Demir R, Haberly L B, Jackson M B
Center for Neuroscience, University of Wisconsin Medical School, Madison Wisconsin 53706, USA.
J Neurosci. 1999 Feb 15;19(4):1294-306. doi: 10.1523/JNEUROSCI.19-04-01294.1999.
When near-threshold electrical stimulation is used to evoke epileptiform discharges in brain slices, a latent period of up to 150 msec elapses before the discharge begins. During this period most neurons are silent, and abnormal electrical activity is difficult to detect with microelectrodes. A fundamental question about epileptiform activity concerns how synchronous discharges arise abruptly in a relatively quiescent slice. This issue was addressed here by using voltage imaging techniques to study epileptiform discharges in rat piriform cortex slices. These experiments revealed two distinct forms of electrical activity during the latent period. (1) A steeply increasing depolarization, referred to here as onset activity, has been described previously and occurs at the site of discharge onset. (2) A sustained depolarization that precedes onset activity, referred to here as plateau activity, has not been described previously. Plateau and onset activity occurred in different subregions of the endopiriform nucleus (a region of high seizure susceptibility). When cobalt or kynurenic acid was applied focally to inhibit electrical activity at the site of plateau activity, discharges were blocked. However, application of these agents to other nearby sites (except the site of onset) failed to block discharges. Plateau activity represents a novel form of electrical activity that precedes and is necessary for epileptiform discharges. Discharges thus are generated in a sequential process by two spatially distinct neuronal circuits. The first circuit amplifies and sustains activity initiated by the stimulus, and the second generates the actual discharge in response to an excitatory drive from the first.
当使用接近阈值的电刺激在脑片中诱发癫痫样放电时，在放电开始前会有长达150毫秒的潜伏期。在此期间，大多数神经元处于静息状态，用微电极很难检测到异常电活动。关于癫痫样活动的一个基本问题是，在相对静止的脑片中，同步放电是如何突然出现的。本文通过使用电压成像技术研究大鼠梨状皮质脑片中的癫痫样放电来解决这个问题。这些实验揭示了潜伏期内两种不同形式的电活动。（1）一种急剧增加的去极化，在此称为起始活动，此前已有描述，发生在放电起始部位。（2）一种在起始活动之前出现的持续去极化，在此称为平台活动，此前尚未有描述。平台活动和起始活动发生在内梨状核的不同亚区域（癫痫易感性高的区域）。当局部应用钴或犬尿烯酸抑制平台活动部位的电活动时，放电被阻断。然而，将这些药物应用于其他附近部位（起始部位除外）未能阻断放电。平台活动代表了一种在癫痫样放电之前出现且对其必不可少的新型电活动形式。因此，放电是由两个空间上不同的神经元回路依次产生的。第一个回路放大并维持由刺激引发的活动，第二个回路则响应来自第一个回路的兴奋性驱动产生实际放电。
