IONIZING-RADIATION INDUCES EXPRESSION OF IMMEDIATE-EARLY GENES IN THERAT-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-j un mRNAs was induced in a scattered cell population in the lateral str iatum, whereas in the piriform cortex the expression of zif-268 mRNA w as decreased. Other brain regions did not show consistent changes in t he mRNA levels. Three hours after radiation the mRNA levels had return ed to normal. Immunocytochemistry showed the number of c-Fos and Jun-B -positive neurones to be increased in the striatum and slightly increa sed in the frontoparietal cortex 1 and 3 h after radiation. The result s show that a subpopulation of neurones is sensitive to ionizing radia tion at the clinically relevant dose of 2 Gy and that the neuronal res ponse to this irradiation involves altered expression of genes encodin g for transcription factors.