Vagal stimulation modulates inflammation through a ghrelin mediated mechanism in traumatic brain injury

Transcutaneous auricular vagus nerve stimulation improves social deficits through the inhibition of IL-17a signaling in a mouse model of autism

Background

Maternal exposure to inflammation is one of the causes of autism spectrum disorder (ASD). Electrical stimulation of the vagus nerve exerts a neuroprotective effect via its anti-inflammatory action. We thus investigated whether transcutaneous auricular vagus nerve stimulation (taVNS) can enhance social abilities in a mouse model of ASD induced by maternal immune activation (MIA).

Methods

ASD mouse model were constructed by intraperitoneal injection of polyinosinic:polycytidylic acid (poly (I:C)). TaVNS with different parameters were tested in ASD mouse model and in C57BL/6 mice, then various behavioral tests and biochemical analyses related to autism were conducted. ASD model mice were injected with an interleukin (IL)-17a antibody into the brain, followed by behavioral testing and biochemical analyses.

Results

TaVNS reduced anxiety, improved social function, decreased the number of microglia, and inhibited M1 polarization of microglia. Additionally, taVNS attenuated the expression of the IL-17a protein in the prefrontal cortex and blood of ASD model mice. To examine the possible involvement of IL-17a in taVNS-induced neuroprotection, we injected an IL-17a antibody into the prefrontal cortex of ASD model mice and found that neutralizing IL-17a decreased the number of microglia and inhibited M1 polarization. Furthermore, neutralizing IL-17a improved social function in autism model mice.

Conclusion

Our study revealed that reduced neuroinflammation is an important mechanism of taVNS-mediated social improvement and neuroprotection against autism. This effect of taVNS could be attributed to the inhibition of the IL-17a pathway.

Using neural biomarkers to personalize dosing of vagus nerve stimulation

BACKGROUND

Vagus nerve stimulation (VNS) is an established therapy for treating a variety of chronic diseases, such as epilepsy, depression, obesity, and for stroke rehabilitation. However, lack of precision and side-effects have hindered its efficacy and extension to new conditions. Achieving a better understanding of the relationship between VNS parameters and neural and physiological responses is therefore necessary to enable the design of personalized dosing procedures and improve precision and efficacy of VNS therapies.

METHODS

We used biomarkers from recorded evoked fiber activity and short-term physiological responses (throat muscle, cardiac and respiratory activity) to understand the response to a wide range of VNS parameters in anaesthetised pigs. Using signal processing, Gaussian processes (GP) and parametric regression models we analyse the relationship between VNS parameters and neural and physiological responses.

RESULTS

Firstly, we illustrate how considering multiple stimulation parameters in VNS dosing can improve the efficacy and precision of VNS therapies. Secondly, we describe the relationship between different VNS parameters and the evoked fiber activity and show how spatially selective electrodes can be used to improve fiber recruitment. Thirdly, we provide a detailed exploration of the relationship between the activations of neural fiber types and different physiological effects. Finally, based on these results, we discuss how recordings of evoked fiber activity can help design VNS dosing procedures that optimize short-term physiological effects safely and efficiently.

CONCLUSION

Understanding of evoked fiber activity during VNS provide powerful biomarkers that could improve the precision, safety and efficacy of VNS therapies.

Dysregulated brain-gut axis in the setting of traumatic brain injury: review of mechanisms and anti-inflammatory pharmacotherapies

Traumatic brain injury (TBI) is a chronic and debilitating disease, associated with a high risk of psychiatric and neurodegenerative diseases. Despite significant advancements in improving outcomes, the lack of effective treatments underscore the urgent need for innovative therapeutic strategies. The brain-gut axis has emerged as a crucial bidirectional pathway connecting the brain and the gastrointestinal (GI) system through an intricate network of neuronal, hormonal, and immunological pathways. Four main pathways are primarily implicated in this crosstalk, including the systemic immune system, autonomic and enteric nervous systems, neuroendocrine system, and microbiome. TBI induces profound changes in the gut, initiating an unrestrained vicious cycle that exacerbates brain injury through the brain-gut axis. Alterations in the gut include mucosal damage associated with the malabsorption of nutrients/electrolytes, disintegration of the intestinal barrier, increased infiltration of systemic immune cells, dysmotility, dysbiosis, enteroendocrine cell (EEC) dysfunction and disruption in the enteric nervous system (ENS) and autonomic nervous system (ANS). Collectively, these changes further contribute to brain neuroinflammation and neurodegeneration via the gut-brain axis. In this review article, we elucidate the roles of various anti-inflammatory pharmacotherapies capable of attenuating the dysregulated inflammatory response along the brain-gut axis in TBI. These agents include hormones such as serotonin, ghrelin, and progesterone, ANS regulators such as beta-blockers, lipid-lowering drugs like statins, and intestinal flora modulators such as probiotics and antibiotics. They attenuate neuroinflammation by targeting distinct inflammatory pathways in both the brain and the gut post-TBI. These therapeutic agents exhibit promising potential in mitigating inflammation along the brain-gut axis and enhancing neurocognitive outcomes for TBI patients.

Non-Invasive Vagal Nerve Stimulation Pre-Treatment Reduces Neurological Dysfunction After Closed Head Injury in Mice

Non-invasive vagus nerve stimulation (nVNS) has recently been suggested as a potential therapy for traumatic brain injury (TBI). We previously demonstrated that nVNS inhibits cortical spreading depolarization, the electrophysiological event underlying migraine aura, and is relevant to TBI. Our past work also suggests a role for interleukin-1 beta (IL-1β) in cognitive deficits after closed head injury (CHI) in mice. We show that nVNS pre-treatment suppresses CHI-associated spatial learning and memory impairment and prevents IL-1β activation in injured neurons, but not endothelial cells. In contrast, nVNS administered 10 min after CHI was ineffective. These data suggest that nVNS prophylaxis might ameliorate neuronal dysfunction associated with CHI in populations at high risk for concussive TBI.

Vagus Nerve Stimulation and Inflammation in Cardiovascular Disease: A State-of-the-Art Review

Vagus nerve stimulation (VNS) has been found to exert anti-inflammatory effects in different clinical settings and has been associated with improvement of clinical outcomes. However, evidence on the mechanistic link between the potential association of inflammatory status with clinical outcomes following VNS is scarce. This review aims to summarize the existing knowledge linking VNS with inflammation and its potential link with major outcomes in cardiovascular diseases, in both preclinical and clinical studies. Existing data show that in the setting of myocardial ischemia and reperfusion, VNS seems to reduce inflammation resulting in reduced infarct size and reduced incidence of ventricular arrhythmias during reperfusion. Furthermore, VNS has a protective role in vascular function following myocardial ischemia and reperfusion. Atrial fibrillation burden has also been reduced by VNS, whereas suppression of inflammation may be a potential mechanism for this effect. In the setting of heart failure, VNS was found to improve systolic function and reverse cardiac remodeling. In summary, existing experimental data show a reduction in inflammatory markers by VNS, which may cause improved clinical outcomes in cardiovascular diseases. However, more data are needed to evaluate the association between the inflammatory status with the clinical outcomes following VNS.

Noninvasive Vagal Nerve Stimulation for Opioid Use Disorder

Background

Opioid Use Disorder (OUD) is an escalating public health problem with over 100,000 drug overdose-related deaths last year most of them related to opioid overdose, yet treatment options remain limited. Non-invasive Vagal Nerve Stimulation (nVNS) can be delivered via the ear or the neck and is a non-medication alternative to treatment of opioid withdrawal and OUD with potentially widespread applications.

Methods

This paper reviews the neurobiology of opioid withdrawal and OUD and the emerging literature of nVNS for the application of OUD. Literature databases for Pubmed, Psychinfo, and Medline were queried for these topics for 1982-present.

Results

Opioid withdrawal in the context of OUD is associated with activation of peripheral sympathetic and inflammatory systems as well as alterations in central brain regions including anterior cingulate, basal ganglia, and amygdala. NVNS has the potential to reduce sympathetic and inflammatory activation and counter the effects of opioid withdrawal in initial pilot studies. Preliminary studies show that it is potentially effective at acting through sympathetic pathways to reduce the effects of opioid withdrawal, in addition to reducing pain and distress.

Conclusions

NVNS shows promise as a non-medication approach to OUD, both in terms of its known effect on neurobiology as well as pilot data showing a reduction in withdrawal symptoms as well as physiological manifestations of opioid withdrawal.

Non-Invasive Vagus Nerve Stimulation Improves Brain Lesion Volume and Neurobehavioral Outcomes in a Rat Model of Traumatic Brain Injury

Abstract Traumatic brain injury (TBI) continues to be a major cause of death and disability worldwide. This study assessed the effectiveness of non-invasive vagus nerve stimulation (nVNS) in reducing brain lesion volume and improving neurobehavioral performance in a rat model of TBI. Animals were randomized into three experimental groups: (1) TBI with sham stimulation treatment (Control), (2) TBI treated with five lower doses (2-min) nVNS, and (3) TBI treated with five higher doses (2 × 2-min) nVNS. We used the gammaCore nVNS device to deliver stimulations. Magnetic resonance imaging studies were performed 1 and 7 days post-injury to confirm lesion volume. We observed smaller brain lesion volume in the lower dose nVNS group compared with the control group on days 1 and 7. The lesion volume for the higher dose nVNS group was significantly smaller than either the lower dose nVNS or the control groups on days 1 and 7 post-injury. The apparent diffusion coefficient differences between the ipsilateral and contralateral hemispheres on day 1 were significantly smaller for the higher dose (2 × 2 min) nVNS group than for the control group. Voxel-based morphometry analysis revealed an increase in the ipsilateral cortical volume in the control group caused by tissue deformation and swelling. On day 1, these abnormal volume changes were 13% and 55% smaller in the lower dose and higher dose nVNS groups, respectively, compared with the control group. By day 7, nVNS dampened cortical volume loss by 35% and 89% in the lower dose and higher dose nVNS groups, respectively, compared with the control group. Rotarod, beam walking, and anxiety performances were significantly improved in the higher-dose nVNS group on day 1 compared with the control group. The anxiety indices were also improved on day 7 post-injury compared with the control and the lower-dose nVNS groups. In conclusion, the higher dose nVNS (five 2 × 2-min stimulations) reduced brain lesion volume to a level that further refined the role of nVNS therapy for the acute treatment of TBI. Should nVNS prove effective in additional pre-clinical TBI models and later in clinical settings, it would have an enormous impact on the clinical practice of TBI in both civilian and military settings, as it can easily be adopted into routine clinical practice.

Continuous vagus nerve stimulation exerts beneficial effects on rats with experimentally induced Parkinson's disease: Evidence suggesting involvement of a vagal afferent pathway

BACKGROUND

Vagus nerve stimulation (VNS) exerts neuroprotective and anti-inflammatory effects in preclinical models of central nervous system disorders, including Parkinson's disease (PD). VNS setting applied for experimental models is limited into single-time or intermittent short-duration stimulation. We developed a VNS device which could deliver continuous stimulation for rats. To date, the effects of vagal afferent- or efferent-selective stimulation on PD using continuous electrical stimulation remains to be determined.

OBJECTIVE

To investigate the effects of continuous and selective stimulation of vagal afferent or efferent fiber on Parkinsonian rats.

METHODS

Rats were divided into 5 group: intact VNS, afferent VNS (left VNS in the presence of left caudal vagotomy), efferent VNS (left VNS in the presence of left rostral vagotomy), sham, vagotomy. Rats underwent the implantation of cuff-electrode on left vagus nerve and 6-hydroxydopamine administration into the left striatum simultaneously. Electrical stimulation was delivered just after 6-OHDA administration and continued for 14 days. In afferent VNS and efferent VNS group, the vagus nerve was dissected at distal or proximal portion of cuff-electrode to imitate the selective stimulation of afferent or efferent vagal fiber respectively.

RESULTS

Intact VNS and afferent VNS reduced the behavioral impairments in cylinder test and methamphetamine-induced rotation test, which were accompanied by reduced inflammatory glial cells in substantia nigra with the increased density of the rate limiting enzyme in locus coeruleus. In contrast, efferent VNS did not exert any therapeutic effects.

CONCLUSION

Continuous VNS promoted neuroprotective and anti-inflammatory effect in experimental PD, highlighting the crucial role of the afferent vagal pathway in mediating these therapeutic outcomes.

Neuromodulation Therapies in Pre-Clinical Models of Traumatic Brain Injury: Systematic Review and Translational Applications

Traumatic brain injury (TBI) has been associated with several lasting impairments that affect quality of life. Pre-clinical models of TBI have been studied to further our understanding of the underlying short-term and long-term symptomatology. Neuromodulation techniques have become of great interest in recent years as potential rehabilitative therapies after injury because of their capacity to alter neuronal activity and neural circuits in targeted brain regions. This systematic review aims to provide an overlook of the behavioral and neurochemical effects of transcranial direct current stimulation (tDCS), transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS) in pre-clinical TBI models. After screening 629 abstracts, 30 articles were pooled for review. These studies showed that tDCS, TMS, DBS, or VNS delivered to rodents restored TBI-induced deficits in coordination, balance, locomotor activity and improved cognitive impairments in memory, learning, and impulsivity. Potential mechanisms for these effects included neuroprotection, a decrease in apoptosis, neuroplasticity, and the restoration of neural circuit abnormalities. The translational value, potential applicability, and the interpretation of these findings in light of outcome data from clinical trials in patients with TBI are discussed.

Wireless optoelectronic devices for vagus nerve stimulation in mice

Objective.Vagus nerve stimulation (VNS) is a promising approach for the treatment of a wide variety of debilitating conditions, including autoimmune diseases and intractable epilepsy. Much remains to be learned about the molecular mechanisms involved in vagus nerve regulation of organ function. Despite an abundance of well-characterized rodent models of common chronic diseases, currently available technologies are rarely suitable for the required long-term experiments in freely moving animals, particularly experimental mice. Due to challenging anatomical limitations, many relevant experiments require miniaturized, less invasive, and wireless devices for precise stimulation of the vagus nerve and other peripheral nerves of interest. Our objective is to outline possible solutions to this problem by using nongenetic light-based stimulation.Approach.We describe how to design and benchmark new microstimulation devices that are based on transcutaneous photovoltaic stimulation. The approach is to use wired multielectrode cuffs to test different stimulation patterns, and then build photovoltaic stimulators to generate the most optimal patterns. We validate stimulation through heart rate analysis.Main results.A range of different stimulation geometries are explored with large differences in performance. Two types of photovoltaic devices are fabricated to deliver stimulation: photocapacitors and photovoltaic flags. The former is simple and more compact, but has limited efficiency. The photovoltaic flag approach is more elaborate, but highly efficient. Both can be used for wireless actuation of the vagus nerve using light impulses.Significance.These approaches can enable studies in small animals that were previously challenging, such as long-termin vivostudies for mapping functional vagus nerve innervation. This new knowledge may have potential to support clinical translation of VNS for treatment of select inflammatory and neurologic diseases.

Effects and neuroprotective mechanisms of vagus nerve stimulation on cognitive impairment with traumatic brain injury in animal studies: A systematic review and meta-analysis

Introduction

Cognitive impairment is the main clinical feature after traumatic brain injury (TBI) and is usually characterized by attention deficits, memory loss, and decreased executive function. Vagus nerve stimulation (VNS) has been reported to show potential improvement in the cognition level after traumatic brain injury in clinical and preclinical studies. However, this topic has not yet been systematically reviewed in published literature. In this study, we present a systematic review and meta-analysis of the effects of VNS on cognitive function in animal models of TBI and their underlying mechanisms.

Methods

We performed a literature search on PubMed, PsycINFO, Web of Science, Embase, Scopus, and Cochrane Library from inception to December 2021 to identify studies describing the effects of VNS on animal models of TBI.

Results

Overall, nine studies were identified in animal models (36 mice, 268 rats, and 27 rabbits). An analysis of these studies showed that VNS can improve the performance of TBI animals in behavioral tests (beam walk test: SMD: 4.95; 95% confidence interval [CI]: 3.66, 6.23; p < 0.00001) and locomotor placing tests (SMD: -2.39; 95% CI: -4.07, -0.71; p = 0.005), whereas it reduced brain edema (SMD: -1.58; 95% CI: -2.85, -0.31; p = 0. 01) and decrease TNF-α (SMD: -3.49; 95% CI: -5.78, -1.2; p = 0.003) and IL-1β (SMD: -2.84; 95% CI: -3.96, -1.71; p < 0.00001) expression level in the brain tissue. However, the checklist for SYRCLE showed a moderate risk of bias (quality score between 30% and 60%), mainly because of the lack of sample size calculation, random assignment, and blinded assessment.

Conclusion

The present review showed that VNS can effectively promote cognitive impairment and neuropathology in animal models of TBI. We hope that the results of this systematic review can be applied to improve the methodological quality of animal experiments on TBI, which will provide more important and conclusive evidence on the clinical value of VNS. To further confirm these results, there is a need for high-quality TBI animal studies with sufficient sample size and a more comprehensive outcome evaluation.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021290797, identifier: CRD42021290797.

The Brain–Gut Axis in Traumatic Brain Injury: Implications for Nutrition Support

Purpose of Review

Early enteral nutrition improves outcomes following traumatic brain injury (TBI). This can prove difficult due to TBI-induced feeding intolerance secondary to disruption of the brain-gut axis, a network composed of central nervous system (CNS) input, autonomic signaling, and immunologic regulation that controls gut and CNS homeostasis. Here, we discuss the pathophysiology of brain–gut axis dysregulation and outline nutrition strategies in patients with TBI.

Recent Findings

Feeding intolerance following TBI is multifactorial; complex signaling between the CNS, sympathetic nervous system, parasympathetic nervous system, and enteric nervous system that controls gut homeostasis is disrupted within hours post-injury. This has profound effects on the immune system and gut microbiome, further complicating post-TBI recovery. Despite this disruption, calorie and protein requirements increase considerably following TBI, and early nutritional supplementation improves survival following TBI. Enteral nutrition has proven more efficacious than parenteral nutrition in TBI patients and should be initiated within 48 hours following admission. Immune-fortified nutrition reduces CNS and gut inflammation and may improve outcomes in TBI patients.

Summary

Although autonomic dysregulation of the brain–gut axis results in feeding intolerance following TBI, early enteral nutrition is of paramount importance. Enteral nutrition reduces post-TBI inflammation and enhances immunologic and gut function. When feasible, enteral nutrition should be initiated within 48 hours following injury.

Involvement of the ghrelin system in the maintenance and reinstatement of cocaine-motivated behaviors: a role of adrenergic action at peripheral β1 receptors

Cocaine addiction is a significant medical and public concern. Despite decades of research effort, development of pharmacotherapy for cocaine use disorder remains largely unsuccessful. This may be partially due to insufficient understanding of the complex biological mechanisms involved in the pathophysiology of this disorder. In the present study, we show that: (1) elevation of ghrelin by cocaine plays a critical role in maintenance of cocaine self-administration and cocaine-seeking motivated by cocaine-conditioned stimuli; (2) acquisition of cocaine-taking behavior is associated with the acquisition of stimulatory effects of cocaine by cocaine-conditioned stimuli on ghrelin secretion, and with an upregulation of ghrelin receptor mRNA levels in the ventral tegmental area (VTA); (3) blockade of ghrelin signaling by pretreatment with JMV2959, a selective ghrelin receptor antagonist, dose-dependently inhibits reinstatement of cocaine-seeking triggered by either cocaine or yohimbine in behaviorally extinguished animals with a history of cocaine self-administration; (4) JMV2959 pretreatment also inhibits brain stimulation reward (BSR) and cocaine-potentiated BSR maintained by optogenetic stimulation of VTA dopamine neurons in DAT-Cre mice; (5) blockade of peripheral adrenergic β1 receptors by atenolol potently attenuates the elevation in circulating ghrelin induced by cocaine and inhibits cocaine self-administration and cocaine reinstatement triggered by cocaine. These findings demonstrate that the endogenous ghrelin system plays an important role in cocaine-related addictive behaviors and suggest that manipulating and targeting this system may be viable for mitigating cocaine use disorder.

Integrative effects of transcutaneous electrical acustimulation on abdominal pain, gastrointestinal motility, and inflammation in patients with early-stage acute pancreatitis

BACKGROUND/AIMS

Gastrointestinal (GI) dysmotility in acute pancreatitis (AP) aggravates inflammation and results in severe complications. This study aimed to explore effects and possible mechanisms of transcutaneous electrical acustimulation (TEA) on abdominal pain, GI dysmotility, and inflammation in AP patients.

METHODS

Forty-two AP patients were blindly randomized to receive TEA (n = 21) at acupoints PC6 and ST36 or Sham-TEA (n = 21) at sham points for 2 days. Symptom scores, gastric slow waves, autonomic functions (assessed by spectral analysis of heart rate variability), circulatory levels of motilin, ghrelin, and TNF-α were measured before and after the treatment. Sixteen healthy controls (HCs) were also included without treatment for the assessment of gastric slow waves and biochemistry.

KEY RESULTS

Compared with Sham-TEA, TEA decreased abdominal pain score (2.57 ± 1.78 vs. 1.33 ± 1.02, p < 0.05), bloating score (5.19 ± 1.21 vs. 0.76 ± 0.99, p < 0.001), the first defecation time (65.79 ± 19.51 h vs. 51.38 ± 17.19 h, p < 0.05); TEA, but not Sham-TEA, improved the percentage of normal gastric slow waves by 41.6% (p < 0.05), reduced AP severity score (5.52 ± 2.04 vs. 3.90 ± 1.90, p < 0.05) and serum TNF-α (7.59 ± 4.80 pg/ml vs. 4.68 ± 1.85 pg/ml, p < 0.05), and upregulated plasma ghrelin (0.85 ± 0.96 ng/ml vs. 2.00 ± 1.71 ng/ml, p = 0.001) but not motilin (33.08 ± 22.65 pg/ml vs. 24.12 ± 13.95 pg/ml, p > 0.05); TEA decreased sympathetic activity by 15.0% and increased vagal activity by 18.3% (both p < 0.05).

CONCLUSIONS & INFERENCES

TEA at PC6 and ST36 administrated at early stage of AP reduces abdominal pain, improves GI motility, and inhibits inflammatory cytokine, TNF-α, probably mediated via the autonomic and ghrelin mechanisms.

Involvement of the ghrelin system in the maintenance of oxycodone self-administration: converging evidence from endocrine, pharmacologic and transgenic approaches

Ghrelin, an orexigenic hormone, has emerged as a critical biological substrate implicated in drug reward. However, the response of the ghrelin system to opioid-motivated behaviors and the role of ghrelin in oxycodone self-administration remain to be studied. Here, we investigated the reciprocal interactions between the endogenous ghrelin system and oxycodone self-administration behaviors in rats and the role of the ghrelin system in brain stimulation reward (BSR) driven by optogenetic stimulation of midbrain reward circuits in mice. Oxycodone self-administration significantly elevated plasma ghrelin, des-acyl ghrelin and growth hormone and showed no effect on plasma LEAP2, a newly identified endogenous ghrelin receptor (GHS-R1a) antagonist. Oxycodone self-administration produced significant decreases in plasma gastric inhibitory polypeptide and insulin. Acquisition of oxycodone self-administration significantly upregulated GHS-R1a mRNA levels in dopamine neurons in the ventral tegmental area (VTA), a brain region critical in drug reward. Pretreatment with JMV2959, a selective GHS-R1a antagonist, dose-dependently reduced oxycodone self-administration and decreased the breakpoint for oxycodone under a progressive ratio reinforcement in Long-Evans rats. The inhibitory effects of JMV2959 on oxycodone self-administration is selectively mediated by GHS-R1a as JMV2959 showed a similar effect in Wistar wildtype but not in GHS-R knockout rats. JMV2959 pretreatment significantly inhibited BSR driven by selective stimulation of VTA dopamine neurons, but not by stimulation of striatal GABA neurons projecting to the VTA in mice. These findings suggest that elevation of ghrelin signaling by oxycodone or oxycodone-associated stimuli is a causal process by which oxycodone motivates oxycodone drug-taking and targeting the ghrelin system may be a viable treatment approach for opioid use disorders.

Transcutaneous Cervical Vagal Nerve Stimulation in Patients with Posttraumatic Stress Disorder (PTSD): A Pilot Study of Effects on PTSD Symptoms and Interleukin-6 Response to Stress

BACKGROUND

Posttraumatic stress disorder (PTSD) is a highly disabling condition associated with alterations in multiple neurobiological systems, including increases in inflammatory and sympathetic function, responsible for maintenance of symptoms. Treatment options including medications and psychotherapies have limitations. We previously showed that transcutaneous Vagus Nerve Stimulation (tcVNS) blocks inflammatory (interleukin (IL)-6) responses to stress in PTSD. The purpose of this study was to assess the effects of tcVNS on PTSD symptoms and inflammatory responses to stress.

METHODS

Twenty patients with PTSD were randomized to double blind active tcVNS (N=9) or sham (N=11) stimulation in conjunction with exposure to personalized traumatic scripts immediately followed by active or sham tcVNS and measurement of IL-6 and other biomarkers of inflammation. Patients then self administered active or sham tcVNS twice daily for three months. PTSD symptoms were measured with the PTSD Checklist (PCL) and the Clinician Administered PTSD Scale (CAPS), clinical improvement with the Clinical Global Index (CGI) and anxiety with the Hamilton Anxiety Scale (Ham-A) at baseline and one-month intervals followed by a repeat of measurement of biomarkers with traumatic scripts. After three months patients self treated with twice daily open label active tcVNS for another three months followed by assessment with the CGI.

RESULTS

Traumatic scripts increased IL-6 in PTSD patients, an effect that was blocked by tcVNS (p<.05). Active tcVNS treatment for three months resulted in a 31% greater reduction in PTSD symptoms compared to sham treatment as measured by the PCL (p=0.013) as well as hyperarousal symptoms and somatic anxiety measured with the Ham-A p<0.05). IL-6 increased from baseline in sham but not tcVNS. Open label tcVNS resulted in improvements measured with the CGI compared to the sham treatment period p<0.05).

CONCLUSIONS

These preliminary results suggest that tcVNS reduces inflammatory responses to stress, which may in part underlie beneficial effects on PTSD symptoms.

Brain-gut axis dysfunction in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a chronic and progressive disease, and management requires an understanding of both the primary neurological injury and the secondary sequelae that affect peripheral organs, including the gastrointestinal (GI) tract. The brain-gut axis is composed of bidirectional pathways through which TBI-induced neuroinflammation and neurodegeneration impact gut function. The resulting TBI-induced dysautonomia and systemic inflammation contribute to the secondary GI events, including dysmotility and increased mucosal permeability. These effects shape, and are shaped by, changes in microbiota composition and activation of resident and recruited immune cells. Microbial products and immune cell mediators in turn modulate brain-gut activity. Importantly, secondary enteric inflammatory challenges prolong systemic inflammation and worsen TBI-induced neuropathology and neurobehavioral deficits. The importance of brain-gut communication in maintaining GI homeostasis highlights it as a viable therapeutic target for TBI. Currently, treatments directed toward dysautonomia, dysbiosis, and/or systemic inflammation offer the most promise.

Vagus nerve stimulation in brain diseases: Therapeutic applications and biological mechanisms

Brain diseases, including neurodegenerative, cerebrovascular and neuropsychiatric diseases, have posed a deleterious threat to human health and brought a great burden to society and the healthcare system. With the development of medical technology, vagus nerve stimulation (VNS) has been approved by the Food and Drug Administration (FDA) as an alternative treatment for refractory epilepsy, refractory depression, cluster headaches, and migraines. Furthermore, current evidence showed promising results towards the treatment of more brain diseases, such as Parkinson's disease (PD), autistic spectrum disorder (ASD), traumatic brain injury (TBI), and stroke. Nonetheless, the biological mechanisms underlying the beneficial effects of VNS in brain diseases remain only partially elucidated. This review aims to delve into the relevant preclinical and clinical studies and update the progress of VNS applications and its potential mechanisms underlying the biological effects in brain diseases.

Potential Antioxidative, Anti-inflammatory and Immunomodulatory Effects of Ghrelin, an Endogenous Peptide from the Stomach in SARS-CoV2 Infection

The current COVID-19 pandemic is one of the most devastating events in recent history. The respiratory effects of this disease include acute respiratory distress syndrome, systemic inflammation, cytokine storm, and pulmonary fibrosis. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is a peptide hormone secreted mainly by the stomach. Interestingly, ghrelin possesses promising antioxidant, anti-and inflammatory effects, making it an attractive agent to reduce the complications of the SARS-CoV-2. In addition, ghrelin exerts a wide range of immunomodulatory and anti-inflammatory effects and can mitigate the uncontrolled cytokine production responsible for acute lung injury by upregulating PPARγ and down-regulating NF-κB expression. Ghrelin has also been reported to enhance Nrf2 expression in inflammatory conditions which led to the suppression of oxidative stress. The current opinion summarizes the evidence for the possible pharmacological benefits of ghrelin in the therapeutic management of SARS-CoV-2 infection.

Development and characterization of a chronic implant mouse model for vagus nerve stimulation

Vagus nerve stimulation (VNS) suppresses inflammation and autoimmune diseases in preclinical and clinical studies. The underlying molecular, neurological, and anatomical mechanisms have been well characterized using acute electrophysiological stimulation of the vagus. However, there are several unanswered mechanistic questions about the effects of chronic VNS, which require solving numerous technical challenges for a long-term interface with the vagus in mice. Here, we describe a scalable model for long-term VNS in mice developed and validated in four research laboratories. We observed significant heart rate responses for at least 4 weeks in 60-90% of animals. Device implantation did not impair vagus-mediated reflexes. VNS using this implant significantly suppressed TNF levels in endotoxemia. Histological examination of implanted nerves revealed fibrotic encapsulation without axonal pathology. This model may be useful to study the physiology of the vagus and provides a tool to systematically investigate long-term VNS as therapy for chronic diseases modeled in mice.

The brain-gut axis: A prime therapeutic target in traumatic brain injury

Traumatic brain injury (TBI) is a significant cause of morbidity and mortality in trauma patients. The primary focus of treating TBI is to prevent additional injury to the damaged brain tissue, known as secondary brain injury. This treatment can include treating the body's inflammatory response. Despite promise in animal models, anti-inflammatory therapy has failed to improve outcomes in human patients, suggesting a more targeted and precise approach may be needed. There is a bidirectional axis between the intestine and the brain that contributes to this inflammation in acute and chronic injury. The mechanisms for this interaction are not completely understood, but there is evidence that neural, inflammatory, endocrine, and microbiome signals all participate in this process. Therapies that target the intestine as a source of inflammation have potential to lessen secondary brain injury and improve outcomes in TBI patients, but to develop these treatments we need to better understand the mechanisms behind this intestinal inflammatory response.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

Transcutaneous vagal nerve stimulation blocks stress-induced activation of Interleukin-6 and interferon-γ in posttraumatic stress disorder: A double-blind, randomized, sham-controlled trial

Posttraumatic stress disorder (PTSD) is a highly disabling condition associated with alterations in multiple neurobiological systems, including increases in inflammatory function. Vagus nerve stimulation (VNS) decreases inflammation, however few studies have examined the effects of non-invasive VNS on physiology in human subjects, and no studies in patients with PTSD. The purpose of this study was to assess the effects of transcutaneous cervical VNS (tcVNS) on inflammatory responses to stress. Thirty subjects with a history of exposure to traumatic stress with (N ​= ​10) and without (N ​= ​20) PTSD underwent exposure to stressful tasks immediately followed by active or sham tcVNS and measurement of multiple biomarkers of inflammation (interleukin-(IL)-6, IL-2, IL-1β, Tumor Necrosis Factor alpha (TNFα) and Interferon gamma (IFNγ) over multiple time points. Stressful tasks included exposure to personalized scripts of traumatic events on day 1, and public speech and mental arithmetic (Mental Stress) tasks on days 2 and 3. Traumatic scripts were associated with a pattern of subjective anger measured with Visual Analogue Scales and increased IL-6 and IFNγ in PTSD patients that was blocked by tcVNS (p ​< ​.05). Traumatic stress had minimal effects on these biomarkers in non-PTSD subjects and there was no difference between tcVNS or sham. No significant differences were seen between groups in IL-2, IL-1β, or TNFα. These results demonstrate that tcVNS blocks behavioral and inflammatory responses to stress reminders in PTSD.

Autonomic balance determines the severity of COVID-19 courses

COVID-19 has left mankind desperately seeking how to manage dramatically rising infection rates associated with severe disease progressions. COVID-19 courses range from mild symptoms up to multiple organ failure and death, triggered by excessively high serum cytokine levels (IL 1β, IL 6, TNF α, IL 8). The vagally driven cholinergic anti-inflammatory pathway (CAP) stops the action of nuclear factor κB (NF-κB), the transcriptional factor of pro-inflammatory cytokines. Thus, well-balanced cytokine release depends on adequate vagal signaling. Coronaviruses replicate using NF-κB transcriptional factor as well. By degrading the cytoplasmatic inhibitor of NF-κB subunits (IκB), coronaviruses induce unrestricted NF-κB expression accelerating both, virus replication and cytokine transcription.

We hypothesize that CAP detriment due to depressed vagal tone critically determines the severity of COVID-19.

The Good, the Bad and the Unknown Aspects of Ghrelin in Stress Coping and Stress-Related Psychiatric Disorders

Ghrelin is a peptide hormone released by specialized X/A cells in the stomach and activated by acylation. Following its secretion, it binds to ghrelin receptors in the periphery to regulate energy balance, but it also acts on the central nervous system where it induces a potent orexigenic effect. Several types of stressors have been shown to stimulate ghrelin release in rodents, including nutritional stressors like food deprivation, but also physical and psychological stressors such as foot shocks, social defeat, forced immobilization or chronic unpredictable mild stress. The mechanism through which these stressors drive ghrelin release from the stomach lining remains unknown and, to date, the resulting consequences of ghrelin release for stress coping remain poorly understood. Indeed, ghrelin has been proposed to act as a stress hormone that reduces fear, anxiety- and depression-like behaviors in rodents but some studies suggest that ghrelin may - in contrast - promote such behaviors. In this review, we aim to provide a comprehensive overview of the literature on the role of the ghrelin system in stress coping. We discuss whether ghrelin release is more than a byproduct of disrupted energy homeostasis following stress exposure. Furthermore, we explore the notion that ghrelin receptor signaling in the brain may have effects independent of circulating ghrelin and in what way this might influence stress coping in rodents. Finally, we examine how the ghrelin system could be utilized as a therapeutic avenue in stress-related psychiatric disorders (with a focus on anxiety- and trauma-related disorders), for example to develop novel biomarkers for a better diagnosis or new interventions to tackle relapse or treatment resistance in patients.

Application of Noninvasive Vagal Nerve Stimulation to Stress-Related Psychiatric Disorders

BACKGROUND

Vagal Nerve Stimulation (VNS) has been shown to be efficacious for the treatment of depression, but to date, VNS devices have required surgical implantation, which has limited widespread implementation.

METHODS

New noninvasive VNS (nVNS) devices have been developed which allow external stimulation of the vagus nerve, and their effects on physiology in patients with stress-related psychiatric disorders can be measured with brain imaging, blood biomarkers, and wearable sensing devices. Advantages in terms of cost and convenience may lead to more widespread implementation in psychiatry, as well as facilitate research of the physiology of the vagus nerve in humans. nVNS has effects on autonomic tone, cardiovascular function, inflammatory responses, and central brain areas involved in modulation of emotion, all of which make it particularly applicable to patients with stress-related psychiatric disorders, including posttraumatic stress disorder (PTSD) and depression, since dysregulation of these circuits and systems underlies the symptomatology of these disorders.

RESULTS

This paper reviewed the physiology of the vagus nerve and its relevance to modulating the stress response in the context of application of nVNS to stress-related psychiatric disorders.

CONCLUSIONS

nVNS has a favorable effect on stress physiology that is measurable using brain imaging, blood biomarkers of inflammation, and wearable sensing devices, and shows promise in the prevention and treatment of stress-related psychiatric disorders.

Mazzola P, Souto EB, Chaud MV. Cachexia: Pathophysiology and Ghrelin Liposomes for Nose-to-Brain Delivery

Cachexia, a severe multifactorial condition that is underestimated and unrecognized in patients, is characterized by continuous muscle mass loss that leads to progressive functional impairment, while nutritional support cannot completely reverse this clinical condition. There is a strong need for more effective and targeted therapies for cachexia patients. There is a need for drugs that act on cachexia as a distinct and treatable condition to prevent or reverse excess catabolism and inflammation. Due to ghrelin properties, it has been studied in the cachexia and other treatments in a growing number of works. However, in the body, exogenous ghrelin is subject to very rapid degradation. In this context, the intranasal release of ghrelin-loaded liposomes to cross the blood-brain barrier and the release of the drug into the central nervous system may be a promising alternative to improve its bioavailability. The administration of nose-to-brain liposomes for the management of cachexia was addressed only in a limited number of published works. This review focuses on the discussion of the pathophysiology of cachexia, synthesis and physiological effects of ghrelin and the potential treatment of the diseased using ghrelin-loaded liposomes through the nose-to-brain route.

Vagus Nerve Stimulation Attenuates Early Traumatic Brain Injury by Regulating the NF-κB/NLRP3 Signaling Pathway

BACKGROUND

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. Oxidative stress, inflammation, and apoptosis are vital pathophysiological features post-TBI.

OBJECTIVES

Research has shown that vagus nerve stimulation (VNS) can attenuate oxidative stress in various diseases. However, the critical role of VNS in TBI is still not completely understood. This study investigated the protective effects and potential mechanism of VNS on TBI.

METHODS

Male Sprague-Dawley rats were randomized into 3 groups: sham, TBI, and TBI + VNS. The TBI model was induced in rats by the free-fall drop method. The vagal nerve trunk was separated, and VNS was performed after establishing the TBI model.

RESULTS

The results showed that VNS significantly ameliorated tissue damage, neurological deficits, and cerebral edema, compared with the sham VNS group. Additionally, VNS alleviated oxidative stress, inflammation, and apoptosis in the pericontusive cortex of rats after TBI. VNS also significantly suppressed expression of the nuclear factor-κB (NF-κB) protein in the nucleus and activation of the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome.

CONCLUSIONS

Taken together, the present study indicates that VNS may attenuate brain damage after TBI by inhibiting oxidative stress, inflammation, and apoptosis, possibly through the NF-κB/NLRP3 signaling pathway.

Non-invasive vagal nerve stimulation decreases brain activity during trauma scripts

Background:

Traumatic stress can have lasting effects on neurobiology and result in psychiatric conditions such as posttraumatic stress disorder (PTSD). We hypothesize that non-invasive cervical vagal nerve stimulation (nVNS) may alleviate trauma symptoms by reducing stress sympathetic reactivity. This study examined how nVNS alters neural responses to personalized traumatic scripts.

Methods:

Nineteen participants who had experienced trauma but did not have the diagnosis of PTSD completed this double-blind sham-controlled study. In three sequential time blocks, personalized traumatic scripts were presented to participants immediately followed by either sham stimulation (n = 8; 0–14 V, 0.2 Hz, pulse width = 5s) or active nVNS (n = 11; 0–30 V, 25 Hz, pulse width = 40 ms). Brain activity during traumatic scripts was assessed using High Resolution Positron Emission Tomography (HR-PET) with radiolabeled water to measure brain blood flow.

Results:

Traumatic scripts resulted in significant activations within the bilateral medial and orbital prefrontal cortex, premotor cortex, anterior cingulate, thalamus, insula, hippocampus, right amygdala, and right putamen. Greater activation was observed during sham stimulation compared to nVNS within the bilateral prefrontal and orbitofrontal cortex, premotor cortex, temporal lobe, parahippocampal gyrus, insula, and left anterior cingulate. During the first exposure to the trauma scripts, greater activations were found in the motor cortices and ventral visual stream whereas prefrontal cortex and anterior cingulate activations were more predominant with later script presentations for those subjects receiving sham stimulation.

Conclusion:

nVNS decreases neural reactivity to an emotional stressor in limbic and other brain areas involved in stress, with changes over repeated exposures suggesting a shift from scene appraisal to cognitively processing the emotional event.

Ghrelin as an anti-inflammatory and protective agent in ischemia/reperfusion injury

Ischemia/reperfusion (I/R) continue to be the most frequent cause of damaged tissues. Injured tissues resulted from the first ischemic insult, which is determined by the interruption in the blood supply, followed by subsequent impairment induced by reperfusion. In addition, ischemia-reperfusion injury is mediated by tumor necrosis factor (TNF) and other cytokines that activate complements and proteases responsible for free radical production. However, earlier studies have reported the protective roles of bioactive peptides during ischemia reperfusion injury. In fact, ghrelin is a peptide hormone discovered since 1999 as GH secretagogue and its production was identified in gastric X/A-like endocrine cells in rats and P/D1 type cells in humans. To date, this peptide receives growing attention due to its pleiotropic action in the organism and its role in maintaining energy homeostasis. Ghrelin is also involved in stress responses, assuming a modulatory action on immune pathways. Previous studies have identified many other functions related to an anti-inflammatory role in ischemia reperfusion injury. Under these challenging conditions, studies described acylated and unacylated ghrelin in activation and/or inhibition processes related to ischemia-reperfusion injury. The aim of this article is to provide a minireview about ghrelin mechanisms involved in the proinflammatory response of I/R injury. However, the regulatory processes of ghrelin in this pathologic event are still very limited and warrant further investigation.

Intestinal barrier dysfunction following traumatic brain injury

Traumatic brain injury (TBI) can cause non-neurological injuries to other organs such as the intestine. Newer studies have shown that paracellular hyperpermeability is the basis of intestinal barrier dysfunction following TBI. Ischemia-reperfusion injury, inflammatory response, abnormal release of neurotransmitters and hormones, and malnutrition contribute to TBI-induced intestinal barrier dysfunction. Several interventions that may protect intestinal barrier function and promote the recovery of TBI have been proposed, but relevant studies are still limited. This review is to clarify the established mechanisms of intestinal barrier dysfunction following TBI and to describe the possible strategies to reduce or prevent intestinal barrier dysfunction.

Acylated ghrelin suppresses the cytokine response to lipopolysaccharide and does so independently of the hypothalamic-pituitary-adrenal axis

Ghrelin, one of the major metabolic hormones involved in controlling energy balance, has recently been shown to have other properties including regulating the hypothalamic-pituitary-adrenal (HPA) axis response to psychological stress and being a potent anti-inflammatory agent. Ghrelin's HPA axis and anti-inflammatory actions have previously been identified as principally due to the acylated form (AG). However, our recent work has also suggested a role for des-acylated ghrelin (DAG) in these functions. Here we hypothesized ghrelin's anti-inflammatory activity is mediated by the HPA axis and this effect is differentially executed by AG and DAG. We gave adult male Wistar rats a concomitant injection of AG or DAG and lipopolysaccharide (LPS) and measured their effects on circulating cytokines, stress hormones and neuronal activation of the paraventricular nucleus of the hypothalamus (PVN). AG, but not DAG significantly suppressed the pro- and anti-inflammatory cytokine response induced by LPS in vivo. DAG also had no effects on any components of the HPA axis. AG, despite stimulating neuronal activation in the PVN in vivo and stimulating ACTH release from the pituitary in vitro, did not affect the HPA axis response to LPS. These findings suggest AG's anti-inflammatory effects are independent of its actions on the HPA axis and have implications for the potential use of this peptide for treatment of inflammatory conditions without compromising HPA axis activity.

A review of vagus nerve stimulation as a therapeutic intervention

In this review, we provide an overview of the US Food and Drug Administration (FDA)-approved clinical uses of vagus nerve stimulation (VNS) as well as information about the ongoing studies and preclinical research to expand the use of VNS to additional applications. VNS is currently FDA approved for therapeutic use in patients aged >12 years with drug-resistant epilepsy and depression. Recent studies of VNS in in vivo systems have shown that it has anti-inflammatory properties which has led to more preclinical research aimed at expanding VNS treatment across a wider range of inflammatory disorders. Although the signaling pathway and mechanism by which VNS affects inflammation remain unknown, VNS has shown promising results in treating chronic inflammatory disorders such as sepsis, lung injury, rheumatoid arthritis (RA), and diabetes. It is also being used to control pain in fibromyalgia and migraines. This new preclinical research shows that VNS bears the promise of being applied to a wider range of therapeutic applications.

Neuroprotective effect of dexmedetomidine in a murine model of traumatic brain injury

No FDA approved pharmacological therapy is available that would reduce cell death following traumatic brain injury (TBI). Dexmedetomidine (Dex) is a highly selective agonist of alpha-2 adrenergic receptors and has demonstrated neuroprotective effects in hippocampal slice cultures undergoing direct impact. However, no one has tested whether Dex, in addition to its sedative action, has neuroprotective effects in an animal model of TBI. Thus, in the present study, we investigated the effects of Dex on an animal model of TBI. Mice received different doses of Dex (1, 10, or 100 µg/kg bodyweight, n = 10 each group) or saline as control at 1 hour and 12 hours following TBI. The mice treated with Dex lost less cortical tissue than the control mice. Further analysis found that Dex treatment reduced cell death in the cortex and the hippocampus measured by Fluoro-Jade B (FJB) staining, prevented axonal degeneration detected by immunostaining with antibody against β-amyloid precursor protein (β-APP), and protected synapses from elimination with synaptophysin staining. Taken together, in an in vivo murine model of TBI, Dex at the dose of 100 µg/kg not only prevented tissue lesion and cell death, but also reduced axonal injury and synaptic degeneration caused by TBI.

Vagus Nerve Stimulation and Other Neuromodulation Methods for Treatment of Traumatic Brain Injury

The objective of this paper is to review the current literature regarding the use of vagus nerve stimulation (VNS) in preclinical models of traumatic brain injury (TBI) as well as discuss the potential role of VNS along with alternative neuromodulation approaches in the treatment of human TBI. Data from previous studies have demonstrated VNS-mediated improvement following TBI in animal models. In these cases, VNS was observed to enhance motor and cognitive recovery, attenuate cerebral edema and inflammation, reduce blood brain barrier breakdown, and confer neuroprotective effects. Yet, the underlying mechanisms by which VNS enhances recovery following TBI remain to be fully elucidated. Several hypotheses have been offered including: a noradrenergic mechanism, reduction in post-TBI seizures and hyper-excitability, anti-inflammatory effects, attenuation of blood-brain barrier breakdown, and cerebral edema. We present other potential mechanisms by which VNS acts including enhancement of synaptic plasticity and recruitment of endogenous neural stem cells, stabilization of intracranial pressure, and interaction with the ghrelin system. In addition, alternative methods for the treatment of TBI including deep brain stimulation, transcranial magnetic stimulation, transcranial direct current stimulation, and focused ultrasound stimulation are discussed. Although the primary source data show that VNS improves TBI outcomes, it remains to be determined if these findings can be translated to clinical settings.

Neuroimmune Modulation of Gut Function

Neuroimmune communications are facilitated by the production of neurotransmitters by immune cells and the generation of immune mediators by immune cells, which form a functional entity called the "neuroimmune synapse." There are several mechanisms that further facilitate neuroimmune interactions including the anatomic proximity between immune cells and nerves, the expression of receptors for neurotransmitters on immune cells and for immune mediators on nerves, and the receptor-mediated activation of intracellular signaling pathways that modulate nerve and immune phenotype and function. The bidirectional communication between nerves and immune cells is implicated in allostasis, a process that describes the continuous adaptation to an ever-changing environment. Neuroimmune interactions are amplified during inflammation by the influx of activated immune cells that significantly alter the microenvironment. In this context, the types of neurotransmitters released by activated neurons or immune cells can exert pro- or anti-inflammatory effects. Dysregulation of the enteric nervous system control of gastrointestinal functions, such as epithelial permeability and secretion as well as smooth muscle contractility, also contribute to the chronicity of inflammation. Persistent active inflammation in the gut leads to neuroimmune plasticity, which is a structural and functional remodeling in both the neural and immune systems. The importance of neuroimmune interactions has made them an emerging target in the development of novel therapies for GI pathologies.

Vagus Nerve Stimulation Exerts the Neuroprotective Effects in Obese-Insulin Resistant Rats, Leading to the Improvement of Cognitive Function

Vagus nerve stimulation (VNS) therapy was shown to improve peripheral insulin sensitivity. However, the effects of chronic VNS therapy on brain insulin sensitivity, dendritic spine density, brain mitochondrial function, apoptosis and cognition in obese-insulin resistant subjects have never been investigated. Male Wistar rats (n = 24) were fed with either a normal diet (n = 8) or a HFD (n = 16) for 12 weeks. At week 13, HFD-fed rats were divided into 2 groups (n = 8/group). Each group was received either sham therapy or VNS therapy for an additional 12 weeks. At the end of treatment, cognitive function, metabolic parameters, brain insulin sensitivity, brain mitochondrial function, brain apoptosis, and dendritic spines were determined in each rat. The HFD-fed with Sham therapy developed brain insulin resistance, brain oxidative stress, brain inflammation, and brain apoptosis, resulting in the cognitive decline. The VNS group showed an improvement in peripheral and brain insulin sensitivity. VNS treatment attenuated brain mitochondrial dysfunction and cell apoptosis. In addition, VNS therapy increased dendritic spine density and improved cognitive function. These findings suggest that VNS attenuates cognitive decline in obese-insulin resistant rats by attenuating brain mitochondrial dysfunction, improving brain insulin sensitivity, decreasing cell apoptosis, and increasing dendritic spine density.

Vagus Nerve Stimulation for Treatment of Inflammation: Systematic Review of Animal Models and Clinical Studies

Vagus nerve stimulation (VNS) has been used since 1997 for treatment of drug-resistant epilepsy. More recently, an off-label use of VNS has been explored in animal models and clinical trials for treatment of a number of conditions involving the innate immune system. The underlying premise has been the notion of the cholinergic antiinflammatory pathway (CAP), mediated by the vagus nerves. While the macroanatomic substrate - the vagus nerve - is understood, the physiology of the pleiotropic VNS effects and the "language" of the vagus nerve, mediated brain-body communication, remain an enigma. Tackling this kind of enigma is precisely the challenge for and promise of bioelectronic medicine. We review the state of the art of this emerging field as it pertains to developing strategies for use of the endogenous CAP to treat inflammation and infection in various animal models and human clinical trials. This is a systematic PubMed review for the MeSH terms "vagus nerve stimulation AND inflammation." We report the diverse profile of currently used VNS antiinflammatory strategies in animal studies and human clinical trials. This review provides a foundation and calls for devising systematic and comparable VNS strategies in animal and human studies for treatment of inflammation. We discuss species-specific differences in the molecular genetics of cholinergic signaling as a framework to understand the divergence in VNS effects between species. Brain-mapping initiatives are needed to decode vagus-carried brain-body communication before hypothesis-driven treatment approaches can be devised.

Transcutaneous Cervical Vagus Nerve Stimulation Ameliorates Acute Ischemic Injury in Rats

BACKGROUND

Direct stimulation of the vagus nerve in the neck via surgically implanted electrodes is protective in animal models of stroke. We sought to determine the safety and efficacy of a non-invasive cervical VNS (nVNS) method using surface electrodes applied to the skin overlying the vagus nerve in the neck in a model of middle cerebral artery occlusion (MCAO).

METHODS

nVNS was initiated variable times after MCAO in rats (n = 33). Control animals received sham stimulation (n = 33). Infarct volume and functional outcome were assessed on day 7. Brains were processed by immunohistochemistry for microglial activation and cytokine levels. The ability of nVNS to activate the nucleus tractus solitarius (NTS) was assessed using c-Fos immunohistochemistry.

RESULTS

Infarct volume was 43.15 ± 3.36 percent of the contralateral hemisphere (PCH) in control and 28.75 ± 4.22 PCH in nVNS-treated animals (p < 0.05). The effect of nVNS on infarct size was consistent when stimulation was initiated up to 4 hours after MCAO. There was no difference in heart rate and blood pressure between control and nVNS-treated animals. The number of c-Fos positive cells was 32.4 ± 10.6 and 6.2 ± 6.3 in the ipsilateral NTS (p < 0.05) and 30.4 ± 11.2 and 5.8 ± 4.3 in the contralateral NTS (p < 0.05) in nVNS-treated and control animals, respectively. nVNS reduced the number of Iba-1, CD68, and TNF-α positive cells and increased the number of HMGB1 positive cells.

CONCLUSIONS

nVNS inhibits ischemia-induced immune activation and reduces the extent of tissue injury and functional deficit in rats without causing cardiac or hemodynamic adverse effects when initiated up to 4 hours after MCAO.

The hippocampus and TNF: Common links between chronic pain and depression

Major depression and chronic pain are significant health problems that seriously impact the quality of life of affected individuals. These diseases that individually are difficult to treat often co-exist, thereby compounding the patient's disability and impairment as well as the challenge of successful treatment. The development of efficacious treatments for these comorbid disorders requires a more comprehensive understanding of their linked associations through common neuromodulators, such as tumor necrosis factor-α (TNFα), and various neurotransmitters, as well as common neuroanatomical pathways and structures, including the hippocampal brain region. This review discusses the interaction between depression and chronic pain, emphasizing the fundamental role of the hippocampus in the development and maintenance of both disorders. The focus of this review addresses the hypothesis that hippocampal expressed TNFα serves as a therapeutic target for management of chronic pain and major depressive disorder (MDD).

Electrical stimulation of the vagus nerve dermatome in the external ear is protective in rat cerebral ischemia

BACKGROUND

Although cervical vagus nerve stimulation is effective for reducing infarct volume in rats, it is not feasible for acute human stroke as it requires surgical incision of the neck. We hypothesized that stimulation of the dermatome in the external ear innervated by the vagus nerve (auricular vagus nerve stimulation; aVNS) reduces infarct volume after transient focal ischemia in rats.

METHODS

Animals were randomized to active aVNS or sham stimulation. For aVNS, electrical stimulation of the left cavum concha (1 h duration) using percutaneous needles was initiated 30 min after induction of ischemia. Behavioral and tissue outcome were measured 24 h after induction of ischemia. In a separate experimental dataset, c-Fos immunohistochemistry was performed to identify the brain regions activated after the stimulation.

RESULTS

Stimulation of the left cavum concha resulted in bilateral c-Fos staining in the nuclei tractus solitarii and the loci coerulei in all animals. There was no c-Fos staining in any part of the brainstem in sham control animals. The mean infarct volume (SD) as calculated by indirect method was 44.20 ± 7.58% in controls and 31.65 ± 9.67% in treated animals (P < 0.0001). The effect of aVNS on tissue outcome was associated with better neurological scores at 24 h after ischemia (P < 0.0001).

CONCLUSIONS

Electric stimulation of the vagus nerve dermatome in the external ear activates brainstem afferent vagal nuclei and reduces infarct volume in rats. This finding has potential to facilitate the development of treatments that leverage the brain's endogenous neuroprotective pathways at the setting of acute ischemic stroke.

Vagus nerve stimulation improves coagulopathy in hemorrhagic shock: a thromboelastometric animal model study

Introduction

Inflammation plays a major role in the multifactorial process of trauma associated coagulopathy. The vagus nerve regulates the cholinergic anti-inflammatory pathway. We hypothesized that efferent vagus nerve stimulation (VNS) can improve coagulopathy by modulating the inflammatory response to hemorrhage.

Methods

Wistar rats (n = 24) were divided in 3 groups: Group (G1) Sham hemorrhagic shock (HS); (G2) HS w/o VNS; (G3) HS followed by division of the vagus nerves and VNS of the distal stumps. Hemorrhage (45% of baseline MAPx15 minutes) was followed by normotensive resuscitation with LR. Vagus nerves were stimulated (3.5 mA, 5 Hz) for 30 sec 7 times. Samples were obtained at baseline and at 60 minutes for thromboelastometry (Rotem®) and cytokine assays (IL-1 and IL-10). ANOVA was used for statistical analysis; significance was set at p < 0.05.

Results

Maximum clot firmness (MCF) significantly decreased in G2 after HS (71.5 ± 1.5 vs. 64 ± 1.6) (p < 0.05). MCF significantly increased in G3 compared to baseline (67.3 ± 2.7 vs. 71.5 ± 1.2) (p < 0.05). G3 also showed significant improvement in Alfa angle, and Clot Formation Time (CFT) compared to baseline. IL-1 increased significantly in group 2 and decrease in group 3, while IL-10 increased in group 3 (p < 0.05).

Conclusions

Electrical stimulation of efferent vagus nerves, during resuscitation (G3), decreases inflammatory response to hemorrhage and improves coagulation.

Ghrelin gene products in acute and chronic inflammation

Ghrelin gene products--the peptides ghrelin, unacylated ghrelin, and obestatin--have several actions on the immune system, opening new perspectives within neuroendocrinology, metabolism and inflammation. The aim of this review is to summarize the available evidence regarding the less known role of these peptides in the machinery of inflammation and autoimmunity, outlining some of their most promising therapeutic applications.