Abstract

ِAim

Tryptophan hydroxylase-2 mRNA (TPH, the rate limiting enzyme in 5-HT synthesis) expression levels display circadian variations in the median and dorsal raphe nuclei. This circadian pattern is under the control of the suprachiasmatic nuclei (SCN), the master clock. Photoperiodic cue is encoded by the SCN which convey the seasonal message to target sites. In the present study, we have investigated the effect of photoperiodic changes on the serotonergic neurons of the raphe nuclei. We have assessed the daily expression of TPH2 mRNA in both median and dorsal raphe nuclei of rats housed either under long photoperiod (18 h light/6 h dark cycle, LP18:6) or short photoperiod (SP6:18). ٌ

Results

Our results demonstrate that under LP18:6, TPH2 mRNA levels display a progressive decrease during the dark period and a maximal expression is reported at the beginning of the light period. The expression pattern of TPH2 mRNA under SP6:18 remains unchanged during the dark period and increases significantly before the light/dark transition. This latter expression pattern is in line with the daily profiles of TPH2 mRNA reported previously under standard lighting regimen (12 h light/12 h dark cycle).

Conclusion

The present results suggest that TPH2 mRNA expression pattern within DR and MR is affected by photoperiod which might in turn affect TPH content and 5‐HT release within the circadian structures, but also in all the serotonergic projection areas of the brain.

中文翻译：

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光周期调节大鼠中缝核色氨酸羟化酶2基因表达的每日分布

摘要

目标

色氨酸羟化酶 2 mRNA（TPH，5-HT 合成中的限速酶）表达水平显示中缝核和中缝背核的昼夜节律变化。这种昼夜节律模式受视交叉上核（SCN），即主时钟的控制。光周期提示由 SCN 编码，将季节性信息传达给目标站点。在本研究中，我们研究了光周期变化对中缝核 5-羟色胺能神经元的影响。我们评估了在长光周期（18 小时光照/6 小时黑暗周期，LP18:6）或短光周期（SP6:18）下饲养的大鼠的中缝核和背缝核中 TPH2 mRNA 的每日表达。⌌

结果

我们的结果表明，在 LP18:6 下，TPH2 mRNA 水平在黑暗期间显示出逐渐降低，并且在光照期开始时报告了最大表达。SP6:18 下 TPH2 mRNA 的表达模式在黑暗期间保持不变，在光/暗过渡之前显着增加。后一种表达模式与先前在标准光照方案（12 小时光照/12 小时黑暗循环）下报告的 TPH2 mRNA 的每日分布一致。

结论

目前的结果表明 DR 和 MR 中的 TPH2 mRNA 表达模式受光周期的影响，这可能反过来影响昼夜节律结构内的 TPH 含量和 5-HT 释放，但也影响大脑的所有 5-羟色胺能投射区域。