The research presented in this Thesis investigated the relationship between hypothalamic gonadotrophin releasing hormone-I (GnRH-I) gene expression and the photoperiodic control of reproduction in the Japanese quail (<i>Coturnix c. japonica</i>). A cDNA encoding quail GnRH-I was cloned and used to develop a competitive RT-PCR assay for GnRH-I mRNA. The assay was validated and used to quantify levels of GnRH-I mRNA in the hypothalamus in a series of photoperiodic experiments. The first question addressed was whether a change in GnRH-I mRNA is involved in photoinduced luteinising hormone (LH) secretion, as inferred from an increase in blood plasma LH after transfer from short to long days. An increase in plasma LH was first seen 20h after dawn of the first long day and was found to be associated with an increase in hypothalamic GnRH-I mRNA. Exposure to one photostimulatory day followed by a return to short days, stimulated a surge of LH secretion which persisted for up to 10 days. This photo-induced carry “over effect” for LH secretion was not associated with a “carry over” effect for increased GnRH-I mRNA. The second question addressed was whether the development of relative photorefractoriness induced by prolonged exposure to long day lengths is associated with a change in hypothalamic GnRH-I mRNA. Relative photorefractoriness was demonstrated by showing that quail maintained on long days (18 hr light/day) for a prolonged period went out of breeding condition when transferred to 13 hr light/day, a photoperiod which is photo-stimulatory for fully photosensitive quail. The development of relative photorefractoriness in quail held on 18hr light/day was not associated with a decrease in plasma LH but was associated with a decrease in hypothalamic GnRH-I mRNA. Since the development of relative photorefractoriness is associated with increased prolactin secretion, a final series of experiments investigated the possibility that prolactin might exert an inhibitory effect on hypothalamic GnRH-I mRNA. Treatment of quail with ovine prolactin for 5 days after photostimulation suppressed the photo-induced increase in GnRH-1 mRNA.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641216 |
| Date | January 2001 |
| Creators | Baines, Elizabeth |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10704 |
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