Zebrafish neurobehavioral phenomics for aquatic neuropharmacology and toxicology research

Ayurvedic processing of α-HgS gives novel physicochemistry and distinct toxicokinetics in zebrafish

Rasasindura (RS) is an Ayurvedic medicine, which contains ∼99% α-HgS. It is used as a rejuvenating agent and commonly used to treat diseases such as syphilis, insomnia, high fever, and nervous disorders. Cinnabar ore (α-HgS) is a well-known mineral, which is readily available. Despite it, Ayurvedic practitioners adopted an involved and tedious procedure for the preparation of RS. In this study, three samples, one was Ayurvedic (RS), the second one was the commercial (HGS), and the third one was cinnabar ore (CN), were physiochemically examined. Zebrafish model was employed for toxicity study with an oral dose of 100 mg/kg/day for the three samples for 10 days. We found that RS conferred novel physicochemical properties, which were not seen in HGS and CN. Significantly, the average crystallite size of RS was lowest (26 nm) as compared to HGS (31 nm) and CN (34 nm), and the rate of increase of crystallite size with temperature was lowest in RS. RS did not show any significant behavioral toxicity in zebrafish, which was seen with the HGS-and CN-treated zebrafish. HGS-and CN-treated zebrafish showed a significantly high (∗∗∗p < 0.001) decrease (77 ± 7.6% and 51 ± 6.5%, respectively) of glutathione (GSH) levels in the brain, however, for RS-treated zebrafish, the change of GSH was insignificant (26 ± 2.5%, p > 0.05). Interestingly, HGS significantly altered the γ-aminobutyric acid (GABA) in brain tissue. Therefore, among all three samples, RS exhibited the lowest toxicity, which can be credited to the distinct toxicokinetics by these samples.

Developmental toxicity of trichloroethylene in zebrafish (Danio rerio)

Trichloroethylene (TCE), an industrial solvent and degreaser, is an environmental toxicant that contaminates over half of Superfund sites, is a known carcinogen, and is linked to congenital defects and neurodegenerative disease. The developmental toxicity of TCE near ecologically relevant levels needs further characterization in order to better assess health risks of exposure. In this study, the toxicodynamics of TCE in the zebrafish (Danio rerio) model was investigated through the establishment of a LC50 concentration and by monitoring the acute developmental toxicity of ecologically relevant concentrations (0, 5, 50, and 500 parts per billion; ppb) of TCE during two different exposure lengths (1-72 hours post fertilization (hpf) and 1-120 hpf). Acute developmental toxicity was assessed by monitoring survival and hatching, larval morphology, larval heart rate, and behavioral responses during an embryonic photomotor response test and a larval visual motor response test. Embryonic exposure to TCE was associated with decreased percent hatch at 48 hpf, altered larval morphology, increased heart rate, and altered behavioral responses during the photomotor response test and visual motor response test. Larval morphology and behavioral alterations were more pronounced in the 1-120 hpf exposure length trials. The observed alterations suggest developmental TCE toxicity is still a concern at regulatory concentrations and that timing of exposure influences developmental toxicity.

The effect of copper on behaviour, memory, and associative learning ability of zebrafish (Danio rerio)

Copper is an essential element in many biological processes, but may exert toxic effects at levels surplus to metabolic requirements. Herein we assess the effect of copper on zebrafish behaviour using two assays, namely the novel tank diving test and a T-maze test with food reward. Novel tank diving tests were conducted on days 0, 4, and 10 of a 10 day Cu exposure (at concentrations of 0.77 μM (25% of the 240 h LC50) and 1.52 μM (50% of the 240 h LC50) to assess the alterations of behavioural responses in repeating novel tank diving assays and the effect of Cu on these patterns. Results demonstrate habituation to novelty, which is an indicator of spatial memory. Copper exposure had no effect on the latency of entry into the upper zones of the tank, nor on the total time spent therein, but did cause a greater number of freezing bouts in comparison to the control group. Additionally, Cu exposure had no effect on the habituation responses of zebrafish. Using the T-maze assay, we tested the effect of prior exposure to Cu for 10 days on subsequent behavioural trainings. The T-maze protocol was based on associative learning, where a visual stimulus (colour) was linked with a natural stimulus (food). Results of the control group showed that zebrafish are able to perform associative learning tasks. Moreover, Cu was found to negatively affect the associative learning capabilities. Specifically, while zebrafish in the control group achieved a significant number of correct choices (leading to food reward) throughout the T-maze training, such a trend was not observed for Cu exposed fish. Thus at the exposure concentrations and exposure times considered herein, Cu has no determinative impact on instinctual behavioural responses of zebrafish in repeated novel tank diving assays but does limit the associative learning capabilities.

Maternal ethanol consumption before paternal fertilization: Stimulation of hypocretin neurogenesis and ethanol intake in zebrafish offspring

There are numerous clinical and pre-clinical studies showing that exposure of the embryo to ethanol markedly affects neuronal development and stimulates alcohol drinking and related behaviors. In rodents and zebrafish, our studies show that embryonic exposure to low-dose ethanol, in addition to increasing voluntary ethanol intake during adolescence, increases the density of hypothalamic hypocretin (hcrt) neurons, a neuropeptide known to regulate reward-related behaviors. The question addressed here in zebrafish is whether maternal ethanol intake before conception also affects neuronal and behavioral development, phenomena suggested by clinical reports but seldom investigated. To determine if preconception maternal ethanol consumption also affects these hcrt neurons and behavior in the offspring, we first standardized a method of measuring voluntary ethanol consumption in AB strain adult and larval zebrafish given gelatin meals containing 10% or 0.1% ethanol, respectively. We found the number of bites of gelatin to be an accurate measure of intake in adults and a strong predictor of blood ethanol levels, and also to be a reliable indicator of intake in larval zebrafish. We then used this feeding paradigm and live imaging to examine the effects of preconception maternal intake of 10% ethanol-gelatin compared to plain-gelatin for 14 days on neuronal development in the offspring. Whereas ethanol consumption by adult female HuC:GFP transgenic zebrafish had no impact on the number of differentiated HuC⁺ neurons at 28 h post-fertilization (hpf), preconception ethanol consumption by adult female hcrt:EGFP zebrafish significantly increased the number of hcrt neurons in the offspring, an effect observed at 28 hpf and confirmed at 6 and 12 days post-fertilization (dpf). This increase in hcrt neurons was primarily present on the left side of the brain, indicating asymmetry in ethanol's actions, and it was accompanied by behavioral changes in the offspring, including a significant increase in novelty-induced locomotor activity but not thigmotaxis measured at 6 dpf and also in voluntary consumption of 0.1% ethanol-gelatin at 12 dpf. Notably, these measures of ethanol intake and locomotor activity stimulated by preconception ethanol were strongly, positively correlated with the number of hcrt neurons. These findings demonstrate that preconception maternal ethanol consumption affects the brain and behavior of the offspring, producing effects similar to those caused by embryonic ethanol exposure, and they provide further evidence that the ethanol-induced increase in hcrt neurogenesis contributes to the behavioral disturbances caused by ethanol.

The interactive effect of copper(II) and conspecific alarm substances on behavioural responses of zebrafish (Danio rerio)

Environmental contaminants such as metal ions can have detrimental effects on aquatic organisms at the molecular, organismal and population levels. In the present work, we examined the interactive effect of Cu(II) and conspecific alarm substance on zebrafish behavioural responses utilizing the novel tank diving assay. To this end, 3 novel tank diving tests (on day 0, 3 and 10 of the experimental phase) were conducted on zebrafish in 4 experimental groups: (1) control: no Cu(II) and no alarm substance, (2) Cu(II) only: exposed to 0.78 μM Cu(II) (25 % of the 240 h LC50) in the home tank for 10 days, (3) alarm substance only: exposed to alarm substance for 6 min concomitant with behavioural testing, and (4) Cu(II) + alarm substance: exposed to 0.78 μM Cu(II) in the home tank for 10 days and treated with alarm substance for 6 min during the behavioural testing. Results showed robust habituation response of zebrafish. Exposure to Cu(II) did not affect the behavioural phenotypes of zebrafish in the novel tank diving test or habituation responses. Alarm substance treatment evoked strong anxiety-like behaviour. Finally, zebrafish in the Cu(II) + alarm substance group lost their sensitivity to alarm substance in repeated novel tank assays throughout the concomitant Cu(II) exposure; this observation is tentatively ascribed to Cu(II)-induced olfactory impairment.

Development of 1,3-thiazole analogues of imidazopyridines as potent positive allosteric modulators of GABAA receptors

Structure-activity relationship studies were conducted in the search for 1,3-thiazole isosteric analogs of imidazopyridine drugs (Zolpidem, Alpidem). Three series of novel γ-aminobutyric acid receptor (GABA_AR) ligands belonging to imidazo[2,1-b]thiazoles, imidazo[2,1-b][1,3,4]thiadiazoles, and benzo[d]imidazo[2,1-b]thiazoles were synthesized and characterized as active agents against GABA_AR benzodiazepine-binding site. In each of these series, potent compounds were discovered using a radioligand competition binding assay. The functional properties of highest-affinity compounds 28 and 37 as GABA_AR positive allosteric modulators (PAMs) were determined by electrophysiological measurements. In vivo studies on zebrafish demonstrated their potential for the further development of anxiolytics. Using the OECD "Fish, Acute Toxicity Test" active compounds were found safe and non-toxic. Structural bases for activity of benzo[d]imidazo[2,1-b]thiazoles were proposed using molecular docking studies. The isosteric replacement of the pyridine nuclei by 1,3-thiazole, 1,3,4-thiadiazole, or 1,3-benzothiazole in the ring-fused imidazole class of GABA_AR PAMs was shown to be promising for the development of novel hypnotics, anxiolytics, anticonvulsants, and sedatives drug-candidates.

Fish behavior: A promising model for aquatic toxicology research

Fish behaviors have great potential as models for the study of pharmacology, genetics, and neuroscience. Zebrafish (Danio rerio), Japanese medaka (Oryzias latipes) and Chinese rare minnow (Gobiocypris rarus) are popular freshwater animal models. However, their behavioral use in aquatic toxicology research is generally hampered by oversimplified behavioral tasks and the fact that they are not well-developed animal models for toxicology. Here, this study presented a comparative analysis of multiple behavioral traits (i.e., anxiety-like behavior, novel object recognition, social preferences, habituation to light-dark stimulus and noise stimulus, and spatial learning and memory). We found that only medaka (d-rR) presented a weak or no response to repeated light-dark stimulus and noise stimulus. In addition, no significant behavioral changes were observed for the three species of juvenile fish models after 7 days of exposure to 0.01% v/v carrier solvents (i.e., ethanol, acetone, and DMSO). In contrast to zebrafish and Chinese rare minnow, medaka showed no significant changes in spatial memory after subacute exposure to 1 mg/L imidacloprid or 2.5 μg/L chlorpyrifos (cpf); instead, a hyperactivity response in the open field test and reduced social time were induced by cpf and imidacloprid, respectively. Our results suggest that: (1) behavioral effects are negligible when using <0.01% v/v carrier solvents for behavioral assessment; (2) given the differences in sensitivities of behavioral responses, a single behavior used alone as an endpoint may be insufficient for estimating the toxic impacts of pesticides or other environmental contaminants. In conclusion, these results could have major implications for aquatic toxicology research and water quality monitoring and ecotoxicological risk assessment.

How toxic is a non-toxic nanomaterial: Behaviour as an indicator of effect in Danio rerio exposed to nanogold

Gold nanoparticles are used as drug delivery vectors based on the assumption that they have low toxicity. Literature has, however, produced conflicting results over the last few years. As such, this study aimed to investigate the toxicological effects of nanogold (nAu) on several indicators that range from subcellular to whole-organism level. Gene regulation, changes in oxidative stress biomarkers and swimming performance were assessed in Danio rerio (zebrafish) following exposures to nAu. Adult zebrafish were exposed in vivo to nAu for 96 h and swimming performance measured post-exposure. Liver tissue was collected for DNA microarray and Real-Time Polymerase Chain Reactions (RT-PCR) analyses to determine changes in gene expression (catalase, superoxide dismutase and metallothioneins) and protein biomarker analyses (catalase, superoxide dismutase, acetylcholine esterase, malondialdehyde, cellular energy allocation and metallothionein) were performed on whole-body samples. Swimming behaviour was assessed in 1.1 L Tecniplast™ tanks for a period of six hours and videos were analysed using Noldus EthoVision software. Critical swimming speed was measured in a Loligo® swimming tunnel. The DNA microarray revealed that fish exposed to 20 mg/L differed most from the control group. At 20 mg/L there was a significant increase in gene expression for all genes analysed but this didn't translate to significant responses in protein biomarker levels except for an increase in protein carbonyl formation. The behaviour results demonstrated significant changes in distance moved, swimming speed, acceleration bouts, zone alterations and time spent within the top zone - responses that are usually observed in fish responding to toxicological stress. Furthermore, the critical swimming speed of exposed fish was decreased significantly compared to the control. Since swimming performance and social interaction among zebrafish is essential to their survival, whole-organism behaviour that suggests a toxicological response after exposure to nAu is in agreement with the genetic responses measured in this study.

Zebrafish neurobehavioral phenomics applied as the behavioral warning methods for fingerprinting endocrine disrupting effect by lead exposure at environmentally relevant level

Environmental lead (Pb) exposure is a great hazard to the public health. Although environmentally relevant Pb poisoning is preventable, insidious Pb contaminants are still a major threat to human health. Herein, we reported that exposure to Pb at environmentally relevant concentration level (1 μg/L, 10 μg/L and 100 μg/L), disturbed the courtship behavior of adult male zebrafish and further altered the transcriptional patterns of key genes involved in testicular steroidogenesis (igf3, amh, piwil1, lhcgr, fshr, cyp11c1, star, cyp19a1a, cyp19a1b) and apoptosis (bax, cytoC, caspase 9, caspase 3, puma). Both the behavioral and the transcriptional profiles share a similar biphasic dose response, with stimulatory effects after low-level exposure and inhibitory effects after high-level exposure. This results revealed the endocrine disrupting effects of Pb even at an environmentally relevant level within the concentration range of ambient water quality criteria (AWQC) and the reliability of locomotion fingerprint as the indicator for detecting the risk induced by Pb pollution. Current research, for the first time, employed the ZebraTower system as the biological early warning system (BEWS) to find that Pb exerted biphasic effects on the courtship behavior and endocrine regulation of male adult zebrafish. Methodologically, we firstly propose an efficient solution to monitor and assess the risk of Pb exposure by combining the (BEWS) and data analyzing methods such as zebrafish phenomics, which would make a contribution to the detection and prevention of environmentally relevant Pb poisoning.

Identification of compounds that rescue otic and myelination defects in the zebrafish adgrg6 (gpr126) mutant

Adgrg6 (Gpr126) is an adhesion class G protein-coupled receptor with a conserved role in myelination of the peripheral nervous system. In the zebrafish, mutation of adgrg6 also results in defects in the inner ear: otic tissue fails to down-regulate versican gene expression and morphogenesis is disrupted. We have designed a whole-animal screen that tests for rescue of both up- and down-regulated gene expression in mutant embryos, together with analysis of weak and strong alleles. From a screen of 3120 structurally diverse compounds, we have identified 68 that reduce versican b expression in the adgrg6 mutant ear, 41 of which also restore myelin basic protein gene expression in Schwann cells of mutant embryos. Nineteen compounds unable to rescue a strong adgrg6 allele provide candidates for molecules that may interact directly with the Adgrg6 receptor. Our pipeline provides a powerful approach for identifying compounds that modulate GPCR activity, with potential impact for future drug design.

Zebrafish behavioral phenomics applied for phenotyping aquatic neurotoxicity induced by lead contaminants of environmentally relevant level

Environmental lead (Pb) exposure is a worldwide threat due to the ubiquitous contamination. Although the adverse effects of Pb on human health have previously been extensively explored, the eco-toxicological effects on aquatic vertebrates still need further investigation. In addition, there is a paucity in the knowledge of behavioral and physiological effects of Pb within the range of environmental relevant concentration (under 100 μg/L) on aquatic organisms such as zebrafish. Herein, we demonstrated that adult male zebrafish (Danio rerio) exposed to Pb at environmental concentration level (1 μg/L, 10 μg/L and 100 μg/L) for 14 days, exhibited obvious neuro-behavioral alteration including disturbed light dark preference, impaired exploratory behaviors and inhibited spatial working memory. The alteration of entire behavioral profiles was further associated with the disturbed expression patterns of mRNA level of key genes involved in neurodevelopment (gap43, syn2a, th, dat, and drd1b), neurotoxic effects (c-fos and gfap), and stress responses (tap, mt1, hsp70, and hsp90). To determine the comprehensively effect of aquatic contaminants on the entire behavioral profiles, behavioral phenomic data were obtained by hierarchical clustering analysis. Overall, we employed behavioral phenomics methods to find that Pb within standard chronic Pb toxic criteria, significantly altered behavioral phenotype and brain physiology, which would exert profound ecological consequences and offer the reference for adjustment of aquatic toxic criteria.

Zebrafish exposure to diphenyl diselenide-loaded polymeric nanocapsules caused no behavioral impairments and brain oxidative stress

Previous findings showed that the nanoencapsulation of diphenyl diselenide [(PhSe)₂], an organoselenium compound, provided superior biological effects and lower toxicological potential than its free form in vitro. However, few studies reported the behavioral and biochemical effects of this nanocapsules formulation in vivo. Zebrafish (Danio rerio) has emerged as a useful animal model to determine the pharmacological and toxicological effects of nanoparticles. Here, we evaluated the behavioral and brain oxidative effects after zebrafish exposure to (PhSe)₂-loaded nanocapsules. Formulations were prepared by interfacial deposition of preformed polymer method and later tested at concentrations ranging from 0.1 to 2.0 μM. Both locomotor and exploratory activities were assessed in the novel tank diving test. Moreover, brain oxidative status was determined by measuring thiobarbituric acid-reactive substance levels, glutathione peroxidase, glutathione redutase and glutathione S-transferase activities. (PhSe)₂-loaded nanocapsules showed no alteration on travelled distance, immobility, and erratic swimming, suggesting the absence of behavioral impairments. Interestingly, the higher concentration tested had anxiolytic-like effects, since animals spent more time in the top area and showed a decreased thigmotaxis behavior. Biochemical analysis demonstrated that the concentrations used in this study did not affect oxidative stress-related parameters in brain samples, reinforcing the low toxicological potential of the formulation. In conclusion, the exposure to (PhSe)₂-loaded nanocapsules caused no locomotor impairments as well as did not modify the oxidative status of zebrafish brain, indicating that this formulation is probably non-toxic and promising for future pharmacological studies.

Making Waves: New Developments in Toxicology With the Zebrafish

The laboratory zebrafish (Danio rerio) is now an accepted model in toxicologic research. The zebrafish model fills a niche between in vitro models and mammalian biomedical models. The developmental characteristics of the small fish are strategically being used by scientists to study topics ranging from high-throughput toxicity screens to toxicity in multi- and transgenerational studies. High-throughput technology has increased the utility of zebrafish embryonic toxicity assays in screening of chemicals and drugs for toxicity or effect. Additionally, advances in behavioral characterization and experimental methodology allow for observation of recognizable phenotypic changes after xenobiotic exposure. Future directions in zebrafish research are predicted to take advantage of CRISPR-Cas9 genome editing methods in creating models of disease and interrogating mechanisms of action with fluorescent reporters or tagged proteins. Zebrafish can also model developmental origins of health and disease and multi- and transgenerational toxicity. The zebrafish has many advantages as a toxicologic model and new methodologies and areas of study continue to expand the usefulness and application of the zebrafish.

Understanding Central Nervous System Effects of Deliriant Hallucinogenic Drugs through Experimental Animal Models

Hallucinogenic drugs potently alter human behavior and have a millennia-long history of use for medicinal and religious purposes. Interest is rapidly growing in their potential as CNS modulators and therapeutic agents for brain conditions. Antimuscarinic cholinergic drugs, such as atropine and scopolamine, induce characteristic hyperactivity and dream-like hallucinations and form a separate group of hallucinogens known as "deliriants". Although atropine and scopolamine are relatively well-studied drugs in cholinergic physiology, deliriants represent the least-studied class of hallucinogens in terms of their behavioral and neurological phenotypes. As such, novel approaches and new model organisms are needed to investigate the CNS effects of these compounds. Here, we comprehensively evaluate the preclinical effects of deliriant hallucinogens in various animal models, their mechanisms of action, and potential interplay with other signaling pathways. We also parallel experimental and clinical findings on deliriant agents and outline future directions of translational research in this field.

The Utility of Zebrafish as a Model for Screening Developmental Neurotoxicity

The developing central nervous system and the blood brain barrier are especially vulnerable and sensitive to different chemicals, including environmental contaminants and drugs. Developmental exposure to these compounds has been involved in several neurological disorders, such as autism spectrum disorders as well as Alzheimer's and Parkinson's diseases. Zebrafish (Danio Rerio) have emerged as powerful toxicological model systems that can speed up chemical hazard assessment and can be used to extrapolate neurotoxic effects that chemicals have on humans. Zebrafish embryos and larvae are convenient for high-throughput screening of chemicals, due to their small size, low-cost, easy husbandry, and transparency. Additionally, zebrafish are homologous to other higher order vertebrates in terms of molecular signaling processes, genetic compositions, and tissue/organ structures as well as neurodevelopment. This mini review underlines the potential of the zebrafish as complementary models for developmental neurotoxicity screening of chemicals and describes the different endpoints utilized for such screening with some studies illustrating their use.

Comparative behavioral toxicology with two common larval fish models: Exploring relationships among modes of action and locomotor responses

Behavioral responses inform toxicology studies by rapidly and sensitively detecting molecular initiation events that propagate to physiological changes in individuals. These behavioral responses can be unique to chemical specific mechanisms and modes of action (MOA) and thus present diagnostic utility. In an initial effort to explore the use of larval fish behavioral response patterns in screening environmental contaminants for toxicity and to identify behavioral responses associated with common chemical specific MOAs, we employed the two most common fish models, the zebrafish and the fathead minnow, to define toxicant induced swimming activity alterations during interchanging photoperiods. Though the fathead minnow (Pimephales promelas) is a common model for aquatic toxicology research and regulatory toxicology practice, this model has received little attention in behavioral studies compared to the zebrafish, a common biomedical model. We specifically compared behavioral responses among 7 different chemicals (1-heptanol, phenol, R-(-)-carvone, citalopram, diazinon, pentylenetetrazole (PTZ), and xylazine) that were selected and classified based on anticipated MOA (nonpolar narcosis, polar narcosis, electrophile, specific mechanism) according to traditional approaches to examine whether these comparative responses differ among chemicals with various structure-based predicted toxicity. Following standardized experimental guidelines, zebrafish embryos and fathead minnow larvae were exposed for 96 h to each compound then were observed using digital behavioral analysis. Behavioral observations included photomotor responses, distance traveled, and stimulatory, refractory and cruising locomotor activity. Though fathead minnow larvae displayed greater behavioral sensitivity to 1-heptanol, phenol and citalopram, zebrafish were more sensitive to diazinon and R-(-)-carvone. Both fish models were equally sensitive to xylazine and PTZ. Further, the pharmaceuticals citalopram and xylazine significantly affected behavior at therapeutic hazard values, and each of the seven chemicals elicited unique behavioral response profiles. Larval fish behaviors appear useful as early tier diagnostics to identify mechanisms and pathways associated with diverse biological activities for chemicals lacking mechanistic data.

Understanding the Role of Environmental Enrichment in Zebrafish Neurobehavioral Models

Environmental stimuli are critical in preclinical research that utilizes laboratory animals to model human brain disorders. The main goal of environmental enrichment (EE) is to provide laboratory animals with better choice of activity and greater control over social and spatial stressors. Thus, in addition to being a useful experimental tool, EE becomes an important strategy for increasing the validity and reproducibility of preclinical data. Although zebrafish (Danio rerio) is rapidly becoming a promising new organism for neuroscience research, the role of EE in zebrafish central nervous system (CNS) models remains poorly understood. Here we discuss EE in preclinical studies using zebrafish and its influence on brain physiology and behavior. Improving our understanding of EE effects in this organism may enhance zebrafish data validity and reliability. Paralleling rodent EE data, mounting evidence suggests the growing importance of EE in zebrafish neurobehavioral models.

Exposure to ayahuasca induces developmental and behavioral alterations on early life stages of zebrafish

Ayahuasca is a psychoactive concoction prepared from the plants Banisteriopsis caapi and Psychotria viridis which are used ancestrally by Amazonian Indian populations and more recently, by Christian religious groups in Brazil and other countries. The aims of the present study were to identify the effects of ayahuasca on zebrafish embryo development and neurobehavior. Toxicity and developmental endpoints for zebrafish embryos were assessed from 0 to 1000 mg/L over 96 h of exposure. The effects on locomotor activity of zebrafish larvae were assessed using a video tracking system (ZebraBox) from 0 to 20 mg/L and after 120 and 144 h of exposure. The LC₅₀ of ayahuasca in zebrafish was determined as 236.3 mg/L. Ayahuasca exposure caused significant developmental anomalies in zebrafish embryos, mainly at the highest concentration tested, including hatching delay, loss of equilibrium, edema and the accumulation of red blood cells. Embryo behavior was also significantly affected, with decreased locomotor activity at the highest concentration tested. These results are in accordance with data obtained in mammal studies highlighting the possible risks of uncontrolled use of ayahuasca. Further research employing more specific behavior analysis could provide additional data on both therapeutic benefits and possible toxicological risk of ayahuasca.

Opportunities and challenges for using the zebrafish to study neuronal connectivity as an endpoint of developmental neurotoxicity

Chemical exposures have been implicated as environmental risk factors that interact with genetic susceptibilities to influence individual risk for complex neurodevelopmental disorders, including autism spectrum disorder, schizophrenia, attention deficit hyperactivity disorder and intellectual disabilities. Altered patterns of neuronal connectivity represent a convergent mechanism of pathogenesis for these and other neurodevelopmental disorders, and growing evidence suggests that chemicals can interfere with specific signaling pathways that regulate the development of neuronal connections. There is, therefore, a growing interest in developing screening platforms to identify chemicals that alter neuronal connectivity. Cell-cell, cell-matrix interactions and systemic influences are known to be important in defining neuronal connectivity in the developing brain, thus, a systems-based model offers significant advantages over cell-based models for screening chemicals for effects on neuronal connectivity. The embryonic zebrafish represents a vertebrate model amenable to higher throughput chemical screening that has proven useful in characterizing conserved mechanisms of neurodevelopment. Moreover, the zebrafish is readily amenable to gene editing to integrate genetic susceptibilities. Although use of the zebrafish model in toxicity testing has increased in recent years, the diverse tools available for imaging structural differences in the developing zebrafish brain have not been widely applied to studies of the influence of gene by environment interactions on neuronal connectivity in the developing zebrafish brain. Here, we discuss tools available for imaging of neuronal connectivity in the developing zebrafish, review what has been published in this regard, and suggest a path forward for applying this information to developmental neurotoxicity testing.

Combining hyperspectral imaging and chemometrics to assess and interpret the effects of environmental stressors on zebrafish eye images at tissue level

Changes on an organism by the exposure to environmental stressors may be characterized by hyperspectral images (HSI), which preserve the morphology of biological samples, and suitable chemometric tools. The approach proposed allows assessing and interpreting the effect of contaminant exposure on heterogeneous biological samples monitored by HSI at specific tissue levels. In this work, the model example used consists of the study of the effect of the exposure of chlorpyrifos-oxon on zebrafish tissues. To assess this effect, unmixing of the biological sample images followed by tissue-specific classification models based on the unmixed spectral signatures is proposed. Unmixing and classification are performed by multivariate curve resolution-alternating least squares (MCR-ALS) and partial least squares-discriminant analysis (PLS-DA), respectively. Crucial aspects of the approach are: (1) the simultaneous MCR-ALS analysis of all images from 1 population to take into account biological variability and provide reliable tissue spectral signatures, and (2) the use of resolved spectral signatures from control and exposed populations obtained from resampling of pixel subsets analyzed by MCR-ALS multiset analysis as information for the tissue-specific PLS-DA classification models. Classification results diagnose the presence of a significant effect and identify the spectral regions at a tissue level responsible for the biological change.

Urbanization, environment and pharmaceuticals: advancing comparative physiology, pharmacology and toxicology

Pharmaceuticals are routinely reported in the environment, which indicates an increasingly urban water cycle and highlights a global megatrend. Physicochemical properties and intrinsic biological activity of medicines routinely differ from conventional organic contaminants; thus, diverging applicability domains often challenge environmental chemistry and toxicology computational tools and biological assays originally developed to address historical chemical stressors. Because pharmacology and toxicology information is more readily available for these contaminants of emerging concern than other chemicals in the environment, and many drug targets are conserved across species, leveraging mammalian drug discovery, safety testing and clinical pharmacology information appears useful to define environmental risks and to design less hazardous industrial chemicals. Research is needed to advance biological read across, which promises to reduce uncertainties during chemical assessment aimed at protecting public health and the environment. Whereas such comparative information has been critical to advance an understanding of pharmaceutical hazards and risks in urban ecosystems, studies of medicines with fish and other ecotoxicological models are reciprocally benefiting basic and translational efforts, advancing comparative mechanistic toxicology, and providing robust comparative bridges for integrating conservation and toxicology.

Alterations of larval photo-dependent swimming responses (PDR): New endpoints for rapid and diagnostic screening of aquatic contamination

Detection and toxicity assessment of waterborne contaminants are crucial for protecting human health and the environment. Development of easy-to-implement, rapid and cost-effective tools to measure anthropogenic effects on watersheds are critical for responsible management, particularly in times of increasing development and urbanization. Traditionally, environmental toxicology has focused on limited endpoints, such as lethality and fertility, which are directly affecting population levels. However, more sensitive readings are needed to assess sub-lethal effects. Monitoring of contaminant-induced behavior alterations was proposed before, but is difficult to implement in the wild and performing it in aquatic laboratory models seem more suited. For this purpose, we adapted a photo-dependent swimming response (PDR) that was previously described in zebrafish larva. We first asked if PDR was present in other aquatic animals. We measured PDR in larvae from two freshwater prawn species (Macrobrachium rosenbergii, MR, and Macrobrachium carcinus, MC) and from another fish the fathead minnow (FHM, Pimephales promelas). In all, we found a strong and reproducible species-specific PDR, which is arguing that this behavior is important, therefore an environmental relevant endpoint. Next, we measured PDR in fish larvae after acute exposure to copper, a common waterborne contaminant. FHM larvae were hyperactive at all tested concentrations in contrast to ZF larvae, which exhibited a concentration-dependent hyperactivity. In addition to this well-accepted anxiety-like behavior, we examined two more: photo-stimulated startle response (PSSR) and center avoidance (CA). Both were significantly increased. Therefore, PDR measures after acute exposure to this waterborne contaminant provided as sensitive readout for its detection and toxicity assessment. This approach represents an opportunity to diagnostically examine any substance, even when present in complex mixtures like ambient surface waters. Mechanistic studies of toxicity using the extensive molecular tool kit of ZF could be a direct extension of such approaches.

Assessing the ecotoxicity of potentially neurotoxic substances - Evaluation of a behavioural parameter in the embryogenesis of Danio rerio

The pollution of the aquatic environment is currently characterised by a large number of contaminants, especially by mixtures of micro-pollutants including neurotoxins. The ecotoxicological consequences of this burden are not yet assessable. Within the present study, a new test method was applied which evaluates behavioural changes in zebrafish (Danio rerio) embryos to quantify the neurotoxic effect of selected chemicals. Changes in the frequency of spontaneous tail movements - a parameter of locomotion - occurring during embryogenesis was assessed as parameter for neurotoxic effects. Embryos were exposed in 24-microwell plates to neurotoxic compounds. Behaviour was examined after 24 h of exposure by videotaping and quantifying spontaneous locomotion. Additionally, acute toxicity was determined after 48 h of exposure by utilising the fish embryo toxicity test. Abamectin, emamectin benzoate, chlorpyrifos-oxon and carbamazepine were analysed using both: the new and classic acute test methods. The results showed the neurotoxic effect of the substances. Furthermore, an increased sensitivity compared to acute toxicity data was shown. The aim of the present study, to illustrate the sensitivity and specificity of the established endpoint to reliably assess adverse, neurotoxic effects of compounds on the model organism Danio rerio and to apply a new test method was achieved. Therefore, the present study is a substantial contribution to an effect-based risk assessment of contaminants in aquatic ecosystems.

Anxiolytic-like effects of noribogaine in zebrafish

Noribogaine is the main psychoactive metabolite of the hallucinogenic drug ibogaine, and is a particularly interesting compound potentially useful to treat dependence and various psychiatric disorders. Here, we report the effects of noribogaine on anxiety and locomotion in zebrafish (Danio rerio), a new promising model organism in neurobehavioral and psychopharmacological research. Adult zebrafish were subjected to the 5min novel tank test (NTT) following an acute, 20-min drug immersion in 1, 5 and 10mg/L noribogaine. Overall, noribogaine produced robust anxiolytic-like behavior in zebrafish (increasing the time spent and transitions to the top half compartment and reducing freezing bouts) without overt effects on fish locomotion. Taken together, these results indicate that noribogaine modulates the components of the acute stress response related to emotionality and anxiety behaviors, implicating this drug as a potentially useful non-sedative anxiolytic agent.

Sodium Selenite Prevents Paraquat-Induced Neurotoxicity in Zebrafish

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

Individual differences in cognition among teleost fishes

Individual differences in cognitive abilities have been thoroughly investigated in humans and to a lesser extent in other mammals. Despite the growing interest in studying cognition in other taxonomic groups, data on individual differences are scarce for non-mammalian species. Here, we review the literature on individual differences in cognitive abilities in teleost fishes. Relatively few studies have directly addressed this topic and have provided evidence of consistent and heritable individual variation in cognitive abilities in fish. We found much more evidence of individual cognitive differences in other research areas, namely sex differences, personality differences, cerebral lateralisation and comparison between populations. Altogether, these studies suggest that individual differences in cognition are as common in fish as in warm-blooded vertebrates. Based on the example of research on mammals, we suggest directions for future investigation in fish.

The Power of Zebrafish in Personalised Medicine

The goal of personalised medicine is to develop tailor-made therapies for patients in whom currently available therapeutics fail. This approach requires correlating individual patient genotype data to specific disease phenotype data and using these stratified data sets to identify bespoke therapeutics. Applications for personalised medicine include common complex diseases which may have multiple targets, as well as rare monogenic disorders, for which the target may be unknown. In both cases, whole genome sequence analysis (WGS) is discovering large numbers of disease associated mutations in new candidate genes and potential modifier genes. Currently, the main limiting factor is the determination of which mutated genes are important for disease progression and therefore represent potential targets for drug discovery. Zebrafish have gained popularity as a model organism for understanding developmental processes, disease mechanisms and more recently for drug discovery and toxicity testing. In this chapter, we will examine the diverse roles that zebrafish can make in the expanding field of personalised medicine, from generating humanised disease models to xenograft screening of different cancer cell lines, through to finding new drugs via in vivo phenotypic screens. We will discuss the tools available for zebrafish research and recent advances in techniques, highlighting the advantages and potential of using zebrafish for high throughput disease modeling and precision drug discovery.

Studies on photodegradation process of psychotropic drugs: a review

Consumption of psychotropic drugs is still increasing, especially in high-income countries. One of the most crucial consequences of this fact is significant release of them to the environment. Considerable amounts of atypical antipsychotics, benzodiazepines, antidepressants, and their metabolites were detected in river, lake, and sea water, as well as in tissues of aquatic organisms. Their ecotoxicity was proved by numerous studies. It should be noticed that interaction between psychotropic pharmaceuticals and radiation may lead to formation of potentially more toxic intermediates. On the other hand, photo-assisted wastewater treatment methods can be used as an efficient way to eliminate them from the environment. Many methods based on photolysis and photocatalysis were proposed and developed recently; nevertheless, the problem is still unsolved. However, according to recent studies, photocatalysis could be considered as the most promising and far more effective than regular photolysis. An overview on photolytic as well as homogenous and heterogeneous photocatalytic degradation methods with the use of various catalysts is presented. The photostability and phototoxicity of pharmaceuticals were also discussed. Various analytical methods were used for the photodegradation research, and this issue was also compared and summarized. Use of high-resolution multistage mass spectrometry (Q-TOF, ion trap, Orbitrap) was suggested. The combined techniques such as LC-MS, GC-MS, and LC-NMR, which enable qualitative and quantitative analyses in one run, proved to be the most valuable in this case. Assembling of MS/MS spectra libraries of drug molecules and their phototransformation products was identified as the future challenge.

Zebrafish Get Connected: Investigating Neurotransmission Targets and Alterations in Chemical Toxicity

Neurotransmission is the basis of neuronal communication and is critical for normal brain development, behavior, learning, and memory. Exposure to drugs and chemicals can alter neurotransmission, often through unknown pathways and mechanisms. The zebrafish (Danio rerio) model system is increasingly being used to study the brain and chemical neurotoxicity. In this review, the major neurotransmitter systems, including glutamate, GABA, dopamine, norepinephrine, serotonin, acetylcholine, histamine, and glutamate are surveyed and pathways of synthesis, transport, metabolism, and action are examined. Differences between human and zebrafish neurochemical pathways are highlighted. We also review techniques for evaluating neurological function, including the measurement of neurotransmitter levels, assessment of gene expression through transcriptomic analysis, and the recording of neurobehavior. Finally examples of chemical toxicity studies evaluating alterations in neurotransmitter systems in the zebrafish model are reviewed.

A detailed proteomic profiling of plasma membrane from zebrafish brain

Zebrafish (Danio rerio) is a well-established model organism in developmental biology and disease modeling. In recent years, an increasing amount of studies used zebrafish to analyze the genetic changes underlying various neurological disorders. The brain plasma membrane proteome represents the major subsets of signaling proteins and promising drug targets, but is often understudied due to traditional experimental difficulties including problems with solubility, detergent removal, or low abundance. Here, we report a comprehensive dataset of the proteins identified in the enriched plasma membrane of the zebrafish brain by applying sequential trypsin/chymotrypsin digestion with multidimensional LC-MS/MS. A total number of 97 017 peptide groups corresponding to 9201 proteins were identified. These were annotated in various molecular functions or neurological disorders. The dataset of the current study provides a useful data source for further utilizing zebrafish in basic and clinical neuroscience.

Role of SULT-mediated sulfation in the biotransformation of 2-butoxyethanol and sorbitan monolaurate: A study using zebrafish SULTs

2-Butoxyethanol and sorbitan monolaurate are major components of oil dispersants that are applied in large quantities to control oil spill in the aquatic environment. An important question is whether aquatic animals are equipped with mechanisms for the detoxification of these oil dispersant compounds. The current study aimed to examine whether zebrafish cytosolic sulfotransferases (SULTs) are capable of sulfating 2-butoxyethanol and sorbitan monolaurate. A systematic analysis of 18 zebrafish SULTs revealed that SULT3 ST1 showed the strongest sulfating activity toward 2-butoxyethanol, while SULT1 ST3 displayed the strongest sulfating activity toward sorbitan monolaurate. The pH-dependence of these two SULTs in mediating the sulfation of 2-butoxyethanol or sorbitan monolaurate was examined. Taken together, these results implied that SULT-mediated sulfation may function in the detoxification of these two oil dispersant compounds.

Exploring Hallucinogen Pharmacology and Psychedelic Medicine with Zebrafish Models

After decades of sociopolitical obstacles, the field of psychiatry is experiencing a revived interest in the use of hallucinogenic agents to treat brain disorders. Along with the use of ketamine for depression, recent pilot studies have highlighted the efficacy of classic serotonergic hallucinogens, such as lysergic acid diethylamide and psilocybin, in treating addiction, post-traumatic stress disorder, and anxiety. However, many basic pharmacological and toxicological questions remain unanswered with regard to these compounds. In this study, we discuss psychedelic medicine as well as the behavioral and toxicological effects of hallucinogenic drugs in zebrafish. We emphasize this aquatic organism as a model ideally suited to assess both the potential toxic and therapeutic effects of major known classes of hallucinogenic compounds. In addition, novel drugs with hallucinogenic properties can be efficiently screened using zebrafish models. Well-designed preclinical studies utilizing zebrafish can contribute to the reemerging treatment paradigm of psychedelic medicine, leading to new avenues of clinical exploration for psychiatric disorders.