Age-dependent effects of embryonic ethanol exposure on anxiety-like behaviours in young zebrafish: A genotype comparison study

An overview of current advances in perinatal alcohol exposure and pathogenesis of fetal alcohol spectrum disorders

The adverse use of alcohol is a serious global public health problem. Maternal alcohol consumption during pregnancy usually causes prenatal alcohol exposure (PAE) in the developing fetus, leading to a spectrum of disorders known as fetal alcohol spectrum disorders (FASD) and even fetal alcohol syndrome (FAS) throughout the lifelong sufferers. The prevalence of FASD is approximately 7.7 per 1,000 worldwide, and is even higher in developed regions. Generally, Ethanol in alcoholic beverages can impair embryonic neurological development through multiple pathways leading to FASD. Among them, the leading mechanism of FASDs is attributed to ethanol-induced neuroinflammatory damage to the central nervous system (CNS). Although the underlying molecular mechanisms remain unclear, the remaining multiple pathological mechanisms is likely due to the neurotoxic damage of ethanol and the resultant neuronal loss. Regardless of the molecular pathway, the ultimate outcome of the developing CNS exposed to ethanol is almost always the destruction and apoptosis of neurons, which leads to the reduction of neurons and further the development of FASD. In this review, we systematically summarize the current research progress on the pathogenesis of FASD, which hopefully provides new insights into differential early diagnosis, treatment and prevention for patents with FASD.

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.

Assessing Chronodisruption Distress in Goldfish: The Importance of Multimodal Approaches

Chronodisruption caused by factors such as light at night and mistimed meals has been linked to numerous physiological alterations in vertebrates and may be an anxiogenic factor affecting welfare. This study aims to investigate whether chronodisruption causes measurable changes in the anxiety responses of goldfish under two conditions: randomly scheduled feeding (RF) and continuous light (LL). Anxiety-like behavior was assessed in the open field with object approach and black/white preference tests, which had been validated using diazepam. An increased thigmotaxis response and decreased object exploration under both chronodisruption protocols indicated anxiety states. Furthermore, locomotor activity was increased in LL fish. The black/white preference test discriminated anxiolysis induced by diazepam but was unable to detect anxiety caused by chronodisruption. Plasma cortisol increased in both RF and LL fish throughout the experiment, confirming that both conditions caused stress. The LL fish also showed an apparently desensitized hypothalamus-pituitary-interrenal HPI axis, with a decrease in pomc and crf expression. Individual analysis found no correlation between anxiety-like behavior and stress axis activation nor between scototaxis and thigmotaxis responses. However, individual differences in sensitivity to each test were detected. Altogether, these results highlight circadian disruption as a stressor for fish and endorse a multiple variable approach for reliably assessing animal discomfort.

The effect of fish density and tank size on the behavior of adult zebrafish: A systematic analysis

The zebrafish has been employed in several fields of biology due to its translational relevance and its simplicity and ease of maintenance. As a result, zebrafish are kept in thousands of laboratories around the world. Current industry standards favor keeping the largest possible number of fish in the smallest possible volume of water to increase efficiency and reduce costs. However, physiological and psychological stress resulting from such crowding may impact a variety of phenotypes, from brain function and behavior to cardiovascular function and cancer. Nevertheless, surprisingly little is known about what constitutes an optimal housing environment for the zebrafish, e.g., no systematic analyses have been performed to test the role of housing density and tank volume despite recent sporadic reports implying negative effects of the standard practice of crowding. Here, we conduct the first proof of concept analysis examining the potential impact of housing density and tank volume on the behavior of zebrafish. We randomly assigned adult zebrafish to one of three tank sizes (1.5, 10, or 50 L) with one of three housing densities (1, 2, or 4 fish/L), a 3 × 3 between subject experimental design, and maintained the fish in their corresponding condition for 2 weeks. Subsequently, we tested the behavior of the fish singly in a novel open tank for 12 min and quantified several of their swim path parameters using a video-tracking system. We found significant additive and interacting effects of tank size and/or housing density on swim path parameters including immobility, swim speed, turn angle, and distance to bottom and to stimulus. Although we had only three fish densities and three tank sizes and we did not explore the effects of more extreme conditions and although the interpretation of the above behavioral effects is speculative at this point, the results already demonstrate that both tank size and housing density exerts significant effects on the zebrafish and thus should be considered in zebrafish husbandry.

Cyclophosphamide alters the behaviors of adult Zebrafish via neurotransmitters and gut microbiota

Cyclophosphamide, one of the earliest prescribed alkylating anticancer drugs, has been frequently detected in aquatic environments. However, its effects on fish behavior and associated mechanisms remain largely unknown. In this study, the behaviors, neurochemicals, and gut microbiota of adult zebrafish were investigated after 2 months of exposure to CP at 0.05, 0.5, 5, and 50 µg/L. Behavioral assays revealed that CP increased locomotion and anxiety, and decreased the cognition of zebrafish. The alteration of neurotransmitters and related gene expressions in the dopamine and gamma-aminobutyric acid pathways induced by CP may be responsible for the observed changes in locomotion and cognition of adult zebrafish. Meanwhile, CP increased the anxiety of adult zebrafish through the serotonin, acetylcholine, and histamine pathways in the brain. In addition, increased abundances of Fusobacteriales, Reyanellales, Staphylococcales, Rhodobacterals, and Patescibateria in the intestine at the CP-50 treatment were observed. The study has demonstrated that CP affects the locomotion, anxiety, and cognition in zebrafish, which might be linked with the dysfunction of neurochemicals in the brain. This study further suggests that the gut-brain axis might interact to modulate fish behaviors upon exposure to CP (maybe other organic pollutants). Further research is warranted to test this hypothesis.