LH分泌的内源性年周期节律：信号分析结合数学建模的见解
Endogenous circannual rhythm in LH secretion: insight from signal analysis coupled with mathematical modelling
摘要：
在绵羊和许多脊椎动物中，繁殖的季节性模式是由每年的光周期来决定的，其特征是日照长度的季节性变化。光周期信息被转化为褪黑激素分泌的昼夜节律曲线。在多个神经元中继（下丘脑内）之后，褪黑激素影响GnRH（促性腺激素释放激素）分泌，进而控制卵巢周期性。GnRH分泌模式反映为LH（促黄体激素）分泌模式，其血浆水平可以很容易地测量。我们解决的问题，是否存在一个内源性的昼夜节律在热带绵羊种群，表现出明确的季节性卵巢活动时，母羊受到温带纬度。我们基于我们的分析LH时间序列收集的过程中，3年的母羊进行了一个恒定的光周期制度。由于动物内和动物间的变异性和不相等的采样时间，内源性节律的存在并不简单。我们使用时频信号处理方法从数据中提取隐藏的节奏。为了进一步研究信号的低频和高频成分，我们设计了一个LH等离子体水平的数学模型，该模型考虑了实验采样时间的影响。该模型使我们能够确认存在一个内源性的昼夜节律，研究光周期的LH分泌（脉冲间隔控制）的脉动模式的作用机制，并得出结论，HF成分主要是由于实验采样协议。
英文摘要：
In sheep as in many vertebrates, the seasonal pattern of reproduction is timed by the annual photoperiodic cycle, characterized by seasonal changes in the daylength. The photoperiodic information is translated into a circadian profile of melatonin secretion. After multiple neuronal relays (within the hypothalamus), melatonin impacts GnRH (gonadotrophin releasing hormone) secretion that in turn controls ovarian cyclicity. The pattern of GnRH secretion is mirrored into that of LH (luteinizing hormone) secretion, whose plasmatic level can be easily measured. We addressed the question of whether there exists an endogenous circannual rhythm in a tropical sheep population that exhibits clear seasonal ovarian activity when ewes are subjected to temperate latitudes. We based our analysis on LH time series collected in the course of 3 years from ewes subjected to a constant photoperiodic regime. Due to intra- and inter- animal variability and unequal sampling times, the existence of an endogenous rhythm is not straightforward. We have used time-frequency signal processing methods to extract hidden rhythms from the data. To further investigate the LF (low frequency) and HF (high frequency) components of the signals, we have designed a mathematical model of LH plasmatic level accounting for the effect of experimental sampling times. The model enables us to confirm the existence of an endogenous circannual rhythm, to investigate the action mechanism of photoperiod on the pulsatile pattern of LH secretion (control of the interpulse interval) and to conclude that the HF component is mainly due to the experimental sampling protocol.
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