CA1 pyramidal neurons undergo intense morphological and electrophysiological changes from the second to third postnatal weeks in rats throughout a critical period associated with the emergence of exploratory behavior. Using whole cell current-clamp recordings in vitro and neurochemical methods, we studied the development of the somatic action potential (AP) waveform and some of the underlying channels in this critical period. At the third postnatal week, APs showed a more hyperpolarized threshold, higher duration and amplitude. Subthreshold depolarization broadened APs and depolarized their peak overshoots more pronouncedly in immature neurons (2 weeks old). These features were mimicked by pharmacologically blocking the fast-inactivating A-type potassium current (I_A) and matched well with the higher concentrations of K_v4.2 and K_v4.3 and the lower concentrations of BK and K_v1.2 channels detected by Western blotting. Repetitive stimulation with high frequency trains (50 Hz) reproduced AP broadening associated to inactivation of the A-type current in immature cells. Moreover, repetitive firing showed changes in AP amplitude consistent with the inactivation of both sodium and potassium subthreshold currents, which resulted in higher AP amplitudes in the more immature neurons. We propose that maturation of AP waveform and excitability in this critical developmental period could be related to the onset of exploratory behaviors.

从出生后第二周到第三周，大鼠CA1锥体神经元在与探究行为有关的关键时期经历了强烈的形态和电生理变化。使用体外全细胞电流钳记录和神经化学方法，我们研究了这个关键时期的体细胞动作电位（AP）波形和一些潜在通道的发展。产后第三周，AP的阈值更加极化，持续时间和振幅更高。在未成熟的神经元（2周龄）中，亚阈值去极化使AP增宽并使其峰过冲更明显。通过药理阻断快速灭活的A型钾电流（I _A），并与Western blotting检测到的较高浓度的K _v 4.2和K _v 4.3以及较低浓度的BK和K _v 1.2通道相匹配。高频刺激（50 Hz）的重复刺激再现了与未成熟细胞中A型电流失活相关的AP增宽。此外，重复发射显示AP振幅的变化与钠和钾亚阈值电流的失活相一致，这会导致较不成熟的神经元中AP振幅更高。我们建议，在这个关键的发育时期，AP波形的成熟和兴奋性可能与探索行为的发生有关。