Nonlinear recurrent inhibition through facilitating serotonin release in the raphe

Area of Science:

• Neuroscience
• Computational Neuroscience
• Molecular Biology

Background:

• Serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) are crucial for mood and behavior.
• The local circuit organization and computational principles within the DRN remain largely uncharacterized.

Purpose of the Study:

• To investigate the processing features of the mouse DRN by examining inputs from the lateral habenula.
• To elucidate the functional role of local circuits in DRN information processing.

Main Methods:

• Utilized cellular electrophysiology and imaging of a genetically encoded 5-HT sensor.
• Employed in vivo optogenetic activation of lateral habenula inputs to the DRN.
• Performed auditory conditioning tasks to assess behavioral disruption.

Main Results:

• Uncovered 5-HT1A receptor-mediated recurrent connections between 5-HT neurons, refuting autoinhibition theories.
• Characterized these connections as slow, stochastic, facilitating, and gating spike output.
• Demonstrated that these features generate nonlinear dynamics, including excitation-driven inhibition and winner-take-all computations.
• Showed that optogenetic activation disrupted reward-conditioned responses.

Conclusions:

• Identified a novel, slow serotonergic recurrent inhibitory network within the DRN.
• This network supports unique computational principles, including excitation-driven inhibition.
• Disruption of this network impacts reward-conditioned behavioral responses.