GABA(B)-MEDIATED PRESYNAPTIC INHIBITION OF EXCITATORY TRANSMISSION AND SYNAPTIC VESICLE DYNAMICS IN CULTURED HIPPOCAMPAL-NEURONS

Local recycling of synaptic vesicle membrane at nerve terminals is nec essary to maintain a readily releasable pool of transmitter. To what e xtent are the dynamics of vesicle recycling subject to modulation? We examined the influence of presynaptic GABA(B) receptors on vesicle dyn amics at single synapses using optical imaging of FM1-43 in cultured r at hippocampal neurons. The kinetics of FM1-43 destaining indicate tha t synapses from a single neuron have a unimodal distribution of releas e probabilities, and GABA(B)-mediated inhibition occurs uniformly at a ll sites. Electrical and optical recordings from single cells show tha t the inhibition of excitatory transmission is entirely accounted for by a rapidly reversible reduction of exocytosis. In contrast, GABA(B) receptors do not alter the rate or extent of endocytosis.