Summary
With the aid of the cobalt labelling technique, frog spinal cord motor neuron dendrites of the subpial dendritic plexus have been identified in serial electron micrographs. Computer reconstructions of various lengths (2.5–9.8 μm) of dendritic segments showed the contours of these dendrites to be highly irregular, and to present many thorn-like projections 0.4–1.8 μm long. Number, size and distribution of synaptic contacts were also determined. Almost half of the synapses occurred at the origins of the thorns and these synapses had the largest contact areas. Only 8 out of 54 synapses analysed were found on thorns and these were the smallest. For the total length of reconstructed dendrites there was, on average, one synapse per 1.2 μm, while 4.4% of the total dendritic surface was covered with synaptic contacts. The functional significance of these distal dendrites and their capacity to influence the soma membrane potential is discussed.
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References
Antal, M. (1984) The application of cobalt labelling to electron microscopic investigations of serial sections.Journal of Neuroscience Methods 12, 69–77.
Antal, M., Tornai, I. &Székely, G. (1980) Longitudinal extent of dorsal root fibres in the spinal cord and brain stem of the frog.Neuroscience 5, 1311–22.
Cajal, S. R. Y. (1909)Histologie du système nerveux de l'homme et des vertébrés, Vol. 1. Paris: Maloine.
Conradi, S. (1969) Ultrastructure of dorsal root boutons on lumbosacral motoneurons of the adult cat, as revealed by dorsal root section.Acta physiologica scandinavica, Suppl.332, 85–115.
Corvaja, N. &Grofová, I. (1972) Vestibulospinal projection in the toad. InProgress in Brain Research, Vol. 37,Basic Aspects of Central Vestibular Mechanisms (edited byBrodal, A. &Pompeiano, O.), pp. 297–307. Amsterdam: Elsevier.
Corvaja, N., Grofová, I. &Pompeiano, O. (1973) The origin, course and termination of vestibulospinal fibers in the toad.Brain, Behavior and Evolution 7, 401–23.
Czéh, G. (1972) The role of dendritic events in the initiation of monosynaptic spikes in the frog motoneurons.Brain Research 39, 505–9.
DeFelipe, J., Hendry, S. H. C., Jones, E. G. &Schmechel, D. (1985) Variability in the terminations of GABAergic chandelier cell axons on initial segments of pyramidal cell axons in the monkey sensory-motor cortex.Journal of Comparative Neurology 231, 364–84.
Duval, M. (1895) Hypothèses sur la physiologie des centres nerveux; Théorie histologique du sommeil.Comptes Rendus Société de Biologie, S1047, 74–7.
Görcs, T., Antal, M., Oláh, É. &Székely, G. (1979) An improved cobalt labeling technique with complex compounds.Acta biologica Academiae scientiarum hungaricae 30, 79–86.
Jack, J. J. B., Redman, S. J. &Wong, K. (1981) The components of synaptic potentials evoked in spinal motoneurones by impulses in single group Ia fibres.Journal of Physiology 321, 111–26.
Kawana, E., Sandri, C. &Akert, K. (1971) Ultrastructure of growth cones in the cerebellar cortex of the neonatal rat and cat.Zeitschrift für Zettforschung und mikroskopische Anatomie 115, 248–98.
Lévai, G., Matesz, C. &Székely, G. (1982) Fine structure of dorsal root terminals in the dorsal horn of the frog spinal cord.Acta biologica Academiae scientiarum hungaricae 33, 231–46.
McGuire, B. A., Hornung, J. P., Gilbert, C. D. &Wiesel, T. N. (1984a) Patterns of synaptic input to layer 4 of cat striate cortex.Journal of Neuroscience 4, 3021–33.
McGuire, B. A., Stevens, J. K. &Sterling, P. (1984b) Microcircuitry of bipolar cells in cat retina.Journal of Neuroscience 4, 2920–38.
Rall, W. (1977) Core conductor theory and cable properties of neurons. InHandbook of Physiology, The Nervous System, Vol. 1, Part I (edited byKandel, E. R.) pp. 39–97. Bethesda MD: American Physiological Society.
Rapisardi, S. C. &Miles, T. P. (1984) Synaptology of retinal terminals in the dorsal lateral geniculate nucleus of the cat.Journal of Comparative Neurology 223, 515–34.
Redman, S. Walmsley, B. (1983) Amplitude fluctuations in synaptic potentials evoked in cat spinal motoneurones at identified group Ia synapses.Journal of Physiology 343, 135–45.
Ruigrok, T. J. H., Crowe, A. &Ten Donkelaar, H. J. (1984) Morphology of lumbar motoneurons innervating hindlimb muscles in the turtlePseudemys scripta elegans: an intracellular horseradish peroxidase study.Journal of Comparative Neurology 230, 413–25.
Sala y Pons, C. (1892) Estructura de la médulla espinal de los batricios. Barcelona. As quoted in Cajal (1909), p. 571.
Schwindt, P. C. (1976) Electrical properties of spinal motoneurons. InFrog Neurobiology (edited byLlinás, R. &Precht, W.), pp. 750–64. Berlin, Heidelberg, New York: Springer-Verlag.
Skoff, R. P. &Hamburger, V. (1974) Fine structure of dendritic and axonal growth cones in embryonic chick spinal cord.Journal of Comparative Neurology 153, 107–48.
Székely, G. (1976) The morphology of motoneurons and dorsal root fibers in the frog's spinal cord.Brain Research 103, 275–90.
Székely, G. &Gallyas, F. (1975) Intensification of cobaltous sulphide precipitate in frog nervous tissue.Acta biologica Academiae scientiarum hungaricae 26, 175–88.
Székely, G. &Kosaras, B. (1976) Dendro-dendritic contacts between frog motoneurons shown with the cobalt labelling technique.Brain Research 108, 194–8.
Székely, G. Lévai, G. &Matesz, K. (1983) Primary afferent terminals in the nucleus of the solitary tract of the frog: an electron microscopic study.Experimental Brain Research 53, 109–17.
Urbán, L. &Székely, G. (1983) Intracellular staining of motoneurons with complex cobalt compounds in the frog.Journal of Neurobiology 14, 157–61.
Vaughn, J. E., Henrikson, C. K. &Grieshaber, J. A. (1974) A quantitative study of synapses on motor neuron dendritic growth cones in developing mouse spinal cord.Journal of Cell Biology 60, 664–72.
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Antal, M., Kraftsik, R., Székely, G. et al. Distal dendrites of frog motor neurons: a computer-aided electron microscopic study of cobalt-filled cells. J Neurocytol 15, 303–310 (1986). https://doi.org/10.1007/BF01611433
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DOI: https://doi.org/10.1007/BF01611433