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

Embryonic alcohol exposure alters cholinergic neurotransmission and memory in adult zebrafish

Alcohol is the most consumed addictive substance worldwide that elicits multiple health problems. Consumption of alcoholic beverages by pregnant women is of great concern because pre-natal exposure can trigger fetal alcohol spectrum disorder (FASD). This disorder can significantly change the embryo's normal development, mainly by affecting the central nervous system (CNS), leading to neurobehavioral consequences that persist until adulthood. Among the harmful effects of FASD, the most reported consequences are cognitive and behavioral impairments. Alcohol interferes with multiple pathways in the brain, affecting memory by impairing neurotransmitter systems, increasing the rate of oxidative stress, or even activating neuroinflammation. Here, we aimed to evaluate the deleterious effects of alcohol on the cholinergic signaling and memory in a FASD zebrafish model, using inhibitory avoidance and novel object recognition tests. Four months after the embryonic exposure to ethanol, the behavioral tests indicated that ethanol impairs memory. While both ethanol concentrations tested (0.5 % and 1 %) disrupted memory acquisition in the inhibitory avoidance test, 1 % ethanol impaired memory in the object recognition test. Regarding the cholinergic system, 0.5 % ethanol decreased ChAT and AChE activities, but the relative gene expression did not change. Overall, we demonstrated that FASD model in zebrafish impairs memory in adult individuals, corroborating the memory impairment associated with embryonic exposure to ethanol. In addition, the cholinergic system was also affected, possibly showing a relation with the cognitive impairment observed.

Neurological Disorders Induced by Drug Use: Effects of Adolescent and Embryonic Drug Exposure on Behavioral Neurodevelopment

Clinical studies demonstrate that the risk of developing neurological disorders is increased by overconsumption of the commonly used drugs, alcohol, nicotine and cannabis. These drug-induced neurological disorders, which include substance use disorder (SUD) and its co-occurring emotional conditions such as anxiety and depression, are observed not only in adults but also with drug use during adolescence and after prenatal exposure to these drugs, and they are accompanied by long-lasting disturbances in brain development. This report provides overviews of clinical and preclinical studies, which confirm these adverse effects in adolescents and the offspring prenatally exposed to the drugs and include a more in-depth description of specific neuronal systems, their neurocircuitry and molecular mechanisms, affected by drug exposure and of specific techniques used to determine if these effects in the brain are causally related to the behavioral disturbances. With analysis of further studies, this review then addresses four specific questions that are important for fully understanding the impact that drug use in young individuals can have on future pregnancies and their offspring. Evidence demonstrates that the adverse effects on their brain and behavior can occur: (1) at low doses with short periods of drug exposure during pregnancy; (2) after pre-conception drug use by both females and males; (3) in subsequent generations following the initial drug exposure; and (4) in a sex-dependent manner, with drug use producing a greater risk in females than males of developing SUDs with emotional conditions and female offspring after prenatal drug exposure responding more adversely than male offspring. With the recent rise in drug use by adolescents and pregnant women that has occurred in association with the legalization of cannabis and increased availability of vaping tools, these conclusions from the clinical and preclinical literature are particularly alarming and underscore the urgent need to educate young women and men about the possible harmful effects of early drug use and to seek novel therapeutic strategies that might help to limit drug use in young individuals.

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.

Maternal Chronic Ethanol Exposure Decreases Stress Responses in Zebrafish Offspring

In humans, prenatal alcohol exposure can cause serious health issues in children, known collectively as Foetal Alcohol Spectrum Disorders (FASD). Despite the high prevalence of FASD and a lack of effective treatments, the underlying mechanisms causing the teratogenic action of ethanol are still obscure. The limitations of human studies necessitate the use of animal models for identifying the underlying processes, but few studies have investigated the effects of alcohol in the female germline. Here, we used the zebrafish Danio rerio to investigate the effects of chronic (repeated for seven days) exposure to alcohol. Specifically, we tested whether the offspring of females chronically exposed to ethanol during oogenesis exhibited hormonal abnormalities when subjected to a stressor (alarm cue) as larvae, and if they exhibited anxiety-like behaviours as adults. Exposure to alarm cue increased whole-body cortisol in control larvae but not in those of ethanol-treated females. Furthermore, adult offspring of ethanol-treated females showed some reduced anxiety-like behaviours. These findings suggest that the offspring of ethanol-treated females had reduced stress responses. This study is the first to investigate how maternal chronic ethanol exposure prior to fertilisation influences hormonal and behavioural effects in a non-rodent model.

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.

Xanthatin Selectively Targets Retinoblastoma by Inhibiting the PLK1-Mediated Cell Cycle

Purpose

Retinoblastoma is the most common primary intraocular malignant tumor in children. Although intra-arterial chemotherapy and conventional chemotherapy have become promising therapeutic approaches for advanced intraocular retinoblastoma, the side effects threaten health and are unavoidable, making the development of targeted therapy an urgent need. Therefore, we intended to find a potential drug for human retinoblastoma by screening an in-house compound library that included 89 purified and well-characterized natural products.

Methods

We screened a panel of 89 natural products in retinoblastoma cell lines to find the inhibitor. The inhibition of the identified inhibitor xanthatin on cell growth was detected through half-maximal inhibitory concentration (IC50), flow cytometry assay, and zebrafish model system. RNA-seq further selected the target gene PLK1.

Results

We reported the discovery of xanthatin as an effective inhibitor of retinoblastoma. Mechanistically, xanthatin selectively inhibited the proliferation of retinoblastoma cells by inducing cell cycle arrest and promoting apoptosis. Interestingly, xanthatin targeted PLK1-mediated cell cycle progression. The efficacy of xanthatin was further confirmed in zebrafish models.

Conclusions

Collectively, our data suggested that xanthatin significantly inhibited tumor growth in vitro and in vivo, and xanthatin could be a potential drug treatment for retinoblastoma.

Zebrafish Models of Craniofacial Malformations: Interactions of Environmental Factors

The zebrafish is an appealing model organism for investigating the genetic (G) and environmental (E) factors, as well as their interactions (GxE), which contribute to craniofacial malformations. Here, we review zebrafish studies on environmental factors involved in the etiology of craniofacial malformations in humans including maternal smoking, alcohol consumption, nutrition and drug use. As an example, we focus on the (cleft) palate, for which the zebrafish ethmoid plate is a good model. This review highlights the importance of investigating ExE interactions and discusses the variable effects of exposure to environmental factors on craniofacial development depending on dosage, exposure time and developmental stage. Zebrafish also promise to be a good tool to study novel craniofacial teratogens and toxin mixtures. Lastly, we discuss the handful of studies on gene–alcohol interactions using mutant sensitivity screens and reverse genetic techniques. We expect that studies addressing complex interactions (ExE and GxE) in craniofacial malformations will increase in the coming years. These are likely to uncover currently unknown mechanisms with implications for the prevention of craniofacial malformations. The zebrafish appears to be an excellent complementary model with high translational value to study these complex interactions.

Zebrafish Shoaling, Its Behavioral and Neurobiological Mechanisms, and Its Alteration by Embryonic Alcohol Exposure: A Review

Social cognition and social behaviors are complex phenomena that involve numerous brain areas and underlying neurobiological mechanisms. Embryonic alcohol exposure may lead to the development of Fetal Alcohol Spectrum Disorder (FASD), a disorder that manifests with varying symptoms including abnormal social behavior and other cognitive deficits. Animal models have been utilized to mimic aspects of the disease and to study potential underlying mechanisms. The zebrafish is a relative newcomer in this field but has been suggested as an optimal compromise between system complexity and practical simplicity for modeling FASD. Importantly, due to external fertilization and development of the embryo outside the mother and subsequent lack of parental care, this species allows precise control of the timing and dose of alcohol delivery during embryonic development. Furthermore, the zebrafish is a highly social species and thus may be particularly appropriate for the analysis of embryonic alcohol-induced alterations in this context. Here, we provide a succinct review focusing on shoaling, a prominent form of social behavior, in zebrafish. We summarize what is known about its behavioral mechanisms and underlying neurobiological processes, and how it is altered by exposure to ethanol during embryonic development. Lastly, we briefly consider possible future directions of research that would help us better understand the relationship between the behavioral expression and molecular basis of embryonic ethanol-induced social deficits in fish and humans.

24-Epibrassinolide protects against ethanol-induced behavioural teratogenesis in zebrafish embryo

Embryonic studies have demonstrated the neurotoxic, teratogenic, and neurobehavioral toxicity of ethanol (EtOH). Although multiple mechanisms may contribute to these effects, oxidative stress has been described as the major damage pathway. In this regard, natural antioxidants have the potential to counteract oxidative stress-induced cellular damage. Therefore, the present study aimed to investigate the potential protective role of 24-epibrassinolide (24-EPI), a natural brassinosteroid with proved antioxidant properties, in EtOH-induced teratogenic effects during early zebrafish development. Embryos (~2 h post-fertilization - hpf) were exposed to 1 % EtOH, co-exposed to 24-EPI (0.01, 0.1 and 1 μM) and to 24-EPI alone (1 μM) for 24 h. Following exposure, biochemical evaluations were made at 26 hpf, developmental analysis was made throughout the embryo-larval period, and behavioural responses were evaluated at 120 hpf. Exposure to 1 % EtOH caused an increase in the number of malformations, which were diminished by 24-EPI. In addition, EtOH induced an accumulation of GSSG and consequent reduction of GSH:GSSG ratio, indicating the involvement of oxidative mechanisms in the EtOH-induced effects. These were reverted by 24-EPI as proved by the GSSG levels and GSH:GSSG ratio that returned to control values. Furthermore, exposure to EtOH resulted in behavioural deficits at 120 hpf as observed by the disrupted response to an aversive stimulus, suggesting the involvement of neurotoxic mechanisms. 24-EPI restored the behavioural deficits observed in a dose-dependent manner. The absence of effects in the embryos exposed solely to 24-EPI showed its safety during the exposure period. In conclusion, EtOH caused developmental teratogenicity and behavioural toxicity by inducing glutathione changes, which were prevented by 24-EPI.

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.