Central mechanisms of emesis: A role for GDF15.

BACKGROUND: Nausea and emesis are ubiquitously reported medical conditions and often present as treatment side effects along with polymorbidities contributing to detrimental life-threatening outcomes, such as poor nutrition, lower quality of life, and unfavorable patient prognosis. Growth differentiation factor 15 (GDF15) is a stress response cytokine secreted by a wide variety of cell types in response to a broad range of stressors. Circulating GDF15 levels are elevated in a range of medical conditions characterized by cachexia and malaise. In recent years, GDF15 has gained scientific and translational prominence with the discovery that its receptor, GDNF family receptor α-like (GFRAL), is expressed exclusively in the hindbrain. GFRAL activation may results in profound anorexia and body weight loss, effects which have attracted interest for the pharmacological treatment of obesity. PURPOSE: This review highlights compelling emerging evidence indicating that GDF15 causes anorexia through the induction of nausea, emesis, and food aversions, which encourage a perspective on GDF15 system function in physiology and behavior beyond homeostatic energy regulation contexts. This highlights the potential role of GDF15 in the central mediation of nausea and emesis following a variety of physiological, and pathophysiological conditions such as chemotherapy-induced emesis, hyperemesis gravidarum, and cyclic vomiting syndrome.

The antiemetic actions of GIP receptor agonism.

Nausea and vomiting are primitive aspects of mammalian physiology and behavior that ensure survival. Unfortunately, both are ubiquitously present side effects of drug treatments for many chronic diseases with negative consequences on pharmacotherapy tolerance, quality of life, and prognosis. One of the most critical clinical examples is the profound emesis and nausea that occur in patients undergoing chemotherapy, which continue to be among the most distressing side effects, even with the use of modern antiemetic medications. Similarly, antiobesity/diabetes medications that target the glucagon-like peptide-1 system, despite their remarkable metabolic success, also cause nausea and vomiting in a significant number of patients. These side effects hinder the ability to administer higher dosages for optimal glycemic and weight management and represent the major reasons for treatment discontinuation. Our inability to effectively control these side effects highlights the need to anatomically, molecularly, and functionally characterize novel neural substrates that drive and inhibit nausea and emesis. Here, we discuss clinical and preclinical evidence that highlights the glucose-dependent insulinotropic peptide receptor system as a novel therapeutic central target for the management of nausea and emesis.

Human OPRM1 and murine Oprm1 promoter driven viral constructs for genetic access to µ-opioidergic cell types.

With concurrent global epidemics of chronic pain and opioid use disorders, there is a critical need to identify, target and manipulate specific cell populations expressing the mu-opioid receptor (MOR). However, available tools and transgenic models for gaining long-term genetic access to MOR+ neural cell types and circuits involved in modulating pain, analgesia and addiction across species are limited. To address this, we developed a catalog of MOR promoter (MORp) based constructs packaged into adeno-associated viral vectors that drive transgene expression in MOR+ cells. MORp constructs designed from promoter regions upstream of the mouse Oprm1 gene (mMORp) were validated for transduction efficiency and selectivity in endogenous MOR+ neurons in the brain, spinal cord, and periphery of mice, with additional studies revealing robust expression in rats, shrews, and human induced pluripotent stem cell (iPSC)-derived nociceptors. The use of mMORp for in vivo fiber photometry, behavioral chemogenetics, and intersectional genetic strategies is also demonstrated. Lastly, a human designed MORp (hMORp) efficiently transduced macaque cortical OPRM1+ cells. Together, our MORp toolkit provides researchers cell type specific genetic access to target and functionally manipulate mu-opioidergic neurons across a range of vertebrate species and translational models for pain, addiction, and neuropsychiatric disorders.

GIP receptor agonism blocks chemotherapy-induced nausea and vomiting.

OBJECTIVE: Nausea and vomiting remain life-threatening obstacles to successful treatment of chronic diseases, despite a cadre of available antiemetic medications. Our inability to effectively control chemotherapy-induced nausea and vomiting (CINV) highlights the need to anatomically, molecularly, and functionally characterize novel neural substrates that block CINV. METHODS: Behavioral pharmacology assays of nausea and emesis in 3 different mammalian species were combined with histological and unbiased transcriptomic analyses to investigate the beneficial effects of glucose-dependent insulinotropic polypeptide receptor (GIPR) agonism on CINV. RESULTS: Single-nuclei transcriptomics and histological approaches in rats revealed a topographical, molecularly distinct, GABA-ergic neuronal population in the dorsal vagal complex (DVC) that is modulated by chemotherapy but rescued by GIPR agonism. Activation of DVCGIPR neurons substantially decreased behaviors indicative of malaise in cisplatin-treated rats. Strikingly, GIPR agonism blocks cisplatin-induced emesis in both ferrets and shrews. CONCLUSION: Our multispecies study defines a peptidergic system that represents a novel therapeutic target for the management of CINV, and potentially other drivers of nausea/emesis.

Screening study of anti-emetics to improve GDF15-induced malaise and anorexia: Implications for emesis control.

Considerable preclinical and clinical attention has focused on the food intake and body weight suppressive effects of growth differentiation factor 15 (GDF15) and its elevated blood levels as a consequence of disease states and disease treatment therapeutics. We have previously reported that exogenous administration of GDF15 induces anorexia through nausea and emesis in multiple species. Importantly, GDF15 signaling as a meditator of chemotherapy-induced anorexia and emesis has recently been demonstrated in both murine and nonhuman primate models. The mechanism, however, by which GDF15 induces malaise and the utility of existing therapeutic targets to counteract its effects remain largely unknown. Using a dose of GDF15 that mimics stimulated levels following chemotherapy administration and reliably induces malaise, we sought to screen anti-emetics that represent distinct pharmacotherapeutic classes hypothesized to reduce GDF15-induced effects in rats. Strikingly, our results showed that none of the tested compounds were effective at preventing GDF15-induced malaise. These results illustrate the complexity of GDF15 signaling mechanism and may have important implications for medical conditions characterized by elevated GDF15 levels and incomplete symptom control, such as chemotherapy-induced nausea and vomiting.

GIPR Agonism Inhibits PYY-Induced Nausea-Like Behavior.

The induction of nausea and emesis is a major barrier to maximizing the weight loss profile of obesity medications, and therefore, identifying mechanisms that improve tolerability could result in added therapeutic benefit. The development of peptide YY (PYY)-based approaches to treat obesity are no exception, as PYY receptor agonism is often accompanied by nausea and vomiting. Here, we sought to determine whether glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) agonism reduces PYY-induced nausea-like behavior in mice. We found that central and peripheral administration of a GIPR agonist reduced conditioned taste avoidance (CTA) without affecting hypophagia mediated by a PYY analog. The receptors for GIP and PYY (Gipr and Npy2r) were found to be expressed by the same neurons in the area postrema (AP), a brainstem nucleus involved in detecting aversive stimuli. Peripheral administration of a GIPR agonist induced neuronal activation (cFos) in the AP. Further, whole-brain cFos analyses indicated that PYY-induced CTA was associated with augmented neuronal activity in the parabrachial nucleus (PBN), a brainstem nucleus that relays aversive/emetic signals to brain regions that control feeding behavior. Importantly, GIPR agonism reduced PYY-mediated neuronal activity in the PBN, providing a potential mechanistic explanation for how GIPR agonist treatment reduces PYY-induced nausea-like behavior. Together, the results of our study indicate a novel mechanism by which GIP-based therapeutics may have benefit in improving the tolerability of weight loss agents.

Hypophagia induced by salmon calcitonin, but not by amylin, is partially driven by malaise and is mediated by CGRP neurons.

OBJECTIVE: The behavioral mechanisms and the neuronal pathways mediated by amylin and its long-acting analog sCT (salmon calcitonin) are not fully understood and it is unclear to what extent sCT and amylin engage overlapping or distinct neuronal subpopulations to reduce food intake. We here hypothesize that amylin and sCT recruit different neuronal population to mediate their anorectic effects. METHODS: Viral approaches were used to inhibit calcitonin gene-related peptide (CGRP) lateral parabrachial nucleus (LPBN) neurons and assess their role in amylin's and sCT's ability to decrease food intake in mice. In addition, to test the involvement of LPBN CGRP neuropeptidergic signaling in the mediation of amylin and sCT's effects, a LPBN site-specific knockdown was performed in rats. To deeper investigate whether the greater anorectic effect of sCT compared to amylin is due do the recruitment of additional neuronal pathways related to malaise multiple and distinct animal models tested whether amylin and sCT induce conditioned avoidance, nausea, emesis, and conditioned affective taste aversion. RESULTS: Our results indicate that permanent or transient inhibition of CGRP neurons in LPBN blunts sCT-, but not amylin-induced anorexia and neuronal activation. Importantly, sCT but not amylin induces behaviors indicative of malaise including conditioned affective aversion, nausea, emesis, and conditioned avoidance; the latter mediated by CGRPLPBN neurons. CONCLUSIONS: Together, the present study highlights that although amylin and sCT comparably decrease food intake, sCT is distinctive from amylin in the activation of anorectic neuronal pathways associated with malaise.

Glucagon-like peptide-1 in diabetes care: Can glycaemic control be achieved without nausea and vomiting?

Introduced less than two decades ago, glucagon-like peptide-1 receptor agonists rapidly reshaped the field of Type 2 diabetes mellitus (T2DM) care by providing glycaemic control in tandem with weight loss. However, FDA-approved GLP-1 receptor agonists are often accompanied by nausea and emesis and, in some lean T2DM patients, by undesired anorexia. Importantly, the hypophagic and emetic effects of GLP-1 receptor agonists are caused by activation of central GLP-1 receptors. This review summarizes two different approaches to mitigate the incidence and severity of nausea and emesis related to GLP-1 receptor agonists: conjugation with vitamin B12 , or related corrin ring-containing compounds ('corrination'), and development of dual agonists of GLP-1 receptors with glucose-dependent insulinotropic polypeptide (GIP). Such approaches could lead to the generation of GLP-1 receptor agonists with improved therapeutic efficacy, thus decreasing treatment attrition, increasing patient compliance and extending treatment to a broader population of T2DM patients. The data reviewed show that it is possible to pharmacologically separate the emetic effects of GLP-1 receptor agonists from their glucoregulatory action. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

GIP Receptor Agonism Attenuates GLP-1 Receptor Agonist-Induced Nausea and Emesis in Preclinical Models.

Glucagon-like peptide 1 receptor (GLP-1R) agonists decrease body weight and improve glycemic control in obesity and diabetes. Patient compliance and maximal efficacy of GLP-1 therapeutics are limited by adverse side effects, including nausea and emesis. In three different species (i.e., mice, rats, and musk shrews), we show that glucose-dependent insulinotropic polypeptide receptor (GIPR) signaling blocks emesis and attenuates illness behaviors elicited by GLP-1R activation, while maintaining reduced food intake, body weight loss, and improved glucose tolerance. The area postrema and nucleus tractus solitarius (AP/NTS) of the hindbrain are required for food intake and body weight suppression by GLP-1R ligands and processing of emetic stimuli. Using single-nuclei RNA sequencing, we identified the cellular phenotypes of AP/NTS cells expressing GIPR and GLP-1R on distinct populations of inhibitory and excitatory neurons, with the greatest expression of GIPR in γ-aminobutyric acid-ergic neurons. This work suggests that combinatorial pharmaceutical targeting of GLP-1R and GIPR will increase efficacy in treating obesity and diabetes by reducing nausea and vomiting.

The Role of GIP in the Regulation of GLP-1 Satiety and Nausea.

Gastric inhibitory peptide (GIP) is best known for its role as an incretin hormone in control of blood glucose concentrations. As a classic satiation signal, however, the literature illustrates a mixed picture of GIP involvement with an at best weak anorectic response profile being reported for GIP receptor (GIPR) signaling. Not surprisingly, the pursuit of exploiting the GIP system as a therapeutic target for diabetes and obesity has fallen behind that of the other gastrointestinal-derived incretin, glucagon-like peptide 1 (GLP-1). However, recent discoveries highlighted here support potential therapeutic advantages of combinatorial therapies targeting GIP and GLP-1 systems together, with perhaps the most surprising finding that GIPR agonism may have antiemetic properties. As nausea and vomiting are the most common side effects of all existing GLP-1 pharmacotherapies, the ability for GIP agonism to reduce GLP-1-induced illness behaviors but retain (if not enhance) weight loss and glycemic control may offer a new era in the treatment of obesity and diabetes.

Olanzapine Administration Reduces Chemotherapy-Induced Nausea Behavior in Rats.

Nausea and vomiting are consistently identified among the most distressing side effects of chemotherapy. In recent years, Olanzapine (OLZ) treatment was added to anti-emetic guidelines as a treatment for chemotherapy-induced nausea and vomiting (CINV), despite little available data supporting a mechanism behind the positive benefits of the drug. Here, we examine whether OLZ reduces cisplatin chemotherapy-induced side effects on food intake and pica behavior in rats (i.e., kaolin intake, a proxy for nausea/emesis). Behavioral experiments tested whether systemic or hindbrain administration of OLZ ameliorated cisplatin-induced pica, anorexia, and body weight loss in rats. We also tested whether systemic OLZ reduces cisplatin-induced neuronal activation in the dorsal vagal complex (DVC), a hindbrain region controlling emesis. Lastly, given their role in regulating feeding and emesis, circulating ghrelin levels and central mRNA expression levels of serotonin (HT) receptor subunits, including 5-HT2C, were measured in brain regions that regulate CINV and energy balance in an exploratory analysis to investigate potential mediators of OLZ action. Our results show that both systemic and hindbrain administration of OLZ attenuated cisplatin-induced kaolin intake and body weight loss, but not anorexia. Systemic OLZ decreased cisplatin-induced c-Fos immunofluorescence in the DVC and prevented cisplatin-induced reductions in circulating ghrelin levels. IP OLZ also blocked cisplatin-induced increases in Htr2c expression in DVC and hypothalamic micropunches. These data suggest hindbrain exposure to OLZ is sufficient to induce reductions in cisplatin-induced pica and that central serotonergic signaling, via 5-HT2C, and changes in circulating ghrelin may be potential mediators of olanzapine anti-emetic action.

Activation of PPG neurons following acute stressors differentially involves hindbrain serotonin in male rats.

Within the hindbrain, serotonin (5-HT) functions as a modulator of the central glucagon-like peptide-1 (GLP-1) system. This interaction between 5-HT and GLP-1 is achieved via 5-HT2C and 5-HT3 receptors and is relevant for GLP-1-mediated feeding behavior. The central GLP-1 system is activated by various stressors, activates the hypothalamic pituitary adrenocortical (HPA) axis, and contributes to stress-related behaviors. Whether 5-HT modulates GLP-1's role in the stress response in unknown. We hypothesized that the serotonergic modulation of GLP-1-producing neurons (i.e., PPG neurons) is stimuli-specific and that stressed-induced PPG activity is one of the modalities in which 5-HT plays a role. In this study, we investigated the roles of 5-HT2C and 5-HT3 receptors in mediating the activation of PPG neurons in the nucleus tractus solitarius (NTS) following exposure to three different acute stressors: lithium chloride (LiCl), noncontingent cocaine (Coc), and novel restraint stress (RES). Results showed that increased c-Fos expression in PPG neurons following LiCl and RES-but not Coc-is dependent on hindbrain 5-HT2C and 5-HT3 receptor signaling. Additionally, stressors that depend on 5-HT signaling to activate PPG neurons (i.e., LiCl and RES) increased c-Fos expression in 5-HT-expressing neurons within the caudal raphe (CR), specifically in the raphe magnus (RMg). Finally, we showed that RMg neurons innervate NTS PPG neurons and that some of these PPG neurons lie in close proximity to 5-HT axons, suggesting RMg 5-HT-expressing neurons are the source of 5-HT input responsible for engaging NTS PPG neurons. Together, these findings identify a direct RMg to NTS pathway responsible for the modulatory effect of 5-HT on the central GLP-1 system-specifically via activation of 5-HT2C and 5-HT3 receptors-in the facilitation of acute stress responses.

Corrination of a GLP-1 Receptor Agonist for Glycemic Control without Emesis.

Glucagon-like peptide-1 receptor (GLP-1R) agonists used to treat type 2 diabetes mellitus often produce nausea, vomiting, and in some patients, undesired anorexia. Notably, these behavioral effects are caused by direct central GLP-1R activation. Herein, we describe the creation of a GLP-1R agonist conjugate with modified brain penetrance that enhances GLP-1R-mediated glycemic control without inducing vomiting. Covalent attachment of the GLP-1R agonist exendin-4 (Ex4) to dicyanocobinamide (Cbi), a corrin ring containing precursor of vitamin B12, produces a "corrinated" Ex4 construct (Cbi-Ex4). Data collected in the musk shrew (Suncus murinus), an emetic mammal, reveal beneficial effects of Cbi-Ex4 relative to Ex4, as evidenced by improvements in glycemic responses in glucose tolerance tests and a profound reduction of emetic events. Our findings highlight the potential for clinical use of Cbi-Ex4 for millions of patients seeking improved glycemic control without common side effects (e.g., emesis) characteristic of current GLP-1 therapeutics.

GDF15 Induces Anorexia through Nausea and Emesis.

Growth differentiation factor 15 (GDF15) is a cytokine that reduces food intake through activation of hindbrain GFRAL-RET receptors and has become a keen target of interest for anti-obesity therapies. Elevated endogenous GDF15 is associated with energy balance disturbances, cancer progression, chemotherapy-induced anorexia, and morning sickness. We hypothesized that GDF15 causes emesis and that its anorectic effects are related to this function. Here, we examined feeding and emesis and/or emetic-like behaviors in three different mammalian laboratory species to help elucidate the role of GDF15 in these behaviors. Data show that GDF15 causes emesis in Suncus murinus (musk shrews) and induces behaviors indicative of nausea/malaise (e.g., anorexia and pica) in non-emetic species, including mice and lean or obese rats. We also present data in mice suggesting that GDF15 contributes to chemotherapy-induced malaise. Together, these results indicate that GDF15 triggers anorexia through the induction of nausea and/or by engaging emetic neurocircuitry.

Myocardial apoptosis and mesenchymal stem cells with acute exercise.

Aerobic exercise confers many health benefits. However, numerous reports have shown that acute aerobic exercise can injure the heart. We tested the general hypothesis that acute moderate-intensity exercise in rodents induces cardiomyocyte damage and stimulates mesenchymal stem cells (MSCs) to increase paracrine-mediated protective effects on cardiomyocytes. A single session of treadmill running (13 m/min, 0% grade, for 45 min) in untrained C57BL/6 male mice (n = 18) increased cleaved poly ADP-ribose polymerase (PARP), a marker of apoptosis, in the myocardium 24 h postexercise. Microarray analysis of mouse myocardium identified 11 relevant apoptotic genes and several shifts in matrix remodeling transcripts over the postexercise window. Postexercise cardiomyocyte death was recapitulated in neonatal rat cardiomyocytes (NRCMs) by culturing cells in 2% plasma harvested from exercised rats. The increased cell death observed in exercise-treated NRCMs was attenuated by ß-adrenergic blockade, but not antioxidant treatment. MSC survival, proliferation, and chemotaxis showed no significant differences between sedentary and exercise plasma conditions, despite increased IL-6, TNF-α, IL-1ß, and IFN-γ secretions from MSCs treated with exercise plasma. NRCM survival was increased nearly 500% when cocultured with MSCs, but this effect was not altered under exercise plasma culture conditions. Our results suggest acute moderate-intensity aerobic treadmill running in exercise-naïve rodents induces temporal cardiomyocyte death due to plasma-borne factors, namely, catecholaminergic stress. Even though exercise conditions prompt an inflammatory response in MSCs, the exercise milieu does not alter the MSC-protective phenotype on cardiomyocytes.

Excitatory Hindbrain-Forebrain Communication Is Required for Cisplatin-Induced Anorexia and Weight Loss.

Cisplatin chemotherapy is commonly used to treat cancer despite severe energy balance side effects. In rats, cisplatin activates nucleus tractus solitarius (NTS) projections to the lateral parabrachial nucleus (lPBN) and calcitonin-gene related peptide (CGRP) projections from the lPBN to the central nucleus of the amygdala (CeA). We demonstrated previously that CeA glutamate receptor signaling mediates cisplatin-induced anorexia and body weight loss. Here, we used neuroanatomical tracing, immunofluorescence, and confocal imaging to demonstrate that virtually all NTS→lPBN and lPBN→CeA CGRP projections coexpress vesicular glutamate transporter 2 (VGLUT2), providing evidence that excitatory projections mediate cisplatin-induced energy balance dysregulation. To test whether lPBN→CeA projection neurons are required for cisplatin-induced anorexia and weight loss, we inhibited these neurons chemogenetically using a retrograde Cre-recombinase-expressing canine adenovirus-2 in combination with Cre-dependent inhibitory Designer Receptors Exclusive Activated by Designer Drugs (DREADDs) before cisplatin treatment. Inhibition of lPBN→CeA neurons attenuated cisplatin-induced anorexia and body weight loss significantly. Using a similar approach, we additionally demonstrated that inhibition of NTS→lPBN neurons attenuated cisplatin-induced anorexia and body weight loss significantly. Together, our data support the view that excitatory hindbrain-forebrain projections are necessary for cisplatin's untoward effects on energy intake, elucidating a key neuroanatomical circuit driving pathological anorexia and weight loss that accompanies chemotherapy treatment. SIGNIFICANCE STATEMENT: Chemotherapy treatments are commonly used to treat cancers despite accompanying anorexia and weight loss that may limit treatment adherence and reduce patient quality of life. Strikingly, we lack a neural understanding of, and effective treatments for, chemotherapy-induced anorexia and weight loss. The current data characterize the excitatory nature of neural projections activated by cisplatin in rats and reveal the necessity of specific hindbrain-forebrain projections for cisplatin-induced anorexia and weight loss. Together, these findings help to characterize the neural mechanisms mediating cisplatin-induced anorexia, advancing opportunities to develop better-tolerated chemotherapies and adjuvant therapies to prevent anorexia and concurrent nutritional deficiencies during cancer treatment.

Physical activity induced protection against breast cancer risk associated with delayed parity.

Epidemiological evidence indicates that physical activity between menarche and first pregnancy is associated with a lower risk of breast cancer among women with at least 20years between these reproductive events. The mechanism by which physical activity during this interval confers protection is unknown. This study used a novel animal model to assess potentially protective effects of physical activity on tumor development in delayed parity. Thirty-six female Sprague Dawley rats received an i.p. injection of 50mg/kg N-methyl-N-nitrosourea (MNU) at 5weeks of age. Estrogen and progesterone pellets were implanted subcutaneously 1week (early parity, EP, n=8) or 4weeks (delayed parity, DP, n=11) following MNU injection. An additional group of DP rats were progressively exercise trained (Ex+DP, n=9) on a treadmill following MNU injection for 7weeks (up to 20m/min at 15% incline for 30min). We observed the greatest tumor latency and smallest tumor burden in Ex+DP animals. Ductal hyperplasia and inflammation of non-tumor bearing mammary glands were only found in DP, and we detected a significant increase in collagen for DP and Ex+DP compared to EP. Exercise induced differential gene expression of cyclin-dependent kinase-inhibitor 1C (Cdkn1c) and urokinase-plasminogen activator (Plau) in mammary tissue of Ex+DP animals compared to DP alone. While there are delayed parity-induced changes in mammary gland collagen and gene expression levels, Ex+DP animals had longer tumor latency, smaller tumor burden, and glandular tissue resistant to ductal hyperplasia. Exercise may induce protection through beneficial regulation of gene expression profiles.

Glucagon-Like Peptide-1 Receptor Activation in the Ventral Tegmental Area Decreases the Reinforcing Efficacy of Cocaine.

Cocaine addiction continues to be a significant public health problem for which there are currently no effective FDA-approved treatments. Thus, there is a clear need to identify and develop novel pharmacotherapies for cocaine addiction. Recent evidence indicates that activation of glucagon-like peptide-1 (GLP-1) receptors in the ventral tegmental area (VTA) reduces intake of highly palatable food. As the neural circuits and neurobiological mechanisms underlying drug taking overlap to some degree with those regulating food intake, these findings suggest that activation of central GLP-1 receptors may also attenuate cocaine taking. Here, we show that intra-VTA administration of the GLP-1 receptor agonist exendin-4 (0.05 µg) significantly reduced cocaine, but not sucrose, self-administration in rats. We also demonstrate that cocaine taking is associated with elevated plasma corticosterone levels and that systemic infusion of cocaine activates GLP-1-expressing neurons in the nucleus tractus solitarius (NTS), a hindbrain nucleus that projects monosynaptically to the VTA. To determine the potential mechanisms by which cocaine activates NTS GLP-1-expressing neurons, we microinjected corticosterone (0.5 µg) directly into the hindbrain fourth ventricle. Intraventricular corticosterone attenuated cocaine self-administration and this effect was blocked in animals pretreated with the GLP-1 receptor antagonist exendin-(9-39) (10 µg) in the VTA. Finally, AAV-shRNA-mediated knockdown of VTA GLP-1 receptors was sufficient to augment cocaine self-administration. Taken together, these findings indicate that increased activation of NTS GLP-1-expressing neurons by corticosterone may represent a homeostatic response to cocaine taking, thereby reducing the reinforcing efficacy of cocaine. Therefore, central GLP-1 receptors may represent a novel target for cocaine addiction pharmacotherapies.

Glutamate Receptors in the Central Nucleus of the Amygdala Mediate Cisplatin-Induced Malaise and Energy Balance Dysregulation through Direct Hindbrain Projections.

Cisplatin chemotherapy is used commonly to treat a variety of cancers despite severe side effects such as nausea, vomiting, and anorexia that compromise quality of life and limit treatment adherence. The neural mechanisms mediating these side effects remain elusive despite decades of clinical use. Recent data highlight the dorsal vagal complex (DVC), lateral parabrachial nucleus (lPBN), and central nucleus of the amygdala (CeA) as potential sites of action in mediating the side effects of cisplatin. Here, results from immunohistochemical studies in rats identified a population of cisplatin-activated DVC neurons that project to the lPBN and a population of cisplatin-activated lPBN calcitonin gene-related peptide (CGRP, a marker for glutamatergic neurons in the lPBN) neurons that project to the CeA, outlining a neuroanatomical circuit that is activated by cisplatin. CeA gene expressions of AMPA and NMDA glutamate receptor subunits were markedly increased after cisplatin treatment, suggesting that CeA glutamate receptor signaling plays a role in mediating cisplatin side effects. Consistent with gene expression results, behavioral/pharmacological data showed that CeA AMPA/kainate receptor blockade attenuates cisplatin-induced pica (a proxy for nausea/behavioral malaise in nonvomiting laboratory rodents) and that CeA NMDA receptor blockade attenuates cisplatin-induced anorexia and body weight loss in addition to pica, demonstrating that glutamate receptor signaling in the CeA is critical for the energy balance dysregulation caused by cisplatin treatment. Together, these data highlight a novel circuit and CGRP/glutamatergic mechanism through which cisplatin-induced malaise and energy balance dysregulation are mediated. SIGNIFICANCE STATEMENT: To treat cancer effectively, patients must follow prescribed chemotherapy treatments without interruption, yet most cancer treatments produce side effects that devastate quality of life (e.g., nausea, vomiting, anorexia, weight loss). Although hundreds of thousands of patients undergo chemotherapies each year, the neural mechanisms mediating their side effects are unknown. The current data outline a neural circuit activated by cisplatin chemotherapy and demonstrate that glutamate signaling in the amygdala, arising from hindbrain projections, is required for the full expression of cisplatin-induced malaise, anorexia, and body weight loss. Together, these data help to characterize the neural circuits and neurotransmitters mediating chemotherapy-induced energy balance dysregulation, which will ultimately provide an opportunity for the development of well tolerated cancer and anti-emetic treatments.

Incretins and amylin: neuroendocrine communication between the gut, pancreas, and brain in control of food intake and blood glucose.

Arguably the most fundamental physiological systems for all eukaryotic life are those governing energy balance. Without sufficient energy, an individual is unable to survive and reproduce. Thus, an ever-growing appreciation is that mammalian physiology developed a redundant set of neuroendocrine signals that regulate energy intake and expenditure, which maintains sufficient circulating energy, predominantly in the form of glucose, to ensure that energy needs are met throughout the body. This orchestrated control requires cross talk between the gastrointestinal tract, which senses the incoming meal; the pancreas, which produces glycemic counterregulatory hormones; and the brain, which controls autonomic and behavioral processes regulating energy balance. Therefore, this review highlights the physiological, pharmacological, and pathophysiological effects of the incretin hormones glucagon-like peptide-1 and gastric inhibitory polypeptide, as well as the pancreatic hormone amylin, on energy balance and glycemic control.