Spatial memory and changes in expression of genes of neurotrophic factors in adult rat brain after fractionated whole brain irradiation

Background: Ionizing radia on causes cogni ve impairment in adult brain. However, the effects of various irradia on protocols with frac onated fixed total dose on hippocampal func on have not yet been studied. Materials and Methods: Frac onated whole brain irradia on with a total dose of 36 Gy was performed according to the following protocols: 2Gy-18 frac ons (2Gy*18), 4Gy-9 frac on (4Gy*9) and 6Gy-6 frac ons (6Gy*6). Changes in spa al memory were studied in Morris water maze tests at 12 th and 17 th day a1er irradia on with a hidden pla2orm and at 38 th day a1er irradia on without a pla2orm. Levels of expression of brain derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) genes were evaluated using qPCR. Results: Expression of genes of neurotrophic factors (BDNF and VEGF) was decreased at 4 th and 8 th week a1er irradia on, the decrease depended on frac ona on. The Morris water maze test with a hidden pla2orm showed improvement in long-term spa al memory at 12 th and 17 th day a1er irradia on. In the Morris water maze test without pla2orm cogni ve deficit was detected only in 6Gy*6 group at 4th week a1er irradia on. Conclusion: Our study shows that different frac ona on protocols affect hippocampal func ons differently, and that the greatest nega ve impact has the protocol with the maximum single dose. In addi on, decrease in expression of genes of neurotrophic factors might play an important role in cogni ve impairment.