5-Hydroxytryptaminergic control of red pigment-dispersing hormone release in the fiddler crab, Uca pugilator: effects of a 5-hydroxytryptamine uptake inhibitor and a 5-hydroxytryptamine receptor blocker on 5-hydroxytryptamine-induced and iproniazid-induced red pigment dispersion

Effects of environmental antidepressants on colour change and locomotor behaviour in juvenile shore crabs, Carcinus maenas

Juvenile crabs of Carcinus maenas thrive in coastal waters reputed to be the receptacle of continental pollution. Amongst the many pollutants encountered, antidepressants, such as fluoxetine (FLX) and venlafaxine (VEN), often detected at the ng•L^-1 range, are particularly worrying because of their action on the levels of monoamines, such as serotonin, noradrenaline and dopamine. In crustaceans, those monoamines are involved in colour change through their action on neuropeptide hormones. In addition, they are known to have a role in different behaviours, such as locomotion. Both colour change and locomotion are strategies used by juvenile crabs to hide and escape from predators. To investigate if the presence of antidepressants may alter behaviours of ecological importance, juvenile crabs were exposed to environmentally realistic concentrations of either 5 ng•L^-1 of FLX alone or in combination with VEN at 5 ng•L^-1. The ability to change colour depending on the environment and the locomotor activity of juvenile crabs were monitored weekly over 25 days. Animals exposed to antidepressants displayed a different pattern of colour change than the controls, especially those exposed to the combination of FLX and VEN at 5 ng•L^-1 each, and were less efficient to adapt to their environment, i.e., they were not as pale and not as dark as controls or crabs exposed to FLX at 5 ng•L^-1. Moreover, juvenile crabs exposed to the combination of antidepressants exhibited an enhanced locomotor activity throughout the exposure period with a higher velocity and distance moved as well as more time spend moving. The alteration of cryptic behaviours, such as colour change and locomotion by antidepressants persistently present in marine environment at low concentrations may have an impact on the survival of juvenile of C. maenas on the long term.

A Crab Is Not a Fish: Unique Aspects of the Crustacean Endocrine System and Considerations for Endocrine Toxicology

Crustaceans-and arthropods in general-exhibit many unique aspects to their physiology. These include the requirement to moult (ecdysis) in order to grow and reproduce, the ability to change color, and multiple strategies for sexual differentiation. Accordingly, the endocrine regulation of these processes involves hormones, receptors, and enzymes that differ from those utilized by vertebrates and other non-arthropod invertebrates. As a result, environmental chemicals known to disrupt endocrine processes in vertebrates are often not endocrine disruptors in crustaceans; while, chemicals that disrupt endocrine processes in crustaceans are often not endocrine disruptors in vertebrates. In this review, we present an overview of the evolution of the endocrine system of crustaceans, highlight endocrine endpoints known to be a target of disruption by chemicals, and identify other components of endocrine signaling that may prove to be targets of disruption. This review highlights that crustaceans need to be evaluated for endocrine disruption with consideration of their unique endocrine system and not with consideration of the endocrine system of vertebrates.

Effects of the antidepressant fluoxetine on pigment dispersion in chromatophores of the common sand shrimp, Crangon crangon: repeated experiments paint an inconclusive picture

The effects of antidepressants in the environment are starting to generate considerable interest due to the fact that neurotransmitters influence a range of biological processes. Crypsis is an important behavioural and physiological response in many crustaceans modulated by monoamine and pigment dispersing/concentrating hormones. This study aimed to develop a test methodology and investigate the effects of the selective serotonin reuptake inhibitor (SSRI), fluoxetine, on a chromatophore index and overall carapace 'darkness' in the common sand shrimp Crangon crangon. Adult shrimp were exposed for either 1 h, 1 day or 1 week across a range of nominal fluoxetine concentrations (10 ng/L, 100 ng/L and 1000 ng/L) and the chromatophore index or carapace percentage 'darkness' was recorded following 30 min on white and black substrates. These experiments were repeated three times using different specimens. Animals became significantly darker (~20%) on darker background and lighter on light backgrounds as one might expect. However, time periods over which the animals were recorded had a significant impact on the colouration suggesting habituation to laboratory conditions. Fluoxetine exposure came up as a significant factor in two of the three trials for the chromatophore index but the results was inconsistent between trials. There was a high degree of correlation between the chromatophore index and the percentage darkness analyses however, there was no significant effects for fluoxetine exposure with the percentage darkness data. We conclude that the effects on antidepressants on colour change remain inconclusive from these experiments and we discuss potential areas to improve the repeatability of the experiments.

Serotonergic regulation of blood glucose levels in the crayfish, Procambarus clarkii: site of action and receptor characterization

The present study investigated the site of action of 5-hydroxytryptamine (5-HT) and pharmacologically characterized the receptors involved in regulating blood glucose levels in the crayfish, Procambarus clarkii. Injection of 5-HT into intact animals increased glucose levels in a dose-dependent manner. In contrast, 5-HT failed to elicit a hyperglycemic response in eyestalk-ablated animals. Effects of several 5-HT receptor agonists and antagonists were examined. 5-CT, oxymetazoline (both 5-HT(1) receptor agonists) and alpha-methyl-5-HT (a 5-HT(2) receptor agonist), but not 1-phenylbiguanide, m-CPBG (both 5-HT(3) receptor agonists), or RS 67333 (a 5-HT(4) receptor agonist), induced hyperglycemic responses in a dose-dependent manner. In addition, 8-OH-DPAT (a 5-HT(1A) receptor agonist), L-694,247 (a 5-HT(1B/1D) receptor agonist), and DOI (a 5-HT(2A) receptor agonist) were effective in significantly increasing the glucose levels, whereas both BW 723C86 (a 5-HT(2B) receptor agonist) and m-CPP (a 5-HT(2C) receptor agonist) were ineffective. Finally, ketanserin (a 5-HT(2A) receptor antagonist), but not p-MPPF (a 5-HT(1A) receptor antagonist), GR 55562 (a 5-HT(1B/1D) receptor antagonist), SB 206553 (a 5-HT(2B/2C) receptor antagonist), or tropisetron (a 5-HT(3) receptor antagonist), was able to block 5-HT-induced hyperglycemia. The combined results support the hypothesis that 5-HT exerts its hyperglycemic effect by enhancing the release of hyperglycemic factor(s) from the eyestalks, and suggest that 5 HT-induced hyperglycemia is mediated by 5-HT(1)- and 5-HT(2)-like receptors.

Effect of 5-hydroxytryptamine antibodies on pigment migration in the erythrophores of the fiddler crab, Uca pugilator: further evidence for 5-hydroxytryptamine as a neurotransmitter that stimulates release of red pigment-dispersing hormone

5-Hydroxytryptamine (5-HT) antibodies inhibit red pigment dispersion in the fiddler crab, Uca pugilator. This observation supports the hypothesis that 5-HT stimulates release of red pigment-dispersing hormone.

Roles of 5-hydroxytryptamine and dopamine as neurotransmitters eliciting release of erythrophorotropic hormones in the fiddler crab, UCA pugilator

This article reviews the endocrinological, pharmacological and biochemical evidence ascribing neurotransmitter roles for 5-hydroxytryptamine (5-HT, serotonin) in eliciting the release of red pigment-dispersing hormone (RPDH) and for dopamine (DA) in stimulating the release of red pigment-concentrating hormone (RPCH) in the fiddler crab, Uca pugilator. 5-HT produces red pigment dispersion in intact crabs, but only indirectly. Likewise, DA evokes red pigment concentration in vivo but it has no effect on red chromatophores (erythrophores) in isolated legs. The data obtained with 5-HT and DA agonists and antagonists on red pigment translocation in vivo and in vitro, are consistent with their neurotransmitter candidacies in evoking the release of these erythrophorotropic hormones.