POTENTIATION OF EVOKED VESICLE TURNOVER AT INDIVIDUALLY RESOLVED SYNAPTIC BOUTONS

We have studied synaptic plasticity in hippocampal cell cultures using a new imaging approach that allows unambiguous discrimination of pres ynaptic function at the level of single synaptic boutons. Employing a protocol designed to test for use-dependent plasticity resembling N-me thyl-D-aspartate receptor-dependent long-term potentiation (NMDA-type LTP), we find that brief tetanic stimuli induce a potentiation of evok ed synaptic vesicle turnover that lasts for at least 1 hr. Induction o f this clearly presynaptic potentiation is blocked by putative postsyn aptic glutamate receptor antagonists, suggesting that a retrograde ind uction signal might be involved. Potentiation appears to occur approxi mately equally at boutons of low and high initial release probabilitie s, and evidently does not involve an increase in the size of the total recycling synaptic vesicle pool.