Ionic basis of neuronal hyperexcitability

在本财政年度，该项目最重要的成就是实施了物理文献中的控制理论策略，用于抑制碱化鱿鱼巨轴突的节律性放电。鱿鱼轴突是强健的起搏器细胞，当细胞内pH值升高到7.8或更高时，在25赫兹下连续放电数小时。当电池在电压箝位条件下保持在该电位时，它们确实有一个被称为- 55mv的“固定点”，在这个固定点上，净膜电流为零。然而，电压钳方法与深部脑刺激无关。而且，不动点是不稳定的。在电压钳关闭后，有节奏的射击立即恢复。我们已经用一种叫做动态箝位的技术抑制了放电，在这种技术中，电压波形被实时监控，与电压成比例的电流信号被延迟注入细胞。延迟的参考点是最近动作电位最大超调的时间。当延时处于无扰动起搏器周期的60%点且反馈增益处于适当水平时，放电立即停止。电池接近其固定点，因此反馈电路注入的电流立即降至零，或接近于零。膜电位远离固定点，因为这一点是不稳定的，但反馈电路施加电流以防止它远离该点超过几mV。这是一种抑制超兴奋性的机制，一旦放电停止，只需要很少的电流。平坦的基线永远不可能达到，但动作电位的激发被消除了。我们目前正在研究这些结果与深部脑刺激方法的相关性。

The most significant accomplishment of this project during the current fiscal year has been the implementation of a control theory strategy from the physics literature for suppressing rhythmic firing in alkalinized squid giant axons. Squid axons are robust pacemaker cells firing at 25 Hz for hours on end when the intracellular pH is elevated to 7.8, or higher. They do have what is known as a "fixed point" at -55 mV where the net membrane current is zero when the cell is held at that potential in voltage clamp conditions. However, voltage clamp methodology is not relevant to deep brain stimulation. Moreover, the fixed point is unstable. Rhythmic firing resumes immediately after the voltage clamp is turned off. We have suppressed firing with a technique knows as a dynamic clamp in which the voltage waveform is monitored in real time and a current signal proportional to the voltage is injected back into the cell with a delay. The reference point for the delay is the time of the maximum overshoot of the most recent action potential. When the delay is at the 60% point of the unperturbed pacemaker cycle and the feedback gain is at the appropriate level, firing stops immediately. The cell is close to its fixed point and so the current injected by the feedback circuit immediately drops to zero, or close to zero. The membrane potential moves away from the fixed point since this point is unstable, but the feedback circuit applies current to keep it from moving more than a few mV away from that point. This is a mechanism for suppressing hyperexcitability in which very little current is required once firing has ceased. A flat baseline can never be achieved, but firing of action potentials is eliminated. We are currently investigating the relevance of these results for deep brain stimulation methodologies.