X-IRRADIATED CNS OF THE SYRIAN HAMSTER 



263 



of the astrocytes" cytoplasm i Fig. 1 ) . All astrocytic processes are considerably 

 enlarged and even more pale and "watery" than usual. Around a small 

 capillary there is disruption of astrocytic membranes, probably due to a 

 combination of artifact and edema. Under different experimental conditions 

 De Robertis et al. 1958 ) have produced similar changes and emphasized the 

 role of the astrocytes in water and ion metabolism of the brain tissue. It 

 seems probable that this astrocytic swelling represents the electron micro- 

 scope equivalent of the sponginess and loosening of the cortical neuropil that 

 is usually considered reflective of edema. This morphologic manifestation of 

 radiation-induced edema is restricted to astrocytic cytoplasm, and other cells 

 within the central nervous system seem to be unaffected. Furthermore, the 

 narrow intercellular gap which represents the only anatomic extracellular 

 space in the brain i Hager. 1959: Horstmann and Meves. 1959) is not in- 

 creased in this situation. The neurons appear normal at this stage. The 

 appearance of mitochondria is somewhat difficult to evaluate, since similar 

 changes in these organelles can occur as the result of incomplete or delayed 

 fixation. 



Figure 2 demonstrates erythrodiapedesis around a small \ein. The red 

 blood cells lie outside the perivascular space and within the intercellular gap. 

 This is more easily seen in Fig. 3. where the erythrocyte is situated between 

 completely intact cell processes, most of which are astrocytic. Contemporarily 

 with the appearance of astrocytic swelling and erythrodiapedetic bleeding, 

 there occurs slight, but probably definite, swelling of the capillary endo- 



l"iu. -. Ucicbial cortfx. 69 hr after exposure to 45,UUU i. Ei\ ihiodiapcdcsis around 

 a small vein outside of the perivascular space. E, erythrocytes lying between astrocytic 

 processes. V, vessel wall; N. nen.e cell. X 4,800. 



