Approaches to Test the Neurotoxicity of Environmental Contaminants in the Zebrafish Model: From Behavior to Molecular Mechanisms

Swimming Into View: Zebrafish Uncover Targets, Mechanisms, and Therapies for Cadmium Toxicity

PURPOSE OF REVIEW

Cadmium (Cd) remains a persistent threat to human and environmental health. To better understand causal relationships between genotype and disease phenotypes, a genetically tractable model, zebrafish (Danio rerio) has emerged. We summarize recent empirical evidence on the targets, mechanisms, and potential therapies for Cd toxicity.

RECENT FINDINGS

Recent results show that waterborne Cd exhibits organ specific accumulation including in the eye, brain, heart, and gonads triggering oxidative stress, inflammation, gut dysbiosis, and altered methylation patterns that persist across generations. Novel mechanisms of Cd toxicity include the gut-brain axis, ionic antagonism, the Wnt/β-catenin pathway, and epigenetics, leading to potential therapeutics such as probiotics, selenium, and antioxidants. Based on the reviewed literature, more studies should examine the effects of dietary Cd on zebrafish behavior, brains, and cardiovascular function. Given that humans and wildlife are chronically exposed to Cd, leading to gonadal Cd accumulation, studies should conduct early-life exposures across the zebrafish lifespan and assess endpoints across generations to capture germline and epigenetic effects and mechanisms. The zebrafish's biomedical toolkit, along with high-content screening, should be utilized to develop and refine therapies.

Zebrafish as a model to assess the neurotoxic potential of propylene glycol ethers

Propylene glycol ethers are increasingly used as organic solvents of choice in domestic products and industrial manufacturing. However, little is known about their potential neurotoxic effects. In the present study, we therefore evaluated the acute toxic and behavioral effects of propylene glycol ethers using zebrafish larvae as a vertebrate model. Studied endpoints included viability, motor behavior, larval photo and locomotor response, and blood-brain barrier permeability (BBB). We observed hyperactivity at lower concentrations and hypoactivity at higher concentrations. Impaired behavioral patterns in exposed larvae suggested an interaction with the nervous system. Mechanistic studies revealed an impact on BBB permeability since a significant increase in extracellular fluorescent tracer permeability into brain parenchyma was observed following exposure. We conclude that the zebrafish model is a predictive screening model to rank organic solvents with respect to their toxic potential. Experiments with ethanol as a reference correlate with literature findings in humans.

Toxic effects of microplastics (polyethylene) exposure on acetylcholinesterase, stress indicators and immunity in Korean Bullhead, Pseudobagrus fulvidraco

Microplastics (MPs) in aquatic environments can have toxic effects on various organisms, including fish. This study exposed Pseudobagrus fulvidraco to polyethylene MPs at 0, 10 mg/L (approximately 9.50 ×108 particles/L), 20 mg/L (approximately 1.9 ×109 particles/L), 5000 mg/L (approximately 4.75 ×1011 particles/L), and 10,000 mg/L (approximately 9.50 ×1011 particles/L) concentrations for 96 h. At relatively lower MPs concentrations (0, 10 and 20 mg/L), no significant changes were observed in acetylcholinesterase (AChE) activity, stress indicators (heat shock protein 70 and cortisol), or immune responses (lysozyme activity and immunoglobulin M levels). However, at higher MPs concentrations (5000 and 10,000 mg/L), AChE activity was significantly inhibited, stress indicators were significantly increased, and immune responses were significantly decreased. Our results indicate that acute exposure of P. fulvidraco to MPs had negligible effects at concentrations below 20 mg/L, whereas significant toxic effects such as AChE activity inhibition, stress responses, and immune suppression were observed at concentrations above 5000 mg/L. Therefore, our study highlights the risks of severe MPs pollution on aquatic ecosystems and fish health.

Utilizing alternative in vivo animal models for food safety and toxicity: A focus on thermal process contaminant acrylamide

Rodent models have traditionally been used to assess the toxicity of food chemicals, but this approach is costly, time-consuming, and raises ethical concerns. Alternatively, non-mammalian models such as Drosophila melanogaster, Danio rerio, and Caenorhabditis elegans have been shown to be suitable for studying the toxicity of food hazards. Their advantages include low cost, short life cycles, adaptability to high-throughput screening, and adherence to the 3R principles of replacement, reduction, and refinement. These models have been extensively studied in the context of acrylamide toxicity, a common food contaminant. This article comprehensively reviews the biological characteristics of non-mammalian models, recent advances and challenges in acrylamide toxicity research using these models, and explores the potential of natural plant compounds in ameliorating acrylamide toxicity. The review aims to guide research using non-mammalian models for food safety assessment.

The Development of Yellow Mealworm (Tenebrio molitor) as a Cheap and Simple Model to Evaluate Acute Toxicity, Locomotor Activity Changes, and Metabolite Profile Alterations Induced by Nanoplastics of Different Sizes

Due to the wide uses of plastic products, nanoplastics are ubiquitous contaminants in the environment. Hence, extensive studies used various models to evaluate the toxicity of nanoplastics. In the present study, we developed yellow mealworm (Tenebrio molitor) as an alternative model to investigate the acute toxicity of nanoplastics. Our results showed that microinjection with 500 mg/kg nanoplastics significantly increased death rate of yellow mealworms after 24 or 48 h, with 100 nm particles being more effective compared with 20 nm ones. Meanwhile, dose-dependent increase of death rate was observed in yellow mealworms after injection with 2-200 mg/kg 100 nm nanoplastics. Exposure to 2 mg/kg 100 nm but not 20 nm nanoplastics also led to hyperactivity of yellow mealworms. Both types of nanoplastics altered metabolite profiles, that 20 nm nanoplastics significantly up-regulated and down-regulated 9 and 12 metabolites, whereas 100 nm nanoplastics significantly up-regulated and down-regulated 16 and 25 metabolites, respectively. Enrichment analysis revealed that 100 nm but not 20 nm nanoplastics significantly affected alpha-linolenic acid metabolism (ko00592) and purine metabolism (ko00230). For the metabolites belonging to these pathways, 100 nm nanoplastics significantly up-regulated stearidonic acid but down-regulated guanine. Combined, these results revealed size-dependent effects of nanoplastics on acute toxicity, hyperactivity and metabolite profile changes in yellow mealworms. These results also indicated the potential uses of yellow mealworms as a cheap and simple model to evaluate the toxicity of nanoplastics.

Tetrachlorantraniliprole induces neurodevelopmental toxicity through oxidative stress-mediated apoptosis and dysregulation of Wnt signaling pathway

Tetrachlorantraniliprole (TCTP) is a novel bisamide insecticide and widely used to protect against lepidopteran insect species. However, the application of TCTP in rice fields often leads to water pollution, posing threats to aquatic organisms and potentially to human health. Few studies have assessed the toxic effects of TCTP on aquatic animals. In this study, we used zebrafish as a model organism to evaluate the toxicity of TCTP. Our findings indicated that TCTP adversely affected the development of zebrafish larvae, impacting parameters such as heart rate, body length, and pericardial edema. Exposure to TCTP resulted in the increased embryo mortality along with higher concentrations of the compound. The expression of neurodevelopment-related genes was inhibited in embryos exposed to TCTP. Hematoxylin and eosin (HE) staining revealed that TCTP caused damage to the brain cells of the embryos. Behavioral analysis showed a reduction in activity of the larvaes, which aligned with a decrease in acetylcholinesterase (AChE) activity. Additionally, RNA sequencing (RNA-seq) was employed to elucidate the mechanisms of toxicity. GO and KEGG analysis identified that the pathways were related to oxidative stress, apoptosis and Wnt signaling. We observed an increase of reactive oxygen species (ROS) and Ca²/Mg²-ATPase activity, while antioxidant enzyme activities (SOD, MDA, CAT, Na/K-ATPase and T-ATPase) were significantly decreased in TCTP-exposed groups. Furthermore, TCTP induced brain cells apoptosis, as evidenced by the upregulation of pro-apoptotic genes (bax, p53, TNFα, caspase3 and caspase9) and the downregulation of anti-apoptotic gene (bcl2). Moreover, TCTP increased the expression of genes involved in Wnt signaling pathway. Notably, oxidative stress and neuronal damage induced by TCTP could be mitigated by astaxanthin, an antioxidant. Additionally, IWR-1, an inhibitor of Wnt signaling pathway, effectively alleviated the upregulation of genes associated with TCTP treatment and inhibited oxidative stress-induced apoptosis. In conclusion, this study demonstrated TCTP-induced defects of neurodevelopment and the brain cells in zebrafish larvae which were primarily driven by oxidative stress-induced apoptosis and dysregulation of Wnt signaling pathway. Importantly, these toxic phenotypes can be rescued by treatment with astaxanthin or IWR-1.

Integrated multi-omics analysis reveals the underlying molecular mechanism for the neurotoxicity of triclosan in zebrafish

Triclosan (TCS) is a primary broad-spectrum antibacterial agent commonly present in the environment. As a new type of environmental endocrine disruptor, it causes range of toxicities, including hepatotoxicity and reproductive toxicity. However, few research has examined the toxicity of long-term TCS-induced exposure in zebrafish at ambient concentrations, in contrast to the early life stage investigations. In the present study, we investigated the behavioral effects of TCS at environmental concentrations (300 μg/L) during constant exposure in zebrafish adults；An integrated transcriptomic and metabolomic analysis was performed to analyze the molecular mechanism underlying behavioral effects of TCS. Our results show that TCS exposure significantly induces behavioral disruptions such as anxiety-like behavior, memory problems, and altered social preferences. Histopathological investigations and neural ultrastructural observations demonstrated that TCS could induce variable levels of pyknosis and vacuolation in the cytoplasm of neurons as well as torn mitochondrial membranes, shrinkage and broken or absent cristae. Transcriptomics indicated that immune- and metabolism-related gene expression patterns were severely disturbed by TCS. Metabolomic analysis revealed 82 distinct metabolites in adult zebrafish exposed to TCS. Lipid metabolism, especially glycerophospholipid metabolism, and amino acid regulation pathways were co-enriched by multi-omics combinatorial analysis. Hence, this study highlights a number of biomarkers for the risk assessment of TCS against non-target organisms, offering a reference dataset for the behavioral toxicity of TCS to zebrafish, and strengthening the early warning, management, and control of TCS pollution.

Tri-iso-butyl phosphate (TiBP) exposure induces neurotoxicity by triggering oxidative stress accompanied by neurotransmitter system disruptions and apoptosis in zebrafish larvae

The current research sheds light on the biological toxicity of organophosphate flame retardants (OPFRs), yet it overlooks the neurotoxicity and potential molecular mechanisms of tris(1,3-dichloro-2-propyl) phosphate (TiBP), a prominent constituent of the OPFRs. To address this, we utilized zebrafish larvae as a model to investigate TiBP's acute toxicity and neurotoxic effects, along with the associated molecular pathways. Our findings revealed that the 96 h and 120 h LC50 values for TiBP were 56.51 mg/L and 48.85 mg/L, respectively. Gradient exposure based on the 120 h LC50 demonstrated that TiBP induced developmental toxicity, characterized by elevated heart rate, reduced body length, and diminished eye distance. Additionally, a decrease in swimming activity was observed in the light test, along with the inhibition of the neuro crest cell development in Tg (HuC:eGFP) and Tg (sox10: eGFP) zebrafish larvae following TiBP exposure, as well as the alterations of neurogenesis and ACh-related genes. Expression of key neurodevelopment genes, including mbpa, gap43, nestin, ngfra, was significantly downregulated. Furthermore, heightened anxiety-like behaviors in open field and phototaxis tests were observed, concomitant with neurotransmitter imbalances. Specifically, there was an increase in DA levels, a decrease in GABA, and an upregulation of AChE activity. These disruptions were primarily mediated through transcriptional dysregulation of neurotransmitter synthesis, transport, and reception. Upon exposure to TiBP, zebrafish larvae exhibited a concentration-dependent increase in both ROS level and apoptosis. An upregulation of antioxidant enzymes and their transcription levels indicated the presence of oxidative stress in the larvae. The induction of ddit3 was congruent with the observed apoptosis, suggesting that it may be triggered by oxidative stress via the ERs-CHOP pathway. In summary, our study indicates that oxidative stress is a pivotal molecular event in the neurotoxicity induced by TiBP, implicating the disruption of the GABAergic, dopaminergic, and cholinergic systems, as well as triggering apoptosis.

Transcriptome networks and physiology related to cardiac function and motor activity are perturbed in larval zebrafish (Danio rerio) following exposure to the antidepressant citalopram

Citalopram is a selective serotonin reuptake inhibitor (SSRI) used to treat depression and is often detected in aquatic environments. Here, we measured the acute toxicity of citalopram at environmentally relevant concentrations to zebrafish embryos/larvae and utilized RNA-seq to reveal potential mechanisms of toxicity. We also assessed behavioral outcomes in larval zebrafish. Zebrafish embryos were exposed continuously to embryo rearing medium (ERM), or one concentration of 0.1, 1, 10, 100, and 1000 μg/L citalopram for 7 days post-fertilization (dpf). No acute toxicity was noted for citalopram over 7-days in developing zebrafish, nor were there any effects on hatch rates; however, exposure resulted in a dose-dependent decrease in heart rate at 2 dpf. Reactive oxygen species were also increased in 7-day old larvae zebrafish exposed to 100 μg/L citalopram. There were 29 genes differentially expressed in fish exposed to 10 μg/L citalopram [FDR <0.05] and 79 genes differentially expressed in fish exposed to 1000 μg/L citalopram [FDR <0.05]. In the 1000 μg/L citalopram treatment, there were several transcripts downregulated related to muscle function, including myhz2, myhz1, and myom1. Twenty-five gene set pathways were shared between exposure concentrations including 'IL6 Expression Targets', 'Thyroid Stimulating Hormone (TSH) Resistance in Congenital Hypothyroidism', and 'GFs/TNF - > Ion Channels.' Enrichment of KEGG pathways revealed that 1000 μg/L citalopram altered processes related to the proteosome and cardiac muscle contractions. Larval zebrafish at 7 dpf showed hypoactivity with exposure to ≥10 μg/L citalopram. This may be related to the downregulation of transcripts involved in muscle function. Overall, our results show that citalopram as a pharmaceutical pollutant may have an adverse influence on aquatic species' ability to survive by reducing their abilities to elude predators (e.g. cardiac output, locomotor activity). This study improves mechanistic understanding of the potential harm citalopram may cause fish and contributes to environmental risk assessments for SSRIs in aquatic species.

Effects of organic and inorganic contaminants and their mixtures on metabolic health and gene expression in developmentally exposed zebrafish

Organic and inorganic chemicals co-occur in household dust, and these chemicals have been determined to have endocrine and metabolic disrupting effects. While there is increasing study of chemical mixtures, the effects of complex mixtures mimicking household dust and other environmental matrices have not been well studied and their potential metabolism disrupting effects are thus poorly understood. Previous research has demonstrated high potency adipogenic effects of residential household dust extracts using in vitro adipogenesis assays. More recent research simplified this to a mixture relevant to household dust and comprised of common co-occurring organic and inorganic contaminants, finding that these complex combinations often exhibited additive or even synergistic effects in cell models. This study aimed to translate our previous in vitro observation to an in vivo model, the developing zebrafish, to evaluate the metabolic effects of early exposure to organic and inorganic chemicals, individually and in mixtures. Zebrafish embryos were exposed from 1 day post fertilization (dpf) to 6 dpf, then metabolic energy expenditure, swimming behavior and gene expression were measured. Globally, we observed that most mixtures did not reflect the effects of individual chemicals; the BFR mixture produced a less potent effect when compared to the individual chemicals, while the PFAS and the inorganic mixtures seemed to have a more potent effect than the individual chemicals. Finally, the environmental mixture, mimicking household dust proportions, was less potent than the inorganic chemical mix alone. Additional work is necessary to better understand the mixture effect of inorganic and organic chemicals combined.

Controlled in vivo intrinsic detrimental effect of d-Limonene channelized by influential proximal interaction through apoptosis and steatosis in embryonic zebrafish (Danio rerio)

Bioaccumulation of d-Limonene in environment due to the aggrandised usage of their natural sources like citrus food wastes and industrial day to day life products has raised concern to their biotoxicity to environment biotic health. Moreover, their after-usage discharge to aquatic system has enhanced the distress of posing threat and needs attention. This study entails mechanistic and molecular evaluation of in-vivo biotoxicity of d-Limonene in zebrafish embryo models. Experimental analysis excavated the controlled concentration-dependent morphological, physiological and cellular in-vivo impact of d-Limonene in zebrafish embryos through significant changes in oxidative stress, steatosis and apoptosis regulated via 6-fold and 5-fold mRNA expression change in p53 and Sod1 genes. Computational evaluation deduced the cellular mechanism of d-limonene biotoxicity as irregularities in oxidative stress, apoptosis and steatosis due of their intrinsic interaction with metabolic proteins like Zhe1a (-4.8 Kcal/mol), Sod1(-5.3 Kcal/mol), p53, caspase3 and apoa1 leading to influential change in structural and functional integrity of the metabolic proteins. The study unravelled the measured in-vivo biotoxicity of d-Limonene at cellular and molecular level to advocate the controlled usage of d-Limonene related natural and industrial product for a sustainable environmental health.

Developing an Approach for Integrating Chemical Analysis and Transcriptional Changes to Assess Contaminants in Water, Sediment, and Fish

Pharmaceuticals in aquatic environments pose threats to aquatic organisms because of their continuous release and potential accumulation. Monitoring methods for these contaminants are inadequate, with targeted analyses falling short in assessing water quality's impact on biota. The present study advocates for integrated strategies combining suspect and targeted chemical analyses with molecular biomarker approaches to better understand the risks posed by complex chemical mixtures to nontarget organisms. The research aimed to integrate chemical analysis and transcriptome changes in fathead minnows to prioritize contaminants, assess their effects, and apply this strategy in Wascana Creek, Canada. Analysis revealed higher pharmaceutical concentrations downstream of a wastewater-treatment plant, with clozapine being the most abundant in fathead minnows, showing notable bioavailability from water and sediment sources. Considering the importance of bioaccumulation factor and biota-sediment accumulation factor in risk assessment, these coefficients were calculated based on field data collected during spring, summer, and fall seasons in 2021. Bioaccumulation was classified as very bioaccumulative with values >5000 L kg-1, suggesting the ability of pharmaceuticals to accumulate in aquatic organisms. The study highlighted the intricate relationship between nutrient availability, water quality, and key pathways affected by pharmaceuticals, personal care products, and rubber components. Prioritization of these chemicals was done through suspect analysis, supported by identifying perturbed pathways (specifically signaling and cellular processes) using transcriptomic analysis in exposed fish. This strategy not only aids in environmental risk assessment but also serves as a practical model for other watersheds, streamlining risk-assessment processes to identify environmental hazards and work toward reducing risks from contaminants of emerging concern. Environ Toxicol Chem 2024;43:2252-2273. © 2024 SETAC.

Evaluation of the citalopram toxicity on early development of zebrafish: Morphological, physiological and biochemical responses

Citalopram, an antidepressant drug have been detected in different environmental matrices due to its high consumption. Previous study has proved that citalopram may alter the behaviour of aquatic organisms at environmentally relevant concentrations. However, scientific knowledge is still lacking on the ecotoxicological effects of citalopram on aquatic organisms. For this reason, the present study is aimed to investigate the potential toxicity of citalopram in terms of development, antioxidant, neurotoxicity, apoptosis, lipogenesis, and bone mineralization in embryonic and larval zebrafish (Danio rerio) at environmentally relevant concentrations. We noticed that citalopram exposure at 1 and 10 μg/L concentration delays hatching and heartbeat at 24, 48, 72 and 96 hpf. Exposure to citalopram also significantly increased mortality at 10 μg/L. Abnormal development with yolk sac edema, pericardial edema and scoliosis were also observed after citalopram treatment. In addition, citalopram significantly (P < 0.001) induced superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and lipid peroxidation (LPO) levels. A significant decrease in acetylcholine esterase (AChE) activity was also observed in citalopram exposed groups. We found significant dose-and time-dependent increases in apoptosis, lipogenesis, and bone mineralization. In conclusion, the findings of the present study can provide new insights on the ecotoxicity of citalopram in the aquatic environment.

Toxicity of zinc oxide nanoparticles: Cellular and behavioural effects

Due to their extensive use, the release of zinc oxide nanoparticles (ZnO NP) into the environment is increasing and may lead to unintended risk to both human health and ecosystems. Access of ZnO NP to the brain has been demonstrated, so their potential toxicity on the nervous system is a matter of particular concern. Although evaluation of ZnO NP toxicity has been reported in several previous studies, the specific effects on the nervous system are not completely understood and, particularly, effects on genetic material and on organism behaviour are poorly addressed. We evaluated the potential toxic effects of ZnO NP in vitro and in vivo, and the role of zinc ions (Zn2+) in these effects. In vitro, the ability of ZnO NP to be internalized by A172 glial cells was verified, and the cytotoxic and genotoxic effects of ZnO NP or the released Zn2+ ions were addressed by means of vital dye exclusion and comet assay, respectively. In vivo, behavioural alterations were evaluated in zebrafish embryos using a total locomotion assay. ZnO NP induced decreases in viability of A172 cells after 24 h of exposure and genetic damage after 3 and 24 h. The involvement of the Zn2+ ions released from the NP in genotoxicity was confirmed. ZnO NP exposure also resulted in decreased locomotor activity of zebrafish embryos, with a clear role of released Zn2+ ions in this effect. These findings support the toxic potential of ZnO NP showing, for the first time, genetic effects on glial cells and proving the intervention of Zn2+ ions.

Cardiotoxicity risk induced by sanitary insecticide Dimefluthrin

Dimefluthrin (DIM) is a commonly utilized sanitary insecticide, predominantly employed for indoor pest management within residential and public environments directly interacting with human habitation. However, the usage of DIM is escalating with increasing mosquito resistance, prompting concerns about its health risks. Here, using zebrafish as a research model, we systematically evaluated DIM's impact on human health. Findings revealed significant health hazards during embryonic development, including reduced hatching rates, shortened body lengths, and organ malformations, notably affecting the heart. It was explored the mechanism of DIM-induced cardiotoxicity in zebrafish, and histopathological analyses revealed that DIM resulted in ventricular linearization in zebrafish embryos. Antioxidant enzyme activities were reduced and cardiac reactive oxygen species (ROS) accumulated after DIM exposure, suggesting clear signs of oxidative stress. Additionally, acridine orange (AO) staining and caspase-3 immunofluorescence demonstrated cardiac apoptosis in Tg (kdrl: EGFP) zebrafish. qPCR analysis implied that DIM induced apoptosis via the p53/Caspase pathway by up-regulating the expression levels of p53, cytochrome C (cyto-C), caspase-9, and caspase-3. Together, our work provided a systematic perspective on the cardiotoxicity of sanitary pesticides, which could offer opportunities for future risk management.

Discovery of a highly selective fluorescent probe for hydrogen peroxide and its biocompatibility evaluation and bioimaging applications in cells and zebrafish

As one of the most widely distributed reactive oxygen species in vivo, hydrogen peroxide plays divergent and important roles in cell growth, differentiation and aging. When the level of hydrogen peroxide in the body is abnormal, it will lead to genome mutation and induce irreversible oxidative modification of proteins, lipids and polysaccharides, resulting in cell death or even disease. Therefore, it is significant to develop a sensitive and specific probe for real-time detection of hydrogen peroxide in vivo. In this study, the response mechanism between hydrogen peroxide and probe QH was investigated by means of HRMS and the probe showed good optical properties and high selectivity to hydrogen peroxide. Note that the evaluating of probe biocompatibility resulted from cytotoxicity test, behavioral test, hepatotoxicity test, cardiotoxicity test, blood vessel toxicity test, immunotoxicity test and neurotoxicity test using cell and transgenic zebrafish models with more than 20 toxic indices. Furthermore, the detection performance of the probe for hydrogen peroxide was evaluated by multiple biological models and the probe was proved to be much essential for the monitoring of hydrogen peroxide in vivo.

Waterborne atenolol disrupts neurobehavioral and neurochemical responses in adult zebrafish

Environmental contamination by pharmaceuticals from industrial waste and anthropogenic activities poses adverse health effects on non-target organisms. We evaluated the neurobehavioral and biochemical responses accompanying exposure to ecological relevant concentrations of atenolol (0, 0.1, 1.0, and 10 µg/L) for seven uninterrupted days in adult zebrafish (Danio rerio). Atenolol-exposed fish exhibited anxiety-like behavior, characterized by significant bottom-dwelling with marked reduction in vertical exploration. Atenolol-exposed fish exhibited marked increase in the duration and frequency of aggressive events without altering their preference for conspecifics. Biochemical data using brain samples indicated that atenolol disrupted antioxidant enzyme activities and induced oxidative stress. Exposure to atenolol markedly decreased ATP and AMP hydrolysis without affecting ADP hydrolysis and acetylcholinesterase (AChE) activity. Atenolol significantly upregulated tryptophan hydroxylase 1 (tph1) mRNA expression but downregulated brain-derived neurotrophic factor (bdnf) mRNA. Collectively, waterborne atenolol elicits aggressive and anxiety-like responses in adult zebrafish, accompanied by oxidative stress, reduced nucleotide hydrolysis, altered tph1 and bdnf mRNA expression, which may impact the survival and health of fish in aquatic environment.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Comparison of developmental toxicity of graphene oxide and graphdiyne to zebrafish larvae

Graphdiyne (GDY) is a new member of family of carbon-based 2D nanomaterials (NMs), but the environmental toxicity is less investigated compared with other 2D NMs, such as graphene oxide (GO). In this study, we compared with developmental toxicity of GO and GDY to zebrafish larvae. It was shown that exposure of zebrafish embryos from 5 h post fertilization to GO and GDY for up to 5 days decreased hatching rate and induced morphological deformity. Behavioral tests indicated that GO and GDY treatment led to hyperactivity of larvae. However, blood flow velocity was not significantly affected by GO or GDY. RNA-sequencing data revealed that both types of NMs altered gene expression profiles as well as gene ontology terms and KEGG pathways related with metabolism. We further confirmed that the NMs altered the expression of genes related with lipid droplets and autophagy, which may be account for the delayed development of zebrafish larvae. At the same mass concentrations, GO induced comparable or even larger toxic effects compared with GDY, indicating that GDY might be more biocompatible compared with GO. These results may provide novel understanding about the environmental toxicity of GO and GDY in vivo.

Behavioral toxicity and neurotoxic mechanisms of PLA-PBAT biodegradable microplastics in zebrafish

Escalation of ecological concern due to biodegradable plastics has attracted the attention of many contemporary researchers. This study searched to investigate the acute and sub-chronic toxicity of polylactic acid (PLA) and polybutyleneadipate-co-terephthalate (PLA-PBAT) bio-microplastics on 3-month-old zebrafish to elucidate their potential toxic mechanisms. Acute toxicity assessments revealed 96 h-LC50 value of 12.69 mg/L for PLA-PBAT. Sub-chronic exposure of over 21 days revealed deviations in critical behavioral patterns and physiological indicators. In treated groups, weight gain and specific growth rates were significantly lower than those obtained for the control group, such that high doses induced significant reductions in total organ coefficient (p < 0.05). A positive correlation was observed between zebrafish mortality and increased doses. Detailed behavioral evaluations revealed a dose-dependent decrease in the speed and range of swimming, along with modifications in shoaling behavior, anxiety-like responses, and avoidance behaviors. Brain tissues transcriptomic analyses revealed the molecular responses underlying sub-chronic exposure to PLA-PBAT. Totally 702 DEGs and 5 KEGG pathways were significantly identified in low-dose group, with the top 2 significant pathways being ribosome pathway and cytokine-cytokine receptor interaction pathway. Totally 650 DEGs and 5 KEGG pathways were significantly identified in medium-dose group, with the top 2 significant pathways being Herpes simplex virus 1 infection pathway and complement and coagulation cascades pathway. Totally 1778 DEGs and 16 KEGG pathways were significantly identified in high-dose group, with the top 2 significant pathways being metabolism of xenobiotics by cytochrome P450 and drug metabolism - cytochrome P450 pathway. Most significantly enriched pathways are associated with immune responses. The validation of key gene in cytokine-cytokine receptor interaction pathway also confirmed its high correlation with behavioral indicators. These results indicate that PLA-PBAT is likely to cause behavioral abnormalities in zebrafish by triggering immune dysregulation in the brain.

Rhodamine B, an organic environmental pollutant induces reproductive toxicity in parental and teratogenicity in F1 generation in vivo

This study investigated the reproductive toxicity of rhodamine B in zebrafish and its transgenerational effects on the F1 generation. In silico toxicity predictions revealed high toxicity of rhodamine B, mainly targeting pathways associated with the reproductive and endocrine systems. In vivo experiments on zebrafish demonstrated that rhodamine B exposure at a concentration of 1.5 mg/L led to significant impairments in fecundity parameters, particularly affecting females. Histopathological analysis revealed distinct changes in reproductive organs, further confirming the reproductive toxicity of rhodamine B, with females being more susceptible than males. Gene expression studies indicated significant suppression of genes crucial for ovulation in rhodamine B-treated female fish, highlighting hormonal imbalance as a potential mechanism of reproductive toxicity. Furthermore, bioaccumulation studies showed the presence of rhodamine B in both adult fish gonads and F1 generation samples, suggesting transgenerational transfer of the dye. Embryotoxicity studies on F1 generation larvae demonstrated reduced survival rates, lower hatching rates, and increased malformations in groups exposed to rhodamine B. Moreover, rhodamine B induced oxidative stress in F1 generation larvae, as evidenced by elevated levels of reactive oxygen species and altered antioxidant enzyme activity. Neurotoxicity assessments revealed reduced acetylcholinesterase activity, indicating potential neurological impairments in F1 generation larvae. Additionally, locomotory defects and skeletal abnormalities were observed in F1 generation larvae exposed to rhodamine B. This study provides comprehensive evidence of the reproductive toxicity of rhodamine B in adult zebrafish and its transgenerational effects on the F1 generation.

Polluted water from a storage dam (Villa Victoria, méxico) induces oxidative damage, AChE activity, embryotoxicity, and behavioral changes in Cyprinus carpio larvae

The Villa Victoria dam is one of the most important storage reservoirs in Mexico since it distributes water to more than 20 million inhabitants in the Metropolitan Zone of Mexico City. In this dam, the common carp (Cyprinus carpio) is an important food resource for the inhabitants, so the aim of this work was to evaluate the oxidative damage (lipoperoxidation, oxidized proteins, antioxidant enzymes activity and gene expression), AChE, embryotoxicity and behavioral changes in C. carpio embryos and larvae exposed to water from Villa Victoria dam for 24, 48, 72 and 96 h. The embryotoxicity was evaluated trough the General Morphology Score (GMS) and the teratogenic index. Behavioral changes in basal locomotor activity and thigmotaxis were evaluated in a DanioVision, Noldus ™. An increase in lipid and protein oxidation as well as modification of CAT, SOD and GPx enzymatic activity was observed during the exposure times. The GMS indicated a low development in the embryos, the teratogenic index was less than 1, however teratogenic effects as yolk edema, fin malformation, head malformation and scoliosis were observed. In parallel, an increase in AChE activity and gene expression was observed reflecting changes in distance traveled of the basal locomotor activity and thigmotaxis at the sampling points. In conclusion, pollutants in water from Villa Victoria dam caused oxidative damage, changes in SOD, CAT, GPx and AChE activity as well as embryotoxicity and modifications in the behavior of C. carpio larvae. This study demonstrates the need to implement restoration programs for this reservoir since, contamination in the Villa Victoria dam could eventually endanger aquatic life and human health.

Behavioral Effects of the Mixture and the Single Compounds Carbendazim, Fipronil, and Sulfentrazone on Zebrafish (Danio rerio) Larvae

Pesticides are often detected in freshwater, but their impact on the aquatic environment is commonly studied based on single compounds, underestimating the potential additive effects of these mixtures. Even at low concentrations, pesticides can negatively affect organisms, altering important behaviors that can have repercussions at the population level. This study used a multi-behavioral approach to evaluate the effects of zebrafish larvae exposure to carbendazim (C), fipronil (F), and sulfentrazone (S), individually and mixed. Five behavioral tests, thigmotaxis, touch sensitivity, optomotor response, bouncing ball test, and larval exploratory behavior, were performed to assess potential effects on anxiety, fear, and spatial and social interaction. Significant changes were observed in the performance of larvae exposed to all compounds and their mixtures. Among the single pesticides, exposure to S produced the most behavioral alterations, followed by F and C, respectively. A synergistic effect between the compounds was observed in the C + F group, which showed more behavioral effects than the groups exposed to pesticides individually. The use of behavioral tests to evaluate pesticide mixtures is important to standardize methods and associate behavioral changes with ecologically relevant events, thus creating a more realistic scenario for investigating the potential environmental impacts of these compounds.

Evaluation of sub-chronic toxicity of melamine via systematic or oral delivery in adult zebrafish based on behavioral endpoints

Melamine-tainted products have been found in the market and raised issues about food safety. Recent studies done in rodents and humans demonstrated the toxicities of melamine, especially in causing kidney damage and bladder stone formation. However, very few studies assessed its behavior toxicity in organisms, including fish. Therefore, in this study, the researchers aim to determine whether sub-chronic exposure to melamine via oral and systematic administration could induce behavioral abnormality in zebrafish. After 14 days of systematic exposure to melamine at doses of 0.1 and 10 ppm levels, zebrafish were subjected to multiple behavioral assays. Results from both exposure routes showed that melamine indeed slightly increased fish locomotion and altered their exploratory behaviors in the novel tank assay. Furthermore, tightened shoaling formation was also displayed by the treated fish in the waterborne exposure group. However, melamine exposure did not cause any obvious alterations in fish behaviors during other behavioral tests. In addition, in comparison with previously published data on the behavior toxicities of several solvents in zebrafish, our phenomic analysis suggests the relatively low behavior toxicities of melamine via either systematic exposure or oral administration to zebrafish compared to those solvents. Nevertheless, our data indicate that the potential neurotoxicity of chronic low-dose melamine should not be ignored.

Recent advances and current challenges of new approach methodologies in developmental and adult neurotoxicity testing

Adult neurotoxicity (ANT) and developmental neurotoxicity (DNT) assessments aim to understand the adverse effects and underlying mechanisms of toxicants on the human nervous system. In recent years, there has been an increasing focus on the so-called new approach methodologies (NAMs). The Organization for Economic Co-operation and Development (OECD), together with European and American regulatory agencies, promote the use of validated alternative test systems, but to date, guidelines for regulatory DNT and ANT assessment rely primarily on classical animal testing. Alternative methods include both non-animal approaches and test systems on non-vertebrates (e.g., nematodes) or non-mammals (e.g., fish). Therefore, this review summarizes the recent advances of NAMs focusing on ANT and DNT and highlights the potential and current critical issues for the full implementation of these methods in the future. The status of the DNT in vitro battery (DNT IVB) is also reviewed as a first step of NAMs for the assessment of neurotoxicity in the regulatory context. Critical issues such as (i) the need for test batteries and method integration (from in silico and in vitro to in vivo alternatives, e.g., zebrafish, C. elegans) requiring interdisciplinarity to manage complexity, (ii) interlaboratory transferability, and (iii) the urgent need for method validation are discussed.

How neurobehavior and brain development in alternative whole-organism models can contribute to prediction of developmental neurotoxicity

Developmental neurotoxicity (DNT) is not routinely evaluated in chemical risk assessment because current test paradigms for DNT require the use of mammalian models which are ethically controversial, expensive, and resource demanding. Consequently, efforts have focused on revolutionizing DNT testing through affordable novel alternative methods for risk assessment. The goal is to develop a DNT in vitro test battery amenable to high-throughput screening (HTS). Currently, the DNT in vitro test battery consists primarily of human cell-based assays because of their immediate relevance to human health. However, such cell-based assays alone are unable to capture the complexity of a developing nervous system. Whole organismal systems that qualify as 3 R (Replace, Reduce and Refine) models are urgently needed to complement cell-based DNT testing. These models can provide the necessary organismal context and be used to explore the impact of chemicals on brain function by linking molecular and/or cellular changes to behavioural readouts. The nematode Caenorhabditis elegans, the planarian Dugesia japonica, and embryos of the zebrafish Danio rerio are all suited to low-cost HTS and each has unique strengths for DNT testing. Here, we review the strengths and the complementarity of these organisms in a novel, integrative context and highlight how they can augment current cell-based assays for more comprehensive and robust DNT screening of chemicals. Considering the limitations of all in vitro test systems, we discuss how a smart combinatory use of these systems will contribute to a better human relevant risk assessment of chemicals that considers the complexity of the developing brain.

Effects of sodium dodecylbenzene sulfonate (SDBS) on zebrafish (Danio rerio) gills and blood

Sodium dodecylbenzene sulfonate (SDBS) is an important surfactant used as a cleaning agent and industrial additive to remove unwanted chemicals which have been detected in the aquatic environment. The aim of this study was to examine the toxicological potential of SDBS on the gills of adult male zebrafish (Danio rerio) exposed to this chemical. For the 96 hr acute exposure, fish were divided into three groups: control, 0.25 mg/L, and 0.5 mg/L of SDBS. After the experiment, morphophysiological analyses (gill histopathology and histochemistry), oxidative stress (determination of gill activities of superoxide dismutase (SOD) and catalase (CAT)), and hematological analyses (leukocyte differentiation) were conducted. Data demonstrated that SDBS at both tested concentrations altered the histopathological index and initiated circulatory disturbances, as well as adverse, progressive, and immunological changes in the gills. In the 0.5 mg/L group, SOD activity decreased significantly, but CAT activity was not altered. Prominent blood changes observed in this group were neutrophilia and lymphocytosis. The number of mucous and chloride cells increased significantly in both groups. Taken together, our findings demonstrated that exposure of D. rerio to SDBS, even for 96 hr, produced adverse morphological and hematological effects associated with a reduction in SOD activity. Our findings indicate that exposure of aquatic species to the anionic surfactant SDBS may lead to adverse consequences associated with oxidative stress. Therefore, this study highlights the risks that this substance may pose to aquatic ecosystems and emphasizes the need for further investigations and strict regulations on its disposal.

Exposure to the antineoplastic ifosfamide alters molecular pathways related to cardiovascular function, increases heart rate, and induces hyperactivity in zebrafish (Danio rerio)

Ifosfamide is an alkylating antineoplastic drug used in chemotherapy, but it is also detected in wastewater. Here, the objectives were to (1) determine teratogenic, cardiotoxic, and mitochondrial toxicity potential of ifosfamide exposure; (2) elucidate mechanisms of toxicity; (3) characterize exposure effects on larval behavior. Survival rate, hatch rate, and morphological deformity incidence were not different amongst treatments following exposure levels up to 1000 µg/L ifosfamide over 7 days. RNA-seq reveled 231 and 93 differentially expressed transcripts in larvae exposed to 1 µg/L and 100 µg/L ifosfamide, respectively. Several gene networks related to vascular resistance, cardiovascular response, and heart rate were affected, consistent with tachycardia observed in exposed embryonic fish. Hyperactivity in larval zebrafish was observed with ifosfamide exposure, potentially associated with dopamine-related gene networks. This study improves ecological risk assessment of antineoplastics by elucidating molecular mechanisms related to ifosfamide toxicity, and to alkylating agents in general.

The concentration of dissolved organic matter impacts the neurobehavior in female zebrafish exposed to cyclophosphamide

Cyclophosphamide (CP) is a broad-spectrum anticancer drug for various cancers and frequently detected in aquatic environments, reaching concentrations up to 22 μg/L. However, there is limited understanding of the toxicities of CP with the presence of dissolved organic matter, a ubiquitous component in aquatic environments, in fish. In this study, we investigated the behaviors, morphological alterations of retina, and related gene transcripts in zebrafish exposed to CP (0 and 50 μg/L) and Humic acid (HA, a main component of DOM) at concentrations of 0, 3, 10, and 30 mg-C/L for 30 days. The results showed that, relative to the zebrafish in CP treatment, HA at 30 mg-C/L increased the locomotion (12.1 % in the light and 7.2 % in the dark) and startle response (9.7 %), while inhibiting the anxiety (12.5 %) and cognition of female zebrafish (24.6 %). The levels of transcripts of neurotransmitter- (tph1b and ache), neuroinflammation-(il-6 and tnfα) and antioxidant-(gpx) related genes in the brain of female adult were also altered by CP with the presence of HA. In addition, HA promoted the transgenerational effects of CP on the neurobehaviors. Therefore, HA can enhance potential neurotoxicity of CP in female fish through alteration neurotransmission related genes. Our findings provide new insights into the toxicity and underlying mechanisms of CP with the presence of dissolved organic matter, thereby contribute to a deeper understanding of the risks posed by CP in aquatic ecosystems.

Mixture of pesticides based on dimethylamine and imidacloprid affects locomotion of adult zebrafish

Numerous chemical compounds are found in aquatic environments; among them are pesticides. Pesticides are widely used worldwide, and this use has progressively increased in recent decades, resulting in the accumulation of potentially toxic compounds in surface waters. Dimethylamine-based herbicides (DBH) and imidacloprid-based insecticides (IBI) have low soil absorption and high water solubility, facilitating the arrival of these compounds in aquatic environments. In this study, our objective was to analyze whether two pesticides, DBH and IBI at environmentally relevant concentrations of 320 μg/L for each compound, and their mixtures impact the behavioral and endocrine parameters of adult zebrafish, verifying the effect of pesticides on exploratory behavior and social and analyzing hormonal parameters related to stress. Acute exposure to the mixture of pesticides reduced fish locomotion. Pesticides alone and in combination did not affect cortisol levels in exposed animals. Pesticides, when tested together, can cause different effects on non-target organisms, and the evaluation of mixtures of these compounds is extremely important.

The Effects of Wastewater Reuse on Smallmouth Bass (Micropterus dolomieu) Relative Abundance in the Shenandoah River Watershed, USA

Municipal and industrial wastewater effluent is an important source of water for lotic systems, especially during periods of low flow. The accumulated wastewater effluent flows-expressed as a percentage of total streamflow (ACCWW%)-contain chemical mixtures that pose a risk to aquatic life; fish may be particularly vulnerable when chronically exposed. Although there has been considerable focus on individual-level effects of exposure to chemical mixtures found in wastewater effluent, scaling up to population-level effects remains a challenging component needed to better understand the potential consequences of exposure in wild populations. This may be particularly important under a changing climate in which wastewater reuse could be essential to maintain river flows. We evaluated the effects of chronic exposure to wastewater effluent, as measured by ACCWW%, on the relative abundance of young-of-year (YOY), juvenile, and adult smallmouth bass (Micropterus dolomieu) populations in the Shenandoah River Watershed (USA). We found that increases in ACCWW% in the previous year and during the prespawn period were negatively correlated with the relative abundance of YOY, resulting in an average 41% predicted decrease in abundance (range = 0.5%-94% predicted decrease in abundance). This lagged effect suggests that adult fish reproductive performance may be compromised by chemical exposure during periods of high ACCWW%. No relationships between ACCWW% and juvenile or adult relative abundance were found, suggesting that negative effects of ACCWW% on YOY abundance may be offset due to compensatory mechanisms following higher ACCWW% exposure. Understanding the effects of wastewater effluent exposure at multiple levels of biological organization will help in the development of management strategies aimed at protecting aquatic life. Environ Toxicol Chem 2024;00:1-11. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Fluorene-induced stress in the benthic oligochaete Tubifex tubifex: A multi-biomarker assessment of toxicological pathways and mechanisms under acute and subchronic exposures

This study examined the multifaceted impacts of fluorene exposure on Tubifex tubifex, encompassing acute (survival analysis and behavioral responses) and subchronic exposure regimens (antioxidant enzyme response and histopathology), molecular docking studies, and generalized read-across analysis. Survival analysis revealed concentration-dependent increases in toxicity over varying time intervals, with LC50 values decreasing from 30.072 mg/L at 24 h to 12.365 mg/L at 96 h, emphasizing the time-sensitive and concentration-responsive nature of the stressor. Behavioral responses were both concentration- and duration-dependent. While Erratic Movement and Clumping Tendency exhibited earlier responses (within 24 h) at lower concentrations, the wrinkling effect and mucus secretion) exhibited delayed onset, suggesting intricate regulatory mechanisms underlying adaptability to environmental challenges; moreover, the wrinkling effect was consistently induced at higher concentrations, indicating greater sensitivity to the toxic effects of fluorene. With sublethal environmentally relevant concentrations-1.24 mg/l and 2.47 mg/L i.e., 10% and 20% 96 h, respectively-the antioxidant enzyme response (i.e., upregulation of SOD, CAT, and GST) with increasing fluorene concentration, revealing a nonlinear, hormetic response, suggested adaptive protection at lower doses but inhibition at higher concentrations. Histopathological examination indicated that higher fluorene concentrations caused cellular proliferation, inflammation, and severe tissue damage in the digestive tract and body wall. Molecular docking studies demonstrated robust interactions between fluorene and major stress biomarker enzymes, disrupting their functions and inducing oxidative stress. Interactions with cytochrome c oxidase suggested interference with cellular energy production. Generalized Read-Across (GenRA) analysis unveiled shared toxicity mechanisms among fluorene and its analogs, involving the formation of reactive epoxides and the influence of cytochrome P450 enzymes. The diverse functional groups of these analogs, particularly chlorine-containing compounds, were implicated in toxicity through lipid peroxidation and membrane damage. Adverse outcome pathways and broader consequences for aquatic ecosystem health are discussed.

Polystyrene microplastics induced disturbances in neuronal arborization and dendritic spine density in mice prefrontal cortex

An increasing use of plastics in daily life leads to the accumulation of microplastics (MPs) in the environment, posing a serious threat to the ecosystem, including humans. It has been reported that MPs cause neurotoxicity, but the deleterious effect of polystyrene (PS) MPs on neuronal cytoarchitectural morphology in the prefrontal cortex (PFC) region of mice brain remains to be established. In the present study, Swiss albino male mice were orally exposed to 0.1, 1, and 10 ppm PS-MPs for 28 days. After exposure, we found a significant accumulation of PS-MPs with a decreased number of Nissl bodies in the PFC region of the entire treated group compared to the control. Morphometric analysis in the PFC neurons using Golgi-Cox staining accompanied by Sholl analysis showed a significant reduction in basal dendritic length, dendritic intersections, nodes, and number of intersections at seventh branch order in PFC neurons of 1 ppm treated PS-MPs. In neurons of 0.1 ppm treated mice, we found only decrease in the number of intersections at the seventh branch order. While 10 ppm treated neurons decreased in basal dendritic length, dendritic intersections, followed by the number of intersections at the third and seventh branch order were observed. As well, spine density on the apical secondary branches along with mRNA level of BDNF was significantly reduced in all the PS-MPs treated PFC neurons, mainly at 1 ppm versus control. These results suggest that PS-MPs exposure affects overall basal neuronal arborization, with the highest levels at 1 and 10 ppm, followed by 0.1 ppm treated neurons, which may be related to the down-regulation of BDNF expression in PFC.

Zebrafish neuromast sensory system: Is it an emerging target to assess environmental pollution impacts?

Environmental pollution poses risks to ecosystems. Among these risks, one finds neurotoxicity and damage to the lateral line structures of fish, such as the neuromast and its hair cells. Zebrafish (Danio rerio) is recommended as model species to be used in ecotoxicological studies and environmental biomonitoring programs aimed at assessing several biomarkers, such as ototoxicity. However, little is known about the history of and knowledge gaps on zebrafish ototoxicity. Thus, the aim of the current study is to review data available in the scientific literature about using zebrafish as animal model to assess neuromast toxicity. It must be done by analyzing the history and publication category, world production, experimental design, developmental stages, chemical classes, neuromasts and hair cell visualization methods, and zebrafish strains. Based on the results, number, survival and fluorescence intensity of neuromasts, and their hair cells, were the parameters oftentimes used to assess ototoxicity in zebrafish. The wild AB strain was the most used one, and it was followed by Tübingen and transgenic strains with GFP markers. DASPEI was the fluorescent dye most often applied as method to visualize neuromasts, and it was followed by Yo-Pro-1 and GFP transgenic lines. Antibiotics, antitumorals, metals, nanoparticles and plant extracts were the most frequent classes of chemicals used in the analyzed studies. Overall, pollutants can harm zebrafish's mechanosensory system, as well as affect their behavior and survival. Results have shown that zebrafish is a suitable model system to assess ototoxicity induced by environmental pollution.

The uses of zebrafish (Danio rerio) as an in vivo model for toxicological studies: A review based on bibliometrics

An in vivo model is necessary for toxicology. This review analyzed the uses of zebrafish (Danio rerio) in toxicology based on bibliometrics. Totally 56,816 publications about zebrafish from 2002 to 2023 were found in Web of Science Core Collection, with Toxicology as the top 6 among all disciplines. Accordingly, the bibliometric map reveals that "toxicity" has become a hot keyword. It further reveals that the most common exposure types include acute, chronic, and combined exposure. The toxicological effects include behavioral, intestinal, cardiovascular, hepatic, endocrine toxicity, neurotoxicity, immunotoxicity, genotoxicity, and reproductive and transgenerational toxicity. The mechanisms include oxidative stress, inflammation, autophagy, and dysbiosis of gut microbiota. The toxicants commonly evaluated by using zebrafish model include nanomaterials, arsenic, metals, bisphenol, and dioxin. Overall, zebrafish provide a unique and well-accepted model to investigate the toxicological effects and mechanisms. We also discussed the possible ways to address some of the limitations of zebrafish model, such as the combination of human organoids to avoid species differences.

4-Methylbenzylidene camphor induced neurobehavioral toxicity in zebrafish (Danio rerio) embryos

4-Methylbenzylidene camphor (4-MBC) is a widely used organic UV filter in personal care products. Extensive use of 4-MBC and its frequent detection in aquatic ecosystems defile the biota with muscular and neuronal impairments. This study investigates the neurobehavioral toxicity of 4-MBC using Danio rerio as a model organism. Embryos were exposed semi-statically to 4-MBC at 5, 50, and 500 μg/L concentrations for 10-day post fertilization (dpf). Embryos exhibited a significant thigmotaxis and decreased startle touch response with altered expression of nervous system mRNA transcripts on 5 & 10 dpf. Compared to the sham-exposed group, 4-MBC treated larvae exhibited changes in the expression of shha, ngn1, mbp, elavl3, α1-tubulin, syn2a, and gap43 genes. Since ngn1 induction is mediated by shh signaling during sensory neuron specification, the elevated protein expression of NGN1 indicates 4-MBC interference in the sonic hedgehog signaling pathway. This leads to sensory neuron impairment and function such as 'sense' as evident from reduced touch response. In addition, larval brain histology with a reduced number of cells in the Purkinje layer emblazing the defunct motor coordination. Predictive toxicity study also showed a higher affinity of 4-MBC to modeled Shh protein. Thus, the findings of the present work highlighted that 4-MBC is potential to induce developmental neurotoxicity at both behavioral and molecular functional perspectives, and developing D. rerio larvae could be considered as a suitable alternate animal model to assess the neurological dysfunction of organic UV filters.

Astaxanthin activates the Nrf2/Keap1/HO-1 pathway to inhibit oxidative stress and ferroptosis, reducing triphenyl phosphate (TPhP)-induced neurodevelopmental toxicity

Triphenyl phosphate (TPhP) serves as a major organophosphorus flame retardant, and its induced neurodevelopmental toxicity has attracted widespread attention, but the mechanism remains unclear. In this study, we involved zebrafish to explore the new mechanism of TPhP inducing oxidative stress and ferroptosis to promote neurodevelopmental toxicity. The results suggested that TPhP affected the embryonic development, reduced the number of new neurons, and led to abnormal neural behavior in zebrafish larvae. TPhP also induced ROS accumulation, activated the antioxidant defense signal Nrf2 and Keap1, and significantly changed the activities of Acetylcholinesterase (AChE), Adenosine triphosphatase (ATPase) and glutathione S-transferase (GST). In addition, TPhP induced ferroptosis in zebrafish, which was reflected in the increase of Fe2+ content, the abnormal expression of GPX4 protein and genes related to iron metabolism (gpx4a, slc7a11, acsl4b, tfa, slc40a1, fth1b, tfr2, tfr1a, tfr1b and ncoa4). Astaxanthin intervention specifically inhibited ROS levels, and reversed SLC7A11 and GPX4 expression levels and Fe2+ metabolism thus alleviating ferroptosis induced by TPhP. Astaxanthin also partially reversed the activity of AChE, GST and the expression of neurodevelopmental-related genes (gap43, gfap, neurog1 and syn2a), so as to partially rescue the embryonic developmental abnormalities and motor behavior disorders induced by TPhP. More interestingly, the expression of mitochondrial apoptosis-related protein BAX, anti-apoptotic protein BCL-2, Caspase3 and Caspase9 was significantly altered in the TPhP exposed group, which could be also reversed by Astaxanthin intervention. In summary, our results suggested that TPhP exposure can induce oxidative stress and ferroptosis, thereby causing neurodevelopment toxicity to zebrafish, while Astaxanthin can partially reverse oxidative stress and reduce the neurodevelopmental toxicity of zebrafish larvae by activating Nrf2/Keap1/HO-1 signaling pathway.

Long-term effects of embryonic exposure to benzophenone-3 on neurotoxicity and behavior of adult zebrafish

Benzophenone-3 (BP-3) is the most widely used ultraviolet filter (UV filter) in industries to avoid UV radiation damage. BP-3 is added to most sunscreens to protect the skin, hair, and lips from sun rays. It results in continuous discharge into aquatic environments, leading to aquatic biota and human's continuous exposure. Consequences of BP-3 exposure on the physiology and behavior of aquatic animals, mainly zebrafish, have been investigated, including their neurotoxic effects. However, little is known about its consequences in long-term developmental endpoints. This study aimed to investigate the long-term effects of embryonic BP-3 exposure on biomarkers of neurotoxicity in zebrafish. For this, we exposed embryos to 5, 10, and 20 μg∙L-1 BP-3 concentration and let fish grow to adulthood (5mpf). We evaluated anxiety-like behavior, social preference, aggressiveness, and enzymatic activity of the antioxidant defenses system and neurotoxic biomarkers (Glutathione S-transferase -GST, catalase -CAT, and acetylcholinesterase -AChE) in adult zebrafish. Enzymatic activities were also investigated in larvae immediately after BP-3 exposure. Animals early exposed to BP-3 presented anxiety-like behaviors and decreased social preference, but aggressiveness was not altered. In general, exposure to BP-3 leads to altered enzymatic activity, which persists into adulthood. GST activity increased in embryos and adults, while CAT activity decreased in both life stages. AChE activity enhanced only at the larval stage (96 hpf). The long-term behavioral and biochemical effects of BP-3 highlight the need for abolishing or restricting the compound from personal care products, which are continually disposed into the environment and threaten the biota and human health.

Comparing Ocular Toxicity of Legacy and Alternative Per- and Polyfluoroalkyl Substances in Zebrafish Larvae

Studies comparing the ocular toxicity potential between legacy and alternative PFAS are lacking. To address this research gap, zebrafish larvae were exposed to both legacy PFAS (i.e., perfluorooctanesulfonic acid [PFOS] and perfluorooctanoic acid [PFOA]) and their corresponding alternatives (i.e., perfluorobutanesulfonic acid [PFBS] and perfluorobutanoic acid [PFBA]). Alterations in their visual behaviors, such as phototactic and optomotor responses (OMR), were assessed at sublethal concentrations. Gene expression variations in visual function-associated pathways were also measured. Visual behavioral assessment revealed that PFOS exposure resulted in concentration-dependent reductions in phototactic responses at 10-1000 μg/L, with PFOA exerting reduction effects only at 100 mg/L. However, their two alternatives had no effect at all tested concentrations. Following an improved contrast-OMR (C-OMR) assessment, PFOS decreased the OMR to a water flow stimulus at 10, 100, and 1000 μg/L. The gene expression analysis revealed that PFOS exposure markedly downregulated most genes involved in the opsins in the photoreceptor and phototransduction cascade, which explains the observed visual behavior changes well. Our findings indicate that PFOS is the most likely PFAS to cause visual toxicity, with PFOA present but less likely, and their substitutes, PFBS and PFBA, cannot be classified as visually toxic to zebrafish.

The hepatotoxicity assessment of micro/nanoplastics: A preliminary study to apply the adverse outcome pathways

Plastic pollution has become a significant global problem over the years, leading to the continuous decomposition and accumulation of micro/nanoplastics (MNPLs) in the environment. As a result, human exposure to these MNPLs is inevitable. The liver, in particular, is highly susceptible to potential MNPL toxicity. In this study, we systematically reviewed the current literature on MNPLs-induced hepatotoxicity and collected data on toxic events occurring at different biological levels. Then, to better understand the cause-mechanism causality, we developed an Adverse Outcome Pathway (AOP) framework for MNPLs-induced hepatotoxicity. The AOP framework provided insights into the mechanism of MNPL-induced hepatotoxicity and highlighted potential health risks such as liver dysfunction and inflammation, metabolism disorders and liver fibrosis. Moreover, we discussed the potential application of emerging toxicological models in the hepatotoxicity study. Liver organoids and liver-on-chips, which can simulate the structure and function of the liver in vitro, offer a promising alternative platform for toxicity testing and risk assessment. We proposed combining the AOP framework with these emerging toxicological models to improve our understanding of the hepatotoxic effects of MNPLs. Overall, this study performed a preliminary exploration of novel toxicological methodologies to assess the hepatotoxicity of MNPLs, providing a deeper understanding of environmental toxicology.

Fenpropathrin causes alterations in locomotion and social behaviors in zebrafish (Danio rerio)

Fenpropathrin is one of the widely used pyrethroid pesticides in agriculture and is frequently detected in the environment, groundwater, and food. While fenpropathrin was found to have neurotoxic effects in mammals, it remains unclear whether it has similar effects on fish. Here, we used adult zebrafish to investigate the impacts of fenpropathrin on fish social behaviors and neural activity. Exposure of adult zebrafish to 500 ppb of fenpropathrin for 72 h increased anxiety levels but decreased physical fitness, as measured by a novel tank diving test and swimming tunnel test. Fish exposed to fenpropathrin appeared to spend more time in the conspecific zone of the tank, possibly seeking greater comfort from their companions. Although learning, memory, and aggressive behavior did not change, fish exposed to fenpropathrin appeared to have shorter fighting durations. The immunocytochemical results showed the tyrosine hydroxylase antibody-labeled dopaminergic neurons in the teleost posterior tuberculum decreased in the zebrafish brain. According to a quantitative polymerase chain reaction (qPCR) analysis of the brain, exposure to fenpropathrin resulted in a decrease in the messenger (m)RNA expression of monoamine oxidase (mao), an enzyme that facilitates the deamination of dopamine. In contrast, the mRNA expression of the sncga gene, which may trigger Parkinson's disease, was found to have increased. There were no changes observed in expressions of genes related to antioxidants and apoptosis between the control and fenpropathrin-exposed groups. We provide evidence to demonstrate the defect of the neurotoxicity of fenpropathrin toward dopaminergic neurons in adult zebrafish.

Developmental and neurobehavioral toxicity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (antioxidant AO2246) during the early life stage of zebrafish

BACKGROUND

2,2'-Methylenebis (4-methyl-6-tert-butylphenol) (AO2246) is a synthetic phenolic antioxidant extensively used in food packaging bags and cosmetics. Recently, AO2246 was detected with unexpectedly high concentrations in plasma and breast milk samples from pregnant and lactating women. Hence, it is essential to conduct a thorough investigation to evaluate the detrimental effects of AO2246 on biota.

OBJECTIVE

To investigate the developmental and behavioral toxicity of AO2246 in zebrafish, as well as the molecular mechanisms underlying these effects.

METHODS

Zebrafish embryos were exposed to AO2246 at concentrations ranging from 0.05 to 10 μM for up to 6 days postfertilization (dpf). Hatching rate, survival rate, heart rate, and body length were measured. Locomotor behavioral and electrophysiologal analyses were performed. Two fluorescence-labeled transgenic zebrafish lines (endothelium-Tg and macrophage/microglia-Tg) were employed. RNA sequencing was carried out.

RESULTS

AO2246 has a 96-hour LC50 value of 3 μM. The exposure of AO2246 resulted in a significant reduction in both hatching rate and heart rate. Analysis of locomotor behavior demonstrated that larvae exposed to AO2246 doses exceeding 2 μM exhibited a significant decrease in both total distance and mean velocity. Electrophysiological recordings demonstrated a noteworthy reduction in spike activity at a concentration of 3 μM, relative to control conditions. The administration of AO2246 at 3 μM elicited morphological reactivity and immune alteration of the midbrain microglia in the macrophage/microglia-transgenic zebrafish line, indicating a potential contribution of neurological disorders to behavioral defects. RNA sequencing analysis revealed altered gene expression profiles at high AO2246 concentrations, particularly the dysregulation of pathways associated with neuronal function.

CONCLUSIONS

The present study demonstrates that AO2246 exposure elicits developmental and neurobehavioral toxicity in zebrafish larvae. Specifically, exposure to AO2246 was found to cause disturbances in neuronal electrophysiological activity and neurological disorders, which ultimately led to the impairment of locomotor behavior in zebrafish larvae.

Toxic effects of exogenous retinoic acid on the neurodevelopment of zebrafish (Danio rerio) embryos

Endogenous retinoic acid (RA) is essential for embryonic development and maintaining adult physiological processes. Human-caused RA residues in the environment threaten the survival of organisms in the environment. We employed zebrafish as a model to explore the developmental impacts of excess RA. We used exogenous RA to raise the amount of RA signal in the embryos and looked at the effects of excess RA on embryonic morphological development. Upregulation of the RA signal significantly reduced embryo hatching and increased embryo malformation. To further understand the neurotoxic impact of RA signaling on early neurodevelopment, we measured the expression of neurodevelopmental marker genes and cell death and proliferation markers in zebrafish embryos. Exogenous RA disrupted stem cell (SC) and neuron marker gene expression and exacerbated apoptosis in the embryos. Furthermore, we looked into the links between the transcriptional coactivator RBM14 and RA signaling to better understand the mechanism of RA neurotoxicity. There was a negative interaction between RA signaling and the transcription coactivator RBM14, and the morpholino-induced RBM14 down-regulation can partially block the effects of RAR antagonist BMS493-induced RA signaling inhibition on embryonic malformation and cell apoptosis. In conclusion, exogenous RA causes neurodevelopmental toxicity, and RBM14 may be involved in this neurotoxic process.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Neurobehavioral effects of fungicides in zebrafish: a systematic review and meta-analysis

Pesticides are widely used in global agriculture to achieve high productivity levels. Among them, fungicides are specifically designed to inhibit fungal growth in crops and seeds. However, their application often results in environmental contamination, as these chemicals can persistently be detected in surface waters. This poses a potential threat to non-target organisms, including humans, that inhabit the affected ecosystems. In toxicologic research, the zebrafish (Danio rerio) is the most commonly used fish species to assess the potential effects of fungicide exposure, and numerous and sometimes conflicting findings have been reported. To address this, we conducted a systematic review and meta-analysis focusing on the neurobehavioral effects of fungicides in zebrafish. Our search encompassed three databases (PubMed, Scopus, and Web of Science), and the screening process followed predefined inclusion/exclusion criteria. We extracted qualitative and quantitative data, as well as assessed reporting quality, from 60 included studies. Meta-analyses were performed for the outcomes of distance traveled in larvae and adults and spontaneous movements in embryos. The results revealed a significant overall effect of fungicide exposure on distance, with a lower distance traveled in the exposed versus control group. No significant effect was observed for spontaneous movements. The overall heterogeneity was high for distance and moderate for spontaneous movements. The poor reporting practices in the field hindered a critical evaluation of the studies. Nevertheless, a sensitivity analysis did not identify any studies skewing the meta-analyses. This review underscores the necessity for better-designed and reported experiments in this field.

A vision for safer food contact materials: Public health concerns as drivers for improved testing

Food contact materials (FCMs) and food contact articles are ubiquitous in today's globalized food system. Chemicals migrate from FCMs into foodstuffs, so called food contact chemicals (FCCs), but current regulatory requirements do not sufficiently protect public health from hazardous FCCs because only individual substances used to make FCMs are tested and mostly only for genotoxicity while endocrine disruption and other hazard properties are disregarded. Indeed, FCMs are a known source of a wide range of hazardous chemicals, and they likely contribute to highly prevalent non-communicable diseases. FCMs can also include non-intentionally added substances (NIAS), which often are unknown and therefore not subject to risk assessment. To address these important shortcomings, we outline how the safety of FCMs may be improved by (1) testing the overall migrate, including (unknown) NIAS, of finished food contact articles, and (2) expanding toxicological testing beyond genotoxicity to multiple endpoints associated with non-communicable diseases relevant to human health. To identify mechanistic endpoints for testing, we group chronic health outcomes associated with chemical exposure into Six Clusters of Disease (SCOD) and we propose that finished food contact articles should be tested for their impacts on these SCOD. Research should focus on developing robust, relevant, and sensitive in-vitro assays based on mechanistic information linked to the SCOD, e.g., through Adverse Outcome Pathways (AOPs) or Key Characteristics of Toxicants. Implementing this vision will improve prevention of chronic diseases that are associated with hazardous chemical exposures, including from FCMs.

Comparative Assessment of the Toxicity of Brominated and Halogen-Free Flame Retardants to Zebrafish in Terms of Tail Coiling Activity, Biomarkers, and Locomotor Activity

BDE-47, a flame retardant that is frequently detected in environmental compartments and human tissues, has been associated with various toxic effects. In turn, information about the effects of aluminum diethyl-phosphinate (ALPI), a halogen-free flame retardant from a newer generation, is limited. This study aims to assess and compare the toxicity of BDE-47 and ALPI to zebrafish by analyzing the tail coiling, locomotor, acetylcholinesterase activities, and oxidative stress biomarkers. At 3000 µg/L BDE-47, the coiling frequency increased at 26-27 h post-fertilization (hpf), but the burst activity (%) and mean burst duration (s) did not change significantly. Here, we considered that the increased coiling frequency is a slight neurotoxic effect because locomotor activity was impaired at 144 hpf and 300 µg/L BDE-47. Moreover, we hypothesized that oxidative stress could be involved in the BDE-47 toxicity mechanisms. In contrast, only at 30,000 µg/L did ALPI increase the catalase activity, while the motor behavior during different developmental stages remained unaffected. On the basis of these findings, BDE-47 is more toxic than ALPI.

Developmental toxicity, immunotoxicity and cardiotoxicity induced by methidathion in early life stages of zebrafish

Methidathion is a highly effective organophosphorus pesticide and is extensively utilized for the control of insects in agricultural production. However, there is little information on the adverse effects and underlying mechanisms of methidathion on aquatic organisms. In this work, embryonic zebrafish were exposed to methidathion at concentrations of 4, 10, and 25 mg/L for 96 h, and morphological changes and activities of antioxidant indicators alterations were detected. In addition, the locomotor behavioral abilities of zebrafish exposed to methidathion were also measured. To further explore the mechanism of the toxic effects of methidathion, gene expression levels associated with cardiac development, cell apoptosis, and the immune system were tested through qPCR assays. The findings revealed that methidathion exposure could induce a decrease in survival rate, hatchability, length of body, and increase in abnormality of zebrafish, as well as cardiac developmental toxicity. The LC50 value of methidathion in zebrafish embryos was determined to be about 30.72 mg/L at 96 hpf. Additionally, methidathion exposure triggered oxidative stress in zebrafish by increasing SOD activity, ROS, and MDA content. Acridine orange (AO) staining indicated that methidathion exposure led to apoptosis, which was mainly distributed in the pericardial region. Furthermore, significant impairments of locomotor activity in zebrafish larvae were induced by methidathion exposure. Lastly, the expression of pro-inflammatory factors including IFN-γ, IL-6, IL-8, CXCL-clc, TLR4, and MYD88 significantly up-regulated in exposed zebrafish. Taken together, the results in this work illustrated that methidathion caused developmental toxicity, cardiotoxicity, and immunotoxicity in embryogenetic zebrafish.

ZIF-8 Nanoparticles Induce Behavior Abnormality and Brain Oxidative Stress in Adult Zebrafish (Danio rerio)

Zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs) are typical metal-organic framework (MOF) materials and have been intensively studied for their potential application in drug delivery and environmental remediation. However, knowledge of their potential risks to health and the environment is still limited. Therefore, this study exposed female and male zebrafish to ZIF-8 NPs (0, 9.0, and 90 mg L^-1) for four days. Subsequently, variations in their behavioral traits and brain oxidative stress levels were investigated. The behavioral assay showed that ZIF-8 NPs at 90 mg/L could significantly decrease the locomotor activity (i.e., hypoactivity) of both genders. After a ball falling stimulation, zebrafish exposed to ZIF-8 NPs (9.0 and 90 mg L^-1) exhibited more freezing states (i.e., temporary cessations of movement), and males were more sensitive than females. Regardless of gender, ZIF-8 NPs exposure significantly reduced the SOD, CAT, and GST activities in the brain of zebrafish. Correlation analysis revealed that the brain oxidative stress induced by ZIF-8 NPs exposure might play an important role in their behavioral toxicity to zebrafish. These findings highlight the necessity for further assessment of the potential risks of MOF nanoparticles to aquatic species and the environment.

Zebrafish as an Animal Model in Cannabinoid Research

Cannabinoids are active substances present in plants of the Cannabis genus. Both the Food and Drug Administration (FDA) and European Medicines Agency (EMA) have approved several medicinal products containing natural cannabinoids or their synthetic derivatives for the treatment of drug-resistant epilepsy, nausea and vomiting associated with cancer chemotherapy, anorexia in AIDS patients, and the alleviation of symptoms in patients with multiple sclerosis. In fact, cannabinoids constitute a broad group of molecules with a possible therapeutic potential that could be used in the management of much more diseases than mentioned above; therefore, multiple preclinical and clinical studies on cannabinoids have been carried out in recent years. Danio rerio (zebrafish) is an animal model that has gained more attention lately due to its numerous advantages, including easy and fast reproduction, the significant similarity of the zebrafish genome to the human one, simplicity of genetic modifications, and body transparency during the early stages of development. A number of studies have confirmed the usefulness of this model in toxicological research, experiments related to the impact of early life exposure to xenobiotics, modeling various diseases, and screening tests to detect active substances with promising biological activity. The present paper focuses on the current knowledge of the endocannabinoid system in the zebrafish model, and it summarizes the results and observations from studies investigating the pharmacological effects of natural and synthetic cannabinoids that were carried out in Danio rerio. The presented data support the notion that the zebrafish model is a suitable animal model for use in cannabinoid research.