Figure 2. CCKBCs and PVBCs inhibit PN firing with similar efficacy.
(A) Representative experiment for testing the capability of a BC to control spike generation in a PN. Sinusoidal current trains were injected into a PN at a theta frequency (3.53 Hz) to initiate firing and three action potentials were evoked at 30 Hz in the presynaptic PVBC 30–40 ms before the peak of the fourth cycle (for details see Materials and methods). Red arrow points to the cycle, when the presynaptic BC was stimulated. Voltage traces are offset for clarity. (B) Summary data of experiments shown in panel A: the firing probability of the PN was significantly suppressed within the cycle when the action potential train was evoked in the presynaptic PVBC. (C) Comparison of the inhibitory efficacy of CCKBCs and PVBCs. The inhibitory efficacy shows the probability of the suppression of action potential generation in the PN by BC firing (i.e.: 1- [PN firing probability during the control sinusoidal current cycles - firing probability when the BC is stimulated]) CCKBC: 76.2 ± 7.1%, n = 25, PVBC: 75.6 ± 6.5%, n = 25, p=0.88, M-W test. (D) The relationship between the inhibitory efficacy and the area of IPSPs. (E) The area of the IPSPs and the charge transfer of the IPSCs are strongly correlated. (F) The relationship between the inhibitory efficacy and IPSC charge transfer, indicating a larger inhibitory efficacy at a larger charge transfer. (G) Representative experiment for testing BCs ability to postpone PN firing. The timing of the evoked action potential in a BC was systematically shifted relative to the peak of the sinusoidal current injected into the PN. (H) The delay in PN firing as a function of the timing of synaptic inhibition in the pair shown in G. Asterisks indicate significant delay in firing compared to the peak of the cycle during the control period (paired sample Wilcoxon signed rank test p<0.05). (I) Pooled data from 7 CCKBC and 6 PVBC pairs. Squares show the average maximal delay (CCKBC: 22.40 ± 4.14 ms, n = 7, PVBC: 23.76 ± 3.16 ms, n = 6, p=0.72, M-W test) and triangles show the average last time point with significant delay in PN firing (CCKBC: −116.21 ± 14.47 ms, PVBC: −102.41 ± 18.58 ms, p=0.94, M-W test). Color codes are the same as in panel C (blue: CCKBCs, orange: PVBCs). Scales: A: 10 mV, 200 ms; G: 10 mV, 50 ms.