Cetas J S, de Venecia R K, McMullen N T
Department of Cell Biology and Anatomy, University of Arizona College of Medicine, PO Box 245044, 1501 N. Campbell Avenue, Tucson, AZ 85724, USA.
Brain Res. 1999 May 29;830(1):203-8. doi: 10.1016/s0006-8993(99)01355-4.
The injection of anterograde tracers into the ventral division of the medial geniculate body (MGV) of both rats and rabbits labels terminal axons in layer I of auditory cortex as well as the more conventional terminal arbors in layers III/IV. Whether these layer I projections represent a separate lemniscal pathway to the molecular layer or arise as collaterals of axons terminating in III/IV has not been addressed. Focal injections of the anterograde tracers biocytin or biotinylated dextran amine were made into the MGV of young rabbits. Serial section reconstruction of single MGV axons in auditory cortex revealed that layer I axons were collaterals of thalamocortical afferents that formed multiple divergent patches within III/IV. MGV collaterals to layer I often coursed tangentially for several millimeters before terminating. In some cases, the layer I collaterals descended to arborize within a thalamocortical patch in layers III/IV. These results suggest considerable radial and tangential divergence in the auditory thalamocortical pathway and argue for an expanded role for layer I in the processing of specific sensory stimuli.
将顺行示踪剂注入大鼠和家兔内侧膝状体腹侧部（MGV），会标记听皮层I层的终末轴突以及III/IV层中更常见的终末分支。这些I层投射是代表一条通向分子层的独立的lemniscal通路，还是作为终止于III/IV层的轴突的侧支产生，尚未得到解决。将顺行示踪剂生物胞素或生物素化葡聚糖胺局部注入幼兔的MGV。对听皮层中单个MGV轴突进行连续切片重建显示，I层轴突是丘脑皮质传入纤维的侧支，这些传入纤维在III/IV层内形成多个发散的斑块。MGV到I层的侧支通常在终止前沿切线方向走行几毫米。在某些情况下，I层侧支会下降到III/IV层的丘脑皮质斑块内形成分支。这些结果表明，听觉丘脑皮质通路中存在相当大的径向和切向发散，并支持I层在特定感觉刺激处理中发挥更大作用的观点。
