van der Beek E M, Wiegant V M, van Oudheusden H J, van der Donk H A, van den Hurk R, Buijs R M
Department of Human and Animal Physiology, Agricultural University, Wageningen, The Netherlands.
Brain Res. 1997 Apr 25;755(1):101-11. doi: 10.1016/s0006-8993(97)00086-3.
The suprachiasmatic nucleus (SCN) is critically involved in the generation and entrainment of circadian rhythms in mammalian species. Both the occurrence and the timing of the luteinizing hormone surge on the afternoon of proestrus in the female rodent are critically dependent on the integrity of the SCN. Recently, we demonstrated the presence of a monosynaptic pathway from the SCN to the gonadotropin releasing hormone (GnRH) neurons in the preoptic area. In addition, we found that interaction between the SCN and the GnRH system may be found close to the SCN, since we observed apposition of SCN efferents and GnRH fibers at the ultrastructural level in that region. The aim of the present study was to investigate the presence of synaptic contacts between GnRH fibers and structures in the SCN and surrounding perichiasmatic area (periSCN). At the light microscopical level, the immunoreactivity for GnRH showed a considerable overlap with the immunoreactivity for vasopressin and vasoactive intestinal peptide, two neuropeptides synthesized by SCN neurons. At the ultrastructural level, we demonstrated synaptic input of GnRH-containing axons on immunocytochemically unidentified structures in the SCN/peri-SCN region. The present results clearly demonstrate that the SCN and periSCN are postsynaptic targets of GnRH fibers. It is hypothesized that the GnRH input in the SCN region represents an anatomical substrate for feedback-control between these systems.
视交叉上核（SCN）在哺乳动物昼夜节律的产生和调节中起着关键作用。雌性啮齿动物发情前期下午促黄体生成素高峰的出现及其时间，都严重依赖于SCN的完整性。最近，我们证明了从SCN到视前区促性腺激素释放激素（GnRH）神经元存在单突触通路。此外，我们发现SCN与GnRH系统之间的相互作用可能在靠近SCN的位置，因为我们在该区域的超微结构水平上观察到SCN传出纤维与GnRH纤维并列。本研究的目的是调查GnRH纤维与SCN及周围视交叉周围区域（periSCN）结构之间是否存在突触联系。在光学显微镜水平上，GnRH的免疫反应性与加压素和血管活性肠肽的免疫反应性有相当大的重叠，这两种神经肽是由SCN神经元合成的。在超微结构水平上，我们证明了含GnRH的轴突对SCN/peri-SCN区域免疫细胞化学未鉴定结构的突触输入。目前的结果清楚地表明，SCN和periSCN是GnRH纤维的突触后靶点。据推测，SCN区域的GnRH输入代表了这些系统之间反馈控制的解剖学基础。
