Role of norepinephrine in mediating stress hormone regulation of long-term memory storage: a critical involvement of the amygdala.

There is extensive evidence indicating that the noradrenergic system of the amygdala, particularly the basolateral nucleus of the amygdala (BLA), is involved in memory consolidation. Infusions of norepinephrine or beta-adrenoceptor agonists into the BLA enhance memory for inhibitory avoidance as well as water maze training. Other findings show that alpha 1-adrenoceptor activation also enhances memory for inhibitory avoidance training through an interaction with beta-adrenergic mechanisms. The central hypothesis guiding the research reviewed in this chapter is that stress hormones released during emotionally arousing experiences activate noradrenergic mechanisms in the BLA, resulting in enhanced memory for those events. Findings from experiments using rats have shown that the memory-modulatory effects of the adrenocortical stress hormones epinephrine and glucocorticoids are mediated by influences involving activation of beta-adrenoceptors in the BLA. In addition, both behavioral and microdialysis studies have shown that the noradrenergic system of the BLA also mediates the influences of other neuromodulatory systems such as opioid peptidergic and GABAergic systems on memory storage. Other findings indicate that this stress hormone-induced activation of noradrenergic mechanisms in the BLA regulates explicit/declarative memory storage in other brain regions.