Pharmacological discrimination of extinction and reconsolidation of contextual fear memory by a potentiator of AMPA receptors

Abstract

Conditioned fear memory, once formed through fear conditioning, is modulated by reexposure of individuals to a conditioned stimulus. The reexposure reactivates the fear memory, which induces reconsolidation of the memory first, and then extinction of the fear response. Both attenuating the former and facilitating the latter are effective in reducing the fear response, and these findings are potentially translatable to the enhancement of exposure therapy for complex anxiety disorders. Currently, there is no drug that is established to modulate either reconsolidation or extinction selectively, which are thought to be independent processes. Here, we report that an extinction-facilitating AMPA potentiator, 4-[2-(phenylsulfonylamino)ethylthio]-2,6-difluoro-phenoxyacetamide (PEPA), does not act on the reconsolidation of fear memory formed by contextual fear conditioning in mice. The freezing rates observed in contextually conditioned mice following short reexposure (3 min) to the context were not influenced by intraperitoneal or intra-amygdala administration of PEPA. The same short reexposure to the context enhanced freezing responses in mice that were similarly administered D-cycloserine (DCS), a drug that facilitates both extinction and reconsolidation, and this enhancement of freezing responses in mice intraperitoneally administered DCS was abolished by propranolol, a drug that suppresses reconsolidation. At the same doses used in the short reexposure experiments, PEPA and DCS facilitated extinction of the fear response induced by long reexposure to the context and suppressed reinstatement of the conditioned fear memory. PEPA and DCS did not affect reextinction. These results suggest that PEPA acts on extinction of contextual fear memory without having detectable influences on its reconsolidation.