Thalamic nucleus reuniens regulates fear memory destabilization upon retrieval.

The neural circuit supporting aversive memory destabilization after retrieval includes the hippocampus, amygdala, and medial prefrontal cortex. The nucleus reuniens (NR) contributes to the functional interaction of these brain regions relevant to cognitive processing. However, the direct participation of this thalamic subregion in memory destabilization is yet to be investigated. The present study addressed this question in contextually fear-conditioned rats. Pre-reactivation infusion of the GABA _A receptor agonist muscimol, the protein degradation inhibitor clasto-lactacystin β-lactone (β-lac), or the glutamate N2B-containing NMDA receptors antagonist ifenprodil into the NR prevented the post-reactivation amnestic effects of both locally infused anisomycin and systemically administered clonidine. In either case, the results suggest a significant disruption in memory destabilization. It is noteworthy that these pharmacological interventions induced no changes in expression or contextual specificity of the memory. Moreover, omitting memory reactivation precluded the muscimol, β-lac, and ifenprodil effects on destabilization and the anisomycin and clonidine effects on reconsolidation. We also quantified the Egr1/Zif268-expressing neurons to investigate the effects of muscimol-induced NR inactivation on the activity-related plasticity locally, and in other brain regions supporting fear memory destabilization-reconsolidation. Relative to controls, there were reduced values in the NR, the dorsal CA1 hippocampus, the prelimbic cortex, and the infralimbic cortex. In contrast, increases happened in the ventral CA1 hippocampus and the basolateral amygdala. These results suggest that NR has a circuit-level influence on this process. Together, present findings demonstrate how the NR can regulate contextual fear memory destabilization upon retrieval.
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