Compartmental model simulations of synaptic kinetics.

<p>Electrotonic attenuation of the synaptic current along the dendrites en route to the soma, results in smaller and slower somatic EPSPs. <b>A, E</b>. A single synaptic contact with a conductance of 3.8 nS was simulated on (<b>A</b>) a spiny stellate or (<b>E</b>) a basket cell dendrite at the location where a putative contact was identified (arrows in <b>B</b> and <b>F</b>, respectively). The decay time constant (τ2) of the conductance in <b>E</b> was faster than in <b>A</b> (1 ms vs. 2.3 ms). The simulated EPSCs and the resulting EPSPs at the synapse are drawn in a thin line. The same EPSPs measured in the soma are drawn with a thick line. In (<b>A</b>) the somatic potential trace was multiplied (×30) to allow direct comparison of the kinetics. The 10% and 90% EPSP amplitudes are marked by the blue lines. Note that the more distal contact simulated in <b>A</b> is more strongly delayed, slowed and attenuated than the proximal contact simulated in <b>E</b>. <b>B–H</b>. A single synaptic activation was simulated successively in all compartments of the spiny stellate (<b>B–E</b>) and smooth basket (<b>F–H</b>) neurons. In each compartment, the latency of the EPSP arrival at the soma and the somatic 10%–90% EPSP rise times were analyzed and compared with the experimentally observed values. The somatic and dendritic compartments were then colored according to the following categories: Black: simulated values lower than the smallest experimentally observed latency or rise time. Grey: simulated values larger than the largest experimentally observed latency or rise time. Blue: simulated values within the range between the smallest and the largest observed values. Red: Mean EPSP latency (average±s.d.). Yellow: Mean EPSP rise time (average±s.d.). Green: Overlapping compartments in which both rise-times and latencies were within the average range. <b>B, F</b>. Latency plots. <b>C, G</b>, Rise time plots. <b>D, H</b>, overlap plots of latencies and rise times. The scale bar is 100 µm. <b>I–L</b>. Simulations were repeated in 5 spiny stellate cells and 1 star pyramid (<b>I, J</b>) and 4 basket cells(<b>K, L</b>) neurons, each presented by a different symbol. <b>I, K</b>, Somatic EPSP latencies plotted against the dendritic distance from the soma for all spiny neurons (<b>I</b>) and basket cell (<b>K</b>) dendrites. <b>J, L</b>, Plots of the rise times at different dendritic distances from the soma. The dashed lines represent the experimental values of the corresponding average+s.d. Red symbols represent the overlap compartments for the latency and rise times in each neuron. Spines in <b>A–D, I–J</b>, were incorporated by scaling Cm and Rm in the dendrites. A faster conductance (as in E) was simulated in <b>F–H, K–L</b>.