Posttraining norepinephrine infusion into the central amygdala differentially enhances later retention in Roman high-avoidance and low-avoidance rats.

Memory-enhancement effects of norepinephrine (NE) were investigated by infusing NE into the central amygdala (CEA) of Roman high-avoidance (RHA) and low-avoidance (RLA) rats after training on active and passive behaviors in the defensive-burying paradigm. During acquisition, both lines spent comparable time in burying behavior. RLA rats, but not RHA rats, also displayed substantial immobility. During retention, the cerebrospinal-fluid-treated RLA rats mostly displayed immobility to the nonelectrified probe, whereas the RHA rats showed neither burying nor immobility. In the RLA rats, high-dose (200 ng), but not low-dose (20 ng), NE infusion enhanced the duration of the passive response (immobility) without affecting the active response. NE given into the CEA of RHA rats caused a selective dose-dependent appearance of the active behavioral component. The results suggest a phenotype-dependent effect of intra-amygdaloid NE on memory processes in the rat.