AgRP Neuron Activity Research Articles

Chemogenetic engagement of different GPCR signaling pathways segregates the orexigenic activity from the control of whole-body glucose metabolism by AGRP Neurons.

BackgroundThe control of energy balance involves neural circuits in the central nervous system, including AGRP neurons in the arcuate nucleus of the hypothalamus (ARC). AGRP neurons are crucial for energy balance and their increased activity during fasting is critical to promote feeding behavior. The activity of these neurons is influenced by multiple signals including those acting on G-protein coupled receptors (GPCR) activating different intracellular signaling pathways. We sought to determine whether discrete G-protein mediated signaling in AGRP neurons, promotes differential regulation of feeding and whole-body glucose homeostasis. Methodology: To test the contribution of Gαq/11 or Gαs signaling, we developed congenital mouse lines expressing the different DREADD receptors (i.e., hM3q and rM3s), in AGRP neurons. Then we elicited chemogenetic activation of AGRP neurons in these mice during the postprandial state to determine the impact on feeding and glucose homeostasis. ResultsActivation of AGRP neurons via hM3q and rM3s promoted hyperphagia. In contrast, only hM3q activation of AGRP neurons of the hypothalamic arcuate nucleus during the postprandial state enhanced whole-body glucose disposal by reducing sympathetic nervous system activity to the pancreas and liver, promoting glucose-stimulated insulin secretion, glycogen deposition and improving glucose tolerance. ConclusionThese data indicate that AGRP neurons regulate food intake and glucose homeostasis through distinct GPCR-dependent signaling pathways and suggest that the transient increase in AGRP neuron activity may contribute to the beneficial effects of fasting on glycemic control.

Chemogenetic activation of arcuate nucleus NPY and NPY/AgRP neurons increases feeding behaviour in mice

Neuropeptide Y (NPY) plays a crucial role in controlling energy homeostasis and feeding behaviour. The role of NPY neurons located in the arcuate nucleus of the hypothalamus (Arc) in responding to homeostatic signals has been the focus of much investigation, but most studies have used AgRP promoter-driven models, which do not fully encompass Arc NPY neurons. To directly investigate NPY-expressing versus AgRP-expressing Arc neurons function, we utilised chemogenetic techniques in NPY-Cre and AgRP-Cre animals to activate Arc NPY or AgRP neurons in the presence of food and food-related stimuli. Our findings suggest that chemogenetic activation of the broader population of Arc NPY neurons, including AgRP-positive and AgRP-negative NPY neurons, has equivalent effects on feeding behaviour as activation of Arc AgRP neurons. Our results demonstrate that these Arc NPY neurons respond specifically to caloric signals and do not respond to non-caloric signals, in line with what has been observed in AgRP neurons. Activating Arc NPY neurons significantly increases food consumption and influences macronutrient selection to prefer fat intake.

AgRP Neurons Encode Circadian Feeding Time

Food intake follows a predictable daily pattern and synchronizes metabolic rhythms. Neurons expressing Agouti-related protein (AgRP) read out physiological energetic state and elicit feeding, but the regulation of these neurons across daily timescales is poorly understood. Using a combination of neuron-dynamics measurements and timed optogenetic activation in mice, we show that daily AgRP-neuron activity was not fully consistent with existing models of homeostatic regulation. Instead of operating as deprivation counter, AgRP-neuron activity primarily followed the circadian rest-activity cycle through a process that required an intact suprachiasmatic nucleus (SCN) and synchronization by light. Imposing novel feeding patterns through time-restricted food access or periodic AgRP-neuron stimulation was suffcient to resynchronize the daily AgRP-neuron activity rhythm and drive anticipatory-like behavior through a process that required DMHPDYN neurons. These results indicate that AgRP-neurons integrate time-of-day information of past feeding experience with current metabolic needs to predict circadian feeding time. This work is supported by NIH to D.A. R01DK126740. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

MicroRNA-33 controls hunger signaling in hypothalamic AgRP neurons

AgRP neurons drive hunger, and excessive nutrient intake is the primary driver of obesity and associated metabolic disorders. While many factors impacting central regulation of feeding behavior have been established, the role of microRNAs in this process is poorly understood. Utilizing unique mouse models, we demonstrate that miR-33 plays a critical role in the regulation of AgRP neurons, and that loss of miR-33 leads to increased feeding, obesity, and metabolic dysfunction in mice. These effects include the regulation of multiple miR-33 target genes involved in mitochondrial biogenesis and fatty acid metabolism. Our findings elucidate a key regulatory pathway regulated by a non-coding RNA that impacts hunger by controlling multiple bioenergetic processes associated with the activation of AgRP neurons, providing alternative therapeutic approaches to modulate feeding behavior and associated metabolic diseases.

249-LB: CRISPR/Cas9-Mediated Deletion of FGF Receptor 1 in AgRP Neurons Results in Obesity and Impaired Glucose Metabolism

Obesity remains a growing epidemic as current treatment approaches have limited success. We have recently identified hypothalamic α-Klotho as a novel metabolic regulator; however, the downstream pathways remain unclear. Using a Cre-dependent CRISPR/Cas9 system alongside transgenic mice to investigate the role of FGFR1 in defined neuron populations of adult mice, we show that deletion of FGFR1 in AgRP neurons results in increased weight gain and adiposity, worsened glucose tolerance, and increased liver lipid accumulation. Mechanistically, deletion of FGFR1 negates pERK signaling and the ability of α-Klotho to reduce fasting-induced AgRP neuron activity in mice. While in hypothalamic cells, knockdown of FGFR1 prevents FOXO1 phosphorylation by α-Klotho, providing evidence of an α-Klotho-FGFR1-PI3K-FOXO1 signaling axis in AgRP neurons. Taken together, our data demonstrate the metabolic role of FGFR1 in AgRP neurons and identify it as a critical regulator of energy and glucose homeostasis. Disclosure D. Shookster: None. H. Huang: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK121215 to H.H.)

Nutrient-sensing AgRP neurons relay control of liver autophagy during energy deprivation

Autophagy represents a key regulator of aging and metabolism in sensing energy deprivation. We find that fasting in mice activates autophagy in the liver paralleled by activation of hypothalamic AgRP neurons. Optogenetic and chemogenetic activation of AgRP neurons induces autophagy, alters phosphorylation of autophagy regulators, and promotes ketogenesis. AgRP neuron-dependent induction of liver autophagy relies on NPY release in the paraventricular nucleus of the hypothalamus (PVH) via presynaptic inhibition of NPY1R-expressing neurons to activate PVHCRH neurons. Conversely, inhibiting AgRP neurons during energy deprivation abrogates induction of hepatic autophagy and rewiring of metabolism. AgRP neuron activation increases circulating corticosterone concentrations, and reduction of hepatic glucocorticoid receptor expression attenuates AgRP neuron-dependent activation of hepatic autophagy. Collectively, our study reveals a fundamental regulatory principle of liver autophagy in control of metabolic adaptation during nutrient deprivation.

Negative energy balance hinders prosocial helping behavior

The internal state of an animal, including homeostatic requirements, modulates its behavior. Negative energy balance stimulates hunger, thus promoting a range of actions aimed at obtaining food. While these survival actions are well established, the influence of the energy status on prosocial behavior remains unexplored. We developed a paradigm to assess helping behavior in which a free mouse was faced with a conspecific trapped in a restrainer. We measured the willingness of the free mouse to liberate the confined mouse under diverse metabolic conditions. Around 42% of adlibitum-fed mice exhibited a helping behavior, as evidenced by the reduction in the latencies to release the trapped cagemate. This behavior was independent of subsequent social contact reward and was associated with changes in corticosterone indicative of emotional contagion. This decision-making process was coupled with reduced blood glucose excursions and higher Adenosine triphosphate (ATP):Adenosine diphosphate (ADP) ratios in the forebrain of helper mice, suggesting that it was a highly energy-demanding process. Interestingly, chronic (food restriction and type 2 diabetes) and acute (chemogenetic activation of hunger-promoting AgRP neurons) situations mimicking organismal negative energy balance and enhanced appetite attenuated helping behavior toward a distressed conspecific. To investigate similar effects in humans, we estimated the influence of glycated hemoglobin (a surrogate of long-term glycemic control) on prosocial behavior (namely charity donation) using the Understanding Society dataset. Our results evidenced that organismal energy status markedly influences helping behavior and that hypothalamic AgRP neurons are at the interface of metabolism and prosocial behavior.

Hypothalamic AgRP neurons exert top-down control on systemic TNF-α release during endotoxemia

Loss of appetite and negative energy balance are common features of endotoxemia in all animals and are thought to have protective roles by reducing nutrient availability to host and pathogen metabolism. Accordingly, fasting and caloric restriction have well-established anti-inflammatory properties. However, in response to reduced nutrient availability at the cellular and organ levels, negative energy balance also recruits distinct energy-sensing brain circuits, but it is not known whether these neuronal systems have a role in its anti-inflammatory effects. Here, we report that hypothalamic AgRP neurons-a critical neuronal population for the central representation of negative energy balance-have parallel immunoregulatory functions. We found that when endotoxemia occurs in fasted mice, the activity of AgRP neurons remains sustained, but this activity does not influence feeding behavior and endotoxemic anorexia. Furthermore, we found that endotoxemia acutely desensitizes AgRP neurons, which also become refractory to inhibitory signals. Mimicking this sustained AgRP neuron activity in fed mice by chemogenetic activation-a manipulation known to recapitulate core behavioral features of fasting-results in reduced acute tumor necrosis factor alpha (TNF-α) release during endotoxemia. Mechanistically, we found that endogenous glucocorticoids play an important role: glucocorticoid receptor deletion from AgRP neurons prevents their endotoxemia-induced desensitization, and importantly, it counteracts the fasting-induced suppression of TNF-α release, resulting in prolonged sickness. Together, these findings provide evidence directly linking AgRP neuron activity to the acute response during endotoxemia, suggesting that these neurons are a functional component of the immunoregulatory effects associated with negative energy balance and catabolic metabolism.

Forkhead Box i2 (Foxi2) Transcription Factor Regulates Systemic Energy Metabolism Via Neuropeptide AgRP

The neuropeptide AgRP is essential for maintaining systemic energy homeostasis. In the current study, we show that hypothalamic Foxi2, as a novel regulator of nutrient sensing, controls systemic energy metabolism by specifically stimulating AgRP expression. Foxi2 was highly expressed in the hypothalamus, and its expression was induced by fasting. Immunofluorescence assays demonstrated that Foxi2 was localized in AgRP neurons. We stereotactically injected adeno-associated virus to selectively overexpress Foxi2 in AgRP-IRES-Cre mice and found that Foxi2 overexpression in AgRP neurons specifically increased AgRP expression, thereby increasing food intake and reducing energy expenditure, subsequently leading to obesity and insulin resistance. Mechanistically, Foxi2 stimulated AgRP expression by directly binding to it and activating its transcription. Furthermore, Foxi2 overexpression activated AgRP neuron activity, as revealed by whole-cell patch-clamp experiments. Conversely, global Foxi2-mutant mice became leaner with age and were resistant to high-fat diet-induced obesity and metabolic disturbances. Collectively, our data suggest that Foxi2 plays an important role in controlling energy metabolism by regulating AgRP expression.

Edinger-Westphal peptidergic neurons enable maternal preparatory nesting.

SummaryOptimizing reproductive fitness in mammalians requires behavioral adaptations during pregnancy. Maternal preparatory nesting is an essential behavior for the survival of the upcoming litter. Brain-wide immediate early gene mapping in mice evoked by nesting sequences revealed that phases of nest construction strongly activate peptidergic neurons of the Edinger-Westphal nucleus in pregnant mice. Genetic ablation, bidirectional neuromodulation, and in vitro and in vivo activity recordings demonstrated that these neurons are essential to modulate arousal before sleep to promote nesting specifically. We show that these neurons enable the behavioral effects of progesterone on preparatory nesting by modulating a broad network of downstream targets. Our study deciphers the role of midbrain CART+ neurons in behavioral adaptations during pregnancy vital for reproductive fitness.

NPY derived from AGRP neurons controls feeding via Y1 and energy expenditure and food foraging behaviour via Y2 signalling

ObjectiveAguti-related protein (AGRP) neurons in the arcuate nucleus of the hypothalamus (ARC), which co-express neuropeptide Y (NPY), are key regulators of feeding and energy homeostasis. However, the precise role NPY has within these neurons and the specific pathways that it control are still unclear. In this article, we aimed to determine what aspects of feeding behaviour and energy homeostasis are controlled by NPY originating from AGRP neurons and which Y-receptor pathways are utilised to fulfil this function. MethodsNovel conditional Agrpcre/+;Npylox/lox knockout mice were generated and comprehensively phenotyped, both under standard chow as well as high-fat-diet conditions. Designer receptor exclusively activated by designer drugs (DREADD) technology was used to assess the altered responses on feeding and energy homeostasis control in the absence of NPY in these neurons. Rescue experiments utilising Npy1r- and Npy2r-selective NPY ligands were performed to assess which component of the energy homeostasis control is dependent by which specific Y-receptor pathway. ResultsWe show that the specific deletion of Npy only in AGRP neurons leads to a paradoxical mild obese phenotype associated with reduced locomotion and energy expenditure and increased feeding and Respiratory Quotient (RQ) that remain elevated under a positive energy balance. The activation of Npy-deficient AGRP neurons via DREADD's is still able to drive feeding, yet with a delayed onset. Additionally, Clozapine-N-oxide (CNO) treatment reduces locomotion without impacting on energy expenditure. Rescue experiments re-introducing Npy1r- and Npy2r-selective NPY ligands revealed that the increased feeding and RQ are mostly driven by Npy1r, whereas energy expenditure and locomotion are controlled by Npy2r signalling. ConclusionTogether, these results demonstrate that NPY originating from AGRP neurons is not only critical to initiate but also for continuously driving feeding, and we for the first time identify which Y-receptor controls which pathway.

Endothelial peroxynitrite causes disturbance of neuronal oscillations by targeting caspase-1 in the arcuate nucleus

Severe anorexia limits the clinical application of cisplatin, and even leads to the discontinuation of treatment. However, the mechanisms underlying cisplatin-induced anorexia are unknown. Herein, we demonstrated that cisplatin could affect neuronal gamma oscillations and induce abnormal neuronal theta-gamma phase-amplitude coupling in the arcuate nucleus (Arc) of the hypothalamus, and these findings were associated with significantly decreased food intake and weight loss in mice. Chemogenetic activation of AgRP neurons in the Arc reversed the cisplatin-induced food intake reduction in mice. We further demonstrated that endothelial peroxynitrite (ONOO−) formation in the Arc induced nitrosative stress following cisplatin treatment via a previously uncharacterized pathway involving neuronal caspase-1 activation. Strikingly, treatment with the ONOO− scavenger uric acid (UA) reversed the reduced action potential (AP) frequency of AgRP neurons and increased the AP frequency of POMC neurons induced by SIN1, a donor of ONOO−, in the Arc, as determined by whole-cell patch-clamp electrophysiological recording. Consistent with these findings, UA treatment effectively alleviated cisplatin-induced dysfunction of neuronal oscillations and neuronal theta-gamma phase-amplitude coupling in the Arc of mice. Taken together, these results suggest, for the first time, that targeting the overproduction of endothelial ONOO− can regulate cisplatin-induced neurotoxicity through neuronal caspase-1, and thereby serve as a potential therapeutic approach to alleviate chemotherapy-induced anorexia and weight loss.

NTS Prlh overcomes orexigenic stimuli and ameliorates dietary and genetic forms of obesity

Calcitonin receptor (Calcr)-expressing neurons of the nucleus tractus solitarius (NTS; CalcrNTS cells) contribute to the long-term control of food intake and body weight. Here, we show that Prlh-expressing NTS (PrlhNTS) neurons represent a subset of CalcrNTS cells and that Prlh expression in these cells restrains body weight gain in the face of high fat diet challenge in mice. To understand the relationship of PrlhNTS cells to hypothalamic feeding circuits, we determined the ability of PrlhNTS-mediated signals to overcome enforced activation of AgRP neurons. We found that PrlhNTS neuron activation and Prlh overexpression in PrlhNTS cells abrogates AgRP neuron-driven hyperphagia and ameliorates the obesity of mice deficient in melanocortin signaling or leptin. Thus, enhancing Prlh-mediated neurotransmission from the NTS dampens hypothalamically-driven hyperphagia and obesity, demonstrating that NTS-mediated signals can override the effects of orexigenic hypothalamic signals on long-term energy balance.

Asprosin—A Fasting-Induced, Glucogenic, and Orexigenic Adipokine as a New Promising Player. Will It Be a New Factor in the Treatment of Obesity, Diabetes, or Infertility? A Review of the Literature

Asprosin is a recently discovered protein released during fasting conditions mainly by adipocytes from white adipose tissue. As a glucogenic peptide, it stimulates the release of glucose from hepatic cells by binding to the OLFR734 receptor and leading to the activation of the G protein-cAMP-PKA pathway. As it crosses the blood–brain barrier, it also acts as an orexigenic peptide that stimulates food intake through activation of AgRP neurons in the hypothalamus; thus, asprosin participates in maintaining the body’s energy homeostasis. Moreover, studies have shown that asprosin levels are pathologically elevated in obesity and related diseases. However, the administration of anti-asprosin antibodies can both normalize its concentration and reduce food intake in obese mice, which makes it an interesting factor to combat obesity and related diseases. Current research also draws attention to the relationship between asprosin and fertility, especially in men. Asprosin improves age- and obesity-related decrease in fertility potential by improving sperm motility. It should also be mentioned that plasma asprosin levels can be differentially modulated by physical activity; intense anaerobic exercise increases asprosin level, while aerobic exercise decreases it. However, further research is necessary to confirm the exact mechanisms of asprosin activity and its potential as a therapeutic target.

Chronic unpredictable stress induces depression-related behaviors by suppressing AgRP neuron activity

Previous studies have shown that AgRP neurons in the arcuate nucleus (ARC) respond to energy deficits and play a key role in the control of feeding behavior and metabolism. Here, we demonstrate that chronic unpredictable stress, an animal model of depression, decreases spontaneous firing rates, increases firing irregularity and alters the firing properties of AgRP neurons in both male and female mice. These changes are associated with enhanced inhibitory synaptic transmission and reduced intrinsic neuronal excitability. Chemogenetic inhibition of AgRP neurons increases susceptibility to subthreshold unpredictable stress. Conversely, chemogenetic activation of AgRP neurons completely reverses anhedonic and despair behaviors induced by chronic unpredictable stress. These results indicate that chronic stress induces maladaptive synaptic and intrinsic plasticity, leading to hypoactivity of AgRP neurons and subsequently causing behavioral changes. Our findings suggest that AgRP neurons in the ARC are a key component of neural circuitry involved in mediating depression-related behaviors and that increasing AgRP neuronal activity coule be a novel and effective treatment for depression.

209-OR: Evidence that Agrp Neuron Activation Drives Cold-Induced Hyperphagia

Although hyperphagic feeding during cold exposure is widely viewed as a response to the negative energy state that results from increased thermogenesis, the underlying mechanisms are unknown. We investigated an alternative hypothesis, that during cold exposure, hyperphagia is mounted in anticipation of homeostatic need, rather than as a compensatory response. In support of this hypothesis, we report that in chow-fed mice acutely housed at 14°C, increases of food intake and thermogenesis occur both rapidly and simultaneously, implying hyperphagia is not mounted as a compensatory response. We next asked whether this cold-induced feeding response involves activation of agouti-related peptide (Agrp) neurons, which are implicated in other forms of hyperphagic feeding. Consistent with this hypothesis, we report that Agrp neurons are activated within 1-2 min of cold exposure and prior to the onset of hyperphagia, as judged by in vivo fiber photometry and confirmed by cFos induction (Agrp+/cFos+, 22°C: 5.3±4.5% vs. 14°C: 20.2±6.1%; p<0.01). To test whether Agrp neuron activation is required for cold-induced hyperphagia, we employed a chemogenetic strategy to silence Agrp neurons. As predicted, their silencing prevented hyperphagic feeding (2h food intake after housing at 14°C: 0.26±0.06 g vs. 0.10±0.04 g; p<0.05), but not the associated thermogenic response (0.63 vs. 0.62 kcal/hr; p=ns) during cold exposure. Interestingly, cold-induced hyperphagia is absent in mice with diet-induced obesity (DIO). Consequently, unlike chow-fed mice, these animals lose weight during cold exposure. These observations suggest that 1) Agrp neurons lie downstream of thermoregulatory neurocircuits, 2) during cold exposure, increased Agrp neuronal firing occurs rapidly as part of a homeostatic response that preserves body temperature and energy stores, and 3) this response appears to be impaired in mice with DIO. Future studies will map the neurocircuitry underlying these responses and clarify how DIO impairs their activation. Disclosure J.D. Deem: None. C.L. Faber: None. C. Pedersen: None. B.N. Phan: None. K. Ogimoto: None. S.A. Larsen: None. M.A. Tran: None. V. Damian: None. K. Kaiyala: None. J. Scarlett: None. M.R. Bruchas: None. M.W. Schwartz: Research Support; Self; Novo Nordisk A/S. G.J. Morton: Research Support; Self; Novo Nordisk A/S. Funding American Diabetes Association (1-19-PDF-103 to J.D.D.); Dick and Julia McAbee Foundation; National Institutes of Health (T32-HL007028-39, R01DK089056, R01DK101997, R01DK124238, R01DK089056, P30DK017047, P30DK035816)

97-OR: Leptin's Hunger-Suppressing Effects Are Mediated by the Hypothalamic-Pituitary-Adrenocortical Axis

Leptin deficiency is known to promote hyperphagia, but the mechanism for this is unknown. Here we show that hypoleptinemia-driven hypercorticosteronemia promotes hyperphagia in fasting (40.3±4.9 kcal consumed in 2 hour after a 48 hour fast vs. 2.4±1.0 kcal after a 6 hour fast, P<0.0001) and poorly-controlled type 1 diabetes (T1D) (28.4±2.5 vs. 13.3±2.9 kcal, P<0.01) in rats. Correcting hypoleptinemia with a 6 hour leptin infusion reversed hypercorticosteronemia and reduced food intake to control rates in both models (48 hour fast+leptin 5.2±2.2 kcal, P<0.0001; T1D+leptin 8.1±1.9 kcal, P<0.0001), while restoring hypercorticosteronemia abrogated the anorexic effect of leptin (48 hour fast+leptin+corticosterone 29.5±3.1 kcal, T1D+leptin+corticosterone 30.0±2.7 kcal, both P<0.001 vs. leptin-treated). Treatment with a glucocorticoid receptor antagonist, mifepristone, reversed hyperphagia (48 hour fast 8.8±4.3 kcal, T1D 15.0±2.3 kcal; both P<0.05). In adrenalectomized mice treated with low-dose corticosterone, food intake following a fast was markedly reduced, whereas high-dose corticosterone restored hyperphagia. Hypercorticosteronemia induced by hypoglycemia drove hyperphagia independent of leptin and insulin (hypoglycemic-hyperinsulinemic: 42.5±2.3 kcal, euglycemic-hyperinsulinemic: 1.8±1.9 kcal, euglycemic-hyperinsulinemic-corticosterone-treated: 32.0±4.6 kcal; both P<0.001 vs. euglycemic) which was reversed by mifepristone (14.6±2.3 kcal, P<0.0001 vs. hypoglycemic). Finally, we show that hypercorticosteronemia increases feeding behavior through corticosterone-mediated stimulation of AgRP neuron activity: overexpression of 11β-hydroxysteroid dehydrogenase 2 in AgRP neurons abrogated the hyperphagic effect of corticosterone. Together these data provide new insights into hypoleptinemia-induced hyperphagia and reveal that corticosterone-driven AgRP neuron activity drives hyperphagia during starvation, T1D, and hypoglycemia. Disclosure R.J. Perry: Research Support; Self; AstraZeneca. J. Resch: None. A.M. Douglass: None. J. Madara: None. J.D. Song: None. C. Wu: None. B. Lowell: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research & Development, Merck & Co., Inc. Advisory Panel; Spouse/Partner; Merck & Co., Inc. Board Member; Self; Novo Nordisk A/S. Consultant; Self; Aegerion Pharmaceuticals, IMetabolic BioPharma Corporation, Longitude Capital, Nimbus Discovery, Inc., Staten Biotechnology B.V. Funding National Institutes of Health (R01DK113984, P30DK059635, T32DK101019, K99/R00CA215315, R01NS087568, UL1TR000142, T32DK007058, R01DK075632, R01DK089044, R01DK096010, R01DK111401)

AGRP neurons modulate fasting-induced anxiolytic effects

Recent studies indicate that activation of hypothalamic Agouti-related protein (Agrp) neurons can increase forage-related/repetitive behavior and decrease anxiety levels. However, the impact of physiological hunger states and food deprivation on anxiety-related behaviors have not been clarified. In the present study, we evaluated changes in anxiety levels induced by physiological hunger states and food deprivation, and identified the neuron population involved. Ad libitum fed and fasted mice were tested in the open field and elevated plus-maze behavioral tests. The DREADD approach was applied to selectively inhibit and stimulate neurons expressing Agrp in hypothalamic arcuate nucleus in Agrp-Cre transgenic mice. We found that anxiety levels were significantly reduced in the late light period when mice have increased need for food and increased Agrp neurons firing, in contrast to the levels in the early light period. Consistently, we also found that anxiety was potently reduced in 24-h fasted mice, relative to 12-h fasted mice or fed ad libitum. Mechanistically, we found that chemogenetic activation of Agrp neurons reduced anxiety in fed mice, and inactivation of Agrp neurons reduced fasting-induced anxiolytic effects. Our results suggest that anxiety levels may vary physiologically with the increasing need for food, and are influenced by acute fasting in a time-dependent manner. Agrp neurons contribute to fasting-induced anxiolytic effects, supporting the notion that Agrp neuron may serve as an entry point for the treatment of energy states-related anxiety disorders.

Regulation of substrate utilization and adiposity by Agrp neurons

The type of nutrient utilized by the organism at any given time—substrate utilization—is a critical component of energy metabolism. The neuronal mechanisms involved in the regulation of substrate utilization in mammals are largely unknown. Here, we found that activation of hypothalamic Agrp neurons rapidly altered whole-body substrate utilization, increasing carbohydrate utilization, while decreasing fat utilization. These metabolic changes occurred even in the absence of caloric ingestion and were coupled to increased lipogenesis. Accordingly, inhibition of fatty acid synthase—a key enzyme that mediates lipogenesis—blunted the effects of Agrp neuron activation on substrate utilization. In pair-fed conditions during positive energy balance, activation of Agrp neurons improved metabolic efficiency, and increased weight gain and adiposity. Conversely, ablation of Agrp neurons impaired fat mass accumulation. These results suggest Agrp neurons regulate substrate utilization, contributing to lipogenesis and fat mass accumulation during positive energy balance.

Activation of Agrp neurons modulates memory-related cognitive processes in mice

Hypothalamic Agrp neurons are critical regulators of food intake in adult mice. In addition to food intake, these neurons have been involved in other cognitive processes, such as the manifestation of stereotyped behaviors. Here, we evaluated the extent to which Agrp neurons modulate mouse behavior in spatial memory-related tasks. We found that activation of Agrp neurons did not affect spatial learning but altered behavioral flexibility using a modified version of the Barnes Maze task. Furthermore, using the Y-maze test to probe working memory, we found that chemogenetic activation of Agrp neurons reduced spontaneous alternation behavior mediated by the neuropeptide Y receptor-5 signaling. These findings suggest novel functional properties of Agrp neurons in memory-related cognitive processes.