LACK OF EFFECT OF ANTIDEPRESSANT DRUGS ON THE LEVELS OF MESSENGER-RNAS ENCODING SEROTONERGIC RECEPTORS, SYNTHETIC ENZYMES AND 5HT TRANSPORTER

Serotonergic transmission is thought to be central to the aetiology of depression and the therapeutic actions of antidepressant drugs, and t he latters' delayed effect has given rise to the hypothesis that an ad aptive change may be involved, possibly at the level of gene expressio n. We have examined this hypothesis by treating rats over a time cours e of up to 32 days with either imipramine, mianserin, fluvoxamine, cit alopram, amoxapine or saline and measuring the levels of mRNAs encodin g the 5HT(1A), 5HT(1B), 5HT(1C) and 5HT(2) receptors, the enzymes tryp tophan hydroxylase and aromatic amino acid decarboxylase, and the 5HT transporter. None of the treatments gave rise to significant changes i n any of the mRNA levels at any time point. These results suggest that the reported changes in 5HT receptor numbers do not occur as a result of changes in the abundance of their encoding mRNAs, and that changes to the latter is not central to the therapeutic effects of antidepres sant drugs.