Constantin Stephanie, Caraty Alain, Wray Susan, Duittoz Anne H
Université de Tours, 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.
Endocrinology. 2009 Jul;150(7):3221-7. doi: 10.1210/en.2008-1711. Epub 2009 Feb 12.
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.
促性腺激素释放激素-1（GnRH-1）的脉冲式释放对于刺激垂体前叶的促性腺细胞至关重要。这种分泌模式似乎是GnRH-1神经元所固有的，然而，这种间歇性释放背后的机制仍然未知。在猴鼻外植体中，GnRH-1群体表现出与GnRH-1释放相同周期的同步钙事件，尽管事件顺序尚不清楚，但表明存在联系。小鼠鼻外植体中的GnRH-1神经元也表现出同步钙事件。在本研究中，使用放射免疫学方法在小鼠鼻外植体中检测了GnRH-1释放，并分析了其与钙信号的关系。GnRH-1神经元早在体外培养3天（div）时就产生间歇性释放，并在整个研究期间（3-21 div）维持这种释放。脉冲频率保持恒定，这表明脉冲发生器在早期发育阶段就开始起作用。相比之下，脉冲幅度在3至7 div之间增加了2倍，在7至14 div之间再次增加，这表明合成和/或分泌机制在成熟。为了评估这些可能性，测量了GnRH-1的总含量。在7至14 div之间仅检测到GnRH-1含量有小幅增加，而在14至21 div之间则出现了大幅增加。这些数据表明，GnRH-1含量在7 div时不是脉冲幅度的限制因素，但分泌机制在3至14 div之间成熟。 kisspeptin-10的应用揭示了GnRH-1神经元将来自天然配体的信号整合到分泌反应中的能力。最后，对培养基和钙成像记录的同步采样表明，同步钙事件和分泌事件是一致的。
