Atrazine alters kisspeptin signaling and downstream neuroendocrine regulation following embryonic exposure in zebrafish.

Atrazine is an herbicide used to control broadleaf and grassy weeds but is also a known endocrine disrupting chemical classified by the US EPA for its effect on the luteinizing hormone (LH) surge. The US EPA's maximum contaminant level (MCL) for atrazine in drinking water is 3 parts per billion (ppb; µg/L), though concentrations may exceed this during peak crop seasons. Because drinking water is the primary exposure route, studying environmentally relevant concentrations near the MCL is critical for understanding public health impacts. Atrazine has been shown in epidemiological and toxicological studies to disrupt neuroendocrine and reproductive functions, including suppression of gonadotropin-releasing hormone (GnRH) neuron activity, leading to decreased LH and follicle-stimulating hormone (FSH) surges. Given the breadth of observed effects, this study hypothesized that atrazine targets an upstream neuroendocrine regulator-the kisspeptin signaling pathway-due to its dual role in reproductive and dopaminergic regulation. Kisspeptin expression was characterized in developing zebrafish, showing increases every 24 h from 1 to 120 h post fertilization (hpf). Zebrafish were exposed during embryogenesis (1-72 hpf) to atrazine at 0, 0.3, 3, or 30 ppb. Immunofluorescence at 120 hpf showed reduced kisspeptin expression in the habenula at 3 ppb and near-complete loss of kiss1/kiss2 expression with brain disorganization at 30 ppb. Kisspeptin, LH, and FSH levels were measured at 168 hpf and 6 months post fertilization (mpf). Age- and sex-dependent alterations were observed. Behavioral tests revealed anxiety-like phenotypes in larvae and adults. These findings indicate atrazine disrupts neuroendocrine and behavioral function through kisspeptin pathway dysfunction.