BDE-47 Causes Depression-like Effects in Zebrafish Larvae via a Non-Image-Forming Visual Mechanism

Depression is a high-incidence mood disorder that is frequently accompanied by sleep disturbances, which can be triggered by the non-image-forming (NIF) visual system. Therefore, we hypothesize that polybrominated diphenyl ethers are known to induce visual impairment that could promote depression by disrupting the NIF visual pathway. In this study, zebrafish larvae were exposed to BDE-47 at environmentally relevant concentrations (2.5 and 25 μg/L). BDE-47 caused melanopsin genes that dominate the NIF visual system that fell at night (p < 0.05) but rose in the morning (p < 0.05). Such bidirectional difference transmitted to clock genes and neuropeptides in the suprachiasmatic nucleus and impacted the adjacent serotonin system. However, indicative factors of depression, including serta, htr1aa, and aanat2, were unidirectionally increased 1.3- to 1.6-fold (p < 0.05). They were consistent with the increase in nighttime thigmotaxis (p < 0.05) and circadian hypoactivity (p < 0.05). The results of melanopsin antagonism also indicated that these consequences were possibly due to the combination of direct photoentrainment by melanopsin and circadian disruption originating from melanopsin. Collectively, our findings revealed that BDE-47 exposure disrupted the NIF visual pathway and resulted in depression-like effects, which may further exert profound health effects like mood disorders.