Benzo[a]pyrene (B[a]P) is commonly associated with oxidative stress-induced neurotoxicity. Retinoic acid (RA) has been shown to exhibit neuroprotection in brain, and disruption of RA signaling via excess or deficient RA can lead to oxidative stress. B[a]P contamination in aquatic environment has been shown to lower the internal RA level. Thus, the present study was conducted in wild-type zebrafish to ameliorate the neurotoxic effect of B[a]P by waterborne RA co-supplementation. Findings showed that B[a]P induced anxiolytic-like behavioral response, and altered antioxidant activity in zebrafish is attenuated by RA. Our study also advocated the neurotoxic potential of RA treatment alone in control condition. Previous findings showed that periventricular gray zone (PGZ) of optic tectum (TeO) in zebrafish brain regulates anxiety-like behavior. The augmented pyknotic neuronal counts in PGZ following B[a]P treatment was ameliorated by RA co-supplementation. Further, presence of B[a]P in the cell milieu is known to induce oxidative stress through increase expression of cytochrome P450 1A1 (CYP1A1), an enzyme necessary for metabolic breakdown of both B[a]P and RA. Any deviation from the required concentration of RA leads to production of reactive oxygen species. Further, low availability of RA in cell milieu is known to decrease the expression of Nrf2, a transcription factor necessary for the expression of several antioxidants and antioxidant enzymes. Recent studies also showed that RA increases glutathione synthesis and exhibits neuroprotective properties in brain cells. The findings of the present study address the potential role of exogenous RA co-supplementation as a therapeutic intervention against B[a]P-induced depletion of RA, causing neurotoxicity in zebrafish.

The aquatic environment provides a sink for the environmental pollutants that have potential to induce oxidative stress by altering neurobehavioral response of aquatic animals. Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon is known to induce oxidative stress in the brain. Withania somnifera has been used traditionally for its neuroprotective effect in experimental models of neurological disorders. The present study is aimed to evaluate the neuroprotective potential of Withania somnifera leaf extract (WSLE) following exposure to waterborne B[a]P. Wild-type zebrafish (Danio rerio) were designated as naive, control (dimethyl sulfoxide), WSLE, B[a]P, and B[a]P + WSLE groups. Behavioral studies showed reversal in scototaxis (anxiety-like) behavior in B[a]P group and was restored by WSLE cosupplementation in B[a]P + WSLE group. B[a]P-induced altered antioxidant status was ameliorated by WSLE in the B[a]P + WSLE group. Previous studies showed that the periventricular gray zone (PGZ) of the optic tectum in zebrafish brain regulates scototaxis (anxiety-like) behavior. Our histopathological observation showed a significant increase in the pyknotic neuronal counts in PGZ of the B[a]P group and was ameliorated by WSLE cosupplementation. The study showed that the reversal in scototaxis behavior following exposure to waterborne B[a]P might be associated with neuromorphological alterations in PGZ, whereas a pioneer ethnopharmacological approach of WSLE cosupplementation showed its neuroprotective role to restore normal scototaxis of zebrafish. Future research directing toward understanding the role of visual circuit involved with impaired scototaxis behavior in zebrafish might provide new pathological outcomes following exposure to B[a]P.

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