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Effects of Prenatal Irradiation with an Accelerated Heavy-Iron Beam on Postnatal Development in Rats: II.. Further Study on Neurophysiologic Alterations
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Organogenesis is a highly radiosensitive period, study of prenatal exposure
to high LET heavy ion beams on postnatal development is important for
clarifying the radiation risk in space and promoting the evidence-based
mechanism research. The effects from heavy ion irradiations are not well
studied as those for low LET radiations such as X-rays in this field, even
the ground-based investigations remain to be addressed. Using the Heavy Ion
Medical Accelerator in Chiba (HIMAC) and Wistar rats, postnatal
neurophysiological development in offspring was investigated following
exposure of pregnant rats to accelerated neon-ion beams with a LET value of
about 30 keV/um at a dose range from 0.1 to 2.0Gy on the 15th day of
gestation. The age for appearance of four physiologic markers and attainment
of five neonatal reflexes, and gain in body weight were monitored. Male
offspring were evaluated as young adults using two behavioral tests
including open field and hole-board dipping tests. The effects of X-rays at
200 kVp measured for the same biological end points were studied for
comparison. For most of the endpoints at early age, significant
neurophysiological alteration was observed even in offspring receiving 0.1
Gy of accelerated neon ions but not X-rays. All offspring receiving 2.0 Gy
of accelerated neon ions died prior to weaning. Offspring prenatally
irradiated with neon ions generally showed higher incidences of prenatal
death, increased preweaning mortality, markedly delayed accomplishment in
physiological markers and reflexes, significantly lower body weight and
reduced ratios of main organ weight to body weight, and altered behavior
compared to those exposed to X-rays at doses of 0.1 to 1.5 Gy. These
findings indicate that irradiations with neon ions at 0.1 to 1.5 Gy on day
15 of gestation caused varied developmental alterations in offspring, and
efficient dose leading to the detrimental effects seemed to be lower than
that of X-rays.