Enhanced hippocampal corticotropin-releasing factor gene expression associated with memory consolidation and memory storage in rats.

Corticotropin-releasing factor (CRF) has been found to play an important role in modulating the learning and memory processes in rats. In the present study, we examined the alteration of CRF mRNA level in rat hippocampus at different stages of the memory process. Results indicated that CRF mRNA is quite homogenously distributed within subdivisions of the hippocampus, with the dentate gyrus (DG) has a relatively lower expression level. By using the one-way inhibitory avoidance learning paradigm, we have selected the good memory (GM) rats (with a retention score of 600) and the poor memory (PM) rats (with retention scores < 80). Results indicated that CRF mRNA level in the hippocampus was significantly increased in GM rats when compared with that in the PM rats at 1 hr, 3 hr and 6 hr after training. It was not markedly altered at 24 hr and 72 hr post-training. However, it was again increased at 21 days post-training in both the hippocampus and the frontal cortex. Further, this effect was demonstrated not to be associated with the acute footshock stress. These results together suggest that enhanced hippocampal CRF gene expression is probably associated with both memory consolidation and memory storage, but is not associated with maintenance of formed memory in rats.