Objective To detemine the effects of ketamine on c fos gene expression in the different brain regions of rats following stress responses Methods Twenty one male Wistar rats were randomly allocated to receiving intraperitoneally 2 ml normal saline (group C or group S,n=7) or ketamine 100mg?kg 1 (group K,n=7) respectively, 5 min later, the stress response was induced with electrical foot shock (2 0mA,1s of duration,once every 30s,over 15min)only in group S and K All rats were decapitated 30min after the stress to extract the total cellular RNA of cerebral cortex, hypothalamus and hippocampus RT PCR technique was applied to determining cDNA amplification products with ? actin mRNA being as an internal control Densities of DNA bands were quantified using image analysis system Results The c fos mRNA levels were markedly elevated in group S as compared with control levels (P0 05).Conclusions The c fos gene involves in molecular modulation of stress responses Ketamine produce different effects on the expression of c fos gene in the different brain regions