Embryonic BPA exposure has transgenerational effects on Medaka

Bisphenol A (BPA), a xenoestrogen, has developmental- and behavior-altering effects in fish through the Gonadotropin releasing hormone (GnRH) neural pathway. Previous studies using transgenic lines of medaka with GnRH3 neurons tagged with green fluorescent protein (GFP) showed that embryonic low dose BPA exposure affected the developing GnRH3 neurons. GnRH3 neurons in medaka are located in extra-hypothalamic regions of the terminal nerve (TN) and trigeminal nerve (TG), with a putative role in modulating allied reproductive behaviors. Here, we examined transgenerational effects of parental low dose BPA exposure (200ug/L) on first generation (F1) offspring. Fertilized medaka embryos (F1) were collected from two distinct parental BPA exposure groups – i) G1, two-week long exposure from egg laying and ii) G2: exposure from 0-6 days post fertilization (dpf), as well as F1 eggs from untreated controls.

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Transparent medaka embryos allow for fluorescent imaging of GnRH3-GFP neurons. Images were taken on dpf 3, 4, and 5 and GnRH3 neuron populations in the TG and TN were assessed. BPA exposure effects were quantized using changes in GnRH neural fluorescence. While an initial increase in GnRH3 fluorescence in both treatment groups as compared to control was seen at 3dpf, a significant decrease in fluorescence was seen at 4dpf for both groups at both TG and TN loci: (G1: -28.04% TG, -32.29% TN; G2: -43.03% TG, -28.92% TN). This trend is in contrast to the observed significant increase in TN fluorescence seen in the parents. G1 and G2 groups both showed delayed hatching rates vs. controls. Overall embryonic brain growth assessed on 3 and 4dpf by measuring eye distance. showed significantly smaller brains in both treatment groups vs. controls (G1: -17.7% 3dpf, -6.76% 4dpf; G3 -14.7% 4dpf 4). This novel study suggests that chronic low dose BPA exposure in parents (briefly during embryonic development) can have transgenerational effects on the GnRH neuronal systems.

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