[Characteristics of the synaptic apparatus of the parietal associative cortex (area 5b) in the cat brain].

An electron microscopic examination of the associative cerebral cortex (area 5b) in cat was performed. The average density of axonal terminal profiles in this area was 263 +/- 16 terminals per 1000 micron2 of the slice area. 75.5% of axonal terminals contained synaptic vesicles and had asymmetric or symmetric contacts with visible active zones. 8.4% of axonal terminals had contacts without visible active zones. 24.5% of axonal terminals contained synaptic vesicles, but had no visible contacts with neighbouring structures. 84.9% of axonal terminals contained round or slightly elongated vesicles, 7.8% --a mixture of round and elongated vesicles and 7.3%--thin elongated vesicles. Among the axonal terminals with visible synaptic contacts 46.6% were of the axo-spine type, 50%--of axo-dendritic type and 3.4%--of axo-somatic type. 77% of axo-somatic terminals contained elongated vesicles and had symmetric contacts and 23% contained round vesicles and had asymmetric contacts.