Chronic exposure to dietary selenomethionine dysregulates the genes involved in serotonergic neurotransmission and alters social and antipredator behaviours in zebrafish (Danio rerio)

Assessment of dietary Selenium and its role in Mercury fate in cultured fish rainbow trout with two sustainable aquafeeds

This study enhances the current limited understanding of the interaction between mercury (Hg) and selenium (Se) species in fish. Rainbow trout (Oncorhynchus mykiss), a model aquaculture fish, was exposed to Hg and Se species through controlled dietary conditions. Over a 6-month feeding trial, the impact of dietary Se on Hg bioaccumulation in fish, including flesh, brain, and liver, was tracked. Twelve dietary conditions were tested, including plant-based diets (0.25 µgSe g-1) and tuna byproduct diets (0.25 µgHg g-1, 8.0 µgSe g-1) enriched with methylmercury and/or Se as selenite or selenomethionine. The tuna byproduct diet resulted in lower Hg levels than the plant-based diets, with muscle Hg content below the European Commission's safe threshold. This study highlights the significant impact of specific Se compounds in the diet, particularly from tuna-based aquafeed, on Hg bioaccumulation. These promising results provide a strong recommendation for future use of fisheries byproducts in sustainable aquafeeds.

Neurobehavioral toxic effects and mechanisms of 2-aminobenzothiazole exposure on zebrafish

2-Aminobenzothiazole (NTH), a benzothiazole derivative, exhibits potent biochemical activities and plays a significant role in modern industry. Widespread and intensive utilization of NTH has led to its detection in aquatic environments, encompassing both groundwater and surface water. Despite its wide usage, the effect of NTH on developmental neurotoxicity in aquatic organisms remains uncharted. Therefore, the aim of this investigation was to create exposure models for short- and long-term studies in order to analyze the neurobehavioral toxic impact of NTH (0, 50, 500, and 5000 μg/L) on zebrafish, which includes motor function, anxiety, and memory performance, as well as to examine the mechanism of neurotoxicity. The results revealed a significant suppression of initial embryonic mobility by NTH. However, during short-term exposure experiments, it did not significantly impact the developmental neurobehavioral functions of zebrafish. In addition, significant effects on zebrafish were observed after long-term exposure to 50 and 500 μg/L NTH, mainly impacting locomotion, social behavior, anxiety, and cognitive functions. Moreover, NTH caused oxidative damage in adult zebrafish brain tissue, which was accompanied by abnormal expression of oxidative damage-related genes. Furthermore, the Real-Time PCR results indicated a significant suppression of genes related to exposure to NTH, specifically those in the GABA synthesis pathway (gabrg2, gad2, gad1b, and abat) and the 5-HT synthesis pathway (tph2, tph1b, pet1, and htr1aa). Taken together, this study demonstrates for the first time that chronic exposure to NTH decreases the expression of genes associated with the zebrafish GABA synthesis pathway and the 5-HT synthesis pathway. This suppression is accompanied by oxidative damage, ultimately resulting in neurobehavioral changes related to motor ability, anxiety, and memory performance.

Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system

Bisphenol S (BPS) is a common endocrine-disrupting chemical globally used in several consumer and industrial products. Although previous studies suggested that BPS induces multiple effects in exposed organisms, very little is known about its intergenerational effect on offspring behavior and/or the potential underlying mechanisms. To this end, adult female zebrafish Danio rerio were exposed to BPS (0, 10, 30 µg/L) and 1 µg/L of 17-β-estradiol (E2) as a positive control for 60 days. Afterwards, female fish were bred with untreated males, and their offspring were raised to 6 months old in control water. Maternal exposure to BPS decreased male offspring anxiety and antipredator behaviors while boldness remained unaffected. Specifically, maternal exposure to 10 and 30 µg/L BPS and 1 µg/L E2 were found to impact male offspring anxiety levels as they decreased the total time that individuals spent in the dark zone in the light/dark box test and increased the total track length in the center of the open field test. In addition, maternal exposure to all concentrations of BPS and E2 disrupted antipredator responses of male offspring by decreasing shoal cohesion in the presence of chemical alarm cues derived from conspecifics, which communicated high risk. To elucidate the possible molecular mechanism underlying these neuro-behavioral effects of BPS, we assessed the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter and monoamine oxidase (MAO). The impaired anxiety and antipredator responses were associated with reduced levels of 5-HT1A subtype and MAO mRNA expression within the brain of adult male offspring. Collectively, the results of this study demonstrate that maternal exposure to environmental concentrations of BPS can interfere with the serotonergic signaling pathway in the developing brain, subsequently leading to the onset of a suite of behavioral deficits in adult offspring.

Neurotoxicity of the Cu(OH)2 Nanopesticide through Perturbing Multiple Neurotransmitter Pathways in Developing Zebrafish

The copper hydroxide [Cu(OH)2] nanopesticide is an emerging agricultural chemical that can negatively impact aquatic organisms. This study evaluated the behavioral changes of zebrafish larvae exposed to the Cu(OH)2 nanopesticide and assessed its potential to induce neurotoxicity. Metabolomic and transcriptomic profiling was also conducted to uncover the molecular mechanisms related to potential neurotoxicity. The Cu(OH)2 nanopesticide at 100 μg/L induced zebrafish hypoactivity, dark avoidance, and response to the light stimulus, suggestive of neurotoxic effects. Altered neurotransmitter-related pathways (serotoninergic, dopaminergic, glutamatergic, GABAergic) and reduction of serotonin (5-HT), dopamine (DA), glutamate (GLU), γ-aminobutyric acid (GABA), and several of their precursors and metabolites were noted following metabolomic and transcriptomic analyses. Differentially expressed genes (DEGs) were associated with the synthesis, transport, receptor binding, and metabolism of 5-HT, DA, GLU, and GABA. Transcripts (or protein levels) related to neurotransmitter receptors for 5-HT, DA, GLU, and GABA and enzymes for the synthesis of GLU and GABA were downregulated. Effects on both the glutamatergic and GABAergic pathways in zebrafish were specific to the nanopesticide and differed from those in fish exposed to copper ions. Taken together, the Cu(OH)2 nanopesticide induced developmental neurotoxicity in zebrafish by inhibiting several neurotransmitter-related pathways. This study presented a model for Cu(OH)2 nanopesticide-induced neurotoxicity in developing zebrafish that can inform ecological risk assessments.

Dopaminergic and serotoninergic neurotoxicity of lanthanide phosphate (TbPO4) in developing zebrafish

Rare earth elements (REEs) are exploited for global use in manufacturing. Such activities result in their release into the environment and the transformation into more stable phosphate deposition. The objective of this study was to evaluate molecular and behavioral changes of zebrafish exposed to the synthesized terbium phosphate (TbPO4) at concentrations of 10, 20, and 50 mg/L and to determine its potential for neurotoxicity. Metabolomics related to neurotransmitters, and assessment of transcripts and proteins were conducted to uncover the molecular mechanisms underlying TbPO4 with emphasis on neurotransmitter systems. Exposure to 20 mg/L TbPO4 induced larval hyperactivity and perturbed the cholinergic system in zebrafish. Based on metabolomics related to neurotransmitters, dopamine (DA), serotonin (5-HT), and many of their precursors and metabolites were decreased in abundance by TbPO4. In addition, the expression levels of transcripts related to the synthesis, transport, receptor binding, and metabolism of DA and 5-HT were analyzed at the mRNA and protein levels. Transcript and protein levels for tyrosine hydroxylase (TH), the rate-limiting enzyme for DA synthesis, were down-regulated in larval fish. Monoamine oxidase (MAO), an enzyme that catabolizes monoamines DA and 5-HT, was also reduced in mRNA abundance. We hypothesize that DA synthesis and monoamine metabolism are associated with behavioral alterations. This study elucidates putative mechanisms and exposure risks to wildlife and humans by characterizing phosphatic REE-induced neurotoxicity in developing zebrafish.

Neurobehavioral disorders induced by environmental zinc in female zebrafish (Danio rerio): Insights from brain and intestine transcriptional and metabolic signatures

Human activities can cause zinc (Zn) contamination of aquatic environments. Zn is an essential trace metal, but effects of environmentally relevant Zn exposure on the brain-intestine axis in fish are poorly understood. Here, six-month-old female zebrafish (Danio rerio) were exposed to environmentally relevant Zn concentrations (0, 1.0, and 1.5 mg/L) for six weeks. Zn significantly accumulated in the brain and intestine, causing anxiety-like behaviors and altered social behaviors. Zn accumulation altered levels of neurotransmitters, including serotonin, glutamate, and γ-aminobutyric acid, in the brain and intestine, and these changes were directly associated with changes in behavior. Zn caused oxidative damage and mitochondrial dysfunction, and impaired NADH dehydrogenase, thereby dysregulating the energy supply in brain Zn exposure resulted in nucleotide imbalance and dysregulation of DNA replication and the cell cycle, potentially impairing the self-renewal of intestinal cells. Zn also disturbed carbohydrate and peptide metabolism in the intestine. These results indicate that chronic exposure to Zn at environmentally relevant concentrations dysregulates the bidirectional interaction of the brain-intestine axis with respect to neurotransmitters, nutrients, and nucleotide metabolites, thereby causing neurological disorder-like behaviors. Our study highlights the necessity to evaluate the negative impacts of chronic environmentally relevant Zn exposure on the health of humans and aquatic animals.

Application of autonomous sensor technology to estimate selenium exposure and a site-specific selenium threshold in a Canadian boreal lake

There is an increasing trend in the use of real-time sensor technology to remotely monitor aquatic ecosystems. Commercially available probes, however, are currently not able to measure aqueous selenium (Se) concentrations. Because of the well-described bioaccumulation potential and associated toxicity of Se in oviparous vertebrates, it is crucial to monitor Se concentrations at sites receiving continuous effluent Se input. This study aimed to estimate Se concentrations in a boreal lake (McClean Lake) downstream from a Saskatchewan uranium mill using real-time electrical conductivity (EC) data measured by autonomous sensors. Additionally, this study aimed to derive a site-specific total aqueous Se (TSe) threshold based on Se concentrations in periphyton and benthic macroinvertebrates sampled from the same lake. To characterize effluent distribution within the lake, eight Smart Water (Libelium) sensor units were programmed to report EC and temperature for five and seven consecutive weeks in 2018 and 2019, respectively. In parallel, periphyton and benthic macroinvertebrates were sampled with Hester-Dendy's artificial substrate samplers (n = 4) at the same sites and subsequently analyzed for Se concentrations. Electrical conductivity was measured with a handheld field meter for sensor data validation and adjusted to the median lake water temperature (13 °C) registered for the deployment periods. Results demonstrated good accuracy of sensor readings relative to handheld field meter readings and the successful use of real-time EC in estimating TSe exposure (r = 0.87; r²  = 0.84). Linear regression equations derived for Se in detritivores versus Se in periphyton and Se in periphyton versus sensor-estimated TSe were used to estimate a site-specific TSe threshold of 0.7 µg/L (±0.2). Moreover, mean Se concentrations in periphyton (16.7 ± 4.4 µg/g dry weight [d.w.]) and benthic detritivores (6.0 ± 0.4 µg/g d.w.) from one of the exposure sites helped identify an area with potential for high Se bioaccumulation and toxicity in aquatic organisms in McClean Lake. Integr Environ Assess Manag 2023;19:395-411. © 2022 SETAC.

Fentanyl Induces Novel Conditioned Place Preference in Adult Zebrafish, Disrupts Neurotransmitter Homeostasis, and Triggers Behavioral Changes

Abuse of new psychoactive substances increases risk of addiction, which can lead to serious brain disorders. Fentanyl is a synthetic opioid commonly used in clinical practice, and behavioral changes resulting from fentanyl addiction have rarely been studied with zebrafish models. In this study, we evaluated the rewarding effects of intraperitoneal injections of fentanyl at concentrations of 10, 100, and 1000 mg/L on the group shoaling behavior in adult zebrafish. Additional behavioral tests on individual zebrafish, including novel tank, novel object exploration, mirror attack, social preference, and T-maze memory, were utilized to evaluate fentanyl-induced neuro-behavioral toxicity. The high doses of 1000 mg/L fentanyl produced significant reward effects in zebrafish and altered the neuro-behavioral profiles: reduced cohesion in shoaling behavior, decreased anxiety levels, reduced exploratory behavior, increased aggression behavior, affected social preference, and suppressed memory in an appetitive associative learning task. Behavioral changes in zebrafish were shown to be associated with altered neurotransmitters, such as elevated glutamine (Gln), gamma-aminobutyric acid (GABA), dopamine hydrochloride (DA), and 5-hydroxytryptamine (5-HT). This study identified potential fentanyl-induced neurotoxicity through multiple neurobehavioral assessments, which provided a method for assessing risk of addiction to new psychoactive substances.

Acute toxicity of broflanilide on neurosecretory system and locomotory behavior of zebrafish (Danio rerio)

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC₅₀) of 0.76 mg/L. However, its effect on fish behavior and the underlying mechanisms are still unclear. The present study evaluated the effects of broflanilide on the zebrafish brain over a 96-h exposure by comparing the histopathological changes and relative expression of targeted genes with the behavioral metrics. The results of the toxicity test showed that broflanilide could cause deformities, such as deformation of the operculum and spinal curvature, at 0.6, 0.82 and 1.15 mg/L. Results also showed tissue damage and apoptosis in the cerebellum under 0.27 and 0.6 mg/L exposure. Additionally, broflanilide affected the neurotransmitters, metabolites and transcripts of genes associated with dopamine, gamma-aminobutyric acid expression. and the signaling pathways in zebrafish brains at 0.60 mg/L after 1 h and 96 h of exposure, while the levels of glutamate, glutamate decarboxylase, GABA transaminase, nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) were also inhibited at 0.27 mg/L after 96 h of exposure. The accumulated swimming distance was significantly longer and the average speed was significantly faster than the control at 0.27 and 0.6 mg/L after 1-h of exposure, while these metrics were lowered at 0.6 mg/L after 96 h of exposure. The study results demonstrates that broflanilide affects the zebrafish brain, neurotransmitters and associated fish behaviors. This study also provides deeper insight into the mechanistic understanding of the effects of broflanilide on the zebrafish brain.

Selenium Distribution and Trophic Transfer in the Periphyton-Benthic Macroinvertebrate Food Chain in Boreal Lakes Downstream from a Milling Operation

Selenium (Se) is an essential micronutrient with a narrow essentiality-toxicity range known to bioaccumulate in aquatic food webs. Selenium uptake and trophic transfer at the base of aquatic food chains represent a great source of uncertainty for Se risk assessment. The goal of the present study was to investigate Se distribution in water and sediment and its subsequent transfer into the periphyton-benthic macroinvertebrate (BMI) food chain in boreal lakes downstream from a Saskatchewan uranium mill. In particular, the present study aimed to assess potential differences in Se bioaccumulation patterns by BMI taxa to contribute to the current knowledge gap. During summer 2018 and 2019, water, sediment, periphyton, and BMI were sampled at two sites in Vulture Lake, seven sites in McClean Lake east basin, and one reference site in McClean Lake west basin. Periphyton and BMI taxa were sampled with artificial substrates (Hester-Dendy) deployed for 5 weeks in 2018 and 7 weeks in 2019; BMI were sorted into the lowest practical achievable taxonomic level and analyzed for total Se concentrations. At the diluted effluent exposure sites, Se concentrations in BMI ranged from 1.3 to 18.0 µg/g dry weight and from 0.3 to 49.3 µg/g dry weight in 2018 and 2019, respectively, whereas concentrations ranged from 0.01 to 3.5 µg/g dry weight at the reference site. Selenium concentrations in periphyton and some BMI taxa sampled near the effluent diffuser (Se < 1 µg/L) reached levels comparable to higher effluent exposure sites (Se > 2 µg/L). Despite differences in Se bioaccumulation among BMI taxa, an approximately one-to-one trophic transfer ratio was observed for benthic primary consumers and benthic predatory taxa. Environ Toxicol Chem 2022;41:2181-2192. © 2022 SETAC.

Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring

Recent studies show that bisphenol S (BPS) induces multiple adverse effects in exposed organisms; however, the maternal effects of BPS exposure remain poorly understood. Here, we expose adult female zebrafish to environmentally relevant concentrations of BPS (0, 1, 10, 30 μg/L) and 1 μg/L of 17-β-estradiol (E2) as a positive control for 60 days. Females were then paired with BPS-unexposed males and their offspring were raised in control water for 6 months. Maternal exposure to BPS was found to alter social behavior and anxiety response in a dose-specific manner in male offspring. Group preferences and social cohesion were significantly reduced by maternal exposure to 1 and 10 μg/L BPS, respectively. Additionally, maternal exposure to 1 and 30 μg/L BPS and E2 decreased offspring stress responses during the novel tank test. The impaired social behavior was associated with elevated arginine-vasotocin (AVT) level as well as with the altered expression of genes involved in AVT signaling pathway (AVT, avpr1aa) and enzymatic antioxidant genes (cat and Mn-sod) in the brain. Collectively, these results suggest that maternal exposure to environmentally relevant concentrations of BPS alters social behavior in zebrafish offspring, which is likely mediated by oxidative stress and disruption of neuropeptide signaling pathways in the brain.

Excessive selenium affects neural development and locomotor behavior of zebrafish embryos

Selenium is an essential micronutrient derived from daily diet to maintain the normal growth and development of vertebrates. Excessive selenium intake will induce cardiovascular toxicity, reproductive toxicity and neurotoxicity. However, there have been few studies of the toxic effects of selenium on neural development and locomotor behavior. In this study, newly fertilized zebrafish embryos were treated with selenium. As a result, selenium treatment at the concentration of 0.5 µM decreased the moving speed and distance and blunted the touch response of zebrafish embryos. TUNEL assay and immunofluorescence analysis revealed that selenium induced nervous system impairment including promoted cell apoptosis, proliferation and neuroinflammation, and decreased neurons in zebrafish embryos. RNA-seq and RT-PCR results indicated that selenium treatment significantly decreased the expression of the dopaminergic neuron, motor neuron, GABAergic neuron and neurotransmitter transport marker genes in zebrafish embryos. The expression of PPAR signaling pathway marker genes was significantly down-regulated in selenium-treated embryos. Two PPAR agonists (rosiglitazone and bezafibrate) and an anti-cancer drug (cisplatin) were tested for their effects to alleviate selenium-induced locomotor defects. Rosiglitazone and bezafibrate could restore the expression of some neural marker genes but could not fully rescue the selenium-induced locomotor behavior defects. The supplementation of cisplatin could restore the dysfunctional locomotor behavior and the abnormal expression of the PPAR and neural marker genes to almost the normal levels. In conclusion, the results of this study reveal that selenium-induced neural development and locomotor behavior defects are caused by multiple complex factors including PPAR signaling, and all the factors might be recovered by cisplatin through unknown mechanisms.

Ferroptosis and Apoptosis Are Involved in the Formation of L-Selenomethionine-Induced Ocular Defects in Zebrafish Embryos

Selenium is an essential trace element for humans and other vertebrates, playing an important role in antioxidant defense, neurobiology and reproduction. However, the toxicity of excessive selenium has not been thoroughly evaluated, especially for the visual system of vertebrates. In this study, fertilized zebrafish embryos were treated with 0.5 µM L-selenomethionine to investigate how excessive selenium alters zebrafish eye development. Selenium-stressed zebrafish embryos showed microphthalmia and altered expression of genes required for retinal neurogenesis. Moreover, ectopic proliferation, disrupted mitochondrial morphology, elevated ROS-induced oxidative stress, apoptosis and ferroptosis were observed in selenium-stressed embryos. Two antioxidants—reduced glutathione (GSH) and N-acetylcysteine (NAC)—and the ferroptosis inhibitor ferrostatin (Fer-1) were unable to rescue selenium-induced eye defects, but the ferroptosis and apoptosis activator cisplatin (CDDP) was able to improve microphthalmia and the expression of retina-specific genes in selenium-stressed embryos. In summary, our results reveal that ferroptosis and apoptosis might play a key role in selenium-induced defects of embryonic eye development. The findings not only provide new insights into selenium-induced cellular damage and death, but also important implications for studying the association between excessive selenium and ocular diseases in the future.

Behavioral genetics of alcohol's effects in three zebrafish (Danio rerio) populations

Alcohol abuse is one of the most dangerous and serious problems for patients and society. Interpopulation studies are important in understanding how genetic background contributes to the effects of alcohol. In this study, we applied a chronic alcohol exposure protocol in three zebrafish populations (Danio rerio; both sexes; AB, TU, and outbred fish - OB). We analyzed the behavioral responses and mRNA expression involved in neurotransmitter metabolism - th1, tph1, ache, ada1, gaba1, gad1b, and bdnf. Locomotion patterns were similar between populations (increased speed after acute alcohol and unaltered locomotion after chronic and withdrawal treatments). All populations exhibited increased expression of genes associated with locomotion (th1, gad1b, and gaba1) after acute alcohol exposure. Anxiety-like responses increased in AB and TU fish during withdrawal and decreased in AB fish after acute alcohol exposure. Genes related to anxiety-like behavior (tph1 and ada1) were overexpressed in AB and TU fish after acute and withdrawal treatments, while OB fish exhibited unaltered responses. Bdnf levels decreased during withdrawal in AB and OB fish, while TU showed upregulated levels in both chronic and withdrawal treatments. Our results suggest that zebrafish populations respond differently to alcohol exposure, which may contribute to understanding the mechanisms underlying alcohol use and dependence. Moreover, we found that a more diverse genetic background (OB) was related to higher variability in behavioral and mRNA expression, demonstrating that inbred populations (AB and TU) may be useful tools in identifying alcohol use and abuse mechanisms.

Immunotoxicity of polychlorinated biphenyls (PCBs) to the marine crustacean species, Scylla paramamosain

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in environments, and they can negatively affect aquatic animal health. After 7 days of PCBs exposure, the activities of catalase, phenoloxidase, and superoxide dismutase and the total hemocyte count in the haemolymph were significantly decreased and the reactive oxygen species (ROS) content and phagocytic rate of hemocytes were significantly increased in mud crab Scylla paramamosain. Additionally, serum lysozyme, glutathione, glutathione-S-transferase, and glutathione peroxidase activities were significantly down-regulated in mud crab after PCBs exposure. The survival rate of crab hemocytes significantly declined as the PCBs concentration increased, indicating that PCBs had a cytotoxic effect on hemocytes. Exposure to increasing concentrations of PCBs also increased the degree of DNA damage in crab hemocytes. After PCBs exposure, the expression levels of P53 and caspase-3 in hemocytes were significantly up-regulated, which suggests that apoptosis was occurring. The apoptosis rate of hemocytes was up-regulated as the PCBs concentration increased, indicating that apoptosis was induced by the PCBs-activated caspase-3 pathway. These data suggest that exposure to PCBs hampered the immune response of mud crabs, most likely by (1) inducing ROS, causing DNA damage, and reducing the viability of hemocytes, (2) reducing the activities of antioxidant enzymes, and (3) inducing phagocytosis and apoptosis of hemocytes. And the final result of PCBs-induced immunotoxicity to mud crabs is the reduced bacterial disease resistance and survival rate of crabs under Vibrio alginolyticus challenge.

Transgenerational effects of selenomethionine on behaviour, social cognition, and the expression of genes in the serotonergic pathway in zebrafish

Elevated levels of contaminants from human activities have become a major threat to animals, particularly within aquatic ecosystems. Selenium (Se) is a naturally occurring element with a narrow range of safe intake, but excessive Se has toxicological effects, as it can bioaccumulate and cause cognitive and behavioural impairments. In this study, we investigated whether exposure to Se would also have transgenerational effects, causing changes in the descendants of exposed individuals. We exposed adult female zebrafish to either a control diet or environmentally relevant concentrations of dietary Se-Met (3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days. Then, females from each treatment group were bred with untreated males, and the offspring (F1-generation) were raised to adulthood (6 months old) without Se exposure. In behavioural tests, offspring that were maternally exposed to 34.1 μg Se/g showed signs of elevated stress, weaker group preferences, and impaired social learning. Maternal exposure to high levels of Se-Met also led to dysregulation of the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter, and monoamine oxidase (MAO). Such perturbations in the serotonergic system, thus, appear to underlie the neurobehavioural deficits that we observed. These findings suggest that Se contamination can have important transgenerational consequences on social behaviour and cognition.

Dietary Seleno-l-Methionine Causes Alterations in Neurotransmitters, Ultrastructure of the Brain, and Behaviors in Zebrafish (Danio rerio)

Elevated concentrations of dietary selenium (Se) cause abnormalities and extirpation of fish inhabiting in Se-contaminated environments. However, its effect on fish behavior and the underlying mechanisms remain largely unknown. In this study, two-month-old zebrafish (Danio rerio) was fed seleno-l-methionine (Se-Met) at environmentally relevant concentrations (i.e., control (2.61), low (5.43), medium (12.16), and high (34.61) μg Se/g dry weight (dw), respectively, corresponding to the C, L, M, and H treatments) for 60 days. Targeted metabolomics, histopathological, and targeted transcriptional endpoints were compared to behavioral metrics to evaluate the effects of dietary exposure to Se-Met . The results showed that the levels of total Se and malondialdehyde in fish brains were increased in a dose-dependent pattern. Meanwhile, mitochondrial damages and decreased activities of the mitochondria respiratory chain complexes were observed in the neurons at the M and H treatments. In addition, dietary Se-Met affected neurotransmitters, metabolites, and transcripts of the genes associated with the dopamine, serotonin, gamma-aminobutyric acid, acetylcholine, and histamine signaling pathways in zebrafish brains at the H treatments. The total swimming distance and duration in the Novel Arm were lowered in fish from the H treatment. This study has demonstrated that dietary Se-Met affects the ultrastructure of the zebrafish brain, neurotransmitters, and associated fish behaviors and may help enhance adverse outcome pathways for neurotransmitter-behavior key events in zebrafish.

Chronic exposure to environmentally realistic levels of diuron impacts the behaviour of adult marine medaka (Oryzias melastigma)

Diuron, a commonly used herbicide and antifouling biocide, has been frequently detected in seawater. The effects of diuron on fish behaviour are currently poorly understood. Herein, the marine medaka (Oryzias melastigma) was continuously exposed to environmentally realistic levels of diuron from the fertilised egg stage to the adult stage. Behavioural evaluation of adult marine medaka indicated that exposure to diuron increased anxiety in the light-dark test and increased predator avoidance. In addition, diuron exposure significantly reduced aggression, social interaction, shoaling, and learning and memory ability. However, only negligible variations in foraging behaviour and in behaviour in the novel tank test were observed. Marine medaka chronically exposed to diuron also showed decreased levels of dopamine in the brain, and changes were observed in the transcription of genes related to dopamine synthesis, degradation and receptors. Exposure to 5000 ng/L diuron caused significant downregulation of the expression of the genes of tyrosine hydroxylase and monoamine oxidase and significantly upregulated the expression of the genes of the D5 dopaminergic receptor. The relative expression of the D4 dopaminergic receptor was significantly upregulated in the 50, 500 and 5000 ng/L diuron-treated groups. These findings highlight the significant neurotoxic effects of diuron and the extent to which this may involve the dopaminergic system of the brain. More broadly, this study reveals the ecological risk associated with environmentally realistic levels of diuron in marine animals.

Chronic exposure to bisphenol S induces oxidative stress, abnormal anxiety, and fear responses in adult zebrafish (Danio rerio)

Bisphenol S (BPS) is increasingly used in a wide range of industrial and consumer products, resulting in its ubiquitous distribution across the environment, including aquatic ecosystems. Although it is commonly known as a weak/moderate estrogenic compound, there has been a growing acknowledgment of the potential of BPS to cause toxicity by inducing oxidative stress. Oxidative stress is a major participant in the development of anxiety-like behaviors in humans and animals. Therefore, the present study was designed to examine the impact of BPS on anxiety-like behavior and fear responses in adult zebrafish and also to elucidate the possible linkage between the BPS neurotoxicity and oxidative status of the brain. To this end, adult male and female zebrafish were exposed to 0 (control), 1, 10, and 30 μg/L of BPS and 1 μg/L of 17-β-estradiol (E2) for 75 days. Following exposure, changes in anxiety and fear-related responses were evaluated by applying a novel tank test and by exposing focal fish to chemical alarm cues. Additionally, we evaluated the expression of multiple antioxidant genes in the zebrafish brain. Our results indicate that BPS, irrespective of exposure concentration, and E2 significantly decreased bottom-dwelling behavior and the latency to enter the upper water column. Furthermore, exposure to the highest concentration of BPS and E2 induced a significant decrease in fear-related responses. The impaired anxiety and reduced fear-related responses were associated with a down-regulation in the transcription of genes involved in enzymatic antioxidant defense. Taken together, our results suggest that chronic exposure to BPS impairs anxiety and fear responses in adult zebrafish, possibly by inducing oxidative stress in the brain.

Bisphenol S exposure alters behavioral parameters in adult zebrafish and offspring

The environmental emission of bisphenol S (BPS), which is globally utilized in the manufacturing of polycarbonates, epoxy resin and thermal paper, has affected the aquatic ecosystem. Thus, effects of BPS exposure on the fitness of aquatic animals have been noted. Here, adult male and female zebrafish were used as aquatic model organisms and separately exposed to environmentally relevant doses of BPS (0, 1, 10 and 100 μg/L) for 14 days. The results showed that BPS changed the body pigment of zebrafish and slowed the maturation of oocytes in the ovary, resulting in a significant decrease in the shoaling behavior of adult zebrafish and the attraction of BPS-treated females during the mating process. Furthermore, in the subgeneration of adult zebrafish exposed to BPS for 7 days, survival behaviors, such as locomotor, phototaxis and feeding behaviors, deviated from normal behaviors. After exposing the adult zebrafish to BPS for an additional 7 days, the above described survival behaviors and light adaptation were disrupted in offspring. Our data, based on intergenerational behavioral studies, demonstrate that BPS affects the behaviors of aquatic animals and the ability of offspring to feed and avoid predators, possibly jeopardizing the survival of aquatic animals.

Effects of chronic exposure to bisphenol-S on social behaviors in adult zebrafish: Disruption of the neuropeptide signaling pathways in the brain

Bisphenol S (BPS), considered to be a safe alternative to Bisphenol A, is increasingly used in a wide variety of consumer and industrial products. However, mounting evidence suggests that BPS can act as a xenoestrogen targeting a wide range of neuro-endocrine functions in animals. At present, very little is known about the impacts of BPS on social behaviors and/or the potential underlying mechanisms. To this end, we exposed adult male and female zebrafish to environmentally relevant concentrations of BPS (0 (control), 1, 10, and 30 μg/L), as well as to 17β-estradiol (E2; 1 μg/L; as positive control) for 75 days. Subsequently, alterations in social behaviors were evaluated by measuring shoal cohesion, group preferences, and locomotor activity. Furthermore, to elucidate the possible molecular mechanism underlying the neuro-behavioral effects of BPS, we also quantified the changes in the mRNA abundance of arginine vasotocin (AVT), isotocin (IT), and their corresponding receptors in the zebrafish brain. The results showed that E2 and BPS (30 μg/L) decreased shoal cohesion in both males and females. Moreover, a marked decline in group preferences was observed in all treatment groups, while locomotor activity remained unaffected. Alterations in the social behaviors were associated with sex-specific changes in the mRNA expression of genes involved in IT and AVT signaling. Taken together, the results of this study suggest that chronic exposure to BPS can impair zebrafish social behaviors via disruption of isotocinergic and vasotocinergic neuro-endocrine systems.

Effects of chronic exposure to selenomethionine on social learning outcomes in zebrafish (Danio rerio): serotonergic dysregulation and oxidative stress in the brain

For many species, social learning is crucial for fitness-related activities, but human-induced environmental changes can impair such learning processes. For instance, mining can release the element, selenium (Se), that is vital for physiological functions but also has toxicological properties at elevated concentrations. In this study, we investigated the effects of chronic exposure to Se on social learning outcomes and potential underlying molecular mechanisms in adult zebrafish. After exposure to different levels of dietary selenomethionine (control, 3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days, we examined the ability of observer fish to follow demonstrators (experienced individuals) in escaping an oncoming trawl. Social learning outcomes were then assessed in the absence of demonstrators. Our results indicated that fish in the highest exposure group (34.1 μg/g) displayed significantly slower escape responses compared to fish in the control and lower exposure groups (3.6 and 12.8 μg Se/g). This impaired behavior was associated with higher oxidative stress and dysregulation in genes that are key in the serotonergic pathway, indicating that oxidative stress and alteration in the serotonergic system lead to impairment of social learning.

Paternal exposure to a common herbicide alters the behavior and serotonergic system of zebrafish offspring

Increasingly, studies are revealing that endocrine disrupting chemicals (EDCs) can alter animal behavior. Early life exposure to EDCs may permanently alter phenotypes through to adulthood. In addition, the effects of EDCs may not be isolated to a single generation − offspring may indirectly be impacted, via non-genetic processes. Here, we analyzed the effects of paternal atrazine exposure on behavioral traits (distance moved, exploration, bottom-dwelling time, latency to enter the top zone, and interaction with a mirror) and whole-brain mRNA of genes involved in the serotonergic system regulation (slc6a4a, slc6a4b, htr1Aa, htr1B, htr2B) of zebrafish (Danio rerio). F0 male zebraFIsh were exposed to atrazine at 0.3, 3 or 30 part per billion (ppb) during early juvenile development, the behavior of F1 progeny was tested at adulthood, and the effect of 0.3 ppb atrazine treatment on mRNA transcription was quantified. Paternal exposure to atrazine significantly reduced interactions with a mirror (a proxy for aggression) and altered the latency to enter the top zone of a tank in unexposed F1 offspring. Bottom-dwelling time (a proxy for anxiety) also appeared to be somewhat affected, and activity (distance moved) was reduced in the context of aggression. slc6a4a and htr1Aa mRNA transcript levels were found to correlate positively with anxiety levels in controls, but we found that this relationship was disrupted in the 0.3 ppb atrazine treatment group. Overall, paternal atrazine exposure resulted in alterations across a variety of behavioral traits and showed signs of serotonergic system dysregulation, demonstrating intergenerational effects. Further research is needed to explore transgenerational effects on behavior and possible mechanisms underpinning behavioral effects.

Altered neurotransmission and neuroimaging biomarkers of chronic arsenic poisoning in wild muskrats (Ondatra zibethicus) and red squirrels (Tamiasciurus hudsonicus) breeding near the City of Yellowknife, Northwest Territories (Canada)

Chronic arsenic poisoning has been shown to be a risk factor for the development of intellectual disability. Numerous human and animal studies have also confirmed that low-level arsenic exposure has deleterious effects on neurotransmission and brain structures which have been further linked to neurobehavioral disorders. The aim of this present work was to comparatively assess structural brain volume changes and alteration of two (2) neurotransmitters, specifically dopamine (DA) and serotonin (5-HT) in the brains of wild muskrats and squirrels breeding in arsenic endemic areas, near the vicinity of the abandoned Giant mine site in Yellowknife and in reference locations between 52 and 105 km from the city of Yellowknife. The levels of DA and 5-HT were measured in the brain tissues, and Magnetic Resonance Imaging (MRI) was used to attempt brain volume measurements. The results revealed that the concentrations of DA and 5-HT were slightly increased in the brains of squirrels from the arsenic endemic areas compared to the reference site. Further, DA and 5-HT were slightly reduced in the brains of muskrats from the arsenic endemic areas compared to the reference location. In general, no statistically significant neurotransmission changes and differences were observed in the brain tissues of muskrats and squirrels from both arsenic endemic areas and non-endemic sites. Although MRI results showed that the brain volumes of squirrels and muskrats were not statistically different between sites after multiple comparison correction; it was noted that core brain regions were substantially affected in muskrats, in particular the hippocampal memory circuit, striatum and thalamus. Squirrel brains showed more extensive neuroanatomical changes, likely due to their relatively smaller body mass, with extensive shrinkage of the core brain structures, and the cortex, even after accounting for differences in overall brain size. The results of this present study constitute the first observation of neuroanatomical changes in wild small mammal species breeding in arsenic endemic areas of Canada.

The zebrafish subcortical social brain as a model for studying social behavior disorders

Social behaviors are essential for the survival and reproduction of social species. Many, if not most, neuropsychiatric disorders in humans are either associated with underlying social deficits or are accompanied by social dysfunctions. Traditionally, rodent models have been used to model these behavioral impairments. However, rodent assays are often difficult to scale up and adapt to high-throughput formats, which severely limits their use for systems-level science. In recent years, an increasing number of studies have used zebrafish (Danio rerio) as a model system to study social behavior. These studies have demonstrated clear potential in overcoming some of the limitations of rodent models. In this Review, we explore the evolutionary conservation of a subcortical social brain between teleosts and mammals as the biological basis for using zebrafish to model human social behavior disorders, while summarizing relevant experimental tools and assays. We then discuss the recent advances gleaned from zebrafish social behavior assays, the applications of these assays to studying related disorders, and the opportunities and challenges that lie ahead.

The Effects of Selenomethionine on the Escape Behaviours of Fathead Minnows

Selenium (Se) is an essential micronutrient for animals and yet becomes toxic with only a small increase in concentration. Toxicological studies have reported various effects of Se on fishes, including developmental impacts and deformities of the musculature and sensory systems. This paper investigates the impact of sublethal concentrations of Se on the ability of the Fathead Minnow (Pimephales promelas) to perform escape responses, a routine behaviour important to predator-prey dynamics. Predation is among the strongest evolutionary driving forces in nature. Changes to this dynamic can have effects that cascade through the ecosystem. We used responses to mechanical and visual stimuli to determine the impact of environmentally relevant concentrations of dietary selenomethionine on the behaviour of minnows. Latency to respond to the stimulus and kinematic performance were assessed. Our results indicated that there was no significant effect of selenomethionine on either the visual response to a threat or burst swimming behaviours of the fast-start response in minnows. Levels of Se in tissues approached that of tissue-specific guidelines set by regulatory bodies across North America. This suggests that current regulations are adequately protecting this key component of predator avoidance in Fathead Minnows.