Noradrenergic activation of the basolateral amygdala modulates consolidation of object recognition memory

Abstract

Noradrenergic activation of the basolateral complex of the amygdala (BLA) modulates the consolidation of memory for many kinds of highly emotionally arousing training tasks. The present experiments investigated whether posttraining noradrenergic activation of the BLA is sufficient to enable memory consolidation of a low-arousing training experience. Sprague-Dawley rats received intra-BLA infusions of norepinephrine, the beta-adrenoceptor antagonist propranolol or saline immediately after either 3 or 10 min of object recognition training. Saline-infused controls exhibited poor 24-h retention when given 3 min of object recognition training and good retention when given 10 min of training. Norepinephrine administered after 3 min of object recognition training produced dose-dependent enhancement of 24-h object recognition memory whereas propranolol administered after 10 min of training produced dose-dependent impairment of memory. These findings provide evidence that posttraining noradrenergic activation of the BLA enhances memory of a low-arousing training experience that would otherwise not induce long-term memory. Thus, regardless of the degree of emotional arousal induced by an experience, noradrenergic activation of the BLA after the experience ensures that it will be better remembered.

Figure 1

Representative photomicrograph illustrating placement of a cannula and needle tip in the BLA. Arrow points to needle tip. The gray area in the diagram represents the different nuclei of the BLA: the lateral nucleus (L), basal nucleus (B) and accessory basal nucleus (AB). CEA, central nucleus of the amygdala.

Figure 2

Noradrenergic activation of the BLA modulates consolidation of object recognition memory. (A) Enhancing effects of posttraining intra-BLA infusions of norepinephrine on 24-h object recognition memory. Saline-infused controls displayed no evidence of memory of 3 min of training. The retention performance of groups given 0.3 or 1.0 µg of norepinephrine was significantly better than that of the saline controls. Data are presented as discrimination index (mean ± SEM; see main text). (B) Impairing effects of posttraining intra-BLA infusions of propranolol on 24-h object recognition memory. All groups received 10 min of training. Saline-infused controls displayed significant memory and propranolol produced dose-dependent impairment of memory. The performance of all three propranolol groups differed significantly from that of the saline controls. * P < 0.05; ** P < 0.01. N = 7–9 rats per group.