Biswas Mohammad Shahangir, Luo Yuanjun, Sarpong Gideon Anokye, Sugihara Izumi
Department of Systems Neurophysiology, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
Center for Brain Integration Research, Tokyo Medical and Dental University, Tokyo, Japan.
J Comp Neurol. 2019 Aug 15;527(12):1966-1985. doi: 10.1002/cne.24662. Epub 2019 Feb 25.
The basilar pontine nucleus (PN) is the key relay point for the cerebrocerebellar link. However, the projection pattern of pontocerebellar mossy fiber axons, which is essential in determining the functional organization of the cerebellar cortex, has not been fully clarified. We reconstructed the entire trajectory of 25 single pontocerebellar mossy fiber axons labeled by localized injection of biotinylated dextran amine into various locations in the PN and mapped all their terminals in an unfolded scheme of the cerebellum in 10 mice. The majority of axons (20/25 axons) entered the cerebellum through the middle cerebellar peduncle contralateral to the origin, while others entered through the ipsilateral pathway. A small number of axons (1/25 axons) had collaterals terminating in the cerebellar nuclei. Axons projected mostly to a combination of lobules, often bilaterally, and terminated in multiple zebrin (aldolase C) stripes, more frequently in zebrin-positive stripes (83.9%) than in zebrin-negative stripes, with 66.5 mossy fiber terminals on the average. Axons originating from the rostral (plus medial and lateral), central and caudal PN mainly terminated in the paraflocculus, crus I and lobule VIb-c, in the simplex lobule, crus II and paramedian lobule, and in lobules II-VIa, VIII and copula pyramidis, respectively. The results suggest that the interlobular branching pattern of pontocerebellar axons determines the group of cerebellar lobules that are involved in a related functional localization of the cerebellum. In the hemisphere, crus I may be functionally distinct from neighboring lobules (simple lobule and crus II) in the mouse cerebellum based on the pontocerebellar axonal projection pattern.
脑桥基底部核团（PN）是大脑与小脑连接的关键中继点。然而，脑桥小脑苔藓纤维轴突的投射模式，这对于确定小脑皮质的功能组织至关重要，尚未完全阐明。我们通过将生物素化葡聚糖胺局部注射到PN的不同位置，重建了25条单根脑桥小脑苔藓纤维轴突的完整轨迹，并在10只小鼠的小脑展开图中绘制了它们所有的终末。大多数轴突（20/25条轴突）通过与起源部位对侧的小脑中脚进入小脑，而其他轴突则通过同侧路径进入。少数轴突（1/25条轴突）有侧支终止于小脑核团。轴突大多投射到多个小叶的组合，通常是双侧的，并终止于多个zebrin（醛缩酶C）条带，在zebrin阳性条带中终止的频率更高（83.9%），而在zebrin阴性条带中较少，平均有66.5个苔藓纤维终末。起源于嘴侧（加内侧和外侧）、中央和尾侧PN的轴突分别主要终止于旁绒球、小脑脚I和小叶VIb - c，单小叶、小脑脚II和旁正中小叶，以及小叶II - VIa、VIII和锥体连合。结果表明，脑桥小脑轴突的小叶间分支模式决定了参与小脑相关功能定位的小脑小叶组。在半球中，基于脑桥小脑轴突投射模式，小鼠小脑的小脑脚I在功能上可能与相邻小叶（单小叶和小脑脚II）不同。
