Summary
Representative examples of lowand high-output neuromuscular synapses between motoneuron and distal accessory flexor muscle of the lobster were selected on the basis of their mean quantal content, and subsequently analysed by serial section electron microscopy. The high-output terminal has twice as many synapses as the low-output terminal. However, since the mean surface area of synapses is significantly smaller in the high-output terminal than in the low-output one, the total synaptic surface area between the two types of terminals is similar. Also, though the high-output terminal possesses a greater number of presynaptic dense bodies than its low-output counterpart, the mean number per synapse is similar for the two terminals. The terminals, however, differ significantly in the size of their dense bodies. Thus both the mean and total surface area of these bodies is greater in the high-output terminal than in the low-output one. Moreover, the mean ratio of dense body area to synaptic area is significantly greater for the high-output terminal than for its low-output counterpart. This difference in dense body area parallels the difference in quantal content of synaptic transmission between the lowand high-output terminals and supports the hypothesis that presynaptic densities represent the ultrastructural correlates of transmitter mobilization and/or release.
Similar content being viewed by others
References
Atwood, H.L.: Organization and synaptic physiology of crustacean neuromuscular systems. Prog. Neurobiol. 7, 291–391 (1976)
Atwood, H.L., Jahromi, S.S.: Fast axon synapses of a crab leg muscle. J. Neurobiol. 9, 1–15 (1978)
Atwood, H.L., Morin, W.A.: Neuromuscular and axo-axonal synapses of the crayfish opener muscle. J. Ultrastruct. Res. 32, 351–369 (1970)
Atwood, H.L., Govind, C.K., Jahromi, S.S.: Excitatory synapses of blue crab gastric mill muscles. Cell Tissue Res. 177, 145–158 (1977)
Atwood, H.L., Govind, C.K., Kwan, I.: Non-homogeneous excitatory synapses of a crab stomach muscle. J. Neurobiol. 9, 17–28 (1978)
Bittner, G.D.: Differentiation of nerve terminals in the crayfish opener muscle and its functional significance. J. Gen. Physiol. 51, 731–758 (1968)
Ceccarelli, B., Hurlbut, W.P., Mauro, A.: Turnover of transmitter and synaptic vesicles at the frog neuromuscular junction. J. Cell Biol. 57, 499–524 (1973)
Cohen, M.J.: The crustacean myochordotonal organ as a proprioceptive system. Comp. Biochem. Physiol. 64, 41–54 (1963)
Del Castillo, J., Katz, B.: Quantal components of the endplate potential. J. Physiol. (Lond.) 124, 560–573 (1954)
DeRosa, R.A., Govind, C.K.: Transmitter output increases in an identifiable lobster motoneuron with growth of its muscle fibers. Nature (Lond.) 273, 676–678 (1978)
Dudel, J., Kuffler, S.W.: The quantal nature of transmission and spontaneous miniature potentials at the crayfish neuromuscular junction. J. Physiol. (Lond.) 155, 514–529 (1961)
Finlayson, L.H., Osborne, M.P.: Secretory activity of neurons and related electrical activity. Adv. Comp. Physiol. Biochem. 6, 165–258 (1975)
Govind, C.K., Chiang, R.G.: Correlation between presynaptic dense bodies and transmitter output at lobster neuromuscular synapses by serial section electron microscopy. Brain Res. 161, 377–388 (1979)
Govind, C.K., Atwood, H.L., Lang, F.: Synaptic differentiation in a regenerating crab-limb muscle. Proc. Natl. Acad. Sci. U.S.A. 70, 822–826 (1973)
Govind, C.K., Meiss, D.E., She, J., Yap-Chung, E.: Fiber composition of the distal accessory flexor muscle in several decapod crustaceans. J. Morphol. 157, 151–160 (1978)
Gray, E.G.: Electron microscopy of presynaptic organelles of the spinal cord. J. Anat. 97, 101–106 (1963)
Hoyle, G., McNeil, P.A.: Correlated physiological and ultrastructural studies on specialized muscles. Ic. Neuromuscular junctions in the eyestalk levator muscles of Podophthalmus vigil (Weber). J. Exp. Zool. 167, 523–550 (1968)
Jahromi, S.S., Atwood, H.L.: Three-dimensional ultrastructure of the crayfish neuromuscular apparatus. J. Cell Biol. 63, 599–613 (1974)
Katz, B.: Nerve, Muscle and Synapse. New York: McGraw Hill Book Co. (1966)
Meiss, D.E., Govind, C.K.: Multiterminal innervation: non-uniform density along single lobster muscle fibers. Brain Res. 160, 163–169 (1979a)
Meiss, D.E., Govind, C.K.: Regional differentiation of neuromuscular synapses in a lobster receptor muscle. J. Exp. Biol. In Press (1979b)
Pfenninger, K.H.: Synaptic morphology and cytochemistry. Progr. Histochem. Cytochem. 5, 1–86 (1973)
Sherman, R.G., Atwood, H.L.: Correlated electrophysiological and ultrastructural studies of a crustacean motor unit. J. Gen. Physiol. 59, 586–615 (1972)
Thomas, R.C., Wilson, V.J.: Marking single neurons by staining with intracellular recording microelectrodes. Science (Wash.) 151, 1538–1539 (1966)
Wernig, A., Stirner, H.: Quantum amplitude distributions point to functional unity of the synaptic ‘active zone’. Nature (Lond.) 269, 820–822 (1977)
Wood, M.R., Pfenninger, K.H., Cohen, M.J.: Two types of presynaptic configurations in insect central synapses: an ultrastructural analysis. Brain Res. 130, 22–45 (1977)
Author information
Authors and Affiliations
Additional information
Supported by grants from the National Research Council and Muscular Dystrophy Association of Canada to C.K. Govind. D.E. Meiss is a post-doctoral fellow of the Muscular Dystrophy Association of Canada. We thank Eva Yap-Chung for her expert and unfailing technical assistance
Rights and permissions
About this article
Cite this article
Govind, C.K., Meiss, D.E. Quantitative comparison of low- and high-output neuromuscular synapses from a motoneuron of the lobster (Homarus americanus). Cell Tissue Res. 198, 455–463 (1979). https://doi.org/10.1007/BF00234190
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00234190