Probes for NPY

Neuropeptide Y (NPY) in the arcuate nucleus (ARC) is known as one of the most critical regulators of feeding. However, how NPY promotes feeding under obese conditions is unclear. Here, we show that positive energy balance, induced by high-fat diet (HFD) or in genetically obese leptin-receptor-deficient mice, leads to elevated Npy2r expression especially on proopiomelanocortin (POMC) neurons, which also alters leptin responsiveness. Circuit mapping identified a subset of ARC agouti-related peptide (Agrp)-negative NPY neurons that control these Npy2r expressing POMC neurons. Chemogenetic activation of this newly discovered circuitry strongly drives feeding, while optogenetic inhibition reduces feeding. Consistent with that, lack of Npy2r on POMC neurons leads to reduced food intake and fat mass. This suggests that under energy surplus conditions, when ARC NPY levels generally drop, high-affinity NPY2R on POMC neurons is still able to drive food intake and enhance obesity development via NPY released predominantly from Agrp-negative NPY neurons.

Activity in the dorsal vagal complex (DVC) is essential to gastric motility regulation. We and others have previously shown that this activity is greatly influenced by local GABAergic signaling primarily due to somatostatin-expressing GABAergic neurons (SST). To further understand the network dynamics associated with gastric motility control in the DVC, we focused on another neuron prominently distributed in this complex, neuropeptide-Y (NPY) neurons. However, the effect of these neurons on gastric motility remains unknown. Here we investigate the anatomical and functional characteristics of the NPY neurons in the nucleus tractus solitarius (NTS) and their interactions with SST neurons using transgenic mice of both sexes. We sought to determine if NPY neurons influence the activity of gastric projecting neurons, synaptically interact with SST neurons, and affect end-organ function. Our results using combined neuroanatomy and optogenetic in vitro and in vivo show that NPY neurons: are part of the gastric vagal circuit as they are trans-synaptically labeled by a viral tracer from the gastric antrum; are primarily excitatory as optogenetic activation of these neurons evoke EPSCs in gastric-antrum projecting neurons; are functionally coupled to each other and reciprocally connected to SST neurons, whose stimulation has a potent inhibitory effect on the action potential firing of the NPY neurons; and affect gastric tone and motility as reflected by their robust optogenetic response in vivo. These findings indicate that interacting NPY and SST neurons are integral to the network that controls vagal transmission to the stomach.Significance StatementThe brainstem neurons in the dorsal nuclear complex are essential for regulating vagus nerve activity that affects the stomach via tone and motility. Two distinct non-overlapping populations of predominantly excitatory neuropeptide Y (NPY) neurons and predominantly inhibitory somatostatin (SST) neurons form reciprocal connections with each other in the nucleus of the tractus solitarius (NTS) and with premotor neurons in the dorsal motor nucleus of the vagus to control gastric mechanics. Light activation and inhibition of NTS. NPY neurons increased and decreased gastric motility, respectively, while both activation and inhibition of NTS SST neurons enhanced gastric motility.

The central nervous system is an active and major regulator of bone structure and remodelling. Specifically, signalling within the hypothalamus has been shown to be critical to ensuring that skeletal functions align with whole body metabolic supply and demand. Here, we identify agouti-related peptide (AgRP), an orexigenic peptide exclusively co-expressed with neuropeptide Y (NPY) in the arcuate nucleus (ARC) of the hypothalamus, as another critical player in the central control of bone homeostasis. Using novel mouse models, we show that AgRP deletion leads to an increase in cortical and trabecular bone mass as a result of an increase in bone thickness despite a lean phenotype, particularly in male mice. Interestingly, male AgRP deficient mice display a significant decrease in pro-opiomelanocortin (POMC) expression in the ARC, but no change in NPY or CART expression, suggesting that the increase in bone mass in AgRP-deficient mice is unlikely to be a result of altered NPY signalling. This is consistent with the observation that bone mass is unchanged in response to the specific deletion of NPY from AgRP expressing neurones. By contrast, POMC expression in the ARC is significantly increased in female AgRP deficient mice, although AgRP deletion results in altered respiratory exchange ratio regulation in response to re-feeding after a fast in both sexes. Taken together, the present study identifies AgRP as being directly involved in the regulation of bone mass and highlights the complexity intrinsic to the neuropeptide regulation of the skeleton.

Spinal motor neurons (MNs) integrate sensory stimuli and brain commands to generate movements. In vertebrates, the molecular identities of the cardinal MN types such as those innervating limb versus trunk muscles are well elucidated. Yet the identities of finer subtypes within these cell populations that innervate individual muscle groups remain enigmatic. Here we investigate heterogeneity in mouse MNs using single-cell transcriptomics. Among limb-innervating MNs, we reveal a diverse neuropeptide code for delineating putative motor pool identities. Additionally, we uncover that axial MNs are subdivided into three molecularly distinct subtypes, defined by mediolaterally-biased Satb2, Nr2f2 or Bcl11b expression patterns with different axon guidance signatures. These three subtypes are present in chicken and human embryos, suggesting a conserved axial MN expression pattern across higher vertebrates. Overall, our study provides a molecular resource of spinal MN types and paves the way towards deciphering how neuronal subtypes evolved to accommodate vertebrate motor behaviors.

Opioid signaling has been shown to be critically important in the neuromodulation of sensory circuits in the superficial spinal cord. Agonists of the mu-opioid receptor (MOR) elicit itch, whereas agonists of the kappa-opioid receptor (KOR) have been shown to inhibit itch. Despite the clear roles of MOR and KOR for the modulation itch, whether the delta-opioid receptor (DOR) is involved in the regulation of itch remained unknown. Here, we show that intrathecal administration of DOR agonists suppresses chemical itch and that intrathecal application of DOR antagonists is sufficient to evoke itch. We identify that spinal enkephalin neurons co-express neuropeptide Y (NPY), a peptide previously implicated in the inhibition of itch. In the spinal cord, DOR overlapped with both the NPY receptor (NPY1R) and KOR, suggesting that DOR neurons represent a site for convergent itch information in the dorsal horn. Lastly, we found that neurons co-expressing DOR and KOR showed significant Fos induction following pruritogen-evoked itch. These results uncover a role for DOR in the modulation of itch in the superficial dorsal horn. Perspective: This article reveals the role of the delta-opioid receptor in itch. Intrathecal administration of delta agonists suppresses itch whereas the administration of delta antagonists is sufficient to induce itch. These studies highlight the importance of delta-opioid signaling for the modulation of itch behaviors, which may represent new targets for the management of itch disorders.

In patients with advanced-stage cancer, cancer-associated anorexia affects treatment success and patient survival. However, the underlying mechanism is poorly understood. Here, we show that Dilp8, a Drosophila homologue of mammalian insulin-like 3 peptide (INSL3), is secreted from tumour tissues and induces anorexia through the Lgr3 receptor in the brain. Activated Dilp8-Lgr3 signalling upregulated anorexigenic nucleobinding 1 (NUCB1) and downregulated orexigenic short neuropeptide F (sNPF) and NPF expression in the brain. In the cancer condition, the protein expression of Lgr3 and NUCB1 was significantly upregulated in neurons expressing sNPF and NPF. INSL3 levels were increased in tumour-implanted mice and INSL3-treated mouse hypothalamic cells showed Nucb2 upregulation and Npy downregulation. Food consumption was significantly reduced in intracerebrospinal INSL3-injected mice. In patients with pancreatic cancer, higher serum INSL3 levels increased anorexia. These results indicate that tumour-derived Dilp8/INSL3 induces cancer anorexia by regulating feeding hormones through the Lgr3/Lgr8 receptor in Drosophila and mammals.