Involvement of norepinephrine in the hyperglycemic responses of the freshwater giant prawn, Macrobrachium rosenbergii, under cold shock

A brief and updated introduction to the neuroendocrine system of crustaceans

The neuroendocrine system of crustaceans is complex and regulates many processes, such as development, growth, reproduction, osmoregulation, behavior, and metabolism. Once stimulated, crustaceans' neuroendocrine tissues modulate the release of monoamines, ecdysteroids, and neuropeptides that can act as hormones or neurotransmitters. Over a few decades, research has unraveled some mechanisms governing these processes, substantially contributing to understanding crustacean physiology. More aspects of crustacean neuroendocrinology are being comprehended with molecular biology, transcriptome, and genomics analyses. Hence, these studies will also significantly enhance the ability to cultivate decapods, such as crabs and shrimps, used as human food sources. In this review, current knowledge on crustacean endocrinology is updated with new findings about crustacean hormones, focusing mainly on the main neuroendocrine organs and their hormones and the effects of these molecules regulating metabolism, growth, reproduction, and color adaptation. New evidence about vertebrate-type hormones found in crustaceans is included and discussed. Finally, this review may assist in understanding how the emerging chemicals of environmental concern can potentially impair and disrupt crustacean's endocrine functions and their physiology.

The impact of chasing stress on the metabolism of the Atlantic Ghost Crab Ocypode quadrata (Fabricius, 1787)

Ocypode quadrata, a Ghost crab species found along the western Atlantic coast, is considered a bioindicator of anthropogenic impact on sandy beaches. Ghost Crabbing, a touristic activity in which ghost crabs are chased just for fun, is a potentially threatening activity for this crab. In crustaceans, metabolites such as glucose and lactate, and the gene expression of crustacean hyperglycemic hormone (CHH) and heat shock proteins (HSPs) increase when the animals are exposed to several types of stress, including alterations in temperature, salinity, or exposure to xenobiotics. This work was developed to identify if being chased by humans would affect these markers of stress in this species of crab. The effects of chasing stress on hemolymph and tissue metabolites and the gene expression levels of CHH and HSP70 were investigated. The levels of lactate in the hemolymph of stressed crabs were six times higher than those of control crabs immediately after chasing and decreased progressively during recovery, indicating an active anaerobic metabolism during the stress. On the contrary, glucose levels in the hemolymph of the stressed crabs increased progressively from 30 to 60 min after chasing, indicating an inverse correlation between glucose and lactate and the conversion of lactate to glucose by gluconeogenesis. In stressed crabs, the levels of triglycerides in the hemolymph decreased 30 min after chasing, while the opposite tended to occur in the hepatopancreas, indicating that during recovery, the crabs use triglycerides as energy source to sustain aerobic metabolism. Finally, this study demonstrates that ghost crabs are stressed by minimum human contact and that "ghost crabbing" must not be encouraged as a tourist activity.

Effects of Low Temperature on Antioxidant and Heat Shock Protein Expression Profiles and Transcriptomic Responses in Crayfish (Cherax destructor)

Low temperature is a critical factor restricting the growth and survival of aquatic animals, but research on the mechanism of response to low temperature in Cherax destructor is limited. C. destructor is one of the most important freshwater crustaceans with strong adaptability in Australia, and it has been commercialized gradually in recent years. Here, growth indicators, antioxidant parameters, anti-stress gene expression, and transcriptome sequencing were used on crayfish following 8 weeks of low-temperature acclimation. The results showed that weight gain, length gain, and molting rates decreased as the temperature decreased. The activity of antioxidant enzymes decreased, while the content of antioxidant substances and the expression of anti-stress genes increased. Transcriptome sequencing identified 589 differentially expressed genes, 279 of which were upregulated and 310 downregulated. The gene functions and pathways for endocrine disorders, glucose metabolism, antioxidant defense, and immune responses were identified. In conclusion, although low-temperature acclimation inhibited the basal metabolism and immune ability of crayfish, it also increased the antioxidant substance content and anti-stress-gene expression to protect the organism from low-temperature damage. This study provided molecular insights into the study of low-temperature responses of low-temperature-tolerant crustacean species.

The effect of banana blossom on growth performance, immune response, disease resistance, and anti-hypothermal stress of Macrobrachium rosenbergii

Banana (Musa acuminata) blossom contains high nutritional value and bioactive compounds. In this study, Macrobrachium rosenbergii were fed with diets containing banana blossom powder (BBP) at 10 and 20 g kg^-1, hot-banana blossom (BBH) extract at 10 and 20 g kg^-1, and the basal diet for 56 days. The growth performance, physiological response and immune parameters were evaluated. The results showed that a significantly higher percentage weight gain (PWG) and percentage length gain (PLG) in prawns fed with BBH diet. The feed efficiency (FE) significantly increased in prawns fed BBP. The prawn fed both BBH and BBP diet showed higher survival rate than control group. The prawn fed with BBH showed a significant increase in total haemocyte count (THC) and different haemocyte count (DHC), whereas phenoloxidase (PO) activity and respiratory bursts (RBs) significant increase in prawns fed both BBP and BBH diet. Furthermore, M. rosenbergii fed with both BBP and BBH diets showed significantly higher phagocytic activity and clearance efficiency against Lactococcus garvieae infection. At the end of the 56 days of feeding trial, the susceptibility of prawns to L. garvieae infection and hypothermal (18 °C) stress were evaluated. The results showed that prawns fed BBH diets had a significantly higher survival rate against L. garvieae than those of fed with the basal diet. Anti-hypothermal stress was observed in prawns fed both BBP and BBH diets showing no significant difference in haemolymph glucose in prawns subjected to 18 °C and 28 °C, whereas the norepinephrine level in haemolymph of prawns fed with BBH diets subjected to 18 °C was significantly lower than in prawns subjected to 28 °C. In summary, we recommend addition of hot-banana blossom extract to the diet of M. rosenbergii at 20 g kg^-1 to promote growth performance, improve physiological function, enhance immunity, increase anti-hypothermal stress, and to increase resistance against L. gavieae.

Novel protein kinase C participates catecholamine biosynthesis and immunocompetence modulation in haemocytes of Litopenaeus vannamei

The catecholamine biosynthesis is required for physiological and immunological responses against stress, and the neuroendocrine-immune regulatory network plays a crucial role in immunocompetence of shrimp. A novel protein kinase C of Litopenaeus vannamei (LvnPKC) is involved in immune defense and signaling transduction in haemocytes, and in the present study, the gene silence technique is conducted to identify the role of LvnPKC on catecholamine biosynthesis and immunocompetence modulation in haemocytes of L. vannamei. The results show that tyrosine significantly increases in haemocytes of LvnPKC-silenced shrimp, and in the meantime, the obvious decrease of L-3, 4-dihydroxyphenylalanine and increase of dopamine as well as the consistent norepinephrine levels are detected. Tyrosine hydroxylase and dopamine β-hydroxylase activities are significantly reduced in haemocytes of LvnPKC-silenced shrimp. Total haemocyte count, hyaline cells and granulocytes insignificantly differ among treatments, and the obvious increase of phenoloxidase activity, respiratory bursts, superoxide dismutase and glutathione peroxidase activities are observed in haemocytes of LvnPKC-silenced shrimp, and furthermore, the downregulated phagocytic activity was observed. It is therefore concluded that the LvnPKC mediates catecholamine biosynthesis and immunocompetence in haemocytes, and plays a crucial role in the neuroendocrine-immune regulatory network.

'Prescribing' psychotropic medication to our rivers and estuaries

SummaryThe influence of pharmaceuticals on the environment is an increasing concern among environmental toxicologists. It is known that their growing use is leading to detectable levels in wastewater, conceivably causing harm to aquatic ecosystems. Psychotropic medication is one such group of substances, particularly affecting high-income countries. While these drugs have a clear place in therapy, there is debate around the risk/benefit ratio in patients with mild mental health problems. Therefore, it is necessary to evaluate the wider implications as risks could extend beyond the individual to non-target organisms, particularly those in rivers and estuaries.Declaration of interestNone.

Metabolic effects of epinephrine on the crab Neohelice granulata

Although widely known for their involvement in the control of carbohydrate and lipid metabolism of vertebrates, the participation of catecholamines (CAs) in the metabolism of invertebrates is less understood. This study was designed to identify the physiological role of Epinephrine (E) in the intermediary metabolism of the burrowing crab Neohelice granulata and how E regulates the metabolism in crabs fed with a high-carbohydrate (HC) or a high-protein (HP) diet. To answer these questions, we evaluated in vivo the effects of E injections on glucose and triglycerides in the hemolymph and tissue glycogen levels of crabs fed with HC or HP diet. An in vitro investigation was carried out to assess the direct effects of E on glycogenolysis, lipolysis and glycolysis pathways in the hepatopancreas, mandibular muscle and anterior and posterior gills of this crab. E injections increased glucose and did not affect triglycerides levels in the hemolymph of either group of crabs, and E decreased glycogen in the hepatopancreas and mandibular muscle only in HP crabs, suggesting that these effects may be mediated by the crustacean hyperglycemic hormone (CHH). When the tissues were incubated with different concentrations of E, the concentration of glucose released to the medium decreased in the hepatopancreas and posterior gills, while glucose oxidation increased in the posterior gills of HP crabs. Incubation with E did not alter any parameter in tissues of HC crabs. These effects suggest that E may be involved in the metabolic response to osmotic stress.

Octopamine enhances the immune responses of freshwater giant prawn, Macrobrachium rosenbergii, via octopamine receptors

Octopamine (OA) is known to play an important role in regulating insect immune responses. In Macrobrachium rosenbergii (18.0 ± 1.7 g), OA at 25.0 and 250.0 pmol/prawn significantly increased THC, semigranular cells (SGCs) and PO activity in hemocytes per 50 μL hemolymph, hyaline cells, granular cells (GCs) and RBs in hemocytes per 10 μL hemolymph, and RBs per hemocyte, and however, significantly decreased PO activity per granulocyte (GC + SGC), which returned to control levels after 4 h of injection. The significantly increased phagocytic activity and clearance efficiency of prawn received OA for 8 h returned to control levels after 16 h of injection. In addition, the significantly increased glucose and decreased lactate were observed within 1 h of OA injection. In the susceptibility test, prawn received OA at 25.0 or 250.0 pmol/prawn for 2 h then challenged with Lactococcus garvieae at 10⁵ colony-forming units/prawn significantly increased the resistance of prawns by 23.3% and 30.0%, respectively, compared to the saline-challenged control after 144 h of challenge. In addition, the changes on immunocompetence induced by OA were observed to be blocked by adrenoceptors antagonists. These results suggest that OA administration at 250.0 pmol/prawn or less causes the mediate a transient up-regulation in immune and physiologic responses to promote the resistance of M. rosenbergii to L. garvieae, which are thought to be mediated by α- and β-adrenergic-like octopamine receptors.

Effects of ammonia-N exposure on the concentrations of neurotransmitters, hemocyte intracellular signaling pathways and immune responses in white shrimp Litopenaeus vannamei

The effects of ammonia-N exposure (transferred from 0.07 to 2, 10 and 20 mg L^-1) on the mechanism of neuroendocrine-immunoregulatory network were investigated in Litopenaeus vannamei. The results showed that biogenic amines (dopamine, noradrenaline, 5-hydroxytryptamine) concentrations in treatment groups increased significantly within 12 h. The gene expression of guanylyl cyclase increased significantly from 3 h to 24 h. And dopamine receptor D₄ and α₂ adrenergic receptor gene expression in treatment groups decreased significantly within 12 h, whereas the mRNA expression of 5-HT₇ receptor increased significantly within 3 h and reached the peak levels at 6 h. The second messengers (cAMP, cGMP) and Calmodulin (CaM) increased significantly in treatment groups after 3 h. The concentrations of protein kinases (PKA, PKG) shared a similar trend in cAMP and cGMP which were up-regulated and reached the peak value at 6 h, while the PKC decreased within 3 h and arrived at its bottom at 6 h. The nuclear factor kappa-b and cAMP-response element binding protein mRNA expression levels of treatment shrimps increased sharply and reached maximum values at 6 h. The total hemocyte count, phagocytic activity, antibacterial activity in treatment groups decreased dramatically within 48 h. Whereas the phenoloxidase activities slightly up-regulated. Then it was decreased significantly up to 48 h. α₂-macroglobulin activity decreased at the first 3 h-stress. Then they up-regulated significantly in 6 h. The results suggest that there are two crucial neuroendocrine substances (biogenic amine and CHH), which play a principal role in adapting to ammonia-N exposure and cause immune response through cAMP-, CaM- and cGMP-dependent pathways.

Involvement of dopamine beta-hydroxylase in the neuroendocrine-immune regulatory network of white shrimp, Litopenaeus vannamei

In shrimp, the biosynthesis of catecholamines, including dopamine and norepinephrine, is required for physiological and immunological responses against stress. Dopamine beta-hydroxylase (DBH), a copper-containing monooxygenase enzyme that plays an important role in catecholamine synthesis of the neuroendocrine regulatory network, was identified in Litopenaeus vannamei. In the present study, the potential role of DBH in the immunocompetence of L. vannamei was further estimated by depleting DBH by pharmaceutical inhibition of disulfiram and a gene silencing technique of L. vannamei DBH-double-stranded (ds)RNA (LvDBH-dsRNA). Immunocompetence was evaluated following the determination of the total hemocyte count, differential hemocyte count, phenoloxidase activity, respiratory bursts, superoxide dismutase activity, phagocytic activity, and the clearance efficiency as well as the susceptibility against Vibrio alginolyticus infection. At 30-120 min after shrimp had received disulfiram, they exhibited significantly reduced total hemocyte count, phenoloxidase activity of hemocytes in hemolymph, respiratory bursts of hemocytes in hemolymph and per hemocyte, phagocytic activity, clearance efficiency, and survival ratio against V. alginolyticus infection, compared to those injected with saline. In addition, the significantly lower total hemocyte count, phagocytic activity, clearance efficiency, and resistance to V. alginolyticus infection were observed in shrimp that received LvDBH-dsRNA at 3 days post injection compared to those injected with diethyl pyrocarbonate-water or non-targeting gene-dsRNA. The DBH depleted L. vannamei revealed immunosuppression and decreased the survival ratio to V. alginolyticus infection, which indicated that DBH played a crucial role in the neuroendocrine-immune regulatory network.

The upregulation of immune responses in tyrosine hydroxylase (TH) silenced Litopenaeus vannamei

Catecholamines (CAs) play a crucial role in maintaining physiological and immune homeostasis in invertebrates and vertebrates under stressful conditions. Tyrosine hydroxylase (TH) is the first and rate-limiting enzyme in CA synthesis. To develop an effective CA-related immunological defense system against stress and pathogen infection, various criteria, were evaluated in TH double-stranded (ds) RNA-injected white shrimp, Litopenaeus vannamei. Specifically, the relative transcript quantification of TH, dopamine β-hydroxylase (DBH), crustacean hyperglycemic hormone (CHH), and other immune-related genes; TH activity in the haemolymph; and the estimation of l-dihydroxyphenylalanine (l-DOPA), glucose, and lactate levels in the haemolymph were examined. TH depletion revealed a significant increase in the total haemocyte count; granular cells; semigranular cells; respiratory bursts (RBs, release of superoxide anion); superoxide dismutase (SOD) activity; phagocytic activity and clearance efficiency; and the expression of lipopolysaccharide and β-1,3-glucan-binding protein and peroxinectin, SOD, crustin, and lysozyme genes. In addition, the reduction of TH gene expression and activity was accompanied by a decline of phenoloxidase (PO) activity per granulocyte, lower glucose and lactate levels, and significantly low expression of DBH and CHH genes. However, the number of hyaline cells, activity of PO, RBs per haemocyte, and expression of POI and POII genes were not significantly different in the LvTH-silenced shrimp. Notably, the survival ratio of LvTH-silenced shrimp was significantly higher than that of shrimp injected with diethyl pyrocarbonate-water and nontargeting dsRNA when challenged with Vibrio alginolyticus. Therefore, the depletion of TH can enhance disease resistance in shrimp by upregulating specific immune parameters but downregulating the levels of carbohydrate metabolites.

Dopamine beta-hydroxylase participate in the immunoendocrine responses of hypothermal stressed white shrimp, Litopenaeus vannamei

Dopamine beta-hydroxylase (DBH) plays a critical role in catecholamine (CA) synthesis of neuroendocrine regulatory network, and is suggested to be involved in the immunoendocrine responses of invertebrate against bacterial challenge. DBH has been identified in white shrimp, Litopenaeus vannamei, and further investigation on its potential function was conducted after hypothermal stress, pharmaceutical inhibition and gene silencing in the present study. Cloned DBH L. vannamei (LvDBH), belonging to the Copper type II, ascorbate-dependent monooxygenases, was characterized by a DOMON domain, a Cu2_monooxygen domain and three glycosylation sites, and its expression was abundant in thoracic ganglia and haemocytes determined by quantitative real-time PCR. The effects of hypothermal stress showed that LvDBH expression in thoracic ganglia, haemocytes and hepatopancreas as well as the DBH contents in haemocytes and dopamine (DA) and norepinephrine (NE) levels in haemolymph are obviously up-regulated. L. vannamei receiving disulfiram for 30-120 min revealed the inhibition of DBH and NE contents in haemocytes and haemolymph respectively, but high level of DA in haemolymph was noticed. Besides, a significant decrease of LvDBH expression in thoracic ganglia, haemocytes and hepatopancreas were also observed. Subsequently, LvDBH expression was successfully silenced in thoracic ganglia, haemocytes and hepatopancreas of shrimp that received LvDBH-dsRNA for 3 days, and meanwhile, a decrease of DBH contents in haemocytes accompanied by decreased levels of NE and DA in haemolymph were also observed. These results indicate that LvDBH possesses the functional domains responsible for CAs synthesis, and therefore, inhibiting DBH contents in haemocytes by disulfiram and by LvDBH-dsRNA resulted in the impaired synthesis of NE from DA in haemolymph. These also suggest that the increased release of DA and NE in haemolymph for potential modulation of physiological or immunological responses is the consequence of the upregulated LvDBH expression and DBH contents in L. vannamei exposed to hypothermal stress.

Roles of dopamine receptors in mediating acute modulation of immunological responses in Macrobrachium rosenbergii

Dopamine (DA) was found to influence the immunological responses and resistance to pathogen infection in invertebrates. To clarify the possible modulation of DA through dopamine receptors (DAR) against acute environmental stress, the levels of DA, glucose and lactate in the haemolymph of Macrobrachium rosenbergii under hypo- and hyperthermal stresses were measured. The changes in immune parameters such as total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and phagocytic activity (PA) were evaluated in prawns which received DAR antagonists (SCH23390, SCH, D1 antagonist; domperidone, DOM, D2 antagonist; chlorpromazine, CH, D1+2 antagonist) followed by hypo- (15 °C) and hyperthermal (34 °C) stresses. In addition, pharmacological analysis of the effect DA modulation was studied in haemocytes incubated with DA and DAR antagonists. The results revealed a significant increase in haemolymph DA accompanied with upregulated levels of glucose and lactate in prawns exposed to both hypo- and hyperthermal stresses in 2 h. In addition, a significant decrease in RBs per haemocyte was noted in prawns which received DAR antagonists when they exposed to hyperthermal stress for 30 min. In in vitro test, antagonism on RBs, SOD and GPx activity of haemocytes were further evidenced through D1, D1, D1+D2 DARs, respectively, in the meantime, no significant difference in PO activity and PA was observed among the treatment groups. These results suggest that the upregulation of DA, glucose and lactate in haemolymph might be the response to acute thermal stress for the demand of energy, and the DAR occupied by its antagonistic action impart no effect on immunological responses except RBs in vivo even though the modulation mediated through D1 DAR was further evidenced in RBs, SOD and GPx activities in vitro. It is therefore concluded that thermal stress mediate stress responses not only through DAR but also via diverse pathways, and DA might modulate the levels of RBs, SOD and GPx activities mainly through D1 DAR.

A first insight into temperature stress-induced neuroendocrine and immunological changes in giant freshwater prawn, Macrobrachium rosenbergii

Haemolymph norepinephrine (NE); total haemocyte count (THC); respiratory bursts (RBs); superoxide dismutase (SOD), phenoloxidase (PO), and phagocytic activity; and prophenoloxidase (proPO)-system-related genes (lipopolysaccharide- and β-1,3-glucan-binding protein: LGBP, proPO, peroxinectin: PE, and α2-macroglobulin: α2-M) in haemocytes of Macrobrachium rosenbergii were investigated after transferring them from 28 °C to 22 °C, 28 °C, and 34 °C respectively. The results revealed that haemolymph NE, hyaline cells (HCs), and PO activity per granulocyte increased from 30 to 120 min of exposure, and however, RBs and phagocytic activity significantly decreased from 30 to 120 min of exposure as well as granular cells (GCs), semigranular cells (SGCs), and SOD activity decreased from 60 to 120 min of exposure for the prawns subjected to temperature stress. The proPO-system-related gene expression markedly increased with 60-120 min of exposure for the prawns transferred from 28 °C to 22 °C and 34 °C, except α2M at 120 min. These results provide a first insight into the effects of temperature stress on haemolymph NE level and immune functions in prawns and suggest that temperature-stress-induced acute modulation in immunity is associated with the release of haemolymph NE in M. rosenbergii.

Norepinephrine and dopamine increase motility, biofilm formation, and virulence of Vibrio harveyi

Vibrio harveyi is one of the major pathogens of aquatic organisms, affecting both vertebrates and invertebrates, and causes important losses in the aquaculture industry. In order to develop novel methods to control disease caused by this pathogen, we need to obtain a better understanding of pathogenicity mechanisms. Sensing of catecholamines increases both growth and production of virulence-related factors in pathogens of terrestrial animals and humans. However, at this moment, knowledge on the impact of catecholamines on the virulence of pathogens of aquatic organisms is lacking. In the present study, we report that in V. harveyi, norepinephrine (NE) and dopamine (Dopa) increased growth in serum-supplemented medium, siderophore production, swimming motility, and expression of genes involved in flagellar motility, biofilm formation, and exopolysaccharide production. Consistent with this, pretreatment of V. harveyi with catecholamines prior to inoculation into the rearing water resulted in significantly decreased survival of gnotobiotic brine shrimp larvae, when compared to larvae challenged with untreated V. harveyi. Further, NE-induced effects could be neutralized by α-adrenergic antagonists or by the bacterial catecholamine receptor antagonist LED209, but not by β-adrenergic or dopaminergic antagonists. Dopa-induced effects could be neutralized by dopaminergic antagonists or LED209, but not by adrenergic antagonists. Together, our results indicate that catecholamine sensing increases the success of transmission of V. harveyi and that interfering with catecholamine sensing might be an interesting strategy to control vibriosis in aquaculture. We hypothesize that upon tissue and/or hemocyte damage during infection, pathogens come into contact with elevated catecholamine levels, and that this stimulates the expression of virulence factors that are required to colonize a new host.

The biological effects of antidepressants on the molluscs and crustaceans: a review

Antidepressants are among the most commonly detected human pharmaceuticals in the aquatic environment. Since their mode of action is by modulating the neurotransmitters serotonin, dopamine, and norepinephrine, aquatic invertebrates who possess transporters and receptors sensitive to activation by these pharmaceuticals are potentially affected by them. We review the various types of antidepressants, their occurrence and concentrations in aquatic environments, and the actions of neurohormones modulated by antidepressants in molluscs and crustaceans. Recent studies on the effects of antidepressants on these two important groups show that molluscan reproductive and locomotory systems are affected by antidepressants at environmentally relevant concentrations. In particular, antidepressants affect spawning and larval release in bivalves and disrupt locomotion and reduce fecundity in snails. In crustaceans, antidepressants affect freshwater amphipod activity patterns, marine amphipod photo- and geotactic behavior, crayfish aggression, and daphnid reproduction and development. We note with interest the occurrence of non-monotonic dose responses curves in many studies on effects of antidepressants on aquatic animals, often with effects at low concentrations, but not at higher concentrations, and we suggest future experiments consider testing a broader range of concentrations. Furthermore, we consider invertebrate immune responses, genomic and transcriptomic sequencing of invertebrate genes, and the ever-present and overwhelming question of how contaminant mixtures could affect the action of neurohormones as topics for future study. In addressing the question, if antidepressants affect aquatic invertebrates at concentrations currently found in the environment, there is strong evidence to suggest the answer is yes. Furthermore, the examples highlighted in this review provide compelling evidence that the effects could be quite multifaceted across a variety of biological systems.

Characterisation of AmphiAmR4, an amphioxus (Branchiostoma floridae) α₂-adrenergic-like G-protein-coupled receptor

Little is known about the evolutionary relationship between vertebrate adrenergic receptors and invertebrate octopamine and tyramine receptors. The complexity of the adrenergic signalling system is believed to be an innovation of the vertebrate lineage but the presence of noradrenaline has been reported in some invertebrate species. The cephalochordate, amphioxus (Branchiostoma floridae), is an ideal model organism for studying the evolution of vertebrate GPCRs, given its unique position at the base of the chordate lineage. Here, we describe the pharmacological characterisation and second messenger coupling abilities of AmphiAmR4, which clusters with α₂-adrenergic receptors in a phylogenetic tree but also shares a high sequence similarity to invertebrate octopamine/tyramine receptors in both BLAST and Hidden Markov Model analyses. Thus, it was of particular interest to determine if AmphiAmR4 displayed similar functional properties to the vertebrate α₂-adrenergic receptors or to invertebrate octopamine or tyramine receptors. When stably expressed in Chinese hamster ovary (CHO) cells, noradrenaline couples the receptor to both the activation of adenylyl cyclase and to the activation of the MAPKinase pathway. Pharmacological studies with a wide range of agonists and antagonists suggest that AmphiAmR4 functions as an α₂-adrenergic-like receptor when expressed in CHO cells.

Norepinephrine regulates prophenoloxidase system-related parameters and gene expressions via α- and β-adrenergic receptors in Litopenaeus vannamei

The total (THC) and differential haemocyte counts (DHC), phenoloxidase (PO) activity, and prophenoloxidase (proPO) system-related genes were investigated in haemocytes of Litopenaeus vannamei that received saline, norepinephrine (NE), and NE co-treated with various adrenergic receptor (AR) antagonists both in vivo and in vitro. Results showed that semi-granular and granular cells of shrimp which received NE, NE + phentolamine (Phe), NE + prazosin (Pra), NE + propanolol (Pro) and NE + metoprolol (Met) significantly decreased, while the PO activity of the shrimp received NE + Phe in vivo was significant higher than all the other treatments. PO activities of haemocytes exposed to saline, Pra + NE, and Met + NE were significantly higher than those of haemocytes exposed to NE, Phe + NE, and Pro + NE in vitro. Similar phenomena in lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP), proPO-I, proPO-II, serine proteinases (SP), and peroxinectin (PE) messenger (m)RNA expressions of haemocytes exposed to saline, NE, and NE co-treated with various AR antagonists were observed both in vivo and in vitro. No significant differences were observed for LGBP and proPO-II mRNA expressions between haemocytes treated with saline and Pra + NE, for proPO-I mRNA expression between haemocytes treated with saline and Met + NE; or for SP and PE mRNA expressions among haemocytes treated with saline, Pra + NE, and Met + NE. These results suggest that stress-induced NE may promote the migration of circulating granulocytes to the site of the injection and the existing proPO mRNA translation which had been stored in granulocytes. NE downregulated the LGBP, proPO-I, proPO-II, SP, and PE gene transcription by haemocytes via α1-, β1-, α1-, α1- and β1-, and α1- and β1-ARs, respectively, which subsequently decreased the PO activity by α1- and β1-ARs in haemocytes of L. vannamei.

Melatonin: neuritogenesis and neuroprotective effects in crustacean x-organ cells

Melatonin has both neuritogenic and neuroprotective effects in mammalian cell lines such as neuroblastoma cells. The mechanisms of action include receptor-coupled processes, direct binding and modulation of calmodulin and protein kinase C, and direct scavenging of free radicals. While melatonin is produced in invertebrates and has influences on their physiology and behavior, little is known about its mechanisms of action. We studied the influence of melatonin on neuritogenesis in well-differentiated, extensively-arborized crustacean x-organ neurosecretory neurons. Melatonin significantly increased neurite area in the first 24h of culture. The more physiological concentrations, 1 nM and 1 pM, increased area at 48 h also, whereas the pharmacological 1 μM concentration appeared to have desensitizing effects by this time. Luzindole, a vertebrate melatonin receptor antagonist, had surprising and significant agonist-like effects in these invertebrate cells. Melatonin receptors have not yet been studied in invertebrates. However, the presence of membrane-bound receptors in this population of crustacean neurons is indicated by this study. Melatonin also has significant neuroprotective effects, reversing the inhibition of neuritogenesis by 200 and 500 μM hydrogen peroxide. Because this is at least in part a direct action not requiring a receptor, melatonin's protection from oxidative stress is not surprisingly phylogenetically-conserved.

Cold shock-induced norepinephrine triggers apoptosis of haemocytes via caspase-3 in the white shrimp, Litopenaeus vannamei

The total haemocyte count (THC), haemolymph norepinephrine (NE) level, caspase-3 mRNA expression and activity levels, and apoptotic haemocyte rate were measured when shrimp Litopenaeus vannamei (20-25 g) were transferred from 28 to 22 degrees C after 0, 2, and 7 days, and the caspase-3 mRNA expression and activity levels and the apoptotic cell rate of haemocytes, in vitro, were determined after incubation with 2 x 10(-8) M NE for 0, 30, 60, and 120 min at 27 +/- 1.0 degrees C. For shrimp transferred from 28 +/- 1.0 to 22 +/- 0.5 degrees C after 2 and 7 days, the THC decreased by 17.9% and 18.0%, but the NE concentration, caspase-3 transcription and activity levels, and apoptotic cell rate increased by 62.5% and 37.3%, 5100.0% and 446.6%, 148.6% and 152.0%, and 88.7% and 200.1%, respectively, compared to those of shrimp held at 28 +/- 0.5 degrees C which served as the control. Similar tendencies were observed for the apoptotic cell rate, and caspase-3 transcription and activity levels of haemocytes exposed to 2 x 10(-8) M NE in vitro. These results suggest that NE plays an important role in the apoptosis of haemocytes in L. vannamei under hypothermal stress, which causes depressive effects on immunological responses.