Chronic Restraint Stress Did Not Alter Active Avoidance Coping or Neuronal Activation Levels of the Medial Prefrontal Cortex or the Nucleus Accumbens in Male Rats

Abstract

Stress is an adaptive response crucial for survival. However, chronic stress can lead to maladaptive behaviors and health issues. Prolonged stress reduces the flexibility of defensive coping behaviors. Previous studies have shown that the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc) play critical roles in maintaining active avoidance instead of freezing behaviors in face of threats. This study aimed to investigate whether chronic stress altered the prelimbic cortex, infralimbic cortex, NAc core and the NAc shell neuronal activation levels and the defensive coping in male rats in face of danger, and we hypothesized that the activation levels of these two brain regions would decrease and the animals would spend more time in freezing. The animals underwent a chronic restraint stress procedure (2 h/day) for consecutive 14 days. Using a cued lever-pressing shock avoidance task, we assessed the avoidance coping and the neuronal activities in the mPFC and the NAc. Our results showed that compared to nonstressed controls, animals that underwent chronic restraint stress were slower in gaining body weight and developed despair-like behaviors in the forced swim test. However, contrary to our hypothesis, chronic restraint stress did not alter active avoidance coping or neuronal activation levels of the mPFC and the NAc.

Keywords

• avoidance behavior
• chronic stress
• freezing
• medial prefrontal cortex
• nucleus accumbens