The medial prefrontal cortex to the medial amygdala connections may affect the anxiety level in aged rats

Background Aging changes brain function and behavior differently in male and female individuals. Changes in the medial prefrontal cortex (mPFC)-medial amygdala (MeA) connectivity affect anxiety-like behavior. Objectives Therefore, this study aimed to investigate the effect of aging and sex on the mPFC-MeA connection and its association with the level of anxiety-like behavior. Methods We divided the Wistar rats into the male and female young rats (2-3-month-old) and male and female old rats (18-20 months old). First, the open field test (OFT) was performed, and then 80 nl of Fluoro-Gold (FG) was injected by stereotaxic surgery in the right or left MeA. After 10 days, the animals were perfused, their brain removed, coronal sections cut, and the number of FG-labeled cells in the right and left mPFC of each sample was estimated. Results Based on our results, old animals revealed less anxiety-like behavior than young ones, and young females were less anxious than young males, too. Interestingly, MeA of old male rats received more fibers from the bilateral mPFC than young ones. Also, this connection was stronger in the young females than young males. Altogether, the present study indicated that old individuals had less anxiety-like behavior and stronger mPFC-MeA connection, and young female rats were less anxious and had a stronger connection of mPFC-amygdala than males of the same age. Conclusion Thus, it seems that there is a negative relationship between anxiety levels based on the rat's performance in the OFT apparatus and the mPFC-MeA connection.