Abstract
Melatonin has been identified in a variety of invertebrate species, but its function is not as well understood as in crustaceans. The effects of melatonin on hemolymph glucose levels and tissue carbohydrate metabolism in the Chinese mitten crab, Eriocheir sinensis, were fully investigated in this study. Moreover, whether the eyestalk (an important endocrine center in invertebrate species) involves in this process or not, also were clarified. Analysis revealed that eyestalk ablation, especially bilateral, caused a significant decrease in the hemolymph glucose level. Moreover, injection of melatonin induced hyperglycemia in a dose-dependent manner both in intact and ablated crabs. Based on the expression of CHH mRNA in the 10 different tissues, eyestalk, thoracic ganglion, intestinal tract and hemolymph were selected to estimate the effect of melatonin on the expression of CHH mRNA. Bilateral eyestalk ablation caused a significant increase in the expression of CHH mRNA in the thoracic ganglion, intestinal tract and hemolymph compared with the controls. In addition, injection of melatonin into intact or ablated crabs elevated the CHH mRNA level in the eyestalk, thoracic ganglion and intestinal tract tissues compared with controls. The hemolymph CHH mRNA after melatonin injection was elevated only in ablated crabs. Administration of melatonin resulted in a significant decrease in total carbohydrates and glycogen levels with an increase in phosphorylase activity levels in the hepatopancreas and muscle in intact and ablated crabs. Our findings demonstrated that melatonin can induce hyperglycemic effects in both intact and ablated crabs, suggesting that this effect is probably not mediated solely via eyestalk.
Highlights
Melatonin (5-methoxy-N-acetyltryptamine, MT), is a highly conserved and ubiquitous molecule present from unicellular organisms to mammals
Injection of melatonin into crabs with or without eyestalks resulted in significant hyperglycemia in a dose-dependent manner, whereas injection of crustacean saline did not evoke any significant change in hemolymph glucose levels (p > 0.05, Figure 2)
Crustacean hyperglycemic hormone (CHH) mRNA expression had tissue-specific characteristic in E. sinensis
Summary
Melatonin (5-methoxy-N-acetyltryptamine, MT), is a highly conserved and ubiquitous molecule present from unicellular organisms to mammals. Hyperglycemia of Melatonin on E. sinensis peripheral tissues such as the cerebroid ganglion (MendozaVargas et al, 2017), intestine (Lardone et al, 2014) and hemolymph (Mendoza-Vargas et al, 2017) in crustaceans (Balzer et al, 1997; Tilden et al, 1997). As an established neurotransmitter in animals, MT has caught the attention of crustacean physiologists in recent years because it regulates a broad range of body functions (Sainath et al, 2013). These functions include limb regeneration (Tilden et al, 1997), circadian rhythms (Mendoza-Vargas et al, 2017), the antioxidant defense system (Geihs et al, 2016) and reproduction (Girish et al, 2015). Melatonin can affect the level of hemolymph glucose (Sainath and Reddy, 2010; Maciel et al, 2014)
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