Strain dependent neurochemical changes induced by embryonic alcohol exposure in zebrafish

Multigenerational effects of alcohol: A behavioral study in three zebrafish populations

Fetal alcohol exposure can result in fetal alcohol spectrum disorder (FASD), which encompasses a range of cognitive and behavioral impairments. Although zebrafish have been used as a reliable model to study FASD, little is known about the ontogeny of this disorder and population differences in subsequent generations not directly exposed to alcohol. In this study, we evaluated the behavioral outcomes of zebrafish populations AB, Outbred (OB), and Tubingen (TU), offspring of parents exposed to alcohol during embryonic development. The offspring of adult fish with FASD (exposed to 1 % alcohol at the embryonic stage) was compared to the offspring of unexposed parental fish (0 % alcohol at the embryo phase). The behavioral profile of the offspring was assessed at 6 days post-fertilization (dpf) and 45 dpf. At 6dpf, the AB FASD offspring exhibited hyperactivity and increased time at the edge of the tank, while the TU and OB FASD offspring showed hypoactivity. At 45dpf, TU fish maintained the larval locomotor pattern, characterized by decreased average speed and total distance traveled and increased immobility. However, AB and OB fish did not show alterations in locomotor activity and anxiety-related responses at 45dpf. Our results demonstrate, for the first time, that FASD zebrafish offspring display behavioral differences, which were most evident during the early ontogenetic phase (6dpf) but may vary throughout animal ontogeny. TU fish exhibited the most consistent behavioral pattern across different developmental stages. These findings provide insights into the multigenerational and persistent behavioral consequences of embryonic alcohol exposure in zebrafish. Further research should focus on other features that can be inherited and the development of treatments for the offspring affected by it.

Utility of the Zebrafish Model for Studying Neuronal and Behavioral Disturbances Induced by Embryonic Exposure to Alcohol, Nicotine, and Cannabis

It is estimated that 5% of pregnant women consume drugs of abuse during pregnancy. Clinical research suggests that intake of drugs during pregnancy, such as alcohol, nicotine and cannabis, disturbs the development of neuronal systems in the offspring, in association with behavioral disturbances early in life and an increased risk of developing drug use disorders. After briefly summarizing evidence in rodents, this review focuses on the zebrafish model and its inherent advantages for studying the effects of embryonic exposure to drugs of abuse on behavioral and neuronal development, with an emphasis on neuropeptides known to promote drug-related behaviors. In addition to stimulating the expression and density of peptide neurons, as in rodents, zebrafish studies demonstrate that embryonic drug exposure has marked effects on the migration, morphology, projections, anatomical location, and peptide co-expression of these neurons. We also describe studies using advanced methodologies that can be applied in vivo in zebrafish: first, to demonstrate a causal relationship between the drug-induced neuronal and behavioral disturbances and second, to discover underlying molecular mechanisms that mediate these effects. The zebrafish model has great potential for providing important information regarding the development of novel and efficacious therapies for ameliorating the effects of early drug exposure.

Ethanol and caffeine age-dependently alter brain and retinal neurochemical levels without affecting morphology of juvenile and adult zebrafish (Danio rerio)

Adolescent alcohol exposure in humans is predictive of adult development of alcoholism. In rodents, caffeine pre-exposure enhances adult responsiveness to ethanol via a pathway targeted by both compounds. Embryonic exposure to either compound adversely affects development, and both compounds can alter zebrafish behaviors. Here, we evaluate whether co-exposure to caffeine and/or alcohol in adolescence exerts neurochemical changes in retina and brain. Zebrafish (Danio rerio) were given daily 20 min treatments to ethanol (1.5% v/v), caffeine (25-100 mg/L), or caffeine + ethanol for 1 week during mid-late adolescence (53-92 days post fertilization (dpf)) or early adulthood (93-142 dpf). Immediately after exposure, anatomical measurements were taken, including weight, heart rate, pigment density, length, girth, gill width, inner and outer eye distance. Brain and retinal tissue were subsequently collected either (1) immediately, (2) after a short interval (2-4d) following exposure, or (3) after a longer interval that included an acute 1.5% ethanol challenge. Chronic ethanol and/or caffeine exposure did not alter anatomical parameters. However, retinal and brain levels of tyrosine hydroxylase were elevated in fish sacrificed after the long interval following exposure. Protein levels of glutamic acid decarboxylase were also increased, with the highest levels observed in 70-79 dpf fish exposed to caffeine. The influence of ethanol and caffeine exposure on neurochemistry demonstrates specificity of their effects during postembryonic development. Using the zebrafish model to assess neurochemistry relevant to reward and anxiety may inform understanding of the mechanisms that reinforce co-addiction to alcohol and stimulants.

Long-term behavioral alterations following embryonic alcohol exposure in three zebrafish populations

Fetal alcohol exposure may lead to a condition known as fetal alcohol spectrum disorder (FASD), which comprises a set of consequences, including cognitive and behavioral impairments. Although zebrafish has been applied as a reliable model for studying FASD, there is no approach to the disorder's ontogeny and population differences. Here, we evaluated the behavioral outcomes of AB, Outbred (OB), and Tübingen (TU) zebrafish populations embryonically exposed to alcohol throughout the development to the adult stage. We exposed 24hpf eggs to 0%, 0.5%, or 1.0% alcohol for 2h. Fish were let grow and locomotor and anxiety-like behaviors were tested in a novel tank at larval - 6dpf, juvenile - 45dpf, and adult- 90dpf stages. At 6dpf, both AB and OB treated with 1.0% alcohol showed hyperactivity, while 0.5% and 1.0% TU fish exhibited hypolocomotion. At 45dpf, AB and TU fish maintained the larval pattern of locomotion. At the adult stage - 90dpf, both AB and TU populations showed increased locomotor activity and anxiogenic responses, while the OB population did not show altered behavior. Our results show for the first time that zebrafish populations exhibit behavioral differences in response to embryonic alcohol exposure and that it varies along animals' ontogeny. AB fish showed the most consistent behavioral pattern through developmental stages, TU fish showed behavioral changes only in adulthood, and OB population showed high interindividual variability. These data reinforce that different populations of zebrafish are better adapted to translational studies, offering reliable results in contrast to domesticated OB populations obtained from farms, which exhibit more variable genomes.

Acute Administration of Ethanol and of a D1-Receptor Antagonist Affects the Behavior and Neurochemistry of Adult Zebrafish

Alcohol abuse represents major societal problems, an unmet medical need resulting from our incomplete understanding of the mechanisms underlying alcohol’s actions in the brain. To uncover these mechanisms, animal models have been proposed. Here, we explore the effects of acute alcohol administration in zebrafish, a promising animal model in alcohol research. One mechanism via which alcohol may influence behavior is the dopaminergic neurotransmitter system. As a proof-of-concept analysis, we study how D1 dopamine-receptor antagonism may alter the effects of acute alcohol on the behavior of adult zebrafish and on whole brain levels of neurochemicals. We conduct these analyses using a quasi-inbred strain, AB, and a genetically heterogeneous population SFWT. Our results uncover significant alcohol x D1-R antagonist interaction and main effects of these factors in shoaling, but only additive effects of these factors in measures of exploratory behavior. We also find interacting and main effects of alcohol and the D1-R antagonist on dopamine and DOPAC levels, but only alcohol effects on serotonin. We also uncover several strain dependent effects. These results demonstrate that acute alcohol may act through dopaminergic mechanisms for some but not all behavioral phenotypes, a novel discovery, and also suggest that strain differences may, in the future, help us identify molecular mechanisms underlying acute alcohol effects.

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

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

Behavioral effects of acute ethanol in larval zebrafish (D. rerio) depend on genotype and volume of experimental well

Ethanol consumption is a worldwide problem. Sensitivity to acute effects of ethanol influences the development of chronic ethanol abuse and ethanol dependence. Environmental and genetic factors have been found to contribute to differential effects of acute ethanol. Animal models have been employed to investigate these factors. An increasingly frequently utilized animal model in ethanol research is the zebrafish. A large proportion of ethanol studies with zebrafish have been conducted with adult zebrafish. However, high throughput drug and mutation screens are particularly well adapted to larval zebrafish. These studies are often carried out using the 96-well-plate that allows monitoring large numbers of fish efficiently. Here, we investigate the effects of acute (30 min long) ethanol exposure in 8-day post-fertilization (dpf) old zebrafish. We compare four genetically distinct populations (strains) of zebrafish, measuring numerous parameters of their swim path in two well sizes, i.e., in the 96-well-plate (small volume wells) and in the 6-well-plate (large volume wells). In general, we found that the highest dose of ethanol (1% vol/vol) reduced swim speed, increased duration of immobility, increased turn angle, and increased intra-individual variance of turn angle, while the intermediate dose (0.5%) had a less strong effect, compared to control. However, we also found that these ethanol effects were strain dependent and, in general, were better detected in the larger volume well. We conclude that larval zebrafish are appropriate for quantification of acute ethanol effects and also for the analysis of environmental and genetic factors that influence these effects. We also speculate that using larger wells will likely increase sensitivity of detection and precision in screening applications.

Exposure of parents to alcohol alters behavior of offspring in zebrafish

Alcoholism and alcohol abuse represent a significant medical and societal problem, and have been thoroughly investigated in humans as well as using animal models. A less well understood aspect of alcohol related disorders is the possible effect of this drug on offspring whose parents were exposed prior to conception. The zebrafish has been successfully employed in alcohol research, however, the effect of exposing the parents to alcohol before fertilization of the eggs on offspring has not been demonstrated in this species. In this proof of concept study, we attempt to address this hiatus. We exposed both adult male and female zebrafish to 0.0% (control) or 0.5% (vol/vol) alcohol chronically for 7 days, subsequently bred the fish within their respective treatment group, collected the fertilized eggs, allowed them to develop, and tested the behavior of free-swimming offspring at their age of 7-9 days post-fertilization. We conducted the analysis in two genetically distinct quasi-inbred strains of zebrafish, AB and TL. Although gross morphology and general activity of the fish appeared unaffected, we found significant behavioral alterations in offspring of alcohol exposed parents compared to offspring of control parents in both strains. These alterations included robustly increased duration and reduced frequency of immobility, increased turn angle, and increased intra-individual variance of turn angle in offspring of alcohol exposed parents in both strains. The mechanisms underlying these behavioral effects or whether the effects are due to exposure of the father, the mother, or both to alcohol are unknown. Nevertheless, our results now set the stage for future studies with zebrafish that will address these questions.

Neurochemical and Behavioral Consequences of Ethanol and/or Caffeine Exposure: Effects in Zebrafish and Rodents

Zebrafish are increasingly being utilized to model the behavioral and neurochemical effects of pharmaceuticals and, more recently, pharmaceutical interactions. Zebrafish models of stress establish that both caffeine and ethanol influence anxiety, though few studies have implemented co-administration to assess the interaction of anxiety and reward-seeking. Caffeine exposure in zebrafish is teratogenic, causing developmental abnormalities in the cardiovascular, neuromuscular, and nervous systems of embryos and larvae. Ethanol is also a teratogen and, as an anxiolytic substance, may be able to offset the anxiogenic effects of caffeine. Co-exposure to caffeine and alcohol impacts neuroanatomy and behavior in adolescent animal models, suggesting stimulant substances may moderate the impact of alcohol on neural circuit development. Here, we review the literature describing neuropharmacological and behavioral consequences of caffeine and/or alcohol exposure in the zebrafish model, focusing on neurochemistry, locomotor effects, and behavioral assessments of stress/anxiety as reported in adolescent/juvenile and adult animals. The purpose of this review is twofold: (1) describe the work in zebrafish documenting the effects of ethanol and/or caffeine exposure and (2) compare these zebrafish studies with comparable experiments in rodents. We focus on specific neurochemical pathways (dopamine, serotonin, adenosine, GABA, adenosine), anxiety-type behaviors (assessed with novel tank, thigmotaxis, shoaling), and locomotor changes resulting from both individual and co-exposure. We compare findings in zebrafish with those in rodent models, revealing similarities across species and identifying conservation of mechanisms that potentially reinforce co-addiction.

Lasting effects of mild embryonic ethanol exposure on voltage-gated ion channels in adult zebrafish brain

The zebrafish is increasingly well utilized in alcohol research, particularly in modeling human fetal alcohol spectrum disorders (FASD). FASD results from alcohol reaching the developing fetus intra utero, a completely preventable yet prevalent and devastating life-long disorder. The hope with animal models, including the zebrafish, is to discover the mechanisms underlying this disease, which may aid treatment and diagnosis. In the past, we developed an embryonic alcohol exposure regimen that is aimed at mimicking the milder, and most prevalent, forms of FASD in zebrafish. We have found numerous lasting alterations in behavior, neurochemistry, neuronal markers and glial cell phenotypes in this zebrafish FASD model. Using the same model (2 h long bath immersion of 24 h post-fertilization old zebrafish eggs into 1% vol/vol ethanol), here we conduct a proof of concept analysis of voltage-gated cation channels, investigating potential embryonic alcohol induced changes in L-, T- and N- type Ca⁺⁺ and the SCN1A Na⁺ channels using Western blot followed by immunohistochemical analysis of the same channels in the pallium and cerebellum of the zebrafish brain. We report significant reduction of expression in all four channel proteins using both methods. We conclude that reduced voltage-gated cation channel expression induced by short and low dose exposure to alcohol during embryonic development of zebrafish may contribute to the previously demonstrated lasting behavioral and neurobiological changes.

Embryonic Exposure to Ethanol Increases Anxiety-Like Behavior in Fry Zebrafish

AIMS

Fetal alcohol spectrum disorder (FASD) is an umbrella term to describe the effects of ethanol (Eth) exposure during embryonic development, including several conditions from malformation to cognitive deficits. Zebrafish (Danio rerio) are a translational model popularly applied in brain disorders and drug screening studies due to its genetic and physiology homology to humans added to its transparent eggs and fast development. In this study, we investigated how early ethanol exposure affects zebrafish behavior during the initial growth phase.

METHODS

Fish eggs were exposed to 0.0 (control), 0.25 and 0.5% ethanol at 24 h post-fertilization. Later, fry zebrafish (10 days old) were tested in a novel tank task and an inhibitory avoidance protocol to inquire about morphology and behavioral alterations.

RESULTS

Analysis of variance showed that ethanol doses of 0.25 and 0.5% do not cause morphological malformations and did not impair associative learning but increased anxiety-like behavior responses and lower exploratory behavior when compared to the control.

CONCLUSION

Our results demonstrate that one can detect behavioral abnormalities in the zebrafish induced by embryonic ethanol as early as 10 days post-fertilization and that alcohol increases anxious behavior during young development in zebrafish.

Sexually dimorphic and asymmetric effects of embryonic ethanol exposure on hypocretin/orexin neurons as related to behavioral changes in zebrafish

Neurons expressing the neuropeptide hypocretin/orexin (Hcrt) in the hypothalamus promote reward-related behaviors including alcohol consumption and are shown in rodents and zebrafish to be stimulated by embryonic exposure to ethanol (EtOH). We used here in zebrafish three-dimensional analyses of the entire population of Hcrt neurons to examine how embryonic EtOH exposure at low-moderate concentrations (0.1% or 0.5% v/v) alters these neurons in relation to behavior. We found that EtOH in the water for 2 h (22-24 h post fertilization) increases the number of Hcrt neurons on the left but not right side of the brain through a stimulation of cell proliferation, this is accompanied by a decrease in locomotor activity under novel conditions but not after habituation, and these effects are evident in both larvae and adults indicating they are long lasting. Our analyses in adults revealed sexually dimorphic effects, with females consuming more EtOH-gelatin and exhibiting more freezing behavior along with an asymmetric increase in Hcrt neurons and males exhibiting increased aggression with no change in Hcrt. These findings suggest that a long lasting, asymmetric increase in Hcrt neurons induced by EtOH results from an asymmetric increase in proliferation specific to Hcrt and contributes to behavioral changes in females.

The Effects of Early Life Stress on the Brain and Behaviour: Insights From Zebrafish Models

The early life period represents a window of increased vulnerability to stress, during which exposure can lead to long-lasting effects on brain structure and function. This stress-induced developmental programming may contribute to the behavioural changes observed in mental illness. In recent decades, rodent studies have significantly advanced our understanding of how early life stress (ELS) affects brain development and behaviour. These studies reveal that ELS has long-term consequences on the brain such as impairment of adult hippocampal neurogenesis, altering learning and memory. Despite such advances, several key questions remain inadequately answered, including a comprehensive overview of brain regions and molecular pathways that are altered by ELS and how ELS-induced molecular changes ultimately lead to behavioural changes in adulthood. The zebrafish represents a novel ELS model, with the potential to contribute to answering some of these questions. The zebrafish offers some important advantages such as the ability to non-invasively modulate stress hormone levels in a whole animal and to visualise whole brain activity in freely behaving animals. This review discusses the current status of the zebrafish ELS field and its potential as a new ELS model.

Contributions of Zebrafish Studies on the Behavioural Consequences of Early Alcohol Exposure: A Systematic Review

BACKGROUND

The consequences of mild to severe exposure to alcohol during brain development is still a matter of debate and scientific investigation. The long-term behavioural effects of ethanol exposure have been related to impaired social skills and cognition. Zebrafish have become a suitable animal model to investigate the effects of early ethanol exposure because it is very feasible to promote drug delivery during early development.

OBJECTIVE

The goal of the current report is to review existing behavioural studies addressing the impact of early alcohol exposure using zebrafish to determine whether these models resemble the behavioural effects of early alcohol exposure in humans.

METHODS

A comprehensive search of biomedical databases was performed using the operation order: "ZEBRAFISH AND BEHAV* AND (ETHANOL OR ALCOHOL)". The eligibility of studies was determined using the PICOS strategy, contemplating the population as zebrafish, intervention as exposure to ethanol, comparison with a non-exposed control animal, and outcomes as behavioural parameters.

RESULTS

The systematic search returned 29 scientific articles as eligible. The zebrafish is presented as a versatile animal model that is useful to study FASD short and long-term behaviour impairments, such as anxiety, impaired sociability, aggressiveness, learning problems, memory impairment, seizure susceptibility, sleep disorders, motivational problems, and addiction.

CONCLUSION

This systematic review serves to further promote the use of zebrafish as a model system to study the pathophysiological and behavioural consequences of early alcohol exposure.

Lasting alterations induced in glial cell phenotypes by short exposure to alcohol during embryonic development in zebrafish

Despite the known teratogenic effects of alcohol (ethanol) on the developing human fetus, the prevalence of fetal alcohol spectrum disorder (FASD) is not decreasing. Appropriate treatment for this life-long disease has not been developed, and even diagnostic biomarkers are unavailable. FASD remains a large unmet medical need. Numerous animal models have been developed to mimic FASD and study potential underlying biological mechanisms. However, most of these models focused on neuronal phenotypes. Given that glial cells represent the majority of cells in the vertebrate brain, and given the increasingly appreciated roles they play in a myriad of neuronal functions as well as CNS disorders, we decided to investigate potential embryonic alcohol exposure induced changes in them. Building upon a previously introduced zebrafish model of milder and most prevalent forms of FASD, we investigated the effect of a 2-hour-long exposure to alcohol (1% vol/vol bath concentration) employed at the 24^th hour postfertilization stage of development of zebrafish on a number of glial cell-related phenotypes. We studied oligodendrocyte, astrocyte as well as microglia-related phenotypes using immunohistochemistry, lipid, and enzyme activity analyses. We report significant changes in wide-spread glial cell phenotypes induced by embryonic alcohol exposure in the zebrafish brain and conclude that the zebrafish will advance our understanding of the mechanisms of this devastating disorder.

Inhibition of ecto-5'-nucleotidase and adenosine deaminase is able to reverse long-term behavioural effects of early ethanol exposure in zebrafish (Danio rerio)

The behavioural impacts of prenatal exposure to ethanol include a lower IQ, learning problems, anxiety and conduct disorders. Several components of the neurochemical network could contribute to the long-lasting effects of ethanol embryonic exposure. Adenosine is an important neuromodulator, that has been indicated to be affected by acute and chronic exposure to ethanol. Here, embryos of zebrafish exposed to 1% ethanol during the developmental stages of gastrula/segmentation or pharyngula exhibited anxiolytic effect, increased aggressiveness, and decreased social interaction. The exposure during pharyngula stage was able to affect all behavioural parameters analysed at 3 months-post fertilization (mpf), while the treatment during gastrula stage affected the anxiety and social interaction parameters. The aggressiveness was the only behavioural effect of early ethanol exposure that lasted to 12 mpf. The use of a specific inhibitor of adenosine production, the inhibitor of ecto-5′-nucleotidase (AMPCP/150 mg/kg), and the specific inhibitor of adenosine degradation, the inhibitor of adenosine deaminase, EHNA (100 mg/kg) did not affect the effects over anxiety. However, AMPCP at 3 mpf, but not EHNA, reversed aggressive parameters. AMPCP also recovered the social interaction parameter at 3 mpf in animals treated in both stages, while EHNA recovered this parameter just in those animals treated with ethanol during the gastrula stage. These results suggest that long-lasting behavioural effects of ethanol can be modulated by intervention on ecto-5′-nucleotidase and adenosine deaminase activities.

Preclinical methodological approaches investigating of the effects of alcohol on perinatal and adolescent neurodevelopment

Despite much evidence of its economic and social costs, alcohol use continues to increase. Much remains to be known as to the effects of alcohol on neurodevelopment across the lifespan and in both sexes. We provide a comprehensive overview of the methodological approaches to ethanol administration when using animal models (primarily rodent models) and their translational relevance, as well as some of the advantages and disadvantages of each approach. Special consideration is given to early developmental periods (prenatal through adolescence), as well as to the types of research questions that are best addressed by specific methodologies. The zebrafish is used increasingly in alcohol research, and how to use this model effectively as a preclinical model is reviewed as well.

Developmental stage-dependent deficits induced by embryonic ethanol exposure in zebrafish: A neurochemical analysis

FASD results from the developing fetus being exposed to alcohol, and is characterized by morphological, behavioural and cognitive deficits. However, the expression, severity and age of onset of these symptoms has been found to show variation. This variation may partly be due to the developmental stage at which alcohol reached the developing fetus. Previously, alcohol was shown to lead to significant concentration dependent behavioural as well as neurochemical changes detected in adult zebrafish when this substance was administered at 24 h post-fertilization (hpf) for 2 h. This alcohol exposure method arguably mimicked the milder, and more prevalent, forms of human FASD. However, whether the observed changes depended upon the developmental stage, i.e., the timing, of alcohol exposure has not been systematically analyzed. Here, we employ the same alcohol dosing regimen, where zebrafish eggs are immersed into 0% or 1% (vol/vol) alcohol for 2 h, but we perform the immersion at 5, 10, 16, 24, 36, or 48 hpf. We previously developed a sensitive HPLC method to quantify neurochemicals, and found levels of dopamine, serotonin and their metabolites DOPAC and 5-HIAA to be affected by embryonic alcohol treatment. Here, using the same method, we compare whole-brain levels of these neurochemicals in the embryonic alcohol exposed and control zebrafish at their age of 30 days post-fertilization (dpf). Consistent with previous reports, we found significant reduction of levels of dopamine, serotonin and their metabolites in the fish exposed to alcohol at 24 hpf. However, we also found significant dependency on the developmental stage at which alcohol was administered with particularly robust impairments when the exposure was at the early or middle of the developmental periods probed. Our results now demonstrate that one can detect functional abnormalities in the zebrafish brain induced by embryonic alcohol as early as 30 dpf and that the neurochemical deficits are dependent upon the developmental stage at which alcohol is administered.

Developmental stage and genotype dependent behavioral effects of embryonic alcohol exposure in zebrafish larvae

Fetal Alcohol Spectrum Disorders (FASD) represent a worldwide problem. The severity and types of symptoms of FASD vary, which may be due to the genotype of the fetus and the developmental stage at which the fetus is exposed to alcohol. The most prevalent forms of FASD present less severe symptoms, including behavioral and cognitive abnormalities, and arise from exposure to low amounts of alcohol consumed infrequently. Treating or diagnosing FASD patients has been difficult because we do not understand the mechanisms underlying FASD. Animal models, including the zebrafish, have been suggested to answer this question. Here, we present a proof of concept analysis studying the behavioral effects of embryonic alcohol exposure in one-week old juvenile zebrafish. We exposed zebrafish embryos at one of five developmental stages (8, 16, 24, 32, or 40 hour post-fertilization) to 0% (control) or 1% (vol/vol) ethanol for 2 h, and tested the behavior of these fish at their age of 7-9 days post-fertilization. We employed two genetically distinct zebrafish populations, a quasi-inbred AB derivative strain, and a genetically variable WT population. We report significant developmental time and genotype dependent effects of alcohol on certain measures of motor function and/or anxiety-like responses. For example, we found embryonic alcohol exposed AB fish to swim faster, vary their speed more, stop moving more often and turn less compared to control fish, alcohol induced changes that were absent or less robust in WT fish. We conclude that our results open new avenues to the identification of genetic mechanisms that mediate or influence alcohol induced developmental alteration of brain function and behavior, which, on the long run, may allow us to identify diagnostic biomarkers and treatment options for human FASD.

Repeated ethanol exposure increases anxiety-like behaviour in zebrafish during withdrawal

Zebrafish (Danio rerio) are quickly becoming an important model organism in behavioural neuroscience and drug addiction research. Conditioned place preference studies show that drugs of abuse produce responses in zebrafish that are similar to mammalian animal models. Repeated administration of ethanol in zebrafish results in withdrawal-induced behavioural responses that vary with dose and exposure duration, requiring additional investigation. Here, we examine the effects of ethanol withdrawal on anxiety-like behaviours in adult zebrafish after a 21-day ethanol dosing schedule at either 0.4% or 0.8%. Anxiety-like behaviour was measured with the novel object approach test; this test involves placing a fish in a circular arena with a novel object in the centre and observing the amount of exploration of the object. We found increased anxiety-like behaviour during ethanol withdrawal. This study adds to the growing body of literature that validates the zebrafish as a model organism in the field of behavioural neuroscience and addiction.

Alcohol exposure during embryonic development: An opportunity to conduct systematic developmental time course analyses in zebrafish

Ethanol affects numerous neurobiological processes depending upon the developmental stage at which it reaches the vertebrate embryo. Exposure time dependency may explain the variable severity and manifestation of life-long symptoms observed in fetal alcohol spectrum disorder (FASD) patients. Characterization of behavioural deficits will help us understand developmental stage-dependency and its underlying biological mechanisms. Here we highlight pioneering studies that model FASD using zebrafish, including those that demonstrated developmental stage-dependency of alcohol effects on some behaviours. We also succinctly review the more expansive mammalian literature, briefly discuss potential developmental stage dependent biological mechanisms alcohol alters, and review some of the disadvantages of mammalian systems versus the zebrafish. We stress that the temporal control of alcohol administration in the externally developing zebrafish gives unprecedented precision and is a major advantage of this species over other model organisms employed so far. We also emphasize that the zebrafish is well suited for high throughput screening and will allow systematic exploration of embryonic-stage dependent alcohol effects via mutagenesis and drug screens.

Persistent increase in ecto‑5'‑nucleotidase activity from encephala of adult zebrafish exposed to ethanol during early development

Prenatal alcohol exposure causes alterations to the brain and can lead to numerous cognitive and behavioral outcomes. Long-lasting effects of early ethanol exposure have been registered in glutamatergic and dopaminergic systems. The purinergic system has been registered as an additional target of ethanol exposure. The objective of this research was to evaluate if the ecto‑5'‑nucleotidase and adenosine deaminase activities and gene expression of adult zebrafish exposed to 1% ethanol during early development could be part of the long-lasting targets of ethanol. Zebrafish embryos were exposed to 1% ethanol in two distinct developmental phases: gastrula/segmentation (5-24 h post-fertilization) or pharyngula (24-48 h post-fertilization). At the end of three months, after checking for morphological outcomes, the evaluation of enzymatic activity and gene expression was performed. Exposure to ethanol did not promote gross morphological defects; however, a significant decrease in the body length was observed (17% in the gastrula and 22% in the pharyngula stage, p < 0.0001). Ethanol exposure during the gastrula/segmentation stage promoted an increase in ecto‑5'‑nucleotidase activity (39.5%) when compared to the control/saline group (p < 0.0001). The ecto‑5'‑nucleotidase gene expression and the deamination of adenosine exerted by ecto and cytosolic adenosine deaminase were not affected by exposure to ethanol in both developmental stages. HPLC experiments did not identify differences in adenosine concentration on the whole encephala of adult animals exposed to ethanol during the gastrula stage or on control animals (p > 0.05). Although the mechanism underlying these findings requires further investigation, these results indicate that ethanol exposure during restricted periods of brain development can have long-term consequences on ecto‑5'‑nucleotidase activity, which could have an impact on subtle sequels of ethanol early exposure.

Lasting changes induced by mild alcohol exposure during embryonic development in BDNF, NCAM and synaptophysin-positive neurons quantified in adult zebrafish

Fetal alcohol spectrum disorder is one of the leading causes of mental health issues worldwide. Analysis of zebrafish exposed to alcohol during embryonic development confirmed that even low concentrations of alcohol for a short period of time may have lasting behavioral consequences at the adult or old age. The mechanism of this alteration has not been studied. Here, we immersed zebrafish embryos into 1% alcohol solution (vol/vol%) at 24 hr post-fertilization (hpf) for 2 hr and analyzed potential changes using immunohistochemistry. We measured the number of BDNF (brain-derived neurotrophic factor) and NCAM (neuronal cell adhesion molecule)-positive neurons and the intensity of synaptophysin staining in eight brain regions: lateral zone of the dorsal telencephalic area, medial zone of the dorsal telencephalic area, dorsal nucleus of the ventral telencephalic area, ventral nucleus of the ventral telencephalic area, parvocellular preoptic nucleus, ventral habenular nucleus, corpus cerebella and inferior reticular formation. We found embryonic alcohol exposure to significantly reduce the number of BDNF- and NCAM-positive cells in all brain areas studied as compared to control. We also found alcohol to significantly reduce the intensity of synaptophysin staining in all brain areas except the cerebellum and preoptic area. These neuroanatomical changes correlated with previously demonstrated reduction of social behavior in embryonic alcohol-exposed zebrafish, raising the possibility of a causal link. Given the evolutionary conservation across fish and mammals, we emphasize the implication of our current study for human health: even small amount of alcohol consumption may be unsafe during pregnancy.

Short exposure to low concentrations of alcohol during embryonic development has only subtle and strain- dependent effect on the levels of five amino acid neurotransmitters in zebrafish

The zebrafish has been successfully employed to model and study the effects of embryonic alcohol exposure. Short exposure to low alcohol concentrations during embryonic development has been shown to significantly disrupt social behavior as well as the dopaminergic and serotoninergic systems in zebrafish. However, analysis of potential effects of embryonic alcohol exposure on other amino acid neurotransmitter systems has not been performed. Here we analyzed neurochemicals obtained from adult AB and TU strain zebrafish that were immersed in 0.00% (control), 0.25%, 0.50%, 0.75% or 1.00% alcohol solution (vol/vol%) at 24 h post-fertilization for 2 h. From whole brain extracts, we quantified glutamate, aspartate, glycine, taurine and GABA levels using high performance liquid chromatography (HPLC). We found embryonic alcohol exposure not to have any significant effect on the levels of glutamate, aspartate, glycine and GABA in both AB and TU zebrafish. AB zebrafish showed a significant elevation of taurine levels, but only in the highest alcohol dose group compared to control. These results, albeit mainly negative, together with prior findings suggest that behavioral abnormalities resulting from embryonic alcohol exposure described before for AB zebrafish may primarily be due to altered dopaminergic and serotoninergic mechanisms. Furthermore, a Principal Component Analysis conducted with all neurochemicals tested in this and in our prior study, found a strain-dependent correlation structure response to embryonic alcohol treatment, confirming that embryonic alcohol effects may be genotype dependent.

Adenosine deaminase activity and gene expression patterns are altered after chronic ethanol exposure in zebrafish brain

Ethanol alters the homeostasis between excitatory and inhibitory neurotransmitters and its intoxication reveals adenosine as responsible to modify several responses including signal transduction. Zebrafish has been recently investigated for knowledge the prolonged effect of ethanol on behavioral and biochemical parameters. The aim of this study was to evaluate the soluble and membrane adenosine deaminase activities and gene expression in zebrafish brain. Animals were exposed to 0.5% ethanol for 7, 14, and 28days. There were no significant changes in ADA activity from soluble fraction after all treatments. However, we verified a decrease of ADA activity in membrane fraction after 28days (44%) of ethanol exposure. ADA1 was not altered whereas mRNA transcript levels for ADAL presented an increase after 28days of ethanol exposure (34%). ADA2-1 showed a decrease (26%) followed by an increase (17%) of transcripts after 14 and 28days of ethanol exposure, respectively. However, ADA2-1 truncated alternative splice isoform (ADA2-1/T) demonstrated a reduction after 28days (20%). ADA2-2 was decreased (22%) followed by an increase (109%) of transcripts after 14 and 18days of ethanol exposure, respectively. Altogether, the purine catabolism promoted by ADA may be an important target of the chronic toxicity induced for ethanol.

Fetal alcohol spectrum disorders: Zebrafish in the analysis of the milder and more prevalent form of the disease

Fetal Alcohol Spectrum Disorders (FASD) represent a large unmet medical need. Exposure of the developing human embryo to alcohol can lead to life-long suffering. Despite the well documented deleterious effects of alcohol on the developing fetus, pregnant women continue to drink alcohol, and FASD remains the leading cause of preventable mental retardation and other behavioral abnormalities. Particularly prevalent are the milder forms of the disease cluster, representing children who do not show obvious physical signs and who may be undiagnosed or misdiagnosed. To develop treatment and diagnostic tools, researchers have turned to animal models. The zebrafish is becoming one of the leading biomedical research organisms that may facilitate discovery of the biological mechanisms underlying this disease and the identification of biomarkers that may be used for diagnosis. Here we review the latest advances of this field, mostly focussing on the discoveries made in our own laboratory and others with zebrafish employed to analyze the effects of moderate to low level of exposure to alcohol. We argue that the zebrafish represents unique advantages, and adding information obtained with this species to the mix of other animal models will significantly increase translational relevance of animal biomedical research for the analysis of human FASD.

Embryonic alcohol exposure leading to social avoidance and altered anxiety responses in adult zebrafish

Fetal Alcohol Spectrum Disorders (FASD) is a syndrome characterized by neurological and behavioral impairments. A recently discovered hallmark of FASD is impaired social behavior. Avoidance of social interaction typical of FASD may be the result of increased anxiety. Previously, the zebrafish was successfully used to model embryonic alcohol induced social abnormalities. Here, we analyzed both anxiety and social responses using a zebrafish FASD model, in adult fish. We exposed zebrafish embryos to low concentrations of ethanol (0.1%; 0.25%; 0.5% and 1% v/v) for 2h at, 24h post-fertilization, to mimic the most prevalent milder FASD cases, and investigated the ensuing alterations in adult, 4-month-old, zebrafish. We studied social interaction in the social preference task and anxiety in the novel tank task. We observed an ethanol dose dependent reduction of time spend in the conspecific zone compared to control, corroborating prior findings. We also found significant changes in the novel tank (e.g. increased bottom dwell time, increased distance to top) suggesting elevated anxiety to control, but we also found, using an anxiolytic drug buspirone, that reduction of anxiety is associated with reduced shoaling. Our results confirm that embryonic alcohol exposure disrupts social behavior, and also show that its effects on anxiety related phenotypes may be genotype, alcohol administration method, experimental procedure and test-context dependent.

Metabolomics and fetal alcohol spectrum disorder

Fetal alcohol spectrum disorder (FASD) is a major public health issue that encompass an array of physical, neurological, and behavioral effects due to alcohol consumption during pregnancy. The classical biomarkers of FASD that are currently used lack sensitivity and specificity, and as such there is an opportunity through the use of novel metabolomics analysis to identify new biomarkers to identify those at risk for FASD, which could more effectively aid in early intervention. The focus of this minireview is to identify current work that is being done in the field of metabolomics in FASD in utero, and to highlight promising metabolites that could act as biomarkers in the future. We will conclude with suggestions for further research, as there is a large gap of knowledge in this particular area of metabolomics.

Behavioral Responses to Novelty or to a Predator Stimulus Are Not Altered in Adult Zebrafish by Early Embryonic Alcohol Exposure

BACKGROUND

Fetal alcohol spectrum disorders (FASD) may vary in symptoms and severity. In the milder and more prevalent forms of the disease, behavioral abnormalities may include impaired social behavior, for example, difficulty interpreting social cues. Patients with FASD remain often undiagnosed due to lack of biomarkers, and treatment is unavailable because the mechanisms of the disease are not yet understood. Animal models have been proposed to facilitate addressing these problems. More recently, short exposure of the zebrafish embryo to low concentrations of alcohol was shown to lead to significant and lasting impairment of behavior in response to social stimuli. The impairment may be the result of abnormal social behavior or altered fear/anxiety. The goal of the current study was to investigate the latter.

METHODS

Here, we employed the alcohol exposure regimen used previously (exposure of 24th hour postfertilization embryos to 0.00, 0.25, 0.50, 0.75, or 1.00% vol/vol alcohol for 2 hours), allowed the fish to reach adulthood, and measured the behavioral responses of these adults to a novel tank (anxiety-related behaviors) as well as to an animated image of a sympatric predator of zebrafish (fear-related behaviors).

RESULTS

We found behavioral responses of embryonic alcohol-exposed adult fish to remain statistically indistinguishable from those of controls, suggesting unaltered anxiety and fear in the embryonic alcohol-treated fish.

CONCLUSIONS

Given that motor and perceptual function was previously shown to be also unaltered in the adults after embryonic alcohol exposure, our current results suggest that the impaired response of these fish to social stimuli may be the result of abnormal social behavior.

The Genetics of Fetal Alcohol Spectrum Disorders

The term "fetal alcohol spectrum disorders" (FASD) defines the full range of ethanol (EtOH)-induced birth defects. Numerous variables influence the phenotypic outcomes of embryonic EtOH exposure. Among these variables, genetics appears to play an important role, yet our understanding of the genetic predisposition to FASD is still in its infancy. We review the current literature that relates to the genetics of FASD susceptibility and gene-EtOH interactions. Where possible, we comment on potential mechanisms of reported gene-EtOH interactions. Early indications of genetic sensitivity to FASD came from human and animal studies using twins or inbred strains, respectively. These analyses prompted searches for susceptibility loci involved in EtOH metabolism and analyses of candidate loci, based on phenotypes observed in FASD. More recently, genetic screens in animal models have provided an additional insight into the genetics of FASD. Understanding FASD requires that we understand the many factors influencing phenotypic outcome following embryonic EtOH exposure. We are gaining ground on understanding some of the genetics behind FASD, yet much work remains to be carried out. Coordinated analyses using human patients and animal models are likely to be highly fruitful in uncovering the genetics behind FASD.

Effects of embryonic ethanol exposure at low doses on neuronal development, voluntary ethanol consumption and related behaviors in larval and adult zebrafish: Role of hypothalamic orexigenic peptides

Embryonic exposure to ethanol is known to affect neurochemical systems in rodents and increase alcohol drinking and related behaviors in humans and rodents. With zebrafish emerging as a powerful tool for uncovering neural mechanisms of numerous diseases and exhibiting similarities to rodents, the present report building on our rat studies examined in zebrafish the effects of embryonic ethanol exposure on hypothalamic neurogenesis, expression of orexigenic neuropeptides, and voluntary ethanol consumption and locomotor behaviors in larval and adult zebrafish, and also effects of central neuropeptide injections on these behaviors affected by ethanol. At 24h post-fertilization, zebrafish embryos were exposed for 2h to ethanol, at low concentrations of 0.25% and 0.5%, in the tank water. Embryonic ethanol compared to control dose-dependently increased hypothalamic neurogenesis and the proliferation and expression of the orexigenic peptides, galanin (GAL) and orexin (OX), in the anterior hypothalamus. These changes in hypothalamic peptide neurons were accompanied by an increase in voluntary consumption of 10% ethanol-gelatin and in novelty-induced locomotor and exploratory behavior in adult zebrafish and locomotor activity in larvae. After intracerebroventricular injection, these peptides compared to vehicle had specific effects on these behaviors altered by ethanol, with GAL stimulating consumption of 10% ethanol-gelatin more than plain gelatin food and OX stimulating novelty-induced locomotor behavior while increasing intake of food and ethanol equally. These results, similar to those obtained in rats, suggest that the ethanol-induced increase in genesis and expression of these hypothalamic peptide neurons contribute to the behavioral changes induced by embryonic exposure to ethanol.

Influences of acute ethanol exposure on locomotor activities of zebrafish larvae under different illumination

Larval zebrafish present unique opportunities to study the behavioral responses of a model organism to environmental challenges during early developmental stages. The purpose of the current study was to investigate the locomotor activities of AB strain zebrafish larvae at 5 and 7 days post-fertilization (dpf) in response to light changes under the influence of ethanol, and to explore potential neurological mechanisms that are involved in ethanol intoxication. AB strain zebrafish larvae at both 5 and 7 dpf were treated with ethanol at 0% (control), 0.1%, 0.25%, 0.5%, 1%, and 2% (v/v%). The locomotor activities of the larvae during alternating light-dark challenges, as well as the locomotor responses immediately following the light transitions, were investigated. The levels of various neurotransmitters were also measured in selected ethanol-treated groups. The larvae at 5 and 7 dpf demonstrated similar patterns of locomotor responses to ethanol treatment. Ethanol treatment at 1% increased the swimming distances of the zebrafish larvae in the dark periods, but had no effect on the swimming distances in the light periods. In contrast, ethanol treatment at 2% increased the swimming distances in the light periods, but did not potentiate the swimming activity in the dark periods, compared to controls. Differences in the levels of neurotransmitters that are involved in norepinephrine, dopamine, and serotonin pathways were also observed in groups with different ethanol treatments. These results indicated the behavioral studies concerning the ethanol effects on locomotor activities of zebrafish larvae could be carried out as early as 5 dpf. The 1% and 2% ethanol-treated zebrafish larvae modeled ethanol effects at different intoxication states, and the differences in neurotransmitter levels suggested the involvement of various neurotransmitter pathways in different ethanol intoxication states.

Impairment of social behaviour persists two years after embryonic alcohol exposure in zebrafish: A model of fetal alcohol spectrum disorders

Zebrafish naturally form social groups called shoals. Previously, we have shown that submerging zebrafish eggs into low concentrations of alcohol (0.00, 0.25, 0.50, 0.75 and 1.00 vol/vol% external bath concentration) during development (24h post-fertilization) for two hours resulted in impaired shoaling response in seven month old young adult zebrafish. Here we investigate whether this embryonic alcohol exposure induced behavioural deficit persists to older age. Zebrafish embryos were exposed either to fresh system water (control) or to 1% alcohol for two hours, 24h after fertilization, and were raised in a high-density tank system. Social behaviour was tested by presenting the experimental fish with a computer animated group of zebrafish images, while automated tracking software measured their behaviour. Control fish were found to respond strongly to animated conspecific images by reducing their distanceand remaining close to the images during image presentation, embryonic alcohol treated fish did not. Our results suggest that the impaired shoaling response of the alcohol exposed fish was not due to altered motor function or visual perception, but likely to a central nervous system alteration affecting social behaviour itself. We found the effects of embryonic alcohol exposure on social behaviour not to diminish with age, a result that demonstrates the deleterious and potentially life-long consequences of exposure to even small amount of alcohol during embryonic development in vertebrates.

Differences in inhibitory avoidance, cortisol and brain gene expression in TL and AB zebrafish

Recently, we established an inhibitory avoidance paradigm in Tupfel Long-Fin (TL) zebrafish. Here, we compared task performance of TL fish and fish from the AB strain; another widely used strain and shown to differ genetically and behaviourally from TL fish. Whole-body cortisol and telencephalic gene expression related to stress, anxiety and fear were measured before and 2 h post-task. Inhibitory avoidance was assessed in a 3-day paradigm: fish learn to avoid swimming from a white to a black compartment where a 3V-shock is given: day 1 (first shock), day 2 (second shock) and day 3 (no shock, sampling). Tupfel Long-Fin fish rapidly learned to avoid the black compartment and showed an increase in avoidance-related spatial behaviour in the white compartment across days. In contrast, AB fish showed no inhibitory avoidance learning. AB fish had higher basal cortisol levels and expression levels of stress-axis related genes than TL fish. Tupfel Long-Fin fish showed post-task learning-related changes in cortisol and gene expression levels, but these responses were not seen in AB fish. We conclude that AB fish show higher cortisol levels and no inhibitory avoidance than TL fish. The differential learning responses of these Danio strains may unmask genetically defined risks for stress-related disorders.

Commentary: catching a conserved mechanism of ethanol teratogenicity

BACKGROUND

Due to its profound impact on human development, ethanol (EtOH) teratogenicity is a field of intense study. The complexity of variables that influence the outcomes of embryonic or prenatal EtOH exposure compels the use of animal models in which these variables can be isolated.

METHODS

Numerous model systems have been used in these studies. The zebrafish is a powerful model system, which has seen a recent increase in usage for EtOH studies.

RESULTS

Those using zebrafish for alcohol studies often face 2 questions: (i) How physiologically relevant are the doses of EtOH administered to zebrafish embryos? and (ii) Will the mechanisms of EtOH teratogenesis be conserved to other model systems and human?

CONCLUSIONS

The current article by Flentke and colleagues () helps to shed important light on these questions and clearly demonstrates that the zebrafish will be a valuable model system with which to understand EtOH teratogenicity.

Embryonic alcohol exposure impairs the dopaminergic system and social behavioral responses in adult zebrafish

BACKGROUND

The zebrafish is a powerful neurobehavioral genetics tool with which complex human brain disorders including alcohol abuse and fetal alcohol spectrum disorders may be modeled and investigated. Zebrafish innately form social groups called shoals. Previously, it has been demonstrated that a single bath exposure (24 hours postfertilization) to low doses of alcohol (0, 0.25, 0.50, 0.75, and 1% vol/vol) for a short duration (2 hours) leads to impaired group forming, or shoaling, in adult zebrafish.

METHODS

In the current study, we immersed zebrafish eggs in a low concentration of alcohol (0.5% or 1% vol/vol) for 2 hours at 24 hours postfertilization and let the fish grow and reach adulthood. In addition to quantifying the behavioral response of the adult fish to an animated shoal, we also measured the amount of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid from whole brain extracts of these fish using high-pressure liquid chromatograph.

RESULTS

Here we confirm that embryonic alcohol exposure makes adult zebrafish increase their distance from the shoal stimulus in a dose-dependent manner. We also show that the shoal stimulus increases the amount of dopamine and 3,4-dihydroxyphenylacetic acid in the brain of control zebrafish but not in fish previously exposed to alcohol during their embryonic development.

CONCLUSIONS

We speculate that one of the mechanisms that may explain the embryonic alcohol-induced impaired shoaling response in zebrafish is dysfunction of reward mechanisms subserved by the dopaminergic system.

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.

Embryonic alcohol exposure impairs associative learning performance in adult zebrafish

The zebrafish has been proposed for modeling fetal alcohol spectrum disorders (FASD). Previous FASD research with zebrafish employed high concentrations of alcohol and/or long exposure periods. Here, we exposed zebrafish eggs to low doses of alcohol (0, 0.25, 0.50, 0.75 and 1.0% (vol/vol); external bath application of which 1/20th may reach the inside of the egg) at 16-h post-fertilization (hpf) and only for a short duration (2h) in the hope to avoid gross morphological aberrations and to mimic the more frequent FASD exposure levels. Upon reaching adulthood the exposed and control zebrafish were tested for their associative learning performance in a plus-maze. Embryonic alcohol exposure led to no gross anatomical abnormalities and did not increase mortality. Unexposed (control) zebrafish showed excellent acquisition of association between a conditioned visual stimulus (CS) and food reward, demonstrated by their preference for the target zone of the maze that contained the CS during a probe trial in the absence of reward. However, alcohol-exposed fish showed no such preference and performed indistinguishable from random chance. Locomotor activity during training and the probe trial or the amount of food consumed during training did not differ between the embryonic alcohol exposed and unexposed (control) fish, suggesting that the impaired learning performance found was unlikely to be caused by altered motivation or motor function. Our results suggest that even very small amounts of alcohol reaching the embryo for only a short duration of time may have long lasting deleterious effects on cognitive function in vertebrates.