Krajnak K, Kashon M L, Rosewell K L, Wise P M
Department of Physiology, University of Kentucky, Lexington 40536-0084, USA.
Endocrinology. 1998 Oct;139(10):4189-96. doi: 10.1210/endo.139.10.6259.
The timing of the preovulatory surge of LH in female rodents is tightly coupled to the environmental light/dark cycle. This coupling is mediated by the circadian pacemaker located in the suprachiasmatic nuclei (SCN). Studies indicate that vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP), which are synthesized in the SCN, transmit circadian information from the SCN to GnRH neurons, thereby regulating the timing of the LH surge. However, to date, the rhythmic expression of these two peptides in the SCN has only been examined in males. The pattern of VIP expression in males is difficult to reconcile with its role in the LH surge. The purpose of the present study was to assess the rhythm of VIP messenger RNA (mRNA) levels in the SCN of female rats under several endocrine conditions. We compared this rhythm to that in males and to AVP mRNA rhythms in all experimental groups. In all groups of females, VIP mRNA levels were rhythmic, with peak expression occurring during the light phase and a nadir occurring during the dark phase. The rhythm was approximately 12 h out of phase compared with that in males. The rhythmic expression of AVP mRNA in the SCN was virtually identical in all groups of animals. Based on these results, we conclude that 1) the rhythm of VIP seen in the SCN of females during the day may serve as a facilitory signal from the SCN to GnRH neurons; 2) the sex-specific pattern of VIP mRNA does not depend on estradiol; and 3) AVP gene expression within the SCN is not sexually differentiated or altered by estradiol.
雌性啮齿动物促排卵前促黄体生成素（LH）激增的时间与环境光/暗周期紧密相关。这种关联是由位于视交叉上核（SCN）的昼夜节律起搏器介导的。研究表明，在SCN中合成的血管活性肠肽（VIP）和精氨酸加压素（AVP）将昼夜节律信息从SCN传递给促性腺激素释放激素（GnRH）神经元，从而调节LH激增的时间。然而，迄今为止，仅在雄性动物中研究了这两种肽在SCN中的节律性表达。雄性动物中VIP的表达模式与其在LH激增中的作用难以协调。本研究的目的是评估在几种内分泌条件下雌性大鼠SCN中VIP信使核糖核酸（mRNA）水平的节律。我们将这种节律与雄性动物的节律以及所有实验组中AVP mRNA的节律进行了比较。在所有雌性动物组中，VIP mRNA水平具有节律性，在光照期出现表达峰值，在黑暗期出现最低点。与雄性动物相比，该节律的相位大约相差12小时。所有动物组中SCN中AVP mRNA的节律性表达几乎相同。基于这些结果，我们得出以下结论：1）白天在雌性动物SCN中观察到的VIP节律可能作为从SCN到GnRH神经元的促进信号；2）VIP mRNA的性别特异性模式不依赖于雌二醇；3）SCN内AVP基因的表达没有性别差异，也不会被雌二醇改变。
