structural and Behavioral Alteration in the 

 Rat Following Cumulative Exposure of the 

 Central Nervous System to X-lrradiation * 



Robert H. Brownson 



Medical College of Virginia, 

 Richmond. J'irginia 



Introduction 



This project is constructed to permit analysis of the cytologic, histochenii- 

 cal. and functional state of the rat's central nervous system. This analysis 

 has been based on short- and lono-term responses demonstrated by the 

 central nervous system to cumulative levels of total-head x-irradiation. The 

 followins,' report is limited to the lonti-term responses. 



Da\ idofT and others !l938) have described the microscopic effects of x- 

 irradiation applied directly to the brain and spinal cord of monkeys. These 

 workers described thickeninu of the blood \essel walls, swelling", gliosis, 

 hypertrophy, and formation of gitter cells in the nemoglial elements. These 

 changes were noted 322 days following exposure in animals receiving 1,856 r. 

 The same authors expressed the opinion that there seemed to be two factors 

 involved in go\erning histologic alterations: the dosage and the time inter\al 

 between irradiation and autopsy. 



Clemente and Hoist i 1954) subjected monkey heads to doses of x-irradi- 

 ation ranging from 6.000 r to 15 r at 188 r per minute. They observed 

 varying degrees of necrobiotic changes such as clumping, chromatolysis. 

 degeneration, and neuronophagia of neurons with only slight changes be- 

 low the 1,500 r le\el. These investigators obser\ed gliosis 4 to 8 months after 

 the date of exposure. Astrocytes were hyperchromatic and inidergoing 

 degeneration, while scattered oligodendroglia demonstrated swelling. 



More recently Berg and Lindgren il958i attempted to chart the extent 

 of cerebral lesions produced by different divided and undivided doses and 

 to determine the time-dose relationships for delayed reactions of brain tissue 

 on application of a single dose and fractionated doses. These in\estigators 

 reported \arious lesions in the rabbit brain : frank necrosis, partial destruc- 



* Supported by National Institutes of Health. 



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