EFFECTS OF MEMBRANE VOLTAGE ON RECEPTIVE-FIELD PROPERTIES OF LATERAL GENICULATE NEURONS IN THE CAT - CONTRIBUTIONS OF THE LOW-THRESHOLD CA-2+ CONDUCTANCE
EFFECTS OF MEMBRANE VOLTAGE ON RECEPTIVE-FIELD PROPERTIES OF LATERAL GENICULATE NEURONS IN THE CAT - CONTRIBUTIONS OF THE LOW-THRESHOLD CA-2+ CONDUCTANCE
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DOI：
10.1152/jn.1992.68.6.2185
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发表时间：
1992-12-01
影响因子：
2.5
通讯作者：
SHERMAN, SM
中科院分区：
文献类型：
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作者：
LU, SM;GUIDO, W;SHERMAN, SM
1. 丘脑中继细胞，包括外侧膝状核的中继细胞，表现出低阈值尖峰（LT 尖峰），这是由于 Ca2+ 电导增加而导致的大去极化。通常，每个 LT 尖峰的峰值是 2 到 7 个动作电位的爆发，我们将其称为 LT 爆发。 LT 尖峰与电压相关，因为如果细胞的静息膜电位去极化程度超过大约 -60 mV，则 LT 尖峰将失活，但如果超极化程度更高，则尖峰失活，并且可以通过去极化（例如来自传入兴奋性突触后电位 (EPSP)）来激活。因此，丘脑中继细胞显示两种响应模式：中继或强直模式，当细胞去极化且 LT 尖峰失活时，导致动作电位的强直放电；和突发模式，当细胞超极化并倾向于用 LT 尖峰及其相关的动作电位突发做出反应时。 2．我们对 LT 尖峰对视觉诱发信号通过膝状体中继细胞传递到视觉皮层的贡献感兴趣。我们对麻醉、麻痹的猫体内膝状体细胞进行细胞内记录，以研究膜电压的影响，从而研究 LT 尖峰的存在或不存在对漂移正弦波光栅响应的影响。我们监测了 14 个膝状神经元（6 个 X、7 个 Y 和 1 个未分类）在 LT 尖峰失活或去失活的不同膜电位下的视觉诱发反应。3．在视觉刺激过程中改变膜电压可以在中继模式和突发模式之间切换每个细胞的响应模式。在突发模式下，LT 尖峰与视觉刺激同相发生，而不是以与视觉刺激不相关的节律间隔发生。对于任何给定的刺激周期，细胞通常以 LT 爆发或强直反应做出反应，并且刺激周期很少引起超过一次 LT 爆发。有时，一个周期会同时引起 LT 爆发和强直反应，但总是先发生 LT 爆发。4．细胞的空间调谐特性作为膜电位的函数并没有显着差异，因为 LT 爆发的调谐与强直反应成分的调谐非常相似。尽管我们没有获得完整的时间调谐特性，但我们确实注意到超极化细胞在几个时间频率下对 LT 爆发做出了可靠的响应。5。在响应线性方面，LT 突发和强直响应分量之间存在一致的差异。我们通过计算响应的基波和二次谐波傅里叶振幅（分别为 F1 和 F2）来测量这一点。 F1 幅度代表响应的线性部分，F2 幅度代表响应非线性的度量。我们发现，对于每个细胞，LT 爆发的 F2 与 F1 比率比强直反应成分要高得多。6。我们发现与 LT 尖峰相关的突发的尖峰间隔小于或等于 4 毫秒。然而。我们注意到了这一点。在相对去极化期间，细胞可以在中继模式期间以突发响应，其尖峰间隔也小于或等于 4 ms。这似乎只是反映了随着细胞变得更加去极化，放电率越来越高。我们将中继发射模式期间的这种突发称为高阈值（HT）突发，因为它们与 1. T 尖峰无关，因此源自与传统动作电位相关的较高阈值。7。最后，我们能够制定可靠的经验标准来区分 LT 爆发和强直反应成分，这些标准仅基于动作电位的时间模式。我们发现，由于 HT 突发，LT 突发的短暂峰间间隔不足以作为标准。然而，LT 突发的另一个特点是在 HT 突发期间没有出现之前的静默期。这个静默期大于或等于 100 毫秒，除非我们使用时间频率 >8 Hz 的视觉刺激；对于更高的频率，我们发现大于或等于 50 ms 的静默期，随后是短暂的尖峰间隔，可以成功识别 LT 突发。这允许使用细胞外记录来研究 LT 尖峰，从而提供一种更实用的方法来定量研究 LT 爆发和紧张反应成分对视觉反应的单独贡献。
1. Thalamic relay cells, including those of the lateral geniculate nucleus, display a low-threshold spike (LT spike), which is a large depolarization due to an increased Ca2+ conductance. Typically riding the crest of each LT spike is a burst of from two to seven action potentials, which we refer to as the LT burst. The LT spike is voltage dependent, because if the cell's resting membrane potential is more depolarized than roughly -60 mV, the LT spike is inactivated, but if more hyperpolarized, the spike is deinactivated and can be activated by a depolarization, such as from an afferent excitatory postsynaptic potential (EPSP). Thalamic relay cells thus display two response modes: a relay or tonic mode, when the cell is depolarized and LT spikes are inactivated, leading to tonic firing of action potentials; and a burst mode, when the cell is hyperpolarized and tends to respond with LT spikes and their associated bursts of action potentials.2. We were interested in the contribution of the LT spike on the transmission of visually evoked signals through geniculate relay cells to visual cortex. We recorded intracellularly from geniculate cells in an anesthetized, paralyzed, in vivo cat preparation to study the effects of membrane voltage, and thus the presence or absence of LT spikes, on responses to drifting sine-wave gratings. We monitored the visually evoked responses of 14 geniculate neurons (6 X, 7 Y, and 1 unclassified) at different membrane potentials at which LT spikes were inactivated or deinactivated.3. Changing membrane voltage during visual stimulation switched the response mode of every cell between the relay and burst modes. In the burst mode, LT spikes occurred in phase with the visual stimulus and not at rhythmic intervals uncorrelated to visual stimuli. To any given stimulus cycle, the cell responded usually with an LT burst or a tonic response, and rarely was more than one LT burst evoked by a stimulus cycle. Occasionally a single cycle evoked both an LT burst and tonic response, but always the LT burst occurred first.4. The spatial tuning characteristics of the cells did not differ dramatically as a function of membrane potential, because the tuning of the LT bursts was quite similar to that of the tonic response component. Although we did not obtain complete temporal tuning properties, we did note that hyperpolarized cells responded reliably with LT bursts at several temporal frequencies.5. A consistent difference was seen between the LT burst and tonic response components in terms of response linearity. We measured this by computing the fundamental and second harmonic Fourier amplitudes of the responses (F1 and F2, respectively). The F1 amplitude represents the linear portion of the response, and the F2 amplitude represents a measure of response nonlinearity. We found that, for every cell, the F2-to-F1 ratio was considerably higher for the LT burst than for the tonic response component.6. We found that the bursts associated with LT spikes had interspike intervals less-than-or-equal-to 4 ms. However. we noted that. during relative depolarization, cells could respond during the relay mode with bursts also having interspike intervals less-than-or-equal-to 4 ms. This seemed simply to reflect increasingly high firing rates as the cell became more depolarized. We refer to this bursting during the relay firing mode as high-threshold (HT) bursts, because they were not associated with 1. T spikes and thus arose from the higher threshold associated with conventional action potentials.7. Finally, we were able to develop reliable empirical criteria to distinguish the LT burst from the tonic response component, criteria that were based solely on the temporal pattern of action potentials. We found that, because of HT bursts, the brief interspike interval of the LT burst was an insufficient criterion. However, the LT burst was also characterized by a prior silent period not seen during HT bursts. This silent period was greater-than-or-equal-to 100 ms, except when we used visual stimuli at temporal frequencies >8 Hz; for higher frequencies, we found that a silent period greater-than-or-equal-to 50 ms followed by brief interspike intervals successfully identified an LT burst. This permits the use of extracellular recording to study LT spiking, thereby providing a more practical means of quantitatively studying the separate contributions of the LT burst and tonic response components to visual responsiveness.