ABSTRACT

Circadian rhythms are an adaptive response of organisms to the environment that enables them to measure time. Circadian rhythms are some of the most studied biological rhythms. Serotonin (5HT) has been proposed as their modulator of circadian rhythms, playing a pivotal role in their establishment. However, 5HT concentrations are altered in insect organisms when they feed on some plant extracts. Insects show a variety of rhythms. The larval stage of the lepidopteran Spodoptera frugiperda is a pest of economically important crops. As a response, plants have developed secondary metabolites, such as azadirachtin, obtained from Azadirachta indica. We assessed the circadian rhythm of 5HT in the brain and digestive tube of larvae of S. frugiperda; furthermore, the effect of A. indica extract on the oscillations was evaluated. 5HT modulates the rhythms of locomotor activity, and if extracts of A. indica alter the concentration of 5HT, it can indirectly alter the rhythms of locomotor activity, as well as peristaltic movements of the intestine. Larvae were exposed to a 12 h:12 h light-dark (LD) photoperiod, and half of them remained for 72 h under constant darkness (DD). Tissue samples were obtained at six different times during a single 24 h period, and the amount of 5HT was quantified by high-performance liquid chromatography (HPLC). Data were statistically compared by a one-way ANOVA followed by a Tukey post hoc test and subjected to Cosinor analysis for assessment of 24 h rhythmicity. The results showed that the A. indica methanolic extract had an effect on the 5HT concentration of the brain and digestive tube of the larvae. In the brain, the 5HT increase in larvae fed with the extract could alter memory, learning, sleep, and locomotor activity processes. Whereas in the intestine, the 5HT decrease in the larvae fed with the extract could decrease peristalsis movements and, therefore, indirectly influence the antifeedant effect.

摘要

昼夜节律是生物体对环境的适应性反应，使它们能够测量时间。昼夜节律是研究最多的生物节律之一。血清素 (5HT) 已被提议作为它们的昼夜节律调节剂，在它们的建立中发挥关键作用。然而，当昆虫以某些植物提取物为食时，它们的 5HT 浓度会发生变化。昆虫表现出多种节奏。鳞翅目草地贪夜蛾的幼虫阶段是重要经济作物的害虫。作为回应，植物已经开发出次生代谢物，例如从印楝中获得的印楝素。我们评估了草地贪夜蛾幼虫大脑和消化管中 5HT 的昼夜节律; 此外，还评估了籼稻提取物对振荡的影响。5HT 调节运动活动的节律，如果A. indica 的提取物改变 5HT 的浓度，它可以间接改变运动活动的节律，以及肠道的蠕动运动。幼虫暴露于 12 小时：12 小时的明暗 (LD) 光周期，其中一半在恒定黑暗 (DD) 下保持 72 小时。在单个 24 小时内在六个不同时间获得组织样本，并通过高效液相色谱 (HPLC) 对 5HT 的量进行定量。通过单向方差分析和 Tukey post hoc 对数据进行统计比较测试并进行余弦分析以评估 24 小时节律。结果表明，籼稻甲醇提取物对幼虫脑和消化管的5HT浓度有影响。在大脑中，用提取物喂养的幼虫的 5HT 增加可能会改变记忆、学习、睡眠和运动活动过程。而在肠道中，用提取物喂养的幼虫的 5HT 减少会减少蠕动运动，因此间接影响拒食效果。