[Synaptogenesis in organotypic tissue cultures of the central nervous system]

The growth cones of differentiating neurone processes and developmental synaptic formation in organotypic rat hippocampus cultures have been studied with the electron microscope. The vesicular structures ("growth" and synaptic vesicle) appearing in growth cones and in terminal axonal boutons, even before specialized synaptic membrane formation, are the earliest indications of synaptogenesis. First immature synapses are formed on day 5--7 on the growth cones. Most of them represent passant axo-dendritic synapses, axo-somatic and axo-spine-dendritic appearing later. Electrophysiological investigations agree with morphological data, showing the stable spontaneous activity to correspond to the time periods when immature synapses are detected in the explants, while the formation of impulse flows of two types (single and packed discharges) exhibits a rapid increase of morphologically mature synapses in the process of cultivation.