Splenic nerve is required for cholinergic antiinflammatory pathway control of TNF in endotoxemia

Neural signaling in the spleen controls B-cell responses to blood-borne antigen

Entry of blood-borne pathogens into the spleen elicits a series of changes in cellular architecture that culminates in the systemic release of protective antibodies. Despite an abundance of work that has characterized these processes, the regulatory mechanisms that coordinate cell trafficking and antibody production are still poorly understood. Here, marginal zone (MZ) B cells responding to streptococcus in the blood were observed to migrate along splenic nerves, arriving at the red pulp venous sinuses where they become antibody-secreting cells. Electrical stimulation of the vagus nerve, which in turn regulates the splenic nerve, arrested B-cell migration and decreased antibody secretion. Thus, neural circuits regulate the first wave of antibody production following B-cell exposure to blood-borne antigen.

CPSI-121 pharmacologically prevents intestinal barrier dysfunction after cutaneous burn through a vagus nerve-dependent mechanism

BACKGROUND

We have recently demonstrated the protective effects of electrical stimulation of the vagus nerve in prevention of gut injury after severe burn. Here we evaluate the potential for a pharmacologic agonist of the vagus nerve as an approach to regulate outcomes in preclinical models. We tested a new generation of guanylhydrazone-derived compounds, CPSI-121; a compound that may activate the parasympathetic nervous system through poorly understood mechanisms to determine whether we could prevent intestinal mucosal barrier breakdown.

METHODS

Male balb/c mice were subjected to a full-thickness, 30% total body surface area steam burn, and the efficacy of CPSI-121 was tested against vagus nerve stimulation (VNS) postburn at 4 hours. Surgical vagotomy was used to disrupt the neuroenteric axis and gut injury prevention was assessed. Gut barrier dysfunction was quantified by permeability to 4-kDa fluorescein isothiocyanate-dextran. Gut injury was assessed by histologic evaluation. Tight junction protein expression (ZO-1 and occludin) was characterized by immunofluorescence and immunoblot.

RESULTS

VNS and CPSI-121 administration significantly reduced the permeability to 4-kDa fluorescein isothiocyanate-dextran and maintained normal histology compared with burn. However, abdominal vagotomy eliminated the protective effects of both VNS and CPSI-121. ZO-1 and occludin expression was similar to sham in VNS and CPSI-121-treated burn animals, but significantly altered in burn-vagotomized animals. Splenectomy did not alter the effect of CPSI-121.

CONCLUSION

Similar to direct electrical VNS, CPSI-121 effectively protects the intestinal mucosal barrier from breakdown after severe burn. We suggest that this could represent a noninvasive therapy to prevent end-organ dysfunction after trauma that would be administered during resuscitation.

Effects of vagus nerve stimulation and vagotomy on systemic and pulmonary inflammation in a two-hit model in rats

Pulmonary inflammation contributes to ventilator-induced lung injury. Sepsis-induced pulmonary inflammation (first hit) may be potentiated by mechanical ventilation (MV, second hit). Electrical stimulation of the vagus nerve has been shown to attenuate inflammation in various animal models through the cholinergic anti-inflammatory pathway. We determined the effects of vagotomy (VGX) and vagus nerve stimulation (VNS) on systemic and pulmonary inflammation in a two-hit model. Male Sprague-Dawley rats were i.v. administered lipopolysaccharide (LPS) and subsequently underwent VGX, VNS or a sham operation. 1 hour following LPS, MV with low (8 mL/kg) or moderate (15 mL/kg) tidal volumes was initiated, or animals were left breathing spontaneously (SP). After 4 hours of MV or SP, rats were sacrificed. Cytokine and blood gas analysis was performed. MV with 15, but not 8 mL/kg, potentiated the LPS-induced pulmonary pro-inflammatory cytokine response (TNF-α, IL-6, KC: p<0.05 compared to LPS-SP), but did not affect systemic inflammation or impair oxygenation. VGX enhanced the LPS-induced pulmonary, but not systemic pro-inflammatory cytokine response in spontaneously breathing, but not in MV animals (TNF-α, IL-6, KC: p<0.05 compared to SHAM), and resulted in decreased pO(2) (p<0.05 compared to sham-operated animals). VNS did not affect any of the studied parameters in both SP and MV animals. In conclusion, MV with moderate tidal volumes potentiates the pulmonary inflammatory response elicited by systemic LPS administration. No beneficial effects of vagus nerve stimulation performed following LPS administration were found. These results questions the clinical applicability of stimulation of the cholinergic anti-inflammatory pathway in systemically inflamed patients admitted to the ICU where MV is initiated.

Interleukin-17A increases neurite outgrowth from adult postganglionic sympathetic neurons

Inflammation can profoundly alter the structure and function of the nervous system. Interleukin (IL)-17 has been implicated in the pathogenesis of several inflammatory diseases associated with nervous system plasticity. However, the effects of IL-17 on the nervous system remain unexplored. Cell and explant culture techniques, immunohistochemistry, electrophysiology, and Ca2+ imaging were used to examine the impact of IL-17 on adult mouse sympathetic neurons. Receptors for IL-17 were present on postganglionic neurons from superior mesenteric ganglia (SMG). Supernatant from activated splenic T lymphocytes, which was abundant in IL-17, dramatically enhanced axonal length of SMG neurons. Importantly, IL-17-neutralizing antiserum abrogated the neurotrophic effect of splenocyte supernatant, and incubation of SMG neurons in IL-17 (1 ng/ml) significantly potentiated neurite outgrowth. The neurotrophic effect of IL-17 was accompanied by inhibition of voltage-dependent Ca2+ influx and was recapitulated by incubation of neurons in a blocker of N-type Ca2+ channels (ω-conotoxin GVIA; 30 nM). IL-17-induced neurite outgrowth in vitro appeared to be independent of glia, as treatment with a glial toxin (AraC; 5 μM) did not affect the outgrowth response to IL-17. Moreover, application of the cytokine to distal axons devoid of glial processes enhanced neurite extension. An inhibitor of the NF-κB pathway (SC-514; 20 μM) blocked the effects of IL-17. These data represent the first evidence that IL-17 can act on sympathetic somata and distal neurites to enhance neurite outgrowth, and identify a novel potential role for IL-17 in the neuroanatomical plasticity that accompanies inflammation.

Innate immune functions of macrophage subpopulations in the spleen

In the different compartments of the spleen, macrophage populations can be found that have different functions depending on their localization. In the lymphoid compartment of the spleen, the white pulp, macrophages are in essence similar to populations found in lymph nodes and other organized secondary lymphoid organs. In the red pulp, large populations of classical scavenger macrophages are found that, in addition to scavenging blood-borne debris, are involved in iron recycling by phagocytosis of effete red blood cells. The most conspicuous macrophage populations of the spleen are located in the marginal zone. Strategically positioned in the bloodstream and adorned with unique sets of pattern recognition receptors, they play an important role in host defense by bridging the innate and adaptive immune systems. In this review, the various macrophage subsets of the spleen are described.

Neuroanatomical evidence demonstrating the existence of the vagal anti-inflammatory reflex in the intestine

BACKGROUND

The cholinergic anti-inflammatory pathway is proposed to be part of the so-called vago-vagal 'inflammatory reflex'. The aim of this study is to provide neuro-anatomical evidence to support the existence of a functional neuronal circuit and its activation in response to intestinal inflammation.

METHODS

The expression of c-fos was evaluated at different levels of the neurocircuitry in the course of postoperative ileus (POI) in a mouse model. Specific activation of the motor neurons innervating the inflamed intestine and the spleen was monitored by retrograde tracing using cholera toxin-b. The role of the vagal afferent pathway nerve was evaluated by selective vagal denervation of the intestine.

KEY RESULTS

Abdominal surgery resulted in subtle inflammation of the manipulated intestine at 24 h (late phase), but not after 2 and 6 h (early) after surgery. This local inflammation was associated with activation of neurons in the nucleus of the solitary tract and in the dorsal nucleus of the vagus. The vagal output mainly targeted the inflamed zone: 42% of motor neurons innervating the intestine expressed c-fos IR in contrast to 7% of those innervating the spleen. Vagal denervation of the intestine abolished c-fos expression in the brain nuclei involved in the neuronal network activated by intestinal inflammation.

CONCLUSIONS & INFERENCES

Our data demonstrate that intestinal inflammation triggers a vagally mediated circuit leading mainly to activation of vagal motor neurons connected to the inflamed intestine. These findings for the first time provide neuro-anatomical evidence for the existence of the endogenous 'inflammatory reflex' and its activation during inflammation.

Neural regulation of inflammation: no neural connection from the vagus to splenic sympathetic neurons

The 'inflammatory reflex' acts through efferent neural connections from the central nervous system to lymphoid organs, particularly the spleen, that suppress the production of inflammatory cytokines. Stimulation of the efferent vagus has been shown to suppress inflammation in a manner dependent on the spleen and splenic nerves. The vagus does not innervate the spleen, so a synaptic connection from vagal preganglionic neurons to splenic sympathetic postganglionic neurons was suggested. We tested this idea in rats. In a preparatory operation, the anterograde tracer DiI was injected bilaterally into the dorsal motor nucleus of vagus and the retrograde tracer Fast Blue was injected into the spleen. On histological analysis 7-9 weeks later, 883 neurons were retrogradely labelled from the spleen with Fast Blue as follows: 89% in the suprarenal ganglia (65% left, 24% right); 11% in the left coeliac ganglion; but none in the right coeliac or either of the superior mesenteric ganglia. Vagal terminals anterogradely labelled with DiI were common in the coeliac but sparse in the suprarenal ganglia, and confocal analysis revealed no putative synaptic connection with any Fast Blue-labelled cell in either ganglion. Electrophysiological experiments in anaesthetized rats revealed no effect of vagal efferent stimulation on splenic nerve activity or on that of 15 single splenic-projecting neurons recorded in the suprarenal ganglion. Together, these findings indicate that vagal efferent neurons in the rat neither synapse with splenic sympathetic neurons nor drive their ongoing activity.

Reflex principles of immunological homeostasis

The reasoning that neural reflexes maintain homeostasis in other body organs, and that the immune system is innervated, prompted a search for neural circuits that regulate innate and adaptive immunity. This elucidated the inflammatory reflex, a prototypical reflex circuit that maintains immunological homeostasis. Molecular products of infection or injury activate sensory neurons traveling to the brainstem in the vagus nerve. The arrival of these incoming signals generates action potentials that travel from the brainstem to the spleen and other organs. This culminates in T cell release of acetylcholine, which interacts with α7 nicotinic acetylcholine receptors (α7 nAChR) on immunocompetent cells to inhibit cytokine release in macrophages. Herein is reviewed the neurophysiological basis of reflexes that provide stability to the immune system, the neural- and receptor-dependent mechanisms, and the potential opportunities for developing novel therapeutic devices and drugs that target neural pathways to treat inflammatory diseases.

Modulation of inflammatory pathways by the immune cholinergic system

Research done in the past years pointed to a novel function of cholinergic transmission. It has been shown that cholinergic transmission can modulate various aspects of the immune function, whether innate or adaptive. Cholinergic transmission affects immune cell proliferation, cytokine production, T helper differentiation and antigen presentation. Theses effects are mediated by cholinergic muscarinic and nicotinic receptors and other cholinergic components present in immune cells, such as acetylcholinesterase (AChE) and cholineacetyltransferase. The α7 nicotinic acetylcholine receptor was designated anti-inflammatory activity and has shown promise in pre-clinical models of inflammatory disorders. We herein describe the various components of the immune cholinergic system, and specifically the immune suppressive effects of α7 activation. This activation can be accomplished either by direct stimulation or indirectly, by inhibition of AChE. Thus, the presence of the immune cholinergic system can pave the way for novel immunomodulatory agents, or to the broadening of use of known cholinergic agents.

Nicotine exerts an anti-inflammatory effect in a murine model of acute lung injury

Activation of the cholinergic anti-inflammatory pathway through direct activation of nicotinic acetylcholine receptors on immune cells can inhibit pro-inflammatory chemokine and cytokine release and thereby protect in a variety of inflammatory diseases. The aim of this study was to investigate whether nicotine treatment protected against acute lung inflammation. Mice challenged with intratracheal lipopolysaccharide (LPS, 50 μg) were treated with nicotine (0.2 or 0.4 mg/kg, sc). After 24 h, bronchoalveolar lavage fluid (BALF) was obtained to measure leukocyte infiltration, lung edema, and pro-inflammatory chemokine (MIP-1α, MIP-2, and eotaxin) and cytokine (IL-1, IL-6, and TNF-α) levels. Nicotine treatment reduced the LPS-mediated infiltration of leukocytes and edema as evidenced by decreased BALF inflammatory cells, myeloperoxidase, and protein. Nicotine also downregulated lung production of pro-inflammatory chemokines and cytokines. These data support the proposal that activation of the cholinergic anti-inflammatory pathway may represent a useful addition to the therapy of acute respiratory distress syndrome.

Novel information on the non-neuronal cholinergic system in orthopedics provides new possible treatment strategies for inflammatory and degenerative diseases

Anti-cholinergic agents are used in the treatment of several pathological conditions. Therapy regimens aimed at up-regulating cholinergic functions, such as treatment with acetylcholinesterase inhibitors, are also currently prescribed. It is now known that not only is there a neuronal cholinergic system but also a non-neuronal cholinergic system in various parts of the body. Therefore, interference with the effects of acetylcholine (ACh) brought about by the local production and release of ACh should also be considered. Locally produced ACh may have proliferative, angiogenic, wound-healing, and immunomodulatory functions. Interestingly, cholinergic stimulation may lead to anti-inflammatory effects. Within this review, new findings for the locomotor system of a more widespread non-neuronal cholinergic system than previously expected will be discussed in relation to possible new treatment strategies. The conditions discussed are painful and degenerative tendon disease (tendinopathy/tendinosis), rheumatoid arthritis, and osteoarthritis.

Acetylcholine-synthesizing T cells relay neural signals in a vagus nerve circuit

Neural circuits regulate cytokine production to prevent potentially damaging inflammation. A prototypical vagus nerve circuit, the inflammatory reflex, inhibits tumor necrosis factor-α production in spleen by a mechanism requiring acetylcholine signaling through the α7 nicotinic acetylcholine receptor expressed on cytokine-producing macrophages. Nerve fibers in spleen lack the enzymatic machinery necessary for acetylcholine production; therefore, how does this neural circuit terminate in cholinergic signaling? We identified an acetylcholine-producing, memory phenotype T cell population in mice that is integral to the inflammatory reflex. These acetylcholine-producing T cells are required for inhibition of cytokine production by vagus nerve stimulation. Thus, action potentials originating in the vagus nerve regulate T cells, which in turn produce the neurotransmitter, acetylcholine, required to control innate immune responses.

Human ghrelin protects animals from renal ischemia-reperfusion injury through the vagus nerve

BACKGROUND

Acute kidney injury secondary to renal ischemia and reperfusion injury is widely prevalent. Ghrelin, which is a stomach-derived peptide, has been shown to be anti-inflammatory. The purpose of this study was to examine whether human ghrelin has any beneficial effects after renal ischemia and reperfusion injury, and if so, whether ghrelin's action in renal ischemia and reperfusion injury is mediated by the vagus nerve.

METHODS

Male adult rats were subjected to renal ischemia and reperfusion by bilateral renal pedicle clamping for 60 min, treated intravenously with human ghrelin (4 nmol/rat) or normal saline (vehicle) immediately after reperfusion. After 24 h, the animals were killed and samples were harvested. In separate groups, subdiaphragmatic vagotomy prior to renal ischemia and reperfusion was performed, treated with human ghrelin or vehicle, and at 24 h, blood and organs were harvested.

RESULTS

Renal ischemia and reperfusion injury caused significant increases in the serum levels of tissue injury markers compared with the sham operation. Human ghrelin treatment attenuated serum creatinine and blood urea nitrogen significantly by 55% and 53%, and liver enzymes (aminotransferase [AST] and alanine aminotransferase [ALT]) by 20% and 24%, respectively, compared with the vehicle-treated groups. Tissue water contents, plasma and kidney interleukin-6, and kidney myeloperoxidase activity were decreased. Bcl-2/Bax ratio was increased, and histology of the kidneys was improved. More importantly, prior vagotomy abolished ghrelin's protective effect in tissue injury markers and tissue water contents in renal ischemia and reperfusion injured animals.

CONCLUSION

Human ghrelin treatment in renal ischemia and reperfusion injured rats attenuated systemic and kidney-specific inflammatory responses. The protection of human ghrelin in renal ischemia and reperfusion injury was mediated by the vagus nerve. These data suggest that ghrelin can be developed as a novel treatment for patients with acute kidney injury induced by renal ischemia and reperfusion injury.

Role of α7 nicotinic acetylcholine receptors in regulating tumor necrosis factor-α (TNF-α) as revealed by subtype selective agonists

Immunological responses to protect against excessive inflammation can be regulated by the central nervous system through the cholinergic anti-inflammatory pathway wherein acetylcholine released from vagus nerves can inhibit inflammatory cytokines. Although a role for the α7 nicotinic acetylcholine receptor (α7 nAChR) in mediating this pathway has been suggested, pharmacological modulation of the pathway by selective agonists remains to be further elucidated. In this study, the role of α7 nAChRs in the regulation of TNF-α release was investigated using high affinity and selective α7 nAChR agonists in mouse peritoneal macrophage and human whole blood in vitro, and in mouse serum in vivo. In mouse peritoneal macrophages, LPS-induced TNF-α release in vitro was inhibited by a selective α7 nAChR agonist, A-833834 (5-[6-(5-Methyl-hexahydro-pyrrolo[3,4-c]pyrrol-2-yl)-pyridazin-3-yl]-1H-indole), and that effect was attenuated by α7 nAChR antagonist methyllycaconitine. The inhibitory effect of A-833834 on LPS-induced TNF-α release was also observed in human whole blood in vitro. I.v. LPS-induced TNF-α release in mouse serum was attenuated following i.p. administration of A-833834. Similarly, i.v. LPS-induced TNF-α release in mouse serum was also attenuated following i.p. administration of A-585539, another α7 nAChR agonist with limited brain penetration, suggesting that these effects are mediated by peripheral α7 nAChRs. A-833834 was also efficacious in suppressing TNF-α release in mouse serum following oral administration in zymosan-induced peritonitis. These studies collectively demonstrate that selectively targeting α7 nAChRs could offer a novel therapeutic modality to treat acute and chronic inflammatory disease states.

Restoring the balance of the autonomic nervous system as an innovative approach to the treatment of rheumatoid arthritis

The immunomodulatory effect of the autonomic nervous system has raised considerable interest over the last decades. Studying the influence on the immune system and the role in inflammation of the sympathetic as well as the parasympathetic nervous system not only will increase our understanding of the mechanism of disease, but also could lead to the identification of potential new therapeutic targets for chronic immune-mediated inflammatory diseases, such as rheumatoid arthritis (RA). An imbalanced autonomic nervous system, with a reduced parasympathetic and increased sympathetic tone, has been a consistent finding in RA patients. Studies in animal models of arthritis have shown that influencing the sympathetic (via α- and β-adrenergic receptors) and the parasympathetic (via the nicotinic acetylcholine receptor α7nAChR or by electrically stimulating the vagus nerve) nervous system can have a beneficial effect on inflammation markers and arthritis. The immunosuppressive effect of the parasympathetic nervous system appears less ambiguous than the immunomodulatory effect of the sympathetic nervous system, where activation can lead to increased or decreased inflammation depending on timing, doses and kind of adrenergic agent used. In this review we will discuss the current knowledge of the role of both the sympathetic (SNS) and parasympathetic nervous system (PNS) in inflammation with a special focus on the role in RA. In addition, potential antirheumatic strategies that could be developed by targeting these autonomic pathways are discussed.

β2-Adrenoreceptors of regulatory lymphocytes are essential for vagal neuromodulation of the innate immune system

The nervous system is classically organized into sympathetic and parasympathetic systems acting in opposition to maintain physiological homeostasis. Here, we report that both systems converge in the activation of β2-adrenoceptors of splenic regulatory lymphocytes to control systemic inflammation. Vagus nerve stimulation fails to control serum TNF levels in either β2-knockout or lymphocyte-deficient nude mice. Unlike typical suppressor CD25(+) cells, the transfer of CD4(+)CD25(-) regulatory lymphocytes reestablishes the anti-inflammatory potential of the vagus nerve and β2-agonists to control inflammation in both β2-knockout and nude mice. β2-Agonists inhibit cytokine production in splenocytes (IC(50)≈ 1 μM) and prevent systemic inflammation in wild-type but not in β2-knockout mice. β2-Agonists rescue wild-type mice from established polymicrobial peritonitis in a clinically relevant time frame. Regulatory lymphocytes reestablish the anti-inflammatory potential of β2-agonists to control systemic inflammation, organ damage, and lethal endotoxic shock in β2-knockout mice. These results indicate that β2-adrenoceptors in regulatory lymphocytes are critical for the anti-inflammatory potential of the parasympathetic vagus nerve, and they represent a potential pharmacological target for sepsis.

Cholinergic regulatory lymphocytes re-establish neuromodulation of innate immune responses in sepsis

Many anti-inflammatory strategies that are successful in treating sepsis in healthy animals fail in clinical trials, in part because sepsis normally involves immunocompromised patients, and massive lymphocyte apoptosis prevents immunomodulation. In this article, we report a new set of regulatory lymphocytes that are able to re-establish the cholinergic anti-inflammatory modulation and to provide therapeutic advantages in sepsis. The vagus nerve controls inflammation in healthy, but not in septic, mice. Likewise, vagus nerve and cholinergic agonists fail to control inflammation in splenectomized and nude animals. Unlike typical suppressor CD25(+) cells, CD4(+)CD25(-) lymphocytes re-establish the anti-inflammatory potential of the vagus nerve and cholinergic agonists in immunocompromised and septic animals. These cholinergic lymphocytes re-establish splenic protection and the potential of cholinergic agonists to rescue immunocompromised animals from established sepsis. The study results revealed these new regulatory lymphocytes as, to our knowledge, the first known physiological target for neuromodulation of the innate immune responses and a potential therapeutic target for sepsis.

Stimulation of alpha7 nicotinic acetylcholine receptor by nicotine attenuates inflammatory response in macrophages and improves survival in experimental model of sepsis through heme oxygenase-1 induction

Activation of nicotinic acetylcholine receptor alpha7 subunit (α7nAChR) by nicotine leads to the improved survival rate in experimental model of sepsis. Previously, we demonstrated that heme oxygenase (HO)-1 inducers or carbon monoxide significantly increased survival of lipopolysaccharide (LPS)-induced and cecal ligation and puncture-induced septic mice by reduction of high mobility group box 1 release, a late mediator of sepsis. However, that activation of α7nAChR by nicotine provides anti-inflammatory action through HO-1 upregulation has not been elucidated. Here we show that HO-1-inducible effect by nicotine was mediated through sequential event-Ca(2+) influx, classical protein kinase C activation, and reactive oxygen species production-which activates phosphoinositol-3-kinase/Akt/Nrf-2 pathway. In addition, HO-1 is required for nicotine-mediated suppression of tumor necrosis factor-α, inducible nitric oxide synthase, and high mobility group box 1 expression induced by LPS in macrophages, as evidenced by the fact that nicotine failed to inhibit production of these mediators when HO-1 was suppressed. Importantly, nicotine-induced survival rate was reduced by inhibition of HO-1 in LPS- and cecal ligation and puncture-treated septic mice. Collectively, these data suggest that activation of α7nAChR by nicotine is critical in the regulation of anti-inflammatory process, which could be mediated through HO-1 expression. Thus, we conclude that activation of α7nAChR by nicotine provides anti-inflammatory action through HO-1 upregulation.

Inflammation and cardiorespiratory control: the role of the vagus nerve

Inflammation and immunity have been implicated in a wide variety of diseases and disorders ranging from asthma to cardiovascular disease to hemorrhagic shock. In this review we will briefly consider the evidence for the neural concomitants of immunomodulation. First, we will briefly review the anatomy and physiology of the cardiorespiratory system. Then we will review the anatomy and physiology of neural-immune communication. The nucleus of the solitary tract is a site of integration of both the afferent and efferent neural regulation of the cardiorespiratory as well as the immune system. Then we will provide an overview of what is known about neuroimmunomodulation from both animal and human studies including neuroimaging and clinical studies. Finally, we will discuss a possible role of this neural circuitry in asthma related health disparities.

The hypothermic response to bacterial lipopolysaccharide critically depends on brain CB1, but not CB2 or TRPV1, receptors

Hypothermia occurs in the most severe cases of systemic inflammation, but the mechanisms involved are poorly understood. This study evaluated whether the hypothermic response to bacterial lipopolysaccharide (LPS) is modulated by the endocannabinoid anandamide(AEA) and its receptors: cannabinoid-1 (CB1), cannabinoid-2 (CB2) and transient receptor potential vanilloid-1 (TRPV1). In rats exposed to an ambient temperature of 22◦C, a moderate dose of LPS (25 - 100 μg kg−1 I.V.) induced a fall in body temperature with a nadir at ∼100 minpostinjection. This response was not affected by desensitization of intra-abdominal TRPV1 receptors with resiniferatoxin (20 μg kg - 1 I.P.), by systemic TRPV1 antagonism with capsazepine(40mg kg−1 I.P.), or by systemic CB2 receptor antagonism with SR144528 (1.4 mg kg−1 I.P.).However, CB1 receptor antagonism by rimonabant (4.6mg kg−1 I.P.) or SLV319 (15mg kg−1 I.P.)blocked LPS hypothermia. The effect of rimonabant was further studied. Rimonabant blocked LPS hypothermia when administered I.C.V. at a dose (4.6 μg) that was too low to produce systemic effects. The blockade of LPS hypothermia by I.C.V. rimonabant was associated with suppression of the circulating level of tumour necrosis factor-α. In contrast to rimonabant,the I.C.V. administration of AEA (50 μg) enhanced LPS hypothermia. Importantly, I.C.V. AEAdid not evoke hypothermia in rats not treated with LPS, thus indicating that AEA modulates LPS-activated pathways in the brain rather than thermo effector pathways. In conclusion, the present study reveals a novel, critical role of brain CB1 receptors in LPS hypothermia. Brain CB1 receptors may constitute a new therapeutic target in systemic inflammation and sepsis.

α7-cholinergic receptor mediates vagal induction of splenic norepinephrine

Classically, sympathetic and parasympathetic systems act in opposition to maintain the physiological homeostasis. In this article, we report that both systems work together to restrain systemic inflammation in life-threatening conditions such as sepsis. This study indicates that vagus nerve and cholinergic agonists activate the sympathetic noradrenergic splenic nerve to control systemic inflammation. Unlike adrenalectomy, splenectomy and splenic neurectomy prevent the anti-inflammatory potential of both the vagus nerve and cholinergic agonists, and abrogate their potential to induce splenic and plasma norepinephrine. Splenic nerve stimulation mimics vagal and cholinergic induction of norepinephrine and re-establishes neuromodulation in α7 nicotinic acetylcholine receptor (α7nAChR)-deficient animals. Thus, vagus nerve and cholinergic agonists inhibit systemic inflammation by activating the noradrenergic splenic nerve via the α7nAChR nicotinic receptors. α7nAChR represents a unique molecular link between the parasympathetic and sympathetic system to control inflammation.

Voluntarily produced increases in heart rate variability modulate autonomic effects of endotoxin induced systemic inflammation: an exploratory study

Exposure of healthy people to lipopolysaccharide (LPS; endotoxin) produces a pro-inflammatory response, subjective symptoms, and decreased heart rate variability (HRV). Given the efficacy of HRV biofeedback (BF) for treating asthma, the large autonomic effects of HRV BF, and the link between vagus nerve activity and inflammation, we hypothesized that HRV BF would dampen the acute manifestations of systemic inflammation induced by LPS challenge. Healthy participants age 18-40 were randomly assigned to four-one-hour training sessions of either HRV BF (n = 6) or a control 15/min paced breathing condition (n = 5) prior to acute experimentally induced LPS exposure. Participants were coached to do the procedures for 10 min each at five hourly time points after LPS injection, and then 2 h later. Subjective symptoms, HRV parameters, and plasma cytokine levels were measured at each time point, 2 h afterward, and the following morning. Participants were able to perform the procedures both during four pre-exposure training sessions and while experiencing LPS-induced symptoms. The HRV BF group showed significant attenuation of the LPS-induced decline in HRV for the 6 h following LPS exposure, suggesting that HRV BF decreased autonomic dysfunction produced by LPS-induced inflammation. HRV BF also reduced symptoms of headache and eye sensitivity to light, but did not affect LPS-induced levels of pro-inflammatory cytokines or symptoms of nausea, muscle aches, or feverishness. Further evaluation of HRV BF appears to be warranted among patients with inflammatory conditions.

The pulse of inflammation: heart rate variability, the cholinergic anti-inflammatory pathway and implications for therapy

Biological therapeutics targeting TNF, IL-1 and IL-6 are widely used for treatment of rheumatoid arthritis, inflammatory bowel disease and a growing list of other syndromes, often with remarkable success. Now advances in neuroscience have collided with this therapeutic approach, perhaps rendering possible the development of nerve stimulators to inhibit cytokines. Action potentials transmitted in the vagus nerve culminate in the release of acetylcholine that blocks cytokine production by cells expressing acetylcholine receptors. The molecular mechanism of this cholinergic anti-inflammatory pathway is attributable to signal transduction by the nicotinic alpha 7 acetylcholine receptor subunit, a regulator of the intracellular signals that control cytokine transcription and translation. Favourable preclinical data support the possibility that nerve stimulators may be added to the future therapeutic armamentarium, possibly replacing some drugs to inhibit cytokines.

Regulation of peripheral inflammation by the central nervous system

In inflammatory disorders such as rheumatoid arthritis, cytokines and danger signals are sensed by the central nervous system, which adapts behavior and physiologic responses during systemic stress. The central nervous system can also signal the periphery to modulate inflammation through efferent hormonal and neuronal pathways. The brain and spinal cord are involved in this bidirectional interaction. A variety of neuronal pathways that modulate synovial inflammation have been implicated, including the sympathetic and the parasympathetic branches of the autonomic system. Another mechanism, the dorsal root reflex, involves antidromic signaling along somatic afferent fibers that influences joint inflammation by releasing neuropeptides and other neuromediators in the periphery. Some of the neurotransmitters and neuroreceptors involved have been identified in preclinical models and represent novel targets for the treatment of rheumatic diseases.

Vagal nerve stimulation protects against burn-induced intestinal injury through activation of enteric glia cells

The enteric nervous system may have an important role in modulating gastrointestinal barrier response to disease through activation of enteric glia cells. In vitro studies have shown that enteric glia activation improves intestinal epithelial barrier function by altering the expression of tight junction proteins. We hypothesized that severe injury would increase expression of glial fibrillary acidic protein (GFAP), a marker of enteric glial activation. We also sought to define the effects of vagal nerve stimulation on enteric glia activation and intestinal barrier function using a model of systemic injury and local gut mucosal involvement. Mice with 30% total body surface area steam burn were used as model of severe injury. Vagal nerve stimulation was performed to assess the role of parasympathetic signaling on enteric glia activation. In vivo intestinal permeability was measured to assess barrier function. Intestine was collected to investigate changes in histology; GFAP expression was assessed by quantitative PCR, by confocal microscopy, and in GFAP-luciferase transgenic mice. Stimulation of the vagus nerve prevented injury-induced intestinal barrier injury. Intestinal GFAP expression increased at early time points following burn and returned to baseline by 24 h after injury. Vagal nerve stimulation prior to injury increased GFAP expression to a greater degree than burn alone. Gastrointestinal bioluminescence was imaged in GFAP-luciferase transgenic animals following either severe burn or vagal stimulation and confirmed the increased expression of intestinal GFAP. Injection of S-nitrosoglutathione, a signaling molecule released by activated enteric glia cells, following burn exerts protective effects similar to vagal nerve stimulation. Intestinal expression of GFAP increases following severe burn injury. Stimulation of the vagus nerve increases enteric glia activation, which is associated with improved intestinal barrier function. The vagus nerve may mediate the signaling that occurs from the central nervous system to the enteric nervous system following gastrointestinal injury.

Non-neuronal regulation and repertoire of cholinergic receptors in organs

Many studies on the cholinergic pathway have indicated that cholinergic receptors, which are widely expressed in various cells, play an important role in all body organs. In this review, we present the concept that cholinergic responses are regulated through a neuronal or non-neuronal mechanism. The neuronal mechanism is a system in which acetylcholine binds to cholinergic receptors on target cells through the nerves. In the non-neuronal mechanism, acetylcholine, produced by neighboring cells in an autocrine/paracrine manner, binds to cholinergic receptors on target cells. Both mechanisms subsequently lead to physiological and pathophysiological responses. We also investigated the subunits/subtypes of cholinergic receptors on target cells, physiological and pathophysiological responses of the organs via cholinergic receptors, and extracellular factors that alter the subtypes/subunits of cholinergic receptors. Collectively, this concept will elucidate how cholinergic responses occur and will help us conduct further experiments to develop new therapeutic agents.

Anti-inflammatory effect of vagus nerve stimulation in a rat model of inflammatory bowel disease

Vagus nerve stimulation of afferents is used as an adjunctive treatment for drug-resistant epilepsy and depression. In addition, anti-inflammatory properties of vagus nerve stimulation have been reported in various experimental models of inflammation but not in colitis. These effects are thought to be mediated via peripheral release of acetylcholine from the vagus and subsequent activation of macrophages. Our aim was to evaluate in rats the anti-inflammatory effects of chronic vagus nerve stimulation on colonic inflammation. Colitis was induced by intracolonic instillation of trinitrobenzene sulfonic acid. Vagus nerve stimulation (left cervical) was performed in freely moving animals 3 h per day for five consecutive days. Assessment of colonic inflammation was obtained using physiological (e.g. body weight, temperature and locomotor activity) parameters, macroscopical (area of lesions), histological, and biological parameters (e.g. myeloperoxidase activity, cytokine and cytokine-related mRNAs), both at the level of the damaged colon and the colon immediately above. A global multivariate index of colitis was then generated for a better characterization of colonic inflammation. Vagus nerve stimulation reduced the degree of body weight loss and inflammatory markers as observed above the lesion by histological score and myeloperoxidase quantification. This anti-inflammatory effect was also demonstrated by the improvement of the multivariate index of colitis. These data argue for an anti-inflammatory role of vagus nerve stimulation chronically performed in freely moving rats with colitis and provide potential therapeutic applications for patients with inflammatory bowel diseases.

Neural aspects of immunomodulation: focus on the vagus nerve

Inflammation and immunity have been implicated in a wide variety of diseases and disorders ranging from Alzheimer's disease to cardiovascular disease to hemorrhagic shock. In this review, we will briefly consider the evidence for the neural concomitants of immunomodulation. First, we will briefly review the anatomy and physiology of neural-immune communication. Evidence for the somatotopic organization of the vagus nerve and for pain processes suggests that such an organization may be relevant for the investigation of the neural concomitants of immunity. Then we will provide an overview of what is known from both animal and human studies including neuroimaging and clinical studies. Finally, we will discuss some of the challenges and opportunities in this exciting area of investigation.

Efferent vagal nerve stimulation attenuates gut barrier injury after burn: modulation of intestinal occludin expression

INTRODUCTION

Severe injury can cause intestinal permeability through decreased expression of tight junction proteins, resulting in systemic inflammation. Activation of the parasympathetic nervous system after shock through vagal nerve stimulation is known to have potent anti-inflammatory effects; however, its effects on modulating intestinal barrier function are not fully understood. We postulated that vagal nerve stimulation improves intestinal barrier integrity after severe burn through an efferent signaling pathway, and is associated with improved expression and localization of the intestinal tight junction protein occludin.

METHODS

Male balb/c mice underwent right cervical vagal nerve stimulation for 10 minutes immediately before 30% total body surface area, full-thickness steam burn. In a separate arm, animals underwent abdominal vagotomy at the gastroesophageal junction before vagal nerve stimulation and burn. Intestinal barrier injury was assessed by permeability to 4 kDa FITC-dextran, histology, and changes in occludin expression using immunoblotting and confocal microscopy.

RESULTS

Cervical vagal nerve stimulation decreased burn-induced intestinal permeability to FITC-dextran, returning intestinal permeability to sham levels. Vagal nerve stimulation before burn also improved gut histology and prevented burn-induced changes in occludin protein expression and localization. Abdominal vagotomy abrogated the protective effects of cervical vagal nerve stimulation before burn, resulting in gut permeability, histology, and occludin protein expression similar to burn alone.

CONCLUSION

Vagal nerve stimulation performed before injury improves intestinal barrier integrity after severe burn through an efferent signaling pathway and is associated with improved tight junction protein expression.

Nicotinic acetylcholine receptor activation reduces skeletal muscle inflammation of mdx mice

Mdx mice develop an inflammatory myopathy characterized at different ages by myonecrosis with scattered inflammatory infiltrates followed by muscular regeneration and later persistent fibrosis. This work aimed to verify the putative anti-inflammatory role of nicotinic acetylcholine receptor (nAChR) in the mdx muscular lesion. Mitigation of myonecrosis and decreased TNFα production were accompanied by increased numbers of F4/80 macrophages expressing nAChRα7. In vivo treatment with nicotine attenuated muscular inflammation characterized by reduced metalloprotease MMP-9 activity, TNFα and NFkB content and increased muscular regeneration. Our data indicate that nAChR activation influences local inflammatory responses in the muscular lesion of mdx mice.

Endotoxin exposure during late pregnancy alters ovine offspring febrile and hypothalamic-pituitary-adrenal axis responsiveness later in life

A growing number of studies indicate that maternal infection during pregnancy is associated with adverse fetal development and neonatal health. In this study, late gestating sheep (day 135) were challenged systemically with saline (0.9%) or Escherichia coli lipopolysaccharide endotoxin (400 ng/kg x 3 consecutive days, or 1.2 microg/kg x 1 day) in order to assess the impact of maternal endotoxemia on the developing fetal neuroendocrine-immune system. During adulthood, cortisol secretion and febrile responses of female offspring and the cortisol response of the male offspring to endotoxin (400 ng/kg), as well as the female cortisol response to adrenocorticotropic hormone (ACTH) challenge, were measured to assess neuroendocrine-immune function. These studies revealed that maternal endotoxin treatment during late gestation altered the female febrile and male and female cortisol response to endotoxin exposure later in life; however, the response was dependent on the endotoxin treatment regime that the pregnant sheep received. The follow-up ACTH challenge suggests that programing of the adrenal gland may be altered in the female fetus during maternal endotoxemia. The long-term health implications of these changes warrant further investigation.

Understanding immunity requires more than immunology

Acetylcholine and related neurotransmitters appeared with unicellular life forms, millions of years before innate immunity. Tools and insights are now available for understanding how the evolving nervous system influenced the development of immunity.

The sympathetic-vagal balance against endotoxemia

The goal of this study was to establish a convenient and effective approach to anti-inflammation treatment by rebalancing the sympathetic-vagal system via vagal nerve stimulation (VNS). We established an endotoxemia model in Sprague-Dawley rats using lipopolysaccharide (LPS) injection. Electrical discharges in the vagal system, including the nucleus tractus solitarii (NTS) and afferent and efferent cervical vagal nerves, were detected. The condition of sympathetic-vagal balance, presented as heart rate variability (HRV) and hepatic norepinephrine/acetylcholine (NE/ACh), was measured following endotoxemia with and without VNS. Discharges in afferent and efferent vagal nerves increased significantly following LPS injection compared with the basis level and corresponding time points in the control group. Discharges in the NTS also increased significantly following LPS injection. The HRV components, including normalized high frequency (HFnm), normalized low frequency (LFnm), LF/HF, and very low frequency (VLF), increased significantly following LPS injection. HFnm values in the LPS + VNS group increased significantly compared with the LPS group. Conversely, LFnm, LF/HF, and VLF in the LPS + VNS group decreased significantly compared with the LPS group. Hepatic NE and ACh significantly decreased within 6 h after LPS injection compared with the basal level and the control groups (P < 0.05). VNS did not significantly improve hepatic NE, but the ACh levels in the LPS + VNS group were higher than those in other groups. Sympathetic and vagal nervous systems are enhanced following endotoxemia. The overexcitation of the sympathetic system leads to sympathetic-vagal disequilibrium. The rebalance of the sympathetic and vagal system is crucial for critically ill patients.

Cholinergic stimulation of the immune system protects against lethal infection by Salmonella enterica serovar Typhimurium

SUMMARY

The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

Intensive Care Unit-acquired infection as a side effect of sedation

Introduction

Sedative and analgesic medications are routinely used in mechanically ventilated patients. The aim of this review is to discus epidemiologic data that suggest a relationship between infection and sedation, to review available data for the potential causes and pathophysiology of this relationship, and to identify potential preventive measures.

Methods

Data for this review were identified through searches of PubMed, and from bibliographies of relevant articles.

Results

Several epidemiologic studies suggested a link between sedation and ICU-acquired infection. Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Furthermore, experimental evidence coming from studies both in humans and animals suggest that sedatives and analgesics present immunomodulatory properties that might alter the immunologic response to exogenous stimuli. Clinical studies comparing different sedative agents do not provide evidence to recommend the use of a particular agent to reduce ICU-acquired infection rate. However, sedation strategies aiming to reduce the duration of mechanical ventilation, such as daily interruption of sedatives or nursing-implementing sedation protocol, should be promoted. In addition, the use of short acting opioids, propofol, and dexmedetomidine is associated with shorter duration of mechanical ventilation and ICU stay, and might be helpful in reducing ICU-acquired infection rates.

Conclusions

Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects, and immunomodulatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Future studies should compare the effect of different sedative agents, and the impact of progressive opioid discontinuation compared with abrupt discontinuation on ICU-acquired infection rates.

Modulation of brain dead induced inflammation by vagus nerve stimulation

Because the vagus nerve is implicated in control of inflammation, we investigated if brain death (BD) causes impairment of the parasympathetic nervous system, thereby contributing to inflammation. BD was induced in rats. Anaesthetised ventilated rats (NBD) served as control. Heart rate variability (HRV) was assessed by ECG. The vagus nerve was electrically stimulated (BD + STIM) during BD. Intestine, kidney, heart and liver were recovered after 6 hours. Affymetrix chip-analysis was performed on intestinal RNA. Quantitative PCR was performed on all organs. Serum was collected to assess TNFalpha concentrations. Renal transplantations were performed to address the influence of vagus nerve stimulation on graft outcome. HRV was significantly lower in BD animals. Vagus nerve stimulation inhibited the increase in serum TNFalpha concentrations and resulted in down-regulation of a multiplicity of pro-inflammatory genes in intestinal tissue. In renal tissue vagal stimulation significantly decreased the expression of E-selectin, IL1beta and ITGA6. Renal function was significantly better in recipients that received a graft from a BD + STIM donor. Our study demonstrates impairment of the parasympathetic nervous system during BD and inhibition of serum TNFalpha through vagal stimulation. Vagus nerve stimulation variably affected gene expression in donor organs and improved renal function in recipients.

The vagus nerve modulates CD4+ T cell activity

The vagus nerve has a counter-inflammatory role in a number of model systems. While the majority of these anti-inflammatory effects have been ascribed to the activation of nicotinic receptors on macrophages, little is known about the role of the vagus in modulating the activity of other cells involved in inflammatory responses. Here, we demonstrate that following subdiaphragmatic vagotomy of mice CD4(+) T cells from the spleen proliferated at a higher rate and produced more pro-inflammatory cytokines, including TNF and IFN-gamma, upon in vitro stimulation. Cell responses were restored to control levels following the administration of nicotine and the treatment of non-vagotomized animals with a nicotinic receptor antagonist could mimic the effect of vagotomy. Our results suggest that vagal input constitutively down-regulates T cell function through action at nicotinic receptors and the role of the vagus in regulating immune responses is more extensive than previously demonstrated.

Stress-related modulation of inflammation in experimental models of bowel disease and post-infectious irritable bowel syndrome: role of corticotropin-releasing factor receptors

The interaction between gut inflammatory processes and stress is gaining increasing recognition. Corticotropin-releasing factor (CRF)-receptor activation in the brain is well established as a key signaling pathway initiating the various components of the stress response including in the viscera. In addition, a local CRF signaling system has been recently established in the gut. This review summarize the present knowledge on mechanisms through which both brain and gut CRF receptors modulate intestinal inflammatory processes and its relevance towards increased inflammatory bowel disease (IBD) activity and post-infectious irritable bowel syndrome (IBS) susceptibility induced by stress.

MicroRNA-132 potentiates cholinergic anti-inflammatory signaling by targeting acetylcholinesterase

MicroRNAs (miRNAs) contribute to both neuronal and immune cell fate, but their involvement in intertissue communication remained unexplored. The brain, via vagal secretion of acetylcholine (ACh), suppresses peripheral inflammation by intercepting cytokine production; therefore, we predicted that microRNAs targeting acetylcholinesterase (AChE) can attenuate inflammation. Here, we report that inflammatory stimuli induced leukocyte overexpression of the AChE-targeting miR-132. Injected locked nucleic acid (LNA)-modified anti-miR-132 oligonucleotide depleted miR-132 amounts while elevating AChE in mouse circulation and tissues. In transfected cells, a mutated 3'UTR miR-132 binding site increased AChE mRNA expression, whereas cells infected with a lentivirus expressing pre-miR-132 showed suppressed AChE. Transgenic mice overexpressing 3'UTR null AChE showed excessive inflammatory mediators and impaired cholinergic anti-inflammatory regulation, in spite of substantial miR-132 upregulation in brain and bone marrow. Our findings identify the AChE mRNA-targeting miR-132 as a functional regulator of the brain-to-body resolution of inflammation, opening avenues for study and therapeutic manipulations of the neuro-immune dialog.

Reflex control of immunity

Inflammation can cause damage and even death. What controls this primitive and potentially lethal innate immune response to injury and infection? Molecular and neurophysiological studies during the past decade have revealed a pivotal answer: immunity is coordinated by neural circuits that operate reflexively. The afferent arc of the reflex consists of nerves that sense injury and infection. This activates efferent neural circuits, including the cholinergic anti-inflammatory pathway, that modulate immune responses and the progression of inflammatory diseases. It might be possible to develop therapeutics that target neural networks for the treatment of inflammatory disorders.