Radiation Malformations Belonging to the Cyclopia–Arrhinencephalia–Otocephalia Group in the Mouse Foetus

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Abstract
Mice were subjected to a single whole-body X-radiation of 200 r. on the 9th day of pregnancy and embryos and foetuses derived from them were examined from the 13th to 19th day of pregnancy. Besides some exencephalias, hydrocephaluses, harelips and cleft-palates, a spectrum of malformations grossly classified into the following three groups was observed at comparatively high frequencies (over 32 per cent.). The first group : an apparently univentricular telencephalon accompanied by a beak-like appearance of the snout and eyes approaching the median. The second group : a reduction in the size of the telencephalon associated with a tapering of the snout and a tendency to synophthalmia. The third group : the tapering snout which may be accompanied by fusing nostrils. Besides, two cases of microtia were found. Microscopic findings suggest that these three groups present a spectrum of malformations belonging to the cyclopia-arrhinencephalia-otocephalia group. However, no typical cyclopias were detected. During the most sensitive developmental stage, the 9th day of pregnancy, 3-5 brain vesicles are formed and the anterior neuropore is closed. That this phase of basic morphogenesis of the nervous system is most sensitive to teratogenic influences is in harmony with both the results of experimental embryologists employing lower vertebrates and those of human pathologists.