Ionizing radiation induces expression of immediate early genes in the rat brain

In situ hybridization histochemistry and immunocytochemistry were used to examine whether therapeutic ionizing radiation induces expression of immediate early genes in the rat brain. One hour following a single dose of 2 or 15 Gy the expression of c-fos and zif-268 but not of c-jun mRNAs was induced in a scattered cell population in the lateral striatum, whereas in the piriform cortex the expression of zif-268 mRNA was decreased. Other brain regions did not show consistent changes in the mRNA levels. Three hours after radiation the mRNA levels had returned to normal. Immunocytochemistry showed the number of c-Fos and Jun-B-positive neurones to be increased in the striatum and slightly increased in the frontoparietal cortex 1 and 3 h after radiation. The results show that a subpopulation of neurones is sensitive to ionizing radiation at the clinically relevant dose of 2 Gy and that the neuronal response to this irradiation involves altered expression of genes encoding for transcription factors.