Haas Julie S, White John A
Department of Biomedical Engineering, Center for BioDynamics, Boston University, Boston, Massachusetts 02215, USA.
J Neurophysiol. 2002 Nov;88(5):2422-9. doi: 10.1152/jn.00598.2002.
Electrophysiologically, stellate cells (SCs) from layer II of the medial entorhinal cortex (MEC) are distinguished by intrinsic 4- to 12-Hz subthreshold oscillations. These oscillations are thought to impose a pattern of slow periodic firing that may contribute to the parahippocampal theta rhythm in vivo. Using stimuli with systematically differing frequency content, we examined supra- and subthreshold responses in SCs with the goal of understanding how their distinctive characteristics shape these responses. In reaction to repeated presentations of identical, pseudo-random stimuli, the reliability (repeatability) of the spiking response in SCs depends critically on the frequency content of the stimulus. Reliability is optimal for stimuli with a greater proportion of power in the 4- to 12-Hz range. The simplest mechanistic explanation of these results is that rhythmogenic subthreshold membrane mechanisms resonate with inputs containing significant power in the 4- to 12-Hz band, leading to larger subthreshold excursions and thus enhanced reliability. However, close examination of responses rules out this explanation: SCs do show clear subthreshold resonance (i.e., selective amplification of inputs with particular frequency content) in response to sinusoidal stimuli, while simultaneously showing a lack of subthreshold resonance in response to the pseudo-random stimuli used in reliability experiments. Our results support a model with distinctive input-output relationships under subthreshold and suprathreshold conditions. For suprathreshold stimuli, SC spiking seems to best reflect the amount of input power in the theta (4-12 Hz) frequency band. For subthreshold stimuli, we hypothesize that the magnitude of subthreshold theta-range oscillations in SCs reflects the total power, across all frequencies, of the input.
在电生理方面，内侧内嗅皮层（MEC）第II层的星状细胞（SCs）具有4至12赫兹的阈下固有振荡特征。这些振荡被认为会产生一种缓慢的周期性放电模式，这可能有助于体内海马旁回的θ节律。我们使用具有系统不同频率成分的刺激，研究了星状细胞的阈上和阈下反应，目的是了解它们的独特特征如何塑造这些反应。在对相同的伪随机刺激进行重复呈现时，星状细胞放电反应的可靠性（可重复性）关键取决于刺激的频率成分。对于在4至12赫兹范围内具有更大功率比例的刺激而言，可靠性最佳。对这些结果最简单的机制解释是，产生节律的阈下膜机制与在4至12赫兹频段具有显著功率的输入发生共振，导致更大的阈下波动，从而提高了可靠性。然而，对反应的仔细检查排除了这种解释：星状细胞在对正弦刺激的反应中确实表现出明显的阈下共振（即对具有特定频率成分的输入进行选择性放大），而在对可靠性实验中使用 的伪随机刺激的反应中却同时表现出缺乏阈下共振。我们的结果支持一个在阈下和阈上条件下具有独特输入 - 输出关系的模型。对于阈上刺激，星状细胞放电似乎最能反映θ（4至12赫兹）频段的输入功率量。对于阈下刺激，我们假设星状细胞阈下θ范围振荡的幅度反映了所有频率输入 的总功率。
