Chronic fluoxetine treatment alters the structure, connectivity and plasticity of cortical interneurons

Area of Science:

• Neuroscience
• Molecular Psychiatry
• Developmental Neuroscience

Background:

• Antidepressants, including fluoxetine, are hypothesized to induce neuronal structural plasticity, mimicking juvenile brain states.
• The mechanisms behind this 'reopening' of critical periods remain unclear, but inhibitory networks are implicated.
• Recent research highlights the role of inhibitory networks in fluoxetine-induced structural plasticity.

Purpose of the Study:

• To investigate the effects of chronic fluoxetine treatment on neuronal structure in the hippocampus and medial prefrontal cortex (mPFC).
• To examine changes in plasticity-related molecules and interneuron morphology following fluoxetine administration.
• To elucidate the role of interneurons in fluoxetine-induced structural plasticity and critical period reopening.

Main Methods:

• Utilized transgenic mice with eGFP-labeled interneurons for detailed analysis.
• Administered chronic fluoxetine treatment to adult mice.
• Analyzed molecular markers (PSA-NCAM, GAD67/65, synaptophysin, parvalbumin) and synaptic structures in the hippocampus and mPFC.
• Quantified dendritic spine density on interneurons in the mPFC.

Main Results:

• Fluoxetine treatment increased expression of plasticity molecules (PSA-NCAM, GAD67/65, synaptophysin).
• Observed a decrease in parvalbumin-expressing interneurons ensheathed by perineuronal nets.
• Noted a trend towards reduced perisomatic inhibitory puncta on pyramidal neurons and increased puncta on interneurons in the mPFC.
• Found increased dendritic spine density on mPFC interneurons after chronic fluoxetine exposure.

Conclusions:

• Chronic fluoxetine treatment induces structural changes in adult cerebral cortex inhibitory neurons.
• These changes may involve alterations in plasticity-related molecules or the extracellular matrix surrounding interneurons.
• The findings suggest a potential mechanism for how fluoxetine influences plasticity, possibly by affecting interneurons crucial for juvenile critical periods.