A Well-Defined Readily Releasable Pool with Fixed Capacity for Storing Vesicles at Calyx of Held
Fig 9
Correlations between steady state supply of reluctant vesicles and short-term plasticity during submaximal stimulation.
Data are color coded by age: magenta circles are from animals aged 14–15 days; green squares were 16–18 days; and blue x’s were 19–21 days. A. Steady state unreleased fraction of the RRP remaining after 100Hz stimulation vs the paired-pulse ratio when synapses were rested (top panel) and vs the half-decay time for responses during the preceding 100Hz stimulation (bottom panel). The steady state fraction was calculated without theory by dividing the cumulative response after the frequency jump by the cumulative response during trials where stimulation was 300Hz from the start. Half-decay time was estimated as the 50% point in the cumulative response when stimulation was 100Hz from the start. In both cases, cumulative responses were calculated after subtracting the steady state (green lines in Fig 7A); calculating the steady state unreleased fraction instead as the index generated for Fig 3D yielded a similar result. Straight lines are best fits; p < 0.001 for both panels. B. Capacity of the low pv subdivision of the RRP assuming the parallel model of vesicle recruitment vs the same measures of short-term plasticity used in Panel (A). The procedure factors out variation in new vesicle recruitment and release (see Lemma 7; upper bound for was used; one experiment was excluded because the recording quality was too low to estimate the steady state response size, which is required for calculating
; p < 0.01 for both correlations; R2 = 64% for the top panel, and 50% for the lower).