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The Journal of Neuroscience, April 1, 2003, 23(7):2618
Synapse Density Regulates Independence at Unitary Inhibitory
Synapses
Linda S.
Overstreet and
Gary L.
Westbrook
Vollum Institute, Oregon Health & Science University,
Portland, Oregon 97201
Neurotransmitter transporters may promote synapse specificity by
limiting spillover between release sites. At GABAergic synapses, transport block prolongs synaptic responses when many inputs are activated, yet it is unclear whether transporters alter signaling by
single axons. We found that unitary IPSCs generated by paired recordings between hippocampal interneurons and granule cells could be
either prolonged or totally unaffected by block of GABA transporters.
This variability was explained by the density of active release sites
rather than the number of active sites. Prolongation by transport block
required release from multiple sites and was enhanced by repetitive
activation. Furthermore, transport-sensitive unitary IPSCs were
accelerated when the release probability was reduced, indicating that
cross talk prolonged the time course of IPSCs even when transport was
intact. Our results suggest that the release site density regulates the
degree of cross talk as well as the contribution of transporters to
GABA clearance. Thus, interplay between release site density and
transporter action determines the independence of unitary inhibitory synapses.
Key words:
synaptic transmission; IPSC; transport; independence; density; NO711; dentate gyrus; GABAA
receptor; granule cell
Copyright © 2003 Society for Neuroscience 0270-6474/03/2372618-09$05.00/0
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