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Elongated profiles of synaptic vesicles in motor endplates. Morphological effects of fixative variations

  • Published:
Journal of Neurocytology

Summary

The effect of different fixation procedures on the ultrastructure and the number of elongated profiles of synaptic vesicles of motor endplates in the rat diaphragm was studied.

With aldehyde fixation, less than 10% of the vesicle profiles are elongated when the fixative contains an isotonic buffer. Increasing or decreasing the molarity of the buffer respectively raises or lowers the percentage of elongated profiles. When the fixative contains a low molarity buffer, raising its molarity with sucrose raises the percentage of elongated profiles even more. By varying the molarity of the buffer rinse after aldehyde fixation, the number of elongated profiles of vesicles can be made to either increase or decrease by respectively increasing and decreasing the molarity of the buffer. Thus after aldehyde fixation, synaptic vesicles are osmotically sensitive and can change shape.

With primary OsO4 fixation, less than 10% of the vesicle profiles are elongated irrespective of the buffer molarity. Thus with OsO4 fixation, synaptic vesicles are no longer osmotically sensitive or able to change shape.

Varying the pH (from 6.0 to 8.0) or the temperature of the fixative (from 4 to 37°C), did not significantly alter the percentage of elongated profiles. However, increasing the temperature of the fixative to 47°C increased the percentage.

These results indicate that certain fixation procedures can produce a high percentage of elongated profiles of vesicles in an excitatory synapse. The possibility is considered that the susceptibility of synaptic vesicles to ‘flattening’ is related to the tonicity of their contents.

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  1. Anatomical Institute, University of Oslo, Karl Johans Gate 47, Oslo 1, Norway

    Helge Korneliussen

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Korneliussen, H. Elongated profiles of synaptic vesicles in motor endplates. Morphological effects of fixative variations. J Neurocytol 1, 279–296 (1972). https://doi.org/10.1007/BF01099939

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  • DOI: https://doi.org/10.1007/BF01099939

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