Aroclor 1254 impairs visual and neurosensory signaling pathways independent of the aryl hydrocarbon receptor in larval zebrafish.

Aroclor 1254 is a mixture of polychlorinated biphenyl (PCB) congeners that are present in aquatic systems originating from coolants, solvents, plasticizers, and shipbreaking. Aroclor 1254 can induce an eye tremor response in early life stage zebrafish (Danio rerio) following exposure to between 22.7 and 4140 µg/L Aroclor 1254 at 102 h post fertilization (hpf), as shown in our recent study. However, the underlying mechanism that induces this response, either acting through the aryl hydrocarbon receptor (AhR) or non-AhR pathways, is not well characterized. As such, transcriptomics, morphology, and targeted behavioral functions were assessed using previously exposed larvae. Transcriptomic profiling was conducted in 102 hpf larvae to elucidate what may be driving this tremor response using in silico bioinformatic software. Subsequent eye tremor responses, a visually mediated behavioral function assay, and eye morphology were assessed in 7 day post fertilization (dpf) larvae after embryonic treatment. Parkinson's signaling pathway, opioid signaling pathway, and the negative regulation of general cell signaling and communication were the top enriched dose-dependent pathways predicted. Eye diameters were significantly decreased in 7 dpf larvae exposed to 173 µg/L Aroclor 1254, whereas the number of eye saccades, assessed with an optokinetic response assay, and eye tremor response behavior were increased following exposure to a concentration of ≥ 173 µg/L Aroclor 1254. This suggests that Aroclor 1254 acts through a cross-talk of visual and neuronal-based mechanisms, and that non-AhR pathways may be more important than AhR pathways in inducing visual effects, which may influence survivorship and recruitment in early life stage wild fish.