Publications

Even though extensively documented in acute experiments, ongoing vagal activity has not been characterized longitudinally over days or weeks in mice, a preferred preclinical model. This study presents a chronic recording model to record compound action potentials (CAPs) from the mouse vagus nerve for up to 6 months in both anesthetized and awake animals, with stable signal-to-noise ratios and half-rise times. The approach allows for longitudinal analysis while tracking individual CAPs across multiple days, their firing rates and phase-locking characteristics with other physiological signals, and in the awake case, movement using unsupervised machine learning models. Results reveal diverse CAP populations with varying degrees of physiological coupling, providing a valuable platform to investigate how vagal activity may be modified based on disease severity and develop closed-loop VNS by predicting flare-ups and tracking stimulation efficacy.

Vagal sensory neurons in the nodose ganglia selectively encode specific cytokines, enabling real-time body-brain communication of immune signals. Using in vivo calcium imaging, vagal sensory neurons within the nodose ganglia exhibit distinct real-time neuronal responses to inflammatory cytokines. Groups of individual nodose ganglia neurons are cytokine-selective, while other neurons respond to multiple cytokines while maintaining distinct cytokine-specific patterns for each, indicating that immune signals have distinct neural representations. Vagal sensory neurons express receptors for cytokines and other immune mediators and transmit cytokine-specific neural action potentials to the brain. In mice with dextran sulfate sodium (DSS)-induced colitis, nodose ganglia neuronal activity and cytokine-specific neuronal responses were both altered, indicating that inflammation changes neural excitability.

Objective: Sensory nerves of the peripheral nervous system (PNS) transmit afferent signals from the body to the brain. These peripheral nerves are composed of distinct subsets of fibers and associated cell bodies, which reside in peripheral ganglia distributed throughout the viscera and along the spinal cord. The vagus nerve (cranial nerve X) is a complex polymodal nerve that transmits a wide array of sensory information, including signals related to mechanical, chemical, and noxious stimuli. To understand how stimuli applied to the vagus nerve are encoded by vagal sensory neurons in the jugular-nodose ganglia, we developed a framework for micro-endoscopic calcium imaging and analysis. Approach: We developed novel methods for in vivo imaging of the intact jugular-nodose ganglion using a miniature microscope (Miniscope) in transgenic mice with the genetically-encoded calcium indicator GCaMP6f.

A fully-implantable recording and stimulation neuromodulation device measuring 2.2 cm³ and weighing 2.8 g is described, with a bidirectional wireless interface allowing simultaneous readout of multiple physiological signals and complete control over stimulation parameters, along with a wirelessly rechargeable battery providing up to 5 days of lifetime on a single charge. The device was designed using only commercially available electrical components and 3D-printed packaging to facilitate widespread adoption and accelerate discovery and translation of future bioelectronic therapeutics. The device was implanted to deliver vagus nerve stimulation in 12 animals and demonstrated a functional neural interface capable of inducing acute bradycardia with functional lifetimes exceeding three weeks.

Bacterial lipopolysaccharide (LPS) induces a multi-organ, Toll-like receptor 4 (TLR4)-dependent acute inflammatory response. Using network analysis, the spatiotemporal dynamics of 20 LPS-induced protein-level inflammatory mediators over 0-48 hours were defined in the heart, gut, lung, liver, spleen, kidney, and systemic circulation in both wild-type and TLR4-null mice. Dynamic Network Analysis suggested that inflammation in the heart is most dependent on TLR4, followed by the liver, kidney, plasma, gut, lung, and spleen. Insights from computational analyses suggest an early role for TLR4-dependent tumor necrosis factor in coordinating multiple signaling pathways in the heart, giving way to later interleukin-17A—possibly derived from pathogenic Th17 cells and effector/memory T cells—in the spleen and blood.

A scalable model for long-term vagus nerve stimulation (VNS) in mice was developed and validated in four research laboratories. Significant heart rate responses were observed for at least 4 weeks in 60-90% of animals. Device implantation did not impair vagus-mediated reflexes, including baroreflex, lung stretch reflex, and feeding reflexes. Histological examination of implanted nerves revealed fibrotic encapsulation without axonal pathology. VNS using this implant significantly suppressed TNF levels in endotoxemia. Because the implant does not interfere with physiological vagus nerve-mediated reflexes and successfully inhibits serum TNF levels in acute endotoxemia, this method may be useful in facilitating mechanistic studies of long-term VNS as therapy for chronic diseases modeled in mice.

A common-mode interference rejection algorithm based on an impedance matching approach was developed for bipolar cuff electrodes. Two unipolar channels were recorded from the two electrode contacts of a bipolar cuff, and the impedance mismatch was estimated and used to correct one of the two channels. Using the impedance adjustment algorithm, ECG artifacts were significantly suppressed relative to the simple subtraction method by an additional 9.2 dB on average. The algorithm successfully reduced the common-mode interference from ECG artifacts, stimulation artifacts, and evoked EMG interference while retaining neural signals.

Vagus nerve stimulation (VNS) is a bioelectronic therapy where selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects. Evidence for directional VNS with anodal block (ABL) has been scarce and inconsistent. Through a series of vagotomies, physiological markers for afferent and efferent fiber activation by VNS were established: stimulus-elicited change in breathing rate (ΔBR) and heart rate (ΔHR), respectively. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ΔBR) whereas cathode caudad caused an efferent pattern of responses. The study provides concrete physiological and neurophysiological evidence that anodal block is a viable mechanism for functionally demonstrable directional biasing in VNS, for a range of clinically relevant stimulation parameters.

Recently developed methods were used to isolate and decode specific neural signals acquired from the surface of the vagus nerve in BALB/c wild type mice to identify those that respond robustly to hypoglycemia. Neural signals in the vagus nerve respond significantly to insulin-induced hypoglycemia and correlate with dropping blood glucose levels. A decoding algorithm was able to reconstruct blood glucose levels with high accuracy (median error 18.6 mg/dl). Hyperglycemia did not induce robust vagus nerve responses, and deletion of TRPV1 nociceptors attenuated the hypoglycemia-dependent vagus nerve signals. These results provide insight to the sensory vagal signaling that encodes hypoglycemic states and suggest a method to measure blood glucose levels by decoding nerve signals.

The bodies have built-in neural reflexes that continuously monitor organ function and maintain physiological homeostasis. While the field of bioelectronic medicine has mainly focused on the stimulation of neural circuits to treat various conditions, recent studies have started to investigate the possibility of leveraging the sensory arm of these reflexes to diagnose disease states. Neural signals emanating from the body's built-in biosensors and propagating through peripheral nerves must be recorded and decoded to identify the presence or levels of relevant biomarkers of disease. This review outlines studies decoding vagus nerve activity as it related to inflammatory, metabolic, and cardiopulmonary biomarkers to enable the development of real-time diagnostic devices and help advance truly closed-loop neuromodulation technologies.

Recent advances reveal that neural reflexes modulate the immune system, but it was previously unknown whether cytokine mediators of immunity mediate specific neural signals. Methods were developed to isolate and decode specific neural signals recorded from the vagus nerve to discriminate between the cytokines IL-1β and TNF. A bipolar cuff electrode recording activity from the surface of the cervical vagus nerve of mice was used. The methodological waveform successfully detects and discriminates between specific cytokine exposures using neural signals, demonstrating that the nervous system maintains physiological homeostasis through reflex pathways that modulate organ function.

We present a novel 3D self-adaptive nerve electrode for high density nerve signal recording and site-specific stimulation. A new pre-shaped flexible spiral structure has been developed in order to achieve tight contact with small nerves without any additional mechanical locking structure or force. This unique structure enables the nerve electrode to adapt and maintain close contact with the nerve without compressing it or restricting its movement. The spiral nerve electrodes (inner diameter = 310 um) with 8 recording channels (electrode diameter = 50 um) were fabricated and successfully applied to the rat vagus nerve (approximate diameter of 350 um) in order to record compound action potentials.