Inducible nitric oxide synthase-derived nitric oxide reduces vagal satiety signalling in obese mice

Multifaceted impact of adipose conditioned media: Obesity-driven promotion of prostate cancer and cancer stem cell dynamics

Obesity is an established risk factor for the development and progression of prostate cancer (PC). This study used adipose conditioned media (ACM) from differentiated adipocytes to assess its effect on PC development and aggressiveness. Due to limited research on ACM's impact on isolated PC stem cells (PCSCs), we also examined CD44+ PCSCs. ACM notably boosted interleukin-1β (IL-1β), IL-6, and IL-8 production in normal prostate epithelial cells and LNCaP cells. It also increased IL-6 and IL-8 production in PC3 and CD44+ LNCaP cells, and IL-1β and IL-6 production in CD44+ PC3 cells. This indicates that ACM induces the production of inflammatory cytokines in both cancer and prostate epithelial cells. Furthermore, ACM promoted proliferation in androgen receptor (AR)-negative PC3 cells, CD44+  PC3 PCSCs, and nonmalignant RWPE cells, without affecting AR-positive LNCaP cells. In addition, ACM-enhanced invasion and migration potential in both PC3 and CD44+  PC3 cells. Western blot analysis indicated the involvement of NF-κB and AKT pathways in ACM-induced proliferation in PC3 cells and NF-κB in PCSCs. In ACM-treated PC3 cells, E-cadherin was downregulated, while N-cadherin, Snail, vimentin, fibronectin, and Twist were upregulated, suggesting ACM-induced invasion via classical epithelial-to-mesenchymal transition (EMT) pathways. In response to ACM, PCSCs exhibited increased expression of E-cadherin, Snail, and vimentin, which are partial EMT markers promoting stemness and resistance to apoptosis. In addition, increased expressions of Nanog, Oct3/4, survivin, and Bcl-2 were observed. Although the molecules we studied have diverse effects on cellular regulation, our data emphasize obesity's multifaceted role in promoting and aggressing PC, notably affecting PCSC populations.

Hydrogen sulfide ameliorates hypertension and vascular dysfunction induced by insulin resistance in rats by reducing oxidative stress and activating eNOS

Hydrogen sulfide (H2S) is a gasotransmitter implied in metabolic diseases, insulin resistance, obesity, and type 2 Diabetes Mellitus. This study aimed to determine the effect of chronic administration of sodium hydrosulfide (NaHS; inorganic H2S donor), L-Cysteine (L-Cys; substrate of H2S producing enzymes) and DL-Propargylglycine (DL-PAG; cystathionine-gamma-lyase inhibitor) on the vascular dysfunction induced by insulin resistance in rat thoracic aorta. For this purpose, 72 animals were divided into two main sets that received: 1) tap water (control group; n = 12); and 2) fructose 15% w/v in drinking water [insulin resistance group (IR); n = 60] for 20 weeks. After 16 weeks, the group 2 was divided into five subgroups (n = 12 each), which received daily i. p. injections during 4 weeks of: 1) non-treatment (control); 2) vehicle (phosphate buffer saline; PBS, 1 ml/kg); 3) NaHS (5.6 mg/kg); 4) L-Cys (300 mg/kg); and (5) DL-PAG (10 mg/kg). Hemodynamic variables, metabolic variables, vascular function, ROS levels and the expression of p-eNOS and eNOS were determined. IR induced: 1) hyperinsulinemia; 2) increased HOMA-index; 3) decreased Matsuda index; 4) hypertension, vascular dysfunction, increased ROS levels; 5) increased iNOS, and 6) decreased CSE, p-eNOS and eNOS expression. Furthermore, IR did not affect contractile responses to norepinephrine. Interestingly, NaHS and L-Cys treatment, reversed IR-induced impairments and DL-PAG treatment decreased and increased the HOMA and Matsuda index, respectively. Taken together, these results suggest that NaHS and L-Cys decrease the metabolic and vascular alterations induced by insulin resistance by reducing oxidative stress and activating eNOS. Thus, hydrogen sulfide may have a therapeutic application.

Dietary Fat Modulation of Gut Microbiota and Impact on Regulatory Pathways Controlling Food Intake

Obesity is a multifactorial disease that continues to increase in prevalence worldwide. Emerging evidence has shown that the development of obesity may be influenced by taxonomic shifts in gut microbiota in response to the consumption of dietary fats. Further, these alterations in gut microbiota have been shown to promote important changes in satiation signals including gut hormones (leptin, ghrelin, GLP-1, peptide YY and CCK) and orexigenic and anorexigenic neuropeptides (AgRP, NPY, POMC, CART) that influence hyperphagia and therefore obesity. In this review, we highlight mechanisms by which gut microbiota can influence these satiation signals both locally in the gastrointestinal tract and via microbiota-gut-brain communication. Then, we describe the effects of dietary interventions and associated changes in gut microbiota on satiety signals through microbiota-dependent mechanisms. Lastly, we present microbiota optimizing therapies including prebiotics, probiotics, synbiotics and weight loss surgery that can help restore beneficial gut microbiota by enhancing satiety signals to reduce hyperphagia and subsequent obesity. Overall, a better understanding of the mechanisms by which dietary fats induce taxonomical shifts in gut microbiota and their impact on satiation signaling pathways will help develop more targeted therapeutic interventions in delaying the onset of obesity and in furthering its treatment.

Position statement on nutrition therapy for overweight and obesity: nutrition department of the Brazilian association for the study of obesity and metabolic syndrome (ABESO-2022)

Obesity is a chronic disease resulting from multifactorial causes mainly related to lifestyle (sedentary lifestyle, inadequate eating habits) and to other conditions such as genetic, hereditary, psychological, cultural, and ethnic factors. The weight loss process is slow and complex, and involves lifestyle changes with an emphasis on nutritional therapy, physical activity practice, psychological interventions, and pharmacological or surgical treatment. Because the management of obesity is a long-term process, it is essential that the nutritional treatment contributes to the maintenance of the individual's global health. The main diet-related causes associated with excess weight are the high consumption of ultraprocessed foods, which are high in fats, sugars, and have high energy density; increased portion sizes; and low intake of fruits, vegetables, and grains. In addition, some situations negatively interfere with the weight loss process, such as fad diets that involve the belief in superfoods, the use of teas and phytotherapics, or even the avoidance of certain food groups, as has currently been the case for foods that are sources of carbohydrates. Individuals with obesity are often exposed to fad diets and, on a recurring basis, adhere to proposals with promises of quick solutions, which are not supported by the scientific literature. The adoption of a dietary pattern combining foods such as grains, lean meats, low-fat dairy, fruits, and vegetables, associated with an energy deficit, is the nutritional treatment recommended by the main international guidelines. Moreover, an emphasis on behavioral aspects including motivational interviewing and the encouragement for the individual to develop skills will contribute to achieve and maintain a healthy weight. Therefore, this Position Statement was prepared based on the analysis of the main randomized controlled studies and meta-analyses that tested different nutrition interventions for weight loss. Topics in the frontier of knowledge such as gut microbiota, inflammation, and nutritional genomics, as well as the processes involved in weight regain, were included in this document. This Position Statement was prepared by the Nutrition Department of the Brazilian Association for the Study of Obesity and Metabolic Syndrome (ABESO), with the collaboration of dietitians from research and clinical fields with an emphasis on strategies for weight loss.

Glucagon-like peptide-1 receptor differentially controls mossy cell activity across the dentate gyrus longitudinal axis

Understanding the role of dentate gyrus (DG) mossy cells (MCs) in learning and memory has rapidly evolved due to increasingly precise methods for targeting MCs and for in vivo recording and activity manipulation in rodents. These studies have shown MCs are highly active in vivo, strongly remap to contextual manipulation, and that their inhibition or hyperactivation impairs pattern separation and location or context discrimination. Less well understood is how MC activity is modulated by neurohormonal mechanisms, which might differentially control the participation of MCs in cognitive functions during discrete states, such as hunger or satiety. In this study, we demonstrate that glucagon-like peptide-1 (GLP-1), a neuropeptide produced in the gut and the brain that regulates food consumption and hippocampal-dependent mnemonic function, might regulate MC function through expression of its receptor, GLP-1R. RNA-seq demonstrated that most, though not all, Glp1r in hippocampal principal neurons is expressed in MCs, and in situ hybridization revealed strong expression of Glp1r in hilar neurons. Glp1r-ires-Cre mice crossed with Ai14D reporter mice followed by co-labeling for the MC marker GluR2/3 revealed that almost all MCs in the ventral DG expressed Glp1r and that almost all Glp1r-expressing hilar neurons were MCs. However, only ~60% of dorsal DG MCs expressed Glp1r, and Glp1r was also expressed in small hilar neurons that were not MCs. Consistent with this expression pattern, peripheral administration of the GLP-1R agonist exendin-4 (5 μg/kg) increased cFos expression in ventral but not dorsal DG hilar neurons. Finally, whole-cell patch-clamp recordings from ventral MCs showed that bath application of exendin-4 (200 nM) depolarized MCs and increased action potential firing. Taken together, this study adds to known MC activity modulators a neurohormonal mechanism that may preferentially affect ventral DG physiology and may potentially be targetable by several GLP-1R pharmacotherapies already in clinical use.

Neuronal Nitric Oxide Synthase Regulates Depression-like Behaviors in Shortening-Induced Obese Mice

Shortening is mainly derived from the partial hydrogenation of palm oil and widely used in fast food. Food processed with shortening contains high levels of industrial trans fatty acids. Studies have shown that there is a correlation between industrial trans fatty acids, obesity, and depression. However, the regulatory effect of neuronal nitric oxide synthase (nNOS) on depression in obese patients is still unknown. The purpose of this study was to explore mood changes in obese mice fed a high shortening diet, and to determine the regulatory effect of nNOS on depressive-like behaviors in obese mice. We used a high shortening diet-induced obesity mouse model to systematically assess the metabolic response, behavioral changes, prefrontal and hippocampal nNOS protein levels, and the effect of nNOS inhibitors (7-nitroindole) on depression-like behavior in obese mice. Interestingly, obese mice on a 9-week high-shortening diet developed short-term spatial working memory impairment and anxiety-like behavior, and obesity may be a risk factor for cognitive impairment and mood disorders. In animals fed a high shortening diet for 12 weeks, obese mice developed depression-like behavior and had significantly elevated levels of nNOS protein expression in the hippocampus and prefrontal lobe. Administration of the nNOS inhibitor 7-nitroindole could improve depression-like behaviors in obese mice, further suggesting that inhibition of nNOS is helpful for depression associated with obesity.

Cannabinoid 1 and mu-Opioid Receptor Agonists Synergistically Inhibit Abdominal Pain and Lack Side Effects in Mice

While effective in treating abdominal pain, opioids have significant side effects. Recent legalization of cannabis will likely promote use of cannabinoids as an adjunct or alternative to opioids, despite a lack of evidence. We aimed to investigate whether cannabinoids inhibit mouse colonic nociception, alone or in combination with opioids at low doses. Experiments were performed on C57BL/6 male and female mice. Visceral nociception was evaluated by measuring visceromotor responses (VMR), afferent nerve mechanosensitivity in flat-sheet colon preparations, and excitability of isolated DRG neurons. Blood oxygen saturation, locomotion, and defecation were measured to evaluate side effects. An agonist of cannabinoid 1 receptor (CB1R), arachidonyl-2'-chloroethylamide (ACEA), dose-dependently decreased VMR. ACEA and HU-210 (another CB1R agonist) also attenuated colonic afferent nerve mechanosensitivity. Additionally, HU-210 concentration-dependently decreased DRG neuron excitability, which was reversed by the CB1R antagonist AM-251. Conversely, cannabinoid 2 receptor (CB2R) agonists did not attenuate VMR, afferent nerve mechanosensitivity, or DRG neuron excitability. Combination of subanalgesic doses of CB1R and µ-opioid receptor agonists decreased VMR; importantly, this analgesic effect was preserved after 6 d of twice daily treatment. This combination also attenuated afferent nerve mechanosensitivity and DRG neuron excitability, which was inhibited by neuronal nitric oxide synthase and guanylate cyclase inhibitors. This combination avoided side effects (decreased oxygen saturation and colonic transit) caused by analgesic dose of morphine. Activation of CB1R, but not CB2R, decreased colonic nociception both alone and in synergy with µ-opioid receptor. Thus, CB1R agonists may enable opioid dose reduction and avoid opioid-related side effects.SIGNIFICANCE STATEMENT One of the most cited needs for patients with abdominal pain are safe and effective treatment options. The effectiveness of opioids in the management of abdominal pain is undermined by severe adverse side effects. Therefore, strategies to replace opioids or reduce the doses of opioids to suppress abdominal pain is needed. This study in mice demonstrates that cannabinoid 1 receptor (CB1R) agonists inhibit visceral sensation. Furthermore, a combination of subanalgesic doses of µ-opioid receptor agonist and CB1R agonist markedly reduce abdominal pain without causing the side effects of high-dose opioids. Thus, CB1R agonists, alone or in combination with low-dose opioids, may be a novel and safe treatment strategy for abdominal pain.

Mechanisms of reduced leptin-mediated satiety signaling during obesity

BACKGROUND/OBJECTIVES

Disrupted leptin signaling in vagal afferent neurons contributes to hyperphagia and obesity. Thus, we tested the hypothesis that intrinsic negative regulators of leptin signaling, suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) underlie dysfunctional leptin-mediated vagal afferent satiety signaling during obesity.

METHODS

Experiments were performed on standard chow-fed control mice, high-fat fed (HFF), or low-fat fed (LFF) mice. SOCS3 and PTP1B expression were quantified using western blot and quantitative PCR. Nodose ganglion neuronal excitability and jejunal afferent sensitivity were measured by patch clamp and extracellular afferent recordings, respectively.

RESULTS

Increased expression of SOCS3 and PTP1B were observed in the jejunum of HFF mice. Prolonged incubation with leptin attenuated nodose ganglion neuronal excitability, and this effect was reversed by inhibition of SOCS3. Leptin potentiated jejunal afferent nerve responses to CCK in LFF mice but decreased them in HFF mice. Inhibition of SOCS3 restored impaired vagal afferent neuronal excitability and afferent nerve responses to satiety mediators during obesity. Two-pore domain K⁺ channel (K_2P) conductance and nitric oxide (NO) production that we previously demonstrated were elevated during obesity were decreased by inhibitions of SOCS3 or PTP1B.

CONCLUSIONS

This study suggests that obesity impairs vagal afferent sensitivity via SOCS3 and PTP1B, likely as a consequence of obesity-induced hyperleptinemia. The mechanisms underlying leptin resistance appear also to cause a more global impairment of satiety-related vagal afferent responsiveness.

Effect of high-fat diet on mechanosensitive transient receptor potential channel activation in vagal afferent neurons

Mechanical stimulation of the gastrointestinal tract is an important stimulus of satiety and can be transduced by transient receptor potential (TRP) channels. Several studies have revealed attenuated vagally-mediated satiety responses including mechanosensitivity in diet-induced obesity; however, ion channels underlying this hyposensitivity have not been fully understood. This study aimed to examine the effect of chronic high-fat diet on activation of selected mechanosensitive TRP channels in vagal afferents. C57/BL6 mice were fed on either a high-fat or low-fat diet for 6-8 weeks. An increase in the intracellular calcium to hypotonic solution and activators of TRPV1, TRPV4, and TRPA1 was measured in nodose neurons using Ca2+-imaging techniques. Jejunal afferent nerve firing induced by mechanical stimulation and TRP channel agonists was measured using in vitro extracellular multiunit afferent recording. In high-fat diet-fed mice, we observed reduced calcium influx and jejunal afferent response induced by mechanical stimuli and agonists of TRPV4 and TRPA1, but not TRPV1. Our data show diet-induced obesity disrupts the activation of TRPV4 and TRPA1, at both the cellular level and the level of nerve terminals in the small intestine, which may partly explain reduced mechanosensitivity of vagal afferents and may contribute to decreased gut-brain satiety signaling in obesity.

Human Nitric Oxide Synthase-Its Functions, Polymorphisms, and Inhibitors in the Context of Inflammation, Diabetes and Cardiovascular Diseases

In various diseases, there is an increased production of the free radicals needed to carry out certain physiological processes but their excessive amounts can cause oxidative stress and cell damage. Enzymes play a major role in the transformations associated with free radicals. One of them is nitric oxide synthase (NOS), which catalyzes the formation of nitric oxide (NO). This enzyme exists in three forms (NOS1, NOS2, NOS3), each encoded by a different gene. The following work presents the most important information on the NOS isoforms and their role in the human body, including NO synthesis in various tissues and cells, intercellular signaling and activities supporting the immune system and regulating blood vessel functions. The role of NOS in pathological conditions such as obesity, diabetes and heart disease is considered. Attention is also paid to the influence of the polymorphisms of these genes, encoding particular isoforms, on the development of these pathologies and the role of NOS inhibitors in the treatment of patients.

Placental Adaptive Changes to Protect Function and Decrease Oxidative Damage in Metabolically Healthy Maternal Obesity

Pregnancy-related disorders, including preeclampsia and gestational diabetes, are characterized by the presence of an adverse intrauterine milieu that may ultimately result in oxidative and nitrosative stress. This scenario may trigger uncontrolled production of reactive oxygen species (ROS) such as superoxide anion (O^●−) and reactive nitrogen species (RNS) such as nitric oxide (NO), along with an inactivation of antioxidant systems, which are associated with the occurrence of relevant changes in placental function through recognized redox post-translational modifications in key proteins. The general objective of this study was to assess the impact of a maternal obesogenic enviroment on the regulation of the placental nitroso-redox balance at the end of pregnancy. We measured oxidative damage markers—thiobarbituric acid-reacting substances (TBARS) and carbonyl groups (C=O) levels; nitrosative stress markers—inducible nitric oxide synthase, nitrosothiol groups, and nitrotyrosine residues levels; and the antioxidant biomarkers—catalase and superoxide dismutase (SOD) activity and expression, and total antioxidant capacity (TAC), in full-term placental villous from both pre-pregnancy normal weight and obese women, and with absence of metabolic complications throughout gestation. The results showed a decrease in C=O and TBARS levels in obese pregnancies. Although total SOD and catalase concentrations were shown to be increased, both activities were significantly downregulated in obese pregnancies, along with total antioxidant capacity. Inducible nitric oxide sintase levels were increased in the obese group compared to the lean group, accompanied by an increase in nitrotyrosine residues levels and lower levels of nitrosothiol groups in proteins such as ERK1/2. These findings reveal a reduction in oxidative damage, accompanied by a decline in antioxidant response, and an increase via NO-mediated nitrative stress in placental tissue from metabolically healthy pregnancies with obesity. All this plausibly points to a placental adaptation of the affected antioxidant response towards a NO-induced alternative pathway, through changes in the ROS/RNS balance, in order to reduce oxidative damage and preserve placental function in pregnancy.

The obesity epidemic in the face of homeostatic body weight regulation: What went wrong and how can it be fixed?

Ever since the pioneering discoveries in the mid nineteen hundreds, the hypothalamus was recognized as a crucial component of the neural system controlling appetite and energy balance. The new wave of neuron-specific research tools has confirmed this key role of the hypothalamus and has delineated many other brain areas to be part of an expanded neural system sub serving these crucial functions. However, despite significant progress in defining this complex neural circuitry, many questions remain. One of the key questions is why the sophisticated body weight regulatory system is unable to prevent the rampant obesity epidemic we are experiencing. Why are pathologically obese body weight levels defended, and what can we do about it? Here we try to find answers to these questions by 1) reminding the reader that the neural controls of ingestive behavior have evolved in a demanding, restrictive environment and encompass much of the brain's major functions, far beyond the hypothalamus and brainstem, 2) hypothesizing that the current obesogenic environment impinges mainly on a critical pathway linking hypothalamic areas with the motivational and reward systems to produce uncompensated hyperphagia, and 3) proposing adequate strategies for prevention and treatment.

Effects of different diets used in diet-induced obesity models on insulin resistance and vascular dysfunction in C57BL/6 mice

The aim of the present study was to compare different diets used to induce obesity in a head-to-head manner with a focus on insulin resistance and vascular dysfunction. Male C57BL/6J mice were put on standard chow diet (SCD), normal-fat diet (NFD), cafeteria diet (CAF) or high-fat diet (HFD) for 12 weeks starting at the age of 6 weeks. Both CAF and HFD led to obesity (weight gain of 179% and 194%, respectively), glucose intolerance and insulin resistance to a comparable extent. In aortas containing perivascular adipose tissue (PVAT), acetylcholine-induced vasodilation was best in the NFD group and worst in the CAF group. Reduced phosphorylation of endothelial nitric oxide synthase at serine 1177 was observed in both CAF and HFD groups. Plasma coagulation activity was highest in the HFD group and lowest in the SCD group. Even the NFD group had significantly higher coagulation activity than the SCD group. In conclusions, CAF and HFD are both reliable mouse diets in inducing visceral obesity, glucose intolerance and insulin resistance. CAF is more effective than HFD in causing PVAT dysfunction and vascular dysfunction, whereas hypercoagulability was mostly evident in the HFD group. Coagulation activity was higher in NFD than NCD group.

Gastric vagal afferent neuropathy following experimental spinal cord injury

Dramatic impairment of gastrointestinal (GI) function accompanies high-thoracic spinal cord injury (T3-SCI). The vagus nerve contains mechano- and chemosensory fibers as well as the motor fibers necessary for the central nervous system (CNS) control of GI reflexes. Cell bodies for the vagal afferent fibers are located within the nodose gangla (NG) and the majority of vagal afferent axons are unmyelinated C fibers that are sensitive to capsaicin through activation of transient receptor potential vanilloid-1 (TRPV1) channels. Vagal afferent fibers also express receptors for GI hormones, including cholecystokinin (CCK). Previously, T3-SCI provokes a transient GI inflammatory response as well as a reduction of both gastric emptying and centrally-mediated vagal responses to GI peptides, including CCK. TRPV1 channels and CCK-A receptors (CCKar) expressed in vagal afferents are upregulated in models of visceral inflammation. The present study investigated whether T3-SCI attenuates peripheral vagal afferent sensitivity through plasticity of TRPV1 and CCK receptors. Vagal afferent response to graded mechanical stimulation of the stomach was significantly attenuated by T3-SCI at 3-day and 3-week recovery. Immunocytochemical labeling for CCKar and TRPV1 demonstrated expression on dissociated gastric-projecting NG neurons. Quantitative assessment of mRNA expression by qRT-PCR revealed significant elevation of CCKar and TRPV1 in the whole NG following T3-SCI in 3-day recovery, but levels returned to normal after 3-weeks. Three days after injury, systemic administration of CCK-8 s showed a significantly diminished gastric vagal afferent response in T3-SCI rats compared to control rats while systemic capsaicin infusion revealed a significant elevation of vagal response in T3-SCI vs control rats. These findings demonstrate that T3-SCI provokes peripheral remodeling and prolonged alterations in the response of vagal afferent fibers to the physiological signals associated with digestion.

Deoxycholic acid activates colonic afferent nerves via 5-HT3 receptor-dependent and -independent mechanisms

Increased bile acids in the colon can evoke increased epithelial secretion resulting in diarrhea, but little is known about whether colonic bile acids contribute to abdominal pain. This study aimed to investigate the mechanisms underlying activation of colonic extrinsic afferent nerves and their neuronal cell bodies by a major secondary bile acid, deoxycholic acid (DCA). All experiments were performed on male C57BL/6 mice. Afferent sensitivity was evaluated using in vitro extracellular recordings from mesenteric nerves in the proximal colon (innervated by vagal and spinal afferents) and distal colon (spinal afferents only). Neuronal excitability of cultured dorsal root ganglion (DRG) and nodose ganglion (NG) neurons was examined with perforated patch clamp. Colonic 5-HT release was assessed using ELISA, and 5-HT immunoreactive enterochromaffin (EC) cells were quantified. Intraluminal DCA increased afferent nerve firing rate concentration dependently in both proximal and distal colon. This DCA-elicited increase was significantly inhibited by a 5-HT₃ antagonist in the proximal colon but not in the distal colon, which may be in part due to lower 5-HT immunoreactive EC cell density and lower 5-HT levels in the distal colon following DCA stimulation. DCA increased the excitability of DRG neurons, whereas it decreased the excitability of NG neurons. DCA potentiated mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. Together, this study suggests that DCA can excite colonic afferents via direct and indirect mechanisms but the predominant mechanism may differ between vagal and spinal afferents. Furthermore, DCA increased mechanosensitivity of high-threshold spinal afferents and may be a mechanism of visceral hypersensitivity.NEW & NOTEWORTHY Deoxycholic acid (DCA) directly excites spinal afferents and, to a lesser extent, indirectly via mucosal 5-HT release. DCA potentiates mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. DCA increases vagal afferent firing in proximal colon via 5-HT release but directly inhibits the excitability of their cell bodies.