The influence of strain, age and other modalities on the radiosensitivity of cerebral microvasculature: A quantitative evaluation

The neonatal rat and its radiation induced cerebral hemorrhages were used to demonstrate the dependancy of the radiation response on the age (developmental stage) and strain (genetic condition). The extent of the radiation damage was quantified by a scoring scale ranging from 0 to 5. Holtzman and Gunn (non-jaundiced heterozygous j/+ and jaundiced homozygous j/j rats were irradiated to the head by 2.5 Gy of X-rays at the age of either 20-30 (ld) or 30-48 hours (2d). The score values for the irradiation age of 1 day were as follows: 1.98, 2.74 and 2.80 for Holtzman, heterozygous and homozygous Gunn rats, respectively. The corresponding values for the irradiation age of 2 days were 0.97, 1.92 and 1.85, respectively. The significant (p<0.001) decrease in radiosensitivity within one day resulted in a dose modifying factor of at least 1.3. comparing the strains there was a significant (p<0.0003) increase in radiosensitivity in Gunn rats as compared to Holzman rats for both radiation age groups. The difference between heterozygous and homozygous Gunn rats was not significant suggesting that the gene j recessive for jaundice might be dominant for the increase in radiosensitivity. (orig.)