472 WALTER R. STAHL 



damage and spreading axonal effects from a small segment of frog sciatic 

 nerve exposed to 10 kr and more. Lebedinsky (1959b) assessed synaptic trans- 

 mission in the irradiated animal under physiologic conditions by testing 

 blinking of the eye following cervical sympathetic stimulation; alterations 

 occurred after doses of a few hundred r. 



In another synaptic study, using a leg withdrawal reflex in the rabbit, 

 Kudritsky (1957) found that 10 r will alter some of the timing parameters, 

 especially the variability of the latent period of response. Similar types of 

 alterations have been reported following 500-1,000 r (Gvozdikova, 1957). 

 Kudritsky has also suggested that there may be adaptation of the organism 

 to radiation and found evidence that pretreatment of a rabbit with several 

 hundred r eliminated its response (noted previously) to a subsequent 10 r 

 test. 



Many indirect factors can enter into an altered CNS response following 

 irradiation such as changes in basic metabolic processes in nerve cells in- 

 volving DNA metabolism (Levinson et al., 1957) or cerebral amino acid 

 metabolism (Minayev and Skvortsova, 1957). No final conclusions seem 

 possible on this point; nucleic acids are known to be fairly radiosensitive 

 in some biologic systems, but maintenance of the membrance potential is 

 expected to be quite stable to slight biochemical damage. 



Many Soviet studies have dealt with various vascular reactions to radi- 

 ation exposure. Lyubimova-Gerasimova (1960) found significant alterations 

 in tone of cerebral vessels following 1,000 r in the rabbit. Several studies 

 discuss blood-brain barrier permeability changes and alterations in capillary 

 properties; these may well play a role in some of the reactions seen after 

 exposure. 



The possible importance of circulating toxic or physiologic substances in 

 radiation reactions has been stressed in many works. Working under Lebe- 

 dinsky, Maslova (1958) and others have produced evidence indicating fluc- 

 tuations in circulating sympathin levels following near-lethal exposures in 

 cats and rabbits. There seems little doubt that under some conditions sym- 

 pathins are increased and that they fluctuate considerably. These substances 

 may well exert a role on almost any aspect of CNS activity. The possible 

 presence of sympathins should be given serious thought in experimental 

 results without a ready interpretation, such as atypical subcortical EEG 

 reactions. Mozzhukin and Pevsner (1959), working under Zedgenidze, 

 showed important changes in pressor reflexes following radiation and sug- 

 gested that altered adrenal medullary activity was responsible. Hypotonia 

 or other vascular reactions may alter reactions in CNS tests. 



Direct radiation injury to an effector organ needs serious thought with 

 CNS studies involving secretory organs. For instance, Lomonos (1957) and 

 Ye. A. Brodskaya (1958) showed that there are changes in the uncondi- 



