The Brilliance of the Zebrafish Model: Perception on Behavior and Alzheimer’s Disease

Comparative Evaluation of Cytotoxicity of Zinc Oxide Nanoparticles Mixed With Herbal Extract as an Intracanal Medicament: A Zebrafish Model Study

Objective In this study, zebrafish embryos are used to study the cytotoxic effects of a novel intracanal medication (ICM) based on zinc oxide nanoparticles (ZnO NPs) loaded with polyherbal extracts (Azadirachta indica and Solanum xanthocarpum). Material and methods In the present study, a green and sustainable method was employed for the synthesis of ZnO NPs mixed with bark and seed extracts of Azadirachta indica and Solanum xanthocarpum to be used as a polyherbal ICM. Formulation of ZnO NPs was confirmed with color change in mixture produced upon dissolving zinc acetate dihydrate in distilled water followed by slow addition of sodium hydroxide solution and herbal extracts. The effects of these green synthesized ZnO NPs were evaluated through a zebrafish embryo toxicity test. Embryos were exposed to different concentrations (25, 50, and 100 µg/mL) of synthesized experimental doses of ZnO NP and compared with the control embryos. Toxicological endpoints, such as the zebrafish embryo's survival rate, hatching rate, and heart rate, were noted and described. Results A concentration-dependent increase in mortality rate and hatching delay followed by declined heart rate was observed in green synthesized ZnO NP-treated embryos. The maximum toxicity was observed with an increase in the concentration of 100 µg/mL of the experimental dose, and at a low concentration of 25 µg/mL, it does not effectively show any developmental alteration in zebrafish embryos. Conclusion A novel polyherbal ICM loaded with ZnO NPs exhibited a dose-dependent effect on the heart rate, hatching, and mortality rate of the embryos. At optimal concentrations, the medication demonstrated minimal developmental malformations and cytotoxic effects, indicating its safety for use. However, increasing concentrations of the medication resulted in severe developmental malformations.

In Vivo Assays for Amyloid-Related Diseases

Amyloid-related diseases, such as Alzheimer's and Parkinson's disease, are devastating conditions caused by the accumulation of abnormal protein aggregates known as amyloid fibrils. While assays involving animal models are essential for understanding the pathogenesis and developing therapies, a wide array of standard analytical techniques exists to enhance our understanding of these disorders. These techniques provide valuable information on the formation and propagation of amyloid fibrils, as well as the pharmacokinetics and pharmacodynamics of candidate drugs. Despite ethical concerns surrounding animal use, animal models remain vital tools in the search for treatments. Regardless of the specific animal model chosen, the analytical methods used are usually standardized. Therefore, the main objective of this review is to categorize and outline the primary analytical methods used in in vivo assays for amyloid-related diseases, highlighting their critical role in furthering our understanding of these disorders and developing effective therapies.

Investigating the Potential of Essential Oils from Citrus reticulata Leaves in Mitigating Memory Decline and Oxidative Stress in the Scopolamine-Treated Zebrafish Model

Petitgrain essential oil (PGEO) is derived from the water distillation process on mandarin (Citrus reticulata) leaves. The chemical constituents of PGEO were analyzed by gas chromatography/mass spectrometry (GC/MS) method which revealed the presence of six compounds (100%). The major peaks were for methyl-N-methyl anthranilate (89.93%) and γ-terpinene (6.25%). Over 19 days, zebrafish (Tubingen strain) received PGEO (25, 150, and 300 μL/L) before induction of cognitive impairment with scopolamine immersion (SCOP, 100 μM). Anxiety-like behavior and memory of the zebrafish were assessed by a novel tank diving test (NTT), Y-maze test, and novel object recognition test (NOR). Additionally, the activity of acetylcholinesterase (AChE) and the extent of the brain's oxidative stress were explored. In conjunction, in silico forecasts were used to determine the pharmacokinetic properties of the principal compounds discovered in PGEO, employing platforms such as SwissADME, Molininspiration, and pKCSM. The findings provided evidence that PGEO possesses the capability to enhance memory by AChE inhibition, alleviate SCOP-induced anxiety during behavioral tasks, and diminish brain oxidative stress.

Zebrafish Model in Illuminating the Complexities of Post-Traumatic Stress Disorders: A Unique Research Tool

Post-traumatic stress disorder (PTSD) is a debilitating psychological condition that may develop in certain individuals following exposure to life-threatening or traumatic events. Distressing symptoms, including flashbacks, are characterized by disrupted stress responses, fear, anxiety, avoidance tendencies, and disturbances in sleep patterns. The enduring effects of PTSD can profoundly impact personal and familial relationships, as well as social, medical, and financial stability. The prevalence of PTSD varies among different populations and is influenced by the nature of the traumatic event. Recently, zebrafish have emerged as a valuable model organism in studying various conditions and disorders. Zebrafish display robust behavioral patterns that can be effectively quantified using advanced video-tracking tools. Due to their relatively simple nervous system compared to humans, zebrafish are particularly well suited for behavioral investigations. These unique characteristics make zebrafish an appealing model for exploring the underlying molecular and genetic mechanisms that govern behavior, thus offering a powerful comparative platform for gaining deeper insights into PTSD. This review article aims to provide updates on the pathophysiology of PTSD and the genetic responses associated with psychological stress. Additionally, it highlights the significance of zebrafish behavior as a valuable tool for comprehending PTSD better. By leveraging zebrafish as a model organism, researchers can potentially uncover novel therapeutic interventions for the treatment of PTSD and contribute to a more comprehensive understanding of this complex condition.

Neurobehavioral toxic effects and mechanisms of 2-aminobenzothiazole exposure on zebrafish

2-Aminobenzothiazole (NTH), a benzothiazole derivative, exhibits potent biochemical activities and plays a significant role in modern industry. Widespread and intensive utilization of NTH has led to its detection in aquatic environments, encompassing both groundwater and surface water. Despite its wide usage, the effect of NTH on developmental neurotoxicity in aquatic organisms remains uncharted. Therefore, the aim of this investigation was to create exposure models for short- and long-term studies in order to analyze the neurobehavioral toxic impact of NTH (0, 50, 500, and 5000 μg/L) on zebrafish, which includes motor function, anxiety, and memory performance, as well as to examine the mechanism of neurotoxicity. The results revealed a significant suppression of initial embryonic mobility by NTH. However, during short-term exposure experiments, it did not significantly impact the developmental neurobehavioral functions of zebrafish. In addition, significant effects on zebrafish were observed after long-term exposure to 50 and 500 μg/L NTH, mainly impacting locomotion, social behavior, anxiety, and cognitive functions. Moreover, NTH caused oxidative damage in adult zebrafish brain tissue, which was accompanied by abnormal expression of oxidative damage-related genes. Furthermore, the Real-Time PCR results indicated a significant suppression of genes related to exposure to NTH, specifically those in the GABA synthesis pathway (gabrg2, gad2, gad1b, and abat) and the 5-HT synthesis pathway (tph2, tph1b, pet1, and htr1aa). Taken together, this study demonstrates for the first time that chronic exposure to NTH decreases the expression of genes associated with the zebrafish GABA synthesis pathway and the 5-HT synthesis pathway. This suppression is accompanied by oxidative damage, ultimately resulting in neurobehavioral changes related to motor ability, anxiety, and memory performance.

A novel Zebrafish model of Alzheimer's disease by Aluminium chloride; involving nitro-oxidative stress, neuroinflammation and cholinergic pathway

Alzheimer's disease (AD) is the most common form of dementia and is a progressive neurodegenerative disorder of the brain. Most AD experimental animal models are pharmacological or transgenic in origin. The existing pharmacological approaches for developing AD are poorly developed and most of them fail to replicate the complete characteristics of disease pathology. Developing a cost-effective and reliable experimental animal model will meet this research gap. Zebrafish (ZF) are progressively emerging as a powerful drug discovery disease model to evaluate central nervous system (CNS) disorders due to their homologous similarities to humans as well as cost-effectiveness. The present research is conceptualized to develop and evaluate a reliable ZF AD model using aluminum chloride (AlCl3). Chronic exposure of 0.04 mM of AlCl3 for 28 days increased the expression of amyloid-β, phosphorylated tau protein and senile plaque development in the ZF brain. The observed changes were associated with learning and memory impairment. Furthermore, decreased brain-derived neurotrophic factor (BDNF) level and elevated oxidative stress indices, pro-inflammatory cytokines levels and acetylcholine esterase (AChE) activity was observed upon exposure to AlCl3 in the ZF brain. Chronic exposure to 0.04 mM of AlCl3 would be a cost-effective ZF AD model for pharmacological screening and may also be used to unravel the molecular mechanism underlying the neuropathology of the disease.

Zebrafish Experimental Animal Models for AD: A Comprehensive Review

AD disease (AD) is a multifaceted and intricate neurodegenerative disorder characterized by intracellular neurofibrillary tangle (NFT) formation and the excessive production and deposition of Aβ senile plaques. While transgenic AD models have been found instrumental in unravelling AD pathogenesis, they involve cost and time constraints during the preclinical phase. Zebrafish, owing to their simplicity, well-defined behavioural patterns, and relevance to neurodegenerative research, have emerged as a promising complementary model. Zebrafish possess glutaminergic and cholinergic pathways implicated in learning and memory, actively contributing to our understanding of neural transmission processes. This review sheds light on the molecular mechanisms by which various neurotoxic agents, including okadaic acid (OKA), cigarette smoke extract, metals, and transgenic zebrafish models with genetic similarities to AD patients, induce cognitive impairments and neuronal degeneration in mammalian systems. These insights may facilitate the identification of effective neurotoxic agents for replicating AD pathogenesis in the zebrafish brain. In this comprehensive review, the pivotal role of zebrafish models in advancing our comprehension of AD is emphasized. These models hold immense potential for shaping future research directions and clinical interventions, ultimately contributing to the development of novel AD therapies.

Zebrafish as a Potential Model for Neurodegenerative Diseases: A Focus on Toxic Metals Implications

In the last century, industrial activities increased and caused multiple health problems for humans and animals. At this moment, heavy metals are considered the most harmful substances for their effects on organisms and humans. The impact of these toxic metals, which have no biological role, poses a considerable threat and is associated with several health problems. Heavy metals can interfere with metabolic processes and can sometimes act as pseudo-elements. The zebrafish is an animal model progressively used to expose the toxic effects of diverse compounds and to find treatments for different devastating diseases that human beings are currently facing. This review aims to analyse and discuss the value of zebrafish as animal models used in neurological conditions, such as Alzheimer's disease (AD), and Parkinson's disease (PD), particularly in terms of the benefits of animal models and the limitations that exist.

An amino-terminal fragment of apolipoprotein E4 leads to behavioral deficits, increased PHF-1 immunoreactivity, and mortality in zebrafish

Although the increased risk of developing sporadic Alzheimer's disease (AD) associated with the inheritance of the apolipoprotein E4 (APOE4) allele is well characterized, the molecular underpinnings of how ApoE4 imparts risk remains unknown. Enhanced proteolysis of the ApoE4 protein with a toxic-gain of function has been suggested and a 17 kDa amino-terminal ApoE4 fragment (nApoE41-151) has been identified in post-mortem human AD frontal cortex sections. Recently, we demonstrated in vitro, exogenous treatment of nApoE41-151 in BV2 microglial cells leads to uptake, trafficking to the nucleus and increased expression of genes associated with cell toxicity and inflammation. In the present study, we extend these findings to zebrafish (Danio rerio), an in vivo model system to assess the toxicity of nApoE41-151. Exogenous treatment of nApoE41-151 to 24-hour post-fertilization for 24 hours resulted in significant mortality. In addition, developmental abnormalities were observed following treatment with nApoE41-151 including improper folding of the hindbrain, delay in ear development, deformed yolk sac, enlarged cardiac cavity, and significantly lower heart rates. A similar nApoE31-151 fragment that differs by a single amino acid change (C>R) at position 112 had no effects on these parameters under identical treatment conditions. Decreased presence of pigmentation was noted for both nApoE31-151- and nApoE41-151-treated larvae compared with controls. Behaviorally, touch-evoked responses to stimulus were negatively impacted by treatment with nApoE41-151 but did not reach statistical significance. Additionally, triple-labeling confocal microscopy not only confirmed the nuclear localization of the nApoE41-151 fragment within neuronal populations following exogenous treatment, but also identified the presence of tau pathology, one of the hallmark features of AD. Collectively, these in vivo data demonstrating toxicity as well as sublethal effects on organ and tissue development support a novel pathophysiological function of this AD associated-risk factor.