Physiological dissociation in hippocampal subregions in response to amygdala stimulation.

Previous studies indicated that the amygdala, when activated by emotional or electrical stimulation, modulates hippocampal-dependent memory processes and synaptic plasticity. Although the modulatory effect of the amygdala has often been generalized to the hippocampal formation, studies suggest that hippocampal subregions may display distinct functional profiles and may respond distinctively to amygdala activation. In this study we assessed the effect of basolateral amygdala (BLA) stimulation on long-term potentiation (LTP)--a synaptic model of memory--induced by a standard (sdTS) or a strong theta stimulation (sgTS) in the hippocampal dentate gyrus (DG) and CA1, in anesthetized rats. The modulatory stimulation was applied 30 s before or after the tetanus stimulation. Results show that while BLA activation impaired CA1 LTP induced with an sdTS, it enhanced LTP in the DG under both sdTS and sgTS conditions. These findings provide evidence for a differential amygdalar control of hippocampal memory subsystems, and may contribute to the understanding of the complexity of memory processes under stressful conditions.