Effect of irradiation at the early fetal stage on adult brain function in the mouse: Locomotor activity

Purpose: To study long-term changes in the adult locomotor activity of mice after exposure to gamma radiation at the early fetal stage of development. Materials and methods: Pregnant Swiss albino mice were exposed locally on the abdominal area to a single dose of 0.25-1.5 Gy of ⁶⁰Co gamma radiation at the dose rate of 1 Gy/min. When the F1 offspring were 6 months old, their locomotor and exploratory behaviour was assessed by the open-field and dark/bright arena tests. Animals were again subjected to the dark/bright arena test at 12 and 18 months of age in order to study the persistence of the effects. Results: Irradiation produced a noticeable disturbance in the normal behaviour pattern of the mice. There was a significant dose-dependent decrease in the open-field activity of 6-month-old mice. In the dark/bright arena test, the time spent and lines crossed in the dark area showed a significant decrease, while their activities in the brightly lit area increased significantly, indicating a reduced aversion to bright light. These effects were evident even at a dose of 0.3 Gy and increased linearly with dose. The significant behavioural changes persisted at 12 months, but at 18 months the difference in the time spent and lines crossed in the dark and bright areas were not significantly different from sham-irradiated control values below 0.5 Gy. Conclusions: These results show that day 14 of gestation in Swiss albino mice is a time of high risk for inducing long-term changes in the adult locomotor function by γ-radiation doses below 1 Gy. Using a range of radiation doses and different observation times we have demonstrated that the effect increases linearly with dose, but there appears to be a threshold of 0.3-0.5 Gy for producing significant persistent changes in the adult ambulatory activity.