Hoffer Zachary S, Hoover John E, Alloway Kevin D
Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania 17033-2255, USA.
J Comp Neurol. 2003 Nov 24;466(4):525-44. doi: 10.1002/cne.10895.
We used a dual anterograde-tracing paradigm to characterize the organization of corticocortical projections from primary somatosensory (SI) barrel cortex. In one group of rats, biotinylated dextran amine (BDA) and Fluoro-Ruby (FR) were injected into separate barrel columns that occupied the same row of barrel cortex; in the other group, the tracers were deposited into barrel columns residing in different rows. The labeled corticocortical terminals in the primary motor (MI) and secondary somatosensory (SII) cortices were plotted, and digital reconstructions of these plots were quantitatively analyzed. In all cases, labeled projections from focal tracer deposits in SI barrel cortex terminated in elongated, row-like strips of cortex that corresponded to the whisker representations of the MI or SII cortical areas. When both tracers were injected into separate parts of the same SI barrel row, FR- and BDA-labeled terminals tended to merge into a single strip of labeled MI or SII cortex. By comparison, when the tracers were placed in different SI barrel rows, both MI and SII contained at least two row-like FR- and BDA-labeled strips that formed mirror image representations of the SI injection sites. Quantitative analysis of these labeling patterns revealed three major findings. First, labeled overlap in SII was significantly greater for projections from the same barrel row than for projections from different barrel rows. Second, in the infragranular layers of MI but not in the supragranular layers, labeled overlap was significantly higher for projections from the same SI barrel row. Finally, in all layers of SII and in the infragranular layers of MI, the amount of labeled overlap was proportional to the proximity of the tracer injection sites. These results indicate that SI projections to MI and SII have an anisotropic organization that facilitates the integration of sensory information received from neighboring barrels that represent whiskers in the same row.
我们采用双顺行示踪范式来描绘初级体感（SI）桶状皮层的皮质-皮质投射组织。在一组大鼠中，将生物素化葡聚糖胺（BDA）和荧光红宝石（FR）注入占据桶状皮层同一排的不同桶状柱中；在另一组中，将示踪剂注入位于不同排的桶状柱中。绘制初级运动（MI）和次级体感（SII）皮层中标记的皮质-皮质终末，并对这些图的数字重建进行定量分析。在所有情况下，SI桶状皮层中局灶性示踪剂沉积的标记投射终止于细长的、行状的皮层条带，这些条带对应于MI或SII皮层区域的胡须表征。当将两种示踪剂都注入同一SI桶状排的不同部分时，FR和BDA标记的终末倾向于合并成一条标记的MI或SII皮层带。相比之下，当将示踪剂置于不同的SI桶状排时，MI和SII都包含至少两条行状的FR和BDA标记条带，它们形成了SI注射部位的镜像表征。对这些标记模式的定量分析揭示了三个主要发现。首先，来自同一桶状排的投射在SII中的标记重叠明显大于来自不同桶状排的投射。其次，在MI的颗粒下层而非颗粒上层，来自同一SI桶状排的投射的标记重叠明显更高。最后，在SII的所有层和MI的颗粒下层，标记重叠的量与示踪剂注射部位的接近程度成正比。这些结果表明，SI向MI和SII的投射具有各向异性组织，这有助于整合从代表同一排胡须的相邻桶状区域接收的感觉信息。
