Melatonin (MEL) is a conserved molecule with respect to its synthesis pathway and functions. In crayfish, MEL content in eyestalks (Ey) increases at night under the photoperiod, and this indoleamine synchronizes the circadian rhythm of electroretinogram amplitude, which is expressed by retinas and controlled by the cerebroid ganglion (CG). The aim of this study was to determine whether MEL content in eyestalks and CG or circulating MEL in hemolymph (He) follows a circadian rhythm under a free-running condition; in addition, it was tested whether MEL might directly influence the spontaneous electrical activity of the CG. Crayfish were maintained under constant darkness and temperature, a condition suitable for studying the intrinsic properties of circadian systems. MEL was quantified in samples obtained from He, Ey, and CG by means of an enzyme-linked immunosorbent assay, and the effect of exogenous MEL on CG spontaneous activity was evaluated by electrophysiological recording. Variation of MEL content in He, Ey, and CG followed a circadian rhythm that peaked at the same circadian time (CT). In addition, a single dose of MEL injected into the crayfish at different CTs reduced the level of spontaneous electrical activity in the CG. Results suggest that the circadian increase in MEL content directly affects the CG, reducing its spontaneous electrical activity, and that MEL might act as a periodical signal to reinforce the organization of the circadian system in crayfish.

中文翻译：

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褪黑激素释放的昼夜节律是增强小龙虾昼夜节律系统时间结构的一种机制。

就其合成途径和功能而言，褪黑激素（MEL）是一个保守的分子。在小龙虾中，在光周期下的夜晚，眼柄中的MEL含量（Ey）会增加，并且这种吲哚胺使视网膜电图振幅的昼夜节律同步，该振幅由视网膜表达并由脑神经节（CG）控制。这项研究的目的是确定眼球和CG中的MEL含量或血淋巴（He）中的循环MEL含量是否在自由运转条件下遵循昼夜节律。此外，还测试了MEL是否会直接影响CG的自发电活动。小龙虾保持在恒定的黑暗和温度下，这是一个适合研究昼夜节律系统内在特性的条件。在从He，Ey，通过酶联免疫吸附测定法测定CG和CG，通过电生理记录评价外源MEL对CG自发活性的影响。He，Ey和CG中MEL含量的变化遵循的昼夜节律在同一昼夜节律时间（CT）达到峰值。此外，在不同的CT处将小剂量的MEL注入小龙虾可降低CG中的自发电活动水平。结果表明，昼夜节律中MEL含量的增加直接影响了CG，降低了其自发的电活动，并且MEL可能作为周期性信号来增强小龙虾中昼夜节律系统的组织。而CG遵循的昼夜节律在同一昼夜节律时间（CT）达到峰值。此外，在不同的CT处将小剂量的MEL注入小龙虾，可降低CG中的自发电活动水平。结果表明，昼夜节律中MEL含量的增加直接影响了CG，降低了其自发的电活动，并且MEL可能作为周期性信号来增强小龙虾中昼夜节律系统的组织。而CG遵循的昼夜节律在同一昼夜节律时间（CT）达到峰值。此外，在不同的CT处将小剂量的MEL注入小龙虾可降低CG中的自发电活动水平。结果表明，昼夜节律中MEL含量的增加直接影响了CG，降低了其自发的电活动，并且MEL可能作为周期性信号来增强小龙虾中昼夜节律系统的组织。