Differential roles of the infralimbic and prelimbic areas of the prefrontal cortex in reconsolidation of a traumatic memory

Abstract

Studies about reconsolidation of conditioned fear memories have shown that pharmacological manipulation at memory reactivation can attenuate or enhance the subsequent expression of the conditioned fear response. Here we examined the effects of a single injection of the mTOR inhibitor rapamycin (Rap) into the infralimbic (IL) and prelimbic (PL) areas [which compose the ventromedial prefrontal cortex (PFC)] on reconsolidation and extinction of a traumatic fear memory. We found opposite effects of Rap infused into the PL and IL on reconsolidation and extinction: intra-PL Rap and systemic Rap impaired reconsolidation and facilitated extinction whereas intra-IL Rap enhanced reconsolidation and impaired extinction. These effects persisted at least 10 days after reactivation. Shock exposure induced anxiety-like behavior and impaired working memory and intra-IL and -PL Rap normalized these effects. Finally, when measured after fear retrieval, shocked rats exhibited reduced and increased phosphorylated p70s6K levels in the IL and basolateral amygdala, respectively. No effect on phosphorylated p70s6K levels was observed in the PL. The study points to the differential roles of the IL and PL in memory reconsolidation and extinction. Moreover, inhibiting mTOR via rapamycin following reactivation of a fear memory may be a novel approach in attenuating enhanced fear memories.

Keywords: Extinction; Inhibitory avoidance; Post-traumatic stress disorder (PTSD); Rapamycin.