Summary
Electron microscopy of the synaptic morphology of synapses in the cerebral ganglion of the adult ascidian (sea squirt) Ciona intestinalis reveals that the synapses are restricted to the central neuropil of the ganglion. Many of the synapses show a polarity of structure such that pre and post synaptic parts can be identified. The vesicles in the presynaptic bag are of two main diameters 80 and 30 nm respectively. The large vesicles have electron dense contents that vary both in their capacity and dimensions.
The pre and postsynaptic membranes are more electron dense than the surrounding membranes, but they are only slightly thicker. Both the pre and post synaptic membranes have electron dense “dots” some 10 nm in diameter associated with their cytoplasmic surfaces. Sometimes the presynaptic membrane has larger peg-like projections between the vesicles. Associated with the post synaptic membrane are tubules some 10 nm in diameter. These tubules may be the “dots” cut obliquely.
The synaptic cleft material is more electron dense than the surrounding intercellular material, and in it there is a dense line made up of granules about 3–5 nm in diameter. This dense line is usually mid way between the pre and post synaptic membranes, but may be nearer the postsynaptic membrane.
No tight junctions between adjacent nerve process profiles have been observed.
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I wish to thank Professors J. Z. Young, F. R. S. and E. G. Gray for much advice and encouragement, also Dr. R. Bellairs for the use of electron microscope facilities and Mr. R. Moss and Mrs. J. Hamilton for skillful technical assistance.
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Dilly, P.N. Synapses in the cerebral ganglion of adult Ciona intestinalis . Z. Zellforsch. 93, 142–150 (1968). https://doi.org/10.1007/BF00325029
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DOI: https://doi.org/10.1007/BF00325029