Porter L L
Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814.
J Comp Neurol. 1991 Oct 15;312(3):404-14. doi: 10.1002/cne.903120308.
Through its complex network of interconnections, each of the functionally specialized subdivisions in the cat primary somatosensory cortex may provide the motor cortex with different input and thus play a unique role in motor behavior. Areas 2 and 3a receive separate peripheral information. Cells in both regions project directly to the cat motor cortex but are thought to target different populations of neurons. In this study the morphology and distribution patterns of the area 3a projection to the motor cortex were compared to previous findings on the projection from area 2. Also, details of the projection from area 3a to area 2 were studied. Injections of Phaseolus vulgaris leucoagglutinin were made into area 3a and fixed brain tissue was processed for immunohistochemical staining of this anterograde tracer. Tissue was examined with the light microscope to determine the patterns of the 3a projections to area 2 and motor cortex, area 4. Axons arising from cells in area 3a terminated in multiple column-like clusters in both motor cortex and area 2. The small number of cells labeled at the injection sites suggested that multiple foci of the 3a fibers are formed by collateral axonal branches of the same neurons. The topography of the projection from area 3a to the motor cortex was more clearly defined than that from area 3a to area 2. Electron microscope analysis determined the laminar distribution and types of synapses formed between area 3a efferents and their target neurons. A high proportion of synapses was found in layer III in both target regions. However, unlike in area 4, labeled terminals were sparse in laminae I and II of area 2. Axospinous synapses were slightly more numerous than axodendritic synapses, but both were distributed similarly throughout the thickness of the cortex. In area 2 the axospinous synapses accounted for 63% of synapses and in area 4 for 57% of synapses. No axosomatic synapses were detected.
通过其复杂的互连网络，猫初级体感皮层中每个功能特化的亚区可能为运动皮层提供不同的输入，从而在运动行为中发挥独特作用。2区和3a区接收不同的外周信息。这两个区域的细胞都直接投射到猫的运动皮层，但被认为针对不同的神经元群体。在本研究中，将3a区向运动皮层的投射的形态和分布模式与先前关于2区投射的研究结果进行了比较。此外，还研究了3a区向2区投射的细节。将菜豆白细胞凝集素注射到3a区，并对固定的脑组织进行处理，以对这种顺行示踪剂进行免疫组织化学染色。用光镜检查组织，以确定3a区向2区和运动皮层（4区）的投射模式。3a区细胞发出的轴突在运动皮层和2区均终止于多个柱状簇。注射部位标记的细胞数量较少，这表明3a纤维的多个焦点是由同一神经元的轴突侧支形成的。3a区向运动皮层的投射的拓扑结构比3a区向2区的投射更清晰。电子显微镜分析确定了3a区传出纤维与其靶神经元之间形成的突触的层状分布和类型。在两个靶区域的III层中发现了高比例的突触。然而，与4区不同的是，2区I层和II层中的标记终末很少。轴棘突触略多于轴树突触，但两者在整个皮层厚度中的分布相似。在2区，轴棘突触占突触的63%，在4区占突触的57%。未检测到轴体突触。
