Increasing the GluN2A/GluN2B Ratio in Neurons of the Mouse Basal and Lateral Amygdala Inhibits the Modification of an Existing Fear Memory Trace.
Reconsolidation updating is a form of memory modification in which an existing memory can become destabilized upon retrieval and subsequently be modified via protein-synthesis-dependent reconsolidation. However, not all memories appear to destabilize upon retrieval and thus are not modifiable via reconsolidation updating approaches and the neurobiological basis for this remains poorly understood. Here, we report that auditory fear memories created with 10 tone-shock pairings are resistant to retrieval-dependent memory destabilization and are associated with an increase in the synaptic GluN2A/GluN2B ratio in neurons of the basal and lateral amygdala (BLA) compared with weaker fear memories created via one or three tone-shock pairings. To increase the GluN2A/GluN2B ratio after learning, we generated a line of mice that expresses an inducible and doxycycline-dependent GFP-GluN2A transgene specifically in α-CaMKII-positive neurons. Our findings indicate that increasing the GluN2A/GluN2B ratio in BLA α-CaMKII-positive neurons after a weak fear memory has consolidated inhibits retrieval-dependent memory destabilization and modification of the fear memory trace. This was associated with a reduction in retrieval-dependent AMPA receptor trafficking, as evidenced by a reduction in retrieval-dependent phosphorylation of GluR1 at serine-845. In addition, we determined that increasing the GluN2A/GluN2B ratio before fear learning significantly impaired long term memory consolidation, whereas short-term memory remained unaltered. An increase in the GluN2A/GluN2B ratio after fear learning had no influence on fear extinction or expression. Our results underscore the importance of NMDAR subunit composition for memory destabilization and suggest a mechanism for why some memories are resistant to modification.



Memory modification using reconsolidation updating is being examined as one of the potential treatment approaches for attenuating maladaptive memories associated with emotional disorders. However, studies have shown that, whereas weak memories can be modified using reconsolidation updating, strong memories can be resistant to this approach. Therefore, treatments targeting the reconsolidation process are unlikely to be clinically effective unless methods are devised to enhance retrieval-dependent memory destabilization. Currently, little is known about the cellular and molecular events that influence the induction of reconsolidation updating. Here, we determined that an increase in the GluN2A/GluN2B ratio interferes with retrieval-dependent memory destabilization and inhibits the initiation of reconsolidation updating.
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Roopashri
R
Holehonnur
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Aarron J
AJ
Phensy
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Lily J
LJ
Kim
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Milica
M
Milivojevic
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Dat
0000-0001-9960-1268
D
Vuong
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Delvin K
DK
Daison
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Saira
0000-0002-5119-8649
S
Alex
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Michael
M
Tiner
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Lauren E
LE
Jones
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080.
Sven
0000-0003-1728-8111
S
Kroener
School of Behavioral and Brain Sciences and Department of Molecular and Cell Biology, The University of Texas at Dallas, Dallas, Texas 75080 Jonathan.Ploski@UTDallas.edu.
Jonathan E
0000-0001-6242-9353
JE
Ploski
D000161:Acoustic Stimulation; D000679:Amygdala / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism; D000076122:Disks Large Homolog 4 Protein; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects; D005239:Fear / Q000523:psychology*; D005260:Female; D051528:Guanylate Kinases / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008568:Memory / Q000502:physiology*; D011939:Mental Recall / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism*
D000841:Anisomycin; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D000076122:Disks Large Homolog 4 Protein; D018683:Excitatory Amino Acid Agents; D051528:Guanylate Kinases; D008565:Membrane Proteins; D011500:Protein Synthesis Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; C501447:Dlg4 protein, mouse; C121001:NR2B NMDA receptor
Glun2A; NMDAR; Pavlovian fear conditioning; amygdala; memory; reconsolidation