DELAYED LOCALIZATION OF SYNELFIN (SYNUCLEIN, NACP) TO PRESYNAPTIC TERMINALS IN CULTURED RAT HIPPOCAMPAL-NEURONS

Synelfin is a presynaptic protein of unknown function that is differen tially regulated in the avian song control circuit during the critical period for song learning; in humans, it gives rise to an amyloidogeni c peptide found in senile plaques of Alzheimer's disease. To gain insi ght into the potential involvement of synelfin in synapse development, we investigated its expression in neurons cultured from the embryonic rat hippocampus. These neurons express a variety of defined synaptic proteins, and form numerous synaptic connections after several days in culture, Synapsin I, a synaptic vesicle-associated protein, was detec ted within one day after the neurons were put in culture, but signific ant immunoreactivity for synelfin was not detected until similar to 5 days in vitro (DIV). By 3 DIV, synapsin-positive puncta (previously sh own to correspond to presynaptic specializations) were detected surrou nding the soma and proximal dendritic processes, whereas comparable ag gregations of synelfin did not appear until several days later. By 14 DIV the punctate concentrations of synelfin and synapsin overlapped co mpletely. Thus synelfin is expressed in these cultured neurons and eve ntually becomes localized to presynaptic terminals, but it is absent f rom these specializations when they first form. We conclude that presy naptic terminals can change in molecular composition, and that synelfi n is associated with later stages in synaptic development or modulatio n. (C) Elsevier Science B.V.