510 BROWN, SASMORE, AND JONES 



central nervous system of burros more sensitive to radiation than that of 

 other species? What are the physiologic aberrations leading to the central 

 nervous system response? Is the neurologic syndrome a direct or indirect 

 efTect? 



We do not believe that the dose rate should be emphasized, because the 

 head-irradiation experiment suggests a threshold for dose rate effect. The 

 Nevada and head-irradiated animals responded in a similar manner except 

 deaths occurred earlier in the Nevada burros, and mortality was slightly 

 higher in the head-irradiated animals at equivalent dose levels, possibly a 

 result of anesthesia. A recent report (Zander, 1959) indicates that anesthesia 

 enhances the mortality effect of irradiation. 



The data presented suggest that vascular changes contributed greatly to 

 the central nervous system effects observed. According to Udall ( 1946), the 

 symptomatology described is related to conditions which cause an increase 

 in intracranial pressure, such as cerebral congestion and hemorrhage, menin- 

 gitis, and encephalitis. Extravasation of plasmatic fluid is often concomitant, 

 and hemorrhages are prominent. It seems likely that the perivascular cuffing 

 with neutrophils is a response to the plasmatic fluid extravasations. 



Alterations in the blood-brain barrier may be an important factor in the 

 biaro's response to irradiation. Rose (1958) reported an accelerated pene- 

 tration of electrolytes into the cerebrospinal fluid and brain of rabbits follow- 

 ing irradiation. This could possibly contribute to an increase in cerebrospinal 

 fluid pressure. Two manometric readings of cerebrospinal fluid pressure 

 taken in moribund, recumbent head-irradiated burros at the lumbrosacral 

 fossa approached 800 mm water. Less than 300 mm is normal. 



Although the primary lesion is \ascular, satellitosis and neurophagia are 

 evidence of neuronal damage. Whether these lesions are results of a direct 

 effect on the neurons, a sequela to vascular damage, or metabolic disturb- 

 ances is not known. 



Summary 



Three irradiation experiments with burros showed pronounced central 

 nervous system disturbances and death at relatively low dose levels. The 

 data suggest that vascular changes contributed greatly to the central nervous 

 system effects observed. 



References 



Arnold, A., Bailey, P., Har\ey, R. A., Hass, L. L., and Laughlin. J. S. 1954. Changes 

 in the central nervous system following irradiation with 23 mev x-rays from the 

 betatron. Radiology 62, 37-46. 



Gangloff, H., and Haley, T. J. 1960. Effects of x-irradiation on spontaneous and 

 evoked brain electrical activity in cats. Radiation Research 12, 694-704. 



