Processamento da memória de medo: dimorfismo sexual e consolidação tardia na amígdala e no córtex pré-frontal medial

Abstract

Not all memories last for the lifetime. Generally speaking, memories with high emotional value during acquisition tend to remain accessible for longer periods. However, the mechanisms that interfere with memory endurance are not fully understood. In this work, we modulated the intensity of memory trace emotional value by altering unconditioned stimulus (US) frequency (1 or 5US) during acquisition of contextual fear memory. In male mice, the memory was present 1 day after conditioning in 1 and 5US groups. We used an immediate early gene, ZiF268, as a marker for neural plasticity during consolidation. Nevertheless, only in the 5US group memory persisted for 30 days. On the other hand, only females in the 5US group expressed conditioned fear. Next, we tested the hypothesis that 1US and 5US protocols differently modulate memory formation during systems consolidation, which results in memories with distinct duration. In order to test it, we analyzed ZiF268 expression 12h after acquisition in two areas known for their involvement in systems consolidation: the medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA). 12h after training, a difference between 1US and 5US expression was found in mPFC, but not in BLA. Our results suggest that high emotional value contextual fear memory (5US) results in diminished plasticity in mPFC during systems consolidation, thus probably resulting in diminished modulation by mPFC over other structures, hence allowing memory to persist for 30 days.