Study identifies mechanism by which antidepressant fluoxetine increases cAMP signaling in brain cells
Researchers have identified a cellular mechanism by which the antidepressant fluoxetine elevates cyclic AMP (cAMP) levels in astrocytes, involving communication between astrocytes and microglia via purinergic signalling. SSRIs like fluoxetine are among the most prescribed drug classes globally, yet their full therapeutic mechanisms have remained poorly understood. The findings suggest that fluoxetine's antidepressant effects depend partly on glial cell interactions rather than serotonin elevation alone, potentially opening new targets for depression treatment.
A new preprint study published on bioRxiv investigated how fluoxetine, a widely used SSRI antidepressant, elevates intracellular cAMP levels in astrocytes — a signalling pathway known to be downregulated in depression. Using FRET-based sensors in primary rat astrocytes, researchers found that fluoxetine increased intracellular cAMP by 28% without altering calcium dynamics. The process was found to depend on serotonin 2B (5-HT2B) receptors triggering a 10% increase in astrocytic ATP release, which microglia then convert to adenosine; adenosine in turn activates astrocytic adenosine 2B (A2B) receptors to drive cAMP elevation. When microglia were depleted from astrocyte cultures, fluoxetine-induced cAMP increases were diminished and extracellular ATP accumulated, confirming the necessity of astrocyte-microglia crosstalk. These findings challenge the traditional serotonin-centric explanation of SSRI action and highlight glial purinergic signalling as a key component of fluoxetine's therapeutic mechanism. SSRI prescriptions have grown approximately 50% over the past decade, making a clearer mechanistic understanding clinically relevant for improving or targeting future treatments.
What's missing
The study was conducted in primary rat astrocyte cultures, and it is unclear whether the same signalling cascade operates in intact human brain tissue or in vivo models. The functional significance of a 10–28% change in ATP release and cAMP elevation for actual antidepressant efficacy in patients has not been established. The study does not address whether this mechanism differs across brain regions, patient populations, or other SSRI compounds beyond fluoxetine.
What different sources said
- bioRxivCenter
Antidepressant fluoxetine engages astrocytic cAMP via purinergic signalling
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