Brain gonadotropin releasing hormone receptors: localization and regulation.

In this review, the current information about the location of GnRH receptor protein and GnRH receptor mRNA in the rat central nervous system is summarized as well as the changes that occur in the GnRH receptor mRNA levels during different endocrine conditions of the animals. The results of these studies show that GnRH receptor protein and mRNA levels change in parallel in the hippocampus, suggesting that pretranscriptional factors control the synthesis of the receptor. In the arcuate and ventromedial nuclei of the hypothalamus, GnRH receptor mRNA levels are highest during the early morning of proestrus and during the morning of an estrogen-progesterone-induced LH surge. The timing of the changes in GnRH receptor mRNA levels indicates that increasing levels of estradiol are responsible for the increase in GnRH receptor synthesis. Binding of GnRH agonist to the brain GnRH receptor causes a dose-dependent increase in inositol phosphates as well as changes in intracellular Ca++ levels of the target neurons. Together, it is suggested that GnRH functions in the brain as a neurotransmitter and/or modulator linking the peripheral endocrine effects of GnRH to actions of the peptide inside the central nervous system where it can facilitate, for example, reproductive behaviors.