Steriade M, Timofeev I
Laboratoire de Neurophysiologie, Faculté de Médecine, Université Laval, Quebec, Canada G1K 7P4.
J Neurosci. 1997 May 15;17(10):3778-95. doi: 10.1523/JNEUROSCI.17-10-03778.1997.
The intrathalamic mechanisms of frequency-dependent augmenting responses were investigated in decorticated cats by means of intracellular recordings from thalamocortical (TC) neurons in ventrolateral (VL) nucleus, including simultaneous impalements from two TC neurons. Pulse trains (10 Hz) applied to VL nucleus elicited two types of augmenting responses: (1) in 68% of cells, the incremental responses occurred on a progressive depolarization associated with the decrease in IPSPs produced by preceding stimuli in the train; (2) in the remaining cells, progressively growing low-threshold (LT) responses resulted from the enhancement of Cl--dependent IPSPs, giving rise to postinhibitory rebound bursts, followed by a self-sustained sequence of spindle waves. Although in some TC cells the augmenting responses developed from LT responses once the latter reached a given level of depolarization, other neurons displayed augmenting responses immediately after the early antidromic spike that depolarized the neuron to the required level, without an intermediate step of LT rebound. Repeated pulse trains led to a progressive and persistent increase in slow depolarizing responses of TC cells, as well as to a persistent and prolonged decrease in the amplitudes of the IPSPs. On the basis of parallel experiments, we propose that the two types of augmentation in TC cells are a result of contrasting responses of thalamic reticular neurons evoked by repetitive thalamic stimuli: decremental responses, which may account for disinhibition leading to depolarizing responses in TC cells, and incremental responses, explaining the progressive hyperpolarization of TC cells. These data demonstrate that frequency-dependent changes in neuronal excitability are present in the thalamus of a decorticated hemisphere and suggest that short-term plasticity processes in the gateway to the cerebral cortex may decisively influence cortical excitability during repetitive responses.
通过对去皮质猫腹外侧（VL）核的丘脑皮质（TC）神经元进行细胞内记录，包括同时对两个TC神经元进行穿刺，研究了频率依赖性增强反应的丘脑内机制。施加到VL核的脉冲序列（10Hz）引发了两种类型的增强反应：（1）在68%的细胞中，增量反应发生在与该序列中先前刺激产生的IPSPs减少相关的渐进性去极化上；（2）在其余细胞中，逐渐增强的低阈值（LT）反应源于Cl-依赖性IPSPs的增强，产生抑制后反弹爆发，随后是一连串自发的纺锤波。虽然在一些TC细胞中，一旦LT反应达到给定的去极化水平，增强反应就从LT反应发展而来，但其他神经元在早期逆向冲动使神经元去极化到所需水平后立即显示出增强反应，而没有LT反弹的中间步骤。重复的脉冲序列导致TC细胞的缓慢去极化反应逐渐持续增加，以及IPSPs幅度持续延长减小。基于平行实验，我们提出TC细胞中的两种增强类型是丘脑网状神经元对重复性丘脑刺激的对比反应的结果：递减反应，可能解释导致TC细胞去极化反应的去抑制，以及增量反应，解释TC细胞的渐进性超极化。这些数据表明，去皮质半球的丘脑中存在神经元兴奋性的频率依赖性变化，并表明大脑皮层通路中的短期可塑性过程可能在重复性反应期间决定性地影响皮层兴奋性。
