The Effect of Atrazine on Fear Behaviors in Rats

Abstract

Atrazine (ATR) is a widely used herbicide in agriculture. Unfortunately, excessive use of ATR has led to the contamination of food and drinking sources (Mosquin et al., 2012; Whitmore and Chen, 2013). Subsequently, this has led to humans becoming exposed to ATR in their daily life. Animal studies have shown that ATR can influence emotionally relevant behaviors such as anxiety in rodents (Ma et al., 2018; Chavez‐Pichardo et al., 2020). However, other emotional behaviors such as fear remain unexplored. To address this gap, rats were exposed to ATR in their drinking water at a dose considered safe for ingestion (0.035mg/kg; Environmental Protection Agency), whereas control animals received filtered water. Both groups had ad libitum access to water for four months. Following exposure, fear was assessed using Pavlovian fear conditioning where rats learn that a tone predicts a shock by exhibiting freezing behavior to the tone. We hypothesized that rats exposed to ATR would show increased fear expression compared to control rats. Anxiety‐like behavior was also examined using the open field test. During fear conditioning no differences were observed in freezing behavior between groups (ATR: 58%, Controls: 59%; n=10; p=0.3714). In the open field test, ATR rats trended towards having more center entries (ATR: 23.8, Controls: 14.8; n=10, p=0.0570) and decreased time spent in corners (ATR: 70.5 s, Controls: 114.2 s; n=10, p=0.0248) compared to controls. These results suggest that ATR does not affect fear behaviors, but it can decrease anxiety‐like behaviors. Future directions aim at examining brain regions key to emotional behaviors, such as the amygdala, using immunohistochemistry. Our findings may help elucidate how prolonged ingestion of atrazine at a dose considered safe for humans may influence emotionally relevant behaviors.