Fig. 8.

Depletion and desensitization model of synaptic depression. A, Simulations based on a presynaptic depletion model that does not include receptor desensitization. Trains of 10 stimuli at 200 Hz with P_R values ranging from 0.02 to 0.75. Smaller responses to stimulus #1 correspond to lower P_R values. Time constant of recovery from depression was 100 msec. EPSCs reached similar steady-state values when P_R ranged from 0.15 to 0.75. Inset on right shows the 10th response on an expanded vertical scale. Note that data points are superimposed from trains withP_R of 0.15 to 0.75. Y values (normalized to EPSC₁) for these four data points ranged from 0.075 to 0.079. B, Desensitization was included in the model as described in Materials and Methods. P_R was varied as inA. Steady-state EPSCs were maximal atP_R = 0.15. Inset shows 10th response on an expanded vertical scale. C, EPSC_SS is plotted versus EPSC₁. Results of the presynaptic model are shown by filled circles; results of simulations incorporating postsynaptic desensitization are shown with open circles.