Change of conduction velocity by regional myelination yields constant latency irrespective of distance between thalamus and cortex
Change of conduction velocity by regional myelination yields constant latency irrespective of distance between thalamus and cortex
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DOI：
10.1073/pnas.0937380100
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发表时间：
2003-05-13
影响因子：
11.1
通讯作者：
Kimura, F
中科院分区：
文献类型：
--
作者：
Salami, M;Itami, C;Kimura, F
大范围的感觉皮质接受来自丘脑小得不成比例的核的输入，这导致丘脑传入神经之间的旅行距离有很大的差异。然而，从丘脑到皮质细胞的潜伏期在整个大脑皮层是非常恒定的(通常约为2毫秒)。在这里，我们发现了一种机制，可以在丘脑皮质传入神经元中产生潜伏期的不变性，而不考虑旅行距离的可变性。通过刺激丘脑腹基底核(VB)和白质(WM)，从小鼠丘脑皮质脑片IV层细胞记录的兴奋性突触后电流计算传导速度(CV)。在成人中，VB到WM的CV(CVVB-WM；3.28+/-0.11m/S)大约是WM到IV层细胞(CVWM-IV；0.33+/-0.05m/S)的10倍。通过刺激白质细胞记录VB细胞的逆行单位反应来确认CVVB-WM。从CVWM-IV中排除突触延迟并不能解释CV的10倍差异。组织化学染色显示，VB to WM髓鞘密度较高，而皮质髓鞘染色较弱。我们还发现，这种形态和生理特征是平行发展的，并在出生后4周左右完成。考虑到VB到WM在传入神经元之间比皮质内区域更长，长度变化更大，这种巨大的CV差异使得传导时间严重依赖于皮质内区域的长度，而皮质内区域的长度相对恒定。我们的发现很可能提供了一种连接多个地点的一般策略，而不考虑大脑中的距离。
The widely spanning sensory cortex receives inputs from the disproportionately smaller nucleus of the thalamus, which results in a wide variety of travelling distance among thalamic afferents. Yet, latency from the thalamus to a cortical cell is remarkably constant across the cortex (typically, approximate to2 ms). Here, we found a mechanism that produces invariability of latency among thalamocortical afferents, irrespective of the variability of travelling distances. The conduction velocity (CV) was calculated from excitatory postsynaptic currents recorded from layer IV cells in mouse thalamocortical slices by stimulating the ventrobasal nucleus of the thalamus (VB) and white matter (WM). In adults, the obtained CV for VB to WM (CVVB-WM; 3.28 +/- 0.11 m/s) was approximate to10 times faster than that of WM to layer IV cells (CVWM-IV; 0.33 +/- 0.05 m/s). The CVVB-WM was confirmed by recording antidromic single-unit responses from VB cells by stimulating WM. Exclusion of synaptic delay from CVWM-IV did not account for the 10-fold difference of CV. By histochemical staining, it was revealed that VB to WM was heavily myelinated, whereas in the cortex staining became substantially weaker. We also found that such morphological and physiological characteristics developed in parallel and were accomplished around postnatal week 4. Considering that VB to WM is longer and more variable in length among afferents than is the intracortical region, such an enormous difference of CV makes conduction time heavily dependent on the length of intracortical region, which is relatively constant. Our finding may well provide a general strategy of connecting multiple sites irrespective of distances in the brain.