The use of probiotics has been recently considered a novel therapeutic strategy to prevent pathologies such as obesity; however, the specific mechanisms of action by which probiotics exert their beneficial effects on metabolic health remain unclear. The aim of the present study was to investigate the short-term effects of a probiotic Lactobacillus rhamnosus supplementation (PROB) on appetite regulation, growth-related markers, and microbiota diversity in zebrafish (Danio rerio) larvae, compared to a group subjected to a constant darkness photoperiod (DARK), as well as to evaluate the effects of both treatments on melatonin receptors' expression. After a 24 h treatment, both PROB and DARK conditions caused a significant increase in leptin a expression. Moreover, mRNA abundances of leptin b and proopiomelanocortin a were elevated in the PROB group, and DARK showed a similar tendency, supporting a negative regulation of appetite markers by the treatments. Moreover, both PROB and DARK also enhanced the abundances of melatonin receptors transcript (melatonin receptor 1 ba and bb) and protein (melatonin receptor 1) suggesting a potential involvement of melatonin in mediating these effects. Nevertheless, treatments did not exhibit a significant effect on the expression of most of the growth hormone/insulin-like growth factor axis genes evaluated. Finally, only the DARK condition significantly modulated gut microbiota diversity at such short time, altogether highlighting the rapid effects of this probiotic on modulating appetite regulatory and melatonin receptors' expression, without a concomitant variation of gut microbiota.

益生菌的使用最近被认为是预防肥胖等疾病的新治疗策略。然而，益生菌对代谢健康发挥有益作用的具体作用机制仍不清楚。本研究的目的是研究益生菌鼠李糖乳杆菌补充剂 (PROB) 对斑马鱼 ( Danio rerio ) 幼虫的食欲调节、生长相关标志物和微生物群多样性的短期影响，与接受益生菌的组相比。恒定黑暗光周期 (DARK)，以及评估两种处理对褪黑激素受体表达的影响。处理 24 小时后，PROB 和 DARK 条件均导致瘦素 a显着增加。表达。此外，瘦素 b和阿黑皮素原 a 的mRNA 丰度在 PROB 组中升高，而 DARK 显示出类似的趋势，支持治疗对食欲标志物的负调节。此外，PROB 和 DARK 还增加了褪黑激素受体转录本（褪黑激素受体 1 ba和bb) 和蛋白质（褪黑激素受体 1）表明褪黑激素可能参与介导这些作用。然而，处理对大多数评估的生长激素/胰岛素样生长因子轴基因的表达没有表现出显着影响。最后，只有 DARK 条件在如此短的时间内显着调节了肠道微生物群的多样性，共同突出了这种益生菌对调节食欲调节和褪黑激素受体表达的快速作用，而没有伴随肠道微生物群的变化。