Diazepam and fluoxetine decrease the stress response in zebrafish

Which emerging micropollutants deserve more attention in wastewater in the post-COVID-19 pandemic period? Based on distribution, risk, and exposure analysis

Aggravated accumulation of emerging micropollutants (EMs) in aquatic environments, especially after COVID-19, raised significant attention throughout the world for safety concerns. This article reviews the sources and occurrence of 25 anti-COVID-19 related EMs in wastewater. It should be pointed out that the concentration of anti-COVID-19 related EMs, such as antivirals, plasticizers, antimicrobials, and psychotropic drugs in wastewater increased notably after the pandemic. Furthermore, the ecotoxicity, ecological, and health risks of typical EMs before and after COVID-19 were emphatically compared and analyzed. Based on the environmental health prioritization index method, the priority control sequence of typical EMs related to anti-COVID-19 was identified. Lopinavir (LPV), venlafaxine (VLX), di(2-ethylhexyl) phthalate (DEHP), benzalkonium chloride (BAC), triclocarban (TCC), di-n-butyl phthalate (DBP), citalopram (CIT), diisobutyl phthalate (DIBP), and triclosan (TCS) were identified as the top-priority control EMs in the post-pandemic period. Besides, some insights into the toxicity and risk assessment of EMs were also provided. This review provides direction for proper understanding and controlling the EMs pollution after COVID-19, and is of significance to evaluate objectively the environmental and health impacts induced by COVID-19.

Anxiolytic-like effects of acute serotonin-releasing agents in zebrafish models of anxiety: experimental study and systematic review

Though commonly used to model affective disorders, zebrafish display notable differences in terms of the structure and function of the brain serotonin system, including responses to pharmacological interventions, as compared to mammals. For example, elevation of brain serotonin following acute administration of serotonin reuptake inhibitors (SRIs) generally has anxiogenic effects, both in the clinical situation and in rodent models of anxiety, but previous research has indicated the opposite in zebrafish. However, several issues remain unresolved. We conducted a systematic review of SRI effects in zebrafish models of anxiety and, on the basis of these results, performed a series of experiments further investigating the influence of serotonin-releasing agents on anxiety-like behaviour in zebrafish, with sex-segregated wild-type animals being administered either escitalopram, or the serotonin releaser fenfluramine, in the light-dark test. In the systematic review, we find that the available literature indicates an anxiolytic-like effect of SRIs in the novel-tank diving test. Regarding the light-dark test, most studies reported no behavioural effects of SRIs, although the few that did generally saw anxiolytic-like responses. In the experimental studies, consistent anxiolytic-like effects were observed with neither sex nor habituation influencing treatment response. We find that the general effect of acute SRI administration in zebrafish indeed appears to be anxiolytic-like, indicating, at least partly, differences in the functioning of the serotonin system as compared to mammals and that caution is advised when using zebrafish to model affective disorders.

An optimized whole-body corticosteroid hormones quantification method by LC-MS/MS for assessing stress levels in European glass eels (Anguilla anguilla)

The European eel (Anguilla anguilla) juvenile stage exhibits facultative estuarine migration. The causes of this behavior are yet unknown but it may have an impact on the population's fate by altering the sex ratio of the population. Recent studies have highlighted potential stress-related issues in glass eels settling in estuaries but studying stress response in small organisms requires sensitive, accurate and precise analytical methods. The aims of the present study are (i) to develop a whole-body Liquid Chromatography-Mass Spectrometry (LC-MS/MS) method for the simultaneous determination of several stress hormones in low-body mass fish; (ii) to apply this method to glass eels to study their responses to acute stress (iii) to test the effect of anxiolytics (diazepam) on these responses. Our results showed that enhanced LC-MS/MS analysis reduced detection limits and improved accuracy and precision for the quantification at the individual level. Following an acute stress, cortisol concentration significantly increased in glass eels and a 15 h diazepam exposure significantly reduced cortisol levels highlighting a marked anxiolytic effect on this species.

Biomarker triterpenoids of Centella asiatica as potential antidepressant agents: Combining in vivo and in silico studies

Although there are various treatments available for depression, some patients may experience resistance to treatment or encounter adverse effects. Centella asiatica (C. asiatica) is an ancient medicinal herb used in Ayurvedic medicine for its rejuvenating, neuroprotective and psychoactive properties. This study aims to explore the antidepressant-like effects of the major constituents found in C. asiatica, i.e., asiatic acid, asiaticoside, madecassic acid, and madecassoside at three doses (1.25, 2.5, and 5 mg/kg, i.p), on the behavioural and cortisol level of unpredictable chronic stress (UCS) zebrafish model. Based on the findings from the behavioural study, the cortisol levels in the zebrafish body after treatment with the two most effective compounds were measured using enzyme-linked immunosorbent assay (ELISA). Furthermore, a molecular docking study was conducted to predict the inhibitory impact of the triterpenoid compounds on serotonin reuptake. The in vivo results indicate that madecassoside (1.25, 2.5, and 5 mg/kg), asiaticoside and asiatic acid (5 mg/kg) activated locomotor behaviour. Madecassoside at all tested doses and asiaticoside at 2.5 and 5 mg/kg significantly decreased cortisol levels compared to the stressed group, indicating the potential regulation effect of madecassoside and asiaticoside on the hypothalamic-pituitary-adrenal axis overactivity. This study highlights the potential benefits of madecassoside and asiaticoside in alleviating depressive symptoms through their positive effects on behaviour and the hypothalamic-pituitary-adrenal (HPA)- axis in a chronic unpredictable stress zebrafish model. Furthermore, the in silico study provided additional evidence to support these findings. These promising results suggest that C. asiatica may be a valuable and cost-effective therapeutic option for depression, and further research should be conducted to explore its potential benefits.

Decreased Brain Serotonin in rbfox1 Mutant Zebrafish and Partial Reversion of Behavioural Alterations by the SSRI Fluoxetine

RBFOX1 functions as a master regulator of thousands of genes, exerting a pleiotropic effect on numerous neurodevelopmental and psychiatric disorders. A potential mechanism by which RBFOX1 may impact these disorders is through its modulation of serotonergic neurotransmission, a common target for pharmacological intervention in psychiatric conditions linked to RBFOX1. However, the precise effects of RBFOX1 on the serotonergic system remain largely unexplored. Here we show that homozygous rbfox1sa15940 zebrafish, which express a shorter, aberrant rbfox1 mRNA, have significantly reduced serotonin levels in telencephalon and diencephalon. We observed that the acute administration of fluoxetine partially reverses the associated behavioural alterations. The hyperactive phenotype and altered shoaling behaviour of the rbfox1sa15940/sa15940 zebrafish could be reversed with acute fluoxetine exposure in the Open Field and the Shoaling test, respectively. However, in the other paradigms, hyperactivity was not diminished, suggesting a distinct intrinsic motivation for locomotion in the different paradigms. Acute fluoxetine exposure did not reverse the alterations observed in the aggression and social novelty tests, suggesting the involvement of other neurological mechanisms in these behaviours. These findings underscore the importance of investigating the intricate working mechanisms of RBFOX1 in neurodevelopmental and psychiatric disorders to gain a better understanding of the associated disorders along with their pharmacological treatment.

Effects of chronic diazepam exposure on the behaviors and oxidative stress homeostasis in the eyes and brains of female Japanese medaka

Diazepam (DZP) residue has been frequently detected in wastewater, surface water, and groundwater due to its extensive use over the decades. In this study, we exposed female Japanese medaka (Oryzias latipes) to environmentally relevant doses of DZP (800 and 8000 ng/L) for 4 weeks, aimed to investigate their behavioral responses and possible links with ocular and brain oxidative stress homeostasis. As a result, DZP exposure could significantly reduce swimming activity (800 ng/L) and anxiety (800 and 8000 ng/L), indicating a sedative effect on medaka. The DZP exposure also significantly increased the social interaction in medaka at 8000 ng/L. Furthermore, exposure to DZP could alter the ocular and brain oxidative stress homeostasis in medaka. The ocular CAT activities significantly increased in the 800 ng/L-DZP groups, and the brain SOD, CAT, GST and MDA levels also significantly increased in both DZP exposure groups. Correlation analysis revealed that the ocular and brain oxidative stress induced by DZP exposure might play an important role in their behavioral toxicity to medaka. Our findings highlight the necessity to clarify the exact link between DZP exposure-induced oxidative stress in the neural and sensor systems and its behavioral toxicity to better assess the risks on nontarget aquatic species.

Developing Peripheral Biochemical Biomarkers of Brain Disorders: Insights from Zebrafish Models

High prevalence of human brain disorders necessitates development of the reliable peripheral biomarkers as diagnostic and disease-monitoring tools. In addition to clinical studies, animal models markedly advance studying of non-brain abnormalities associated with brain pathogenesis. The zebrafish (Danio rerio) is becoming increasingly popular as an animal model organism in translational neuroscience. These fish share some practical advantages over mammalian models together with high genetic homology and evolutionarily conserved biochemical and neurobehavioral phenotypes, thus enabling large-scale modeling of human brain diseases. Here, we review mounting evidence on peripheral biomarkers of brain disorders in zebrafish models, focusing on altered biochemistry (lipids, carbohydrates, proteins, and other non-signal molecules, as well as metabolic reactions and activity of enzymes). Collectively, these data strongly support the utility of zebrafish (from a systems biology standpoint) to study peripheral manifestations of brain disorders, as well as highlight potential applications of biochemical biomarkers in zebrafish models to biomarker-based drug discovery and development.

Chemical and Visual Cues as Modulators of the Stress Response to Social Isolation in the Marine Medaka, Oryzias melastigma

The marine medaka is emerging as a potential behavioral model organism for ocean studies, namely on marine ecotoxicology. However, not much is known on the behavior of the species and behavioral assays lack standardization. This study assesses the marine medaka as a potential model for chemical communication. We investigated how short exposure to visual and chemical cues mediated the stress response to social isolation with the light/dark preference test (LDPT) and the open field test (OFT). After a 5-day isolation period, and 1 h before testing, isolated fish were randomly assigned to one of four groups: (1) placed in visual contact with conspecifics; (2) exposed to a flow of holding water from a group of conspecifics; (3) exposed to both visual and chemical cues from conspecifics; or (4) not exposed to any stimuli (controls). During the LDPT, the distance traveled and transitions between zones were more pronounced in animals exposed to the conspecific's chemical stimuli. The time spent in each area did not differ between the groups, but a clear preference for the bright area in all animals indicates robust phototaxis. During the OFT, animals exposed only to chemical cues initially traveled more than those exposed to visual or both stimuli, and displayed lower thigmotaxis. Taken together, results show that chemical cues play a significant role in exploratory behavior in this species and confirm the LDPT and OFT as suitable tests for investigating chemical communication in this species.

Extinction and reinstatement of methamphetamine-induced conditioned place preference in zebrafish

Conditioned place preference (CPP) paradigm in zebrafish has been used to measure drug reward, but there is limited research on CPP reinstatement to determine relapse vulnerability. The present study aimed to investigate extinction and reinstatement of methamphetamine (MA)-induced CPP in zebrafish and evaluate the model's predictive validity. Zebrafish received different doses of MA (0-60 mg/kg) during CPP training. The preferred dose of MA at 40 mg/kg was used for extinction via either confined or nonconfined procedures. The extinguished CPP was reinstated by administering a priming dose of MA (20 mg/kg) or various stressors. To assess persistent susceptibility to reinstatement, MA CPP and reinstatement were retested following 14 days of abstinence. In addition, the effects of SCH23390, naltrexone, and clonidine on MA CPP during acquisition, expression, or reinstatement phases were monitored. MA induced CPP in a dose-dependent manner. Both nonconfined and confined extinction procedures time-dependently reduced the time spent on the MA-paired side. A priming dose of MA, chasing stress, or yohimbine reinstated the extinguished CPP. After 14 days of abstinence, the MA CPP remained extinguished and was significantly reinstated by MA priming or chasing stress. Similar to the observations in rodents, SCH23390 suppressed the acquisition of MA CPP, naltrexone reduced the expression and MA priming-induced reinstatement, while clonidine prevented stress-induced reinstatement of MA CPP. This work expanded the zebrafish CPP paradigm to include extinction and reinstatement phases, demonstrating predictive validity and highlighting its potential as a valuable tool for exploring drug relapse.

The occurrence of typical psychotropic drugs in the aquatic environments and their potential toxicity to aquatic organisms - A review

Psychotropic drugs (PDs) and their bioactive metabolites often persist in aquatic environments due to their typical physical properties, which made them resistant to removal by traditional wastewater treatment plants (WWTPs). Consequently, such drugs and/or their metabolites are frequently detected in both aquatic environments and organisms. Even at low concentrations, these drugs can exhibit toxic effects on non-target organisms including bony fish (zebrafish (Danio rerio) and fathead minnows) and bivalves (freshwater mussels and clams). This narrative review focuses on the quintessential representatives of three different categories of PDs-antiepileptics, antidepressants, and antipsychotics. The data regarding their concentrations occurring in the environment, patterns of distribution, the degree of enrichment in various tissues of aquatic organisms, and the toxicological effects on them are summarized. The toxicological assessments of these drugs included the evaluation of their effects on the reproductive, embryonic development, oxidative stress-related, neurobehavioral, and genetic functions in various experimental models. However, the mechanisms underlying the toxicity of PDs to aquatic organisms and their potential health risks to humans remain unclear. Most studies have focused on the effects caused by acute short-term exposure due to limitations in the experimental conditions, thus making it necessary to investigate the chronic toxic effects at concentrations that are in coherence with those occurring in the environment. Additionally, this review aims to raise awareness and stimulate further research efforts by highlighting the gaps in the understanding of the mechanisms behind PD-induced toxicity and potential health risks. Ultimately, the study underscores the importance of developing advanced remediation methods for the removal of PDs in WWTPs and encourages a broader discussion on mitigating their environmental impacts.

A psychiatric drug found in waste-water plant effluents alters the migratory behavior of critically endangered Anguilla anguilla juveniles

Migratory fishes cross or settle in several environments potentially polluted. Psychiatric drugs, which represent one growing pollution and are found in discharges from waste-water treatment plants, may alter individual behaviors. Here, we assessed behavioral alterations in the upstream migratory behavior of Anguilla anguilla caused by diazepam, an anxiolytic. We monitored the swimming activity, swimming behavior, and boldness to assess whether diazepam impacts them or not. Our 7-day behavioral follow-up allowed us to test the kinetics of the potential effects of diazepam. We found diazepam reduced swimming activity and altered individual swimming behavior, with fewer individuals swimming against the current, so swimming upstream. Those effects varied over time and were stronger at the end of our monitoring, suggesting chemical pollutants encountered in estuaries may act as a chemical burden for individuals, despite metabolisation. We also found diazepam favored bolder behavior in glass eels. Our results provide new knowledge on chemical pollution and psychiatric drugs inducing behavioral alterations. Those alterations may have ecological and evolutionary consequences for glass eels, by diminishing predator avoidance and impacting spatial colonization, and thus, local density.

The zebrafish for preclinical psilocybin research

In this review, we discuss the possible utility of zebrafish in research on psilocybin, a psychedelic drug whose recreational use as well as possible clinical application are gaining increasing interest. First, we review behavioral tests with zebrafish, focussing on anxiety and social behavior, which have particular relevance in the context of psilocybin research. Next, we briefly consider methods of genetic manipulations with which psilocybin's phenotypical effects and underlying mechanisms may be investigated in zebrafish. We briefly review the known mechanisms of psilocybin, and also discuss what we know about its safety and toxicity profile. Last, we discuss examples of how psilocybin may be employed for testing treatment efficacy in preclinical research for affective disorders in zebrafish. We conclude that zebrafish has a promising future in preclinical research on psychedelic drugs.

Tank color influences the response of tomato clownfish (Amphiprion frenatus) to an acute stress challenge

The trade of aquarium organisms is growing worldwide. This market depends on a continuous supply of healthy and colorful aquatic animals, but this sector has few initiatives. However, in the last decade, there has been a growing interest in researching captive breeding of these animals, aiming to develop a more sustainable aquarium hobby. Larviculture is an important phase in the cultivation process because the larvae are more sensitive to stress and variations in the bulk of variables, such as temperature, salinity, nutritional management, light intensity and spectrum, and environmental background colors. Because background color could be a promoter variable of proper welfare, we tested whether it affects the endocrine response of tomato clownfish Amphiprion frenatus larvae to an acute stress challenge. We show that background color influences the endocrine stress axis responsiveness in tomato clownfish. When fish were subjected to a standard acute stressor of 61 days after hatching, only fish adapted to white walls increased the whole-body cortisol levels. From the results presented herein, we recommend that white tanks be avoided for A. frenatus larviculture. Both, the less stress level and the good welfare condition of larvae reared in colored tanks may have robust, practical applications since almost all clownfish in the ornamental aquarium trade come from captive breeding.

Hazard and health risk assessment of exposure to pharmaceutical active compounds via toxicological evaluation by zebrafish

The uncontrolled or continuous release of effluents from wastewater treatment plants leads to the omnipresence of pharmaceutical active compounds (PhACs) in the aquatic media. Today, this is a confirmed problem becoming a main subject of twin public and scientific concerns. However, still little information is available about the long-term impacts of these PhACs on aquatic organisms. In this review, efforts were made to reveal correlation between the occurrence in the environment, ecotoxicological and health risks of different PhACs via toxicological evaluation by zebrafish (Danio rerio). This animal model served as a bioindicator for any health impacts after the exposure to these contaminants and to better understand the responses in relation to human diseases. This review paper focused on the calculation of Risk Quotients (RQs) of 34 PhACs based on environmental and ecotoxicological data available in the literature and prediction from the ECOSAR V2.2 software. To the best of the authors' knowledge, this is the first report on the risk assessment of PhACs by the two different methods as mentioned above. RQs showed greater difference in potential environmental risks of the PhACs. These differences in risk values underline the importance of environmental and experimental factors in exposure conditions and the interpretation of RQ values. While the results showed high risk to Danio rerio of the majority of PhACs, risk qualification of the others varied between moderate to insignifiant. Further research is needed to assess pharmaceutical hazards when present in wastewater before discharge and monitor the effectiveness of treatment processes. The recent new advances in the morphological assessment of toxicant-exposed zebrafish larvae for the determination of test compounds effects on the developmental endpoints were also discussed. This review emphasizes the need for strict regulations on the release of PhACs into environmental media in order to minimize their toxicity to aquatic organisms.

Solfeggio-frequency music exposure reverses cognitive and endocrine deficits evoked by a 24-h light exposure in adult zebrafish

Music therapy has long been used as a non-pharmacological intervention to improve cognitive function and mood in humans. Mounting rodent evidence also supports beneficial impact of music exposure on animal cognitive performance. The zebrafish (Danio rerio) is an important emerging aquatic animal model in translational biomedical and neuroscience research. Here, we evaluate the effects of intermittent (2-h or 6-h twice daily) and continuous (24-h) solfeggio-frequency music exposure on behavioral, cognitive and endocrine parameters in adult zebrafish whose circadian rhythm was disturbed by a 24-h light exposure. Overall, while a 24-h light exposure evokes overt cognitive deficits and elevates zebrafish whole-body cortisol levels, these effects were reversed by solfeggio-frequency music exposure for 2 or 6h twice daily, and by continuous 24-h exposure). Collectively, these findings suggest a positive modulation of cognitive and endocrine responses in adult zebrafish by environmental enrichment via the long-term exposure to music, and reinforces zebrafish as a robust, sensitive model organism for neurocognitive and neuroendocrine research.

Effects of common antiepileptic drugs on teleost fishes

Antiepileptic drugs (AEDs) are globally prescribed to treat epilepsy and many other psychiatric disorders in humans. Their high consumption, low metabolic rate in the human body and low efficiency of wastewater treatment plants (WWTPs) in eliminating these chemicals results in the frequent occurrence of these pharmaceutical drugs in aquatic systems. Therefore, aquatic organisms, including ecologically and economically important teleost fishes, may be inadvertently exposed to these chemicals. Due to their physiological similarity with humans, fishes may be particularly vulnerable to AEDs. Almost all AED drugs are detectable in natural aquatic ecosystems, but diazepam (DZP) and carbamazepine (CBZ) are among the most widely detected AEDs to date. Recent studies suggest that these drugs have a substantial capacity to induce neurotoxicity and behavioral abnormality in fishes. Here we review the current state of knowledge regarding the potential mode of action of DZP and CBZ as well as that of some other AEDs on teleosts and put observable behavioral effects into a mechanistic context. We find that following their intended mode of action in humans, AEDs also disrupt the GABAergic, glutamatergic and serotonergic systems as well as parasympathetic neurotransmitters in fishes. Moreover, AEDs have non-specific modes of action in teleosts ranging from estrogenic activity to oxidative stress. These physiological changes are often accompanied by dose-dependent disruptions of anxiety, locomotor activity, social behaviors, food uptake, and learning and memory, but DZP and CBZ consistently induced anxiolytic effects. Thereby, AED exposure severely compromises individual fitness across teleost fish species, which may lead to population and ecosystem impairment. We also showcase promising avenues for future research by highlighting where we lack data when it comes to effects of certain AEDs, AED concentrations and behavioral endpoints.

Effects of fluoxetine on fish: What do we know and where should we focus our efforts in the future?

Fluoxetine is one of the most studied and detected selective serotonin reuptake inhibitors in the aquatic environment, found at concentrations ranging from ng/L to μg/L. Its presence in this environment can induce effects on aquatic organisms that may compromise their fitness. Several experimental studies have demonstrated that fluoxetine can induce neurotoxicity, genetic and biochemical changes, and cause behavioral dysfunction in a wide range of fish species. However, contradictory results can be found. There is thus the need for a comprehensive review of the current state of knowledge on the effects of fluoxetine on fish at different levels of biological organization, highlighting inclusive patterns and discussing the potential causes for the contradictory results, that can be found in the available literature. This review also aims to explore and identify the main gaps in knowledge and areas for future research. We conclude that environmentally relevant concentrations of fluoxetine (e.g., from 0.00345 μg/L) produced adverse effects and often this concentration range is not addressed in conventional environmental risk assessment strategies. Its environmental persistence and ionizable properties reinforce the need for standardized testing with representative aquatic models, targeting endpoints sensitive to the specific mode of action of fluoxetine, in order to assess and rank its actual environmental risk to aquatic ecosystems.

Good practices in the rearing and maintenance of zebrafish (Danio rerio) in Brazilian laboratories

Abstract Good Laboratory Practice (GLP) is a management quality control system that encompasses the organizational process and conditions under which non-clinical health and environmental studies are carried out. According to the World Health Organization, GLP must contain five topics: resources, characterization, rules, results, and quality control. This work aims to address a review according to WHO standards of implementing Good Laboratory Practices in zebrafish (Danio rerio) vivariums. Considering that the promotion of one health (animal, human, and environmental) associated with an education plan, protocols, and records are fundamental to guarantee the safety and integrity of employees, animals, and the environment as well as reliability in the results generated. In a way, Brazil still needs improvements related to the well-being of aquatic organisms (national laws, international agreements, corporate programs, and others), especially concerning its use in research and technological development. In this way, the implementation of GLPs provides valuable guidance for improving animal welfare and worker safety, facilitating the standardization of research.

Boas práticas na criação e manutenção de zebrafish (Danio rerio) em laboratório no Brasil

Resumo As Boas Práticas de Laboratório (BPL) são um sistema de controle de qualidade gerencial que abrange o processo organizacional e as condições sob as quais os estudos não clínicos de saúde e meio ambiente são desenvolvidos. Conforme a Organização Mundial da Saúde (OMS) as BPL devem conter cinco tópicos: recursos, caracterização, regras, resultados e controle de qualidade. O objetivo deste trabalho foi apresentar uma revisão conforme o padrão da OMS para a implementação das BPL em biotério de zebrafish. Considerando que a promoção da saúde única (animal, humana e ambiental) associada a um plano de educação, protocolos e registros são fundamentais para garantir a segurança e a integridade dos trabalhadores/pesquisadores, animais e meio ambiente assim como confiabilidade nos resultados gerados. De certa forma o Brasil ainda necessita de melhorias relacionadas ao bem-estar de organismos aquáticos (leis nacionais, acordos internacionais, programas corporativos e outros); especialmente em relação à utilização deste na pesquisa e desenvolvimento tecnológico. Desta forma, a implementação de BPL fornece uma orientação valiosa para a melhoria do bem-estar animal, e segurança do trabalhador vindo a facilitar a padronização da pesquisa.

Impact of pharmaceutical products on zebrafish: An effective tool to assess aquatic pollution

Overuse of pharmaceuticals products (PPs) and sometimes ineffective wastewater purification systems have led to the accumulation of these residues in aquatic systems. Raising concerns about the likely harmful effects of these substances both to ecosystems and to human health. Animals as model organisms are nowadays increasingly used to track the health of environmental system around the world. They can be used to understand biological processes, to obtain information on the health status of the environment, and to better understand the effects of xenobiotics on organisms. Among model organisms, the zebrafish (Danio rerio) is one of the best models for studying evolution biology, cancer, toxicology, drug discovery, and genetics. This fish is a multipurpose model organism, due to its easy of maintenance and keeping and the transparency of the embryo during the early stages of development. In this paper, the toxicological effects of typical PPs, and their effects on zebrafish are reviewed. Many PPs have been found to be toxic or even fatal to zebrafish. Showing how these pharmaceuticals compound can affect zebrafish from the larval stage and even in the adult stage. Zebrafish is thus a model for how we can better understand how medications affect not only individual fish but the entire aquatic ecosystem, bringing about perturbations in their behaviour and putting their survival at risk.

Baicalein prevents stress-induced anxiety behaviors in zebrafish model

Baicalein is a flavonoid mainly obtained from plants with wide range of biological activities, including neuroprotection. An acute and unexpected chronic stress (UCS) protocol has recently been adapted to zebrafish, a popular vertebrate model in brain research. The present study was aimed to evaluate baicalein's anti-anxiety potential in a zebrafish model by induction, which included neuropharmacological evaluation to determine behavioural parameters in the novel tank diving test (NTDT) and light-dark preference test (LDPT). The toxicity was also assessed using the brine shrimp lethality assay, and the 50% lethal concentration (LC50) was determined. The animals were then stressed for 7 days before being treated with different doses of baicalein (1 and 2 mg/L) for another 7 days in UCS condition. Due to acute stress and UCS, the frequency of entries and time spent in the 1) top region and 2) light area of the novel tank reduced significantly, indicating the existence of elevated anxiety levels. The biological activity of baicalein was demonstrated by its high LC50 values (1,000 μg/ml). Additionally, baicalein administration increased the frequency of entries and duration spent in the light region, indicating a significant decrease in anxiety levels. Overall, the present results showed that baicalein has a therapeutic advantage in reversing the detrimental consequences of UCS and acute stress, making it is a promising lead molecule for new drug design, development, and therapy for stress.

Incorporating ventilatory activity into a novel tank test for evaluating drug effects on zebrafish

The effects of ethanol and caffeine exposure on zebrafish, Danio rerio, were investigated using a combination of measurements of behavioral and physiologic responses in a novel tank situation. Ventilation activity as a physiologic measure was measured remotely by monitoring ventilation-related bioelectric signals from freely moving zebrafish in the test tank. The directions of the behavioral responses, except for outer area preference, were substantially the same in both ethanol- and caffeine-treated fish and qualitatively indistinguishable, suggesting that relying solely on behavioral measures may lead to inappropriate interpretation of drug effects when depending on limited behavioral parameters. By incorporating ventilation activity-related physiologic measures into the quantification of drug effects in novel tank tests, more-accurate evaluations of differences in the effects of moderate doses of anxiolytic ethanol and anxiogenic caffeine were possible. Here, we propose that combining physiologic measures such as ventilation rate and its variability with behavioral measures makes it possible to characterize the effects of environmental challenges on zebrafish in a multi-dimensional and more-detailed manner.

Synthetic estrogen bioaccumulates and changes the behavior and biochemical biomarkers in adult zebrafish

Estrogen is considered to be an endocrine disrupter and is becoming increasingly more prevalent in the daily life of humans. In some cases, estrogen is not fully metabolized by organisms and may be excreted in either its original form or in organic complex forms, into water residue systems reaching concentrations of 0.05 ng.L^-1 to 75 ng.L^-1. However, estrogen 17α-ethinylestradiol (EE2), which is used in oral contraceptives, is very difficult to remove from water. Here, we evaluated whether the synthetic hormone, EE2, affects the nervous system and the behavior of adult zebrafish. We established a range of concentrations (0.05, 0.5, 5, 50, and 75 ng.L^-1), in addition to the control, to evaluate the effect of this compound and its bioaccumulation in zebrafish tissues. Here we show that EE2 bioaccumulates in fish and can change its behavior with an increased time in the upper zone (novel tank test) and far from the shoal segment (social preference test), demonstrating a clear anxiolytic pattern. The anxiolytic effect of EE2 can be harmful as it can affect the stress response of the species. The results presented herein reinforce the idea that the presence of EE2 in environmental water can be dangerous for non-target animals.

The psychoactive effects of Bryophyllum pinnatum (Lam.) Oken leaves in young zebrafish

Bryophyllum pinnatum (Lam.) Oken (BP) is a plant that is used worldwide to treat inflammation, infections, anxiety, restlessness, and sleep disorders. While it is known that BP leaves are rich in flavonoids, the extent of the beneficial and toxic effects of its crude extracts remains unclear. Although some neurobehavioral studies using leaf extracts have been conducted, none has examined the effects of water-extracted leaf samples. The zebrafish is a powerful animal model used to gain insights into the efficacy and toxicity profiles of this plant due to its high fecundity, external development, and ease of performing behavioral assays. In this study, we performed behavioral testing after acute exposure to different concentrations of aqueous extract from leaves of B. pinnatum (LABP) on larval zebrafish, investigating light/dark preference, thigmotaxis, and locomotor activity parameters under both normal and stressed conditions. LABP demonstrated dose-and time-dependent biphasic effects on larval behavior. Acute exposure (25 min) to 500 mg/L LABP resulted in decreased locomotor activity. Exposure to 300 mg/L LABP during the sleep cycle decreased dark avoidance and thigmotaxis while increasing swimming velocity. After sleep deprivation, the group treated with 100 mg/L LABP showed decreased dark avoidance and increased velocity. After a heating stressor, the 30 mg/L and 300 mg/L LABP-treated groups showed decreased dark avoidance. These results suggest both anxiolytic and psychoactive effects of LABP in a dose-dependent manner in a larval zebrafish model. These findings provide a better understanding of the mechanisms underlying relevant behavioral effects, consequently supporting the safe and effective use of LABP for the treatment of mood disorders.

A cross-species comparative approach to assessing multi- and transgenerational effects of endocrine disrupting chemicals

A wide range of chemicals have been identified as endocrine disrupting chemicals (EDCs) in vertebrate species. Most studies of EDCs have focused on exposure of both male and female adults to these chemicals; however, there is clear evidence that EDCs have dramatic effects when mature or developing gametes are exposed, and consequently are associated with in multigenerational and transgenerational effects. Several publications have reviewed such actions of EDCs in subgroups of species, e.g., fish or rodents. In this review, we take a holistic approach synthesizing knowledge of the effects of EDCs across vertebrate species, including fish, anurans, birds, and mammals, and discuss the potential mechanism(s) mediating such multi- and transgenerational effects. We also propose a series of recommendations aimed at moving the field forward in a structured and coherent manner.

Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior

Antidepressant (AD) drugs are widely prescribed for the treatment of psychiatric disorders, including depression and anxiety disorders. The continuous use of ADs causes significant quantities of these bioactive chemicals to enter the aquatic ecosystems mainly through wastewater effluent discharge. This may result in many aquatic organisms being inadvertently affected by these drugs. Fluoxetine (FLX) and venlafaxine (VEN) are currently among the most widely detected ADs in aquatic systems. A growing body of experimental evidence demonstrates that FLX and VEN have a substantial capacity to induce neurotoxicity and cause behavioral dysfunctions in a wide range of teleost species. At the same time, these studies often report seemingly contradictory results that are confounding in nature. Hence, we clearly require comprehensive reviews that attempt to find overarching patterns and establish possible causes for these variable results. This review aims to explore the current state of knowledge regarding the neurobehavioral effects of FLX and VEN on fishes. This study also discusses the potential mechanistic linkage between the neurotoxicity of ADs and behavioral dysfunction and identifies key knowledge gaps and areas for future research.

Formation and occurrence of disinfection byproducts of benzodiazepine drug estazolam in drinking water of Beijing

Estazolam (EZ) is a long-acting benzodiazepine (BZD) drug with high clinical consumption in China to treat anxiety, depression and other syndromes. Recently, it has been found as a leading potentially inappropriate medication among hospitalized elderly patients, increasing the risk of falls. It is discharged into the aquatic environment after use and has been frequently detected, ultimately affecting the safety of drinking water. In the present study, the reaction of EZ during chlorination disinfection was investigated in detail with regard to its transformation and kinetics. By means of ultra-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS), four main disinfection byproducts (DBPs) were tentatively identified, and the transformation pathways were speculated to be cleavage at the imine linkage and oxidation on the diazepinone ring. The chlorination reaction rate in the pseudo-first-order kinetic model was significantly affected by free available chlorine (FAC) and pH. The increase in pH value led to a decrease in the reaction rate, while a higher dosage of chlorine resulted in a faster kinetic rate. We further estimated the potential toxicities of EZ and its DBPs using quantitative structure-activity relationship (QSAR) software tools. DBPs exhibited much higher toxicity than EZ and exhibited developmental toxicity and mutagenicity. Finally, a total of 108 drinking water samples were collected in the wet and dry seasons to determine actual residue changes in real environmental conditions. The detection frequency was 29% for EZ, and the highest concentration of 0.60 ng L^-1 was found for its DBPs in tap water. No seasonal variations in concentration were observed. Overall, the results indicate that EZ and its DBPs may persist in drinking water, posing potential risks to public health.

Anti-stress effects of the glucagon-like peptide-1 receptor agonist liraglutide in zebrafish

Stress-related disorders are extremely harmful and cause significant impacts on the individual and society. Despite the limited evidence regarding glucagon-like peptide-1 receptor (GLP-1R) and mental disorders, a few clinical and preclinical studies suggest that modulating this system could improve symptoms of stress-related disorders. This study aimed to investigate the effects of liraglutide, a GLP-1R agonist, on neurobehavioral phenotypes and brain oxidative status in adult zebrafish. Acute liraglutide promoted anxiolytic-like effects in the light/dark test, while chronic treatment blocked the impact of unpredictable chronic stress on behavioral and physiological parameters. Taken together, our study demonstrates that liraglutide is active on the zebrafish brain and may counteract some of the effects induced by stress. More studies are warranted to further elucidate the potential of GLP-1R agonists for the management of brain disorders.

Aqueous stability and degradation of psychiatric and neuroactive compounds and its biological activity in Daphnia magna

Pharmaceuticals and other emerging contaminants are continuously released into the aquatic environment, considered as 'pseudo-persistent' pollutants. Many compounds degrade fast in the environment, but sometimes their transformation products (TPs) are equally or even more toxic than the parental compounds, raising concern about the potential risks to the environment. In this way, the crustacean Daphnia magna (D. magna) is one of the most widely used organisms in aquatic toxicology studies, since it is an interesting non-vertebrate model to study via neurotransmitters the toxicological consequences of contaminants. In this study, the stability in water of 17 neuroactive compounds using ultra-high-performance liquid chromatography (UHPLC) coupled to a MS/MS detector was evaluated. In order to assess the stability of the compounds, samples of 1 ng μL^-1 were analyzed at different times (0, 24 and 48 h). No degradation was observed for most of the studied compounds, except for apomorphine and 6-hydroxydopamine that were degraded completely in the first 24 h. The behavioral assay was based in the automatized delivery of visible light stimuli. Most of the tested compounds altered motile responses to light significantly. The pharmaceuticals memantine, imidacloprid, fluoxetine, deprenyl, diazepam, apomorphine and 6-hydroxydopamine decreased motile responses to light. Conversely, pilocarpine, scopolamine, nicotine and p-chlorophenylalanine increased motile responses. Despite the observed degradation of apomorphine and 6-hydroxydopamine, their degradation products (APO-TP1 and 6OH-TP1) were stable and so their effects on behavior. This study shows that a degradation or transformation of the main pollutant is not always linked to a decrease in its toxicity.

Social status modulates the behavioral and physiological consequences of a chemical pollutant in animal groups

The social environment (i.e., the suite of social interactions that occur among individuals that can result in variation in social ranks) is a commonly overlooked aspect of biology when scientists evaluate the effects of chemical contaminants. The social environment, however, represents the arena in which individual-level performance shapes group- or population-level outcomes and may therefore mediate many of the ultimate consequences of chemicals for wildlife. Here, we evaluated the role that the social environment plays in determining the consequences of pollutant exposure. We exposed groups of juvenile brown trout (Salmo trutta) to an emerging pharmaceutical pollutant that is commonly detected in freshwaters (the benzodiazepine, oxazepam) and allowed them to form dominance hierarchies. Exposure affected dominant and subordinate fish differently, causing fish to become less aggressive at high doses and subordinate fish to become more competitively successful at low doses. These perturbations had further consequences for growth, fin damage, and survival. Exposure also modulated physiological stress in the hierarchy, and social status itself affected how much oxazepam was absorbed in tissues, potentially creating a dynamic feedback loop that further influences the asymmetric effects of exposure on differing social statuses. Many effects followed a "U-shaped" dose-response curve, highlighting the importance of nonlinear, low-dose effects. Altogether, we show that social structure in animal groups can interact with and modulate the effects of an environmental contaminant. We underscore the need to account for an organism's natural ecological context, including their social environment, in future experiments and environmental risk assessments to predict the effects of chemical contaminants on wildlife.

Understanding how stress responses and stress-related behaviors have evolved in zebrafish and mammals

Stress response is essential for the organism to quickly restore physiological homeostasis disturbed by various environmental insults. In addition to well-established physiological cascades, stress also evokes various brain and behavioral responses. Aquatic animal models, including the zebrafish (Danio rerio), have been extensively used to probe pathobiological mechanisms of stress and stress-related brain disorders. Here, we critically discuss the use of zebrafish models for studying mechanisms of stress and modeling its disorders experimentally, with a particular cross-taxon focus on the potential evolution of stress responses from zebrafish to rodents and humans, as well as its translational implications.

Human Drug Pollution in the Aquatic System: The Biochemical Responses of Danio rerio Adults

Simple Summary

The release of medicinal products for human use in the aquatic environment is now a serious problem, and can be fatal for the organisms that live there. Danio rerio is a freshwater fish that provides the possibility to study the effects of these pollutants on the health of aquatic organisms. The results of the various existing scientific studies are scarce and conflicting. Here, we review the scientific studies that have analyzed these effects, highlighting that the impacts of drugs are evident in the biochemical responses of these animals.

Abstract

To date, drug pollution in aquatic systems is an urgent issue, and Danio rerio is a model organism to study the toxicological effects of environmental pollutants. The scientific literature has analyzed the effect of human drug pollution on the biochemical responses in the tissues of D. rerio adults. However, the information is still scarce and conflicting, making it difficult to understand its real impact. The scientific studies are not consistent with each other and, until now, no one has grouped their results to create a baseline of knowledge of the possible impacts. In this review, the analysis of literature data highlights that the effects of drugs on adult zebrafishes depend on various factors, such as the tissue analyzed, the drug concentration and the sex of the individuals. Furthermore, the most influenced biochemical responses concern enzymes (e.g., antioxidants and hydrolase enzymes) and total protein and hormonal levels. Pinpointing the situation to date would improve the understanding of the chronic effects of human drug pollution, helping both to reduce it in the aquatic systems and then to draw up regulations to control this type of pollution.

Evaluating the effect of fluoxetine on mesophilic anaerobic dark biohydrogen fermentation of excess sludge

Recently, the influence behavior of new pollutants in the environment has been widely concerned. However, the effect of antidepressants widely detected in excess sludge (ES) on biohydrogen production from anaerobic dark fermentation has never been explored. To fill this gap, fluoxetine (FLX), a typical antidepressant, was selected to evaluate its effect on ES mesophilic anaerobic dark biohydrogen fermentation. The results showed that FLX reduced biohydrogen production even at low content (0.1 mg/Kg). The biohydrogen yield was only 12.8 mL/g in the 1.8 mg/Kg (based on total suspended solids) FLX group, decreased by about 34.7%, compared with the control group (without FLX). Further mechanism investigation implied that high levels (more than 0.6 mg/Kg) of FLX reduced every step associated with the biohydrogen production. FLX reduced the concentration of ammonia nitrogen and phosphate in fermentation broth. FLX also had a significant negative effect on enzyme activity in ES dark fermentation.

Melatonin administration attenuates acute stress by inducing sleep state in zebrafish (Danio rerio)

Melatonin plays a fundamental homeostatic role in basic biological functions, and an anti-stress role has been also proposed for this hormone. This study aimed to evaluate hormonal, enzymatic and behavioral parameters of zebrafish that received administration of melatonin and were submitted to acute stress. A total of 120 wild-type zebrafish were divided into five groups: naïve control (N), negative control group (Stress/C), positive control treated with diazepam (Stress/Diaz), treatment with melatonin at dose 1 (Stress/Melt. 1) and treatment with melatonin at dose 2 (Stress/Melt. 2). The exposure to treatments (diazepam or melatonin) was performed prior to the acute stress protocol, based on a chase by a fishing net during 5 min followed by exposure to the air for 1 min. The body cortisol levels were assessed, as well as oxidative stress (thiobarbituric acid reactive substances, reactive species of oxygen and antioxidant activity), and fish behavior (open field test). Melatonin was able to modulate acute stress effects on zebrafish by inhibiting cortisol increasing levels, reducing locomotor parameters, inducing a sleep state, reducing lipid peroxidation and stimulating antioxidant enzymatic activity.

The effects of two stressors on working memory and cognitive flexibility in zebrafish (Danio rerio): The protective role of D1/D5 agonist on stress responses

Acute stressors are recurrent in multiple species' lives and can facilitate or impair cognition. The use of zebrafish (Danio rerio) as a translational species to understand the mechanisms by which stress induces different behavioral phenotypes has been widely studied. Two acute stressors are recognized when using this species: (1) conspecific alarm substance (CAS); and (2) net chasing. Here, we tested if CAS or net chasing would affect working memory and cognitive flexibility by testing performance in the FMP Y-maze after exposure to stress. We observed that CAS altered zebrafish behavioral phenotypes by increasing repetitive behavior; meanwhile, animals showed different patterns of repetitive behavior when exposed to net chasing, depending on the chasing direction. Because D1 receptors were previously studied as a potential mechanism underlying stress responses in different species, here, we pretreated fish with a D1/D5 agonist (SKF-38393) to assess whether this system plays a role in repetitive behavior in the FMP Y-maze. The pretreatment with D1/D5 agonist significantly decreased repetitive behavior in CAS exposed animals, and cortisol levels for both stressed groups, suggesting that the dopaminergic system plays an important role in zebrafish stress-related responses.

A chemical prioritization process: Applications to contaminants of emerging concern in freshwater ecosystems (Phase I)

Contaminants of emerging concern (CECs), such as pharmaceuticals, personal care products, and hormones, are frequently found in aquatic ecosystems around the world. Information on sublethal effects from exposure to commonly detected concentrations of CECs is lacking and the limited availability of toxicity data makes it difficult to interpret the biological significance of occurrence data. However, the ability to evaluate the effects of CECs on aquatic ecosystems is growing in importance, as detection frequency increases. The goal of this study was to prioritize the chemical hazards of 117 CECs detected in subsistence species and freshwater ecosystems on the Grand Portage Indian Reservation and adjacent 1854 Ceded Territory in Minnesota, USA. To prioritize CECs for management actions, we adapted Minnesota Pollution Control Agency's Aquatic Toxicity Profiles framework, a tool for the rapid assessment of contaminants to cause adverse effects on aquatic life by incorporating chemical-specific information. This study aimed to 1) perform a rapid-screening assessment and prioritization of detected CECs based on their potential environmental hazard; 2) identify waterbodies in the study region that contain high priority CECs; and 3) inform future monitoring, assessment, and potential remediation in the study region. In water samples alone, 50 CECs were deemed high priority. Twenty-one CECs were high priority among sediment samples and seven CECs were high priority in fish samples. Azithromycin, DEET, diphenhydramine, fluoxetine, miconazole, and verapamil were high priority in all three media. Due to the presence of high priority CECs throughout the study region, we recommend future monitoring of particular CECs based on the prioritization method used here. We present an application of a chemical hazard prioritization process and identify areas where the framework may be adapted to meet the objectives of other management-related assessments.

Interspecies Behavioral Variability of Medaka Fish Assessed by Comparative Phenomics

Recently, medaka has been used as a model organism in various research fields. However, even though it possesses several advantages over zebrafish, fewer studies were done in medaka compared to zebrafish, especially with regard to its behavior. Thus, to provide more information regarding its behavior and to demonstrate the behavioral differences between several species of medaka, we compared the behavioral performance and biomarker expression in the brain between four medaka fishes, Oryzias latipes, Oryzias dancena, Oryzias woworae, and Oryzias sinensis. We found that each medaka species explicitly exhibited different behaviors to each other, which might be related to the different basal levels of several biomarkers. Furthermore, by phenomics and genomic-based clustering, the differences between these medaka fishes were further investigated. Here, the phenomic-based clustering was based on the behavior results, while the genomic-based clustering was based on the sequence of the nd2 gene. As we expected, both clusterings showed some resemblances to each other in terms of the interspecies relationship between medaka and zebrafish. However, this similarity was not displayed by both clusterings in the medaka interspecies comparisons. Therefore, these results suggest a re-interpretation of several prior studies in comparative biology. We hope that these results contribute to the growing database of medaka fish phenotypes and provide one of the foundations for future phenomics studies of medaka fish.

Unconventional anxiety pharmacology in zebrafish: Drugs beyond traditional anxiogenic and anxiolytic spectra

Anxiety is the most prevalent brain disorder and a common cause of human disability. Animal models are critical for understanding anxiety pathogenesis and its pharmacotherapy. The zebrafish (Danio rerio) is increasingly utilized as a powerful model organism in anxiety research and anxiolytic drug screening. High similarity between human, rodent and zebrafish molecular targets implies shared signaling pathways involved in anxiety pathogenesis. However, mounting evidence shows that zebrafish behavior can be modulated by drugs beyond conventional anxiolytics or anxiogenics. Furthermore, these effects may differ from human and/or rodent responses, as such 'unconventional' drugs may affect zebrafish behavior despite having no such profiles (or exerting opposite effects) in humans or rodents. Here, we discuss the effects of several putative unconventional anxiotropic drugs (aspirin, lysergic acid diethylamide (LSD), nicotine, naloxone and naltrexone) and their potential mechanisms of action in zebrafish. Emphasizing the growing utility of zebrafish models in CNS drug discovery, such unconventional anxiety pharmacology may provide important, evolutionarily relevant insights into complex regulation of anxiety in biological systems. Albeit seemingly complicating direct translation from zebrafish into clinical phenotypes, this knowledge may instead foster the development of novel CNS drugs, eventually facilitating innovative treatment of patients based on novel 'unconventional' targets identified in fish models.

Putative anxiolytic-like behavioral effects of acute paracetamol in adult zebrafish

Typically triggered by stress, anxiety disorders are most common and widespread mental illnesses. The zebrafish (Danio rerio) is rapidly becoming an important aquatic model species in stress research and central nervous system (CNS) drug screening. Paracetamol is currently the most prescribed medication for pain and fever, and is among the most used drugs globally. However, its CNS effects, especially on anxiety, in both clinical and animal studies remain poorly understood. Capitalizing on zebrafish as a powerful model system, here we evaluate the effects of paracetamol on anxiety-like behavior in adult fish, and its changes following an acute stress exposure. Overall, we report an anxiolytic-like profile of acute paracetamol treatment, and its alleviation of stress-evoked anxiety, in adult short-fin wild type zebrafish. Collectively, these findings suggest complex neuroactive effects of paracetamol, and reinforce the growing importance of zebrafish models for drug screening, including the search for novel putative anti-stress therapies.

Traces of tramadol in water impact behaviour in a native European fish

Tramadol is a widely used analgesic with additional antidepressant and anxiolytic effects. This compound has been reported in continental waters reaching concentrations of µg/L as a consequence of its inefficient removal in sewage treatment plants and increasing use over time. In this study, European chubs (Squalius cephalus) were exposed to 1 µg/L of tramadol in water for 42 days with a subsequent 14 days of depuration. Our results revealed that chubs exposed to this analgesic underwent changes in their behaviour as compared to the control group. The behavioural outcome was also influenced by the individual concentration of tramadol in brain tissue. In particular, experimental fish presented anxiolytic-like effects, characterized by less bold and less social individuals. Exposed animals were less frequently out of the shelter and moved a shorter distance, indicating that they explored the new environment less during the boldness test. In the novel object recognition experiment, although they distinguished the new item, they examined it less and displayed a reduced activity. Shoal cohesion was disrupted as observed in an increased distance between individuals. After the depuration phase, this alteration remained whereas the boldness effect disappeared. Moreover, the degree of behavioural changes was correlated with the concentration of the substance in brain. According to our findings, chronic presence of tramadol in the environment can impact the fitness of exposed aquatic fauna by altering evolutionary crucial behaviours.

Effect of levodopa/carbidopa on stress response in zebrafish

The dopaminergic system of zebrafish is complex and the numerous pathways and receptors in the central nervous system (CNS) are being extensively studied. A critical factor for the synthesis, activation and release of catecholamines (CAs) is the presence of tyrosine hydroxylase, an enzyme which converts L-tyrosine into levodopa. Levodopa thus is the intermediary in the synthesis of dopamine (DA) and norepinephrine (NE) and promotes its release; therefore, CAs play an important role in the CNS with hormonal functions. Here, we use levodopa/carbidopa to clarify the involvement of the dopaminergic pathway in the stress response in zebrafish submitted to an acute stress challenge. Acute stress was induced by chasing fish with a net for 2 min and assessed by measuring whole-body cortisol levels. Two experiments were carried out, the first with exposure to levodopa/carbidopa and the second with exposure to AMPT and levodopa/carbidopa. Levodopa/carbidopa balances the stress response through its action on the zebrafish hypothalamic-pituitary-adrenal (HPA) axis. Changes in cortisol levels suggest that DA was related to the balance of the stress response and that NE decreased this response. These effects were specific to stress since levodopa/carbidopa did not induce changes in cortisol in non-stressed fish.

Acute and chronic effects of diazepam on the polychaete Hediste diversicolor: Antioxidant, metabolic, pharmacologic, neurotoxic and behavioural mechanistic traits

Pharmaceutical drugs are widespread environmental contaminants, but data about their adverse effects are still limited to a few compounds. This study analyzed the acute (96 h) and chronic (28 days) impacts of environmentally realistic levels of diazepam (acute exposure: 0.001, 0.01, 0.1, 1, 10 μg/L; chronic exposure: 0.1, 1, 10, 100, 1000 ng/L), in the polychaete Hediste diversicolor, by measuring behavioral and biochemical (catalase [CAT], glutathione-S-transferases [GSTs], cholinesterases [ChEs], glutathione peroxidase [GPx], lipid peroxidation [TBARS]) parameters. Acute exposure to diazepam altered behavioral traits, decreasing burrowing times and causing hyperactivity, whilst burrowing time increased and hypoactivity resulted after chronic exposure. All biomarkers were affected after the chronic exposure, with the exception of lipid peroxidation. Our data demonstrate that realistic levels of diazepam may impair behavioral and biochemical traits in polychaetes, suggesting that diazepam exposure presents a significant challenge to the environment that supports these organisms.

Understanding neurobehavioral effects of acute and chronic stress in zebrafish

Stress is a common cause of neuropsychiatric disorders, evoking multiple behavioral, endocrine and neuro-immune deficits. Animal models have been extensively used to understand the mechanisms of stress-related disorders and to develop novel strategies for their treatment. Complementing rodent and clinical studies, the zebrafish (Danio rerio) is one of the most important model organisms in biomedicine. Rapidly becoming a popular model species in stress neuroscience research, zebrafish are highly sensitive to both acute and chronic stress, and show robust, well-defined behavioral and physiological stress responses. Here, we critically evaluate the utility of zebrafish-based models for studying acute and chronic stress-related CNS pathogenesis, assess the advantages and limitations of these aquatic models, and emphasize their relevance for the development of novel anti-stress therapies. Overall, the zebrafish emerges as a powerful and sensitive model organism for stress research. Although these fish generally display evolutionarily conserved behavioral and physiological responses to stress, zebrafish-specific aspects of neurogenesis, neuroprotection and neuro-immune responses may be particularly interesting to explore further, as they may offer additional insights into stress pathogenesis that complement (rather than merely replicate) rodent findings. Compared to mammals, zebrafish models are also characterized by increased availability of gene-editing tools and higher throughput of drug screening, thus being able to uniquely empower translational research of genetic determinants of stress and resilience, as well as to foster innovative CNS drug discovery and the development of novel anti-stress therapies.

Effect of fluoxetine on enhanced biological phosphorus removal using a sequencing batch reactor

In this work, the potential impact of emerging pollutant Fluoxetine (FLX) on enhanced biological phosphorus removal (EBPR) was systematically investigated using the sequencing batch reactor. The experimental results showed that even 200 μg/L FLX had no significant effect on EBPR during the short-term exposure. However, in the long-term exposure test, high dosage of FLX inhibited EBPR. 200 μg/L FLX induced biological phosphorus removal efficiency dropped to 71.3 ± 2.1%, significantly lower than that of the blank. The mechanism investigation showed that high concentration of FLX reduced anaerobic phosphorus release and oxic phosphorus absorption, and the consumption of organic matter during the anaerobic period. In addition, FLX decreased the synthesis of intracellular polymer polyhydroxyalkanoates (PHA), but promoted the metabolism of glycogen and polyhydroxyvalerate. FLX reduced the activity of key enzymes in EBPR and the relative abundance of Accumulibacter, but improved the relative abundance of Candidatus Competibacter.

The effects of daily mitotane or diazepam treatment on the formation of chronic stress symptoms in newly captured wild house sparrows

Wild animals brought into captivity frequently experience chronic stress and typically need a period of time to adjust to the conditions of captivity (restraint, artificial lighting, altered diet, human presence, etc.), to which they may never fully acclimate. Changes in mass, the hypothalamic-pituitary-adrenal axis and heart rate parameters have been observed over the first week in newly captive house sparrows (Passer domesticus). In this study, we tested the effects of two drugs, diazepam and mitotane, in preventing the chronic stress symptoms caused by captivity, compared with oil-injected control animals. Diazepam is an anxiolytic that is widely prescribed in humans and other animals and has been shown in some cases to reduce physiological stress. Mitotane is an agent that causes chemical adrenalectomy, reducing the body's capacity to produce glucocorticoid hormones. Our mitotane treatment did not cause the expected change in corticosterone concentrations. Baseline corticosterone was higher after a week in captivity regardless of the treatment group, while stress-induced corticosterone did not significantly increase above baseline after a week in captivity in any treatment group. However, mitotane treatment did have some physiological effects, as it reduced the resting heart rate and the duration of the heart rate response to a sudden noise. It also prevented the increase in nighttime activity that we observed in control animals. There was no effect of diazepam on corticosterone, resting heart rate, activity or heart rate response to a sudden noise, and no effect of either treatment on the sympathetic vs parasympathetic control of the resting heart rate. Together, these data suggest that mitotane, but not diazepam, can have a modest impact on helping house sparrows adapt to captive conditions. Easing the transition to captivity will likely make conservation efforts, such as initiating captive breeding programs, more successful.

Do environmentally relevant concentrations of fluoxetine and citalopram impair stress-related behavior in zebrafish (Danio rerio) embryos?

Selective serotonin reuptake inhibitors (SSRIs) have been shown to interfere with various physiological functions of aquatic organisms, yet the neuroactive potential of low concentrations of SSRIs in the aquatic environment is unclear. The current study investigated the effects of fluoxetine and citalopram on the visual motor response (VMR) of 107 h old zebrafish (Danio rerio) embryos. Results document a reduction in stress-related swimming activity of zebrafish embryos at environmentally relevant concentration levels, with fluoxetine being more effective than citalopram. Further experiments were designed to elucidate (1) if the lower neuroactive potential of citalopram is due to differences in uptake kinetics, (2) if the metabolite of fluoxetine, norfluoxetine, contributes to the neuroactive potential of fluoxetine, (3) and how SSRIs and their metabolites interact in equimolar mixtures. At the stage of 120 h, zebrafish embryos accumulate citalopram at significantly lower rates (up to 127 times) than fluoxetine. Moreover, it was demonstrated that norfluoxetine reduces the embryonic VMR similarly to fluoxetine resulting in additive effects of these substances on stress-related behavior in zebrafish embryos. In contrast, the interaction of fluoxetine, norfluoxetine and citalopram varied with test concentrations of the equimolar mixtures. Findings provide evidence that environmentally relevant concentrations of fluoxetine reduce stress-related behavior of zebrafish embryos, while these effects may be enhanced by the interaction of multiple SSRIs and their metabolites in environmental exposure scenarios.

Fluoxetine chronic exposure affects growth, behavior and tissue structure of zebrafish

Fluoxetine (FLX) is among the top 100 pharmaceutical prescribed annually worldwide and consequently is often detected in wastewater treatment plant effluent and surface waters, in concentrations up to 2.7 and 0.33 μg/L, respectively. Despite the presence of FLX in surface waters, little is known about its chronic effects in fish. Thus, this study aimed at investigating the chronic toxicity of FLX to Danio rerio adults. Rate of weight gain, behavior (feeding and swimming activity) and tissue organization (liver and intestine) were evaluated, after 30 days exposure. A lower rate of weight gain was observed at 100 μg/L FLX. The food intake time decreased, showing a decrease in fish appetite. The preference for the upper aquarium layer was observed at 10 and 100 μg/L of FLX, indicating an inhibition of the stress level (anxiolytic effect). Mild to moderate damage of hepatic tissue and a decrease epithelium height and increase in villus height of intestine were observed in fish exposed to concentrations as low as 0.01 μg/L. Based on obtained results, chronic exposure of fish to FLX could affect swimming and feeding behavior and alter morphological structure of liver and intestine tissues at environmental levels.

Dopamine and serotonin mediate the impact of stress on cleaner fish cooperative behavior

Stress is known to modulate behavioral responses and rapid decision-making processes, especially under challenging contexts which often occur in social and cooperative interactions. Here, we evaluated the effects of acute stress on cooperative behavior of the Indo-Pacific cleaner wrasse (Labroides dimidiatus) and the implications of pre-treatment with monoaminergic compounds: the selective serotonin reuptake inhibitor - fluoxetine, the 5-HT_1A receptor antagonist - WAY-100,635, the D₁ receptor agonist - SKF-38393, and the D₁ receptor antagonist - SCH-23390. We demonstrated that stress decreased the predisposal to interact and increased cortisol levels in cleaners, which are alleviated by fluoxetine and the dopaminergic D₁ antagonist. Overall, our findings highlight the crucial influence of stress on cooperative behavior.