Hippocampal signaling pathways are involved in stress-induced impairment of memory formation in rats

Abstract

Stress is a potent modulator of hippocampal-dependent memory formation. The aim of the present study was to assess the role of hippocampal signaling pathways in stress-induced memory impairment in male Wistar rats. The animals were exposed to acute elevated platform (EP) stress and memory formation was measured by a step-through type passive avoidance task. The results indicated that post-training or pre-test exposure to EP stress impaired memory consolidation or retrieval respectively. Using western blot analysis, it was found that memory retrieval was associated with the increase in the levels of phosphorylated cAMP-responsive element binding protein (P-CREB), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and its downstream targets in the hippocampus. In contrast, the stress exposure decreased the hippocampal levels of these proteins. In addition, stress-induced impairment of memory consolidation or retrieval was associated with the decrease in the P-CREB/CREB ratio and the PGC-1α level in the hippocampus. On the other hand, the hippocampal level of nuclear factor E2-related factor 2 (Nrf2) and gamma-glutamylcysteine synthetase (γ-GCS) which are the master regulators of defense system were decreased by the stress exposure. The increased hippocampal levels of Nrf2 and it׳s downstream was observed during memory retrieval, while stress-induced impairment of memory consolidation or retrieval inhibited this hippocampal signaling pathway. Overall, these findings suggest that down-regulation of CREB/PGC-1α signaling cascade and Nrf2 antioxidant pathways in the hippocampus may be associated with memory impairment induced by stress.