Taste aversion memory reconsolidation is independent of its retrieval
Highlights
► AMPA receptors inhibition in the amygdala impaired retrieval of taste aversion memory regardless of memory strength. ► Inhibition of retrieval did not affect anisomycin disruption of reconsolidation. ► Retrieval does not trigger destabilization required for memory reconsolidation. ► Relevant updated information causes stored memory to render labile and susceptible for reconsolidation.
Introduction
Memories stabilize over time through a protein synthesis-dependent process named consolidation (McGaugh, 2000). However upon activation, consolidated memories return to a labile state and undergo a consolidation-like process referred to as reconsolidation (Nader & Einarsson, 2010). Mainly, reconsolidation is sustained by the now widely reported observation that after a memory trace is activated, it is susceptible to disruption by the same treatments that disrupt memory during consolidation, e.g., protein synthesis inhibitors (Nader & Einarsson, 2010). Memory reconsolidation is an opportunity to modify or even erase memories, making manipulation of reconsolidation a plausible therapeutic tool for treating people with anxiety disorders, like PTSD or phobias. Therefore, to describe the relevant parameters that trigger reconsolidation is of general interest in the field.
It has been considered that retrieval is one condition to be essential to initiate reconsolidation (Nader & Einarsson, 2010). However, no experimental evidence support this notion and, on the contrary, one work reported that indeed, reconsolidation occurs in the absence of retrieval (Ben Mamou, Gamache, & Nader, 2006). In that study CNQX, an AMPA receptor antagonist, was shown to disrupt retrieval of fear conditioning when infused in the amygdala of rats. Then, CNQX and the protein synthesis inhibitor anisomycin were infused together into the amygdala. Retrieval was again disrupted and anisomycin impaired memory reconsolidation, indicating that memory can be activated and turn labile without memory retrieval (Ben Mamou et al., 2006). To provide further evidence on this regard, we examined whether transient pharmacological disruption of memory retrieval impedes reconsolidation in the widely used associative conditioning task, taste aversion.
Taste aversion was obtained by intraperitoneal injection of LiCl after intake of a novel saccharin taste solution. As a result taste-aversion association is induced and, on the next presentation saccharin solution was recognized as an aversive tastant and consumption was reduced (Bermudez-Rattoni, 2004). To assess effects on reconsolidation, memory was strengthened by repeating taste-aversion training on the next day (Fig. 1, solid circles). Protocols that update memory by strengthening have successfully been used to evaluate reconsolidation (Garcia-DeLaTorre et al., 2009, Lee, 2008, Rodriguez-Ortiz et al., 2005, Rodriguez-Ortiz et al., 2008).
Section snippets
Subjects
Male Wistar rats from Instituto de Fisiología Celular breeding colony weighing between 270 and 310 g at the beginning of experiment were housed individually in plastic cages on a 12 h/12 h light/dark cycle. All manipulations were performed during light cycle. Food was freely available throughout experiments. Every effort was made to reduce the number of animals used and all experiments were performed in accordance with the Ministry of Health of Mexico.
Surgery and microinjections
Animals under ketamine/xylazine (22/2.6 mg/rat)
Retrieval is not necessary to initiate taste aversion memory reconsolidation
Previous work has shown that AMPA (αamino-3-hydroxyl-5-methyl-4-isoxazole-propionate) receptors inhibition in the amygdala of rats specifically disrupts retrieval of conditioned fear and conditioned taste aversion without affecting memory acquisition or consolidation (Ben Mamou et al., 2006, Yasoshima et al., 2005). Accordingly, we infused NBQX (2,3-dioxo-6nitro-1,2,3,4-tetrahydrobenzo [f]quinoxaline-7-sulfonamide) in the amygdala of rats before acquisition of a second taste aversion. Fig. 1A
Discussion
In the present report we observe that inhibition of retrieval did not impede incorporation of information to long-term memory. This finding indicates that retrieval and long-term storage of updated information are dissociable processes. This idea seems counterintuitive since stored memory must turn active in order to incoming information be integrated to long-term memory, and retrieval looks like the most adequate mechanism to activate memory (Lewis, 1979). However from our results, memory can
Acknowledgments
We thank for comments to Dr. Yadin Dudai and we thank Perla Moreno, Oreste Carbajal and Patricia Delgado for their technical assistance. CONACYT-México 060478, 155242 and DGAPA IN216709 supported this study.
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