Neurotoxicity of 4-nonylphenol in adult zebrafish: Evaluation of behaviour, oxidative stress parameters and histopathology of brain

Nonylphenol and its derivatives use as plasticizer or additives in manufacturing industries. Effluents originated from industrial areas are being added to soil, ground water, river and marine water intentionally or unintentionally. Complex mixture of these contaminants enter the food chain and produce sub-lethal deleterious effects mainly on nervous and reproductive systems of aquatic animals and human beings. The information pertaining to oxidative stress-mediated alterations in brain of zebrafish would be helpful to understand the toxicity potential of such compounds in aquatic animals. The aim of the present study was to evaluate the behavioural changes, status of oxidative stress markers; sod, cat, and NF-E2-related factor 2 (nrf2) mRNA gene expression profile; and histopathological changes in the brain of adult zebrafish exposed to 4-nonylphenol (4NP) at concentration of 100 and 200 μg/L of water for 21 days. Zebrafish were divided into four groups viz; control (C1), vehicle (C2, ethanol 10 μg/L of water), treatment 1 (T1, 4-NP, 100 μg/L) and treatment 2 (T2, 4-NP, 200 μg/L). Both exposure levels of 4-NP adversely affected the exploratory behaviour of zebrafish and produced anxiety-like symptom. Concentration-dependent reduction in activity of superoxide dismutase and catalase; and glutathione level, with increased level of malondialdehyde recorded in the brain of exposed zebrafish. Gene expression analysis showed down regulation of sod, cat, nrf2 genes in brain of zebrafish from toxicity groups indicating 4-NP induced oxidative stress in brain. However, noticeable histological alterations were not observed in 4-NP exposed brain of zebrafish.