Chemobehavioural phenomics and behaviour-based psychiatric drug discovery in the zebrafish

Aquatic blues: modeling depression and antidepressant action in zebrafish

Depression is a serious psychiatric condition affecting millions of patients worldwide. Unipolar depression is characterized by low mood, anhedonia, social withdrawal and other severely debilitating psychiatric symptoms. Bipolar disorder manifests in alternating depressed mood and 'hyperactive' manic/hypomanic states. Animal experimental models are an invaluable tool for research into the pathogenesis of bipolar/unipolar depression, and for the development of potential treatments. Due to their high throughput value, genetic tractability, low cost and quick reproductive cycle, zebrafish (Danio rerio) have emerged as a promising new model species for studying brain disorders. Here, we discuss the developing utility of zebrafish for studying depression disorders, and outline future areas of research in this field. We argue that zebrafish represent a useful model organism for studying depression and its behavioral, genetic and physiological mechanisms, as well as for anti-depressant drug discovery.

Developing zebrafish models relevant to PTSD and other trauma- and stressor-related disorders

While post-traumatic stress disorder (PTSD) and other trauma- and stress-related disorders (TSRDs) represent a serious societal and public health concern, their pathogenesis is largely unknown. Given the clinical complexity of TSRD development and susceptibility, greater investigation into candidate biomarkers and specific genetic pathways implicated in both risk and resilience to trauma becomes critical. In line with this, numerous animal models have been extensively used to better understand the pathogenic mechanisms of PTSD and related TSRD. Here, we discuss the rapidly increasing potential of zebrafish as models of these disorders, and how their use may aid researchers in uncovering novel treatments and therapies in this field.

Aquatic toxicology of fluoxetine: understanding the knowns and the unknowns

Fluoxetine is one of the most prescribed psychotropic medications, and is an agent of increasing interest for environmental toxicology. Fish and other aquatic organisms are excellent models to study neuroactive small molecules like fluoxetine. However, prone to variance due to experimental factors, data obtained in these models need to be interpreted with caution, using proper experimental protocols, study designs, validated endpoints as well as well-established models and tests. Choosing the treatment protocol and dose range for fluoxetine and other serotonergic drugs is critical for obtaining valid test results and correct data interpretation. Here we discuss the value of aquatic models to study fluoxetine effects, based on prior high-quality research, and outline the directions of future translational studies in the field. We review fluoxetine-evoked phenotypes in acute vs. chronic protocols, discussing them in the contact of complex role of serotonin in behavioral regulation. We conclude that zebrafish and other aquatic models represent a useful in-vivo tool for fluoxetine pharmacology and (eco)toxicology research.

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.

Discovering novel neuroactive drugs through high-throughput behavior-based chemical screening in the zebrafish

Most neuroactive drugs were discovered through unexpected behavioral observations. Systematic behavioral screening is inefficient in most model organisms. But, automated technologies are enabling a new phase of discovery-based research in central nervous system (CNS) pharmacology. Researchers are using large-scale behavior-based chemical screens in zebrafish to discover compounds with new structures, targets, and functions. These compounds are powerful tools for understanding CNS signaling pathways. Substantial differences between human and zebrafish biology will make it difficult to translate these discoveries to clinical medicine. However, given the molecular genetic similarities between humans and zebrafish, it is likely that some of these compounds will have translational utility. We predict that the greatest new successes in CNS drug discovery will leverage many model systems, including in vitro assays, cells, rodents, and zebrafish.

Identification of marine neuroactive molecules in behaviour-based screens in the larval zebrafish

High-throughput behavior-based screen in zebrafish is a powerful approach for the discovery of novel neuroactive small molecules for treatment of nervous system diseases such as epilepsy. To identify neuroactive small molecules, we first screened 36 compounds (1–36) derived from marine natural products xyloketals and marine isoprenyl phenyl ether obtained from the mangrove fungus. Compound 1 demonstrated the most potent inhibition on the locomotor activity in larval zebrafish. Compounds 37–42 were further synthesized and their potential anti-epilepsy action was then examined in a PTZ-induced epilepsy model in zebrafish. Compound 1 and compounds 39, 40 and 41 could significantly attenuate PTZ-induced locomotor hyperactivity and elevation of c-fos mRNA in larval zebrafish. Compound 40 showed the most potent inhibitory action against PTZ-induced hyperactivity. The structure-activity analysis showed that the OH group at 12-position played a critical role and the substituents at the 13-position were well tolerated in the inhibitory activity of xyloketal derivatives. Thus, these derivatives may provide some novel drug candidates for the treatment of epilepsy.

Larval zebrafish model for FDA-approved drug repositioning for tobacco dependence treatment

Cigarette smoking remains the most preventable cause of death and excess health care costs in the United States, and is a leading cause of death among alcoholics. Long-term tobacco abstinence rates are low, and pharmacotherapeutic options are limited. Repositioning medications approved by the U.S. Food and Drug Administration (FDA) may efficiently provide clinicians with new treatment options. We developed a drug-repositioning paradigm using larval zebrafish locomotion and established predictive clinical validity using FDA-approved smoking cessation therapeutics. We evaluated 39 physician-vetted medications for nicotine-induced locomotor activation blockade. We further evaluated candidate medications for altered ethanol response, as well as in combination with varenicline for nicotine-response attenuation. Six medications specifically inhibited the nicotine response. Among this set, apomorphine and topiramate blocked both nicotine and ethanol responses. Both positively interact with varenicline in the Bliss Independence test, indicating potential synergistic interactions suggesting these are candidates for translation into Phase II clinical trials for smoking cessation.

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.

The spinning task: a new protocol to easily assess motor coordination and resistance in zebrafish

The increasing use of adult zebrafish in behavioral studies has created the need for new and improved protocols. Our investigation sought to evaluate the swimming behavior of zebrafish against a water current using the newly developed Spinning Task. Zebrafish were individually placed in a beaker containing a spinning magnetic stirrer and their latency to be swept into the whirlpool was recorded. We characterized that larger fish (>4 cm) and lower rpm decreased the swimming time in the Spinning Task. There was also a dose-related reduction in swimming after acute treatment with haloperidol, valproic acid, clonazepam, and ethanol, which alter coordination. Importantly, at doses that reduced swimming time in the Spinning Task, these drugs influenced absolute turn angle (ethanol increased and the other drugs decreased), but had no effect of distance travelled in a regular water tank. These results suggest that the Spinning Task is a useful protocol to add information to the assessment of zebrafish motor behavior.

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.

Fear, anxiety, and control in the zebrafish

Emotional responses are triggered by environmental signals and involve profound changes at multiple levels, from molecular to behavior. Much has been learnt about two emotions, fear and anxiety, by studying mammalian models. In particular, neural circuits and the corresponding molecular mechanisms essential for the learning and retention of fear, as well as the activation of anxiety, are well known. In contrast, little is known about how these emotions are terminated. The zebrafish is a newcomer to the world of emotion research. A number of assays for fear and anxiety now exist, but the underlying neural circuitry is largely undefined. Recent experiments, however, appear to provide a hint as to how anxiety is downregulated. In particular, they point to an essential role for a circuit involving the posterior septum, medial habenula, and interpeduncular nucleus. This evolutionarily conserved circuit may fulfill a similar function in mammals.

Behavioral screening for neuroactive drugs in zebrafish

The larval zebrafish has emerged asa vertebrate model system amenable to small molecule screens for probing diverse biological pathways. Two large-scale small molecule screens examined the effects of thousands of drugs on larval zebrafish sleep/wake and photomotor response behaviors. Both screens identified hundreds of molecules that altered zebrafish behavior in distinct ways. The behavioral profiles induced by these small molecules enabled the clustering of compounds according to shared phenotypes. This approach identified regulators of sleep/wake behavior and revealed the biological targets for poorly characterized compounds. Behavioral screening for neuroactive small molecules in zebrafish is an attractive complement to in vitro screening efforts, because the complex interactions in the vertebrate brain can only be revealed in vivo.

Predicting adult fish acute lethality with the zebrafish embryo: relevance of test duration, endpoints, compound properties, and exposure concentration analysis

The zebrafish embryo toxicity test has been proposed as an alternative for the acute fish toxicity test, which is required by various regulations for environmental risk assessment of chemicals. We investigated the reliability of the embryo test by probing organic industrial chemicals with a wide range of physicochemical properties, toxicities, and modes of toxic action. Moreover, the relevance of using measured versus nominal (intended) exposure concentrations, inclusion of sublethal endpoints, and different exposure durations for the comparability with reported fish acute toxicity was explored. Our results confirm a very strong correlation of zebrafish embryo to fish acute toxicity. When toxicity values were calculated based on measured exposure concentrations, the slope of the type II regression line was 1 and nearly passed through the origin (1 to 1 correlation). Measured concentrations also explained several apparent outliers. Neither prolonged exposure (up to 120 h) nor consideration of sublethal effects led to a reduced number of outliers. Yet, two types of compounds were less lethal to embryos than to adult fish: a neurotoxic compound acting via sodium channels (permethrin) and a compound requiring metabolic activation (allyl alcohol).

In vivo chemical screening for modulators of hematopoiesis and hematological diseases

In vivo chemical screening is a broadly applicable approach not only for dissecting genetic pathways governing hematopoiesis and hematological diseases, but also for finding critical components in those pathways that may be pharmacologically modulated. Both high-throughput chemical screening and facile detection of blood-cell-related phenotypes are feasible in embryonic/larval zebrafish. Two recent studies utilizing phenotypic chemical screens in zebrafish have identified several compounds that promote hematopoietic stem cell formation and reverse the hematopoietic phenotypes of a leukemia oncogene, respectively. These studies illustrate efficient drug discovery processes in zebrafish and reveal novel biological roles of prostaglandin E2 in hematopoietic and leukemia stem cells. Furthermore, the compounds discovered in zebrafish screens have become promising therapeutic candidates against leukemia and included in a clinical trial for enhancing hematopoietic stem cells during hematopoietic cell transplantation.

A larval zebrafish model of bipolar disorder as a screening platform for neuro-therapeutics

Modelling neurological diseases has proven extraordinarily difficult due to the phenotypic complexity of each disorder. The zebrafish has become a useful model system with which to study abnormal neurological and behavioural activity and holds promise as a model of human disease. While most of the disease modelling using zebrafish has made use of adults, larvae hold tremendous promise for the high-throughput screening of potential therapeutics. The further development of larval disease models will strengthen their ability to contribute to the drug screening process. Here we have used zebrafish larvae to model the symptoms of bipolar disorder by treating larvae with sub-convulsive concentrations of the GABA antagonist pentylenetetrazol (PTZ). A number of therapeutics that act on different targets, in addition to those that have been used to treat bipolar disorder, were tested against this model to assess its predictive value. Carbamazepine, valproic acid, baclofen and honokiol, were found to oppose various aspects of the PTZ-induced changes in activity. Lidocaine and haloperidol exacerbated the PTZ-induced activity changes and sulpiride had no effect. By comparing the degree of phenotypic rescue with the mechanism of action of each therapeutic we have shown that the low-concentration PTZ model can produce a number of intermediate phenotypes that model symptoms of bipolar disorder, may be useful in modelling other disease states, and will help predict the efficacy of novel therapeutics.

Behavioral barcoding in the cloud: embracing data-intensive digital phenotyping in neuropharmacology

For decades, studying the behavioral effects of individual drugs and genetic mutations has been at the heart of efforts to understand and treat nervous system disorders. High-throughput technologies adapted from other disciplines (e.g., high-throughput chemical screening, genomics) are changing the scale of data acquisition in behavioral neuroscience. Massive behavioral datasets are beginning to emerge, particularly from zebrafish labs, where behavioral assays can be performed rapidly and reproducibly in 96-well, high-throughput format. Mining these datasets and making comparisons across different assays are major challenges for the field. Here, we review behavioral barcoding, a process by which complex behavioral assays are reduced to a string of numeric features, facilitating analysis and comparison within and across datasets.

Distinct models of induced hyperactivity in zebrafish larvae

The analysis of behavioural hyperactivity can provide insights into how perturbations in normal activity may be linked to the altered function of the nervous system and possibly the symptoms of disease. As a small vertebrate zebrafish have numerous experimental advantages that are making them a powerful model for these types of studies. While the majority of behavioural studies have focused on adult zebrafish, it has become apparent that larvae can also display complex stereotypical patterns of behaviour. Here we have used three compounds (pentylenetetrazole (PTZ), aconitine and 4-aminopyridine) that have different neuronal targets (GABA, sodium and potassium channels), to induce distinct patterns of hyperactivity in larvae. Our studies have revealed that each compound produces a number of distinct concentration-dependent activity patterns. This work has shown for the first time that at sub-convulsive concentrations, PTZ can reverse the normal behavioural response to alternating periods of light and dark in zebrafish larvae. It also appears that both PTZ and 4-aminopyridine produce distinct changes in the normal startle response patterns immediately following light/dark transitions that may be the result of an elevation in stress/anxiety. Aconitine produces a general elevation in activity that eliminates the normal response to light and dark. In addition to differences in the patterns of behaviour each compound also produces a unique pattern of c-fos (an immediate early gene) expression in the brain. While more work is required to make direct links between region specific neuronal activity and individual behaviours, these models provide a framework with which to study and compare mechanistically different types of inducible behaviours.

Developmental exposure to valproate and ethanol alters locomotor activity and retino-tectal projection area in zebrafish embryos

Given the minimal developmental neurotoxicity data available for the large number of new and existing chemicals, there is a critical need for alternative methods to identify and prioritize chemicals for further testing. We outline a developmental neurotoxicity screening approach using zebrafish embryos. Embryos were exposed to nominal concentrations of either valproate or ethanol then examined for lethality, malformation, nervous system structure and locomotor activity. Developmental valproate exposure caused locomotor activity changes at concentrations that did not result in malformations and showed a concentration-dependent decrease in retino-tectal projection area in the optic tectum. Developmental ethanol exposure also affected retino-tectal projection area at concentrations below those concentrations causing malformations. As both valproate and ethanol are known human developmental neurotoxicants, these results add to the growing body of evidence showing the potential utility of zebrafish in screening compounds for mammalian developmental neurotoxicity.

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 profiling of zebrafish embryos exposed to a panel of 60 water-soluble compounds

The zebrafish is a powerful whole animal model which is complementary to in vitro and mammalian models. It has been shown to be applicable to the high-throughput behavioral screening of compound libraries. We have analysed 60 water-soluble toxic compounds covering a range of common drugs, toxins and chemicals, and representing various pharmacological mechanisms. Wild-type zebrafish larvae were cultured individually in defined buffer in 96 well plates. They were exposed for a 96h period starting at 24h post fertilization (hpf). A logarithmic concentration series was used for range-finding, followed by a narrower geometric series for LC(50) determination. LC(50) values were determined at 24h intervals and behavioral testing was carried out on day 5. We used the visual motor response test, in which movement of individual larvae was analysed using automated video-tracking. For all compounds, LC(50) values were found to decrease as the embryo developed. The majority of compounds (57/60) produced an effect in both the basal (lights on) and challenge phases (lights off) of the behavioral assay. These effects were either (i) suppression of locomotor activity (monotonic concentration-response); (ii) stimulation then suppression (biphasic response); (iii) stimulation (monotonic response). We conclude that behavioral assays with zebrafish embryos could be useful for pharmaceutical efficacy and toxicity screening. The precise phenotypic outcome obtained with behavioral assay varies with compound class.

Zebrafish embryos and larvae: a new generation of disease models and drug screens

Technological innovation has helped the zebrafish embryo gain ground as a disease model and an assay system for drug screening. Here, we review the use of zebrafish embryos and early larvae in applied biomedical research, using selected cases. We look at the use of zebrafish embryos as disease models, taking fetal alcohol syndrome and tuberculosis as examples. We discuss advances in imaging, in culture techniques (including microfluidics), and in drug delivery (including new techniques for the robotic injection of compounds into the egg). The use of zebrafish embryos in early stages of drug safety-screening is discussed. So too are the new behavioral assays that are being adapted from rodent research for use in zebrafish embryos, and which may become relevant in validating the effects of neuroactive compounds such as anxiolytics and antidepressants. Readouts, such as morphological screening and cardiac function, are examined. There are several drawbacks in the zebrafish model. One is its very rapid development, which means that screening with zebrafish is analogous to "screening on a run-away train." Therefore, we argue that zebrafish embryos need to be precisely staged when used in acute assays, so as to ensure a consistent window of developmental exposure. We believe that zebrafish embryo screens can be used in the pre-regulatory phases of drug development, although more validation studies are needed to overcome industry scepticism. Finally, the zebrafish poses no challenge to the position of rodent models: it is complementary to them, especially in early stages of drug research.

Assessing locomotor activity in larval zebrafish: Influence of extrinsic and intrinsic variables

The U.S. Environmental Protection Agency is evaluating methods to screen and prioritize large numbers of chemicals for developmental toxicity. We are exploring methods to detect developmentally neurotoxic chemicals using zebrafish behavior at 6 days of age. The behavioral paradigm simultaneously tests individual larval zebrafish under both light and dark conditions in a 96-well plate using a video tracking system. We have found that many variables affect the level or pattern of locomotor activity, including age of the larvae, size of the well, and the presence of malformations. Some other variables, however, do not appear to affect larval behavior including type of rearing solution (10% Hank's vs. 1:3 Danieau vs 60 mg/kg Instant Ocean vs 1× and 1:10× EPA Moderately Hard Water). Zebrafish larval behavior using a microtiter plate format may be an ideal endpoint for screening developmentally neurotoxic chemicals, but it is imperative that many test variables be carefully specified and controlled.

The use of the zebrafish model in stress research

The study of the causes and mechanisms underlying psychiatric disorders requires the use of non-human models for the test of scientific hypotheses as well as for use in pre-clinical drug screening and discovery. This review argues in favor of the use of zebrafish as a novel animal model to study the impact of early (stressful) experiences on the development of differential stress phenotypes in later life. This phenomenon is evolutionary conserved among several vertebrate species and has relevance to the etiology of psychiatric disorders. Why do we need novel animal models? Although significant progress has been achieved with the use of traditional mammalian models, there are major pitfalls associated with their use that impedes progress on two major fronts: 1) uncovering of the molecular mechanisms underlying aspects of compromised (stress-exposed) brain development relevant to the etiology of psychiatric disorders, and 2) ability to develop high-throughput technology for drug discovery in the field of psychiatry. The zebrafish model helps resolve these issues. Here we present a conceptual framework for the use of zebrafish in stress research and psychiatry by addressing three specific domains of application: 1) stress research, 2) human disease mechanisms, and 3) drug discovery. We also present novel methodologies associated with the development of the zebrafish stress model and discuss how such methodologies can contribute to remove the main bottleneck in the field of drug discovery.

Zebrafish behavioural assays of translational relevance for the study of psychiatric disease

Understanding the pathogenesis of the complex behavioural disorders that constitute psychiatric disease is a major challenge for biomedical research. Assays in rodents have contributed significantly to our understanding of the neural basis of behavioural disorders and continue to be one of the main focuses for the development of novel therapeutics. Now, owing to their genetic tractability and optical transparency (allowing in vivo imaging of circuit function) and the rapid expansion of genetic tools, zebrafish are becoming increasingly popular for behavioural genetic research. The increased development of behavioural assays in zebrafish raises the possibility of exploiting the advantages of this system to identify molecular mechanisms contributing to behavioural phenotypes associated with psychiatric disorders as well as potential therapeutics. This mini-review describes behavioural paradigms in zebrafish that can be used to address endophenotypes associated with psychiatric disease. The content reflects the interests of the author and covers tests of cognitive functions, response choice and inhibition, social interaction and executive function.

Antipsychotic drugs reverse MK-801-induced cognitive and social interaction deficits in zebrafish (Danio rerio)

Schizophrenia is a severe mental illness characterized by positive and negative symptoms and cognitive deficits. Reduction of glutamatergic neurotransmission by NMDA receptor antagonists mimics symptoms of schizophrenia. Modeling social interaction and cognitive impairment in animals can be of great benefit in the effort to develop novel treatments for negative and cognitive symptoms of schizophrenia. Studies have demonstrated that these behavioral changes are, in some cases, sensitive to remediation by antipsychotic drugs. The zebrafish has been proposed as a candidate to study the in vivo effects of several drugs and to discover new pharmacological targets. In the current study we investigated the ability of antipsychotic drugs to reverse schizophrenia-like symptoms produced by the NMDA receptor antagonist MK-801. Results showed that MK-801 (5μM) given pre-training hindered memory formation while both atypical antipsychotics sulpiride (250μM) and olanzapine (50μM) improved MK-801-induced amnesia. The same change was observed in the social interaction task, where atypical antipsychotics reversed the MK-801-induced social interaction deficit whereas the typical antipsychotic haloperidol (9μM) was ineffective to reverse those behavioral deficits. Therefore, MK-801-treated zebrafish showed some behavioral features observed in schizophrenia, such as cognitive and social interaction deficits, which were reverted by current available atypical drugs.

Using the zebrafish photomotor response for psychotropic drug screening

Because psychotropic drugs affect behavior, we can use changes in behavior to discover psychotropic drugs. The original prototypes of most neuroactive medicines were discovered in humans, rodents and other model organisms. Most of these discoveries were made by chance, but the process of behavior based drug discovery can be made more systematic and efficient. Fully automated platforms for analyzing the behavior of embryonic zebrafish capture digital video recordings of animals in each individual well of a 96-well plate before, during, and after a series of stimuli. To analyze systematically the thousands of behavioral recordings obtained from a large-scale chemical screen, we transform these behavioral recordings into numerical barcodes, providing a concise and interpretable summary of the observed phenotypes in each well. Systems-level analysis of these behavioral phenotypes generate testable hypotheses about the molecular mechanisms of poorly understood drugs and behaviors. By combining the in vivo relevance of behavior-based phenotyping with the scale and automation of modern drug screening technologies, systematic behavioral barcoding represents a means of discovering psychotropic drugs and provides a powerful, systematic approach for unraveling the complexities of vertebrate behavior.

Investigating regeneration and functional integration of CNS neurons: lessons from zebrafish genetics and other fish species

Zebrafish possess a robust, innate CNS regenerative ability. Combined with their genetic tractability and vertebrate CNS architecture, this ability makes zebrafish an attractive model to gain requisite knowledge for clinical CNS regeneration. In treatment of neurological disorders, one can envisage replacing lost neurons through stem cell therapy or through activation of latent stem cells in the CNS. Here we review the evidence that radial glia are a major source of CNS stem cells in zebrafish and thus activation of radial glia is an attractive therapeutic target. We discuss the regenerative potential and the molecular mechanisms thereof, in the zebrafish spinal cord, retina, optic nerve and higher brain centres. We evaluate various cell ablation paradigms developed to induce regeneration, with particular emphasis on the need for (high throughput) indicators that neuronal regeneration has restored sensory or motor function. We also examine the potential confound that regeneration imposes as the community develops zebrafish models of neurodegeneration. We conclude that zebrafish combine several characters that make them a potent resource for testing hypotheses and discovering therapeutic targets in functional CNS regeneration. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.

In the swim of things: recent insights to neurogenetic disorders from zebrafish

The advantage of zebrafish as a model to study human pathologies lies in the ease of manipulating gene expression in vivo. Here we focus on recent progress in our understanding of motor neuron diseases and neurodevelopmental disorders and discuss how novel technologies will permit further disease models to be developed. Together these advances set the stage for this simple functional model, with particular advantages for transgenesis, multigenic analyses and chemical biology, to become uniquely suited for advancing the functional genomics of neurological and possibly psychiatric diseases - from understanding the genetics and cell biology of degenerative and developmental disorders to the discovery of therapeutics.

Small molecule screening in zebrafish: an in vivo approach to identifying new chemical tools and drug leads

In the past two decades, zebrafish genetic screens have identified a wealth of mutations that have been essential to the understanding of development and disease biology. More recently, chemical screens in zebrafish have identified small molecules that can modulate specific developmental and behavioural processes. Zebrafish are a unique vertebrate system in which to study chemical genetic systems, identify drug leads, and explore new applications for known drugs. Here, we discuss some of the advantages of using zebrafish in chemical biology, and describe some important and creative examples of small molecule screening, drug discovery and target identification.

Using zebrafish to assess the impact of drugs on neural development and function

BACKGROUND: Zebrafish is becoming an increasingly attractive model organism for understanding biology and developing therapeutics, because as a vertebrate, it shares considerable similarity with mammals in both genetic compositions and tissue/organ structures, and yet remains accessible to high throughput phenotype-based genetic and small molecule compound screening. OBJECTIVE/METHOD: The focus of this review is on the nervous system, which is arguably the most complex organ and known to be afflicted by more than six hundred disorders in humans. I discuss the past, present, and future of using zebrafish to assess the impact of small molecule drugs on neural development and function, in light of understanding and treating neurodevelopmental disorders such as autism, neurodegenerative disorders including Alzheimer's, Parkinson's, and Hungtington's disease, and neural system dysfunctions such as anxiety/depression and addiction. CONCLUSION: These studies hold promise to reveal fundamental mechanisms governing nervous system development and function, and to facilitate small molecule drug discovery for the many types of neurological disorders.

Zebrafish embryos as models for embryotoxic and teratological effects of chemicals

The experimental virtues of the zebrafish embryo such as small size, development outside of the mother, cheap maintenance of the adult made the zebrafish an excellent model for phenotypic genetic and more recently also chemical screens. The availability of a genome sequence and several thousand mutants and transgenic lines together with gene arrays and a broad spectrum of techniques to manipulate gene functions add further to the experimental strength of this model. Pioneering studies suggest that chemicals can have in many cases very similar toxicological and teratological effects in zebrafish embryos and humans. In certain areas such as cardiotoxicity, the zebrafish appears to outplay the traditional rodent models of toxicity testing. Several pilot projects used zebrafish embryos to identify new chemical entities with specific biological functions. In combination with the establishment of transgenic sensor lines and the further development of existing and new automated imaging systems, the zebrafish embryos could therefore be used as cost-effective and ethically acceptable animal models for drug screening as well as toxicity testing.