Amygdala is critical for stress-induced modulation of hippocampal long-term potentiation and learning

Stress is a biologically significant factor shown to influence synaptic pla sticity and memory functioning in the hippocampus. This study examined the role of the amygdala, a brain structure implicated in coordinating stress b ehaviors and modulating memory consolidation, in mediating stress effects o n hippocampal longterm potentiation (LTP) and memory in rats. Electrolytic lesions of the amygdala effectively blocked the adverse physiological and b ehavioral effects of restraint and tailshock stress, without impeding the i ncrease in corticosterone secretion to stress. Physiologically, hippocampal slices from stressed animals exhibited impaired LTP relative to slices fro m unstressed control animals, whereas hippocampal slices from stressed anim als with amygdalar lesions exhibited normal LTP. Behaviorally, stressed ani mals were impaired in retention of a hippocampal-dependent hidden platform version of the Morris water maze task, and this impairment was blocked by a mygdalar lesions. In a fixed location-visible platform water maze task that can be acquired by independent hippocampal and nonhippocampal memory syste ms, stress enhanced the use of nonhippocampal-based memory to acquire the t ask. These results indicate that an intact amygdala is necessary for the ex pression of the modulatory effects of stress on hippocampal LTP and memory.