Differential effects of anxiogenic drugs on place and response learning: Role of basolateral amygdala

The basolateral amygdala (BLA) is involved in emotion and the emotional modulation of memory. Emotional arousal can impair or enhance memory depending on the nature of the arousal and on the type of learning involved. Two systems subject to amygdala modulation include hippocampally-mediated "place" learning, and caudate-mediated "response" learning. These have been shown to exhibit competitive interference. Previous studies of amygdala modulation of multiple memory systems have used tasks that can be solved using either the caudate or hippocampal-system. The current series of experiments examined the effects of emotional arousal (induced with anxiogenic drugs) on the relative use of place or response learning in a task that can be solved successfully with both ("combined task"). The nature of the observed differential involvement of place and response learning was further explored with tasks that can be solved using only one or the other (place and response tasks).; Induction of an anxiety state with the anxiogenic noradrenergic alpha-2 antagonists, yohimbine and RS 79948-197, affected place and response learning differently: pretraining i.p. injections of these drugs did not significantly affect acquisition in the combined task; however, a probe trial revealed that drug animals utilized a response strategy, while controls were essentially split between use of a place and response strategy. Infusions of RS 79948-197 directly into the BLA were administered to examine whether it mediates this effect, given its well-established involvement in emotion and anxiety, and its role in modulating both response and place learning. It was found that BLA infusions of RS 79948-197 were sufficient to produce the response preference. The experiment was repeated using posttraining infusions of RS 79948-197, to examine whether the observed effects were due to non-mnemonic processes (e.g., drug effects on attention, perception, or motor performance). The same pattern of results was obtained, suggesting that actions on consolidation were sufficient to achieve the response preference demonstrated by drug animals.; To test whether the combined task results reflected an impairing effect of heightened arousal on hippocampal place learning, rats were run in tasks directly assessing place and response learning. Animals receiving posttraining intra-BLA infusions of RS 79948-197 showed impairment in the place task, and enhancement in the response task. These results suggest that heightened emotional arousal, mediated by the BLA, can impair hippocampal function, thereby reducing competitive interference between hippocampas-mediated place and caudate-mediated response systems, resulting in an enhancement in response learning.