Figure 1. HCN1^f/fcre EC layer III neurons are hyperexcitable despite a hyperpolarized RMP.

(a) Typical electrophysiological recordings obtained from HCN1^f/wt and HCN1^f/fcre EC layer III neuron somata at the normal RMP. The traces were obtained by applying a series of 400 ms hyperpolarizing and depolarizing current steps from −100 pA to + 200 pA as shown in the schematic. Note that the HCN1^f/fcre neuron RMP is substantially more hyperpolarized compared with that of the HCN1f^/wt neuron. The scale shown applies to both traces. (b) Representative traces obtained when 100 pA hyperpolarizing pulses were applied from a fixed potential of −70 mV to measure the R_N. (c–e) Graphs depicting the mean RMP values, average numbers of action potentials elicited with 400 ms depolarizing current pulses applied either at the RMP (solid lines) or at −70 mV (dashed lines) and mean R_N measured at −70 mV using 100 pA hyperpolarizing current steps respectively. (f) Example single and 50 Hz trains of αEPSPs obtained by injecting alpha waveforms (see Methods) in HCN1^f/wt and HCN1^f/fcre neuron somata. The traces were obtained at a fixed potential of −70 mV. (g,h) Bar graphs showing the mean amplitude and decay time constant (τ) of single αEPSPs in HCN1^f/wt and HCN1^f/fcre neurons respectively. (i) The average summation ratios of 20 Hz (open squares) and 50 Hz (solid squares) trains of αEPSPs in HCN1^f/wt and HCN1^f/fcre neuron somata. The numbers of observations for each point are indicated in parenthesis. The significance (p) values are shown for all comparisons except for the graph in (d). Here, asterisks denote significance at p < 0.05 when compared with appropriate controls.