Neurobehavioral effects of fungicides in zebrafish: a systematic review and meta-analysis.

Pesticides are widely used in global agriculture to achieve high productivity levels. Among them, fungicides are specifically designed to inhibit fungal growth in crops and seeds. However, their application often results in environmental contamination, as these chemicals can persistently be detected in surface waters. This poses a potential threat to non-target organisms, including humans, that inhabit the affected ecosystems. In toxicologic research, the zebrafish (Danio rerio) is the most commonly used fish species to assess the potential effects of fungicide exposure, and numerous and sometimes conflicting findings have been reported. To address this, we conducted a systematic review and meta-analysis focusing on the neurobehavioral effects of fungicides in zebrafish. Our search encompassed three databases (PubMed, Scopus, and Web of Science), and the screening process followed predefined inclusion/exclusion criteria. We extracted qualitative and quantitative data, as well as assessed reporting quality, from 60 included studies. Meta-analyses were performed for the outcomes of distance traveled in larvae and adults and spontaneous movements in embryos. The results revealed a significant overall effect of fungicide exposure on distance, with a lower distance traveled in the exposed versus control group. No significant effect was observed for spontaneous movements. The overall heterogeneity was high for distance and moderate for spontaneous movements. The poor reporting practices in the field hindered a critical evaluation of the studies. Nevertheless, a sensitivity analysis did not identify any studies skewing the meta-analyses. This review underscores the necessity for better-designed and reported experiments in this field.

Effects of N-acetylcysteine and acetyl-L-carnitine on acute PTZ-induced seizures in larval and adult zebrafish.

BACKGROUND: Epilepsy is a prevalent neurological disease, affecting approximately 1-2% of the global population. The hallmark of epilepsy is the occurrence of epileptic seizures, which are characterized by predictable behavioral changes reflecting the underlying neural mechanisms of the disease. Unfortunately, around 30% of patients do not respond to current pharmacological treatments. Consequently, exploring alternative therapeutic options for managing this condition is crucial. Two potential candidates for attenuating seizures are N-acetylcysteine (NAC) and Acetyl-L-carnitine (ALC), as they have shown promising neuroprotective effects through the modulation of glutamatergic neurotransmission. METHODS: This study aimed to assess the effects of varying concentrations (0.1, 1.0, and 10 mg/L) of NAC and ALC on acute PTZ-induced seizures in zebrafish in both adult and larval stages. The evaluation of behavioral parameters such as seizure intensity and latency to the crisis can provide insights into the efficacy of these substances. RESULTS: Our results indicate that both drugs at any of the tested concentrations were not able to reduce PTZ-induced epileptic seizures. On the other hand, the administration of diazepam demonstrated a notable reduction in seizure intensity and increased latencies to higher scores of epileptic seizures. CONCLUSION: Consequently, we conclude that, under the conditions employed in this study, NAC and ALC do not exhibit any significant effects on acute seizures in zebrafish.

Chemically-induced epileptic seizures in zebrafish: A systematic review.

The use of zebrafish as a model organism is gaining evidence in the field of epilepsy as it may help to understand the mechanisms underlying epileptic seizures. As zebrafish assays became popular, the heterogeneity between protocols increased, making it hard to choose a standard protocol to conduct research while also impairing the comparison of results between studies. We conducted a systematic review to comprehensively profile the chemically-induced seizure models in zebrafish. Literature searches were performed in PubMed, Scopus, and Web of Science, followed by a two-step screening process based on inclusion/exclusion criteria. Qualitative data were extracted, and a sample of 100 studies was randomly selected for risk of bias assessment. Out of the 1058 studies identified after removing duplicates, 201 met the inclusion criteria. We found that the most common chemoconvulsants used in the reviewed studies were pentylenetetrazole (n = 180), kainic acid (n = 11), and pilocarpine (n = 10), which increase seizure severity in a dose-dependent manner. The main outcomes assessed were seizure scores and locomotion. Significant variability between the protocols was observed for administration route, duration of exposure, and dose/concentration. Of the studies subjected to risk of bias assessment, most were rated as low risk of bias for selective reporting (94%), baseline characteristics of the animals (67%), and blinded outcome assessment (54%). Randomization procedures and incomplete data were rated unclear in 81% and 68% of the studies, respectively. None of the studies reported the sample size calculation. Overall, these findings underscore the need for improved methodological and reporting practices to enhance the reproducibility and reliability of zebrafish models for studying epilepsy. Our study offers a comprehensive overview of the current state of chemically-induced seizure models in zebrafish, highlighting the common chemoconvulsants used and the variability in protocol parameters. This may be particularly valuable to researchers interested in understanding the underlying mechanisms of epileptic seizures and screening potential drug candidates in zebrafish models.

Micronized Curcumin Causes Hyperlocomotion in Zebrafish Larvae.

Zebrafish larvae have been widely used in neuroscience and drug research and development. In the larval stage, zebrafish present a broad behavioral repertoire and physiological responses similar to adults. Curcumin (CUR), a major component of Curcuma longa L. (Zingiberaceae), has demonstrated the ability to modulate several neurobiological processes relevant to mental disorders in animal models. However, the low bioavailability of this compound can compromise its in vivo biological potential. Interestingly, it has been shown that micronization can increase the biological effects of several compounds. Thus, in this study, we compared the effects of acute exposure for 30 min to the following solutions: water (control), 0.1% DMSO (vehicle), 1 µM CUR, or 1 µM micronized curcumin (MC) in zebrafish larvae 7 days post-fertilization (dpf). We analyzed locomotor activity (open tank test), anxiety (light/dark test), and avoidance behavior (aversive stimulus test). Moreover, we evaluated parameters of oxidative status (thiobarbituric acid reactive substances and non-protein thiols levels). MC increased the total distance traveled and absolute turn angle in the open tank test. There were no significant differences in the other behavioral or neurochemical outcomes. The increase in locomotion induced by MC may be associated with a stimulant effect on the central nervous system, which was evidenced by the micronization process.

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

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

N-acetylcysteine protects against motor, optomotor and morphological deficits induced by 6-OHDA in zebrafish larvae.

BACKGROUND: Parkinson's disease (PD) is the second most common neurodegenerative disorder. In addition to its highly debilitating motor symptoms, non-motor symptoms may precede their motor counterparts by many years, which may characterize a prodromal phase of PD. A potential pharmacological strategy is to introduce neuroprotective agents at an earlier stage in order to prevent further neuronal death. N-acetylcysteine (NAC) has been used against paracetamol overdose hepatotoxicity by restoring hepatic concentrations of glutathione (GSH), and as a mucolytic in chronic obstructive pulmonary disease by reducing disulfide bonds in mucoproteins. It has been shown to be safe for humans at high doses. More recently, several studies have evidenced that NAC has a multifaceted mechanism of action, presenting indirect antioxidant effect by acting as a GSH precursor, besides its anti-inflammatory and neurotrophic effects. Moreover, NAC modulates glutamate release through activation of the cystine-glutamate antiporter in extra-synaptic astrocytes. Its therapeutic benefits have been demonstrated in clinical trials for several neuropsychiatric conditions but has not been tested in PD models yet. METHODS: In this study, we evaluated the potential of NAC to prevent the damage induced by 6-hydroxydopamine (6-OHDA) on motor, optomotor and morphological parameters in a PD model in larval zebrafish. RESULTS: NAC was able to prevent the motor deficits (total distance, mean speed, maximum acceleration, absolute turn angle and immobility time), optomotor response impairment and morphological alterations (total length and head length) caused by exposure to 6-OHDA, which reinforce and broaden the relevance of its neuroprotective effects. DISCUSSION: NAC acts in different targets relevant to PD pathophysiology. Further studies and clinical trials are needed to assess this agent as a candidate for prevention and adjunctive treatment of PD.