Participation of corticosterone and adrenaline in the re-exposure to the context fear conditioning task: effects on memory persistence?

Abstract

The cognitive processes (learning and memory) are essential for our adaptation to environment changes and consequently for our survival. There are several studies that indicate that adrenal hormones - glucocorticoids (GC) and adrenaline - participate in the regulation of memory functions during stress situations. It is interesting to notice the interaction of complementarity that exists between these two systems when it comes to aversive memories. GC act as modulators of cognitive processes, facilitating or impairing these processes, depending on their circulating levels. High or low levels of this hormone impair performance and intermediate levels are related to an improvement in performance. The administration of metyrapone (a GC synthesis inhibitor) 90 min before retrieval of a contextual fear memory impairs this memory function, but results in an increase in fear response in a subsequent re-exposure, suggesting that a reduction of GC concentration in a situation that should produce an increase in its secretion (first re-exposure) can release the adrenergic system modulation by negative feedback, thus causing a hyper-secretion of adrenaline, which can lead to increased fear in the second re-exposure. The aim of this study is to investigate the function of these stress response systems in the retrieval and memory persistence of contextual fear task. (AU)