Antidromic Compound Action Potentials Research Articles

The Fifth Bioelectronic Medicine Summit Hosted by the Feinstein Institutes for Medical Research (Manhasset, NY) and Columbia Engineering (NY, NY) at The Garden City Hotel, Garden City, NY 11530 on October 11-12th, 2022- Bioelectronic Medicine: Today’s Tools, Tomorrow’s Therapies

Poster session abstractsP1. Clinical feasibility of liver-targeted peripheral ultrasound neuromodulation (pFUS) using interleaved B-mode imaging and pulsed ultrasound stimuli in type 2 diabeticsJeffrey Ashe1, John Graf1, Radhika Madhavan1, Kirk Wallace1, Victoria Cotero1, Samantha Abate1, Ram Krishna Pandey1, Raimund Herzog2, Porindla Sridhar Narayan1, David Shoudy1, Ying Fan1, Tzu-Jen Kao1, Chris Puleo1 1 GE Research, Niskayuna, NY, USA; 2 Yale University, New Haven, CT, USA Correspondence: Chris PuleoRecently it has been shown that mechanical shear waves produced by focused ultrasound pulses result in activation of mechanosensitive ion channels and modulate peripheral nerve activity. The activity of multiple classes of ion channels can be affected by the pulsed ultrasound stimuli, and these ion channels show cell and tissue specific expression and activation patterns. Unlike electromagnetic stimuli, ultrasound penetrates deeply through biological tissue and can be focused to millimeter-to-centimeter-sized volumes without affecting neighboring tissue. Furthermore, ultrasound pulses can be non-invasively image-targeted to specific anatomical locations with technologies used safely for decades in diagnostic imaging applications. However, while peripheral neuromodulation with ultrasound has been demonstrated in multiple in vitro and pre-clinical models, the methods have not yet been reported in humans. Herein, we demonstrate the use of a modified diagnostic imaging system for testing pulsed ultrasound neuromodulation in human subjects. Specifically, we test pulsed ultrasound stimulation of the hepatoportal plexus using stimulation parameters previously found to restore glucose homeostasis and improve insulin resistance in multiple pre-clinical models of type 2 diabetes. We demonstrate image-targeted neuromodulation by interleaving B-mode imaging pulses with focused pulsed stimuli and apply both human expert-based and post-hoc deep learning-based image object detection to quantify the on-target versus off-target stimulus dose (i.e., the duration of time and spatial average intensity of pulses that were aligned to the anatomical target). Finally, we report the first safety and feasibility outcomes in subjects with type 2 diabetes and discuss these outcomes in relation to our previous pre-clinical results.P3. Toward closed-loop bioelectronics: wireless power and data communication using magnetoelectric technologyFatima Alrashadan1, Zhanghao Yu1, Joshua Woods1, Kaiyuan Yang1, Jacob T. Robinson1,2,3 1Department of Electrical and Computer Engineering, Rice University, Houston, Texas, USA; 2Department of Bioengineering, Rice University, Houston, Texas, USA; 3Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA Correspondence: Jacob T. RobinsonImplantable bioelectronics has opened up a promising avenue to treat many drug-resistance neurological and psychiatric disorders by interfering directly with the nervous system. These devices deliver controlled electric stimulations to modulate the electrical activities of the nervous system or record the electrical, chemical, and physical properties for better diagnosis. Integrating implantable devices with wireless power, bidirectional communication, and biosensing functionalities could allow for the design of next-generation bioelectronics that features adaptive closed-loop systems and distributed networks of implants. Different wireless power transfer techniques (WPT) including radiofrequency (RF), inductive coupling, ultrasound, and light have demonstrated the ability to power medical implants, however, with performance trade-offs in terms of implant size, misalignment tolerance, bidirectional communication link, and the amount of power that can be delivered safely through biological tissues.Magnetoelectric (ME) is an emerging technology that has shown the potential to wirelessly power miniaturized implants (ME-BIT) to stimulate different nerve targets while demonstrating high efficiency at mm-size, high power delivery (> 1 mW) without safety issues, and high misalignment tolerance. These features are empowered by using ME material that has high power density, low mechanical resonance frequency, and high permeability to concentrate magnetic flux inside the material. However, to enable using the ME technology to design adaptive closed-loop systems, there is still a need to develop a bidirectional data communication link. One possible solution is to integrate the ME implant with one of the existing communication modalities, including, RF, near field coupling, ultrasound, or infrared, however, the addition of new components will increase the device footprint and constrain the power budget.Here, we propose a low-power communication system that utilizes the unique characteristic of the magnetoelectric material itself to establish a bidirectional link between the ME-BIT and an external transceiver. Specifically, we use the backscattered field generated by the ME film when excited by an external magnetic field as a carrier signal. To modulate this signal to encode digital data, we use an integrated circuit to change the electrical loading conditions across the ME film terminals. This carrier signal travels losslessly through the biological tissues and can be received using a magnetic receiver outside the body.Our system comprises an implantable ME-BIT (ME transducer + IC) and a custom portable transceiver. With design optimizations in data modulation and recovery, the proposed system archives an 8-kbps data rate at the 335-kHz carrier frequency, and a TRX-implant distance greater than 2 cm for a bit error rate less than 1E-3. Furthermore, we validated the proposed system for wireless stimulation and sensing and conducted Ex-vivo tests through a 1.5-cm porcine tissue.P4. High frequency electrical stimulation attenuates neuronal release of high mobility group box 1 (HMGB1) and ameliorates neuropathic painHuan Yang1, Timir B. Datta-Chaudhuri1,2,3, Sam J. George1, Bilal Haider1, Jason Wong1 Michael Brines1, Kevin J. Tracey1,2,3, and Sangeeta S. Chavan1,2,3 1Institute for Bioelectronic Medicine, Feinstein Institutes for Medical Research, 350 Community Drive, Manhasset, NY 11030, USA; 2Elmezzi Graduate School of Molecular Medicine, Feinstein Institute for Medical Research, Northwell Health, Manhasset, NY, USA; 3Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Hempstead, New York, USA Correspondence: Sangeeta S. ChavanChronic pain presents a major unmet clinical problem. High-frequency electrical nerve stimulation (HFES) has achieved clinical success as an analgesic modality for pain management, but the underlying mechanism is unknown. We reasoned that HFES may inhibit neuroinflammatory mediator release by sensory neurons to reduce pain. HMGB1, a key mediator of injury- and infection-elicited inflammation, is involved in the pathogenesis of persistent pain. We recently reported that neuronal HMGB1 is required for mediating inflammation and hyperalgesia following nerve injury (Yang H et al., PNAS, 118:1-9, 2021). Here we assessed the effects of HFES in modulating HMGB1 release by sensory neurons. Using microelectrode arrays (MEAs) in cultured dorsal root ganglia (DRG) harvested from transgenic mice that express light-sensitive channel rhodopsin in sensory neurons, we observe that light-evoked HMGB1 release from DRGs is significantly reduced with HFES exposure (10 kHz, 2 mA, rectangular symmetric, biphasic, charge balanced) (HMGB1 levels in unstimulated group = 5.3 + 0.5 ng/ml; in light stimulated group = 25.8 + 6.0 vs. light + HFES = 8.2 + 2.1* pg/ml, N=6, *: P<0.01 vs. light stimulated group). In agreement, in vivo studies showed that HFES (20.6 kHz, 10 min/per day X 3 consecutive days) significantly reduces mechanical hyperalgesia and levels of HMGB1 in the inflamed paws in C57BL/6 mice that subjected to chronic constriction injury (CCI) of the sciatic nerve. HMGB1 levels in sham surgery group = 10.6 + 1.1 ng/mg protein, in CCI group = 29.0 + 3.9 vs. CCI + HFES = 12.8 + 1.6* ng/mg protein, N=10 mice per group, *P<0.001 vs. CCI group. Similar beneficial effects by HFES were observed in Sprague-Dawley rats subjected to sciatic nerve injury. Together, these results support the mechanistic insight that HFES may reset sensory neurons into a less pro-inflammatory state via inhibiting the release of neuroinflammatory mediators such as HMGB1 (supported in part by funding from TrueRelief, Santa Monica, CA; grants from NIH, NIGMS 1R35GM118182 to KJT and R01GM132672 to SSC).P5. Solid state batteries enable miniaturisation of active implanted medical devicesDenis Pasero 1Ilika, Unit 10a The Quadrangle, Abbey Park Industrial Estate, Romsey, UKCorrespondence: Denis PaseroPurpose: A new generation of miniaturised, implanted, active medical devices, possibly introduced via a catheter, is being developed by disruptive product designers. Conventional medical batteries are packaged within metallic cans for safety purposes; they are also typically primary (non-rechargeable) and must contain the whole energy required during the life of the device they power from first day of implantation. For these reasons, miniaturisation of conventional medical batteries is limited to a few 10’s of cm3. New active implanted sensing devices are being designed with less than 1 cm3 in volume, including implanted cardiac sensors, neuromodulation therapy devices, smart orthopaedics and orthodontics sensors. Millimeter-scale solid state batteries, which do not need significant packaging, have been developed to uniquely enable miniaturisation of next generation implantable devices.Methods: Solid state batteries were fabricated by physical vapour deposition and sputtering. Key developments to increase energy density used the following methods: Implement photolithography as a method for patterning the batteries sub-layers at the micron-level, enabling miniature features Thin down the substrate, i.e. the mechanical support for the batteries, enabling high energy density Stack and interconnect single cells on top of each other, to multiply the energy of the resulting battery for a same footprint Increase the cathode thickness in order to store more energy The rechargeable batteries have been developed on Ilika’s first volume manufacturing line, opened in Southampton, Hampshire in 2021, the first of its kind in the UK.Results: Ilika’s first solid state batteries were produced, down to 15 mm2 footprint and total thickness 1 mm. The batteries consisted of 6 stacked cells, interconnected in parallel, yielding a total capacity of 300 uAh and nominal voltage of 3.5V. The arial energy density of the stacked battery was measured to be approximately 12.5 uAh/mm2. Internal resistance of the full stack was measured to be about a sixth that of each single cell forming the stack, enabling peak power of a few mA. These batteries could be recharged in as little as 8 min with heating of the battery less than 2°C upon fast charging. These batteries are going through their final development stage and will go through full medical certification in 2023.Discussion: A novel technique for stacking and interconnecting solid state cells was shown to significantly increase the energy density and decrease the internal resistance of the battery stack. This development could enable further development in implanted medical sensors by providing an energy source of minimal size (mm-scale footprint and um-scale thickness), appropriate energy density for increasing functionalities and long life avoiding the risk and cost of removal.Use of rechargeable batteries for in-the-body applications have historically suffered from patient compliance with regards to regular charging. Whilst a new conversation with the patient is required, the benefit of miniaturising non-life-critical sensors which can be recharged in less than 10 minutes, is expected to outweigh the need for regular recharging.P7. Flexible, scalable high channel count stereo-electrode for recording in the human brainKeundong Lee,1 Angelique C. Paulk,2 Yun Goo Ro,1 Karen Tonsfeldt,1 Youngbin Tchoe,1 Andrew M. Bourhis,1 Jihwan Lee,1 Daniel R. Cleary,1 John S. Pezaris,2 Yoav Kfir,2 Sydney S. Cash,2 Shadi A. Dayeh1 1Integrated Electronics and Biointerfaces Laboratory, Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA 92093, USA; 2Department of Neurology, Harvard Medical School, Boston, MA, USA; Center for Neurotechnology and Neurorecovery, Department of Neurology, Massachusetts General Hospital, Boston, MA 02114, USA Correspondence: Shadi A. DayehOver the past decade, stereotactically placed electrodes have become the gold standard for deep brain recording and stimulation for a wide variety of neurological and psychiatric diseases. Current devices, however, are highly limited in their spatial resolution and ability to record from small populations let alone individual neurons. Here, we report on a novel, reconfigurable, monolithically integrated human-grade flexible depth electrode with a maximum of 128 channels and able to record from 10 cm of brain tissue. This thin, stylet-guided depth electrode is capable of recording local field potentials and single unit neuronal activity (action potentials) as validated across species and represents a major new advance in manufacturing and design approaches for a mainstay technology in clinical neurology.P8. NINDS and trans-NIH funding opportunities for technology development and translationEric Hudak, Megan Frankowski, Brooks Gross, Nick LanghalsDivision of Translational Research, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA Correspondence: Eric HudakThe mission of the NINDS Division of Translational Research (DTR) is to accelerate basic research findings toward patient use for neurological disorders and stroke by providing funding, expertise, and resources to the research community. DTR provides funding and resources through grants, cooperative agreements, and contracts to academic and industry researchers to advance early-stage neurological technologies, devices, and therapeutic approaches to industry adoption (i.e. investor funding and corporate partnerships).The Translational Neural Devices (TND) program within DTR has created a variety of programs that support the design, implementation, and management of research activities critical to translational challenges in the treatment of neurological disease. In addition, TND plays an active role in the NIH BRAIN Initiative, Blueprint MedTech Program, SPARC Program, and HEAL Initiative.NINDS TND is actively managing programs that support neural device therapeutics and training through grants, contracts, and consultants. These programs cover all stages of translational research from early device development and optimization to preclinical development and early clinical development. Funding opportunities and resources are actively supporting translational research in preclinical discovery and development of new therapeutic interventions for neurological disorders and stroke, as well as neuropsychiatric disorders and neurotraumatic injuries (BRAIN Initiative) and pain (HEAL Initiative). An overview of the NINDS Translational Neural Devices program and related Trans-NIH funding opportunities and resources will be presented.P9. Bioelectronic devices for in vivo recordings of metabolic information from the vagus nerveAmparo Guemes, Poppy Oldroyd, Alejandro Carnicer-Lombarte, Sam Hilton, George MalliarasBioelectronic Laboratory, Department of Engineering, University of Cambridge, Cambridge, UK Correspondence: Amparo GuemesIntroduction: Closed-loop bioelectronic medicine, which uses electrical recording and stimulation to interface with peripheral nerves, is becoming a promising strategy for the treatment of chronic diseases [1]. This multidisciplinary work presents the opportunities of bioelectronics for improving metabolic control in Type 1 diabetes by decoding metabolic clues from the cervical vagus nerve recordings.Methods: Interfacing with peripheral nerves and organs for reliable recording poses difficult challenges due to invasiveness and high risk of body rejection. Here, we compare the ability of two types of sub-millimetre cuff devices to record metabolic information from the vagus nerve: thin-film flexible devices were chosen given their potential for chronic implantation, and gold microwires were used as gold-standard. Both type of devices were implanted in vivo around the cervical vagus nerve of Sprague-Dawley rats anaesthetised under urethane. For the microwires, a region of 1mm was exposed towards the tip of PTFE coated gold microwires (75um diameter) and placed around the nerve for cuff recordings. Conformable bioelectronic devices were fabricated using thin-film technology based on conductive polymer PEDOT:PSS microelectrodes on parylene-C for high-resolution recording [2]. The devices include two ring microelectrodes to cover the circumference of the vagus nerve and 6 small contacts (100umx100um) to increase spatial resolution. In this work, we also present an improved strategy to extract information from neurograms under different metabolic conditions. The decoding methodology applies band-pass filtering (400Hz-4Khz), ECG removal based on continuous wavelet transformation (CWT), identification of action potentials and extraction of waveforms, dimensionality reduction, clustering of waveforms, extraction of metrics (spike rate, spike amplitude, inter-spike-interval), and correlation with metabolic events.Results: We have validated the ability to record nerve activity and decode metabolic information through implantation of both gold microwires and flexible devices on the vagus nerve of rodents after metabolic challenges. Using both types of devices, we predominantly found an increase in the overall firing rate or at least in one of the identified clusters corresponding to a decrease in glucose levels. No meaningful changes in the firing rate were observed on increasing or stable blood glucose concentrations. To verify that the detected spikes were of neural nature, a lidocaine bath at the exposed site was used at the end of the experiments that caused the successful elimination of the neural response.Conclusion: We demonstrate the design, fabrication, and acute implementation of new bioelectronic neural probes for recording signals from the surface of the vagus nerve. Gold microwires can be used as a gold-standard electrophysiological tool for acute recording from the vagus nerve of rats under anaesthesia, but bioelectronic flexible thin-film devices based on conductive polymers provide the best way for minimally invasive chronic implantation in awake animals. This study explores the development of new technology to interface with small peripheral nerves, and contributes to increase our understanding on the role the nervous systems plays in metabolism.[1] Guemes, A., Etienne-Cummings, R., and Georgiou, P. Bioelectronic Medicine 6(1). (2020).[2] D. Khodagholy, et al., Adv. Mat. 2011, vol 23, H268-H272.P10. A system for investigating bioelectronic therapies using a multicontact nerve cuff electrode and an implanted stimulator/recorderJoern Rickert1, Martin Schuettler1, Ivor Gillbe2, Ronny Pfeifer1, Timothy Denison3 1CorTec, Freiburg, Germany; 2Bioinduction Ltd., Bristol, UK; 3Institute of Biomedical Engineering, Department of Engineering Sciences, University of Oxford, Oxford, UK; MRC Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK Correspondence: Timothy DenisonIntroduction: The field of bioelectronic medicine has moved quickly in the past years from fundamental research on rodents to first clinical studies, e.g., for treatment of rheumatic arthritis or hypertension. New applications are on the horizon but the transfer from fundamental research to clinical studies requires hardware suitable for large animal or human use, which is not commonly available today. Here, we describe a platform suitable for investigating new biomedical treatment paradigms in large animals and humans.Methods and Materials: The platform combines the Picostim ultracompact stimulator/recorder implant system by Bioinduction (Bristol, UK), the DyNeuMo research application developed in partnership between Bioinduction and Oxford, and the AirRay electrode technology developed by CorTec (Freiburg, Germany).Results: The Picostim implant is powered by a rechargeable battery and features 8 channels of electrical stimulation (up to 15mA), neural recording, and a 3-axis accelerometer. The implant is very compact at just 7cc and is programmed remotely using an external wireless controller. The implant allows smart adaptive therapy employing circadian, motion and neural signal feedback, which are combined and processed in real time on the implant.The nerve interface consists of a novel self-sizing spiral nerve cuff electrode with 8 contacts. Two of the contacts are ring shaped, arranged at the ends of the cuff. The remaining 6 contacts are dot-shaped and describe a segmented ring in the middle of the cuff. The cuff is 18mm in length and has an inner diameter of 2.5mm. It is made from laser-micromachined soft silicone (PMDS) and platinum iridium contacts. The cuffs are attached to multi-lumen polyurethane-based cables/connectors.Conclusions: Combined, the platform can be used to develop new and more precise treatments using recording and fascicle selective stimulation on the vagus nerve as well as other nerves. Currently, preclinical versions of the system are undergoing tests and validations, and clinical versions are planned. Here, we present the technical details of the system and its application.P11. Non-invasive 40Hz sensory stimulation as a potential novel therapeutic intervention for neurodegenerative diseasesMihály Hajós1,2, Aylin Cimenser1, Xia Da1, Alyssa Boasso1, Chandran V. Seshagiri1, Holly Mrozak1, Evan Hempel1, J. Thomas Megerian1,3, Brent Vaughan1, Zach Malchano1 1Cognito Therapeutics, Cambridge, MA, USA; 2Yale University School of Medicine, New Haven, CT, USA; 3Thompson Autism Center, CHOC Children’s, Orange, CA, USA Correspondence: Mihály HajósRecent experimental findings have shown that synchronized 40 Hz gamma oscillation of neuronal networks, generated by optogenetic or sensory (e.g., visual and/or auditory) stimulation, effectively reduce pathological hallmarks of Alzheimer’s disease (AD) in transgenic mice expressing AD-related human pathological genes (Adaikkan & Tsai, 2020). Daily one-hour exposure to 40Hz visual and auditory stimulation showed reductions in brain AD plaques, hyperphosphorylated tau, neurodegeneration and brain atrophy. Treatment also prevented synaptic loss and dysfunction, leading to improved learning abilities in transgenic mice. These results initiated the development and validation of non-invasive, 40Hz sensory stimulation as a potential therapeutic intervention for AD and potentially other neurodegenerative diseases. In a 6-month long phase I/II randomized, controlled, US-based multi-center clinical trial (Overture trial; NCT03556280) the feasibility, safety, tolerability, adherence rates and efficacy of gamma sensory stimulation were evaluated using Cognito Therapeutics Gamma Sensory Stimulation System in patients with clinical presentation of AD spectrum. Participants with Mini-Mental State Examination (MMSE) scores of 14-26, were randomized 2:1 to receive daily, one-hour, 40Hz noninvasive audio-visual stimulation or sham stimulation.A total of 135 subjects were screened, of whom 74 were randomized and 53 completed (20 sham arm, 33 active arm). Daily use of the Gamma Sensory Stimulation System was confirmed to be safe with minimal side effects. MRI data demonstrated absence of Amyloid-Related Imaging Abnormalities (ARIA) in all subjects. High adherence to daily therapy was established based on device-recorded usage. Among clinical instruments assessing cognitive and functional abilities, Alzheimer's Disease Cooperative Study - Activities of Daily Living (ADCS-ADL) and MMSE scores demonstrated the most effective outcomes of the therapy. Changes in ADCS-ADL scores were statistically significant between the sham and treatment arms (P<0.0003), indicating a significant slowing in functional decline by the treatment. Similarly, participants in the active arm showed a significantly reduced decline in MMSE scores compared to sham arm subjects (p<0.013). Nighttime active durations (assessed by actigraphy) were significantly (p<0.03) reduced in the treatment arm and the opposite change was observed in the sham arm. Quantitative MRI analysis revealed a significantly reduced whole brain (p<0.01), and occipital lobe (p<0.03) volume loss, and a significantly attenuated reduction in occipital cortical thickness (p<0.01) in the active arm relative to the sham arm participants. A separate MRI analysis revealed a significant (p<0.004) preservation of white matter in active treatment arm participants compared to ADNI1 controls.Our results demonstrate that long-term, daily 40Hz sensory stimulation is safe and well tolerated. Based on the treatment’s excellent safety profile, together with beneficial clinical outcome results observed in the Overture trial, pivotal clinical trials have been planned to support clinical efficacy of gamma sensory stimulation in AD. In addition, based on significant reduction in white matter loss and brain atrophy, effects of gamma sensory stimulation should be explored in other neurodegenerative diseases as well.P13. Evoked synaptic excitatory potentials (ESAPs): a novel electrophysiological biomarker for spinal cord stimulationMahima Sharma1, Vividha Bhaskar1, Lillian Yang1, Nigel Gebodh1, Tianhe Zhang2, Rosana Esteller2, John Martin1, Marom Bikson1 1Department of Biomedical Engineering, The City College of New York, NY, USA; 2Boston Scientific Neuromodulation, Valencia, California, USA Correspondence: Marom BiksonIntroduction: Spinal cord stimulation (SCS) produces varied responses evoked by epidural electrical stimulation. Evoked responses occurring within 2 ms of stimulation are the electrically evoked compound action potentials (ECAP) that measure the activity of dorsal column axons but not necessarily a spinal circuit response. We identify a separate electrophysiological signal that occur 2-3 ms after SCS that directly reflects synaptic activity in the spinal grey matter.Methods: Anesthetized female Sprague Dawley rats (250-280g) were implanted with epidural spinal cord stimulation (SCS) leads, epidural motor cortex stimulation electrodes, epidural recoding lead, and intra-spinal penetrating recording electrode arrays, as well as electromyography (EMG) electrodes. We stimulated motor cortex or the epidural spinal cord with a train of 20 pulses (200- 40 μs pulse width, 1 Hz) and simultaneously recorded responses from epidural and intraspinal electrodes.Results: Low frequency (1 Hz) SCS produces characteristic ECAP (composed of P1, N1, and P2 waves lasting <2 ms) as well as an additional S-wave starting after the N2 and lasting ~6 ms. The S-wave has a distinct dose response and spinal topography compared to the ECAPs. CNQX (a highly selective competitive antagonist of AMPA) blocked the S-wave and its intraspinal analog but not ECAPS. Given its distinct synaptic origin, we term S-wave response an Evoked Synaptic Excitatory Potential (ESAP). Increasing SCS frequency to 50 Hz dampened ESAPs but not ECAPs, suggesting habituation.Conclusions: We recorded a sparsely, if ever, characterized evoked spinal synaptic response (ESAPs) in addition to dorsal column ECAPs that may shed insight into SCS underlying mechanisms.P15. Focused ultrasound stimulation at the spleen does not produce hemodynamic changes and does not elicit antidromic compound action potentials in the splenic nerveStefanos Zafeiropoulos1,2, Naveen Jayaprakash1, Stavros Zanos1,2 1 Elmezzi Graduate School of Molecular Medicine at Northwell Health, 350 Community Drive, Manhasset, NY 11030 USA; 2 Institute for Bioelectronic Medicine, Feinstein Institutes for Medical Research at Northwell Health, 350 Community Drive, Manhasset, NY 11030 USA Correspondence: Stavros ZanosBackground: Focused ultrasound stimulation (FUS) of nerve terminals at the spleen has anti-inflammatory effects (Cotero, 2019) and, for that reason, it may have therapeutic value in various diseases (Zachs2019, Ahmed 2020). However, its mechanism of action is still unclear. Splenic nerve stimulation elicits compound action potentials (CAPs) in the splenic nerve and transiently increases systemic arterial blood pressure (Donega, 2021). It is unknown if splenic FUS produces hemodynamic effects or elicits antidromic CAPs in the splenic nerve.Methods: Healthy rats (n=4) were anesthetized and FUS of the spleen was applied for 12 minutes at 0.83 MPa. Before, during and after FUS delivery, we measured right ventricular pressure, systemic blood pressure, and heart rate. At the same timepoints, we recorded neural activity from the splenic nerve; an i.v. LPS injection (10 μg) was performed as positive control to validate splenic nerve recordings, as LPS is known to activate the splenic nerve (MacNeil, 1996).Results: Right ventricular systolic pressure remained stable over the time course of the experiment (pre-FUS: 31.38 ± 1.35 mmHg, during FUS: 31.39 ± 1.17, post-FUS: 31.35 ± 1.35). Similarly, mean arterial pressure (pre-FUS 88.10 ± 1.95 mmHg, during FUS: 86.35 ± 1.66, post-FUS: 86.42 ± 2.71) and heart rate (pre-FUS: 254.89 ± 10.65, during FUS: 255.66 ± 12.43, post-FUS: 254.71 ± 12.9) did not change significantly. The rate of spontaneous CAPs recorded from the splenic nerve did not change with FUS (baseline: 0.28 ± 0.25 spikes/s, during FUS: 0.25 ± 0.22; paired

SPARC: Current Steering To Selectively Recruit Nerves Of The Lower Urinary Tract

Lack of bladder control has a substantial impact on quality of life, with consequences ranging from sleep deprivation and embarrassment to bladder and kidney infection. Current methods to address lower urinary tract (LUT) dysfunction, including pharmacological interventions and catheterization, are insufficient to restore bladder control and may lead to rehospitalization, especially after spinal cord injury. Previously, we have used epidural spinal cord stimulation (SCS) to selectively recruit nerves innervating the LUT, a promising result that suggests this method of stimulation could be used to address LUT dysfunction. Epidural SCS has been in use clinically for pain relief for over 50 years, and is a minimally‐invasive way to access these neural pathways. However, current clinical leads have large electrodes that make it difficult to spatially limit the region targeted by SCS. Here, we use a high‐density epidural spinal cord electrode and multipolar stimulation patterns to reduce off‐target neural recruitment and refine the selective activation of LUT nerves.We placed a high‐density epidural spinal cord electrode (MicroLeads Inc) at three locations of the sacral spinal cord and cauda equina in cats under isoflurane anesthesia. To record antidromic compound action potentials evoked by SCS, we recorded from nerve cuffs (MicroLeads Inc) on the sciatic nerve, pelvic nerve, as well as the pudendal nerve and its branches. To measure muscle recruitment during stimulation, we recorded electromyogram (EMG) activity from the external urethral sphincter, external anal sphincter, pelvic floor and gluteus. Using catheters in the bladder and urethra, we measured pressure changes during stimulation. We stimulated on all electrodes of the spinal cord arrays individually, as well as in bipolar and tripolar sets of electrodes to determine the effect of current steering on LUT nerve recruitment.We were able to recruit LUT nerves with all configurations of stimulation electrodes. However, monopolar stimulation resulted in substantial selective recruitment of the off‐target sciatic nerve, representing 59% of selective responses at the most rostral sacral location, 72% at the more caudal sacral location, and 27% at the cauda equina. By using bipolar and tripolar stimulation across the same electrodes, we were able to steer current so that electrodes selective for the sciatic nerve with monopolar stimulation were selective for LUT responses. Additionally, recruitment thresholds of monopolar stimulation were typically lower, between 50–1000 μA, than those of multipolar stimulation, which ranged from 100–2800 μA. We were also able to change the EMG recruitment with changes in electrode configurations, allowing targeting of functionally‐relevant muscles.We were able to map the recruitment of LUT nerves and muscles across several levels of the spinal cord using both monopolar and multipolar stimulation. By using these stimuli to access LUT nerves and muscles, we hope to systematically modify function in the LUT, providing a potential route to treat LUT dysfunction.Support or Funding InformationNIH SPARC award 1OT2OD024908 and Craig H. Neilsen Foundation, award 476681

Effects of Combined Electrical Stimulation of the Dorsal Column and Dorsal Roots on Wide-Dynamic-Range Neuronal Activity in Nerve-Injured Rats.

Electrical stimulation at the dorsal column (DC) and dorsal root (DR) may inhibit spinal wide-dynamic-range (WDR) neuronal activity in nerve-injured rats. The objective of this study was to determine if applying electrical conditioning stimulation (CS) at both sites provides additive or synergistic benefits. By conducting in vivo extracellular recordings of WDR neurons in rats that had undergone L5 spinal nerve ligation, we tested whether combining 50 Hz CS at the two sites in either a concurrent (2.5 min) or alternate (5 min) pattern inhibits WDR neuronal activity better than CS at DC alone (5 min). The intensities of CS were determined by recording antidromic compound action potentials to graded stimulation at the DC and DR. We measured the current thresholds that resulted in the first detectable Aα/β waveform (Ab0) and the peak Aα/β waveform (Ab1) to select CS intensity at each site. The same number of electrical pulses and amount of current were delivered in different patterns to allow comparison. At a moderate intensity of 50% (Ab0 + Ab1), different patterns of CS all attenuated the C-component of WDR neurons in response to graded intracutaneous electrical stimuli (0.1-10 mA, 2 msec) and inhibited windup in response to repetitive noxious stimuli (0.5 Hz). However, the inhibitory effects did not differ significantly between different patterns. At the lower intensity (Ab0), no CS inhibited WDR neurons. These findings suggest that combined stimulation of DC and DR may not be superior to DC stimulation alone for inhibition of WDR neurons.

The optimal distance between two electrode tips during recording of compound nerve action potentials in the rat median nerve.

The distance between the two electrode tips can greatly influence the parameters used for recording compound nerve action potentials. To investigate the optimal parameters for these recordings in the rat median nerve, we dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spacings. Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part. When the distance between two stimulating electrode tips was increased, the threshold and supramaximal stimulating intensity of compound nerve action potentials were gradually decreased, but the amplitude was not changed significantly. When the distance between two recording electrode tips was increased, the amplitude was gradually increased, but the threshold and supramaximal stimulating intensity exhibited no significant change. Different distances between recording and stimulating sites did not produce significant effects on the aforementioned parameters. A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve. In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference (however also required a higher threshold and higher supramaximal stimulus), was found to be superior to the antidromic compound action potential.

Bipolar spinal cord stimulation attenuates mechanical hypersensitivity at an intensity that activates a small portion of A-fiber afferents in spinal nerve-injured rats

Spinal cord stimulation (SCS) is used clinically to treat neuropathic pain states, but the precise mechanism by which it attenuates neuropathic pain remains to be established. The profile of afferent fiber activation during SCS and how it may correlate with the efficacy of SCS-induced analgesia are unclear. After subjecting rats to an L5 spinal nerve ligation (SNL), we implanted a miniature quadripolar electrode similar to that used clinically. Our goal was to determine the population and number of afferent fibers retrogradely activated by SCS in SNL rats by recording the antidromic compound action potential (AP) at the sciatic nerve after examining the ability of bipolar epidural SCS to alleviate mechanical hypersensitivity in this model. Notably, we compared the profiles of afferent fiber activation to SCS between SNL rats that exhibited good SCS-induced analgesia (responders) and those that did not (nonresponders). Additionally, we examined how different contact configurations affect the motor threshold (MoT) and compound AP threshold. Results showed that three consecutive days of SCS treatment (50 Hz, 0.2 ms, 30 min, 80-90% of MoT), but not sham stimulation, gradually alleviated mechanical hypersensitivity in SNL rats. The MoT obtained in the animal behavioral study was significantly less than the Aα/β-threshold of the compound AP determined during electrophysiological recording, suggesting that SCS could attenuate mechanical hypersensitivity with a stimulus intensity that recruits only a small fraction of the A-fiber population in SNL rats. Although both the MoT and compound AP threshold were similar between responders and nonresponders, the size of the compound AP waveform at higher stimulation intensities was larger in the responders, indicating a more efficient activation of the dorsal column structure in responders.

Metabotropic glutamate receptor 1 activity generates persistent, N‐methyl‐d‐aspartate receptor‐dependent depression of hippocampal pyramidal cell excitability

Metabotropic glutamate receptors (mGluRs) are involved in many forms of neuronal plasticity. In the hippocampus, they have well-defined roles in long-lasting forms of both synaptic and intrinsic plasticity. Here, we describe a novel form of long-lasting intrinsic plasticity that we call (S)-3,5-dihydroxyphenylglycine (DHPG)-mediated long-term depression of excitability (DHPG-LDE), and which is generated following transient pharmacological activation of group I mGluRs. In extracellular recordings from hippocampal slices, DHPG-LDE was expressed as a long-lasting depression of antidromic compound action potentials (cAPs) in CA1 or CA3 cells following a 4-min exposure to the group I mGluR agonist (S)-DHPG. A similar phenomenon was also seen for orthodromic fibre volleys evoked in CA3 axons. In single-cell recordings from CA1 pyramids, DHPG-LDE was manifest as persistent failures in antidromic action potential generation. DHPG-LDE was blocked by (S)-(+)-a-amino-4-carboxy-2-methylbenzeneacetic acid (LY367385), an antagonist of mGluR1, but not 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), an mGluR5 inhibitor. Although insensitive to antagonists of alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate/kainate and gamma-aminobutyric acid(A) receptors, DHPG-LDE was blocked by antagonists of N-methyl-D-aspartate (NMDA) receptors. Similarly, in single-cell recordings, DHPG-mediated antidromic spike failures were eliminated by NMDA receptor antagonism. Long after (S)-DHPG washout, DHPG-LDE was reversed by mGluR1 antagonism. A 4-min application of (S)-DHPG also produced an NMDA receptor-dependent persistent depolarization of CA1 pyramidal cells. This depolarization was not solely responsible for DHPG-LDE, because a similar level of depolarization elicited by raising extracellular K(+) increased the amplitude of the cAP. DHPG-LDE did not involve HCN channels or protein synthesis, but was eliminated by blockers of protein kinase C or tyrosine phosphatases.

Role of primary afferents in spinal cord stimulation-induced vasodilation: characterization of fiber types

Selected patients with peripheral vascular disease can be treated with spinal cord stimulation (SCS) to improve blood flow in the limbs. However, the mechanisms producing these effects remain unclear. The present study was designed to investigate if SCS produces cutaneous vasodilation via antidromic activation of the unmyelinated C-fibers and/or the small myelinated fibers. SCS was applied to anesthetized rats with a ball electrode at the L2–L3 spinal level. In Protocol 1, effects of capsaicin were examined. Blood flow changes in the hindpaw induced by SCS were measured in the footpad with laser Doppler flowmeters. Topical application of capsaicin (1%) on the tibial nerve did not affect SCS-induced vasodilation at 30 and 60% of motor threshold (MT). However, the duration of vasodilation induced by SCS at 90% MT and at 10 times MT was significantly reduced after capsaicin application on the tibial nerve. In Protocol 2, antidromic compound action potentials (CAPs) of the tibial nerve were recorded in response to SCS. CAPs of the large and the small myelinated afferent fibers were observed in response to SCS at all intensities. However, even with SCS at ten times MT, CAPs of C-fibers could not be detected in the tibial nerve. In Protocol 3, antidromic CAPs of the dorsal root were measured in response to SCS. Antidromic CAPs of C-fibers in dorsal roots were evoked by SCS at ≥90% of MT. It is concluded that SCS-induced vasodilation at ≤60% of MT may be mediated via only the myelinated fibers, whereas vasodilation at ≥90% of MT may also involve antidromic activation of some unmyelinated C-fibers.

The effect of pulpward pressure on the response to 50% lidocaine (lignocaine) applied to exposed dentine in cats

The responses of intradental nerves can be blocked by 50% lidocaine applied to exposed, etched dentine. The aim here was to analyse electrophysiologically the contribution of pulpward pressure to the anaesthetic effect of lidocaine applied to exposed dentine. In 17 adult cats with intact lower canines, approximately 1 mm of the coronal tip of the canine was removed and the exposed dentine acid-etched. Pulpward pressure was applied to the exposed dentine through a chamber fixed to the tip of the tooth. Cervical and coronal electrodes of silver wire and Ag/AgCl mixture were placed, the cervical 2 mm from the gingival margin of the canine and the coronal into the coronal pulp chamber. The inferior alveolar nerve was surgically exposed and single pulpal nerve fibres responding to electrical stimulation of the canine were identified. The chamber was filled with 50% lidocaine solution, and 0 (atmospheric pressure), 1.3, 5.0 or 10.0 kPa pressure was applied to the chamber for 20 min. Orthodromic and antidromic action potentials were compared before and after the lidocaine application. When lidocaine was applied at 0, 1.3 or 5.0 kPa ( n=5 each) for 20 min, all the orthodromic responses to cathodal electrical stimulation with the coronal electrode were blocked. Almost all orthodromic responses (12/15) remained unblocked when the cathodal electrical stimulation was applied with the cervical electrode. Applying 10.0 kPa pressure to the lidocaine solution blocked all the pulpal nerve responses ( n=5) to both stimulation modes. The amplitude of the antidromic compound action potential was significantly decreased when the applied pressure was increased. These results suggest that increased pulpward pressure may effectively force anaesthetic solution more rapidly through the dentinal tubules into the pulp.

Respiratory activity in glossopharyngeal, vagus and accessory nerves and pharyngeal constrictors in newborn rat in vitro.

1. Previously, in a brainstem-spinal cord-rib preparation from neonatal rats we demonstrated that a decrement in extracellular pH (from about 7.4 to 7.1) caused expiratory activity in an internal intercostal muscle (IIM) during the first half of the expiratory phase (Ea). As the initial step in finding nerves or muscles firing during the second half of the expiratory phase (Eb), the patterns of activity in the glossopharyngeal, vagus and accessory nerves were examined in the present study. 2. Since the emerging motor rootlets of these three nerves (> 20; collected into about 10 bundles before the jugular foramen) are distributed in a continuous fashion from rostral to caudal levels of the brainstem, visual identification was impossible. Therefore, antidromic compound action potentials evoked by stimulation of the glossopharyngeal nerve (IX), the pharyngeal branch of the vagus nerve (PhX), the superior laryngeal nerve (SLN), the cervical vagus nerve (CX) and the accessory nerve (XI) were recorded from the peripheral stumps of the various rootlets. Nerve rootlets could be categorised into rostral, intermediate and caudal groups (rostIX-XI, intIX-XI, caudIX-XI). The rostIX-XI rootlets showed their largest potential on IX stimulation, while the intIX-XI and caudIX-XI rootlets showed their largest potentials on CX stimulation. The intIX-XI rootlets showed larger potentials on PhX and SLN stimulation than the caudIX-XI rootlets. 3. Activity was recorded simultaneously from the central stumps of the rootlets in the above three groups. Most rootlets showed inspiratory bursts. Under low pH conditions, all representatives of group rostIX-XI, most of intIX-XI and about half of caudIX-XI showed additional bursts during the Ea phase. Groups intIX-XI and caudIX-XI but not rostIX-XI also showed discrete bursts during the Eb phase in some preparations. In general, expiratory activity was prominent in intIX-XI. The spinal branch of XI showed no consistent respiratory activity. 4. Since the intIX-XI rootlets showed Eb bursts and large antidromic potentials on stimulation of PhX and SLN (which innervate the inferior pharyngeal constrictor muscle (IPC)), electromyograms were recorded from the rostral and caudal parts of IPC (rIPC and cIPC). Under low pH conditions, cIPC showed bursts during the Ea and Eb phases, while rIPC showed bursts predominantly during the Eb phase. 5. These results indicate that recording from rIPC would be a useful way of examining the neuronal mechanisms responsible for Eb phase activity.

Pulsed Nd:YAG laser irradiation of the tooth pulp in the cat: I. Effect of spot lasing.

The purpose of the present study was to evaluate physiologically pulpal nerve responses and to elucidate histopathologically the pulp tissue reactions to "spot irradiation" with a pulsed Nd:YAG laser. Antidromic compound action potentials and the pulpal blood flow (PBF) were recorded from the canine tooth of a sodium pentobarbitone-anesthetized cat. The laser irradiation-induced pulp tissue changes were histologically investigated. The coronal antidromic compound action potentials disappeared in all the teeth tested during lasing, and the time needed to erase them was significantly shortened with increases in lasing power (P < 0.05). The radicular PBF increased when spot irradiation was performed, and the coronal PBF also temporarily increased with low-powered lasing. Histologic investigation revealed that spot irradiation with the laser produced severe damage in the pulp tissue in a dose-dependent manner. The present study suggests that spot irradiation with a pulsed Nd:YAG laser risks producing nerve injury and irreversible tissue damage in the pulp with lasing for the purpose of desensitizing hypersensitive dentin.

A technique for estimating activity in whole nerve trunks applied to the cervical sympathetic trunk, in the rabbit

The changes in sympathetic outflow may be evaluated from the amplitude of the antidromic compound action potential (ACAP) according to the collision technique described by Douglas and Ritchie (Douglas, W.W. and Ritchie J.M., A technique for recording functional activity in specific groups of medullated and non-medullated fibers in whole nerve trunks. J. Physiol., 138 (1957) 19–30). This technique was revised, taking into account the depressant action exerted by antidromic stimulation on sympathetic preganglionic neurones (SPNs). Cervical sympathetic nerve (CSN) of rabbits was used as experimental model. Stimulation frequencies of 0.2–0.5 Hz were found to be sufficiently low to avoid depressant actions on CSN spontaneous activity; they were employed to test the sensitivity of the technique during different experimental manoeuvres, such as changes in pulmonary-ventilation, baroreceptor unloading and arousal stimuli. In addition a procedure was devised to calibrate the ACAP amplitude: high frequency antidromic stimulation was used to induce a complete and transient inhibition of SPNs which allows to record the ACAP maximum amplitude. ACAPs recorded in various experimental conditions can then be expressed as percentage of this value.

GABAergic modulation of axonal conduction in the developing rat retinotectal pathway

The effect of γ-aminobutyric acid (GABA) on nerve conduction was investigated in the developing rat optic nerves in vitro. Antidromic compound action potentials (CAP) were suppressed by GABA, with increasing attenuation in older preparations. Enhancement of CAP amplitude using bicuculline was observed in postnatal days 4–5 suggesting the presence of endogenous GABA activity. Our findings suggest that the role of electrical activity in the refinement of the retinotectal projection could be limited by the GABAergic action on axonal conduction.

The effect of H‐wave therapy upon conduction in the human superficial radial nerve in vivo

This study was designed to investigate the putative neurophysiological effects of so-called 'H-wave therapy' (HWT), a form of electrical stimulation, upon conduction latencies in the human superficial radial nerve. Antidromic compound action potentials were recorded from the superficial radial nerve in the dominant forearms of thirty-two healthy human volunteers, who were randomly assigned to a control or one. of three HWT groups (2, 16 or 60 Hz). HWT was applied under double-blind conditions for three consecutive 5 min periods. Action potentials were recorded pre-HWT and immediately after each period of stimulation, i.e. at 5, 10 and 15 min. Analysis of results showed significant increases in negative and positive peak latencies in the 16 Hz and, to a greater extent, in the 60 Hz groups when compared with controls. No changes in conduction latency were observed in the low frequency 2 Hz group. The results of this study demonstrate that HWT applied at frequencies of 16 and 60 Hz may produce a direct, localized effect upon conduction in underlying peripheral nerves.

Effects of osmotic pressure on intrathecal and epidural lidocaine anesthesia

Lidocaine (1%), either in plain distilled water or in 10% dextrose, was intrathecally or epidurally administered to urethane-chloralose anesthetized cats. Electrical stimulation was applied to the gracile tract at a cervical level, and the resultant antidromic compound action potentials were recorded from the sural nerve. Lidocaine dissolved in plain distilled water was more effective than lidocaine dissolved in 10% dextrose solution in suppressing the compound action potentials. Lidocaine-free plain distilled water or dextrose solution caused partial suppression of the compound action potentils. The suppression was more marked following plain distilled water application than following application of 5% or 10% dextrose.

The antidromic compound action potential of the auditory nerve.

1. The antidromic compound action potential (ACAP) of the auditory nerve was evoked by shocks to the auditory nerve root and recorded at the round window of the cochlea in anesthetized guinea pigs. The goal of this study was to determine the characteristics of the ACAP and compare these characteristics with those of the orthodromic, sound-evoked compound action potential (CAP). 2. The ACAP consists of an initial complex of a positive peak (p1) followed by a negative peak (n1). In contrast, the CAP consists of a negative peak (N1) followed by a positive peak (P1). These differences in waveform are likely due to the differences in conduction direction, antidromic for the ACAP vs. orthodromic for the CAP. 3. After the initial complex, the ACAP has a second complex of peaks (p2, n2) at a latency of approximately 1 ms; this complex is much smaller in amplitude than the initial complex (p1, n1). It is likely that the initial ACAP complex reflects firing of auditory-nerve fibers whereas the second complex reflects firing of neurons further centrally, perhaps in the cochlear nucleus, that are activated by orthodromic firing of auditory-nerve fibers. 4. Experiments with shock pairs are consistent with the idea that for auditory nerve fibers, the absolute refractory period is < 0.5 ms, and the relative refractory period is between 0.5 and at least 5 ms. 5. Experiments with click-shock pairs indicate that a shock interferes with the response to a click when the click and shock are given at about the same time.(ABSTRACT TRUNCATED AT 250 WORDS)

Tooth Pulp Deafferentation Is Not Associated with Changes in Primary Afferent Depolarization of Facial Afferent Endings in the Brain Stem

Previous studies have demonstrated that tooth pulp deafferentation is associated with statistically significant alterations in the low-threshold facial mechanoreceptive field properties of brain stem neurons in trigeminal (V) subnucleus oralis. A loss of spinal afferent-induced presynaptic inhibition as a consequence of a decrease in primary afferent depolarization (PAD) following spinal nerve deafferentation has been invoked as a mechanism underlying deafferentation-induced somatosensory neuroplasticity. Therefore, this study was initiated to determine if these pulp deafferentation-induced neuroplastic changes could be accounted for by an alteration in PAD of low-threshold facial afferent endings in subnucleus oralis of anesthetized rats. In control (unoperated) rats ( n = 7) and rats ( n = 7) that had undergone mandibular pulp deafferentation 6-10 days previously, antidromic compound action potentials evoked by test stimulation in V subnucleus oralis were recorded in branches of the infraorbital (IO) and supraorbital (SO) nerves, and conditioning stimuli were applied to some of the same nerves. PAD of the afferent endings in oralis of these nerve branches was documented in all animals, and there was no significant difference between the two groups in the incidence or any of the other features of PAD. The features of the PAD were consistent with those described in several previous studies of normal animals. These findings indicate that the reported deafferentation-induced loss of spinal presynaptic regulatory mechanisms cannot be entrapolated to all forms of deafferentation injury and that the mechanoreceptive field changes that can occur in central V somatosensory neurons as a result of tooth pulp deafferentation may not reflect an alteration in PAD.

Electrophysiological study of dorsal column function in streptozocin-induced diabetic rats: comparison with 2,5-hexanedione intoxication

Dorsal column function and peripheral motor and sensory conduction velocities (MCV, SCV) were evaluated in experimental diabetic rats and compared with those in 2,5-hexanedione (2,5-HD) intoxicated rats. Hyperglycemia was induced by a single injection of streptozocin, and electrophysiological studies were performed 4 and 12 weeks after the injection. For 8 weeks 2,5-HD was administered daily by drinking water to make the 2,5-HD neuropathy rats. Age-matched rats were used as control. In diabetic rats, gracile surface potentials evoked by electrical stimulation of the lumbosacral trunk remained normal during the experimental period, whereas the N and P waves of the evoked potentials were suppressed and the duration of the N wave was prolonged in the 2,5-HD rats. In 4-week diabetic rats, the antidromic compound action potentials of the gracile tract recorded at the most proximal site of lumbosacral trunk were normal. In 12-week diabetic rats, the gracile tract conduction velocity (GTCV) was decreased, although the duration of these potentials was normal. By contrast, the GTCV was decreased and the duration was markedly prolonged in 2,5-HD rats. These findings might indicate that temporal dispersion of incoming volleys in the gracile tract is increased in 2,5-HD rats, but not in diabetic rats. These results suggest that diabetic myelopathy exists that but the magnitude and progression of this condition are quite different from those of 2,5-HD intoxication, typical dying-back-type neuropathy and that the dorsal column is less vulnerable than the peripheral nerve in diabetes mellitus.

Peripheral Vasodilatation after Spinal Cord Stimulation: Animal Studies of Putative Effector Mechanisms

Spinal cord stimulation has been reported to relieve ischemic pain and to enhance peripheral circulation. To elucidate the still unknown mechanisms behind these effects, changes in the peripheral blood flow in the skin of the hind paw after stimulation applied to the dorsal column was studied in the normal rat. A substantial flow increase, monitored by laser Doppler technique, was observed in response to stimulation with an intensity comparable to that used clinically in man, recruiting only low-threshold neuronal elements. The response remained after transection of the dorsal roots, as well as after spinal cord section rostrally to the stimulating electrode. Furthermore, monitoring of antidromic compound action potentials in a peripheral nerve indicated that the stimulus intensity applied to dorsal columns recruited solely low-threshold, large-diameter fibers. Stimulation failed to produce an increase in blood flow in addition to that produced by guanethidine and hexamethonium, but high-intensity dorsal column or dorsal root stimulation still was effective. The results indicate that spinal mechanisms are essential and that antidromic activation of primary afferent fibers is unlikely to account for the peripheral vasodilatation induced by low-intensity spinal cord stimulation. Our observations suggest a transitory inhibition of sympathetic vasoconstriction as the principal underlying mechanism.

Enkephalins, substance P, bradykinin and angiotensin II: Differential sites of action on the hypothalamo-neurohypophysial system

To test the hypothesis that enkephalins, substance P, bradykinin and angiotensin II could act as neurohumoral modulators of hypothalamic function, these peptides (0.01-20 microgram) were injected into the general circulation of anesthetized rats, and changes in hypothalamo-neurohypophysial activity were determined by continuously monitoring the amplitude of antidromic compound action potentials (CAP) in the hypothalamo-hypophysial tract. A decrease of CAP amplitude was taken to indicate an increase of orthodromic impulse traffic. All peptides elicited a CAP decrease. On a molar basis when injected i.v., the enkephalin analog FK 33-824 was the most effective substance, followed by substance P, Leu-enkephalin and angiotensin II. Enkephalins and substance P injected through the internal carotid artery, were 2-5 times more effective than when injected i.v., whereas bradykinin was most effective when it reached the brain through a vertebral route. Angiotensin II produced the same CAP decrease irrespective of the route of administration and, in contradistinction to the other peptides, its effect was not abolished by stalk section. Tachyphylaxis and reversibility with naloxone was observed only for the enkephalins. The data suggest that sites of action are the hypothalamus for enkephalins and substance P, the neurohypophysis for angiotensin II, and the hindbrain for bradykinin.

Osmosensitivity of the hepatic portal vein area and vasopressin release in rats.

1. The role of intraperitoneal osmoreceptors in hypothalamo-neurohypophyseal control was studied in urethane- or nembutal-anaesthetized rats. Plasma samples were taken for radioimmunoassay of arginine vasopressin, and the electrical activity of single supraoptic endocrine neurones and of the hypothalamo-neurohypophyseal tract were monitored during superfusion of the hepatic portal vein with hypo-, iso- and hypertonic solutions. 2. Plasma arginine vasopressin increased within 1 min following superfusion with 0.3-0.9 osmolal NaCl solutions in a dose-related manner from basal levels of 30 pg/ml, to 170 pg/ml. Prior superfusion with xylocaine or intravenous infusions of 800 micrograms atropine-methyl bromate abolished this response, although vasopressin was still released to nicotine in atropine-blocked rats. 3. Portal vein superfusions had no significant effects on arterial blood pressure, plasma osmolality and plasma Na concentrations. 4. Forty supraoptic neurones were antidromically activated from the neural lobe/stalk region. Superfusions of the portal vein with NaCl solutions (0.33-1.20 osmole/kg, 37 degrees C, 5-120 sec) stimulated seven out of eight phasically firing and eight out of twenty-four continuously firing neurones. One phasically active, ten continuously firing and four silent cells were not affected, and six continuously firing neurones were inhibited by the superfusions. 5. The amplitude decreases of antidromic compound action potentials in the hypothalamo-neurohypophyseal tract, reflecting an increase of the orthodromic nerve impulse traffic, ranged from 17 to 22% for superfusions with 1.2 osmolal NaCl or LiCl solutions, from 8 to 11% for 1.2 osmolal Na isethionate or choline Cl and from 3 to 9% for 1.2 osmolal glucose; there was no effect when 1.2 osmolal urea and isotonic or hypotonic NaCl solutions were applied. 6. Responses of the amplitude of compound action potentials to superfusions with 1.2 osmolal NaCl solutions or with 0.1 mumole ACh, but not to electrical stimulation of the portal vein or its superfusion with 1.2 osmolal KCl, were abolished by prior application of 0.3 mumole atropine sulphate. Prior superfusions with xylocaine abolished the responses to all stimuli above. 7. These results suggest that within the hepatic portal vein area there are osmosensitive receptor cells and/or nerve terminals which activate the hypothalamoneurohypophyseal system through a peripheral cholinergic mechanism.