Targeting of gonadotropin-releasing hormone to the median eminence: Evidence of the action of chemotropic factors.
Item
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Title
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Targeting of gonadotropin-releasing hormone to the median eminence: Evidence of the action of chemotropic factors.
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Identifier
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AAI9732940
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identifier
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9732940
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Creator
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Lapostolle-Rogers, Marie-Christine.
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Contributor
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Adviser: Marie J. Gibson
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience
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Abstract
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The projection of gonadotropin-releasing hormone (GnRH) neurons to the median eminence of the medial basal hypothalamus (MBH), where the hormone is secreted into the portal circulation to stimulate pituitary gonadotropins, is essential to reproductive function. This pathway, established early in development, is also seen when preoptic area (POA)-derived GnRH cell-containing grafts are placed in the third ventricle of hypogonadal mice (hpg). Evidence, derived from experiments on hpg mice receiving GnRH neurons containing grafts, suggested the existence of diffusible factors directing the GnRH axonal projection to the median eminence. The present work includes two parts: In an in vitro study, I elucidate some of the mechanisms responsible for the projection of GnRH axons, using organotypic cultures. In vivo, I established that GnRH axons from embryonic POA grafts placed in the mammillary bodies projected to the median eminence.;Using organotypic cultures in insert chambers, we showed that GnRH axons specifically grew in higher number and extended farther from the POA explant towards the MBH co-explant than other tissues. This effect was significant after 4 days in culture and maintained for 10 days in culture. Staining for growth associated protein 43 (GAP-43) labels a general population of neurons elongating their axons. In contrast to its effect on GnRH axons, the MBH did not induce a differential outgrowth of those axons labeled with GAP-43. The importance of contact-mediated guidance with glial elements was also assessed. Only erratic associations were seen between GnRH and glial processes extending on the membrane. However, GnRH axons consistently traveled in the company of GAP-43-labeled axons. We suggest that while employing an axonal substrate, GnRH axons follow diffusible chemoattractive signal(s) secreted by the MBH. In vivo, we implanted POA grafts in the mammillary bodies region, which never contains GnRH cell bodies in mice. One animal with grafts exclusively in the mammillary bodies had gonadal development and his median eminence was innervated. Other grafts innervated the median eminence from mammillary bodies and lateral hypothalamic locations. These findings suggest the existence of a gradient of diffusible factor chemotropic for GnRH axons released by the median eminence, capable of directing GnRH outgrowth in vitro and also in vivo from ectopic caudal locations.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
