I _h in cell bodies and dimorphic terminals of Hcn-deficient mice. Representative traces of I_h generated from voltage steps between −144 and −64 mV in 10-mV increments recorded from cell bodies (A, C, E, and G) or dimorphic terminals (B, D, F, and H). (A and B) Representative traces from wild-type mice. (C–H) Representative traces from Hcn1 (C and D)-, Hcn2 (E and F)-, or Hcn1/2 (G and H)-deficient neurons. I_h was completely absent in Hcn1/2 calyx terminals (H) but remained in cell bodies (G). The residual current in H is likely the fast potassium inward rectifier I_K1. (I–P) Biophysical properties from wild-type and Hcn1-, Hcn2-, and Hcn1/2-deficient neuron cell bodies (I, K, M, and O) and calyx terminals (J, L, N, and P). Asterisks indicate statistical significance relative to wild-type: *, P < 0.05; **, P < 0.01; ***, P < 0.001. The number of samples is shown inside the bars for each condition. Error bars indicate mean ± SEM.