Behavioral and Histologic Effects of Head 

 Irradiation in Newborn Rats 



James N. Vamazaki. Leslie R. Bennett, and Carmine D. Clemente 



Univeruty of California, Los Angeles Medical Center and \.A. Hospitals, 

 Los Angeles and Sepulveda, California 



Introduction 



The efiect ot ioniziiiii radiation on the nei\ous systt-ni durinti \aiioiis 

 stages of its o^rowth and de\eIopinent has elicited a broad spectrum of 

 pathoio<_;ic responses. Early e.xperirnents clearly demonstrated the relative 

 \ ulnerability to radium and x-ray of the brain in youni^ guinea pigs. rats, 

 doys, rabbits, and kittens compared to the adult i Danysz. 1903: Turner 

 and Geort;e. 1910). resultiny in stunted iirowth and abnorn:ial neurologic 

 findings. The teratogenic effects of ionizing radiation in the embryo has 

 received the attention of many excellent studies clarifying the differential 

 response during the various stages of development from the earliest embry- 

 onic stage to the end of gestation i Bagg. 1922: Job ct al.. 1935: VVarkany 

 and Schraffenberger. 1947: Russell and Kussell. 1954: Hicks. 1950, 1953a.b. 

 1954a,b). The nature of the cerebral anomalies depended less on the dose 

 ot radiation than on the time of gestation when administered. The degree 

 ot sensitivity has been related to the extieme sensitivity of the undifteren- 

 tiated multi-potential cell in the \ery early embryonic stage and later in 

 gestation to the early neural cell or neuroblast ( Rugh and Grupp. 1959: 

 Hicks. 1950, 1953a.b. 1954a.b). 



Regardless of the ease with which the embryonic central nervous system 

 can be damaged, an increasing gradient of radioresistance develops as gesta- 

 tion progresses. The degree ot this sensitivity is demonstrated by the fact 

 that 15 r can produce exencephalia in the very early embryo (Rugh and 

 Grupp. 1959). In contrast, the minimal dose which has caused pathologic 

 lesions in the adult monkeys has been 1.500 r when slight neinonal damage 

 was seen, but some of the animals after 4 to 8 months had elapsed developed 

 focal seizures. With larger doses there occurred blood brain barrier changes, 

 astrocytic and neuronal damage with lesions, particularly affecting the hypo- 

 thalamus and the medulla. Several neurologic signs of varying severity 

 developed according to the radiation dose (Clemente and Hoist, 1954: 



59 



