Mastick G S, Easter S S
Department of Biology, University of Michigan, Ann Arbor 48109-1048, USA.
Dev Biol. 1996 Jan 10;173(1):79-94. doi: 10.1006/dbio.1996.0008.
We investigated the potential role of rostral-caudal and dorsal-ventral subdivisions of the early rostral brain by relating these subdivisions to the early patterning of neuron cell bodies and their axon projections. The earliest neurons were mapped using the lipophilic axon tracers diI and diO on embryos fixed on embryonic days 9.5-10.5 (E9.5-E10.5); neuromeric boundaries were marked by diO. The tracts were small in number, were organized orthogonally (2 dorsal-ventral and 4 rostral-caudal), and originated from groups of cell bodies which we term "sources." Two parallel longitudinal axon systems, one dorsal (the tract of the postoptic commissure and the mesencephalic tract of the trigeminal nerve) and one ventral (the mammillotegmental tract and the medial longitudinal fasciculus), projected caudally from the prosencephalon into the rhombencephalon. We argue that the dorsal longitudinal pathway marked the boundary between the alar and basal plates along the entire neuraxis. The dorsal-ventral axons coursed circumferentially and either crossed the midline (forming the posterior and ventral tegmental commissures) or turned caudally without crossing the midline. The dorsal-ventral axons were not generally restricted to the interneuromeric boundaries, as others have suggested. Earlier, all neighboring neurons projected their axons together; later, nearby neurons projected into different pathways. Some tracts originated in single neuromeres, while other tracts had origins in two or more neuromeres. The dorsal longitudinal axons altered course at several of the borders, but the ventral longitudinal axons did not. In summary, the early subdivisions appeared to influence some, but not all, aspects of tract formation.
我们通过将早期脑嘴侧的头-尾和背-腹分区与神经元细胞体及其轴突投射的早期模式相关联，研究了这些分区的潜在作用。最早的神经元是在胚胎第9.5 - 10.5天（E9.5 - E10.5）固定的胚胎上使用亲脂性轴突示踪剂二碘荧光素（diI）和二氧荧光素（diO）进行定位的；神经节边界用diO标记。这些束数量较少，呈正交排列（2个背-腹和4个头-尾方向），并起源于我们称为“源”的细胞体群。两个平行的纵向轴突系统，一个位于背侧（视交叉后束和三叉神经中脑束），一个位于腹侧（乳头体被盖束和内侧纵束），从端脑向尾侧投射到后脑。我们认为背侧纵向通路标志着沿整个神经轴的翼板和基板之间的边界。背-腹轴突沿圆周方向走行，要么穿过中线（形成后连合和腹侧被盖连合），要么不穿过中线而转向尾侧。背-腹轴突一般并不像其他人所认为的那样局限于神经节间边界。早期，所有相邻神经元一起投射它们的轴突；后来，附近的神经元投射到不同的通路。一些束起源于单个神经节，而其他束起源于两个或更多神经节。背侧纵向轴突在几个边界处改变走行，但腹侧纵向轴突没有。总之，早期分区似乎影响了束形成的一些方面，但不是全部。
