Constructing the habituome for phenotype-driven zebrafish research

Therapeutic effects of nanosilibinin in valproic acid-zebrafish model of autism spectrum disorder: Focusing on Wnt signaling pathway and autism spectrum disorder-related cytokines

In this study, we delved into the intricate world of autism spectrum disorder (ASD) and its connection to the disturbance in the Wnt signaling pathway and immunological abnormalities. Our aim was to evaluate the impact of silibinin, a remarkable modulator of both the Wnt signaling pathway and the immune system, on the neurobehavioral and molecular patterns observed in a zebrafish model of ASD induced by valproic acid (VPA). Because silibinin is a hydrophobic molecule and highly insoluble in water, it was used in the form of silibinin nanoparticles (nanosilibinin, NS). After assessing survival, hatching rate, and morphology of zebrafish larvae exposed to different concentrations of NS, the appropriate concentrations were chosen. Then, zebrafish embryos were exposed to VPA (1 μM) and NS (100 and 200 μM) at the same time for 120 h. Next, anxiety and inattentive behaviors and the expression of CHD8, CTNNB, GSK3beta, LRP6, TNFalpha, IL1beta, and BDNF genes were assessed 7 days post fertilization. The results indicated that higher concentrations of NS had adverse effects on survival, hatching, and morphological development. The concentrations of 100 and 200 μM of NS could ameliorate the anxiety-like behavior and learning deficit and decrease ASD-related cytokines (IL1beta and TNFalpha) in VPA-treated larvae. In addition, only 100 μM of NS prevented raising the gene expression of Wnt signaling-related factors (CHD8, CTNNB, GSK3beta, and LRP6). In conclusion, NS treatment for the first 120 h showed therapeutic effect on an autism-like phenotype probably via reducing the expression of pro-inflammatory cytokines genes and changing the expression of Wnt signaling components genes.

Behavioral effects of visual stimuli in adult zebrafish using a novel eight-tank imaging system

Introduction

Animals respond to various environmental cues. Animal behavior is complex, and behavior analysis can greatly help to understand brain function. Most of the available behavioral imaging setups are expensive, provide limited options for customization, and allow for behavioral imaging of one animal at a time.

Methods

The current study takes advantage of adult zebrafish as a model organism to study behavior in a novel behavioral setup allowing one to concurrently image 8 adult zebrafish.

Results

Our results indicate that adult zebrafish show a unique behavioral profile in response to visual stimuli such as moving lines. In the presence of moving lines, the fish spent more time exploring the tank and spent more time toward the edges of the tanks. In addition, the fish moved and oriented themselves against the direction of the moving lines, indicating a negative optomotor response (OMR). With repeated exposure to moving lines, we observed a reduced optomotor response in adult zebrafish.

Discussion

Our behavioral setup is relatively inexpensive, provides flexibility in the presentation of various animated visual stimuli, and offers improved throughput for analyzing behavior in adult zebrafish. This behavioral setup shows promising potential to quantify various behavioral measures and opens new avenues to understand complex behaviors.

Zebrafish (Danio rerio) as a translational model for neuro-immune interactions in the enteric nervous system in autism spectrum disorders

Autism spectrum disorders (ASD) affect about 1% of the population and are strongly associated with gastrointestinal diseases creating shortcomings in quality of life. Multiple factors contribute to the development of ASD and although neurodevelopmental deficits are central, the pathogenesis of the condition is complex and the high prevalence of intestinal disorders is poorly understood. In agreement with the prominent research establishing clear bidirectional interactions between the gut and the brain, several studies have made it evident that such a relation also exists in ASD. Thus, dysregulation of the gut microbiota and gut barrier integrity may play an important role in ASD. However, only limited research has investigated how the enteric nervous system (ENS) and intestinal mucosal immune factors may impact on the development of ASD-related intestinal disorders. This review focuses on the mechanistic studies that elucidate the regulation and interactions between enteric immune cells, residing gut microbiota and the ENS in models of ASD. Especially the multifaceted properties and applicability of zebrafish (Danio rerio) for the study of ASD pathogenesis are assessed in comparison to studies conducted in rodent models and humans. Advances in molecular techniques and in vivo imaging, combined with genetic manipulation and generation of germ-free animals in a controlled environment, appear to make zebrafish an underestimated model of choice for the study of ASD. Finally, we establish the research gaps that remain to be explored to further our understanding of the complexity of ASD pathogenesis and associated mechanisms that may lead to intestinal disorders.

Behavioral profile of adult zebrafish acutely exposed to a selective dopamine uptake inhibitor, GBR 12909

BACKGROUND

The dopamine transporter (DAT) is the main regulator of dopamine concentration in the extrasynaptic space. The pharmacological inhibition of the DAT results in a wide spectrum of behavioral manifestations, which have been identified so far in a limited number of species, mostly in rodents.

AIM

Here, we used another well-recognized model organism, the zebrafish (Danio rerio), to explore the behavioral effects of GBR 12909, a highly-affine selective DAT blocker.

METHODS

We evaluated zebrafish locomotion, novelty-related exploration, spatial cognition, and social phenotypes in the novel tank, habituation and shoaling tests, following acute 20-min water immersion in GBR 12909.

RESULTS

Our findings show hypolocomotion, anxiety-like state, and impaired spatial cognition in fish acutely treated with GBR 12909. This behavioral profile generally parallels that of the DAT knockout rodents and zebrafish, and it overlaps with behavioral effects of other DAT-inhibiting drugs of abuse, such as cocaine and D-amphetamine.

CONCLUSION

Collectively, our data support the utility of zebrafish in translational studies on DAT targeting neuropharmacology and strongly implicate DAT aberration as an important mechanisms involved in neurological and psychiatric diseases.

Two Locomotor Traits Show Different Patterns of Developmental Plasticity Between Closely Related Clonal and Sexual Fish

The capacity to compensate for environmental change determines population persistence and biogeography. In ectothermic organisms, performance at different temperatures can be strongly affected by temperatures experienced during early development. Such developmental plasticity is mediated through epigenetic mechanisms that induce phenotypic changes within the animal's lifetime. However, epigenetic modifiers themselves are encoded by DNA so that developmental plasticity could itself be contingent on genetic diversity. In this study, we test the hypothesis that the capacity for developmental plasticity depends on a species' among-individual genetic diversity. To test this, we exploited a unique species complex that contains both the clonal, genetically identical Amazon molly (Poecilia formosa), and the sexual, genetically diverse Atlantic molly (Poecilia mexicana). We predicted that the greater among-individual genetic diversity in the Atlantic molly may increase their capacity for developmental plasticity. We raised both clonal and sexual mollies at either warm (28°C) or cool (22°C) temperatures and then measured locomotor capacity (critical sustained swimming performance) and unforced movement in an open field across a temperature gradient that simulated environmental conditions often experienced by these species in the wild. In the clonal Amazon molly, differences in the developmental environment led to a shift in the thermal performance curve of unforced movement patterns, but much less so in maximal locomotor capacity. In contrast, the sexual Atlantic mollies exhibited the opposite pattern: developmental plasticity was present in maximal locomotor capacity, but not in unforced movement. Thus our data show that developmental plasticity in clones and their sexual, genetically more diverse sister species is trait dependent. This points toward mechanistic differences in how genetic diversity mediates plastic responses exhibited in different traits.

Different influences of anxiety models, environmental enrichment, standard conditions and intraspecies variation (sex, personality and strain) on stress and quality of life in adult and juvenile zebrafish: A systematic review

Antagonist and long-lasting environmental manipulations (EM) have successfully induced or reduced the stress responses and quality of life of zebrafish. For instance, environmental enrichment (EE) generally reduces anxiety-related behaviours and improves immunity, while unpredictable chronic stress (UCS) and aquarium-related stressors generate the opposite effects. However, there is an absence of consistency in outcomes for some EM, such as acute exposure to stressors, social enrichment and some items of structural enrichment. Therefore, considering intraspecies variation (sex, personality, and strain), increasing intervention complexity while improving standardisation of protocols and contemplating the possibility that EE may act as a mild stressor on a spectrum between too much (UCS) and too little (standard conditions) stress intensity or stimulation, would reduce the inconsistencies of these outcomes. It would also help explore the mechanism behind stress resilience and to standardise EM protocols. Thus, this review critically analyses and compares knowledge existing over the last decade concerning environmental manipulations for zebrafish and the influences that sex, strain, and personality may have on behavioural, physiological, and fitness-related responses.

Swimming in the maze: An overview of maze apparatuses and protocols to assess zebrafish behavior

Most preclinical behavioral assays use rodents as model animals, leaving room for species-specific biases that could be avoided by an expanded cross-species approach. In this context, zebrafish emerges as an alternative model organism to study neurobiological mechanisms of anxiety, preference, learning, and memory, as well as other phenotypes with relevance to neuropsychiatric disorders. In recent years, several zebrafish studies using different types of mazes have been published. However, the protocols and apparatuses' shapes and dimensions vary widely in the literature. This variation may puzzle researchers attempting to implement maze behavioral assays and challenges the reproducibility across institutions. This review aims to provide an overview of the behavioral paradigms assessed in different types of mazes in zebrafish reported in the last couple of decades. Also, this review aims to contribute to a better characterization of multi-behavioral assessment in zebrafish.

Impacts of polystyrene microplastics on the behavior and metabolism in a marine demersal teleost, black rockfish (Sebastes schlegelii)

After nano- (0.5 μm) or micro- (15 μm) polystyrene (PS) microplastics exposure, the behavior, metabolism and energy reserve in marine demersal fish (Sebastes schlegelii) were evaluated. The behavior of fish was accurately recorded by video behavior tracking technology. Results showed that changes in behavior (e.g. cluster, the reduction of swimming speed and range of movement) were significantly greater in 15-μm PS-exposed fish, which may affect hunting behavior and exploration competence. Oxygen consumption and ammonia excretion of fish was significantly greater in 15-μm PS treatment than in 0.5-μm PS treatment, suggesting respiration and metabolism stress. Moreover, the abnormal behavior, respiration and ammonia excretion of PS-exposed fish had recovered modestly. In addition, abnormal symptoms of bile, liver and lumen of intestine were detected in 15-μm PS exposure. Importantly, the growth and gross energy of fish were reduced in 15-μm PS exposure than 0.5-μm PS exposure. Both 0.5-μm and 15-μm PS exposures led to significantly lower protein and lipid contents, suggesting energy reserve and nutrition quality reduction of fish. Overall, microplastics had the negative impact at greater levels than nanoplastics. Altered behavior, energy reserve and nutritional quality of fish indicated the potential risk on biological functions, the development of fishery and food safety.

Differences in stress reactivity between zebrafish with alternative stress coping styles

Animals experience stress in a variety of contexts and the behavioural and neuroendocrine responses to stress can vary among conspecifics. The responses across stressors often covary within an individual and are consistently different between individuals, which represent distinct stress coping styles (e.g. proactive and reactive). While studies have identified differences in peak glucocorticoid levels, less is known about how cortisol levels differ between stress coping styles at other time points of the glucocorticoid stress response. Here we quantified whole-body cortisol levels and stress-related behaviours (e.g. depth preference, movement) at time points representing the rise and recovery periods of the stress response in zebrafish lines selectively bred to display the proactive and reactive coping style. We found that cortisol levels and stress behaviours are significantly different between the lines, sexes and time points. Further, individuals from the reactive line showed significantly higher cortisol levels during the rising phase of the stress response compared with those from the proactive line. We also observed a significant correlation between individual variation of cortisol levels and depth preference but only in the reactive line. Our results show that differences in cortisol levels between the alternative stress coping styles extend to the rising phase of the endocrine stress response and that cortisol levels may explain variation in depth preferences in the reactive line. Differences in the timing and duration of cortisol levels may influence immediate behavioural displays and longer lasting neuromolecular mechanisms that modulate future responses.

Zebrafish models for personalized psychiatry: Insights from individual, strain and sex differences, and modeling gene x environment interactions

Currently becoming widely recognized, personalized psychiatry focuses on unique physiological and genetic profiles of patients to best tailor their therapy. However, the role of individual differences, as well as genetic and environmental factors, in human psychiatric disorders remains poorly understood. Animal experimental models are a valuable tool to improve our understanding of disease pathophysiology and its molecular mechanisms. Due to high reproduction capability, fully sequenced genome, easy gene editing, and high genetic and physiological homology with humans, zebrafish (Danio rerio) are emerging as a novel powerful model in biomedicine. Mounting evidence supports zebrafish as a useful model organism in CNS research. Robustly expressed in these fish, individual, strain, and sex differences shape their CNS responses to genetic, environmental, and pharmacological manipulations. Here, we discuss zebrafish as a promising complementary translational tool to further advance patient-centered personalized psychiatry.

Embryonic alcohol exposure leading to social avoidance and altered anxiety responses in adult zebrafish

Fetal Alcohol Spectrum Disorders (FASD) is a syndrome characterized by neurological and behavioral impairments. A recently discovered hallmark of FASD is impaired social behavior. Avoidance of social interaction typical of FASD may be the result of increased anxiety. Previously, the zebrafish was successfully used to model embryonic alcohol induced social abnormalities. Here, we analyzed both anxiety and social responses using a zebrafish FASD model, in adult fish. We exposed zebrafish embryos to low concentrations of ethanol (0.1%; 0.25%; 0.5% and 1% v/v) for 2h at, 24h post-fertilization, to mimic the most prevalent milder FASD cases, and investigated the ensuing alterations in adult, 4-month-old, zebrafish. We studied social interaction in the social preference task and anxiety in the novel tank task. We observed an ethanol dose dependent reduction of time spend in the conspecific zone compared to control, corroborating prior findings. We also found significant changes in the novel tank (e.g. increased bottom dwell time, increased distance to top) suggesting elevated anxiety to control, but we also found, using an anxiolytic drug buspirone, that reduction of anxiety is associated with reduced shoaling. Our results confirm that embryonic alcohol exposure disrupts social behavior, and also show that its effects on anxiety related phenotypes may be genotype, alcohol administration method, experimental procedure and test-context dependent.

Energetic cost determines voluntary movement speed only in familiar environments

Locomotor performance is closely related to fitness. However, in many ecological contexts, animals do not move at their maximal locomotor capacity, but adopt a voluntary speed that is lower than maximal. It is important to understand the mechanisms that underlie voluntary speed, because these determine movement patterns of animals across natural environments. We show that voluntary speed is a stable trait in zebrafish (Danio rerio), but there were pronounced differences between individuals in maximal sustained speed, voluntary speed and metabolic cost of locomotion. We accept the hypothesis that voluntary speed scales positively with maximal sustained swimming performance (Ucrit), but only in unfamiliar environments (1st minute in an open-field arena versus 10th minute) at high temperature (30°C). There was no significant effect of metabolic scope on Ucrit Contrary to expectation, we rejected the hypothesis that voluntary speed decreases with increasing metabolic cost of movement, except in familiar spatial (after 10 min of exploration) and thermal (24°C but not 18 or 30°C) environments. The implications of these data are that the energetic costs of exploration and dispersal in novel environments are higher than those for movement within familiar home ranges.

A sensitive biomarker for the detection of aquatic contamination based on behavioral assays using zebrafish larvae

An effective biological early warning system for the detection of water contamination should employ undemanding species that rapidly react to the presence of contaminants in their environment. The demonstrated reaction should be comprehensible and unambiguously evidential of the contamination event. This study utilized 96h post fertilization zebrafish larvae and tested their behavioral response to acute exposure to low concentrations of cadmium chloride (CdCl2) (5.0, 2.5, 1.25, 0.625mg/L) and permethrin (0.05, 0.029, 0.017, 0.01μg/L). We hypothesize that the number of larvae that show advanced trajectories in a group corresponds with water contamination, as the latter triggers avoidance behavior in the organisms. The proportion of advanced trajectories in the control and treated groups during the first minute of darkness was designated as a segregation parameter. It was parametrized and a threshold value was set using one CdCl2 trial and then applied to the remaining CdCl2 and permethrin replicates. For all cases, the method allowed distinguishing between the control and treated groups within two cycles of light: dark. The calculated parameter was statistically significantly different between the treated and control groups, except for the lowest CdCl2 concentration (0.625mg/L) in one replicate. This proof-of-concept study shows the potential of the proposed methodology for utilization as part of a multispecies biomonitoring system.

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.

Behavioural toxicity assessment of silver ions and nanoparticles on zebrafish using a locomotion profiling approach

Zebrafish (Danio rerio) is not only a widely used species in the Fish Embryo Toxicity (FET) test but also an emerging model in behavioural ecotoxicology. By using automatic behaviour tracking technology, locomotion of developing zebrafish (ZF) larvae can be accurately recorded and potentially used in an ecotoxicological context to detect toxicant-induced behavioural alterations. In this study, we explored if and how quantitative locomotion data can be used for sub-lethal toxicity testing within the FET framework. We exposed ZF embryos to silver ions and nanoparticles, which previously have been reported to cause neurodevelopmental toxicity and behavioural retardation in early-life stages of ZF. Exposure to a broad range of silver (Ag(+) and AgNPs) concentrations was conducted, and developmental toxicity was assessed using FET criteria. For behavioural toxicity assessment, locomotion of exposed ZF eleutheroembryos (120hpf) was quantified according to a customised behavioural assay in an automatic video tracking system. A set of repeated episodes of dark/light stimulation were used to artificially stress ZF and evoke photo-motor responses, which were consequently utilized for locomotion profiling. Our locomotion-based behaviour profiling approach consisted of (1) dose-response ranking for multiple and single locomotion variables; (2) quantitative assessment of locomotion structure; and (3) analysis of ZF responsiveness to darkness stimulation. We documented that both silver forms caused adverse effects on development and inhibited hatchability and, most importantly, altered locomotion. High Ag(+) and AgNPs exposures significantly suppressed locomotion and a clear shift in locomotion towards inactivity was reported. Additionally, we noted that low, environmentally relevant Ag(+) concentrations may cause subordinate locomotive changes (hyperactivity) in developing fish. Overall, it was concluded that our locomotion-based behaviour-testing scheme can be used jointly with FET and can provide endpoints for sub-lethal toxicity. When combined with multivariate data analysis, this approach facilitated new insights for handling and analysis of data generated by automatized behavioural tracking systems.

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.

Role of nitric oxide in the behavioral and neurochemical effects of IB-MECA in zebrafish

RATIONALE

The adenosine A3 receptor and the nitric oxide (NO) pathway regulate the function and localization of serotonin transporters (SERTs). These transporters regulate extracellular serotonin levels, which are correlated with defensive behavior.

OBJECTIVE

The purpose of this study was to understand the role of the A3AR on anxiety and arousal models in zebrafish, and whether this role is mediated by the nitrergic modulation of serotonin uptake.

METHODS

The effects of IB-MECA (0.01 and 0.1 mg/kg) were assessed in a series of behavioral tasks in adult zebrafish, as well as on extracellular serotonin levels in vivo and serotonin uptake in brain homogenates. Finally, the interaction between IB-MECA and drugs blocking voltage-dependent calcium channels (VDCCs), NO synthase, and SERT was analyzed.

RESULTS

At the lowest dose, IB-MECA decreased bottom dwelling and scototaxis, while at the highest dose, it also decreased shoaling, startle probability, and melanophore responses. These effects were accompanied by an increase in brain extracellular serotonin levels. IB-MECA also concentration-dependently increased serotonin uptake in vitro. The effects of IB-MECA on extracellular 5-HT, scototaxis, and geotaxis were blocked by L-NAME, while only the effects on 5-HT and scototaxis were blocked by verapamil. In vitro, the increase in 5-HT uptake was dependent on VDCCs and NO. Finally, fluoxetine blocked the effect of IB-MECA on scototaxis, but not geotaxis.

CONCLUSION

These results suggest that the effect of IB-MECA on scototaxis are mediated by a VDCC-NO-SERT pathway. While NO seems to mediate the effects of IB-MECA on geotaxis, neither VDCCs nor SERT seems to be involved in this process.

Fingerprinting of psychoactive drugs in zebrafish anxiety-like behaviors

A major hindrance for the development of psychiatric drugs is the prediction of how treatments can alter complex behaviors in assays which have good throughput and physiological complexity. Here we report the development of a medium-throughput screen for drugs which alter anxiety-like behavior in adult zebrafish. The observed phenotypes were clustered according to shared behavioral effects. This barcoding procedure revealed conserved functions of anxiolytic, anxiogenic and psychomotor stimulating drugs and predicted effects of poorly characterized compounds on anxiety. Moreover, anxiolytic drugs all decreased, while anxiogenic drugs increased, serotonin turnover. These results underscore the power of behavioral profiling in adult zebrafish as an approach which combines throughput and physiological complexity in the pharmacological dissection of complex behaviors.

PFOS induces behavioral alterations, including spontaneous hyperactivity that is corrected by dexamfetamine in zebrafish larvae

Perfluorooctane sulfonate (PFOS) is a widely spread environmental contaminant. It accumulates in the brain and has potential neurotoxic effects. The exposure to PFOS has been associated with higher impulsivity and increased ADHD prevalence. We investigated the effects of developmental exposure to PFOS in zebrafish larvae, focusing on the modulation of activity by the dopaminergic system. We exposed zebrafish embryos to 0.1 or 1 mg/L PFOS (0.186 or 1.858 µM, respectively) and assessed swimming activity at 6 dpf. We analyzed the structure of spontaneous activity, the hyperactivity and the habituation during a brief dark period (visual motor response), and the vibrational startle response. The findings in zebrafish larvae were compared with historical data from 3 months old male mice exposed to 0.3 or 3 mg/kg/day PFOS throughout gestation. Finally, we investigated the effects of dexamfetamine on the alterations in spontaneous activity and startle response in zebrafish larvae. We found that zebrafish larvae exposed to 0.1 mg/L PFOS habituate faster than controls during a dark pulse, while the larvae exposed to 1 mg/L PFOS display a disorganized pattern of spontaneous activity and persistent hyperactivity. Similarly, mice exposed to 0.3 mg/kg/day PFOS habituated faster than controls to a new environment, while mice exposed to 3 mg/kg/day PFOS displayed more intense and disorganized spontaneous activity. Dexamfetamine partly corrected the hyperactive phenotype in zebrafish larvae. In conclusion, developmental exposure to PFOS in zebrafish induces spontaneous hyperactivity mediated by a dopaminergic deficit, which can be partially reversed by dexamfetamine in zebrafish larvae.

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.

Anxiolytic drug discovery: what are the novel approaches and how can we improve them?

INTRODUCTION

Contemporary biological psychiatry uses experimental (animal) models to increase our understanding of affective disorder pathogenesis. Despite the well-recognized spectrum nature of affective disorders, modern anxiolytic drug discovery mainly targets specific pathways and molecular determinants within a single phenotypic domain. However, greater understanding of the integrative mechanisms and pathogenesis is essential in order to develop new effective therapies.

AREAS COVERED

In this review, the authors emphasize the importance of a 'domain interplay-oriented' approach to experimental affective research. They also highlight the need to expand the scope of anxiolytic drug targets to better understand the pathogenesis of anxiety-spectrum disorders.

EXPERT OPINION

There is the potential to markedly improve the utility of animal models for affective disorders. First, the authors suggest that one such way would be by analyzing the systems of several domains and their interplay to better understand disease pathogenesis. Further, it could also be improved by expanding the range of model species and by extending the spectrum of anxiolytic drug targets; this would help to focus on emerging and unconventional systems to better develop new therapies.

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.

Perspectives on zebrafish models of hallucinogenic drugs and related psychotropic compounds

Among different classes of psychotropic drugs, hallucinogenic agents exert one of the most prominent effects on human and animal behaviors, markedly altering sensory, motor, affective, and cognitive responses. The growing clinical and preclinical interest in psychedelic, dissociative, and deliriant hallucinogens necessitates novel translational, sensitive, and high-throughput in vivo models and screens. Primate and rodent models have been traditionally used to study cellular mechanisms and neural circuits of hallucinogenic drugs' action. The utility of zebrafish ( Danio rerio ) in neuroscience research is rapidly growing due to their high physiological and genetic homology to humans, ease of genetic manipulation, robust behaviors, and cost effectiveness. Possessing a fully characterized genome, both adult and larval zebrafish are currently widely used for in vivo screening of various psychotropic compounds, including hallucinogens and related drugs. Recognizing the growing importance of hallucinogens in biological psychiatry, here we discuss hallucinogenic-induced phenotypes in zebrafish and evaluate their potential as efficient preclinical models of drug-induced states in humans.

Behavioral and neurochemical changes in the zebrafish leopard strain

The zebrafish leopard phenotype (leo) displays abnormal pigmentation and shows increased anxiety-like behavior. The neurochemical changes associated with this anxious phenotype are not known. Here, we demonstrate that leo show increased anxiety-like behavior in the light/dark box and in the novel tank test. This anxious phenotype is rescued by acute treatment with a dose of a serotonin reuptake inhibitor, fluoxetine, that is inactive in wild-type animals. Moreover, leo show decreased tissue levels of serotonin, increased serotonin turnover and slightly increased monoamine oxidase activity. These results suggest that the anxious phenotype observed in leo zebrafish is caused by a decrease in serotonin uptake. This work could open an important avenue in defining the neurochemical underpinning of natural variation in anxiety disorders.

Dissociating the effects of habituation, black walls, buspirone and ethanol on anxiety-like behavioral responses in shoaling zebrafish. A 3D approach to social behavior

Understanding the different patterns of anxiety-like behavioral responses is of great interest for pharmacological and genetic research. Here we report the effects of 3.5-hr habituation, buspirone and ethanol on those responses in shoaling zebrafish (Danio rerio). Since in these experiments we used a container with white walls, the effects of black-vs.-white walls were tested in a separate experiment. An important objective was to determine whether factors unrelated to anxiety played a role in modulating the responses. The anxiety-like behavioral responses studied here are social cohesion, distance from bottom and bottom-dwell time, radial distribution (to study thigmotaxis), transparent-wall preference (to study escape responses), locomotion and freezing. The experimental conditions yielded distinctly different response patterns. Thigmotaxis was the most obvious response to white walls and it was significantly reduced after 3.5-hr habituation. It was not affected by any of the drugs. The reduction of social cohesion after 3.5-hr habituation and in the 0.5% ethanol group was probably the most interesting effect seen in this study. A role of anxiety herein was suggested but could not be established with certainty. Other hypotheses were also discussed. The large increase of distance-from-bottom resulting in swimming close to the water surface, which occurred in both buspirone groups and in the 0.5%-ethanol group, is most likely not an anxiolytic response, because of the discrepancy with the in the literature well-established time-course and the absence of any effect of 3.5-hr habituation or black walls on vertical measures. Finally, locomotion and duration freezing could not be specifically taken as indicators for the state of anxiety and the results concerning transparent-wall preference were not sufficient clear. We conclude that the neuronal and ethological mechanisms underlying the effects of habituation, white-aversion, buspirone and ethanol on anxiety-like behavioral responses are complex and need further exploration.