Lee Charles C, Sherman S Murray
Department of Neurobiology, University of Chicago, Chicago, Illinois 60637, USA.
J Neurophysiol. 2008 Jul;100(1):317-26. doi: 10.1152/jn.90391.2008. Epub 2008 Apr 24.
The thalamus is an essential structure in the mammalian forebrain conveying information topographically from the sensory periphery to primary neocortical areas. Beyond this initial processing stage, "higher-order" thalamocortical connections have been presumed to serve only a modulatory role, or are otherwise functionally disregarded. Here we demonstrate that these "higher-order" thalamic nuclei share similar synaptic properties with the "first-order" thalamic nuclei. Using whole cell recordings from layer 4 neurons in thalamocortical slice preparations in the mouse somatosensory and auditory systems, we found that electrical stimulation in all thalamic nuclei elicited large, glutamatergic excitatory postsynaptic potentials (EPSPs) that depress in response to repetitive stimulation and that fail to activate a metabotropic glutamate response. In contrast, the intracortical inputs from layer 6 to layer 4 exhibit facilitating EPSPs. These data suggest that higher-order thalamocortical projections may serve a functional role similar to the first-order nuclei, whereas both are physiologically distinct from the intracortical layer 6 inputs. These results suggest an alternate route for information transfer between cortical areas via a corticothalamocortical pathway.
丘脑是哺乳动物前脑的一个重要结构，它将来自感觉外周的信息按拓扑结构传递到初级新皮质区域。在这个初始处理阶段之后，“高阶”丘脑皮质连接被认为仅起调节作用，或者在功能上被忽视。在这里，我们证明这些“高阶”丘脑核与“一阶”丘脑核具有相似的突触特性。利用小鼠体感和听觉系统丘脑皮质切片标本中第4层神经元的全细胞记录，我们发现所有丘脑核的电刺激都会引发大的、谷氨酸能兴奋性突触后电位（EPSP），这些电位在重复刺激时会衰减，并且不会激活代谢型谷氨酸反应。相比之下，从第6层到第4层的皮质内输入表现出EPSP增强。这些数据表明，高阶丘脑皮质投射可能具有与一阶核类似的功能作用，而两者在生理上都与皮质内第6层输入不同。这些结果提示了一条通过皮质-丘脑-皮质通路在皮质区域之间进行信息传递的替代途径。
