Development of neuromuscular synapses

1983 ◽  
Vol 63 (3) ◽  
pp. 915-1048 ◽  
Author(s):  
M. R. Bennett
Keyword(s):  
Motor Unit ◽  
Muscle Cells ◽  
Terminal Branch ◽  
Quantal Release ◽  
Synaptic Site ◽  
Neuromuscular Synapses ◽  
A Site ◽  
Threshold Amount ◽  
Neuron Soma ◽  
Secretory Capacity

Quantal secretion at nerve terminals in mature muscles depends on the number of terminal branches and the size of release sites (sect. VB4). The physical length of SBL determines the length of terminal branch that can be laid down in a reinnervation experiment (sect. IVA4). A limit is set on the total length of terminal branches formed by a motoneuron; this limit is determined by the amount of TF (sect. IVB) made available from the neuron soma to the peripheral branches of the neuron (sect. VC). As a result of this limit, not all SBL needs to be occupied at a site by terminal branches. The SBL eventually disappears if it is not occupied by terminal branches (sect. IVA2). If a muscle is relatively inactive, it synthesizes and releases at synaptic sites additional amounts of NGF, which stimulates the growth of additional terminal branches. These may secrete sufficient amounts of AF to induce the formation of new SRs with associated SBL. In these circumstances a new synaptic site is formed or an extension of an existing site is created. If the size of a motor unit is decreased, the enhanced release of TF at the remaining terminals ensures that each occupies all the SBL at the synaptic site. Furthermore the enhanced release of AF per terminal induces more SBL, allowing additional terminal branches on the muscle cells to be established. Neither of these changes occurs unless the threshold amount of NGF is available from the muscle to stabilize the terminals. If this condition is met, an increase in quantal release per terminal occurs after reducing the size of a motor unit (sect. VC). An increase in quantal release per terminal also occurs after inactivation of a muscle. Such inactivation leads to an enhanced release of NGF per synaptic site (sect. VA4). Extra terminals may then form if sufficient TF is available; these may innervate existing but empty synaptic sites. In rare circumstances the extra terminal may induce SBL and innervate these new sites if sufficient AF is available. In both cases the quantal release per terminal increases. During development the secretory capacity of the axon terminal depends on the muscle cells with which it synapses. This secretory capacity can be enhanced either by increasing the number of terminal branch pairs or by increasing the secretory capacity of individual release sites. If two terminals innervate a synaptic site, their individual secretory capacity is reduced--in these circumstances the terminal's secretory capacity depends on the amount of NGF available to the terminal; two terminals must share their NGF.

scholarly journals Activation of cAMP signaling transiently inhibits apoptosis in vascular smooth muscle cells in a site upstream of caspase-3

1999 ◽  
Vol 6 (7) ◽  
pp. 661-672 ◽  
Author(s):  
Sergei N Orlov ◽  
Nathalie Thorin-Trescases ◽  
Nickolai O Dulin ◽  
Than-Vinh Dam ◽  
Maria A Fortuno ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Caspase 3 ◽  
Muscle Cells ◽  
Camp Signaling ◽  
A Site

scholarly journals Nerve-Muscle Interaction In Vitro

1973 ◽  
Vol 62 (3) ◽  
pp. 255-270 ◽  
Author(s):  
J. H. Steinbach ◽  
A.J. Harris ◽  
J. Patrick ◽  
D. Schubert ◽  
S. Heinemann
Keyword(s):  
Nerve Cell ◽  
Muscle Cell ◽  
Acetylcholine Receptors ◽  
Muscle Cells ◽  
Acetylcholine Sensitivity ◽  
Release Of Acetylcholine ◽  
Clonal Lines ◽  
Nerve Muscle ◽  
A Site

Nerve and muscle cells from clonal lines interact in vitro, resulting in the association on the muscle surface of an area of increased acetylcholine sensitivity with a site of nerve-muscle contact. This localization of acetylcholine sensitivity on the muscle cell to a site of contact between nerve and muscle was found to occur when acetylcholine receptors on the muscle had been blocked with α-neurotoxin. Localization was also found to occur when the nerve cell had been prevented from releasing acetylcholine. It is concluded that neither the presence of active acetylcholine receptors on the muscle, nor the release of acetylcholine from the nerve, was required for the events leading to the localization of acetylcholine sensitivity in vitro.

Effects of the First Twenty MEIC Reference Chemicals on Viability, Glucose Consumption and Spontaneous Contractility of Primary Cultured Rat Skeletal Muscle Cells

1992 ◽  
Vol 20 (2) ◽  
pp. 222-225
Author(s):  
Michael Gulden ◽  
Jutta Finger
Keyword(s):  
Skeletal Muscle ◽  
Biological Activities ◽  
Glucose Consumption ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Cytotoxic Action ◽  
Rat Skeletal Muscle ◽  
Site Specific ◽  
Excitable Membranes ◽  
A Site

Primary cultured rat skeletal muscle cells were used to determine concentration-dependent effects of the first twenty MEIC chemicals on three endpoints, spontaneous contractility and viability after 1 and 24 hours, and glucose consumption during 24 hours of exposure. The contractions of cultured muscle cells depend on spontaneous electrical activity of the excitable cell membranes. The majority of the test compounds inhibited contractility at concentrations which affected neither viability nor glucose consumption. Most of these compounds are known to interact with excitable membranes in a site-specific or non-site-specific manner, thereby causing therapeutically intended or toxic effects. The results indicate that inhibition of spontaneous contractility of cultured skeletal muscle cells may reflect important non-cytotoxic biological activities of test chemicals which might be more relevant for their acute toxicity than cytotoxic action.

Identification of multiple proteins that interact with functional regions of the human cardiac alpha-actin promoter

1989 ◽  
Vol 9 (8) ◽  
pp. 3269-3283
Author(s):  
T A Gustafson ◽  
L Kedes
Keyword(s):  
Transcription Factor ◽  
Muscle Cells ◽  
Tata Box ◽  
Actin Gene ◽  
Functional Importance ◽  
Cell Biol ◽  
Proximal Site ◽  
Gel Shift ◽  
A Site ◽  
Alpha Actin

5' Sequences of the human cardiac alpha-actin gene are involved in the tissue-specific and developmental regulation of the gene. Deletion analyses combined with transient expression experiments in muscle cells have demonstrated three primary regions of functional importance (A. Minty and L. Kedes, Mol. Cell. Biol. 6:2125-2136, 1986; T. Miwa and L. Kedes, Mol. Cell. Biol. 7:2803-2813, 1987), and we have previously demonstrated binding of a protein indistinguishable from serum response factor (SRF) to the most proximal region (T.A. Gustafson, T. Miwa, L.M. Boxer, and L. Kedes, Mol. Cell. Biol. 8:4110-4119, 1988). In this report, we examine protein interaction with the remainder of the promoter. Gel shift and footprinting assays revealed that at least seven distinct nuclear proteins interacted with known and putative regulatory regions of the promoter. The transcription factor Sp1 bound to eight sites, as demonstrated by footprinting assays and gel shift analysis with purified Sp1. Purified CCAAT box-binding transcription factor CTF/NF-I and Sp1 were shown to interact with the far-upstream regulatory element at -410, and footprint analysis showed extensive overlap of these two sites. Two unidentified proteins with similar but distinct footprints interacted with the second region of functional importance at -140, which contains the second CArG motif [CC(A + T rich)6GG], and these proteins were shown to be distinct from SRF. SRF was found to bind to the remaining three CArG boxes, two of which were closely interdigitated with Sp1 sites. In addition, CArG box 4 was found to interact with SRF and another distinct protein whose footprint was contained within the SRF-binding site. Sequences surrounding the TATA box were also shown to bind proteins. Sp1 was shown to bind to a site immediately downstream from the TATA box and to a site within the first exon. Thus, each of the three functional upstream regions, as defined by transfection assays, was shown to interact with five factors: Sp1 and CTF/NF-I at the upstream site, two unidentified proteins at the central site, and SRF at the most proximal site. These results suggest that expression of the cardiac actin gene in muscle cells is controlled by complex interactions among multiple upstream and intragenic elements.

Quantal Secretion and Nerve-Terminal Cable Properties at Neuromuscular Junctions in an Amphibian (Bufo marinus)

1999 ◽  
Vol 81 (3) ◽  
pp. 1135-1146 ◽  
Author(s):  
G. T. Macleod ◽  
L. Farnell ◽  
W. G. Gibson ◽  
M. R. Bennett
Keyword(s):  
Nerve Terminal ◽  
Neuromuscular Junctions ◽  
Motor Nerve ◽  
Current Injection ◽  
Bufo Marinus ◽  
Motor Nerve Terminal ◽  
Terminal Branch ◽  
Quantal Release ◽  
Cable Properties ◽  
Test Electrode

Quantal secretion and nerve-terminal cable properties at neuromuscular junctions in an amphibian ( Bufo marinus). The effect of a conditioning depolarizing current pulse (80–200 μs) on quantal secretion evoked by a similar test pulse at another site was examined in visualized motor-nerve terminal branches of amphibian endplates ( Bufo marinus). Tetrodotoxin (200 nM) and cadmium (50 μM) were used to block voltage-dependent sodium and calcium conductances. Quantal release at the test electrode was depressed at different distances (28–135 μm) from the conditioning electrode when the conditioning and test pulses were delivered simultaneously. This depression decreased when the interval between conditioning and test current pulses was increased, until, at an interval of ∼0.25 ms, it was negligible. At no time during several thousand test-conditioning pairs, for electrodes at different distances apart (28–135 μm) on the same or contiguous terminal branches, did the electrotonic effects of quantal release at one electrode produce quantal release at the other. Analytic and numerical solutions were obtained for the distribution of transmembrane potential at different sites along terminal branches of different lengths for current injection at a point on a terminal branch wrapped in Schwann cell, in the absence of active membrane conductances. Solutions were also obtained for the combined effects of two sites of current injection separated by different time delays. This cable model shows that depolarizing current injections of a few hundred microseconds duration produce hyperpolarizations at ∼30 μm beyond the site of current injection, with these becoming larger and occurring at shorter distances the shorter the terminal branch. Thus the effect of a conditioning depolarizing pulse at one site on a subsequent test pulse at another more than ∼30 μm away is to substantially decrease the absolute depolarization produced by the latter, provided the interval between the pulses is less than a few hundred microseconds. It is concluded that the passive cable properties of motor nerve terminal branches are sufficient to explain the effects on quantal secretion by a test electrode depolarization of current injections from a spatially removed conditioning electrode.

Anatomy and development of the somatic musculature of the nematode Ascaris

1976 ◽  
Vol 64 (3) ◽  
pp. 773-788 ◽  
Author(s):  
A. O. Stretton
Keyword(s):  
Action Potentials ◽  
Light And Electron Microscopy ◽  
Muscle Cells ◽  
Serial Sections ◽  
Cell Numbers ◽  
Striking Increase ◽  
Neuromuscular Synapses ◽  
System A ◽  
Somatic Musculature ◽  
Number Of Cells

The musculature of the nematode Ascaris has been studied by the examination of serial sections by light and electron microscopy. The muscle cells of nematodes are unusual in that they send branches to the neurones in contrast to the more usual situation in other animals where neurones send processes to the muscles. The neuromuscular synapses are made at the ends of the arms. Muscle cells receive multiple innervations and perform integration of the combined inputs. The action potentials are initiated near the ends of the arms so each arm acts as an integrative centre. It is shown that it is common for a muscle cell to have several arms, raising the possibility that each arm may integrate different combinations of neuronal inputs. In the second larval stage the total number of muscle cells is 83. The adult has approximately 5 X 10(4) muscle cells. The very striking increase in cell numbers of the musculature is not matched by a corresponding increase in the number of cells in the nervous system. A model for the way in which a small number of neurones can co-ordinate the activity of an increasing population of muscle cells is presented.

The arrangement and ultrastructure of the musculature, nerves and epidermis, in the tail of the cercaria of Cryptocotyle lingua (Creplin) from Littorina littorea (L.)

1975 ◽  
Vol 190 (1099) ◽  
pp. 165-186 ◽  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Synaptic Vesicles ◽  
Transverse Section ◽  
Tail Length ◽  
Muscle Cells ◽  
Striated Muscles ◽  
Neuromuscular Synapses ◽  
Straight Line ◽  
T Tubules ◽  
Fibrillar Region

The ultrastructure of the caudal muscles of the cercaria of Cryptocotyle lingua is related to the rapid swimming movements. Dorsal and ventral striated longitudinal muscle cells extend in a straight line along the tail length each containing a single myofibril, U-shaped in transverse section and divided into sarcomeres. A-, I- and H-bands are recognizable and the fragmented Z-band consists of a row of dense bars to which the thin myofilaments are attached. A pair of proximal ventro-lateral striated muscles may be responsible for the figure of eight pattern of movement. Large mitochondria are abundant in the non-fibrillar region of the muscle cells. Tubular sarcoplasmic reticulum envelops the myofibril giving off branches at the Z-bands which extend into and across the myofibril alternating with the dense bars. T-tubules are absent but cisternae of the sarcoplasmic reticulum form numerous dyadic junctions with the sarcolemma. Dorsal and ventral motor caudal nerves arise from a nerve plexus behind the tail root; axo-axonal and neuromuscular synapses are frequent. Clear and dense synaptic vesicles occur in the presynaptic terminals.

scholarly journals Identification of multiple proteins that interact with functional regions of the human cardiac alpha-actin promoter.

1989 ◽  
Vol 9 (8) ◽  
pp. 3269-3283 ◽  
Author(s):  
T A Gustafson ◽  
L Kedes
Keyword(s):  
Transcription Factor ◽  
Muscle Cells ◽  
Tata Box ◽  
Actin Gene ◽  
Functional Importance ◽  
Cell Biol ◽  
Proximal Site ◽  
Gel Shift ◽  
A Site ◽  
Alpha Actin

5' Sequences of the human cardiac alpha-actin gene are involved in the tissue-specific and developmental regulation of the gene. Deletion analyses combined with transient expression experiments in muscle cells have demonstrated three primary regions of functional importance (A. Minty and L. Kedes, Mol. Cell. Biol. 6:2125-2136, 1986; T. Miwa and L. Kedes, Mol. Cell. Biol. 7:2803-2813, 1987), and we have previously demonstrated binding of a protein indistinguishable from serum response factor (SRF) to the most proximal region (T.A. Gustafson, T. Miwa, L.M. Boxer, and L. Kedes, Mol. Cell. Biol. 8:4110-4119, 1988). In this report, we examine protein interaction with the remainder of the promoter. Gel shift and footprinting assays revealed that at least seven distinct nuclear proteins interacted with known and putative regulatory regions of the promoter. The transcription factor Sp1 bound to eight sites, as demonstrated by footprinting assays and gel shift analysis with purified Sp1. Purified CCAAT box-binding transcription factor CTF/NF-I and Sp1 were shown to interact with the far-upstream regulatory element at -410, and footprint analysis showed extensive overlap of these two sites. Two unidentified proteins with similar but distinct footprints interacted with the second region of functional importance at -140, which contains the second CArG motif [CC(A + T rich)6GG], and these proteins were shown to be distinct from SRF. SRF was found to bind to the remaining three CArG boxes, two of which were closely interdigitated with Sp1 sites. In addition, CArG box 4 was found to interact with SRF and another distinct protein whose footprint was contained within the SRF-binding site. Sequences surrounding the TATA box were also shown to bind proteins. Sp1 was shown to bind to a site immediately downstream from the TATA box and to a site within the first exon. Thus, each of the three functional upstream regions, as defined by transfection assays, was shown to interact with five factors: Sp1 and CTF/NF-I at the upstream site, two unidentified proteins at the central site, and SRF at the most proximal site. These results suggest that expression of the cardiac actin gene in muscle cells is controlled by complex interactions among multiple upstream and intragenic elements.

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