Long-term structural plasticity of hippocampal dendritic spines following contextual fear memory reactivation

Abstract

Dendritic spines are plastic structures exhibiting a high degree of morphological variability. Certain morphometric parameters, such as volume, positively correlate with the strength of the synapse in which they participate. Memories, too, are subject to change over time and with experiences. In particular, the presence of a reminder of a learning event can trigger the labilization of the memory trace, followed by a re-stabilization process termed reconsolidation. The underlying mechanisms behind the labilization/reconsolidation processes are of great interest, as they are thought of as possible targets for the treatment of post-traumatic stress disorders. Dendritic spines have long been considered the physical sites for memory formation and storage. Our work aimed at studying the long-term spine morphological plasticity associated with labilization/reconsolidation in the dorsal hippocampus, a brain region relevant for the formation of contextual memories. Our results suggest that labilization/reconsolidation does not affect spine density, but rather induces changes in spine morphology. Furthermore, we show that some of these changes are prevented by the inhibition of the transcription factor NF-κB inhibition. Finally, we found that NF-κB negative modulation also affects spine morphology in animals that were not exposed to recall but have undergone the training session, suggesting that there may be a late surge of NF-κB activity resulting from the consolidation itself.