A study of direct and indirect radiation damage upon the developing ear in Amblystoma

Abstract

The primary purpose of this study is to determine the relative effects of direct and indirect radiation damage on the development of the ear in the salamander. The terms direct effect and indirect effect are employed here in their general biological sense; a brief discussion of their significance may be found in an earlier paper (Piatt, Raventos and Kusner, '59,. Secondary attention is directed to the effects of reduced temperature on the post-irradiation development of the ear. Interest in the temperature factor arose as a necessary by-product of the experimental procedure and its bearing on the results of this paper is discussed under the appropriate sections below.The results of other investigators who have dealt with the question of direct vs. indirect effects of radiation damage are frequently at variance. Wood and Prime ('15) found that mouse tumors subjected to radium treatment die in vitro after one hour but are only slowed in their growth when left in vivo. They suggest that toxic substances produced by radium irradiation accumulate in the in vitro cultures but are eliminated in the in vivo transplants, thus accounting for death in the former and survival in the latter. If this be so, then the indirect effect of the liberated toxins is decisive in causing death of tumor cells. On the other hand, Strangeways and Hopwood ('26) x-irradiated embryonic chick tissues in vitro and observed either absence or reduction of mitotic figures after 80 minutes incubation. They interpret this effect as a direct one since total body irradiation was not employed. Duryee ('47, '49) x-irradiated ovarian eggs of Amphibia. Irradiation of the entire egg caused considerably more damage to the nucleus than when nuclei isolated from the cytoplasm were irradiated. Also, non-irradiated nuclei mixed with irradiated cell brei showed intermediate degrees of nuclear damage. These results are interpreted as evidence for indirect radiation damage. On the other hand, Strangeways and Fell ('27) found that extracts of x-irradiated chick embryos added to in vitro cultures of non-irradiated tissues had no ill effect on these tissues. In the same study, though, they did interpret part of their data as supporting indirect radiation effects since explants from embryos made 80 minutes after irradiation grew better than explants made 24 hours after irradiation.Vintemberger ('28) x-irradiated just one of the blastomeres of the two-cell stage in the frog. The non-irradiated blastomere continued to develop and formed approximately half an embryo. Rugh and Clugston ('55) performed the same experiment using Fundulus eggs irradiated with alpha particles. The irradiated blastomere was subsequently discarded but the non-irradiated half developed normally to the gastrula stage when mechanical difficulties prevented it from continuing normal development. Taken together the results of these two experiments suggest that contact of irradiated and non-irradiated cells causes no indirect radiation damage to the latter.Experiments on indirect radiation effe...