Freeze-etched postsynaptic membranes in the visual cortex reveal different types of synapses including mixed synapses.

The intramembranous structure of the postsynaptic membranes in the rat visual cortex was examined. Simple, complex and mixed synapses were differentiated according to the shape of the postsynaptic particle aggregations. The present data support the existence of all intermediate stages schematically presented in the hypothesis describing a synapse division. The advantage of the freeze-etching technique for the study of the shape of the active zones is emphasized.