206 NORBERT SCHUMMELFEDER 



was more severe at higher dose levels. In other experiments on the macaque, in 

 which 10,000 r Co*'° (gamma) radiation to the head alone or to the whole 

 body was used, Vogel et al. (1958) also observed pyknosis of granule cells 

 in the cerebellum. Both Haymaker et al. (1958) and Vogel et al. (1958), 

 whose animals survived no longer than one week, observed that the pyknosis 

 of granule cells was reversible by about the 3rd day. In a subsequent study 

 of the effects of cobalt'"^ (gamma) radiation on the cerebellum of macaque 

 monkeys at the same dose levels, Wilson (1960) confirmed the observation 

 that under these conditions the granule cell pyknosis is transitory and 

 reversible, but he found that pyknosis was somewhat briefer than reported 

 by the other authors. Similar results have been obtained in rabbits after 

 exposed to a Co"" source (Vogel, 1959) and in guinea pigs after x-irradiation 

 (Alvord and Brace, 1957). Vogel (1959) noted that after a dose of 15,000 r 

 gamma radiation from a Co''" source, granule cell pyknosis was evident in 

 15 hours and that by the 10th day practically all the granule cells of exposed 

 folia had disappeared. According to Hicks (1953; Hicks and Montgomery, 

 1952; Hicks and Wright, 1954; Hicks et al.. 1956) the same holds for rats 

 and mice. In these animals they found that nerve cells or cerebellar tissue 

 could readily be damaged by x-rays, depending on the dose. 



Our observations coincide with those of Hicks et al. { 1956) on the mouse. 

 We have shown that sufficiently intense x-irradiation of the cerebellar tissue 

 results in primary tissue changes. Incidence, pattern, and course of these 

 changes are clearly related to the x-ray dose. Under the conditions of oiu' 

 experiments, nuclear pyknosis in irradiated granule cells of adult mice is a 

 sign of irreversible cellular change leading to cellular necrosis. In this respect 

 our observations on mice do not coincide with those of Haymaker et al. 

 (1958), Vogel et al. (1958), and Wilson (1960) on macaque monkeys. We 

 are imablc to explain this difTerence, but points to be taken into considera- 

 tion are species and age of the animals, nature of irradiation, radiation 

 energy and rate of dosage. 



There is still little knowledge of the earliest histopathologic and histo- 

 chemical changes occurring in the cerebellum following irradiation or in the 

 sequence in which the changes develop. Our histochemical investigations 

 show that during early radiation damage of cerebellar tissue following high 

 x-irradiation dose, changes occur in the nucleic-acid-containing components 

 of granule and Purkinje cells. Particularly in Purkinje cells, alterations occur 

 in the cytoplasmic RNA that are secondary eflfects due to regressive cellular 

 alterations, since swelling of the nerve cells was observed initially and de- 

 crease in cytoplasmic nucleic acid content later on. The change in the 

 structural organization of the nuclear DNA in the pyknotic granular cells is 

 possibly also a secondary effect due to the increased density of the pyknotic 

 nuclei. But it could also represent a primary change in the physicochemical 



