Flavell Charlotte R, Cerminara Nadia L, Apps Richard, Lumb Bridget M
School of Physiology and Pharmacology, University of Bristol, Bristol, UK.
J Comp Neurol. 2014 Jun 15;522(9):2179-90. doi: 10.1002/cne.23527.
The gracile nucleus (GN) and lateral part of rostral dorsal accessory olive (rDAO) are important relays for indirect, postsynaptic dorsal column, and direct ascending pathways, respectively, that terminate as climbing fibers in the "hindlimb-receiving" parts of the C1 and C3 zones in the cerebellar cortex. While the spinal cells of origin of that project to GN and rDAO are from largely separate territories in the spinal cord, previous studies have indicated that there could be an area of overlap between these two populations in the medial dorsal horn. Given the access of these two ascending tracts to sensory (thalamic) versus sensorimotor (precerebellar) pathways, the present study therefore addresses the important question of whether or not individual neurons have the potential to contribute axons to both ascending pathways. A double-fluorescent tracer strategy was used in rats (red Retrobeads and Fluoro-Ruby or green Retrobeads and Fluoro-Emerald) to map the spatial distribution of cells of origin of the two projections in the lumbar spinal cord. The two pathways were found to receive input from almost entirely separate territories within the lumbar cord (levels L3-L5). GN predominantly receives input from lamina IV, while rDAO receives its input from three cell populations: medial laminae V-VI, lateral lamina V, and medial laminae VII-VIII. Cells that had axons that branched to supply both GN and rDAO represented only about 1% of either single-labeled cell population. Overall, the findings therefore suggest functional independence of the two ascending pathways.
薄束核（GN）和延髓背侧副橄榄核吻侧部外侧（rDAO）分别是间接、突触后背柱和直接上行通路的重要中继站，这些通路在小脑皮质C1和C3区的“后肢接受”部分以攀缘纤维的形式终止。虽然投射到GN和rDAO的脊髓起源细胞主要来自脊髓中不同的区域，但先前的研究表明，这两个细胞群在背内侧角可能存在重叠区域。鉴于这两条上行通路分别通向感觉（丘脑）和感觉运动（小脑前）通路，因此本研究探讨了一个重要问题，即单个神经元是否有可能向这两条上行通路都发出轴突。在大鼠中采用双荧光示踪策略（红色Retrobeads和Fluoro-Ruby或绿色Retrobeads和Fluoro-Emerald）来绘制两条投射通路在腰段脊髓起源细胞的空间分布。结果发现，这两条通路几乎完全从腰段脊髓（L3-L5节段）内不同的区域接收输入。GN主要从IV层接收输入，而rDAO从三个细胞群接收输入：内侧V-VI层、外侧V层和内侧VII-VIII层。轴突分支并同时供应GN和rDAO的细胞仅占单个标记细胞群的1%左右。因此，总体而言，这些发现表明这两条上行通路具有功能独立性。
