Effect of late fetal irradiation on adult behavior of mouse: Dose-responserelationship

Pregnant Swiss mice were exposed to 0.3-1.5 Gy of gamma radiation on day 17 of gestation and allowed to deliver the offspring. When the F1 mice were 6 months old, they were subjected to a number of behavioral tests. Open-fiel d and dark-bright arena tests were conducted to study locomotor and explora tory activities. Learning and memory were tested by holeboard activity, con ditioned avoidance response, and radial arm maze performance. After all the tests, 20 animals (10 males and 10 females) from each group were killed, a nd their brain weight was taken. The open-field and dark-bright arena tests showed a significant dose-dependent decrease in the locomotor and explorat ory activities. Reduction in time spent in the dark area and higher locomot or activity in the bright area indicated a reduced aversion to bright light . But the emotional activities like rearing and grooming did not change. Th e learning and memory functions also showed a significant impairment, even at 0.3 Gy. The deficit in the performance in the holeboard test, conditione d avoidance response, as well as maze-learning efficiency, decreased linear ly with increase in radiation dose. The brain weight showed a linear dose-d ependent decrease. But the brain/body weight ratio was not significantly af fected even at 1.5 Gy. These results demonstrate that exposure of a mouse o n day 17 of gestation to radiation doses below 1.0 Gy can induce significan t impairment in the adult brain function, without producing any notable eff ects on brain morphology. This study also suggests that the retardation of higher brain function by exposures during the late fetal period may have a threshold of around 0.3 Gy. (C) 1999 Elsevier Science Inc. All rights reser ved.