Departments of Molecular and Integrative Physiology.
Departments of Molecular and Integrative Physiology
J Neurosci. 2023 Oct 4;43(40):6717-6730. doi: 10.1523/JNEUROSCI.2355-22.2023. Epub 2023 Aug 3.
In vertebrates, the pulsatile release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus triggers secretion of anterior pituitary gonadotropins, which activate steroidogenesis, and steroids in turn exert typically homeostatic negative feedback on GnRH release. Although long-term episodic firing patterns of GnRH neurons in brain slices resemble the pulsatile release of GnRH and LH , neither the relationship between GnRH neuron firing and release nor whether this relationship is influenced by gonadal feedback are known. We combined fast-scan cyclic voltammetry and patch-clamp to perform simultaneous measurements of neuropeptide release with either spontaneous action potential firing or in response to neuromodulator or action-potential-spike templates in brain slice preparations from male mice. GnRH release increased with higher frequency spontaneous firing to a point; release reached a plateau after which further increases in firing rate did not elicit further increased release. Kisspeptin, a potent GnRH neuron activator via a Gq-coupled signaling pathway, triggered GnRH release before increasing firing rate, whether globally perfused or locally applied. Increasing the number of spikes in an applied burst template increased release; orchidectomized mice had higher sensitivity to the increased action potential number than sham-operated mice. Similarly, Ca currents triggered by these burst templates were increased in GnRH neurons of orchidectomized mice. These results suggest removal of gonadal feedback increases the efficacy of the stimulus-secretion coupling mechanisms, a phenomenon that may extend to other steroid-sensitive regions of the brain. Pulsatile secretion of GnRH plays a critical role in fertility. The temporal relationship between GnRH neuron action potential firing and GnRH release remains unknown as does whether this relationship is influenced by gonadal feedback. By combining techniques of fast-scan cyclic voltammetry and patch-clamp we, for the first time, monitored GnRH concentration changes during spontaneous and neuromodulator-induced GnRH neuron firing. We also made the novel observation that gonadal factors exert negative feedback on excitation-secretion coupling to reduce release in response to the same stimulus. This has implications for the control of normal fertility, central causes of infertility, and more broadly for the effects of sex steroids in the brain.
在脊椎动物中，下丘脑神经元中促性腺激素释放激素 (GnRH) 的脉冲式释放触发了前垂体促性腺激素的分泌，从而激活了类固醇生成，而类固醇反过来又对 GnRH 的释放产生典型的同源负反馈。尽管脑片中原发性 GnRH 神经元的长期间歇性放电模式类似于 GnRH 和 LH 的脉冲式释放，但 GnRH 神经元放电与释放之间的关系以及这种关系是否受到性腺反馈的影响尚不清楚。我们结合快速扫描循环伏安法和膜片钳技术，在来自雄性小鼠的脑片制备物中，对神经肽释放进行了同步测量，这些脑片既可以自发产生动作电位，也可以响应神经调质或动作电位尖峰模板。GnRH 释放随着自发性放电频率的增加而增加，但达到一个点后，释放达到平台期，之后进一步增加放电率不会引起进一步增加的释放。 kisspeptin 通过 Gq 偶联信号通路强烈激活 GnRH 神经元，在增加放电率之前触发 GnRH 释放，无论是全身性灌注还是局部应用。在应用爆发模板中增加尖峰数量会增加释放；与假手术组相比，去势组小鼠对增加的动作电位数量更为敏感。同样，去势组小鼠 GnRH 神经元中由这些爆发模板触发的 Ca 电流也增加了。这些结果表明，去除性腺反馈会增加刺激-分泌偶联机制的效率，这种现象可能扩展到大脑的其他类固醇敏感区域。 GnRH 的脉冲式分泌对生育能力起着至关重要的作用。GnRH 神经元动作电位放电与 GnRH 释放之间的时间关系尚不清楚，也不清楚这种关系是否受到性腺反馈的影响。通过结合快速扫描循环伏安法和膜片钳技术，我们首次监测了自发性和神经调质诱导的 GnRH 神经元放电期间 GnRH 浓度的变化。我们还观察到一个新现象，即性腺因素对兴奋-分泌偶联产生负反馈，以减少对相同刺激的释放。这对正常生育能力的控制、不孕的中枢原因，以及更广泛地对大脑中性类固醇的影响都有意义。
