloride (curare), was added to the culture dish. After 48 h of exposure, the inhibitors were removed by repeated dilution of the culture medium and electrophysiological analyses were performed. 4. Cholinoceptive assay cells were manipulated into contact with the presynaptic neurons to assess secretory properties along neuronal processes. Assay cells were used to control for variations in postsynaptic sensitivity that could result from long-term exposure to activity inhibitors. 5. These analyses demonstrated that inhibition of TTX-sensitive presynaptic activity and inhibition of curare-sensitive postsynaptic activation both blocked the induction of excitation-secretion coupling typically induced in these motoneurons by appropriate target contact. Neuron B5, which rapidly acquires functional synaptic properties in vitro, was unaffected in its secretory function by 48 h of activity inhibition. 6. Acquisition of secretory competence was not suppressed due to a reduction in the viability or long-term changes in excitability of the activity-inhibited neurons, as indicated by analyses of electrophysiological properties. 7. Although target-contact and activity both participated in the induction of secretory modifications in neuron B19, target-mediated changes did not involve retrograde effects on presynaptic neuronal excitability. 8. We hypothesize that contact-mediated mechanisms govern the initiation of presynaptic modifications in B19, however, our data indicate that the acquisition of functional excitation-secretion coupling also involves activity-dependent mechanisms. Although the mechanistic role of activity remains undefined, our results suggest that the activation of the target muscle plays a critical role in a retrograde signaling pathway underlying maturation of a functional secretory apparatus in target-contacted neuronal processes.

scholarly journals New insights into the morphology and evolution of the ventral pharynx and jaws in Histriobdellidae (Eunicida, Annelida)

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Alexander Tzetlin ◽  
Nataliya Budaeva ◽  
Elena Vortsepneva ◽  
Conrad Helm
Keyword(s):  
Fine Structure ◽  
3D Reconstruction ◽  
Muscle Fibers ◽  
Comparative Analyses ◽  
Maxillary Protraction ◽  
Jaw Apparatus ◽  
Different Parts ◽  
Comprehensive Study

AbstractThe jaw apparatus in several annelid families represents a powerful tool for systematic approaches and evolutionary investigations. Nevertheless, for several taxa, this character complex has scarcely been investigated, and complete comparative analyses of all annelid jaws are lacking. In our comprehensive study, we described the fine structure of the jaw apparatus and the ventral pharyngeal organ (VPO) in Histriobdella homari – a minute ectocommensal of lobsters putatively belonging to the Eunicida – using different comparative morphological approaches, including SEM, TEM, CLSM and subsequent 3D reconstruction. The H. homari jaw apparatus is composed of ventral paired mandibles and dorsal symmetrical maxillae consisting of numerous dental plates, ventral carriers and an unpaired dorsal rod, and the general assemblage and arrangement of the different parts are highly comparable to those of other eunicid families. The jaw ultrastructure of histriobdellids resembles that of the families Dorvilleidae and (juvenile) Onuphidae. Furthermore, our data reveal that in the process of development of the jaw apparatus, the mandibles, maxillae II and unpaired dorsal rod are formed first, and the remaining maxillae and ventral carriers appear later. Notably, the muscular apparatus differs from that in Dorvilleidae and Onuphidae in terms of the number and arrangement of muscle fibers encompassing the jaws – not only because of the very small size of Histriobdella but also because histriobdellid maxillary protraction occurs due to straightening of the dorsal rod and thus requires a different muscular scaffold. Based on our investigations, the arrangement of the muscular apparatus of the jaws, the presence of paired ventral carriers and the dorsal rod, and the morphology of the ventral pharyngeal organ represent a histriobdellid autapomorphy. Our datasets form a basis for further comparative analyses to elucidate the evolution of Eunicida and jaw-bearing Annelida.

scholarly journals SARCOLEMMAL INVAGINATIONS CONSTITUTING THE T SYSTEM IN FISH MUSCLE FIBERS

1964 ◽  
Vol 22 (3) ◽  
pp. 675-696 ◽  
Author(s):  
Clara Franzini-armstrong ◽  
Keith R. Porter
Keyword(s):  
Fine Structure ◽  
Osmium Tetroxide ◽  
Striated Muscle ◽  
Muscle Fibers ◽  
Fish Muscle ◽  
Structural Features ◽  
The Body ◽  
Glutaraldehyde Fixation ◽  
Striated Muscle Fibers ◽  
T System

Striated muscle fibers from the body and tail myotomes of a fish, the black Mollie, have been examined with particular attention to the sarcoplasmic reticulum (SR) and transverse tubular (or T) system. The material was fixed in osmium tetroxide and in glutaraldehyde, and the images provided by the two kinds of fixatives were compared. Glutaraldehyde fixes a fine structure that is broadly comparable with that preserved by osmium tetroxide alone but differs in some significant details. Especially significant improvements were obtained in the preservation of the T system, that is, the system of small tubules that pervades the fiber at every Z line or A-I junction level. As a result of this improved glutaraldehyde fixation, the T system is now clearly defined as an entity of fine structure distinct from the SR but uniquely associated with the SR and myofibrils. Glutaraldehyde fixation also reveals that the T system is a sarcolemmal derivative that retains its continuity with the sarcolemma and limits a space that is in direct communication with the extracellular environment. These structural features favor the conclusion that the T system plays a prominent role in the fast intracellular conduction of the excitatory impulse. The preservation of other elements of muscle fine structure, including the myofibrils, seems for reasons discussed, to be substantially improved by glutaraldehyde.

scholarly journals Neural regulation of acetylcholinesterase mRNAs at mammalian neuromuscular synapses.

1994 ◽  
Vol 127 (4) ◽  
pp. 1061-1069 ◽  
Author(s):  
R N Michel ◽  
C Q Vu ◽  
W Tetzlaff ◽  
B J Jasmin
Keyword(s):  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Synaptic Proteins ◽  
Trophic Factors ◽  
Mammalian Skeletal Muscle ◽  
Mrna Levels ◽  
Adult Muscle ◽  
Neuromuscular Synapses ◽  
Evoked Activity

We examined the role of innervation on acetylcholinesterase (AChE) gene expression within mammalian skeletal muscle fibers. First, we showed the selective accumulation of AChE mRNAs within the junctional vs extrajunctional sarcoplasm of adult muscle fibers using a quantitative reverse transcription PCR assay and demonstrated by in situ hybridization experiments that AChE transcripts are concentrated immediately beneath the postsynaptic membrane of the neuromuscular junction. Next, we determined the influence of nerve-evoked activity vs putative trophic factors on the synaptic accumulation of AChE mRNA levels in muscle fibers paralyzed by either surgical denervation or selective blockage of nerve action potentials with chronic superfusion of tetrodotoxin. Our results indicated that muscle paralysis leads to a marked decrease in AChE transcripts from the postsynaptic sarcoplasm, yet the extent of this decrease is less pronounced after tetrodotoxin inactivation than after denervation. These results suggest that although nerve-evoked activity per se appears a key regulator of AChE mRNA levels, the integrity of the synaptic structure or the release of putative trophic factors contribute to maintaining the synaptic accumulation of AChE transcripts at adult neuromuscular synapses. Furthermore, the pronounced downregulation of AChE transcripts in paralyzed muscles stands in sharp contrast to the well-documented increase in nicotinic acetylcholine receptor mRNAs under these conditions, and indicates that expression of the genes encoding these two synaptic proteins are subjected to different regulatory mechanisms in adult muscle fibers in vivo.

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