Metabolic modulation of tumours with engineered bacteria for immunotherapy.

The availability of L-arginine in tumours is a key determinant of an efficient anti-tumour T cell response1-4. Consequently, increases of typically low L-arginine concentrations within the tumour may greatly potentiate the anti-tumour responses of immune checkpoint inhibitors, such as programmed death-ligand 1 (PD-L1)-blocking antibodies5. However, currently no means are available to locally increase intratumoural L-arginine levels. Here we used a synthetic biology approach to develop an engineered probiotic Escherichia coli Nissle 1917 strain that colonizes tumours and continuously converts ammonia, a metabolic waste product that accumulates in tumours6, to L-arginine. Colonization of tumours with these bacteria increased intratumoural L-arginine concentrations, increased the number of tumour-infiltrating T cells and had marked synergistic effects with PD-L1 blocking antibodies in the clearance of tumours. The anti-tumour effect of these bacteria was mediated by L-arginine and was dependent on T cells. These results show that engineered microbial therapies enable metabolic modulation of the tumour microenvironment leading to enhanced efficacy of immunotherapies.

In vivo microstimulation with cathodic and anodic asymmetric waveforms modulates spatiotemporal calcium dynamics in cortical neuropil and pyramidal neurons of male mice.

Electrical stimulation has been critical in the development of an understanding of brain function and disease. Despite its widespread use and obvious clinical potential, the mechanisms governing stimulation in the cortex remain largely unexplored in the context of pulse parameters. Modeling studies have suggested that modulation of stimulation pulse waveform may be able to control the probability of neuronal activation to selectively stimulate either cell bodies or passing fibers depending on the leading polarity. Thus, asymmetric waveforms with equal charge per phase (i.e., increasing the leading phase duration and proportionately decreasing the amplitude) may be able to activate a more spatially localized or distributed population of neurons if the leading phase is cathodic or anodic, respectively. Here, we use two-photon and mesoscale calcium imaging of GCaMP6s expressed in excitatory pyramidal neurons of male mice to investigate the role of pulse polarity and waveform asymmetry on the spatiotemporal properties of direct neuronal activation with 10-Hz electrical stimulation. We demonstrate that increasing cathodic asymmetry effectively reduces neuronal activation and results in a more spatially localized subpopulation of activated neurons without sacrificing the density of activated neurons around the electrode. Conversely, increasing anodic asymmetry increases the spatial spread of activation and highly resembles spatiotemporal calcium activity induced by conventional symmetric cathodic stimulation. These results suggest that stimulation polarity and asymmetry can be used to modulate the spatiotemporal dynamics of neuronal activity thus increasing the effective parameter space of electrical stimulation to restore sensation and study circuit dynamics.

Assessing the impact of CKD on outcomes in septic shock patients receiving standard Vs reduced initial fluid volume.

OBJECTIVE: To determine if following fluid resuscitation recommendations in the Surviving Sepsis Campaign guidelines affects hospital length of stay (LOS) in chronic kidney disease (CKD) patients who present to the emergency department with sepsis-induced hypotension or septic shock. DESIGN: Retrospective, single center, cohort study. SETTING: 433-bed community hospital with a 35-bed emergency department in central Kentucky. PATIENTS: Adults (≥18 years of age) who presented to the emergency department with severe sepsis or septic shock, as defined by the Centers for Medicare and Medicaid Services (CMS), with documented CKD and at least one episode of hypotension within 6 h of presentation. A total of 106 patients were included in the study. MEASUREMENTS AND MAIN RESULTS: Patients were stratified into two groups based on the total volume of weight-based crystalloid fluid bolus initiated within the first three hours of hypotension onset (<27 mL/kg and ≥ 27 mL/kg). There was a statistically significant reduction in the primary outcome of median LOS among patients who received less than 27 mL/kg of a crystalloid fluid bolus (5.1 vs 7.7 days, p = .003). Likewise, there was a statistically significant reduction in the secondary outcome of total cost per case in the reduced fluid volume cohort (p = .019. No significant differences were found in other secondary outcomes, including vasopressor requirements, ICU admission rate, and normalization of MAP at 6 h. CONCLUSION: The results of this single-center, retrospective study indicate that CKD patients who receive guideline-directed fluid resuscitation (≥27 mL/kg) for sepsis-induced hypotension or septic shock experience a longer hospital LOS compared to those who receive a reduced initial fluid volume.

Calcium activation of cortical neurons by continuous electrical stimulation: Frequency dependence, temporal fidelity, and activation density.

Electrical stimulation of the brain has become a mainstay of fundamental neuroscience research and an increasingly prevalent clinical therapy. Despite decades of use in basic neuroscience research and the growing prevalence of neuromodulation therapies, gaps in knowledge regarding activation or inactivation of neural elements over time have limited its ability to adequately interpret evoked downstream responses or fine-tune stimulation parameters to focus on desired responses. In this work, in vivo two-photon microscopy was used to image neuronal calcium activity in layer 2/3 neurons of somatosensory cortex (S1) in male C57BL/6J-Tg(Thy1-GCaMP6s)GP4.3Dkim/J mice during 30 s of continuous electrical stimulation at varying frequencies. We show frequency-dependent differences in spatial and temporal somatic responses during continuous stimulation. Our results elucidate conflicting results from prior studies reporting either dense spherical activation of somas biased toward those near the electrode, or sparse activation of somas at a distance via axons near the electrode. These findings indicate that the neural element specific temporal response local to the stimulating electrode changes as a function of applied charge density and frequency. These temporal responses need to be considered to properly interpret downstream circuit responses or determining mechanisms of action in basic science experiments or clinical therapeutic applications.

A Materials Roadmap to Functional Neural Interface Design.

Advancement in neurotechnologies for electrophysiology, neurochemical sensing, neuromodulation, and optogenetics are revolutionizing scientific understanding of the brain while enabling treatments, cures, and preventative measures for a variety of neurological disorders. The grand challenge in neural interface engineering is to seamlessly integrate the interface between neurobiology and engineered technology, to record from and modulate neurons over chronic timescales. However, the biological inflammatory response to implants, neural degeneration, and long-term material stability diminish the quality of interface overtime. Recent advances in functional materials have been aimed at engineering solutions for chronic neural interfaces. Yet, the development and deployment of neural interfaces designed from novel materials have introduced new challenges that have largely avoided being addressed. Many engineering efforts that solely focus on optimizing individual probe design parameters, such as softness or flexibility, downplay critical multi-dimensional interactions between different physical properties of the device that contribute to overall performance and biocompatibility. Moreover, the use of these new materials present substantial new difficulties that must be addressed before regulatory approval for use in human patients will be achievable. In this review, the interdependence of different electrode components are highlighted to demonstrate the current materials-based challenges facing the field of neural interface engineering.

A selective inhibitor of PRMT5 with in vivo and in vitro potency in MCL models.

Protein arginine methyltransferase-5 (PRMT5) is reported to have a role in diverse cellular processes, including tumorigenesis, and its overexpression is observed in cell lines and primary patient samples derived from lymphomas, particularly mantle cell lymphoma (MCL). Here we describe the identification and characterization of a potent and selective inhibitor of PRMT5 with antiproliferative effects in both in vitro and in vivo models of MCL. EPZ015666 (GSK3235025) is an orally available inhibitor of PRMT5 enzymatic activity in biochemical assays with a half-maximal inhibitory concentration (IC50) of 22 nM and broad selectivity against a panel of other histone methyltransferases. Treatment of MCL cell lines with EPZ015666 led to inhibition of SmD3 methylation and cell death, with IC50 values in the nanomolar range. Oral dosing with EPZ015666 demonstrated dose-dependent antitumor activity in multiple MCL xenograft models. EPZ015666 represents a validated chemical probe for further study of PRMT5 biology and arginine methylation in cancer and other diseases.

Pharmacy-Driven Dexmedetomidine Stewardship and Appropriate Use Guidelines in a Community Hospital Setting.

BACKGROUND: Dexmedetomidine is a widely utilized agent in the intensive care unit (ICU) because it does not suppress respiratory drive and may be associated with less delirium than midazolam or propofol. Cost of dexmedetomidine therapy and debate as to the proper duration of use has brought its use to the forefront of discussion. OBJECTIVE: To validate the efficacy and cost savings associated with pharmacy-driven dexmedetomidine appropriate use guidelines and stewardship in mechanically ventilated patients. METHODS: This was a retrospective cohort study of adult patients who received dexmedetomidine for ICU sedation while on mechanical ventilation at a 433-bed not-for-profit community hospital. Included patients were divided into pre-enactment (PRE) and postenactment (POST) of dexmedetomidine guideline groups. RESULTS: A total of 100 patients (50 PRE and 50 POST) were included in the analysis. A significant difference in duration of mechanical ventilation (11.1 vs 6.2 days, P = 0.006) and incidence of reintubation (36% vs 18% of patients, P = 0.043) was seen in the POST group. Aggregate use of dexmedetomidine 200-µg vials (37.1 vs 18.4 vials, P = 0.010) and infusion days (5.4 vs 2.5 days, P = 0.006) were significantly lower in the POST group. Dexmedetomidine acquisition cost savings were calculated at $374 456.15 in the POST group. There was no difference between the PRE and POST groups with regard to ICU length of stay, expected mortality, and observed mortality. CONCLUSIONS: Pharmacy-driven dexmedetomidine appropriate use guidelines decreased the use of dexmedetomidine and increased cost savings at a community hospital without adversely affecting clinical outcomes.

Validation and Clinical Evaluation of a Novel Method To Measure Miltefosine in Leishmaniasis Patients Using Dried Blood Spot Sample Collection.

To facilitate future pharmacokinetic studies of combination treatments against leishmaniasis in remote regions in which the disease is endemic, a simple cheap sampling method is required for miltefosine quantification. The aims of this study were to validate a liquid chromatography-tandem mass spectrometry method to quantify miltefosine in dried blood spot (DBS) samples and to validate its use with Ethiopian patients with visceral leishmaniasis (VL). Since hematocrit (Ht) levels are typically severely decreased in VL patients, returning to normal during treatment, the method was evaluated over a range of clinically relevant Ht values. Miltefosine was extracted from DBS samples using a simple method of pretreatment with methanol, resulting in >97% recovery. The method was validated over a calibration range of 10 to 2,000 ng/ml, and accuracy and precision were within ±11.2% and ≤7.0% (≤19.1% at the lower limit of quantification), respectively. The method was accurate and precise for blood spot volumes between 10 and 30 µl and for Ht levels of 20 to 35%, although a linear effect of Ht levels on miltefosine quantification was observed in the bioanalytical validation. DBS samples were stable for at least 162 days at 37°C. Clinical validation of the method using paired DBS and plasma samples from 16 VL patients showed a median observed DBS/plasma miltefosine concentration ratio of 0.99, with good correlation (Pearson'sr= 0.946). Correcting for patient-specific Ht levels did not further improve the concordance between the sampling methods. This successfully validated method to quantify miltefosine in DBS samples was demonstrated to be a valid and practical alternative to venous blood sampling that can be applied in future miltefosine pharmacokinetic studies with leishmaniasis patients, without Ht correction.

An Open-Source 3D-Printed Hindlimb Stabilization Apparatus for Reliable Measurement of Stimulation-Evoked Ankle Flexion in Rat.

Currently there are numerous methods to evaluate peripheral nerve stimulation interfaces in rats, with stimulation-evoked ankle torque being one of the most prominent. Commercial rat ankle torque measurement systems and custom one-off solutions have been published in the literature. However, commercial systems are proprietary and costly and do not allow for customization. One-off lab-built systems have required specialized machining expertise, and building plans have previously not been made easily accessible. Here, detailed building plans are provided for a low-cost, open-source, and basic ankle torque measurement system from which additional customization can be made. A hindlimb stabilization apparatus was developed to secure and stabilize a rat's hindlimb, while allowing for simultaneous ankle-isometric torque and lower limb muscle electromyography (EMG). The design was composed mainly of adjustable 3D-printed components to accommodate anatomical differences between rat hindlimbs. Additionally, construction and calibration procedures of the rat hindlimb stabilization apparatus were demonstrated in this study. In vivo torque measurements were reliably acquired and corresponded to increasing stimulation amplitudes. Furthermore, implanted leads used for intramuscular EMG recordings complemented torque measurements and were used as an additional functional measurement in evaluating the performance of a peripheral nerve stimulation interface. In conclusion, an open-source and noninvasive platform, made primarily with 3D-printed components, was constructed for reliable data acquisition of evoked motor activity in rat models. The purpose of this apparatus is to provide researchers a versatile system with adjustable components that can be tailored to meet user-defined experimental requirements when evaluating motor function of the rat hindlimbs.

Can Electrical Stimulation Prevent Recurrence of Keloid Scars? A Scoping Review.

Objective: Keloids represent a symptomatic, aberrant healing process that is difficult to treat with high recurrence rates spanning from 55% to 100% if treated via excision without adjuvant therapy. Electrical stimulation (ES) has demonstrated findings that suggest it could reduce the recurrence rate of keloids after resection. Therefore, the aim of this study is to conduct a scoping review to investigate ES as an adjuvant therapy for decreasing keloid recurrence after excision. Approach: A scoping review was performed using PubMed and Web of Science databases. The search strategy encompassed terms linking keloids and various aspects of electrical stimulation. Results: Our search yielded 2,229 articles, of which 115 articles were analyzed as full text and 1 article met inclusion criteria. Despite this, ES has demonstrated other evidence that suggests its utility. ES has been shown to counter keloidic features by reducing mast cell counts, shifting wound composition from M2 to M1 macrophages, promoting angiogenesis, and controlling fibroblast orientation and location. An alternating current will orient fibroblasts perpendicular to the current without unintended migration. Innovation: Our study indicates that, based on a compilation of clinical and preclinical in vitro data, the optimal scenario for ES in the role of keloid treatment is after excision with a biphasic pulsed application and square waveform. Conclusions: ES could serve as a multifaceted, adjuvant treatment after keloid excision, steering the healing process away from keloid-associated characteristics. Its cost-effectiveness means it could be adopted globally, providing a strategy to mitigate the burden of keloids irrespective of other available treatments or economic conditions.

Computational modeling of dorsal root ganglion stimulation using an Injectrode.

Objective.Minimally invasive neuromodulation therapies like the Injectrode, which is composed of a tightly wound polymer-coated Platinum/Iridium microcoil, offer a low-risk approach for administering electrical stimulation to the dorsal root ganglion (DRG). This flexible electrode is aimed to conform to the DRG. The stimulation occurs through a transcutaneous electrical stimulation (TES) patch, which subsequently transmits the stimulation to the Injectrode via a subcutaneous metal collector. However, it is important to note that the effectiveness of stimulation through TES relies on the specific geometrical configurations of the Injectrode-collector-patch system. Hence, there is a need to investigate which design parameters influence the activation of targeted neural structures.Approach.We employed a hybrid computational modeling approach to analyze the impact of Injectrode system design parameters on charge delivery and neural response to stimulation. We constructed multiple finite element method models of DRG stimulation, followed by the implementation of multi-compartment models of DRG neurons. By calculating potential distribution during monopolar stimulation, we simulated neural responses using various parameters based on prior acute experiments. Additionally, we developed a canonical monopolar stimulation and full-scale model of bipolar bilateral L5 DRG stimulation, allowing us to investigate how design parameters like Injectrode size and orientation influenced neural activation thresholds.Main results.Our findings were in accordance with acute experimental measurements and indicate that the minimally invasive Injectrode system predominantly engages large-diameter afferents (Aß-fibers). These activation thresholds were contingent upon the surface area of the Injectrode. As the charge density decreased due to increasing surface area, there was a corresponding expansion in the stimulation amplitude range before triggering any pain-related mechanoreceptor (Aδ-fibers) activity.Significance.The Injectrode demonstrates potential as a viable technology for minimally invasive stimulation of the DRG. Our findings indicate that utilizing a larger surface area Injectrode enhances the therapeutic margin, effectively distinguishing the desired Aßactivation from the undesired Aδ-fiber activation.

Characterization of idiopathic chronic diarrhea and associated intestinal inflammation and preliminary observations of effects of vagal nerve stimulation in a non-human primate.

BACKGROUND: Diarrhea is commonly associated with irritable bowel syndrome, inflammatory bowel disease, microscopic colitis, and other gastrointestinal dysfunctions. Spontaneously occurring idiopathic chronic diarrhea is frequent in rhesus macaques, but has not been used as a model for the investigation of diarrhea or its treatment. We characterized this condition and present preliminary data demonstrating that left vagal nerve stimulation provides relief. METHODS: Stool consistency scores were followed for up to 12 years. Inflammation was assessed by plasma C-reactive protein, [18F]fluorodeoxyglucose (FDG) uptake, measured by positron emission tomography (PET), multiplex T cell localization, endoscopy and histology. The vagus was stimulated for 9 weeks in conscious macaques, using fully implanted electrodes, under wireless control. KEY RESULTS: Macaques exhibited recurrent periods of diarrhea for up to 12 years, and signs of inflammation: elevated plasma C-reactive protein, increased bowel FDG uptake and increased mucosal T helper1 T-cells. The colon and distal ileum were endoscopically normal, and histology revealed mild colonic inflammation. Application of vagal nerve stimulation to conscious macaques (10 Hz, 30 s every 3 h; 24 h a day for 9 weeks) significantly reduced severity of diarrhea and also reduced inflammation, as measured by FDG uptake and C-reactive protein. CONCLUSIONS AND INFERENCES: These macaques exhibit spontaneously occurring diarrhea with intestinal inflammation that can be reduced by VNS. The data demonstrate the utility of this naturally occurring primate model to study the physiology and treatments for chronic diarrhea and the neural control circuits influencing diarrhea and inflammation that are not accessible in human subjects.

The role of spinal cord neuroanatomy and the variances of epidurally evoked spinal responses.

BACKGROUND: Spinal cord stimulation (SCS) has demonstrated multiple benefits in treating chronic pain and other clinical disorders related to sensorimotor dysfunctions. However, the underlying mechanisms are still not fully understood, including how electrode placement in relation to the spinal cord neuroanatomy influences epidural spinal recordings (ESRs). To characterize this relationship, this study utilized stimulation applied at various anatomical sections of the spinal column, including at levels of the intervertebral disc and regions correlating to the dorsal root entry zone. METHOD: Two electrode arrays were surgically implanted into the dorsal epidural space of the swine. The stimulation leads were positioned such that the caudal-most electrode contact was at the level of a thoracic intervertebral segment. Intraoperative cone beam computed tomography (CBCT) images were utilized to precisely determine the location of the epidural leads relative to the spinal column. High-resolution microCT imaging and 3D-model reconstructions of the explanted spinal cord illustrated precise positioning and dimensions of the epidural leads in relation to the surrounding neuroanatomy, including the spinal rootlets of the dorsal and ventral columns of the spinal cord. In a separate swine cohort, implanted epidural leads were used for SCS and recording evoked ESRs. RESULTS: Reconstructed 3D-models of the swine spinal cord with epidural lead implants demonstrated considerable distinctions in the dimensions of a single electrode contact on a standard industry epidural stimulation lead compared to dorsal rootlets at the dorsal root entry zone (DREZ). At the intervertebral segment, it was observed that a single electrode contact may cover 20-25% of the DREZ if positioned laterally. Electrode contacts were estimated to be ~0.75 mm from the margins of the DREZ when placed at the midline. Furthermore, ventral rootlets were observed to travel in proximity and parallel to dorsal rootlets at this level prior to separation into their respective sides of the spinal cord. Cathodic stimulation at the level of the intervertebral disc, compared to an 'off-disc' stimulation (7 mm rostral), demonstrated considerable variations in the features of recorded ESRs, such as amplitude and shape, and evoked unintended motor activation at lower stimulation thresholds. This substantial change may be due to the influence of nearby ventral roots. To further illustrate the influence of rootlet activation vs. dorsal column activation, the stimulation lead was displaced laterally at ~2.88 mm from the midline, resulting in variances in both evoked compound action potential (ECAP) components and electromyography (EMG) components in ESRs at lower stimulation thresholds. CONCLUSION: The results of this study suggest that the ECAP and EMG components of recorded ESRs can vary depending on small differences in the location of the stimulating electrodes within the spinal anatomy, such as at the level of the intervertebral segment. Furthermore, the effects of sub-centimeter lateral displacement of the stimulation lead from the midline, leading to significant changes in electrophysiological metrics. The results of this pilot study reveal the importance of the small displacement of the electrodes that can cause significant changes to evoked responses SCS. These results may provide further valuable insights into the underlying mechanisms and assist in optimizing future SCS-related applications.

Hedgehog-Gli pathway activation during kidney fibrosis.

The Hedgehog (Hh) signaling pathway regulates tissue patterning during development, including patterning and growth of limbs and face, but whether Hh signaling plays a role in adult kidney remains undefined. In this study, using a panel of hedgehog-reporter mice, we show that the two Hh ligands (Indian hedgehog and sonic hedgehog ligands) are expressed in tubular epithelial cells. We report that the Hh effectors (Gli1 and Gli2) are expressed exclusively in adjacent platelet-derived growth factor receptor-ß-positive interstitial pericytes and perivascular fibroblasts, suggesting a paracrine signaling loop. In two models of renal fibrosis, Indian Hh ligand was upregulated with a dramatic activation of downstream Gli effector expression. Hh-responsive Gli1-positive interstitial cells underwent 11-fold proliferative expansion during fibrosis, and both Gli1- and Gli2-positive cells differentiated into α-smooth muscle actin-positive myofibroblasts. In the pericyte-like cell line 10T1/2, hedgehog ligand triggered cell proliferation, suggesting a possible role for this pathway in the regulation of cell cycle progression of myofibroblast progenitors during the development of renal fibrosis. The hedgehog antagonist IPI-926 abolished Gli1 induction in vivo but did not decrease kidney fibrosis. However, the transcriptional induction of Gli2 was unaffected by IPI-926, suggesting the existence of smoothened-independent Gli activation in this model. This study is the first detailed description of paracrine hedgehog signaling in adult kidney, which indicates a possible role for hedgehog-Gli signaling in fibrotic chronic kidney disease.

Vagus nerve stimulation using an endovascular electrode array.

Objective. Vagus nerve stimulation (VNS), which involves a surgical procedure to place electrodes directly on the vagus nerve (VN), is approved clinically for the treatment of epilepsy, depression, and to facilitate rehabilitation in stroke. VNS at surgically implanted electrodes is often limited by activation of motor nerve fibers near and within the VN that cause neck muscle contraction. In this study we investigated endovascular VNS that may allow activation of the VN at locations where the motor nerve fibers are not localized.Approach. We used endovascular electrodes within the nearby internal jugular vein (IJV) to electrically stimulate the VN while recording VN compound action potentials (CAPs) and neck muscle motor evoked potentials (MEPs) in an acute intraoperative swine experiment.Main Results. We show that the stimulation electrode position within the IJV is critical for efficient activation of the VN. We also demonstrate use of fluoroscopy (cone beam CT mode) and ultrasound to determine the position of the endovascular stimulation electrode with respect to the VN and IJV. At the most effective endovascular stimulation locations tested, thresholds for VN activation were several times higher than direct stimulation of the nerve using a cuff electrode; however, this work demonstrates the feasibility of VNS with endovascular electrodes and provides tools to optimize endovascular electrode positions for VNS.Significance. This work lays the foundation to develop endovascular VNS strategies to stimulate at VN locations that would be otherwise too invasive and at VN locations where structures such as motor nerve fibers do not exist.

Deep-learning segmentation of fascicles from microCT of the human vagus nerve.

Introduction: MicroCT of the three-dimensional fascicular organization of the human vagus nerve provides essential data to inform basic anatomy as well as the development and optimization of neuromodulation therapies. To process the images into usable formats for subsequent analysis and computational modeling, the fascicles must be segmented. Prior segmentations were completed manually due to the complex nature of the images, including variable contrast between tissue types and staining artifacts. Methods: Here, we developed a U-Net convolutional neural network (CNN) to automate segmentation of fascicles in microCT of human vagus nerve. Results: The U-Net segmentation of ~500 images spanning one cervical vagus nerve was completed in 24 s, versus ~40 h for manual segmentation, i.e., nearly four orders of magnitude faster. The automated segmentations had a Dice coefficient of 0.87, a measure of pixel-wise accuracy, thus suggesting a rapid and accurate segmentation. While Dice coefficients are a commonly used metric to assess segmentation performance, we also adapted a metric to assess fascicle-wise detection accuracy, which showed that our network accurately detects the majority of fascicles, but may under-detect smaller fascicles. Discussion: This network and the associated performance metrics set a benchmark, using a standard U-Net CNN, for the application of deep-learning algorithms to segment fascicles from microCT images. The process may be further optimized by refining tissue staining methods, modifying network architecture, and expanding the ground-truth training data. The resulting three-dimensional segmentations of the human vagus nerve will provide unprecedented accuracy to define nerve morphology in computational models for the analysis and design of neuromodulation therapies.

Computational modeling of dorsal root ganglion stimulation using an Injectrode.

Objective: Minimally invasive neuromodulation therapies like the Injectrode, which is composed of a tightly wound polymer-coated platinum/iridium microcoil, offer a low-risk approach for administering electrical stimulation to the dorsal root ganglion (DRG). This flexible electrode is aimed to conform to the DRG. The stimulation occurs through a transcutaneous electrical stimulation (TES) patch, which subsequently transmits the stimulation to the Injectrode via a subcutaneous metal collector. However, effectiveness of stimulation relies on the specific geometrical configurations of the Injectrode-collector-patch system. Hence, there is a need to investigate which design parameters influence the activation of targeted neural structures. Approach: We employed a hybrid computational modeling approach to analyze the impact of the Injectrode system design parameters on charge delivery and the neural response to stimulation. We constructed multiple finite element method models of DRG stimulation and multi-compartment models of DRG neurons. We simulated the neural responses using parameters based on prior acute preclinical experiments. Additionally, we developed multiple human-scale computational models of DRG stimulation to investigate how design parameters like Injectrode size and orientation influenced neural activation thresholds. Main results: Our findings were in accordance with acute experimental measurements and indicated that the Injectrode system predominantly engages large-diameter afferents (Aß-fibers). These activation thresholds were contingent upon the surface area of the Injectrode. As the charge density decreased due to increasing surface area, there was a corresponding expansion in the stimulation amplitude range before triggering any pain-related mechanoreceptor (Aδ-fibers) activity. Significance: The Injectrode demonstrates potential as a viable technology for minimally invasive stimulation of the DRG. Our findings indicate that utilizing a larger surface area Injectrode enhances the therapeutic margin, effectively distinguishing the desired Aß activation from the undesired Aδ-fiber activation.

Quantifying changes in local basal ganglia structural connectivity in the 6-hydroxydopamine model of Parkinson's Disease using correlational tractography.

In recent years, tractography based on diffusion magnetic resonance imaging (dMRI) has become a popular tool for studying microstructural changes resulting from brain diseases like Parkinson's Disease (PD). Quantitative anisotropy (QA) is a parameter that is used in deterministic fiber tracking as a measure of connection between brain regions. It remains unclear, however, if microstructural changes caused by lesioning the median forebrain bundle (MFB) to create a Parkinsonian rat model can be resolved using tractography based on ex-vivo diffusion MRI. This study aims to fill this gap and enable future mechanistic research on structural changes of the whole brain network rodent models of PD. Specifically, it evaluated the ability of correlational tractography to detect structural changes in the MFB of 6-hydroxydopamine (6-OHDA) lesioned rats. The findings reveal that correlational tractography can detect structural changes in lesioned MFB and differentiate between the 6-OHDA and control groups. Imaging results are supported by behavioral and histological evidence demonstrating that 6-OHDA lesioned rats were indeed Parkinsonian. The results suggest that QA and correlational tractography is appropriate to examine local structural changes in rodent models of neurodegenerative disease. More broadly, we expect that similar techniques may provide insight on how disease alters structure throughout the brain, and as a tool to optimize therapeutic interventions.

Spatially selective stimulation of the pig vagus nerve to modulate target effect versus side effect.

Electrical stimulation of the cervical vagus nerve using implanted electrodes (VNS) is FDA-approved for the treatment of drug-resistant epilepsy, treatment-resistant depression, and most recently, chronic ischemic stroke rehabilitation. However, VNS is critically limited by the unwanted stimulation of nearby neck muscles-a result of non-specific stimulation activating motor nerve fibers within the vagus. Prior studies suggested that precise placement of small epineural electrodes can modify VNS therapeutic effects, such as cardiac responses. However, it remains unclear if placement can alter the balance between intended effect and limiting side effect. We used an FDA investigational device exemption approved six-contact epineural cuff to deliver VNS in pigs and quantified how epineural electrode location impacts on- and off-target VNS activation. Detailed post-mortem histology was conducted to understand how the underlying neuroanatomy impacts observed functional responses. Here we report the discovery and characterization of clear neuroanatomy-dependent differences in threshold and saturation for responses related to both effect (change in heart rate) and side effect (neck muscle contractions). The histological and electrophysiological data were used to develop and validate subject-specific computation models of VNS, creating a well-grounded quantitative framework to optimize electrode location-specific activation of nerve fibers governing intended effect versus unwanted side effect.