Summary
Synaptosomes (nerve-ending particles) prepared from rat cerebral cortex were examined after fixation in glutaraldehyde and block-staining with PTA, in order to investigate the nature of the contact region between the presynaptic component of synaptosomes and their postsynaptic membranes or processes. Two types of synaptosome are described. Type A is distinguished by discontinuous synaptic membrane specializations. It has presynaptic dense projections, postsynaptic densities and, within the cleft, an intermediate band which is intermittently thickened to form cleft densities. The membrane specializations and the cleft densities are situated alongside each other, and together constitute a synaptic subunit. In Type B both synaptic membranes are thickened along their length of apposition, each thickening also forming projections into the adjacent cytoplasm. Within the cleft there are two longitudinally-running bands with, between them, a number of transverse bars.
The classification of synaptosomes into Types A and B is discussed, particular attention being paid to their possible relationship to excitatory and inhibitory synapses. The value of investigating synaptic organization in terms of the contact region of synaptosomes is stressed.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Aghajanian, G.K., andF.E. Bloom: The formation of synaptic junctions in developing rat brain: a quantitative electron microscopic study. Brain Res.6, 716–727 (1967).
Akert, K., K. Pfenninger, andC. Sandri: The fine structure of synapses in the subfornical organ of the cat. Z. Zellforsch.81, 537–556 (1967).
Andersen, P., J.C. Eccles, andY. Loyning: Recurrent inhibition in the hippocampus with identification of the inhibitory cell and its synapses. Nature (Lond.)198, 541–542 (1963).
— —, andP.E. Voorhoeve: Inhibitory synapses on somas of Purkinje cells in the cerebellum. Nature (Lond.)199, 655–656 (1963).
Blackstad, T.W., andP.R. Flood: Ultrastructure of hippocampal axo-somatic synapses. Nature (Lond.)198, 542–543 (1963).
Bloom, F.E., andG.K. Aghajanian: Cytochemistry of synapses: a selective staining method for electron microscopy. Science154, 1575–1577 (1966).
— —: Fine structural and cytochemical analysis of the staining of synaptic junctions with phosphotungstic acid. J. Ultrastruct. Res.22, 361–375 (1968).
Clementi, F., V.P. Whittaker, andM.N. Sheridan: The yield of synaptosomes from the cerebral cortex of guinea pigs estimated by a polystyrene bead ‘tagging’ procedure. Z. Zellforsch.72, 126–138 (1966).
Colonnier, M.: Synaptic patterns on different cell types in the different laminae of the cat visual cortex. An electron microscope study. Brain Res.9, 268–287 (1968).
De Robertis, E.: Electron microscope and chemical study of binding sites of brain biogenic amines. In: Progress in brain research (ed.H.E. Himwich andW.A. Himwich), vol. 8, p. 118–136. Amsterdam: Elsevier 1964.
—, andS. Fiszer: Ultrastructure and cholinergic binding capacity of junctional complexes isolated from rat brain. Brain Res.5, 45–56 (1967).
—, andH.S. Bennett: Some features of the submicroscopic morphology of synapses in frog and earthworm. J. biophys. biochem. Cytol.1, 47–58 (1955).
—, andL. Salganicoff: Electron microscope observations on nerve endings isolated from rat brain. Anat. Rec.139, 220 (1961).
— — — —: Cholinergic and non-cholinergic nerve endings in rat brain. I. J. Neurochem.9, 23–35 (1962).
—, andL.M. Zieher: Isolation of synaptic vesicles and structural organization of the acetylcholine system within brain nerve endings. J. Neurochem.10, 225–235 (1963).
Eccles, J.C.: The physiology of synapses, p. 17–19. Berlin-Göttingen-Heidelberg-New York: Springer 1964.
Gobel, S.: Electron microscopical studies of the cerebellar molecular layer. J. Ultrastruct. Res.21, 430–458 (1968).
Gray, E.G.: Axo-somatic and axo-dendritic synapses of the cerebral cortex: an electron microscope study. J. Anat. (Lond.)93, 420–433 (1959).
—: The granule cells, mossy synapses and Purkinje spine synapses of the cerebellum: Light and electron microscope observations. J. Anat. (Lond.)95, 345–356 (1961).
—: Electron microscopy of presynaptic organelles of the spinal cord. J. Anat. (Lond.)97, 101–106 (1963).
—: Problems of interpreting the fine structure of vertebrate and invertebrate synapses. Int. Rev. Gen. exp. Zool.2, 139–170 (1966).
—, andR.W. Guillery: Synaptic morphology in the normal and degenerating nervous system. Int. Rev. Cytol.19, 111–182 (1966).
—, andV.P. Whittaker: The isolation of synaptic vesicles from the central nervous system. J. Physiol. (Lond.)153, 35–37P (1960).
— —: The isolation of nerve endings from brain: an electron microscopic study of cell fragments derived by homogenization and centrifugation. J. Anat. (Lond.)96, 79–87 (1962).
—, andJ.Z. Young: Electron microscopy of synaptic structure inOctopus brain. J. Cell Biol.21, 87–103 (1964).
Hamlyn, L.H.: Electron microscopy of mossy fibre endings in Ammon's Horn. Nature (Lond.)190, 645–646 (1961).
—: The fine structure of the mossy fibre endings in the hippocampus of the rabbit. J. Anat. (Lond.)96, 112–120 (1962).
—: An electron microscope study of pyramidal neurons in the Ammon's Horn of the rabbit. J. Anat. (Lond.)97, 189–201 (1963).
Israel, M., andV.P. Whittaker: The isolation of mossy fibre endings from the granular layer of the cerebellar cortex. Experientia (Basel)21, 325–326 (1965).
Jones, D.G.: An electron-microscope study of subcellular fractions ofOctopus brain. J. Cell Sci.2, 573–586 (1967).
—: The fine structure of the synaptic membrane adhesions on octopus synaptosomes. Z. Zellforsch.88, 457–469 (1968).
- Specializations of the synaptic region on rat synaptosomes. J. Anat. (Lond.), in press (1969).
Loos, H. van der: Fine structure of synapses in the cerebral cortex. Z. Zellforsch.60, 815–825 (1963).
Luft, J.H.: Permanganate—a new fixative for electron microscopy. J. biophys. biochem. Cytol.2, 799–801 (1956).
Palay, S.L.: Synapses in the central nervous system. J. biophys. biochem. Cytol., Suppl.2, 193–202 (1956).
—: The morphology of the central nervous system. Exp. Cell Res., Suppl.5, 275–293 (1958).
Reynolds, E.S.: The use of lead citrate at high pH as an electron-opaque stain in electron microscopy. J. Cell Biol.17, 208–211 (1963).
Robertson, J.D.: The ultrastructure of cell membranes and their derivatives. Biochem. Soc. Symp.16, 3–43 (1959).
Sabatini, D.D., K. Bensch, andR.J. Barrnett: Cytochemistry and electron microscopy. The preservation of cellular ultrastructure and enzymic activity by aldehyde fixation. J. Cell Biol.17, 19–58 (1963).
Whittaker, V.P.: The isolation and characterization of acetylcholine-containing particles from brain. Biochem. J.72, 694–706 (1959).
—: The binding of acetylcholine by brain particlesin vitro. In: Mechanisms of release of biogenic amines (ed.U.S. von Euler, S. Rosell, andB. Uvnas), p. 147–163. Oxford: Pergamon 1966.
—: The morphology of fractions of rat forebrain synaptosomes separated on continuous sucrose density gradients. Biochem. J.106, 412–417 (1968).
—, andM.N. Sheridan: The morphology and acetylcholine content of isolated cerebral cortical synaptic vesicles. J. Neurochem.12, 363–372 (1965).
Author information
Authors and Affiliations
Additional information
I would like to thank ProfessorsJ. Z. Young, F. R. S. andE. G. Gray for their advice, and also ProfessorK. Akert for very kindly reading the manuscript. I am grateful to Mr.S. Waterman for photographic assistance, and to Mrs.J. Astafiev for drawing the text figure.
Rights and permissions
About this article
Cite this article
Jones, D.G. The morphology of the contact region of vertebrate synaptosomes. Z.Zellforsch 95, 263–279 (1969). https://doi.org/10.1007/BF00968457
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00968457