STRESS-INDUCED EXPRESSION OF THE C-FOS PROTOONCOGENE IN THE HIPPOCAMPAL-FORMATION

To investigate the effects of stress on c-fos mRNA expression, rats we re submitted to forced immobilization for 15, 30, 60 or 120 min before sacrifice. In situ hybridization was performed on sections containing the dorsal hippocampus with a P-32-labelled 50-base oligonucleotide p robe (10(7)-10(9) cpm/mug) complementary to nucleotides 370-319 of rat c-fos. Forced restraint induced a time-dependent increase in c-fos mR NA expression which was most pronounced in the dentate gyrus and CA1-C A3 regions of the hippocampal formation, and which peaked after 30 min of immobilization (72.7 +/- 1.0 vs 24.1 +/- 0.8 cpm/mm2 in unrestrain ed animals). A positive but weaker signal was also detected in the amy gdala, pyriform cortex and other parts of the cerebral cortex and habe nulae. These results suggest that the hippocampal formation is activat ed during stress.