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 necessary to maintain a readily releasable pool of transmitter. To what extent are the dynamics of vesicle recycling subject to modulation? We examined the influence of presynaptic GABA(B) receptors on vesicle dynamics at single synapses using optical imaging of FM1-43 in cultured rat hippocampal neurons. The kinetics of FM1-43 destaining indicate that synapses from a single neuron have a unimodal distribution of release probabilities, and GABA(B)-mediated inhibition occurs uniformly at all sites. Electrical and optical recordings from single cells show that 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.