EFFECTS OX BLOOD-BRAIN BARRIER, CEREBRAL BLOOD VESSELS 423 



partially or completely occluded. In these reoions, few. if any, normal- 

 looking nemons could be found. In another animal, sacrificed 10 days after 

 the beam was directed at the brain stem, there were frank hemorrhagic areas 

 in the midbrain ( Fig. 6C ) and peri\ascular globules (Fig. 6D I in the brain 

 stem, similar to those reported by Brightman I 1959). 



Vascular and parenchymal damage was also observed in the cerebellum 

 following alpha particle radiation. This was characterized by spongy loss of 

 cerebellar cortical tissue, thickening of the meningeal and inxaginating 

 vessels, and \acuolization of the Purkinje cell layer ( Figs. 7A-D i . 



In these higher radiation dose experiments, it is difficult to say that the 

 entire neuropathology observed is the result of an altered circulatory system. 

 On the other hand, it is impossible to believe that the neurons in a portion 

 of the neuraxis with such badly damaged vessels could react physiologically. 



Summary 



In this communication we wished to slant our attentions to the reactivity 

 of the vasculature in the brain and spinal cord to ionizing radiations. Studies 

 dealing with the influence of x-ravs on the blood-brain barrier were re- 

 viewed, and pathologic changes in central nervous system blood \essels due 

 to x-rays and to alpha particle radiation were described. 



It is felt that x-iadiation dosages under 1.000 r administered to the brains 

 of adult animals fail to reveal marked histopathologic findings, even though 

 these ha\e been observed following this radiation dosage in newborn animals. 

 Nevertheless, the effect of these relati\-ely low doses may become manifested 

 in nein^al dysfunction through changes in the surrounding medium of 

 neuronal pools. Thus, we feel that one of the effects of low dosage radiation 

 is an increase in the permeability of cerebral \essels. 



With higher x-ray doses (4,500 or 6,000 r) and with alpha particle radia- 

 tion (10,000 rad) to the central nervous system, histopathologic findings 

 have been obser\ed not only in the cerebral vasculatme. but also in neurons 

 and neuroglia. Vascular damage was evident by thickening and hyalinization 

 of the vessel walls. Perivascular infiltration of leucocytes and complete occlu- 

 sion of larger and smaller vessels were often observed. Neuronal damage was 

 evident by morphologic changes in the cytoplasm and nuclei of remaining 

 cells and by spongy loss of neuronal elements in the areas irradiated. Neiu'ons 

 showing \acuolization and ghost cells were frequently observed. Although at 

 these higher dosages it was difficult to maintain that the neuronal pathology 

 was only the direct result of altered circulation, it is felt that vascular 

 pathology cannot be imderestimated in an analysis of the response of the 

 central nervous svstem to ionizing radiations. 



