Svirskis Gytis, Kotak Vibhakar, Sanes Dan H, Rinzel John
Center for Neural Science, New York University, New York, New York 10003, USA.
J Neurosci. 2002 Dec 15;22(24):11019-25. doi: 10.1523/JNEUROSCI.22-24-11019.2002.
Neurons possess multiple voltage-dependent conductances specific for their function. To investigate how low-threshold outward currents improve the detection of small signals in a noisy background, we recorded from gerbil medial superior olivary (MSO) neurons in vitro. MSO neurons responded phasically, with a single spike to a step current injection. When bathed in dendrotoxin (DTX), most cells switched to tonic firing, suggesting that low-threshold potassium currents (I(KLT)) participated in shaping these phasic responses. Neurons were stimulated with a computer-generated steady barrage of random inputs, mimicking weak synaptic conductance transients (the "noise"), together with a larger but still subthreshold postsynaptic conductance, EPSG (the "signal"). DTX reduced the signal-to-noise ratio (SNR), defined as the ratio of probability to fire in response to the EPSG and the probability to fire spontaneously in response to noise. The reduction was mainly attributable to the increase of spontaneous firing in DTX. The spike-triggered reverse correlation indicated that, for spike generation, the neuron with I(KLT) required faster inward current transients. This narrow temporal integration window contributed to superior phase locking of firing to periodic stimuli before application of DTX. A computer model including Hodgkin-Huxley type conductances for spike generation and for I(KLT) (Rathouz and Trussell, 1998) showed similar response statistics. The dynamic low-threshold outward current increased SNR and the temporal precision of integration of weak subthreshold signals in auditory neurons by suppressing false positives.
神经元具有多种与其功能相关的电压依赖性电导。为了研究低阈值外向电流如何在嘈杂背景下改善小信号的检测，我们在体外记录了沙鼠内侧上橄榄核（MSO）神经元的活动。MSO神经元对阶跃电流注入呈现相位反应，产生单个动作电位。当用树突毒素（DTX）处理时，大多数细胞转变为紧张性放电，这表明低阈值钾电流（I(KLT)）参与了这些相位反应的形成。用计算机生成的稳定随机输入序列刺激神经元，模拟微弱的突触电导瞬变（“噪声”），同时施加一个较大但仍低于阈值的突触后电导，即兴奋性突触后电流（EPSG，“信号”）。DTX降低了信噪比（SNR），信噪比定义为对EPSG产生动作电位的概率与对噪声自发产生动作电位的概率之比。这种降低主要归因于DTX处理后自发放电的增加。触发动作电位的反向相关性表明，对于动作电位的产生，具有I(KLT)的神经元需要更快的内向电流瞬变。这种狭窄的时间整合窗口有助于在施加DTX之前，神经元对周期性刺激的放电具有更好的锁相性。一个包含用于动作电位产生和I(KLT)的霍奇金-赫胥黎型电导的计算机模型（Rathouz和Trussell，1998）显示了类似的反应统计结果。动态低阈值外向电流通过抑制误报，提高了听觉神经元中微弱阈下信号的信噪比和时间整合精度。
