Are inhibitory synaptic conductances on thalamic relay neurons inhomogeneous? Are synapses from individual a!erents clustered?

Standard and dynamic current clamps were used to emulate dendritic GABA-Aergic postsynaptic currents (IPSCs) in a reconstructed thalamic relay neuron. The variability of somatically recorded single events was an order of magnitude smaller than reported in experimental work, suggesting that experimentally observed variability of miniature IPSCs re#ects variable synaptic strength rather than "ltering. Additionally, to evoke physiologic unitary-IPSCs at 0.8 probability-of-release, it was necessary to partially cluster synapses. This induced nonlinear summation * bringing unitary amplitudes down to the observed range. We conclude that synaptic strength is inhomogeneous and that inhibitory a!erents might form synapses in clusters. ( 2000 Elsevier Science B.V. All rights reserved.