The expressions of Bcl-2, Bax and thioredoxin (Trx) mRNAs after kainic acid (KA) injection with or without melatonin pre-treatment were examined by real-time quantitative reverse transcription polymerase chain reaction in rat hippocampus. Bcl-2, Bax, and Trx mRNA expressions after KA injection were significantly increased. Additionally, it was observed that melatonin or melatonin pre-treatment had no significant effect on the regulation of Trx mRNA. Pre-treatment with melatonin at the 30th minute before KA injection resulted in a significant depletion in Bcl-2, Bax and Trx mRNA expressions. However, our results showed that melatonin pre-treatment increases the ratio of Bcl-2 to Bax mRNA in short-term period. (C) 2004 Elsevier Ireland Ltd. All rights reserved.