Thyroid Endocrine Disruption and Neurotoxicity of Gestodene in Adult Female Mosquitofish (Gambusia Affinis)

The occurrence of progestins in various aquatic environments and their potential negative impact on aquatic ecosystems have attracted increasing attention. Here, the effects of gestodene (GES) on the thyroid endocrine system and nerve system were studied in the mosquitofish ( Gambusia affinis ). Adult female fish were exposed to GES at 0 (control), 4.4, 40.8, 378.7 ng/L for 60 days. The results showed that exposure to 378.7 ng/L GES caused a significant decrease in growth of fish compared with the control. The behavioral tests revealed that a marked reduction in the total distance (50.6%) and velocity (40.1 - 61.9%) was observed in the 378.7 ng/L GES treatment. The levels of T3 were significantly increased by GES in a dose-dependent manner, while those of T4 were slightly decreased. The AChE activity was decreased significantly in the 4.42 and 40.78 ng/L GES treatment, but increased significantly at 378.67 ng/L. In the brain, a strong increase of the transcriptional levels of Bdnf , Trh and Dio2 was observed in the fish from the 378.7 ng/L treatment. In addition, chronic exposure to GES caused colloid depletion, follicular collapse and epithelial hyperplasia in the thyroid, and angiectasis, congestion and vacuolar necrosis in the brain. These findings help better understand the effects of GES and the associated underlying mechanism in G. affinis .