Dopamine in crayfish and other crustaceans: distribution in the central nervous system and physiological functions

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.

Effects of Chronic Exposure to Low Doses of Rotenone on Dopaminergic and Cholinergic Neurons in the CNS of Hemigrapsus sanguineus

Rotenone, as a common pesticide and insecticide frequently found in environmental samples, may be present in aquatic habitats worldwide. Exposure to low concentrations of this compound may cause alterations in the nervous system, thus contributing to Parkinsonian motor symptoms in both vertebrates and invertebrates. However, the effects of chronic exposure to low doses of rotenone on the activity of neurotransmitters that govern motor functions and on the specific molecular mechanisms leading to movement morbidity remain largely unknown for many aquatic invertebrates. In this study, we analyzed the effects that rotenone poisoning exerts on the activity of dopamine (DA) and acetylcholine (ACh) synthesis enzymes in the central nervous system (CNS) of Asian shore crab, Hemigrapsus sanguineus (de Haan, 1835), and elucidated the association of its locomotor behavior with Parkinson's-like symptoms. An immunocytochemistry analysis showed a reduction in tyrosine hydroxylase (TH) in the median brain and the ventral nerve cord (VNC), which correlated with the subsequent decrease in the locomotor activity of shore crabs. We also observed a variation in cholinergic neurons' activity, mostly in the ventral regions of the VNC. Moreover, the rotenone-treated crabs showed signs of damage to ChAT-lir neurons in the VNC. These data suggest that chronic treatment with low doses of rotenone decreases the DA level in the VNC and the ACh level in the brain and leads to progressive and irreversible reductions in the crab's locomotor activity, life span, and changes in behavior.

Development of Serotonergic and Dopaminergic Neuronal Networks of the Central Nervous System in King Crab, Paralithodes camtschaticus

This article presents recent findings as regards distribution of cells producing serotonin and dopamine in the larval central nervous system at different developmental stages, including four pelagic larval stages (zoea I-IV), a semibenthic postlarval stage glaucothoe (megalopa), benthic juveniles, and adult red king crabs, Paralithodes camtschaticus, made by using immunocytochemistry and confocal laser scanning microscopy. We have shown that the serotonergic and dopaminergic neurons are present long before the onset of metamorphosis. In the red king crab b larval nervous system, the changes become particularly pronounced during the first metamorphosis from zoea IV to glaucothoe, which may be related to the development of the segmental appendages and maturation of motor behaviors in decapods. This work presents the distribution and dynamics of the development of serotonergic and dopaminergic neuronal networks in king crab show, the potential roles of serotonin and dopamine in the modulation of olfactory and visual processing in the early stages of larval development, and also the mechanosensory and chemosensory processing in the glaucothoe stage during settlement and in their transition from a pelagic to benthic lifestyle.

Serotonin and dopamine regulate the aggressiveness of swimming crabs (Portunus trituberculatus) in different ways

Bioamines act as a pivotal part in the regulation of aggressive behavior in animals as a type of neuroendocrine, but the patterns of how they regulate aggressiveness in crustaceans are still unclear due to species-specific responses. To determine the effects of serotonin (5-HT) and dopamine (DA) on the aggressiveness of swimming crabs (Portunus trituberculatus), we quantified their behavioral and physiological characteristics. The results showed that an injection of 5-HT at 0.5 mmol L^-1 and 5 mmol L^-1 could significantly enhance the aggressiveness of swimming crabs, as well as an injection of DA at 5 mmol L^-1. The regulation of 5-HT and DA on aggressiveness is dose-dependent, and these two bioamines have different concentration thresholds that can trigger aggressiveness changes. 5-HT could up-regulate the 5-HTR1 gene expression and increase lactate content at the thoracic ganglion as the aggressiveness enhances, suggesting that 5-HT may activate related receptors and neuronal excitability to regulate aggressiveness. As a result of DA injection at 5 mmol L^-1, lactate content in the chela muscle and hemolymph increased, glucose content in the hemolymph increased, and the CHH gene was significantly up-regulated. Pyruvate kinase and hexokinase enzyme activities in the hemolymph increased, which accelerated the glycolysis process. These results demonstrate that DA regulates the lactate cycle, which provides substantial short-term energy for aggressive behavior. Both 5-HT and DA can mediate aggressive behavior in the crab by activating calcium regulation in muscle tissue. We conclude that the enhancement of aggressiveness is a process of energy consumption, in which 5-HT acts on the central nervous system to induce aggressive behavior, and DA affects muscle and hepatopancreas tissue to provide a large amount of energy. This study expands upon the knowledge of regulatory mechanisms of aggressiveness in crustaceans and offers a theoretical foundation for enhancing crab culture management.

The dynamic range of voltage-dependent gap junction signaling is maintained by Ih-induced membrane potential depolarization

Like their chemical counterparts, electrical synapses show complex dynamics such as rectification and voltage dependence that interact with other electrical processes in neurons. The consequences arising from these interactions for the electrical behavior of the synapse, and the dynamics they create, remain largely unexplored. Using a voltage-dependent electrical synapse between a descending modulatory projection neuron (MCN1) and a motor neuron (LG) in the crustacean stomatogastric ganglion, we find that the influence of the hyperpolarization-activated inward current (Ih) is critical to the function of the electrical synapse. When we blocked Ih with CsCl, the apparent voltage dependence of the electrical synapse shifted by 18.7 mV to more hyperpolarized voltages, placing the dynamic range of the electrical synapse outside of the range of voltages used by the LG motor neuron (-60.2 mV to -44.9 mV). With dual electrode current- and voltage-clamp recordings, we demonstrate that this voltage shift is not due to a change in the properties of the gap junction itself, but is a result of a sustained effect of Ih on the presynaptic MCN1 axon terminal membrane potential. Ih-induced depolarization of the axon terminal membrane potential increased the electrical postsynaptic potentials and currents. With Ih present, the axon terminal resting membrane potential is depolarized, shifting the dynamic range of the electrical synapse toward the functional range of the motor neuron. We thus demonstrate that the function of an electrical synapse is critically influenced by a voltage-dependent ionic current (Ih).NEW & NOTEWORTHY Electrical synapses and voltage-gated ionic currents are often studied independently from one another, despite mounting evidence that their interactions can alter synaptic behavior. We show that the hyperpolarization-activated inward ionic current shifts the voltage dependence of electrical synaptic transmission through its depolarizing effect on the membrane potential, enabling it to lie within the functional membrane potential range of a motor neuron. Thus, the electrical synapse's function critically depends on the voltage-gated ionic current.

Plastic additive oleamide elicits hyperactivity in hermit crabs

Numerous studies have estimated the abundance of plastics in our oceans and warned of its threat to wildlife. However, mechanisms underlying its attractiveness to marine life remain unclear. Though visual similarities to food sources have been suggested, recent studies show that biofouled plastics release dimethyl sulfide which marine fauna mistake for food whilst foraging. Our study shows that the plastic additive oleamide (9-octadecenamide) attracts hermit crabs (Pagurus bernhardus). Respiration rate increases significantly in response to low concentrations of oleamide, and hermit crabs show a behavioral attraction comparable to their response to the feeding stimulant betaine. Oleamide has a striking resemblance to the necromone oleic acid, a chemical released by arthropods during decomposition. As scavengers, hermit crabs may misidentify oleamide as a food source, creating an olfactory trap. As such, our short communication demonstrates that additive leaching may play a significant role in the attraction of marine life to plastic.

Biochemical and metabolic responses of the deep-sea mussel Bathymodiolus platifrons to cadmium and copper exposure

Greater interest in commercial deep-sea mining has been accompanied by mounting environmental concerns, including metal contamination resulting from mining activities. However, little is known about the toxic effects of metal exposure on deep-sea life. Given its ability to accumulate metals from the surrounding environment, its wide distribution at both vents and seeps, and its high abundance, the deep-sea mussel Bathymodiolus platifrons could serve as an ideal model to investigate the toxicological responses of deep-sea organisms to metal exposure. Here, we evaluated metal accumulation, traditional metal-related biomarkers, namely acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase, catalase, reduced glutathione, metallothioneins, and malondialdehyde, as well as metabolic profiles in the gills of B. platifrons after a 7-day exposure to copper (100 μg/L), cadmium (500 μg/L), or copper-plus-cadmium treatments (100 μg/L Cu and 500 μg/L Cd). Metal exposure concentrations selected in this study can be found in deep-sea hydrothermal environments. Metal exposure resulted in significant metal accumulation in the gills of the mussel, indicating that B. platifrons has promise for use as an indicator of deep-sea metal pollution levels. Traditional biomarkers (AKP, ACP, and measured antioxidants) revealed cellular injury and oxidative stress in mussels following metal exposure. Metabolic responses in the three treatment groups indicated that metal exposure perturbed osmoregulation, energy metabolism, and nucleotide metabolism in mussels, in a response marked by differentially altered levels of amino acids, hypotaurine, betaine, succinate, glucose 6-phosphate, fructose 6-phosphate, guanosine, guanosine 5'-monophosphate, and inosine. Nevertheless, several uniquely altered metabolites were found in each treatment exposure group, suggesting dissimilar modes of toxicity between the two metal types. In the Cd-exposed group, the monosaccharide D-allose, which is involved in suppressing mitochondrial ROS production, was downregulated, a response consistent with oxidative stress in Cd-exposed B. platifrons. In the Cu-exposed group, the detected alterations in dopamine, dopamine-related, and serotonin-related metabolites together suggest disturbed neurotransmission in Cu-exposed B. platifrons. In the Cu-plus-Cd group, we detected a decline in fatty acid levels, implying that exposure to both metals jointly exerted a negative influence on the physiological functioning of the mussel. To the best of our knowledge, this is the first study to investigate changes in metabolite profiles in Bathymodiolus mussels exposed to metal. The findings reported here advance our understanding of the adverse impact of metal exposure on deep-sea life and can inform deep-sea mining assessments through the use of multiple biomarkers.

Opposing effects of dopamine on agonistic behaviour in crayfish

The effects of dopamine on the agonistic behaviour of crayfish were analysed. When dopamine concentrations of 1 μmol l-1 were injected into large crayfish, individuals were beaten by smaller opponents, despite their physical advantage. Injection of 10 μmol l-1 dopamine into small animals increased their rate of winning against larger opponents. Injection of a D1 receptor antagonist prohibited the onset of a 'loser' effect in subordinate animals, suggesting that the inhibitory effect of dopamine on larger animals is mediated by D1 receptors. Similarly, injection of a D2 receptor antagonist prohibited the onset of a 'winner' effect in dominant animals, suggesting that the facilitating effect of dopamine on small animals is mediated by D2 receptors. Since the inhibitory effect of 1 μmol l-1 dopamine was similar to that seen with 1 μmol l-1 octopamine and the facilitating effect of 10 μmol l-1 dopamine was similar to that of 1 μmol l-1 serotonin, functional interactions among dopamine, octopamine and serotonin were analyzed by co-injection of amines with their receptor antagonists in various combinations. The inhibitory effect of 1 μmol l-1 dopamine disappeared when administered with D1 receptor antagonist, but remained when combined with octopamine receptor antagonist. Octopamine effects disappeared when administered with either D1 receptor antagonist or octopamine receptor antagonist, suggesting that the dopamine system is downstream of octopamine. The facilitating effect of 10 μmol l-1 dopamine disappeared when combined with serotonin 5HT1 receptor antagonist or D2 receptor antagonist. Serotonin effects also disappeared when combined with D2 receptor antagonist, suggesting that dopamine and serotonin activate each other through parallel pathways.

Synthetic cathinones and their phenethylamine analogues produce distinct psychomotor and reward behavior in crayfish

Synthetic cathinones share potent sympathomimetic properties with amphetamines due to their shared phenethylamine backbone. Despite recent work focused on understanding the behavioral effects of synthetic cathinones, a systematic comparison of neuropharmacology, behavior, and physiological effects with other stimulants, has remained elusive. In the present study, we explore the behavioral effects of cathinones in crayfish, a model system which combines a well characterized behavioral paradigm for addiction-like behaviors, a modularly organized nervous system, the lack of a formal blood-brain barrier, and experimental tractability. The objective of this study was to characterize the psychomotor and rewarding effects of methylated cathinones (methylone, mephedrone), and their non β-ketone substituted amphetamine analogs (4-methylmethamphetamine, 4-MMA and 3,4-methylenedioxymethamphetamine MDMA) in crayfish. Our results suggest that these drugs produce psychostimulation, which sensitizes upon repeated drug administration. Furthermore, crayfish demonstrated a conditioned substrate preference for mephedrone and 4-MMA drug-pairings at a 10 μg/g dose, a preference which persisted even through a series of extinction trials. Our study indicates that synthetic cathinones and substituted amphetamine analogues produce distinct behavioral effects in an invertebrate system which consists of a relatively simple neuronal organization. The present findings provide an evolutionary context to our understanding about how drugs of abuse initiate reward at levels far beyond those specific to humans.

Identification of putative amine receptor complement in the eyestalk of the crayfish, Procambarus clarkii

In decapod crustaceans, the amines dopamine, octopamine, serotonin, and histamine are known to serve as locally released and/or circulating neuromodulators. While many studies have focused on determining the modulatory actions of amines on decapod nervous systems, comparatively little is known about the identity of the receptors through which they exert their actions. Here, a crayfish, Procambarus clarkii, tissue-specific transcriptome was used to identify putative amine receptors in the eyestalk, a structure composed largely of the eyestalk ganglia, including the neuroendocrine X-organ-sinus gland system, and retina. Transcripts encoding 17 distinct putative amine receptors, three dopamine (one dopamine 1-like, one dopamine 2-like, and one dopamine/ecdysteroid-like), five octopamine (one alpha-like, three beta-like, and one octopamine/tyramine-like), three serotonin (two type-1-like and one type-7-like), and six histamine (five histamine-gated chloride channel A-like and one histamine-gated chloride channel B-like) were identified in the assembly. Comparison of the nucleotide sequence of the transcript encoding one predicted type-1-like serotonin receptor with that cloned previously from the P. clarkii nervous system shows the two sequences to be essentially identical, providing increased support for the validity of the transcripts used to deduce the proteins reported here. Reciprocal BLAST and structural/functional domain analyses support the protein family annotations ascribed to the putative P. clarkii receptors. These data represent the first large-scale description of amine receptors from P. clarkii, and as such provide a new resource for initiating gene-based studies of aminergic control of physiology/behavior at the level of receptors in this species.

Characterization of locomotor response to psychostimulants in the parthenogenetic marbled crayfish (Procambarus fallax forma virginalis): A promising model for studying the neural and molecular mechanisms of drug addiction

Although scientific research using mammalian models has made great strides in uncovering the enigmatic neural and molecular mechanisms orchestrating the state of drug addiction, a complete understanding has thus far eluded researchers. The complexity of the task has led to the use of invertebrate model systems to complement the research of drug-induced reward in mammalian systems. Invertebrates, such as crayfish, offer excellent model systems to help reveal the underlying mechanisms of drug addiction as they retain the ancestral neural reward circuit that is evolutionarily conserved across taxa, and they possess relatively few, large neurons, laid out in an accessible, modularly organized nervous system. Crayfish offer the benefits of delineated developmental life stages, a large body size suitable for a variety of experimental methods, and stereotyped behaviors. Unique among crayfish is the parthenogenetic marbled crayfish (Procambarus fallax forma virginalis), a species of asexually reproducing, genetically identical clones. With the benefits of reduced individual variation, high fecundity, and easy lab husbandry, the marbled crayfish would make a particularly powerful addition to the animal model repertoire. Here we characterize the locomotor response of juvenile P. f. f. virginalis exposed to the psychostimulant, d-amphetamine sulfate. Custom video-tracking software was used to record the movement patterns of juveniles exposed to water infused with varying concentrations of d-amphetamine sulfate. ANOVA demonstrated that crayfish locomotion was significantly impacted by drug concentration. These psychostimulant effects provide the foundation of P. f. f. virginalis as a model for parsing the neural and molecular mechanisms of drug addiction.

Dopamine binding directly up-regulates (Na+, K+)-ATPase activity in the gills of the freshwater shrimp Macrobrachium amazonicum

We examined the effects of exogenous dopamine on gill (Na⁺, K⁺)-ATPase activity in vitro in microsomal preparations from juvenile or adult freshwater shrimp, Macrobrachium amazonicum. Dopamine had no effect on enzyme activity in juveniles but stimulated activity in adult shrimp gills by ≈35%. Stimulation of the gill (Na⁺, K⁺)-ATPase in adult shrimps by 100 mmol L^-1 dopamine was characterized kinetically by varying ATP, MgATP, and Na⁺ and K⁺ concentrations, together with inhibition by ouabain. Dopamine stimulated ATP hydrolysis by ≈40% obeying Michaelis-Menten kinetics, reaching V_M = 190.5 ± 15.7 nmol Pi min^-1 mg^-1 protein, K_M remaining unaltered. Stimulation by Na⁺ (≈50%) and K⁺ (≈25%) revealed distinct kinetic profiles: although K_M values were similar, Na⁺ stimulation followed cooperative kinetics, contrasting with the Michaelian kinetics seen for K⁺. Stimulation by MgATP increased activity by ≈30% with little change in K_M. Similar saturation profiles were seen for ouabain inhibition with very similar calculated K_I values. Our findings suggest that dopamine may be involved in hemolymph sodium homeostasis by directly binding to the gill (Na⁺, K⁺)-ATPase at a site different from ouabain, thus stimulating enzyme activity in an ontogenetic stage-specific manner. However, dopamine binding does not affect enzyme affinity for cations and ouabain. This is the first report of the direct action of dopamine in stimulating the crustacean gill (Na⁺, K⁺)-ATPase.

Evidence that dopamine is involved in neuroendocrine regulation, gill intracellular signaling pathways and ion regulation in Litopenaeus vannamei

The transport of ions and ammonia in the gills may be regulated by neuroendocrine factors, in order to explore the regulation mechanism of dopamine (DA), hemolymph neuroendocrine hormones, gill intracellular signaling pathways, ion and ammonia transporters, as well as hemolymph osmolality and ammonia concentration were investigated in Litopenaeus vannamei after 10−7 and 10−6 mol shrimp−1 DA injection. The data displayed a significant increase in crustacean hyperglycemic hormone (CHH) concentration at 1-12 h and a transient significant decrease in corticotrophin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and cortisol concentrations under DA stimulation. The up-regulation of guanylyl cyclase (GC) mRNA, cyclic guanosine monophosphate (cGMP) and protein kinase G (PKG) concentrations, together with down-regulation of DA receptor D4 mRNA and up-regulation of cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), diacylglycerol (DAG) and protein kinase C (PKC) concentrations suggested an activation of complicated intracellular signaling pathway. The expression of cyclic AMP response element-binding protein (CREB), FXYD2 and 14-3-3 protein mRNA was significantly increased by PKA regulation. The increase in Na+/K+-ATPase (NKA) activity and the stabilization of V-type H+-ATPase (V-ATPase) activity are accompanied by an up-regulation of K+-channel, Na+/K+/2Cl− cotransporter (NKCC), Rh protein and vesicle associated membrane protein (VAMP) mRNA, resulting in an increase in hemolymph osmolality and a decrease in hemolymph ammonia concentration. These results suggest that DA stimulates the secretion of CHH and inhibits the release of cortisol, which activates intracellular signaling factors to facilitate ion and ammonia transport across the gills, and may not affect intracellular acidification.

Effect of psychiatric drugs on Daphnia magna oxylipin profiles

Neuro-active pharmaceuticals have been reported to act as endocrine disruptors enhancing reproduction in the model crustacean Daphnia manga at environmental concentrations of ng/L. Oxylipins and more specifically eicosanoids, which are lipid mediators formed from polyunsaturated fatty acids (PUFAs), are known to regulate reproduction together with other physiological processes in insects. In D. magna, the biosynthesis of eicosanoids and their putative role in the regulation of reproduction has been studied using transcriptomics, genomics and exposures to cyclooxygenase inhibitors. Quantification of eicosanoids and oxylipins derived from PUFAs upon exposure to pharmaceuticals is therefore crucial for a better understanding of the mode of action of neuro-active pharmaceuticals on aquatic invertebrates. The aim of this study was to investigate shifts in the oxylipin profile in D. magna adults upon exposure to environmental concentrations of the three psychiatric drugs, fluoxetine, diazepam and carbamazepine, with known effects of enhancing offspring production. Oxylipin profiles were determined in whole organism tissues using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Up to 28 different oxylipins belonging to arachidonic (AA), linoleic acid (LA), α-linoleic acid (α-LA) and eicosapentaenoic acid (EPA) pathways were detected and quantified in D. magna adults. Exposure to the selected psychiatric drugs showed that fluoxetine enhanced the accumulation of the cyclooxygenase (COX) product 12-hydroxyheptadecatrienoic acid (12-HHTrE), whereas diazepam increased the concentration of eicosanoids belonging to the lipoxygenase (LOX) and cytochrome P450 (CYP) pathways (HETEs, EpOMEs, HODEs, HOTrEs and HEPEs) from the AA, LA, αLA and EPA pathways. Carbamazepine had little effect and only one LA-derived compound from the LOX pathway (13-HODE) increased significantly. This means that despite having different modes of action in humans, fluoxetine and diazepam up-regulated eicosanoid pathways in D. magna, closely related to known biologically active products that regulate reproduction in insects.

Independent and simultaneous effect of crustacean hyperglycemic hormone and dopamine on the hemocyte intracellular signaling pathways and immune responses in white shrimp Litopenaeus vannamei

Immune responses and intracellular signaling pathways were examined after hemolymph of Litopenaeus vannamei being incubated in Crustacean hyperglycemic hormone (CHH), dopamine (DA) and DA antagonist (Y). The results showed that the effect CHH and CHH + DA + Y on viability of hemocytes were no significant changes compared to the control group. However, in DA, DA + Y and CHH + DA groups, the viability of hemocytes decreased significantly. The phagocytic activity and the antibacterial activity of CHH group were increased significantly within 12h. Whereas the CHH + DA, DA were significantly lower than the control. PO in haemolymph was up-regulated after CHH and DA incubation. The proPO has the opposite change in all groups. In addition, DA + Y, CHH + DA + Y has a similar trend with the DA and CHH respectively. Furthermore, a significant increase of cAMP, CaM and cGMP were found in treatment groups except for the CaM concentration of the CHH group and the cGMP concentration of DA group. There is no significant change observed in the CHH group about CaM concentration. Whereas the cGMP of DA group decreased within 12h. The results suggest that DA could depress the immune responses by cAMP-, CaM-pathways. However, the CHH is on the contrary, which transduced the signals from cAMP, cGMP to PKA, PKC and PKG to enhance the immune response parameters.

Crayfish Self-Administer Amphetamine in a Spatially Contingent Task

Natural reward is an essential element of any organism’s ability to adapt to environmental variation. Its underlying circuits and mechanisms guide the learning process as they help associate an event, or cue, with the perception of an outcome’s value. More generally, natural reward serves as the fundamental generator of all motivated behavior. Addictive plant alkaloids are able to activate this circuitry in taxa ranging from planaria to humans. With modularly organized nervous systems and confirmed vulnerabilities to human drugs of abuse, crayfish have recently emerged as a compelling model for the study of the addiction cycle, including psychostimulant effects, sensitization, withdrawal, reinstatement, and drug reward in conditioned place preference paradigms. Here we extend this work with the demonstration of a spatially contingent, operant drug self-administration paradigm for amphetamine. When the animal enters a quadrant of the arena with a particular textured substrate, a computer-based control system delivers amphetamine through an indwelling fine-bore cannula. Resulting reward strength, dose-response, and the time course of operant conditioning were assessed. Individuals experiencing the drug contingent on their behavior, displayed enhanced rates of operant responses compared to that of their yoked (non-contingent) counterparts. Application of amphetamine near the supra-esophageal ganglion elicited stronger and more robust increases in operant responding than did systemic infusions. This work demonstrates automated implementation of a spatially contingent self-administration paradigm in crayfish, which provides a powerful tool to explore comparative perspectives in drug-sensitive reward, the mechanisms of learning underlying the addictive cycle, and phylogenetically conserved vulnerabilities to psychostimulant compounds.

Identification, Quantitation, and Imaging of the Crustacean Peptidome

Crustaceans serve as a useful, simplified model for studying peptides and neuromodulation, as they contain numerous neuropeptide homologs to mammals and enable electrophysiological studies at the single-cell and neural circuit levels. In particular, crustaceans contain well-defined neural networks, including the stomatogastric ganglion, esophageal ganglion, commissural ganglia, and several neuropeptide-rich organs, such as the brain, pericardial organs, and sinus glands. Due to the lack of a genomic database for crustacean peptides, an important step of crustacean peptidomics involves the discovery and identification of novel peptides and the construction of a database, more recently with the aid of mass spectrometry (MS). Herein, we present a general workflow and detailed methods for MS-based peptidomic analysis of crustacean tissue samples and circulating fluids. In conjunction with profiling, quantitation can also be performed with isotopic or isobaric labeling. Information regarding the localization patterns and changes of peptides can be studied via mass spectrometry imaging. Combining these sample preparation strategies and MS analytical techniques allows for a multifaceted approach to obtaining deep knowledge of crustacean peptidergic signaling pathways.

Cyclic AMP-regulated opposing and parallel effects of serotonin and dopamine on phototaxis in the Marmorkrebs (marbled crayfish)

Phototactic behaviours are observed from prokaryotes to amphibians and are a basic form of orientation. We showed that the marbled crayfish displays phototaxis in which the behavioural response reversed from negative to positive depending on external light conditions. Animals reared in a 12-L/12-D light cycle showed negative phototaxis during daytime and positive phototaxis during night-time. Animals reared under constant light conditioning showed negative phototaxis during day- and night-time, while animals reared under constant dark conditioning showed positive phototaxis during day- and night-time. Injection of serotonin leads to a reversal of negative to positive phototaxis in both light/dark-reared and light/light-reared animals while injection of dopamine induced reversed negative phototaxis in dark/dark-reared animals. Four hours of dark adaptation were enough for light/dark-reared animals to reverse phototaxis from negative to positive. Injection of a serotonin 5HT₁ receptor antagonist blocked the reverse phototaxis while serotonin 5HT₂ receptor antagonists had no effects. Similarly, dark/dark-reared animals reversed to showing negative phototaxis after 4 h of light adaptation. Injection of a dopamine DA₁ receptor antagonist blocked this reverse phototaxis, while dopamine DA₂ receptor antagonists had no effects. Injection of a cAMP analogue into light/dark-reared animals blocked reverse phototaxis after dark adaptation, while adenylate cyclase inhibitor in dark/dark-reared animals blocked reverse phototaxis after light adaptation. These results strongly suggest that serotonin mediates positive phototaxis owing to decreased cAMP levels, while dopamine-mediated negative phototaxis occurs due to increased cAMP levels. Supporting this, the ratio of serotonin to dopamine in the brain was much higher in dark/dark-reared than light/dark-reared animals.

Manganese tissue accumulation and tyrosine hydroxylase immunostaining response in the Neotropical freshwater crab, Dilocarcinus pagei, exposed to manganese

Manganese (Mn) is an essential metal for the development and function of the mammalian brain; however, excess Mn accumulation may cause neurological abnormalities resembling Parkinson's disease due to reductions in brain dopamine levels. Because dopamine also regulates many functions in crustaceans, this study examined the effects of Mn accumulation in Dilocarcinus pagei, a Neotropical freshwater crab. Following a 72-h exposure to graded concentrations of MnCl₂, Mn accumulation was assessed in several tissues. Glycaemia and the tyrosine hydroxylase (TH) immunostaining response were also examined as indicators of catecholaminergic function and catecholaminergic cell integrity, respectively. Tissue Mn accumulation was variable and occurred in the following order: gills > hepatopancreas > claw muscle > haemolymph. Exposure to 2 mM Mn reduced the gill levels of calcium, copper and iron, whereas Mn at all concentrations decreased zinc levels. All Mn-exposed animals showed lower copper levels in the hepatopancreas and haemolymph. Exposure to 2.0 mM Mn increased the haemolymph calcium. Mn exposure had no effect on glycaemia, whereas exposure to low Mn concentrations reduced the TH immunostaining response. Analysis of the central nervous system revealed the greatest Mn effect in the cerebral ganglion and the least effect in the abdominal ganglia. These results suggest the operation of an adaptive mechanism for tissue accumulation that could be responsible for the lack of an association between Mn concentrations and metal accumulation. The findings also suggest that Mn, calcium, iron and zinc share a transporter in gill cells and that Mn resistance is greater in the TH-positive cells of this crustacean than in mammalian cells.

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.

Expression and distribution of neuropeptides in the nervous system of the crab Carcinus maenas and their roles in environmental stress

Environmental fluctuations, such as salinity, impose serious challenges to marine animal survival. Neuropeptides, signaling molecules involved in the regulation process, and the dynamic changes of their full complement in the stress response have yet to be investigated. Here, a MALDI-MS-based stable isotope labeling quantitation strategy was used to investigate the relationship between neuropeptide expression and adaptability of Carcinus maenas to various salinity levels, including high (60 parts per thousand [p.p.t.]) and low (0 p.p.t.) salinity, in both the crustacean pericardial organ (PO) and brain. Moreover, a high salinity stress time course study was conducted. MS imaging (MSI) of neuropeptide localization in C. maenas PO was also performed. As a result of salinity stress, multiple neuropeptide families exhibited changes in their relative abundances, including RFamides (e.g. APQGNFLRFamide), RYamides (e.g. SSFRVGGSRYamide), B-type allatostatins (AST-B; e.g. VPNDWAHFRGSWamide), and orcokinins (e.g. NFDEIDRSSFGFV). The MSI data revealed distribution differences in several neuropeptides (e.g. SGFYANRYamide) between color morphs, but salinity stress appeared to not have a major effect on the localization of the neuropeptides.

Characterization of a prawn OA/TA receptor in Xenopus oocytes suggests functional selectivity between octopamine and tyramine

Here we report the characterization of an octopamine/tyramine (OA/TA or TyrR1) receptor (OA/TA_Mac) cloned from the freshwater prawn, Macrobrachium rosenbergii, an animal used in the study of agonistic social behavior. The invertebrate OA/TA receptors are seven trans-membrane domain G-protein coupled receptors that are related to vertebrate adrenergic receptors. Behavioral studies in arthropods indicate that octopaminergic signaling systems modulate fight or flight behaviors with octopamine and/or tyramine functioning in a similar way to the adrenalins in vertebrate systems. Despite the importance of octopamine signaling in behavioral studies of decapod crustaceans there are no functional data available for any of their octopamine or tyramine receptors. We expressed OA/TA_Mac in Xenopus oocytes where agonist-evoked trans-membrane currents were used as readouts of receptor activity. The currents were most effectively evoked by tyramine but were also evoked by octopamine and dopamine. They were effectively blocked by yohimbine. The electrophysiological approach we used enabled the continuous observation of complex dynamics over time. Using voltage steps, we were able to simultaneously resolve two types of endogenous currents that are affected over different time scales. At higher concentrations we observe that octopamine and tyramine can produce different and opposing effects on both of these currents, presumably through the activity of the single expressed receptor type. The pharmacological profile and apparent functional-selectivity are consistent with properties first observed in the OA/TA receptor from the insect Drosophila melanogaster. As the first functional data reported for any crustacean OA/TA receptor, these results suggest that functional-selectivity between tyramine and octopamine is a feature of this receptor type that may be conserved among arthropods.

Catecholamine levels in groundwater and stream amphipods and their response to temperature stress

Temperature stress in invertebrates is known to be reflected by changes in catecholamine levels. However, the mechanisms of stress response are not fully understood. Groundwater and surface water amphipods are expected to be differently adapted to temperature elevations due to the different temperature regimes in their habitats and consequently, show a different stress response. No data have been published so far regarding the effects of stress on catecholamine patterns in groundwater invertebrates and accordingly, comparisons with surface water fauna are also missing. In this study, we compared the average catecholamine levels in two taxonomically related amphipod species: Niphargus inopinatus, living in groundwater with constant water temperatures throughout the year, and Gammarus pulex, a surface water stream amphipod frequently exposed to diurnal and seasonal temperature fluctuations. Furthermore, we tracked the immediate changes in whole-animal catecholamine levels in response to heat stress in both species. Pronounced differences in the catecholamine levels of the two species became apparent, with the average dopamine (DA) level of N. inopinatus being almost 1000 times higher than that in G. pulex. The noradrenaline (NA) concentrations in N. inopinatus were on average two orders of magnitude higher than in G. pulex, and for adrenaline (A), the difference constituted one order of magnitude. When exposed to short-term heat stress, both species showed a response in terms of catecholamine levels, but the observed patterns were different. In N. inopinatus, temperature stress was reflected by the appearance of adrenaline, while in G. pulex a significant increase in noradrenaline levels occurred in the treatment with the highest temperature elevation.

Dopaminergic tone regulates transient potassium current maximal conductance through a translational mechanism requiring D1Rs, cAMP/PKA, Erk and mTOR

Background

Dopamine (DA) can produce divergent effects at different time scales. DA has opposing immediate and long-term effects on the transient potassium current (I_A) within neurons of the pyloric network, in the Panulirus interruptus stomatogastric ganglion. The lateral pyloric neuron (LP) expresses type 1 DA receptors (D1Rs). A 10 min application of 5-100 μM DA decreases LP I_A by producing a decrease in I_A maximal conductance (G_max) and a depolarizing shift in I_A voltage dependence through a cAMP-Protein kinase A (PKA) dependent mechanism. Alternatively, a 1 hr application of DA (≥5 nM) generates a persistent (measured 4 hr after DA washout) increase in I_A G_max in the same neuron, through a mechanistic target of rapamycin (mTOR) dependent translational mechanism. We examined the dose, time and protein dependencies of the persistent DA effect.

Results

We found that disrupting normal modulatory tone decreased LP I_A. Addition of 500 pM-5 nM DA to the saline for 1 hr prevented this decrease, and in the case of a 5 nM DA application, the effect was sustained for >4 hrs after DA removal. To determine if increased cAMP mediated the persistent effect of 5nM DA, we applied the cAMP analog, 8-bromo-cAMP alone or with rapamycin for 1 hr, followed by wash and TEVC. 8-bromo-cAMP induced an increase in I_A G_max, which was blocked by rapamycin. Next we tested the roles of PKA and guanine exchange factor protein activated by cAMP (ePACs) in the DA-induced persistent change in I_A using the PKA specific antagonist Rp-cAMP and the ePAC specific agonist 8-pCPT-2′-O-Me-cAMP. The PKA antagonist blocked the DA induced increases in LP I_A G_max, whereas the ePAC agonist did not induce an increase in LP I_A G_max. Finally we tested whether extracellular signal regulated kinase (Erk) activity was necessary for the persistent effect by co-application of Erk antagonists PD98059 or U0126 with DA. Erk antagonism blocked the DA induced persistent increase in LP I_A.

Conclusions

These data suggest that dopaminergic tone regulates ion channel density in a concentration and time dependent manner. The D1R- PKA axis, along with Erk and mTOR are necessary for the persistent increase in LP I_A induced by high affinity D1Rs.

Investigating candidate neuromodulatory systems underlying parasitic manipulation: concepts, limitations and prospects

Studies addressing the functional basis of parasitic manipulation suggest that alteration of the neuromodulatory system is a common feature of manipulated hosts. Screening of the neuromodulatory system has so far been carried out by performing ethopharmacological analysis, biochemical quantification of neurotransmitters and neuromodulators, and/or immunocytochemistry. Here, we review the advantages and limitations of such approaches through the analysis of case studies. We further address whether the analysis of candidate neuromodulatory systems fits the current view of manipulation as being multidimensional. The benefits in combining ethopharmacology with more recent molecular tools to investigate candidate neuromodulatory pathways is also emphasized. We conclude by discussing the value of a multidisciplinary study of parasitic manipulation, combining evolutionary (parasite transmission), behavioural (syndrome of manipulation) and neuroimmunological approaches.

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.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Neurobiology of the crustacean swimmeret system

The crustacean swimmeret system includes a distributed set of local circuits that individually control movements of one jointed limb. These modular local circuits occur in pairs in each segmental ganglion, and normally operate synchronously to produce smoothly coordinated cycles of limb movements on different body segments. The system presents exceptional opportunities for computational and experimental investigation of neural mechanisms of coordination because: (a) The system will express in vitro the periodic motor pattern that normally drives cycles of swimmeret movements during forward swimming. (b) The intersegmental neurons which encode information that is necessary and sufficient for normal coordination have been identified, and their activity can be recorded. (c) The local commissural neurons that integrate this coordinating information and tune the phase of each swimmeret are known. (d) The complete set of synaptic connections between coordinating neurons and these commissural neurons have been described. (e). The synaptic connections onto each local pattern-generating circuit through which coordinating information tunes the circuit's phase have been discovered. These factors make possible for the first time a detailed, comprehensive cellular and synaptic explanation of how this neural circuit produces an effective, behaviorally significant output. This paper is the first comprehensive review of the system's neuroanatomy and neurophysiology, its local and intersegmental circuitry, its transmitter pharmacology, its neuromodulatory control mechanisms, and its interactions with other motor systems. Each of these topics is covered in detail in an attempt to provide a complete review of the literature as a foundation for new research. The series of hypotheses that have been proposed to account for the system's properties are reviewed critically in the context of experimental tests of their validity.

Opposite actions of dopamine on aversive and appetitive memories in the crab

The understanding of how the reinforcement is represented in the central nervous system during memory formation is a current issue in neurobiology. Several studies in insects provide evidence of the instructive role of biogenic amines during the learning and memory process. In insects it was widely accepted that dopamine (DA) mediates aversive reinforcements. However, the idea of DA being exclusively involved in aversive memory has been challenged in recent studies. Here, we study the involvement of DA during aversive and appetitive memories in the crab Chasmagnathus. We found that DA-receptor antagonists impair aversive memory consolidation, in agreement with previous reports in insects, while administration of DA facilitates memory formation after a weak training protocol. In contrast, DA treatment during appetitive training was found to impair formation of long-term appetitive memory. In addition, as a first step in elucidating the neuroanatomical correlates of DA action on memory, we mapped dopaminergic neurons in the central nervous system of the crab. Results of the current study, together with those obtained in a previous work about the role of octopamine (OA), suggest that both amines (DA and OA) play a dual action in memory processes. On the one hand, DA and OA mediate the aversive and the appetitive signals, respectively, throughout training, while on the other hand, they interfere with the formation of memory of the opposite sign (DA in appetitive and OA in aversive). Our results support a new understanding about the way appetitive and aversive stimuli are processed during memory formation to ensure adaptive behavior.

Distribution and changes of serotonin and dopamine levels in the central nervous system and ovary of the Pacific white shrimp, Litopenaeus vannamei, during ovarian maturation cycle

We investigated changes in serotonin (5-HT) and dopamine (DA) levels and in their distribution patterns in the central nervous system (CNS) and ovary during the ovarian maturation cycle in the Pacific white shrimp, Litopenaeus vannamei. The concentrations of these two neurotransmitters were determined by using high performance liquid chromatography with electrochemical detection. The 5-HT concentration exhibited a gradual increase in the brain and thoracic ganglia during early ovarian stages I, II, and III, reaching a maximum at the mature ovarian stage IV, whereas DA showed its highest concentration at ovarian stage II in the brain and thoracic ganglia and then declined to its lowest concentration at ovarian stage IV. In the ovaries, 5-HT was lowest at ovarian stage I and gradually increased to a peak at ovarian stage IV. Conversely, the concentration of DA was highest at ovarian stages I and II and lowest at ovarian stage IV. In the brain, 5-HT immunoreactivity (-ir) from stage IV and DA-ir from stage II were distributed extensively in neurons of clusters 6, 11, and 17, in fibers, and in the anterior and posterior medial protocerebral, olfactory, antenna II, and tegumentary neuropils. In the circumesophageal, subesophageal, thoracic, and abdominal ganglia, both 5-HT-ir and DA-ir were detected in neuropils and surrounding neurons and fibers. 5-HT-ir and DA-ir were more intense in the thoracic ganglia than in other parts of the CNS. In the ovary, 5-HT-ir exhibited high intensity in late oocytes, whereas DA-ir was more intense in early oocytes. Thus, opposing changes occur in the levels of these two neurotransmitters and in their specific localizations in the CNS and ovary during ovarian maturation, indicating their important involvement in female reproduction.

Metabolomics of microliter hemolymph samples enables an improved understanding of the combined metabolic and transcriptional responses of Daphnia magna to cadmium

Omic technologies offer unprecedented opportunities to better understand mode(s)-of-toxicity and downstream secondary effects by providing a holistic view of the molecular changes underlying physiological disruption. Crustacean hemolymph represents a largely untapped biochemical resource for such toxicity studies. We sought to characterize changes in the hemolymph metabolome and whole-body transcriptome to reveal early processes leading to chronic toxicity in the indicator species, Daphnia magna, after 24-h sublethal cadmium exposure (18 μg/L, corresponding to 1/10 LC(50)). We first confirmed that metabolites can be detected and identified in small volumes (∼3-6 μL) of D. magna hemolymph using Fourier transform ion cyclotron resonance mass spectrometry and NMR spectroscopy. Subsequently, mass spectrometry based metabolomics of hemolymph identified disruption to two major classes of metabolites: amino acids and fatty acids. These findings were compared to differentially expressed genes identified by a D. magna 44k oligonucleotide microarray, which included decreased levels of digestive enzymes and increased expression of cuticle proteins and oxidative stress response genes. The combination of metabolic and transcriptional changes revealed through KEGG pathway analysis and gene ontology, respectively, enabled a more complete understanding of how cadmium disrupts nutrient uptake and metabolism, ultimately resulting in decreased energy reserves and chronic toxicity.

Drug-sensitive reward in crayfish: an invertebrate model system for the study of SEEKING, reward, addiction, and withdrawal

In mammals, rewarding properties of drugs depend on their capacity to activate appetitive motivational states. With the underlying mechanisms strongly conserved in evolution, invertebrates have recently emerged as a powerful new model in addiction research. In crayfish natural reward has proven surprisingly sensitive to human drugs of abuse, opening an unlikely avenue of research into the basic biological mechanisms of drug addiction. In a series of studies we first examined the presence of natural reward systems in crayfish, then characterized its sensitivity to a wide range of human drugs of abuse. A conditioned place preference (CPP) paradigm was used to demonstrate that crayfish seek out those environments that had previously been paired with the psychostimulants cocaine and amphetamine, and the opioid morphine. The administration of amphetamine exerted its effects at a number of sites, including the stimulation of circuits for active exploratory behaviors (i.e., SEEKING). A further study examined morphine-induced reward, extinction and reinstatement in crayfish. Repeated intra-circulatory infusions of morphine served as a reward when paired with distinct visual or tactile cues. Morphine-induced CPP was extinguished after repeated saline injections. Following this extinction phase, morphine-experienced crayfish were once again challenged with the drug. The priming injections of morphine reinstated CPP at all tested doses, suggesting that morphine-induced CPP is unrelenting. In an exploration of drug-associated behavioral sensitization in crayfish we concurrently mapped measures of locomotion and rewarding properties of morphine. Single and repeated intra-circulatory infusions of morphine resulted in persistent locomotory sensitization, even 5 days following the infusion. Moreover, a single dose of morphine was sufficient to induce long-term behavioral sensitization. CPP for morphine and context-dependent cues could not be disrupted over a drug free period of 5 days. This work demonstrates that crayfish offer a comparative and complementary approach in addiction research. Serving as an invertebrate animal model for the exposure to mammalian drugs of abuse, modularly organized and experimentally accessible nervous systems render crayfish uniquely suited for studying (1) the basic biological mechanisms of drug effects, (2) to explore how the appetitive/seeking disposition is implemented in a simple neural system, and (3) how such a disposition is related to the rewarding action of drugs of abuse. This work aimed to contribute an evolutionary, comparative context to our understanding of a key component in learning, and of natural reward as an important life-sustaining process.

Immunohistochemical mapping of histamine, dopamine, and serotonin in the central nervous system of the copepod Calanus finmarchicus (Crustacea; Maxillopoda; Copepoda)

Calanoid copepods constitute an important group of marine planktonic crustaceans that often dominate the metazoan biomass of the world's oceans. In proportion to their ecological importance, little is known about their nervous systems. We have used immunohistochemical techniques in a common North Atlantic calanoid to localize re-identifiable neurons that putatively contain the biogenic amines histamine, dopamine, and serotonin. We have found low numbers of such cells and cell groups (approximately 37 histamine pairs, 22 dopamine pairs, and 12 serotonin pairs) compared with those in previously described crustaceans. These cells are concentrated in the anterior part of the central nervous system, the majority for each amine being located in the three neuromeres that constitute the brain (protocerebrum, deutocerebrum, and tritocerebrum). Extensive histamine labeling occurs in several small compact protocerebral neuropils, three pairs of larger, more posterior, paired, dense neuropils, and one paired diffuse tritocerebral neuropil. The most concentrated neuropil showing dopamine labeling lies in the putative deutocerebrum, associated with heavily labeled commissural connections between the two sides of the brain. The most prominent serotonin neuropil is present in the anterior medial part of the brain. Tracts of immunoreactive fibers of all three amines are prominent in the cephalic region of the nervous system, but some projections into the most posterior thoracic regions have also been noted.

Cell specific dopamine modulation of the transient potassium current in the pyloric network by the canonical D1 receptor signal transduction cascade

Dopamine (DA) modifies the motor pattern generated by the pyloric network in the stomatogastric ganglion (STG) of the spiny lobster, Panulirus interruptus, by directly acting on each of the circuit neurons. The 14 pyloric neurons fall into six cell types, and DA actions are cell type specific. The transient potassium current mediated by shal channels (I(A)) is a common target of DA modulation in most cell types. DA shifts the voltage dependence of I(A) in opposing directions in pyloric dilator (PD) versus lateral pyloric (LP) neurons. The mechanism(s) underpinning cell-type specific DA modulation of I(A) is unknown. DA receptors (DARs) can be classified as type 1 (D1R) or type 2 (D2R). D1Rs and D2Rs are known to increase and decrease intracellular cAMP concentrations, respectively. We hypothesized that the opposing DA effects on PD and LP I(A) were due to differences in DAR expression patterns. In the present study, we found that LP expressed somatodendritic D1Rs that were concentrated near synapses but did not express D2Rs. Consistently, DA modulation of LP I(A) was mediated by a Gs-adenylyl cyclase-cAMP-protein kinase A pathway. Additionally, we defined antagonists for lobster D1Rs (flupenthixol) and D2Rs (metoclopramide) in a heterologous expression system and showed that DA modulation of LP I(A) was blocked by flupenthixol but not by metoclopramide. We previously showed that PD neurons express D2Rs, but not D1Rs, thus supporting the idea that cell specific effects of DA on I(A) are due to differences in receptor expression.

D(2) receptors receive paracrine neurotransmission and are consistently targeted to a subset of synaptic structures in an identified neuron of the crustacean stomatogastric nervous system

Dopamine (DA) modulates motor systems in phyla as diverse as nematodes and arthropods up through chordates. A comparison of dopaminergic systems across a broad phylogenetic range should reveal shared organizing principles. The pyloric network, located in the stomatogastric ganglion (STG), is an important model for neuromodulation of motor networks. The effects of DA on this network have been well characterized at the circuit and cellular levels in the spiny lobster, Panulirus interruptus. Here we provide the first data about the physical organization of the DA signaling system in the STG and the function of D(2) receptors in pyloric neurons. Previous studies showed that DA altered intrinsic firing properties and synaptic output in the pyloric dilator (PD) neuron, in part by reducing calcium currents and increasing outward potassium currents. We performed single cell reverse transcriptase-polymerase chain reaction (RT-PCR) experiments to show that PD neurons exclusively expressed a type 2 (D(2alphaPan)) DA receptor. This was confirmed by using confocal microscopy in conjunction with immunohistochemistry (IHC) on STG whole-mount preparations containing dye-filled PD neurons. Immunogold electron microscopy showed that surface receptors were concentrated in fine neurites/terminal swellings and vesicle-laden varicosities in the synaptic neuropil. Double-label IHC experiments with tyrosine hydroxylase antiserum suggested that the D(2alphaPan) receptors received volume neurotransmissions. Receptors were further mapped onto three-dimensional models of PD neurons built from Neurolucida tracings of confocal stacks from the IHC experiments. The data showed that D(2alphaPan) receptors were selectively targeted to approximately 40% of synaptic structures in any given PD neuron, and were nonuniformly distributed among neurites.

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.

Cloning and immunoreactivity of the 5-HT 1Mac and 5-HT 2Mac receptors in the central nervous system of the freshwater prawn Macrobrachium rosenbergii

Biogenic amines are implicated in several mental disorders, many of which involve social interactions. Simple model systems, such as crustaceans, are often more amenable than vertebrates for studying mechanisms underlying behaviors. Although various cellular responses of biogenic amines have been characterized in crustaceans, the mechanisms linking these molecules to behavior remain largely unknown. Observed effects of serotonin receptor agonists and antagonists in abdomen posture, escape responses, and fighting have led to the suggestion that biogenic amine receptors may play a role in modulating interactive behaviors. As a first step in understanding this potential role of such receptors, we have cloned and fully sequenced two serotonin receptors, 5-HT(1Mac) and 5-HT(2Mac), from the CNS of the freshwater prawn Macrobrachium rosenbergii and have mapped their CNS immunohistochemical distribution. 5-HT(1Mac) was found primarily on the membranes of subsets of cells in all CNS ganglia, in fibers that traverse all CNS regions, and in the cytoplasm of a small number of cells in the brain and circum- and subesophageal ganglia (SEG), most of which also appear to contain dopamine. The pattern of 5-HT(2Mac) immunoreactivity was found to differ significantly; it was found mostly in the central neuropil area of all ganglia, in glomeruli of the brain's olfactory lobes, and in the cytoplasm of a small number of neurons in the SEG, thoracic, and some abdominal ganglia. The observed differences in terms of localization, distribution within cells, and intensity of immunoreactive staining throughout the prawn's CNS suggest that these receptors are likely to play different roles.

Changes in the levels of serotonin and dopamine in the central nervous system and ovary, and their possible roles in the ovarian development in the giant freshwater prawn, Macrobrachium rosenbergii

Serotonin or 5-hydroxytryptamine (5-HT) and dopamine (DA) are the two key neurotransmitters that control gonadal development in decapod crustaceans. This study investigated changes in the levels of 5-HT and DA in the CNS and ovary during different phases of the ovarian cycle of the freshwater prawn, Macrobrachium rosenbergii. The levels of 5-HT and DA were quantified by using High Performance Liquid Chromatography with electrochemical detection (HPLC-ECD). Moreover, changes of vitellogenin (Vg) concentrations in the hemolymph after treatment with 5-HT and DA (at doses of 2.5 x 10(-6) and 2.5 x 10(-7)mol per prawn) were also examined. 5-HT exhibited a gradual increase in concentration in the brain and thoracic ganglia from ovarian stage I (0.12+/-0.01 nmol/mg, 0.22+/-0.01 nmol/mg, respectively) to reach a maximum (0.66+/-0.03 nmol/mg, 1.48+/-0.03 nmol/mg, respectively) at ovarian stage IV. In contrast, DA in the brain and thoracic ganglia showed the highest concentrations at ovarian stage II (0.20+/-0.01 nmol/mg, 1.27+/-0.06 nmol/mg, respectively) and then decreased to the lowest concentrations (0.06+/-0.01 nmol/mg, 0.28+/-0.04 nmol/mg, respectively) at ovarian stage IV. The ovarian concentration of 5-HT was 0.53+/-0.11 nmol/mg at ovarian stage I and gradually increased to 1.63+/-0.16 nmol/mg at ovarian stage IV. In contrast, the concentration of DA was highest at ovarian stage I (29.05+/-1.31 nmol/mg), and lowest at the ovarian stage IV (11.43+/-0.74 nmol/mg). Injecting 5-HT into prawns significantly increased Vg concentration in the hemolymph at ovarian stage IV compared to control groups, and injecting DA into prawns had the opposite effect. The inverse relationship between 5-HT and DA levels in neural ganglia and ovaries, and their opposing effects on hemolymph Vg levels suggest that these two transmitters play opposite regulatory roles in controlling ovarian maturation and oocyte development in this species.

Drug-seeking behavior in an invertebrate system: evidence of morphine-induced reward, extinction and reinstatement in crayfish

Several lines of evidence suggest that exploring the neurochemical basis of reward in invertebrate species may provide clues for the fundamental behavioral and neurobiology underpinnings of drug addiction. How the presence of drug-sensitive reward relates to a decrease in drug-seeking behavior and reinstatement of drug-seeking behavior in invertebrate systems is not known. The present study of a conditioned place preference (CPP) paradigm in crayfish (Orconectes rusticus) explores morphine-induced reward, extinction and reinstatement. Repeated intra-circulatory infusions of 2.5 microg/g, 5.0 microg/g and 10.0 microg/g doses of morphine over 5 days serve as a reward when paired with a distinct visual or tactile environment. Morphine-induced CPP was extinguished after repeated saline injections for 5 days in the previously morphine-paired compartment. After the previously established CPP had been eliminated during the extinction phase, morphine-experienced crayfish were challenged with 2.5 microg/g, 5.0 microg/g and 10.0 microg/g, respectively. The priming injections of morphine reinstated CPP in all training doses, suggesting that morphine-induced CPP is unrelenting, and that with time, it can be reinstated by morphine following extinction in an invertebrate model just like in mammals. Together with other recent studies, this work demonstrates the advantage of using crayfish as an invertebrate animal model to investigate the basic biological processes that underline exposure to mammalian drugs of abuse.