Influence of gestational age to low-level gamma irradiation on postnatal behavior in mice

The present investigation was carried out to study the effects of in utero exposure to low-level gamma radiation (0.25, 0.35, or 0.50 Gy) on the postn atal neurophysiology and neurochemistry of the mouse. Pregnant Swiss albino mice were irradiated on days 11.5, 12.5, 14.5, or 17.5 post coitus (PC) an d allowed to deliver. Locomotor and exploratory activities, learning and me mory functions, and emotional activities were tested at 3 months of age usi ng behavior tests. A representative group of animals was killed and hippoca mpal biogenic amines, noradrenaline, dopamine, serotonin (5-HT), arid 5-HT' s metabolite 5-hydroxy indoleactetic acid (5-HIAA), were measured. Exposure to 0.25 Gy at any of the gestation days did not produce any significant im pairment in brain functions. However, an increase in gamma irradiation to 0 .50 Gy on all the gestation days produced significant impairment in locomot or (open-field test) and anxiolytic (light and dark area test) activities, learning (hole board test), memory functions (active avoidance test), and e motional activity (rearings). The late fetal period is relatively resistant to radiation-induced impairment of brain functions. Both of the organogene sis gestation days showed a higher sensitivity than the fetal gestation day s studied. Even a lower dose of 0.35 Gy when exposed on the late organogene sis days 11.5 and 12.5 PC, produced significant reduction in locomotor and exploratory activities. Day 11.5 PC showed a higher sensitivity than the ot her PC days studied. Biogenic amines did not show significant change after any of the exposures on any of the gestation days. The results suggest a th reshold between 0.25 to 0.35 Gy for postnatal neurobehavior changes. (C) 20 00 Elsevier Science Inc. All rights reserved.