G-protein-coupled receptor 75 (GPR75) has emerged as an important mediator in diet-induced obesity (DIO) and a promising therapeutic target for anti-obesity drugs. However, the anatomical location of GPR75 in the brain remains unclear, hindering the understanding of GPR75 biology in DIO. Here, we generated a new GPR75-GFP-Ires-Cre knockin mouse strain, in which the Cre expression is driven by the endogenous GPR75 promoter and the GFP is fused with the C-terminal of the GPR75 protein. Both Cre and GFP were confirmed to be colocalized with the endogenous GPR75 expression. In addition, the GPR75-GFP fusion protein remains functionally normal with unaltered susceptibility to DIO. Moreover, using this mouse strain, we found that GPR75 is broadly expressed throughout the brain and mainly localized to the cytoplasm of brain neurons. This new genetic tool can therefore be used to study the neural basis for GPR75 in mediating DIO.

IntroductionAnimals rely on defensive avoidance of exposed or potentially threatening environments as a fundamental survival strategy, often expressing this behavior as thigmotaxis, or a preference for the periphery of an open space. However, researchers still do not understand how neural circuits coordinate avoidance behavior with competing physiological drives such as feeding. In this study, we investigate how corticotropin-releasing factor (CRF)-expressing neurons in the bed nucleus of the stria terminalis (BNST) integrate environmental avoidance and feeding behavior.MethodsWe used adult male and female mice and applied fiber photometry to monitor BNST CRF neuronal activity in vivo. We performed both acute and chronic manipulations of these neurons to test their causal role in behavior. We used behavioral assays to measure avoidance (thigmotaxis) and food intake. We also conducted anatomical tracing to identify projections from BNST CRF neurons to hypothalamic regions and used axon terminal optogenetic stimulation to test the functional contributions of specific pathways.ResultsBNST CRF neurons increased their activity in response to diverse stressors. When we activated these neurons, mice showed increased periphery-oriented behavior and reduced food intake. Anatomical tracing revealed that BNST CRF neurons project to key hypothalamic regions, including the lateral hypothalamus (LH) and paraventricular hypothalamic nucleus (PVH). When we stimulated BNST CRF→LH projections, we observed both increased avoidance behavior and suppressed feeding. In contrast, stimulating BNST CRF→PVH projections did not significantly alter either behavior.DiscussionOur findings identify BNST CRF neurons as a circuit node that integrates stress and feeding-related signals to bias behavioral output. Specifically, BNST CRF projections to the LH drive the coupling of avoidance and feeding suppression. These results provide new insight into how the brain coordinates competing motivational states such as avoidance and feeding.

Sensory perception is shaped by experience, giving stimuli behavioral significance. Basal forebrain (BF) cholinergic neurons in mice, which are crucial for arousal and motivation, also regulate sensory processing. Within BF nuclei, glutamatergic (vGlut2BF) neurons receive cholinergic input and modulate behaviors, but their roles in encoding sensory significance remain unclear. Using in vivo calcium imaging, we found that vGlut2BF neurons initially poorly encoded odor identity. However, their response to conditioned odors increased following associative learning, and their population activity more distinctly encoded paired stimuli, reflecting emergent value representation. Furthermore, pairing stimulation or inhibition of vGlut2BF neurons with specific odors altered odor preferences, suggesting that appropriately timed vGlut2BF neuronal activity is sufficient to influence valence assignment. Our findings reveal that vGlut2BF neurons transform sensory input into motivationally significant stimuli, positioning the BF as a key hub for linking sensory processing with motivational states and experience-driven plasticity. Neural mechanisms underlying motivation-driven behaviors are not fully understood. Here authors show that non-cholinergic neurons in rodent basal forebrain link sensory stimuli with motivational states and experience-driven plasticity.

Anorexia nervosa (AN) is a debilitating, often lethal, restrictive-type eating disorder without an effective cure. The underlying neural basis of AN has remained elusive without an animal model that has represented all typical AN symptoms. Here we show that aberrant activation of mediobasal hypothalamic (MBH) glutamatergic neurons led to lethal self-starvation, hyperactivity, anhedonia, social phobia, and increased anxiety, all of which represent typical symptoms of AN. These symptoms were selectively exhibited by targeted activation of MBH neurons expressing steroidogenic factor (SF1) and estrogen receptor alpha (ERa). Moreover, the elicited AN symptoms by activation of MBH glutamatergic or SF1/ERa neurons were rescued by removing release of glutamate or brain-derived neurotrophic factor (BDNF) from these neurons. Importantly, BDNF overexpression in SF1/ERa neurons promoted typical AN symptoms, which were suppressed by removing glutamate release. Thus, our findings identify aberrantly enhanced BDNF and consequent augmented glutamate release from SF1/ERa neurons as a neural basis underlying AN.

Stress and diet are known to synergistically promote risks of obesity but the underlying neural basis remains elusive. Corticotropin-releasing hormone neurons in the paraventricular hypothalamus (PVHCRH) are stress responsive and release both CRH and glutamate. Here we generated a mouse model with gain or loss of release in CRH or glutamate from PVHCRH neurons. While these models showed no changes in body weight when fed chow, they exhibited contrasting effects when fed high-fat high-caloric diets (HFD). Whereas disrupting glutamate release from PVHCRH neurons led to diet-induced obesity (DIO), that of CRH caused no impact. Conversely, augmented CRH release led to DIO while that of glutamate caused no impact. The observed DIO in both cases was associated with an increased drive for HFD, but without obvious changes in behavioral signs of anxiety. Our results suggest PVHCRH neurons as a key mediator for the exerbated DIO induced by maladaptive stress responses.

Homeotherms maintain a steady body temperature through thermoregulation, a process critical for survival during fasting, in which the brain has to defend energy-costly body temperature while reducing energy expenditure to conserve energy reserve; however, the neural basis for defending body temperature remains unclear. Here, we demonstrated that AgRP neuron lesion led to lethality during time-restricted feeding on chow but not on HFD, and caused no obvious impact on HFD-induced obesity or obesity-reducing responses to glucagon-like peptide-1 receptor agonism. The lesion disrupted adaptive feeding behaviors during time-restricted feeding and reduced motivational feeding on chow. Notably, the lethality was caused by hypothermia instead of reduced food intake. The lesion also caused failure in body temperature maintenance during acute fasting in cold. Fasting-induced activation in AgRP neurons was abrogated when mice were placed in a warm environment. Our results identify the physiological role for AgRP neurons in defending body temperature during restricted availability of low-calorie diets but dispensable for body weight regulation with food ad libitum.

An appropriate stress response is essential for properly responding to, coping with, and subsequently recovering from disturbing environmental stimuli. However, how the brain dynamically encodes the scalability of stress responses remains poorly understood. Here, we found that, GABAergic neurons in the arcuate nucleus (Arc, denoted as ArcGABA neurons) send direct inputs to corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVH, denoted as PVHCRH neurons), the primary regulators of the hypothalamic-pituitary-adrenal (HPA) axis. Although PVHCRH neurons exhibited time-locked activation in response to various environmental stressors, both GABA release onto PVHCRH neurons and the activity of PVHCRH-projecting ArcGABA neurons were selectively reduced during exposure to prolonged, high-intensity stressors, but not following exposure to transient, low-intensity stressors. Notably, GABA release onto PVHCRH neurons was positively correlated with PVHCRH-projecting ArcGABA neuron activity, yet anticorrelated with PVHCRH neuronal activity in response to the same prolonged, high-intensity stressors. Selective silencing of PVHCRH- projecting ArcGABA neurons was sufficient to elevate HPA axis activity and stress levels, phenocopying the effect of direct of PVHCRH neuron activation. Conversely, selective activation of PVHCRH-projecting ArcGABA neurons reduced both HPA axis activity and stress levels, this effect was completely abolished by concurrent excitation of PVHCRH neurons. Molecular identity screening further revealed that these PVHCRH-projecting ArcGABA neurons are not subsets expressing agouti-related peptide (AgRP) and tyrosine hydroxylase (TH) markers. Collectively, these findings indicate that the non-AgRP/TH ArcGABA→PVHCRH neurocircuit serves as a critical neural substrate that directly encodes the scalability of stress responses to environmental stressors by modulating inhibitory GABA release in a stimulus intensity-dependent manner.

Background: The global obesity crisis and the limited success of current treatments underscore the need to identify novel regulatory pathways. While central administration of α-Klotho exerts anti-obesity effects in rodents through AgRP neurons, the intracellular signaling mechanisms that mediate this process remain undefined. Methods: To define the role of FGFR1 within the α-Klotho signaling pathway in AgRP neurons, we performed a targeted deletion of the receptor in adult mice using an AAV-mediated CRISPR/Cas9 system alongside transgenic models. Results: Deletion of FGFR1 in AgRP neurons disrupted energy homeostasis, promoting weight gain induced by a high-fat diet. Electrophysiological recordings revealed that FGFR1 loss increased the intrinsic firing rate of AgRP neurons and abolished the suppressive effect of α-Klotho on their activity. At the molecular level, FGFR1 knockdown decreased phosphorylation of the transcription factor FOXO1 and elevated AgRP mRNA expression. Conclusions: Our results define a crucial FGFR1 signaling axis in AgRP neurons that coordinately regulates their electrical activity and peptide expression, thereby establishing FGFR1 as an essential regulator of energy homeostasis.

Motion sickness is associated with thermoregulation and metabolic control, but the underlying neural circuitry remains largely unknown. Here we show that neurons in the medial vestibular nuclei parvocellular part (MVePC) mediate the hypothermic responses induced by motion. Reactivation of motion-sensitive MVePC neurons recapitulates motion sickness in mice. We show that motion-activated neurons in the MVePC are glutamatergic (MVePCGlu), and that optogenetic stimulation of MVePCGlu neurons mimics motion-induced hypothermia by signalling to the lateral parabrachial nucleus (LPBN). Acute inhibition of MVePC-LPBN circuitry abrogates motion-induced hypothermia. Finally, we show that chronic inhibition of MVePCGlu neurons prevents diet-induced obesity and improves glucose homeostasis without suppressing food intake. Overall, these findings highlight MVePCGlu neurons as a potential target for motion-sickness treatment and obesity control. Glutamatergic neurons in the parvocellular part of the medial vestibular nucleus mediate motion-induced hypothermia and can be targeted to prevent diet-induced obesity.

In this presentation, I will briefly cover key factors that contribute to variations in feeding behaviors including food intake measurement methods, and external and internal environments. In addition, brain mechanisms that control feeding behaviors and consequent body weight changes will also be covered. Examples on using various methods for feeding studies will be illustrated. Audience will gain a grasp of current research front on feeding and body weight research in rodents.

Olfactory perception of food odors is a key determinant of eating behavior, including triggering appetite, facilitating food seeking and influencing food choice. While transient food-related olfactory cues stimulate appetite and provoke cravings in states of hunger, emerging evidence implies that prolonged and sustained exposure to food-derived odor (FO) suppresses feeding. However, the mechanisms by which olfaction induces hypophagia remain elusive. In this study, we show that prolonged FO exposure significantly suppresses food intake in male mice. We identified a subset of neurons in the ventral subiculum (vSub) that are specifically activated by FO. We further discovered that these FO-activated neurons in the vSub receive excitatory inputs from the olfactory bulb (OB) and send glutamatergic projections to the ventromedial hypothalamus (VMH). Inhibition of the OB → vSub → VMH circuit abolished the FO-induced reduction in food intake, while activation of this circuit suppressed feeding and reduced body weight. Together, these findings reveal a neurobiological circuitry that mediates the influence of olfactory signals on food intake regulation.

Overconsumption of a palatable Western diet, a condition linked to central leptin resistance, contributes extensively to the current obesity epidemic. In this context, intensive efforts have focused on detailing the molecular mechanisms underlying leptin resistance. Here, we demonstrate that chronic inhibition of hypothalamic arcuate GABAergic neurons (ArcGABA) effectively reduced diet-induced obesity (DIO). Interestingly, palatable food exposure increased the activity level of ArcGABA neurons, which do not express the leptin receptor (non-LepR neurons; nonresponsive to leptin). Chronic activation of ArcGABA non-LepR neurons led to massive obesity, which was associated with normal leptin-induced pSTAT3 signaling but phenotypic leptin resistance; i.e., high leptin levels failing to reduce obesity. In contrast, chronic inhibition of ArcGABA non-LepR neurons effectively prevented and reversed DIO, suggesting a potential anti-obesity treatment strategy. These results reveal that obesogenic stimulation of ArcGABA non-LepR neurons, even with intact leptin-pSTAT3 signaling, results in obesity, identifying a novel neural basis underlying leptin resistance.

Circadian rhythms are internal biological rhythms driving temporal tissue-specific, metabolic programs. Loss of the circadian transcription factor BMAL1 in the paraventricular nucleus (PVN) of the hypothalamus reveals its importance in metabolic rhythms, but its functions in individual PVN cells are poorly understood. Here, loss of BMAL1 in the PVN results in arrhythmicity of processes controlling energy balance and alters peripheral diurnal gene expression. BMAL1 chromatin immunoprecipitation sequencing (ChIP-seq) and single-nucleus RNA sequencing (snRNA-seq) reveal its temporal regulation of target genes, including oxytocin (OXT), and restoring circulating OXT peaks in BMAL1-PVN knockout (KO) mice rescues absent activity rhythms. While glutamatergic neurons undergo day/night changes in expression of genes involved in cell morphogenesis, astrocytes and oligodendrocytes show gene expression changes in cytoskeletal organization and oxidative phosphorylation. Collectively, our findings show diurnal gene regulation in neuronal and non-neuronal PVN cells and that BMAL1 contributes to diurnal OXT secretion, which is important for systemic diurnal rhythms.

Glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) have proven to be highly effective in reducing obesity across species and ages, gaining unmet popularity in clinical treatments against obesity. Although extensive research efforts have been made to explore how the brain regulates body weight homeostasis including the effect brought up by GLP-1 and its synthetic analogs GLP-1RAs, the identity of neurons and neural pathways that are responsible for the observed anti-obesity effect of GLP-1RAs remain largely elusive. Excitingly, three recent high-profile studies presented compelling evidence that each argues for the importance of GLP-1Rs in the dorsomedial hypothalamus, hindbrain, or lateral septum, respectively, in mediating the anti-obesity effect of GLP-1RAs. While these studies clearly illustrated the contributions of each of these distinct brain regions involved in GLP-1RAs in body weight regulation, the presented results also suggest the complexity of the involved brain neural network. This commentary briefly introduces these studies and highlights key knowledge gaps that require further investigation.

Dopaminergic (DA) neurons are known to play a key role in controlling behaviors. While DA neurons in other brain regions are extensively characterized, those in zona incerta (ZITH or A13) receive much less attention and their function remains to be defined. Here it is shown that optogenetic stimulation of these neurons elicited intensive self-grooming behaviors and promoted place preference, which can be enhanced by training but cannot be converted into contextual memory. Interestingly, the same stimulation increased DA release to periaqueductal grey (PAG) neurons and local PAG antagonism of DA action reduced the elicited self-grooming. In addition, A13 neurons increased their activity in response to various external stimuli and during natural self-grooming episodes. Finally, monosynaptic retrograde tracing showed that the paraventricular hypothalamus represents one of the major upstream brain regions to A13 neurons. Taken together, these results reveal that A13 neurons are one of the brain sites that promote appetitive self-grooming involving DA release to the PAG.

Obesity results from excessive caloric input associated with overeating and presents a major public health challenge. The hypothalamus has received significant attention for its role in governing feeding behavior and body weight homeostasis. However, extrahypothalamic brain circuits also regulate appetite and consumption by altering sensory perception, motivation, and reward. We recently discovered a population of basal forebrain cholinergic (BFc) neurons that regulate appetite suppression. Through viral tracing methods in the mouse model, we found that BFc neurons densely innervate the basolateral amygdala (BLA), a limbic structure involved in motivated behaviors. Using channelrhodopsin-assisted circuit mapping, we identified cholinergic responses in BLA neurons following BFc circuit manipulations. Furthermore, in vivo acetylcholine sensor and genetically encoded calcium indicator imaging within the BLA (using GACh3 and GCaMP, respectively) revealed selective response patterns of activity during feeding. Finally, through optogenetic manipulations in vivo, we found that increased cholinergic signaling from the BFc to the BLA suppresses appetite and food intake. Together, these data support a model in which cholinergic signaling from the BFc to the BLA directly influences appetite and feeding behavior.

Obesity is a growing global health epidemic with limited orally administered therapeutics. Serotonin (5-HT) is one neurotransmitter which remains an excellent target for new weight-loss therapies, but a gap remains in understanding the mechanisms involved in 5-HT produced in the dorsal Raphe nucleus (DRN) and its involvement in meal initiation. Using an optogenetic feeding paradigm, we showed that the 5-HTDRN➔arcuate nucleus (ARH) circuit plays a role in meal initiation. Incorporating electrophysiology and ChannelRhodopsin-2-Assisted Circuit Mapping, we demonstrated that 5-HTDRN neurons receive inhibitory input partially from GABAergic neurons in the DRN, and the 5-HT response can be enhanced by hunger. Additionally, deletion of the GABAA receptor subunit in 5-HT neurons inhibits meal initiation with no effect on the satiation process. Finally, we identified the role of dopaminergic inputs via dopamine receptor D2 in enhancing the response to GABA-induced feeding. Thus, our results indicate that 5-HTDRN neurons are inhibited by synergistic inhibitory actions of GABA and dopamine, for the initiation of a meal.

Light plays an essential role in a variety of physiological processes, including vision, mood, and glucose homeostasis. However, the intricate relationship between light and an animal's feeding behavior has remained elusive. Here, we found that light exposure suppresses food intake, whereas darkness amplifies it in male mice. Interestingly, this phenomenon extends its reach to diurnal male Nile grass rats and healthy humans. We further show that lateral habenula (LHb) neurons in mice respond to light exposure, which in turn activates 5-HT neurons in the dorsal Raphe nucleus (DRN). Activation of the LHb→5-HTDRNcircuit in mice blunts darkness-induced hyperphagia, while inhibition of the circuit prevents light-induced anorexia. Together, we discovered a light-responsive neural circuit that relays the environmental light signals to regulate feeding behavior in mice.