SEQUENCE OF X-RAY DAMAGE IN MOUSE CEREBELLUM 207 



quality of the DNA caused by the action of ionizino radiation. Further 

 in\estigations are necessary to clarify this problem. As brought out by the 

 acridine orange fluorescence technique, the increased resistance of pyknotic 

 nuclei to depolymerizing and hydrolysing agents allow clear identification of 

 damaged irradiated pyknotic cell nuclei. 



Summary 



Dexelopment and course of radiation lesions in the cerebellum in mice 

 were studied after exposure to single doses of x-rays, 250 to 60,000 r, applied 

 to one cerebellar hemisphere through apertures 3 X ^ mm or 0.5 X 2 mm 

 in diameter. Degree and sexerity of radiation damage in the cerebellum was 

 correlated in terms of tinre-intensity relationships with the x-ray dose. 



After a dose of 60.000 r. morphologic changes of different cerebellar struc- 

 tures (e.g.. nerve cells of the molecidar layer and Purkinje and granule cells) 

 were visible as early as 30 minutes following exposine and were fully dcxel- 

 oped at 60 minutes. Within 90 hours, complete necrosis of the irradiated 

 cerebellar area with concomitant resorptive and reparative changes was 

 observed. C'ystic liquefaction eventually occurred. 



After less intense x-ray doses, 60,000 to 10,000 r. similar radiation lesions 

 were observed, but the latent period of their inception was longer. Exposure 

 to doses below 10,000 r down to 4,000 r residted in necrosis of the granidar 

 layer and in destruction of single nene cells in other parts of the cerebellar 

 cortex. The latent time was more prolonged. Radiation damage finally resulted 

 in the formation of a glial scar. 



At x-ray doses below 4,000 r. only single nerve cells or cell groups were 

 damaged, and the latent period was correspondingly lengthened. In such 

 lesions, proliferation of glial elements and capillaries ultimately occurred, 

 and hyalinosis developed in the walls of distended blood vessels. Since no evi- 

 dence of vascular alterations was observed before development of nerve cell 

 lesions, the visible radiation damage was interpreted as due to a direct effect 

 of the ionizing radiation on the cellular elements of cerebellar tissue. 



The acridine orange fluorescence tcchniciue was used to determine whether 

 alterations occin- in the structural organization of the DNA in pyknotic 

 nuclei of irradiated granule cells and in the RNA content of Purkinje cells. 

 Our results indicated that after irradiation DNA of pyknotic nuclei in the 

 granular layer is not depolymerized to a noticeable degree. These pyknotic 

 nuclei were more resistant than normal to treatment with depolymerizing 

 and hydrolysing chemical agents and DNase. Without fiuther experimenta- 

 tion it is difficult to say whether this increased resistance of irradiated, 

 pyknotic nuclei is an immediate and specific effect due to the action of ioniz- 

 ing radiation on the DNA or whether it is a nonspecific effect due to in- 



