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Development of Gonadotropin-Releasing Hormone-1 Secretion in Mouse Nasal Explants

Université de Tours (S.C., A.C., A.H.D.), Physiologie de la Reproduction et des Comportements, Institut National de la Recherche Agronomique Unité Mixte de Recherche 6175 Centre National de la Recherche Scientifique, Nouzilly 37380, France; Cellular and Developmental Neurobiology Section (S.C., S.W.), National Institute of Neurological Disorders and Stroke/National Institutes of Health, Bethesda, Maryland 20892; and Centre for Neuroendocrinology (S.C.), Department of Physiology, University of Otago, Dunedin 9054, New Zealand

Address all correspondence and requests for reprints to: Stéphanie Constantin, Centre for Neuroendocrinology, Department of Physiology, University of Otago, Dunedin 9054, New Zealand. E-mail: const95p{at}otago.ac.nz.

Pulsatile release of GnRH-1 is critical to stimulate gonadotropes of the anterior pituitary. This secretory pattern seems to be inherent to GnRH-1 neurons, however, the mechanisms underlying such episodical release remain unknown. In monkey nasal explants, the GnRH-1 population exhibits synchronized calcium events with the same periodicity as GnRH-1 release, suggesting a link, though the sequence of events was unclear. GnRH-1 neurons in mouse nasal explants also exhibit synchronized calcium events. In the present work, GnRH-1 release was assayed in mouse nasal explants using radioimmunology and its relationship with calcium signaling analyzed. GnRH-1 neurons generated episodical release as early as 3 d in vitro (div) and maintained such release throughout the period studied (3–21 div). The pulse frequency remained constant, suggesting that the pulse generator is operative at an early developmental stage. In contrast, pulse amplitude increased 2-fold between 3 and 7 div, and again between 7 and 14 div, suggesting maturation in synthesizing and/or secretory mechanisms. To evaluate these possibilities, total GnRH-1 content was measured. Only a small increase in GnRH-1 content was detected between 7 and 14 div, whereas a large increase occurred between 14 and 21 div. These data indicate that GnRH-1 content was not a limiting factor for the amplitude of the pulses at 7 div but that the secretory mechanisms mature between 3 and 14 div. The application of kisspeptin-10 revealed the ability of GnRH-1 neurons to integrate signals from natural ligands into a secretory response. Finally, simultaneous sampling of medium and calcium imaging recordings indicated that the synchronized calcium events and secretory events are congruent.