Post-training disruption of Arc protein expression in the anterior cingulate cortex impairs long-term memory for inhibitory avoidance training.

The activity-regulated-cytoskeletal-associated protein (Arc) has a well established role in memory consolidation and synaptic plasticity in the hippocampus and amygdala. However the role of Arc within the anterior cingulate cortex (ACC), an area of the brain involved in processing memory for pain, has yet to be examined. Here we sought to determine if Arc protein within neurons of the rat ACC is necessary for the consolidation of a single-trial, contextual inhibitory avoidance (IA) task. Immunohistochemistry and western blotting revealed an increase in Arc protein within the ACC following IA training in a shock-specific manner, suggesting that ACC Arc expression may play a critical role in the consolidation of the aversive task. To directly test this hypothesis, male Sprague-Dawley rats were trained on the IA task and given post-training intra-ACC infusions of Arc antisense oligodeoxynucleotides (ODNs), designed to suppress Arc translation, or control scrambled ODNs that do not suppress Arc translation. Memory retention was tested 48h after training. Arc antisense-induced disruption of Arc protein expression in the ACC impaired long-term memory for the IA task as compared to rats given intra-ACC infusions of the scrambled control ODNS, suggesting that Arc expression in the ACC is important for the consolidation of emotional memory. Results further indicate that knock down of Arc 6h after training impairs IA memory. This is consistent with time course findings indicating elevated Arc expression at 3 and 6h after IA training but not 12 or 48h. Taken together, these findings support the hypothesis that Arc expression in the ACC participates in synaptic plasticity that underlies long-term memory.