Methylene Blue Facilitates Memory Retention in Zebrafish in a Dose-Dependent Manner

Behavioral neuroscience in zebrafish: unravelling the complexity of brain-behavior relationships

This paper reviews the utility of zebrafish (Danio rerio) as a model system for exploring neurobehavioral phenomena in preclinical research, focusing on physiological processes, disorders, and neurotoxicity biomarkers. A comprehensive review of the current literature was conducted to summarize the various behavioral characteristics of zebrafish. The study examined the etiological agents used to induce neurotoxicity and the biomarkers involved, including Aβ42, tau, MMP-13, MAO, NF-Кβ, and GFAP. Additionally, the different zebrafish study models and their responses to neurobehavioral analysis were discussed. The review identified several key biomarkers of neurotoxicity in zebrafish, each impacting different aspects of neurogenesis, inflammation, and neurodegeneration. Aβ42 was found to alter neuronal growth and stem cell function. Tau's interaction with tubulin affected microtubule stability and led to tauopathies under pathological conditions. MMP-13 was linked to oxidative assault and sensory neuron degeneration. MAO plays a role in neurotransmitter metabolism and neurotoxicity conversion. NF-Кβ was involved in pro-inflammatory pathways, and GFAP was indicative of neuroinflammation and astroglial activation. Zebrafish provide a valuable model for neurobehavioral research, adhering to the "3Rs" philosophy. Their neurotoxicity biomarkers offer insights into the mechanisms of neurogenesis, inflammation, and neurodegeneration. This model system aids in evaluating physiological and pathological conditions, enhancing our understanding of neurobehavioral phenomena and potential therapeutic interventions.

Chemo-kindling in adult zebrafish alters spatial cognition but not social novelty recognition

In the past decades, zebrafish have gathered immense attention and importance in the field of neurological sciences. In the case of epilepsy, zebrafish have appeared as a promising acute animal model for the screening and identification of potential antiepileptic molecules. However, the necessity for establishing competent chronic models of epilepsy in zebrafish is apparent. In this regard, recently we developed a chemo-kindling zebrafish model with a better clinical resemblance. In the present study, an attempt to examine the effect of pentylenetetrazole (PTZ)-induced kindling on the cognitive functions of zebrafish was made. In brief, adult zebrafish were repetitively given a sub-effective concentration of PTZ, till the onset of clonic-tonic seizures, entitled as kindled. Thereafter, T-maze test and social recognition memory test were conducted to evaluate spatial memory and social novelty recognition memory of the fish. At the end, both the groups were sacrificed and the brains were isolated to estimate neurotransmitter and gene expression levels. It was observed that PTZ kindling induced spatial cognition deficits and lower social exploration in zebrafish. However, it didn't change the novelty recognition memory of kindled zebrafish. The results of genes and neurotransmitters estimations in the brain also supported the behavioural findings. The results concluded that PTZ kindling alters spatial cognitive functions in adult zebrafish without affecting the social novelty recognition memory.

Mechanism of action and neurotoxic effects of chronic exposure to bisphenol F in adult zebrafish

Although bisphenol F (BPF), the main replacement for bisphenol A, has been commonly used in polycarbonate production, its neurotoxicity and the underlying mechanisms remain poorly understood. To address this knowledge gap, this study aimed to assess the neurotoxicity caused by chronic exposure to BPF and to identify its underlying mechanisms. We exposed adult zebrafish chronically to BPF at environmentally relevant concentrations (0.001, 0.01, and 0.1 mg/L) for 4 weeks. The results revealed that with BPF crossing the blood-brain barrier and bioaccumulating in brain tissues, chronic exposure to BPF resulted in anxiety-like behaviors and disruptions in learning and memory function in adult zebrafish. Furthermore, BPF toxicity in the zebrafish brain involved the dysregulation of metabolic pathways for choline and kynurenine in neurotransmitter systems and for 17β-estradiol, cortisol, pregnenolone-sulfate, and Dehydroepiandrosterone (DHEA)-sulfate in neurosteroid systems. RNA-seq analysis revealed that BPF exposure affected metabolic pathways, calcium signaling pathways, neuroactive ligand-receptor interactions, tight junctions, gap junctions, and the gonadotropin-releasing hormone signaling pathway. Our results indicate that chronic exposure to BPF alters the neurochemical profile of the brain and causes neurobehavioral effects, such as anxiety and cognitive decline. Overall, the multimodal approach, including behavioral and neurochemical profiling technologies, has great potential for the comprehensive assessment of potential risks posed by environmental pollutants to human and ecosystem health.

Zebrafish: A Pharmacological Model for Learning and Memory Research

Learning and memory are essential to organism survival and are conserved across various species, especially vertebrates. Cognitive studies involving learning and memory require using appropriate model organisms to translate relevant findings to humans. Zebrafish are becoming increasingly popular as one of the animal models for neurodegenerative diseases due to their low maintenance cost, prolific nature and amenability to genetic manipulation. More importantly, zebrafish exhibit a repertoire of neurobehaviors comparable to humans. In this review, we discuss the forms of learning and memory abilities in zebrafish and the tests used to evaluate the neurobehaviors in this species. In addition, the pharmacological studies that used zebrafish as models to screen for the effects of neuroprotective and neurotoxic compounds on cognitive performance will be summarized here. Lastly, we discuss the challenges and perspectives in establishing zebrafish as a robust model for cognitive research involving learning and memory. Zebrafish are becoming an indispensable model in learning and memory research for screening neuroprotective agents against cognitive impairment.

Color Discrimination Provides Insight into the Relationship between Personality Cognition and Brain Morphology in the Western Mosquitofish (Gambusia affinis)

Recent studies on the differences in cognitive ability between individuals focused on two aspects: one is whether the individual differences in cognitive ability are related to brain size, the other is whether they pertain to certain personality traits. To explore these two hypotheses, we tested the personality traits, cognitive abilities, and brain volumes of western mosquitofish (Gambusia affinis). First, a color preference test was conducted to select two unbiased colors for G. affinis for subsequent cognitive tests. The results showed that G. affinis had a great preference for red and green to yellow and blue; therefore, the red-green combination was selected for the study of cognitive abilities. Then, we explored the relationship among cognition, personality, and brain morphology through cognitive abilities tests, personality traits, and brain volume measurements. We found that there was a trade-off among cognition, personality, and brain morphology. For example, more active individuals found food faster, but had also poor memory; Those individuals with larger corpus cerebelli were bolder while they were less likely to find food; The individuals that found food faster were more active and had a smaller inferior lobe. The color preference test provides a reliable way for selecting unbiased colors for behavioral studies in G. affinis. Meanwhile, our study indicates that there exists a balance mechanism among cognition, personality, and brain morphology.

The Potentials of Methylene Blue as an Anti-Aging Drug

Methylene blue (MB), as the first fully man-made medicine, has a wide range of clinical applications. Apart from its well-known applications in surgical staining, malaria, and methemoglobinemia, the anti-oxidative properties of MB recently brought new attention to this century-old drug. Mitochondrial dysfunction has been observed in systematic aging that affects many different tissues, including the brain and skin. This leads to increaseding oxidative stress and results in downstream phenotypes under age-related conditions. MB can bypass Complex I/III activity in mitochondria and diminish oxidative stress to some degree. This review summarizes the recent studies on the applications of MB in treating age-related conditions, including neurodegeneration, memory loss, skin aging, and a premature aging disease, progeria.

Amelioration of cognitive deficit in zebrafish by an undescribed anthraquinone from Juglans regia L.: An in-silico, in-vitro and in-vivo approach

An undescribed anthraquinone assigned as 1-Hydroxy-5,5-dimethyl-5,6,7,8-tetrahydro-9,10-anthraquinone (compound 1) was isolated from ethylacetate extract of Juglans regia L. The structure of the compound was established on the basis of 1D, 2D NMR (HSQC, HMBC, COSY), ESI-QTOF-MS/MS spectroscopy. The molecular docking studies of compound 1 indicated similar molecular interactions as that of co-crystalized inhibitor. Compound 1 showed hydrogen bonds with residues PHE295, GLY121, π-σ interactions with TYR 341, π-π interactions with HIS 447 residues, and π-alkyl with TRP86 and TYR 337. On the basis of in-silico interaction studies of compound 1 with proteins, it was tested using acetylcholinesterase inhibition assay, acrylamide-induced neurotoxicity test of zebrafish larva, and scopolamine-induced cognitive deficit model of adult zebrafish. The compound 1 showed potent acetylcholinesterase inhibition activity, prevented acrylamide-induced neurotoxicity and improved learning and memory functions in T-maze test. The results established compound 1 to be a potential neuroprotective natural product for amelioration of cognitive impairment.

Swimming in the maze: An overview of maze apparatuses and protocols to assess zebrafish behavior

Most preclinical behavioral assays use rodents as model animals, leaving room for species-specific biases that could be avoided by an expanded cross-species approach. In this context, zebrafish emerges as an alternative model organism to study neurobiological mechanisms of anxiety, preference, learning, and memory, as well as other phenotypes with relevance to neuropsychiatric disorders. In recent years, several zebrafish studies using different types of mazes have been published. However, the protocols and apparatuses' shapes and dimensions vary widely in the literature. This variation may puzzle researchers attempting to implement maze behavioral assays and challenges the reproducibility across institutions. This review aims to provide an overview of the behavioral paradigms assessed in different types of mazes in zebrafish reported in the last couple of decades. Also, this review aims to contribute to a better characterization of multi-behavioral assessment in zebrafish.

Reduning injection and its effective constituent luteoloside protect against sepsis partly via inhibition of HMGB1/TLR4/NF-κB/MAPKs signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Reduning injection (RDN), a popular traditional Chinese medicine, formulated by three herbs (i.e., Artemisia carvifolia Buch.-Ham. ex Roxb., Lonicera japonica Thunb., and Gardenia jasminoides J. Ellis), has been widely used to treat upper respiratory infectious diseases in China.

AIM OF THE STUDY

To investigate the protective effect of RDN on both lipopolysaccharides (LPS)- and cecal ligation and puncture (CLP)-induced septic mice. To identify the potentially effective constituent, and to determine its protective effect and underlying mechanism in vivo and in vitro.

MATERIALS AND METHODS

Male C57BL/6 mice were used to establish septic model by tail intravenous injection of 4 mg/kg LPS or CLP surgery. After modeling, mice were administered by tail intravenous injection of RDN in the dose of 16 or 8 mL/kg/day. The mortality, histopathology, plasma levels of inflammatory cytokines were evaluated respectively. In addition, we screened the potentially effective substances of RDN against sepsis by detecting the nitric oxide (NO) production in LPS-stimulated Raw 264.7 cells and verified the effect of luteoloside in CLP-induced septic mice subsequently. Finally, the underlying mechanisms of RDN and luteoloside were investigated in the inflammatory model in vitro.

RESULTS

Administration of RDN significantly reduced the mortality and increased the survival rate in both LPS- and CLP-induced septic mice. Meanwhile, RDN reduced the release of inflammatory cytokines accompanied by alleviating the organs damage of lung, liver, and kidney in CLP-induced septic mice. Moreover, several components from Gardenia jasminoides J. Ellis extract (ZZ) or Lonicera japonica Thunb and Artemisia carvifolia Buch.-Ham. ex Roxb extract (JQ) as well as the constituents of luteoloside, quercetin, and caffeic acid were screened out to have obvious anti-inflammatory activity, which may be the potentially effective substances of RDN against sepsis. We further verified the protective role of luteoloside in CLP-induced septic mice. In addition, RDN and luteoloside significantly inhibited both the secretion and translocation of mobility group box (HMGB)1, and HMGB1-mediated activation of TLR4/NF-κB/MAPKs signaling pathways.

CONCLUSION

RDN and its effective constituent luteoloside exhibited a significant protective effect against sepsis, which were potential candidate drugs for treatment of sepsis. The mechanism of antisepsis partly was related to inhibition of HMGB1/TLR4/NF-κB/MAPKs signaling pathways. The results provide an evidence base for the follow-up clinical application of RDN in treatment of sepsis.

Methylene Blue Preserves Cytochrome Oxidase Activity and Prevents Neurodegeneration and Memory Impairment in Rats With Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion in neurocognitive disorders diminishes cytochrome oxidase activity leading to neurodegenerative effects and impairment of learning and memory. Methylene blue at low doses stimulates cytochrome oxidase activity and may thus counteract the adverse effects of cerebral hypoperfusion. However, the effects of methylene blue on cytochrome oxidase activity during chronic cerebral hypoperfusion have not been described before. To test this hypothesis, rats underwent bilateral carotid artery occlusion or sham surgery, received daily 4 mg/kg methylene blue or saline injections, and learned a visual water task. Brain mapping of cytochrome oxidase activity was done by quantitative enzyme histochemistry. Permanent carotid occlusion for 1 month resulted in decreased cytochrome oxidase activity in visual cortex, prefrontal cortex, perirhinal cortex, hippocampus and amygdala, and weaker interregional correlation of cytochrome oxidase activity between these regions. Methylene blue preserved cytochrome oxidase activity in regions affected by carotid occlusion and strengthened their interregional correlations of cytochrome oxidase activity, which prevented neurodegenerative effects and facilitated task-specific learning and memory. Brain-behavior correlations revealed positive correlations between performance and brain regions in which cytochrome oxidase activity was preserved by methylene blue. These results are the first to demonstrate that methylene blue prevents neurodegeneration and memory impairment by preserving cytochrome oxidase activity and interregional correlation of cytochrome oxidase activity in brain regions susceptible to chronic hypoperfusion. This demonstration provides further support for the hypothesis that lower cerebral blood flow results in an Alzheimer's-like syndrome and that stimulating cytochrome oxidase activity with low-dose methylene blue is neuroprotective.

DMSO effects larval zebrafish (Danio rerio) behavior, with additive and interaction effects when combined with positive controls

Embryonic and larval zebrafish (Danio rerio) behavior is commonly used to identify neurotoxic compounds. Here, we investigated whether sub-lethal exposures to the common solvents dimethyl sulfoxide (DMSO, 0.01-1%) and methanol (MeOH, 0.01-1%), or the anti-fungal agent methylene blue (MB, 0.0001-0.0005%), can influence larval behavior in a simple light/dark paradigm conducted in 96-well plates. In addition, we tested whether the media volume within the behavioral arena or the zebrafish strain, AB wild type, AB Tübingen (AB/TU), or Tüpfel long-fin (TL), could also influence larval behavior. Following the single exposures, we co-exposed larvae to DMSO and either MB or two other compounds with known behavioral effects in larval zebrafish, flutamide and perfluorooctanesulfonic acid (PFOS). We found ≥0.55% DMSO and 0.0005% MB significantly affected larval behavior, but there was no effect of MeOH. Similarly, TL showed less movement compared to AB and AB/TU strains, whereas lower media volumes also significantly reduced larval movement. However, all strains responded similarly to DMSO and MB. In the co-exposure studies, we found either additive or interaction effects between DMSO and either MB, flutamide, or PFOS, depending on the behavioral endpoint measured. In addition, media volume had no effect on the DMSO concentration response curve, but again we observed additive effects on behavior. In conclusion, methodology can lead to alterations in baseline locomotor activity and compounds can have additive or interaction effects on behavioral endpoints. However, we found no evidence that strain effects should be a concern when deciding on solvents for a simple light/dark behavioral test in larval zebrafish.

Alzheimer's disease in the zebrafish: where can we take it?

With the ever-growing geriatric population, research on brain diseases such as dementia is more imperative now than ever. The most prevalent of all dementias is Alzheimer's disease, a progressive neurodegenerative disease that presents with deficits in memory, cognition, motor skills, and a general decline in the quality of life. The social and economic burden associated with Alzheimer's disease is tremendous and is projected to grow even greater over the coming years. There is a specific need to elucidate and improve the treatments available, not only to alleviate the symptoms related to dementias such as Alzheimer's but also to prevent the formation of the disease. This is an effort that can be expedited and made more efficient by utilizing an animal model such as the zebrafish. This paper reviews the utility of zebrafish in Alzheimer's research by examining research on a sampling of the treatments available for the disease, specifically donepezil, memantine, and methylene blue. The human model and the shortcomings of the rodent model are also discussed.

Heme oxygnease-1 induction by methylene blue protects RAW264.7 cells from hydrogen peroxide-induced injury

Although methylene blue (MB) has showed strong antioxidant effect, its effect related with heme oxygenase-1 (HO-1) is still unclear. Thus, we investigated the effects of MB on HO-1 protein content and enzyme activity, and its protective effect against hydrogen peroxide (H₂O₂)-induced oxidative damage in RAW264.7 macrophage. The cell viability and the release of lactate dehydrogenase of RAW264.7 were determined. The mitochondrial functions were valuated through these indexes: content of adenosine triphosphate, superoxide dismutase, concentration of reactive oxygen species and mitochondrial membrane potential. Meanwhile, high content screening tested generation of ROS, MMP and intracellular concentration of calcium ion. qRT-PCR valuated macrophage phenotype markers expression. Lastly, flow cytometry and caspase-3 detection analyzed RAW264.7 apoptosis. Our data showed that (1) Both pretreatment and posttreatment of MB increased HO-1 protein content and enzyme activity; (2) MB rescued cells from H₂O₂-induced mitochondrial dysfunction; (3) High content screening revealed that MB alleviated the changes including generation of reactive oxygen species, mitochondrial membrane potential and intracellular concentration of calcium ion in H₂O₂ exposed RAW264.7; (4) MB attenuated H₂O₂-induced apoptosis; (5) MB pretreatment decreased the expression of M1 macrophage markers (Tnf and Nos2) while increasing the expression of M2 macrophage markers (Mrc1 and Il10); (6) The beneficial effect of MB was abolished by zinc protoporphyrin IX (HO-1 activity inhibitor) or HO-1 siRNA. In summary, MB protects RAW264.7 cells from H2O2-induced injury through up-regulation HO-1.