Acute net stress of young adult zebrafish (Danio rerio) is not sufficient to increase anxiety-like behavior and whole-body cortisol

Acute clomipramine exposure elicits dose-dependent surfacing behavior in adult zebrafish (Danio rerio)

Chronic treatment with clomipramine, a tricyclic antidepressant drug, reduces symptoms of obsessive-compulsive disorder (OCD) and can influence the activity of the hypothalamic-pituitary-adrenal axis. However, little is known regarding the effects of acute clomipramine on the immediate expression of stress responses. Serotonergic drugs can elicit surfacing, a behavioral profile potentially related to toxicity in fish, although surfacing has not yet been observed after clomipramine exposure. The present study investigated the impact of acute exposure to clomipramine on basal and stress-induced behaviors in the novel tank test and cortisol levels in mixed-sex, wild-type, adult zebrafish (Danio rerio). The findings show clomipramine-exposed groups (regardless of stress exposure) spent much more time in the top of the novel tank and had significantly less overall motor activity in the behavioral task compared to the fish not exposed to the drug. Then, the dose-dependent effects of acute clomipramine on activity in the surface of the novel tank (top third of the top half) were investigated further. Clomipramine dose-dependently increased surface-dwelling and elicited a dose-dependent hypoactivity in overall motor behavior. There were no statistically significant differences in whole-body cortisol levels in either experiment. Like other serotonin-acting drugs, clomipramine strongly elicited surface-dwelling and depressed motor behavior in adult zebrafish. Additional testing is needed to elucidate whether surfacing represents a toxic state and how serotonin regulates surfacing.

Methamphetamine effects in zebrafish (Danio rerio) depend on behavioral endpoint, dose and test session duration

Research using zebrafish (Danio rerio) has begun to provide novel information in many fields, including the behavioral pharmacology of drug use and misuse. There have been limited studies on the effects of methamphetamine in adult zebrafish and the parameters of exposure (dose, test session length) have not been well-documented. Behavior following drug exposure is generally measured during relatively short sessions (6-10 min is common) in a novel tank environment. Many procedural variables (isolation, netting, novel tank) elicit anxiety-like behavior that is most apparent during the initial portion of a test session. This anxiety-like behavior might mask the initial effects of methamphetamine. During longer test sessions, these anxiety-like responses would be expected to habituate and drug effects should become more apparent. To test this idea, we measured several locomotor activity responses for 50-min following a range of methamphetamine doses (0.1-3.0 mg/L via immersion in methamphetamine solution). Methamphetamine failed to alter swimming velocity, distance travelled, or freezing time. In contrast, methamphetamine produced a dose-dependent decrease in time spent in the bottom of the tank, an increase in the number of visits to the top of the tank, and an increase in the number of transitions along the sides of the tank. The effects of methamphetamine were apparent 10-20 min following exposure and generally persisted throughout the session. These findings indicate that longer test sessions are required to measure methamphetamine-induced changes in behavior in zebrafish, as has been shown in other laboratory animals. The results also suggest that anxiety-like responses associated with various procedural aspects (netting, isolation, novel test apparatus) likely interfere with the ability to observe many behavioral effects of methamphetamine in zebrafish. Based on the current results, habituation to testing procedures to reduce anxiety-like behaviors is recommended in determining the effects of methamphetamine in zebrafish.

Low toxicity of magnetite-based modified bionanocomposites with potential application for wastewater treatment: Evaluation in a zebrafish animal model

In recent years, the escalating concerns surrounding environmental pollution and the need for sustainable wastewater treatment solutions have underscored the significance of developing technologies that can efficiently treat wastewater while also reducing negative ecological effects. In this context, our study aims to contribute to the advancement of sustainable technologies for wastewater treatment, by investigating the effects that bare magnetite nanoparticles and those functionalized with the enzyme laccase could have in an aquatic animal, zebrafish, at various life cycle stages. Exposure to magnetite nanoparticles shows some effects on embryo hatching, survival rates, or larval behavior at higher concentrations. For both treatments, the hatching percentages were close to 80% compared to 93% for the control group. At the end of the observations in larvae, survival in all the evaluated groups was higher than 90%. Additionally, we evaluated the accumulation of nanoparticles in various stages of zebrafish. We found that, although there was accumulation during embryonic stages, it did not affect normal development or subsequent hatching. Iron levels in different organs such as gills, muscles, gastrointestinal tract, and brain were also evaluated in adults. Animals treated with a mix of food and nanoparticles at 10 μg/mL (Food group) presented a higher concentration of iron accumulation in muscle, gastrointestinal tract, and gills compared to the untreated control group. Although iron levels increased depending on the dose and exposure method applied, they were not statistically significant from the control groups. Our findings suggest that bionanocomposites evaluated here can be considered safe for removal of contaminants in wastewater without toxic effects or detrimental accumulation fish's health.

Extinction and reinstatement of methamphetamine-induced conditioned place preference in zebrafish

Conditioned place preference (CPP) paradigm in zebrafish has been used to measure drug reward, but there is limited research on CPP reinstatement to determine relapse vulnerability. The present study aimed to investigate extinction and reinstatement of methamphetamine (MA)-induced CPP in zebrafish and evaluate the model's predictive validity. Zebrafish received different doses of MA (0-60 mg/kg) during CPP training. The preferred dose of MA at 40 mg/kg was used for extinction via either confined or nonconfined procedures. The extinguished CPP was reinstated by administering a priming dose of MA (20 mg/kg) or various stressors. To assess persistent susceptibility to reinstatement, MA CPP and reinstatement were retested following 14 days of abstinence. In addition, the effects of SCH23390, naltrexone, and clonidine on MA CPP during acquisition, expression, or reinstatement phases were monitored. MA induced CPP in a dose-dependent manner. Both nonconfined and confined extinction procedures time-dependently reduced the time spent on the MA-paired side. A priming dose of MA, chasing stress, or yohimbine reinstated the extinguished CPP. After 14 days of abstinence, the MA CPP remained extinguished and was significantly reinstated by MA priming or chasing stress. Similar to the observations in rodents, SCH23390 suppressed the acquisition of MA CPP, naltrexone reduced the expression and MA priming-induced reinstatement, while clonidine prevented stress-induced reinstatement of MA CPP. This work expanded the zebrafish CPP paradigm to include extinction and reinstatement phases, demonstrating predictive validity and highlighting its potential as a valuable tool for exploring drug relapse.

Baicalein prevents stress-induced anxiety behaviors in zebrafish model

Baicalein is a flavonoid mainly obtained from plants with wide range of biological activities, including neuroprotection. An acute and unexpected chronic stress (UCS) protocol has recently been adapted to zebrafish, a popular vertebrate model in brain research. The present study was aimed to evaluate baicalein's anti-anxiety potential in a zebrafish model by induction, which included neuropharmacological evaluation to determine behavioural parameters in the novel tank diving test (NTDT) and light-dark preference test (LDPT). The toxicity was also assessed using the brine shrimp lethality assay, and the 50% lethal concentration (LC50) was determined. The animals were then stressed for 7 days before being treated with different doses of baicalein (1 and 2 mg/L) for another 7 days in UCS condition. Due to acute stress and UCS, the frequency of entries and time spent in the 1) top region and 2) light area of the novel tank reduced significantly, indicating the existence of elevated anxiety levels. The biological activity of baicalein was demonstrated by its high LC50 values (1,000 μg/ml). Additionally, baicalein administration increased the frequency of entries and duration spent in the light region, indicating a significant decrease in anxiety levels. Overall, the present results showed that baicalein has a therapeutic advantage in reversing the detrimental consequences of UCS and acute stress, making it is a promising lead molecule for new drug design, development, and therapy for stress.

Revealing the Increased Stress Response Behavior through Transcriptomic Analysis of Adult Zebrafish Brain after Chronic Low to Moderate Dose Rates of Ionizing Radiation

Simple Summary

The increasing use of radiopharmaceuticals for medical diagnostics and radiotherapy raises concerns regarding health risks for both humans and the environment. Additionally, in the context of major nuclear accidents like in Chernobyl and Fukushima, very little is known about the effects of chronic exposure to low and moderate dose rates of ionizing radiation (IR). Many studies demonstrated the sensibility of the developmental brain, but little data exists for IR at low dose rates and their impact on adults. In this study, we characterized the molecular mechanisms that orchestrate stress behavior caused by chronic exposure to low to moderate dose rates of IR using the adult zebrafish model. We observed the establishment of a congruent stress response at both the molecular and individual levels.

Abstract

High levels of ionizing radiation (IR) are known to induce neurogenesis defects with harmful consequences on brain morphogenesis and cognitive functions, but the effects of chronic low to moderate dose rates of IR remain largely unknown. In this study, we aim at defining the main molecular pathways impacted by IR and how these effects can translate to higher organizational levels such as behavior. Adult zebrafish were exposed to gamma radiation for 36 days at 0.05 mGy/h, 0.5 mGy/h and 5 mGy/h. RNA sequencing was performed on the telencephalon and completed by RNA in situ hybridization that confirmed the upregulation of oxytocin and cone rod homeobox in the parvocellular preoptic nucleus. A dose rate-dependent increase in differentially expressed genes (DEG) was observed with 27 DEG at 0.05 mGy/h, 200 DEG at 0.5 mGy/h and 530 DEG at 5 mGy/h. Genes involved in neurotransmission, neurohormones and hypothalamic-pituitary-interrenal axis functions were specifically affected, strongly suggesting their involvement in the stress response behavior observed after exposure to dose rates superior or equal to 0.5 mGy/h. At the individual scale, hypolocomotion, increased freezing and social stress were detected. Together, these data highlight the intricate interaction between neurohormones (and particularly oxytocin), neurotransmission and neurogenesis in response to chronic exposure to IR and the establishment of anxiety-like behavior.

Analysis of neuroendocrine factors in response to conditional stress in zebrafish Danio rerio (Cypriniformes: Cyprinidae)

Challenges in the aquatic environment disrupt the homeostasis mechanisms of many teleost fishes. Induction of stress affects the circulating levels of catecholamine and has an impact on development and reproduction. It is not known how osmotic and hypoxic stress could affect the catecholamine and serotonin levels in zebrafish despite its well-known action in the vertebrate brain. This study thus investigates how serotonin (5-HT), epinephrine (E), norepinephrine (NE), and dopamine (DA) in the brain of female zebrafish respond to hypoxic (air) and osmotic conditions (salinity of 10 ppt). Analysis of zebrafish brain utilizing HPLC with PDA detector using reverse-phase PrimeSep column indicated that osmotic stress, air response and its combination modified 5-HT, NE and E levels. The tested stressors elevated 5-HT (>2.8 μM) while lowering NE (<3.00 μM) and E (<1.02 μM) levels in the brain as opposed to exposure to non-stressed fish. In addition, reproductive markers such as vitellogenin (Vtg1) and estrogen receptor (ERα) mRNA expression in the brain were up-regulated after osmotic stress, whereas air exposure down-regulated ERα mRNA expression but up-regulated Vtg1 compared to non-stressed fish. Overall, the data indicate that acute osmotic stress and air exposure that lowered catecholamine E and NE and elevated 5-HT levels could up-regulate mRNA expression of ERα and Vtg1 genes in the zebrafish brain, thus presenting evidence for a role of neurotransmitters on reproductive signals during acute conditional stress in the brain of wild zebrafish.

Understanding how stress responses and stress-related behaviors have evolved in zebrafish and mammals

Stress response is essential for the organism to quickly restore physiological homeostasis disturbed by various environmental insults. In addition to well-established physiological cascades, stress also evokes various brain and behavioral responses. Aquatic animal models, including the zebrafish (Danio rerio), have been extensively used to probe pathobiological mechanisms of stress and stress-related brain disorders. Here, we critically discuss the use of zebrafish models for studying mechanisms of stress and modeling its disorders experimentally, with a particular cross-taxon focus on the potential evolution of stress responses from zebrafish to rodents and humans, as well as its translational implications.

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.

Exposure to aluminium causes behavioural alterations and oxidative stress in the brain of adult zebrafish

Aluminium (Al) water pollution is an increasing environmental problem. Accordingly, this study aimed to find out more about its toxic effects on aquatic organisms. Adult zebrafish were exposed to 11 mg/L of Al and the behavioural responses and its correlation with brain oxidative stress, antioxidant-defences, changes in metabolism and neurotransmission were assessed at 10, 15 and 20 days of exposure. The behavioural and locomotory responses, suggest an increase in the anxiety state, especially observed in animals exposed to Al for 15 days. The reactive oxygen species increased in a time-dependent trend, while the oxidative damage varied over exposure time. The activity of antioxidant enzymes, as superoxide dismutase, glutathione peroxidase and glutathione S-transferases, and the metallothioneins levels increased after short-term exposures and tended to decrease or stabilize at longer times. The results contribute to understand the toxic mechanisms activated by Al highlighting correlations like behavioural disorders and oxidative state.

The effects of two stressors on working memory and cognitive flexibility in zebrafish (Danio rerio): The protective role of D1/D5 agonist on stress responses

Acute stressors are recurrent in multiple species' lives and can facilitate or impair cognition. The use of zebrafish (Danio rerio) as a translational species to understand the mechanisms by which stress induces different behavioral phenotypes has been widely studied. Two acute stressors are recognized when using this species: (1) conspecific alarm substance (CAS); and (2) net chasing. Here, we tested if CAS or net chasing would affect working memory and cognitive flexibility by testing performance in the FMP Y-maze after exposure to stress. We observed that CAS altered zebrafish behavioral phenotypes by increasing repetitive behavior; meanwhile, animals showed different patterns of repetitive behavior when exposed to net chasing, depending on the chasing direction. Because D1 receptors were previously studied as a potential mechanism underlying stress responses in different species, here, we pretreated fish with a D1/D5 agonist (SKF-38393) to assess whether this system plays a role in repetitive behavior in the FMP Y-maze. The pretreatment with D1/D5 agonist significantly decreased repetitive behavior in CAS exposed animals, and cortisol levels for both stressed groups, suggesting that the dopaminergic system plays an important role in zebrafish stress-related responses.

Effects of polystyrene nanoplastics on Ctenopharyngodon idella (grass carp) after individual and combined exposure with zinc oxide nanoparticles

The toxicity of polystyrene nanoparticles (PS NPs) and ZnO nanoparticles (ZnO NPs), in combination is poorly known. Thus, the aim of the current study was to evaluate the effects of PS NPs (760 μg/L) on Ctenopharyngodon idella exposed to it, both in separate and in combination with ZnO NPs (760 μg/L), based on behavioral, biochemical and genotoxic biomarkers. Current data have indicated that PS NPs, for a short exposure period (3 days), both in separate and in combination with nanoparticles, have affected animals' response to the mirror test. On the other hand, all treatments have equally induced C. idella inactivity towards alarm substances and DNA damage. There was increased oxidative stress, mainly in groups exposed to PS NPs (in combination, or not, with nanoparticles); although increased, the evaluated antioxidant levels did not appear to be enough to inhibit the effects of treatment-induced production of free radicals. Together, these results are likely co-responsible for the observed changes. The current study did not observe antagonistic, synergistic or additive effect on animals exposed to the combination between PS NPs and ZnO NPs; however, this outcome should not discourage the performance of similar studies focused on assessing the (eco)toxicity of pollutant mixtures comprising nanomaterials.

Understanding neurobehavioral effects of acute and chronic stress in zebrafish

Stress is a common cause of neuropsychiatric disorders, evoking multiple behavioral, endocrine and neuro-immune deficits. Animal models have been extensively used to understand the mechanisms of stress-related disorders and to develop novel strategies for their treatment. Complementing rodent and clinical studies, the zebrafish (Danio rerio) is one of the most important model organisms in biomedicine. Rapidly becoming a popular model species in stress neuroscience research, zebrafish are highly sensitive to both acute and chronic stress, and show robust, well-defined behavioral and physiological stress responses. Here, we critically evaluate the utility of zebrafish-based models for studying acute and chronic stress-related CNS pathogenesis, assess the advantages and limitations of these aquatic models, and emphasize their relevance for the development of novel anti-stress therapies. Overall, the zebrafish emerges as a powerful and sensitive model organism for stress research. Although these fish generally display evolutionarily conserved behavioral and physiological responses to stress, zebrafish-specific aspects of neurogenesis, neuroprotection and neuro-immune responses may be particularly interesting to explore further, as they may offer additional insights into stress pathogenesis that complement (rather than merely replicate) rodent findings. Compared to mammals, zebrafish models are also characterized by increased availability of gene-editing tools and higher throughput of drug screening, thus being able to uniquely empower translational research of genetic determinants of stress and resilience, as well as to foster innovative CNS drug discovery and the development of novel anti-stress therapies.

Early Mistreatment Contributes to Social Behavior Disorders in Zebrafish

Adverse experiences during childhood have been the focus of a series of studies due to the psychological damage observed in individuals who suffered abuse during their youth. Studies with model animals that can mimic these observations can significantly contribute to understanding the mechanisms behind this phenomenon. In our experiments, young zebrafish (20 dpf) were exposed to aggressive alcoholized male adults for 30 min for 10 days. At 30 dpf, the animals were tested for shoal formation, and at 60 dpf, locomotion and aggression were evaluated. Animals that suffered oppression from adults showed greater group cohesion and lower attack emission and higher distance from the image in the mirror test. Locomotor parameters were not changed. These results show that the stress caused by aggression exposure in the juvenile phase led to increased fear and avoidance behavior later in life. Moreover, we confirm the importance of the zebrafish as a sensitive tool for studies on the effects of early mistreatment and its consequences to adult behavior.

Progressive impairment of learning and memory in adult zebrafish treated by Al2O3 nanoparticles when in embryos

Al₂O₃ Nanoparticles (Al₂O₃-NPs) have been widely used because of their unique physical and chemical properties, and Al₂O₃-NPs can be released into the environment directly or indirectly. Our previous research found that 13 nm Al₂O₃-NPs can induce neural cell death and autophagy in primarily cultured neural cells in vitro. The aim of this study was to determine where Al₂O₃-NPs at 13 nm particle size can cause neural cells in vivo and assess related behavioural changes and involved potential mechanisms. Zebrafish from embryo to adult were selected as animal models. Learning and memory as functional indicators of neural cells in zebrafish were measured during the development from embryo to adult. Our results indicate that Al₂O₃-NPs treatment in zebrafish embryos stages can cause the accumulation of aluminium content in zebrafish brain tissue, leading to progressive impaired neurodevelopmental behaviours and latent learning and memory performance. Additionally, oxidative stress and disruption of dopaminergic transmission in zebrafish brain tissues are correlated with the dose-dependent and age-dependent accumulation of aluminium content. Moreover, the number of neural cells in the telencephalon tissue treated with Al₂O₃-NPs significantly declined, and the ultramicroscopic morphology indicated profound autophagy alternations. The results suggest that Al₂O₃-NPs has dose-dependent and time-dependent progressive damage on learning and memory performance in adult zebrafish when treated in embryos. This is the first study of the effects of Al₂O₃-NPs on learning and memory during the development of zebrafish from embryo to adult.

The zebrafish tail immobilization (ZTI) test as a new tool to assess stress-related behavior and a potential screen for drugs affecting despair-like states

BACKGROUND

Affective disorders, especially depression and anxiety, are highly prevalent, debilitating mental illnesses. Animal experimental models are a valuable tool in translational affective neuroscience research. A hallmark phenotype of clinical and experimental depression, the learned helplessness, has become a key target for 'behavioral despair'-based animal models of depression. The zebrafish (Danio rerio) has recently emerged as a promising novel organism for affective disease modeling and CNS drug screening. Despite being widely used to assess stress and anxiety-like behaviors, there are presently no clear-cut despair-like models in zebrafish.

NEW METHOD

Here, we introduce a novel behavioral paradigm, the zebrafish tail immobilization (ZTI) test, as a potential tool to assess zebrafish despair-like behavior. Conceptually similar to rodent 'despair' models, the ZTI protocol involves immobilizing the caudal half of the fish body for 5 min, leaving the cranial part to move freely, suspended vertically in a small beaker with water.

RESULTS

To validate this model, we used exposure to low-voltage electric shock, alarm pheromone, selected antidepressants (sertraline and amitriptyline) and an anxiolytic drug benzodiazepine (phenazepam), assessing the number of mobility episodes, time spent 'moving', total distance moved and other activity measures of the cranial part of the body, using video-tracking. Both electric shock and alarm pheromone decreased zebrafish activity in this test, antidepressants increased it, and phenazepam was inactive. Furthermore, a 5-min ZTI exposure increased serotonin turnover, elevating the 5-hydroxyindoleacetic acid/serotonin ratio in zebrafish brain, while electric shock prior to ZTI elevated both this and the 3,4-dihydroxyphenylacetic acid/dopamine ratios. In contrast, preexposure to antidepressants sertraline and amitriptyline lowered both ratios, compared to the ZTI test-exposed fish.

COMPARISON WITH EXISTINGMETHOD(S)

The ZTI test is the first despair-like experimental model in zebrafish.

CONCLUSIONS

Collectively, this study suggests the ZTI test as a potentially useful protocol to assess stress-/despair-related behaviors, potentially relevant to CNS drug screening and behavioral phenotyping of zebrafish.

Effects of chronic prazosin, an alpha-1 adrenergic antagonist, on anxiety-like behavior and cortisol levels in a chronic unpredictable stress model in zebrafish (Danio rerio)

Post-traumatic stress disorder (PTSD) is often associated with significant neuroendocrine dysfunction and a variety of other symptoms. Today, there are limited efficacious treatment options for PTSD, none of which directly target the dysfunction observed with the hypothalamic-pituitary-adrenal (HPA) axis. The development of new pharmacological treatments is expensive and time consuming; thus, there is utility in repurposing compounds already approved for use in other conditions. One medication in particular that has shown promise for the alleviation of PTSD symptoms is prazosin, an alpha-1 adrenergic receptor antagonist used to treat hypertension. While there have been many studies indicating the efficacy of prazosin in the treatment of PTSD symptoms, no studies fully elucidate mechanisms elicited by this treatment, nor is it clear if prazosin normalizes neuroendocrine dysfunction associated with trauma exposure. The use of zebrafish (Danio rerio) has been growing in popularity, in part, due to the homology of the stress response system with mammals. In this study, the zebrafish model was utilized to determine behavioral and biological changes induced by chronic unpredictable stress (CUS) and how these effects could be modulated by chronic prazosin treatment. The results indicated that 7d of CUS increased anxiety-like behavior in the novel tank test and decreased basal levels of cortisol. Chronic (7d) prazosin treatment decreased anxiety-like behaviors overall but did not appear to affect CUS-induced changes in behavior and basal cortisol levels. This suggests that the clinical effectiveness of prazosin may not normalize dysregulated stress responses prevalent in many patients with PTSD, but that prazosin-induced relief from anxiety in stress-related conditions may involve an alternative mechanism other than by normalizing neuroendocrine dysfunction.