A small fish with a big future: zebrafish in behavioral neuroscience

Ontogeny of working memory and behavioural flexibility in the free movement pattern (FMP) Y-maze in zebrafish

The acquisition of executive skills such as working memory, decision-making and adaptive responding occur at different stages of central nervous system development. Zebrafish (Danio rerio) are increasingly used in behavioural neuroscience for complex behavioural tasks, and there is a critical need to understand the ontogeny of their executive functions. Zebrafish across developmental stages (4, 7, 14, 30 and 90 days post fertilisation (dpf)), were assessed to track development of working memory (WM) and behavioural flexibility (BF) using the free movement pattern Y-maze (FMP Y-maze). Several differences in both WM and BF were identified during the transition from yolk-dependent to independent feeding. Specifically, WM is evident in all age groups, even from 4 dpf. However, BF is not developed until larvae start free feeding, and show significant improvement thereafter, with young adults (90 dpf) demonstrating the most well-defined BF. We demonstrate, for the first time, objective WM processes in 4 dpf zebrafish larvae. This suggests that those wishing to study WM in zebrafish may be able to do so from 4 dpf, thus drastically increasing throughput. In addition, we show that zebrafish follow distinct stages of cognitive development and age-related changes during the early developmental period. Finally, our findings indicate distinct WM and BF mechanisms, which may be useful to study for translational purposes.

Calcium Imaging Characterize the Neurobiological Effect of Terahertz Radiation in Zebrafish Larvae

(1) Objective: To explore the neurobiological effects of terahertz (THz) radiation on zebrafish larvae using calcium (Ca2+) imaging technology. (2) Methods: Zebrafish larvae at 7 days post fertilization (dpf) were exposed to THz radiation for 10 or 20 min; the frequency was 2.52 THz and the amplitude 50 mW/cm2. The behavioral experiments, neural Ca2+ imaging, and quantitative polymerase chain reaction (qPCR) of the dopamine-related genes were conducted following the irradiation. (3) Results: Compared with the control group, the behavioral experiments demonstrated that THz radiation significantly increased the distance travelled and speed of zebrafish larvae. In addition, the maximum acceleration and motion frequency were elevated in the 20 min radiation group. The neural Ca2+ imaging results indicated a substantial increase in zebrafish neuronal activity. qPCR experiments revealed a significant upregulation of dopamine-related genes, such as drd2b, drd4a, slc6a3 and th. (4) Conclusion: THz radiation (2.52 THz, 50 mW/cm2, 20 min) upregulated dopamine-related genes and significantly enhanced neuronal excitability, and the neurobiological effect of THz radiation can be visualized using neural Ca2+ imaging in vivo.

A novel gene trap line for visualization and manipulation of erbb3b+ neural crest and glial cells in zebrafish

Glia are a diverse and essential cell type in the vertebrate nervous system. Transgenic tools and fluorescent reporter lines are critical resources to investigate how glial subtypes develop and function. However, despite the many lines available in zebrafish, the community still lacks the ability to label all unique stages of glial development and specific subpopulations of cells. To address this issue, we screened zebrafish gene and enhancer trap lines to find a novel reporter for peripheral glial subtypes. From these, we generated the gSAIzGFFD37A transgenic line that expresses GFP in neural crest cells and central and peripheral glia. We found that the gene trap construct is located within an intron of erbb3b, a gene essential for glial development. Additionally, we confirmed that GFP+ ​cells express erbb3b along with sox10, a known glial marker. From our screen, we have identified the gSAIzGFFD37A line as a novel and powerful tool for studying glia in the developing zebrafish, as well as a new resource to manipulate erbb3b+ ​cells.

Vesicular monoamine transporter 2 (SLC18A2) regulates monoamine turnover and brain development in zebrafish

AIM

We aimed at identifying potential roles of vesicular monoamine transporter 2, also known as Solute Carrier protein 18 A2 (SLC18A2) (hereafter, Vmat2), in brain monoamine regulation, their turnover, behaviour and brain development using a novel zebrafish model.

METHODS

A zebrafish strain lacking functional Vmat2 was generated with the CRISPR/Cas9 system. Larval behaviour and heart rate were monitored. Monoamines and their metabolites were analysed with high-pressure liquid chromatography. Amine synthesising and degrading enzymes, and genes essential for brain development, were analysed with quantitative PCR, in situ hybridisation and immunocytochemistry.

RESULTS

The 5-bp deletion in exon 3 caused an early frameshift and was lethal within 2 weeks post-fertilisation. Homozygous mutants (hereafter, mutants) displayed normal low locomotor activity during night-time but aberrant response to illumination changes. In mutants dopamine, noradrenaline, 5-hydroxytryptamine and histamine levels were reduced, whereas levels of dopamine and 5-hydroxytryptamine metabolites were increased, implying elevated monoamine turnover. Consistently, there were fewer histamine, 5-hydroxytryptamine and dopamine immunoreactive cells. Cellular dopamine immunostaining, in wild-type larvae more prominent in tyrosine hydroxylase 1 (Th1)-expressing than in Th2-expressing neurons, was absent in mutants. Despite reduced dopamine levels, mutants presented upregulated dopamine-synthesising enzymes. Further, in mutants the number of histidine decarboxylase-expressing neurons was increased, notch1a and pax2a were downregulated in brain proliferative zones.

CONCLUSION

Lack of Vmat2 increases monoamine turnover and upregulates genes encoding amine-synthesising enzymes, including histidine decarboxylase. Notch1a and pax2a, genes implicated in stem cell development, are downregulated in mutants. The zebrafish vmat2 mutant strain may be a useful model to study how monoamine transport affects brain development and function, and for use in drug screening.

Abnormal brain development of monoamine oxidase mutant zebrafish and impaired social interaction of heterozygous fish

Monoamine oxidase (MAO) deficiency and imbalanced levels of brain monoamines have been associated with developmental delay, neuropsychiatric disorders and aggressive behavior. Animal models are valuable tools to gain mechanistic insight into outcomes associated with MAO deficiency. Here, we report a novel genetic model to study the effects of mao loss of function in zebrafish. Quantitative PCR, in situ hybridization and immunocytochemistry were used to study neurotransmitter systems and expression of relevant genes for brain development in zebrafish mao mutants. Larval and adult fish behavior was evaluated through different tests. Stronger serotonin immunoreactivity was detected in mao^+/− and mao^−/− larvae compared with their mao^+/+ siblings. mao^−/− larvae were hypoactive, and presented decreased reactions to visual and acoustic stimuli. They also had impaired histaminergic and dopaminergic systems, abnormal expression of developmental markers and died within 20 days post-fertilization. mao^+/− fish were viable, grew until adulthood, and demonstrated anxiety-like behavior and impaired social interactions compared with adult mao^+/+ siblings. Our results indicate that mao^−/− and mao^+/− mutants could be promising tools to study the roles of MAO in brain development and behavior.

This article has an associated First Person interview with the first author of the paper.

Summary: We assessed developmental, neurochemical and behavioral alterations displayed by mao^+/− and mao^−/− zebrafish, establishing that these model organisms are promising tools to study the consequences of MAOA/B deficiency.

Exposure to a high dose of amoxicillin causes behavioral changes and oxidative stress in young zebrafish

Autistic spectrum disorder (ASD) is a group of early-onset neurodevelopmental disorders characterized by impaired social and communication skills. Autism is widely described as a behavioral syndrome with multiple etiologies where may exhibit neurobiological, genetic, and psychological deficits. Studies have indicated that long term use of antibiotics can alter the intestinal flora followed by neuroendocrine changes, leading to behavioral changes. Indeed, previous studies demonstrate that a high dose of amoxicillin can change behavioral parameters in murine animal models. The objective was to evaluate behavioral and oxidative stress parameters in zebrafish exposed to a high dose of amoxicillin for 7 days. Young zebrafish were exposed to a daily concentration of amoxicillin (100 mg/L) for 7 days. Subsequently, the behavioral analysis was performed, and the brain content was dissected for the evaluation of oxidative stress parameters. Zebrafish exposed to a high dose of amoxicillin showed locomotor alteration and decreased social interaction behavior. In addition, besides the significant decrease of sulfhydryl content, there was a marked decrease in catalase activity, as well as an increased superoxide dismutase activity in brain tissue. Thus, through the zebrafish model was possible to note a central effect related to the exposition of amoxicillin, the same as observed in murine models. Further, the present data reinforce the relation of the gut-brain-axis and the use of zebrafish as a useful tool to investigate new therapies for autistic traits.

Zebrafish Shoaling, Its Behavioral and Neurobiological Mechanisms, and Its Alteration by Embryonic Alcohol Exposure: A Review

Social cognition and social behaviors are complex phenomena that involve numerous brain areas and underlying neurobiological mechanisms. Embryonic alcohol exposure may lead to the development of Fetal Alcohol Spectrum Disorder (FASD), a disorder that manifests with varying symptoms including abnormal social behavior and other cognitive deficits. Animal models have been utilized to mimic aspects of the disease and to study potential underlying mechanisms. The zebrafish is a relative newcomer in this field but has been suggested as an optimal compromise between system complexity and practical simplicity for modeling FASD. Importantly, due to external fertilization and development of the embryo outside the mother and subsequent lack of parental care, this species allows precise control of the timing and dose of alcohol delivery during embryonic development. Furthermore, the zebrafish is a highly social species and thus may be particularly appropriate for the analysis of embryonic alcohol-induced alterations in this context. Here, we provide a succinct review focusing on shoaling, a prominent form of social behavior, in zebrafish. We summarize what is known about its behavioral mechanisms and underlying neurobiological processes, and how it is altered by exposure to ethanol during embryonic development. Lastly, we briefly consider possible future directions of research that would help us better understand the relationship between the behavioral expression and molecular basis of embryonic ethanol-induced social deficits in fish and humans.

Sleep deprivation impairs learning and memory by decreasing protein O-GlcNAcylation in the brain of adult zebrafish

Sleep is an evolutionarily conserved physiological process implicated in the consolidation of learning and memory (L/M). Here, we report that sleep deprivation (SD)-induced cognitive deficits in zebrafish are mediated through reduction in O-GlcNAcylation of brain. Microarray-based gene expression profiling of zebrafish brain demonstrated significant changes in genes involved in metabolism by SD or fear conditioning (FC), compared to the control group. In particular, it was observed that a marked decrease in the number of genes involved in carboxylic acid and organic acid metabolic processes in the brains of SD group compared to control group. SD downregulated O-GlcNAc transferase (OGT) and O-GlcNAcylation, while the expression of O-GlcNAcase was upregulated. FC activated protein kinase A (PKA) and phosphorylated cAMP response element binding protein (p-CREB), an effect that was greatly inhibited by SD. Moreover, FC upregulated expressions of OGT and increased O-GlcNAcylation in the brains of normal but not SD zebrafish. Intriguingly, upregulation of O-GlcNAcylation by glucosamine restored defects in L/M functions and PKA/p-CREB activity in SD group. Our findings highlight the O-GlcNAcylation changes in the brain during the L/M process and further provide a foundation for future studies seeking the molecular and biochemical mechanisms by which HBP of glucose metabolism affects cognitive function.

Dose dependent behavioral effects of acute alcohol administration in zebrafish fry

The zebrafish is becoming increasingly utilized in behavioral neuroscience as it appears to strike a good compromise between practical simplicity and system complexity. Particularly in alcohol (ethanol) research, the zebrafish has been employed as a translationally relevant model organism. However, the majority of studies investigating the effects of alcohol on brain function and behavior has used adult zebrafish. In the current study, we utilize 6-8 post-fertilization day old larval zebrafish (fry) to investigate the effects of a 40 min-long, acute, immersion into the alcohol bath. We measure the behavioral responses of the fry during the immersion session in relatively large arenas, the petri dish, instead of the often employed 96 well plate, and report on significant modification of behavior induced by alcohol. For example, we found the intermediate dose of alcohol (0.5%, vol/vol) to exert a stimulant effect manifesting as slight elevation of swim speed, robust increase of turning, temporal variability of swim speed and turning, and diminished frequency of staying immobile. We also found the high dose of 1% alcohol to elicit an opposite response, a sedative effect. This biphasic dose response of alcohol mimics what has been found in mammals, including humans, and thus we conclude that a few day-old zebrafish fry may be a cost effective and efficient tool with which one can screen for small molecules or mutations with alcohol-effect modifying properties.

Larval zebrafish model for studying the effects of valproic acid on neurodevelopment: An approach towards modeling autism

INTRODUCTION

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder of early onset, characterized by impaired sociability, cognitive function and stereotypies. The etiology of ASD involves a multidimensional link between genetic, neurobiological and environmental factors. Since existing, comprehensive animal models for ASD are time consuming and laborious, the need for simple, quick approaches to study subsets of ASD-associated characteristics has always been in demand for better understanding of disease. The aim of the present study was to develop a cost and time effective zebrafish model with quantifiable parameters to facilitate mechanistic studies as well as high-throughput screening of new molecules for autism.

METHODS

Zebrafish embryos were treated with valproic acid (75 μM) beginning at 4-h post fertilization to 5-days post fertilization. A series of behavioral tests (anxiety, inattentive behavior and circling behavior) and molecular studies were performed as surrogate parameters of ASD-like characteristic on the larvae at 7-dayspost fertilization for a quick screen. The study was followed by validation of model by screening positive control and negative control drugs. The social interaction test was performed on 21-days post fertilization to confirm that the surrogate phenotypes were indicative of social deficit (a core symptom of ASD).

RESULTS

The model showed a significant behavioral impairment (2-4fold difference) in valproic acid treated larvae compared to control larvae, which was further supported by alterations in select high-risk genes and proteins, implicated in human ASD. Reversal of behavioral impairments using standard drugs marketed for symptomatic treatment in ASD and no effect on behaviors when treated with paracetamol (negative control) signifies the role of model in preliminary drug screening.

CONCLUSION

The model shows robust parameters to study behavior, molecular mechanism and drug screening approach in a single frame. Thus, we postulate that our 7-day larval model could be a useful preliminary screening tool to identify novel targets as well as potential drugs for autism and also can be applied to develop a high-throughput screening approach.

Bold zebrafish (Danio rerio) express higher levels of delta opioid and dopamine D2 receptors in the brain compared to shy fish

Individual variation in coping with environmental challenges is a well-known phenomenon across vertebrates, including teleost fish. Dopamine is the major transmitter in the brain reward networks, and important for motivational processes and stress coping. Functions of the endogenous opioid system are not well studied in teleosts. However, in mammals the activity in the brain reward networks is regulated by the endogenous opioid system. This study aimed at investigating if there was a correlation between risk-taking behavior and the expression of dopamine and opioid receptors in the zebrafish (Danio rerio) brain. Risk-taking behavior was assessed in a novel tank diving test, and the most extreme high risk taking, i.e. bold, and low risk taking, i.e. shy, fish were sampled for qPCR analysis of whole brain gene expression. The expression analysis showed a significantly higher expression of the dopamine D2 receptors (drd2a and drd2b) and the delta opioid receptor (DOR; oprd1b) in bold compared to shy fish. Besides reward and reinforcing properties, DORs are also involved in emotional responses. Dopamine D2 receptors are believed to be important for active stress coping in rodents, and taken together the results of the current study suggest similar functions in zebrafish. However, additional experiments are required to clarify how dopamine and opioid receptor activation affect behavior and stress coping in this species.

The Use of Larval Zebrafish (Danio rerio) Model for Identifying New Anxiolytic Drugs from Herbal Medicine

Anxiety is a widespread psychiatric disorder. The search for a cure is still continuing since many of the synthetic drugs were inefficient in completely treating anxiety, yet caused some dangerous side effects until many of the drugs were withdrawn from the market. One promising source of new anxiolytics could be herbal medicines. The challenge is to screen plant extracts. Rodent models can be used for this purpose but are expensive. Moreover, rodent tests are costly and consume relatively large quantities of sample. For this reason, alternative animal models may be useful. Zebrafish larvae have many advantages for screening natural products. The main advantage is that they can be produced cheaply and in large numbers. Several studies have shown that the zebrafish is a good model for studying drugs that affect anxiety. This review focuses on the use of animal models, including zebrafish larvae, for studying anxiety and screening for herbal medicines that modulate anxiety. Finally, future prospects of the zebrafish larva as an alternative model in this field are also discussed.

Diazepam fails to alter anxiety-like responses but affects motor function in a white-black test paradigm in larval zebrafish (Danio rerio)

The growing popularity of zebrafish in psychopharmacology and behavioral brain research is partly due to the practicality and simplicity of drug administration in this species. Several drugs may be administered to zebrafish by immersing the fish in the drug solution. Furthermore, numerous drugs developed for mammals, including humans, have been found to show a similar effect profile in the zebrafish. Thus, the zebrafish has been suggested as a potentially useful animal screening tool. Despite decades of drug development, anxiety still represents a major unmet medical need, and the search for anxiolytic compounds is continuing. The zebrafish has been proposed for high throughput screens for anxiolytic compounds, and the effects of anxiolytic compounds on the behavior of zebrafish have started to be explored. Diazepam (Valium®) is a frequently prescribed human anxiolytic, a GABA_A receptor agonist, has also started to be tested in zebrafish, but with occasional contradicting results. Here, we investigate the effects of diazepam in larval (6-day post-fertilization old) zebrafish in a black-white preference paradigm. We found significant white preference and thigmotaxis (edge preference) in our control fish, anxiety-like responses that habituated over time. However, unexpectedly, we observed no anxiolytic effects of diazepam on these behaviors, and only detected significant motor activity reducing effect of the drug. We discuss the complex interpretation of light/dark tests in zebrafish, and also speculate about the possibility of differential GABAergic mechanisms that diazepam affects in larval vs adult zebrafish.

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.

Quantitative investigation of the mechanisms of microplastics and nanoplastics toward zebrafish larvae locomotor activity

This study investigated the direct and indirect toxic effects of microplastics and nanoplastics toward zebrafish (Danio rerio) larvae locomotor activity. Results showed that microplastics alone exhibited no significant effects except for the upregulated zfrho visual gene expression; whereas nanoplastics inhibited the larval locomotion by 22% during the last darkness period, and significantly reduced larvae body length by 6%, inhibited the acetylcholinesterase activity by 40%, and upregulated gfap, α1-tubulin, zfrho and zfblue gene expression significantly. When co-exposed with 2μg/L 17 α-ethynylestradiol (EE2), microplastics led to alleviation on EE2's inhibition effect on locomotion, which was probably due to the decreased freely dissolved EE2 concentration. However, though nanoplastics showed stronger adsorption ability for EE2, the hypoactivity phenomenon still existed in the nanoplastics co-exposure group. Moreover, when co-exposed with a higher concentration of EE2 (20μg/L), both plastics showed an enhanced effect on the hypoactivity. Principal component analysis was performed to reduce data dimensions and four principal components were reconstituted in terms of oxidative stress, body length, nervous and visual system related genes explaining 84% of total variance. Furthermore, oxidative damage and body length reduction were evaluated to be main reasons for the hypoactivity. Therefore, nanoplastics alone suppressed zebrafish larvae locomotor activity and both plastic particles can change the larvae swimming behavior when co-exposed with EE2. This study provides new insights into plastic particles' effects on zebrafish larvae, improving the understanding of their environmental risks to the aquatic environment.

Developmental profiling of ASD-related shank3 transcripts and their differential regulation by valproic acid in zebrafish

SHANK3 is a scaffolding protein that binds to various synaptic proteins at the postsynaptic density (PSD) of excitatory glutamatergic synapses. SHANK3 is not only strongly implicated in autism spectrum disorders (ASD) but also plays a critical role in human Phelan-McDermid syndrome (22q13.3 deletion syndrome). Accumulated experimental evidence demonstrates that the zebrafish model system is useful for studying the functions of ASD-related gene during early development. However, many basic features of shank3 transcript expression in zebrafish remain poorly understood. Here, we investigated temporal, spatial, and isoform-specific expression patterns of shank3 during zebrafish development on the basis of previous researches and the differential effects of each shank3 transcript expression after exposure to valproic acid (VPA), an ASD-associated drug. At first, we observed that both shank3a and shank3b were barely expressed at very early ages (before 24 h post-fertilization (hpf)), whereas their expression levels were increased and mainly enriched in the nervous system after 24 hpf. Secondly, all of the six shank3 transcripts gradually increased during the first 7 hpf and then decreased. Subsequently, they exhibited a second increasing peak between 1 month post-fertilization (mpf) and adulthood. Thirdly, VPA treatment affected the isoform-specific expression of zebrafish shank3. In particular, the mRNA expression levels of those isoforms that contain a SAM domain were significantly increased, whereas the mRNA expression level of those which contained an ANK domain but without a SAM domain was decreased. To conclude, our findings support the molecular diversity of shank3 in zebrafish and provide a molecular framework to understand the isoform-specific function of shank3 in zebrafish.

The Difference between Anxiolytic and Anxiogenic Effects Induced by Acute and Chronic Alcohol Exposure and Changes in Associative Learning and Memory Based on Color Preference and the Cause of Parkinson-Like Behaviors in Zebrafish

We describe an interdisciplinary comparison of the effects of acute and chronic alcohol exposure in terms of their disturbance of light, dark and color preferences and the occurrence of Parkinson-like behavior in zebrafish through computer visual tracking, data mining, and behavioral and physiological analyses. We found that zebrafish in anxiolytic and anxious states, which are induced by acute and chronic repeated alcohol exposure, respectively, display distinct emotional reactions in light/dark preference tests as well as distinct learning and memory abilities in color-enhanced conditional place preference (CPP) tests. Additionally, compared with the chronic alcohol (1.0%) treatment, acute alcohol exposure had a significant, dose-dependent effect on anxiety, learning and memory (color preference) as well as locomotive activities. Acute exposure doses (0.5%, 1.0%, and 1.5%) generated an “inverted V” dose-dependent pattern in all of the behavioral parameters, with 1.0% having the greatest effect, while the chronic treatment had a moderate effect. Furthermore, by measuring locomotive activity, learning and memory performance, the number of dopaminergic neurons, tyrosine hydroxylase expression, and the change in the photoreceptors in the retina, we found that acute and chronic alcohol exposure induced varying degrees of Parkinson-like symptoms in zebrafish. Taken together, these results illuminated the behavioral and physiological mechanisms underlying the changes associated with learning and memory and the cause of potential Parkinson-like behaviors in zebrafish due to acute and chronic alcohol exposure.

Inhibition of phosphorylated tyrosine hydroxylase attenuates ethanol-induced hyperactivity in adult zebrafish (Danio rerio)

Zebrafish have been successfully employed in the study of the behavioural and biological effects of ethanol. Like in mammals, low to moderate doses of ethanol induce motor hyperactivity in zebrafish, an effect that has been attributed to the activation of the dopaminergic system. Acute ethanol exposure increases dopamine (DA) in the zebrafish brain, and it has been suggested that tyrosine hydroxylase, the rate-limiting enzyme of DA synthesis, may be activated in response to ethanol via phosphorylation. The current study employed tetrahydropapaveroline (THP), a selective inhibitor of phosphorylated tyrosine hydroxylase, for the first time, in zebrafish. We treated zebrafish with a THP dose that did not alter baseline motor responses to examine whether it can attenuate or abolish the effects of acute exposure to alcohol (ethanol) on motor activity, on levels of DA, and on levels of dopamine's metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). We found that 60-minute exposure to 1% alcohol induced motor hyperactivity and an increase in brain DA. Both of these effects were attenuated by pre-treatment with THP. However, no differences in DOPAC levels were found among the treatment groups. These findings suggest that tyrosine hydroxylase is activated via phosphorylation to increase DA synthesis during alcohol exposure in zebrafish, and this partially mediates alcohol's locomotor stimulant effects. Future studies will investigate other potential candidates in the molecular pathway to further decipher the neurobiological mechanism that underlies the stimulatory properties of this popular psychoactive drug.

Model of voluntary ethanol intake in zebrafish: effect on behavior and hypothalamic orexigenic peptides

Recent studies in zebrafish have shown that exposure to ethanol in tank water affects various behaviors, including locomotion, anxiety and aggression, and produces changes in brain neurotransmitters, such as serotonin and dopamine. Building on these investigations, the present study had two goals: first, to develop a method for inducing voluntary ethanol intake in individual zebrafish, which can be used as a model in future studies to examine how this behavior is affected by various manipulations, and second, to characterize the effects of this ethanol intake on different behaviors and the expression of hypothalamic orexigenic peptides, galanin (GAL) and orexin (OX), which are known in rodents to stimulate consumption of ethanol and alter behaviors associated with alcohol abuse. Thus, we first developed a new model of voluntary intake of ethanol in fish by presenting this ethanol mixed with gelatin, which they readily consume. Using this model, we found that individual zebrafish can be trained in a short period to consume stable levels of 10% or 20% ethanol (v/v) mixed with gelatin and that their intake of this ethanol-gelatin mixture leads to pharmacologically relevant blood ethanol concentrations which are strongly, positively correlated with the amount ingested. Intake of this ethanol-gelatin mixture increased locomotion, reduced anxiety, and stimulated aggressive behavior, while increasing expression of GAL and OX in specific hypothalamic areas. These findings, confirming results in rats, provide a method in zebrafish for investigating with forward genetics and pharmacological techniques the role of different brain mechanisms in controlling ethanol intake.

Induction of social behavior in zebrafish: live versus computer animated fish as stimuli

The zebrafish offers an excellent compromise between system complexity and practical simplicity and has been suggested as a translational research tool for the analysis of human brain disorders associated with abnormalities of social behavior. Unlike laboratory rodents zebrafish are diurnal, thus visual cues may be easily utilized in the analysis of their behavior and brain function. Visual cues, including the sight of conspecifics, have been employed to induce social behavior in zebrafish. However, the method of presentation of these cues and the question of whether computer animated images versus live stimulus fish have differential effects have not been systematically analyzed. Here, we compare the effects of five stimulus presentation types: live conspecifics in the experimental tank or outside the tank, playback of video-recorded live conspecifics, computer animated images of conspecifics presented by two software applications, the previously employed General Fish Animator, and a new application Zebrafish Presenter. We report that all stimuli were equally effective and induced a robust social response (shoaling) manifesting as reduced distance between stimulus and experimental fish. We conclude that presentation of live stimulus fish, or 3D images, is not required and 2D computer animated images are sufficient to induce robust and consistent social behavioral responses in zebrafish.

Developing zebrafish models of autism spectrum disorder (ASD)

Autism spectrum disorder (ASD) is a serious neurodevelopmental disorder with complex symptoms and unclear, multi-factorial pathogenesis. Animal (rodent) models of ASD-like behavior are extensively used to study genetics, circuitry and molecular mechanisms of ASD. The evolutionarily conserved nature of social behavior and its molecular pathways suggests that alternative experimental models can be developed to complement and enhance the existing rodent ASD paradigms. The zebrafish (Danio rerio) is rapidly becoming a popular model organism in neuroscience and biological psychiatry to study brain function, model human brain disorders and explore their genetic or pharmacological modulation. Representing highly social animals, zebrafish emerge as a strong potential model organism to study normal and pathological social phenotypes, as well as several other ASD-like symptoms. Here, we discuss the developing utility of zebrafish in modeling ASD as a new emerging field in translational neuroscience and drug discovery.

Zebrafish as an emerging model for studying complex brain disorders

The zebrafish (Danio rerio) is rapidly becoming a popular model organism in pharmacogenetics and neuropharmacology. Both larval and adult zebrafish are currently used to increase our understanding of brain function, dysfunction, and their genetic and pharmacological modulation. Here we review the developing utility of zebrafish in the analysis of complex brain disorders (including, e.g., depression, autism, psychoses, drug abuse, and cognitive deficits), also covering zebrafish applications towards the goal of modeling major human neuropsychiatric and drug-induced syndromes. We argue that zebrafish models of complex brain disorders and drug-induced conditions are a rapidly emerging critical field in translational neuroscience and pharmacology research.

Towards a comprehensive catalog of zebrafish behavior 1.0 and beyond

Zebrafish (Danio rerio) are rapidly gaining popularity in translational neuroscience and behavioral research. Physiological similarity to mammals, ease of genetic manipulations, sensitivity to pharmacological and genetic factors, robust behavior, low cost, and potential for high-throughput screening contribute to the growing utility of zebrafish models in this field. Understanding zebrafish behavioral phenotypes provides important insights into neural pathways, physiological biomarkers, and genetic underpinnings of normal and pathological brain function. Novel zebrafish paradigms continue to appear with an encouraging pace, thus necessitating a consistent terminology and improved understanding of the behavioral repertoire. What can zebrafish 'do', and how does their altered brain function translate into behavioral actions? To help address these questions, we have developed a detailed catalog of zebrafish behaviors (Zebrafish Behavior Catalog, ZBC) that covers both larval and adult models. Representing a beginning of creating a more comprehensive ethogram of zebrafish behavior, this effort will improve interpretation of published findings, foster cross-species behavioral modeling, and encourage new groups to apply zebrafish neurobehavioral paradigms in their research. In addition, this glossary creates a framework for developing a zebrafish neurobehavioral ontology, ultimately to become part of a unified animal neurobehavioral ontology, which collectively will contribute to better integration of biological data within and across species.

Antipredatory behavior of zebrafish: adaptive function and a tool for translational research

The zebrafish is gaining popularity in behavioral brain research. It may be a cost-effective tool with which we can improve our understanding of the biological and genetic mechanisms of human brain function and dysfunction. Some, myself and collaborators included, have argued that such translational relevance may be best achieved if one considers the ecology and species-specific characteristics of the study organism. In this review, I focus on our own studies investigating zebrafish fear responses, which may be utilized in analyzing the mechanisms of fear and anxiety, and which may be used for screening anxiolytic drugs. I review how zebrafish respond to their natural and synthetic alarm substance as well as to other fear-inducing stimuli, including sympatric and allopatric predatory fish, sympatric or allopatric harmless fish, moving (animated) images of predatory fish and moving images of abstract shapes. I discuss the behavioral responses these stimuli elicit, summarize the methods of the quantification of the behaviors, and speculate about their possible adaptive nature. Although we utilize complex visual stimuli and do not yet know what key features zebrafish may be sensitive to, our results, together with those published by others, imply that this simple vertebrate may have a bright future in behavioral brain research.

Sight of conspecific images induces changes in neurochemistry in zebrafish

Zebrafish are gaining popularity in behavioural brain research as this species combines practical simplicity with system complexity. The dopaminergic system has been thoroughly investigated using mammals. Dopamine plays important roles in motor function and reward. Zebrafish have dopamine receptors homologous to mammalian counterparts, and dopamine receptor antagonists as well as alcohol have been shown to exert significant effects on this species as measured using HPLC or behavioural methods. The sight of conspecifics was previously shown to be rewarding in zebrafish but whether this stimulus affects the dopaminergic system has not been studied. Here, we present animated images of zebrafish to the experimental zebrafish subject for varying lengths of time and quantify the amount of dopamine, DOPAC, serotonin and 5HIAA extracted from the subject's brain immediately after the stimulus presentation using HPLC with electrochemical detection. We find conspecific images to induce a robust behavioural response (attraction) in experimental zebrafish. Importantly, dopamine and DOPAC levels significantly increased in response to the presentation of conspecific images but not to scrambled images. Last, serotonin and 5HIAA levels did not significantly change in response to the conspecific images. We conclude that our findings, together with pervious studies, now conclusively demonstrate that the behavioural response induced by the appearance of conspecifics is mediated, at least partly, by the dopaminergic system in zebrafish.