Background: The hippocampus, a key brain area for learning and memory, can express clock genes with circadian fashion. The neurotrophic factors are important for cognitive function in the hippocampus. The expression of circadian clock gene and neurotrophic factor in the hippocampus would be necessary to achieve and optimize daily memory performance.

Objective: It is of interest to examine the daily expression patterns of neurotrophic factor genes and the link between these genes and clock genes in rat hippocampus.

Material and Method: Daily expression profiles of four clock genes (Per1, Cry1, Bmal1, and Rev-erb alpha) and four neurotrophic factor genes (BDNF, NGF, NT-3, and VEGF) were analyzed in the rat hippocampus at 6 hours apart by real-time PCR.

Results: The mRNAs of BDNF, NGF, and VEGF, but not NT-3 in hippocampus were expressed in circadian manner as well as those of clock genes. Correlation analysis revealed strong relationships between the expression of VEGF and Per1, VEGF and Rev-erb alpha, BDNF and Bmal1, and BDNF and Cry1.

Conclusion: The present study suggests that VEGF and BDNF are clock-controlled genes relating to specific clock genes. Therefore, further investigation on the molecular mechanisms linking cognitive processes and circadian clock in hippocampus could be necessary to clarify their functions.

Keywords: Hippocampus, Clock genes, Neurotrophic factors, BDNF, NGF, NT-3, VEGF, Circadian