Skip to main content
SpringerLink
Log in

Structure and ultrastructure of the frog motor endplate

A freeze-etching study

  • Published:
Cell and Tissue Research Aims and scope Submit manuscript

Summary

The frog motor endplate in its simplest form consists of an elongated, slender nerve ending embedded in a gutter-like depression of the sarcolemma. This nerve terminal contains the usual synaptic organelles. It is covered by a thin coating of Schwann cell cytoplasm which embraces the terminal with thin finger-like processes from both sides, thereby sub-dividing it into 300–1000 regularly spaced compartments. The individual synaptic compartments correspond to the strings of varicosities or grape-like configurations of motor nerve terminals in endplates of other species and in the cerebral neuropil of vertebrates.

Each compartment contains one or more bar-like densities of the presynaptic membrane, ‘active zones’, which are associated with the attachment sites between synaptic vesicles and plasmalemma. Active zones have a regular transverse arrangement and occur at specific loci opposite the junctional folds. The attachment sites for synaptic vesicles are at the edges of the bars which are bilaterally delineated by a double row of 10 nm particles attached to the A-face. The structural appearance of vesicle attachment sites in freeze-etch replicas corresponds to that of micropinocytosis. The active zones are often fragmented and the frequency of their association with vesicle attachment sites is highly variable.

The junctional folds are characterized by “specific sites” in which intramembranous particle aggregations occur at relatively high packing density (7500/μm2). These sites are located opposite the active zones at the juxtaneural lips, a location where one would expect ACh-sensitive receptors on the postsynaptic membrane.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Akert, K., Moor, H., Pfenninger, K., Sandri, C.: Contribution of new impregnation methods and freeze-etching to the problems of synaptio fine structure. In: Mechanism of synaptic transmission (ed. K. Akert and P. Waser). Progr. Brain Res. 31, 223–240 (1969)

  • Akert, K., Peper, K.: Ultrastructure of chemical synapses: a comparison between synaptic membrane complexes of the motor endplate and the synaptic junction in the CNS. Golgi Centennial Symposium (ed. M. Santini). New York: Raven Press 1974 (in press)

    Google Scholar 

  • Betz, W., Sakmann, B.: “Disjunction” of frog neuromuscular synapses by treatment with proteolytic enzymes. Nature (Lond.), New Biol. 232, 94–95 (1971)

    Google Scholar 

  • Betz, W., Sakmann, B.: Effects of proteolytic enzymes on function and structure of frog neuromuscular junction. J. Physiol. (Lond.) 230, 673–688 (1973)

    Google Scholar 

  • Birks, R., Huxley, H. E., Katz, B.: The fine structure of the neuromuscular junction of the frog. J. Physiol. (Lond.) 150, 134–144 (1960)

    Google Scholar 

  • Ceccarelli, S., Hurlbut, W. P., Mauro, A.: Depletion of vesicles from frog neuromuscular junctions by prolonged tetanic stimulation. J. Cell Biol. 54, 30–38 (1972)

    Google Scholar 

  • Cole, W. V.: Motor endings in striated muscle of vertebrates. J. comp. Neurol. 102, 671–716 (1955)

    Google Scholar 

  • Couteaux, R.: Sur les gouttières synaptiques du muscle strié. C. R. Soc. Biol. (Paris) 140, 270–271 (1946)

    Google Scholar 

  • Couteaux, R.: Contribution à l'étude de la synapse myoneurale. Rev. canad. Biol. 6, 563–711 (1947)

    Google Scholar 

  • Couteaux, R.: Localization of cholinesterase at neuromuscular junctions. Int. Rev. Cytol. 4, 335–375 (1955)

    Google Scholar 

  • Couteaux, R.: Morphological and cytochemical observations on the post-synaptic membrane at motor end-plates and ganglionic synapses. Exp. Cell Res., Suppl. 5, 294–322 (1958)

    Google Scholar 

  • Couteaux, R.: Motor end-plate structure. In: The structure and function of muscle. Vol. 2: Structure (ed. G. H. Bourne), p. 337–380, New York and London: Academic Press 1960

    Google Scholar 

  • Couteaux, R.: Principaux critéres morphologiques et cytochimiques utilisables aujourd'hui pour définir les divers types de synapses. Actualités Neurophysiol., 3° sér., 145–173 (1961)

  • Couteaux, R.: The differentiation of synaptic areas. Proc. roy. Soc. B 158, 457–480 (1963)

    Google Scholar 

  • Couteaux, R., Pécot-Dechavassine, M.: L'ouverture des vésicules synaptiques au niveau des “zones actives”. In: Septième Congr. Internat, de Microscopie Electronique, Grenoble, vol. 3, 709–710 (1970a)

    Google Scholar 

  • Couteaux, R., Pécot-Dechavassine, M.: Vésicules synaptiques et poches au niveau des “zones actives” de la jonction neuromusculaire. C. R. Acad. Sc. (Paris) 271, 2346–2349 (1970b)

    Google Scholar 

  • Dreyer, F., Peper, K.: A monolayer preparation of innervated skeletal muscle fibres of the M. cutaneus pectoris of the frog. Pflügers Arch. 348, 257–262 (1974)

    Google Scholar 

  • Dreyer, F., Peper, K., Akert, K., Sandri, C., Moor, H.: Ultrastructure of the “active zone” in the frog neuromuscular junction. Brain Res. 62, 373–380 (1973)

    Google Scholar 

  • Hall, Z. W., Kelly, R. B.: Enzymatic detachment of endplate acetylcholinesterase from muscle. Nature (Lond.), New Biol. 232, 62–63 (1971)

    Google Scholar 

  • Heuser, J. E., Reese, T. S.: Evidence for recycling of synaptic vesicle membrane during transmitter release at the frog neuromuscular junction. J. Cell Biol. 57, 315–344 (1973)

    Google Scholar 

  • Katz, B.: The release of neural transmitter substances. Liverpool: University Press 1969

    Google Scholar 

  • Koelliker, A.: Untersuchungen über die letzten Endigungen der Nerven. Mit 4 Kupfertafeln. Leipzig: W. Engelmann 1862

    Google Scholar 

  • Koenig, J., Pécot-Dechavassine, M.: Relations entre l'apparition des potentiels miniatures et l'ultrastructure des plaques motrices en voie de réinnervation et de néoformation chez le rat. Brain Res. 27, 43–57 (1971)

    Google Scholar 

  • Kuehne, W.: Über die peripherischen Endorgane der motorischen Nerven. Mit 5 Tafeln. Leipzig: W. Engelmann 1862

    Google Scholar 

  • Kuehne, W.: Die Verbindung der Nervenscheiden mit dem Sarkolemm. Z. Biol. 19, 501–534 (1883)

    Google Scholar 

  • Kuehne, W.: Neue Untersuchungen über motorische Nervenendigungen. Z. Biol. 23, 1–148 (1887)

    Google Scholar 

  • McMahan, U. J., Spitzer, N. C., Peper, K.: Visual identification of nerve terminals in living isolated skeletal muscle. Proc. roy. Soc. B 181, 421–430 (1972)

    Google Scholar 

  • McNutt, N. S., Weinstein, R. S.: Membrane ultrastructure at mammalian intercellular junctions. In: Progress in biophysics and molecular biology (ed. J.A.V. Butler and D. Noble), vol. 26, p. 47–101. Oxford: Pergamon 1973

    Google Scholar 

  • Moor, H.: Recent progress in the freeze-etching technique. Phil. Trans. B. 261, 121–131 (1971)

    Google Scholar 

  • Moor, R., Muehlethaler, K.: Fine structure in frozen-etched yeast cells. J. Cell Biol. 17, 609–628 (1963)

    Google Scholar 

  • Nickel, E., Potter, L. T.: Ultrastructure of isolated membranes of Torpedo electric tissue. Brain Res. 57, 508–517 (1973)

    Google Scholar 

  • Reger, J. P.: The fine structure of neuromuscular synapse of gastrocnemii from mouse and frog. Anat. Rec. 130, 7–24 (1958)

    Google Scholar 

  • Retzius, G.: Zur Kenntnis der motorischen Nervenendigungen. Biol. Untersuchungen, N. F. 3, 41–52 (1892)

    Google Scholar 

  • Robertson, J. D.: Some features of the ultrastructure of reptilian skeletal muscle. J.biophys. biochem. Cytol. 2, 369–380 (1956)

    Google Scholar 

  • Robertson, J. D.: The ultrastructure of a reptilian myoneural junction. J. biophys. biochem. Cytol. 2, 381–394 (1956)

    Google Scholar 

  • Sandri, C., Akert, K., Livingston, R. B., Moor, H.: Particle aggregations at specialized sites in freeze-etched postsynaptic membranes. Brain Res. 41, 1–16 (1972)

    Google Scholar 

  • Satir, B., Schooley, C., Satir, P.: Membrane fusion in a model system. Mucocyst secretion in Tetrahymena. J. Cell Biol. 56, 153–176 (1973)

    Google Scholar 

  • Streit, P., Akert, K., Sandri, C., Livingston, R. B., Moor, H.: Dynamic ultrastructure of presynaptic membranes at nerve terminals in the spinal cord of rats. Anesthetized and unanesthetized preparations compared. Brain Res. 48, 11–26 (1972)

    Google Scholar 

  • Waser, P. G.: On receptors in the postsynaptic membrane of the motor endplate. In: Ciba Foundation Symposium on Molecular Properties of Drug Receptors, p. 59–75. London: Churchill 1970

    Google Scholar 

  • Zacks, S. I.: The motor endplate, p. 321. Philadelphia and London: Saunders 1964

    Google Scholar 

Download references

Author information

Authors and Affiliations

  1. II. Physiologisches Institut der Universität des Saarlandes, D-665, Homburg/Saar, Germany

    K. Peper & F. Dreyer

  2. Brain Research Institute, University of Zürich, Switzerland

    C. Sandri & K. Akert

  3. Laboratory of Electron microscopy, Department of General Botany, Federal Institute of Technology, Zürich, Switzerland

    H. Moor

Authors
  1. K. Peper
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. F. Dreyer
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. C. Sandri
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. K. Akert
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. H. Moor
    View author publications

    You can also search for this author in PubMed Google Scholar

Additional information

This work was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 38, Projekt N), The Swiss National Foundation for Scientific Research (Grants Nr. 3 82372 and 3 77472) and the Dr. Eric Slack-Gyr Foundation Zürich.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Peper, K., Dreyer, F., Sandri, C. et al. Structure and ultrastructure of the frog motor endplate. Cell Tissue Res. 149, 437–455 (1974). https://doi.org/10.1007/BF00223024

Download citation

  • Received:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF00223024

Key words

Search

Navigation