Enriched environment prevents oxidative stress in zebrafish submitted to unpredictable chronic stress

Environmental enrichment improves behaviors rather than the growth and physiology of rock bream Oplegnathus fasciatus

Environmental enrichment has the potential to improve the welfare and post-release survival of hatchery fish stocked for conservation purposes. However, the effectiveness of environmental enrichment is partly dependent on the fish species, life stage, and specific enrichment structure used. To enhance the effectiveness of environmental enrichment, it is crucial to focus on characteristic differences in enrichment structures, such as type and level. This study investigated how differences in enrichment type and level affected physiological and behavioral aspects of the welfare of pre-release juvenile rock bream Oplegnathus fasciatus by evaluating growth performance, basal and stressed cortisol levels, antioxidant enzyme activities, and exploratory behaviors regarding anxiety and flexibility. Fish were reared for 4 weeks in different enrichment treatments: barren, low-level cover structure, high-level cover structure, low-level interference structure (LI), and high-level interference structure (HI). The results revealed that fish reared with the LI treatment showed less anxiety and greater flexibility with respect to exploratory behaviors, without oxidative damage being detected. Despite exhibiting less anxiety as well, fish reared in the HI treatment had oxidative damage, indicated by lower superoxide dismutase activity, compared to those in the barren treatment. In addition, none of these enrichment structures enhanced growth performance or mitigate chronic and acute stress responses. Overall, the low-level interference structure may be more favorable in promoting the behavioral welfare of the fish. Application of this type and level of enrichment may increase the survival of the hatchery fish after release, which is critical to stocking success.

A systematic review of the impact of environmental enrichment in zebrafish

Environmental enrichment (EE) consists of a series of interventions carried out in the home environment to promote greater exposure to sensory stimuli and mimic the natural habitat of laboratory-housed animals, providing environments closer to those found in nature. Some studies have shown the positive effects of EE in zebrafish housed in a laboratory environment. However, this evidence is still recent and accompanied by contradictory results. Furthermore, there is great variability in the protocols applied and in the conditions of the tests, tanks and materials used to generate an enriched environment. This substantial variability can bring many uncertainties to the development of future studies and hinder the reproducibility and replicability of research. Here, in this context, we carried out a systematic review of the literature, aiming to provide an overview of the EE protocols used in zebrafish research. The literature search was performed in PubMed, Scopus and Web of Science and the studies were selected on the basis of predefined inclusion/exclusion criteria. A total of 901 articles were identified in the databases, and 27 of those studies were included in this review. We conducted data extraction and risk-of-bias analysis in the included studies. Among these studies, the effect of EE was evaluated in two different ways: (1) for animal welfare and (2) as an intervention to prevent behavioral, biochemical, molecular, developmental and breeding dysfunctions. Although the EE protocols in zebrafish presented a series of experimental differences, the results showed that the benefits of the EE for zebrafish were consistent. According to the results described here, the use of EE in the zebrafish home tank improves welfare and may reduce sources of bias in scientific research. However, it is still necessary to develop standardized protocols to improve the application of EE in scientific studies using zebrafish.

Systematic review and meta-analysis of 10 years of unpredictable chronic stress in zebrafish

The zebrafish (Danio rerio) is a model animal that is being increasingly used in neuroscience research. A decade ago, the first study on unpredictable chronic stress (UCS) in zebrafish was published, inspired by protocols established for rodents in the early 1980s. Since then, several studies have been published by different groups, in some cases with conflicting results. Here we conducted a systematic review to identify studies evaluating the effects of UCS in zebrafish and meta-analytically synthetized the data of neurobehavioral outcomes and relevant biomarkers. Literature searches were performed in three databases (PubMed, Scopus and Web of Science) with a two-step screening process based on inclusion/exclusion criteria. The included studies underwent extraction of qualitative and quantitative data, as well as risk-of-bias assessment. Outcomes of included studies (n = 38) were grouped into anxiety/fear-related behavior, locomotor function, social behavior or cortisol level domains. UCS increased anxiety/fear-related behavior and cortisol levels while decreasing locomotor function, but a significant summary effect was not observed for social behavior. Despite including a substantial number of studies, the high heterogeneity and the methodological and reporting problems evidenced in the risk-of-bias analysis made it difficult to assess the internal validity of most studies and the overall validity of the model. Our review thus evidences the need to conduct well-designed experiments to better evaluate the effects of UCS on diverse behavioral patterns displayed by zebrafish.

Housing Conditions Affect Adult Zebrafish (Danio rerio) Behavior but Not Their Physiological Status

Zebrafish is a valuable model for neuroscience research, but the housing conditions to which it is exposed daily may be impairing its welfare status. The use of environmental enrichment and the refinement of methodology for cortisol measurement could reduce stress, improving its welfare and its suitability as an animal model used in stress research. Thus, this study aimed to evaluate (I) the influence of different housing conditions on zebrafish physiology and behavior, and (II) skin mucus potential for cortisol measurement in adult zebrafish. For this, AB zebrafish were raised under barren or enriched (PVC pipes and gravel image) environmental conditions. After 6 months, their behavior was assessed by different behavioral paradigms (shoaling, white-black box test, and novel tank). The physiological response was also evaluated through cortisol levels (whole-body homogenates and skin mucus) and brain oxidative stress markers. The results revealed that enriched-housed fish had an increased nearest neighbors' distance and reduced activity. However, no effect on body length or stress biomarkers was observed; whole-body and skin mucus cortisol levels had the same profile between groups. In conclusion, this study highlights the skin mucus potential as a matrix for cortisol quantification, and how housing conditions could influence the data in future studies.

Structural environmental enrichment and the way it is offered influence cognitive judgement bias and anxiety-like behaviours in zebrafish

Environmental enrichment in zebrafish generally reduces anxiety-related behaviours, improves learning in maze trials and increases health and biological fitness. However, certain types of enrichment or certain conditions induce the opposite effects. Therefore, it is essential to study the characteristics of environmental enrichment that modulate these effects. This study aims to investigate if structural environmental enrichment and the way it is offered influence cognitive judgement bias and anxiety-like behaviours in adult zebrafish. The fish were assigned to six housing manipulations: constant barren, constant enrichment, gradual gain of enrichment, gradual loss of enrichment, sudden gain of enrichment and sudden loss of enrichment. We then transposed the cognitive judgment bias paradigm, formerly used in studies on other animals to measure the link between emotion and cognition, to objectively assess the impact of these manipulations on the zebrafish's interpretation of ambiguous stimuli, considering previous experiences and related emotional states. We used two battery tests (light/dark and activity tests), which measured anxiety-related behaviours to check if these tests covariate with cognitive bias results. The fish with a sudden gain in enrichment showed a pessimistic bias (interpreted ambiguous stimuli as negative). In addition, the fish that experienced a sudden gain and a gradual loss in enrichment showed more anxiety-like behaviours than the fish that experienced constant conditions or a gradual gain in enrichment. The data provide some proof that structural environmental enrichment and the way it is presented can alter zebrafish's cognitive bias and anxiety-like behaviours.

Ochratoxin A induces locomotor impairment and oxidative imbalance in adult zebrafish

Ochratoxin A (OTA) is a mycotoxin produced by species of filamentous fungi widely found as a contaminant in food and with high toxic potential. Studies have shown that this toxin causes kidney and liver damage; however, data on the central nervous system effects of exposure to OTA are still scarce. Thus, this study aimed to investigate the effects of exposure to OTA on behavioral and neurochemical parameters in adult zebrafish. The animals were treated with different doses of OTA (1.38, 2.77, and 5.53 mg/kg) with intraperitoneal injections and submitted to behavioral evaluations in the open tank and social interaction tests. Subsequently, they were euthanized, and the brains were used to assess markers associated with oxidative status. In the open tank test, OTA altered distance traveled, absolute turn angle, mean speed, and freezing time. However, no significant effects were observed in the social interaction test. Moreover, OTA also increased glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GR) levels and decreased non-protein thiols (NPSH) levels in the zebrafish brain. This study showed that OTA can affect behavior and neurochemical levels in zebrafish.

Deferoxamine Supplementation Abolished Iron-Related Toxicity of Ilex paraguariensis Extract: Behavioral and Biochemical Evaluation in Adult Zebrafish (Danio rerio)

Ilex paraguariensis (Herb mate) is a native plant from South America, widely consumed through the infusion of dried leaves. The presence of antioxidant properties in herb mate may be relevant and contribute to evaluating the effect of its compounds against oxidative stress, which could cause neurodegenerative diseases. Despite having health benefits, there are reports of the presence of heavy metals in extracts obtained from the infusion. One of these metals is iron (Fe), found in large amounts in herb mate. To reverse the cumulative effects of metals and Fe in the body, the use of Deferoxamine (Dfx) is indicated, being a potent chelator of Fe. In this work, we aimed to evaluate the antioxidant potential of the micro-encapsulated extract of I. paraguariensis (MEIP) supplemented with Dfx on zebrafish behavior and biochemical biomarkers. To evaluate the effect per se and the supplementation, four groups were established: the first group was the control (water); the second, fish treated with MEIP; the third group was formed of fish treated with Dfx; while the fourth group was treated with both MEIP and Dfx. When applied alone, Dfx presents an anxiogenic-like pattern on zebrafish (Danio rerio), while the MEIP shows an anxiolytic-like behavior. The antioxidant enzymes are re-modulated close to control when the MEIP + Dfx is applied. The cholinergic system shows an activation of the signaling, as well as the heme radical group formation, which is not affected by the Dfx-chelating effect. Thus, the supplementation of MEIP with Dfx is important to transform this extract into one that is safer and healthier for human consumption.

Behavioral and cortisol analysis of the anti-stress effect of Polygonum minus (Huds) extracts in chronic unpredictable stress (CUS) zebrafish model

The World Health Organization (WHO) recorded approximately 350 million people worldwide have suffered from mental health disorders, such as depression, anxiety, schizophrenia, and addictive behaviors. The search for new drugs from nature has drawn on many biological resources and human practices. In this study, leaves of Polygonum minus standardized extract (Biokesum®), 1 and 100 mg/L were used to evaluate the anti-stress effect in the chronic unpredictable stress (CUS) zebrafish model. Five groups of zebrafish were manipulated in this study, comprising control, chronic unpredictable stress (CUS), CUS + Biokesum® 1 mg/L (4 days, 20 min/day, immersion) CUS + Biokesum® 100 mg/L (4 days, 20 min/day, immersion) and CUS + fluoxetine 0.6 mg/L (4 days, 20 min/day, immersion). Four different behavioral tests were used, i.e. open-field test, social interaction test, light and dark test, and exploratory test. After four consecutive days of treatment, the zebrafish were sacrificed for whole-body cortisol analysis. The exploratory test showed a significant change upon P. minus treatment (one-way ANOVA; p = 0.0011). Cortisol analysis showed a decrease of cortisol level after treatment with the extract and fluoxetine, without significant difference. These results showed that zebrafish is a reliable model to study the anti-stress effect of compounds or herbal extract.

Anti-stress effects of the glucagon-like peptide-1 receptor agonist liraglutide in zebrafish

Stress-related disorders are extremely harmful and cause significant impacts on the individual and society. Despite the limited evidence regarding glucagon-like peptide-1 receptor (GLP-1R) and mental disorders, a few clinical and preclinical studies suggest that modulating this system could improve symptoms of stress-related disorders. This study aimed to investigate the effects of liraglutide, a GLP-1R agonist, on neurobehavioral phenotypes and brain oxidative status in adult zebrafish. Acute liraglutide promoted anxiolytic-like effects in the light/dark test, while chronic treatment blocked the impact of unpredictable chronic stress on behavioral and physiological parameters. Taken together, our study demonstrates that liraglutide is active on the zebrafish brain and may counteract some of the effects induced by stress. More studies are warranted to further elucidate the potential of GLP-1R agonists for the management of brain disorders.

Different influences of anxiety models, environmental enrichment, standard conditions and intraspecies variation (sex, personality and strain) on stress and quality of life in adult and juvenile zebrafish: A systematic review

Antagonist and long-lasting environmental manipulations (EM) have successfully induced or reduced the stress responses and quality of life of zebrafish. For instance, environmental enrichment (EE) generally reduces anxiety-related behaviours and improves immunity, while unpredictable chronic stress (UCS) and aquarium-related stressors generate the opposite effects. However, there is an absence of consistency in outcomes for some EM, such as acute exposure to stressors, social enrichment and some items of structural enrichment. Therefore, considering intraspecies variation (sex, personality, and strain), increasing intervention complexity while improving standardisation of protocols and contemplating the possibility that EE may act as a mild stressor on a spectrum between too much (UCS) and too little (standard conditions) stress intensity or stimulation, would reduce the inconsistencies of these outcomes. It would also help explore the mechanism behind stress resilience and to standardise EM protocols. Thus, this review critically analyses and compares knowledge existing over the last decade concerning environmental manipulations for zebrafish and the influences that sex, strain, and personality may have on behavioural, physiological, and fitness-related responses.

How do zebrafish (Danio rerio) respond to MK-801 and amphetamine? Relevance for assessing schizophrenia-related endophenotypes in alternative model organisms

Schizophrenia pathophysiology has been associated with dopaminergic hyperactivity, NMDA receptor hypofunction, and redox dysregulation. Most behavioral assays and animal models to study this condition were developed in rodents, leaving room for species-specific biases that could be avoided by cross-species approaches. As MK-801 and amphetamine are largely used in mice and rats to mimic schizophrenia features, this study aimed to compare the effects of these drugs in several zebrafish (Danio rerio) behavioral assays. Male and female adult zebrafish were exposed to MK-801 (1, 5, and 10 μM) or amphetamine (0.625, 2.5, and 10 mg/L) and observed in paradigms of locomotor activity and social behavior. Oxidative parameters were quantified in brain tissue. Our results demonstrate that MK-801 disrupted social interaction, an effect that resembles the negative symptoms of schizophrenia. It also altered locomotion in a context-dependent manner, with hyperactivity when fish were tested in the presence of social cues and hypoactivity when tested alone. On the other hand, exposure to amphetamine was devoid of effects on locomotion and social behavior, while it increased lipid peroxidation in the brain. Key outcomes induced by MK-801 in rodents, such as social interaction deficit and locomotor alterations, were replicated in zebrafish, corroborating previous studies and reinforcing the use of zebrafish to study schizophrenia-related endophenotypes. More studies are necessary to assess the predictive validity of preclinical paradigms with this species and ultimately optimize the screening of potential novel treatments.

Physical enrichment research for captive fish: Time to focus on the DETAILS

Growing research effort has shown that physical enrichment (PE) can improve fish welfare and research validity. However, the inclusion of PE does not always result in positive effects and conflicting findings have highlighted the many nuances involved. Effects are known to depend on species and life stage tested, but effects may also vary with differences in the specific items used as enrichment between and within studies. Reporting fine-scale characteristics of items used as enrichment in studies may help to reveal these factors. We conducted a survey of PE-focused studies published in the last 5 years to examine the current state of methodological reporting. The survey results suggest that some aspects of enrichment are not adequately detailed. For example, the amount and dimensions of objects used as enrichment were frequently omitted. Similarly, the ecological relevance, or other justification, for enrichment items was frequently not made explicit. Focusing on ecologically relevant aspects of PE and increasing the level of detail reported in studies may benefit future work and we propose a framework with the acronym DETAILS (Dimensions, Ecological rationale, Timing of enrichment, Amount, Inputs, Lighting and Social environment). We outline the potential importance of each of the elements of this framework with the hope it may aid in the level of reporting and standardization across studies, ultimately aiding the search for more beneficial types of PE and the development of our understanding and ability to improve the welfare of captive fish and promote more biologically relevant behaviour.

Zebrafish as a tool in the study of sleep and memory-related disorders

Sleep is an evolutionarily conserved phenomenon, being an essential biological necessity for the learning process and memory consolidation. The brain displays two types of electrical activity during sleep: slow-wave activity or non-rapid eye movement (NREM) sleep and desynchronized brain wave activity or rapid eye movement (REM) sleep. There are many theories about "Why we need to sleep?" among them the synaptic homeostasis. This theory proposes that the role of sleep is the restoration of synaptic homeostasis, which is destabilized by synaptic strengthening triggered by learning during waking and by synaptogenesis during development. Sleep diminishes the plasticity load on neurons and other cells to normalize synaptic strength. In contrast, it re-establishes neuronal selectivity and the ability to learn, leading to the consolidation and integration of memories. The use of zebrafish as a tool to assess sleep and its disorders is growing, although sleep in this animal is not yet divided, for example, into REM and NREM states. However, zebrafish are known to have a regulated daytime circadian rhythm. Their sleep state is characterized by periods of inactivity accompanied by an increase in arousal threshold, preference for resting place, and the "rebound sleep effect" phenomenon, which causes an increased slow-wave activity after a forced waking period. In addition, drugs known to modulate sleep, such as melatonin, nootropics, and nicotine, have been tested in zebrafish. In this review, we discuss the use of zebrafish as a model to investigate sleep mechanisms and their regulation, demonstrating this species as a promising model for sleep research.

Enrichment for Laboratory Zebrafish-A Review of the Evidence and the Challenges

Simple Summary

The zebrafish is one of the most commonly used animals in scientific research, but there remains a lack of consensus over good practice for zebrafish housing and care. One such area which lacks agreement is whether laboratory zebrafish should be provided with environmental enrichment—additions or modifications to the basic laboratory environment which aim to improve welfare, such as plastic plants in tanks. The need for the provision of appropriate environmental enrichment has been recognised in other laboratory animal species, but some scientists and animal care staff are hesitant to provide enrichment for zebrafish, arguing that there is little or no evidence that enrichment can benefit zebrafish welfare. This review aims to summarise the current literature on the effects of enrichment on zebrafish physiology, behaviour and welfare, and identifies some forms of enrichment which are likely to benefit zebrafish. It also considers the possible challenges that might be associated with introducing more enrichment, and how these might be addressed.

Abstract

Good practice for the housing and care of laboratory zebrafish Danio rerio is an increasingly discussed topic, with focus on appropriate water quality parameters, stocking densities, feeding regimes, anaesthesia and analgesia practices, methods of humane killing, and more. One area of current attention is around the provision of environmental enrichment. Enrichment is accepted as an essential requirement for meeting the behavioural needs and improving the welfare of many laboratory animal species, but in general, provision for zebrafish is minimal. Some of those involved in the care and use of zebrafish suggest there is a ‘lack of evidence’ that enrichment has welfare benefits for this species, or cite a belief that zebrafish do not ‘need’ enrichment. Concerns are also sometimes raised around the practical challenges of providing enrichments, or that they may impact on the science being undertaken. However, there is a growing body of evidence suggesting that various forms of enrichment are preferred by zebrafish over a barren tank, and that enriched conditions can improve welfare by reducing stress and anxiety. This review explores the effects that enrichment can have on zebrafish behaviour, physiology and welfare, and considers the challenges to facilities of providing more enrichment for the zebrafish they house.

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.

The Influence of Behavioral, Social, and Environmental Factors on Reproducibility and Replicability in Aquatic Animal Models

The publication of reproducible, replicable, and translatable data in studies utilizing animal models is a scientific, practical, and ethical necessity. This requires careful planning and execution of experiments and accurate reporting of results. Recognition that numerous developmental, environmental, and test-related factors can affect experimental outcomes is essential for a quality study design. Factors commonly considered when designing studies utilizing aquatic animal species include strain, sex, or age of the animal; water quality; temperature; and acoustic and light conditions. However, in the aquatic environment, it is equally important to consider normal species behavior, group dynamics, stocking density, and environmental complexity, including tank design and structural enrichment. Here, we will outline normal species and social behavior of 2 commonly used aquatic species: zebrafish (Danio rerio) and Xenopus (X. laevis and X. tropicalis). We also provide examples as to how these behaviors and the complexity of the tank environment can influence research results and provide general recommendations to assist with improvement of reproducibility and replicability, particularly as it pertains to behavior and environmental complexity, when utilizing these popular aquatic models.

Non-pharmacological and pharmacological approaches for psychiatric disorders: Re-appraisal and insights from zebrafish models

Acute and chronic stressors are common triggers of human mental illnesses. Experimental animal models and their cross-species translation to humans are critical for understanding of the pathogenesis of stress-related psychiatric disorders. Mounting evidence suggests that both pharmacological and non-pharmacological approaches can be efficient in treating these disorders. Here, we analyze human, rodent and zebrafish (Danio rerio) data to compare the impact of non-pharmacological and pharmacological therapies of stress-related psychopathologies. Emphasizing the likely synergism and interplay between pharmacological and environmental factors in mitigating daily stress both clinically and in experimental models, we argue that environmental enrichment emerges as a promising complementary therapy for stress-induced disorders across taxa. We also call for a broader use of novel model organisms, such as zebrafish, to study such treatments and their potential interplay.

Protective Effects of Spirulina platensis, Voluntary Exercise and Environmental Interventions Against Adolescent Stress-Induced Anxiety and Depressive-Like Symptoms, Oxidative Stress and Alterations of BDNF and 5HT-3 Receptors of the Prefrontal Cortex in Female Rats

BACKGROUND AND PURPOSE

Ample evidence indicates that chronic adolescence stress is associated with an increased risk of developing neuropsychiatric disorders in adulthood. Given the importance of the effective therapeutic ways to overcome adolescent stress-related deficits, the present study investigated the effects of Spirulina platensis (SP), environmental enrichment (EE), and voluntary exercise (EX) and their combination on anxiety or depression-like behaviors, oxidative stress, and alterations of BDNF and 5HT-3 receptors in the prefrontal cortex (PFC) induced by adolescent stress in adult female rats.

METHODS

During the adolescent period (PNDs30-40), rats were subjected to restraint stress. Then, the animals were subjected to SP treatment (200 mg/kg/day), EX, EE, and the combined treatments (SP+EX, and SP+EE) for 15 days between PNDs41-55. Subsequently, anxiety or depression-like behaviors, BDNF levels, oxidative stress markers and mRNA expression of BDNF and 5HT₃ in the PFC were assessed.

RESULTS

Stressed rats demonstrated enhanced anxiety levels and depression-like behaviors in adulthood. Regarding the oxidative stress markers, stressed rats exhibited significantly higher levels of malondialdehyde, a lipid peroxidation product, higher activities of antioxidant enzymes (glutathione peroxidase and superoxide dismutase) and significantly lower total antioxidant reactivity capacity in the PFC. Additionally, adolescent stress significantly increased 5HT3 receptor mRNA expression and decreased BDNF content and its mRNA expression in the PFC. Treatments with SP, EX, EE, and the combined interventions alleviated these deficits.

CONCLUSION

Our findings indicate that appropriate interventions during the adolescent period can protect against adolescent stress-induced behavioral, and biochemical defects and oxidative stress damage in adulthood.

Effects of N-acetylcysteine amide on anxiety and stress behavior in zebrafish

Anxiety disorders are highly prevalent and a leading cause of disability worldwide. Their etiology is related to stress, an adaptive response of the organism to restore homeostasis, in which oxidative stress and glutamatergic hyperactivity are involved. N-Acetylcysteine (NAC) is a multitarget approved drug proved to be beneficial in the treatment of various mental disorders. Nevertheless, NAC has low membrane permeability and poor bioavailability and its limited delivery to the brain may explain inconsistencies in the literature. N-Acetylcysteine amide (AD4) is a synthetic derivative of NAC in which the carboxyl group was modified to an amide. The amidation of AD4 improved lipophilicity and blood-brain barrier permeability and enhanced its antioxidant properties. The purpose of this study was to investigate the effects of AD4 on behavioral and biochemical parameters in zebrafish anxiety models. Neither AD4 nor NAC induced effects on locomotion and anxiety-related parameters in the novel tank test. However, in the light/dark test, AD4 (0.001 mg/L) increased the time spent in the lit side in a concentration 100 times lower than NAC (0.1 mg/L). In the acute restraint stress protocol, NAC and AD4 (0.001 mg/L) showed anxiolytic properties without meaningful effects on oxidative status. The study suggests that AD4 has anxiolytic effects in zebrafish with higher potency than the parent compound. Additional studies are warranted to characterize the anxiolytic profile of AD4 and its potential in the management of anxiety disorders.

Propiconazole induces abnormal behavior and oxidative stress in zebrafish

The use of pesticides has been growing along with the demand for agricultural products. These compounds, however, are not restricted to the field, spreading easily through the soil, contaminating groundwater and reaching urban centers. Propiconazole is a triazole fungicide that has been increasingly used in agriculture. However, there are few data about its effects on non-target organisms. This study aimed to evaluate the effects of propiconazole in zebrafish. The animals were exposed for 96 h to different concentrations of propiconazole (425, 850, 1700, 8500 ng/L), then submitted to the novel tank test for behavioral analyses. The brains were collected for evaluation of oxidative stress parameters. Exposure to propiconazole (1700 and 8500 ng/L) decreased the number of crossings, entries, and time spent in the top, and increased the time spent in the bottom area of the tank. We also observed an increase in the activities of superoxide dismutase and catalase in zebrafish brain exposed to propiconazole at 425, 850, and 1700 ng/L. We conclude that propiconazole alters normal fish behavior and disrupts oxidative status. More studies are necessary to elucidate the exact mechanism underlying the effects of propiconazole on non-target-organisms.

Withdrawal effects following repeated ethanol exposure are prevented by N-acetylcysteine in zebrafish

Alcohol abuse is a highly prevalent condition that substantially contributes to global morbidity and mortality. Most available pharmacological treatments offer little efficacy as relapse rates are high, due in part to the symptoms experienced during abstinence. The roles of oxidative stress and glutamatergic transmission in alcohol withdrawal have been demonstrated in several studies, suggesting that restoration of oxidative status and glutamatergic function may represent a new pharmacological target to prevent the behavioral and biochemical alterations observed during withdrawal. A well-known antioxidant and glutamatergic modulator, N-acetylcysteine (NAC), has shown promise in treating a variety of psychiatric conditions, including substance use disorders, and is a promising molecule in the management of alcohol withdrawal syndrome. Thus, the aim of this study was to investigate whether NAC is able to prevent the expression of behavioral and biochemical alterations induced by ethanol withdrawal in chronically exposed zebrafish. Animals were exposed to ethanol (1% v/v, 20 min) or control water, followed by treatment with NAC (1 mg/L, 10 min) or control water daily for 8 days; 24 h later, experimental animals were submitted to the novel tank test (NTT). Ethanol withdrawal decreased the distance traveled and increased the number of immobile episodes, indicating locomotor deficits; moreover, withdrawal decreased the number of entries and time spent in the top area, while increasing time spent in the bottom area, indicating anxiety-like behavior. Alcohol withdrawal also increased lipid peroxidation (TBARS) and decreased non-protein reduced sulfhydryl (NPSH) and superoxide dismutase (SOD) and catalase (CAT) activities. NAC attenuated these locomotor deficits and prevented the manifestation of anxiety-like behavior as well as the oxidative damage observed following ethanol withdrawal. Given its favorable safety profile, additional clinical and preclinical studies are warranted to unravel the long-term effects of NAC in the context of alcohol abuse and the exact mechanisms involved. Nevertheless, our study adds to the existing body of evidence supporting the clinical evaluation of NAC in substance abuse disorders.

Acetyl-L-carnitine as a putative candidate for the treatment of stress-related psychiatric disorders: Novel evidence from a zebrafish model

Stress-related psychiatric disorders are mental conditions that affect mood, cognition and behavior and arise because of the impact of prolonged stress on the central nervous system (CNS). Acetyl-L-carnitine (ALC) is an acetyl ester of L-carnitine that easily crosses the blood-brain barrier and was recently found to be decreased in patients with major depressive disorder. ALC plays a role in energy metabolism and is widely consumed as a nutritional supplement to improve physical performance. In this study, our objective was to evaluate the effects of ALC treatment (0.1 mg/L, 10 min) for 7 days on behavior and oxidative stress in zebrafish subjected to unpredictable chronic stress (UCS) protocol. Behavioral outcomes were assessed in the novel tank test, and parameters of oxidative status (lipid peroxidation and antioxidant defenses) were evaluated in the brain using colorimetric methods. According to our previous findings, UCS increased anxiety-like behavior and lipid peroxidation, while it decreased non-protein thiol levels and superoxide dismutase activity. However, ALC reversed the anxiety-like behavior and oxidative damage in stressed animals, while it was devoid of effect in control animals. Although our data reinforce the neuroprotective potential of ALC in the treatment of psychiatric disorders related to stress, further investigations are required to clarify its mechanisms of action and confirm its efficacy.