Chapin J K, Sadeq M, Guise J L
Department of Physiology and Biophysics, Hahnemann University, Philadelphia, Pennsylvania 19102.
J Comp Neurol. 1987 Sep 15;263(3):326-46. doi: 10.1002/cne.902630303.
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 whether 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.(ABSTRACT TRUNCATED AT 400 WORDS)
通过使用逆行和顺行运输的神经解剖示踪剂（包括辣根过氧化物酶、小麦胚芽凝集素、PHA-L和3H-亮氨酸）的离散注射，研究了大鼠初级体感（SI）皮层内的皮质-皮质连接。相对于大鼠SI内的细胞构筑分区，定义了切线连接和垂直连接，具体如下：（1）“颗粒区”（GZs），其特征是IV层有密集的颗粒聚集体，接收大部分直接的腹后（VP）丘脑皮质终末；（2）“颗粒周围区”（PGZs），即紧邻GZs的颗粒较少的皮质基质；（3）“颗粒减少区”（DZs），位于SI中央且在其外侧的较大的颗粒减少区域。在颗粒区记录的感受野小且离散，而在颗粒周围区，尤其是颗粒减少区，它们表现出复杂的感觉汇聚。本研究的一个主要目的是确定SI内的皮质内连接模式是否与这些观察到的生理差异相符。一般来说，颗粒周围区和颗粒减少区比颗粒区包含更丰富的皮质-皮质连接系统。例如，在颗粒周围区进行离散的示踪剂注射，会在相邻的颗粒周围区产生标记“壁”，而相邻的颗粒区相对空白。然而，颗粒区充满了相邻颗粒周围区神经元的树突分支。由于这些树突大概可以接受直接的VP丘脑皮质接触，它们代表了丘脑感觉信息可能传递到颗粒周围区的一条途径。进一步传递到颗粒减少区可能由颗粒周围区和颗粒减少区之间发现的一种按地形组织的相互连接系统来实现。在冠状切片中，由逆行或顺行示踪剂的相对远距离注射产生的标记通常呈柱状分布，并位于颗粒周围区和颗粒减少区。在这些区域内，顺行标记由垂直取向的轴突组成，这些轴突在所有层中发出终末的侧支。逆行神经元标记（几乎完全由锥体细胞组成）在颗粒上层中最多。在注射部位附近，标记倾向于从这些柱扩散到相邻颗粒区的颗粒上和颗粒下层。（摘要截断于400字）
