FLUORESCEIN AS INDICATOR OF BRAIN INJURY 379 



was killed at 24 hours after irradiation with 11.000 rad. There was a 6 mm 

 wide band of intense !4-|-) fluorescence extending 34 of the way to the bot- 

 tom of the section in the fresh specimen. The photograph illustrates the 

 isolated patches of lightly stained tissue seen in the gray matter and the 

 mottled appearance of the white matter in the path of the beam. Figure 7B 

 shows the lightly staining patches in the gray matter enlarged 32 times. By 

 48 hours the entire irradiated area had become liquescent. 



Figure 7C shows a rat brain 24 days after the same dose and aperture as 

 used in the monkeys in Fig. 7A and 7B. Without magnification, or with the 

 help of low magnification, it can be seen that in the cortex there is a de- 

 crease in staining quality of the ground substance with some capillaiy 

 dilatation. No changes were recognized in the corpus callosum. Figure 7D is 

 a higher power magnification of the area of the cortex showing changes. 

 Microscopic examination of the brains of rats from the same group autopsied 

 at 20 days or less after irradiation showed no recognizable morphologic 

 changes. By 44 days after irradiation, the irradiated area had undergone 

 hemorrhagic necrosis with a lethal subarachnoid hemorrhage occurring in 

 some animals, a degree of pathology grossly comparable to that found in the 

 monkey after 48 hours. A detailed study of the histopathology of such lesions 

 has been presented by Janssen et al. '1961). 



Two methods of more accurately quantitating the extent of injury, using 

 fluorescein as an indicator and as a method of evaluating the acciuacy of 

 the arbitrary \isual grading of the lesions. ha\e been suggested. Photograph- 

 ing the lesion, using standardized conditions under ultraviolet light, as in 

 Fig. 6. and quantitating the film, using a micro-densitometer. could be done. 

 Pieces of tissue of uniform size taken from the center of the lesion ha\e been 

 analyzed for fluorescein content using a fluorospectrophotometer in a few 

 cases. The values obtained for tissue which had been graded 1+, 2+, and 

 4+ were 62. 78. and 460 jjsz fluorescein. 



Discussion 



The use of fluorescein staining as a criterion of brain injury following 

 irradiation has been described in detail because it combines the advantages 

 of being cjuick. simple. semiquantitati\e, and remarkably sensitixe for brain, 

 rather than because of any basic physiologic or biochemical significance of 

 the property of staining per se. The simplest explanation for the fact that 

 the tissue takes up the dye onlv after injury would seem to be that the mem- 

 branes of injured cells became permeable to substances which they would 

 normally exclude. However, when considering brain tissue, one cannot ignore 

 the so-called blood-brain barrier phenomenon which has been the subject of 

 so much controversv i Clemente and Richardson. 1961 ) . This study does not 



