| Abstract | Thyroid disrupting compounds are ubiquitous in every-day life and are commonly found in aquatic environmentts where they have the potential to impact aquatic species. These compounds can inhibit thyroid hormone synthesis and are most well-known for leading to delayed development and altered metamorphosis. However, a recent study by Bryant (2021) found that fathead minnows exposed to propylthiouracil (PTU, a known thyroid disrupting compound) during development experienced altered reproductive behavior upon maturation with significant reductions in competition, courtship and nest care behaviors. The mechanisms linking thyroid disruption to altered reproduction behavior remain unknown; thus, the principle objective of this study was to determine how the expression of genes known to play a role in sexual differentiation of the brain and neural development are impacted by early-life-stage thyroid disruption. In the present study, a subset of fish from the same group of fish utilized in the Bryant (2021) study were used to analyze the expression of aromatase, estrogen receptor alpha, estrogen receptor beta, androgen receptor, tyrosine hydroxylase, dopamine receptor 2, and basic transcription element binding protein in the brain. All three of the genes involved in neurogenesis, tyh, dr2, and bteb, exhibited a significant increase in expression in the high exposure group (70 mg PTU/L) compared to the control group. While these gene expression changes suggest alterations in neural development, the sample population did not exhibit altered feeding behavior or C-start response (both indicative of neural development in general); thus, it is unlikely that the observed alterations in reproductive behavior can be attributed to such gene expression changes. Of the genes involved in sexual differentiation and sex steroid hormone signaling, only era deminstrated a significant increase in expression in the high exposure group (70 mg PTU/L) compared to the control group indicating that altered estrogen signaling could be linked to the observed alterations in reproductive behavior. |
