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

Sex, drugs, and zebrafish: Acute exposure to anxiety-modulating compounds in a modified novel tank dive test

This study investigated the effects of anxiogenic and anxiolytic drugs on zebrafish (Danio rerio) behaviour using a modified novel tank dive test with higher walls and a narrower depth. Zebrafish were administered chondroitin sulfate, beta-carboline, delta-9-tetrahydrocannabinol (THC), ethanol, and beta-caryophyllene, and their behaviours were evaluated for geotaxis, swimming velocity, and immobility. Both anxiogenic and anxiolytic compounds generally increased bottom-dwelling behaviour, suggesting that the tank's modified dimensions significantly influence zebrafish responses. EC50 values for ethanol showed a lower threshold for velocity reduction compared to zone preference. Chondroitin sulfate uniquely caused a sex-specific increase in male swimming velocity, whereas no other sex-differences were observed with any compound. Interestingly, the presence of drug-treated fish did not alter the behaviour of observer fish, suggesting limited social buffering effects. The findings underscore the complexity of zebrafish behavioural phenotypes and highlight the need for considering tank dimensions and multiple behavioural parameters to accurately assess the effects of anxiety-modulating drugs. This study demonstrates the utility of the modified novel tank dive test in providing nuanced insights into the behavioural effects of different pharmacological agents in zebrafish.

Chronic Behavioral and Neurochemical Effects of Four Novel N-Benzyl-2-phenylethylamine Derivatives Recently Identified as "Psychoactive" in Adult Zebrafish Screens

Potently affecting human and animal brain and behavior, hallucinogenic drugs have recently emerged as potentially promising agents in psychopharmacotherapy. Complementing laboratory rodents, the zebrafish (Danio rerio) is a powerful model organism for screening neuroactive drugs, including hallucinogens. Here, we tested four novel N-benzyl-2-phenylethylamine (NBPEA) derivatives with 2,4- and 3,4-dimethoxy substitutions in the phenethylamine moiety and the -F, -Cl, and -OCF3 substitutions in the ortho position of the phenyl ring of the N-benzyl moiety (34H-NBF, 34H-NBCl, 24H-NBOMe(F), and 34H-NBOMe(F)), assessing their behavioral and neurochemical effects following chronic 14 day treatment in adult zebrafish. While the novel tank test behavioral data indicate anxiolytic-like effects of 24H-NBOMe(F) and 34H-NBOMe(F), neurochemical analyses reveal reduced brain norepinephrine by all four drugs, and (except 34H-NBCl) - reduced dopamine and serotonin levels. We also found reduced turnover rates for all three brain monoamines but unaltered levels of their respective metabolites. Collectively, these findings further our understanding of complex central behavioral and neurochemical effects of chronically administered novel NBPEAs and highlight the potential of zebrafish as a model for preclinical screening of small psychoactive molecules.

Cannabinoid type-2 receptors modulate terpene induced anxiety-reduction in zebrafish

Terpenes are the most extensive and varied group of naturally occurring compounds mostly found in plants, including cannabis, and have an array of potential therapeutic benefits for pathological conditions. The endocannabinoid system can potently modulate anxiety in humans, rodents, and zebrafish. The 'entourage effect' suggests terpenes may target cannabinoid CB1 and CB2 receptors, among others, but this requires further investigation. In this study we first tested for anxiety-altering effects of the predominant 'Super-Class' terpenes, bisabolol (0.001%, 0.0015%, and 0.002%) and terpinolene (TPL; 0.01%, 0.05%, and 0.1%), in zebrafish with the open field test. Bisabolol did not have an effect on zebrafish behaviour or locomotion. However, TPL caused a significant increase in time spent in the inner zone and decrease in time spent in the outer zone of the arena indicating an anxiolytic (anxiety decreasing) effect. Next, we assessed whether CB1 and CB2 receptor antagonists, rimonabant and AM630 (6-Iodopravadoline) respectively, could eliminate or reduce the anxiolytic effects of TPL (0.1%) and β-caryophyllene (BCP; 4%), another super-class terpene previously shown to be anxiolytic in zebrafish. Rimonabant and AM630 were administered prior to terpene exposure and compared to controls and fish exposed to only the terpenes. AM630, but not rimonabant, eliminated the anxiolytic effects of both BCP and TPL. AM630 modulated locomotion on its own, which was potentiated by terpenes. These findings suggest the behavioural effects of TPL and BCP on zebrafish anxiety-like behaviour are mediated by a selective preference for CB2 receptor sites. Furthermore, the CB2 pathways mediating the anxiolytic response are likely different from those altering locomotion.

Transcriptional Alterations Induced by Delta-9 Tetrahydrocannabinol in the Brain and Gonads of Adult Medaka

With the legalization of marijuana smoking in several states of the United States and many other countries for medicinal and recreational use, the possibility of its release into the environment cannot be overruled. Currently, the environmental levels of marijuana metabolites are not monitored on a regular basis, and their stability in the environment is not well understood. Laboratory studies have linked delta 9-tetrahydrocannabinol (Δ⁹-THC) exposure with behavioral abnormalities in some fish species; however, their effects on endocrine organs are less understood. To understand the effects of THC on the brain and gonads, we exposed adult medaka (Oryzias latipes, Hd-rR strain, both male and female) to 50 ug/L THC for 21 days spanning their complete spermatogenic and oogenic cycles. We examined transcriptional responses of the brain and gonads (testis and ovary) to Δ⁹-THC, particularly molecular pathways associated with behavioral and reproductive functions. The Δ⁹-THC effects were more profound in males than females. The Δ⁹-THC-induced differential expression pattern of genes in the brain of the male fish suggested pathways to neurodegenerative diseases and pathways to reproductive impairment in the testis. The present results provide insights into endocrine disruption in aquatic organisms due to environmental cannabinoid compounds.

Cannabidiol improves haloperidol-induced motor dysfunction in zebrafish: a comparative study with a dopamine activating drug

BACKGROUND

Cannabidiol (CBD) extracted from the cannabis plant is believed to have a medicinal value due to its neuroprotective effect via anti-inflammatory and antioxidant action. Recent behavioral studies in rats have reported that CBD mediates serotonin (5-HT1A) receptor action to improve motor dysfunction induced by dopamine (D2) receptor blockade. In particular, its effect on D2 receptor blockade in the striatum is an important function associated with neurological disorders resulting from various extrapyramidal motor dysfunctions. Dopaminergic neurodegeneration associated with this site is known for inducing Parkinson's disease (PD), which often affects the elderly. It is also known to cause drug-induced Parkinsonism. This study examines the ameliorating effect of CBD, which does not act directly on D2 receptors, against drug-induced motor dysfunction induced by the antipsychotic drug (haloperidol).

METHODS

We created a drug-induced Parkinsonism model in zebrafish larvae using an antipsychotic drug (haloperidol). We evaluated the distance traveled and repetitive light-stimulation response. Furthermore, we examined whether administration of several concentrations of CBD ameliorates symptoms of the Parkinsonism model and compared its effects with those of antiparkinsonian drug ropinirole.

RESULTS

CBD concentrations equal to half of haloperidol's resulted in an almost complete reversal of haloperidol-induced motor dysfunction, as measured by the distance traveled by the zebrafish and their response to light-stimulus. While ropinirole also significantly reversed haloperidol's effects at the same concentration as CBD, CBD was more effective than ropinirole.

CONCLUSIONS

CBD-induced motor dysfunction improvement via D2 receptor blockade is a potential novel mechanism for the treatment of haloperidol-induced motor dysfunction.

A Review on the Bioactivity of Cannabinoids on Zebrafish Models: Emphasis on Neurodevelopment

For centuries, the cannabis plant has been used as a source of food, fiber, and medicine. Recently, scientific interest in cannabis has increased considerably, as its bioactive compounds have shown promising potential in the treatment of numerous musculoskeletal and neurological diseases in humans. However, the mechanisms that underlie its possible effects on neurodevelopment and nervous-system functioning remain poorly understood and need to be further investigated. Although the bulk of research on cannabis and cannabinoids is based on in vitro or rodent models, the zebrafish has now emerged as a powerful in vivo model for drug-screening studies and translational research. We here review the available literature on the use of cannabis/cannabinoids in zebrafish, and particularly in zebrafish models of neurological disorders. A critical analysis suggests that zebrafish could serve as an experimental tool for testing the bioactivity of cannabinoids, and they could thus provide important insights into the safety and efficacy of different cannabis-extract-based products. The review showed that zebrafish exhibit similar behaviors to rodents following cannabinoid exposure. The authors stress the importance of analyzing the full spectrum of naturally occurring cannabinoids, rather than just the main ones, THC and CBD, and they offer some pointers on performing behavioral analysis in zebrafish.

Zebrafish larvae: A new model to study behavioural effects and metabolism of fentanyl, in comparison to a traditional mice model

In an effort to find alternatives to study in vivo the so-called New Psychoactive Substances (NPS), the present work was undertaken to investigate the use of zebrafish larvae as animal model in pharmaco-toxicology, providing behavioural and metabolism information. For this purpose, fentanyl, the progenitor of an extremely dangerous group of NPS, was administered at different doses to zebrafish larvae (1, 10, 50, 100 µM) in comparison to mice (0.1, 1, 6, 15 mg/kg), as a well-established animal model. A behavioural assay was performed at the time of the peak effect of fentanyl, showing that the results in larvae are consistent with those observed in mice. On the other hand, several morphological abnormalities (namely yolk sac edema, abnormal pericardial edema, jaw defect and spinal curvature) were found in larvae mostly at high fentanyl doses (50, 100 µM). Larva extract and mice urine were analyzed by using liquid chromatography coupled to high resolution mass spectrometry to identify the metabolic pathways of fentanyl. The main metabolites detected were norfentanyl and hydroxyfentanyl in both the tested models. In conclusion, the present study provides evidence that fentanyl effects on zebrafish larvae and metabolism are similar to rodents and consequently support the hypothesis of using zebrafish larvae as a suitable rapid screening tool to investigate new drugs, and particularly NPS.

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.

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.

Behavioral Effects of Developmental Exposure to JWH-018 in Wild-Type and Disrupted in Schizophrenia 1 (disc1) Mutant Zebrafish

Synthetic cannabinoids can cause acute adverse psychological effects, but the potential impact when exposure happens before birth is unknown. Use of synthetic cannabinoids during pregnancy may affect fetal brain development, and such effects could be moderated by the genetic makeup of an individual. Disrupted in schizophrenia 1 (DISC1) is a gene with important roles in neurodevelopment that has been associated with psychiatric disorders in pedigree analyses. Using zebrafish as a model, we investigated (1) the behavioral impact of developmental exposure to 3 μM 1-pentyl-3-(1-naphthoyl)-indole (JWH-018; a common psychoactive synthetic cannabinoid) and (2) whether disc1 moderates the effects of JWH-018. As altered anxiety responses are seen in several psychiatric disorders, we focused on zebrafish anxiety-like behavior. Zebrafish embryos were exposed to JWH-018 from one to six days post-fertilization. Anxiety-like behavior was assessed using forced light/dark and acoustic startle assays in larvae and novel tank diving in adults. Compared to controls, both acutely and developmentally exposed zebrafish larvae had impaired locomotion during the forced light/dark test, but anxiety levels and response to startle stimuli were unaltered. Adult zebrafish developmentally exposed to JWH-018 spent less time on the bottom of the tank, suggesting decreased anxiety. Loss-of-function in disc1 increased anxiety-like behavior in the tank diving assay but did not alter sensitivity to JWH-018. Results suggest developmental exposure to JWH-018 has a long-term behavioral impact in zebrafish, which is not moderated by disc1.

Putative Activation of the CB1 Cannabinoid Receptors Prevents Anxiety-Like Behavior, Oxidative Stress, and GABA Decrease in the Brain of Zebrafish Submitted to Acute Restraint Stress

Anxiety disorder is a well-recognized condition observed in subjects submitted to acute stress. Although the brain mechanisms underlying this disorder remain unclear, the available evidence indicates that oxidative stress and GABAergic dysfunction mediate the generation of stress-induced anxiety. Cannabinoids are known to be efficient modulators of behavior, given that the activation of the cannabinoid receptors type-1 (CB1 receptors) induces anxiolytic-like effects in animal models. In the present study, we aimed to describe the effects of the stimulation of the CB1 receptors on anxiety-like behavior, oxidative stress, and the GABA content of the brains of zebrafish submitted to acute restraint stress (ARS). The animals submitted to the ARS protocol presented evident anxiety-like behavior with increased lipid peroxidation in the brain tissue. The evaluation of the levels of GABA in the zebrafish telencephalon presented decreased levels of GABA in the ARS group in comparison with the control. Treatment with ACEA, a specific CB1 receptor agonist, prevented ARS-induced anxiety-like behavior and oxidative stress in the zebrafish brain. ACEA treatment also prevented a decrease in GABA in the telencephalon of the animals submitted to the ARS protocol. Overall, these preclinical data strongly suggest that the CB1 receptors represent a potential target for the development of the treatment of anxiety disorders elicited by acute stress.

A critical review on the detection, occurrence, fate, toxicity, and removal of cannabinoids in the water system and the environment

Cannabinoids are a group of organic compounds found in cannabis. Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), the two major constituents of cannabinoids, and their metabolites are contaminants of emerging concern due to the limited information on their environmental impacts. As well, their releases to the water systems and environment are expected to increase due to recent legalization. Solid-phase extraction is the most common technique for the extraction and pre-concentration of cannabinoids in water samples as well as a clean-up step after the extraction of cannabinoids from solid samples. Liquid chromatography coupled with mass spectrometry is the most common technique used for the analysis of cannabinoids. THC and its metabolites have been detected in wastewater, surface water, and drinking water. In particular, 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (THC-COOH) has been detected at concentrations up to 2590 and 169 ng L^-1 in untreated and treated wastewater, respectively, 79.9 ng L^-1 in surface water, and 1 ng L^-1 in drinking water. High removal of cannabinoids has been observed in wastewater treatment plants; this is likely a result of adsorption due to the low aqueous solubility of cannabinoids. Based on the estrogenicity and cytotoxicity studies and modelling, it has been predicted that THC and THC-COOH pose moderate risk for adverse impact on the environment. While chlorination and photo-oxidation have been shown to be effective in the removal of THC-COOH, they also produce by-products that are potentially more toxic than regulated disinfection by-products. The potential of indirect exposure to cannabinoids and their metabolites through recreational water is of great interest. As cannabinoids and especially their by-products may have adverse impacts on the environment and public health, more studies on their occurrence in various types of water and environmental systems, as well as on their environmental toxicity, would be required to accurately assess their impact on the environment and public health.

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.

Analyzing cannabinoid-induced abnormal behavior in a zebrafish model

In this study, we investigated locomotor activity and responses to repeated light and dark stimuli to assess cannabinoid-induced abnormal behavior in zebrafish larvae (Danio rerio), as an alternative to standard rodent models. To induce the desired responses, we used cannabidiol and WIN55,212-2, two major cannabinoid components. A repeated light and dark test was used to assess how drug exposure influences locomotory responses. Larvae were examined after moderate cannabidiol and WIN55,212-2 exposure and at 24 h after transfer to untreated water. We found that cannabidiol did not produce a dose-dependent inhibitory effect on locomotor activity, with both 0.5 and 10 μg/mL concentrations reducing movement velocity and the total distance moved. However, 10 μg/mL cannabidiol was observed to attenuate the responses of larvae exposed to darkness. No differences were detected between the control and cannabidiol-treated groups after 24 h in fresh water. Fish treated with WIN55,212-2 at 0.5 and 1 μg/mL showed virtually no activity, even in darkness, whereas a concentration of 10 μg/mL induced mortality. A 24-h period in fresh water had the effect of reversing most of the drug-induced immobilization, even in the WIN55,212-2-treated groups. Larvae were also evaluated for their responses to cannabidiol subsequent to an initial exposure to WIN55,212-2, and it was accordingly found that treatment with cannabidiol could attenuate WIN55,212-2-induced abnormal immobilization, whereas equivalent doses of cannabidiol and WIN55,212-2 produced a mixed response. In conclusion, the behavioral effects of the two cannabinoids cannabidiol and WIN55,212-2 appear to be ratio dependent. Furthermore, the repeated light and dark test could serve as a suitable method for assaying drug-induced behavior.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

Transformation potential of cannabinoids during their passage through engineered water treatment systems: A perspective

Cannabinoids are incipient contaminants with limited literature in the context of water treatment. With increasing positive public opinion toward legalization and their increasing use as a pharmaceutical, cannabinoids are expected to become a critical class of pollutant that requires attention in the water treatment industry. The destructive removal of cannabinoids via chlorination and other oxidation processes used in drinking water and wastewater treatment requires careful investigation, because the oxidation and disinfection byproducts (DBPs) may pose significant risks for public health and the environment. Understanding transformation of cannabinoids is the first step toward the development of management strategies for this emerging class of contaminant in natural and engineered aquatic systems. This perspective reviews the current understanding of cannabinoid occurrence in water and its potential transformation pathways during the passage through drinking water and wastewater treatment systems with chlorination process. The article also aims to identify research gaps on this topic, which demand attention from the environmental science and engineering community.

Potential of the zebrafish model for the forensic toxicology screening of NPS: A comparative study of the effects of APINAC and methiopropamine on the behavior of zebrafish larvae and mice

The increased diffusion of the so-called novel psychoactive substances (NPS) and their continuous change in structure andconceivably activity has led to the need of a rapid screening method to detect their biological effects as early as possible after their appearance in the market. This problem is very felt in forensic pathology and toxicology, so the preclinical study is fundamental in the approach to clinical and autopsy cases of difficult interpretation intoxication. Zebrafish is a high-throughput suitable model to rapidly hypothesize potential aversive or beneficial effects of novel molecules. In the present study, we measured and compared the behavioral responses to two novel neuroactive drugs, namely APINAC, a new cannabimimetic drug, and methiopropamine (MPA), a methamphetamine-like compound, on zebrafish larvae (ZL) and adult mice. By using an innovative statistical approach (general additive models), it was found that the spontaneous locomotor activity was impaired by the two drugs in both species: the disruption extent varied in a dose-dependent and time-dependent manner. Sensorimotor function was also altered: i) the visual object response was reduced in mice treated with APINAC, whereas it was not after exposure to MPA; ii) the visual placing responses were reduced after treatment with both NPS in mice. Furthermore, the visual motor response detected in ZL showed a reduction after treatment with APINAC during light-dark and dark-light transition. The same pattern was found in the MPA exposed groups only at the dark-light transition, while at the transition from light to dark, the individuals showed an increased response. In conclusion, the present study highlighted the impairment of spontaneous motor and sensorimotor behavior induced by MPA and APINAC administration in both species, thus confirming the usefulness of ZL as a model for a rapid behavioural-based drug screening.

The psychoactive cathinone derivative pyrovalerone alters locomotor activity and decreases dopamine receptor expression in zebrafish (Danio rerio)

INTRODUCTION

Pyrovalerone (4-methyl-β-keto-prolintane) is a synthetic cathinone (beta-keto-amphetamine) derivative. Cathinones are a concern as drugs of abuse, as related street drugs such as methylenedioxypyrovalerone have garnered significant attention. The primary mechanism of action of cathinones is to inhibit reuptake transporters (dopamine and norepinephrine) in reward centers of the central nervous system.

METHODS

We measured bioenergetic, behavioral, and molecular responses to pyrovalerone (nM-µM) in zebrafish to evaluate its potential for neurotoxicity and neurological impairment.

RESULTS

Pyrovalerone did not induce any mortality in zebrafish larvae over a 3- and 24-hr period; however, seizures were prevalent at the highest dose tested (100 µM). Oxidative phosphorylation was not affected in the embryos, and there was no change in superoxide dismutase 1 expression. Following a 3-hr treatment to pyrovalerone (1-100 µM), larval zebrafish (6d) showed a dose-dependent decrease (70%-90%) in total distance moved in a visual motor response (VMR) test. We interrogated potential mechanisms related to the hypoactivity, focusing on the expression of dopamine-related transcripts as cathinones can modulate the dopamine system. Pyrovalerone decreased the expression levels of dopamine receptor D1 (~60%) in larval zebrafish but did not affect the expression of tyrosine hydroxylase, dopamine active transporter, or any other dopamine receptor subunit examined, suggesting that pyrovalerone may regulate the expression of dopamine receptors in a specific manner.

DISCUSSION

Further studies using zebrafish are expected to reveal new insight into molecular mechanisms and behavioral responses to cathinone derivates, and zebrafish may be a useful model for understanding the relationship between the dopamine system and bath salts.

Developmental Effects of Cannabidiol and Δ9-Tetrahydrocannabinol in Zebrafish

Cannabidiol (CBD) has gained much attention in the past several years for its therapeutic potential in the treatment of drug-resistant epilepsy, such as Dravet syndrome. Although CBD has shown anecdotal efficacy in reducing seizure frequency, little is known regarding the potential adverse side effects of CBD on physiology, development, organogenesis, or behavior. The goal of this project was to compare the relative morphological, behavioral, and gene expression phenotypes resulting after a developmental exposure to Δ9-tetrahydrocannabinol (THC) or CBD. Zebrafish were exposed from blastula through larval stage (96 h postfertilization [hpf]) to 0.3, 0.6, 1.25, 2.5, 5 mg/l (1, 2, 4, 8, 16 µM) THC or 0.07, 0.1, 0.3, 0.6, 1.25 mg/l CBD (0.25, 0.5, 1, 2, 4 µM). Despite the similarity in THC and CBD dysmorphologies, ie, edemas, curved axis, eye/snout/jaw/trunk/fin deformities, swim bladder distention, and behavioral abnormalities, the LC50 for CBD (0.53 mg/l) was nearly 7 times lower than THC (3.65 mg/l). At 96 hpf, c-fos, dazl, and vasa were differentially expressed following THC exposure, but only c-fos expression was significantly increased by CBD. Cannabidiol was more bioconcentrated compared with THC despite higher THC water concentrations. This work supports the potential for persistent developmental impacts of cannabinoid exposure, but more studies are needed to assess latent effects and their molecular mechanisms of toxicity.

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.

Ethanol and cannabinoids interact to alter behavior in a zebrafish fetal alcohol spectrum disorder model

BACKGROUND

Recent work suggests that endocannabinoids (eCBs) may signal through the sonic hedgehog signaling pathway. We therefore hypothesized that combined ethanol and eCB exposure during defined stages of zebrafish embryogenesis will produce deficits comparable to human fetal alcohol spectrum disorder (FASD).

METHODS

Zebrafish embryos were exposed to ethanol or cannabinoid agonists alone or in combination at defined developmental stages and assessed for changes in brain morphology or expression of marker genes such as pax6a. Juvenile fish were then assessed for risk-taking/anxiety-like behavior using the novel tank dive test.

RESULTS

Either chronic or acute exposure to high doses of the CB1R agonist ACEA resulted in FASD phenotypes. However, acute subthreshold doses of CB1R agonist alone, or combined with 0.5% ethanol, did not induce morphological phenotypes, but did induce dysmorphogenesis when combined with acute 1% ethanol. Phenotypes were rescued using the CB1R antagonist SR141716A. In addition, JZL195, a dual inhibitor of FAAH and MAGL, two degradative enzymes for eCBs, induced FASD phenotypes in the presence of subthreshold ethanol, confirming the activation of common signaling pathways by ethanol and eCBs. We next analyzed the effects of ethanol and CB1R agonist on juvenile zebrafish behavior and show that ACEA or ethanol alone did not alter behavior, but combined ACEA and ethanol increased risk-taking behavior.

CONCLUSIONS

These studies demonstrate that pathological and behavioral phenotypes associated with FASD are induced by exposure to CB1R agonists and suggest that combined exposure to lower levels of alcohol and marijuana may be capable of inducing FASD-like morphological and behavioral impairments.

Multigenerational consequences of early-life cannabinoid exposure in zebrafish

While Δ⁹-tetrahydrocannabinol (THC) has been widely studied in the realm of developmental and reproductive toxicology, few studies have investigated potential toxicities from a second widely used cannabis constituent, cannabidiol (CBD). CBD is popularized for its therapeutic potential for reducing seizure frequencies in epilepsy. This study investigated developmental origins of health and disease (DOHaD) via multigenerational gene expression patterns, behavior phenotypes, and reproductive fitness of a subsequent F1 following an F0 developmental exposure of zebrafish (Danio rerio) to THC (0.024, 0.12, 0.6 mg/L; 0.08, 0.4, 2 μM) or CBD (0.006, 0.03, 0.15 mg/L; 0.02, 0.1, 0.5 μM). Embryonic exposure at these concentrations did not cause notable morphological abnormalities in either F0 or F1 generations. However, during key developmental stages (14, 24, 48, 72, and 96 h post fertilization) THC and CBD caused differential expression of c-fos, brain-derived neurotrophic factor (bdnf), and deleted-in-azoospermia like (dazl), while in F1 larvae only CBD differentially expressed dazl. Larval photomotor behavior was reduced (F0) or increased (F1) by THC exposure, while CBD had no effect on F0 larvae, but decreased activity in the unexposed F1 larvae. These results support our hypothesis of cannabinoid-related developmental neurotoxicity. As adults, F0 fecundity was reduced, but it was not in F1 adults. Conversely, in the adult open field test there were no significant effects in F0 fish, but a significant reduction in the time in periphery was seen in F1 fish from the highest THC exposure group. The results highlight the need to consider long-term ramifications of early-life exposure to cannabinoids.

Zebrafish models relevant to studying central opioid and endocannabinoid systems

The endocannabinoid and opioid systems are two interplaying neurotransmitter systems that modulate drug abuse, anxiety, pain, cognition, neurogenesis and immune activity. Although they are involved in such critical functions, our understanding of endocannabinoid and opioid physiology remains limited, necessitating further studies, novel models and new model organisms in this field. Zebrafish (Danio rerio) is rapidly emerging as one of the most effective translational models in neuroscience and biological psychiatry. Due to their high physiological and genetic homology to humans, zebrafish may be effectively used to study the endocannabinoid and opioid systems. Here, we discuss current models used to target the endocannabinoid and opioid systems in zebrafish, and their potential use in future translational research and high-throughput drug screening. Emphasizing the high degree of conservation of the endocannabinoid and opioid systems in zebrafish and mammals, we suggest zebrafish as an excellent model organism to study these systems and to search for the new drugs and therapies targeting their evolutionarily conserved mechanisms.

Selective and Context-Dependent Social and Behavioral Effects of Δ9-Tetrahydrocannabinol in Weakly Electric Fish

Cannabinoid (CB) receptors are widespread in the nervous system and influence a variety of behaviors. Weakly electric fish have been a useful model system in the study of the neural basis of behavior, but we know nothing of the role played by the CB system. Here, we determine the overall behavioral effect of a nonselective CB receptor agonist, namely Δ9-tetrahydrocannabinol (THC), in the weakly electric fish Apte-ronotus leptorhynchus. Using various behavioral paradigms involving social stimuli, we show that THC decreases locomotor behavior, as in many species, and influences communication and social behavior. Across the different experiments, we found that the propensity to emit communication signals (chirps) and seek social interactions was affected in a context-dependent manner. We explicitly tested this hypothesis by comparing the behavioral effects of THC injection in fish placed in a novel versus a familiar social and physical environment. THC-injected fish were less likely to chirp than control fish in familiar situations but not in novel ones. The tendency to be in close proximity to other fish was affected only in novel environments, with control fish clustering more than THC-injected ones. By identifying behaviors affected by CB agonists, our study can guide further comparative and neurophysiological studies of the role of the CB system using a weakly electric fish as a model.

Analysis of the Uptake, Metabolism, and Behavioral Effects of Cannabinoids on Zebrafish Larvae

The Cannabis sativa plant contains numerous phytocannabinoids and terpenes with known or potential biological activity. For decades, plant breeders have been breeding the Cannabis plant to control for a desired ratio of the major cannabinoids. A high-throughput in vivo model to understand the relationship between the chemical composition of different strains and their therapeutic potential then becomes of value. Measuring changes in the behavioral patterns of zebrafish larvae is an established model with which to test the biological activity of neuroactive compounds. However, there is currently little information regarding the uptake kinetics and metabolism of compounds by larvae. In this study, we chose to compare the uptake kinetics and metabolism of Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) alone or in combination with their effects on larval behavior. We have shown that both compounds have distinct behavioral patterns and concentration response profiles. Additionally, the uptake kinetics observed for each compound appears to correlate with the change in behavior observed in the behavioral assays. When combinations of THC and CBD were tested there were shifts in both the behavioral activity and the uptake kinetics of each compound compared with when they were tested alone. Finally, the THC/CBD-derived metabolites detected in the larvae are similar to those found in mammalian systems. This study thus provides a model for further testing of additional cannabinoids and potentially plant extracts.

The endocannabinoid gene faah2a modulates stress-associated behavior in zebrafish

The ability to orchestrate appropriate physiological and behavioral responses to stress is important for survival, and is often dysfunctional in neuropsychiatric disorders that account for leading causes of global disability burden. Numerous studies have shown that the endocannabinoid neurotransmitter system is able to regulate stress responses and could serve as a therapeutic target for the management of these disorders. We used quantitative reverse transcriptase-polymerase chain reactions to show that genes encoding enzymes that synthesize (abhd4, gde1, napepld), enzymes that degrade (faah, faah2a, faah2b), and receptors that bind (cnr1, cnr2, gpr55-like) endocannabinoids are expressed in zebrafish (Danio rerio). These genes are conserved in many other vertebrates, including humans, but fatty acid amide hydrolase 2 has been lost in mice and rats. We engineered transcription activator-like effector nucleases to create zebrafish with mutations in cnr1 and faah2a to test the role of these genes in modulating stress-associated behavior. We showed that disruption of cnr1 potentiated locomotor responses to hyperosmotic stress. The increased response to stress was consistent with rodent literature and served to validate the use of zebrafish in this field. Moreover, we showed for the first time that disruption of faah2a attenuated the locomotor responses to hyperosmotic stress. This later finding suggests that FAAH2 may be an important mediator of stress responses in non-rodent vertebrates. Accordingly, FAAH and FAAH2 modulators could provide distinct therapeutic options for stress-aggravated disorders.

ABIN-1 Negatively Regulates μ-Opioid Receptor Function

The μ-opioid receptor (MOR) is a G_i/o protein-coupled receptor that mediates analgesic, euphoric, and reward effects. Using a bacterial two-hybrid screen, we reported that the carboxyl tail of the rat MOR associates with A20-binding inhibitor of nuclear factor κB (ABIN-1). This interaction was confirmed by direct protein-protein binding and coimmunoprecipitation of MOR and ABIN-1 proteins in cell lysates. Saturation binding studies showed that ABIN-1 had no effect on MOR binding. However, the interaction of ABIN-1 and MOR inhibited the activation of G proteins induced by DAMGO ([d-Ala2,N-Me-Phe4,Gly5-ol]-Enkephalin). MOR phosphorylation, ubiquitination, and internalization induced by DAMGO were decreased in Chinese hamster ovary cells that coexpressed MOR and ABIN-1. The suppression of forskolin-stimulated adenylyl cyclase by DAMGO was also inhibited by the interaction of ABIN-1 with MOR. In addition, extracellular signal-regulated kinase activation was also negatively regulated by overexpression of ABIN-1. These data suggest that ABIN-1 is a negative coregulator of MOR activation, phosphorylation, and internalization in vitro. ABIN-1 also inhibited morphine-induced hyperlocomotion in zebrafish larvae (AB strain). By utilization of an antisense morpholino oligonucleotide (MO) gene knockdown technology, the ABIN-1 MO-injected zebrafish larvae showed a significant increase (approximately 60%) in distance moved compared with control MO-injected larvae after acute morphine treatment (P < 0.01). Taken together, ABIN-1 negatively regulates MOR function in vitro and in vivo.

Role of the endocannabinoid system in vertebrates: Emphasis on the zebrafish model

The endocannabinoid system (eCBs), named after the plant Cannabis sativa, comprises cannabinoid receptors, endogenous ligands known as "endocannabinoids", and enzymes involved in the biosynthesis and degradation of these ligands, as well as putative transporters for these ligands. ECBs proteins and small molecules have been detected in early embryonic stages of many vertebrate models. As a result, cannabinoid receptors and endogenous as well as exogenous cannabinoids influence development and behavior in many vertebrate species. Understanding the precise mechanisms of action for the eCBs will provide an invaluable guide towards elucidation of vertebrate development and will also help delineate how developmental exposure to marijuana might impact health and cognitive/executive functioning in adulthood. Here we review the developmental roles of the eCBs in vertebrates, focusing our attention on the zebrafish model. Since little is known regarding the eCBs in zebrafish, we provide new data on the expression profiles of eCBs genes during development and in adult tissue types of this model organism. We also highlight exciting areas for future investigations, including the synaptic regulation of eCBs, its role in reward and addiction, and in nervous system development and plasticity.

Modafinil decreases anxiety-like behaviour in zebrafish

Modafinil (2-((diphenylmethyl)sulfinyl)acetamide), a selective dopamine and norepinephrine transporter inhibitor, is most commonly prescribed for narcolepsy but has gained recent interest for treating a variety of disorders. Zebrafish (Danio rerio) are becoming a model of choice for pharmacological and behavioural research. To investigate the behavioural effects of modafinil on anxiety, we administered doses of 0, 2, 20, and 200 mg/L for 30 minutes then tested zebrafish in the novel approach test. In this test, the fish was placed into a circular arena with a novel object in the center and motion-tracking software was used to quantify the time the fish spent in the outer area of the arena (thigmotaxis zone), middle third of the arena (transition zone) and center of the arena, as well as total distance traveled, immobility and meandering. Modafinil caused a decrease in time spent in the thigmotaxis zone and increased time spent in the transition zone across all doses. Modafinil did not significantly alter the time spent in the center zone (near the novel object), the distance moved, meandering, or the duration of time spent immobile. We also validated this test as a measure of anxiety with the administration of ethanol (1%) which decreased time spent in the thigmotaxis zone and increased time spent in the transition zone. These results suggest that modafinil decreases anxiety-like behaviour in zebrafish.

Up-regulation of immunomodulatory effects of mouse bone-marrow derived mesenchymal stem cells by tetrahydrocannabinol pre-treatment involving cannabinoid receptor CB2

Chronic pain is commonly and closely correlated with inflammation. Both cannabinoid signaling and mesenchymal stem cells (MSCs) have been demonstrated to reduce inflammatory pain. Although cannabinoid signaling is essential for mesenchymal stem cell survival and differentiation, little is known about its role in modulatory effect of MSCs on inflammation and pain sensitivity. Here we showed that mouse bone-marrow derived MSCs (BM-MSCs) expressed both cannabinoid receptor type 1 and 2 (CB1 and CB2). CB2 expression level in BM-MSCs increased with their maturation. In addition, we found that tetrahydrocannabinol (THC) activated CB2 receptor and ERK signaling, consequently enhancing the modulation of MSCs on inflammation-associated cytokine release from lipopolysaccharides-stimulated microglia. Consistent with in vitro data, THC pretreatment enhanced the immunomodulatory effects of BM-MSC on thermal hyperalgesia and mechanical allodynia in chronic constriction injury model, by decreasing the release of pro-inflammation cytokines. Our study revealed the crucial role of THC in promoting the immunomodulatory effects of MSCs and proposed a new strategy to alleviate pain based on stem cells therapy.

Cannabinoid modulation of zebrafish fear learning and its functional analysis investigated by c-Fos expression

It has been shown that zebrafish fear learning proceeds in the same way as reported for rodents. However, in zebrafish fear learning it is possible to substitute the use of electric shocks as unconditioned stimulus and utilize the inborn fear responses to the alarm substance Schreckstoff, instead. The skin extract Schreckstoff elicits typical fear reactions such as preferred bottom dwelling, swimming in a tighter shoal, erratic movements and freezing. This natural fear behavior can be transferred from Schreckstoff to any other sensory stimulus by associative conditioning (fear learning). We presented Schreckstoff simultaneously with a red light stimulus and tested the effectiveness of fear learning during memory retrieval. The two brain regions known to be relevant for learning in zebrafish are the medial and the lateral pallium of the dorsal telencephalon, both containing rich expressions of the endocannabinoid receptor CB1. To test the influence of the zebrafish endocannabinoid system on fear acquisition learning, an experimental group of ten fish was pretreated with the CB1 receptor agonist THC (Δ⁹-tetrahydrocannabinol; 100nM for 1h). We found that CB1 activation significantly inhibited acquisition of fear learning, possibly by impairing stimulus encoding processes in pallial areas. This was supported by analyzes of c-Fos expression in the brains of experimental animals. Schreckstoff exposure during fear acquisition learning and memory retrieval during red light presentation increased the number of labelled cells in pallial structures, but in no other brain region investigated (e.g. striatum, thalamus, and habenula). THC administration before fear conditioning significantly decreased c-Fos expression in these structures to a level similar to the control group without Schreckstoff experience, suggesting that Schreckstoff induced fear learning requires brain circuits restricted mainly to pallial regions of the dorsal telencephalon.

Concentration, population, and context-dependent effects of AM251 in zebrafish

RATIONALE

The function of the cannabinoid type 1 receptor (CB1-R) is poorly understood in zebrafish, and numerous inconsistent effects have been reported on it in the literature.

OBJECTIVE

The objective of the present study is to determine whether differences in the reported effects of CB1-R antagonism on anxiety-like behavioural responses, dopaminergic and serotonergic responses are due to concentration, context-dependent and/or population (genotype-related) effects.

METHOD

Two genetically distinct populations of zebrafish (AB and short fin (SF)) were treated with different concentrations of AM251 (0, 0.1, 1mg/L), and behavioural responses were quantified under two different contexts: one, following habituation and two, subsequently in a novel environment. The levels of dopamine, serotonin and their metabolites 3,4-dihydroxyindole acetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) were quantified from whole-brain tissue.

RESULTS

We demonstrate that a 60-min exposure to AM251 (0, 0.1, 1mg/L) does not alter behavioural performance following habituation in either populations. However, when subsequently transferred to a novel environment, zebrafish that were pre-treated with the highest dose of AM251 (1mg/L) exhibited increased anxiety-like behavioural responses including elevated absolute turn angle, freezing and bottom dwelling. We found that exposure to the highest dose of AM251 (1mg/L) for 60min increased serotonin in fish of both populations tested. In contrast, exposure to 0.1mg/L AM251 decreased, whereas to 1mg/L AM251 increased dopamine, DOPAC and 5-HIAA in fish of both populations.

CONCLUSION

Our results demonstrate a genotype-independent effect of AM251 but imply that the inconsistent findings obtained after pharmacological blockade of CB1-Rs in zebrafish may be due to a combination of concentration- and environmental context-dependent effects.

Effects of β-diketone antibiotic mixtures on behavior of zebrafish (Danio rerio)

To date, few data are available on neurotoxicity of β-diketone antibiotics (DKAs) from the perspective of animal behavior. Herein, the effects of long-term DKAs exposure on zebrafish (Danio rerio) behavior were assessed for locomotor activity, anxiety, social interaction and their related molecular mechanisms. DKAs exposure to zebrafish consisted of six DKA species, including ofloxacin, ciprofloxacin, enrofloxacin, doxycycline, chlortetracycline and oxytetracycline, with equal weight concentration and equal volume. DKAs at 6.25 mg/L significantly increased the time spent in the upper portion of the test tank (+40%) and the number of line crossings (±42%), indicating occurrence of anxiolytic behavior. For conditioned place preference test, long-term DKAs exposure at 6.25 mg/L increased the number of motionless positions in the non-preferred white side (+31%), number of transitions to the white side (+221%) and time spent in the white side (+35%) in relation to the control. DKAs at 6.25 mg/L significantly increased zebrafish shoaling behavior (+38%) resulting from an anxiety-like state, but 25 mg/L DKAs exposure decreased zebrafish social cohesion (-41%) possibly due to an autism-like state. With increasing DKAs-exposure concentration, the signal intensity of (1)O2 gradually decreased, leading to insufficient energy supply and movement functional disorders. Based on GO functional annotation and metabolic pathway analysis, 11 genes closely associated with locomotor behavior were identified. Using qRT-PCR, we confirmed that DKAs exposure led to changes in the transcriptional levels of 11 locomotor-related genes. These results suggest that behavior is a potential strategy for evaluating mechanisms underlying the neurochemical basis triggered by stress in zebrafish.

Using zebrafish in systems toxicology for developmental toxicity testing

With the high cost and the long-term assessment of developmental toxicity testing in mammals, the vertebrate zebrafish has become a useful alternative model organism for high-throughput developmental toxicity testing. Zebrafish is also very favorable for the 3R perspective in toxicology; however, the methodologies used by research groups vary greatly, posing considerable challenges to integrative analysis. In this review, we discuss zebrafish developmental toxicity testing, focusing on the methods of chemical exposure, the assessment of morphological abnormalities, housing conditions and their effects on the production of healthy embryos, and future directions. Zebrafish as a systems toxicology model has the potential to elucidate developmental toxicity pathways, and to provide a sound basis for human health risk assessments.

Elucidating cannabinoid biology in zebrafish (Danio rerio)

The number of annual cannabinoid users exceeds 100,000,000 globally and an estimated 9% of these individuals will suffer from dependency. Although exogenous cannabinoids, like those contained in marijuana, are known to exert their effects by disrupting the endocannabinoid system, a dearth of knowledge exists about the potential toxicological consequences on public health. Conversely, the endocannabinoid system represents a promising therapeutic target for a plethora of disorders because it functions to endogenously regulate a vast repertoire of physiological functions. Accordingly, the rapidly expanding field of cannabinoid biology has sought to leverage model organisms in order to provide both toxicological and therapeutic insights about altered endocannabinoid signaling. The primary goal of this manuscript is to review the existing field of cannabinoid research in the genetically tractable zebrafish model-focusing on the cannabinoid receptor genes, cnr1 and cnr2, and the genes that produce enzymes for synthesis and degradation of the cognate ligands anandamide and 2-arachidonylglycerol. Consideration is also given to research that has studied the effects of exposure to exogenous phytocannabinoids and synthetic cannabinoids that are known to interact with cannabinoid receptors. These results are considered in the context of either endocannabinoid gene expression or endocannabinoid gene function, and are integrated with findings from rodent studies. This provides the framework for a discussion of how zebrafish may be leveraged in the future to provide novel toxicological and therapeutic insights in the field of cannabinoid biology, which has become increasingly significant given recent trends in cannabis legislation.

Aquatic blues: modeling depression and antidepressant action in zebrafish

Depression is a serious psychiatric condition affecting millions of patients worldwide. Unipolar depression is characterized by low mood, anhedonia, social withdrawal and other severely debilitating psychiatric symptoms. Bipolar disorder manifests in alternating depressed mood and 'hyperactive' manic/hypomanic states. Animal experimental models are an invaluable tool for research into the pathogenesis of bipolar/unipolar depression, and for the development of potential treatments. Due to their high throughput value, genetic tractability, low cost and quick reproductive cycle, zebrafish (Danio rerio) have emerged as a promising new model species for studying brain disorders. Here, we discuss the developing utility of zebrafish for studying depression disorders, and outline future areas of research in this field. We argue that zebrafish represent a useful model organism for studying depression and its behavioral, genetic and physiological mechanisms, as well as for anti-depressant drug discovery.

Casting a wider fish net on animal models in neuropsychiatric research

Neuropsychiatric disorders, such as schizophrenia, are associated with abnormal brain development. In this review, we discuss how studying dimensional components of these disorders, or endophenotypes, in a wider range of animal models will deepen our understanding of how interactions between biological and environmental factors alter the trajectory of neurodevelopment leading to aberrant behavior. In particular, we discuss some of the advantages of incorporating studies of brain and behavior using a range of teleost fish species into current neuropsychiatric research. From the perspective of comparative neurobiology, teleosts share a fundamental pattern of neurodevelopment and functional brain organization with other vertebrates, including humans. These shared features provide a basis for experimentally probing the mechanisms of disease-associated brain abnormalities. Moreover, incorporating information about how behaviors have been shaped by evolution will allow us to better understand the relevance of behavioral variation to determine their physiological underpinnings. We believe that exploiting the conservation in brain development across vertebrate species, and the rich diversity of fish behavior in lab and natural populations will lead to significant new insights and a holistic understanding of the neurobiological systems implicated in neuropsychiatric disorders.

Fingerprinting of psychoactive drugs in zebrafish anxiety-like behaviors

A major hindrance for the development of psychiatric drugs is the prediction of how treatments can alter complex behaviors in assays which have good throughput and physiological complexity. Here we report the development of a medium-throughput screen for drugs which alter anxiety-like behavior in adult zebrafish. The observed phenotypes were clustered according to shared behavioral effects. This barcoding procedure revealed conserved functions of anxiolytic, anxiogenic and psychomotor stimulating drugs and predicted effects of poorly characterized compounds on anxiety. Moreover, anxiolytic drugs all decreased, while anxiogenic drugs increased, serotonin turnover. These results underscore the power of behavioral profiling in adult zebrafish as an approach which combines throughput and physiological complexity in the pharmacological dissection of complex behaviors.

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.