Influence of the estrous cycle on c-fos and CRH gene transcription in the brain of endotoxin-challenged female rats.
Influence of the estrous cycle on c-fos and CRH gene transcription in the brain of endotoxin-challenged female rats.
复制标题
发情周期对内毒素攻击雌性大鼠大脑中 c-fos 和 CRH 基因转录的影响。
作者：
R. Nappi;M. Bonneau;S. Rivest
本研究旨在探讨排卵周期是否干扰全身免疫激活的急性时相反应对雌性大鼠脑内即刻早期基因c-fos和应激相关神经肽促肾上腺皮质激素释放激素(CRH)转录的影响。在整个动情前期和动情间期2天(09.00，12.00，15.00h)，成年大鼠一次性腹腔注射内毒素(LPS，200微克/100g体重)或溶媒溶液，3h后(12.00，15.00，18.00h)处死。冰冻切片制作成30微米切片，分别用35S标记的外显子和内含子探针进行原位杂交组织化学检测c-fos mRNA和CRH初级转录本(异核)。注射脂多糖诱导c-fos基因在终板/视前内侧区、视上核、下丘脑室旁核的小细胞和巨细胞分裂、弓状核和正中隆起、杏仁中央核、蓝斑、孤束核、最后区和延髓腹外侧区等多个核团和区域表达。有趣的是，c-fos mRNA的表达强度取决于发情周期的不同阶段和/或一天中的不同时间。事实上，在上述几个结构中，内毒素在发情前期的上午比下午和发情间期-2诱导更明显的c-fos信号。内毒素处理后，CRH初级转录物在下丘脑室旁核的小细胞分裂中显著增加，在发情前期早晨杂交信号最强，此时CRH免疫反应阳性神经元中有大量c-fos阳性细胞共存。在发情前期和发情间歇期的中午和下午早些时候，处死动物的PVN中AVP hnRNA的水平也显著增加。这些结果表明，调节生殖周期性的神经内分泌事件影响内毒素诱导的早期基因c-fos在大脑选择性结构中的激活，以及对直接参与HPA轴调节的神经元的刺激。在排卵周期的特定阶段，雌性哺乳动物的性腺状态可能对机体在外来物质存在时的整合起着至关重要的作用，以防止过度的免疫反应。雌性动物在免疫原过程中调节神经元回路激活强度的能力很可能是一种优雅的性别二型性，参与了符合生理需求的反应的调整。
The purpose of this study was to investigate whether the ovulatory cycle interferes with the effect of the acute-phase response of a systemic immune activation on the transcription of the immediate early gene c-fos and the stress-related neuropeptide corticotropin-releasing hormone (CRH) in the brains of female rats. Throughout the day of proestrus and diestrus-2 (09.00, 12.00, 15.00 h), adult rats received either a single intraperitoneal injection of the endotoxin lipopolysaccharide (LPS, 200 micrograms/100 g body weight) or the vehicle solution and were killed 3 h later (12.00, 15.00, 18.00 h). Frozen brains were mounted on a microtome, cut in 30-micron slices and then processed for the detection of c-fos mRNA and CRH primary transcript (heteronuclear [hnRNA]) by means of in situ hybridization histochemistry using 35S-labeled exonic and intronic probes, respectively. LPS injection induced a profound expression of c-fos mRNA in the several nuclei and areas of the brain, such as the organum vasculosum of the lamina terminalis/medial preoptic area, supraoptic nucleus, parvo- and magnocellular divisions of the hypothalamic paraventricular nucleus (PVN), arcuate nucleus/median eminence, central nucleus of the amygdala, locus coeruleus, nucleus of the solitary tract, area postrema and ventrolateral medulla. Interestingly, the intensity of expression of c-fos mRNA depended on the phase of the estrous cycle and/or the time of the day. Indeed, in several of the structures described above, LPS induced a more pronounced c-fos signal in the morning of proestrus than the afternoon and diestrus-2. CRH primary transcript was significantly increased by LPS treatment selectively in the parvocellular division of the PVN and the highest hybridization signal was observed in the morning of proestrus, a period where a large number of c-fos-positive cells were colocalized in CRH-immunoreactive neurons. A significant increase in the levels of AVP hnRNA was also observed in the parvocellular PVN of animals sacrificed at noon and early afternoon of both pro- and diestrus days. These results provide evidence that the neuroendocrine events regulating the reproductive cyclicity influence the endotoxin-induced activation of the early gene c-fos in selective structures of the brain and the stimulation of neurons directly involved in the regulation of the HPA axis. It is possible that the gonadal status of female mammals plays a crucial role in the integration of the organism in the presence of foreign material in preventing an exaggerated immune response during particular phases of the ovulatory cycle. The capacity of female animals to modulate the intensity through which the neuronal circuitry activated during immunogenic processes is likely to be an elegant sexual dimorphism participating in the adjustment of the responses in line with the physiological demand.