Using Extinction-Renewal to Circumvent the Memory Strength Boundary Condition in Fear Memory Reconsolidation.

Reconsolidation is a process by which memories are destabilized, updated, and then restabilized. Strong memories are resistant to undergoing reconsolidation. Here, we addressed whether an overtrained fear memory could be made susceptible to reconsolidation by first extinguishing, and then renewing, the memory. Rats were trained with ten tone-footshock pairings, followed by eight days of tone extinction in the training context. The next day, rats were placed into a second context and memory for the tone was renewed/reactivated with a single tone presentation. Immediately following reactivation, rats received an injection of midazolam or vehicle. Rats were then tested for freezing to the tone in a third context. Midazolam had no effect in rats that did not undergo tone extinction, but significantly attenuated freezing to the tone in extinguished rats. Thus, rats that received tone extinction underwent tone memory reconsolidation following its renewal. In a second experiment, we administered the reactivation session and midazolam injections prior to extinction. Midazolam had no effect and rats extinguished at a rate similar to controls. These data suggest that strong emotional memories are capable of updating following weakening of memory expression through extinction.

Combined administration of MK-801 and cycloheximide produces a delayed potentiation of fear discrimination memory extinction.

Mixed evidence exists regarding the role of N-methyl-D-aspartate (NMDA) receptors in memory reconsolidation. We provide no evidence that NMDA receptors are involved with memory reconsolidation, but instead demonstrate that prereactivation systemic MK-801 injection, combined with postreactivation intrabasolateral amygdala (BLA) cycloheximide infusion, produces a delayed potentiation of extinction learning. These data suggest that an interaction between NMDA antagonism and protein synthesis inhibition may enhance extinction by exerting effects outside of the intended reconsolidation manipulation window. The present work demonstrates a novel pharmacological enhancement of extinction, and underscores the importance of employing proper control procedures in reconsolidation research. (PsycINFO Database Record