Learning-dependent BDNF levels in the rat medial prefrontal cortex: approach vs. withdrawal

This article presents a comparison of changes in molecular markers of systemogenesis related to behavioral motivation: approach versus avoidance, differing in their stress levels. We conducted an immunohistochemical study of brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex of adult Long-Evans rats. Two groups were trained in a bar-pressing task: 1) to activate a food dispenser and obtain food (approach); 2) to terminate a shock and avoid pain (avoidance). The avoidance group showed significantly fewer BDNF-immunopositive cells in the prelimbic and infralimbic prefrontal cortex compared to the approach group. Furthermore, BDNF levels correlated with individual differences in anxiety and exploratory activity. We conclude that the medial prefrontal cortex is involved in both approach and avoidance behaviors, but to a significantly lesser extent in avoidance. The potential role of stress-induced neuroinflammation in these differences is discussed.