Zebrafish models to study drug abuse-related phenotypes.

Mounting evidence implicates the zebrafish (Danio rerio) as a promising model species for reward and addiction research. Modeling drug abuse-related behavior in both adult and larval zebrafish produced a wealth of clinically translatable data, also demonstrating their sensitivity to various drugs of abuse and the ability to develop tolerance. Several studies have also applied withdrawal paradigms to model the adverse effects of drug abuse in zebrafish. In this review, we summarize recent findings of a wide spectrum of zebrafish drug abuse-related behavioral and physiological phenotypes, discuss the existing challenges, and outline potential future directions of research in this field.

Behavioral effects of MDMA ('ecstasy') on adult zebrafish.

3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') is a potent psychedelic drug inducing euphoria and hypersociability in humans, as well as hyperactivity and anxiety in rodents. Adult zebrafish (Danio rerio) have become a widely used species in neurobehavioral research. Here, we explore the effects of a wide range (0.25-120 mg/l) of acute MDMA doses on zebrafish behavior in the novel tank test. Although MDMA was inactive at lower doses (0.25-10 mg/l), higher doses reduced bottom swimming and immobility (40-120 mg/l) and impaired intrasession habituation (10-120 mg/l). MDMA also elevated brain c-fos expression, collectively confirming the usage of zebrafish models for screening of hallucinogenic compounds.

The role of omega-3 polyunsaturated fatty acids eicosapentaenoic and docosahexaenoic acids in the treatment of major depression and Alzheimer's disease: Acting separately or synergistically?

Omega-3 polyunsaturated fatty acids (n-3-PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may improve or prevent some psychiatric and neurodegenerative diseases in both experimental and clinical studies. As important membrane components, these PUFAs benefit brain health by modulating neuroimmune and apoptotic pathways, changing membrane function and/or competing with n-6 PUFAs, the precursors of inflammatory mediators. However, the exact role of each fatty acid in neuroimmune modulation and neurogenesis, the interaction between EPA and DHA, and the best EPA:DHA ratios for improving brain disorders, remain unclear. It is also unknown whether EPA, as a DHA precursor, acts directly or via DHA. Here, we discuss recent evidence of EPA and DHA effects in the treatment of major depression and Alzheimer's disease, as well as their potential synergistic action on anti-inflammatory, antioxidant and neurotrophic processes in the brain. We further analyze the cellular and molecular mechanisms by which EPA, DHA or their combination may benefit these diseases. We also outline the limitations of current studies and suggest new genetic models and novel approaches to overcome these limitations. Finally, we summarize future strategies for translational research in this field.

Building neurophenomics in zebrafish: Effects of prior testing stress and test batteries.

The zebrafish (Danio rerio) is a promising model organism for neurophenomics - a new field of neuroscience linking neural phenotypes to various genetic and environmental factors. However, the effects of prior experimental manipulations on zebrafish performance in different behavioral paradigms remain unclear. Here, we examine the influence of selected stressful procedures and test batteries on adult zebrafish anxiety-like behaviors in two commonly used models - the novel tank (NTT) and the light-dark box (LDB) tests. While no overt behavioral differences between outbred short-fin wild-type (WT) and mutant 'pink' glowfish were seen in both tests under baseline (control) conditions, an acute severe stressor (a 30-min car transportation) detected significantly lower mutant fish anxiety-like behavior in these tests. In contrast, WT zebrafish showed no overt NTT or LDB responses following a mild stressor (5-min 40-Wt light) exposure, also showing no differences in batteries of NTT and LDB run immediately one after another, or with a 1-day interval. Collectively, these findings suggest that zebrafish may be relatively less sensitive (e.g., than other popular species, such as rodents) to the test battery effect, and show that stronger stressors may be needed (to complement low-to-moderate stress aquatic screens) to better reveal phenotypical variance in zebrafish assays. Strengthening the value of zebrafish models in neurophenotyping research, this study indicates the potential of using more test batteries and a wider spectrum of pre-test stressors in zebrafish behavioral assays.

Genetic and environmental modulation of neurodevelopmental disorders: Translational insights from labs to beds.

Neurodevelopmental disorders (NDDs) are a heterogeneous group of prevalent neuropsychiatric illnesses with various degrees of social, cognitive, motor, language and affective deficits. NDDs are caused by aberrant brain development due to genetic and environmental perturbations. Common NDDs include autism spectrum disorder (ASD), intellectual disability, communication/speech disorders, motor/tic disorders and attention deficit hyperactivity disorder. Genetic and epigenetic/environmental factors play a key role in these NDDs with significant societal impact. Given the lack of their efficient therapies, it is important to gain further translational insights into the pathobiology of NDDs. To address these challenges, the International Stress and Behavior Society (ISBS) has established the Strategic Task Force on NDDs. Summarizing the Panel's findings, here we discuss the neurobiological mechanisms of selected common NDDs and a wider NDD+ spectrum of associated neuropsychiatric disorders with developmental trajectories. We also outline the utility of existing preclinical (animal) models for building translational and cross-diagnostic bridges to improve our understanding of various NDDs.

Understanding autism and other neurodevelopmental disorders through experimental translational neurobehavioral models.

Neurodevelopmental disorders (NDDs) are highly prevalent and severely debilitating brain illnesses caused by aberrant brain growth and development. Resulting in cognitive, social, motor, language and affective disabilities, common NDDs include autism spectrum disorder (ASD), intellectual disability, communication/speech disorders, motor/tic disorders and attention deficit hyperactivity disorder. Affecting neurogenesis, glia/neuronal proliferation and migration, synapse formation and myelination, aberrant neural development occurs over a substantial period of time. Genetic, epigenetic, and environmental factors play a key role in NDD pathogenesis. Animal models are an indispensable tool to study NDDs. Paralleling clinical findings, we comprehensively evaluate various preclinical tests and models which target key (social, cognitive, motor) neurobehavioral domains of ASD and other common NDDs. Covering both traditional (rodent) and alternative NDD models, we outline the emerging areas of research and emphasize how preclinical models play a key role in gaining translational and mechanistic insights into NDDs and their therapy.

Zebrafish neurobehavioral phenomics for aquatic neuropharmacology and toxicology research.

Zebrafish (Danio rerio) are rapidly emerging as an important model organism for aquatic neuropharmacology and toxicology research. The behavioral/phenotypic complexity of zebrafish allows for thorough dissection of complex human brain disorders and drug-evoked pathological states. As numerous zebrafish models become available with a wide spectrum of behavioral, genetic, and environmental methods to test novel drugs, here we discuss recent zebrafish phenomics methods to facilitate drug discovery, particularly in the field of biological psychiatry. Additionally, behavioral, neurological, and endocrine endpoints are becoming increasingly well-characterized in zebrafish, making them an inexpensive, robust and effective model for toxicology research and pharmacological screening. We also discuss zebrafish behavioral phenotypes, experimental considerations, pharmacological candidates and relevance of zebrafish neurophenomics to other 'omics' (e.g., genomic, proteomic) approaches. Finally, we critically evaluate the limitations of utilizing this model organism, and outline future strategies of research in the field of zebrafish phenomics.

Improving treatment of neurodevelopmental disorders: recommendations based on preclinical studies.

INTRODUCTION: Neurodevelopmental disorders (NDDs) are common and severely debilitating. Their chronic nature and reliance on both genetic and environmental factors makes studying NDDs and their treatment a challenging task. AREAS COVERED: Herein, the authors discuss the neurobiological mechanisms of NDDs, and present recommendations on their translational research and therapy, outlined by the International Stress and Behavior Society. Various drugs currently prescribed to treat NDDs also represent a highly diverse group. Acting on various neurotransmitter and physiological systems, these drugs often lack specificity of action, and are commonly used to treat multiple other psychiatric conditions. There has also been relatively little progress in the development of novel medications to treat NDDs. Based on clinical, preclinical and translational models of NDDs, our recommendations cover a wide range of methodological approaches and conceptual strategies. EXPERT OPINION: To improve pharmacotherapy and drug discovery for NDDs, we need a stronger emphasis on targeting multiple endophenotypes, a better dissection of genetic/epigenetic factors or "hidden heritability," and a careful consideration of potential developmental/trophic roles of brain neurotransmitters. The validity of animal NDD models can be improved through discovery of novel (behavioral, physiological and neuroimaging) biomarkers, applying proper environmental enrichment, widening the spectrum of model organisms, targeting developmental trajectories of NDD-related behaviors and comorbid conditions beyond traditional NDDs. While these recommendations cannot be addressed all in once, our increased understanding of NDD pathobiology may trigger innovative cross-disciplinary research expanding beyond traditional methods and concepts.

Cytokine and endocrine parameters in mouse chronic social defeat: implications for translational 'cross-domain' modeling of stress-related brain disorders.

Mounting clinical and experimental evidence implicates various cytokines in stress-related affective brain disorders. Here, we analyze behavioral phenotypes in C57BL/6J male mice following the chronic social defeat stress paradigm, and examine their serum cytokines and corticosterone levels. Loser mice experiencing 20 days of daily 15-min social confrontations demonstrate elevated levels of pro-inflammatory cytokines interleukin IL-7 and vascular endothelial growth factor (VEGF), as well as a trend to increase IL-6 and IL-15. We also found higher levels of an anti-inflammatory cytokine IL-10 in the winner mice, with unaltered serum IL-2, IL-4, IL-1a, MCP-1 and corticosterone levels between the groups. Overall, our results suggest that animal affective-like states correlate with specific cytokine profiles, including some cytokines (e.g., VEGF, IL-7 or IL-15) whose role in neuropsychiatric disorders is only beginning to emerge. This study emphasizes the importance of integrative analyses of neural and immune phenotypes in stress and stress-related neurobehavioral disorders. These findings may also help foster the search for new therapeutic and preventative strategies that target selected cytokines and their signaling pathways.

Perspectives on experimental models of serotonin syndrome in zebrafish.

Serotonin syndrome (SS) is a serious life-threatening disorder associated with elevated brain serotonergic function. With the growing use of serotonergic drugs, SS affects a large portion of general population, becoming a major biomedical concern. SS-like behaviors have also been reported in animals following administration of serotonergic drugs. Although clinical and rodent studies have provided significant insight into the etiology of SS, its exact mechanisms and risk factors remain poorly understood. The need to develop more efficient psychotropic drugs also requires extensive high-throughput screening of novel compounds using sensitive in-vivo tests. The use of zebrafish (Danio rerio) in neuroscience research is rapidly expanding due to their homology to humans, robust behavioral and physiological responses, genetic tractability, and low costs. Here we discuss the potential of zebrafish models to study SS-related phenotypes induced by selected serotonergic drugs. Overall, zebrafish exposed to serotonergic agents and their combinations exhibit a characteristic top dwelling (surfacing behavior) and hypolocomotion which may represent potential markers of SS-like states in zebrafish. This behavior in zebrafish models positively correlates with brain concentrations of serotonin, suggesting the developing utility of zebrafish (and other aquatic models) for studying SS. Future research is expected to foster high-throughput screening of drug interactions, and pharmacogenetics studies identifying zebrafish mutations implicated in pathological SS-like states.

Unique and potent effects of acute ibogaine on zebrafish: the developing utility of novel aquatic models for hallucinogenic drug research.

An indole alkaloid, ibogaine is the principal psychoactive component of the iboga plant, used by indigenous peoples in West Africa for centuries. Modulating multiple neurotransmitter systems, the drug is a potent hallucinogen in humans, although its psychotropic effects remain poorly understood. Expanding the range of model species is an important strategy for translational neuroscience research. Here we exposed adult zebrafish (Danio rerio) to 10 and 20mg/L of ibogaine, testing them in the novel tank, light-dark box, open field, mirror stimulation, social preference and shoaling tests. In the novel tank test, the zebrafish natural diving response (geotaxis) was reversed by ibogaine, inducing initial top swimming followed by bottom dwelling. Ibogaine also attenuated the innate preference for dark environments (scototaxis) in the light-dark box test. While it did not exert overt locomotor or thigmotaxic responses in the open field test, the drug altered spatiotemporal exploration of novel environment, inducing clear preference of some areas over others. Ibogaine also promoted 'mirror' exploration in the mirror stimulation test, disrupted group cohesion in the shoaling test, and evoked strong coloration responses due to melanophore aggregation, but did not alter brain c-fos expression or whole-body cortisol levels. Overall, our results support the complex pharmacological profile of ibogaine and its high sensitivity in zebrafish models, dose-dependently affecting multiple behavioral domains. While future investigations in zebrafish may help elucidate the mechanisms underlying these unique behavioral effects, our study strongly supports the developing utility of aquatic models in hallucinogenic drug research. High sensitivity of three-dimensional phenotyping approaches applied here to behavioral effects of ibogaine in zebrafish provides further evidence of how 3D reconstructions of zebrafish swimming paths may be useful for high-throughput pharmacological screening.

Constructing the habituome for phenotype-driven zebrafish research.

Intra-session habituation to novelty reflects spatial working memory (related to exploration and cognition), and is observed in various species, including zebrafish (Danio rerio). With the growing understanding of complex zebrafish behaviors, the extent to which they habituate remains unclear. Here we perform a large-scale characterization of zebrafish novelty-evoked (novel tank and open field) behaviors, to establish their grouping based on intra-session habituation and sensitivity to anxiolytic or anxiogenic manipulations. We also assess multiple behaviors in high- and low-anxiety sub-cohorts of a large heterogeneous zebrafish population, comparing their habituation profiles. Overall, our analyses demonstrate that anxiety responsivity and the ability to habituate show little correlation for multiple zebrafish behaviors, suggesting that they most likely represent distinct behavioral phenomena in novel environments. Using these data, we also present the habituome--a new conceptual approach to study affective and cognitive responses in zebrafish by examining a big set of their habituation phenotypes. Given marked similarity in animal novelty exploration, this approach may also be used to construct habituomes in other model organisms, including rodents and humans.

Potential translational targets revealed by linking mouse grooming behavioral phenotypes to gene expression using public databases.

Rodent self-grooming is an important, evolutionarily conserved behavior, highly sensitive to pharmacological and genetic manipulations. Mice with aberrant grooming phenotypes are currently used to model various human disorders. Therefore, it is critical to understand the biology of grooming behavior, and to assess its translational validity to humans. The present in-silico study used publicly available gene expression and behavioral data obtained from several inbred mouse strains in the open-field, light-dark box, elevated plus- and elevated zero-maze tests. As grooming duration differed between strains, our analysis revealed several candidate genes with significant correlations between gene expression in the brain and grooming duration. The Allen Brain Atlas, STRING, GoMiner and Mouse Genome Informatics databases were used to functionally map and analyze these candidate mouse genes against their human orthologs, assessing the strain ranking of their expression and the regional distribution of expression in the mouse brain. This allowed us to identify an interconnected network of candidate genes (which have expression levels that correlate with grooming behavior), display altered patterns of expression in key brain areas related to grooming, and underlie important functions in the brain. Collectively, our results demonstrate the utility of large-scale, high-throughput data-mining and in-silico modeling for linking genomic and behavioral data, as well as their potential to identify novel neural targets for complex neurobehavioral phenotypes, including grooming.

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.

Understanding spatio-temporal strategies of adult zebrafish exploration in the open field test.

Zebrafish (Danio rerio) are emerging as a useful model organism for neuroscience research. Mounting evidence suggests that various traditional rodent paradigms may be adapted for testing zebrafish behavior. The open field test is a popular rodent test of novelty exploration, recently applied to zebrafish research. To better understand fish novelty behavior, we exposed adult zebrafish to two different open field arenas for 30 min, assessing the amount and temporal patterning of their exploration. While (similar to rodents) zebrafish scale their locomotory activity depending on the size of the tank, the temporal patterning of their activity was independent of arena size. These observations strikingly parallel similar rodent behaviors, suggesting that spatio-temporal strategies of animal exploration may be evolutionarily conserved across vertebrate species. In addition, we found interesting oscillations in zebrafish exploration, with the per-minute distribution of their horizontal activity demonstrating sinusoidal-like patterns. While such patterning is not reported for rodents and other higher vertebrates, a nonlinear regression analysis confirmed the oscillation patterning of all assessed zebrafish behavioral endpoints in both open field arenas, revealing a potentially important aspect of novelty exploration in lower vertebrates.

Modeling anxiety using adult zebrafish: a conceptual review.

Zebrafish (Danio rerio) are rapidly emerging as a useful animal model in neurobehavioral research. Mounting evidence shows the suitability of zebrafish to model various aspects of anxiety-related states. Here, we evaluate established and novel approaches to uncover the molecular substrates, genetic pathways and neural circuits of anxiety using adult zebrafish. Experimental approaches to modeling anxiety in zebrafish include novelty-based paradigms, pharmacological and genetic manipulations, as well as innovative video-tracking, 3D-reconstructions, bioinformatics-based searchable databases and omics-based tools. Complementing traditional rodent models of anxiety, we provide a conceptual framework for the wider application of zebrafish and other aquatic models in anxiety research. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Alterations in grooming activity and syntax in heterozygous SERT and BDNF knockout mice: the utility of behavior-recognition tools to characterize mutant mouse phenotypes.

Serotonin transporter (SERT) and brain-derived neurotrophic factor (BDNF) are key modulators of molecular signaling, cognition and behavior. Although SERT and BDNF mutant mouse phenotypes have been extensively characterized, little is known about their self-grooming behavior. Grooming represents an important behavioral domain sensitive to environmental stimuli and is increasingly used as a model for repetitive behavioral syndromes, such as autism and attention deficit/hyperactivity disorder. The present study used heterozygous ((+/-)) SERT and BDNF male mutant mice on a C57BL/6J background and assessed their spontaneous self-grooming behavior applying both manual and automated techniques. Overall, SERT(+/-) mice displayed a general increase in grooming behavior, as indicated by more grooming bouts and more transitions between specific grooming stages. SERT(+/-) mice also aborted more grooming bouts, but showed generally unaltered activity levels in the observation chamber. In contrast, BDNF(+/-) mice displayed a global reduction in grooming activity, with fewer bouts and transitions between specific grooming stages, altered grooming syntax, as well as hypolocomotion and increased turning behavior. Finally, grooming data collected by manual and automated methods (HomeCageScan) significantly correlated in our experiments, confirming the utility of automated high-throughput quantification of grooming behaviors in various genetic mouse models with increased or decreased grooming phenotypes. Taken together, these findings indicate that mouse self-grooming behavior is a reliable behavioral biomarker of genetic deficits in SERT and BDNF pathways, and can be reliably measured using automated behavior-recognition technology.

Perspectives of zebrafish models of epilepsy: what, how and where next?

Epilepsy is a complex brain disorder with multiple underlying causes and poorly understood pathogenetic mechanisms. Animal models have been indispensable tools in experimental epilepsy research. Zebrafish (Danio rerio) are rapidly emerging as a promising model organism to study various brain disorders. Seizure-like behavioral and neurophysiological responses can be evoked in larval and adult zebrafish by various pharmacological and genetic manipulations, collectively emphasizing the growing utility of this model for studying epilepsy. Here, we discuss recent developments in using zebrafish models to study the seizure-like behavior involved in epilepsy, outlining current challenges and strategies for further translational research in this field.

The Zebrafish Neurophenome Database (ZND): a dynamic open-access resource for zebrafish neurophenotypic data.

Zebrafish (Danio rerio) are widely used in neuroscience research, where their utility as a model organism is rapidly expanding. Low cost, ease of experimental manipulations, and sufficient behavioral complexity make zebrafish a valuable tool for high-throughput studies in biomedicine. To complement the available repositories for zebrafish genetic information, there is a growing need for the collection of zebrafish neurobehavioral and neurological phenotypes. For this, we are establishing the Zebrafish Neurophenome Database (ZND; www.tulane.edu/∼znpindex/search ) as a new dynamic online open-access data repository for behavioral and related physiological data. ZND, currently focusing on adult zebrafish, combines zebrafish neurophenotypic data with a simple, easily searchable user interface, which allow scientists to view and compare results obtained by other laboratories using various treatments in different testing paradigms. As a developing community effort, ZND is expected to foster innovative research using zebrafish by federating the growing body of zebrafish neurophenotypic data.

Behavioral and physiological effects of RDX on adult zebrafish.

1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) is a nitroamine explosive, with common toxic effects including seizures. Here, we explore the behavioral effects of acute RDX exposure in adult zebrafish Danio rerio, a rapidly developing model in neuroscience and neurotoxicology research. Overall, a 30-min exposure to RDX low dose of 0.1 mM evoked behavioral activation in zebrafish, while a higher dose of 1 mM markedly reduced exploration, increased freezing and evoked seizure-like responses (i.e., bouts of hyperactivity, spasms, and corkscrew swimming). Likewise, whole-body cortisol levels were also significantly elevated in fish exposed to 1 mM (but not 0.1 mM) RDX. In line with clinical and animal data, our study demonstrates the dose-dependent behavioral activation and pro-convulsant effects of RDX in zebrafish-based models.