State-dependent central synaptic regulation by GLP-1 is essential for energy homeostasis

Central glucagon-like peptide-1 (GLP-1), secreted by a distinct population of nucleus tractus solitarius neurons, suppresses feeding but the exact mechanisms of action in the brain remain unclear. Here, we investigate a descending circuit formed by GLP-1 receptor (GLP-1R) neurons in the paraventricular hypothalamic nucleus (PVN^GLP-1R) projecting to the dorsal vagal complex (DVC) of the brain stem in mice. PVN^GLP-1R→DVC synapses release glutamate and are augmented by GLP-1. Chemogenetic activation of PVN^GLP-1R→DVC suppresses feeding. Under an energy deficit (that is, hunger) state, synaptic strength is weaker but is more profoundly augmented by GLP-1R activation than under energy-replete state. In an obese condition, the dynamic synaptic changes in this circuit are disrupted. Optogenetic activation of PVN^GLP-1R→DVC projections suppresses food intake energy state dependently, and blocking its synaptic release or ablating GLP-1Rs in the presynaptic neurons impairs metabolic health. These findings indicate that the state-dependent synaptic regulation by GLP-1 in PVN^GLP-1R→DVC descending circuit is important for energy homeostasis.