Serotonin neurons integrate GABA and dopamine inputs to regulate meal initiation

Area of Science:

• Neuroscience
• Neurobiology
• Endocrinology

Background:

• Obesity is a global health crisis with few oral treatments.
• Serotonin (5-HT) is a promising target for weight-loss therapies.
• Mechanisms of 5-HT in meal initiation, particularly from the dorsal Raphe nucleus (DRN), are not fully understood.

Purpose of the Study:

• To investigate the role of the 5-HT^DRN➔arcuate nucleus (ARH) circuit in meal initiation.
• To elucidate the inhibitory mechanisms regulating 5-HT^DRN neuron activity.
• To identify the influence of hunger and dopaminergic signaling on this circuit.

Main Methods:

• Optogenetic feeding paradigms to study meal initiation.
• Electrophysiology and ChannelRhodopsin-2-Assisted Circuit Mapping (ChRmine) to analyze neuronal activity.
• Genetic manipulation to delete GABA_A receptor subunits in 5-HT neurons.
• Assessment of dopaminergic input via dopamine receptor D2.

Main Results:

• The 5-HT^DRN➔ARH circuit is critical for initiating meals.
• 5-HT^DRN neurons receive inhibitory input from GABAergic neurons, modulated by hunger.
• GABA_A receptor deletion in 5-HT neurons impaired meal initiation but not satiation.
• Dopamine receptor D2 signaling enhances GABA-induced feeding responses.

Conclusions:

• Serotonin neurons in the DRN are key regulators of meal initiation.
• Synergistic inhibition by GABA and dopamine controls 5-HT^DRN neuron activity.
• This circuit represents a potential therapeutic target for obesity and eating disorders.