Deletion of postsynaptic NL3 causes an increase in glutamate release probability at synapses on PV interneurons. (a) Representative traces (top) and plot (bottom) show increased input-output relationship of AMPAR EPSCs in cells lacking NL3 for incremental stimulation intensities (in V) 2.5, 5,7.5,10, 12.5, 15, 17.5 and 20 (PV-Cre, 12.3 ± 7.1, 49.8 ± 21.6, 114.9 ± 34.7, 181.1 ± 56.5, 241.3 ± 68.8, 252.4 ± 78.5, 224.6 ± 62.1, 215.1 ± 56.4, n = 7 cells; NL3fl/PV-Cre, 4.9 ± 2.0, 74.5 ± 12.5, 189.7 ± 32.5, 319.8 ± 55.8, 446.8 ± 59.7, 563.4 ± 77.6, 576.5 ± 75.3, 521.2 ± 72.7, n = 7 cells; p= 0.33, 0.34, 0.14, 0.10, 0.02, 0.01, 0.003, 0.006 for each stimulus intensity) (b) Representative average traces (top) and plot (bottom) show reduced paired pulse ratios at inter-stimulus intervals of 20, 50, 100 and 200 ms in cells lacking NL3 (PV-Cre, 2.5 ± 0.1, 2.2 ± 0.1, 1.6 ± 0.1, 1.4 ± 0.1, n = 11 cells; NL3fl/PV-Cre, 1.8 ± 0.1, 1.6 ± 0.1, 1.4 ± 0.1, 1.1 ± 0.1, n = 12 cells; p < 0.01, 0.01, 0.05, 0.05 for each inter-stimulus interval). (c–d) (top) sample traces showing spontaneous EPSCs. (bottom) cumulative distribution plot for AMPAR sEPSC amplitudes (c) and frequency (d) showing unchanged sEPSC amplitude and increased sEPSC frequency as a result of NL3 deletion (p = 0.3, Mann-Whitney test for amplitude, p = 0.03 Mann-Whitney test for frequency). Inset shows average sEPSC amplitudes (c) (PV-Cre, 20.5 ± 0.9 pA, n= 10 cells; NL3fl/PV-Cre, 22.1 ± 1.8 pA, n= 10 cells) and mEPSC frequency (d) (PV-Cre, 17.9 ± 1.4 Hz, n = 10 cells; NL3fl/PV-Cre, 23.6 ± 1.6 Hz, n= 10 cells) (e) Representative traces (top) for 1st, 10th, 50th and 120th NMDAR EPSC at +40 mV following 10 min wash-in of 40 μM MK-801 and summary time course (bottom) showing an accelerated block of NMDAR EPSC in cells lacking NL3. (f) Double exponential fit for the weighted decay time constant of MK-801 block (top) in PV-Cre and NL3fl/PV-Cre cells and summary bar graph with mean decay time constant of MK 801 block (bottom) (PV-Cre, τw = 215 ± 25 ms, n = 6 cells; NL3fl/PV-Cre, 112 ± 19 ms, n = 5 cells; p < 0.05 ).