Modulation of experimental arthritis by vagal sensory and central brain stimulation

Vagotomy accelerates the onset of symptoms during early disease progression and worsens joint-level pathogenesis in a male rat model of chronic knee osteoarthritis

Objective

Low vagal tone is common in osteoarthritis (OA) comorbidities and results in greater peripheral inflammation. Characterizing vagal tone's role in OA pathogenesis may offer insights into OA's influences beyond the articular joint. We hypothesized that low vagal tone would accelerate onset of OA-related gait changes and worsen joint damage in a rat knee OA model.

Methods

Knee OA was induced in male Sprague Dawley rats by transecting the medial collateral ligament and medial meniscus. Then, left cervical vagus nerve transection (VGX, n ​= ​9) or sham VGX (non-VGX, n ​= ​6) was performed. Gait and tactile sensitivity were assessed at baseline and across 12 weeks, with histology and systemic inflammation evaluated at endpoint.

Results

At week 4, VGX animals showed limping gait characteristics through shifted stance times from their OA to non-OA limb (p ​= ​0.055; stance time imbalance ​= ​1.6 ​± ​1.6%) and shifted foot strike locations (p ​< ​0.001; spatial symmetry ​= ​48.4 ​± ​0.835%), while non-VGX animals walked with a balanced and symmetric gait. Also at week 4, while VGX animals had a mechanical sensitivity (50% withdrawal threshold) of 13.97 ​± ​7.70 compared to the non-VGX animal sensitivity of 29.74 ​± ​9.43, this difference was not statistically significant. Histologically, VGX animals showed thinner tibial cartilage and greater subchondral bone area than non-VGX animals (p ​= ​0.076; VGX: 0.80 ​± ​0.036 ​mm2; non-VGX: 0.736 ​± ​0.066 ​mm2). No group differences in systemic inflammation were observed at endpoint.

Conclusions

VGX resulted in quicker onset of OA-related symptoms but remained unchanged at later timepoints. VGX also had thinner cartilage and abnormal bone remodeling than non-VGX. Overall, low vagal tone had mild effects on OA symptoms and joint remodeling, and not at the level seen in common OA comorbidities.

Disrupted autonomic pathways in spinal cord injury: Implications for the immune regulation

Spinal Cord Injury (SCI) disrupts critical autonomic pathways responsible for the regulation of the immune function. Consequently, individuals with SCI often exhibit a spectrum of immune dysfunctions ranging from the development of damaging pro-inflammatory responses to severe immunosuppression. Thus, it is imperative to gain a more comprehensive understanding of the extent and mechanisms through which SCI-induced autonomic dysfunction influences the immune response. In this review, we provide an overview of the anatomical organization and physiology of the autonomic nervous system (ANS), elucidating how SCI impacts its function, with a particular focus on lymphoid organs and immune activity. We highlight recent advances in understanding how intraspinal plasticity that follows SCI may contribute to aberrant autonomic activity in lymphoid organs. Additionally, we discuss how sympathetic mediators released by these neuron terminals affect immune cell function. Finally, we discuss emerging innovative technologies and potential clinical interventions targeting the ANS as a strategy to restore the normal regulation of the immune response in individuals with SCI.

Vagus nerve stimulation enhances remyelination and decreases innate neuroinflammation in lysolecithin-induced demyelination

BACKGROUND

Current treatments for Multiple Sclerosis (MS) poorly address chronic innate neuroinflammation nor do they offer effective remyelination. The vagus nerve has a strong regulatory role in inflammation and Vagus Nerve Stimulation (VNS) has potential to affect both neuroinflammation and remyelination in MS.

OBJECTIVE

This study investigated the effects of VNS on demyelination and innate neuroinflammation in a validated MS rodent model.

METHODS

Lysolecithin (LPC) was injected in the corpus callosum (CC) of 46 Lewis rats, inducing a demyelinated lesion. 33/46 rats received continuously-cycled VNS (cVNS) or one-minute per day VNS (1minVNS) or sham VNS from 2 days before LPC-injection until perfusion at 3 days post-injection (dpi) (corresponding with a demyelinated lesion with peak inflammation). 13/46 rats received cVNS or sham from 2 days before LPC-injection until perfusion at 11 dpi (corresponding with a partial remyelinated lesion). Immunohistochemistry and proteomics analyses were performed to investigate the extend of demyelination and inflammation.

RESULTS

Immunohistochemistry showed that cVNS significantly reduced microglial and astrocytic activation in the lesion and lesion border, and significantly reduced the Olig2+ cell count at 3 dpi. Furthermore, cVNS significantly improved remyelination with 57.4 % versus sham at 11 dpi. Proteomic gene set enrichment analyses showed increased activation of (glutamatergic) synapse pathways in cVNS versus sham, most pronounced at 3 dpi.

CONCLUSION

cVNS improved remyelination of an LPC-induced lesion. Possible mechanisms might include modulation of microglia and astrocyte activity, increased (glutamatergic) synapses and enhanced oligodendrocyte clearance after initial injury.

Skeletal interoception in osteoarthritis

The interoception maintains proper physiological conditions and metabolic homeostasis by releasing regulatory signals after perceving changes in the internal state of the organism. Among its various forms, skeletal interoception specifically regulates the metabolic homeostasis of bones. Osteoarthritis (OA) is a complex joint disorder involving cartilage, subchondral bone, and synovium. The subchondral bone undergoes continuous remodeling to adapt to dynamic joint loads. Recent findings highlight that skeletal interoception mediated by aberrant mechanical loads contributes to pathological remodeling of the subchondral bone, resulting in subchondral bone sclerosis in OA. The skeletal interoception is also a potential mechanism for chronic synovial inflammation in OA. In this review, we offer a general overview of interoception, specifically skeletal interoception, subchondral bone microenviroment and the aberrant subchondral remedeling. We also discuss the role of skeletal interoception in abnormal subchondral bone remodeling and synovial inflammation in OA, as well as the potential prospects and challenges in exploring novel OA therapies that target skeletal interoception.

The immunomodulatory effect of oral NaHCO3 is mediated by the splenic nerve: multivariate impact revealed by artificial neural networks

Stimulation of the inflammatory reflex (IR) is a promising strategy for treating systemic inflammatory disorders. Recent studies suggest oral sodium bicarbonate (NaHCO3) as a potential activator of the IR, offering a safe and cost-effective treatment approach. However, the mechanisms underlying NaHCO3-induced anti-inflammatory effects remain unclear. We investigated whether oral NaHCO3's immunomodulatory effects are mediated by the splenic nerve. Female rats received NaHCO3 or water (H2O) for four days, and splenic immune markers were assessed using flow cytometry. NaHCO3 led to a significant increase (p < 0.05, and/or partial eta squared > 0.06) in anti-inflammatory markers, including CD11bc + CD206 + (M2-like) macrophages, CD3 + CD4 + FoxP3 + cells (Tregs), and Tregs/M1-like ratio. Conversely, proinflammatory markers, such as CD11bc + CD38 + TNFα + (M1-like) macrophages, M1-like/M2-like ratio, and SSChigh/SSClow ratio of FSChighCD11bc + cells, decreased in the spleen following NaHCO3 administration. These effects were abolished in spleen-denervated rats, suggesting the necessity of the splenic nerve in mediating NaHCO3-induced immunomodulation. Artificial neural networks accurately classified NaHCO3 and H2O treatment in sham rats but failed in spleen-denervated rats, highlighting the splenic nerve's critical role. Additionally, spleen denervation independently influenced Tregs, M2-like macrophages, Tregs/M1-like ratio, and CD11bc + CD38 + cells, indicating distinct effects from both surgery and treatment. Principal component analysis (PCA) further supported the separate effects. Our findings suggest that the splenic nerve transmits oral NaHCO3-induced immunomodulatory changes to the spleen, emphasizing NaHCO3's potential as an IR activator with therapeutic implications for a wide spectrum of systemic inflammatory conditions.

Diminazene aceturate attenuates systemic inflammation via microbiota gut-5-HT brain-spleen sympathetic axis in male mice

The sympathetic arm of the inflammatory reflex is the efferent pathway through which the central nervous system (CNS) can control peripheral immune responses. Diminazene aceturate (DIZE) is an antiparasitic drug that has been reported to exert protective effects on various experimental models of inflammation. However, the pathways by which DIZE promotes a protective immunomodulatory effects still need to be well established, and no studies demonstrate the capacity of DIZE to modulate a neural reflex to control inflammation. C57BL/6 male mice received intraperitoneal administration of DIZE (2 mg/Kg) followed by lipopolysaccharide (LPS, 5 mg/Kg, i.p.). Endotoxemic animals showed hyperresponsiveness to inflammatory signals, while those treated with DIZE promoted the activation of the inflammatory reflex to attenuate the inflammatory response during endotoxemia. The unilateral cervical vagotomy did not affect the anti-inflammatory effect of DIZE in the spleen and serum. At the same time, splenic denervation attenuated tumor necrosis factor (TNF) synthesis in the spleen and serum. Using broad-spectrum antibiotics for two weeks showed that LPS modulated the microbiota to induce a pro-inflammatory profile in the intestine and reduced the serum concentration of tryptophan and serotonin (5-HT), while DIZE restored serum tryptophan and increased the hypothalamic 5-HT levels. Furthermore, the treatment with 4-Chloro-DL-phenylalanine (pcpa, an inhibitor of 5-HT synthesis) abolished the anti-inflammatory effects of the DIZE in the spleen. Our results indicate that DIZE promotes microbiota modulation to increase central 5-HT levels and activates the efferent sympathetic arm of the inflammatory reflex to control splenic TNF production in endotoxemic mice.

Exploring the impact of integrated polyvagal exercises and knee reinforcement in females with grade II knee osteoarthritis: a randomized controlled trial

This study aimed to compare the effects of knee strengthening exercises to those of polyvagal theory-based exercises combined with knee strengthening exercises on selected outcomes in women with grade II knee osteoarthritis (OA). A randomized controlled trial was conducted, in which 60 female participants diagnosed with grade II knee OA, with a mean age of 57.27 ± 7.81 years and knee pain rated between 4 and 7 on the visual analog scale (VAS), were assigned to either the knee strengthening exercise group (Group 1, n = 30) or the polyvagal theory-based exercise plus knee strengthening exercise group (Group 2, n = 30). Pre- and posttreatment assessment of outcome variables, including WOMAC scores (joint pain, joint stiffness, functional limitations, and the overall index), WHOQOL scores (overall quality of life, general health, physical, psychological, social, and environmental domains), and heart rate variability (HRV, time and frequency domains), were analyzed. Group 2 demonstrated significantly greater reductions in joint pain, stiffness, and functional limitations than Group 1 after the intervention. Group 2 presented with significantly improved WOMAC scores, indicating better overall outcomes. Group 2 showed significant improvements in the psychological and social domains regarding quality of life. There were no significant differences in the physical domain or the environmental domain. Group 2 showed a significant increase in high-frequency power (HF) and a significant decrease in the LF/HF ratio, suggesting improved autonomic regulation. A combination of polyvagal exercise and knee strengthening training resulted in superior outcomes compared to knee strengthening exercises alone in women with grade II knee OA. These findings support the potential effectiveness of incorporating polyvagal exercises as an adjunctive intervention for osteoarthritis management.

Pharmacological and Electroceutical Targeting of the Cholinergic Anti-Inflammatory Pathway in Autoimmune Diseases

Continuous dialogue between the immune system and the brain plays a key homeostatic role in various immune responses to environmental cues. Several functions are under the control of the vagus nerve-based inflammatory reflex, a physiological mechanism through which nerve signals regulate immune functions. In the cholinergic anti-inflammatory pathway, the vagus nerve, its pivotal neurotransmitter acetylcholine, together with the corresponding receptors play a key role in modulating the immune response of mammals. Through communications of peripheral nerves with immune cells, it modulates proliferation and differentiation activities of various immune cell subsets. As a result, this pathway represents a potential target for treating autoimmune diseases characterized by overt inflammation and a decrease in vagal tone. Consistently, converging observations made in both animal models and clinical trials revealed that targeting the cholinergic anti-inflammatory pathway using pharmacologic approaches can provide beneficial effects. In parallel, bioelectronic medicine has recently emerged as an alternative approach to managing systemic inflammation. In several studies, nerve electrostimulation was reported to be clinically relevant in reducing chronic inflammation in autoimmune diseases, including rheumatoid arthritis and diabetes. In the future, these new approaches could represent a major therapeutic strategy for autoimmune and inflammatory diseases.

Autonomic Regulation of Inflammation in Conscious Animals

Bioelectronic medicine is a novel field in modern medicine based on the specific neuronal stimulation to control organ function, cardiovascular, and immune homeostasis. However, most studies addressing neuromodulation of the immune system have been conducted on anesthetized animals, which can affect the nervous system and neuromodulation. Here, we review recent studies involving conscious experimental rodents (rats and mice) to better understand the functional organization of neural control of immune homeostasis. We highlight typical experimental models of cardiovascular regulation, such as electrical activation of the aortic depressor nerve or the carotid sinus nerve, bilateral carotid occlusion, the Bezold-Jarisch reflex, and intravenous administration of the bacterial endotoxin lipopolysaccharide. These models have been used to investigate the relationship between neuromodulation of the cardiovascular and immune systems in conscious rodents (rats and mice). These studies provide critical information about the neuromodulation of the immune system, particularly the role of the autonomic nervous system, i.e., the sympathetic and parasympathetic branches acting both centrally (hypothalamus, nucleus ambiguus, nucleus tractus solitarius, caudal ventrolateral medulla, and rostral ventrolateral medulla), and peripherally (particularly spleen and adrenal medulla). Overall, the studies in conscious experimental models have certainly highlighted to the reader how the methodological approaches used to investigate cardiovascular reflexes in conscious rodents (rats and mice) can also be valuable for investigating the neural mechanisms involved in inflammatory responses. The reviewed studies have clinical implications for future therapeutic approaches of bioelectronic modulation of the nervous system to control organ function and physiological homeostasis in conscious physiology.

Electroacupuncture activated local sympathetic noradrenergic signaling to relieve synovitis and referred pain behaviors in knee osteoarthritis rats

Introduction

Recent research has focused on the local control of articular inflammation through neuronal stimulation to avoid the systemic side effects of conventional pharmacological therapies. Electroacupuncture (EA) has been proven to be useful for inflammation suppressing and pain reduction in knee osteoarthritis (KOA) patients, yet its mechanism remains unclear.

Methods

In the present study, the KOA model was established using the intra-articular injection of sodium monoiodoacetate (MIA) (1 mg/50 μL) into the knee cavity. EA was delivered at the ipsilateral ST36-GB34 acupoints. Hind paw weight-bearing and withdrawl thresholds were measured. On day 9, the histology, dep enrichment proteins, cytokines contents, immune cell population of the synovial membrane of the affected limbs were measured using HE staining, Masson staining, DIA quantitative proteomic analysis, flow cytometry, immunofluorescence staining, ELISA, and Western Blot. The ultrastructure of the saphenous nerve of the affected limb was observed using transmission electron microscopy on the 14th day after modeling.

Results

The result demonstrated that EA intervention during the midterm phase of the articular inflammation alleviated inflammatory pain behaviors and cartilage damage, but not during the early phase. Mid-term EA suppressed the levels of proinflammatory cytokines TNF-α, IL-1β, and IL-6 in the synovium on day 9 after MIA by elevating the level of sympathetic neurotransmitters Norepinephrine (NE) in the synovium but not systemic NE or systemic adrenaline. Selective blocking of the sympathetic function (6-OHDA) and β2-adrenergic receptor (ICI 118,551) prevented the anti-inflammatory effects of EA. EA-induced increment of the NE in the synovium inhibited the CXCL1-CXCR2 dependent overexpression of IL-6 in the synovial macrophages in a β2-adrenergic receptor (AR)-mediated manner.

Discussion

These results revealed that EA activated sympathetic noradrenergic signaling to control local inflammation in KOA rats and contributed to the development of novel therapeutic neurostimulation strategies for inflammatory diseases.

Neuromodulation as a Potential Disease-Modifying Therapy for Osteoarthritis

PURPOSE OF REVIEW

The following review discusses the therapeutic potential of targeting the autonomic nervous system (ANS) for osteoarthritis (OA) treatment and encourages the field to consider the candidacy of bioelectronic medicine as a novel OA treatment strategy.

RECENT FINDINGS

The study of OA pathogenesis has focused on changes occurring at the joint level. As such, treatments for OA have been aimed at the local joint environment, intending to resolve local inflammation and decrease pain. However, OA pathogenesis has shown to be more than joint wear and tear. Specifically, OA-related peripheral and central sensitization can prompt neuroplastic changes in the nervous system beyond the articular joint. These neuroplastic changes may alter physiologic systems, like the neuroimmune axis. In this way, OA and related comorbidities may share roots in the form of altered neuroimmune communication and autonomic dysfunction. ANS modulation may be able to modify OA pathogenesis or reduce the impact of OA comorbidities. Moreover, blocking chronic nociceptive drive from the joint may help to prevent maladaptive nervous system plasticity in OA.

Aberrant functional connectivity between anterior cingulate cortex and left insula in association with therapeutic response to biologics in inflammatory arthritis

BACKGROUND

Brain activity is reported to be associated with individual pain susceptibility and inflammatory status, possibly contributing to disease activity assessment in inflammatory arthritis (IA) including rheumatoid arthritis (RA) and spondyloarthritis (SpA). However, what alteration of brain function associated with disease activity and therapeutic effectiveness in IA remains unclear. We aimed to identify the alterations of brain functional connectivity (FC) shared in both RA and SpA, and evaluate its relationship to anti-rheumatic treatment response using functional magnetic resonance imaging (MRI).

PATIENTS AND METHODS

Structural and resting-state functional MRI data were acquired from patients with IA, patients with osteoarthritis (OA) and heathy controls (HCs). Two datasets were adopted to derive (51 IA, 56 OA, and 17 HCs) and validate (31 IA) the observations. 33 IA patients in the derivation dataset and all the patients in validation dataset required biological treatment and were clinically evaluated before and after therapy. Via whole-brain pair-wise FC analyses, we analyzed IA-specific FC measures relevant to therapeutic response to biologics.

RESULTS

The value of FC between left insular cortex (IC) and anterior cingulate cortex (ACC) was significantly low in IA patients compared with OA patients and HCs. We demonstrated that the FC between left anterior long insular gyrus as a subdivision of IC and ACC was significantly associated with therapeutic response to biologics regarding the improvement of patients' global assessment (PGA) in both derivation and validation datasets.

CONCLUSION

Disease-specific resting-state FC provides a means to assess the therapeutic improvement of PGA and would be a clinical decision-making tool with predictability for treatment response in both RA and SpA.

Neurogenic Hypotension and Bradycardia Modulated by Electroacupuncture in Hypothalamic Paraventricular Nucleus

Electroacupuncture (EA) stimulates somatic median afferents underlying P5-6 acupoints and modulates parasympathoexcitatory reflex responses through central processing in the brainstem. Although decreases in blood pressure and heart rate by the neural-mediated Bezold-Jarisch reflex responses are modulated by EA through opioid actions in the nucleus tractus solitarius and nucleus ambiguus, the role of the hypothalamus is unclear. The hypothalamic paraventricular nucleus (PVN) is activated by sympathetic afferents and regulates sympathetic outflow and sympathoexcitatory cardiovascular responses. In addition, the PVN is activated by vagal afferents, but little is known about its regulation of cardiopulmonary inhibitory hemodynamic responses. We hypothesized that the PVN participates in the Bezold-Jarisch reflex responses and EA inhibits these cardiopulmonary responses through the PVN opioid system. Rats were anesthetized and ventilated, and their heart rate and blood pressures were monitored. Application of phenylbiguanide every 10 min close to the right atrium induced consistent depressor and bradycardia reflex responses. Unilateral microinjection of the depolarization blockade agent kainic acid or glutamate receptor antagonist kynurenic acid in the PVN reduced these reflex responses. In at least 70% of the rats, 30 min of bilateral EA at P5-6 acupoints reduced the depressor and bradycardia responses for at least 60 min. Blockade of the CCK-1 receptors converted the non-responders into EA-responders. Unilateral PVN-microinjection with naloxone reversed the EA inhibition. Vagal-evoked activity of the PVN cardiovascular neurons was reduced by 30 min EA (P5-6) through opioid receptor activation. These data indicate that PVN processes inhibitory cardiopulmonary reflexes and participates in EA-modulation of the neural-mediated vasodepression and bradycardia.

Effect of Transauricular Vagus Nerve Stimulation on Rebound Pain After Ropivacaine Single Injection Femoral Nerve Block for Anterior Cruciate Ligament Reconstruction: A Randomized Controlled Trial

Purpose

The aim of this study was to investigate whether transauricular vagus nerve stimulation (taVNS) could reduce the incidence of rebound pain in patients undergoing anterior cruciate ligament reconstruction (ACLR) under general anesthesia combined with preoperative femoral nerve block.

Methods

In total, 78 patients were enrolled in this prospective, randomized, double-blind, and sham-controlled study. Patients were randomly assigned to 2 groups (n=39): Group taVNS received taVNS (1h /1time, 6times) within the first 12 h after surgery; Group SS received sham stimulation (SS) in the same manner. Pain scores at 0, 4, 8, 12, 24, 48 h after surgery were assessed with Numeric Pain Rating Scale (NRS). The incidence, duration and onset of rebound pain were recorded. In addition, additional analgesic requirements and side effects in the first 48 h postoperatively, as well as sleep disturbance on the night of surgery, were examined.

Results

The incidence and duration of rebound pain were lower in the taVNS group than in the SS group (P=0.025 and P=0.015, respectively). Pain scores at 8 h and 12 h postoperatively were significantly lower in the taVNS group compared with the SS group (P<0.05). The number of times to press the patient-controlled analgesia (PCA) pump and the number of patients requiring additional analgesic were significantly lower in the taVNS group than in the SS group until 12 h after surgery (P=0.021 and P=0.004, respectively). The number of patients with sleep disturbance in the taVNS group was lower than that in the SS group (P=0.030).

Conclusion

The taVNS exerts beneficial effect on rebound pain after femoral nerve block in patients undergoing ACLR, which reduces the incidence and duration of rebound pain, the need for postoperative additional analgesic, and the number of complications.

Sciatic-Vagal Nerve Stimulation by Electroacupuncture Alleviates Inflammatory Arthritis in Lyme Disease-Susceptible C3H Mice

Lyme disease is caused by Borrelia burgdorferi, and the pathogenesis of the disease is complex with both bacterial and host factors contributing to inflammatory responses. Lyme disease affects different organs including joints and results in arthritis. Immune responses stimulated by B. burgdorferi through toll-like receptors cause infiltration of leukocytes, which produce inflammatory cytokines and facilitate spirochete clearance. However, arthritic manifestations and chronic fatigue syndrome-like symptoms persist long after completion of antibiotic treatment regimens in a significant number of patients. To counter the effects of inflammation, treatment by non-steroidal anti-inflammatory drugs, hydroxychloroquine, or synovectomy to eradicate inflammatory arthritis in the involved joint could be employed; however, they often have long-term consequences. Acupuncture has been used for a long time in Asian medicine to diminish pain during various ailments, but the effects and its mechanism are just beginning to be explored. Control of inflammation by neuronal stimulation has been exploited as a systemic therapeutic intervention to arrest inflammatory processes. Our objective was to determine whether activation of the sciatic-vagal network by electroacupuncture on ST36 acupoint, which is used to control systemic inflammation in experimental models of infectious disorders such as endotoxemia, can also alleviate Lyme arthritis symptoms in mice. This aim was further strengthened by the reports that sciatic-vagal neuronal network stimulation can lead to dopamine production in the adrenal medulla and moderate the production of inflammatory factors. We first assessed whether electroacupuncture affects spirochete colonization to attenuate Lyme arthritis. Interestingly, bioluminescent B. burgdorferi burden detected by live imaging and qPCR were similar in electroacupuncture- and mock-treated mice, while electroacupuncture induced a lasting anti-inflammatory effect on mice. Despite the discontinuation of treatment at 2 weeks, the simultaneous decrease in neutrophils in the joints and inflammatory cytokine levels throughout the body at 4 weeks suggests a systemic and persistent effect of electroacupuncture that attenuates Lyme arthritis. Our results suggest that electroacupuncture-mediated anti-inflammatory responses could offer promising healthcare benefits in patients suffering from long-term Lyme disease manifestations.

Autonomic Nervous System Dysregulation and Osteoarthritis Pain: Mechanisms, Measurement, and Future Outlook

PURPOSE OF REVIEW

The autonomic nervous system is an important regulator of stress responses and exhibits functional changes in chronic pain states. This review discusses potential overlap among autonomic dysregulation, osteoarthritis (OA) progression, and chronic pain. From this foundation, we then discuss preclinical to clinical research opportunities to close gaps in our knowledge of autonomic dysregulation and OA. Finally, we consider the potential to generate new therapies for OA pain via modulation of the autonomic nervous system.

RECENT FINDINGS

Recent reviews provide a framework for the autonomic nervous system in OA progression; however, research is still limited on the topic. In other chronic pain states, functional overlaps between the central autonomic network and pain processing centers in the brain suggest relationships between concomitant dysregulation of the two systems. Non-pharmacological therapeutics, such as vagus nerve stimulation, mindfulness-based meditation, and exercise, have shown promise in alleviating painful symptoms of joint diseases, and these interventions may be partially mediated through the autonomic nervous system. The autonomic nervous system appears to be dysregulated in OA progression, and further research on rebalancing autonomic function may lead to novel therapeutic strategies for treating OA pain.

The carotid body detects circulating tumor necrosis factor-alpha to activate a sympathetic anti-inflammatory reflex

Recent evidence has suggested that the carotid bodies might act as immunological sensors, detecting pro-inflammatory mediators and signalling to the central nervous system, which, in turn, orchestrates autonomic responses. Here, we confirmed that the TNF-α receptor type I is expressed in the carotid bodies of rats. The systemic administration of TNF-α increased carotid body afferent discharge and activated glutamatergic neurons in the nucleus tractus solitarius (NTS) that project to the rostral ventrolateral medulla (RVLM), where many pre-sympathetic neurons reside. The activation of these neurons was accompanied by an increase in splanchnic sympathetic nerve activity. Carotid body ablation blunted the TNF-α-induced activation of RVLM-projecting NTS neurons and the increase in splanchnic sympathetic nerve activity. Finally, plasma and spleen levels of cytokines after TNF-α administration were higher in rats subjected to either carotid body ablation or splanchnic sympathetic denervation. Collectively, our findings indicate that the carotid body detects circulating TNF-α to activate a counteracting sympathetic anti-inflammatory mechanism.

Vagus Nerve Stimulation as a Potential Therapy in Early Alzheimer's Disease: A Review

Cognitive dysfunction in Alzheimer's disease (AD) is caused by disturbances in neuronal circuits of the brain underpinned by synapse loss, neuronal dysfunction and neuronal death. Amyloid beta and tau protein cause these pathological changes and enhance neuroinflammation, which in turn modifies disease progression and severity. Vagal nerve stimulation (VNS), via activation of the locus coeruleus (LC), results in the release of catecholamines in the hippocampus and neocortex, which can enhance synaptic plasticity and reduce inflammatory signalling. Vagal nerve stimulation has shown promise to enhance cognitive ability in animal models. Research in rodents has shown that VNS can have positive effects on basal synaptic function and synaptic plasticity, tune inflammatory signalling, and limit the accumulation of amyloid plaques. Research in humans with invasive and non-invasive VNS devices has shown promise for the modulation of cognition. However, the direct stimulation of the vagus nerve afforded with the invasive procedure carries surgical risks. In contrast, non-invasive VNS has the potential to be a broadly available therapy to manage cognitive symptoms in early AD, however, the magnitude and specificity of its effects remains to be elucidated, and the non-inferiority of the effects of non-invasive VNS as compared with invasive VNS still needs to be established. Ongoing clinical trials with healthy individuals and patients with early AD will provide valuable information to clarify the potential benefits of non-invasive VNS in cognition and AD. Whether invasive or non-invasive VNS can produce a significant improvement on memory function and whether its effects can modify the progression of AD will require further investigation.

Cervical Vagus Nerve Stimulation Improves Neurologic Outcome After Cardiac Arrest in Mice by Attenuating Oxidative Stress and Excessive Autophagy

BACKGROUND

Cerebral ischemia and reperfusion (I/R) induces oxidative stress and activates autophagy, leading to brain injury and neurologic deficits. Cervical vagus nerve stimulation (VNS) increases cerebral blood flow (CBF). In this study, we investigate the effect of VNS-induced CBF increase on neurologic outcomes after cardiac arrest (CA).

MATERIALS AND METHODS

A total of 40 male C57Bl/6 mice were subjected to ten minutes of asphyxia CA and randomized to vagus nerve isolation (VNI) or VNS treatment group. Eight mice received sham surgery and VNI. Immediately after resuscitation, 20 minutes of electrical stimulation (1 mA, 1 ms, and 10 Hz) was started in the VNS group. Electrocardiogram, blood pressure, and CBF were monitored. Neurologic and histologic outcomes were evaluated at 72 hours. Oxidative stress and autophagy were assessed at 3 hours and 24 hours after CA.

RESULTS

Baseline characteristics were not different among groups. VNS mice had better behavioral performance (ie, open field, rotarod, and neurologic score) and less neuronal death (p < 0.05, vs VNI) in the hippocampus. CBF was significantly increased in VNS-treated mice at 20 minutes after return of spontaneous circulation (ROSC) (p < 0.05). Furthermore, levels of 8-hydroxy-2'-deoxyguanosine in the blood and autophagy-related proteins (ie, LC-3Ⅱ/Ⅰ, Beclin-1, and p62) in the brain were significantly decreased in VNS mice. Aconitase activity was also reduced, and the p-mTOR/mTOR ratio was increased in VNS mice.

CONCLUSIONS

Oxidative stress induced by global brain I/R following CA/ROSC leads to early excessive autophagy and impaired autophagic flux. VNS promoted CBF recovery, ameliorating these changes. Neurologic and histologic outcomes were also improved.

Effect of Transcutaneous Vagus Nerve Stimulation in Erosive Hand Osteoarthritis: Results from a Pilot Trial

Beyond its effect on vegetative functions, the activation of the vagus nerve inhibits inflammation and reduces pain signaling. The aim of this open-label pilot study was to determine the efficacy and tolerance of transcutaneous auricular VNS (taVNS) on erosive hand osteoarthritis (EHOA) symptoms. Symptomatic EHOA patients with hand pain VAS ≥ 40/100 mm and ≥1 interphalangeal swollen joint(s) were included. The taVNS was performed for 4 weeks using an auricular electrode applied one hour per day and connected to a TENS device with pre-established settings. Clinical efficacy was evaluated by changes between baseline and at 4 weeks with hand pain VAS and the functional index FIHOA score, using a Wilcoxon t-test. The treatment tolerance was also evaluated. Eighteen patients (median age 69 years old, 83% women) were analyzed. At baseline, hand pain VAS was 60 mm [IQR 50; 78.2] and FIHOA 15 [10.7; 20.2]. After 4 weeks, taVNS significantly reduced hand pain VAS, with a median decrease of 23.5 mm [7.7; 37.2] (p = 0.001), as well as FIHOA, with a median decrease of 2 points [0.75; 5.2] (p = 0.01). No serious adverse events were reported. One patient stopped taVNS because of auricular discomfort. This first proof-of-concept trial indicated that taVNS is feasible and may decrease joint inflammation and clinical symptoms in EHOA, arguing for a randomized controlled study versus sham stimulation.

The role of the cholinergic anti-inflammatory pathway in autoimmune rheumatic diseases

The cholinergic anti-inflammatory pathway (CAP) is a classic neuroimmune pathway, consisting of the vagus nerve, acetylcholine (ACh)-the pivotal neurotransmitter of the vagus nerve-and its receptors. This pathway can activate and regulate the activities of immune cells, inhibit cell proliferation and differentiation, as well as suppress cytokine release, thereby playing an anti-inflammatory role, and widely involved in the occurrence and development of various diseases; recent studies have demonstrated that the CAP may be a new target for the treatment of autoimmune rheumatic diseases. In this review, we will summarize the latest progress with the view of figuring out the role of the cholinergic pathway and how it interacts with inflammatory reactions in several autoimmune rheumatic diseases, and many advances are results from a wide range of experiments performed in vitro and in vivo.

The Regulation Effect of α7nAChRs and M1AChRs on Inflammation and Immunity in Sepsis

The inflammatory storm in the early stage and immunosuppression in the late stage are responsible for the high mortality rates and multiple organ dysfunction in sepsis. In recent years, studies have found that the body's cholinergic system can spontaneously and dynamically regulate inflammation and immunity in sepsis according to the needs of the body. Firstly, the vagus nerve senses and regulates local or systemic inflammation by means of the Cholinergic Anti-inflammatory Pathway (CAP) and activation of α7-nicotinic acetylcholine receptors (α7nAChRs); thus, α7nAChRs play important roles for the central nervous system (CNS) to modulate peripheral inflammation; secondly, the activation of muscarinic acetylcholine receptors 1 (M1AChRs) in the forebrain can affect the neurons of the Medullary Visceral Zone (MVZ), the core of CAP, to regulate systemic inflammation and immunity. Based on the critical role of these two cholinergic receptor systems in sepsis, it is necessary to collect and analyze the related findings in recent years to provide ideas for further research studies and clinical applications. By consulting the related literature, we draw some conclusions: MVZ is the primary center for the nervous system to regulate inflammation and immunity. It coordinates not only the sympathetic system and vagus system but also the autonomic nervous system and neuroendocrine system to regulate inflammation and immunity; α7nAChRs are widely expressed in immune cells, neurons, and muscle cells; the activation of α7nAChRs can suppress local and systemic inflammation; the expression of α7nAChRs represents the acute or chronic inflammatory state to a certain extent; M1AChRs are mainly expressed in the advanced centers of the brain and regulate systemic inflammation; neuroinflammation of the MVZ, hypothalamus, and forebrain induced by sepsis not only leads to their dysfunctions but also underlies the regulatory dysfunction on systemic inflammation and immunity. Correcting the neuroinflammation of these regulatory centers and adjusting the function of α7nAChRs and M1AChRs may be two key strategies for the treatment of sepsis in the future.

Bidirectional communication between neural and immune systems

The immune and nervous systems share many features, including receptor and ligand expression, enabling efficient communication between the two. Accumulating evidence suggests that the communication is bidirectional, with the neural system regulating immune cell functions and vice versa. Steroid hormones from the hypothalamus-pituitary-adrenal gland axis are examples of systemic regulators for this communication. Neural reflexes describe regional regulation mechanisms that are a historically new concept that helps to explain how the neural and body systems including immune system communicate. Several recently identified neural reflexes, including the inflammatory reflex and gateway reflex, significantly impact the activation status of the immune system and are associated with inflammatory diseases and disorders. Either pro-inflammatory or anti-inflammatory effects can be elicited by these neural reflexes. On the other hand, the activities of immune cells during inflammation, for example the secretion of inflammatory mediators, can affect the functions of neuronal systems via neural reflexes and modulate biological outputs via specific neural pathways. In this review article, we discuss recent advances in the understanding of bidirectional neuro-immune interactions, with a particular focus on neural reflexes.

Vagus nerve stimulation activates two distinct neuroimmune circuits converging in the spleen to protect mice from kidney injury

Acute kidney injury is highly prevalent and associated with high morbidity and mortality, and there are no approved drugs for its prevention and treatment. Vagus nerve stimulation (VNS) alleviates inflammatory diseases including kidney disease; however, neural circuits involved in VNS-induced tissue protection remain poorly understood. The vagus nerve, a heterogeneous group of neural fibers, innervates numerous organs. VNS broadly stimulates these fibers without specificity. We used optogenetics to selectively stimulate vagus efferent or afferent fibers. Anterograde efferent fiber stimulation or anterograde (centripetal) sensory afferent fiber stimulation both conferred kidney protection from ischemia-reperfusion injury. We identified the C1 neurons-sympathetic nervous system-splenic nerve-spleen-kidney axis as the downstream pathway of vagus afferent fiber stimulation. Our study provides a map of the neural circuits important for kidney protection induced by VNS, which is critical for the safe and effective clinical application of VNS for protection from acute kidney injury.

Neuroimmune Circuits Activated by Vagus Nerve Stimulation

The interaction between the nervous system and the immune system has recently been well-recognized. Vagus nerve stimulation (VNS) presents potential as an anti-inflammatory therapy through activation of neuroimmune pathways. Detailed understanding of the neuroimmune pathways VNS evokes is critical in order to successfully use it in the clinic for the treatment of acute kidney injury, in which inflammation plays an important role. In this review, we describe recent findings regarding VNS-induced neuroimmune pathways responsible for anti-inflammation and tissue protection.

Activation of hypothalamic AMPK ameliorates metabolic complications of experimental arthritis

OBJECTIVE

To investigate whether thermogenesis and the hypothalamus may be involved in the physiopathology of experimental arthritis (EA).

METHODS

EA was induced in Lewis male rats by intradermal injection of Freund's complete adjuvant (FCA). Food intake, body weight, plasma cytokines, thermographic analysis, gene and protein expression of thermogenic markers in brown (BAT) and white (WAT) adipose tissue and hypothalamic AMP-activated protein kinase (AMPK) were analyzed. Virogenetic activation of hypothalamic AMPK was performed.

RESULTS

We first demonstrate that EA is associated with increased BAT thermogenesis and browning of subcutaneous WAT (sWAT) leading to elevated energy expenditure. Moreover, rats suffering EA show inhibition of hypothalamic AMPK, a canonical energy sensor modulating energy homeostasis at central level. Notably, specific genetic activation of AMPK in the ventromedial nucleus of the hypothalamus (VMH; a key site modulating energy metabolism) reverses the effect of EA on energy balance, brown fat and browning, as well as promoting an amelioration of the inflammatory status.

CONCLUSION

Overall, these data indicate that EA promotes a central catabolic state that can be targeted and reversed by the activation of hypothalamic AMPK. This might open new therapeutic alternatives to treat rheumatoid arthritis (RA)-associated metabolic comorbidities, improving RA-patients overall prognosis.

Neuroimmune interactions in painful TMD: Mechanisms and treatment implications

The underlying mechanisms and treatment of painful temporomandibular disorders (TMDs) are important but understudied topics in craniofacial research. As a group of musculoskeletal diseases, the onset of painful TMD is proved to be a result of disturbance of multiple systems. Recently, emerging evidence has revealed the involvement of neuroimmune interactions in painful TMD. Inflammatory factors play an important role in peripheral sensitization of temporomandibular joint (TMJ), and neurogenic inflammation in turn enhances TMJs dysfunction in TMD. Furthermore, centralized neuroimmune communications contribute to neuron excitability amplification, leading to pain sensitization, and is also responsible for chronic TMD pain and other CNS symptoms. Therapeutics targeting neuroimmune interactions may shed light on new approaches for treating TMD. In this review, we will discuss the role of neuroimmune interactions in the onset of painful TMD from the peripheral and centralized perspectives, and how understanding this mechanism could provide new treatment options. Insights into the neuroimmune interactions within TMJs and painful TMD would broaden the knowledge of mechanisms and treatments of this multifactorial disease.

Acetylcholine ameliorated hypoxia-induced oxidative stress and apoptosis in trophoblast cells via p38 MAPK/NF-κB pathway

Hypoxia-induced oxidative stress and apoptosis of trophoblast are involved in the pathogenesis of preeclampsia (PE). Extensive research reports that the principal vagal neurotransmitter acetylcholine (ACh) shows anti-oxidative and anti-apoptotic effects in various diseases models. However, the role of ACh in hypoxic trophoblast remains unknown. Here, we examined the apoptotic levels of human placenta and explored the role(s) of ACh on cobalt chloride (CoCl2)-treated (trophoblast-derived) HTR-8/SVneo cells for mimicking hypoxic injuries. Cell counting kit-8 (CCK-8), dihydroethidium (DHE) probe, western blotting, immunofluorescence staining, migration and invasion assay were employed in the current study. Our data showed that placentas from PE women exhibited increased level of reactive oxygen species (ROS) and apoptotic index than those in normal pregnancy. Our in vitro study showed that CoCl2 enhanced ROS generation and apoptosis in HTR-8/SVneo cells through the activation of the p38 mitogen-activated protein kinase (p38 MAPK)/nuclear factor-κB (NF-κB) pathway. ACh significantly decreased hypoxia-induced ROS generation and the resulting apoptosis, accompanied by lowered phosphorylation of p38 MAPK and NF-κB. Western blotting analysis further confirmed that ACh decreased the ratio of pp38 MAPK/p38 MAPK, p-NF-κB/NF-κB, Bax/Bcl-2 and cleaved caspase-3/caspase-3. Besides, ACh promoted cell invasion and migration ability under hypoxic conditions. Atropine, the muscarinic receptor antagonist, abolished ACh's effects mentioned above. Overall, our data showed that ACh exerted protective effects on hypoxia-induced oxidative stress and apoptosis in trophoblast cells via muscarinic receptors, indicating that improved vagal activity may be of therapeutic value in PE management.

Pyridostigmine ameliorates preeclamptic features in pregnant rats by inhibiting tumour necrosis factor-α synthetsis and antagonizing tumour necrosis factor-α-related effects

OBJECTIVE

Preeclampsia is a hypertensive disorder of pregnancy marked by an excessive inflammatory response. The anti-inflammatory effect of pyridostigmine (PYR) was previously reported; however, its role in hypertensive pregnancies remains unclear. We hypothesized that PYR could attenuate increased blood pressure and other pathological features in preeclampsia models.

METHODS

The expression of tumour necrosis factor (TNF)-α was evaluated in normal and preeclampsia pregnant women. PYR (20 mg/kg) was administered daily to reduced uterine perfusion pressure (RUPP) and TNF-α (150 ng/day) infused rats from gestation day 14 to GD19. In a cell culture experiment, the effect of acetylcholine (ACh) on TNF-α-stimulated primary human umbilical endothelial cells (HUVEC) was assessed.

RESULTS

Preeclampsia women had higher placental TNF-α expression than normal pregnant women. Mean arterial pressure (MAP) in the RUPP group was higher than in the Sham group. PYR inhibited serum and placental acetylcholinesterase activity in rats, and reduced MAP, placental oxidative stress, apoptosis and inflammation in the RUPP group but not in the Sham group. In addition, PYR significantly attenuated the TNF-α-induced increase in MAP, placental oxidative stress and apoptosis. Moreover, TNF-α decreased cell viability and increased the number of TUNEL-positive nuclei of HUVEC, which could largely be abolished by ACh treatment.

CONCLUSION

Collectively, PYR ameliorated hypertension and other preeclampsia-like symptoms in rat models of preeclampsia not only by inhibiting the synthesis of TNF-α but also by acting against TNF-α-induced detrimental effects directly, which is worthy of further investigation and may be used as a potential agent for preeclampsia management.

Driving β2- While Suppressing α-Adrenergic Receptor Activity Suppresses Joint Pathology in Inflammatory Arthritis

Objective

Hypersympathetic activity is prominent in rheumatoid arthritis, and major life stressors precede onset in ~80% of patients. These findings and others support a link between stress, the sympathetic nervous system and disease onset and progression. Here, we extend previous research by evaluating how selective peripherally acting α/β2-adrenergic drugs affect joint destruction in adjuvant-induced arthritis.

Methods

Complete Freund's adjuvant induced inflammatory arthritis in male Lewis rats. Controls received no treatment. Arthritic rats then received vehicle or twice-daily treatment with the α-adrenergic antagonist, phentolamine (0.5 mg/day) and the β2-adrenergic agonist, terbutaline (1200 µg/day, collectively named SH1293) from day (D) of disease onset (D12) through acute (D21) and severe disease (D28). Disease progression was assessed in the hind limbs using dorsoplantar widths, X-ray analysis, micro-computed tomography, and routine histology on D14, D21, and D28 post-immunization.

Results

On D21, SH1293 significantly attenuated arthritis in the hind limbs, based on reduced lymphocytic infiltration, preservation of cartilage, and bone volume. Pannus formation and sympathetic nerve loss were not affected by SH1293. Bone area and osteoclast number revealed high- and low-treatment-responding groups. In high-responding rats, treatment with SH1293 significantly preserved bone area and decreased osteoclast number, data that correlated with drug-mediated joint preservation. SH1293 suppressed abnormal bone formation based on reduced production of osteophytes. On D28, the arthritic sparing effects of SH1293 on lymphocytic infiltration, cartilage and bone sparing were maintained at the expense of bone marrow adipocity. However, sympathetic nerves were retracted from the talocrural joint.

Conclusion and Significance

Our findings support a significant delay in early arthritis progression by treatment with SH1293. Targeting sympathetic neurotransmission may provide a strategy to slow disease progression.

Bioelectronics in the brain-gut axis: focus on inflammatory bowel disease (IBD)

Accumulating evidence shows that intestinal homeostasis is mediated by cross-talk between the nervous system, enteric neurons and immune cells, together forming specialized neuroimmune units at distinct anatomical locations within the gut. In this review, we will particularly discuss how the intrinsic and extrinsic neuronal circuitry regulates macrophage function and phenotype in the gut during homeostasis and aberrant inflammation, such as observed in inflammatory bowel disease (IBD). Furthermore, we will provide an overview of basic and translational IBD research using these neuronal circuits as a novel therapeutic tool. Finally, we will highlight the different challenges ahead to make bioelectronic neuromodulation a standard treatment for intestinal immune-mediated diseases.

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.

Acupuncture modulates immunity in sepsis: Toward a science-based protocol

Sepsis is a serious medical condition in which immune dysfunction plays a key role. Previous treatments focused on chemotherapy to control immune function; however, a recognized effective compound or treatment has yet to be developed. Recent advances indicate that a neuromodulation approach with nerve stimulation allows developing a therapeutic strategy to control inflammation and improve organ functions in sepsis. As a quick, non-invasive technique of peripheral nerve stimulation, acupuncture has emerged as a promising therapy to provide significant advantages for immunomodulation in acute inflammation. Acupuncture obtains its regulatory effect by activating the somatic-autonomic-immune reflexes, including the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex and the somatic-vagal-adrenal reflex, which produces a systemic effect. The peripheral nerve stimulation also induces local reflexes such as the somatic-sympathetic-lung-reflex, which then produces local effects. These mechanisms offer scientific guidance to design acupuncture protocols for immunomodulation and inflammation control, leading to an evidence-based comprehensive therapy recommendation.

Non-invasive peripheral focused ultrasound neuromodulation of the celiac plexus ameliorates symptoms in a rat model of inflammatory bowel disease

NEW FINDINGS

What is the central question of this study? Does peripheral non-invasive focused ultrasound targeted to the celiac plexus improve inflammatory bowel disease? What is the main finding and its importance? Peripheral non-invasive focused ultrasound targeted to the celiac plexus in a rat model of ulcerative colitis improved stool consistency and reduced stool bloodiness, which coincided with a longer and healthier colon than in animals without focused ultrasound treatment. The findings suggest that this novel neuromodulatory technology could serve as a plausible therapeutic approach for improving symptoms of inflammatory bowel disease.

ABSTRACT

Individuals suffering from inflammatory bowel disease (IBD) experience significantly diminished quality of life. Here, we aim to stimulate the celiac plexus with non-invasive peripheral focused ultrasound (FUS) to modulate the enteric cholinergic anti-inflammatory pathway. This approach may have clinical utility as an efficacious IBD treatment given the non-invasive and targeted nature of this therapy. We employed the dextran sodium sulfate (DSS) model of colitis, administering lower (5%) and higher (7%) doses to rats in drinking water. FUS on the celiac plexus administered twice a day for 12 consecutive days to rats with severe IBD improved stool consistency scores from 2.2 ± 1 to 1.0 ± 0.0 with peak efficacy on day 5 and maximum reduction in gross bleeding scores from 1.8 ± 0.8 to 0.8 ± 0.8 on day 6. Similar improvements were seen in animals in the low dose DSS group, who received FUS only once daily for 12 days. Moreover, animals in the high dose DSS group receiving FUS twice daily maintained colon length (17.7 ± 2.5 cm), while rats drinking DSS without FUS exhibited marked damage and shortening of the colon (13.8 ± 0.6 cm) as expected. Inflammatory cytokines such as interleukin (IL)-1β, IL-6, IL-17, tumour necrosis factor-α and interferon-γ were reduced with DSS but coincided with control levels after FUS, which is plausibly due to a loss of colon crypts in the former and healthier crypts in the latter. Lastly, overall, these results suggest non-invasive FUS of peripheral ganglion can deliver precision therapy to improve IBD symptomology.

The Joint-Brain Axis: Insights From Rheumatoid Arthritis on the Crosstalk Between Chronic Peripheral Inflammation and the Brain

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by erosive polyarthritis. Beyond joint pathology, RA is associated with neuropsychiatric comorbidity including depression, anxiety, and an increased risk to develop neurodegenerative diseases in later life. Studies investigating the central nervous system (CNS) in preclinical models of RA have leveraged the understanding of the intimate crosstalk between peripheral and central immune responses. This mini review summarizes the current knowledge of CNS comorbidity in RA patients and known underlying cellular mechanisms. We focus on the differential regulation of CNS myeloid and glial cells in different mouse models of RA reflecting different patterns of peripheral immune activation. Moreover, we address CNS responses to anti-inflammatory treatment in human RA patients and mice. Finally, to illustrate the bidirectional communication between the CNS and chronic peripheral inflammation, we present the current knowledge about the impact of the CNS on arthritis. A comprehensive understanding of the crosstalk between the CNS and chronic peripheral inflammation will help to identify RA patients at risk of developing CNS comorbidity, setting the path for future therapeutic approaches in both RA and neuropsychiatric diseases.

Exploring the Mechanism on the Medullary Visceral Zone Inhibiting the Cholinergic Anti-inflammatory Pathway Induced by Sepsis

Inflammatory storm is an important pathological mechanism of multiple organ dysfunction, and it is associated with most deaths in septic patients, deserving to be studied. Recent findings have confirmed that the Medullary Visceral Zone (MVZ) regulates inflammation and immunity through the cholinergic anti-inflammatory pathway (CAP), but how sepsis affects the MVZ and leads to uncontrolled inflammation remain unclear. The current study reported that sepsis induced MVZ to inhibit CAP which underlies the inflammation storm. Our studies have shown that the rat models of sepsis prepared by cecal ligation and puncture had a higher inflammatory level, higher mortality, and higher Murine Sepsis Score. In septic rats, some indicators of heart rate variability (HRV) such as SDNN, HF band, RMSSD, SD1, and SD2 significantly reduced. In MVZ of septic rats, many cholinergic and catecholaminergic neurons showed apoptotic, with low expressions of tyrosine hydroxylase and choline acetyltransferase. The α7nAChR agonist GTS-21 can improve these pathologies, while the α7nAChR antagonist MLA is the opposite. Our study demonstrates for the first time that cholinergic and catecholaminergic neurons in MVZ went through significant apoptosis and inactiveness in sepsis, which contributes to the inhibition of CAP and acceleration of the inflammation storm in early sepsis. Intervening with CAP has a significant effect on the activity and apoptosis of MVZ neurons while altering systemic inflammation and immunity; in addition, for the first time, we confirmed that some indicators of HRV such as SDNN, HF band, RMSSD, SD1, and SD2 can reflect the activity of CAP, but the CAP interference had little effect on these indicators.

Comparison between the cervical and abdominal vagus nerves in mice, pigs, and humans

BACKGROUND

Vagus nerve (VN) stimulation is currently evaluated as a novel approach to treat immune-mediated disorders. The optimal stimulation parameters, however, largely depend on the VN composition potentially impacting on its clinical translation. Hence, we evaluated whether morphological differences exist between the cervical and abdominal VNs across different species.

MATERIALS AND METHODS

The cervical and abdominal VNs of mouse, pig, and humans were stained for major basic protein and neurofilament F to identify the percentage and size of myelinated and non-myelinated fibers.

RESULTS

The percentage of myelinated fibers was comparable between species, but was higher in the cervical VN compared with the abdominal VN. The cervical VN contained 54 ± 4%, 47 ± 7%, and 54 ± 7% myelinated fibers in mouse, pig, and humans, respectively. The myelinated fibers consisted of small-diameter (mouse: 71%, pig: 80%, and humans: 63%), medium-diameter (mouse: 21%, pig: 18%, and humans: 33%), and large-diameter fibers (mouse: 7%, pig: 2%, and humans: 4%). The abdominal VN predominantly contained unmyelinated fibers (mouse: 93%, pig: 90%, and humans: 94%). The myelinated fibers mainly consisted of small-diameter fibers (mouse: 99%, pig: 85%, and humans: 74%) and fewer medium-diameter (mouse: 1%, pig: 13%, and humans: 23%) and large-diameter fibers (mouse: 0%, pig: 2%, and humans: 3%).

CONCLUSION

The VN composition was largely similar with respect to myelinated and unmyelinated fibers in the species studied. Human and porcine VNs had a comparable diameter and similar amounts of fibrous tissue and contained multiple fascicles, implying that the porcine VN may be suitable to optimize stimulation parameters for clinical trials.

Role of the parasympathetic nervous system in cancer initiation and progression

The nervous system plays an important role in cancer initiation and progression. Accumulated evidences clearly show that the sympathetic nervous system exerts stimulatory effects on carcinogenesis and cancer growth. However, the role of the parasympathetic nervous system in cancer has been much less elucidated. Whereas retrospective studies in vagotomized patients and experiments employing vagotomized animals indicate the parasympathetic nervous system has an inhibitory effect on cancer, clinical studies in patients with prostate cancer indicate it has stimulatory effects. Therefore, the aim of this paper is a critical evaluation of the available data related to the role of the parasympathetic nervous system in cancer.

Central angiotensin-(1-7) attenuates systemic inflammation via activation of sympathetic signaling in endotoxemic rats

Angiotensin-(1-7) [Ang-(1-7)] is an angiotensin-derived neuropeptide with potential anti-hypertensive and anti-inflammatory properties. However, a possible action of Ang-(1-7) in neuroimmune interactions to regulate inflammatory response has not been explored. Thus, the aim of this study was to determine whether the intracerebroventricular (i.c.v.) administration of Ang-(1-7) can modulate systemic inflammation via sympathetic efferent circuits. Wistar male rats received systemic administration of lipopolysaccharide (LPS) (1.5 mg/Kg). Ang-(1-7) (0.3 nmol in 2 µL) promoted the release of splenic norepinephrine and attenuated tumor necrosis factor (TNF) and nitric oxide (NO), but increased interleukin-10 (IL-10), levels in the serum, spleen, and liver in endotoxemic rats. Furthermore, 6-hydroxydopamine-induced chemical sympathectomy (100 mg/Kg, intravenous) or i.c.v. administration of Mas receptor antagonist A779 (3 nmol in 2 µL) abolished the anti-inflammatory effects of central Ang-(1-7) injection. Moreover, this treatment did not alter the plasmatic LPS-induced corticosterone and vasopressin. The administration of Ang-(1-7) reverted the low resistance in response to catecholamines of rings of thoracic aorta isolated from endotoxemic rats, treated or not, with this peptide by a mechanism dependent on the regulation of NO released from perivascular adipose tissue. Together, our results indicate that Ang-(1-7) regulates systemic inflammation and vascular hyporesponsiveness in endotoxemia via activation of a central Mas receptors/sympathetic circuits/norepinephrine axis and provide novel mechanistic insights into the anti-inflammatory Ang-(1-7) properties.

Splenic artery loops: Potential splenic plexus stimulation sites for neuroimmunomodulatory-based anti-inflammatory therapy?

INTRODUCTION

The splenic plexus might represent a novel neuroimmunomodulatory therapeutic target as electrical stimulation of this tissue has been shown to have beneficial anti-inflammatory effects. Tortuous splenic artery segments (splenic artery loops), including their surrounding nerve plexus, have been evaluated as potential stimulation sites in humans. At present, however, our understanding of these loops and their surrounding nerve plexus is incomplete. This study aims to characterize the dimensions of these loops and their surrounding nerve tissue.

MATERIALS AND METHODS

Six formaldehyde fixed human cadavers were dissected and qualitative and quantitative macro- and microscopic data on splenic artery loops and their surrounding nerve plexus were collected.

RESULTS

One or multiple loops were observed in 83% of the studied specimens. These loops, including their surrounding nerve plexus could be easily dissected free circumferentially thereby providing sufficient space for further surgical intervention. The splenic plexus surrounding the loops contained a significant amount of nerves that contained predominantly sympathetic fibers.

CONCLUSION

The results of this study support that splenic artery loops could represent suitable electrical splenic plexus stimulation sites in humans. Dimensions with respect to loop height and width, provide sufficient space for introduction of surgical instruments and electrode implantation, and, the dissected neurovascular bundles contain a substantial amount of sympathetic nerve tissue. This knowledge may contribute to further development of surgical techniques and neuroelectrode interface design.

Vagus nerve stimulation and Neurotrophins: a biological psychiatric perspective

Since 2004, vagus nerve stimulation (VNS) has been used in treatment-resistant or treatment-intolerant depressive episodes. Today, VNS is suggested as possible therapy for a larger spectrum of psychiatric disorders, including schizophrenia, obsessive compulsive disorders, and panic disorders. Despite a large body of literature supports the application of VNS in patients' treatment, the exact mechanism of action of VNS remains not fully understood. In the present study, the major knowledges on the brain areas and neuronal pathways regulating neuroimmune and autonomic response subserving VNS effects are reviewed. Furthermore, the involvement of the neurotrophins (NTs) Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) in vagus nerve (VN) physiology and stimulation is revised. The data on brain NGF/BDNF synthesis and in turn on the activity-dependent plasticity, connectivity rearrangement and neurogenesis, are presented and discussed as potential biomarkers for optimizing stimulatory parameters for VNS. A vagus nerve-neurotrophin interaction model in the brain is finally proposed as a working hypothesis for future studies addressed to understand pathophysiology of psychiatric disturbance.

A new algorithm for drift compensation in multi-unit recordings of action potentials in peripheral autonomic nerves over time

BACKGROUND

Peripheral autonomic nerves control visceral organs and convey information regarding their functional states and are, therefore, potential targets for new therapeutic and diagnostic approaches. Conventionally recorded multi-unit nerve activity in vivo undergoes slow differential drift of signal and noise amplitudes, making accurate monitoring of nerve activity for more than tens of minutes problematic.

NEW METHOD

We describe an on-line drift compensation algorithm that utilizes recursive least-squares to estimate the relative change in spike amplitude due to changes in the nerve-electrode interface over time.

RESULTS

We tested and refined our approach using simulated data and in vivo recordings from nerves supplying the small intestine under control conditions and in response to gut inflammation over several hours. The algorithm is robust to changes in recording conditions and signal-to-noise ratio and applicable to both single and multi-unit recordings. In uncompensated records, drift prevented "spike families" and single units from being discriminated accurately over hours. After rescaling, these were successfully tracked throughout recordings (up to 3 h).

COMPARISON WITH EXISTING METHODS

Existing methods are subjective or compensate for drift using spatial information and spike shape data which is not practical in multi-unit peripheral nerve recordings. In contrast, this method is objective and applicable to data from a single differential multi-unit recording. In comparisons using simulated data the algorithm performed as well as or better than existing methods.

CONCLUSIONS

Results suggest our drift compensation algorithm is widely applicable and robust, though conservative, when differentiating prolonged responses from drift in signal. Extracellular nerve recordings; drift compensation; chronic nerve recordings; closed-loop; multi-unit activity; spike discrimination; recursive least squares; real-time.

The greater inflammatory pathway-high clinical potential by innovative predictive, preventive, and personalized medical approach

BACKGROUND AND LIMITATIONS

Impaired wound healing (WH) and chronic inflammation are hallmarks of non-communicable diseases (NCDs). However, despite WH being a recognized player in NCDs, mainstream therapies focus on (un)targeted damping of the inflammatory response, leaving WH largely unaddressed, owing to three main factors. The first is the complexity of the pathway that links inflammation and wound healing; the second is the dual nature, local and systemic, of WH; and the third is the limited acknowledgement of genetic and contingent causes that disrupt physiologic progression of WH.

PROPOSED APPROACH

Here, in the frame of Predictive, Preventive, and Personalized Medicine (PPPM), we integrate and revisit current literature to offer a novel systemic view on the cues that can impact on the fate (acute or chronic inflammation) of WH, beyond the compartmentalization of medical disciplines and with the support of advanced computational biology.

CONCLUSIONS

This shall open to a broader understanding of the causes for WH going awry, offering new operational criteria for patients' stratification (prediction and personalization). While this may also offer improved options for targeted prevention, we will envisage new therapeutic strategies to reboot and/or boost WH, to enable its progression across its physiological phases, the first of which is a transient acute inflammatory response versus the chronic low-grade inflammation characteristic of NCDs.

Anatomical and clinical implications of vagal modulation of the spleen

The vagus nerve coordinates most physiologic functions including the cardiovascular and immune systems. This mechanism has significant clinical implications because electrical stimulation of the vagus nerve can control inflammation and organ injury in infectious and inflammatory disorders. The complex mechanisms that mediate vagal modulation of systemic inflammation are mainly regulated via the spleen. More specifically, vagal stimulation prevents organ injury and systemic inflammation by inhibiting the production of cytokines in the spleen. However, the neuronal regulation of the spleen is controversial suggesting that it can be mediated by either monosynaptic innervation of the splenic parenchyma or secondary neurons from the celiac ganglion depending on the experimental conditions. Recent physiologic and anatomic studies suggest that inflammation is regulated by neuro-immune multi-synaptic interactions between the vagus and the splanchnic nerves to modulate the spleen. Here, we review the current knowledge on these interactions, and discuss their experimental and clinical implications in infectious and inflammatory disorders.

Role of sensory neurons, neuroimmune pathways, and transient receptor potential vanilloid 1 (TRPV1) channels in a murine model of breast cancer metastasis

Sensory nerves sensitive to capsaicin are afferent nerve fibers which contain TRPV1 channels. Activation of these channels induces release of neuropeptides which regulate local blood flow and immune response. Inactivation of sensory neurons either with high-dose capsaicin treatment or local ablation of vagal sensory nerve activity markedly increases metastasis of breast carcinoma formed by 4T1 derivative cells. These cancer cells also induce an extensive systemic inflammatory response. Further findings have documented that lack of local sensory neuromediators alters phenotype of cancer cells within primary tumor leading to overgrowth of metastatic subsets. This might be due to decreases in local and systemic immune response to growing tumor. Specifically, Substance P, one of the most abundant sensory neuropeptides, enhances anti-tumoral immune response evoked by radiotherapy under in vivo conditions. These findings further suggest that activation of TRPV1 channels on sensory neurons may induce an anti-tumoral immune response. We are testing this hypothesis. Our initial results as reported here demonstrate anti-inflammatory consequences of low-dose systemic capsaicin treatment. In conclusion, sensory nerve fibers sensitive to capsaicin have important roles in defense against metastatic breast carcinoma; hence, controlled activation of these neural pathways might be effective in cancer therapy. Specifically, activation of sensory fibers of left vagus nerve using a perineuronal stimulation may inhibit metastasis of breast carcinoma. Likewise, pharmacological modulators of TRPV1 channels may induce anti-tumoral immune response. Exact players of this newly explored defense system are, however, only partly validated, and further studies are required.

Proinflammatory α-Adrenergic Neuronal Regulation of Splenic IFN-γ, IL-6, and TGF-β of Mice from Day 15 onwards in Arthritis

INTRODUCTION

In arthritic mice, a sympathetic influence is proinflammatory from the time point of immunization until the onset of disease (days 0-32), but reasons are unknown. Disruption of the major anti-inflammatory pathway through Gαs-coupled receptors probably play a role. For example, noradrenaline cannot operate via anti-inflammatory β2-adrenoceptors but through proinflammatory α1/2-ad-renoceptors. This might happen, first, through a loss of sympathetic nerve fibers in inflamed tissue with low neurotransmitter levels (noradrenaline only binds to high-affinity α-adrenoceptors) and, second, through an alteration in G-protein receptor coupling with a predominance of α-adrenergic signaling. We hypothesized that both mechanisms play a role in the course of collagen type II-induced arthritis (CIA) in the spleen in mice.

METHODS

In CIA mice, nerve fiber density in the spleen was quantified by immunohistochemistry techniques. The functional impact of sympathetic nerve fibers in the spleen was studied by a micro-superfusion technique of spleen slices with a focus on the secretion of IFN-γ and IL-6 (proinflammatory) and TGF-β (anti-inflammatory).

RESULTS

During CIA, sympathetic nerve fibers get increasingly lost from day14 until day 55 after immunization. The influence of electrically released noradrenaline diminishes in the course of arthritis. At all investigated time points (days 14, 32, and 55), only proinflammatory neuronal α-adrenergic effects on cytokine secretion were demonstrated (i.e., stimulation of IFN-γ and IL-6 and inhibition of TGF-β).

CONCLUSION

Sympathetic nerve fibers are rapidly lost in the spleen, and only proinflammatory α-adrenergic neuronal regulation of cytokine secretion takes place throughout the course of arthritis. These results support a predominance of a proinflammatory α-adrenergic sympathetic influence in arthritis.

Regulation of murine arthritis by systemic, spinal, and intra-articular adrenoceptors

BACKGROUND

The regulation of the immune system by the sympathetic nervous system is allowing the design of novel treatments for inflammatory disorders such as arthritis. In this study, we have analyzed the effects of α- and β-adrenoceptor agonists injected subcutaneously, intrathecally, or intra-articularly in zymosan-induced arthritis.

METHODS

Murine arthritis was induced by intra-articular (knee joint) injection of zymosan. α1 (phenylephrine), α2 (clonidine), β1 (dobutamine), or β2 (salbutamol)-adrenoceptor agonists were injected subcutaneously (sc), intrathecally (it), or intra-articularly (ia) to activate peripheral, spinal, or intra-articular adrenoceptors and to study their effects on articular edema formation and neutrophil migration into the synovial cavity.

RESULTS

Treatments with phenylephrine did not affect the edema formation, but it increased neutrophil migration when injected subcutaneously (155.3%) or intra-articularly (187.7%). Treatments with clonidine inhibited neutrophil migration (59.9% sc, 68.7% it, 42.8% ia) regardless of the route of administration, but it inhibited edema formation only when injected intrathecally (66.7%) or intra-articularly (36%) but not subcutaneously. Treatments with dobutamine inhibited both edema (42.0% sc, 69.5% it, 61.6% ia) and neutrophil migration (28.4% sc, 70.3% it, 82.4% ia) in a concentration dependent manner. Likewise, all the treatments with salbutamol also inhibited edema formation (89.9% sc, 62.4% it, 69.8% ia) and neutrophil migration (76.6% sc, 39.1% it, 71.7% ia).

CONCLUSION

Whereas the β-adrenoceptor agonists induced anti-inflammatory effects regardless of their route of administration, α1- and α2-adrenoceptor agonists induced either pro- and anti-inflammatory effects, respectively.

The role of neutrophils in neuro-immune modulation

Neutrophils are peripheral immune cells that represent the first recruited innate immune defense against infections and tissue injury. However, these cells can also induce overzealous responses and cause tissue damage. Although the role of neutrophils activating the immune system is well established, only recently their critical implications in neuro-immune interactions are becoming more relevant. Here, we review several aspects of neutrophils in the bidirectional regulation between the nervous and immune systems. First, the role of neutrophils as a diffuse source of acetylcholine and catecholamines is controversial as well as the effects of these neurotransmitters in neutrophil's functions. Second, neutrophils contribute for the activation and sensitization of sensory neurons, and thereby, in events of nociception and pain. In addition, nociceptor activation promotes an axon reflex triggering a local release of neural mediators and provoking neutrophil activation. Third, the recruitment of neutrophils in inflammatory responses in the nervous system suggests these immune cells as innovative targets in the treatment of central infectious, neurological and neurodegenerative disorders. Multidisciplinary studies involving immunologists and neuroscientists are required to define the role of the neurons-neutrophils communication in the pathophysiology of infectious, inflammatory, and neurological disorders.