Nita D A, Steriade M, Amzica F
Laboratoire de neurophysiologie, Faculté de médecine, Université Laval, Quebec, Canada G1K 7P4.
J Physiol. 2003 Oct 1;552(Pt 1):325-32. doi: 10.1113/jphysiol.2003.050310. Epub 2003 Aug 22.
The intrinsic properties of thalamic neurons are influenced by synaptic activities in ascending pathways and corticofugal projections, as well as by the actions of neurotransmitters released by generalised modulatory systems. We focused on the effects of corticothalamic projections on the hyperpolarisation-activated cation current Ih. Intracellular recordings of thalamocortical neurons in the dorsal lateral geniculate (dLG) nucleus were performed in cats under ketamine-xylazine anaesthesia. At variance with the conventional way of recording intracellularly from thalamic neurons after partial or total ablation of the grey and white matter overlying the dLG, we preserved intact corticothalamic neuronal loops. Stimulating electrodes inserted into the optic tract and light-emitting-diodes as photic stimulation were used to identify the dLG neurons. The expression of the depolarising sag due to Ih depended on the state of cortical networks. Thalamic dLG Ih, induced by hyperpolarising current steps, was detected during the periods of cortical disfacilitation that occur during the cortical slow (< 1 Hz) oscillation, whereas Ih was absent during the active (depolarised) periods. The possibility that the excitatory corticothalamic projections could preclude the generation of the Ih was tested by applying a concentrated K+ solution (3 M) to the primary visual cortex. The same dLG neurons that did not display Ih before application of K+ were able to produce hyperpolarisation-activated depolarising sags during K+-induced cortical depression. Our data suggest that the thalamic clock-like delta oscillation, which results from an interplay between Ih and the low-threshold calcium current (IT), as described in preparations without cerebral cortex, is prevented in dLG neurons when corticothalamic loops are intact.
丘脑神经元的内在特性受上行通路和皮质传出投射中的突触活动影响，也受广义调制系统释放的神经递质作用的影响。我们重点研究了皮质丘脑投射对超极化激活阳离子电流Ih的影响。在氯胺酮-赛拉嗪麻醉下，对猫的背外侧膝状体（dLG）核中的丘脑皮质神经元进行细胞内记录。与在dLG上方灰质和白质部分或全部切除后从丘脑神经元进行细胞内记录的传统方法不同，我们保留了完整的皮质丘脑神经元环路。将刺激电极插入视束，并使用发光二极管进行光刺激来识别dLG神经元。由Ih引起的去极化下陷的表达取决于皮质网络的状态。在皮质慢波（<1 Hz）振荡期间发生的皮质去易化期间，通过超极化电流阶跃诱导的丘脑dLG Ih被检测到，而在活跃（去极化）期间则不存在Ih。通过将浓缩的K+溶液（3 M）应用于初级视觉皮层，测试了兴奋性皮质丘脑投射可能阻止Ih产生的可能性。在应用K+之前未显示Ih的相同dLG神经元在K+诱导的皮质抑制期间能够产生超极化激活的去极化下陷。我们的数据表明，如在没有大脑皮层的标本中所描述的，由Ih和低阈值钙电流（IT）之间的相互作用产生的丘脑时钟样δ振荡，在皮质丘脑环路完整时在dLG神经元中被阻止。
