Effect of dexamethasone on the expression of immediate early genes c-fos and c-jun in different regions of the neonatal brain

Abstract

The ratio of the expression levels of the immediate early genes c-jun and c-fos that encode components of the AP-1 transcription complex determines the direction of changes in the expression of genes controlled by the complex, including changes induced by glucocorticoids. The aim of the present work was to assess the levels of mRNA encoded by genes c-jun and c-fos and the ratio of expression levels of these genes in various regions of the neonatal rat brain after the administration of dexamethasone, a selective ligand of the glucocorticoid receptor. The level of mRNA encoded by the immediate early gene c-fos in the hippocampus and prefrontal cortex of 3-day-old rat pups was elevated at 30, 60, and 120 min after dexamethasone administration. The basal level of c-fos gene expression in the brainstem was higher than in the cortex and hippocampus, and administration of the hormone was followed by a reduction in the amount of transcript detectable in the brainstem after 2 h. As a result, the ratio of c-jun to c-fos transcript levels in the brainstem of neonatal rats was doubled after dexamethasone administration. The dexamethasone-induced shift of the ratio of c-jun to c-fos transcript levels in the brainstem of neonatal rats towards a predominance of c-jun reported for the first time in the present work may induce the expression of genes that contain AP-1 response elements in the promoters, since the glucocorticoid receptor can be involved in protein-protein interactions with the Jun/Jun homodimer of the AP-1 complex.