Fine structure of synaptic contacts in the first order giant fibre system of the squid
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Masses of uniform boutons with characteristics of chemically transmitting synapses cover the soma and dendrites of the first order giant cell. They are filled with small round agranular zinc iodide-osmium positive synaptic vesicles. Only a few boutons contain large granular vesicles.
Zones with large round agranular zinc iodide-osmium negative synaptic vesicles and a 15 nm wide cleft between the synaptic membranes occur in the contact area of the first to the second order giant axon. However, there are also large zones with gap junctions, characterized by the absence of synaptic vesicles and a narrow, less than 5 nm wide cleft between the apposed membranes. It is postulated that the first to second order giant synapse transmits both chemically and electrically.
Key-WordsSynapse ultrastructure Giant axons Squid
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