MAP kinase activation by fluoxetine and its relation to gene expression in cultured rat astrocytes

Chronic treatments with antidepressants active on major depressive disorders influence pathways involved in cell survival and plasticity. As astrocytes seem to play a key role ill the protection of brain cells, we investigated in these cells the rapid effects of the antidepressant fluoxetine (Prozac(R)) on signaling cascades and gene induction, which probably play a role in neuroprotection. We shove here that fluoxetine alone activates the extracellular signal-regulated-protein kinase (Erk) and p38 mitogen-associated protein (MAP) kinase cascades. RT-PCR revealed that genes, modulated in brain by long-term fluoxetine treatment, are rapidly induced (detectable after 2-4 h) by fluoxetine in cultured astrocytes: brain-derived nerve factor (BDNF) and its receptors, glial-derived nerve factor (GDNF) and deiodinase 3 (D3). Induction of D3 by fluoxetine is inhibited by U0126 and SB203580, suggesting that Erk and p38 MAP kinases are involved. Glial-derived nerve factor (GDNF) induction by fluoxetine is prevented by U0126, suggesting that Erk is implicated. Brain-derived nerve factor (BDNF) induction seems mediated by other signaling pathways. In conclusion, we show that fluoxetine alone rapidly activates mitogen activated protein (MAP) kinase cascades in rat astrocytes and that genes involved in neuroprotection are induced in a few hours in a MAP kinase-dependent or -independent manner.