Figure 5. Slow Recovery From Synaptic Depression in rbp.

(A) Sample EPSCs evoked by 60-Hz stimulation after a prolonged period of rest (no stimulation for at least 30s; ‘baseline’) and at inter-train intervals (‘ITI’) of 1s (middle) and 10s (right) of a wild type (top) and a drbp synapse (bottom) at 15 mM [Ca²⁺]_e.

(B) Peak amplitudes of the first EPSC of the second ‘test’ train (top) and cumulative EPSC amplitudes (bottom) as a function of ITI of a wild-type (left) and a rbp mutant synapse (right) under baseline conditions (‘− PhTX’). Average data and individual data for each synapse are shown in dark and light colors, respectively. Average data were fitted with a double-exponential function (blue).

(C) Representative EPSC recovery time courses of the indicated genotypes in the presence of PhTX (‘+ PhTX’).

(D) 1^st EPSC: Average slow time constants (‘τ_slow’; left) and fast time constants (‘τ_fast’; right) of exponential fits to the first EPSC amplitudes of the second train (‘1^st EPSC’) of the indicated genotypes at 15 mM [Ca²⁺]_e and 3 mM [Ca²⁺]_e. wt (15mM [Ca²⁺]_e, n=4; 3mM [Ca²⁺]_e, n=7), drbp (15mM [Ca²⁺]_e, n=7) under baseline conditions. cum. EPSC: Average cumulative EPSC amplitudes of the same data set. We did not detect significant changes in the amplitudes of the slow and the fast exponential component for 1^st EPSC and cumulative EPSC data between genotypes.

(E) Average recovery time constants of the 1^st EPSC (left) and cum. EPSC in wild type in the absence and presence of PhTX (‘−/+ PhTX’) at 3mM [Ca²⁺]_e (n=7). There were no significant changes in recovery time constants in the absence and presence of PhTX (all p≥0.29).

(F) Average recovery time constants of the 1^st EPSC (left) and cum. EPSC in drbp in the absence and presence of PhTX (‘−/+ PhTX’) at 15mM [Ca²⁺]_e (n=7). Note the significant slowing of τ_slow upon PhTX application (left; p=0.037).