Targeting the Autonomic Nervous System for Risk Stratification, Outcome Prediction and Neuromodulation in Ischemic Stroke

Ischemic stroke is a worldwide major cause of mortality and disability and has high costs in terms of health-related quality of life and expectancy as well as of social healthcare resources. In recent years, starting from the bidirectional relationship between autonomic nervous system (ANS) dysfunction and acute ischemic stroke (AIS), researchers have identified prognostic factors for risk stratification, prognosis of mid-term outcomes and response to recanalization therapy. In particular, the evaluation of the ANS function through the analysis of heart rate variability (HRV) appears to be a promising non-invasive and reliable tool for the management of patients with AIS. Furthermore, preclinical molecular studies on the pathophysiological mechanisms underlying the onset and progression of stroke damage have shown an extensive overlap with the activity of the vagus nerve. Evidence from the application of vagus nerve stimulation (VNS) on animal models of AIS and on patients with chronic ischemic stroke has highlighted the surprising therapeutic possibilities of neuromodulation. Preclinical molecular studies highlighted that the neuroprotective action of VNS results from anti-inflammatory, antioxidant and antiapoptotic mechanisms mediated by α7 nicotinic acetylcholine receptor. Given the proven safety of non-invasive VNS in the subacute phase, the ease of its use and its possible beneficial effect in hemorrhagic stroke as well, human studies with transcutaneous VNS should be less challenging than protocols that involve invasive VNS and could be the proof of concept that neuromodulation represents the very first therapeutic approach in the ultra-early management of stroke.

The role of surgery in the management of Lennox-Gastaut syndrome: A systematic review and meta-analysis of the clinical evidence

Lennox-Gastaut syndrome (LGS) is a severe form of childhood onset epilepsy in which patients require multiple medications and may be candidates for palliative surgical intervention. In this meta-analysis, we sought to evaluate the impact of palliative vagus nerve stimulation (VNS), corpus callosotomy (CC), and resective surgery (RS) by analyzing their impact on seizure control, antiepileptic drug (AED) usage, quality of life (QOL), behavior, cognition, prognostic factors, and complications. A systematic search of PubMed MEDLINE, Scopus, and Cochrane Database of Systematic Reviews was performed to find articles that met the following criteria: (1) prospective/retrospective study with original data, (2) at least one LGS surgery patient aged less than 18 years, and (3) information on seizure frequency reduction (measured as percentage, Engel class, or qualitative comment). Seizures were analyzed quantitatively in a meta-analysis of proportions and a random-effects model, whereas other outcomes were analyzed qualitatively. Forty studies with 892 LGS patients met the selection criteria, with 19 reporting on CC, 17 on VNS, four on RS, two on RS + CC, one on CC + VNS, and one on deep brain stimulation. CC seizure reduction rate was 74.1% (95% confidence interval [CI] = 64.5%-83.7%), and VNS was 54.6% (95% CI = 42.9%-66.3%), which was significantly different (p < .001). RS seizure reduction was 88.9% (95% CI = 66.1%-99.7%). Many VNS patients reported alertness improvements, and most had no major complications. VNS was most effective for atonic/tonic seizures; higher stimulation settings correlated with better outcomes. CC patients reported moderate cognitive and QOL improvements; disconnection syndrome, transient weakness, and respiratory complications were noted. Greater callosotomy extent correlated with better outcomes. AED usage most often did not change after surgery. RS showed considerable QOL improvements for patients with localized seizure foci. In the reported literature, CC appeared to be more effective than VNS for seizure reduction. VNS may provide a similar or higher level of QOL improvement with lower aggregate risk of complications. Patient selection, anatomy, and seizure type will inform decision-making.

Activation of the Cholinergic Anti-Inflammatory Pathway as a Novel Therapeutic Strategy for COVID-19

The outbreak of coronavirus disease 2019 (COVID-19) underlined the urgent need for alleviating cytokine storm. We propose here that activating the cholinergic anti-inflammatory pathway (CAP) is a potential therapeutic strategy. However, there is currently no approved drugs targeting the regulatory pathway. It is evident that nicotine, anisodamine and some herb medicine, activate the CAP and exert anti-inflammation action in vitro and in vivo. As the vagus nerve affects both inflammation and specific immune response, we propose that vagus nerve stimulation by invasive or non-invasive devices and acupuncture at ST36, PC6, or GV20, are also feasible approaches to activate the CAP and control COVID-19. It is worth to investigate the efficacy and safety of the strategy in patients with COVID-19.

Sudarshan Kriya Yoga: A Breath of Hope during COVID-19 Pandemic

Important counter measures to combat an infectious disease pandemic include vaccination, antiviral therapy, and immunomodulation therapy. Vaccinations are disease specific and moreover strain specific, so the protection provided is also specific and limited. Antiviral therapies are costly and require bulk production of drugs, hence globally there is an increased interest toward low-risk, cost-effective complementary alternative therapies, such as Yoga and Ayurveda to tackle the infectious pandemic, coronavirus disease 2019 (COVID-19). There is clinical evidence available on the potential complementary role of yogic practices in the management of noncommunicable and communicable diseases. Various online databases were searched for articles published between 2000 and 2020. Databases explored were Medline, EMBASE, Indian Citation Index, PsycINFO, Index Medicus for South-East Asia Region, and Google Scholar. All search results were screened, and articles related to keywords such as COVID-19, yoga therapy, and Sudarshan Kriya Yoga (SKY) were selected for data extraction. Quality of the studies included was evaluated on the basis of the construct validity, content validity, relevance, bias, credibility relating to information, and data sources. SKY is a unique yogic practice that includes specific sequential breathing techniques. It balances the autonomic nervous system and thus can alleviate anxiety, routine stress, depression, stress-related medical disorders, and posttraumatic stress. It potentiates natural host immune defenses that are essential to tackle a plethora of microbial infections. This narrative review article provides an overview of potential therapeutic benefits that SKY can offer to the population at large during this COVID-19 pandemic.

Transcutaneous Vagal Nerve Stimulation in Treatment-Resistant Depression: A Feasibility Study

BACKGROUND

Major depression (MD) contributes significantly to the global burden of disease with up to one-third of patients being treatment resistant. Therefore, the development of new treatment options for treatment-resistant depression (TRD) is needed. Vagus nerve stimulation (VNS) has shown mood improvements in patients with TRD. However, due to high costs related to the implantation and the invasive nature of VNS, an application with transcutaneous VNS (t-VNS) has been developed stimulating a vagal nerve branch in the earlobe (Arnold's nerve). A few studies with t-VNS in MD has shown a possible antidepressant effect, but feasibility is poorly described and patients with TRD have not been investigated.

OBJECTIVES

As the full antidepressant effect of t-VNS takes months we wanted to assess feasibility and side effects of daily treatments.

MATERIALS AND METHODS

Single-arm feasibility trial assessing compliance, usability, side effects, cognitive speed, and depression in a four-week period with a recommended t-VNS stimulation duration of four hours per day in patients with TRD. The primary outcome was compliance with 80% of the recommended daily treatment time.

RESULTS

Compliance threshold was reached for 80.0% of the 20 included participants. Usability was acceptable. Side effects were few, mild or moderate, mostly as local effects at the contact point in the ear. The device was difficult to use for some participants. A statistically significant reduction in depression severity and an increase in cognitive speed were seen with unchanged suicidal ideation and sleep.

CONCLUSIONS

We would recommend larger long-term randomized studies of t-VNS to access any antidepressant effect in TRD. The design of the device might be improved for higher usability.

Effects of acute transcutaneous vagus nerve stimulation on emotion recognition in adolescent depression

BACKGROUND

Transcutaneous vagus nerve stimulation (tVNS) is a promising therapeutic option for major depressive disorder (MDD) in adults. Alternative third-line treatments for MDD in adolescents are scarce. Here we aimed to assess the effects of acute tVNS on emotion recognition in adolescents with MDD.

METHODS

Adolescents (14-17 years) with MDD (n = 33) and non-depressed controls (n = 30) received tVNS or sham-stimulation in a cross-sectional, case-control, within-subject cross-randomized controlled trial, while performing different tasks assessing emotion recognition. Correct responses, response times, and errors of omission and commission on three different computerized emotion recognition tasks were assessed as main outcomes. Simultaneous recordings of electrocardiography and electro dermal activity, as well as sampling of saliva for the determination of α-amylase, were used to quantify the effects on autonomic nervous system function.

RESULTS

tVNS had no effect on the recognition of gradually or static expressed emotions but altered response inhibition on the emotional Go/NoGo-task. Specifically, tVNS increased the likelihood of omitting a response toward sad target-stimuli in adolescents with MDD, while decreasing errors (independent of the target emotion) in controls. Effects of acute tVNS on autonomic nervous system function were found in non-depressed controls only.

CONCLUSIONS

Acute tVNS alters the recognition of briefly presented facial expressions of negative valence in adolescents with MDD while generally increasing emotion recognition in controls. tVNS seems to specifically alter early visual processing of stimuli of negative emotional valence in MDD. These findings suggest a potential therapeutic benefit of tVNS in adolescent MDD that requires further evaluation within clinical trials.

Vagus Nerve Stimulation Decreases Pancreatitis Severity in Mice

Background

Vagus nerve stimulation (VNS) is effective in reducing inflammation in various diseases, such as rheumatoid arthritis, colitis and acute kidney injury. The anti-inflammatory effect of vagus nerve in these diseases necessitates the interactions of neural activation and α7 nicotinic acetylcholine receptors (α7nAChRs) on splenic macrophages. In this study, we aimed to investigate the effect of VNS on severity in experimental acute pancreatitis (AP).

Methods

Two independent AP models were used, which induced in ICR mice with caerulein or pancreatic duct ligation (PDL). Thirty minutes after modeling, the left cervical carotid sheath containing the vagus nerve was electrically stimulated for 2 min. Plasma lipase and amylase activities, TNF-α levels and pancreas histologic damage were evaluated. In caerulein mice, the percentages of α7nAChR⁺ macrophage in pancreas and spleen were assessed by flow cytometry. Furthermore, splenectomy and adoptive transfer of VNS-conditioned α7nAChR splenocytes were performed in caerulein mice to evaluate the role of spleen in the protective effect of VNS.

Results

VNS reduced plasma lipase and amylase activities, blunted the concentrations of TNF-α and protected against pancreas histologic damage in two AP models. Survival rates were improved in the PDL model after VNS. In caerulein AP mice, VNS increased the percentages of α7nAChR⁺ macrophages in pancreas and spleen. Adoptive transfer of VNS-treated α7nAChR splenocytes provided protection against pancreatitis in recipient mice. However, splenectomy did not abolish the protective effect of VNS.

Conclusions

VNS reduces disease severity and attenuates inflammation in AP mice. This effect is independent of spleen and is probably related to α7nAChR on macrophage.

Effect of Long-Term Treatment with Vagus Nerve Stimulation on Mood and Quality of Life in Korean Patients with Drug-Resistant Epilepsy

BACKGROUND AND PURPOSE

This study aimed to determine the long-term effects of vagus nerve stimulation (VNS) treatment on suicidality, mood-related symptoms, and quality of life (QOL) in patients with drug-resistant epilepsy (DRE). We also investigated the relationships among these main effects, clinical characteristics, and VNS parameters.

METHODS

Among 35 epilepsy patients who underwent VNS implantation consecutively in our epilepsy center, 25 patients were recruited to this study for assessing the effects of VNS on suicidality, mood-related symptoms, and QOL. The differences in these variables between before and after VNS treatment were analyzed statistically using paired t-tests. Multiple linear regression analyses were also performed to determine how the patients' demographic and clinical characteristics influenced the variables that showed statistically significant changes after long-term VNS treatment.

RESULTS

After VNS, our patients showed significant improvements not only in the mean seizure frequency but also in suicidality, depression, and QOL. The reduction in depression was associated with the improvement in QOL and more-severe depression at baseline. The reduction in suicidality was associated with higher suicidality at baseline, smaller changes in depression, and less-severe depression at baseline. Improved QOL was associated with lower suicidality at baseline.

CONCLUSIONS

This study found that VNS decreased the mean seizure frequency in patients with DRE, and also improved their depression, suicidality, and QOL. These results provide further evidence for therapeutic effect of VNS on psychological comorbidities of patients with DRE.

An economic evaluation of vagus nerve stimulation as an adjunctive treatment to anti-seizure medications for the treatment of drug-resistant epilepsy in England

INTRODUCTION

Anti-seizure medications (ASMs) are commonly used to prevent recurring epileptic seizures, but around a third of people with epilepsy fail to achieve an adequate response. Vagus nerve stimulation (VNS) is clinically recommended for people with drug-resistant epilepsy (DRE) who are not suitable for surgery, but the cost-effectiveness of the intervention has not recently been evaluated. The study objective is to estimate costs and quality-adjusted life-years (QALYs) associated with using VNS as an adjunct to ongoing ASM therapy, compared to the strategy of using only ASMs in the treatment of people with DRE, from an English National Health Service perspective.

METHODS

A cohort state transition model was developed in Microsoft Excel to simulate costs and QALYs of the VNS + ASM and ASM only strategies. Patients could transition between five health states, using a 3-month cycle length. Health states were defined by an expected percentage reduction in seizure frequency, derived from randomized control trial data. Costs included the VNS device as well as its installation, setup, and removal; ASM therapy; adverse events associated with VNS (dyspnea, hoarseness, and cough); and health-state costs associated with epilepsy including hospitalizations, emergency department visits, neurologist visits, and primary care visits. A range of sensitivity analyses, including probabilistic sensitivity analysis, were run to assess the impact of parameter and structural uncertainty.

RESULTS

In the base case, VNS + ASM had an estimated incremental cost-effectiveness ratio (ICER) of £17,771 per QALY gained compared to ASMs alone. The cost-effective ICER was driven by relative reductions in expected seizure frequency and the differences in health care resource use associated therewith. Sensitivity analyses found that the amount of resource use per epilepsy-related health state was a key driver of the cost component.

CONCLUSIONS

VNS is expected to be a cost-effective intervention in the treatment of DRE in the English National Health Service.

The Vagal Autonomic Pathway of COVID-19 at the Crossroad of Alzheimer's Disease and Aging: A Review of Knowledge

Coronavirus Disease 2019 (COVID-19) pandemic-triggered mortality is significantly higher in older than in younger populations worldwide. Alzheimer's disease (AD) is related to aging and was recently reported to be among the major risk factors for COVID-19 mortality in older people. The symptomatology of COVID-19 indicates that lethal outcomes of infection rely on neurogenic mechanisms. The present review compiles the available knowledge pointing to the convergence of COVID-19 complications with the mechanisms of autonomic dysfunctions in AD and aging. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is prone to neuroinvasion from the lung along the vagus nerve up to the brainstem autonomic nervous centers involved in the coupling of cardiovascular and respiratory rhythms. The brainstem autonomic network allows SARS-CoV-2 to trigger a neurogenic switch to hypertension and hypoventilation, which may act in synergy with aging- and AD-induced dysautonomias, along with an inflammatory "storm". The lethal outcomes of COVID-19, like in AD and unhealthy aging, likely rely on a critical hypoactivity of the efferent vagus nerve cholinergic pathway, which is involved in lowering cardiovascular pressure and systemic inflammation tone. We further discuss the emerging evidence supporting the use of 1) the non-invasive stimulation of vagus nerve as an additional therapeutic approach for severe COVID-19, and 2) the demonstrated vagal tone index, i.e., heart rate variability, via smartphone-based applications as a non-serological low-cost diagnostic of COVID-19. These two well-known medical approaches are already available and now deserve large-scale testing on human cohorts in the context of both AD and COVID-19.

Saudi Arabian Consensus Statement on Vagus Nerve Stimulation for Refractory Epilepsy

Vagus nerve stimulation (VNS) is an approved adjunctive therapy for refractory epilepsy and used in patients who are not candidates for resective epilepsy surgery. In Saudi Arabia, VNS device implantation is being performed since 2008 by several comprehensive epilepsy programs, but with variable protocols. Therefore, to standardize the use of VNS, a task force was established to create a national consensus. This group consisted of epileptologists, epilepsy surgeons and a VNS nurse coordinator working in comprehensive epilepsy centers and dealing with refractory epilepsy cases. The group intensively reviewed the literature using Medline, EMBASE, Web of Science and Cochrane Library, in addition to physician's manual. Evidence is reported as three stages: preimplantation and patient selection, a perioperative phase involving all stakeholders and post-operative care with specific programming pathways.

Vagus Nerve Stimulation Transiently Mitigates Chemotherapy-Induced Peripheral Neuropathy in Rats

Background

Chemotherapy-induced peripheral neuropathy is a severe side effect of chemotherapeutic agents. Vagus nerve stimulation attenuates neuroinflammation by activating the cholinergic anti-inflammatory pathway and thus may attenuate CIPN.

Methods

Adult male Sprague-Dawley rats received intraperitoneal paclitaxel injection (2 mg/kg) every other day for a total of 4 injections. Three weeks later, the left cervical vagus nerve was exposed under general anesthesia, and the rats randomly received 20-min stimulation (1 V, 2 ms, 5 Hz, 30 s ON/5 min OFF) or sham stimulation. Heat and mechanical pain sensitivity was evaluated using Hargreaves and von Frey tests before and after treatment (n=12 per group per time point). Additionally, rats receiving paclitaxel or saline but no surgery were included. Expression of representative pro- and anti-inflammatory cytokines in dorsal root ganglia was assessed by Western blotting assays and immunohistochemistry.

Results

Paclitaxel significantly reduced the sensitivity for heat (withdrawal latency: paclitaxel 6.16 ± 0.54 s vs saline 9.93 ± 0.78 s, p<0.001) and mechanical pain (withdrawal frequency: paclitaxel 32.22 ± 15.51% vs saline 3.33 ± 4.92%, p<0.001). Compared with sham-stimulated rats, rats receiving vagus nerve stimulation had significantly higher sensitivity for heat (withdrawal latency: VNS 10.28 ± 1.15 s vs sham 6.27 ± 0.56 s, p<0.001) and mechanical pain (withdrawal frequency: VNS 10.00 ± 9.54% vs Sham 31.67 ± 18.99%, p=0.003) on +1 day, but not 7 days later (withdrawal latency: VNS 6.97 ± 1.13 s vs Sham 6.23 ± 0.79 s, p=0.080; withdrawal frequency: VNS 21.67 ± 11.93% vs Sham 23.33 ± 7.79%, p=0.689). Western blotting assays and immunohistochemistry revealed that interleukin-10 level was elevated in the dorsal root ganglia of rats receiving vagus nerve stimulation while no apparent changes in NF-κB or TNF-α levels were observed.

Conclusion

Vagus nerve stimulation could transiently attenuate paclitaxel-induced hyperalgesia in rats. Future studies are needed to investigate whether stimulation with different protocols could achieve durable effects.

Complex sleep-disordered breathing after vagus nerve stimulation: broadening the spectrum of adverse events of special interest

Two young males with refractory epilepsy of unknown aetiology were referred for vagus nerve stimulation (VNS). Sleep disturbances emerged following VNS parameter changes. In Patient 1, video-polysomnogram (PSG) disclosed snoring and catathrenia in non-REM sleep. Central apnoea also occurred, but more rarely. In Patient 2, video-PSG showed mixed apnoea with desaturation and episodes of stridor followed by a catathrenia-like sound. A drug-induced sleep endoscopy (DISE) revealed, during VNS OFF time, glossoptosis, "trap door" of the epiglottis, and paresis of the left side of the larynx and ipsilateral vocal cords. During ON time, there were periods of pharyngeal collapse, in which video-PSG revealed patterns suggestive of both obstructive and central sleep apnoea. All these sleep-related phenomena were coincident with VNS ON time. In the first patient, VNS parameter adjustment was sufficient to successfully reverse all the symptoms, whereas the other patient required concomitant treatment with continuous positive airway pressure. The data broaden our knowledge about sleep disorders related to VNS, in particular stridor and catathrenia. We suggest that central sleep apnoea may be associated with laryngeal occlusion. DISE may be considered in selected cases as a valuable clinical tool to evaluate, in a single session, the effectiveness of multiple VNS parameter changes on respiration and laryngeal side effects. [Published with video sequences].

Celiac Vagus Nerve Stimulation Recapitulates Angiotensin II-Induced Splenic Noradrenergic Activation, Driving Egress of CD8 Effector Cells

Angiotensin II (AngII) is a peptide hormone that affects the cardiovascular system, not only through typical effects on the vasculature, kidneys, and heart, but also through less understood roles mediated by the brain and the immune system. Here, we address the hard-wired neural connections within the autonomic nervous system that modulate splenic immunity. Chronic AngII infusion triggers burst firing of the vagus nerve celiac efferent, an effect correlated with noradrenergic activation in the spleen and T cell egress. Bioelectronic stimulation of the celiac vagus nerve, in the absence of other challenges and independently from afferent signals to the brain, evokes the noradrenergic splenic pathway to promote release of a growth factor mediating neuroimmune crosstalk, placental growth factor (PlGF), and egress of CD8 effector T cells. Our findings also indicate that the neuroimmune interface mediated by PlGF and necessary for transducing the neural signal into an effective immune response is dependent on α-adrenergic receptor signaling.

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Bioelectronic stimulation of celiac vagus nerve primes a splenic immune response

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Vagus nerve stimulation selectively drives the egress of CD8+ effector T cells

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Placental growth factor (PlGF) is a key mediator of the splenic neuroimmune coupling

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Vagus nerve stimulation induces splenic PlGF through α-adrenergic receptors signaling

Therapeutic effects of children with refractory epilepsy after vagus nerve stimulation in Taiwan

BACKGROUND

Vagus nerve stimulation (VNS) is used as an add-on treatment for epilepsy. This study aimed to use Taiwanese nationwide registry data to analyze the therapeutic effects of VNS in children with refractory epilepsy (RE) and try to explore predictive factors of VNS treatment effectiveness.

METHODS

This retrospective study collected data from December 2007 to December 2014. Patient variables included gender, age, VNS implantation date, epilepsy duration, seizure frequency, seizure type, etiology, and antiepileptic drug (AED) history. We divided patients into three groups: Group I as seizure frequency >80 times per month, Group II as seizure frequency 24-80 times per month, and Group III as seizure frequency <24 times per month. Multivariate regression analysis was performed to determine predictors of seizure frequency reduction after VNS treatment.

RESULTS

A total of 80 patients were included in this study. Three or more AED types were prescribed for 61 (77.1%) patients. Seizure frequency decreased significantly at 12 and 24 months after VNS treatment. The mean seizure reduction rates were 44.6% and 50.1% at 12 and 24 months after VNS treatment, with the difference between them reaching statistical significance (p = 0.001). In multivariate linear regression, high seizure frequency (Group I) was a positive predictor of seizure frequency reduction (p < 0.001). The most common complication was coughing (eight patients, 10%) and no patient had early withdrawal or premature termination of VNS use due to complications.

CONCLUSION

VNS is an effective palliative treatment for children with RE for different seizure types. Seizure reduction rate at 24 months after VNS was better than at 12 months after VNS. High seizure frequency can be regarded as a positive predictor for seizure frequency reduction in children with RE treated with VNS.

The Effectiveness of Vagus Nerve Stimulation in Drug-Resistant Epilepsy Correlates with Vagus Nerve Stimulation-Induced Electroencephalography Desynchronization

Introduction: VNS is an adjunctive neuromodulation therapy for patients with drug-refractory epilepsy. The antiseizure effect of VNS is thought to be related to a diffuse modulation of functional connectivity but remains to be confirmed.

Aim: To investigate electroencephalographic (EEG) metrics of functional connectivity in patients with drug-refractory epilepsy treated by vagus nerve stimulation (VNS), between VNS-stimulated “ON” and nonstimulated “OFF” periods and between responder (R) and nonresponder (NR) patients.

Methods: Scalp-EEG was performed for 35 patients treated by VNS, using 21 channels and 2 additional electrodes on the neck to detect the VNS stimulation. Patients were defined as VNS responders if a reduction of seizure frequency of ∼50% was documented. We analyzed the synchronization in EEG time series during “ON” and “OFF” periods of stimulation, using average phase lag index (PLI) in signal space and phase-locking value (PLV) between 10 sources. Based on graph theory, we computed brain network models and analyzed minimum spanning tree (MST) for responder and nonresponder patients.

Results: Among 35 patients treated by VNS for a median time of 7 years (range 4 months to 22 years), 20 were R and 15 were NR. For responder patients, PLI during ON periods was significantly lower than that during OFF periods in delta (p = 0.009), theta (p = 0.02), and beta (p = 0.04) frequency bands. For nonresponder patients, there were no significant differences between ON and OFF periods. Moreover, variations of seizure frequency with VNS correlated with the PLI OFF/ON ratio in delta (p = 0.02), theta (p = 0.04), and beta (p = 0.03) frequency bands. Our results were confirmed using PLV in theta band (p < 0.05). No significant differences in MST were observed between R and NR patients.

Conclusion: The correlation between VNS-induced interictal EEG time-series desynchronization and decrease in seizure frequency suggested that VNS therapeutic impact might be related to changes in interictal functional connectivity.

Sex Differences in Vagus Nerve Stimulation Effects on Rat Cardiovascular and Immune Systems

Background

Investigations into the benefits of vagus nerve stimulation (VNS) through pre-clinical and clinical research have led to promising findings for treating several disorders. Despite proven effectiveness of VNS on conditions such as epilepsy and depression, understanding of off-target effects and contributing factors such as sex differences can be beneficial to optimize therapy design.

New Methods

In this article, we assessed longitudinal effects of VNS on cardiovascular and immune systems, and studied potential sex differences using a rat model of long-term VNS. Rats were implanted with cuff electrodes around the left cervical vagus nerve for VNS, and wireless physiological monitoring devices for continuous monitoring of cardiovascular system using electrocardiogram (ECG) signals. ECG morphology and heart rate variability (HRV) features were extracted to assess cardiovascular changes resulting from VNS in short-term and long-term timescales. We also assessed VNS effects on expression of inflammatory cytokines in blood during the course of the experiment. Statistical analysis was performed to compare results between Treatment and Sham groups, and between male and female animals from Treatment and Sham groups.

Results

Considerable differences between male and female rats in cardiovascular effects of VNS were observed in multiple cardiovascular features. However, the effects seemed to be transient with approximately 1-h recovery after VNS. While short-term cardiovascular effects were mainly observed in male rats, females in general showed more significant long-term effects even after VNS stopped. We did not observe notable changes or sex differences in systemic cytokine levels resulting from VNS.

Comparison With Existing Methods

Compared to existing methods, our study design incorporated wireless physiological monitoring and systemic blood cytokine level analysis, along with long-term VNS experiments in unanesthetized rats to study sex differences.

Conclusion

The contribution of sex differences for long-term VNS off-target effects on cardiovascular and immune systems was assessed using awake behaving rats. Although VNS did not change the concentration of inflammatory biomarkers in systemic circulation for male and female rats, we observed significant differences in cardiovascular effects of VNS characterized using ECG morphology and HRV analyses.

Quantified Morphology of the Cervical and Subdiaphragmatic Vagus Nerves of Human, Pig, and Rat

It is necessary to understand the morphology of the vagus nerve (VN) to design and deliver effective and selective vagus nerve stimulation (VNS) because nerve morphology influences fiber responses to electrical stimulation. Specifically, nerve diameter (and thus, electrode-fiber distance), fascicle diameter, fascicular organization, and perineurium thickness all significantly affect the responses of nerve fibers to electrical signals delivered through a cuff electrode. We quantified the morphology of cervical and subdiaphragmatic VNs in humans, pigs, and rats: effective nerve diameter, number of fascicles, effective fascicle diameters, proportions of endoneurial, perineurial, and epineurial tissues, and perineurium thickness. The human and pig VNs were comparable sizes (∼2 mm cervically; ∼1.6 mm subdiaphragmatically), while the rat nerves were ten times smaller. The pig nerves had ten times more fascicles-and the fascicles were smaller-than in human nerves (47 vs. 7 fascicles cervically; 38 vs. 5 fascicles subdiaphragmatically). Comparing the cervical to the subdiaphragmatic VNs, the nerves and fascicles were larger at the cervical level for all species and there were more fascicles for pigs. Human morphology generally exhibited greater variability across samples than pigs and rats. A prior study of human somatic nerves indicated that the ratio of perineurium thickness to fascicle diameter was approximately constant across fascicle diameters. However, our data found thicker human and pig VN perineurium than those prior data: the VNs had thicker perineurium for larger fascicles and thicker perineurium normalized by fascicle diameter for smaller fascicles. Understanding these differences in VN morphology between preclinical models and the clinical target, as well as the variability across individuals of a species, is essential for designing suitable cuff electrodes and stimulation parameters and for informing translation of preclinical results to clinical application to advance the therapeutic efficacy of VNS.

Vagus nerve stimulation for treatment-resistant depression: is this therapy distinct from other antidepressant treatments?

BACKGROUND

The treatment-resistant depression (TRD) is a very disabling disease.

OBJECTIVE

The aim of this article is to provide an overview of the therapeutic activity of vagus nerve stimulation (VNS) therapy system in TRD. We summarised the progress made during the last decade in this area.

METHODS

We conducted a non-systematic review on the efficacy and safety of the VNS therapy for this disease. We analysed the results from acute and long-term studies that utilised this technique. Major electronic databases were searched.

RESULTS

The patients with TRD may show acute and long-term benefit when treated with this technique. There are promising results for VNS therapy for these patients. The level of evidence as an acute treatment option is only 3, but as chronic treatment is 2. This therapy should be offered as an added long-term treatment option for patients with chronic and recurrent difficult to treat depression.

CONCLUSIONS

The antidepressant effects of this procedure remain controversial. The clinical trials have produced mixed results, but VNS therapy for TRD has two distinct features that differentiate it from other antidepressant treatments: a sustained therapeutic response obtained in highly resistant depressive disorders, a favourable safety profile and guaranteed compliance.

Impact of Cardiac-Based Vagus Nerve Stimulation Closed-Loop Stimulation on the Seizure Outcome of Patients With Generalized Epilepsy: A Prospective, Individual-Control Study

OBJECTIVES

We designed a prospective, individual-controlled study to evaluate the effect of cardiac-based VNS (cbVNS) in a cohort of patients with generalized epilepsy (GE).

MATERIALS AND METHODS

Twenty patients were included. They were followed up for six months under regular VNS (rVNS) and subsequently for six months during cbVNS. Stimulation parameters were 500 μsec, 30 Hz, and up to 2.5 mA. Seizure frequency was documented after two, four, and six months during the rVNS and cbVNS phases. Patients with at least 50% seizure frequency reduction were considered responders. The total and relative amount of stimulation cycles generated by both rVNS and cbVNS activation were documented. Findings during rVNS were compared to baseline and cbVNS data were compared to those during rVNS.

RESULTS

There was a significant decrease in mean seizure frequency (61% [95% CI, 48-74]; p < 0.001) during the rVNS phase compared to baseline. There was no additional significant (16% [95% CI, 4-35]; p = 0.097) mean seizure frequency reduction during cbVNS compared to the rVNS phase. Fifteen patients (75%) were considered responders after rVNS. Four patients (20%) were considered responders after six months of cbVNS. During the cbVNS phase, the mean total number of cycles/day was 346, 354, and 333 for months two, four, and six, respectively; the cycles generated by rVNS were 142, 138, and 146 for months two, four, and six, respectively; and cycles generated by cbVNS were 204, 215, and 186 for months two, four, and six, respectively. There was no relationship between the mean total number of cycles (-6[95% CI, -85 to 72]; p = 0.431), the mean number of auto-stimulation cycles (27[95% CI,-112 to 166]; p = 0.139), the mean number of regular cycles (-33[95% CI,-123 to 57]; p = 0.122), or the mean percentage of auto-stimulation cycles (13[95% CI,19- 45]; p = 0.109) and outcome during the cbVNS phase. Eight patients showed some decrease in seizure frequency during cbVNS.

CONCLUSIONS

rVNS was effective in reducing seizure frequency in patients with generalized epilepsy, but activation of the cbVNS feature did not add significantly to rVNS efficacy. On the other hand, although not statistically significant, 40% of the patients showed some reduction in seizure frequency, which might prove useful at an individual level.

Vagus Nerve Stimulation Provides Multiyear Improvements in Autonomic Function and Cardiac Electrical Stability in the ANTHEM-HF Study

BACKGROUND

Patients with heart failure with reduced left ventricular ejection fraction (LVEF) (HFrEF) experience long-term deterioration of autonomic function and cardiac electrical stability linked to increased mortality risk. The Autonomic Neural Regulation Therapy to Enhance Myocardial Function in Heart Failure (ANTHEM-HF) trial reported improved heart rate variability (HRV) and heart rate turbulence (HRT) and reduced T-wave alternans (TWA) after 12 months of vagus nerve stimulation (VNS). We investigated whether the benefits of chronic VNS persist in the long term.

METHODS AND RESULTS

Effects of chronic VNS on heart rate, HRV, HRT, TWA, R-wave and T-wave heterogeneity (RWH, TWH), and nonsustained ventricular tachycardia (NSVT) incidence were evaluated in all ANTHEM-HF patients with ambulatory ECG data at 24 and 36 months (n = 25). Autonomic markers improved significantly at 24 and 36 months compared to baseline [heart rate, square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), standard deviation of the normal-to-normal intervals (SDNN), HF-HRV, HRT slope, P < 0.05]. Peak TWA levels remained reduced at 24 and 36 months (P < 0.0001). Reductions in RWH and TWH at 6 and 12 months persisted at 24 and 36 months (P < 0.01). NSVT decreased at 12, 24, and 36 months (P < 0.025). No sudden cardiac deaths, ventricular fibrillation, or sustained ventricular tachycardia occurred.

CONCLUSION

In symptomatic patients with HFrEF, chronic VNS appears to confer wide-ranging, persistent improvements in autonomic tone (HRV), baroreceptor sensitivity (HRT), and cardiac electrical stability (TWA, RWH, TWH).

A 12-month pilot study outcomes of vagus nerve stimulation in Crohn's disease

BACKGROUND

The vagus nerve has anti-inflammatory properties. We aimed to investigate vagus nerve stimulation (VNS) as a new therapeutic strategy targeting an intrinsic anti-inflammatory pathway in a pilot study in Crohn's disease patients. The main objectives addressed the questions of long-term safety, tolerability, and anti-inflammatory effects of this therapy. This study is the continuation of previous reported findings at 6 months.

METHODS

Nine patients with moderate active disease underwent VNS. An electrode wrapped around the left cervical vagus nerve was continuously stimulated over 1 year. Clinical, biological, endoscopic parameters, cytokines (plasma, gut), and mucosal metabolites were followed-up.

KEY RESULTS

After 1 year of VNS, five patients were in clinical remission and six in endoscopic remission. C-reactive protein (CRP) and fecal calprotectin decreased in six and five patients, respectively. Seven patients restored their vagal tone and decreased their digestive pain score. The patients' cytokinergic profile evolved toward a more "healthy profile": Interleukins 6, 23, 12, tumor necrosis factor α, and transforming growth factorβ1 were the most impacted cytokines. Correlations were observed between CRP and tumor necrosis factor α, and some gut mucosa metabolites as taurine, lactate, alanine, and beta-hydroxybutyrate. VNS was well tolerated.

CONCLUSION & INFERENCES

Vagus nerve stimulation appears as an innovative and well-tolerated treatment in moderate Crohn's disease. After 12 months, VNS has restored a homeostatic vagal tone and reduced the inflammatory state of the patients. VNS has probably a global modulatory effect on the immune system along with gut metabolic regulations. This pilot study needs replication in a larger randomized double-blinded control study.

Digital Cardiovascular Biomarker Responses to Transcutaneous Cervical Vagus Nerve Stimulation: State-Space Modeling, Prediction, and Simulation

Background

Transcutaneous cervical vagus nerve stimulation (tcVNS) is a promising alternative to implantable stimulation of the vagus nerve. With demonstrated potential in myriad applications, ranging from systemic inflammation reduction to traumatic stress attenuation, closed-loop tcVNS during periods of risk could improve treatment efficacy and reduce ineffective delivery. However, achieving this requires a deeper understanding of biomarker changes over time.

Objective

The aim of the present study was to reveal the dynamics of relevant cardiovascular biomarkers, extracted from wearable sensing modalities, in response to tcVNS.

Methods

Twenty-four human subjects were recruited for a randomized double-blind clinical trial, for whom electrocardiography and photoplethysmography were used to measure heart rate and photoplethysmogram amplitude responses to tcVNS, respectively. Modeling these responses in state-space, we (1) compared the biomarkers in terms of their predictability and active vs sham differentiation, (2) studied the latency between stimulation onset and measurable effects, and (3) visualized the true and model-simulated biomarker responses to tcVNS.

Results

The models accurately predicted future heart rate and photoplethysmogram amplitude values with root mean square errors of approximately one-fifth the standard deviations of the data. Moreover, (1) the photoplethysmogram amplitude showed superior predictability (P=.03) and active vs sham separation compared to heart rate; (2) a consistent delay of greater than 5 seconds was found between tcVNS onset and cardiovascular effects; and (3) dynamic characteristics differentiated responses to tcVNS from the sham stimulation.

Conclusions

This work furthers the state of the art by modeling pertinent biomarker responses to tcVNS. Through subsequent analysis, we discovered three key findings with implications related to (1) wearable sensing devices for bioelectronic medicine, (2) the dominant mechanism of action for tcVNS-induced effects on cardiovascular physiology, and (3) the existence of dynamic biomarker signatures that can be leveraged when titrating therapy in closed loop.

Trial Registration

ClinicalTrials.gov NCT02992899; https://clinicaltrials.gov/ct2/show/NCT02992899

International Registered Report Identifier (IRRID)

RR2-10.1016/j.brs.2019.08.002

Feasibility of Non-Invasive Vagus Nerve Stimulation (gammaCore VET™) for the Treatment of Refractory Seizure Activity in Dogs

Idiopathic epilepsy is the most common chronic neurologic condition in dogs. Approximately 20–30% of those dogs are refractory to standard medical therapy and commonly experience side effects from antiepileptic drugs. Non-invasive vagus nerve stimulation (nVNS) has been frequently used in human medicine as an adjunct seizure therapy with low incidence of adverse events. Canine studies are limited to invasive surgical implants with no non-invasive evaluations currently published. We investigated the feasibility and efficacy of nVNS (gammaCore VET) as an adjunct treatment for refractory epilepsy in dogs. In total, 14 client-owned dogs completed the trial of either 8- or 16-week treatment periods during which they received 90–120 s stimulation three times per day in the region of the left cervical vagus nerve. Owners recorded seizure type (focal or generalized) and frequency as well as any adverse effects. Out of 14 dogs, nine achieved a reduction in seizure frequency and four were considered responders with a 50% or greater reduction in seizures from baseline to the final treatment period. However, there was no statistically significant difference in overall seizure frequency (p = 0.53) or percent change in seizure frequency between groups (p = 0.75). Adverse effects occurred in 25% of dogs originally enrolled, with reports of a hoarse bark and limb trembling, lethargy, behavioral changes, and an increase in seizure frequency. Non-invasive VNS was found to be safe and easy to administer with mild adverse events. It is considered a feasible treatment option as an adjunct therapy in refractory seizures and should be further investigated.

[Application of scalp electroencephalogram in treatment of refractory epilepsy with vagus nerve stimulation]

Electroencephalogram (EEG) has been an important tool for scientists to study epilepsy and evaluate the treatment of epilepsy for half a century, since epilepsy seizures are caused by the diffusion of excessive discharge of brain neurons. This paper reviews the clinical application of scalp EEG in the treatment of intractable epilepsy with vagus nerve stimulation (VNS) in the past 30 years. It mainly introduces the prediction of the therapeutic effect of VNS on intractable epilepsy based on EEG characteristics and the effect of VNS on EEG of patients with intractable epilepsy, and expounds some therapeutic mechanisms of VNS. For predicting the efficacy of VNS based on EEG characteristics, EEG characteristics such as epileptiform discharge, polarity of slow cortical potential changes, changes of EEG symmetry level and changes of EEG power spectrum are described. In view of the influence of VNS treatment on patients' EEG characteristics, the change of epileptiform discharge, power spectrum, synchrony, brain network and amplitude of event-related potential P300 are described. Although no representative EEG markers have been identified for clinical promotion, this review paves the way for prospective studies of larger patient populations in the future to better apply EEG to the clinical treatment of VNS, and provides ideas for predicting VNS efficacy, assessing VNS efficacy, and understanding VNS treatment mechanisms, with broad medical and scientific implications.

Health Technology Assessment Report on Vagus Nerve Stimulation in Drug-Resistant Epilepsy

Background: Vagus nerve stimulation (VNS) is a palliative treatment for medical intractable epileptic syndromes not eligible for resective surgery. Health technology assessment (HTA) represents a modern approach to the analysis of technologies used for healthcare. The purpose of this study is to assess the clinical, organizational, financial, and economic impact of VNS therapy in drug-resistant epilepsies and to establish the congruity between costs incurred and health service reimbursement. Methods: The present study used an HTA approach. It is based on an extensive detailed bibliographic search on databases (Medline, Pubmed, Embase and Cochrane, sites of scientific societies and institutional sites). The HTA study includes the following issues: (a) social impact and costs of the disease; (b) VNS eligibility and clinical results; (c) quality of life (QoL) after VNS therapy; (d) economic impact and productivity regained after VNS; and (e) costs of VNS. Results: Literature data indicate VNS as an effective treatment with a potential positive impact on social aspects and on quality of life. The diagnosis-related group (DRG) financing, both on national and regional levels, does not cover the cost of the medical device. There was an evident insufficient coverage of the DRG compared to the full cost of implanting the device. Conclusions: VNS is a palliative treatment for reducing seizure frequency and intensity. Despite its economic cost, VNS should improve patients’ quality of life and reduce care needs.

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.

Effects of transcutaneous vagus nerve stimulation in individuals aged 55 years or above: potential benefits of daily stimulation

Ageing is associated with attenuated autonomic function. Transcutaneous vagal nerve stimulation (tVNS) improved autonomic function in healthy young participants. We therefore investigated the effects of a single session of tVNS (studies 1 and 2) and tVNS administered daily for two weeks (study 3) in volunteers aged ≥ 55 years. tVNS was performed using modified surface electrodes on the tragus and connected to a transcutaneous electrical nerve stimulation (TENS) machine. Study 1: participants (n=14) received a single session of tVNS and sham. Study 2: all participants (n=51) underwent a single session of tVNS. Study 3: participants (n=29) received daily tVNS for two weeks. Heart rate variability and baroreflex sensitivity were derived. Quality of life (QoL), mood and sleep were assessed in study 3. tVNS promoted increases in measures of vagal tone and was associated with greater increases in baroreflex sensitivity than sham. Two weeks of daily tVNS improved measures of autonomic function, and some aspects of QoL, mood and sleep. Importantly, findings showed that improvements in measures of autonomic balance were more pronounced in participants with greater baseline sympathetic prevalence. This suggests it may be possible to identify individuals who are likely to encounter significant benefits from tVNS.

Vagus Nerve Stimulation as a Gateway to Interoception

The last two decades have seen a growing interest in the study of interoception. Interoception can be understood as a hierarchical phenomenon, referring to the body-to-brain communication of internal signals, their sensing, encoding, and representation in the brain, influence on other cognitive and affective processes, and their conscious perception. Interoceptive signals have been notoriously challenging to manipulate in experimental settings. Here, we propose that this can be achieved through electrical stimulation of the vagus nerve (either in an invasive or non-invasive fashion). The vagus nerve is the main pathway for conveying information about the internal condition of the body to the brain. Despite its intrinsic involvement in interoception, surprisingly little research in the field has used Vagus Nerve Stimulation to explicitly modulate bodily signals. Here, we review a range of cognitive, affective and clinical research using Vagus Nerve Stimulation, showing that it can be applied to the study of interoception at each level of its hierarchy. This could have considerable implications for our understanding of the interoceptive dimension of cognition and affect in both health and disease, and lead to development of new therapeutic tools.

Sources of off-target effects of vagus nerve stimulation using the helical clinical lead in domestic pigs

Objective

Clinical data suggest that efficacious vagus nerve stimulation (VNS) is limited by side effects such as cough and dyspnea that have stimulation thresholds lower than those for therapeutic outcomes. VNS side effects are putatively caused by activation of nearby muscles within the neck, via direct muscle activation or activation of nerve fibers innervating those muscles. Our goal was to determine the thresholds at which various VNS-evoked effects occur in the domestic pig—an animal model with vagus anatomy similar to human—using the bipolar helical lead deployed clinically.

Approach

Intrafascicular electrodes were placed within the vagus nerve to record electroneurographic (ENG) responses, and needle electrodes were placed in the vagal-innervated neck muscles to record electromyographic (EMG) responses.

Main results

Contraction of the cricoarytenoid muscle occurred at low amplitudes (~0.3 mA) and resulted from activation of motor nerve fibers in the cervical vagus trunk within the electrode cuff which bifurcate into the recurrent laryngeal branch of the vagus. At higher amplitudes (~1.4 mA), contraction of the cricoarytenoid and cricothyroid muscles was generated by current leakage outside the cuff to activate motor nerve fibers running within the nearby superior laryngeal branch of the vagus. Activation of these muscles generated artifacts in the ENG recordings that may be mistaken for compound action potentials representing slowly conducting Aδ-, B-, and C-fibers.

Significance

Our data resolve conflicting reports of the stimulation amplitudes required for C-fiber activation in large animal studies (>10 mA) and human studies (<250 μA). After removing muscle-generated artifacts, ENG signals with post-stimulus latencies consistent with Aδ- and B-fibers occurred in only a small subset of animals, and these signals had similar thresholds to those that caused bradycardia. By identifying specific neuroanatomical pathways that cause off-target effects and characterizing the stimulation dose-response curves for on- and off-target effects, we hope to guide interpretation and optimization of clinical VNS.

Implementing Mobile HRV Biofeedback as Adjunctive Therapy During Inpatient Psychiatric Rehabilitation Facilitates Recovery of Depressive Symptoms and Enhances Autonomic Functioning Short-Term: A 1-Year Pre-Post-intervention Follow-Up Pilot Study

OBJECTIVE

New treatment options for depression are warranted, due to high recurrence rates. Recent research indicates benefits of heart rate variability biofeedback (HRVBF) on symptom recovery and autonomic functioning in depressed individuals. Slow-paced breathing-induced amplification of vagus nerve activity is the main element of HRVBF. Thus, the latter represents a safe and non-invasive complementary depression treatment. However, its efficacy in patients undergoing inpatient psychiatric rehabilitation receiving highly comprehensive treatments has not been evaluated.

METHODS

Ninety-two inpatients were randomly assigned to an intervention group (IG) or control group (CG). While the latter received the standard treatment only, adjunctive HRVBF was provided to the IG over 5 weeks. Depression severity and heart rate variability (HRV) were assessed before (pre) and after 5 weeks (post). Moreover, 1-year follow-up depression scores were available for 30 participants.

RESULTS

Although depression improved in both groups, the IG exhibited significantly larger improvements at post-assessment ( η p 2 = 0.065) and significant increases in resting LF-HRV (d = 0.45) and cardiorespiratory coherence (d = 0.61). No significant effects for RMSSD, SDNN, HF-HRV, or HR were found (ps > 0.05). Additionally, the IG showed a medium- to large-sized reduction in resting respiratory rate from 13.2 to 9.8 breaths per minute (p < 0.001, d = 0.86), with the CG exhibiting only a small decrease from 13.5 to 12.4 (p = 0.49; d = 0.35). While the IG exhibited significantly lower depression scores at post-assessment (p = 0.042, d = 0.79), this effect decreased during follow-up (p = 0.195, d = 0.48).

CONCLUSION

HRVBF as adjuvant therapy during inpatient psychiatric rehabilitation facilitated depression recovery. Additionally, amplified LF-HRV as well as cardiorespiratory coherence at rest and a decrease in resting breathing frequency was observed in the HRVBF group. These findings emphasize HRVBF's value as complementary therapy regardless of concurrent treatments. Moreover, these incremental benefits could serve as resource even after the actual training period. However, the additional antidepressant gains vanish during the long-term follow-up, indicating the need for more intense training or regular practice afterward, respectively. Thus, future studies are warranted to examine how the initial benefits of HRVBF during inpatient psychiatric rehabilitation can be preserved post discharge.

Potential of Electrical Neuromodulation for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a common chronic inflammatory disease of the digestive tract that is often debilitating. It affects patients' quality of life and imposes a financial burden. Despite advances in treatment with medications such as biologics, a large proportion of patients do not respond to medical therapy or develop adverse events. Therefore, alternative treatment options such as electrical neuromodulation are currently being investigated. Electrical neuromodulation, also called bioelectronic medicine, is emerging as a potential new treatment for IBD. Over the past decade, advancements have been made in electrical neuromodulation. A number of electrical neuromodulation methods, such as vagus nerve stimulation, sacral nerve stimulation, and tibial nerve stimulation, have been tested to treat IBD. A series of animal and clinical trials have been performed to evaluate efficacy with promising results. Although the exact underlying mechanisms of action for electrical neuromodulation remain to be explored, this modality is promising. Further randomized controlled trials and basic experiments are needed to investigate efficacy and clarify intrinsic mechanisms.

Optogenetic Stimulation of Vagal Efferent Activity Preserves Left Ventricular Function in Experimental Heart Failure

•

This study was designed to determine the effect of selective optogenetic simulation of vagal efferent activity on left ventricular function in an animal (rat) model of MI-induced heart failure.

•

Optogenetic stimulation of dorsal brainstem vagal pre-ganglionic neurons transduced to express light-sensitive channels preserved LV function and exercise capacity in animals with MI.

•

The data suggest that activation of vagal efferents is critically important to deliver the therapeutic benefit of VNS in chronic heart failure.

Large clinical trials designed to test the efficacy of vagus nerve stimulation (VNS) in patients with heart failure did not demonstrate benefits with respect to the primary endpoints. The nonselective nature of VNS may account for the failure to translate promising results of preclinical and earlier clinical studies. This study showed that optogenetic stimulation of vagal pre-ganglionic neurons transduced to express light-sensitive channels preserved left ventricular function and exercise capacity in a rat model of myocardial infarction−induced heart failure. These data suggested that stimulation of vagal efferent activity is critically important to deliver the therapeutic benefit of VNS in heart failure.

Neuroimmune Communication in the Kidney

Recent studies have clarified the interaction between nervous systems and immunity regarding the manner in which local inflammation is regulated and systemic homeostasis is maintained. The cholinergic anti-inflammatory pathway (CAP) is a neuroimmune pathway activated by vagus nerve stimulation. Following afferent vagus nerve stimulation, signals are transmitted to immune cells in the spleen, including β2-adrenergic receptor-positive CD4-positive T cells and α7 nicotinic acetylcholine receptor-expressing macrophages. These immune cells release the neurotransmitters norepinephrine and acetylcholine, inducing a series of reactions that reduce proinflammatory cytokines, relieving inflammation. CAP contributes to various inflammatory diseases such as endotoxemia, rheumatoid arthritis, and inflammatory bowel disease. Moreover, emerging studies have revealed that vagus nerve stimulation ameliorates kidney damage in an animal model of acute kidney injury. These studies suggest that the link between the nervous system and kidneys is associated with the pathophysiology of kidney injury. Here, we review the current knowledge of the neuroimmune circuit and kidney disease, as well as potential for therapeutic strategies based on this knowledge for treating kidney disease in clinical settings.

Acute effects of vagus nerve stimulation parameters on gastric motility assessed with magnetic resonance imaging

BACKGROUND

Vagus nerve stimulation (VNS) is an emerging bioelectronic therapy for regulating food intake and controlling gastric motility. However, the effects of different VNS parameters and polarity on postprandial gastric motility remain incompletely characterized.

METHODS

In anesthetized rats (N = 3), we applied monophasic electrical stimuli to the left cervical vagus and recorded compound nerve action potential (CNAP) as a measure of nerve response. We evaluated to what extent afferent or efferent pathway could be selectively activated by monophasic VNS. In a different group of rats (N = 13), we fed each rat a gadolinium-labeled meal and scanned the rat stomach with oral contrast-enhanced magnetic resonance imaging (MRI) while the rat was anesthetized. We evaluated the antral and pyloric motility as a function of pulse amplitude (0.13, 0.25, 0.5, 1 mA), width (0.13, 0.25, 0.5 ms), frequency (5, 10 Hz), and polarity of VNS.

KEY RESULTS

Monophasic VNS activated efferent and afferent pathways with about 67% and 82% selectivity, respectively. Primarily afferent VNS increased antral motility across a wide range of parameters. Primarily efferent VNS induced a significant decrease in antral motility as the stimulus intensity increased (R = -.93, P < .05 for 5 Hz, R = -.85, P < .05 for 10 Hz). The VNS with either polarity tended to promote pyloric motility to a greater extent given increasing stimulus intensity.

CONCLUSIONS AND INFERENCES

Monophasic VNS biased toward the afferent pathway is potentially more effective for facilitating occlusive contractions than that biased toward the efferent pathway.

Neuromodulation, Specialized Proresolving Mediators, and Resolution of Pain

The current crises in opioid abuse and chronic pain call for the development of nonopioid and nonpharmacological therapeutics for pain relief. Neuromodulation-based approaches, such as spinal cord stimulation, dorsal root ganglion simulation, and nerve stimulation including vagus nerve stimulation, have shown efficacy in achieving pain control in preclinical and clinical studies. However, the mechanisms by which neuromodulation alleviates pain are not fully understood. Accumulating evidence suggests that neuromodulation regulates inflammation and neuroinflammation-a localized inflammation in peripheral nerves, dorsal root ganglia/trigeminal ganglia, and spinal cord/brain-through neuro-immune interactions. Specialized proresolving mediators (SPMs) such as resolvins, protectins, maresins, and lipoxins are lipid molecules produced during the resolution phase of inflammation and exhibit multiple beneficial effects in resolving inflammation in various animal models. Recent studies suggest that SPMs inhibit inflammatory pain, postoperative pain, neuropathic pain, and cancer pain in rodent models via immune, glial, and neuronal modulations. It is noteworthy that sham surgery is sufficient to elevate resolvin levels and may serve as a model of resolution. Interestingly, it has been shown that the vagus nerve produces SPMs and vagus nerve stimulation (VNS) induces SPM production in vitro. In this review, we discuss how neuromodulation such as VNS controls pain via immunomodulation and neuro-immune interactions and highlight possible involvement of SPMs. In particular, we demonstrate that VNS via auricular electroacupuncture effectively attenuates chemotherapy-induced neuropathic pain. Furthermore, auricular stimulation is able to increase resolvin levels in mice. Thus, we propose that neuromodulation may control pain and inflammation/neuroinflammatioin via SPMs. Finally, we discuss key questions that remain unanswered in our understanding of how neuromodulation-based therapies provide short-term and long-term pain relief.

Cardiac autonomic modulation in drug-resistant epilepsy patients after vagus nerve stimulation therapy

The positive effect of vagus nerve stimulation (VNS) in patients with drug-resistant epilepsy is considered to be mediated by the afferent pathways of the vagus nerve, but the efferent pathways may influence the cardiac autonomic activity.

AIM OF THE STUDY

To assess the effects of VNS on cardiac autonomic modulation in epilepsy patients, over three months of neurostimulation.

CLINICAL RATIONALE FOR THE STUDY

Linear and non-linear heart rate variability (HRV) analysis can provide information on the sympathovagal balance and reveal particularities of the central control of the autonomic cardiovascular function.

MATERIALS AND METHODS

Using Biopac Acquisition System, we analysed HRV parameters in resting condition and during sympathetic and parasympathetic activation tests in five patients with drug-resistant epilepsy, who underwent VNS procedure.

RESULTS

During the sympathetic and vagal activation tests, all five patients presented normal responses of cardiac autonomic activity, reflected in RMSSD, HFnu and LF/HF dynamics in both HRV evaluations. No bradycardia, cardiac arrhythmia or orthostatic hypotension was registered during the two evaluations.

CONCLUSIONS

Our results indicate that VNS appears not to alter the cardiac autonomic function after three months of neurostimulation. HRV analysis is a useful tool for evaluating cardiac autonomic modulation in epilepsy patients during VNS therapy.

CLINICAL IMPLICATIONS

Patients with decreased HRV should be periodically monitored. Cardiac changes in patients with epilepsy are important because of the additional risk of arrhythmias mediated through the autonomic dysfunction.

Effect of vagus nerve stimulation for the treatment of drug-resistant epilepsy: A protocol of systematic review and meta-analysis

BACKGROUND

Drug-resistant epilepsy (DRE) is a very tricky disorder, which greatly affects quality of life in such patients. Relevant studies suggested that vagus nerve stimulation (VNS) has potential benefits for DRE. However, there are inconsistent conclusions. The purpose of this study is to investigate whether VNS is effective and safety for DRE.

METHODS

To collect comprehensive randomized controlled trials (RCTs), the following electronic databases will be retrieved: MEDLINE, EMBASE, Cochrane Library, Web of Science, PsycINFO, CINAHL, AMED, and China National Knowledge Infrastructure from the commencement of each electronic database up to the present with no language restrictions. Two authors will independently carry out all procedures of literature selection, information collection, and risk of bias assessment. Any objections will be worked out by a third author through consultation. The risk of bias for each included trial will be identified using Cochrane risk of bias tool, and statistical analysis will be performed utilizing RevMan 5.3 software.

RESULTS

This study will synthesize the data from the present eligible high quality RCTs to assess whether VNS is effective and safety for DRE.

CONCLUSION

This study will provide systematic evidence of VNS for the treatment of patients with DRE.

SYSTEMATIC REVIEW REGISTRATION

INPLASY202040086.

A proposed guideline for vagus nerve stimulator handling in palliative care and after death

Vagus nerve stimulation (VNS) is often used for patients with drug-resistant epilepsy. Although this intervention may improve seizure control and mood, a number of factors must be considered when patients with VNS near end of life. We reviewed relevant literature to create a proposed guideline for management of patients with VNS in palliative care and after death. VNS has multiple possible side effects, including cough and swallowing difficulties. For patients with neurologic disease in palliative care, such adverse effects can severely affect quality of life and increase the risk for complications such as aspiration pneumonia. Patients with VNS should be screened regularly for such side effects, and VNS parameters should be adjusted if they are identified. If a patient requires urgent cardiac resuscitation involving external defibrillation, the VNS should be interrogated immediately afterwards to evaluate its function. During defibrillation, paddles should be placed perpendicular to the VNS, and as far as possible away from it. The VNS can be acutely turned off by taping the magnet to the patient's chest, thereby preventing any possible interference with restoration of a normal heart rhythm. After death, any staff involved with handling the body should be notified that a VNS is in place. The device must be removed prior to cremation, as it can explode with high heat. If the cause of death is unclear, a full postmortem examination should be undertaken, per sudden unexpected death in epilepsy guidelines. If there is concern about device malfunction, the device should be returned to the manufacturer for evaluation.

A Randomized Crossover Trial

Background

Individuals are able to perform goal-directed behaviors thanks to executive functions. According to the neurovisceral integration model, executive functions are upregulated by brain areas such as the prefrontal and cingulate cortices, which are also crucially involved in controlling cardiac vagal activity. An array of neuroimaging studies already showed that these same brain areas are activated by transcutaneous vagus nerve stimulation (tVNS). Despite evidence toward effects of tVNS on specific executive functions such as inhibitory control, there have been no studies investigating what type of inhibition is improved by tVNS by systematically addressing them within the same experiment. Furthermore, the effect of tVNS on another core executive function, cognitive flexibility, has not yet been investigated.

Objective

We investigated the effects of tVNS on core executive functions such as inhibitory control and cognitive flexibility.

Methods

Thirty-two participants (nine women, M _age = 23.17) took part in this study. Vagally mediated heart rate variability parameters (root mean square of successive differences, RMSSD, and high frequency, HF) were measured while participants performed four different cognitive tasks that mainly rely on different aspects of both the aforementioned executive functions.

Results

Despite clear conflict effects in the four tasks, only performance on the task used to measure set-shifting paradigm was improved by tVNS, with switch costs being lower during tVNS than during sham stimulation. Furthermore, HF increased during each of the cognitive flexibility tasks, although HF during tVNS did not differ from HF during sham stimulation.

Conclusion

The results indicate for the first time (a) that tVNS can increase cognitive flexibility in a set-shifting paradigm, and (b) that tVNS may exert a stronger effect on cognitive flexibility than inhibition. The present study provides only partial evidence for the neurovisceral integration model. Future studies should address further paradigms that demand cognitive flexibility, thus investigating this new hypothesis on the specificity of the tVNS effects on cognitive flexibility.

Pharyngolaryngeal spasm-induced dysphagia in an epileptic patient undergoing vagus nerve stimulation therapy

Vagus nerve stimulation for refractory epilepsy may induce laryngeal side effects such as dysphonia and dysphagia. Careful tuning of the stimulation parameters and collaboration between epileptologists and otolaryngologists can help significantly reduce side effects.

Critical Review of Transcutaneous Vagus Nerve Stimulation: Challenges for Translation to Clinical Practice

Several studies have illustrated that transcutaneous vagus nerve stimulation (tVNS) can elicit therapeutic effects that are similar to those produced by its invasive counterpart, vagus nerve stimulation (VNS). VNS is an FDA-approved therapy for the treatment of both depression and epilepsy, but it is limited to the management of more severe, intervention-resistant cases as a second or third-line treatment option due to perioperative risks involved with device implantation. In contrast, tVNS is a non-invasive technique that involves the application of electrical currents through surface electrodes at select locations, most commonly targeting the auricular branch of the vagus nerve (ABVN) and the cervical branch of the vagus nerve in the neck. Although it has been shown that tVNS elicits hypo- and hyperactivation in various regions of the brain associated with anxiety and mood regulation, the mechanism of action and influence of stimulation parameters on clinical outcomes remains predominantly hypothetical. Suppositions are largely based on correlations between the neurobiology of the vagus nerve and its effects on neural activity. However, tVNS has also been investigated for several other disorders, including tinnitus, migraine and pain, by targeting the vagus nerve at sites in both the ear and the neck. As most of the described methods differ in the parameters and protocols applied, there is currently no firm evidence on the optimal location for tVNS or the stimulation parameters that provide the greatest therapeutic effects for a specific condition. This review presents the current status of tVNS with a focus on stimulation parameters, stimulation sites, and available devices. For tVNS to reach its full potential as a non-invasive and clinically relevant therapy, it is imperative that systematic studies be undertaken to reveal the mechanism of action and optimal stimulation modalities.

The Immediate Effects of Vagus Nerve Stimulation in Intractable Epilepsy: An Intra-operative Electrocorticographic Analysis

The purpose of this study was to investigate whether and how vagus nerve stimulation (VNS) reduces the epileptogenic activity in the bilateral cerebral cortex in patients with intractable epilepsy. We analyzed the electrocorticograms (ECoGs) of five patients who underwent callosotomy due to intractable epilepsy even after VNS implantation. We recorded ECoGs and analyzed power spectrum in both VNS OFF and ON phases. We counted the number of spikes and electrodes with epileptic spikes, distinguishing unilaterally and bilaterally hemispherically spread spikes as synchronousness of the epileptic spikes in both VNS OFF and ON phases. There were 24.80 ± 35.55 and 7.20 ± 9.93 unilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.157), and 35.8 ± 29.21 and 10.6 ± 13.50 bilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.027). The number of electrodes with unilaterally and bilaterally spread spikes in the VNS OFF and ON phases was 3.84 ± 2.13 and 3.59 ± 1.82 (P = 0.415), and 8.20 ± 3.56 and 6.89 ± 2.89 (P = 0.026), respectively. The ECoG background power spectra recordings in the VNS OFF and ON phases were also analyzed. The spectral power tended to be greater in the high-frequency band at VNS ON phase than OFF phase. This study showed the reduction of epileptogenic spikes and spread areas of the spikes by VNS as immediate effects, electrophysiologically.

Functional vagotopy in the cervical vagus nerve of the domestic pig: implications for the study of vagus nerve stimulation

OBJECTIVE

Given current clinical interest in vagus nerve stimulation (VNS), there are surprisingly few studies characterizing the anatomy of the vagus nerve in large animal models as it pertains to on-and off-target engagement of local fibers. We sought to address this gap by evaluating vagal anatomy in the pig, whose vagus nerve organization and size approximates the human vagus nerve.

APPROACH

Here we combined microdissection, histology, and immunohistochemistry to provide data on key features across the cervical vagus nerve in a swine model, and compare our results to other animal models (mouse, rat, dog, non-human primate) and humans.

MAIN RESULTS

In a swine model we quantified the nerve diameter, number and diameter of fascicles, and distance of fascicles from the epineural surface where stimulating electrodes are placed. We also characterized the relative locations of the superior and recurrent laryngeal branches of the vagus nerve that have been implicated in therapy limiting side effects with common electrode placement. We identified key variants across the cohort that may be important for VNS with respect to changing sympathetic/parasympathetic tone, such as cross-connections to the sympathetic trunk. We discovered that cell bodies of pseudo-unipolar cells aggregate together to form a very distinct grouping within the nodose ganglion. This distinct grouping gives rise to a larger number of smaller fascicles as one moves caudally down the vagus nerve. This often leads to a distinct bimodal organization, or 'vagotopy'. This vagotopy was supported by immunohistochemistry where approximately half of the fascicles were immunoreactive for choline acetyltransferase, and reactive fascicles were generally grouped in one half of the nerve.

SIGNIFICANCE

The vagotopy observed via histology may be advantageous to exploit in design of electrodes/stimulation paradigms. We also placed our data in context of historic and recent histology spanning multiple models, thus providing a comprehensive resource to understand similarities and differences across species.

Acute Cardiovascular Responses to Vagus Nerve Stimulation after Experimental Spinal Cord Injury

Pairing vagus nerve stimulation (VNS) with rehabilitation has emerged as a potential strategy to enhance plasticity and improve recovery in a range of neurological disorders. A recent study highlights the therapeutic promise of VNS in promoting motor recovery after spinal cord injury (SCI). We investigated the safety of acute VNS in a rat model of chronic SCI. We measured the cardiovascular response to various VNS paradigms following chronic high-thoracic SCI that is known to deleteriously impact cardiovascular control. Dose-response experiments with continuous VNS revealed an SCI-dependent increase in sensitivity for heart rate (HR) and blood pressure (BP) compared with controls. A clinically relevant intermittent VNS resulted in transient reduction in HR in rats with SCI; however, BP remained unaltered. In all experiments, the effect lasted only while the VNS stimulus train was present, as HR and BP restored to baseline values as soon as VNS ended. No prolonged episodes of persisting hypotension were seen in either group. Further, VNS did not trigger autonomic dysreflexia or exacerbate the severity of autonomic dysreflexia when induced during or after stimulation sessions. Overall, these findings provide initial evidence that intermittent VNS at parameters used for targeted plasticity therapy (30 Hz, 0.8 mA) appears safe and supports further investigation of this potential therapy for use following SCI.

Transcutaneous Vagus Nerve Stimulation in Patients With Severe Traumatic Brain Injury: A Feasibility Trial

OBJECTIVES

Preclinical studies have shown that surgically implanted vagus nerve stimulation (VNS) promotes recovery of consciousness and cognitive function following experimental traumatic brain injury (TBI). The aim of this study is to report the feasibility and safety of a noninvasive transcutaneous vagus nerve stimulation (tVNS) in patients with persistent impairment of consciousness following severe TBI.

MATERIALS AND METHODS

The feasibility of tVNS was evaluated in five patients presenting with diffuse axonal injury and reduced dominant EEG activity one month following severe TBI. tVNS was applied to the left cymba conchae of the external ear using a skin electrode four hours daily for eight weeks. Possible effects of tVNS on physiological parameters and general side effects were recorded. In addition, we report the rate of recovery using coma recovery scale revised (CRS-R).

RESULTS

The tVNS regime of four hours daily for eight weeks was feasible and well tolerated with little side effects and no clinically relevant effects on physiological parameters. Three patients showed improvements (>3 points) in the CRS-R following eight weeks tVNS.

CONCLUSION

We demonstrated that tVNS is a feasible and safe VNS strategy for patients following severe TBI. Controlled studies are needed to clarify whether tVNS has a potential to promote recovery of consciousness following severe TBI.

Relation of Fractionated Atrial Potentials With the Vagal Innervation Evaluated by Extracardiac Vagal Stimulation During Cardioneuroablation

BACKGROUND

Vagal hyperactivity is directly related to several clinical conditions as reflex/functional bradyarrhythmias and vagal atrial fibrillation (AF). Cardioneuroablation provides therapeutic vagal denervation through endocardial radiofrequency ablation for these cases. The main challenges are neuromyocardium interface identification and the denervation control and validation. The finding that the AF-Nest (AFN) ablation eliminates the atropine response and decreases RR variability suggests that they are related to the vagal innervation.

METHOD

Prospective, controlled, longitudinal, nonrandomized study enrolling 62 patients in 2 groups: AFN group (AFN group 32 patients) with functional or reflex bradyarrhythmias or vagal AF treated with AFN ablation and a control group (30 patients) with anomalous bundles, ventricular premature beats, atrial flutter, atrioventricular nodal reentry, and atrial tachycardia, treated with conventional ablation (non-AFN ablation). In AFN group, ablation delivered at AFN detected by fragmentation/fractionation of the endocardial electrograms and by 3-dimensional anatomic location of the ganglionated plexus. Vagal response was evaluated before, during, and postablation by 5 s noncontact vagal stimulation at the jugular foramen, through the internal jugular veins (extracardiac vagal stimulation [ECVS]), analyzing 15 s mean heart rate, longest RR, pauses, and atrioventricular block. All patients had current guidelines arrhythmia ablation indication.

RESULTS

Preablation ECVS induced sinus pauses, asystole, and transient atrioventricular block in both groups showing a strong vagal response (P=0.96). Postablation ECVS in the AFN group showed complete abolishment of the cardiac vagal response in all cases (pre/postablation ECVS=P<0.0001), demonstrating robust vagal denervation. However, in the control group, vagal response remained practically unchanged postablation (P=0.35), showing that non-AFN ablation promotes no significant denervation.

CONCLUSIONS

AFN ablation causes significant vagal denervation. Non-AFN ablation causes no significant vagal denervation. These results suggest that AFNs are intrinsically related to vagal innervation. ECVS was fundamental to stepwise vagal denervation validation during cardioneuroablation. Visual Overview A visual overview is available for this article.

Transcutaneous Auricular Vagus Nerve Stimulation-Paired Rehabilitation for Oromotor Feeding Problems in Newborns: An Open-Label Pilot Study

Neonates born premature or who suffer brain injury at birth often have oral feeding dysfunction and do not meet oral intake requirements needed for discharge. Low oral intake volumes result in extended stays in the hospital (>2 months) and can lead to surgical implant and explant of a gastrostomy tube (G-tube). Prior work suggests pairing vagus nerve stimulation (VNS) with motor activity accelerates functional improvements after stroke, and transcutaneous auricular VNS (taVNS) has emerged as promising noninvasive form of VNS. Pairing taVNS with bottle-feeding rehabilitation may improve oromotor coordination and lead to improved oral intake volumes, ultimately avoiding the need for G-tube placement. We investigated whether taVNS paired with oromotor rehabilitation is tolerable and safe and facilitates motor learning in infants who have failed oral feeding. We enrolled 14 infants [11 premature and 3 hypoxic-ischemic encephalopathy (HIE)] who were slated for G-tube placement in a prospective, open-label study of taVNS-paired rehabilitation to increase feeding volumes. Once-daily taVNS was delivered to the left tragus during bottle feeding for 2 weeks, with optional extension. The primary outcome was attainment of oral feeding volumes and weight gain adequate for discharge without G-tube while also monitoring discomfort and heart rate (HR) as safety outcomes. We observed no adverse events related to stimulation, and stimulation-induced HR reductions were transient and safe and likely confirmed vagal engagement. Eight of 14 participants (57%) achieved adequate feeding volumes for discharge without G-tube (mean treatment length: 16 ± 6 days). We observed significant increases in feeding volume trajectories in responders compared with pre-stimulation (p < 0.05). taVNS-paired feeding rehabilitation appears safe and may improve oral feeding in infants with oromotor dyscoordination, increasing the rate of discharge without G-tube, warranting larger controlled trials.

A Feasibility Study to Investigate Chemogenetic Modulation of the Locus Coeruleus by Means of Single Unit Activity

Aim

Selective chemogenetic modulation of locus coeruleus (LC) neurons would allow dedicated investigation of the role of the LC-NA pathway in brain excitability and disorders such as epilepsy. This study investigated the feasibility of an experimental set-up where chemogenetic modification of the brainstem locus coeruleus NA neurons is aimed at and followed by LC unit activity recording in response to clozapine.

Methods

The LC of male Sprague-Dawley rats was injected with 10 nl of adeno-associated viral vector AAV2/7-PRSx8-hM3Dq-mCherry (n = 19, DREADD group) or AAV2/7-PRSx8-eGFP (n = 13, Controls). Three weeks later, LC unit recordings were performed in anesthetized rats. We investigated whether clozapine, a drug known to bind to modified neurons expressing hM3Dq receptors, was able to increase the LC firing rate. Baseline unit activity was recorded followed by subsequent administration of 0.01 and 0.1 mg/kg of clozapine in all rats. hM3Dq-mcherry expression levels were investigated using immunofluorescence staining of brainstem slices at the end of the experiment.

Results

Unit recordings could be performed in 12 rats and in a total of 12 neurons (DREADDs: n = 7, controls: n = 5). Clozapine 0.01 mg/kg did not affect the mean firing rate of recorded LC-neurons; 0.1 mg/kg induced an increased firing rate, irrespective whether neurons were recorded from DREADD or control rats (p = 0.006). Co-labeling of LC neurons and mCherry-tag showed that 20.6 ± 2.3% LC neurons expressed the hM3Dq receptor. Aspecific expression of hM3Dq-mCherry was also observed in non-LC neurons (26.0 ± 4.1%).

Conclusion

LC unit recording is feasible in an experimental set-up following manipulations for DREADD induction. A relatively low transduction efficiency of the used AAV was found. In view of this finding, the effect of injected clozapine on LC-NA could not be investigated as a reliable outcome parameter for activation of chemogenetically modified LC neurons. The use of AAV2/7, a vector previously applied successfully to target dopaminergic neurons in the substantia nigra, leads to insufficient chemogenetic modification of the LC compared to transduction with AAV2/9.