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Title: Ovarian steroids and the generation of the preovulatory GnRH surge in the ewe
Author: Harris, J. G.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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Work in chapter 3 aimed to determine whether changes in GnRH biosynthesis, as monitored by the cellular content of GnRH mRNA, occur during the oestradiol-induced GnRH surge. Results of this study detected a significant decrease during the 8-10 hour period prior to surge secretion. The significance of these changes in GnRH mRNA with regard to the successful generation of a GnRH surge remains to be determined, however it does suggest that the oestradiol-induced effects on GnRH biosynthesis and secretion are not temporally linked. How oestradiol can exert this effect is a fascinating question. In the 4th chapter, we utilised microdialysis techniques both to monitor and modulate the GABAergic environment within the POA prior to surge generation. Results showed that a decrease in extracellular GABA concentrations in the vicinity of GnRH neurones occurred prior to surge secretion. However, the infusion of the GABAA agonist - muscimol during the period from oestradiol insertion to the expected time of the surge did not alter the timing or characteristics of the LH surge. The final series of studies in this thesis (chapter 5) were designed to look further at the mechanisms by which progesterone can block the ability of evaluated oestradiol levels to generate the GnRH surge. In conclusion, these studies all implicate important changes in the steroidal control of the GnRH neurosecretory system which occur some time in advance of surge generation. This implies that GnRH surge secretion does not involve the simple activation of GnRH neurones at the time of surge secretion, but rather, involves a complex interplay of mechanisms which occur well in advance of surge secretion. This series of studies has begun to entangle some of the mechanisms involved in the steroidal control of the GnRH surge, and also developed models with which to study this phenomenon further.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available