Are inhibitory synaptic conductances on thalamic relay neurons inhomogeneous? Are synapses from individual afferents clustered?

Standard and dynamic current clamps were used to emulate dendritic GABA-Aer gic postsynaptic currents (IPSCs) in a reconstructed thalamic relay neuron. The variability of somatically recorded single events was an order of magn itude smaller than reported in experimental work, suggesting that experimen tally observed variability of miniature IPSCs reflects variable synaptic st rength rather than filtering. Additionally, to evoke physiologic unitary-IP SCs at 0.8 probability-of-release, it was necessary to partially cluster sy napses. This induced nonlinear summation - bringing unitary amplitudes down to the observed range. We conclude that synaptic strength is inhomogeneous and that inhibitory afferents might form synapses in clusters. (C) 2000 El sevier Science B.V. All rights reserved.