Figure 3. Dab1 Knockdown Reduces Ih Selectively in Distal Dendrites of CA1 PNs.

(A) Whole cell current clamp voltage recordings from soma of Cre-GFP− (A₁) and Cre-GFP+ (A₂) CA1 PNs. Voltage responses are shown to a series of hyperpolarizing and depolarizing current pulses. Arrows point to pronounced voltage sag following strongest hyperpolarization responses in Cre-GFP−and Cre-GFP+ neurons. Scale bars represent 20 mV, 0.2 s.

(B) Whole cell current clamp recordings from proximal dendrites of Cre-GFP− (B₁) and Cre-GFP+ (B₂) CA1 neurons. Scale bars, 50 mV, 0.1 s.

(C) Whole cell current clamp recordings from distal dendrites of Cre-GFP− (C₁) and Cre-GFP+ (C₂) CA1 neurons. Scale bars, 50 mV, 0.1 s. Note pronounced voltage sag with strongest hyperpolarizations in recordings from GFP- but not GFP+ PN distal dendrites.

(D) Whole cell current clamp voltage recordings from distal dendrites in Cre-GFP− (D₁) and Cre-GFP+ (D₂) neurons before (black traces) and after application of 10 μM ZD7288 (red traces). Scale bars, 50 mV, 0.1 s.

(E) Resting membrane potential (RMP in mV) of Cre-GFP− (control, magenta) and Cre-GFP+ (Dab1 knockdown, green) neurons. Dab1 knockdown caused a significant negative shift in the RMP in distal dendrites (p = 0.036) and a significant positive shift in RMP in the soma (p = 0.006). Number of cells for each condition are displayed on graph.

(F) Dab1 knockdown caused a significant increase in mean input resistance (Rin) selectively in distal dendrites (p = 0.003).

(G) Dab1 knockdown significantly increased the voltage sag ratio (V_sag ratio) in the soma (p = 0.004) and significantly decreased V_sag ratio in the distal dendrites (p = 0.0002). V_sag ratio was measured as (V_peak – V_steady-state)/V_peak × 100%, where V_peak is the maximal hyperpolarized voltage and V_steady-state is the steady-state voltage in response to a given hyperpolarizing current step relative to membrane holding potential.

(H) V_sag ratio measured in distal dendrites of Cre-GFP− and Cre-GFP+ neurons before and after application of ZD7288. ZD7288 significantly decreased sag only in Cre-GFP− neurons (paired t test, p < 0.0001). Plot shows individual cells, min to max (whiskers), median (line), and 25^th to 75^th percentiles (box).

(I) Rin measured in distal dendrites of Cre-GFP− and Cre-GFP+ neurons before and after application of ZD7288. ZD7288 significantly increased Rin in Cre-GFP− neurons (paired t test, p < 0.0001). In the presence of ZD7288, Rin was significantly greater in Cre-GFP+ neurons than in Cre-GFP− neurons (p = 0.035). (J) RMP in distal dendrites of Cre-GFP− and Cre-GFP+ neurons before and after application of ZD7288 (red traces). ZD7288 caused a significant negative shift in the RMP of Cre-GFP− neurons (paired t test, p = 0.001). In the presence of ZD7288, RMP was significantly more negative in Cre-GFP+ neurons than in GFP-neurons (p = 0.036).

See also Figure S7.