Behavioral Effects of Cranial Irradiation of 



Rats* 



William J. Arnold 



University of Nebraska, 

 Lincoln, Nebraska 



This paper summarizes the results of a series of experiments, carried out 

 over a period of several years, dealing with the effects of irradiation on a 

 variety of behavioral processes, including emotionality, maze learning and 

 retention, instrumental learning, discrimination learning, formation of a 

 learning set, motivation, visual exploration, and general (locomotor) activity. 

 Details of the irradiation techniques used in these experiments have been 

 published elsewhere (Arnold, 1952; Blair and Arnold, 1956; Blair, 1958) 

 and need not be repeated here. Briefly, each rat was individually irradiated 

 in a lead exposure chamber. For some experiments, the whole head of the 

 rat was exposed to 300, 800, 2,000 or 2,500 r, while, for other experiments, 

 only an oval area (11 X 13 mm) directly over the brain was exposed to 

 5,000 r. 



Gross EflFects, Lethality, and Tooth Deformities 



The results of some of the behavioral tests can best be understood against 

 a background of the gross effects of cranial irradiation. Preliminary work 

 showed that, for 90-day-old rats, 2,500 r whole head irradiation and 5,000 r 

 brain area irradiation were near the maximum practical doses. Beyond these, 

 the mortality rate was prohibitive. All animals developed symptoms of radia- 

 tion sickness similar to those reported for much lower doses of total body 

 irradiation. They stopped eating and lost weight, reaching a minimum 

 weight 10 to 20 days after irradiation. Weight loss and lethality were posi- 

 tively related to dosage and inversely related to age when irradiated. A dose 

 of 5,000 r to the brain area of 90-day-old rats shortened their life span by 

 about one third. 



Tooth deformities developed after irradiation. They were most severe in 



* Most of the research reported in this paper was supported by the Atomic Energy 

 Commission. 



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