Involvement of amygdala pathways in the influence of post-training intra-amygdala norepinephrine and peripheral epinephrine on memory storage

Abstract

These experiments examined the role of two major amygdala afferent-efferent pathways--the stria terminalis (ST) and the ventral amygdalofugal pathway (VAF)--in mediating the effects, on memory storage, of post-training intra-amygdala injections of norepinephrine (NE) and subcutaneous (s.c.) injections of epinephrine (E). Rats with either ST lesions or VAF transections and sham-operated rats were trained on a one-trial step-through inhibitory avoidance task and immediately after training received intra-amygdala injections of NE or a buffer solution. Other groups of VAF-transected animals received post-training s.c. injections of E or saline. ST lesions blocked the memory-enhancing effect of intra-amygdala injections of a low dose of NE (0.2 microgram) as well as the amnestic effect of a high dose of NE (5.0 microgram). In contrast, VAF transections did not block the memory-enhancing effect of NE (0.2 microgram). However, VAF transections attenuated the memory-enhancing effect of s.c. injections of E: the effective dose of E was shifted from 0.1 to 0.5 mg/kg. These findings, considered together with previous evidence that ST lesions block the memory-enhancing effect of peripheral E injections, suggest that the VAF is involved in mediating the central influence of peripheral E on amygdala functioning, while the ST is involved in mediating amygdala influences on memory storage elsewhere in the brain.