Fuentealba Pablo, Crochet Sylvain, Timofeev Igor, Steriade Mircea
Laboratoire de Neurophysiologie, Faculté de Médecine, Université Laval, Québec G1K 7P4, Canada.
J Neurophysiol. 2004 May;91(5):1990-8. doi: 10.1152/jn.01105.2003.
To study the interactions between thalamic and cortical inputs onto neocortical neurons, we used paired-pulse stimulation (PPS) of thalamic and cortical inputs as well as PPS of two cortical or two thalamic inputs that converged, at different time intervals, onto intracellularly recorded cortical and thalamocortical neurons in anesthetized cats. PPS of homosynaptic cortico-cortical pathways produced facilitation, depression, or no significant effects in cortical pathways, whereas cortical responses to thalamocortical inputs were mostly facilitated at both short and long intervals. By contrast, heterosynaptic interactions between either cortical and thalamic, or thalamic and cortical, inputs generally produced decreases in the peak amplitudes and depolarization area of evoked excitatory postsynaptic potentials (EPSPs), with maximal effect at approximately 10 ms and lasting from 60 to 100 ms. All neurons tested with thalamic followed by cortical stimuli showed a decrease in the apparent input resistance (R(in)), the time course of which paralleled that of decreased responses, suggesting that shunting is the factor accounting for EPSP's decrease. Only half of neurons tested with cortical followed by thalamic stimuli displayed changes in R(in). Spike shunting in the thalamus may account for those cases in which decreased synaptic responsiveness of cortical neurons was not associated with decreased R(in) because thalamocortical neurons showed decreased firing probability during cortical stimulation. These results suggest a short-lasting but strong shunting between thalamocortical and cortical inputs onto cortical neurons.
为了研究丘脑和皮层输入对新皮层神经元的相互作用，我们在麻醉猫中，对丘脑和皮层输入采用配对脉冲刺激（PPS），以及对汇聚到细胞内记录的皮层和丘脑皮层神经元上的两个皮层或两个丘脑输入在不同时间间隔进行PPS。同突触皮质 - 皮质通路的PPS在皮质通路中产生易化、抑制或无显著影响，而皮层对丘脑皮层输入的反应在短间隔和长间隔时大多表现为易化。相比之下，皮层与丘脑或丘脑与皮层输入之间的异突触相互作用通常会使诱发的兴奋性突触后电位（EPSP）的峰值幅度和去极化面积减小，在约10毫秒时效果最大，持续60至100毫秒。所有接受丘脑刺激后再给予皮层刺激测试的神经元，其表观输入电阻（R（in））均降低，其时间进程与反应降低的时间进程平行，这表明分流是EPSP降低的原因。只有一半接受皮层刺激后再给予丘脑刺激测试的神经元显示R（in）有变化。丘脑中的锋电位分流可能解释了那些皮层神经元突触反应性降低但R（in）未降低的情况，因为丘脑皮层神经元在皮层刺激期间放电概率降低。这些结果表明，丘脑皮层和皮层输入对皮层神经元之间存在短暂但强烈的分流。
