CSMD3-deficient mice manifest aberrant increased excitability in cerebellar PCs. A, Representative images showing a patch-clamp recorded PC. Left, Light-field image of a patch-clamped cell; middle, biocytin labeling for the patch-clamp recorded cell (red); right, colocalization of biocytin with calbindin (cerebellar PCs marker, green) immunostaining. Scale bars: left, 10 µm; middle and right, 50 µm. B, C, Current-clamp recording of the simple spike firing of depolarized current-evoked PCs. B, Representative traces of PCs simple spike firing evoked by a 300 pA depolarized current (duration, 500 ms) injected into the cells. Calibration: 25 mV, 100 ms. C, Summary of PC spike firing frequency evoked by a series of depolarized currents injected to the cells from 0 to 600 pA in 100 pA increments (wild-type group: n = 15 cells from 3 mice; CSMD3^−/− group: n = 18 cells from 3 mice; CSMD3^−/− vs WT: F_(11,360) = 2.98; p < 0.0001). D, E, Current-clamp recording of spontaneous PC spike firing. D, Representative traces of spontaneous PC spike firing in the wild-type and CSMD3^−/− mice. Calibration: 20 mV, 100 ms. E, Summary of the spontaneous PCs spike firing frequency (wild-type group: n = 11 cells from 6 mice; CSMD3^−/− group: n = 15 cells from 3 mice; CSMD3^−/− vs WT: t₍₂₃₎ = 0.10, p = 0.9199). F, Rheobase of PC spike firing evoked by a depolarized current injection in the wild-type and CSMD3^−/− groups (wild-type group: n = 15 cells from 3 mice; CSMD3^−/− group: n = 18 cells from 3 mice; CSMD3^−/− vs WT: t₍₃₁₎ = 3.03, p = 0.0049). G, Schematic illustrating parameters reflecting the intrinsic membrane properties of PCs by an evoked AP. H, Phase plots of PCs APs evoked by a series of depolarized currents injection in the wild-type and CSMD3^−/− mice. I, J, Summary of threshold potential and action potential half-width in the wild-type and CSMD3^−/− mice (wild-type group: n = 15 cells from 3 mice; CSMD3^−/− group: 18 cells from 3 mice; t₍₃₁₎ = 5.95, p < 0.0001 (I); t₍₃₁₎ = 2.50, p = 0.0181 (J), CSMD3^−/− vs WT). K, L, Summary graphs showing the ISI between the first and the second AP and the AP amplitude (wild-type group: n = 15 cells from 3 mice; CSMD3^−/− group: n = 18 cells from 3 mice; CSMD3^−/− vs WT: t₍₃₁₎ = 3.02, p = 0.005 (K); t₍₃₁₎ = 1.33, p = 0.1923 (L). M, Representative traces illustrating the configuration for measuring the R_in of PCs. A hyperpolarizing current pulse (500 ms) in −50 pA was delivered to the cell to measure membrane R_in. N, Summary graph showing the R_in of PCs in wild-type and CSMD3^−/− mice (n = 15–18 cells from 3 mice/group; CSMD3^−/− vs WT: t₍₃₁₎ = 1.41, p = 0.1637). Data are presented as the mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, two-way ANOVA with Sidak's post hoc test (C); two-tailed unpaired t test for (E, F, I, J, K, L, N).