Morphological Characterization of a Cortico-cortical relay in the cat sensorimotor cortex.
Morphological Characterization of a Cortico-cortical relay in the cat sensorimotor cortex.
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猫感觉运动皮层皮质-皮质中继的形态特征。
DOI：
10.1093/cercor/7.2.100
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Porter,LL
中科院分区：
文献类型：
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作者：
Porter,LL
大脑皮层回路的一个特征是连接不同功能区域的复杂纤维网络。我们对形成这些通路的神经元之间的特定关系的了解是有限的。初级体感皮层（SI）和初级运动皮层（MI）之间的皮质-皮质连接是研究的重点。目的有两个：首先，确定区域间皮质-皮质连接的特征；第二，确定是否存在支持外周信号在传递到运动皮层之前在体感觉环境中被整合的途径。在SI 2区发现了投射到运动皮层的神经元。这些神经元的形态特征和它们从3a区接收的输入模式被确定。将荧光逆行示踪剂“快蓝”注射到电生理学定义的运动皮层前爪表征区，并将顺行示踪剂右旋四甲基罗丹明（DR）注射到3a区体位匹配的区域。在固定组织切片中，鉴定出位于3a区产生的标记轴突场中的2区标记神经元。其中一些被标记的细胞用充满路西法黄（LY）的微管刺穿，并用LY离子电泳注射进行细胞内标记。投射到运动皮层的2区细胞主要位于第II-III层。它们都被归类为锥体神经元，在形态上相似。它们的顶端树突大部分不超过第二层。它们的顶端枝簇在第II-III层中有2-4个分支，而基生树突则有更多的三级基生树突分支。光镜（LM）检查显示ly -填充轮廓和dr -标记轴突之间存在对应。沿dr标记轴突和树突轴或棘的1度、2度和3度分支的顶端和1度和2度分支的基部观察到相应的肿胀。相对位置主要在标记的树枝状轴的近端。与远端树突的相对较少，其中一些是树突棘。没有观察到与躯体相关。在单个细胞中只观察到1或2个异位。皮层-皮层突触输入模式从3a区产生到这一细胞群是由这些LM发现预测的。进行了超微结构分析，以确认接触的存在和预测的连接模式。分别用电子密度逆行示踪剂和顺行示踪剂对投射到运动皮层的2区神经元和投射到2区的3a区轴突进行了识别。在一系列连续的超薄切片中检查位于标记轴突区域的标记神经元。电子显微镜分析显示了类似的模式，但与LM研究预测的相比，突触输入密度略高（每个目标细胞1-8个接触）。这些结果揭示了一个特定的密度和模式的皮质-皮质输入到一个确定的皮质-皮质投射神经元群体。单个靶细胞仅从功能不同但与躯体相关的皮层区域接收稀疏输入。输入到细胞的模式是出乎意料的，因为大多数轴突接触近端树突的轴。这种连接的这一方面可能说明了皮层回路的一个独特特征，它有助于定义其功能角色。这些结果在定义皮层功能方面的意义在于……
One feature of the cerebral cortex circuitry is the complex network of fibers which links its different functional regions. Our knowledge of the specific relationships between neurons which form these pathways is limited. The cortico-cortical connections between primary somatosensory cortex (SI) and primary motor cortext (MI) were the focus of the study. The aims were twofold: first, to identify characteristics of inter-areal cortico-cortical connections; and second, to determine if pathways exist which support the notion that peripheral signals are integrated in the somatosensory cortext before being relayed to the motor cortex. Neurons in area 2 of SI, which projected to the motor cortex were identified. The morphological characteristics of these neurons and the pattern of input that they received from the area 3a were determined. The fluorescent retrograde tracer, fast blue, was injected into the electrophysiologically defined forepaw representation of motor cortex and the anterograde tracer, dextran-tetramethylrhodamine (DR), was injected into the somatotopically matched region of area 3a. Labeled neurons in area 2 which were located in a field of labeled axons arising from area 3a were identified in fixed tissue sections. Some of these labeled cells were impaled with a Lucifer yellow (LY)-filled micropipette and were intracellulary labeled by iontophoretic injection of LY Cells in area 2 that projected to the motor cortex were located primarily in layers II-III. They were all classified as pyramidal neurons and were morphologically similar. Their apical dendrites for the most part did not extend beyond layer II. Their apical tufts exhibited 2-4 branches within layers II-III, while basal dendrites exhibited more numerous tertiary basal dendritic branches. Light microscopic (LM) examination revealed the presence of appositions between LY-filled profiles and DR-labeled axons. Appositions were observed between swellings along DR-labeled axons and dendritic shafts or spines of 1 degrees, 2 degrees and 3 degrees branches of apical and 1 degrees and 2 degrees branches of basal dendrites. The appositions were primarily on proximal segments of labeled dendritic shafts. Fewer appositions with distal dendrites were observed and some of these were with dendritic spines. No appositions with the somata were observed. Only one or two appositions were observed for individual cells. The pattern of cortico-cortical synaptic input arising from area 3a onto this population of cells was predicted from these LM findings. An ultrastructural analysis was performed to confirm the existence of contacts and the predicted pattern of connectivity. Neurons in area 2 which projected to the motor cortex, and area 3a axons which projected to area 2, were identified with electron dense retrograde and anterograde tracers respectively. Labeled neurons located in a field of labeled axons were examined throughout a sequential series of ultrathin sections. Electron microscopic analysis revealed a similar pattern, but with a slightly higher density of synaptic input (1-8 contacts per target cell) than that predicted from the LM studies. These results revealed a specific density and pattern of coritco-cortical input onto an identified population of cortico-cortical projection neurons. Individual target cells received only sparse input from a functionally different but somatotopically related region of the cortex. The pattern of input onto cells was unexpected in that most axons contacted the shafts of proximal dendrites. This aspect of the connection may exemplify a unique feature of the cortical circuit which helps to define its functional role. The significance of these results in defining cortical function is that the …