Melatonin as a Signaling Molecule for Metabolism Regulation in Response to Hypoxia in the Crab Neohelice granulata

Abstract

Melatonin has been identified in a variety of crustacean species, but its function is not as well understood as in vertebrates. The present study investigates whether melatonin has an effect on crustacean hyperglycemic hormone (CHH) gene expression, oxygen consumption (VO2) and circulating glucose and lactate levels, in response to different dissolved-oxygen concentrations, in the crab Neohelice granulata, as well as whether these possible effects are eyestalk- or receptor-dependent. Melatonin decreased CHH expression in crabs exposed for 45 min to 6 (2, 200 or 20,000 pmol·crab−1) or 2 mgO2·L−1 (200 pmol·crab−1). Since luzindole (200 nmol·crab−1) did not significantly (p > 0.05) alter the melatonin effect, its action does not seem to be mediated by vertebrate-typical MT1 and MT2 receptors. Melatonin (200 pmol·crab−1) increased the levels of glucose and lactate in crabs exposed to 6 mgO2·L−1, and luzindole (200 nmol·crab−1) decreased this effect, indicating that melatonin receptors are involved in hyperglycemia and lactemia. Melatonin showed no effect on VO2. Interestingly, in vitro incubation of eyestalk ganglia for 45 min at 0.7 mgO2·L−1 significantly (p < 0.05) increased melatonin production in this organ. In addition, injections of melatonin significantly increased the levels of circulating melatonin in crabs exposed for 45 min to 6 (200 or 20,000 pmol·crab−1), 2 (200 and 20,000 pmol·crab−1) and 0.7 (200 or 20,000 pmol·crab−1) mgO2·L−1. Therefore, melatonin seems to have an effect on the metabolism of N. granulata. This molecule inhibited the gene expression of CHH and caused an eyestalk- and receptor-dependent hyperglycemia, which suggests that melatonin may have a signaling role in metabolic regulation in this crab.

The Hyperglycemic Effect of Melatonin in the Chinese Mitten Crab, Eriocheir sinensis

“…The present data demonstrate that both unilateral and bilateral eyestalk ablation can induce significantly low hemolymph glucose levels, especially bilateral ablation. These results are in agreement with earlier results in N. granulata (Maciel et al, 2014 ) and O. senex senex (Sainath and Reddy, 2010 ).…”

“…Therefore, eyestalk ablation is a classical operation to induce growth or precocious maturation of the gonad in commercial brood production (Sainath and Reddy, 2011 ). The effects of eyestalk ablation on hemolymph glucose levels have been reported in the crabs, Neohelice granulata (Maciel et al, 2014 ), a freshwater edible crab, Oziotelphusa senex senex (Sainath and Reddy, 2010 ) and the fiddler crab, Uca pugilator (Tilden et al, 2001 ). However, the role of the eyestalk in hemolymph glucose physiology has still not been extensively examined in E. sinensis .…”

“…These functions include limb regeneration (Tilden et al, 1997 ), circadian rhythms (Mendoza-Vargas et al, 2017 ), the anti-oxidant defense system (Geihs et al, 2016 ) and reproduction (Girish et al, 2015 ). Moreover, melatonin can also affect the level of hemolymph glucose (Sainath and Reddy, 2010 ; Maciel et al, 2014 ).…”

Melatonin Uptake by Cells: An Answer to Its Relationship with Glucose?

“…Most of the studies have been accomplished in crustaceans. Thus, in the crab Eriocheir sinensis , melatonin injection provoked hyperglycemia by inducing crustacean hyperglycemic hormone (CHH) mRNA synthesis and a similar effect was observed in Uca pugilator [ 190 ] and in Neohelice granulata [ 100 ], thus demonstrating an ancient relationship between melatonin and glucose.…”

Nanoencapsulated Melaleuca alternifolia essential oil exerts anesthetic effects in the brachyuran crab using Neohelice granulate

“…For immersion tests, EOs, eugenol, and menthol were previously dissolved in ethanol at a ratio of 1:10 (stock solution) before they were added to the water. For injection or gavage tests, eugenol and menthol were used after being dissolved in ethanol or diluted in physiological solution for crustaceans (Maciel et al 2014). Terpinen-4-ol and nanoencapsulated TTO were used pure or diluted in physiological solution.…”