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Central neurochemical mechanisms involved in the generation of the preovulatory GnRH surge in normally cycling female rats

Year: 2001
Type: dissertation
Abstract: A number o f central neurotransmitters have been implicated in the cyclic control of gonadotropin-releasing hormone (GnRH) secretion from the median eminence (ME) of the basal hypothalamus (BH) in normally cycling female rats.The large surge of this hormone released on the afternoon of proestrus stimulates secretion o f luteinizing hormone (LH) from the pituitary, thereby driving ovulation.Among the central neurotransmitters thought to play a stimulatory role in the preovulatory, proestrous release o f GnRH are norepinephrine (NE), oxytocin (OT), and nitric oxide (NO).The purpose of this research was to investigate the role o f these neurotransmitters in stimulating GnRH release from BH explants in vitro, in order to better understand how they may be working in vivo.It was found that OT stimulated GnRH release from BH explants, but not ME fragments harvested on the afternoon of proestrus from normally cycling female rats.This suggests that the connectivity o f the intact BH is required for OT to stimulate proestrous GnRH release.The ability o f OT to stimulate proestrous GnRH release from BH explants was blocked by OT receptor antagonism, and by NO synthase (NOS) inhibition.NE was also found to stimulate GnRH release from proestrous BH explants.Alpha-1, but not alpha-2 adrenergic receptor antagonism blocked the ability of NE to stimulate proestrous GnRH release from BH explants.OT receptor antagonism attenuated, but did not entirely block the effect of NE on GnRH release.When used in combination, NE/OT synergistically stimulated GnRH release from proestrous BH explants.This is the first report of this effect.NE/OT-induced stimulation o f proestrous GnRH release from BH explants was blocked by OT receptor antagonism, and by inhibition of NOS.The results suggest that combined NE/OT stimulate GnRH release from proestrous BH explants in a synergistic manner, using OT-receptor and NO mediated mechanisms.
Language: English
Field: Medicine
Open Access status: green
OpenAlex ID: W2468239699
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