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Effects of X-Radiation on Mouse Fetus during Gestation: Emphasis on Distribution of Cerebral Lesions, Part II

National Institute of Neurological Diseases and Blindness, National Institutes of Health, Bethesda, Maryland

Correspondence: For reprints contact: A. S. Dekaban, Section of Child Neurology, National Institute of Neurological Diseases and Blindness, Building 10, Room 4N-250, National Institutes of Health, Bethesda, Maryland 20014.

ABSTRACT

A total of 152 female mice were irradiated on consecutive days of pregnancy between the 7th and 18th gestational day (g.d.). This resulted in 876 irradiated newborns. Exposure to irradiation on the 7th and 8th g.d. led to death and absorption of the majority of the fetuses; however, those which survived were largely normal at birth and only a small proportion had organ-type brain abnormality. Irradiation on 9 g.d. produced an increased number of cerebral abnormalities which included dysraphism, hydrocephalus, microencephaly and arrhinencephaly. Following irradiation between 10 and 12 g.d. entirely different cerebral lesions were found to occur; they included heterotopias, deformities of various structures, cellular deficiency and compensatory dilatation of the ventricles. From the 13th g.d. onward these lesions became smaller and less frequent, and after the 15th g.d. only mi!d architectonic imperfections were present. The heterotopias were most prominent in the subependymal region when irradiation occurred on the 10th and 11th g.d., in the white matter after exposure on the 12th g.d. and in the cerebral cortext following irradiation on the 13th and 14th g.d.

Different functional regions (subdivisions) of the brain showed a varied degree of sensitivity to irradiation in general and especially in different gestational stages. Diencephalon, olfactory system and a part of the limbic system had a low sensitivity in the range of irradiation used; the hippocampus and basal ganglia were moderately sensitive between 10 and 12 g.d. The neopallium and mesocortex were the most sensitive structures and severe damage was caused by irradiation between 10 and 13 g.d. while milder abnormalities occurred after exposure between 14 and 16 g.d. Most of the mice with cerebral lesions had small heads and their bodies were stunted. Tentative correlation of the stages of brain development in the mouse and man has been offered. Also a prediction of the type of cerebral lesions that may result from irradiation of the human fetus at various stages of pregnancy is suggested.