An experimental study of radiation-induced cognitive dysfunction in an adult rat model

The objectives of this study were to establish an adult rat model for the l ate onset of radiation-induced cognitive dysfunction and to compare behavio ural dysfunction with histopathological changes. While under anaesthesia, 3 0 rats (experimental group) were irradiated with a total dose of 40 Gy, giv en as eight fractions in 24 days. Another 30 rats (control group) underwent sham irradiation. The cognitive functions of all rats were evaluated at 6, 9 and 12 months after irradiation using the Morris water maze and passive avoidance tasks. Histopathological examination of these rats was carried ou t after the evaluation of cognitive functions was complete. At 6 and 9 mont hs after irradiation there were no significant differences between the cont rol and irradiated groups in passive avoidance and water maze tests. At 12 months after irradiation, the passive avoidance task revealed a deteriorati on of cognitive function in the experimental group. Histopathological obser vations revealed no abnormal findings in the irradiated brains at the light microscope level. Late onset cognitive dysfunction following cranial irrad iation was observed in an adult rat model. Pathological investigations show ed no abnormalities in the irradiated brains. These findings indicate that radiation-induced cognitive dysfunction can precede morphological changes i n the brain or that they arise without them. The present model seems useful for elucidating the pathogenesis of radiation-induced cognitive dysfunctio n and for developing methods for therapy and prophylaxis.