AgRP/NPY Neuron Excitability Is Modulated by Metabotropic Glutamate Receptor 1 During Fasting

Regulation of body weight and food intake by AGRP neurons during opioid dependence and abstinence in mice

Dysregulation of body weight maintenance and opioid dependence are often treated as independent disorders. Here, we assessed the effects of both acute and long-term administration of morphine with and without chemogenetic activation of agouti-related peptide (AGRP)-expressing neurons in the arcuate nucleus (ARCAGRP neurons) to elucidate whether morphine and neuronal activation affect feeding behavior and body weight. First, we characterized interactions of opioids and energy deficit in wild-type mice. We observed that opioid administration attenuated both fasting-induced refeeding and ghrelin-stimulated feeding. Moreover, antagonism of opioid receptors blocked fasting-induced refeeding behavior. Next, we interfaced chemogenetics with opioid dependence. For chemogenetic experiments of ARCAGRP neurons, we conducted a priori behavioral qualification and post-mortem FOS immunostaining verification of arcuate activation following ARCAGRP chemogenetic activation. We administered clozapine during short-term and long-term morphine administration paradigms to determine the effects of dependence on food intake and body weight. We found that morphine occluded feeding behavior characteristic of chemogenetic activation of ARCAGRP neurons. Notably, activation of ARCAGRP neurons attenuated opioid-induced weight loss but did not evoke weight gain during opioid dependence. Consistent with these findings, we observed that morphine administration did not block fasting-induced activation of the ARC. Together, these results highlight the strength of opioidergic effects on body weight maintenance and demonstrate the utility of ARCAGRP neuron manipulations as a lever to influence energy balance throughout the development of opioid dependence.

Local Drd1-neurons input to subgroups of arcuate AgRP/NPY-neurons

Obesity is a pandemic afflicting more than 300 million people worldwide, driven by consumption of calorically dense and highly rewarding foods. Dopamine (DA) signaling has been implicated in neural responses to highly palatable nutrients, but the exact mechanisms through which DA modulates homeostatic feeding circuits remains unknown. A subpopulation of arcuate (ARC) agouti-related peptide (AgRP)/neuropeptide Y (NPY) (ARCAgRP/NPY+) neurons express the D(1A) dopamine receptor (Drd1) and are stimulated by DA, suggesting one potential avenue for dopaminergic regulation of food intake. Using patch clamp electrophysiology, we evaluated the responses of ARC Drd1-expressing (ARCDrd1+) neurons to overnight fasting and leptin. Collectively, ARCDrd1+ neurons were less responsive to caloric deficit than ARCAgRP/NPY+ neurons; however, ARCDrd1+ neurons were inhibited by the satiety hormone leptin. Using Channelrhodopsin-2-Assisted Circuit Mapping, we identified novel subgroups of ARCDrd1+ neurons that inhibit or excite ARCAgRP/NPY+ neurons. These findings suggest dopamine receptive neurons have multimodal actions in food intake circuits.

Central α-Klotho Suppresses NPY/AgRP Neuron Activity and Regulates Metabolism in Mice

α-Klotho is a circulating factor with well-documented antiaging properties. However, the central role of α-klotho in metabolism remains largely unexplored. The current study investigated the potential role of central α-klotho to modulate neuropeptide Y/agouti-related peptide (NPY/AgRP)-expressing neurons, energy balance, and glucose homeostasis. Intracerebroventricular administration of α-klotho suppressed food intake, improved glucose profiles, and reduced body weight in mouse models of type 1 and 2 diabetes. Furthermore, central α-klotho inhibition via an anti-α-klotho antibody impaired glucose tolerance. Ex vivo patch clamp electrophysiology and immunohistochemical analysis revealed that α-klotho suppresses NPY/AgRP neuron activity, at least in part, by enhancing miniature inhibitory postsynaptic currents. Experiments in hypothalamic GT1-7 cells observed that α-klotho induces phosphorylation of AKT^ser473, ERK^{thr202/tyr204}, and FOXO1^ser256 as well as blunts AgRP gene transcription. Mechanistically, fibroblast growth factor receptor 1 (FGFR1) inhibition abolished the downstream signaling of α-klotho, negated its ability to modulate NPY/AgRP neurons, and blunted its therapeutic effects. Phosphatidylinositol 3 kinase (PI3K) inhibition also abolished α-klotho's ability to suppress food intake and improve glucose clearance. These results indicate a prominent role of hypothalamic α-klotho/FGFR1/PI3K signaling in the modulation of NPY/AgRP neuron activity and maintenance of energy homeostasis, thus providing new insight into the pathophysiology of metabolic disease.

The Role of Neuropeptide Y and Peptide YY in the Development of Obesity via Gut-brain Axis

Obesity is one of the main challenges of public health in the 21st century. Obesity can induce a series of chronic metabolic diseases, such as diabetes, dyslipidemia, hypertension and nonalcoholic fatty liver, which seriously affect human health. Gut-brain axis, the two-direction pathway formed between enteric nervous system and central nervous system, plays a vital role in the occurrence and development of obesity. Gastrointestinal signals are projected through the gut-brain axis to nervous system, and respond to various gastrointestinal stimulation. The central nervous system regulates visceral activity through the gut-brain axis. Brain-gut peptides have important regulatory roles in the gut-brain axis. The brain-gut peptides of the gastrointestinal system and the nervous system regulate the gastrointestinal movement, feeling, secretion, absorption and other complex functions through endocrine, neurosecretion and paracrine to secrete peptides. Both neuropeptide Y and peptide YY belong to the pancreatic polypeptide family and are important brain-gut peptides. Neuropeptide Y and peptide YY have functions that are closely related to appetite regulation and obesity formation. This review describes the role of the gutbrain axis in regulating appetite and maintaining energy balance, and the functions of brain-gut peptides neuropeptide Y and peptide YY in obesity. The relationship between NPY and PYY and the interaction between the NPY-PYY signaling with the gut microbiota are also described in this review.