A recent McGaugh review in Trends in Cognitive Science (Volume 10, Issue 8 , August 2006, Pages 345-347) discusses a PNAS paper by Anderson and colleagues demonstrating that emotionally arousing stimuli enhance long-term memory of immediately preceding neutral stimuli. This fits with with extensive evidence from both human and animal studies indicating that arousal-induced modulation of memory is mediated by β-noradrenergic activation of the amygdala.
(By the way, in my July 20 post on involvement of the Locus Ceruleus in the retrieval of emotional memories I inexplicably neglected to mention that this cluster of nerve cells in the lower brain synthesizes noradrenaline (norepinephrine). Its axons, which project to the amygdala and other cortical areas, can 'spritz' large areas of the cortex during arousal, to enhance both the storage and retrieval of emotional memories.)
McGaugh gives a simplified graphic to summarize the main idea:
Figure - Schematic representation of modulation of memory consolidation by emotional arousal-induced release of adrenal stress hormones and noradrenergic activation of the amygdala. Emotional arousal activates the release of noradrenaline in the basolateral amygdala as well as the release of adrenal stress hormones. The stress hormones then provide increased and sustained noradrenergic activation in the amygdala. The amygdala activation modulates memory consolidation via projections to other brain systems processing memory. (Credit TICS)