Abstract
We assessed brain abnormalities in rats exposed prenatally to radiation (X-rays) using magnetic resonance imaging (MRI) and histological experiments. Pregnant rats were divided into 4 groups: the control group (n = 3) and 3 groups that were exposed to different radiation doses (0.5, 1.0, or 1.5 Gy; n = 3 each). Brain abnormalities were assessed in 32 neonatal male rats (8 per group). Ex vivo T2-weighted imaging and diffusion tensor imaging (DTI) were performed using 11.7-T MRI. The expression of markers of myelin production (Kluver–Barrera staining, KB), nonpyramidal cells (calbindin-D28k staining, CaBP), and pyramidal cells (staining of the nonphosphorylated heavy-chain neurofilament SMI-32) were histologically evaluated. Decreased brain volume, increased ventricle volume, and thinner cortices were observed by MRI in irradiated rats. However, no abnormalities in the cortical 6-layered structure were observed via KB staining in radiation-exposed rats. The DTI color-coded map revealed a dose-dependent reduction in the anisotropic signal (vertical direction), which did not represent reduced numbers of pyramidal cells; rather, it indicated a signal reduction relative to the vertical direction because of low nerve cell density in the entire cortex. We conclude that DTI and histological experiments are useful tools for assessing cortical and hippocampal abnormalities after prenatal exposure to radiation in rats.
Highlights
Many studies of survivors of prenatal exposure to the atomic bombings of Hiroshima and Nagasaki have shown that exposure to ionizing radiation during pregnancy has harmful effects on the development of the human central nervous system (CNS) [1,2,3]
Several reports based on in vivo magnetic resonance imaging (MRI) have shown that CNS damage, such as vessel malformation and ventricular dilatation, was present in rats exposed to radiation prenatally [8] [9]
The Corpus callosum (CC) and External capsule (EC) of rats exposed to 0.5 and 1.0 Gy of radiation prenatally were thinner than those of the control rats. These results show decreased brain volume, increased ventricle volume, thinner cortex, thinner CC, and thinner EC in irradiated rats and all effects were dose dependent
Summary
Many studies of survivors of prenatal exposure to the atomic bombings of Hiroshima and Nagasaki have shown that exposure to ionizing radiation during pregnancy has harmful effects on the development of the human central nervous system (CNS) [1,2,3]. Exposure of an embryo to radiation can cause various diseases, such as hydrocephalus and microcephaly [3]. These CNS alterations have been observed in animal models after prenatal X-ray irradiation at day 15 of pregnancy in rats and at day 13 of pregnancy in mice [4]. Brain abnormalities, such as hippocampal atrophy and ventricular dilatation, have been observed in rodents after exposure to radiation [5,6]. Several reports based on in vivo magnetic resonance imaging (MRI) have shown that CNS damage, such as vessel malformation and ventricular dilatation, was present in rats exposed to radiation prenatally [8] [9]
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