Dissecting a disynaptic central amygdala-parasubthalamic nucleus neural circuit that mediates cholecystokinin-induced eating suppression

Objective: Cholecystokinin (CCK) plays a critical role in regulating eating and metabolism. Previous studies have mapped a multi-synapse neural pathway from the vagus nerve to the central nucleus of the amygdala (CEA) that mediates the anorexigenic effect of CCK. However, the neural circuit downstream of the CEA is still unknown due to the complexity of the neurons in the CEA. Here we sought to determine this circuit using a novel approach.

Methods: It has been established that a specific population of CEA neurons, marked by protein kinase C-delta (PKC-δ), mediates the anorexigenic effect of CCK by inhibiting other CEA inhibitory neurons. Taking advantage of this circuit, we dissected the neural circuit using a unique approach based on the idea that neurons downstream of the CEA should be disinhibited by CEA^PKC-δ+ neurons while being activated by CCK. We also used optogenetic assisted electrophysiology circuit mapping and in vivo chemogenetic manipulation methods to determine the circuit structure and function.

Results: We found that neurons in the parasubthalamic nucleus (PSTh) are activated by the activation of CEA^PKC-δ+ neurons and by the peripheral administration of CCK. We demonstrated that CEA^PKC-δ+ neurons inhibit the PSTh-projecting CEA neurons; accordingly, the PSTh neurons can be disynaptically disinhibited or "activated" by CEA^PKC-δ+ neurons. Finally, we showed that chemogenetic silencing of the PSTh neurons effectively attenuates the eating suppression induced by CCK.

Conclusions: Our results identified a disynaptic CEA-PSTh neural circuit that mediates the anorexigenic effect of CCK and thus provide an important neural mechanism of how CCK suppresses eating.