Structure and ultrastructure of the frog motor endplate

Peper, K.; Dreyer, Florian; Sandri, C.; Akert, K.; Moor, H.

doi:10.1007/bf00223024

Cited by 153 publications

(73 citation statements)

References 23 publications

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“…Our results confirm and extend the observations derived from freeze-fracture of adult vertebrate endplates (3)(4)(5) and electric fish electroplaques (20)(21)(22) (3)(4)(5) and to the density of q-bungarotoxin binding sites within hot spots on cultured rat myotubes (23).…”

Section: Resultssupporting

confidence: 89%

“…Electron microscopic autoradiography of endplates exposed to 125I-labeled a-bungarotoxin indicates that the receptors are restricted to the tops of the postqunctional folds (2). In freeze-fracture replicas, these regions contain tightly packed arrays of intramembranous particles (IMPs) (3)(4)(5). Because the density of IMPs on the protoplasmic (P) fracture face corresponds to the density of toxin binding sites (6), it is likely that the IMPs represent some component of the AcCho receptor.…”

mentioning

confidence: 99%

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Clusters of intramembranous particles on cultured myotubes at sites that are highly sensitive to acetylcholine.

Yee¹,

Fischbach²,

Karnovsky³

1978

Proc. Natl. Acad. Sci. U.S.A.

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Electrophysiological and autoradiographic studies have shown that the distribution of acetylcholine (AcCho) receptors on uninnervated cultured chicken muscle cells is not uniform. Regions of high receptor density (hot spots) 10-40 times more sensitive than surrounding areas are localized as discrete patches or clusters about 10 ,um in diameter on myotube muscle membranes. Hot spots were also found on fusion-arrested mononucleated myoblasts. We have developed a method for freeze-fracturing monolayer cultures that allows the unambiguous reidentification of membrane patches previously assayed for AcCho sensitivity. The freeze-fractured membranes at physiologically defined hot spots contain aggregates of many (10-20) small clusters of large (10-19 nm in diameter) intramembranous particles. Clusters are found on both fracture faces, but the particle density is much greater on the protoplasmic (P) face than on the extracellular (E) face (about 2000/14m2 vs. 700/jum2). Some of the particles appear to be composed of five or six "subunits" arranged cylindrically around a central dark dot. Because the aggregates are present at sites of high AcCho sensitivity, it is likely that the intramembranous particles are in some way related to the AcCho receptor molecule.At the adult skeletal neuromuscular junction, acetylcholine (AcCho) receptors are clustered in the immediate subsynaptic membrane (1). Electron microscopic autoradiography of endplates exposed to 125I-labeled a-bungarotoxin indicates that the receptors are restricted to the tops of the postqunctional folds (2). In freeze-fracture replicas, these regions contain tightly packed arrays of intramembranous particles (IMPs) (3)(4)(5). Because the density of IMPs on the protoplasmic (P) fracture face corresponds to the density of toxin binding sites (6), it is likely that the IMPs represent some component of the AcCho receptor.AcCho receptors are also clustered on uninnervated embryonic myotubes maintained in culture (7,8 MATERIALS AND METHODSCells. Muscle fragments minced from embryonic chicken pectoral muscle were triturated in a Ca2+ , Mg2+ , and enzyme-free salt solution (Puck's DG) by repeated passage through a fire-polished pasteur pipette. The mononucleated muscle precursor cells thus obtained were plated onto collagen-coated glass coverslips (Gold Seal no. 0; diameter, 4 mm). The cells were maintained in Eagle's minimal essential medium (88% vol/vol) supplemented with glutamine (2 mM), heatinactivated horse serum (10% vol/vol), and chicken embryo extract (2% vol/vol).The reidentification of previously identified myotubes in freeze-fracture replicas was facilitated in three ways: (i) the cells

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Section: Resultssupporting

confidence: 89%

mentioning

confidence: 99%

Clusters of intramembranous particles on cultured myotubes at sites that are highly sensitive to acetylcholine.

Yee¹,

Fischbach²,

Karnovsky³

1978

Proc. Natl. Acad. Sci. U.S.A.

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“…There were limitations in the stains that were available to distinguish among these cells at the NMJ and, as argued above for Remak fibers, an inability to resolve them in light microscopy. Now from electron micrographs (Birks et al, 1960a;Heuser and Reese, 1973;Slater, 1968, 1970;Peper et al, 1974;Robertson, 1956), the filling of individual cells with fluorescent dyes using microelectrodes (McMahan et al, 1972), and most recently from immunostaining (Astrow et al, 1994(Astrow et al, , 1998Reynolds and Woolf, 1992;Young et al, 2005) and use of GFP transgenes (Kang et al, 2000(Kang et al, , 2007Zuo et al, 2004) (see Fig. 2), it is apparent that NMSCs cover the synapse.…”

Section: Schwann Cells At the Neuromuscular Junctionsmentioning

confidence: 99%

Biology and pathology of nonmyelinating Schwann cells

Griffin

Thompson

2008

Glia

252

202

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The CNS contains relatively few unmyelinated nerve fibers, and thus benefits from the advantages that are conferred by myelination, including faster conduction velocities, lower energy consumption for impulse transmission, and greater stability of point-to-point connectivity. In the PNS many fibers or regions of fibers the Schwann do not form myelin. Examples include C fibers nociceptors, postganglionic sympathetic fibers, and the Schwann cells associated with motor nerve terminals at neuromuscular junctions. These examples retain a degree of plasticity and a capacity to sprout collaterally that is unusual in myelinated fibers. Nonmyelin-forming Schwann cells, including those associated with uninjured fibers, have the capacity to act as the ''first responders'' to injury or disease in their neighborhoods. V V C

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“…binding was not detected in muscles that had been successfully denervated . In the frog cutaneous pectoris muscle, NMJs are easy to identify because of their characteristic structure (14,31,38) . The motor axon loses its myelin sheet at some distance from the muscle fiber .…”

Section: Experiments On Frog Nmimentioning

confidence: 99%

Specific localization of the alpha-latrotoxin receptor in the nerve terminal plasma membrane.

Valtorta¹,

Madeddu²,

Meldolesi³

et al. 1984

The Journal of Cell Biology

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The receptor for a-latrotoxin, the major protein component of the black widow spider venom, was investigated by the use of the purified toxin and of polyclonal, monospecific anti-a-latrotoxin antibodies . Experiments on rat brain synaptosomes (where the existence of a-latrotoxin receptors was known from previous studies) demonstrated that the toxin-receptor complex is made stable by glutaraldehyde fixation . At saturation, each such complex was found to bind on the average five antitoxin antibody molecules . In frog cutaneous pectoris muscles, the existence of a finite number of high-affinity receptors was revealed by binding experiments with ' 25 1-a-latrotoxin (Kd = 5 x 10-10 M; borax = 1 .36 ± 0.16 [SEJ x 109 sites/mg tissue, dry weight) . Nonpermeabilized muscles were first treated with a-latrotoxin, and then washed, fixed, dissociated into individual fibers, and treated with anti -a-latrotoxin antibodies and finally with rhodamine-conjugated sheep anti-rabbit antibodies. In these preparations, muscle fibers and unmyelinated preterminal nerve branches were consistently negative, whereas bright specific fluorescent images, indicative of concentrated a-latrotoxin binding sites, appeared in the junctional region . These images closely correspond in size, shape, and localization to endplates decorated by the acetylcholinesterase reaction . The presynaptic localization of the specific fluorescence found at frog neuromuscular junctions is supported by two sets of findings: (a) fluorescent endplate images were not seen in muscles that had been denervated ; and (b) the distribution of fluorescence in many fibers treated with alatrotoxin at room temperature was the one expected from swollen terminal branches. Swelling of terminals is a known morphological change induced by a-latrotoxin in this preparation . When muscles were treated with either proteolytic enzymes (trypsin, collagenase) or detergents (Triton X-100) before exposure to a-latrotoxin, the specific fluorescent endplate images failed to appear. Taken together these findings indicate that the a-latrotoxin receptor is an externally exposed protein highly concentrated in the nerve terminal plasma membrane . Its density (number per unit area) at the frog neuromuscular junction can be calculated to be 2,400/um 2.The presynaptic membrane is the portion of the neuronal plasmalemma that surrounds synaptic terminals, where the release of neurotransmitters occurs by fusion of synaptic vesicles (exocytosis) . A number of other important functions (e .g., the recycling of the vesicle membrane, the high-affinity uptake processes of neurotransmitters or transmitter precursors, and the initiation of retrograde transport) are also localized at this level. It is generally agreed that these functional specializations of the presynaptic membrane occur as a consequence ofits molecular dissimilarity with respect to the rest 124 F.

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Structure and ultrastructure of the frog motor endplate

Cited by 153 publications

References 23 publications

Clusters of intramembranous particles on cultured myotubes at sites that are highly sensitive to acetylcholine.

Clusters of intramembranous particles on cultured myotubes at sites that are highly sensitive to acetylcholine.

Biology and pathology of nonmyelinating Schwann cells

Specific localization of the alpha-latrotoxin receptor in the nerve terminal plasma membrane.

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