003 ± 0.004 ΔG/R [±SD] in spines, n = 22, 4 cells; 0.002 ± 0.002 ΔG/R in spiny branchlets, n = 18, 4 cells). The average spatial profile of the CFCT was obtained by pooling data from 13 cells. In the smooth dendrites, the CFCT remained constant up to ∼70 μm from the soma and decreased markedly in more distal parts (Figure 1E).

Half-maximum occurred at 91 μm from the soma with a steepness of 18 μm (exponential space constant of the logistic fit). In contrast, the amplitude of the CFCTs in spiny branchlets and in spines decreased approximately exponentially with distance from the soma (space constant; λ = 54.5 μm) (Figure 1F). This spatial profile of calcium influx is reminiscent of the electrotonic distribution of membrane potentials in Purkinje cells upon proximal depolarization (Roth and Häusser, 2001), suggesting that calcium

transients result from electrotonic Vorinostat activation of calcium channels in spiny dendrites. In Purkinje cells of Cav3.1 knockout (KO) mice, lacking the main T-type subunit, the amplitude of the CFCTs was reduced to 31% of wild-type (WT) mice (n = 23 cells, p < 0.001) in smooth dendrites and to 25% of WT (n = 24 cell, p < 0.001) in spines and spiny branchlets Enzalutamide mw (Figures 1G and 1H). In contrast, the CFCTs were not significantly inhibited in Cav2.3 KO mice lacking R-type calcium channels (Figures 1G and 1H). The role of Cav3 channels was confirmed by pharmacological block with 1 μM mibefradil (McDonough and Bean, 1998), which reduced

the CFCTs to 61% (p = 0.012) (Figure 1G) and to 46% (p < 0.001) of control in smooth dendrites and in spines and spiny branchlets (Figure 1H), respectively. The spatial profile of the CFCTs recorded from Cav3.1 KO mice was similar to that observed in WT mice, with a half decrement at 93.5 μm (steepness of 16.3 μm) in the smooth dendrites and a λ = 56.3 μm in the spiny dendrites (Figures 1I and 1J). In conclusion, electrotonic filtering of the CF excitatory postsynaptic potential (EPSP) in spiny branchlets reduces calcium signaling at distal PF synapses, which is mainly mediated by T-type channels. We explored whether PF input-mediated glutamatergic signaling might promote CF-evoked dendritic calcium electrogenesis. Selective mGluR1 activation by DHPG potentiated CFCTs by 350% ± 80% in spiny branchlets and by 320% ± STK38 120% in smooth dendrites (n = 8 cells; paired data) (Figures 2A–2D). This effect developed in a few tens of seconds, as DHPG penetrated into the slice and was accompanied by a slower increase of basal calcium concentration (slope 4% ± 1%.min−1 [±SD]) (Figure 2B). The somatic complex spike remained unchanged (Figure S2), confirming that 20 μM DHPG did not depress the CF EPSP (Maejima et al., 2005). Strikingly, the potentiated CFCT no longer showed decrease with distance from the soma (Figure 2E), an effect that cannot be attributed to dye saturation (see Supplemental Information).