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  • 1
    Electronic Resource
    Electronic Resource
    A comparison of active zone structure in frog neuromuscular junctions from two fast muscles with different synaptic efficacy (1986)
    Springer
    Journal of neurocytology 15 (1986), S. 525-534 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To search for ultrastructural correlates of differences in synaptic safety factor and neurotransmitter release, neuromuscular junctions from the cutaneous pectoris and cutaneous dorsi muscles of the grass frogRana pipiens were freeze fractured. Synaptic efficacy in these muscles was determined by the extent to which isometric twitch tension could be blocked by lowering [Ca2+] in the bathing solution. We found that junctions in the cutaneous pectoris were significantly more effective than those of the cutaneous dorsi. Morphometric analysis of 16 junctions from each type of muscle showed significant differences in some aspects of active zone structure. Cutaneous pectoris terminals had longer active zone segments and active zones spaced more closely together. This resulted in 20% more active zone length per unit terminal length in the cutaneous pectoris. Cutaneous dorsi terminals had active zones that were more often segmented into two or more sections at a single junctional fold. Mean active zone length per junctional fold and the number of active zone particles per micrometre of active zone length were not significantly different. As a result of the somewhat larger terminal width in the cutaneous dorsi, the percentage of terminal width occupied by active zone was greater in the cutaneous pectoris. As an attempt to indirectly estimate active zone spacing with the light microscope, we applied rhodamine-conjugated alpha bungarotoxin to neuromuscular junctions from the cutaneous pectoris and cutaneous dorsi. No significant difference in the spacing of fluorescently labelled acetylcholine receptor bands was found between the two types of junctions. Our results indicated that the greater active zone length per unit terminal length in the cutaneous pectoris was associated with its increased synaptic efficacy. In addition the continuity and particle organization of active zones may have contributed to the observed differences in synaptic safety factor at frog neuromuscular junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01611734
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  • 2
    Electronic Resource
    Electronic Resource
    Absence of sterol-specific complexes at active zones of degenerating and regenerating frog neuromuscular junctions (1986)
    Springer
    Journal of neurocytology 15 (1986), S. 231-240 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Freeze-fracture combined with filipin treatment has been used as a cytochemical probe for membrane cholesterol. As previously shown at the frog neuromuscular junction, distinctive sterol-specific complexes were formed on the presynaptic membrane after filipin treatment, except at active zones. The absence of sterol-specific complexes from active zones was confirmed using two other cytochemical agents — digitonin and saponin. We also studied the maintenance and differentiation of the presynaptic membrane heterogeneity revealed by membrane cholesterol probes at degenerating and regenerating neuromuscular junctions. During degeneration, active zones in frog nerve terminals were disorganized, but still lacked sterol-specific complexes. After engulfing the degenerating nerve terminals, Schwann cells occupied the synaptic gutters and displayed a uniform distribution of sterol-specific complexes. Schwann cell ridges opposite the postjunctional folds also had prominent sterol-specific complexes in regions formerly occupied by active zones. By 2 weeks after nerve crush, nerve terminals reinvaded the endplate region and active zones began to regenerate. While the intramembrane particles of the early regenerating active zones were not arranged in the normal double-rowed organization, filipin-sterol complexes were nevertheless excluded from these primitive active zones. Areas of nerve terminal membrane opposite to junctional folds but lacking active zones were covered with filipin-sterol complexes. These results show that the normal double-rowed organization is not required for the expression of the membrane heterogeneity associated with the active zone. In addition, the absence of sterol-specific complexes is closely associated with the active zone particles and not simply the membrane regions opposite to the postjunctional folds. The membrane heterogeneity does not seem to be directly linked with the functional state of the active zone since it is still associated with degenerating active zones after transmission failure has occurred.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01611659
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Freeze-Fracture of physiologically identified neuromuscular junctions from single frog muscle fibers (1986)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 4 (1986), S. 147-156 
    Details
    ISSN: 0741-0581
    Keywords: Identified neuromuscular junctions ; Freeze fracture ; Active zones ; Synaptic efficacy ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: We developed a technique for freeze-fracturing single physiologically identified neuromuscular junctions. This technique permits direct comparison of quantal content with morphological variables such as active zone length per unit terminal length for the same cell. The technique was developed to elucidate the structural basis for variability in transmitter release at the neuromuscular junction. The procedures were as follows: (1) record quantal content by conventional intracellular recordings; (2) mark cells for identification by fluorescent dye injection; (3) fix and stain endplate cholinesterase; (4) glycerinate and remove single fibers from the muscle; (5) draw endplate morphology; (6) freeze-fracture single muscle fibers; (7) examine in a transmission electron microscope; and (8) photograph and measure nerve terminal membrane ultrastructure. We found that approximately 15% of freeze-fractured single muscle fibers exhibited nerve terminal active zones. To demonstrate the usefulness of this technique, physiological and morphological information from an identified junction is presented. Freeze-fracture of identified cells has several advantages over thin sections, which cannot accurately show such things as active zone length, spacing, or intramembrane particles. This technique also has applications to the study of active zone ultrastructure in situations where neurotransmitter release is known to differ from normal levels. In addition, direct correlations between membrane structure and function can be studied in other preparations by this method.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060040210
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    Paper (German National Licenses)
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