EFFECTS OF HEAD IRRADIATION IN NEWBORN RATS 63 



iesp(.'cti\ely. The difference in brain in\ol\ement between the animals radi- 

 ated durino the first 5 days ot Hfe compared to the older animals is demon- 

 stiated by the followino examples: 



500 r: Rat No. 32 was irradiated on the 5th day of life. Tremors were 

 first noted at 6 weeks. These became progressively more severe, and in- 

 coordination and weakness of the hind limbs were noted from the 3rd 

 month. The eyes and head were small, and cataracts developed in one eye. 

 Of 7 animals radiated after the 8th day, only rat No. 18 developed any 

 neurolo2;ic siijn. a mild tremor first noted at the 10th month. 



1000 r: Animals ladiated on the first days of life at this dose level denron- 

 strate the marked vulnerability of the brain at this age. By the 2nd week 

 of life they could easily be separated from their control litter mates by their 

 small size, weighing an average of 18 gm in comparison to 39 gm for the 

 controls. Marked tremor was alieady present, eyes were narrowed and small, 

 the animals tended to drag their hind limbs and encountered difficulty in 

 righting themselves. Other animals revealed a marked hypeiactivity. darting 

 about the cage in a purposeless, random manner. 



The incidence and severity of the pathologic findings correlated closely 

 with the neurologic findings in the irradiated animals. 



The most consistent and outstanding finding was the difk-retwje in size of 

 the cerebellum in the irradiated animal in comparison to the controls. When 

 the cranial vault is lemoved in a newborn rat. the cerebellum is in close 

 approximation to the inferior coUiculi ot the brain stem. Within a week 

 after birth, the hemispheric colliculi are overgrown by the developing cere- 

 bellum and cerebral cortex in the normal animal, whereas in the irradiated 

 animals the colliculi are verv prominent even 3 weeks after birth. The 

 ceiebellum remaining is underdeveloped. Petechial hemorrhages were noted 

 on the surface of the cerebral cortex, although noticeably absent elsewhere. 

 When the irradiated brain was cut. the tissue had a more gelatinous 

 consistency than the normal brain. 



In animals allowed to survive lor longer periods of time, the generally 

 retarded size of the brain was striking in addition to a distortion in the 

 configuration of the cerebellum. The meninges often appeared thickened 

 and fibrous, and the diua was firmly adherent to the brain surface, although 

 it was possible to separate it from the cerebral cortex. The posterior part 

 of the cortex often was depressed as if the cortex were thinner in this area. 



In the animals sacrificed 48 to 72 hours after irradiation, widespread 

 changes in the vasculature in the brain and brain stem were noted, and 

 more specific lesions were identified in the choroid plexus and meninges. 

 Vascular lesions occmred after dosages of at least 500 r in animals irradiated 

 within the first 5 days postnatally and in animals administered 1.000 r 

 between the 5th and 10th postnatal days. The most common vascular 



