Leergaard T B, Lakke E A, Bjaalie J G
Department of Anatomy, University of Oslo, Norway.
J Comp Neurol. 1995 Oct 9;361(1):77-94. doi: 10.1002/cne.903610107.
We have explored basic rules guiding the early development of topographically organized projections, employing the rat corticopontine projection as a model system. Using anterograde in vivo tracing with 1,1',dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), we studied the distribution of labelled fibers in the pontine nuclei in relation to cortical site of origin during the first postnatal week. Labelled corticopontine fibers enter the pontine nuclei in distinct, sharply defined zones. The putative terminal fibers typically occupy lamella-like subspaces. Related to changes in cortical site of origin, we describe mediolateral, internal to external, and caudorostral distribution gradients in the pontine nuclei. Fibers originating in the anterolateral cortex occupy an internal central core, while implantations at increasing distance from the anterolateral cortex produce 1) more externally located lamellae, and 2) a caudal to rostral shift in fiber location. Previous investigations have shown that pontocerebellar neurons migrate into the ventral pons in a temporal sequence (Altman and Bayer [1987] J. Comp. Neurol. 257:529). The earliest arriving neurons occupy the central core and later arriving neurons settle in more externally and rostrally located subspaces. We hypothesize that the earliest arriving corticopontine fibers grow into the then only available zone of pontocerebellar neurons (central core), attracted by a diffusible chemotropic cue. Later arriving fibers grow into correspondingly later and more externally and rostrally located contingents of pontocerebellar neurons. Thus, we propose that the topographical organization in the early postnatal corticopontine projection is determined by simple temporal and spatial gradients operative within source (cerebral cortex) and target region (pontine nuclei).
我们以大鼠皮质脑桥投射作为模型系统，探索了指导拓扑组织投射早期发育的基本规则。使用1,1',二辛基-3,3,3',3'-四甲基吲哚羰花青高氯酸盐（DiI）进行顺行体内追踪，我们研究了出生后第一周内标记纤维在脑桥核中的分布与皮质起源部位的关系。标记的皮质脑桥纤维进入脑桥核时分布在不同的、界限清晰的区域。推测的终末纤维通常占据片状的子空间。与皮质起源部位的变化相关，我们描述了脑桥核中的中外侧、内至外以及尾侧至吻侧的分布梯度。起源于前外侧皮质的纤维占据内部中央核心，而在距前外侧皮质距离增加的部位植入则会产生：1）更靠外侧的片状结构，以及2）纤维位置从尾侧向吻侧的移动。先前的研究表明脑桥小脑神经元按时间顺序迁移到腹侧脑桥（阿尔特曼和拜尔[1987]《比较神经学杂志》257:529）。最早到达的神经元占据中央核心，较晚到达的神经元定居在更靠外侧和吻侧的子空间。我们假设最早到达的皮质脑桥纤维生长到当时仅有的脑桥小脑神经元区域（中央核心），这是由一种可扩散的化学趋向性信号吸引所致。较晚到达的纤维生长到相应较晚且更靠外侧和吻侧的脑桥小脑神经元群体中。因此，我们提出出生后早期皮质脑桥投射中的拓扑组织是由源（大脑皮质）和靶区域（脑桥核）内起作用的简单时间和空间梯度所决定的。
