480 WALTER R. STAHL 



curred after radiation, one might expect that nervous system drugs or CNS 

 surgery would radically alter the course of radiation sickness. While many 

 agents, including some with actions on the nervous system, can alter radi- 

 ation dose-effect curves slightly, there is no evidence that they alter them 

 in major ways. It is of basic importance that the most significant delayed 

 radiation effects, namely genetic mutations, simulated aging, somatic muta- 

 tions, and cancer induction, are all mechanisms in which the organism does 

 not adapt to a noxious environmental influence, but suffers innate injury. 

 On the other hand, Soviet scientists take a broad view of nervous control 

 and may include any neurohumoral and all hormonal mechanisms in the 

 category of CNS adaptive responses. Thus, pituitary hormonal changes have 

 been scrutinized for importance in radiation sickness. 



The possible role of nerve damage in aging phenomena and in production 

 of cancer becomes of special interest from this viewpoint. It is well estab- 

 lished that tumors do not have a normal innervation, but it is by no means 

 clear that this is of causal significance. Zubareva (1959) reported on the 

 detailed histology of nerves in spontaneous breast tumors in mice, and 

 Sheveleva (1959) studied nervous influences on the development of a 

 Brown-Pearce implanted tumor in rabbits. Similar work is often found in 

 the Soviet Bulletin of Experimental Biology aiid Medicine. 



Dzharak'yan (1957) has suggested that postirradiation leucopenia is in 

 part due to faulty splenic nerve activity resulting from radiation damage 

 to nerve endings. Many studies have dealt with vascular mechanisms in 

 irradiated animals and commonly report major alterations in tone following 

 several hundred r; this may in part be due to altered levels of circulating 

 sympathins, but direct damage to the vessels and their innervation is also 

 proposed. Cyclic alterations in the secretory activity of the gut are rep>orted 

 by Uspensky (1959) and are said to be due to altered "trophic control" 

 predominantly. This will have to be qualified on the basis of known direct 

 radiation injury to mucosal cells. 



Many of these studies implicate the autonomic nervous system in radiation 

 injury. Soviet authors, especially Lebedinsky, have pointed out that the 

 radiation syndrome involves changes in vascular phenomena, thermoregula- 

 tion, cardiac activity, respiration, capillary permeability, and numerous 

 other autonomic phenomena. He observed changes in hypothalamic stimu- 

 lation thresholds for these after irradiation. Studies by others have shown 

 changes in the excitability level of the vagal centers after irradiation 

 (Gromovskaya, 1959) and similar phenomena. 



Still another aspect of radiation sickness is the specific role of the pitu- 

 itary-adrenal axis after irradiation. Results remain contradictory, but some 

 Soviet workers feel they have shown a distinct stress reaction to radiation 

 injury. Possibly this reaction obtains only in some species and at some doses, 



