IONIZING RADIATIONS: EFFECTS ON EMBRYO, FETUS 21 



All of these anomalies could be attributed to deficiencies during develop- 

 ment caused by ionizing radiations. 



Their explanations of these central nervous system malformations included 

 the following direct statements: 



"There was a selective extirpation effect on certain primiti\e cells. . . . 

 A patchy deficiency of cells. . . . Numerous dead cells spilled into the 

 ventricles. . . . Virtually all of the primitive migratory cells in transit were 

 killed. . . . The residual mitotic colony of lining cells was thrown into dis- 

 order because their support, the matrix of radiosensiti\e cells forming much 

 of the wall, was gone." 



The entire emphasis of this study seemed to be on the deficiencies follow- 

 ing fetal irradiation. 



The appearance of rosettes has often been described in both the neural 

 retina and in the de\eloping cortex following fetal irradiation. The presence 

 of rosettes is proof that cells have been desegregated and that those still 

 viable attempt neural organization. In the case of irradiation, the desegrega- 

 tion is due to the killing of radiosensitive cells, which are then removed, 

 leaving loosely scattered, but \iable cells. It has been shown recently (Mos- 

 cona, 1960) that presumptive nerve, cartilage, and liver cells of mouse and 

 chick embryos may be desegregated (disaggregated) by trypzinization and 

 mixed together, only to reaggregate with respect to whether they were 

 nervous, cartilage, or liver, and irrespective of whether they came from the 

 mouse or the chick. In other words, presumptive ner\e cells show an aflfinity 

 for eacli other, regardless of their genetic source. When they come together 

 without sustentacular materials, they tend to form rosettes which are an 

 expression of disorganization. The rosettes are therefore not a peculiarity of 

 post irradiation, nor of the mouse or rat, but rather of neural disorganization. 

 A single rosette has been formed of neuroblasts from both the mouse and 

 the chick embiyos. These structures, usually temporary in the irradiated and 

 developing embryo, simply represent a stage in the reorganization of viable 

 nerve cells which are inadequate in number to accomplish structural 

 normality (Figs. 36-43 and Table V). 



Our current studies are utilizing low doses to determine the effect of 

 ionizing radiations on the developing central nervous system as demonstrated 

 by beha\ ior, electroencephalographic records at \ arious stages of maturation, 

 and electron microscope and neuropathologic studies of the postnatal brain. 

 It may develop that it will be the experimental psychologist who will spot 

 the specific developmental stages most drastically affected by ionizing radia- 

 tions. If our society is primarily concerned with the function of the central 

 nervous system, we may be dealing with radiation changes which are beyond 

 analysis by the conventional neuropathologic techniques or by the electron 

 microscope. We expect to have information on this during the next year. 



