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Title: The role of endogenous opioids and brain neurotransmitters in the generation of the LH surge in the rat
Author: Yilmaz, Bayram
ISNI:       0000 0001 3575 2366
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1997
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It has been suggested that a multiplicity of neurotransmitter systems regulate the release of gonadotrophin-releasing hormone (GnRH) from their neurons in the hypothalamus which in turn control luteinising hormone (LH) secretion from the anterior pituitary. An example of such neurotransmitter systems is that secreting the endogenous opioid peptides which have a profound inhibitory influence on the LH secretion. Recently, it has been reported that a reduction in the activity of these peptides in the hypothalamus may be the initial neural stimulus for the generation of the pre-ovulatory LH surge which induces ovulation. Furthermore, this inhibitory opioidergic action may involve alterations in the activity of monoaminergic neurons which make synaptic contacts with the GnRH neurons in the hypothalamus. Naloxone-, the opioid antagonist, induced LH release can be prevented by prior administration of a-adrenergic blockers. The central noradrenergic system is believed to be an essential component of the GnRH pulse-generating mechanism. The present study was undertaken to determine (i) the modulating effects of specific mu-, kappa- and delta-opioid receptor agonists and antagonists on hypothalamic monoaminergic content and on LH release and (ii) the inter-relationship between the opioid peptidergic and aminergic systems in the control of GnRH activity. The results indicate that multiple opioid receptor subtypes are involved in the opioid suppression of the pre-ovulatory LH surge. It appears that opioid modulation of noradrenaline, dopamine and serotonin release and/or turnover within the specific areas of the hypothalamus via mu-, kappa- and delta-opioid receptors is inhibitory at the time of the LH surge. This study supports the concept that an increase in the hypothalamic noradrenergic activity is a critical event in triggering the surge release of GnRH and LH. Both the dopaminergic and serotonergic neurotransmitter systems may also facilitate the pre-ovulatory LH surge, although their effects are thought to be of minor importance in this process. In view of the unexpected interference by both urethane and ketamine anaesthesia on plasma LH levels, it is recommended that use of general anaesthetics in neuroendocrine studies should be avoided if at all possible.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Gonadotrophin-releasing hormone; Oestrous cycle