Rosanova Mario, Timofeev Igor
Department of Anatomy and Physiology, School of Medicine, Laval University, Québec, Canada G1K 7P4.
J Physiol. 2005 Jan 15;562(Pt 2):569-82. doi: 10.1113/jphysiol.2004.071381. Epub 2004 Nov 4.
The slow oscillation (SO) generated within the corticothalamic system is composed of active and silent states. The studies of response variability during active versus silent network states within thalamocortical system of human and animals provided inconsistent results. To investigate this inconsistency, we used electrophysiological recordings from the main structures of the somatosensory system in anaesthetized cats. Stimulation of the median nerve (MN) elicited cortical responses during all phases of SO. Cortical responses to stimulation of the medial lemniscus (ML) were virtually absent during silent periods. At the ventral-posterior lateral (VPL) level, ML stimuli elicited either EPSPs in isolation or EPSPs crowned by spikes, as a function of membrane potential. Response to MN stimuli elicited compound synaptic responses and spiked at any physiological level of membrane potential. The responses of dorsal column nuclei neurones to MN stimuli were of similar latency, but the latencies of antidromic responses to ML stimuli were variable. Thus, the variable conductance velocity of ascending prethalamic axons was the most likely cause of the barrages of synaptic events in VPL neurones mediating their firing at different level of the membrane potential. We conclude that the preserved ability of the somatosensory system to transmit the peripheral stimuli to the cerebral cortex during all the phases of sleep slow oscillation is based on the functional properties of the medial lemniscus and on the intrinsic properties of the thalamocortical cells. However the reduced firing ability of the cortical neurones during the silent state may contribute to impair sensory processing during sleep.
皮质丘脑系统中产生的慢振荡（SO）由活跃状态和静息状态组成。对人和动物丘脑皮质系统中活跃与静息网络状态下反应变异性的研究结果并不一致。为了探究这种不一致性，我们对麻醉猫体感系统的主要结构进行了电生理记录。在SO的所有阶段，正中神经（MN）刺激均可诱发皮质反应。在静息期，几乎没有对内侧丘系（ML）刺激的皮质反应。在腹后外侧（VPL）水平，ML刺激根据膜电位的不同，要么单独诱发兴奋性突触后电位（EPSP），要么诱发伴有锋电位的EPSP。对MN刺激的反应在任何膜电位生理水平下均诱发复合突触反应并产生锋电位。背柱核神经元对MN刺激的反应潜伏期相似，但对ML刺激的逆向反应潜伏期则存在差异。因此，丘脑前上行轴突可变的传导速度最有可能是导致VPL神经元在不同膜电位水平发放时出现大量突触事件的原因。我们得出结论，体感系统在睡眠慢振荡的所有阶段将外周刺激传递至大脑皮质的能力得以保留，这是基于内侧丘系的功能特性以及丘脑皮质细胞的内在特性。然而，皮质神经元在静息状态下发放能力的降低可能会导致睡眠期间感觉处理受损。
