Temporal expression of brain-derived neurotrophic factor (BDNF) mRNA in the rat hippocampus after treatment with selective and mixed monoaminergic antidepressants.

Strong evidence suggests that antidepressants work by induction of neuroplastic changes mediated through regulation of brain-derived neurotrophic factor (BDNF). This study was undertaken to investigate the time-course of the effect of three antidepressants; fluoxetine, imipramine and venlafaxine, which differentially affect monoamine reuptake, on BDNF mRNA expression in the hippocampus. The consequences of increased BDNF in the hippocampus are still indefinite. Here, we also determined the effects on the expression of two other genes (synaptophysin and growth-associated protein-43 (GAP-43)) known to be involved in synapse formation and axonal growth and likely regulated by BDNF. The effects were determined in rats after sub-chronic (7 days) and chronic (14 and 21 days) treatment using semi-quantitative in situ hybridisation. BDNF mRNA levels in the dentate gyrus (DG) were increased after treatment with venlafaxine (7, 14 and 21 days) and imipramine (14 and 21 days), but not after treatment with fluoxetine, indicating that stimulation of BDNF mRNA expression is dependent on the pharmacological profile and on the time-course of drug treatment. A transient increase in synaptophysin mRNA was observed after treatment with venlafaxine and fluoxetine whereas imipramine had no effect. In the CA3 region a reduction of GAP-43 mRNA was observed after treatment with imipramine (21 days) and fluoxetine (7 and 14 days). These results suggest that venlafaxine and imipramine, but not fluoxetine, induce neuroplastic effects in the hippocampus through stimulation of BDNF mRNA expression, and that the effect on BDNF is not directly translated into regulation of synaptophysin and GAP-43 mRNA.