Biology subjects

Williams, J. C.

Publications and source records attributed to Williams, J. C..

26 records · Page 2Linked to original sources

bioRxiv2020

Sources of Off-Target Effects of Vagus Nerve Stimulation Using the Helical Clinical Lead in Domestic Pigs

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. 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. 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 A{delta}-, B-, and C-fibers. Our data resolve conflicting reports of the stimulation amplitudes required for C-fiber activation in large animal studies (>10 mA) and human studies (<250 {micro}A). After removing muscle-generated artifacts, ENG signals with post-stimulus latencies consistent with A{delta}- 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.

neuroscience↗

bioRxiv2019

Motion denoising of multiband resting state functional connectivity MRI data: An improved volume censoring method

Simultaneous multi-slice (multiband) accelerated functional magnetic resonance imaging (fMRI) provides dramatically improved temporal and spatial resolution for resting-state functional connectivity (RSFC) studies of the human brain in health and disease. However, multiband acceleration also poses unique challenges for denoising of subject motion induced data artifacts, the presence of which is a major confound in RSFC research that substantively diminishes reliability and reproducibility. We comprehensively evaluated existing and novel approaches to volume censoring-based motion denoising in the Human Connectome Project (HCP) dataset. We show that assumptions underlying common metrics for evaluating motion denoising pipelines, especially those based on quality control-functional connectivity (QC-FC) correlations and differences between high- and low-motion participants, are problematic, and appear to be inappropriate in their current widespread use as indicators of comparative pipeline performance and as targets for investigators to use when tuning pipelines for their own datasets. We further develop two new quantitative metrics that are instead agnostic to QC-FC correlations and other measures that rely upon the null assumption that no true relationships exist between trait measures of subject motion and functional connectivity, and demonstrate their use as benchmarks for comparing volume censoring methods. Finally, we develop and validate quantitative methods for determining dataset-specific optimal volume censoring parameters prior to the final analysis of a dataset, and provide straightforward recommendations and code for all investigators to apply this optimized approach to their own RSFC datasets.

neuroscience↗

bioRxiv2019

Functional Vagotopy in the Cervical Vagus Nerve of the Domestic Pig: Implications for Vagus Nerve Stimulation

Given current clinical interest in vagus nerve stimulation, 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 domestic pig, whose vagus nerve organization and size approximates the human cervical vagus nerve. We provide data on key features across the cervical vagus nerve including 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 vagus nerve stimulation 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 cervical vagus nerve. This often leads to a distinct bimodal organization, or vagotopy that may be advantageous to exploit in design of electrodes/stimulation paradigms. Finally, we placed our data in context of historic and recent histology spanning mouse, rat, canine, pig, non-human primate and human models, thus providing a comprehensive resource to understand similarities and differences across species.

neuroscience↗

bioRxiv2019

Is Vagus Stimulation Brain Washing?

Vagal nerve stimulation (VNS) is an FDA approved treatment method for intractable epilepsy, treatment resistant depression, cluster headaches and migraine with over 100,000 patients having received vagal nerve implants to date. Moreover, evidence in the literature has led to a growing list of possible clinical indications, with several small clinical trials applying VNS to treat conditions ranging from neurodegenerative diseases to arthritis, anxiety disorders, and obesity. Despite the growing list of therapeutic applications, the fundamental mechanisms by which VNS achieves its beneficial effects are poorly understood and an area of active research. In parallel, the glymphatic and meningeal lymphatic systems have recently been proposed and experimentally validated to explain how the brain maintains a healthy homeostasis without a traditionally defined lymphatic system. In particular, the glymphatic system relates to the interchange of cerebrospinal fluid (CSF) and interstitial fluid (ISF) whose net effect is to wash through the brain parenchyma removing metabolic waste products and misfolded proteins from the interstitium. Of note, clearance is sensitive to adrenergic signaling, and a primary driver of CSF influx into the parenchyma appears to be cerebral arterial pulsations and respiration. As VNS has well-documented effects on cardiovascular and respiratory physiology as well as brain adrenergic signaling, we hypothesized that VNS delivered at clinically derived parameters would increase CSF influx in the brain. To test this hypothesis, we injected a low molecular weight (3 kD) lysine-fixable fluorescent tracer (TxRed) into the CSF system of mice with a cervical vagus nerve cuff implant and measured the amount of CSF penetrance following VNS. We found that the clinical VNS group showed a significant increase in CSF dye penetrance as compared to the naive control and sham groups. This study demonstrates that VNS therapeutic strategies already being applied in the clinic today may induce intended effects and/or unwanted side effects by altering CSF/ISF exchange in the brain. This may have broad ranging implications in the treatment of various CNS pathologies.\n\nOne Sentence SummaryCervical vagus nerve stimulation using clinically derived parameters enhances movement of cerebrospinal fluid into the brain parenchyma presenting a previously unreported effect of vagus nerve stimulation with potential clinical utility.

neuroscience↗

bioRxiv2019

Conformational Flexibility of p150Glued(1-191) Subunit of Dynactin Assembled with Microtubules

Microtubule-associated proteins (MAPs) perform diverse functions in cells. These functions are dependent on their interactions with microtubules. Dynactin, a cofactor of dynein motor, assists the binding of dynein to various organelles and is crucial to the long-distance processivity of dynein-based complexes. The largest subunit of dynactin, the p150glued, contains a N-terminus segment that is responsible for the microtubule-binding interactions and long-range processivity of dynactin. We employed solution and magic angle spinning NMR spectroscopy to characterize the structure and dynamics of the p150glued N-terminal region, both free and in complex with polymerized microtubules. This 191-residue region encompasses the CAP-Gly domain, the basic domain and serine-proline-rich (SP-rich) domain. We demonstrate that the basic and SP-rich domains are intrinsically disordered in solution and significantly enhance the binding affinity to microtubules as these regions contain the second microtubule-binding site on the p150Glued subunit. The majority of the basic and SP-rich domains are predicted to be random-coil, while the segments S111-I116, A124-R132 and K144-T146 in the basic domain contain short -helical or {beta}-sheet structures. These three segments possibly encompass the microtubule binding site. Surprisingly, the protein retains high degree of flexibility upon binding to microtubules except for the regions that are directly involved in the binding interactions with microtubules. This conformational flexibility may be essential for the biological functions of the p150Glued subunit.\n\nSTATEMENT OF SIGNIFICANCEMicrotubule-associated proteins (MAPs) perform diverse functions in cells. Many of them comprises intrinsically disordered regions, whose structural flexibility are central to microtubule-based cellular functions of MAPs. We employed solution and magic angle spinning NMR spectroscopy to characterize the structure and dynamics of the p150glued N-terminal region encompassing the CAP-Gly domain, the basic domain and serine-proline-rich (SP-rich) domain, both free and in complex with polymerized microtubules. The results reveal that the basic and SP-rich domains are largely unstructured and retains high degree of flexibility upon binding to microtubules except for the regions that are possibly involved in the binding interactions with microtubules. This approach is informative for dynamics studies of intrinsically disordered MAPs and other disordered proteins in large biological assemblies.

biophysics↗

bioRxiv2019

A Truly Injectable Neural Stimulation Electrode Made From an In-Body Curing Polymer/Metal Composite

Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, we have developed a novel electrode that begins as an uncured, flowable pre-polymer that can be injected around a neuroanatomical target to minimize surgical manipulation. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, we performed detailed electrochemical and microscopy characterization of its material properties and validated the feasibility of using it to electrically stimulate the nervous system in rats and swine. The silicone-metal-particle composite performed very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSCC) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of being simpler than traditional electrode designs, less invasive, and more cost-effective, the Injectrode has the potential to increase the adoption of neuromodulation therapies for existing and new indications.

bioengineering↗

bioRxiv2019

μECoG Recordings Through a Thinned Skull

The studies described in this paper for the first time characterize the acute and chronic performance of optically transparent thin-film {micro}ECoG grids implanted on a thinned skull as both an electrophysiological complement to existing thinned skull preparation for optical recordings/manipulations, and a less invasive alternative to epidural or subdurally placed {micro}ECoG arrays. In a longitudinal chronic study, {micro}ECoG grids placed on top of a thinned skull maintain impedances comparable to epidurally placed {micro}ECoG grids that are stable for periods of at least one month. Optogenetic activation of cortex is also reliably demonstrated through the optically transparent ECoG grids acutely placed on the thinned skull. Finally, spatially distinct electrophysiological recordings were evident on {micro}ECoG electrodes placed on a thinned skull separated by 500-750{micro}m, as assessed by stimulation evoked responses using optogenetic activation of cortex as well as invasive and epidermal stimulation of the sciatic and median nerve at chronic time points. Neural signals were collected through a thinned skull in multiple species, demonstrating potential utility in neuroscience research applications such as in vivo imaging, optogenetics, calcium imaging, and neurovascular coupling.

neuroscience↗

bioRxiv2017

OptoGap: an optogenetics-enabled assay for quantification of cell-cell coupling in multicellular cardiac tissue

Intercellular electrical coupling is an essential means of communication between cells. It is important to obtain quantitative knowledge of such coupling between cardiomyocytes and nonexcitable cells when, for example, pathological electrical coupling between myofibroblasts and cardiomyocytes yields increased arrhythmia risk or during the integration of donor (e.g. cardiac progenitor) cells with native cardiomyocytes in cell-therapy approaches. Currently, there is no direct method for assessing heterocellular coupling within multicellular tissue. Here we demonstrate experimentally and computationally a new contactless assay for electrical coupling, OptoGap, based on selective illumination of inexcitable cells that express optogenetic actuators and optical sensing of the response of coupled excitable cells, e.g. cardiomyocytes, that are light-insensitive. Cell-cell coupling is quantified by the energy required to elicit an action potential via junctional current from the light-stimulated cell(s). The proposed technique is experimentally validated against the standard indirect approach, GapFRAP, using light-sensitive cardiac fibroblasts and non-transformed cardiomyocytes in a two-dimensional setting. Its potential applicability to the complex three-dimensional setting of the native heart is corroborated by computational modeling and proper calibration.\n\nIntercellular coupling is a fundamental form of communication between cells, essential for the synchronization of physiological processes in different organs. Pathologically altered coupling or the emergence of de novo coupling between native and donor cells are problems of interest in many cardiac applications, e.g. during cell delivery and cell integration for cardiac repair therapy1,2. In particular, interactions between cardiomyocytes and fibroblasts are of interest, especially the pro-arrhythmic increase in coupling as the latter transition to myofibroblasts3-6.\n\nElectrical coupling in cardiac tissue is mediated primarily by low-resistance paths formed by gap-junctional proteins (connexins), that can link cardiomyocytes (CMs) to each other and to non-cardiomyocytes (nCMs), such as fibroblasts. Qualitative and quantitative methods, e.g. immunofluorescence, messenger RNA and Western blots, are often used to assay connexin expression levels as a surrogate measure of coupling, but they do not provide functional information. A method for direct quantification of cell-cell coupling within the multicellular tissue context is highly desirable.

bioengineering↗