Migration of LHRH neurons from nasal to forebrain region--an analysis of molecular mechanisms of neuronal migration

嗅觉胎盘切除术后，没有LHRH免疫反应细胞到达前脑，这表明嗅觉神经束中央投射的可用性是鸡胚胎LHRH神经元正常迁移到前脑的先决条件。在ON中央投射缺失的情况下，LHRH神经元偏离其正常的迁移路线，向眼神经内侧分支迁移，这对高度多涎化的NCAM （NCAM- h）呈阳性。这种迁移LHRH神经元的“流浪”现象表明，这些“流浪”的LHRH神经元的迁移需要一定的结构支持，并表明它们的迁移路线和命运并没有完全在它们位于嗅觉基板的前体细胞中被编程。在对人类胚胎的研究中，5w胚胎中未检测到LHRH神经元。在6w胚胎中，LHRH神经元位于犁鼻器官基座对应的嗅上皮内侧、犁鼻末端神经复合体内侧和前脑腹侧。这些神经元件强烈表达NCAM-H。在包括人类胚胎在内的体内和体外研究中，迁移的LHRH神经元与表达ncam - h的神经元件共存一直得到证实。最近，在LHRH神经元迁移过程中，在LHRH神经元、嗅上皮、ON和腹侧前脑中发现了一种神经蛋白多糖（6B4蛋白多糖/磷酸聚糖），即细胞表面相关的细胞外基质。由于已知磷酸磷脂与NCAM结合，因此在胚胎发育过程中，磷酸磷脂与NCAM的结合可能参与了LHRH神经元从鼻区向前脑区的迁移。

No LHRH-immunoreactive cells arrive into the forebrain following olfactory placodectomy, suggesting that the availability of the central projection of the olfactory nerve (ON) bundle is prerequisite for the normal migration of LHRH neurons into the forebrain in chick embryos.In the cases in which the central projection of the ON is absent, LHRH neurons are deviated from their regular migratory course to the medial branch of ophthalmic nerve which is positive to highly polysialylated NCAM (NCAM-H). This straying phenomenon of migrating LHRH neurons indicates that some structural support are needed for the migration of these straying LHRH neurons, and suggests that their migratory route and destiny are not completely programd in their precursor cells in the olphactory placode.In the studies on human embryos, LHRH neurons are not detectable in the 5w-embryos. In the 6w-embryos, LHRH neurons in the medial part of the olfactory epithelium corresponding to the vomeronasal organ anlage, the medial part of the ON-vomeronasal-terminal nerve complex and in the ventral forebrain. These neural elements strongly express NCAM-H.In vivo and in vitro studies including those on human embryos, the coexistence of migrating LHRH neurons and NCAM-H-expressing neural elements is always confirmed. Recently, a neural proteoglycan (6B4 proteoglycan/phosphacan), cell surface-associated extracellular matrix, is found in the LHRH neurons, the olfactory epithelium, the ON and the ventral forebrain during ther migration of LHRH neurons. Since phosphacan is known to bind NCAM,it is possible that the binding of phosphacan with NCAM may be involved in the migration of LHRH neurons from the nasal to forebrain region during embryonic development.