c-Fos expression reveals aberrant neural network activity during cued fear conditioning in APPswe transgenic mice.

The neural circuitry underlying emotional learning and memory is known to involve both the amygdala and hippocampus. Both of these structures undergo anatomical and functional changes during the course of Alzheimer's disease. The present study used expression of the immediate early gene c-Fos to examine the effect of amyloid-induced synaptic pathology on neural activity in the hippocampus and amygdala immediately following Pavlovian fear conditioning. Tg2576 mice underwent cued fear conditioning and the regional interdependencies of c-Fos expression in the hippocampus and the amygdala were assessed using structural equation modelling. Tg2576 mice displayed normal acquisition of conditioned freezing to a punctate auditory cue paired with shock. However, the analysis of c-Fos expression indicated abnormal regional activity in the hippocampal dentate gyrus of Tg2576 mice. Structural equation modelling also supported the view that activity within the amygdala was independent of hippocampal activity in Tg2576 mice (unlike control mice) and regional interaction between the dentate gyrus and CA3 region was disrupted. The results provide novel insight into the effects of excess amyloid production on brain region interdependencies underpinning emotional learning.