Migration of LHRH neurons born in the olfactory placode into the forebrain in the chick embryo

（1）用荧光碳菁染料DiI标记3.5-4.0天鸡胚嗅板上皮细胞。DiI标记的细胞首先出现在嗅上皮和嗅神经中，在染料应用后第1天，第2天或第4天，标记细胞依次出现在吻侧内侧前脑和隔-视前区。DiI标记细胞的分布模式与LHRH神经元的分布模式相似。DiI和LHRH双染证实，DiI标记的细胞同时表达LHRH，为LHRH神经元在发育过程中从嗅基板向隔-视前区迁移提供了证据。(2)In在嗅板不完全切除的胚胎中，在嗅上皮碎片和停止向前脑延伸轴突的NCAM-H阳性嗅神经残余中检测到少量表达NCAM-H的LHRH免疫反应（ir）细胞。嗅神经中枢投射的缺乏导致LHRH-ir细胞停滞，前脑中未发现LHRH-ir细胞。此外，迁移的LHRH-ir细胞偏离发育不良的嗅神经，迁移到三叉神经眼神经的NCAM-H阳性内侧鼻分支。这些结果提示LHRH神经元迁移的结构支持是重要的，LHRH神经元的迁移途径和靶点并不完全由嗅板LHRH神经元的前体细胞所决定。由于迁移的LHRL-ir细胞从来没有独立的NCAM-H阳性神经元在体内和体外，可能需要成功的LHRH神经元迁移和NCAM-H之间的相互作用。

(1)The epithelial cells of the olfactory placode of the chick embryoswere labeled with a fluorescent carbocyanine dye DiI at embryonic days 3.5-4.0. The DiI-labeled cells were first detected in the olfactory epithelium and olfactory nerve one day after the application of DiI.Two or four days after the dye application, the labeled cells sequentially appeared in the rostral medial forebrain, and in the septo-preoptic area. The distribution pattern of DiI-labeled cells closely resembled that of LHRH neurons. Double staining for DiI and LHRH demonstrated that DiI-labeled cells co-expressed LHRH.These results provide evidence for the actual migration of LHRH neurons from the olfactory placode to the septo-preoptic area during the development.(2)In the embryos with a incomplete placodectomy, a small number of LHRH-immunoreactive (ir) cells expressing NCAM-H were detected in the olfactory epithelial fragments and in the NCAM-H-positive olfactory nerve remnants which ceased to extend their axons to the forebrain. The lack of the central projection of the olfactory nerve caused stagnation of LHRH-ir cells, no LHRH-ir cells being found in the forebrain. Furthermore, the migrating LHRH-ir cells deviated from the poorly developed olfactory nerve and migrated into the NCAM-H-positive medial nasal branch of the ophthalmic nerve of the trigeminal nerve. These results suggest the importance of the structual support for the migration of LHRH neurons, and that the migration route and target of LHRH neurons are not exactly programd in the precursor cells of LHRH neurons in the olfactory placode. Since the migrating LHRL-ir cells were never independent of NCAM-H-positive neural elements in vivo and in vitro, the possible interaction between the migration of LHRH neurons and NCAM-H may be needed for successful LHRH neuronal migration.