Figure 1.

Short-term plasticity. (A) A sequence of excitatory postsynaptic currents in response to afferent fiber stimulation at 200 Hz (data provided by H. Taschenberger; EPSCs were recorded in the presence of 1 mM kynurenic acid in the bath solution to minimize AMPAR desensitization and saturation and stimulation artifacts were blanked for clarity). (B) Schematic diagram of the expectations for normalized EPSC amplitudes of such an experiment based on Eq. 1. (Gray circles) Amplitude values, which were calculated as the product of p_succ and p_occ. The value p_succ was assumed to double its initial value during facilitation, while p_occ decreases due to vesicle consumption. The product shows the same pattern of facilitation, followed by depression, as the train of EPSCs to the left. (C) A simple diagram of a single-pool model. A pool of vesicles occupying N release sites is assumed to be depleted by release, which is triggered by a train of stimuli at frequency f. Each stimulus depletes a fraction, p_succ, of the remaining vesicles and the vacated sites are reoccupied with a rate constant k₊. If N is the number of sites and n is the time-dependent number of release-ready vesicles, then $\text{d}n/\text{d}t=\left(N-n\right)\times k_{+}-n\times p_{\text{succ}}\times f$.