Figure 3. Syn II deletion increases the RRP size of synchronously released GABA vesicles.

(a) Representative responses from WT (black) and KO (grey) neurons induced by stimulation of the medial perforant path for 2 s at 40 Hz. Stimulation artifacts were removed for clarity. (b) Plot of the normalized amplitude (means±s.e.m.) versus time showing the multiple-pulse depression during the 40-Hz train in WT (black) and KO (grey) neurons. (c) Cumulative amplitude profile of a 2-s train at 40 Hz. Data points from the last second of the response were fitted by linear regression and the line was extrapolated to time 0 to estimate the RRP_syn. (d) Mean values (±s.e.m.) of the amplitude of the first eIPSC in the train, RRP_syn and P_ves for WT (black bars) and KO (open bars) neurons. (e) Cumulative area profile of a 2-s train at 40 Hz. Data points from the last second of the response were fitted by linear regression and the line was extrapolated to time 0 to estimate the RRP_tot. (f) Mean values (±s.e.m.) of the first eIPSC area in the train and RRP_tot for WT (black bars) and KO (open bars) neurons. For electrophysiology experiments: **P<0.01, two-tailed unpaired Student’s t-test and *P<0.05, Welch’s t-test. n=16 and n=14 neurons from WT (5 mice) and KO (8 mice), respectively. (g) Micrographs of GABA-immunopositive synaptic terminals (stained by 10 nm gold particles) making contact with granule cell dendrites in the molecular layer of the dentate gyrus of WT and KO slices. Scale bar, 200 nm. (h) Mean values (±s.e.m.) of the density of total SVs and the number of docked SVs in presynaptic terminals of WT (black bars) and KO (open bars) neurons. For EM experiments: *P<0.05, unpaired Student’s t-test; n=100/39 synapses from 4 WT mice and 69/72 synapses from 4 KO mice.