Journal of Neurocytology

, Volume 17, Issue 1, pp 3–12 | Cite as

Structural components in the synaptic cleft captured by freeze-substitution and deep etching of directly frozen cerebellar cortex

  • Takao Ichimura
  • Paulo H. Hashimoto


Structural components in the synaptic cleft were examined in cerebellar excitatory synapses by conventional electron microscopy and by rapid freezing followed by freeze-substitution or deep etching. Two transverse components and one parallel element were identified in the clefts of rapidly frozen and freeze-substituted synapses: (i) bridging fibrils, 4–6 nm in diameter, that span the cleft; (ii) columnar pegs, 4–6 nm wide and 8–15 nm high, projecting from the postsynaptic surface; and (iii) intervening fine fibrils running parallel to the apposed synaptic membranes. These were more clearly visible in deep-etched synapses, although the postsynaptic pegs were difficult to distinguish from intramembrane particles in the cross-fractured postsynaptic membranes. Deep etching also revealed other fibrils on the cytoplasmic surface of the postsynaptic membrane. These appear to contact the membrane surface or the intramembrane particles. Freeze-substituted materials also displayed the fibrillar components in the postsynaptic dense fuzz, but failed to display the presynaptic dense projections typically observed in thin sections or deep-etched replicas of the conventionally fixed materials. The bridging fibrils are likely to play a mechanical role in holding the synapse together, while the short pegs may be integral parts of the receptor molecules.


Fibril Cerebellar Cortex Synaptic Cleft Postsynaptic Membrane Excitatory Synapse 
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Copyright information

© Chapman and Hall Ltd 1988

Authors and Affiliations

  • Takao Ichimura
    • 1
  • Paulo H. Hashimoto
    • 1
  1. 1.Department of AnatomyOsaka University Medical SchoolKitakuJapan

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