Dissociating retrieval-dependent contextual aversive memory processes in female rats: Are there cycle-dependent differences?

Upon retrieval, aversive associative memories may engage alternative processes depending on the conditioned stimulus exposure length. Generally, a short session maintains it through reconsolidation, and a long session inhibits it because of extinction learning. However, various experimental interventions have produced no memory changes when given after intermediate conditioned stimulus exposure events. The lack of effectiveness in the latter case has been explained by a stage of transition from reconsolidation to extinction, during which both phases are engaged but neither prevails. Alternatively, it would represent a novel, intermediate phase between reconsolidation and extinction. By combining a varying time of exposure to the paired context with the amnesic agent midazolam, and the introduction of a reinstatement procedure in the protocol to investigate the occurrence of extinction and/or reconsolidation, we aimed at addressing this question in female rats. Midazolam disrupted the reconsolidation of the original aversive memory and the consolidation of extinction memory when given after short (2 or 5 min, but not 1 min) and long (30 min) exposure to the paired context, respectively. There was reinstatement in the latter case only. Midazolam produced no memory changes when given after a session of 7 or 10 min, with reinstatement data suggesting the absence of reconsolidation in both cases. Noteworthy, drug effects on reconsolidation or extinction and the lack of action on the intermediate process were similar across the estrous cycle. Altogether, it was possible to check and dissociate three retrieval-dependent contextual fear memory processes using a more nuanced approach in females.
(Copyright © 2019 IBRO. Published by Elsevier Ltd. All rights reserved.)