Figure 4.

Basket cell ephaptic coupling is absent in the Kcna1^V408A/+ cerebellum. (a) Cumulative event plots, constructed from 100 trials, showing ChR2-expressing basket cell activity (top) in response to threshold light stimulation. Below: connected Purkinje cell activity after pinceau-positive or pinceau-negative basket cell stimulation (2 example cells for each condition, 100 repeated trials). (b) Duration of Purkinje cell inhibition in response to basket cell light activation for pinceau-positive and negative pairs (interval with > 20% change in instantaneous Purkinje cell activity). (c) Plot of average change in Purkinje cell frequency following basket cell light stimulation in visually scored pinceau connections (pinceau-positive n = 11, pinceau-negative n = 7; shading represents 95% CI). (d) Instantaneous change in Purkinje cell firing frequency in 400 μs bins following basket cell light activation with the GABA_A receptor blocker picrotoxin (100 μM; pinceau-positive n = 8, pinceau-negative n = 6). (e) Baseline-normalized Purkinje cell firing 2 ms after basket cell light activation in the presence of picrotoxin (Eph), plotted with the normalized Purkinje cell firing rate prior to picrotoxin addition 5 ms after light activation (Syn). Lines connect data from individual Purkinje cells (* p = 0.018, n.s. = not significant). (f) Plot of light-induced change in Purkinje cell firing frequency in response to basket cell excitation in 1 ms intervals relative to light onset in Kcna1^V408A/+ cerebellum (wild type n = 12, Kcna1^V408A/+ n = 9). (g) Normalized minimum in Purkinje cell firing rate following basket cell optogenetic excitation in Kcna1^V408A/+ and control cerebellum. (h) Purkinje cell activity at pinceau-positive connections from Kcna1^V408A/+ cerebellum in the presence of 100 μM picrotoxin in response to optogenetic basket cell stimulation. Mean change in frequency plotted in 400 μs intervals (wild type n = 8, Kcna1^V408A/+ n = 7). (i) Plot of baseline-normalized Purkinje cell firing rate for individual cells during the 2 ms interval following light-on at pinceau-positive connections (** p = 0.010).