CHANGES IN THE NEURONAL PLASMA-MEMBRANE DURING SYNAPTOGENESIS

During synaptogenesis the plasma membrane of neurons undergoes conside rable changes and large portions of it develop to synaptic membranes. This transformation is brought about by biochemical and morphological changes. The aim of the present investigation was to study by morpholo gical methods the in vivo changes of some basic components of the neur onal membranes during the early postnatal period, when active synaptog enesis occurs. The cerebral cortex of Wistar rats was used for prepara tion of either growth cones (up to postnatal day 10) or synaptosomes ( postnatal days 14-30). Our studies were focused on the changes occurri ng in integral membrane proteins and cholesterol domains, and in certa in carbohydrate residues and anionic sites. In the first days after bi rth relatively few intramembranous particles are found in the plasma m embranes of growth cones, few and small cholesterol domains, scarce le ctin-binding and anionic sites. During the following days there is a c lear tendency for increase of the number of all of the studied structu res until the appearance of typical synaptic membranes. Throughout the studied developmental period the protein and the cholesterol molecule s were found to occupy distinct membrane domains. The structure of the developing neuronal membrane, poor on proteins and cholesterol, and i ts maturation to the fully functional synaptic membrane is discussed.