Summary
Dorsal root fibers were labeled with cobaltous chloride iontophoresis for electron microscopic investigations. In the base of the dorsal horn, where most of the coarser collaterals of dorsal root fibers terminate, many dorsal root terminals were found in postsynaptic relation to synapsing profiles. According to their morphological characteristics, three kinds of presynaptic terminals could be discerned in these complex synapses: axon terminals with spheric vesicles, axon terminals with flattered vesicles and presynaptic dendrites. These latter terminals contained relatively few flattened vesicles accumulated adjacent to a short synaptic articulation surface, and they were rich in cytoplasmic organelles. The functional significance of these structural specializations in the mediation of dorsal root potentials and recurrent inhibition is discussed.
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Barker, J.L., Nicoll, R.A., Padjen, A.: Studies on convulsants in the isolated frog spinal cord. II. Effects on root potentials. J. Physiol. (Lond.) 245, 537–548 (1975)
Barron, D.H., Matthews, B.H.C.: The interpretation of potential changes in the spinal cord. J. Physiol. (Lond.) 92, 276–321 (1938)
Brookhart, J.M., Kubota, K.: Studies of the integrative function of the motor neurone. In: Brain Mechanisms, Progress in Brain Research, Vol. 1 (eds. Moruzzi et al.). Amsterdam: Eisevier 1963
Conradi, S.: On motoneuron synaptology in adult cats. Acta physiol. scand. Suppl. 332, 1–115 (1969)
Czéh, G.: The role of dendritic events in the initiation of monosynaptic spikes in the frog motoneurons. Brain Res. 39, 505–509 (1972)
Czéh, G.: Dendritic responses of frog motoneurons produced by antidromic activation. Neuroscience 1, 469–475 (1976)
Czéh, G.: Ventral root elicited depression of the dorsal root evoked response in frog motoneurons. Exp. Brain Res. 27, 441–449 (1977)
Dowling, J.E.: Synaptic arrangements in the vertebrate retina: The photoreceptor synapse. In: Synaptic Transmission and Neuronal Interaction (ed. M.V.L. Bennett). New York: Raven Press 1974
Eccles, J.C.: The mechanism of synaptic transmission. Ergebn. Physiol. 51, 299–430 (1961)
Eccles, J.C.: Presynaptic inhibition in the spinal cord. In: Physiology of Spinal Neurons. Progress in Brain Research, Vol. 12 (eds. J.C. Eccles and J.P. Schadé). Amsterdam: Elsevier 1964
Eccles, J.C. Malcolm, J.L.: Dorsal root potentials of the spinal cord. J. Neurophysiol. 9, 139–160 (1946)
Glusman, S., Rudomin, P.: Presynaptic modulation of synaptic effectiveness of afferent and ventrolateral tract fibers in the frog spinal cord. Exp. Neurol. 45, 474–490 (1974)
Glusman, S., Vázquez, G., Rudomin, P.: Ultrastructural observations in the frog spinal cord in relation to the generation of primary afferent depolarization. Neurosci. Letters 2, 137–145 (1976)
Gray, E.G.: A morphological basis for presynaptic inhibition? Nature (Lond.) 193, 82–83 (1962)
Grinnell, A.D.: Electrical interaction between antidromically stimulated frog motoneurones and dorsal root afferents: enhancement by gallamine and TEA. J. Physiol. (Lond.) 210, 17–43 (1970)
Khattab, F.J.: A complex synaptic apparatus in spinal cord of cats. Experientia (Basel) 24, 690–691 (1968)
Magherini, P.C., Precht, W., Schwindt, P.C.: Evidence for electrotonic coupling between frog motoneurons in the in situ spinal cord. J. Neurophysiol. 39, 474–500 (1976)
Meij, H.S., Holemans, K.C.: Inhibitory interaction between motoneurones of adjacent segments in the frog spinal cord. Exp. Neurol. 23, 174–185 (1969)
Rall, W.: Dendritic neuron theory and dendro-dendritic synapses in a simple cortical system. In: The Neurosciences: Second Study Program (eds. F.O. Schmitt et al.). New York: Rockefeller University Press 1970
Ralston III, H.J.: The organization of the substantia gelatinosa Rolandi in the cat lumbosacral cord. Z. Zellforsch. 57, 1–23 (1965)
Réthelyi, M.: Ultrastructural synaptology of Clarke's column. Exp. Brain Res. 11, 159–174 (1970)
Réthelyi, M., Szentágothai, J.: The large synaptic complexes of the substantia gelatinosa. Exp. Brain Res. 7, 258–274 (1969)
Schmidt, R.F.: Control of the access of afferent activity to somatosensory pathways. In: Handbook of Sensory Physiology, Vol. II, Somatosensory System (ed. A Iggo). Berlin-Heidelberg-New York: Springer 1973
Shepherd, G.M.: The olfactory bulb as a simple cortical system: experimental analysis and functional implications. In: The neurosciences: Second Study Program (eds. F.O. Schmitt et al.). New York: Rockefeller University Press 1970
Székely, G.: The morphology of motoneurons and dorsal root fibers in the frog's spinal cord. Brain Res. 103, 275–290 (1976)
Székely, G., Gallyas, F.: Intensification of cobaltous sulphide precipitate in frog nervous tissue. Acta biol. Acad. Sci. hung. 26, 175–188 (1975)
Székely, G., Kosaras, B.: Dendro-dendritic contacts between frog motoneurons shown with the cobalt labeling technique. Brain Res. 108, 194–198 (1976)
Timm, F.: Der histochemische Nachweis der normalen Schwermetalle der Leber. Histochemie 2, 150–162 (1960)
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Székely, G., Kosaras, B. Electron microscopic identification of postsynaptic dorsal root terminals: a possible substrate of dorsal root potentials in the frog spinal cord. Exp Brain Res 29, 531–539 (1977). https://doi.org/10.1007/BF00236190
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DOI: https://doi.org/10.1007/BF00236190