Neonatal exposure to a moderate dose of ionizing radiation causes behavioural defects and altered levels of tau protein in mice.

Medical use of ionizing radiation (IR) has great benefits for treatment and diagnostic imaging, but procedures as computerized tomography (CT) may deliver a significant radiation dose to the patient. Recently, awareness has been raised about possible non-cancer consequences from low dose exposure to IR during critical phases of perinatal and/or neonatal brain development. In the present study neonatal NMRI mice were whole body irradiated with a single dose of gamma radiation (0; 350 and 500 mGy) on postnatal day 10 (PND 10). At 2 and 4 months of age, mice of both sexes were observed for spontaneous behaviour in a novel home environment. The neuroproteins CaMKII, GAP-43, synaptophysin and total tau in male mouse cerebral cortex and hippocampus were analysed 24h post-irradiation and in adults at 6 months of age exposed to 0 or 500 mGy on PND 10. A significantly dose-response related deranged spontaneous behaviour in 2- and 4-month-old mice was observed, where both males and females displayed a modified habituation, indicating reduced cognitive function. The dose of 350 mGy seems to be a tentative threshold. Six-month-old male mice showed a significantly increased level of total tau in cerebral cortex after irradiation to 500 mGy compared to controls. This demonstrates that a single moderate dose of IR, given during a defined critical period of brain development, is sufficient to cause persistently reduced cognitive function. Moreover, an elevation of tau protein was observed in male mice displaying reduced cognitive function.