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The functional significance of neurokinin 3 receptor signaling in gonadotropin-releasing hormone neurons


Gonadotropin-releasing hormone (GnRH) is a decapeptide hormone secreted by hypothalamic neurons that is essential for puberty and reproduction. Human studies identified a critical role for the neurokinin 3 receptor (NK3R) and its ligand, neurokinin B (NKB), in puberty. NK3R is expressed in multiple cells within the GnRH neuron network, including GnRH neurons themselves. To date, in vivo studies have not been able to discriminate between the direct and indirect effects of NKB on GnRH neurons. The goal of this thesis is to determine the functional significance of NKB signaling directly to NK3R-expressing GnRH neurons. We show that GT1-7 cells, an in vitro model of the mature differentiated GnRH neuron, express NK3R, and acute treatment with senktide, a NK3R agonist, induces GnRH peptide secretion. Moreover, senktide induces the repression of GnRH gene transcription by a mechanism that involves Fos induction, AP-1 complex formation, and direct binding of Fos protein to a novel AP-1 half-site in enhancer 1. We also find that senktide induces c-Fos gene transcription by a mechanism that involves STAT (-310 bp) and SRF (-345 bp) binding sites. Finally, we identify the PKC pathway acting downstream from the NK3R in GnRH neurons. In summary, NKB signaling directly to NK3R- expression GnRH neurons activates GnRH secretion and represses GnRH transcription by a mechanism that involves a PKC pathway-dependent induction of Fos gene transcription and enhanced Fos protein binding to a novel AP-1 site identified in enhancer 1

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