Anxiolytic effects of diphenyl diselenide on adult zebrafish in a novelty paradigm

Developing a novel quantitative parameter for characterizing spatial distribution of fish following exposure to chemicals and wastewater: Behavioral Gini coefficient

While the spatial distribution pattern of fish is increasingly used for toxicological test of chemicals or wastewater, no ideal parameter is available for quantitative assessment of spatial distribution, especially uneven distribution with multiple hotspots. Here, to develop a quantitative assessment parameter for spatial distribution, the zebrafish were exposed to ethanol, pentylenetetrazole (PTZ), paraquat dichloride (paraquat) and wastewater, followed by a behavioral test in a narrow tank. Behavioral data was acquired and analyzed by idTracker and MATLAB. By comparing the effects of all treatments on behavior parameters, we confirmed that the spatial distribution was more easily altered rather than general locomotor parameters, e.g. 0.7-70 mg/L PTZ and 5-20 mg/L paraquat being effective for altering spatial distribution but having little effects on general locomotor parameters. Based on the heatmap, i.e., the cumulative proportion of grids and that of frequency in grids, we calculated the behavioral Gini coefficient (Gb) for quantitative assessment of fish spatial distribution. The Gini coefficient ranged from zero to 1, with larger values meaning poorer evenness of spatial distribution. Of note, Gb showed smaller coefficient of variations (CV) with 3%-19% between replicate tanks in all treatments than the highest frequency (4%-79%), displaying well robustness. Especially, Gb addressed the challenge of the complicated heatmap with multiple hotspots. Overall, the behavioral Gini coefficient we established is an ideal parameter to quantitatively assess spatial distribution of fish shoal, which is expected to be applied in toxicity testing for chemicals and wastewater and automatic quality monitoring for surface water and aquaculture water.

Diphenyl Diselenide Attenuates Mitochondrial Damage During Initial Hypoxia and Enhances Resistance to Recurrent Hypoxia

Hypoxia plays a significant role in the development of various cerebral diseases, many of which are associated with the potential risk of recurrence due to mitochondrial damage. Conventional drug treatments are not always effective for hypoxia-related brain diseases, necessitating the exploration of alternative compounds. In this study, we investigated the potential of diphenyl diselenide [(PhSe)2] to ameliorate locomotor impairments and mitigate brain mitochondrial dysfunction in zebrafish subjected to hypoxia. Additionally, we explored whether these improvements could confer resistance to recurrent hypoxia. Through a screening process, an appropriate dose of (PhSe)2 was determined, and animals exposed to hypoxia received a single intraperitoneal injection of 100 mg/kg of the compound or vehicle. After 1 h from the injection, evaluations were conducted on locomotor deficits, (PhSe)2 content, mitochondrial electron transport system, and mitochondrial viability in the brain. The animals were subsequently exposed to recurrent hypoxia to assess the latency time to hypoxia symptoms. The findings revealed that (PhSe)2 effectively crossed the blood-brain barrier, attenuated locomotor deficits induced by hypoxia, and improved brain mitochondrial respiration by modulating complex III. Furthermore, it enhanced mitochondrial viability in the telencephalon, contributing to greater resistance to recurrent hypoxia. These results demonstrate the beneficial effects of (PhSe)2 on both hypoxia and recurrent hypoxia, with cerebral mitochondria being a critical target of its action. Considering the involvement of brain hypoxia in numerous pathologies, (PhSe)2 should be further tested to determine its effectiveness as a potential treatment for hypoxia-related brain diseases.

Genotoxicity and cytotoxicity potential of organoselenium compounds in human leukocytes in vitro

In the current work, cytotoxicity and genotoxicity of different organoselenium compounds were examined using Trypan blue exclusion and alkaline comet assays with silver staining respectively. Leukocytes were subjected to a 3-hour incubation with organoselenium compounds at concentrations of 1, 5, 10, 25, 50, and 75 μM, or with the control vehicle (DMSO), at a temperature of 37 °C. The viability of the cells was evaluated using the Trypan blue exclusion method, while DNA damage was analyzed through the alkaline comet assay with silver staining. The exposure of leukocytes to different organoselenium compounds including i.e. (Z)-N-(pyridin-2-ylmethylene)-1-(2-((2-(1-((E)-pyridin-2-ylmethyleneamino)ethyl)phenyl)diselanyl)phenyl)ethanamine (C1), 2,2'(1Z,1'E)-(1,1'-(2,2'-diselanediylbis(2,1-phenylene))bis(ethane-1,1-diyl)) bis(azan-1-yl-1-ylidene)bis -methan-1-yl-1-ylidene)diphenol (C2), and dinaphthyl diselenide (NapSe)2, At concentrations ranging from 1 to 5 μM, no significant DNA damage was observed, as indicated by the absence of a noteworthy increase in the Damage Index (DI). Our results suggest that the organoselenium selenium compounds tested were not genotoxic and cytotoxic to human leukocytes in vitro at lower concentration. This study offers further insights into the genotoxicity profile of these organochalcogens in human leukocytes. Their genotoxicity and cytotoxicity effects at higher concentration are probably mediated through reactive oxygen species generation and their ability to catalyze thiol oxidation.

The zebrafish for preclinical psilocybin research

In this review, we discuss the possible utility of zebrafish in research on psilocybin, a psychedelic drug whose recreational use as well as possible clinical application are gaining increasing interest. First, we review behavioral tests with zebrafish, focussing on anxiety and social behavior, which have particular relevance in the context of psilocybin research. Next, we briefly consider methods of genetic manipulations with which psilocybin's phenotypical effects and underlying mechanisms may be investigated in zebrafish. We briefly review the known mechanisms of psilocybin, and also discuss what we know about its safety and toxicity profile. Last, we discuss examples of how psilocybin may be employed for testing treatment efficacy in preclinical research for affective disorders in zebrafish. We conclude that zebrafish has a promising future in preclinical research on psychedelic drugs.

Assessing the exploratory profile of two zebrafish populations: influence of anxiety-like phenotypes and independent trials on homebase-related parameters and exploration

Anxiety is a protective behavior when animals face aversive conditions. The open field test (OFT) is used to assess the spatio-temporal dynamics of exploration, in which both homebase formation and recognition of environmental cues may reflect habituation to unfamiliar conditions. Because emotional- and affective-like states influence exploration patterns and mnemonic aspects, we aimed to verify whether the exploratory behaviors of two zebrafish populations showing distinct baselines of anxiety differ in two OFT sessions. Firstly, we assessed the baseline anxiety-like responses of short fin (SF) and leopard (LEO) populations using the novel tank test (NTT) and light-dark test (LDT) in 6-min trials. Fish were later tested in two consecutive days in the OFT, in which the spatial occupancy and exploratory profile were analyzed for 30min. In general, LEO showed pronounced diving behavior and scototaxis in the NTT and LDT, respectively, in which an "anxiety index" corroborated their exacerbated anxiety-like behavior. In the OFT, the SF population spent less time to establish the homebase in the 1^st trial, while only LEO showed a markedly reduction in the latency to homebase formation in the 2^nd trial. Both locomotion and homebase-related activities were decreased in the 2^nd trial, in which animals also revealed increased occupancy in the center area of the apparatus. Moreover, we verified a significant percentage of homebase conservation for both populations, while only SF showed reduced the number of trips and increased the average length of trips. Principal component analyses revealed that distinct factors accounted for total variances between trials for each population tested. While homebase exploration was reduced in the 2^nd trial for SF, an increased occupancy in the center area and hypolocomotion were the main factors that contribute to the effects observed in LEO during re-exposure to the OFT. In conclusion, our novel data support the homebase conservation in zebrafish subjected to independent OFT sessions, as well as corroborate a population-dependent effect on specific behavioral parameters related to exploration.

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.

Silibinin and Naringenin against Bisphenol A-Induced Neurotoxicity in Zebrafish Model-Potential Flavonoid Molecules for New Drug Design, Development, and Therapy for Neurological Disorders

Bisphenol A (BPA), a well-known xenoestrogen, is commonly utilised in the production of polycarbonate plastics. Based on the existing evidence, BPA is known to induce neurotoxicity and behavioural issues. Flavonoids such as silibinin and naringenin have been shown to have biological activity against a variety of illnesses. The current research evaluates the neuropharmacological effects of silibinin and naringenin in a zebrafish model against neurotoxicity and oxidative stress caused by Bisphenol A. In this study, a novel tank diving test (NTDT) and light−dark preference test (LDPT) were used in neurobehavioural investigations. The experimental protocol was planned to last 21 days. The neuroprotective effects of silibinin (10 μM) and naringenin (10 μM) in zebrafish (Danio rerio) induced by BPA (17.52 μM) were investigated. In the brine shrimp lethality assay, the 50% fatal concentrations (LC50) were 34.10 μg/mL (silibinin) and 91.33 μg/mL (naringenin) compared to the standard potassium dichromate (13.15 μg/mL). The acute toxicity investigation found no mortality or visible abnormalities in the silibinin- and naringenin-treated groups (LC50 > 100 mg/L). The altered scototaxis behaviour in LDPT caused by BPA was reversed by co-supplementation with silibinin and naringenin, as shown by decreases in the number of transitions to the light zone and the duration spent in the light zone. Our findings point to BPA’s neurotoxic potential in causing altered scototaxis and bottom-dwelling behaviour in zebrafish, as well as the usage of silibinin and naringenin as potential neuroprotectants.

Behavioral Effects of Buspirone in Juvenile Zebrafish of Two Different Genetic Backgrounds

Anxiety continues to represent a major unmet medical need. Despite the availability of numerous anxiolytic drugs, a large proportion of patients do not respond well to current pharmacotherapy, or their response diminishes with chronic drug application. To discover novel compounds and to investigate the mode of action of anxiolytic drugs, animal models have been proposed. The zebrafish is a novel animal model in this research. It is particularly appropriate, as it has evolutionarily conserved features, and drug administration can be employed in a non-invasive manner by immersing the fish into the drug solution. The first step in the analysis of anxiolytic drugs with zebrafish is to test reference compounds. Here, we investigate the effects of buspirone hydrochloride, an anxiolytic drug often employed in the human clinic. We utilize two genetically distinct populations of zebrafish, AB_SK, derived from the quasi-inbred AB strain, and WT, a genetically heterogeneous wild-type population. We placed juvenile (10–13-day, post-fertilization, old) zebrafish singly in petri dishes containing one of four buspirone concentrations (0 mg/L control, 5 mg/L, 20 mg/L or 80 mg/L) for 1 h, with each fish receiving a single exposure to one concentration, a between subject experimental design. Subsequently, we recorded the behavior of the zebrafish for 30 min using video-tracking. Buspirone decreased distance moved, number of immobility episodes and thigmotaxis, and it increased immobility duration and turn angle in a quasi-linear dose dependent but genotype independent manner. Although it is unclear whether these changes represent anxiolysis in zebrafish, the results demonstrate that behavioral analysis of juvenile zebrafish may be a sensitive and simple way to quantify the effects of human anxiolytic drugs.

Effects of intraspecific chemical cues on the behaviour of the bloodfin tetra Aphyocharax anisitsi (Ostariophysi: Characidae)

Chemical communication can induce a multitude of behaviours when detected by fish olfactory systems, from parental care, predation and alarm signalling, to foraging, schooling, reproduction, and migration. Chemical cues provide information that visual traits cannot and fish can respond to chemical cues without any additional sensory cue. In this way, pheromones play an essential role in the fitness of fishes. Given that Aphyocharax anisitsi inhabits environments characterized by cloudy and highly vegetated waters, it is interesting to evaluate the olfactory contribution in their communication. Here, we investigated the relevance of chemical cues in the types of behaviours triggered in A anisitsi by two experimental contexts: 1) non-social and olfactory context (conspecific-chemical cues), and 2) social context (conspecific female or male presence). Non-social context experiments suggest that males of A. anisitsi respond to both male and female-chemical cues even in the absence of other sensory inputs. The high olfactory sensitivity of characids in general and of A. anisitsi, in particular, could facilitate vital functions, such as foraging and conspecific recognition in habitats that impose severe restrictions on the visual system.

A comprehensive review on the neuropathophysiology of selenium

As an essential micronutrient, selenium (Se) exerts its biological function as a catalytic entity in a variety of enzymes. From a toxicological perspective, however, Se can become extremely toxic at concentrations slightly above its nutritional levels. Over the last few decades, there has been a growing level of concern worldwide regarding the adverse effects of both inorganic and organic Se compounds on a broad spectrum of neurological functions. A wealth of evidence has shown that exposure to excess Se may compromise the normal functioning of various key proteins, neurotransmitter systems (the glutamatergic, dopaminergic, serotonergic, and cholinergic systems), and signaling molecules involved in the control and regulation of cognitive, behavioral, and neuroendocrine functions. Elevated Se exposure has also been suspected to be a risk factor for the development of several neurodegenerative and neuropsychiatric diseases. Nonetheless, despite the various deleterious effects of excess Se on the central nervous system (CNS), Se neurotoxicity and negative behavioral outcomes are still disregarded at the expense of its beneficial health effects. This review focuses on the current state of knowledge regarding the neurobehavioral effects of Se and discusses its potential mode of action on different aspects of the central and peripheral nervous systems. This review also provides a brief history of Se discovery and uses, its physicochemical properties, biological roles in the CNS, environmental occurrence, and toxicity. We also review potential links between exposure to different forms of Se compounds and aberrant neurobehavioral functions in humans and animals, and identify key knowledge gaps and hypotheses for future research.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Differential effects of ethanol on behavior and GABAA receptor expression in adult zebrafish (Danio rerio) with alternative stress coping styles

Variation in stress responses between individuals are linked to factors ranging from stress coping styles to sensitivity of neurotransmitter systems. Many anxiolytic compounds (e.g. ethanol) can increase stressor engagement through modulation of neurotransmitter systems and are used to investigate stress response mechanisms. There are two alternative suites of correlated behavioral and physiological responses to stressors (stress coping styles) that differ in exploration tendencies: proactive and reactive stress coping styles. By chronically treating individuals differing in stress coping style with ethanol, a GABA-acting drug, we assessed the role of the GABAergic system on the behavioral stress response. Specifically, we investigated resulting changes in stress-related behavior (i.e. exploratory behavior) and whole-brain GABAA receptor subunits (gabra1, gabra2, gabrd, & gabrg2) in response to a novelty stressor. We found that ethanol-treated proactive individuals showed lower stress-related behaviors than their reactive counterparts. Proactive individuals showed significantly higher expression of gabra1, gabra2, and gabrg2 compared to reactive individuals and ethanol treatment resulted in upregulation of gabra1 and gabrg2 in both stress coping styles. These results suggest that impacts of ethanol on stress-related behaviors vary by stress coping style and that expression of select GABAA receptor subunits may be one of the underlying mechanisms.

Cannabinol in the spotlight: Toxicometabolomic study and behavioral analysis of zebrafish embryos exposed to the unknown cannabinoid

Cannabinol (CBN) is a degradation product of the cannabis metabolite Δ9-tetrahydrocannabinol. The CBN concentration in cannabis leaves ranges between 0.1 and 1.6% (w/w of dry weight); it increases as the plant ages and its formation is affected by the storage conditions. As CBN has not been extensively studied so far, the need to examine its impact in vivo is imperative due to the increasing use of cannabis globally. In the study herein, the CBN toxicity, effects on heart physiology, morphological malformations, behavioral changes and alterations in metabolic pathways of zebrafish larvae upon CBN exposure to sublethal concentrations were examined. The LD₅₀ value was estimated at 1.12 mg/l. At the same time, malformations in zebrafish larvae increased significantly in a dose-dependent manner and exposure to CBN concentrations greater than 0.75 mg/l provoked abnormalities like pericardial edema, yolk sac anomalies and tail bending. Concentrations above this threshold resulted in elongated and shorter in width hearts and in separation of ventricle from atrium. The total movement distance and velocity were increased in dark and decreased in light conditions, in a concentration-dependent manner. Our results showed that CBN acts both as a stimulant and a sedative, with larvae to exhibit altered velocity and bradycardia, respectively. The metabolomic analysis revealed alterations mainly to amino acids, which are related to acute toxicity and hint towards systemic metabolic and neuropathophysiological changes. Taken together, our data indicate increased toxic effects as CBN exposure concentration increases, which should be taken into consideration when studying the impact of cannabis on organisms.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

Photoinduced metal-free α-selenylation of ketones

Herein, we report an efficient photoinduced α-selenylation of ketones without metal, additives or under photosensitizer-free conditions, providing a green protocol using light energy to synthesize a variety of α-selenoketones. This new methodology proved to be a mild, simple and eco-friendly tool for the efficient synthesis of the desired products.

Herein, we report an efficient photoinduced α-selenylation of ketones without metal, additives or under photosensitizer-free conditions, providing a green protocol using light energy to synthesize a variety of α-selenoketones.

Zebrafish models of diabetes-related CNS pathogenesis

Diabetes mellitus (DM) is a common metabolic disorder that affects multiple organ systems. DM also affects brain processes, contributing to various CNS disorders, including depression, anxiety and Alzheimer's disease. Despite active research in humans, rodent models and in-vitro systems, the pathogenetic link between DM and brain disorders remains poorly understood. Novel translational models and new model organisms are therefore essential to more fully study the impact of DM on CNS. The zebrafish (Danio rerio) is a powerful novel model species to study metabolic and CNS disorders. Here, we discuss how DM alters brain functions and behavior in zebrafish, and summarize their translational relevance to studying DM-related CNS pathogenesis in humans. We recognize the growing utility of zebrafish models in translational DM research, as they continue to improve our understanding of different brain pathologies associated with DM, and may foster the discovery of drugs that prevent or treat these diseases.

Long-term effects of oxytetracycline exposure in zebrafish: A multi-level perspective

Oxytetracycline (OTC) is a broad-spectrum antibiotic widely used in livestock production. Like many other pharmaceuticals, OTC is not completely metabolized by the organism and thus, increasing amounts of the compound are being detected in the aquatic environment. The assessment of the environmental risk of pharmaceuticals is hindered by their very low concentrations and specific modes of action and thus relevant exposure scenarios and sensitive endpoints are needed. Thus, this work aimed to study the long-term effect of OTC exposure in zebrafish (at behavior and biochemical levels) and associated bacterial communities (fish gut and water bacterial communities). Results revealed that at behavioral level, boldness increase (manifested by increased exploratory behavior of a new environment) was observed in fish exposed to low OTC concentrations. Moreover, changes in fish swimming pattern were observed in light periods (increased stress response: hyperactivity and freezing) probably due to photo-sensibility conferred by OTC exposure. Effects at biochemical level suggest that long-term exposure to OTC interfere with cellular energy allocation mainly by reducing lipids levels and increasing energy consumption. Moreover, evidences of oxidative damage were also observed (reduced levels of TG, GST and CAT). The analysis of water and gut microbiome revealed changes in the structure and diversity of bacterial communities potentially leading to changes in communities' biological function. Some of the effects were observed at the lowest concentration tested, 0.1 μg/L which is a concentration already detected in the environment and thus clearly demonstrating the need of a serious ecotoxicological assessment of OTC effects on non-target organisms.

Zebrafish exposure to diphenyl diselenide-loaded polymeric nanocapsules caused no behavioral impairments and brain oxidative stress

Previous findings showed that the nanoencapsulation of diphenyl diselenide [(PhSe)₂], an organoselenium compound, provided superior biological effects and lower toxicological potential than its free form in vitro. However, few studies reported the behavioral and biochemical effects of this nanocapsules formulation in vivo. Zebrafish (Danio rerio) has emerged as a useful animal model to determine the pharmacological and toxicological effects of nanoparticles. Here, we evaluated the behavioral and brain oxidative effects after zebrafish exposure to (PhSe)₂-loaded nanocapsules. Formulations were prepared by interfacial deposition of preformed polymer method and later tested at concentrations ranging from 0.1 to 2.0 μM. Both locomotor and exploratory activities were assessed in the novel tank diving test. Moreover, brain oxidative status was determined by measuring thiobarbituric acid-reactive substance levels, glutathione peroxidase, glutathione redutase and glutathione S-transferase activities. (PhSe)₂-loaded nanocapsules showed no alteration on travelled distance, immobility, and erratic swimming, suggesting the absence of behavioral impairments. Interestingly, the higher concentration tested had anxiolytic-like effects, since animals spent more time in the top area and showed a decreased thigmotaxis behavior. Biochemical analysis demonstrated that the concentrations used in this study did not affect oxidative stress-related parameters in brain samples, reinforcing the low toxicological potential of the formulation. In conclusion, the exposure to (PhSe)₂-loaded nanocapsules caused no locomotor impairments as well as did not modify the oxidative status of zebrafish brain, indicating that this formulation is probably non-toxic and promising for future pharmacological studies.

Fellutamide B Synthetic Path Intermediates with in Vitro Neuroactive Function Shows Mood-Elevating Effect in Stress-Induced Zebrafish Model

Fellutamide B is reported to have cytotoxic and proteasome inhibitory activity. Interestingly, fellutamide B and its simplified analogues have also been observed for the neurotrophic activity by stimulating the synthesis and secretion of neurotrophins. Owing to the interesting structural and potent neurotrophic role of fellutamide B (a lipopeptide aldehyde), we have assessed the synthetic path intermediates (compounds A-D) of fellutamide B for their neuroactive potential (in vitro and in vivo). We have observed few compounds (comp #A-D) to have potential neurite outgrowth activity in Neuro2a cells with no observable negative effect on the cell viability. In addition, most compounds (comp #A, C, and D) have shown neurogenic activity ex vivo in hippocampal neurosphere culture, with increased acetyl H3 and acetyl H4 induction ability (comp #C). Furthermore, the intermediate product comp #C has shown anxiolytic and antidepressant-like activity in novel tank test and social interaction test, in the chronic unpredictable stress model of zebrafish mood disorder, inducing BDNF gene expression in the telencephalon region of the fish brain. Our results thus demonstrate that the fellutamide B synthetic path intermediates have potential neurotrophic, neurogenic, and mood-elevating effects and thus good prospect to be developed as potential therapeutics to treat psychiatric disorders.

Hyperglycemia elicits anxiety-like behaviors in zebrafish: Protective role of dietary diphenyl diselenide

Diabetes mellitus (DM) is a chronic metabolic disease that may comorbid with various psychiatric disorders, such as anxiety and depression. The search for effective therapeutics to alleviate hyperglycemia and complications resulting from DM is continuous. Here we investigate the effects of diphenyl diselenide (DD), an organoselenium compound with several pharmacological properties, in a zebrafish model of hyperglycemia. Fish were fed for 74 days with a diet containing 3 mg/Kg DD, a concentration chosen after experiments based in a dose-response curve (DD 1, 2 and 3 mg/Kg) that did not cause overt toxicity (mortality, weight loss and neurobehavioral deficits). In the last 14 days of the experimental period, fish were concomitantly exposed to a glucose solution (111 mM). Afterwards, blood glucose levels, brain selenium (Se) content, and behavioral analysis aiming to assess anxiety-like behaviors and locomotor/exploratory activities were performed. In the novel tank diving test, glucose decreased vertical exploration and fish spent less time in the lit area when tested in the light-dark test, suggesting increased anxiety-like behavior. Moreover, DD decreased blood glucose levels in hyperglycemic fish as well as prevented the development of anxiety-related symptoms. DD diet alone did not change glycemia and behavioral parameters, but increased Se levels in the brain without affecting the cellular viability. Collectively, our findings highlight the growing utility of this zebrafish hyperglycemia model as a valuable strategy for further research in DM field and neuroprotective approaches.

Diazepam fails to alter anxiety-like responses but affects motor function in a white-black test paradigm in larval zebrafish (Danio rerio)

The growing popularity of zebrafish in psychopharmacology and behavioral brain research is partly due to the practicality and simplicity of drug administration in this species. Several drugs may be administered to zebrafish by immersing the fish in the drug solution. Furthermore, numerous drugs developed for mammals, including humans, have been found to show a similar effect profile in the zebrafish. Thus, the zebrafish has been suggested as a potentially useful animal screening tool. Despite decades of drug development, anxiety still represents a major unmet medical need, and the search for anxiolytic compounds is continuing. The zebrafish has been proposed for high throughput screens for anxiolytic compounds, and the effects of anxiolytic compounds on the behavior of zebrafish have started to be explored. Diazepam (Valium®) is a frequently prescribed human anxiolytic, a GABA_A receptor agonist, has also started to be tested in zebrafish, but with occasional contradicting results. Here, we investigate the effects of diazepam in larval (6-day post-fertilization old) zebrafish in a black-white preference paradigm. We found significant white preference and thigmotaxis (edge preference) in our control fish, anxiety-like responses that habituated over time. However, unexpectedly, we observed no anxiolytic effects of diazepam on these behaviors, and only detected significant motor activity reducing effect of the drug. We discuss the complex interpretation of light/dark tests in zebrafish, and also speculate about the possibility of differential GABAergic mechanisms that diazepam affects in larval vs adult zebrafish.

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

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

Sodium Selenite Prevents Paraquat-Induced Neurotoxicity in Zebrafish

Considering the antioxidant properties of sodium selenite (Na₂SeO₃) and the involvement of oxidative stress events in paraquat-induced neurotoxicity, this study investigated the protective effect of dietary Na₂SeO₃ on biochemical and behavioral parameters of zebrafish exposed to paraquat (PQ). Fish were pretreated with a Na₂SeO₃ diet for 21 days and then PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days. In the novel tank test, the Na₂SeO₃ diet prevented the locomotor impairments, as well as the increase in the time spent in the top area of the tank, and the exacerbation of freezing episodes. In the preference for conspecifics and in the mirror-induced aggression (MIA) tasks, Na₂SeO₃ prevented the increase in the latency to enter the area closer to conspecifics and the agonistic behavior of PQ-treated animals, respectively. Na₂SeO₃ prevented the increase of carbonylated protein (CP), reactive oxygen species (ROS), and nitrite/nitrate (NOx) levels, as well as the decrease in non-protein thiols (NPSH) levels. Regarding the antioxidant enzymatic defenses, Na₂SeO₃ prevented the increase in catalase (CAT) and glutathione peroxidase (GPx) activities caused by PQ. Altogether, dietary Na₂SeO₃ improves behavioral and biochemical function impaired by PQ treatment in zebrafish, by modulating not only redox parameters, but also anxiety- and aggressive-like phenotypes in zebrafish.

Unveiling the neurotoxicity of methylmercury in fish (Diplodus sargus) through a regional morphometric analysis of brain and swimming behavior assessment

The current study aims to shed light on the neurotoxicity of MeHg in fish (white seabream - Diplodus sargus) by the combined assessment of: (i) MeHg toxicokinetics in the brain, (ii) brain morphometry (volume and number of neurons plus glial cells in specific brain regions) and (iii) fish swimming behavior (endpoints associated with the motor performance and the fear/anxiety-like status). Fish were surveyed for all the components after 7 (E7) and 14 (E14) days of dietary exposure to MeHg (8.7μgg^-1), as well as after a post-exposure period of 28days (PE28). MeHg was accumulated in the brain of D. sargus after a short time (E7) and reached a maximum at the end of the exposure period (E14), suggesting an efficient transport of this toxicant into fish brain. Divalent inorganic Hg was also detected in fish brain along the experiment (indicating demethylation reactions), although levels were 100-200 times lower than MeHg, which pinpoints the organic counterpart as the great liable for the recorded effects. In this regard, a decreased number of cells in medial pallium and optic tectum, as well as an increased hypothalamic volume, occurred at E7. Such morphometric alterations were followed by an impairment of fish motor condition as evidenced by a decrease in the total swimming time, while the fear/anxiety-like status was not altered. Moreover, at E14 fish swam a greater distance, although no morphometric alterations were found in any of the brain areas, probably due to compensatory mechanisms. Additionally, although MeHg decreased almost two-fold in the brain during post-exposure, the levels were still high and led to a loss of cells in the optic tectum at PE28. This is an interesting result that highlights the optic tectum as particularly vulnerable to MeHg exposure in fish. Despite the morphometric alterations reported in the optic tectum at PE28, no significant changes were found in fish behavior. Globally, the effects of MeHg followed a multiphasic profile, where homeostatic mechanisms prevented circumstantially morphometric alterations in the brain and behavioral shifts. Although it has become clear the complexity of matching brain morphometric changes and behavioral shifts, motor-related alterations induced by MeHg seem to depend on a combination of disruptions in different brain regions.

Alcohol-induced behavioral changes in zebrafish: The role of dopamine D2-like receptors

RATIONALE

The dopaminergic system has been proposed to mediate alcohol-induced locomotor activity, yet the mechanisms underlying this behavioral response remain poorly understood.

OBJECTIVES

This study was conducted to investigate the role of dopamine D2-like receptors in mediating alcohol-induced behavioral responses.

METHODS

In experiment 1, we examined the effects of high concentrations (0, 2.5, 5, 10 μM) of haloperidol on motor responses. In experiment 2, we examined the effects of low concentrations (0, 0.625, 1.25, 2.5 μM) of haloperidol on anxiety-like behavioral responses using the novel tank test. In experiment 3, we examined the effect of pre-treating zebrafish with different concentrations of haloperidol (0, 0.625, 2.5 μM) and subsequently exposing them to 0 or 1 % alcohol.

RESULTS

In experiment 1, haloperidol induced an inverted U-shaped concentration-dependent increase in locomotor activity. In experiment 2, haloperidol (2.5 μM) reduced the absolute turn angle and freezing behavior in a new environment. In experiment 3, acute alcohol exposure significantly increased locomotor activity and decreased anxiety-like behavioral responses. Pre-treating zebrafish with the lower dose of haloperidol (0.625 μM) abolished the alcohol-induced locomotor activity, without altering anxiety-like behavioral responses. However, pre-treating with the higher dose of haloperidol (2.5 μM) abolished both alcohol-induced increase of locomotor activity and reduction of anxiety-like behavioral responses.

CONCLUSION

The results suggest alcohol-induced locomotor hyperactivity in zebrafish is mediated via activation of dopamine D2-like receptors, whereas anxiety-like behavioral responses may only be altered by a high haloperidol concentration, at which dose the drug may affect receptors other than D2-R.

Neurobehavioral and biochemical changes in Nauphoeta cinerea following dietary exposure to chlorpyrifos

The present study aimed to increase our understanding about the mode of toxic action of organophosphate pesticides in insects by evaluating the biochemical and neurobehavioral characteristics in Nauphoeta cinerea exposed to chlorpyrifos (CPF)-contaminated diet. The insects were exposed for 35 consecutive days to CPF at 0.078, 0.15625, 0.3125 and 0.625μg/g feed. Locomotor behavior was assessed for a 10-min trial in a novel arena and subsequently, biochemical analyses were carried out using the cockroaches' heads. In comparison to control, CPF-exposed cockroaches showed significant decreases in the total distance traveled, body rotation, turn angle and meandering, along with significant increase in the number of falls, time and episodes of immobility. The marked decrease in the exploratory profiles of CPF-exposed cockroaches was confirmed by track plots, whereas occupancy plot analyses showed a progressive dispersion at 0.15625μg/g feed group. Moreover, the heads of CPF-exposed cockroaches showed marked decrease in acetylcholinesterase activity and antioxidant status with concomitant significant elevation in dichlorofluorescein oxidation and lipid peroxidation levels in CPF-treated cockroaches. Gas Chromatography-Mass Spectrometry analyses revealed bioaccumulation of CPF in cockroaches exposed to concentrations above 0.078μg/g feed. The findings from this investigation showed N. cinerea as a value model organism for the risk assessment of environmental organophosphate contamination in insects.

Neuroprotection of luteolin against methylmercury-induced toxicity in lobster cockroach Nauphoeta cinerea

Luteolin (3', 4', 5, 7-tetrahydroxyflavone) is a polyphenolic compound found in foods of plant origin and has been reported to possess antioxidant and neuroprotective properties. However, there is dearth of information on the beneficial effects of luteolin on methylmercury (MeHg), a long-established neurotoxic compound in animals and humans. This study evaluated the effect of luteolin on MeHg-induced behavioral and biochemical deficits, using lobster cockroach Nauphoeta cinerea as an alternative and complementary animal model. The insects were exposed for 35 consecutive days to either MeHg alone (0.05 mg/g feed) or in combination with luteolin at 0.25, 0.5 and 1.0 mg/g feed. Locomotor behavior was assessed using video-tracking software during a 10-min trial in a novel arena and subsequently, biochemical analyses were carried out using the cockroaches' heads. Luteolin supplementation dose-dependently reversed the MeHg-induced locomotor deficits and enhanced the exploratory profiles of MeHg-exposed cockroaches as confirmed by track and occupancy plot analyses. Luteolin reversed the MeHg-induced acetylcholinesterase activity inhibition, decreased dichlorofluorescein oxidation and lipid peroxidation levels, but increased total thiol level and catalase and glutathione S-transferase activities in the treated cockroaches. In conclusion, luteolin prevented oxidative stress indices and neurobehavioral deficits in a Nauphoeta cinerea model of MeHg toxicity.

Copper acutely impairs behavioral function and muscle acetylcholinesterase activity in zebrafish (Danio rerio)

Copper is a heavy metal found at relatively high concentrations in surface waters around the world. Copper is a micronutrient at low concentrations and is essential to several organisms. At higher concentrations copper can become toxic, which reveal the importance of studying the toxic effects of this metal on the aquatic life. Thus, the objective of this study was to evaluate the toxic effects of copper on the behavior and biochemical parameters of zebrafish (Danio rerio). Zebrafish were exposed for 24h at a concentration of 0.006 mg/L Cu. After the exposure period, behavioral profile of animals was recorded through 6 min using two different apparatuses tests: the Novel Tank and the Light-Dark test. After behavioral testing, animals were euthanized with a solution of 250 mg/L of tricaine (MS-222). Brain, muscle, liver and gills were extracted for analysis of parameters related to oxidative stress and accumulation of copper in these tissues. Acetylcholinesterase (AChE) activity was determined in brain and muscle. Results showed acute exposure to copper induces significant changes in behavioral profile of zebrafish by changing locomotion and natural tendency to avoid brightly lit area. On the other hand, there were no significant effects on parameters related to oxidative stress. AChE activity decreased significantly in zebrafish muscle, but there were no significant changes in cerebral AChE activity. Copper levels in tissues did not increase significantly compared to the controls. Taken together, these results indicate that a low concentration of copper can acutely affect behavioral profile of adult zebrafish which could be partially related to an inhibition on muscle AChE activity. These results reinforce the need of additional tests to establishment of safe copper concentrations to aquatic organisms and the importance of behavioral parameters in ecotoxicological studies.

Biochemical and behavioral deficits in the lobster cockroach Nauphoeta cinerea model of methylmercury exposure

Methylmercury (MeHg) is well-known for its neurodevelopmental effects both in animals and in humans.