EFFECTS OF HIGH-DOSE RADIATION ON BRAIN 



259 



Fig. 7. Electron micrograph of karyorrectic granule cell of a dog 24 hours after 

 exposure to 15,000 r of gamma radiation. There is fragmentation of the nuclear mem- 

 brane and extrusion of the cytoplasmic constituents. Approximately X 15.000. 



electron microscope showed most of the lirannle ceUs to ha\e fine structure 

 that was essentially normal. Minor stigmata were present in some, indenta- 

 tions of the nuclear membranes bein^ the most conspicuous. 



In general, the altered neurons in radiated dogs were not notably different 

 from those in rabbits. The initial cytologic changes were, as in rabbits, shink- 

 age of the nuclei, clumping of the nuclear granules, folding and redundancy 

 of the nuclear membranes, and expansion of the cytoplasm. In addition, and 

 apparently as a further progression of these changes, there was fragmentation 

 and disintegration of the nuclear membranes of some of the contracted 

 nuclei (Fig. 7). 



Comment 



The findings make it clear that exposiue of the granule cells in the intact 

 animal or in tissue culture to ionizing radiation initiates rapid volumetric 



