MIGRATION OF THE LHRH NEURONS FROM THE NASAL REGION TO THE FOREBRAIN.

在鸡胚胎中，LHRH神经元起源于嗅觉胎盘，并在胚胎3.5-11天迁移到前脑。对LHRH神经元正常发育的研究表明，LHRH神经元在脑内存在两条主要的迁移途径。LHRH神经元迁移的主要途径在很大程度上与嗅觉相关纤维的走向相对应。在这条通路的最尾部，也就是隔区发育的地方，许多LHRH神经元向腹侧视前区的方向转向腹侧。这些LHRH神经元偏离了嗅觉相关纤维。LHRH神经元从神经纤维中的分散表明，另一种引导线索有助于LHRH神经元向视前区的迁移。根据这些发现，LHRH神经元在视前区和隔区具有不同的特征。为了检测LHRH神经元的出生日期是否影响它们的最终位置，在不同时期向鸡蛋中注射了单剂量的BrdU。出生于E2.5-4.5的LHRH神经元分布于E11.5和E18.5的整个终末分布区。而e5.5-6.5出生的LHRH神经元在腹侧视前区未观察到。晚期产生的LHRH神经元可能不能沿着视前区的方向移动。当晚期生成的LHRH神经元向视前区迁移时，LHRH神经元迁移的结构和化学引导底物可能会丢失。Netrin-1是一种可扩散的分子，引导各种轴突和细胞迁移。E7.5时，netrin-1mRNA在下丘脑腹侧强表达，但在背内侧前脑不表达。Netrin-1可能是LHRH神经元从背侧隔前区向腹侧视前区迁移的候选分子。

In the chick embryo, LHRH neurons originate in the olfactory placode and migrate to the forebrain during embryonic days(E) 3.5-11. Examination of the normal development of LHRH neurons indicates that two major pathways of LHRH neuron migration exist in the brain. The main pathway of LHRH neuron migration largely corresponds to the course of the olfactory related fibers. At the most caudal level of this pathway, where the septal area develops, many LHRH neurons turn ventrally in direction of the ventral preoptic area. These LHRH neurons deviate from the olfactory related fibers. The dispersion of LHRH neurons from the nerve fibers implicates that another guidance cues contribute to the migration of LHRH neurons towards the preoptic area. From these findings, it is proposed that a character of LHRH neurons in the preoptic area differs from that in the septal area.To examine whether the birthdate of LHRH neurons influences their final locations, a single dose of BrdU was injected into eggs at different stages. LHRH neurons born at E2.5-4.5 were found in the entire final distribution areas at E11.5 and E18.5. In contrast, LHRH neurons born at E5.5-6.5 were not observed in the ventral preoptic region. It might be possible that late-generated LHRH neurons could not move in direction to the preoptic area. Structural and chemical guidance substrates for LHRH neuron migration might be lost at that time when late-generated LHRH neurons migrate toward the preoptic area.Netrin-1 is a diffusible molecule that guides various axons and cells migration. Netrin-1 mRNA was strongly expressed in the ventral hypothalamus but not in the dorsomedial forebrain at E7.5. Netrin-1 may be a candidate molecule for LHRH neuron migration from the dorsal preseptal area to the ventral preoptic area.