FLUORESCEIN AS INDICATOR OF BRAIN INJURY 381 



rat. However, monkeys s,iven 3.000 rad showed no staining with fluorescein, 

 suooesting that the dose response ctirve for monkeys woidd have a steeper 

 slope than that for tlie rat when plotted as in Fia. 4. but that the monkey 

 may not show a "greater radiosensitivity of brain tissue at lower radiation 

 doses. The work of Hager ct al. (1961 ) using x-ray indicates that the ham- 

 ster brain is probably cjuite radiosensitive. 



In an attempt to rule out the possibility that the data collected in this 

 study pertained to the age of animal and aperture size, age and size of 

 aperture were investigated. Rats 22 days old showed the same response as 

 did rats 120 days old. There was no demonstrable difference in biologic 

 efTecti\eness with apertiae sizes ranging from 0.5 to 4 mm. These studies 

 tend to emphasize the species diflferences found and broaden their interpreta- 

 tion, but are not intended to imply that a^e and size of lesion are not im- 

 portant factors in more extreme situations. Hicks 1953) has demonstrated 

 that the adidt ner\ous system is radioresistant and the embryonic nervous 

 system radiosensiti\e, and Lindgren (1958) has stated that in clinical prac- 

 tice it has pro\ed ad\isable to reduce the adult dose by 25''r for treating 

 brain lesions in 5-year-old children and by 50''r when treating 2-year-old 

 children. Zeman ct al. \ 1959) have demonstrated that in order to produce 

 a lesion in the brain when the aperture is narrowed 25 p.) . an extremely 

 high dose must be delixered to the tissue. Hicks ct al. < 1958) has demon- 

 strated differences in radiosensitivity between strains of mice and difTerences 

 in pathologic and physiologic effects when the intensity of the radiation is 

 varied (Hicks ct al., 1956) . 



Summary 



Soluble fluorescein U.S. P. ( Uranine ) , a dye routinely used by physicians 

 as a convenient and sensitive indicator of damage to corneal epitheliimi. has 

 been found to be an ecjually con\enient. semiquantitative, and sensiti\"e indi- 

 cator of injiny to brain tissue following localized irradiation with a beam of 

 alpha particles from the 184 in. cyclotron. Permeability of the tissue to 

 fluorescein represents a physiologic or biochemical alteration of the cell, 

 which occurs before any morphologic changes demonstrable by light mi- 

 croscopy. The time of onset and intensity of fluorescein staining are different 

 for different doses of irradiation. 7 he minimimi effecti\e dose was 5.000 or 

 6.000 rad. A species difference in radiosensitivity of brain tissue was demon- 

 strated both by the fluorescein technicjue and by histologic morphology. The 

 brain of rabbits and monkeys is considerably more sensitive to alpha particle 

 irradiation than is that of rats. 



