Objective      To investigate the optimal dose of X-ray exposure to establish rat model of disorders of cortical development (DCDs).        Methods      Pregnant Sprague-Dawley rats were exposed to X-ray at different radiation doses at embryonic day 17. The rats were divided into different groups according to the radiation doses

Group A 125 cGy

Group B 150 cGy

Group C 175 cGy

Group D 200 cGy

and Group E 225 cGy. The following indexes were observed in all groups. The survival rate of rat offspring in each group were calculated. Morris water maze test were adopted to test the learning and memory capacity of rat offsprings in each group on P28d. The changes of brain pathology in cerebral cortex and hippocampus was observed to confirm the types of DCDs on P56d. Kainic acid were used to induce seizure and their seizure threshold and mortality induced by seizure were studied on P63d.       Results      1) The survival rate of rat offsprings among the control group and groups A

B

and C were comparatively high. 2) Morris water maze test showed that the escape latency and times of crossing platform of rat offsprings in the groups C and D were always longer than those of the control group(P0.05). The incidence rate of DCDs of offsprings in the groups C and D reached 100%. 4)The latent period of Kainic acid inducing seizure was shortened in the groups B and C (P0.05)

but the time of epileptic state and the mortality induced by seizure of rat offspring in the two groups were the same as that of control group(P0.05) in kainic acid inducing seizure on P63d.       Conclusion      X-ray exposure is a good way to establish DCDs model. The model induced by 175 cGy X-ray is of high survival rate

mental retardation

lower threshold of epileptic seizure and typically pathologic changes of DCDs.