Behavioral effects of MDMA ('ecstasy') on adult zebrafish

Unveil the toxicity induced on early life stages of zebrafish (Danio rerio) exposed to 3,4-methylenedioxymethamphetamine (MDMA) and its enantiomers

The increased detection of the recreational drug 3,4-methylenedioxymethamphetamine (MDMA) in aquatic ecosystems, has raised concern worldwide about its possible negative impacts on wildlife. MDMA is produced as racemate but its enantioselective effects on non-target organisms are poorly understood. Therefore, this study aimed to provide a comprehensive study of the toxicity of MDMA and its enantiomers in the early life stages of zebrafish (Danio rerio). Zebrafish embryos (≈3 h post fertilization) were exposed to different concentrations (0.02, 0.2, 2, 20, and 200 μg/L) of (R,S)-MDMA and both pure enantiomers. Both enantiomers induced effects on embryonic development, DNA integrity, and behaviour and enantioselective effects were noted. (S)-MDMA exhibits higher toxic effects on embryonic development level with increased mortality and severity of teratogenic effects, and behavioural abnormalities in acoustic startle-habituation response. (R)-MDMA affected general activity and avoidance behaviour, showing greater inhibitory effects on behavioural activity. Additionally, (R,S)-MDMA induced higher genotoxic effects than the two isolated enantiomers. These results are of concern at populational levels since effects on mortality, development, and behaviour were observed even at environmentally relevant concentrations, which can cause a reduction of larval viability and in the number of individuals in each generation, and an increase in the risk of predation of the organisms. Yet, the bioaccumulation studies showed that MDMA is not accumulated in zebrafish. Therefore, this work demonstrated for the first time the occurrence of MDMA enantiotoxicity in the early life stages of zebrafish, which should be considered in further environmental risk assessments involving fish species or other non-target aquatic organisms.

Acute clomipramine exposure elicits dose-dependent surfacing behavior in adult zebrafish (Danio rerio)

Chronic treatment with clomipramine, a tricyclic antidepressant drug, reduces symptoms of obsessive-compulsive disorder (OCD) and can influence the activity of the hypothalamic-pituitary-adrenal axis. However, little is known regarding the effects of acute clomipramine on the immediate expression of stress responses. Serotonergic drugs can elicit surfacing, a behavioral profile potentially related to toxicity in fish, although surfacing has not yet been observed after clomipramine exposure. The present study investigated the impact of acute exposure to clomipramine on basal and stress-induced behaviors in the novel tank test and cortisol levels in mixed-sex, wild-type, adult zebrafish (Danio rerio). The findings show clomipramine-exposed groups (regardless of stress exposure) spent much more time in the top of the novel tank and had significantly less overall motor activity in the behavioral task compared to the fish not exposed to the drug. Then, the dose-dependent effects of acute clomipramine on activity in the surface of the novel tank (top third of the top half) were investigated further. Clomipramine dose-dependently increased surface-dwelling and elicited a dose-dependent hypoactivity in overall motor behavior. There were no statistically significant differences in whole-body cortisol levels in either experiment. Like other serotonin-acting drugs, clomipramine strongly elicited surface-dwelling and depressed motor behavior in adult zebrafish. Additional testing is needed to elucidate whether surfacing represents a toxic state and how serotonin regulates surfacing.

Methamphetamine effects in zebrafish (Danio rerio) depend on behavioral endpoint, dose and test session duration

Research using zebrafish (Danio rerio) has begun to provide novel information in many fields, including the behavioral pharmacology of drug use and misuse. There have been limited studies on the effects of methamphetamine in adult zebrafish and the parameters of exposure (dose, test session length) have not been well-documented. Behavior following drug exposure is generally measured during relatively short sessions (6-10 min is common) in a novel tank environment. Many procedural variables (isolation, netting, novel tank) elicit anxiety-like behavior that is most apparent during the initial portion of a test session. This anxiety-like behavior might mask the initial effects of methamphetamine. During longer test sessions, these anxiety-like responses would be expected to habituate and drug effects should become more apparent. To test this idea, we measured several locomotor activity responses for 50-min following a range of methamphetamine doses (0.1-3.0 mg/L via immersion in methamphetamine solution). Methamphetamine failed to alter swimming velocity, distance travelled, or freezing time. In contrast, methamphetamine produced a dose-dependent decrease in time spent in the bottom of the tank, an increase in the number of visits to the top of the tank, and an increase in the number of transitions along the sides of the tank. The effects of methamphetamine were apparent 10-20 min following exposure and generally persisted throughout the session. These findings indicate that longer test sessions are required to measure methamphetamine-induced changes in behavior in zebrafish, as has been shown in other laboratory animals. The results also suggest that anxiety-like responses associated with various procedural aspects (netting, isolation, novel test apparatus) likely interfere with the ability to observe many behavioral effects of methamphetamine in zebrafish. Based on the current results, habituation to testing procedures to reduce anxiety-like behaviors is recommended in determining the effects of methamphetamine in zebrafish.

Daphnia magna an emerging environmental model of neuro and cardiotoxicity of illicit drugs

Cocaine, methamphetamine, ectasy (3,4-methylenedioxy amphetamine (MDMA)) and ketamine are among the most consumed drugs worldwide causing cognitive, oxidative stress and cardiovascular problems in humans. Residue levels of these drugs and their transformation products may still enter the aquatic environment, where concentrations up to hundreds of ng/L have been measured. In the present work we tested the hypothesis that psychotropic effects and the mode of action of these drugs in D. magna cognitive, oxidative stress and cardiovascular responses are equivalent to those reported in humans and other vertebrate models. Accordingly we expose D. magna juveniles to pharmacological and environmental relevant concentrations. The study was complemented with the measurement of the main neurotransmitters involved in the known mechanisms of action of these drugs in mammals and physiological relevant amino acids. Behavioural cognitive patters clearly differentiate the 3 psychostimulant drugs (methamphetamine, cocaine, MDMA) from the dissociative one ketamine. Psychostimulant drugs at pharmacological doses (10-200 μM), increased basal locomotion activities and responses to light, and decreased habituation to it. Ketamine only increased habituation to light. The four drugs enhanced the production of reactive oxygen species in a concentration related manner, and at moderate concentrations (10-60 μM) increased heartbeats, diminishing them at high doses (200 μM). In chronic exposures to environmental low concentrations (10-1000 ng/L) the four drugs did not affect any of the behavioural responses measured but methamphetamine and cocaine inhibited reproduction at 10 ng/L. Observed effects on neurotransmitters and related metabolites were in concern with reported responses in mammalian and other vertebrate models: cocaine and MDMA enhanced dopamine and serotonin levels, respectively, methamphetamine and MDMA decreased dopamine and octopamine, and all but MDMA decreased 3 MT levels. Drug effects on the concentration of up to 10 amino acids evidence disruptive effects on neurotransmitter synthesis, the urea cycle, lipid metabolism and cardiac function.

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.

Exposure to 3,4-methylenedioxymethamphetamine (MDMA) induced biochemical but not behavioral effects in Daphnia magna

Among amphetamine like stimulants (ATS), the 3,4-methylenedioxymethamphetamine (MDMA) is often detected in sewage and surface waters, representing a potential threat for organisms because of its peculiar mechanism of action (i.e., stimulatory and hallucinogenic). The present study aimed at investigating biochemical (i.e., oxidative stress and energetic biomarkers) and behavioral (i.e., swimming activity) effects induced by a 21-days exposure to two concentrations (50 ng/L and 500 ng/L) of MDMA towards Daphnia magna. The amount of reactive oxygen species (ROS), the activity of antioxidant (SOD, CAT, GPx) and detoxifying (GST) enzymes and lipid peroxidation were measured as oxidative stress-related endpoints. Total energy content was estimated from the measurement of protein, carbohydrate and lipid content to assess energy reserves. The modulation of swimming activity was assessed as behavioral endpoint. Slight effects of MDMA exposure on oxidative stress responses and energy reserves were observed, while no alterations of the swimming behavior was noted.

Therapeutic effects of methimazole on 3,4-methylenedioxymethamphetamine-induced hyperthermia and serotonergic neurotoxicity

3,4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug, however over 200 studies demonstrate that acute (e.g. hyperthermia, rhabdomyolysis) and chronic (e.g. neurotoxicity) toxicity effects of MDMA were observed in different animals. Methimazole (MMI), an inhibitor of thyroid hormone synthesis, was found to significantly reduce the HSP72 expression of heat stress induced in fibroblasts. Hence, we attempted to understand the effects of MMI on MDMA induced changes in vivo. Male SD rats were randomly divided into four groups as follows:(a) water-saline (b) water-MDMA (c) MMI-saline and (d) MMI-MDMA group. In the temperature analysis test, MMI was found to alleviate MDMA-induced hyperthermia and increase the heat loss index (HLI), revealing its peripheral vasodilation effect. PET experiment suggested that MDMA induced elevated glucose uptake by skeletal muscles, which was resolved by MMI pretreatment. IHC staining (serotonin transporter, SERT) showed the evidence of neurotoxicity caused by MDMA (serotonin fiber loss), which was alleviated by MMI. Furthermore, the animal behaviour test (forced swimming test, FST) showed higher swimming time but lower immobility time in MMI-MDMA and MMI-saline groups. Taken together, treatment of MMI shows benefits such as lowered body temperature, alleviation of neurotoxicity and excited behaviour. However, further investigations should be conducted in the future to provide in-depth evidence for its clinical use.

Toxicity of the 3,4-Methylenedioxymethamphetamine and Its Enantiomers to Daphnia magna after Isolation by Semipreparative Chromatography

MDMA (3,4-methylenedioxymethamphetamine) is a chiral psychoactive recreational drug sold in illicit markets as racemate. Studies on the impact of MDMA on aquatic organisms are scarce. While enantioselectivity in toxicity in animals and humans has been reported, none is reported on aquatic organisms. This study aimed to investigate the ecotoxicological effects of MDMA and its enantiomers in Daphnia magna. For that, enantiomers (enantiomeric purity > 97%) were separated by liquid chromatography using a homemade semipreparative chiral column. Daphnids were exposed to three concentrations of (R,S)-MDMA (0.1, 1.0 and 10.0 µg L^-1) and two concentrations of (R)- and (S)-enantiomers (0.1 and 1.0 µg L^-1) over the course of 8 days. Morphophysiological responses were dependent on the substance form and daphnia development stage, and they were overall not affected by the (R)-enantiomer. Changes in swimming behaviour were observed for both the racemate and its enantiomers, but enantioselective effects were not observed. Reproductive or biochemical changes were not observed for enantiomers whereas a significant decrease in acetylcholinesterase and catalase activity was noted at the highest concentration of (R,S)-MDMA (10 µg L^-1). Overall, this study showed that sub-chronic exposure to MDMA racemate and its enantiomers can interfere with morphophysiological and swimming behaviour of D. magna. In general, the (R)-enantiomer demonstrated less toxicity than the (S)-enantiomer.

Zebrafish - The Neurobehavioural Model in Trend

Zebrafish (Danio rerio) is currently in vogue as a prevalently used experimental model for studies concerning neurobehavioural disorders and associated fields. Since the 1960s, this model has succeeded in breaking most barriers faced in the hunt for an experimental model. From its appearance to its high parity with human beings genetically, this model renders itself as an advantageous experimental lab animal. Neurobehavioural disorders have always posed an arduous task in terms of their detection as well as in determining their exact etiology. They are still, in most cases, diseases of interest for inventing or discovering novel pharmacological interventions. Thus, the need for a harbinger experimental model for studying neurobehaviours is escalating. Ensuring the same model is used for studying several neuro-studies conserves the results from inter-species variations. For this, we need a model that satisfies all the pre-requisite conditions to be made the final choice of model for neurobehavioural studies. This review recapitulates the progress of zebrafish as an experimental model with its most up-to-the-minute advances in the area. Various tests, assays, and responses employed using zebrafish in screening neuroactive drugs have been tabulated effectively. The tools, techniques, protocols, and apparatuses that bolster zebrafish studies are discussed. The probable research that can be done using zebrafish has also been briefly outlined. The various breeding and maintenance methods employed, along with the information on various strains available and most commonly used, are also elaborated upon, supplementing Zebrafish's use in neuroscience.

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 behavioral and Neurochemical Effects of Novel N-Benzyl-2-Phenylethylamine Derivatives in Adult Zebrafish

Hallucinogenic drugs potently affect brain and behavior and have also recently emerged as potentially promising agents in pharmacotherapy. Complementing laboratory rodents, the zebrafish (Danio rerio) is a powerful animal model organism for screening neuroactive drugs, including hallucinogens. Here, we test a battery of ten novel N-benzyl-2-phenylethylamine (NBPEA) derivatives with the 2,4- and 3,4-dimethoxy substitutions in the phenethylamine moiety and the -OCH₃, -OCF₃, -F, -Cl, and -Br substitutions in the ortho position of the phenyl ring of the N-benzyl moiety, assessing their acute behavioral and neurochemical effects in the adult zebrafish. Overall, substitutions in the Overall, substitutions in the N-benzyl moiety modulate locomotion, and substitutions in the phenethylamine moiety alter zebrafish anxiety-like behavior, also affecting the brain serotonin and/or dopamine turnover. The 24H-NBOMe(F) and 34H-NBOMe(F) treatment also reduced zebrafish despair-like behavior. Computational analyses of zebrafish behavioral data by artificial intelligence identified several distinct clusters for these agents, including anxiogenic/hypolocomotor (24H-NBF, 24H-NBOMe, and 34H-NBF), behaviorally inert (34H-NBBr, 34H-NBCl, and 34H-NBOMe), anxiogenic/hallucinogenic-like (24H-NBBr, 24H-NBCl, and 24H-NBOMe(F)), and anxiolytic/hallucinogenic-like (34H-NBOMe(F)) drugs. Our computational analyses also revealed phenotypic similarity of the behavioral activity of some NBPEAs to that of selected conventional serotonergic and antiglutamatergic hallucinogens. In silico functional molecular activity modeling further supported the overlap of the drug targets for NBPEAs tested here and the conventional serotonergic and antiglutamatergic hallucinogens. Overall, these findings suggest potent neuroactive properties of several novel synthetic NBPEAs, detected in a sensitive in vivo vertebrate model system, the zebrafish, raising the possibility of their potential clinical use and abuse.

Artificial intelligence-driven phenotyping of zebrafish psychoactive drug responses

Zebrafish (Danio rerio) are rapidly emerging in biomedicine as promising tools for disease modelling and drug discovery. The use of zebrafish for neuroscience research is also growing rapidly, necessitating novel reliable and unbiased methods of neurophenotypic data collection and analyses. Here, we applied the artificial intelligence (AI) neural network-based algorithms to a large dataset of adult zebrafish locomotor tracks collected previously in a series of in vivo experiments with multiple established psychotropic drugs. We first trained AI to recognize various drugs from a wide range of psychotropic agents tested, and then confirmed prediction accuracy of trained AI by comparing several agents with known similar behavioral and pharmacological profiles. Presenting a framework for innovative neurophenotyping, this proof-of-concept study aims to improve AI-driven movement pattern classification in zebrafish, thereby fostering drug discovery and development utilizing this key model organism.

Effects of common environmental endocrine-disrupting chemicals on zebrafish behavior

Environmental endocrine-disrupting chemicals (EDCs), a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Therefor, this review focused on the use of the zebrafish as a model to explore the effect of different EDCs on behavior, as well as the molecular mechanisms that drive these effects. Furthermore, our study summarizes the current knowledge on the neuromodulatory effects of different EDCs in zebrafish. This study also reviews the current state of zebrafish behavior research, in addition to the potential mechanisms of single and mixed pollutant-driven behavioral dysregulation at the molecular level, as well as the applications of zebrafish behavior experiments for neuroscience research. This review broadens our understanding of the influence of EDCs on zebrafish behavior and provides guidance for future research.

Developmental exposure to MDMA (ecstasy) in zebrafish embryos reproduces the neurotoxicity adverse outcome 'lower motor activity' described in humans

The recreational use of MDMA (ecstasy) by pregnant women is associated with impaired neuromotor function in infants, but the Adverse Outcome Pathway behind this effect is not clear yet. We present for the first time the evaluation of developmental neurotoxic (DNT) effects of MDMA in zebrafish embryos. The aim of the study was to determine whether the zebrafish model reproduces the adverse outcome occurring in humans. We have studied the DNT effects of MDMA in zebrafish within a range of 5-250 μM performing different behavioural tests: spontaneous tail-coiling and light-dark locomotor response; after exposing the embryos to 4 different scenarios combining changes in pH, in starting exposure time and exposure duration. In these scenarios we evaluated the effects of MDMA in general embryonic development and compared the concentrations producing them with those inducing specific DNT effects. As a result, we have established the experimental conditions leading to the adverse outcome "lower motor activity" in zebrafish without producing general developmental delay or general toxicity. The experimental condition chosen opens the door to use this model in future mechanistic investigations to better characterize the Adverse Outcome Pathway associated with the adverse effects caused by MDMA prenatal exposure in humans.

THC-induced behavioral stereotypy in zebrafish as a model of psychosis-like behavior

High doses of the Cannabis constituent Δ9-tetrahydrocannabinol (THC) increase the risk of psychosis in humans. Highly accessible animal models are needed to address underlying mechanisms. Using zebrafish with a conserved endocannabinoid system, this study investigates the acute effects of THC on adult zebrafish behavior and the mechanisms involved. A concentration-dependent THC-induced behavioral stereotypy akin to THC's effect in rats and the psychotropics phencyclidine and ketamine in zebrafish was established. Distinctive circular swimming during THC-exposure was measured using a novel analytical method that we developed, which detected an elevated Repetition Index (RI) compared to vehicle controls. This was reduced upon co-administration of N-methyl-D-aspartate (NMDA) receptor agonist NMDA, suggesting that THC exerts its effects via biochemical or neurobiological mechanisms associated with NMDA receptor antagonism. Co-treatment of γ-aminobutyric acid receptor antagonist pentylenetetrazol also showed signs of reducing the RI. Since THC-induced repetitive behavior remained in co-administrations with cannabinoid receptor 1 inverse agonist AM251, the phenotype may be cannabinoid receptor 1-independent. Conversely, the inverse cannabinoid receptor 2 agonist AM630 significantly reduced THC-induced behavioral stereotypy, indicating cannabinoid receptor 2 as a possible mediator. A significant reduction of the THC-RI was also observed by the antipsychotic sulpiride. Together, these findings highlight this model's potential for elucidating the mechanistic relationship between Cannabis and psychosis.

Gene alteration in zebrafish exposed to a mixture of substances of abuse

A recent surge in the use and abuse of diverse prescribed psychotic and illicit drugs necessitates the surveillance of drug residues in source water and the associated ecological impacts of chronic exposure to the aquatic organism. Thirty-six psychotic and illicit drug residues were determined in discharged wastewater from two centralized municipal wastewater treatment facilities and two wastewater receiving creeks for seven consecutive days in Kentucky. Zebrafish (Danio rerio) larvae were exposed to the environmental relevant mixtures of all drug residues, all illicit drugs, and all prescribed psychotic drugs. The extracted RNA from fish homogenates was sequenced, and differentially expressed sequences were analyzed for known or predicted nervous system expression, and screened annotated protein-coding genes to the true environmental cocktail mixture. Illicit stimulant (cocaine and one metabolite), opioids (methadone, methadone metabolite, and oxycodone), hallucinogen (MDA), benzodiazepine (oxazepam and temazepam), carbamazepine, and all target selective serotonin reuptake inhibitors including sertraline, fluoxetine, venlafaxine, and citalopram were quantified in 100% of collected samples from both creeks. The high dose cocktail mixture exposure group revealed the largest group of differentially expressed genes: 100 upregulated and 77 downregulated (p ≤ 0.05; q ≤ 0.05). The top 20 differentially expressed sequences in each exposure group comprise 82 unique transcripts corresponding to 74% annotated genes, 7% non-coding sequences, and 19% uncharacterized sequences. Among 61 differentially expressed sequences that corresponded to annotated protein-coding genes, 23 (38%) genes or their homologs are known to be expressed in the nervous system of fish or other organisms. Several of the differentially expressed sequences are associated primarily with the immune system, including several major histocompatibility complex class I and interferon-induced proteins. Interleukin-1 beta (downregulated in this study) abnormalities are considered a risk factor for psychosis. This is the first study to assess the contributions of multiple classes of psychotic and illicit drugs in combination with developmental gene expression.

A Systematic Review of the MDMA Model to Address Social Impairment in Autism

BACKGROUND

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterised by repetitive behaviours, cognitive rigidity/inflexibility, and social-affective impairment. Unfortunately, no gold-standard treatments exist to alleviate the core socio-behavioural impairments of ASD. Meanwhile, the prosocial empathogen/entactogen 3,4-methylene-dioxy-methamphetamine (MDMA) is known to enhance sociability and empathy in both humans and animal models of psychological disorders.

OBJECTIVE

We review the evidence obtained from behavioural tests across the current literature, showing how MDMA can induce prosocial effects in animals and humans, where controlled experiments were able to be performed.

METHODS

Six electronic databases were consulted. The search strategy was tailored to each database. Only English-language papers were reviewed. Behaviours not screened in this review may have affected the core ASD behaviours studied. Molecular analogues of MDMA have not been investigated.

RESULTS

We find that the social impairments may potentially be alleviated by postnatal administration of MDMA producing prosocial behaviours in mostly the animal model.

CONCLUSION

MDMA and/or MDMA-like molecules appear to be an effective pharmacological treatment for the social impairments of autism, at least in animal models. Notably, clinical trials based on MDMA use are now in progress. Nevertheless, larger and more extended clinical studies are warranted to prove the assumption that MDMA and MDMA-like molecules have a role in the management of the social impairments of autism.

Psychopharmacological characterization of an emerging drug of abuse, a synthetic opioid U-47700, in adult zebrafish

3,4-Dichloro-N-[2-(dimethylamino)cyclohexyl]-N-methylbenzamide (U-47700) is a selective μ-opioid receptor agonist originally synthesized as a prospective analgesic drug. Several times more potent than morphine, U-47700 has high abuse potential and may cause clinical neurotoxicity, euphoria, respiratory depression and occasional mortality. U-47700 also evokes analgesia, sedation and euphoria-like states in both humans and rodents. Despite the growing use and abuse of U-47700, its psychopharmacological and toxicological profiles in vivo remain poorly understood. The zebrafish (Danio rerio) is rapidly becoming a popular aquatic model organism for central nervous system (CNS) disease modeling and drug discovery. Here, we examine acute (1, 5, 10, 25 and 50 mg/L for 20-min) and chronic (0.1, 0.5 and 1 mg/L for 14 days) effects of U-47700 in adult zebrafish. Overall, we found overt sedation evoked in fish by acute, and hyperlocomotion with an anxiolytic-like action by chronic, drug treatments. Acute treatment with 1 and 10 mg/L U-47700 also resulted in detectable amounts of this drug in the brain samples, supporting its permeability through the blood-brain barrier. Collectively, these findings emphasize complex dose- and treatment-dependent CNS effects of U-47700 following its acute and chronic administration. Our study also supports high sensitivity of zebrafish to U-47700, and suggests these aquatic models as promising in-vivo screens for probing potential CNS effects evoked by novel synthetic opioid drugs.

Combining Neurobehavioral Analysis and In Vivo Photoaffinity Labeling to Understand Protein Targets of Methamphetamine in Casper Zebrafish

Photoaffinity labeling (PAL) remains one of the most widely utilized methods of determining protein targets of drugs. Although useful, the scope of this technique has been limited to in vitro applications because of the inability of UV light to penetrate whole organisms. Herein, pigment-free Casper zebrafish were employed to allow in vivo PAL. A methamphetamine-related phenethylamine PAL probe, designated here as 2, demonstrated dose-dependent effects on behavior similar to methamphetamine and permitted concentration-dependent labeling of protein binding partners. Click chemistry was used to analyze binding partners via fluoroimaging. Conjugation to a biotin permitted streptavidin pull-down and proteomic analysis to define direct binding partners of the methamphetamine probe. Bioinformatic analysis revealed the probe was chiefly bound to proteins involved in phagocytosis and mitochondrial function. Future applications of this experimental paradigm combining examination of drug-protein binding interactions alongside neurobehavioral readouts via in vivo PAL will significantly enhance our understanding of drug targets, mechanism(s) of action, and toxicity/lethality.

Review on the occurrence and biological effects of illicit drugs in aquatic ecosystems

Illicit drugs (IDs) and their metabolites are recognized as contaminants of emerging concern. After consumption, illicit drugs are partially metabolized and excreted unchanged in urine and feces or as active metabolites reaching wastewater treatment plants (WWTPs). Furthermore, most WWTPs are insufficient in the treatment of effluents containing IDs, which may be released into aquatic ecosystems. Once in the water or sediment, these substances may interact and affect non-target organisms and some evidences suggest that illicit drugs may exhibit pseudo-persistence because of a continuous environmental input, resulting in long-term exposure to aquatic organisms that may be negatively affected by these biologically active compounds. We reviewed the literature on origin and consumption, human metabolism after consumption, aquatic occurrences, and toxicity of the major groups of illicit drugs (opioids, cannabis, synthetic drugs, and cocaine). As a result, it could be concluded that illicit drugs and their metabolites are widespread in diverse aquatic ecosystems in levels able to trigger sublethal effects to non-target organisms, besides to concentrate in seafood. This class of emerging contaminants represents a new environmental concern to academics, managers, and policymakers, whose would be able to assess risks and identify proper responses to reduce environmental impacts.

Opioid Neurobiology, Neurogenetics and Neuropharmacology in Zebrafish

Despite the high prevalence of medicinal use and abuse of opioids, their neurobiology and mechanisms of action are not fully understood. Experimental (animal) models are critical for improving our understanding of opioid effects in vivo. As zebrafish (Danio rerio) are increasingly utilized as a powerful model organism in neuroscience research, mounting evidence suggests these fish as a useful tool to study opioid neurobiology. Here, we discuss the zebrafish opioid system with specific focus on opioid gene expression, existing genetic models, as well as its pharmacological and developmental regulation. As many human brain diseases involve pain and aberrant reward, we also summarize zebrafish models relevant to opioid regulation of pain and addiction, including evidence of functional interplay between the opioid system and central dopaminergic and other neurotransmitter mechanisms. Additionally, we critically evaluate the limitations of zebrafish models for translational opioid research and emphasize their developing utility for improving our understanding of evolutionarily conserved mechanisms of pain-related, addictive, affective and other behaviors, as well as for fostering opioid-related drug discovery.

Zebrafish: an emerging real-time model system to study Alzheimer's disease and neurospecific drug discovery

Zebrafish (Danio rerio) is emerging as an increasingly successful model for translational research on human neurological disorders. In this review, we appraise the high degree of neurological and behavioural resemblance of zebrafish with humans. It is highly validated as a powerful vertebrate model for investigating human neurodegenerative diseases. The neuroanatomic and neurochemical pathways of zebrafish brain exhibit a profound resemblance with the human brain. Physiological, emotional and social behavioural pattern similarities between them have also been well established. Interestingly, zebrafish models have been used successfully to simulate the pathology of Alzheimer’s disease (AD) as well as Tauopathy. Their relatively simple nervous system and the optical transparency of the embryos permit real-time neurological imaging. Here, we further elaborate on the use of recent real-time imaging techniques to obtain vital insights into the neurodegeneration that occurs in AD. Zebrafish is adeptly suitable for Ca²⁺ imaging, which provides a better understanding of neuronal activity and axonal dystrophy in a non-invasive manner. Three-dimensional imaging in zebrafish is a rapidly evolving technique, which allows the visualisation of the whole organism for an elaborate in vivo functional and neurophysiological analysis in disease condition. Suitability to high-throughput screening and similarity with humans makes zebrafish an excellent model for screening neurospecific compounds. Thus, the zebrafish model can be pivotal in bridging the gap from the bench to the bedside. This fish is becoming an increasingly successful model to understand AD with further scope for investigation in neurodevelopment and neurodegeneration, which promises exciting research opportunities in the future.

Using model fish to study the biological mechanisms of cooperative behaviour: A future for translational research concerning social anxiety disorders?

Human societies demand of its composing members the development of a wide array of social tools and strategies. A notable example is human outstanding ability to cooperate with others, in all its complex forms, depicting the reality of a highly demanding social framework in which humans need to be integrated as to attain physical and mental benefits. Considering the importance of social engagement, it's not entirely unexpected that most psychiatric disorders involve some disruption of normal social behaviour, ranging from an abnormal absence to a significant increase of social functioning. It is however surprising that knowledge on these social anxiety disorders still remains so limited. Here we review the literature focusing on the social and cooperative toolbox of 3 fish model species (cleaner fishes, guppies and zebrafish) which are amenable systems to test for social disorders. We build on current knowledge based on ethological information, arising from studies on cooperative behaviour in cleanerfishes and guppies, while profiting from the advantages of the intense use of zebrafish, to create novel paradigms aiming at the major socio-cognitive modules/dimensions in fish species. This focus may enable the discovery of putative conserved endpoints which are relevant for research into social disorders. We suggest that cross-species, cross-domain, functional and genetic approaches could provide a wider array of information on the neurobiological bases of social and cooperative behaviour, crucial to understanding the neural bases of social disorders and key to finding novel avenues towards treatment.

The Non-Peptide Arginine-Vasopressin v1a Selective Receptor Antagonist, SR49059, Blocks the Rewarding, Prosocial, and Anxiolytic Effects of 3,4-Methylenedioxymethamphetamine and Its Derivatives in Zebra Fish

3,4-Methylenedioxymethamphetamine (MDMA) and its derivatives, 2,5-dimethoxy-4-bromo-amphetamine hydrobromide (DOB) and para-methoxyamphetamine (PMA), are recreational drugs whose pharmacological effects have recently been attributed to serotonin 5HT_2A/C receptors. However, there is growing evidence that the oxytocin (OT)/vasopressin system can modulate some the effects of MDMA. In this study, MDMA (2.5-10 mg/kg), DOB (0.5 mg/kg), or PMA (0.005, 0.1, or 0.25 mg/kg) were administered intramuscularly to adult zebra fish, alone or in combination with the V_1a vasopressin antagonist, SR49059 (0.01-1 ng/kg), before carrying out conditioned place preference (CPP), social preference, novel tank diving, and light-dark tests in order to evaluate subsequent rewarding, social, and emotional-like behavior. The combination of SR49059 and each drug progressively blocked: (1) rewarding behavior as measured by CPP in terms of time spent in drug-paired compartment; (2) prosocial effects measured on the basis of the time spent in the proximity of a nacre fish picture; and (3) anxiolytic effects in terms of the time spent in the upper half of the novel tank and in the white compartment of the tank used for the light-dark test. Antagonism was obtained at SR49059 doses which, when given alone, did not change motor function. In comparison with a control group, receiving vehicle alone, there was a three to five times increase in the brain release of isotocin (the analog of OT in fish) after treatment with the most active doses of MDMA (10 mg/kg), DOB (0.5 mg/kg), and PMA (0.1 mg/kg) as evaluated by means of bioanalytical reversed-phase high-performance liquid chromatography. Taken together, these findings show that the OT/vasopressin system is involved in the rewarding, prosocial, and anxiolytic effects of MDMA, DOB, and PMA in zebra fish and underline the association between this system and the behavioral alterations associated with disorders related to substance abuse.

Abuse potential of methylenedioxymethamphetamine (MDMA) and its derivatives in zebrafish: role of serotonin 5HT2-type receptors

RATIONALE

The synthetic phenethylamines are recreational drugs known to produce psychostimulant effects. However, their abuse potential has not been widely studied.

OBJECTIVES

Here, we investigated the rewarding and the hallucinatory effects of 2,5-dimetoxy-4-bromo-amphetamine hydrobromide (DOB) and para-methoxyamphetamine (PMA) in comparison with the classical 3,4-methylenedioxymethamphetamine (MDMA). In addition, the role of serotonin 5-HT2-like receptor on the abovementioned effects was evaluated.

METHODS

Zebrafish were intramuscularly (i.m.) treated with a wide range of doses of DOB (0.1-20 mg/kg), PMA (0.0005-2 mg/kg), or MDMA (0.5-160 mg/kg). Animals were submitted to a conditioned place preference (CPP) task, to investigation of the rewarding properties, and to the evaluation of hallucinatory behavior in terms of appearance of a trance-like behavior. The serotonin 5-HT2 subtype receptor antagonist ritanserin (0.025-2.5 mg/kg) in association with the maximal effective dose of MDMA, DOB, and PMA was given i.m., and the effect on CPP or hallucinatory behavior was evaluated.

RESULTS

MDMA and its derivatives exhibited CPP in a biphasic fashion, being PMA the most potent. This effect was accompanied, for DOB (2 mg/kg) and PMA (0.1 mg/kg), by a trance-like hallucinatory behavior. MDMA at a high dose as 160 mg/kg did not induce any hallucinatory behavior. Ritanserin significantly blocked the rewarding and hallucinatory effects suggesting the involvement of serotonin 5HT2 subtype receptor.

CONCLUSION

Collectively, these findings demonstrate for the first time that the rewarding properties of DOB and PMA are accompanied by hallucinatory behavior through a serotonergic system and reinforce zebrafish as an emerging experimental model for screening new hallucinogens.

Exploring Hallucinogen Pharmacology and Psychedelic Medicine with Zebrafish Models

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

Vesicular monoamine transporter 2 (Vmat2) knockdown elicits anxiety-like behavior in zebrafish

Vesicular monoamine transporter 2 (Vmat2) is widely distributed in the central nervous system, and responsible for uptaking transmitters into the vesicles. However, whether Vmat2-deficiency is related to the anxiety is rarely investigated, especially in zebrafish. Here, we reported Vmat2 heterzygous mutant zebrafish displayed anxiety-like behavior. The mutants spent less time in the top area and took longer latency to the top in the novel tank test. Consistently, they showed dark avoidance in the light/dark box test, with longer duration in the light zone and increased number of crossing between the two zones. Monoamine concentration analysis showed that the levels of monoamine neurotransmitters including dopamine (DA), 5-hydroxy tryptamine (5-HT) and norepinephrine (NE), as well as their metabolites were decreased in VMAT mutants. Taken together, these findings suggest that Vmat2 heterzygous mutant zebrafish may serve as a new model of anxiety, which may be related with the low level of DA, 5-HT and NE.

Zebrafish neurobehavioral phenomics for aquatic neuropharmacology and toxicology research

Zebrafish (Danio rerio) are rapidly emerging as an important model organism for aquatic neuropharmacology and toxicology research. The behavioral/phenotypic complexity of zebrafish allows for thorough dissection of complex human brain disorders and drug-evoked pathological states. As numerous zebrafish models become available with a wide spectrum of behavioral, genetic, and environmental methods to test novel drugs, here we discuss recent zebrafish phenomics methods to facilitate drug discovery, particularly in the field of biological psychiatry. Additionally, behavioral, neurological, and endocrine endpoints are becoming increasingly well-characterized in zebrafish, making them an inexpensive, robust and effective model for toxicology research and pharmacological screening. We also discuss zebrafish behavioral phenotypes, experimental considerations, pharmacological candidates and relevance of zebrafish neurophenomics to other 'omics' (e.g., genomic, proteomic) approaches. Finally, we critically evaluate the limitations of utilizing this model organism, and outline future strategies of research in the field of zebrafish phenomics.

Serotonergic modulation of zebrafish behavior: towards a paradox

Due to the fish-specific genome duplication event (~320-350 mya), some genes which code for serotonin proteins were duplicated in teleosts; this duplication event was preceded by a reorganization of the serotonergic system, with the appearance of the raphe nuclei (dependent on the isthmus organizer) and prosencephalic nuclei, including the paraventricular and pretectal complexes. With the appearance of amniotes, duplicated genes were lost, and the serotonergic system was reduced to a more complex raphe system. From a comparative point of view, then, the serotonergic system of zebrafish and that of mammals shows many important differences. However, many different behavioral functions of serotonin, as well as the effects of drugs which affect the serotonergic system, seem to be conserved among species. For example, in both zebrafish and rodents acute serotonin reuptake inhibitors (SSRIs) seem to increase anxiety-like behavior, while chronic SSRIs decrease it; drugs which act at the 5-HT1A receptor seem to decrease anxiety-like behavior in both zebrafish and rodents. In this article, we will expose this paradox, reviewing the chemical neuroanatomy of the zebrafish serotonergic system, followed by an analysis of the role of serotonin in zebrafish fear/anxiety, stress, aggression and the effects of psychedelic drugs.

Aquatic toxicology of fluoxetine: understanding the knowns and the unknowns

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

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

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

Anxiolytic drug discovery: what are the novel approaches and how can we improve them?

INTRODUCTION

Contemporary biological psychiatry uses experimental (animal) models to increase our understanding of affective disorder pathogenesis. Despite the well-recognized spectrum nature of affective disorders, modern anxiolytic drug discovery mainly targets specific pathways and molecular determinants within a single phenotypic domain. However, greater understanding of the integrative mechanisms and pathogenesis is essential in order to develop new effective therapies.

AREAS COVERED

In this review, the authors emphasize the importance of a 'domain interplay-oriented' approach to experimental affective research. They also highlight the need to expand the scope of anxiolytic drug targets to better understand the pathogenesis of anxiety-spectrum disorders.

EXPERT OPINION

There is the potential to markedly improve the utility of animal models for affective disorders. First, the authors suggest that one such way would be by analyzing the systems of several domains and their interplay to better understand disease pathogenesis. Further, it could also be improved by expanding the range of model species and by extending the spectrum of anxiolytic drug targets; this would help to focus on emerging and unconventional systems to better develop new therapies.

The behavioral effects of acute Δ⁹-tetrahydrocannabinol and heroin (diacetylmorphine) exposure in adult zebrafish

The use of psychotropic drugs in clinical and translational brain research continues to grow, and the need for novel experimental models and screens is becoming widely recognized. Mounting evidence supports the utility of zebrafish (Danio rerio) for studying various pharmacological manipulations, as an alternative model complementing the existing rodent paradigms in this field. Here, we explore the effects of acute 20-min exposure to two commonly abused psychotropic compounds, Δ(9)-tetrahydrocannabinol (THC) and heroin, on adult zebrafish behavior in the novel tank test. Overall, THC administration (30 and 50 mg/L) produces an anxiogenic-like reduction of top swimming, paralleled with a slower, continuous bottom swimming. In contrast, heroin exposure (15 and 25 mg/L) evoked a hyperlocomotor response (with rapid bouts of bottom swimming and frequent 'bouncing' motions) without altering anxiety-sensitive top/bottom endpoints. The behavioral effects of these two compounds in zebrafish seem to parallel the respective rodent and human findings. Collectively, this emphasizes the growing significance of novel emerging aquatic models in translational drug abuse research and small molecule screening.

Perspectives on zebrafish models of hallucinogenic drugs and related psychotropic compounds

Among different classes of psychotropic drugs, hallucinogenic agents exert one of the most prominent effects on human and animal behaviors, markedly altering sensory, motor, affective, and cognitive responses. The growing clinical and preclinical interest in psychedelic, dissociative, and deliriant hallucinogens necessitates novel translational, sensitive, and high-throughput in vivo models and screens. Primate and rodent models have been traditionally used to study cellular mechanisms and neural circuits of hallucinogenic drugs' action. The utility of zebrafish ( Danio rerio ) in neuroscience research is rapidly growing due to their high physiological and genetic homology to humans, ease of genetic manipulation, robust behaviors, and cost effectiveness. Possessing a fully characterized genome, both adult and larval zebrafish are currently widely used for in vivo screening of various psychotropic compounds, including hallucinogens and related drugs. Recognizing the growing importance of hallucinogens in biological psychiatry, here we discuss hallucinogenic-induced phenotypes in zebrafish and evaluate their potential as efficient preclinical models of drug-induced states in humans.

Behavioral effects of bidirectional modulators of brain monoamines reserpine and d-amphetamine in zebrafish

Brain monoamines play a key role in the regulation of behavior. Reserpine depletes monoamines, and causes depression and hypoactivity in humans and rodents. In contrast, d-amphetamine increases brain monoamines' levels, and evokes hyperactivity and anxiety. However, the effects of these agents on behavior and in relation to monoamine levels remain poorly understood, necessitating further experimental studies to understand their psychotropic action. Zebrafish (Danio rerio) are rapidly emerging as a promising model organism for drug screening and translational neuroscience research. Here, we have examined the acute and long-term effects of reserpine and d-amphetamine on zebrafish behavior in the novel tank test. Overall, d-amphetamine (5 and 10mg/L) evokes anxiogenic-like effects in zebrafish acutely, but not 7 days later. In contrast, reserpine (20 and 40 mg/L) did not evoke overt acute behavioral effects, but markedly reduced activity 7 days later, resembling motor retardation observed in depression and/or Parkinson's disease. Three-dimensional 'temporal' (X, Y, time) reconstructions of zebrafish locomotion further supports these findings, confirming the utility of 3D-based video-tracking analyses in zebrafish models of drug action. Our results show that zebrafish are highly sensitive to drugs bi-directionally modulating brain monoamines, generally paralleling rodent and clinical findings. Collectively, this emphasizes the potential of zebrafish tests to model complex brain disorders associated with monoamine dysregulation.

Psychopharmacological effects of acute exposure to kynurenic acid (KYNA) in zebrafish

A metabolite of the kynurenine pathway, kynurenic acid (KYNA) is an important endogenous neuromodulator and neuroprotector, that also exerts neurotropic effects following exogenous administration. In humans and animals, KYNA regulates affective and cognitive responses, acting mainly as an antagonist of glutamatergic receptors. However, the complete psychopharmacological profile of KYNA (which includes the activity of several neurotransmitter receptors) is poorly understood, and merit further studies. Aquatic models are rapidly emerging as useful tools in translational psychopharmacology research. Here, we exposed adult zebrafish (Danio rerio) to exogenous KYNA for 20 min, and assessed their behavior in the novel tank test. Exposure to KYNA (20 mg/L) in this paradigm evoked overt effects in fish, including decreased latency to enter the top half of the tank, increased number of top entries and longer top duration. In contrast, locomotor activity indices (swimming distance and velocity) were not affected by KYNA in this study. Overall, our results show KYNA has an anxiolytic-like pharmacological effect in zebrafish, and therefore strongly support the utility of zebrafish models in neurotropic drug screening, including drugs acting at central glutamatergic system. Robust phenotypic differences evoked by KYNA, revealed here using three-dimensional (3D) reconstructions of zebrafish locomotion in X, Y and time (Z) coordinates, confirm this notion, also demonstrating the value of 3D-based phenotyping approaches for high-throughput drug screening using zebrafish models.

Spatial distribution of illicit drugs in surface waters of the natural park of Pego-Oliva Marsh (Valencia, Spain)

BACKGROUND, AIM AND SCOPE

The Pego-Oliva Marsh is the second most important wetland in the Valencian Community (Spain). It is included in the RAMSAR agreement and represents one key point for migratory birds. Emerging contaminants from the human pressure, such as pharmaceuticals, illicit drugs and personal care product, are not included in the list of priority contaminants of the Water Framework Directive yet, and are neither monitored nor controlled. However, pollution of emerging contaminants can threaten the environment and even human health. In order to understand the status of the emerging contamination and recommend future rationalization of countermeasures, the occurrence of illicit drugs was investigated.

MATERIAL AND METHODS

Samples were collected at 23 sites from the main irrigation channels and the marsh. Illicit drugs were extracted using solid phase extraction and determined by liquid chromatography tandem mass spectrometry. The method detection limits ranged from 0.01 to 1.54 ng l(-1) and the recoveries from 57% to 120%.

RESULTS AND DISCUSSION

3,4-Methylenedioxymethamphetamine, ketamine, morphine, benzoylecgonine, cocaine, methadone, 6-acetylmorphine and nor-9-carboxy-tetrahydrocannabinol were detected. The mean concentrations were 0.62, 21.33, 1.30, 1.92, 2.25, 0.32, 0.04 and 0.07 ng l(-1), respectively. The highest concentrations were in the north of Pego-Oliva Marsh.

CONCLUSIONS

The pollution status by illicit drugs of the Pego-Oliva Marsh has been established. However, contamination levels in all the area of the natural park were low compared with those reported in other superficial waters.