Fig. 2.

I_h recorded under whole-cell voltage clamp from CA3 (A) and CA1 (B) hippocampal pyramidal neurons at three stages of development: P1, P5, and P20. Currents were elicited by 12-sec-long hyperpolarizations from −60 to −120 mV (in steps of −10 mV) from a holding potential of −50 mV, followed by a step to −65 mV to record tail currents. All recordings were made in the presence of Ba²⁺ (0.5 mm; to blockI_K(ir)), TTX, CNQX, AP-5, and bicuculline. A Ba²⁺-insensitive instantaneous current was seen in some older neurons; it was not studied further.