Fluoxetine induces vasodilatation of cerebral arterioles by co-modulating NO/muscarinic signalling.
Bottom Line: Ischaemic stroke patients treated with Selective Serotonin Reuptake Inhibitors (SSRI) show improved motor, cognitive and executive functions, but the underlying mechanism(s) are incompletely understood.Here, we report that cerebral arterioles in the rat brain superfused with therapeutically effective doses of the SSRI fluoxetine showed consistent, dose-dependent vasodilatation (by 1.2 to 1.6-fold), suppressible by muscarinic and nitric oxide synthase (NOS) antagonists [atropine, NG-nitro-l-arginine methyl ester (l-NAME)] but resistant to nicotinic and serotoninergic antagonists (mecamylamine, methylsergide).In vitro, fluoxetine suppressed recombinant human acetylcholinesterase (rhAChE) activity only in the presence of albumin.
Affiliation: Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.Show MeSH
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Mentions: Supporting this notion, cultured mouse b.End.3 brain endothelial cells loaded with the Ca2+ fluorescent dye, fluo 4-AM showed that fluoxetine (10 μM) induced a rapid and robust increase in intracellular calcium ([Ca2+]i, 1.5 ± 0.3 mmol, Fig. 3A). Because ACh has been shown to increase [Ca2+]i in endothelium  and to enhance NO production in peripheral blood vessels,  we further tested for [Ca2+]i increases in response to high ACh levels (10 mM). The fluoxetine effect was more robust than that of the rapidly degradable ACh (data not shown) and was prevented by atropine (Fig. 3B), suggesting that fluoxetine directly activates muscarinic receptors on endothelial cells. When treated with the NO fluorescent dye DAF-2DA, cultured b.End.3 cells displayed atropine-sensitive NO elevation in the presence of 50 μM fluoxetine (Fig. 3C), and NO labelling was particularly intense in cellular regions surrounding the nucleus (Fig. 3D).
Affiliation: Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.