CORTICOCORTICAL CONNECTIONS WITHIN THE PRIMARY SOMATOSENSORY CORTEX OF THE RAT
CORTICOCORTICAL CONNECTIONS WITHIN THE PRIMARY SOMATOSENSORY CORTEX OF THE RAT
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DOI：
10.1002/cne.902630303
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发表时间：
1987-09-15
影响因子：
2.5
通讯作者：
GUISE, JLU
中科院分区：
文献类型：
--
作者：
CHAPIN, JK;SADEQ, M;GUISE, JLU
用HRP、WGA、PHA-L和~ 3 H-亮氨酸等神经解剖示踪剂，研究了大鼠初级躯体感觉皮质（SI）内皮质-皮质的联系。相对于大鼠SI内的细胞结构划分，定义了切向和垂直连接，具体而言：（1）“颗粒区”（GZ），其特征在于其致密的IV层颗粒聚集体，其接收大部分直接腹后（VP）丘脑皮质末端，（2）“颗粒周区”（PGZ），仅围绕GZ的较少颗粒的皮质基质，（3）“颗粒异常区”（DZs），即位于SI中心和SI侧面的较大颗粒异常区。在颗粒区记录的感受野是小的和离散的，而在颗粒周围区，特别是在dysgranular区，他们表现出复杂的感觉会聚。本研究的一个主要目的是确定SI内皮质内连接的模式与这些观察到的生理差异是否相容。在一般情况下，perigranular和dysgranular区包含更丰富的系统皮质连接比颗粒区。例如，颗粒周围区中的离散示踪剂注射在整个相邻的颗粒周围区中产生标记的“壁”，而相邻的颗粒区相对空。然而，颗粒区充满了树突状分支的神经元在相邻的颗粒周区。由于这些树突可能接受直接VP丘脑皮质接触，他们代表了一个路径，通过该丘脑的感觉信息可能被传输到颗粒周围区。进一步传输到dysgranular区可能是subserved的地形组织系统的相互连接，发现颗粒周围区和dysgranular区之间。在冠状面，标记产生的相对较远的注射逆行或顺行示踪剂一般出现在柱状分布，并定位在颗粒周围区和dysgranular区。在这些区域内，orthograde标签包括垂直定向的轴突发射侧喷终端在所有层。逆行神经元标记（几乎完全由锥体细胞组成）是最大的颗粒上层。在注射部位近端，标记倾向于从这些微柱扩散到相邻颗粒区的颗粒上层和颗粒下层。这些连接的细胞基础通过长距离跟踪单轴突（通过细胞外HRP或PHA-L注射填充）通过厚切片来评估。第三层金字塔的轴突以U形轨迹行进，首先在局部分支，然后下降到深层皮质层并进一步分支，然后穿过深层皮质层或白色物质到达其终止区。结果表明，颗粒周围区和颗粒区的神经元可以接收投射到颗粒区IV层的VP丘脑皮质信息，并且这些信息可以传递到（1）邻近颗粒区和颗粒周围区的深层，（2）遍及附近颗粒周围区的所有层，以及（3）地形学上更远的颗粒异常区。这是一致的神经生理学研究结果，即感受野是最小的颗粒层IV，最大的层V，并在所有层的颗粒周围区和dysgranular区。
Corticocortical connections within the primary somatosensory (SI) cortex of rat were investigated by using discrete injections of retro- and orthogradely transported neuroanatomical tracers (including HRP, WGA, PHA-L, and 3H-leucine). Tangential and vertical connections were defined with respect to the cytoarchitectonic divisions within the rat SI, specifically: (1) the "granular zones" (GZs), characterized by their dense layer IV granular aggregates, which receive the majority of direct ventroposterior (VP) thalamocortical terminations, (2) the "perigranular zones" (PGZs), the less-granular cortical matrix just surrounding the GZs, and (3) the "dysgranular zones" (DZs), the larger dysgranular regions lying centrally within and just lateral to the SI. Receptive fields recorded in the granular zones are small and discrete, whereas in the perigranular zones and especially in dysgranular zones they exhibit complex sensory convergence. A major aim of this study was to determine with the pattern of intracortical connectivity within the SI is compatible with these observed physiological differences. In general, the perigranular and dysgranular zones contained more profuse systems of corticocortical connections than did the granular zones. For example, discrete tracer injections in the perigranular zones produced "walls" of labelling throughout the adjacent perigranular zones, while adjacent granular zones were relatively empty. Nevertheless, the granular zones were filled with dendritic branches of neurons in adjacent perigranular zones. Since these dendrites could presumably receive direct VP thalamocortical contacts, they represent one path through which this thalamic sensory information might be transmitted to the perigranular zones. Further transmission to the dysgranular zones might be subserved by a topographically organized system of reciprocal interconnections that was found between the perigranular zones and dysgranular zones. In coronal sections, labelling produced by relatively distant injections of either retro or orthograde tracers generally appeared in a columnar distribution, and was localized in perigranular zones and dysgranular zones. Within these zones, orthograde labelling consisted of vertically oriented axons emitting collateral sprays of terminals in all layers. Retrograde neuronal labelling (composed almost exclusively of pyramidal cells) was greatest in supragranular layers. Proximal to the injection site, labelling tended to spread out from these columns into supra- and infragranular layers in adjacent granular zones. The cellular basis for these connections was assessed by following single axons (filled by extracellular HRP or PHA-L injections) for long distances through thick sections. Axons of layer III pyramids travelled in a U-shaped trajectory, first ramifying locally, then descending to the deep cortical layers and ramifying further before coursing through deep cortical layers or white matter to their termination zones. It was concluded that neurons in the perigranular zones as well as the granular zones may receive VP thalamocortical information projecting to layer IV in the granular zones, and that this may be transmitted (1) to deep layers of adjacent granular zones and perigranular zones, (2) throughout all layers of nearby perigranular zones, and (3) to topographically more distant dysgranular zones. This is consistent with neurophysiological findings that receptive fields are smallest in granular zone layer IV, and largest in layer V, and in all layers in perigranular zones and in dysgranular zones.