Summary
Working with glutaraldehyde fixed, PTA stained rat cerebral cortex, the authors compared the ultrastructural features of synaptosomes with those of intact synaptic junctions. In general there is close correspondence between the two, although the cleft densities and postsynaptic focal densities of synaptosomes show a greater degree of focalization than their counterparts in synaptic junctions. The dense projections have similar profiles in both preparations, but are more difficult to distinguish clearly in synaptosomes on account of the closer packing of the presynaptic network around their apices. The limiting membrane of the presynaptic terminal is usually visible in synaptosomes, but not in synaptic junctions.
Comparing the preparations quantitatively reinforces the qualitative findings, and points to their overall similarity. However a number of the indices in synaptosomes are significantly smaller than the corresponding ones in synaptic junctions, and this points to the operation of a shrinkage factor during fractionation procedures. This is confined to the pre- and post-synaptic components and does not affect the intervening contact region. Histograms of the size distributions of the indices are similar to those obtained for intact synaptic junctions, the majority displaying two peaks.
It is concluded that synaptosomes accurately reproduce the major ultrastructural features of synaptic junctions.
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We would like to thank Mrs. C. Blackshaw for technical help, Mrs. G. Kay for drawing the diagram and Mr. D. Stuart for photographic assistance.
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Jones, D.G., Brearley, R.F. Further studies on synaptic junctions. Z.Zellforsch 125, 432–447 (1972). https://doi.org/10.1007/BF00306652
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DOI: https://doi.org/10.1007/BF00306652