Chronic waterborne exposure to benzo[a]pyrene induces locomotor dysfunction and development of neurodegenerative phenotypes in zebrafish.

Benzo[a]pyrene (B[a]P), a prototype of polycyclic aromatic hydrocarbons (PAHs), is an ubiquitous and notable anthropogenic toxicant. The escalating load of anthropogenic organic pollutants on water bodies and its momentous impact on aquatic life may lead to the development of potent neurodegenerative diseases. Thus, the present study was conducted on zebrafish model to address the potential role of B[a]P in inducing neurodegenerative disease like phenotypes. Waterborne B[a]P exposure was performed for a stipulated period of 21 days at a concentration of 0.4 μg/ml. Separate groups of zebrafish were subjected to methylphenidate hydrochloride (MPH: 0.15 mg/L) bath exposure to study the effect on their behaviour before B[a]P exposure. The findings of the present study advocate that chronic exposure to B[a]P significantly impairs the locomotor activity in zebrafish, which showed reduction in total distance travelled and velocity. Histopathological observation by cresyl violet staining showed that there was significant increase in pyknotic neuronal counts in the diencephalon and telencephalic region of zebrafish brain after B[a]P exposure. Protein expression study showed that there was a significant increase in α-synuclein and decrease in UCH-L1, PSEN2, Nurr1 and NeuN expression in whole brain lysate of B[a]P-exposed zebrafish. Tyrosine hydroxylase (TH), as a marker of dopaminergic neurons, was significantly reduced in the B[a]P-exposed group. MPH co-supplementation significantly ameliorated the B[a]P induced altered expression of Parkinson's relevant proteins in zebrafish brain. These findings advocate that the locomotor impairment following chronic B[a]P exposure is associated with development of neurodegenerative phenotypes typically affecting the dopaminergic system in zebrafish.