Splenic Nerve Research Articles

Galvanic vestibular stimulation-induced activation of C1 neurons in medulla oblongata protects against acute lung injury.

Autonomic nerves, including the sympathetic and parasympathetic nerves, control the immune system along with their physiological functions. On the peripheral side, the interaction between the splenic sympathetic nerves and immune cells is important for the anti-inflammatory effects. However, the central mechanism underlying these anti-inflammatory effects remains unclear. C1 neurons respond to stressors and subsequently determine the outflow of the autonomic nervous system. We have previously shown that C1 neurons protect against acute kidney injury and found a signaling connection between peripheral vestibular organs and C1 neurons. Thus, we hypothesized that hypergravity load or galvanic vestibular stimulation (GVS) might protect against acute lung injury. We showed that C1 neurons are histologically and functionally activated by stimulating the peripheral vestibular organs. Protection against acute lung injury that was induced by a 2 G load disappeared due to vestibular lesions or the deletion of C1 neurons. This GVS-induced protective effect was also eliminated by the deletion of the C1 neurons. Furthermore, GVS increased splenic sympathetic nerve activity in conscious mice, and splenic sympathetic denervation abolished the GVS-induced protection against acute lung injury. Therefore, the activated pathway between C1 neurons and splenic sympathetic nerves is indispensable for GVS-induced protection against acute lung injury.

Unilateral Cervical Vagotomy Modulates Immune Cell Profiles and the Response to a Traumatic Brain Injury.

TBI induces splenic B and T cell expansion that contributes to neuroinflammation and neurodegeneration. The vagus nerve, the longest of the cranial nerves, is the predominant parasympathetic pathway allowing the central nervous system (CNS) control over peripheral organs, including regulation of inflammatory responses. One way this is accomplished is by vagus innervation of the celiac ganglion, from which the splenic nerve innervates the spleen. This splenic innervation enables modulation of the splenic immune response, including splenocyte selection, activation, and downstream signaling. Considering that the left and right vagus nerves have distinct courses, it is possible that they differentially influence the splenic immune response following a CNS injury. To test this possibility, immune cell subsets were profiled and quantified following either a left or a right unilateral vagotomy. Both unilateral vagotomies caused similar effects with respect to the percentage of B cells and in the decreased percentage of macrophages and T cells following vagotomy. We next tested the hypothesis that a left unilateral vagotomy would modulate the splenic immune response to a traumatic brain injury (TBI). Mice received a left cervical vagotomy or a sham vagotomy 3 days prior to a fluid percussion injury (FPI), a well-characterized mouse model of TBI that consistently elicits an immune and neuroimmune response. Flow cytometric analysis showed that vagotomy prior to FPI resulted in fewer CLIP+ B cells, and CD4+, CD25+, and CD8+ T cells. Vagotomy followed by FPI also resulted in an altered distribution of CD11bhigh and CD11blow macrophages. Thus, transduction of immune signals from the CNS to the periphery via the vagus nerve can be targeted to modulate the immune response following TBI.

Effects of spleen nerve denervation on depression–like phenotype, systemic inflammation, and abnormal composition of gut microbiota in mice after administration of lipopolysaccharide: A role of brain–spleen axis

BackgroundAccumulating evidence suggests the role of brain–spleen axis as well as brain–gut–microbiota axis in inflammation-related depression. The spleen mediates anti-inflammatory effects of the vagus nerve which plays a role in depression. However, the role of spleen nerve in inflammation-related depression remains unclear. MethodsThe effects of the splenic nerve denervation (SND) in the depression-like phenotype, systemic inflammation, and abnormal composition of gut microbiota in adult mice after administration of lipopolysaccharide (LPS) were examined. ResultsLPS (0.5 mg/kg) caused depression-like phenotype, systemic inflammation, splenomegaly, increased expression of Iba1 (ionized calcium-binding adapter molecule 1) and decreased expression of postsynaptic density protein-95 (PSD-95) in the hippocampus in the sham-operated mice. In contrast, LPS did not produce depression-like phenotype, and abnormal expressions of Iba1 and PSD-95 in the hippocampus in the SND-operated mice. Furthermore, SND significantly blocked LPS-induced increased plasma levels of pro-inflammatory cytokine interleukin-6 although SND did not affect LPS-induced splenomegaly and increased plasma levels of tumor necrosis factor-α in mice. There were significant changes in several microbiota among the four groups. Interestingly, there were correlations between the relative abundance of several microbiota and Iba1 (or PSD-95) expression in the hippocampus. In addition, expression of Iba1 in the hippocampus was correlated with the relative abundance of several microbiota. LimitationsDetailed mechanisms are unclear. ConclusionsThese results suggest that the splenic nerve plays a role in inflammation-related depression, microglial activation in the hippocampus, and that gut microbiota may regulate microglial function in the brain via gut–microbiota–brain axis.

Electrical stimulation of the splenic nerve bundle ameliorates dextran sulfate sodium-induced colitis in mice

BackgroundVagus nerve stimulation has been suggested to affect immune responses, partly through a neuronal circuit requiring sympathetic innervation of the splenic nerve bundle and norepinephrine (NE) release. Molecular and cellular mechanisms of action remain elusive. Here, we investigated the therapeutic value of this neuromodulation in inflammatory bowel disease (IBD) by applying electrical splenic nerve bundle stimulation (SpNS) in mice with dextran sulfate sodium (DSS)-induced colitis.MethodsCuff electrodes were implanted around the splenic nerve bundle in mice, whereupon mice received SpNS or sham stimulation. Stimulation was applied 6 times daily for 12 days during DSS-induced colitis. Colonic and splenic tissues were collected for transcriptional analyses by qPCR and RNA-sequencing (RNA-seq). In addition, murine and human splenocytes were stimulated with lipopolysaccharide (LPS) in the absence or presence of NE. Single-cell RNA-seq data from publicly available data sets were analyzed for expression of β-adrenergic receptors (β-ARs).ResultsColitic mice undergoing SpNS displayed reduced colon weight/length ratios and showed improved Disease Activity Index scores with reduced Tumor Necrosis Factor α mRNA expression in the colon compared with sham stimulated mice. Analyses of splenocytes from SpNS mice using RNA-seq demonstrated specific immune metabolism transcriptome profile changes in myeloid cells. Splenocytes showed expression of β-ARs in myeloid and T cells. Cytokine production was reduced by NE in mouse and human LPS-stimulated splenocytes.ConclusionsTogether, our results demonstrate that SpNS reduces clinical features of colonic inflammation in mice with DSS-induced colitis possibly by inhibiting splenic myeloid cell activation. Our data further support exploration of the clinical use of SpNS for patients with IBD.

НЕРВНЫЕ И ГУМОРАЛЬНЫЕ ПУТИ ВЛИЯНИЯ ЭНДОТОКСИНОВ КИШКИ НА ИНТЕРОЦЕПТИВНЫЕ РЕФЛЕКТОРНЫЕ РЕАКЦИИ

In acute experiments on rats, an increase and decrease in afferent activity in the mesenteric nerves of the intestine as well as vagus under the diaphragm, depending on the site of lipopolysaccharide (LPS, 10 μg) injection into the intestinal lumen, has been established. In addition, the effect of endotoxin on the gastrointestinal tract (GIT) is manifested in a reflex change in the efferent nerve impulses. The reactions of the cervical sympathetic, splenic, cranial and caudal mesenteric nerves as well as vagus under the diaphragm are represented by an increase or decrease in the spontaneous activity of efferent fibers and depend on the zone of LPS infusion in the GIT. In general, inhibitory responses to endotoxin predominate, especially in the mesenteric nerves. According to experiments, the reflex responses of sympathetic efferent fibers caused by balloon distension of the colon are regularly weakened or completely suppressed after the infusion of LPS into the lumen of this organ. Under conditions of complete external decentralization of the GIT by transection of the vagus, all mesenteric nerves and the colon at the border with the rectum, the effects of modulation of the activity of both peripheral and central nervous structures under the influence of LPS are preserved due to the humoral pathway included in the complex neurotransmitter mechanism for controlling autonomic functions.

Optogenetic stimulation of cholinergic neuronal endings in the celiac‐superior mesenteric ganglion complex suppresses inflammation in murine endotoxemia

The vagus nerve plays a key role in the regulation of inflammation within the inflammatory reflex (Annu Rev Immunol, 2018, 36:783). In this major physiological neuroimmunoregulatory mechanism, efferent vagus nerve cholinergic axons interact with catecholaminergic neurons of the splenic nerve in the celiac‐superior mesenteric ganglion (CSMG) complex(Proc Natl Acad Sci USA, 2020, 117(47):29803).Previous studies utilizing electrical and optogenetic neuromodulation have demonstrated that vagus nerve cholinergic signalling suppresses pro‐inflammatory cytokine levels during endotoxemia and other inflammatory conditions. However, the specific role of cholinergic axonal terminals in the CSMG complex in this regulation remained enigmatic. To provide insight, we investigated the effect of selective optogenetic stimulation of cholinergic neuronal endings in the CSMG complex on cytokine and chemokine levels during murine endotoxemia. We used transgenic female 10–14‐week‐old mice expressing channelrhodopsin 2 coupled with yellow fluorescent protein on cholinergic, i.e., choline acetyltransferase positive neurons (ChAT‐ChR2‐eYFP). Anesthetized mice were subjected to abdominal surgery and the CSMG complex was localized medial to the upper pole left kidney and along the branch of the abdominal aorta, above the left renal vein. Blue laser light stimulation at 473nm was delivered in square pulses for 10mins at 20Hz, 25% duty cycle through an optic fiber cannula placed in contact with the CSMG complex. 30mins following optogenetic stimulation or sham stimulation, lipopolysaccharide (0.25mg/kg) was injected intraperitoneally and 90mins later mice were euthanized and blood, and spleen were collected and processed for cytokine and chemokines. Optogenetic stimulation of the CSMG complex in ChAT‐ChR2 mice (n=14) suppressed serum pro‐inflammatory cytokines and chemokines compared with sham stimulation (n=13), including TNF(401.7 ± 102.9 pg/ml vs 766.1 ± 207.2 pg/ml; P<0.0001) and MIP‐1α (6,523 ± 3,041 pg/ml vs 10,672 ± 3,915 pg/ml, P=0.0066), while the serum levels of the anti‐inflammatory cytokine IL‐10 were significantly increased (30,779 ± 10,035 pg/ml vs 22,979 ± 9,669 pg/ml, P=0.0427). There was also a significant reduction in splenic TNF levels in the stimulated vs the sham group(P=0.0023). Of note, optogenetic stimulation of the CSMG complex in littermate mice that do not express ChR2 on cholinergic neurons did not alter serum and splenic cytokine levels. These results provide the first experimental evidence that selective stimulation of cholinergic neuronal endings in the CSMG complex attenuates cytokine and chemokine levels. Future studies examining the specific contribution of vagal and sympathetic preganglionic cholinergic neurons in the CSMG complex in the regulation of immune responses will be instrumental for developing new targeted therapeutic anti‐inflammatory approaches.

Vagus Nerve Stimulation Reduces Indomethacin-Induced Small Bowel Inflammation.

Crohn’s disease is a chronic, idiopathic condition characterized by intestinal inflammation and debilitating gastrointestinal symptomatology. Previous studies of inflammatory bowel disease (IBD), primarily in colitis, have shown reduced inflammation after electrical or pharmacological activation of the vagus nerve, but the scope and kinetics of this effect are incompletely understood. To investigate this, we studied the effect of electrical vagus nerve stimulation (VNS) in a rat model of indomethacin-induced small intestinal inflammation. 1 min of VNS significantly reduced small bowel total inflammatory lesion area [(mean ± SEM) sham: 124 ± 14 mm2, VNS: 62 ± 14 mm2, p = 0.002], intestinal peroxidation and chlorination rates, and intestinal and systemic pro-inflammatory cytokine levels as compared with sham-treated animals after 24 h following indomethacin administration. It was not known whether this observed reduction of inflammation after VNS in intestinal inflammation was mediated by direct innervation of the gut or if the signals are relayed through the spleen. To investigate this, we studied the VNS effect on the small bowel lesions of splenectomized rats and splenic nerve stimulation (SNS) in intact rats. We observed that VNS reduced small bowel inflammation also in splenectomized rats but SNS alone failed to significantly reduce small bowel lesion area. Interestingly, VNS significantly reduced small bowel lesion area for 48 h when indomethacin administration was delayed. Thus, 1 min of electrical activation of the vagus nerve reduced indomethacin-induced intestinal lesion area by a spleen-independent mechanism. The surprisingly long-lasting and spleen-independent effect of VNS on the intestinal response to indomethacin challenge has important implications on our understanding of neural control of intestinal inflammation and its potential translation to improved therapies for IBD.

Age-Related Variation in Sympathetic Nerve Distribution in the Human Spleen.

Introduction: The cholinergic anti-inflammatory pathway (CAIP) has been proposed as an efferent neural pathway dampening the systemic inflammatory response via the spleen. The CAIP activates the splenic neural plexus and a subsequent series of intrasplenic events, which at least require a close association between sympathetic nerves and T cells. Knowledge on this pathway has mostly been derived from rodent studies and only scarce information is available on the innervation of the human spleen. This study aimed to investigate the sympathetic innervation of different structures of the human spleen, the topographical association of nerves with T cells and age-related variations in nerve distribution.Materials and Methods: Spleen samples were retrieved from a diagnostic archive and were allocated to three age groups; neonates, 10–25 and 25–70 years of age. Sympathetic nerves and T cells were identified by immunohistochemistry for tyrosine hydroxylase (TH) and the membrane marker CD3, respectively. The overall presence of sympathetic nerves and T cells was semi-automatically quantified and expressed as total area percentage. A predefined scoring system was used to analyze the distribution of nerves within different splenic structures.Results: Sympathetic nerves were observed in all spleens and their number appeared to slightly increase from birth to adulthood and to decrease afterward. Irrespective to age, more than halve of the periarteriolar lymphatic sheaths (PALSs) contained sympathetic nerves in close association with T cells. Furthermore, discrete sympathetic nerves were observed in the capsule, trabeculae and red pulp and comparable to the total amount of sympathetic nerves, showed a tendency to decrease with age. No correlation was found between the number of T cells and sympathetic nerves.Conclusion: The presence of discrete sympathetic nerves in the splenic parenchyma, capsule and trabecular of human spleens could suggest a role in functions other than vasoregulation. In the PALS, sympathetic nerves were observed to be in proximity to T cells and is suggestive for the existence of the CAIP in humans. Since sympathetic nerve distribution shows interspecies and age-related variation, and our general understanding of the relative and spatial contribution of splenic innervation in immune regulation is incomplete, it remains difficult to estimate the anti-inflammatory potential of targeting splenic nerves in patients.

Platinized graphene fiber electrodes uncover direct spleen-vagus communication

Neural interfacing nerve fascicles along the splenic neurovascular plexus (SNVP) is needed to better understand the spleen physiology, and for selective neuromodulation of this major organ. However, their small size and anatomical location have proven to be a significant challenge. Here, we use a reduced liquid crystalline graphene oxide (rGO) fiber coated with platinum (Pt) as a super-flexible suture-like electrode to interface multiple SNVP. The Pt-rGO fibers work as a handover knot electrodes over the small SNVP, allowing sensitive recording from four splenic nerve terminal branches (SN 1–4), to uncover differential activity and axon composition among them. Here, the asymmetric defasciculation of the SN branches is revealed by electron microscopy, and the functional compartmentalization in spleen innervation is evidenced in response to hypoxia and pharmacological modulation of mean arterial pressure. We demonstrate that electrical stimulation of cervical and sub-diaphragmatic vagus nerve (VN), evokes activity in a subset of SN terminal branches, providing evidence for a direct VN control over the spleen. This notion is supported by adenoviral tract-tracing of SN branches, revealing an unconventional direct brain-spleen projection. High-performance Pt-rGO fiber electrodes, may be used for the fine neural modulation of other small neurovascular plexus at the point of entry of major organs as a bioelectronic medical alternative.

A comparative anatomical and histological study on the presence of an apical splenic nerve in mice and humans.

The cranial pole of the mouse spleen is considered to be parasympathetically innervated by a macroscopic observable nerve referred to as the apical splenic nerve (ASN). Electrical stimulation of the ASN resulted in increased levels of splenic acetylcholine, decreased lipopolysaccharide‐induced levels of systemic tumor necrosis factor alpha and mitigated clinical symptoms in a mouse model of rheumatoid arthritis. If such a discrete ASN would be present in humans, this structure is of interest as it might represent a relatively easily accessible electrical stimulation target to treat immune‐mediated inflammatory diseases. So far, it is unknown if a human ASN equivalent exists. This study aimed to provide a detailed description of the location and course of the ASN in mice. Subsequently, this information was used for a guided exploration of an equivalent structure in humans. Microscopic techniques were applied to confirm nerve identity and compare ASN composition.Six mice and six human cadavers were used to study and compare the ASN, both macro‐ and microscopically. Macroscopic morphological characteristics of the ASN in both mice and humans were described and photographs were taken. ASN samples were resected, embedded in paraffin, cut in 5 μm thin sections where after adjacent sections were stained with a general, sympathetic and parasympathetic nerve marker, respectively. Neural identity and nerve fiber composition was then evaluated microscopically.Macroscopically, the ASN could be clearly identified in all mice and was running in the phrenicosplenic ligament connecting the diaphragm and apical pole of the spleen. If a phrenicosplenic ligament was present in humans, a similar configuration of potential neural structures was observed. Since the gastrosplenic ligament was a continuation of the phrenicosplenic ligament, this ligament was explored as well and contained white, potential discrete nerve‐like structures as well which could represent an ANS equivalent. Microscopic evaluation of the ASN in mice and human showed that this structure did not represent a nerve, but most likely connective tissue strains.White nerve‐like structures, which could represent the ASN, were macroscopically observed in the phrenicosplenic ligament in both mice and human and in the gastrosplenic ligament in humans. The microscopic investigation did not confirm their neural identity and therefore, this study disclaims the existence of a parasympathetic ASN in both mice and human.

Splenic Denervation Attenuates Repeated Social Defeat Stress-Induced T Lymphocyte Inflammation

BackgroundPosttraumatic stress disorder (PTSD) is a devastating psychological disorder. Patients with PTSD canonically demonstrate an increased risk for inflammatory diseases as well as increased sympathetic tone and norepinephrine outflow. Yet, the exact etiology and causal nature of these physiologic changes remain unclear. Previously, we demonstrated that exogenous norepinephrine alters mitochondrial superoxide in T lymphocytes to produce a proinflammatory T helper 17 phenotype and observed similar T helper 17 polarization in a preclinical model of PTSD. Therefore, we hypothesized sympathetic-driven neuroimmune interactions could mediate psychological trauma–induced T lymphocyte inflammation. MethodsRepeated social defeat stress (RSDS) is a preclinical murine model that recapitulates the behavioral, autonomic, and inflammatory aspects of PTSD. Targeted splenic denervation was performed to deduce the contribution of splenic sympathetic nerves to RSDS-induced inflammation. Denervation or sham operation was performed in 85 C57BL/6J mice, followed by RSDS or control paradigms. Animals were assessed for behavioral, autonomic, inflammatory, and redox profiles. ResultsDenervation did not alter the antisocial or anxiety-like behavior induced by RSDS. In circulation, denervation/RSDS animals exhibited diminished levels of T lymphocyte–specific cytokines (interleukin 2 [IL-2], IL-17A, and IL-22) compared with intact animals, whereas other nonspecific inflammatory cytokines (e.g., IL-6, tumor necrosis factor α, and IL-10) were unaffected by denervation. Importantly, denervation specifically ameliorated the increases in RSDS-induced T lymphocyte mitochondrial superoxide, T helper 17 polarization, and proinflammatory gene expression with minimal impact to non–T lymphocyte immune populations. ConclusionsOverall, our data suggest that sympathetic nerves regulate RSDS-induced splenic T lymphocyte inflammation but play less of a role in the behavioral and non–T lymphocyte inflammatory phenotypes induced by this psychological trauma paradigm.

UPEC kidney infection triggers neuro-immune communication leading to modulation of local renal inflammation by splenic IFNγ.

Bacterial infection results in a veritable cascade of host responses, both local and systemic. To study the initial stages of host-pathogen interaction in living tissue we use spatially-temporally controlled in vivo models. Using this approach, we show here that within 4 h of a uropathogenic Escherichia coli (UPEC) infection in the kidney, an IFNγ response is triggered in the spleen. This rapid infection-mediated inter-organ communication was found to be transmitted via nerve signalling. Bacterial expression of the toxin α-hemolysin directly and indirectly activated sensory neurons, which were identified in the basement membrane of renal tubules. Nerve activation was transmitted via the splenic nerve, inducing upregulation of IFNγ in the marginal zones of the spleen that led to increasing concentrations of IFNγ in the circulation. We found that IFNγ modulated the inflammatory signalling generated by renal epithelia cells in response to UPEC infection. This demonstrates a new concept in the host response to kidney infection; the role of nerves in sensing infection and rapidly triggering a systemic response which can modulate inflammation at the site of infection. The interplay between the nervous and immune systems is an exciting, developing field with the appealing prospect of non-pharmaceutical interventions. Our study identifies an important role for systemic neuro-immune communication in modulating inflammation during the very first hours of a local bacterial infection in vivo.

Human-relevant near-organ neuromodulation of the immune system via the splenic nerve

Neuromodulation of immune function by stimulating the autonomic connections to the spleen has been demonstrated in rodent models. Consequently, neuroimmune modulation has been proposed as a new therapeutic strategy for the treatment of inflammatory conditions. However, demonstration of the translation of these immunomodulatory mechanisms in anatomically and physiologically relevant models is still lacking. Additionally, translational models are required to identify stimulation parameters that can be transferred to clinical applications of bioelectronic medicines. Here, we performed neuroanatomical and functional comparison of the mouse, rat, pig, and human splenic nerve using in vivo and ex vivo preparations. The pig was identified as a more suitable model of the human splenic innervation. Using functional electrophysiology, we developed a clinically relevant marker of splenic nerve engagement through stimulation-dependent reversible reduction in local blood flow. Translation of immunomodulatory mechanisms were then assessed using pig splenocytes and two models of acute inflammation in anesthetized pigs. The pig splenic nerve was shown to locally release noradrenaline upon stimulation, which was able to modulate cytokine production by pig splenocytes. Splenic nerve stimulation was found to promote cardiovascular protection as well as cytokine modulation in a high- and a low-dose lipopolysaccharide model, respectively. Importantly, splenic nerve-induced cytokine modulation was reproduced by stimulating the efferent trunk of the cervical vagus nerve. This work demonstrates that immune responses can be modulated by stimulation of spleen-targeted autonomic nerves in translational species and identifies splenic nerve stimulation parameters and biomarkers that are directly applicable to humans due to anatomical and electrophysiological similarities.

Splenic Nerve Neuromodulation Reduces Inflammation and Promotes Resolution in Chronically Implanted Pigs.

Neuromodulation of the immune system has been proposed as a novel therapeutic strategy for the treatment of inflammatory conditions. We recently demonstrated that stimulation of near-organ autonomic nerves to the spleen can be harnessed to modulate the inflammatory response in an anesthetized pig model. The development of neuromodulation therapy for the clinic requires chronic efficacy and safety testing in a large animal model. This manuscript describes the effects of longitudinal conscious splenic nerve neuromodulation in chronically-implanted pigs. Firstly, clinically-relevant stimulation parameters were refined to efficiently activate the splenic nerve while reducing changes in cardiovascular parameters. Subsequently, pigs were implanted with a circumferential cuff electrode around the splenic neurovascular bundle connected to an implantable pulse generator, using a minimally-invasive laparoscopic procedure. Tolerability of stimulation was demonstrated in freely-behaving pigs using the refined stimulation parameters. Longitudinal stimulation significantly reduced circulating tumor necrosis factor alpha levels induced by systemic endotoxemia. This effect was accompanied by reduced peripheral monocytopenia as well as a lower systemic accumulation of CD16+CD14high pro-inflammatory monocytes. Further, lipid mediator profiling analysis demonstrated an increased concentration of specialized pro-resolving mediators in peripheral plasma of stimulated animals, with a concomitant reduction of pro-inflammatory eicosanoids including prostaglandins. Terminal electrophysiological and physiological measurements and histopathological assessment demonstrated integrity of the splenic nerves up to 70 days post implantation. These chronic translational experiments demonstrate that daily splenic nerve neuromodulation, via implanted electronics and clinically-relevant stimulation parameters, is well tolerated and is able to prime the immune system toward a less inflammatory, pro-resolving phenotype.

Therapeutic Potential of Vagus Nerve Stimulation for Inflammatory Bowel Diseases.

The vagus nerve is a mixed nerve, comprising 80% afferent fibers and 20% efferent fibers. It allows a bidirectional communication between the central nervous system and the digestive tract. It has a dual anti-inflammatory properties via activation of the hypothalamic pituitary adrenal axis, by its afferents, but also through a vago-vagal inflammatory reflex involving an afferent (vagal) and an efferent (vagal) arm, called the cholinergic anti-inflammatory pathway. Indeed, the release of acetylcholine at the end of its efferent fibers is able to inhibit the release of tumor necrosis factor (TNF) alpha by macrophages via an interneuron of the enteric nervous system synapsing between the efferent vagal endings and the macrophages and releasing acetylcholine. The vagus nerve also synapses with the splenic sympathetic nerve to inhibit the release of TNF-alpha by splenic macrophages. It can also activate the spinal sympathetic system after central integration of its afferents. This anti-TNF-alpha effect of the vagus nerve can be used in the treatment of chronic inflammatory bowel diseases, represented by Crohn’s disease and ulcerative colitis where this cytokine plays a key role. Bioelectronic medicine, via vagus nerve stimulation, may have an interest in this non-drug therapeutic approach as an alternative to conventional anti-TNF-alpha drugs, which are not devoid of side effects feared by patients.

Research progress of exploring the treatment of sepsis based on cholinergic anti-inflammatory pathway

The cholinergic anti-inflammatory pathway (CAP) is an important neuroimmunomodulatory mechanism that innervates the spleen through vagus nerve efferent and splenic nerve relay, and acts on macrophages by transforming adrenergic stimulation into cholinergic signal by spleen T cells, which plays an anti-inflammatory effect, and maintains the balance of inflammatory response. Due to the critical role of the imbalance of pro-inflammatory and anti-inflammatory responses in the physiological process of sepsis, regulating the activity of the CAP has become an important focus in the treatments of sepsis. Based on the understanding of the CAP, vagus nerve stimulation, drug agonists mimicking cholinergic signals, and acupuncture are currently applied in the research and exploration of sepsis treatment. This article summarizes the recent progress and prospects of the CAP mechanism, biological effects, and application in sepsis treatment.

Identification of a brainstem locus that inhibits tumor necrosis factor

In the brain, compact clusters of neuron cell bodies, termed nuclei, are essential for maintaining parameters of host physiology within a narrow range optimal for health. Neurons residing in the brainstem dorsal motor nucleus (DMN) project in the vagus nerve to communicate with the lungs, liver, gastrointestinal tract, and other organs. Vagus nerve-mediated reflexes also control immune system responses to infection and injury by inhibiting the production of tumor necrosis factor (TNF) and other cytokines in the spleen, although the function of DMN neurons in regulating TNF release is not known. Here, optogenetics and functional mapping reveal cholinergic neurons in the DMN, which project to the celiac-superior mesenteric ganglia, significantly increase splenic nerve activity and inhibit TNF production. Efferent vagus nerve fibers terminating in the celiac-superior mesenteric ganglia form varicose-like structures surrounding individual nerve cell bodies innervating the spleen. Selective optogenetic activation of DMN cholinergic neurons or electrical activation of the cervical vagus nerve evokes action potentials in the splenic nerve. Pharmacological blockade and surgical transection of the vagus nerve inhibit vagus nerve-evoked splenic nerve responses. These results indicate that cholinergic neurons residing in the brainstem DMN control TNF production, revealing a role for brainstem coordination of immunity.

Morphometric analysis of the splenic artery using contrast-enhanced computed tomography (CT)

PurposeTo evaluate the morphology and course of the splenic artery, which might impact the surgical implantation of systems that stimulate the nerves surrounding the splenic artery. Experimental studies indicate that these nerves play an important part in immune modulation, and might be a potential target in the treatment of autoimmune diseases.MethodsThis retrospective cohort study made use of contrast-enhanced CT images from 40 male and 40 female patients (age 30–69) that underwent a CT examination of the aorta, kidneys or pancreas. Anatomic features were described including total splenic artery length, calibers, tortuosity, the presence of arterial loops and the branching pattern of the splenic artery.ResultsNo age-gender-related differences could be found related to tortuosity or branching pattern. The length of splenic artery in contact with pancreatic tissue decreased with increasing age, but was not different between genders. Artery diameters were wider in male compared to female subjects. Loops of variable directions, that represent a part of the artery that curls out of the pancreatic tissue, were identified in each age-gender category and were present in nearly all subjects (86%).ConclusionThis study suggests that although some anatomic features of the splenic artery are subject to factors as age and gender, the tortuosity of the splenic artery is not age dependent. Most subjects had one or multiple loops, which can serve as a target for neuromodulatory devices. Future studies should investigate whether splenic nerve stimulation is safe and feasible.

Quantification of clinically applicable stimulation parameters for precision near-organ neuromodulation of human splenic nerves

Neuromodulation is a new therapeutic pathway to treat inflammatory conditions by modulating the electrical signalling pattern of the autonomic connections to the spleen. However, targeting this sub-division of the nervous system presents specific challenges in translating nerve stimulation parameters. Firstly, autonomic nerves are typically embedded non-uniformly among visceral and connective tissues with complex interfacing requirements. Secondly, these nerves contain axons with populations of varying phenotypes leading to complexities for axon engagement and activation. Thirdly, clinical translational of methodologies attained using preclinical animal models are limited due to heterogeneity of the intra- and inter-species comparative anatomy and physiology. Here we demonstrate how this can be accomplished by the use of in silico modelling of target anatomy, and validation of these estimations through ex vivo human tissue electrophysiology studies. Neuroelectrical models are developed to address the challenges in translation of parameters, which provides strong input criteria for device design and dose selection prior to a first-in-human trial.

Splenic sympathetic signaling contributes to acute neutrophil infiltration of the injured spinal cord

BackgroundAlterations in the immune system are a complication of spinal cord injury (SCI) and have been linked to an excessive sympathetic outflow to lymphoid organs. Still unknown is whether these peripheral immune changes also contribute for the deleterious inflammatory response mounted at the injured spinal cord.MethodsWe analyzed different molecular outputs of the splenic sympathetic signaling for the first 24 h after a thoracic compression SCI. We also analyzed the effect of ablating the splenic sympathetic signaling to the innate immune and inflammatory response at the spleen and spinal cord 24 h after injury.ResultsWe found that norepinephrine (NE) levels were already raised at this time-point. Low doses of NE stimulation of splenocytes in vitro mainly affected the neutrophils’ population promoting an increase in both frequency and numbers. Interestingly, the interruption of the sympathetic communication to the spleen, by ablating the splenic nerve, resulted in reduced frequencies and numbers of neutrophils both at the spleen and spinal cord 1 day post-injury.ConclusionCollectively, our data demonstrates that the splenic sympathetic signaling is involved in the infiltration of neutrophils after spinal cord injury. Our findings give new mechanistic insights into the dysfunctional regulation of the inflammatory response mounted at the injured spinal cord.