Drinks like a fish: zebra fish (Danio rerio) as a behavior genetic model to study alcohol effects

Glyphosate and Roundup® alter morphology and behavior in zebrafish

Glyphosate has become the most widely used herbicide in the world, due to the wide scale adoption of transgenic glyphosate resistant crops after its introduction in 1996. Glyphosate may be used alone, but it is commonly applied as an active ingredient of the herbicide Roundup®. This pesticide contains several adjuvants, which may promote an unknown toxicity. The indiscriminate application poses numerous problems, both for the health of the applicators and consumers, and for the environment, contaminating the soil, water and leading to the death of plants and animals. Zebrafish (Danio rerio) is quickly gaining popularity in behavioral research, because of physiological similarity to mammals, sensitivity to pharmacological factors, robust performance, low cost, short spawning intervals, external fertilization, transparency of embryos through larval stages, and rapid development. The aim of this study was evaluate the effects of glyphosate and Roundup® on behavioral and morphological parameters in zebrafish larvae and adults. Zebrafish larvae at 3days post-fertilization and adults were exposed to glyphosate (0.01, 0.065, and 0.5mg/L) or Roundup® (0.01, 0.065, and 0.5mg/L) for 96h. Immediately after the exposure, we performed the analysis of locomotor activity, aversive behavior, and morphology for the larvae and exploratory behavior, aggression and inhibitory avoidance memory for adult zebrafish. In zebrafish larvae, there were significant differences in the locomotor activity and aversive behavior after glyphosate or Roundup® exposure when compared to the control group. Our findings demonstrated that exposure to glyphosate at the concentration of 0.5mg/L, Roundup® at 0.065 or 0.5mg/L reduced the distance traveled, the mean speed and the line crossings in adult zebrafish. A decreased ocular distance was observed for larvae exposed at 0.5mg/L of glyphosate. We verified that at 0.5mg/L of Roundup®-treated adult zebrafish demonstrated a significant impairment in memory. Both glyphosate and Roundup® reduced aggressive behavior. Our data suggest that there are small differences between the effects induced by glyphosate and Roundup®, altering morphological and behavioral parameters in zebrafish, suggesting common mechanisms of toxicity and cellular response.

Prenatal cocaine exposure disrupts the dopaminergic system and its postnatal responses to cocaine

Impaired attention is the hallmark consequence of prenatal cocaine exposure (PCE), affecting brain development, learning, memory and social adaptation starting at an early age. To date, little is known about the brain structures and neurochemical processes involved in this effect. Through focusing on the visual system and employing zebrafish as a model, we show that PCE reduces expression of dopamine receptor Drd1, with levels reduced in the optic tectum and other brain regions, but not the telencephalon. Organism-wide, PCE results in a 1.7-fold reduction in the expression of the dopamine transporter (dat), at baseline. Acute cocaine administration leads to a 2-fold reduction in dat in drug-naive larvae but not PCE fish. PCE sensitizes animals to an anxiogenic-like behavioral effect of acute cocaine, bottom-dwelling, while loss of DAT due to genetic knockout (DATKO) leads to bottom-dwelling behavior at baseline. Neuronal calcium responses to visual stimuli in both PCE and DATKO fish show tolerance to acute cocaine in the principal regions of visual attention, the telencephalon and optic tectum. The zebrafish model can provide a sensitive assay by which to elucidate the molecular mechanisms and brain region-specific consequences of PCE, and facilitate the search for effective therapeutic solutions.

Fetal alcohol spectrum disorders: Zebrafish in the analysis of the milder and more prevalent form of the disease

Fetal Alcohol Spectrum Disorders (FASD) represent a large unmet medical need. Exposure of the developing human embryo to alcohol can lead to life-long suffering. Despite the well documented deleterious effects of alcohol on the developing fetus, pregnant women continue to drink alcohol, and FASD remains the leading cause of preventable mental retardation and other behavioral abnormalities. Particularly prevalent are the milder forms of the disease cluster, representing children who do not show obvious physical signs and who may be undiagnosed or misdiagnosed. To develop treatment and diagnostic tools, researchers have turned to animal models. The zebrafish is becoming one of the leading biomedical research organisms that may facilitate discovery of the biological mechanisms underlying this disease and the identification of biomarkers that may be used for diagnosis. Here we review the latest advances of this field, mostly focussing on the discoveries made in our own laboratory and others with zebrafish employed to analyze the effects of moderate to low level of exposure to alcohol. We argue that the zebrafish represents unique advantages, and adding information obtained with this species to the mix of other animal models will significantly increase translational relevance of animal biomedical research for the analysis of human FASD.

Repeated ethanol exposure alters social behavior and oxidative stress parameters of zebrafish

Repeated ethanol (EtOH) consumption induces neurological disorders in humans and is considered an important public health problem. The physiological effects of EtOH are dose- and time-dependent, causing relevant changes in the social behavior. In addition, alcohol-induced oxidative stress has been proposed as a key mechanism involved in EtOH neurotoxicity. Here we investigate for the first time whether repeated EtOH exposure (REE) alters the social behavior of zebrafish and influences brain oxidation processes. Animals were exposed to water (control group) or 1% (v/v) EtOH (EtOH group) for 8 consecutive days (20min per day). EtOH was added directly to the tank water. At day 9, the social behavior and biochemical parameters were assessed. REE increased shoal cohesion by reducing inter-fish and farthest neighbor distances. SOD and CAT activities, as well as NPSH levels decreased in brain tissue. Moreover, REE increased lipid peroxidation suggesting oxidative damage. In summary, changes in oxidation processes may play a role in the CNS effects of EtOH, influencing the social behavior of zebrafish. Furthermore, in a translational neuroscience perspective, our data reinforces the utility of zebrafish to clarify the biochemical and behavioral effects of intermittent EtOH administration.

Cd36 is a candidate lipid sensor involved in the sensory detection of fatty acid in zebrafish

Recently more and more evidences raise the possibility for the taste system in the role of the perception of lipids in mammals, and the fatty acid receptor CD36 has been proved to be as an important candidate receptor of fat taste. Fish has different taste modality with mammals. No information was known about the function of cd36 in fish taste till now. Here, using in situ hybridization and immunofluorescence technologies, we showed that fish cd36/Cd36 localized in taste buds. Real-time PCR technology demonstrated that, in zebrafish cd36 (zcd36)-transfected cells, linoleic acid (LA) increased the expression level of tryptophan hydroxylase-1 (TPH-1), which encodes the enzyme involved in the biosynthesis of monoamine neurotransmitter of 5-HT. Moreover, the LA-induced up-regulation expression of TPH-1 was significantly curtailed by SSO, a specific inhibitor of LCFA binding to CD36, suggesting zCd36 is implicated in the LA-induced release of neurotransmitter. Importantly, we observed that zcd36 gene knockout zebrafish reduced the preference for LA contrast to wild-type zebrafish. Together, our findings indicate that Cd36 is a candidate lipid sensor involved in the sensory detection of fatty acid in zebrafish.

Quantitative Responses of Adult Zebrafish to Changes in Ambient Illumination

The use of zebrafish models to study central nervous system aging and late-onset neurological diseases will be facilitated by assays allowing rapid evaluation of neurological phenotypes in adult zebrafish. We analyzed groups of 12 adult zebrafish swimming simultaneously in single-animal arenas, and quantified their responses to changes in ambient illumination. Under these conditions, stereotypical locomotor patterns were observed and readily quantified using open source software. Continuous, low-velocity movements were observed during 10-min periods of darkness, whereas intermittent high-velocity movements occurred in bright light. At 80%-90% of abrupt light-to-dark or dark-to-light transitions, adult zebrafish produced a synchronous short-latency (20-22 ms) turn, followed by a propulsive movement with a high transient maximum velocity (400-500 mm/s). Between 5 and 35 months of age, latency increased by ∼10%, and peak velocity decreased by ∼30%, suggesting that the response declines in aged adults. Light transition responses can be measured rapidly and automatically in multiple adult zebrafish simultaneously, providing a convenient quantitative method for evaluating sensorimotor function in adult zebrafish models of neurological disease.

Understanding taurine CNS activity using alternative zebrafish models

Taurine is a highly abundant "amino acid" in the brain. Despite the potential neuroactive role of taurine in vertebrates has long been recognized, the underlying molecular mechanisms related to its pleiotropic effects in the brain remain poorly understood. Due to the genetic tractability, rich behavioral repertoire, neurochemical conservation, and small size, the zebrafish (Danio rerio) has emerged as a powerful candidate for neuropsychopharmacology investigation and in vivo drug screening. Here, we summarize the main physiological roles of taurine in mammals, including neuromodulation, osmoregulation, membrane stabilization, and antioxidant action. In this context, we also highlight how zebrafish models of brain disorders may present interesting approaches to assess molecular mechanisms underlying positive effects of taurine in the brain. Finally, we outline recent advances in zebrafish drug screening that significantly improve neuropsychiatric translational researches and small molecule screens.

Stress responses to conspecific visual cues of predation risk in zebrafish

Chemical communication relating to predation risk is a trait common among fish species. Prey fish under threat of predation can signal risk to conspecific fish, which then exhibit defensive responses. Fish also assess predation risk by visual cues and change their behavior accordingly. Here, we explored whether these behavioral changes act as visual alarm signals to conspecific fish that are not initially under risk. We show that shoals of zebrafish (Danio rerio) visually exposed to a predator display antipredator behaviors. In addition, these defensive maneuvers trigger antipredator reactions in conspecifics and, concomitantly, stimulate the hypothalamus-pituitary-interrenal axis, leading to cortisol increase. Thus, we conclude that zebrafish defensive behaviors act as visual alarm cues that induce antipredator and stress response in conspecific fish.

Tebuconazole alters morphological, behavioral and neurochemical parameters in larvae and adult zebrafish (Danio rerio)

In this study, we evaluated the effects of tebuconazole on morphology and exploratory larvae behavior and adult locomotion. Furthermore, we analyzed the effects of this fungicide on AChE activity and gene expression in zebrafish larvae and in the adult zebrafish brain. Tebuconazole (4 mg/L) increased the ocular distance in larvae and reduced the distance travelled, absolute turn angle, line crossing and time outside area in exposed larvae. Moreover, adult zebrafish that were exposed to this fungicide (4 and 6 mg/L) showed a decrease in distance travelled and mean speed when compared to the control group. However, tebuconazole did not alter the number of line crossings or time spent in the upper zone. Tebuconazole inhibited AChE activity at concentrations of 4 mg/L for larvae and 4 and 6 mg/L in the adult zebrafish brain. However, this fungicide did not alter AChE gene expression in the adult zebrafish brain but increased AChE mRNA transcript levels in larvae. These findings demonstrated that tebuconazole could modulate the cholinergic system by altering AChE activity and that this change may be associated with the reduced locomotion of these animals.

Zebrafish models in neuropsychopharmacology and CNS drug discovery

Despite the high prevalence of neuropsychiatric disorders, their aetiology and molecular mechanisms remain poorly understood. The zebrafish (Danio rerio) is increasingly utilized as a powerful animal model in neuropharmacology research and in vivo drug screening. Collectively, this makes zebrafish a useful tool for drug discovery and the identification of disordered molecular pathways. Here, we discuss zebrafish models of selected human neuropsychiatric disorders and drug-induced phenotypes. As well as covering a broad range of brain disorders (from anxiety and psychoses to neurodegeneration), we also summarize recent developments in zebrafish genetics and small molecule screening, which markedly enhance the disease modelling and the discovery of novel drug targets.

Good night, sleep tight: The effects of sleep deprivation on spatial associative learning in zebrafish

Learning and memory are vital to an animal's survival, and numerous factors can disrupt cognitive performance. Sleep is an evolutionarily conserved physiological process known to be important for the consolidation of learning and memory. The zebrafish has emerged as a powerful model organism sharing organizational and functional characteristics with other vertebrates, providing great translational relevance. In our study, we used a simple spatial associative learning task to quantify the effects of sleep deprivation (partial vs. total) on learning performance in zebrafish, using an animated conspecific shoal image as a reward. Control animals maintained on a regular light:dark cycle were able to acquire the association between the unconditioned and conditioned stimulus, reinforcing zebrafish as a valid and reliable model for appetitive conditioning tasks. Notably, sleep deprivation did not alter the perception of and response to the conspecific image. In contrast, although partial sleep deprivation did not impair cognitive performance, total sleep deprivation significantly impaired performance on the associative learning task. Our results suggest that sleep is important for learning and memory, and that the effects of sleep deprivation on these processes can be investigated in zebrafish.

Dopaminergic control of anxiety in young and aged zebrafish

Changes in the expression of the dopamine transporter (DAT), or the sensitivity of dopamine receptors, are associated with aging and substance abuse and may underlie some of the symptoms common to both conditions. In this study, we explored the role of the dopaminergic system in the anxiogenic effects of aging and acute cocaine exposure by comparing the behavioral phenotypes of wild type (WT) and DAT knockout zebrafish (DAT-KO) of different ages. To determine the involvement of specific dopamine receptors in anxiety states, antagonists to D1 (SCH23390) and D2/D3 (sulpiride) were employed. We established that DAT-KO results in a chronic anxiety-like state, seen as an increase in bottom-dwelling and thigmotaxis. Similar effects were produced by aging and acute cocaine administration, both leading to reduction in DAT mRNA abundance (qPCR). Inhibition of D1 activity counteracted the anxiety-like effects associated with DAT deficit, independent of its origin. Inhibition of D2/D3 receptors reduced anxiety in young DAT-KO, and enhanced the anxiogenic effects of cocaine in WT, but did not affect aged WT or DAT-KO fish. These findings provide new evidence that the dopaminergic system plays a critical role in anxiety-like states, and suggest that adult zebrafish provide a sensitive diurnal vertebrate model for elucidating the molecular mechanisms of anxiety and a platform for anxiolytic drug screens.

Time-dependent interacting effects of caffeine, diazepam, and ethanol on zebrafish behaviour

Zebrafish have become a popular animal model for behavioural pharmacology due to their small size, rapid development, and amenability to high throughput behavioural drug screens. Furthermore, water-soluble compounds can be administered via immersion of the fish in the drug solution, which provides a non-invasive drug delivery method. Numerous studies have demonstrated stimulant effects of alcohol. Diazepam and caffeine, on the other hand have been found to have inhibitory effect on locomotor activity in zebrafish. However, the time-dependent changes induced by these psychoactive drugs are rarely reported, and potential drug interactions have not been examined in zebrafish, despite the translational relevance of this question. In the current study, we examine time- and dose-dependent changes in zebrafish following exposure to caffeine, diazepam, and ethanol quantifying four different behavioural parameters over a 30min recording session. We subsequently analyze potential drug-drug interactions by co-administering the three drugs in different combinations. Our time-course and dose-response analyses for each of the three drugs represent so far the most detailed studies available serving as a foundation for future psychopharmacology experiments with zebrafish. Furthermore, we report significant interactions between the three drugs corroborating findings obtained with rodent models as well as in humans, providing translational relevance for the zebrafish model.

Sodium Selenite Prevents Paraquat-Induced Neurotoxicity in Zebrafish

Considering the antioxidant properties of sodium selenite (Na₂SeO₃) and the involvement of oxidative stress events in paraquat-induced neurotoxicity, this study investigated the protective effect of dietary Na₂SeO₃ on biochemical and behavioral parameters of zebrafish exposed to paraquat (PQ). Fish were pretreated with a Na₂SeO₃ diet for 21 days and then PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days. In the novel tank test, the Na₂SeO₃ diet prevented the locomotor impairments, as well as the increase in the time spent in the top area of the tank, and the exacerbation of freezing episodes. In the preference for conspecifics and in the mirror-induced aggression (MIA) tasks, Na₂SeO₃ prevented the increase in the latency to enter the area closer to conspecifics and the agonistic behavior of PQ-treated animals, respectively. Na₂SeO₃ prevented the increase of carbonylated protein (CP), reactive oxygen species (ROS), and nitrite/nitrate (NOx) levels, as well as the decrease in non-protein thiols (NPSH) levels. Regarding the antioxidant enzymatic defenses, Na₂SeO₃ prevented the increase in catalase (CAT) and glutathione peroxidase (GPx) activities caused by PQ. Altogether, dietary Na₂SeO₃ improves behavioral and biochemical function impaired by PQ treatment in zebrafish, by modulating not only redox parameters, but also anxiety- and aggressive-like phenotypes in zebrafish.

Long-term behavioral change as a result of acute ethanol exposure in zebrafish: Evidence for a role for sonic hedgehog but not retinoic acid signaling

BACKGROUND

Developmental exposure to ethanol is recognized to produce long-term neurobehavioral impairment in multiple animal models. However, the molecular mechanisms underlying these deficits remain poorly understood. The present study was undertaken to ascertain whether two well-characterized targets of prenatal alcohol exposure, sonic hedgehog (Shh) and retinoic acid (RA), that induce the hallmark morphological phenotypes of fetal alcohol spectrum disorders (FASD), are involved in the generation of behavioral alterations as a result of alcohol exposure.

METHODS

Zebrafish embryos were exposed to ethanol (0%, 1%, 3%) at either 8-10 or 24-27h post-fertilization (hpf) and then evaluated during adolescence in the novel tank dive test to assess anxiety and risk-taking behavior. Overt signs of dysmorphogenesis were also scored and behavioral and morphological changes were compared for embryos treated with alcohol alone or in combination with subthreshold doses of shh or alhh1a3 morpholinos (MOs).

RESULTS

Ethanol treated fish displayed altered tank diving behavior that was not exacerbated by combined MO treatment. While treatment of embryos with either shha mRNA or RA prior to ethanol exposure only ameliorated the altered tank diving response in the case of shha mRNA overexpression, dysmorphogenesis was rescued by both treatments.

CONCLUSION

These results suggest that the effects of ethanol exposure on changes in anxiety and risk-taking behavior in adolescent zebrafish is manifested by a blunting of Shh, but not RA, signaling during early development.

Animated images in the analysis of zebrafish behavior

This invited review is based upon a recent oral paper I presented at the Virtual Reality Symposium of the 34th International Ethological Conference (2015, Cairns, Australia), and as such it describes studies conducted mainly in my own laboratory. It reviews how we utilized visual stimuli for inducing behavioral responses in the zebrafish with a focus on shoaling, group forming behavior. The zebrafish is gaining increasing popularity in neuroscience. With this interest, its behavior is also more frequently studied. One of the many advantages of the zebrafish over traditional laboratory rodents is that this species is diurnal, and it relies heavily upon its visual system. Thus, similarly to our own species, zebrafish respond to visual stimuli in a robust and easily quantifiable manner. For the past decade, we have been exploring how to use such visual stimuli, and have developed numerous paradigms with which we can induce and quantify a variety of behavioral responses, including shoaling. This review summarizes some of these studies, and discusses questions including whether one should use live fish as stimulus, whether and how one could present animated (moving images) of fish, and how one could optimize a range of stimulus presentation parameters to elicit the most robust responses in zebrafish. Although the zebrafish is a relative newcomer in ethology and behavioral neuroscience, and although many of our findings only represent the first steps in this research, our results suggest that the behavioral analysis of the zebrafish will have an important place in biomedical research.

Behavioural effect of low-dose BPA on male zebrafish: Tuning of male mating competition and female mating preference during courtship process

The ubiquity of environmental pollution by endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA) is progressively considered as a major threat to aquatic ecosystems worldwide. Numerous toxicological studies have proved that BPA are hazardous to aquatic environment, along with alterations in the development and physiology of aquatic vertebrates. However, generally, there is a paucity in knowledge of behavioural and physiological effects of BPA with low concentration, for example, 0.22 nM (50 ng/L) and 2.2 nM (500 ng/L). Here we show that treatment of adult male zebrafish (Danio rerio) with 7 weeks low-dose (0.22 nM-2.2 nM) BPA, resulted in alteration in histological structure of testis tissue and abnormality in expression levels of genes involved in testicular steroidogenesis. Furthermore, low-dose BPA treatment decreased the male locomotion during courtship; and was associated with less courtship behaviours to female but more aggressive behaviours to mating competitor. Interestingly, during the courtship test, we observed that female preferred control male to male under low-dose BPA exposure. Subsequently, we found that the ability of female to chose optimal mating male through socially mutual interaction and dynamics of male zebrafish, which was based on visual discrimination. In sum, our results shed light on the potential behavioural and physiological effect of low-dose BPA exposure on courtship behaviours of zebrafish, which could exert profound consequences on natural zebrafish populations.

Zebrafish (Danio rerio) behaviour is largely unaffected by elevated pCO2

Ocean acidification, the decrease in ocean pH caused by anthropogenic emission of carbon dioxide, can cause behavioural disturbances in marine teleost species. We investigated whether AB-strain zebrafish (Danio rerio) show similar behavioural disturbances in the presence of elevated CO₂, because this model species could open up a toolbox to investigate the physiological and neurological mechanisms of CO₂ exposure. We found no effect of elevated CO₂ (~1600 μatm) on the behaviour of zebrafish in the open field test, indicating that zebrafish are largely insensitive to this elevated CO₂ level. In the detour test of lateralization, however, zebrafish exposed to elevated CO₂ swam more often to the right, whereas individuals exposed to control CO₂ (~400 μatm) had no preference for left or right. This may indicate that some behaviours of some freshwater fishes can be altered by elevated CO₂ levels. Given that elevated CO₂ levels often occur in recirculating aquaculture and aquarium systems, we recommend that dissolved CO₂ levels are measured and, if necessary, the aquarium water should be aerated, in order to exclude CO₂ level as a confounding factor in experiments.

ZEBRAFISH AS AN IN VIVO MODEL FOR SUSTAINABLE CHEMICAL DESIGN

Heightened public awareness about the many thousands of chemicals in use and present as persistent contaminants in the environment has increased the demand for safer chemicals and more rigorous toxicity testing. There is a growing recognition that the use of traditional test models and empirical approaches is impractical for screening for toxicity the many thousands of chemicals in the environment and the hundreds of new chemistries introduced each year. These realities coupled with the green chemistry movement have prompted efforts to implement more predictive-based approaches to evaluate chemical toxicity early in product development. While used for many years in environmental toxicology and biomedicine, zebrafish use has accelerated more recently in genetic toxicology, high throughput screening (HTS), and behavioral testing. This review describes major advances in these testing methods that have positioned the zebrafish as a highly applicable model in chemical safety evaluations and sustainable chemistry efforts. Many toxic responses have been shown to be shared among fish and mammals owing to their generally well-conserved development, cellular networks, and organ systems. These shared responses have been observed for chemicals that impair endocrine functioning, development, and reproduction, as well as those that elicit cardiotoxicity and carcinogenicity, among other diseases. HTS technologies with zebrafish enable screening large chemical libraries for bioactivity that provide opportunities for testing early in product development. A compelling attribute of the zebrafish centers on being able to characterize toxicity mechanisms across multiple levels of biological organization from the genome to receptor interactions and cellular processes leading to phenotypic changes such as developmental malformations. Finally, there is a growing recognition of the links between human and wildlife health and the need for approaches that allow for assessment of real world multi-chemical exposures. The zebrafish is poised to be an important model in bridging these two conventionally separate areas of toxicology and characterizing the biological effects of chemical mixtures that could augment its role in sustainable chemistry.

Embryonic alcohol exposure promotes long-term effects on cerebral glutamate transport of adult zebrafish

Ethanol is a widely consumed substance throughout the world. During development it can substantially damage the human fetus, whereas the developing brain is particularly vulnerable. The brain damage induced by prenatal alcohol exposure may lead to a variety of long-lasting behavioral and neurochemical problems. However, there are no data concerning the effects of developmental ethanol exposure on the glutamatergic system, where extracellular glutamate acts as signaling molecule. Here we investigated the effect of ethanol exposure for 2h (concentrations of 0.0%, 0.1%, 0.25%, 0.50%, and 1.00%) in embryos at 24h post-fertilization (hpf) by measuring the functionality of glutamate transporters in the brain of adult (4 months) zebrafish. However, ethanol 0.1%, 0.25% and 0.50% decreased transport of glutamate to 81.96%, 60.65% and 45.91% respectively, when compared with the control group. Interestingly, 1.00% was able to inhibit the transport activity to 68.85%. In response to the embryonic alcohol exposure, we found impairment in the function of cerebral glutamate transport in adult fish, contributing to long-term alteration in the homeostasis glutamatergic signaling.

Environmental concentrations of prednisolone alter visually mediated responses during early life stages of zebrafish (Danio rerio)

The development of the eye in vertebrates is dependent upon glucocorticoid signalling, however, specific components of the eye are sensitive to synthetic glucocorticoids. The presence of synthetic glucocorticoids within the aquatic environment may therefore have important consequences for fish, which are heavily reliant upon vision for mediating several key behaviours. The potential ethological impact of synthetic glucocorticoid oculotoxicity however has yet to be studied. Physiological and behavioural responses which are dependent upon vision were selected to investigate the possible toxicity of prednisolone, a commonly occurring synthetic glucocorticoid within the environment, during early life stages of zebrafish. Although exposure to prednisolone did not alter the morphology of the external eye, aggregation of melanin within the skin in response to increasing light levels was impeded and embryos exposed to prednisolone (10 μg/l) maintained a darkened phenotype. Exposure to prednisolone also increased the preference of embryos for a dark environment within a light dark box test in a concentration dependent manner. However the ability of embryos to detect motion appeared unaffected by prednisolone. Therefore, while significant effects were detected in several processes mediated by vision, changes occurred in a manner which suggest that vision was in itself unaffected by prednisolone. Neurological and endocrinological changes during early ontogeny are considered as likely candidates for future investigation.

Fishing for Fetal Alcohol Spectrum Disorders: Zebrafish as a Model for Ethanol Teratogenesis

Fetal Alcohol Spectrum Disorders (FASD) describes a wide array of ethanol-induced developmental defects, including craniofacial dysmorphology and cognitive impairments. It affects ∼1 in 100 children born in the United States each year. Due to the pleiotropic effects of ethanol, animal models have proven critical in characterizing the mechanisms of ethanol teratogenesis. In this review, we focus on the utility of zebrafish in characterizing ethanol-induced developmental defects. A growing number of laboratories have focused on using zebrafish to examine ethanol-induced defects in craniofacial, cardiac, ocular, and neural development, as well as cognitive and behavioral impairments. Growing evidence supports that genetic predisposition plays a role in these ethanol-induced defects, yet little is understood about these gene-ethanol interactions. With a high degree of genetic amenability, zebrafish is at the forefront of identifying and characterizing the gene-ethanol interactions that underlie FASD. Because of the conservation of gene function between zebrafish and humans, these studies will directly translate to studies of candidate genes in human populations and allow for better diagnosis and treatment of FASD.

Chronic alcohol exposure induces muscle atrophy (myopathy) in zebrafish and alters the expression of microRNAs targeting the Notch pathway in skeletal muscle

Muscle wasting is estimated to affect 40-60% of alcoholics, and is more common than cirrhosis among chronic alcohol abusers. The molecular and cellular mechanisms underlying alcohol-related musculoskeletal dysfunction are, however, poorly understood. Muscle-specific microRNAs (miRNAs) referred to as myoMirs are now known to play a key role in both myogenesis and muscle atrophy. Yet, no studies have investigated a role for myoMirs in alcohol-related skeletal muscle damage. We developed a zebrafish model of chronic ethanol exposure to better define the mechanisms mediating alcohol-induced muscle atrophy. Adult fish maintained at 0.5% ethanol for eight weeks demonstrated significantly reduced muscle fiber cross-sectional area (∼12%, P < 0.05) compared to fish housed in normal water. Zebrafish miRNA microarray revealed marked changes in several miRNAs with ethanol treatment. Importantly, miR-140, a miRNA that shows 100% sequence homology with miR-140 from both mouse and human, is decreased 10-fold in ethanol treated fish. miR-140 targets several members of the Notch signaling pathway such as DNER, JAG1, and Hey1, and PCR data show that both Hey1 and Notch 1 are significantly up-related (3-fold) in muscle of ethanol treated fish. In addition, miR-146a, which targets the Notch antagonist Numb, is elevated in muscle from ethanol-treated fish. Upregulation of Notch signaling suppresses myogenesis and maintains muscle satellite cell quiescence. These data suggest that miRNAs targeting Notch are likely to play important roles in alcohol-related myopathy. Furthermore, zebrafish may serve as a useful model for better understanding the role of microRNAs in alcohol-related tissue damage.

Acute alcohol exposure increases tyrosine hydroxylase protein expression and dopamine synthesis in zebrafish

Zebrafish have become a popular animal model for investigating the effects of alcohol on the brain and behaviour. Acute exposure to alcohol has been shown to alter dopaminergic signalling in zebrafish, but the underlying mechanisms have not been well defined. In the current study, we characterize the effects of alcohol on the zebrafish dopaminergic system by focusing on tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Using western blot analysis, we demonstrate that a 60min exposure to 1% alcohol increases tyrosine hydroxylase protein expression in the zebrafish brain. Enzymatic activity assays confirmed that alcohol also increases tyrosine hydroxylase enzymatic activity, whereas HPLC analysis demonstrated increased levels of whole-brain dopamine and its metabolite DOPAC. In addition to activation of the dopaminergic system, behavioural analysis revealed accompanying increase of distance traveled following 1% alcohol exposure. These findings suggest that acute alcohol exposure elevates dopamine synthesis via increased tyrosine hydroxylase protein expression. Our results support the hypothesis that alcohol alters dopaminergic signalling in the zebrafish brain in a similar manner as compared to mammals.

Resilience assessment of a biological early warning system based on the locomotor behavior of zebrafish (Danio rerio)

With the development of new tools such as biological early warning systems, it becomes extremely important to test their reliability and detection capability. This work aimed at testing the sturdiness of a video tracking system by determining whether the detection capability does not deteriorate over time, after successive exposures of the zebrafish to three different toxicants, namely sodium hypochlorite, bisphenol A, and ethanol. Zebrafish were exposed to the three tested compounds separately (one fish, one toxicant) once a day, for 1 h and 30 m over 9 days, to 9 % of the 96 h LC50 of the respective toxicant. The behavior analysis was based on nine movement descriptor parameters of the fish, namely: angular velocity; linear velocity; spatial dispersion; linear acceleration; and angular acceleration. A statistical method was developed using self-organizing map (SOM), correspondence analysis, and linear and orthogonal multiple regression models. The results indicated that the system was able to successfully detect the three toxicants. With ethanol, the detection capability was maintained, but in the case of the sodium hypochlorite and bisphenol A, a deterioration of the detection capability occurred over the 9 days. This effect may be due to the induction of detoxification mechanisms and physiological acclimation, or due to the accumulation of adverse effects caused by the repeated exposure to the toxicants. Future works, especially those focusing on the application of similar early warning systems in real-world scenarios, should regularly exchange the sentinel organisms, to avoid degradation of the detection capability, as verified with two of the three tested compounds.

Effect of Ionic Liquids on Zebrafish (Danio rerio) Viability, Behavior, and Histology; Correlation between Toxicity and Ionic Liquid Aggregation

The effect of 11 common amidinium, imidazolium, and phosphonium based ionic liquids (ILs) on zebrafish (Danio rerio) and Chinese hamster ovary cells (CHO) was investigated with specific emphasis on the effect of anion and cation chain length and aggregation of phosphonium based ILs. Viability and behavioral alteration in the locomotor activity and place preference, after IL treatment of 5 days postfertilization larvae, was recorded. Behavior and histological damage evaluation was performed for adult fish in order to get insight into the long-term effects of two potential biomass-dissolving ILs, [DBNH][OAc] and [P4441][OAc]. To get an understanding of how IL aggregation is linked to the toxicity of ILs, median effective concentrations (EC50) and critical micelle concentrations (CMC) were determined. The long-chain ILs were significantly more toxic than the short-chain ones, and the anion chain length was shown to be less significant than the cation chain length when assessing the impact of ILs on the viability of the organisms. Furthermore, most of the ILs were as monomers when the EC50 was reached. In addition, the ILs used in the long-term tests showed no significant effect on the zebrafish behavior, breeding, or histology, within the used concentration range.

Copper at low levels impairs memory of adult zebrafish (Danio rerio) and affects swimming performance of larvae

Metal contamination at low levels is an important issue because it usually produces health and environmental effects, either positive or deleterious. Contamination of surface waters with copper (Cu) is a worldwide event, usually originated by mining, agricultural, industrial, commercial, and residential activities. Water quality criteria for Cu are variable among countries but allowed limits are generally in the μg/L range, which can disrupt several functions in the early life-stages of fish species. Behavioral and biochemical alterations after Cu exposure have also been described at concentrations close to the allowed limits. Aiming to search for the effects of Cu in the range of the allowed limits, larvae and adult zebrafish (Danio rerio) were exposed to different concentrations of dissolved Cu (nominally: 0, 5, 9, 20 and 60μg/L; measured: 0.4, 5.7, 7.2 16.6 and 42.3μg/L, respectively) for 96h. Larvae swimming and body length, and adult behavior and biochemical biomarkers (activity of glutathione-related enzymes in gills, muscle, and brain) were assessed after Cu exposure. Several effects were observed in fish exposed to 9μg/L nominal Cu, including increased larvae swimming distance and velocity, abolishment of adult inhibitory avoidance memory, and decreased glutathione S-transferase (GST) activity in gills of adult fish. At the highest Cu concentration tested (nominally: 60μg/L), body length of larvae, spatial memory of adults, and gill GST activity were decreased. Social behavior (aggressiveness and conspecific interaction), and glutathione reductase (GR) activity were not affected in adult zebrafish. Exposure to Cu, at concentrations close to the water quality criteria for this metal in fresh water, was able to alter larvae swimming performance and to induce detrimental effects on the behavior of adult zebrafish, thus indicating the need for further studies to reevaluate the currently allowed limits for Cu in fresh water.

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

Alcohol-induced behavioral changes in zebrafish: The role of dopamine D2-like receptors

RATIONALE

The dopaminergic system has been proposed to mediate alcohol-induced locomotor activity, yet the mechanisms underlying this behavioral response remain poorly understood.

OBJECTIVES

This study was conducted to investigate the role of dopamine D2-like receptors in mediating alcohol-induced behavioral responses.

METHODS

In experiment 1, we examined the effects of high concentrations (0, 2.5, 5, 10 μM) of haloperidol on motor responses. In experiment 2, we examined the effects of low concentrations (0, 0.625, 1.25, 2.5 μM) of haloperidol on anxiety-like behavioral responses using the novel tank test. In experiment 3, we examined the effect of pre-treating zebrafish with different concentrations of haloperidol (0, 0.625, 2.5 μM) and subsequently exposing them to 0 or 1 % alcohol.

RESULTS

In experiment 1, haloperidol induced an inverted U-shaped concentration-dependent increase in locomotor activity. In experiment 2, haloperidol (2.5 μM) reduced the absolute turn angle and freezing behavior in a new environment. In experiment 3, acute alcohol exposure significantly increased locomotor activity and decreased anxiety-like behavioral responses. Pre-treating zebrafish with the lower dose of haloperidol (0.625 μM) abolished the alcohol-induced locomotor activity, without altering anxiety-like behavioral responses. However, pre-treating with the higher dose of haloperidol (2.5 μM) abolished both alcohol-induced increase of locomotor activity and reduction of anxiety-like behavioral responses.

CONCLUSION

The results suggest alcohol-induced locomotor hyperactivity in zebrafish is mediated via activation of dopamine D2-like receptors, whereas anxiety-like behavioral responses may only be altered by a high haloperidol concentration, at which dose the drug may affect receptors other than D2-R.

Routine handling methods affect behaviour of three-spined sticklebacks in a novel test of anxiety

Fish are increasingly popular subjects in behavioural and neurobiological research. It is therefore important that they are housed and handled appropriately to ensure good welfare and reliable scientific findings, and that species-appropriate behavioural tests (e.g. of cognitive/affective states) are developed. Routine handling of captive animals may cause physiological stress responses that lead to anxiety-like states (e.g. increased perception of danger). In fish, these may be particularly pronounced when handling during tank-to-tank transfer involves removal from water into air. Here we develop and use a new combined scototaxis (preference for dark over light areas) and novel-tank-diving test, alongside conventional open-field and novel-object tests, to measure the effects of transferring three-spined sticklebacks (Gasterosteus aculeatus) between tanks using a box or net (in and out of water respectively). Preference tests for dark over light areas confirmed the presence of scototaxis in this species. Open-field and novel-object tests failed to detect any significant differences between net and box-handled fish. However, the combined diving and scototaxis detected consistent differences between the treatments. Net-handled fish spent less time on the dark side of the tank, less time in the bottom third, and kept a greater distance from the 'safe' bottom dark area than box-handled fish. Possible explanations for this reduction in anxiety-like behaviour in net-handled fish are discussed. The combined diving and scototaxis test may be a sensitive and taxon-appropriate method for measuring anxiety-like states in fish.

Oxytocin reversed MK-801-induced social interaction and aggression deficits in zebrafish

Changes in social behavior occur in several neuropsychiatric disorders such as schizophrenia and autism. The interaction between individuals is an essential aspect and an adaptive response of several species, among them the zebrafish. Oxytocin is a neuroendocrine hormone associated with social behavior. The aim of the present study was to investigate the effects of MK-801, a non-competitive antagonist of glutamate NMDA receptors, on social interaction and aggression in zebrafish. We also examined the modulation of those effects by oxytocin, the oxytocin receptor agonist carbetocin and the oxytocin receptor antagonist L-368,899. Our results showed that MK-801 induced a decrease in the time spent in the segment closest to the conspecific school and in the time spent in the segment nearest to the mirror image, suggesting an effect on social behavior. The treatment with oxytocin after the exposure to MK-801 was able to reestablish the time spent in the segment closest to the conspecific school, as well as the time spent in the segment nearest to the mirror image. In addition, in support of the role of the oxytocin pathway in modulating those responses, we showed that the oxytocin receptor agonist carbetocin reestablished the social and aggressive behavioral deficits induced by MK-801. However, the oxytocin receptor antagonist L-368,899 was not able to reverse the behavioral changes induced by MK-801. This study supports the critical role for NMDA receptors and the oxytocinergic system in the regulation of social behavior and aggression which may be relevant for the mechanisms associated to autism and schizophrenia.

Chronic Treatment with Paraquat Induces Brain Injury, Changes in Antioxidant Defenses System, and Modulates Behavioral Functions in Zebrafish

Paraquat (PQ) administration consists in a chemical model that mimics phenotypes observed in Parkinson's disease (PD), due to its ability to induce changes in dopaminergic system and oxidative stress. The aim of this study was to evaluate the actions of PQ in behavioral functions of adult zebrafish and its influence on oxidative stress biomarkers in brain samples. PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days (one injection every 3 days). PQ-treated group showed a significant decrease in the time spent in the bottom section and a shorter latency to enter the top area in the novel tank test. Moreover, PQ-exposed fish showed a significant decrease in the number and duration of risk assessment episodes in the light-dark test, as well as an increase in the agonistic behavior in the mirror-induced aggression (MIA) test. PQ induced brain damage by decreasing mitochondrial viability. Concerning the antioxidant defense system, PQ increased catalase (CAT) and glutathione peroxidase (GPx) activities, as well as the non-protein sulfhydryl content (NPSH), but did not change ROS formation and decreased lipid peroxidation. We demonstrate, for the first time, that PQ induces an increase in aggressive behavior, alters non-motor patterns associated to defensive behaviors, and changes redox parameters in zebrafish brain. Overall, our findings may serve as useful tools to investigate the interaction between behavioral and neurochemical impairments triggered by PQ administration in zebrafish.

Son et lumière: Sound and light effects on spatial distribution and swimming behavior in captive zebrafish

Aquatic and terrestrial habitats are heterogeneous by nature with respect to sound and light conditions. Fish may extract signals and exploit cues from both ambient modalities and they may also select their sound and light level of preference in free-ranging conditions. In recent decades, human activities in or near water have altered natural soundscapes and caused nocturnal light pollution to become more widespread. Artificial sound and light may cause anxiety, deterrence, disturbance or masking, but few studies have addressed in any detail how fishes respond to spatial variation in these two modalities. Here we investigated whether sound and light affected spatial distribution and swimming behavior of individual zebrafish that had a choice between two fish tanks: a treatment tank and a quiet and light escape tank. The treatments concerned a 2 × 2 design with noisy or quiet conditions and dim or bright light. Sound and light treatments did not induce spatial preferences for the treatment or escape tank, but caused various behavioral changes in both spatial distribution and swimming behavior within the treatment tank. Sound exposure led to more freezing and less time spent near the active speaker. Dim light conditions led to a lower number of crossings, more time spent in the upper layer and less time spent close to the tube for crossing. No interactions were found between sound and light conditions. This study highlights the potential relevance for studying multiple modalities when investigating fish behavior and further studies are needed to investigate whether similar patterns can be found for fish behavior in free-ranging conditions.