MRC Toxicology Unit, Hodgkin Building, University of Leicester, Leicester LE1 9HN, UK.
Neuron. 2011 Sep 8;71(5):911-25. doi: 10.1016/j.neuron.2011.06.028.
Offset responses upon termination of a stimulus are crucial for perceptual grouping and gap detection. These gaps are key features of vocal communication, but an ionic mechanism capable of generating fast offsets from auditory stimuli has proven elusive. Offset firing arises in the brainstem superior paraolivary nucleus (SPN), which receives powerful inhibition during sound and converts this into precise action potential (AP) firing upon sound termination. Whole-cell patch recording in vitro showed that offset firing was triggered by IPSPs rather than EPSPs. We show that AP firing can emerge from inhibition through integration of large IPSPs, driven by an extremely negative chloride reversal potential (E(Cl)), combined with a large hyperpolarization-activated nonspecific cationic current (I(H)), with a secondary contribution from a T-type calcium conductance (I(TCa)). On activation by the IPSP, I(H) potently accelerates the membrane time constant, so when the sound ceases, a rapid repolarization triggers multiple offset APs that match onset timing accuracy.
刺激终止时的偏移反应对于感知分组和间隙检测至关重要。这些间隙是声音通信的关键特征，但能够产生快速听觉刺激偏移的离子机制一直难以捉摸。偏移发射发生在脑干上的上橄榄核复合体 (SPN) 中，该核在声音期间受到强大的抑制，并在声音终止时将其转换为精确的动作电位 (AP) 发射。体外全细胞膜片钳记录显示，偏移发射是由 IPSP 而非 EPSP 触发的。我们表明，AP 发射可以通过整合由极其负的氯离子反转电位 (E(Cl))驱动的大 IPSP 从抑制中产生，与大的超极化激活非特异性阳离子电流 (I(H))相结合，具有来自 T 型钙电流 (I(TCa))的次要贡献。在 IPSP 的激活下，I(H)有力地加速了膜时间常数，因此当声音停止时，快速去极化触发多个与起始时间精度匹配的偏移 AP。
