Subdiaphragmatic Vagal Research Articles

Brain Endothelial Cells Regulate Glucagon-Like Peptide 1 Entry Into the Brain via a Receptor-Mediated Process.

Glucagon-like peptide 1 (GLP-1) in addition to regulating glucose-dependent insulin and glucagon secretion exerts anorexic and neuroprotective effects. While brain-derived GLP-1 may participate in these central actions, evidence suggests that peripherally derived GLP-1 plays an important role and GLP-1 analogs are known to cross the blood brain barrier. To define the role of brain microvascular endothelial cells in GLP-1 entry into the brain, we infused labeled GLP-1 or exendin-4 into rats intravenously and examined their appearance and protein kinase A activities in various brain regions. We also studied the role of endothelial cell GLP-1 receptor and its signaling in endothelial cell uptake and transport of GLP-1. Systemically infused labeled GLP-1 or exendin-4 appeared rapidly in various brain regions and this was associated with increased protein kinase A activity in these brain regions. Pretreatment with GLP-1 receptor antagonist reduced labeled GLP-1 or exendin-4 enrichment in the brain. Sub-diaphragmatic vagus nerve resection did not alter GLP-1-mediated increases in protein kinase A activity in the brain. Rat brain microvascular endothelial cells rapidly took up labeled GLP-1 and this was blunted by either GLP-1 receptor antagonism or protein kinase A inhibition but enhanced through adenylyl cyclase activation. Using an artificially assembled blood brain barrier consisting of endothelial and astrocyte layers, we found that labeled GLP-1 time-dependently crossed the barrier and the presence of GLP-1 receptor antagonist blunted this transit. We conclude that GLP-1 crosses the blood brain barrier through active trans-endothelial transport which requires GLP-1 receptor binding and activation.

SPARC: Biophysical Modeling of Vagus Nerve Stimulation for Translational Scaling of Stimulation Parameters Across Species

Vagus nerve stimulation (VNS) is used clinically to treat epilepsy, depression, and obesity, and is under investigation for other applications. In many cases, the stimulation parameters used in preclinical VNS studies did not translate to successful clinical outcomes. We propose that differences in nerve morphology across preclinical models (e.g., rats and pigs) and humans, as well as variance within those populations, contribute to variance in therapeutic response due to variable levels of neural activation or block. Therefore, we quantified vagal morphology across species and simulated excitation and block thresholds using computational models.We quantified the morphology of the cervical and subdiaphragmatic vagus nerves (VN) in rats, pigs, and humans. The human and pig VNs had similar effective diameters (~3.7 mm at the cervical level and ~2.4 mm at the subdiaphragmatic level), although the pig nerves had almost 10x more fascicles (~41 fascicles for pig VN vs. ~5.8 fascicles for human VN). Conversely, the rat nerves were ~10x smaller (0.265 mm diameter at the cervical level and 0.147 mm at the subdiaphragmatic level) and had only one or a couple of fascicles. For our rat samples, the ratio of perineurium thickness to fascicle diameter corresponded well to the previous estimate of 3% of the fascicle diameter (Grinberg et al., 2008). Conversely, for our human samples, the perineurium was substantially thicker (~8.0% and ~21% at the cervical and subdiaphragmatic levels, respectively), and the ratio of perineurium thickness to fascicle diameter decreased with increased fascicle diameter.We designed and implemented a computational pipeline to construct volume conductor finite element models (FEMs) in COMSOL for multiple vagus nerve samples from each species, instrumented with a cuff electrode as used preclinically or clinically. We coupled the FEMs to models of mammalian myelinated and unmyelinated fibers in NEURON to quantify excitation and block thresholds. The intensity of VNS stimulation required to achieve activation of 50% of the 5.7 to 10 μm model myelinated fibers in human models were ~5–10x greater than in rat nerve samples, and intensities to activate 0.8 μm model unmyelinated fibers were ~20x greater. Further, thresholds of excitation and block varied across individuals within a species and were governed by species‐ and individual‐specific factors such as fascicle diameter and fascicle organization within the nerve. Human and pig cervical models show comparable within‐species variability (the highest thresholds to activate 50% of model nerve fibers were ~2x larger than the lowest) and greater variability than across the rat cervical models (the highest thresholds to activate 50% of model nerve fibers were ~1.25x larger than lowest).Morphologically‐based computational models of the cervical and subdiaphragmatic VN in rats, pigs, and humans indicate that cross‐ and within‐species differences in nerve morphology are important considerations for understanding differences in VNS responses between individuals and that substantial translation scaling of stimulation intensity is required to achieve comparable responses in different species.Support or Funding InformationFunding: This work was supported by the NIH SPARC Program (OT2‐OD025340).

Dexmedetomidine alleviates sleep-restriction-mediated exaggeration of postoperative immunosuppression via splenic TFF2 in aged mice

Major abdominal procedures could induce dysfunction in the immune system and lead to postoperative immunosuppression. Sleep dysfunction is associated with impaired immune activity. However, the effects of postoperative sleep dysfunction on postoperative immune function remain unclear. In this study, we found that sleep-restriction (SR) after surgery increased the spleen weight and the percentage of myeloid-derived suppressor cells (MDSCs) in the spleen, and inhibited splenic CD8+ T cells activity, which was via inhibiting subdiaphragmatic vagus nerve (SVN)-mediated trefoil factor 2 (TFF2) expression in the spleen of aged mice. Dexmedetomidine could alleviate SR-induced these changes via modulating gut microbiota, which acted through SVN. Moreover, we showed essential roles of splenic TFF2 in attenuating SR-induced reduced protective ability against Escherichia coli (E. coli) pneumonia, increased expression of IL-4 and IL-13 in the lung and M2 polarization of alveolar macrophages (AMs), and decreased phagocytic activity of AMs. Dexmedetomidine improved SR-induced reduced protective ability against E. coli pneumonia via splenic TFF2, and subsequently decreasing IL-4 and IL-13 expression in the lung via modulating gut microbiota/SVN, increasing the compromised phagocytic activity of AMs, and ultimately decreasing M2 polarization of AMs. Taken together, dexmedetomidine-induced increase in splenic TFF2 expresssion could alleviate SR-induced exaggeration of postoperative immunosuppression.

Vagal Nerve Stimulation for Glycemic Control in a Rodent Model of Type 2 Diabetes.

Vagal nerve stimulation (VNS) has been reported to reduce body weight and improve sympathovagal imbalance in both basic and clinical studies. Its effects on glycemic control were however unclear. The aims of this study were to investigate the effects of VNS with various parameters on blood glucose and its possible mechanisms in rats. A hyperglycemic rodent model induced by glucagon was used initially to optimize the VNS parameters; then, a type 2 diabetic rodent model induced by high-fat diet combined with streptozotocin was used to validate the VNS method. The VNS electrodes were implanted at the dorsal subdiaphragmatic vagus; three subcutaneous electrodes were implanted at the chest area for recording electrocardiogram in rats induced by glucagon. (1) VNS with short pulse width of 0.3ms but not 3ms reduced blood glucose during an oral glucose tolerance test (OGTT), with a 38.4% reduction at 15min and 26.9% at 30min (P < 0.05, vs. sham-VNS respectively). (2) VNS at low frequency of 5Hz but not 14Hz or 40Hz reduced blood glucose during the OGTT (P < 0.05, vs. sham-VNS). (3) Intermittent VNS was more potent than continuous VNS (P < 0.01). (4) No difference was found between unilateral VNS and bilateral VNS. (5) VNS enhanced vagal activity (P = 0.005). (6) The hypoglycemic effect of VNS was blocked by glucagon-like peptide-1 (GLP-1) antagonist exendin-4. VNS at 5Hz reduces blood glucose in diabetic rats by enhancing vagal efferent activity and the release of GLP-1.

Abdominal vagal deafferentation alters affective behaviors in rats

BackgroundThere is growing evidence for a role of abnormal gut-brain signaling in disorders involving altered mood and affect, including depression. Studies using vagus nerve stimulation (VNS) suggest that the disruption of vagal afferent signaling may contribute to these abnormalities. To test this hypothesis, we used a rat model of subdiaphragmatic vagal deafferentation (SDA), the most complete and selective vagal deafferentation method existing to date, to study the consequences of complete disconnection of abdominal vagal afferents on affective behaviors. MethodsSDA- and Sham-operated male rats were subjected to several tests that are commonly used in preclinical rodent models to assess the presence of anhedonic behavior, namely the novel object-induced exploration test, the novelty-suppressed eating test, and the sucrose preference test. In addition, we compared SDA and Sham rats in a social interaction test and the forced swim test to assess sociability and behavioral despair, respectively. ResultsCompared to Sham controls, SDA rats consistently displayed signs of anhedonic behavior in all test settings used. SDA rats also showed increased immobility and reduced swimming in the forced swim test, whereas they did not differ from Sham controls with regards to social approach behavior. LimitationsThis study was conducted in male rats only. Hence, possible sex-specific effects of SDA on affective behaviors remained unexamined. ConclusionsOur findings demonstrate that hedonic behavior and behavioral despair are subject to visceral modulation through abdominal vagal afferents. These data are compatible with preclinical models and clinical trials showing beneficial effects of VNS on depression-like and affective behaviors.

Exercise activates vagal induction of dopamine and attenuates systemic inflammation

Physical exercise is one of the most important factors improving quality of life, but it is not feasible for patients with morbidity or limited mobility. Most previous studies focused on high-intensity or long-term exercise that causes metabolic stress or physiological adaption, respectively. Here, we studied how moderate-intensity swimming affects systemic inflammation in 6–8 week old C57BL/6J male mice during endotoxemia. One-hour swimming prevented hypokalemia, hypocalcemia, attenuated serum levels of inflammatory cytokines, increased anti-inflammatory cytokines but affected neither IL6 nor glycemia before or after the endotoxic challenge. Exercise attenuated serum TNF levels by inhibiting its production in the spleen through a mechanism mediated by the subdiaphragmatic vagus nerve but independent of the splenic nerve. Exercise increased serum levels of dopamine, and adrenalectomy prevented the potential of exercise to induce dopamine and to attenuate serum TNF levels. Dopaminergic agonist type-1, fenoldopam, inhibited TNF production in splenocytes. Conversely, dopaminergic antagonist type-1, butaclamol, attenuated exercise control of serum TNF levels. These results suggest that vagal induction of dopamine may contribute to the anti-inflammatory potential of physical exercise.

Oleoylethanolamide-induced anorexia in rats is associated with locomotor impairment.

The endogenous peroxisome proliferator‐activated receptor alpha (PPAR‐α) agonist Oleoylethanolamide (OEA) inhibits eating in rodents, mainly by delaying the onset of meals. The underlying mechanisms of OEA‐induced anorexia, however, remain unclear. Animals treated with high OEA doses were shown to display signs of discomfort and impaired locomotion. Therefore, we first examined whether the impaired locomotion may contribute to OEA's anorectic effect. Second, it is controversial whether abdominal vagal afferents are necessary for OEA's anorectic effect. Thus, we explored alternative peripheral neural pathways mediating IP OEA's anorectic effect by performing a celiac‐superior mesenteric ganglionectomy (CGX) or a subdiaphragmatic vagal deafferentation (SDA) alone or in combination. Exogenously administered OEA at a commonly used dose (10 mg/kg BW, IP) concurrently reduced food intake and compromised locomotor activity. Attempts to dissociate both phenomena using the dopamine D2/D3 receptor agonist Quinpirole (1 mg/kg BW, SC) failed because Quinpirole antagonized both, OEA‐induced locomotor impairment and delay in eating onset. CGX attenuated the prolongation of the latency to eat by IP OEA, but neither SDA nor CGX prevented IP OEA‐induced locomotor impairment. Our results indicate that IP OEA's anorectic effect may be secondary to impaired locomotion rather than due to physiological satiety. They further confirm that vagal afferents do not mediate exogenous OEA's anorectic effects, but suggest a role for spinal afferents in addition to an alternative, nonneuronal signaling route.

Abdominal Vagal Afferents Modulate the Brain Transcriptome and Behaviors Relevant to Schizophrenia.

Reduced activity of vagal efferents has long been implicated in schizophrenia and appears to be responsible for diminished parasympathetic activity and associated peripheral symptoms such as low heart rate variability and cardiovascular complications in affected individuals. In contrast, only little attention has been paid to the possibility that impaired afferent vagal signaling may be relevant for the disorder's pathophysiology as well. The present study explored this hypothesis using a model of subdiaphragmatic vagal deafferentation (SDA) in male rats. SDA represents the most complete and selective vagal deafferentation method existing to date as it leads to complete disconnection of all abdominal vagal afferents while sparing half of the abdominal vagal efferents. Using next-generation mRNA sequencing, we show that SDA leads to brain transcriptional changes in functional networks annotating with schizophrenia. We further demonstrate that SDA induces a hyperdopaminergic state, which manifests itself as increased sensitivity to acute amphetamine treatment and elevated accumbal levels of dopamine and its major metabolite, 3,4-dihydroxyphenylacetic acid. Our study also shows that SDA impairs sensorimotor gating and the attentional control of associative learning, which were assessed using the paradigms of prepulse inhibition and latent inhibition, respectively. These data provide converging evidence suggesting that the brain transcriptome, dopamine neurochemistry, and behavioral functions implicated in schizophrenia are subject to visceral modulation through abdominal vagal afferents. Our findings may encourage the further establishment and use of therapies for schizophrenia that are based on vagal interventions.SIGNIFICANCE STATEMENT The present work provides a better understanding of how disrupted vagal afferent signaling can contribute to schizophrenia-related brain and behavioral abnormalities. More specifically, it shows that subdiaphragmatic vagal deafferentation (SDA) in rats leads to (1) brain transcriptional changes in functional networks related to schizophrenia, (2) increased sensitivity to dopamine-stimulating drugs and elevated dopamine levels in the nucleus accumbens, and (3) impairments in sensorimotor gating and the attentional control of associative learning. These findings may encourage the further establishment of novel therapies for schizophrenia that are based on vagal interventions.

Extracellular pH monitoring for use in closed-loop vagus nerve stimulation

Objective. Vagal nerve stimulation (VNS) has shown potential benefits for obesity treatment; however, current devices lack physiological feedback, which limit their efficacy. Changes in extracellular pH (pHe) have shown to be correlated with neural activity, but have traditionally been measured with glass microelectrodes, which limit their in vivo applicability. Approach. Iridium oxide has previously been shown to be sensitive to fluctuations in pH and is biocompatible. Iridium oxide microelectrodes were inserted into the subdiaphragmatic vagus nerve of anaesthetised rats. Introduction of the gut hormone cholecystokinin (CCK) or distension of the stomach was used to elicit vagal nerve activity. Main results. Iridium oxide microelectrodes have sufficient pH sensitivity to readily detect changes in pHe associated with both CCK and gastric distension. Furthermore, a custom-made Matlab script was able to use these changes in pHe to automatically trigger an implanted VNS device. Significance. This is the first study to show pHe changes in peripheral nerves in vivo. In addition, the demonstration that iridium oxide microelectrodes are sufficiently pH sensitive as to measure changes in pHe associated with physiological stimuli means they have the potential to be integrated into closed-loop neurostimulating devices.

GLP-1 Elicits an Intrinsic Gut–Liver Metabolic Signal to Ameliorate Diet-Induced VLDL Overproduction and Insulin Resistance

Perturbations in hepatic lipid and very-low-density lipoprotein (VLDL) metabolism are involved in the pathogenesis of obesity and hepatic insulin resistance. The objective of this study is to delineate the mechanism of subdiaphragmatic vagotomy in preventing obesity, hyperlipidemia, and insulin resistance. By subjecting the complete subdiaphragmatic vagotomized mice to various nutritional conditions and investigating hepatic de novo lipogenesis pathway, we found that complete disruption of subdiaphragmatic vagal signaling resulted in a significant decrease of circulating VLDL-triglyceride compared with the mice obtained sham procedure. Vagotomy further prevented overproduction of VLDL-triglyceride induced by an acute fat load and a high-fat diet-induced obesity, hyperlipidemia, hepatic steatosis, and glucose intolerance. Mechanistic studies revealed that plasma glucagon-like peptide-1 was significantly raised in the vagotomized mice, which was associated with significant reductions in mRNA and protein expression of SREBP-1c (sterol regulatory element-binding protein 1c), SCD-1 (stearoyl-CoA desaturase-1), and FASN (fatty acid synthase), as well as enhanced hepatic insulin sensitivity. In vitro, treating mouse primary hepatocytes with a glucagon-like peptide-1 receptor agonist, exendin-4, for 48 hours inhibited free fatty acid, palmitic acid treatment induced de novo lipid synthesis, and VLDL secretion from hepatocytes. Elevation of glucagon-like peptide-1 in vagotomized mice may prevent VLDL overproduction and insulin resistance induced by high-fat diet. These novel findings, for the first time, delineate an intrinsic gut-liver regulatory circuit that is mediated by glucagon-like peptide-1 in regulating hepatic energy metabolism.

Cognitive effects of subdiaphragmatic vagal deafferentation in rats

Vagal afferents are a crucial neuronal component of the gut-brain axis and mediate the information flow from the viscera to the central nervous system. Based on the findings provided by experiments involving vagus nerve stimulation, it has been suggested that vagal afferent signaling may influence various cognitive functions such as recognition memory and cognitive flexibility. Here, we examined this hypothesis using a rat model of subdiaphragmatic vagal deafferentation (SDA), the most complete and selective abdominal vagal deafferentation method existing to date. We found that SDA did not affect working memory in a nonspatial alternation task, nor did it influence short-, intermediate-, and long-term object recognition memory. SDA did also not affect the acquisition of positively reinforced left-right discrimination learning, but it facilitated the subsequent reversal left-right discrimination learning. The SDA-induced effects on reversal learning emerged in the absence of concomitant changes in motivation towards the positive reinforcer, indicating selective effects on cognitive flexibility. Taken together, these findings suggest that the relative contribution of vagal afferent signaling to cognitive functions is limited. At the same time, our study demonstrates that cognitive flexibility, at least in the domains of positively reinforced learning, is subjected to visceral modulation through abdominal vagal afferents.

Anorexia-cachexia syndrome in hepatoma tumour-bearing rats requires the area postrema but not vagal afferents and is paralleled by increased MIC-1/GDF15.

BackgroundThe cancer‐anorexia‐cachexia syndrome (CACS) negatively affects survival and therapy success in cancer patients. Inflammatory mediators and tumour‐derived factors are thought to play an important role in the aetiology of CACS. However, the central and peripheral mechanisms contributing to CACS are insufficiently understood. The area postrema (AP) and the nucleus tractus solitarii are two important brainstem centres for the control of eating during acute sickness conditions. Recently, the tumour‐derived macrophage inhibitory cytokine‐1 (MIC‐1) emerged as a possible mediator of cancer anorexia because lesions of these brainstem areas attenuated the anorectic effect of exogenous MIC‐1 in mice.MethodsUsing a rat hepatoma tumour model, we examined the roles of the AP and of vagal afferents in the mediation of CACS. Specifically, we investigated whether a lesion of the AP (APX) or subdiaphragmatic vagal deafferentation (SDA) attenuate anorexia, body weight, muscle, and fat loss. Moreover, we analysed MIC‐1 levels in this tumour model and their correlation with tumour size and the severity of the anorectic response.ResultsIn tumour‐bearing sham‐operated animals mean daily food intake significantly decreased. The anorectic response was paralleled by a significant loss of body weight and muscle mass. APX rats were protected against anorexia, body weight loss, and muscle atrophy after tumour induction. In contrast, subdiaphragmatic vagal deafferentation did not attenuate cancer‐induced anorexia or body weight loss. Tumour‐bearing rats had substantially increased MIC‐1 levels, which positively correlated with tumour size and cancer progression and negatively correlated with food intake.ConclusionsThese findings demonstrate the importance of the AP in the mediation of cancer‐dependent anorexia and body weight loss and support a pathological role of MIC‐1 as a tumour‐derived factor mediating CACS, possibly via an AP‐dependent action.

Gut–brain nutrient sensing in food reward

For the past several decades, vagal and hormonal gut–brain negative feedback signaling mechanisms that promote satiety and subsequent suppression of food intake have been explored. In addition, a separate positive feedback process termed “appetition,” involving postoral signaling from the gut to the brain, has been shown to promote food intake and produce flavor–nutrient preference conditioning. Afferent fibers emerging from the vagus nerve form the main pathway by which information is relayed from the abdominal viscera to the hindbrain and eventually other higher brain regions involved in food intake. Using a specialized subdiaphragmatic vagal deafferentation technique, it was observed that gut vagal and splanchnic afferents play a role in the negative feedback control of satiety after nutrient intake; however, these afferents are not required for nutrient reinforcement or flavor–nutrient preference conditioning, thereby highlighting the distinction between the processes of satiation and appetition. By linking these physiological and behavioral processes to a neurochemical mechanism, it was found that striatal dopamine release induced by intragastric glucose infusion is involved in sweet appetite conditioning. The mechanisms underlying appetition are still being investigated but may involve other nondopaminergic neurochemical systems and/or presently undiscovered hormonal mediators. Future work to delineate the biological mechanisms whereby appetition drives increased intake and conditioned food preference in response to ingestion should take a multifaceted approach by integrating hormonal, neurophysiological, and behavioral techniques.

Su1554 Effects and Mechanisms of the Subdiaphragmatic Vagus Nerve Stimulation on the Postoperative Ileus in a Rodent Model

Su1554 Effects and Mechanisms of the Subdiaphragmatic Vagus Nerve Stimulation on the Postoperative Ileus in a Rodent Model

L-arginine promotes gut hormone release and reduces food intake in rodents.

AimsTo investigate the anorectic effect of L‐arginine (L‐Arg) in rodents.MethodsWe investigated the effects of L‐Arg on food intake, and the role of the anorectic gut hormones glucagon‐like peptide‐1 (GLP‐1) and peptide YY (PYY), the G‐protein‐coupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents.ResultsOral gavage of L‐Arg reduced food intake in rodents, and chronically reduced cumulative food intake in diet‐induced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. L‐Arg stimulated GLP‐1 and PYY release in vitro and in vivo. Pharmacological blockade of GLP‐1 and PYY receptors did not influence the anorectic effect of L‐Arg. L‐Arg‐mediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of L‐Arg suppressed food intake in rats.Conclusions L‐Arg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of L‐Arg is unlikely to be mediated by GLP‐1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of L‐Arg suppressed food intake in rats, suggesting that L‐Arg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which L‐Arg suppresses food intake and its utility in the treatment of obesity.

Gut vagal afferents are necessary for the eating-suppressive effect of intraperitoneally administered ginsenoside Rb1 in rats

Ginsenoside Rb1 (Rb1) reduces food intake in both lean and high-fat diet induced-obese rats; however, the sites and/or mediation of the eating-suppressive effect of Rb1 have not previously been identified. We hypothesized that intraperitoneally (ip) administered Rb1 exerts its anorectic action by enhancing sensitivity to satiation signals, such as cholecystokinin (CCK), and/or that it acts through vagal afferent nerves that relay the satiating signaling to the hindbrain. To test these hypotheses, we gave ip bolus doses of Rb1 (2.5–10.0mg/kg) and CCK-8 (0.125–4.0μg/kg) alone or in combination and assessed food intake in rats. Low doses of Rb1 (2.5mg/kg) or CCK-8 (0.125μg/kg) alone had no effect on food intake whereas higher doses did. When these subthreshold doses of Rb1 and CCK-8 were co-administered, the combination significantly reduced food intake relative to saline controls, and this effect was attenuated by lorglumide, a selective CCK1-receptor antagonist. Interestingly, lorglumide blocked food intake induced by an effective dose of CCK-8 alone, but not by Rb1 alone, suggesting that Rb1's anorectic effect is independent of the CCK1 receptor. To determine whether peripherally administered Rb1 suppresses feeding via abdominal vagal nerves, we evaluated the effect of ip Rb1 injection in subdiaphragmatic vagal deafferentation (SDA) and control rats. Rb1's effect on food intake was significantly attenuated in SDA rats, compared with that in SHAM controls. These data indicate that the vagal afferent system is the major pathway conveying peripherally administered Rb1's satiation signal.

Subdiaphragmatic vagus nerve activity and hepatic venous glucose are differentially regulated by the central actions of insulin in Wistar and SHR.

Glucose is the most important energy substrate for the maintenance of tissues function. The liver plays an essential role in the control of glucose production, since it is able to synthesize, store, and release glucose into the circulation under different situations. Hormones like insulin and catecholamines influence hepatic glucose production (HGP), but little is known about the role of the central actions of physiological doses of insulin in modulating HGP via the autonomic nervous system in nonanesthetized rats especially in SHR where we see a high degree of insulin resistance and metabolic dysfunction. Wistar and SHR received ICV injection of insulin (100 nU/μL) and hepatic venous glucose concentration (HVGC) was monitored for 30 min, as an indirect measure of HGP. At 10 min after insulin injection, HVGC decreased by 27% in Wistar rats, with a negligible change (3%) in SHR. Pretreatment with atropine totally blocked the reduction in HVGC, while pretreatment with propranolol and phentolamine induced a decrease of 8% in HVGC after ICV insulin injection in Wistar. Intracarotid infusion of insulin caused a significant increase in subdiaphragmatic vagus nerve (SVN) activity in Wistar (12 ± 2%), with negligible effects on the lumbar splanchnic sympathetic nerve (LSSN) activity (−6 ± 3%). No change was observed in SVN (−2 ± 2%) and LSSN activities (2 ± 3%) in SHR after ICA insulin infusion. Taken together, these results show, in nonanesthetized animals, the importance of the parasympathetic nervous system in controlling HVGC, and subdiaphragmatic nerve activity following central administration of insulin; a mechanism that is impaired in the SHR.

Central action of Insulin on the Modulation of Autonomic Balance to Control Hepatic Glucose of Wistar and SHR: Any Interaction Between Hypothalamic Paraventricular Nucleus and Dorsal Vagal Complex?

Insulin is an important to control of glucose level, but little is known about its action on modulation of autonomic nervous system (ANS) to control of glicemia, especially in hypertension. Here, Wistar and SHR had ICV injection of insulin (100 nU/µL) and hepatic glucose (HG) decreased by 27% in Wistar, with no change (3%) in SHR. Pretreatment with atropine blocked the fall in the HG, while propranolol + phentolamine attenuated the decreasing (8%) in HG after insulin ICV in Wistar rats. An intracarotid infusion of insulin was able to increase the subdiaphragmatic vagus nerve (SVN) activity in Wistar (12±2%) with no changes in the lumbar splanchnic sympathetic nerve (LSSN) activity (-6±3%). No change was observed in SVN and LSSN (-2±2% and 2±3%, respectively) in SHR. Wistar rats were subjected to injection of Fluorogold (FG) in the DMV, and 10 days after received insulin for analysis of FOS expression. An increase in the Fos labeled cells was found in the PVN of insulin treated rats compared to the control group (412±44 vs 132±53 cells/mm2). In the cases of the FG injection in the DMV, a number of FG + Fos double labeled cells were found in the PVN. In conclusion, icv insulin selectively activates parasympathetic pathways in Wistar, but not in SHR, and this effect may result from a refined integration between PVN and DMV neuronal circuitry coordinating the sympatho-vagal balance for metabolic and cardiovascular adjustments. Financial support: FAPESP # 2013-06206-0; CNPQ.

Brain-derived neurotrophic factor immunoreactive vagal sensory neurons innervating the gastrointestinal tract of the rat

We have determined whether brain-derived neurotrophic factor immunoreactive (BDNF-ir) neurons in the vagal ganglia innervate the gastrointestinal tract. Many BDNF-ir neurons were medium in size and located throughout the jugular and nodose ganglia. When Fluorogold was injected into the wall of the cervical esophagus, many retrogradely Fluorogold-labeled neurons were found in both the jugular ganglion and the nodose ganglion. When Fluorogold was injected into the body of the stomach or applied to the cut end of the subdiaphragmatic vagus nerve, numerous Fluorogold-labeled neurons were found mostly in the nodose ganglion. Double-labeling combining immunohistochemistry for BDNF and retrograde tracing with Fluorogold showed that more than 90% of the neurons in the jugular ganglion and the nodose ganglion projecting to the cervical esophagus contained BDNF-like immunoreactivity. In the cases of both Fluorogold injection into the stomach and Fluorogold application to the subdiaphragmatic vagus nerve, almost all Fluorogold-labeled neurons in the nodose ganglion contained BDNF-like immunoreactivity. These results indicated that almost all vagal sensory neurons located in either the jugular ganglion or the nodose ganglion that innervate the gastrointestinal tract are BDNF-ir neurons.

Vagal afferents are not necessary for the satiety effect of the gut lipid messenger oleoylethanolamide.

The endogenous lipid messenger oleoylethanolamide (OEA) inhibits eating and modulates fat metabolism supposedly through the activation of peroxisome proliferator-activated receptor-α (PPARα) and vagal sensory fibers. We tested in adult male rats whether OEA stimulates fatty acid oxidation (FAO) and ketogenesis and whether it increases plasma levels of the satiating gut peptides glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). We also explored whether OEA still inhibits eating after subdiaphragmatic vagal deafferentation (SDA). We found that intraperitoneally injected OEA (10 mg/kg body wt) reduced (P < 0.05) food intake mainly by increasing meal latency and that this effect was stronger in rats fed a 60% high-fat diet (HFD) than in chow-fed rats. OEA increased (P < 0.05) postprandial plasma nonesterified fatty acids and β-hydroxybutyrate (BHB) in the hepatic portal vein (HPV) and vena cava (VC) 30 min after injection, which was more pronounced in HFD- than in chow-fed rats. OEA also increased the protein expression of the key ketogenetic enzyme, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, in the jejunum of HFD-fed rats, but not in the liver or duodenum of either diet group. Furthermore, OEA decreased GLP-1 and PYY concentrations (P < 0.05) in the HPV and VC 30 min after administration. Finally, OEA reduced food intake in SDA and sham-operated rats similarly. Our findings indicate that neither intact abdominal vagal afferents nor prandial increases in GLP-1 or