Figure 5.

Fractional destaining of GABAergic boutons. The fractional destaining rate, f (see Materials and Methods), is an estimate of the average amount of release induced by an action potential in a given interval. A, Top graphs show group data for f as a function of stimulus number. f remained constant throughout 2 Hz stimulation (left) but transiently increased with 10 Hz stimulation (right). The stimulus trains in A1 started at t = 0; thus, the first f value that could be obtained is after 15 sec of stimulation. To compare f after equal numbers of stimuli, f was calculated after 150 and 300 stimuli for the individual boutons that made up the group data in these plots. Representative data from two slices are shown replotted in A2, where each line represents an individual bouton. Most individual values of f increase (mean f = 0.52) between 150 and 300 stimuli with 10 Hz stimulation (n = 112 boutons) but not with 2 Hz stimulation (mean f = 0.19; 63 boutons). The filled circles represent the means of the groups. B, Group data (n = 4 slices; 278 boutons) showing effects of 10 μm nifedipine on destaining induced by 10 Hz stimulation in the presence of agatoxin. Data in C are from 101 individual boutons (○) and the mean of those boutons (•) from a single slice showing that the transient enhancement of f is blocked (mean f = 0.22) by nifedipine. Graph in the bottom right shows that nifedipine (○) blocked the transient enhancement of f. Control data (•) are replotted from A (bottom) for comparison.