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

点击翻译按钮获取中文摘要

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.