Dufourny Laurence, Lomet Didier
INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France; CNRS, UMR 7247, F-37380 Nouzilly, France; Université de Tours, F-37041 Tours, France; IFCE, F-37380 Nouzilly, France.
INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France; CNRS, UMR 7247, F-37380 Nouzilly, France; Université de Tours, F-37041 Tours, France; IFCE, F-37380 Nouzilly, France.
Gen Comp Endocrinol. 2017 Dec 1;254:68-74. doi: 10.1016/j.ygcen.2017.09.017. Epub 2017 Sep 18.
Seasonal reproduction is under the control of gonadal steroid feedback, itself synchronized by day-length or photoperiod. As steroid action on GnRH neurons is mostly indirect and therefore exerted through interneurons, we looked for neuroanatomical interactions between kisspeptin (KP) neurons and somatostatin (SOM) neurons, two populations targeted by sex steroids, in three diencephalic areas involved in the central control of ovulation and/or sexual behavior: the arcuate nucleus (ARC), the preoptic area (POA) and the ventrolateral part of the ventromedial hypothalamus (VMHvl). KP is the most potent secretagogue of GnRH secretion while SOM has been shown to centrally inhibit LH pulsatile release. Notably, hypothalamic contents of these two neuropeptides vary with photoperiod in specific seasonal species. Our hypothesis is that SOM inhibits KP neuron activity and therefore indirectly modulate GnRH release and that this effect may be seasonally regulated. We used sections from ovariectomized estradiol-replaced ewes killed after photoperiodic treatment mimicking breeding or anestrus season. We performed triple immunofluorescent labeling to simultaneously detect KP, SOM and synapsin, a marker for synaptic vesicles. Sections from the POA and from the mediobasal hypothalamus were examined using a confocal microscope. Randomly selected KP or SOM neurons were observed in the POA and ARC. SOM neurons were also observed in the VMHvl. In both the ARC and POA, nearly all KP neurons presented numerous SOM contacts. SOM neurons presented KP terminals more frequently in the ARC than in the POA and VMHvl. Quantitative analysis failed to demonstrate major seasonal variations of KP and SOM interactions. Our data suggest a possible inhibitory action of SOM on all KP neurons in both photoperiodic statuses. On the other hand, the physiological significance of KP modulation of SOM neuron activity and vice versa remain to be determined.
季节性繁殖受性腺类固醇反馈的控制，而性腺类固醇反馈本身又由日长或光周期同步。由于类固醇对促性腺激素释放激素（GnRH）神经元的作用大多是间接的，因此是通过中间神经元发挥作用，我们在参与排卵和/或性行为中枢控制的三个间脑区域，即弓状核（ARC）、视前区（POA）和腹内侧下丘脑腹外侧部分（VMHvl），寻找亲吻素（KP）神经元和生长抑素（SOM）神经元之间的神经解剖学相互作用，这两类神经元是性类固醇作用的靶点。KP是GnRH分泌最有效的促分泌素，而SOM已被证明可在中枢抑制促黄体生成素（LH）的脉冲式释放。值得注意的是，在特定的季节性物种中，这两种神经肽的下丘脑含量会随光周期而变化。我们的假设是，SOM抑制KP神经元的活动，从而间接调节GnRH的释放，并且这种作用可能受季节性调节。我们使用了来自经光周期处理模拟繁殖或发情季节后处死的去卵巢并补充雌二醇的母羊的切片。我们进行了三重免疫荧光标记，以同时检测KP、SOM和突触素（一种突触小泡标记物）。使用共聚焦显微镜检查来自POA和下丘脑中间基底部的切片。在POA和ARC中随机选择KP或SOM神经元进行观察。在VMHvl中也观察到了SOM神经元。在ARC和POA中，几乎所有的KP神经元都有大量SOM接触。SOM神经元在ARC中比在POA和VMHvl中更频繁地呈现KP终末。定量分析未能证明KP和SOM相互作用存在主要的季节性变化。我们的数据表明，在两种光周期状态下，SOM可能对所有KP神经元都有抑制作用。另一方面，KP对SOM神经元活动的调节以及反之亦然的生理意义仍有待确定。
