Noradrenergic actions in the basolateral complex of the amygdala modulate Arc expression in hippocampal synapses and consolidation of aversive and non-aversive memory.

ABSTRACT

The basolateral complex of the amygdala (BLA) plays a role in the modulation of emotional memory consolidation through its interactions with other brain regions. In rats, memory enhancing infusions of the ß-adrenergic receptor agonist clenbuterol into the BLA immediately after training enhances expression of the protein product of the immediate early gene Arc in the dorsal hippocampus and memory-impairing intra-BLA treatments reduce hippocampal Arc expression. We have proposed that the BLA may modulate memory consolidation through an influence on the local translation of synaptic plasticity proteins, like Arc, in recently active synapses in efferent brain regions. To date, all work related to this hypothesis is based on aversive memory tasks such as inhibitory avoidance (IA). To determine whether BLA modulation of hippocampal Arc protein expression is specific to plasticity associated with inhibitory avoidance memory, or a common mechanism for multiple types of memory, we tested the effect of intra-BLA infusions of clenbuterol on memory and hippocampal synaptic Arc expression following IA or object recognition training. Results indicate that intra-BLA infusions of clenbuterol enhance memory for both tasks; however, Arc expression in hippocampal synaptoneurosomes was significantly elevated only in rats trained on the aversive IA task. These findings suggest that regulation of Arc expression in hippocampal synapses may depend on co-activation of arousal systems. To test this hypothesis, a "high arousal" version of the OR task was used where rats were not habituated to the testing conditions. Posttraining intra-BLA infusions of clenbuterol enhanced consolidation of the high-arousing version of the task and significantly increased Arc protein levels in dorsal hippocampus synaptic fractions. These findings suggest that the BLA modulates multiple forms of memory and affects the synaptic plasticity-associated protein Arc in synapses of the dorsal hippocampus when emotional arousal is elevated.