Okamura H, Kawakami F, Tamada Y, Geffard M, Nishiwaki T, Ibata Y, Inouye S T
Department of Anatomy, Kyoto Prefectural University of Medicine, Japan.
Brain Res Mol Brain Res. 1995 Apr;29(2):358-64. doi: 10.1016/0169-328x(94)00278-m.
Neuronal activity of the suprachiasmatic nucleus (SCN) is known to be regulated by two major extrinsic factors conveyed by three anatomically distinct pathways to the SCN: photic stimulus by the direct retinohypothalamic tract (RHT) and the indirect geniculohypothalamic tract (GHT), and information from the brainstem by ascending forebrain serotonergic (5-hydroxytryptamine: 5-HT) tract. It has been shown that VIP mRNA level in neurons of the SCN is altered by external light, but remains stable in constant darkness. In the present study, by using the in situ hybridization technique combined with computer-assisted image analysis, we examined VIP mRNA expression in the SCN of rats in which the two major factors were eliminated, i.e. photic stimulus by exposing animals in total darkness and 5-HT transmission by three-day successive administration of p-chlorophenyl-alanine methylester (an inhibitor of tryptophan hydroxylase, 200 mg/kg, daily). In saline-treated controls, VIP mRNA levels remained almost constant throughout the day. In contrast, in PCPA-treated rats, a significant rhythm of VIP mRNA was observed with a peak at CT 4 and a trough at CT 20. These observations suggest that the removal of photic and 5-HT influence induces VIP mRNA rhythm in the SCN, indicating that VIP mRNA is controlled not only by photic information but also by the circadian clock.
已知视交叉上核（SCN）的神经元活动受两条主要外在因素调节，这两条因素通过三条解剖结构不同的通路传递至SCN：直接视网膜下丘脑束（RHT）和间接膝状体下丘脑束（GHT）传递的光刺激，以及来自脑干的上行前脑血清素能（5-羟色胺：5-HT）束传递的信息。研究表明，SCN神经元中的血管活性肠肽（VIP）mRNA水平会受外界光照影响而改变，但在持续黑暗环境中保持稳定。在本研究中，我们采用原位杂交技术结合计算机辅助图像分析，检测了消除这两种主要因素后的大鼠SCN中VIP mRNA的表达情况，即通过将动物置于完全黑暗环境中消除光刺激，以及通过连续三天给予对氯苯丙氨酸甲酯（色氨酸羟化酶抑制剂，200mg/kg，每日）来阻断5-HT传递。在生理盐水处理的对照组中，VIP mRNA水平全天几乎保持恒定。相比之下，在接受对氯苯丙氨酸（PCPA）处理的大鼠中，观察到VIP mRNA有显著节律，在CT4时达到峰值，在CT20时达到谷值。这些观察结果表明，去除光刺激和5-HT的影响会诱导SCN中VIP mRNA的节律，这表明VIP mRNA不仅受光信息控制，还受生物钟控制。
