Hypothalamic neurons that co-express agouti-related protein (AgRP), neuropeptide Y and γ-aminobutyric acid (GABA) are known to promote feeding and weight gain by integration of various nutritional, hormonal, and neuronal signals1,2. Ablation of these neurons in mice leads to cessation of feeding that is accompanied by activation of Fos in most regions where they project3,4,5,6. Previous experiments have indicated that the ensuing starvation is due to aberrant activation of the parabrachial nucleus (PBN) and it could be prevented by facilitating GABAA receptor signalling in the PBN within a critical adaptation period5. We speculated that loss of GABA signalling from AgRP-expressing neurons (AgRP neurons) within the PBN results in unopposed excitation of the PBN, which in turn inhibits feeding. However, the source of the excitatory inputs to the PBN was unknown. Here we show that glutamatergic neurons in the nucleus tractus solitarius (NTS) and caudal serotonergic neurons control the excitability of PBN neurons and inhibit feeding. Blockade of serotonin (5-HT3) receptor signalling in the NTS by either the chronic administration of ondansetron or the genetic inactivation of Tph2 in caudal serotonergic neurons that project to the NTS protects against starvation when AgRP neurons are ablated. Likewise, genetic inactivation of glutamatergic signalling by the NTS onto N-methyl d-aspartate-type glutamate receptors in the PBN prevents starvation. We also show that suppressing glutamatergic output of the PBN reinstates normal appetite after AgRP neuron ablation, whereas it promotes weight gain without AgRP neuron ablation. Thus we identify the PBN as a hub that integrates signals from several brain regions to bidirectionally modulate feeding and body weight.
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We thank G. Froelick, J. Wang and K. Battani for help with histology; A. Rainwater for help with mouse breeding; A. Quintana for propagating CAV2-Cre virus and preparing AAV1-CreGFP virus; and A. Guler and M. Carter for helpful comments on the manuscript. This work was supported in part by National Institutes of Health grant DA024908 to R.D.P.
The authors declare no competing financial interests.
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Wu, Q., Clark, M. & Palmiter, R. Deciphering a neuronal circuit that mediates appetite. Nature 483, 594–597 (2012). https://doi.org/10.1038/nature10899
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