414 



CLEMENTE AND RICHARDSON 



Fig. 1. (A.) A section of monkey parietal cortex impregnated to show astrocytes by 

 the Cajal gold sublimate method. Note the myriad numbers of astrocytic processes 

 surrounding the capillary forming the so-called perivascular glial membrane. X 150. 

 (B.) An electron micrographic demonstration of the perivascular astrocytic processes. 

 Notice the virtually complete encasement of the capillary by the watery-looking cyto- 

 plasmic projections of the nearby astrocyte. Approximately X 1,500. (Figure 1-B was 

 loaned to the authors by Drs. D. Pease, E. Maynard, and R. Schultz. ) 



As is the case with the blood-brain barrier, pathologic, chemical, and 

 physical insults are capable of breaking down the blood-aqueous humor 

 barrier and the blood-cerebrospinal fluid barrier. The most obvious mani- 

 festation of a breakdown in the blood-fluid barriers is an increase in protein 

 in the central humor (Davson, 1960). Again, it has been shown that ex- 

 posure to x-rays afTects the permeability characteristics of these blood-humor 

 barriers. An increase in permeability of the blood-cerebrospinal fluid barrier 

 was observed by Tatsumi as early as 1933 and by Hsu ct al. in 1936. 



In a series of 37 monkeys, Clemente and Hoist (1953, 1954) observed 

 changes in permeability of cerebral vessels following single doses of x-irradi- 

 ation ranging from 1,500 to 6,000 r. Trypan blue injected intraperitoneally 

 demonstrated a profound functional impairment of the blood-brain barrier, 

 especially in the brain stem and hypothalamus, and was best visualized after 

 doses of 4,500 and 6,000 r (Fig. 2). Neuroglial, neuronal, and vascular dam- 



