Vertebral malformation in the mouse foetus caused by X-radiation of the mother during pregnancy

Abstract

ABSTRACT Mice of the ddN and CF1 strains were exposed to a single dose of 200 r. X-radiation between the 8th and 13th day of pregnancy, and the foetal skeletons were examined on the 19th day of pregnancy. The phenomenon of a head-to-tail gradient shift in vertebral malformations as the stage of pregnancy at radiation advanced was less marked in the result in the ddN strain, but in the CF1 strain it was of similar proportions to that obtained by hypoxia. However, after X-radiation, malformations in the cervical and thoracic vertebrae presented two peaks of susceptibility. The first peak in malformation frequency may result from an effect of X-radiation upon the early somite stage or it may be an indirect effect. The second peak may originate from a direct effect upon the primordium, i.e. upon the sclerotome itself. The incidence of cervical malformations was higher in the group treated on the 8th or 9th day, and in the group treated on the 11th day of pregnancy. The malformations presented such characteristics as enlarged rami of the posterior arch of the 1st cervical vertebra or, in the latter group, fusion of the cervical vertebrae. There were also differences in the frequency of involvement of the vertebrae in these two strains which may be due to differences in the rate of differentiation of the vertebral primordium. Other differences were seen in the incidence of cervical ribs, of absence of the 13th rib, and of lumbar ribs. Such regional differentiation seems to be influenced by the genetic constitution.