Compound Action Potential Recordings Research Articles

Multifunctional Nanomesh Enables Cellular-Resolution, Elastic Neuroelectronics.

Silicone-based devices have the potential to achieve an ideal interface with nervous tissue but suffer from scalability, primarily due to the mechanical mismatch between established electronic materials and soft elastomer substrates. This study presents a novel approach using conventional electrode materials through multifunctional nanomesh to achieve reliable elastic microelectrodes directly on polydimethylsiloxane (PDMS) silicone with an unprecedented cellular resolution. This engineered nanomesh features an in-plane nanoscale mesh pattern, physically embodied by a stack of three thin-film materials by design, namely Parylene-C for mechanical buffering, gold (Au) for electrical conduction, and Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) for improved electrochemical interfacing. Nanomesh elastic neuroelectronics are validated using single-unit recording from the small and curvilinear epidural surface of mouse dorsal root ganglia (DRG) with device self-conformed and superior recording quality compared to plastic control devices requiring manual pressing is demonstrated. Electrode scaling studies from in vivo epidural recording further revealed the need for cellular resolution for high-fidelity recording of single-unit activities and compound action potentials. In addition to creating a minimally invasive device to effectively interface with DRG sensory afferents at a single-cell resolution, this study establishes nanomeshing as a practical pathway to leverage traditional electrode materials for a new class of elastic neuroelectronics.

Nerve Preparation and Recordings for Pharmacological Tests of Sensory and Nociceptive Fiber Conduction Ex Vivo.

Measuring signal propagation through nerves is a classical electrophysiological technique established decades ago to evaluate sensory and motor functions in the nervous system. The whole-nerve preparation provides a valuable model to investigate nerve function ex vivo; however, it requires specific knowledge to ensure successful and stable measurements. Although the methodology for sciatic nerve recordings has long existed, a method for reliable and long-lasting recordings from myelinated and non-myelinated (nociceptive) fibers still needs to be adapted for pharmacological testing. This protocol takes benefits from epineurium sheath removal for pharmacological tests and provides a detailed description of how to make accurate nerve preparations, from the dissection and handling of nerves to epineurium cleaning, fabrication of adaptable suction electrodes for appropriate fiber stimulation and recordings, setting of electrophysiological protocols for compound action potential (CAP) recordings to distinguish between myelinated and non-myelinated (nociceptive) fibers, and finally to the analysis of the datasets of CAP components. We also demonstrate the feasibility of CAP recordings from individual branches in epineurium-free nerve preparations and provide clues to help retain nerve viability and maintain stable recordings over time. Although a sciatic nerve preparation was used here, the methodology can be applied to other nerve-type preparations. Key features • Detailed and simplified protocol for peripheral nerve preparation for recording sensory inputs ex vivo. • Recordings from myelinated and non-myelinated (nociceptive) fibers can be performed hours after nerve preparation. • The protocol involves the epineurium removal to facilitate drug permeability into nerve tissue for pharmacological tests. • The protocol allows physiological and pathological studies (pain/chronic pain conditions).

Protective vs. Therapeutic Effects of Mitochondria-Targeted Antioxidant MitoTEMPO on Rat Sciatic Nerve Crush Injury: A Comprehensive Electrophysiological Analysis.

Protective vs. Therapeutic Effects of Mitochondria-Targeted Antioxidant MitoTEMPO on Rat Sciatic Nerve Crush Injury: A Comprehensive Electrophysiological Analysis. Peripheral nerve injuries often result in long-lasting functional deficits, prompting the need for effective interventions. MitoTEMPO (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride) is a mitochondria-targeted antioxidant that has shown protective and therapeutic effects against pathologies associated with reactive oxygen species. This study explores the utilization of MitoTEMPO as a therapeutic and protective agent for sciatic nerve crush injuries. By employing advanced mathematical approaches, the study seeks to comprehensively analyze nerve conduction parameters, nerve excitability, and the distribution of nerve conduction velocities to gauge the potential. Forty Wistar-Albino rats were randomly divided into following groups: (I) SHAM-animals subjected to sham operation and treated intraperitoneally (i.p.) with vehicle (bidistilled water) for 14 days; (II) CI (crush injury)-animals subjected to CI and treated with vehicle 14 days; (III) MiP-animals subjected to 7 days i.p. MitoTEMPO treatment before CI (0.7 mg/kg/day dissolved in vehicle) and, only vehicle for 7 days after CI, protective MitoTEMPO; and (IV) MiT-animals i.p. treated with only vehicle for 7 days before CI and 7 days with MitoTEMPO (0.7 mg/kg/day dissolved in vehicle) after CI, therapeutic MitoTEMPO. Nerve excitability parameters were measured, including rheobase and chronaxie, along with compound action potential (CAP) recordings. Advanced mathematical analyses were applied to CAP recordings to determine nerve conduction velocities and distribution patterns. The study revealed significant differences in nerve excitability parameters between groups. Nerve conduction velocity was notably reduced in the MiP and CI groups, whereas CAP area values were diminished in the MiP and CI groups compared to the MiT group. Furthermore, CAP velocity was lower in the MiP and CI groups, and maximum depolarization values were markedly lower in the MiP and CI groups compared to the SHAM group. The distribution of nerve conduction velocities indicated alterations in the composition of nerve fiber groups following crush injuries. In conclusion, postoperative MitoTEMPO administration demonstrated promising results in mitigating the detrimental effects of nerve crush injuries.

Motor Activity-Induced White Matter Repair in White Matter Stroke.

Subcortical white matter stroke (WMS) is a progressive disorder which is demarcated by the formation of small ischemic lesions along white matter tracts in the CNS. As lesions accumulate, patients begin to experience severe motor and cognitive decline. Despite its high rate of incidence in the human population, our understanding of the cause and outcome of WMS is extremely limited. As such, viable therapies for WMS remain to be seen. This study characterizes myelin recovery following stroke and motor learning-based rehabilitation in a mouse model of subcortical WMS. Following WMS, a transient increase in differentiating oligodendrocytes occurs within the peri-infarct in young male adult mice, which is completely abolished in male aged mice. Compound action potential recording demonstrates a decrease in conduction velocity of myelinated axons at the peri-infarct. Animals were then tested on one of three distinct motor learning-based rehabilitation strategies (skilled reach, restricted access to a complex running wheel, and unrestricted access to a complex running wheel) for their capacity to induce repair. These studies determined that unrestricted access to a complex running wheel alone increases the density of differentiating oligodendrocytes in infarcted white matter in young adult male mice, which is abolished in aged male mice. Unrestricted access to a complex running wheel was also able to enhance conduction velocity of myelinated axons at the peri-infarct to a speed comparable to naive controls suggesting functional recovery. However, there was no evidence of motor rehabilitation-induced remyelination or myelin protection.SIGNIFICANCE STATEMENT White matter stroke is a common disease with no medical therapy. A form of motor rehabilitation improves some aspects of white matter repair and recovery.

The efficacy of a TrkB monoclonal antibody agonist in preserving the auditory nerve in deafened guinea pigs

The auditory nerve typically degenerates following loss of cochlear hair cells or synapses. In the case of hair cell loss neural degeneration hinders restoration of hearing through a cochlear implant, and in the case of synaptopathy suprathreshold hearing is affected, potentially degrading speech perception in noise. It has been established that neurotrophins such as brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) can mitigate auditory nerve degeneration. Several potential BDNF mimetics have also been investigated for neurotrophic effects in the cochlea. A recent in vitro study showed favorable effects of M3, a TrkB monoclonal antibody agonist, when compared with BDNF. In the present study we set out to examine the effect of M3 on auditory nerve preservation in vivo. Thirty-one guinea pigs were bilaterally deafened, and unilaterally treated with a single 3-µl dose of 7 mg/ml, 0.7 mg/ml M3 or vehicle-only by means of a small gelatin sponge two weeks later. During the experiment and analyses the experimenters were blinded to the three treatment groups. Four weeks after treatment, we assessed the treatment effect (1) histologically, by quantifying survival of SGCs and their peripheral processes (PPs); and (2) electrophysiologically, with two different paradigms of electrically evoked compound action potential (eCAP) recordings shown to be indicative of neural health: single-pulse stimulation with varying inter-phase gap (IPG), and pulse-train stimulation with varying inter-pulse interval. We observed a consistent and significant preservative effect of M3 on SGC survival in the lower basal turn (approximately 40% more survival than in the untreated contralateral cochlea), but also in the upper middle and lower apical turn of the cochlea. This effect was similar for the two treatment groups. Survival of PPs showed a trend similar to that of the SGCs, but was only significantly higher for the highest dose of M3. The protective effect of M3 on SGCs was not reflected in any of the eCAP measures: no statistically significant differences were observed between groups in IPG effect nor between the M3 treatment groups and the control group using the pulse-train stimulation paradigm. In short, while a clear effect of M3 was observed on SGC survival, this was not clearly translated into functional preservation.

Modulation of auditory processing by non-auditory brain areas: Effects of acoustic trauma

Acoustic trauma (AT) induced hearing loss elicits plasticity in the form of altered spontaneous firing throughout the central auditory pathway, including at the level of the medial geniculate nucleus (MGN). Non-auditory areas such as the prefrontal cortex (PFC) and amygdala are thought to modulate auditory processing in the MGN, which may play a role in sensory gating. In our laboratory, we investigated the functionality of inputs from the PFC and amygdala on MGN activity in different animal models (rat and guinea pig) both without and with AT. The effects of AT on auditory thresholds were investigated using auditory brainstem response (ABR) recordings or compound action potential recordings of the auditory nerve. To test circuitry functionality, we used single neuron recordings in the MGN combined with electrical stimulation of the PFC or amygdala. Our data showed, first, that electrical stimulation of either the PFC or amygdala resulted in a variety of effects within the MGN (facilitation, inhibition, or no effect) and, second, that AT and subsequent hearing loss significantly increased the magnitude of inhibition. This change in inhibition may represent a compensatory mechanism in response to the increased spontaneous activity in the central auditory pathway known to occur following hearing loss.

Evoked compound action potentials during spinal cord stimulation: effects of posture and pulse width on signal features and neural activation within the spinal cord

Objective. Evoked compound action potential (ECAP) recordings have emerged as a quantitative measure of the neural response during spinal cord stimulation (SCS) to treat pain. However, utilization of ECAP recordings to optimize stimulation efficacy requires an understanding of the factors influencing these recordings and their relationship to the underlying neural activation. Approach. We acquired a library of ECAP recordings from 56 patients over a wide assortment of postures and stimulation parameters, and then processed these signals to quantify several aspects of these recordings (e.g., ECAP threshold (ET), amplitude, latency, growth rate). We compared our experimental findings against a computational model that examined the effect of variable distances between the spinal cord and the SCS electrodes. Main results. Postural shifts strongly influenced the experimental ECAP recordings, with a 65.7% lower ET and 178.5% higher growth rate when supine versus seated. The computational model exhibited similar trends, with a 71.9% lower ET and 231.5% higher growth rate for a 2.0 mm cerebrospinal fluid (CSF) layer (representing a supine posture) versus a 4.4 mm CSF layer (representing a prone posture). Furthermore, the computational model demonstrated that constant ECAP amplitudes may not equate to a constant degree of neural activation. Significance. These results demonstrate large variability across all ECAP metrics and the inability of a constant ECAP amplitude to provide constant neural activation. These results are critical to improve the delivery, efficacy, and robustness of clinical SCS technologies utilizing these ECAP recordings to provide closed-loop stimulation.

ID: 214352 Microdissection of the Swine Spinal Cord to Reveal Lumbar and Thoracic Rootlets

Spinal cord epidural stimulation (SCS) is a safe and effective therapy of chronic pain. The most common complication for SCS is lead migration, resulting in inefficient stimulation. In addition, the shunting of current or activation of the dorsal rootlets may result in contraction of back muscles, via activation of motor fibers recruited at lower stimulation amplitudes. Activation of these rootlets could cause electromyography (EMG) bleed-through into the evoked compound action potential (ECAPs) recordings, as well as cause side effect during SCS therapy. In some cases, motor activation may limit the range of stimulation to levels below what is required for pain therapy.

Auditory nerve responses to combined optogenetic and electrical stimulation in chronically deaf mice

Objective. Optogenetic stimulation of the auditory nerve offers the ability to overcome the limitations of cochlear implants through spatially precise stimulation, but cannot achieve the temporal precision nor temporal fidelity required for good hearing outcomes. Auditory midbrain recordings have indicated a combined (hybrid) stimulation approach may permit improvements in the temporal precision without sacrificing spatial precision by facilitating electrical activation thresholds. However, previous research has been conducted in undeafened or acutely deafened animal models, and the impact of chronic deafness remains unclear. Our study aims to compare the temporal precision of auditory nerve responses to optogenetic, electrical, and combined stimulation in acutely and chronically deafened animals. Methods. We directly compare the temporal fidelity (measured as percentage of elicited responses) and precision (i.e. stability of response size and timing) of electrical, optogenetic, and hybrid stimulation (varying sub-threshold or supra-threshold optogenetic power levels combined with electrical stimuli) through compound action potential and single-unit recordings of the auditory nerve in transgenic mice expressing the opsin ChR2-H134R in auditory neurons. Recordings were conducted immediately or 2–3 weeks following aminoglycoside deafening when there was evidence of auditory nerve degeneration. Main results. Results showed that responses to electrical stimulation had significantly greater temporal precision than optogenetic stimulation (p < 0.001 for measures of response size and timing). This temporal precision could be maintained with hybrid stimulation, but only when the optogenetic stimulation power used was below or near activation threshold and worsened with increasing optical power. Chronically deafened mice showed poorer facilitation of electrical activation thresholds with concurrent optogenetic stimulation than acutely deafened mice. Additionally, responses in chronically deafened mice showed poorer temporal fidelity, but improved temporal precision to optogenetic and hybrid stimulation compared to acutely deafened mice. Significance. These findings show that the improvement to temporal fidelity and temporal precision provided by a hybrid stimulation paradigm can also be achieved in chronically deafened animals, albeit at higher levels of concurrent optogenetic stimulation levels.

Combined brain-derived neurotrophic factor and neurotrophin-3 treatment is preferred over either one separately in the preservation of the auditory nerve in deafened guinea pigs.

Severe hearing loss or deafness is often caused by cochlear hair cell loss and can be mitigated by a cochlear implant (CI). CIs target the auditory nerve, consisting of spiral ganglion cells (SGCs), which degenerate gradually, following hair cell loss. In animal models, it has been established that treatment with the neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) reduce SGC degeneration. In this study, we aimed to investigate whether treatment with both BDNF and NT-3 (Cocktail) is superior to treatment with each neurotrophin separately regarding cell preservation and neural responsiveness to electrical stimulation. To this end, deafened guinea pigs received neurotrophic treatment in their right ear via a gelatin sponge on the perforated round window membrane, followed by cochlear implantation 4 weeks later in the same ear for electrophysiological recordings to various stimulation paradigms. Normal-hearing and deafened untreated guinea pigs were included as positive and negative controls, respectively. Substantial SGC loss occurred in all deafened animals. Each of the neurotrophic treatments led to enhanced SGC survival mainly in the basal turn of the cochlea, gradually decreasing toward the apex. The Cocktail treatment resulted in the highest SGC survival in the treated ear, followed by BDNF, with the least protection of SGCs following NT-3 treatment. Survival of the SGC’s peripheral processes (PPs) followed the same trend in response to the treatment. However, survival of SGCs and PPs in the contralateral untreated ears was also highest in the Cocktail group. Consequently, analysis of the ratio between the treated and untreated ears showed that the BDNF group, which showed low SGC survival in the untreated ear, had the highest relative SGC survival of the three neurotrophin-treated groups. Neurotrophic treatment had positive effects in part of the electrically evoked compound action-potential recording paradigms. These effects were only observed for the BDNF or Cocktail treatment. We conclude that treatment with either BDNF or a cocktail of BDNF and NT-3 is preferred to NT-3 alone. Furthermore, since the Cocktail treatment resulted in better electrophysiological responsiveness and overall higher SGC survival than BDNF alone, we are inclined to recommend the Cocktail treatment rather than BDNF alone.

Periventricular leukomalaci (PVL) is critically dependent upon the presence of extracellular ions (Ca2+ and Na+)

This work is clarifying the role of extracellular ions in PVL in neonates. Ischaemic injury of adult brainwas critically dependent upon the presence of extracellular Ca²+ as revealed by a range of studies (Styset al., 1992). Along with they found that two extracellular ions were essential for the development ofpermanent loss of function during ischaemia in adult brain: Ca²⁺ and Na⁺. The dependence of ischaemicinjury in adult upon both Ca²⁺ and Na⁺ indicates that these ions are potentially toxic to cell viability bycausing permanent loss to axonal function. Therefore, the effects of these two ions during 90 minoxygen-glucose deprivation (OGD), (the practical model of ischaemia) in neonatal brain wereinvestigated using electrophysiology techniques for compound action potential (CAP) recording. Thisproduced the interesting finding that removal of either Ca²⁺ or Na⁺ from the extracellular spaceprotected the neonatal brain from ischaemic injury during OGD. When Ca²⁺ or Na⁺ were removed fromthe extracellular space during 90 min OGD, the CAP declined at the end of OGD. Afterward, the CAPrecovered following restoration of normal conditions. The results of this study indicated that,extracellular Ca²⁺ and Na⁺ are essential for the development of permanent loss of function during OGDin neonatal brain.

ID:16038 Closed-Loop SCS: EVOKE RCT Long-Term & Secondary Outcomes at 12 Months

Evoked compound action potential (ECAP) recording provides an objective measure of dorsal column activation during spinal cord stimulation (SCS) and can assist in the programing of the SCS system. When using the ECAP in a closed-loop SCS (CL-SCS), the stimulation output is automatically adjusted to maintain a desired ECAP amplitude (i.e. consistent level of dorsal column activation). The efficacy of CL-SCS has been shown first in the Australian AVALON open-label study (ACTRN12615000713594) followed by the US EVOKE double-blinded RCT (NCT02924129).

Impact of Atorvastatin on Skeletal Muscle Mitochondrial Activity, Locomotion and Axonal Excitability-Evidence from ApoE-/- Mice.

The cardiovascular benefit of statins is well established. However, only 20% of high-risk patients remain adequately adherent after 5 years of treatment. Among reasons for discontinuation, statin associated-muscle pain symptoms are the most prevalent. Aim of the present study was to evaluate the impact of high dose atorvastatin on skeletal muscle mitochondrial activity, aerobic and anaerobic exercise, and axonal excitability in a murine model of atherosclerosis. ApoE-/- mice were fed 12 weeks a high-fat high-cholesterol diet alone or containing atorvastatin (40 mg/Kg/day). Outcomes were the evaluation of muscle mitochondrial functionality, locomotion, grip test, and axonal excitability (compound action potential recording analysis of Aα motor propioceptive, Aβ mechanoceptive and C nociceptive fibres). Atorvastatin led to a reduction in muscle mitochondrial biogenesis and mitochondrial ATP production. It did not affect muscular strength but led to a time-dependent motor impairment. Atorvastatin altered the responsiveness of mechanoceptive and nociceptive fibres, respectively, the Aβ and C fibres. These findings point out to a mild sensitization on mechanical, tactile and pain sensitivity. In conclusion, although the prevalence of muscular side effects from statins may be overestimated, understanding of the underlying mechanisms can help improve the therapeutic approach and reassure adherence in patients needing-to-be-treated.

122 ECAP-Controlled Closed-Loop Spinal Cord Stimulation (CL SCS): Double-Blind, Randomized Trial for the Treatment of Chronic Pain – 24-Month Outcomes

INTRODUCTION: Evoked compound action potential (ECAP) recording provides an objective measure of spinal cord (SC) activation during SCS and can assist in programing of the SCS system. ECAP-controlled CL SCS, in which the stimulation output is automatically adjusted to maintain a desired ECAP amplitude, has been shown to provide effective pain relief in an open-label study (ACTRN12615000713594). METHODS: 134 subjects were enrolled and randomized after trial leads were implanted. The primary endpoint evaluated =50% reduction in overall back and leg pain measured by the Visual Analog Scale (VAS). Opioid usage and other patient-reported outcomes (PROs) including emotional/physical functioning, sleep quality, and quality of life were also collected. Additionally, objective neurophysiological data, including SC activation and time spent in the therapeutic range, were collected. RESULTS: Herein the Evoke Study Group reports the 24-month outcomes from this ongoing RCT. The proportion of implanted subjects with =50% overall back and leg pain reduction at 24 months was statistically superior in the CL vs. OL group (84.0% vs. 65.9% subjects, respectively; p = 0.040). Long-term improvements in all other PROs, including POMS, ODI, PSQI, EQ-5D-5L, and SF-12, were also demonstrated. Opioids were reduced or eliminated in 66.7% (CL) and 60.9% (OL), respectively. The most frequent level of SC activation was three times greater for CL (median ECAP Amplitude: 22.5 µV CL vs. 7.5 µV OL). SC activation was better maintained within the therapeutic range with CL (median: 93.9% CL vs. 46.1% OL). There were no differences in the safety profiles between treatment groups, and the type, nature, and severity of adverse events were similar to other SCS studies. CONCLUSION: In this ongoing study, ECAP-controlled CL SCS provided statistically superior pain relief and greater improvement in other PROs compared with OL SCS at 24 months. CL delivered greater levels of SC activation and better maintained SC activation in the subject’s therapeutic range.

A Prospective Multicenter Case Series Utilizing Intraoperative Neuromonitoring With Evoked Compound Action Potentials to Confirm Spinal Cord Stimulation Lead Placement

ObjectivesThe use of intraoperative neuromonitoring (IONM) has been adapted to address issues of safety and proper lead positioning in spinal cord stimulation. This multicenter case series seeks to incorporate the use of evoked compound action potential (ECAP) and late response (LR) recording and compare it with the results obtained with IONM, specifically electromyography (EMG), for the confirmation of lead placement. This study aimed to establish a correlation between ECAPs, LR, and EMG and publish human recordings of ECAPs and LR during their use with IONM. Materials and MethodsStandard neuromonitoring protocols were followed at two institutions, with two separate physicians and with seven patients, as part of a larger ongoing study registered with ClinicalTrials.gov (NCT02924129). Stimulation and recording were performed, top and bottom, on each percutaneous lead. Stimulation amplitude was increased considering ECAP, LR, and EMG thresholds. ResultsECAPs, LRs, and EMG signals were observed in all patients. The onset of LR signals on implanted electrodes and EMG signal on subdermal electrodes was well correlated (rs = 0.94, p < 0.001), with a median LR:EMG value of 1.06 (N = 21). LR:EMG for the top (mean = 0.97, N = 8) vs bottom (mean = 1.15, N = 13) of the lead was compared using a paired Wilcoxon signed rank test and an independent samples Mann-Whitney test, revealing a marginally significant and a statistically significant difference (p = 0.078 and p = 0.015, respectively). Mean LR:ECAP was >2 in all locations and approximately 3.5 overall. LR:ECAP between the top and bottom of the lead was significantly different (Wilcoxon test, p < 0.01, N = 12). ConclusionsLR correlated with EMG; leads with bilateral (not necessarily symmetric) EMG activity showed LR:ECAP > 1.5. An LR:ECAP of <1, with LR/EMG generated before the ECAP, indicated that the lead is too lateral. The use of ECAP and LR has the potential of maintaining objective lead placement, without the need for needle placement with IONM.

Postoperative pain facilitates rat C-fibre activity-dependent slowing and induces thermal hypersensitivity in a sex-dependent manner

BackgroundPostoperative pain is a common clinical problem that, in preclinical studies, has almost exclusively been studied in males. Altered C-fibre activity-dependent slowing (ADS) is a potential underlying mechanism, given it is altered after tissue inflammation and nerve injury, but this has not been explored post-incision. We therefore investigated the effect of hind-paw incision on C-fibre ADS in both sexes and the involvement of voltage-gated sodium channels (NaV) as they contribute to ADS. We also assessed mechanical and thermal sensitivity post-incision in both sexes. MethodsDorsal roots were isolated from hind-paw incision (2–4 days post-surgery) or naive (control) juvenile rats of both sexes. Compound action potential recordings were made to assess C-fibre ADS in response to ×40 stimuli at 2 and 10 Hz and repeated in the presence of 20 nM tetrodotoxin/vehicle. Data were quantified by the normalised change in latency (negative peak) and width (positive-to-positive peak) of the triphasic C-fibre response. Hind-paw mechanical withdrawal thresholds and thermal withdrawal latencies were measured pre- and post-incision. ResultsIncision facilitates C-fibre ADS in both sexes, with more pronounced facilitation in females. Tetrodotoxin induces sex- and injury-dependent changes in C-fibre ADS that were distinct between latency and width measures. Hind-paw incision induced comparable mechanical hypersensitivity in both sexes but less peak heat hypersensitivity in females. ConclusionsHind-paw incision induces sex-dependent changes in C-fibre activity-dependent slowing, which likely contribute to the observed sex difference in peak thermal hypersensitivity. This may reflect sex- and incision-induced differences in functional expression of NaV channels that differs by C-fibre subtype.

Microglial depletion abolishes ischemic preconditioning in white matter.

Ischemic preconditioning (IPC) is a phenomenon whereby a brief, non-injurious ischemic exposure enhances tolerance to a subsequent ischemic challenge. The mechanism of IPC has mainly been studied in rodent stroke models where gray matter (GM) constitutes about 85% of the cerebrum. In humans, white matter (WM) is 50% of cerebral volume and is a critical component of stroke damage. We developed a novel CNS WM IPC model using the mouse optic nerve (MON) and identified the involved immune signaling pathways. Here we tested the hypothesis that microglia are necessary for WM IPC. Microglia were depleted by treatment with the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX5622. MONs were exposed to transient ischemia in vivo, acutely isolated 72 h later, and subjected to oxygen-glucose deprivation (OGD) to simulate a severe ischemic injury (i.e., stroke). Functional and structural axonal recovery was assessed by recording compound action potentials (CAPs) and by microscopy using quantitative stereology. Microglia depletion eliminated IPC-mediated protection. In control mice, CAP recovery was improved in preconditioned MONs compared with non-preconditioned MONs, however, in PLX5622-treated mice, we observed no difference in CAP recovery between preconditioned and non-preconditioned MONs. Microgliadepletion also abolished IPC protective effects on axonal integrity and survival of mature (APC+ ) oligodendrocytes after OGD. IPC-mediated protection was independent of retinal injury suggesting it results from mechanistic processes intrinsic to ischemia-exposed WM. We conclude that preconditioned microglia are critical for IPC in WM. The "preconditioned microglia" phenotype might protect against other CNS pathologies and is a neurotherapeutic horizon worth exploring.

Computational modelling of nerve stimulation and recording with peripheral visceral neural interfaces

Objective. Neuromodulation of visceral nerves is being intensively studied for treating a wide range of conditions, but effective translation requires increasing the efficacy and predictability of neural interface performance. Here we use computational models of rat visceral nerve to predict how neuroanatomical variability could affect both electrical stimulation and recording with an experimental planar neural interface. Approach. We developed a hybrid computational pipeline, Visceral Nerve Ensemble Recording and Stimulation (ViNERS), to couple finite-element modelling of extracellular electrical fields with biophysical simulations of individual axons. Anatomical properties of fascicles and axons in rat pelvic and vagus nerves were measured or obtained from public datasets. To validate ViNERS, we simulated pelvic nerve stimulation and recording with an experimental four-electrode planar array. Main results. Axon diameters measured from pelvic nerve were used to model a population of myelinated and unmyelinated axons and simulate recordings of electrically evoked single-unit field potentials (SUFPs). Across visceral nerve fascicles of increasing size, our simulations predicted an increase in stimulation threshold and a decrease in SUFP amplitude. Simulated threshold changes were dominated by changes in perineurium thickness, which correlates with fascicle diameter. We also demonstrated that ViNERS could simulate recordings of electrically-evoked compound action potentials (ECAPs) that were qualitatively similar to pelvic nerve recording made with the array used for simulation. Significance. We introduce ViNERS as a new open-source computational tool for modelling large-scale stimulation and recording from visceral nerves. ViNERS predicts how neuroanatomical variation in rat pelvic nerve affects stimulation and recording with an experimental planar electrode array. We show ViNERS can simulate ECAPS that capture features of our recordings, but our results suggest the underlying NEURON models need to be further refined and specifically adapted to accurately simulate visceral nerve axons.

In Vivo Whole-Nerve Electrophysiology Setup, Action Potential Recording, and Data Analyses in a Rodent Model.

In vivo rodent, whole peripheral nerve models are useful for studying the electrical conduction of sensory and motor fibers under normal physiological conditions as well as for assessing neurological outcomes after the application of physical alterations or pharmacological agents to the nervous system. Significant literature has focused on single-neuron and central nervous system electrophysiology protocol development. However, creation and development of in vivo whole-nerve electrophysiological recording protocols are sparse in the scientific literature. Here, detailed protocols for designing and building an in vivo whole-nerve electrophysiology system are described, including straightforward techniques to create working stimulation and recording electrodes that may be adapted to numerous study designs. Further, we include details for rodent anesthesia, surgical dissection (for the sciatic nerve), compound action potential signal optimization, data acquisition, data analyses, and troubleshooting tips. © 2021 Wiley Periodicals LLC. Basic Protocol 1: In vivo electrophysiology system wiring, hardware, and software setups Support Protocol 1: Design and 3D printing of electrophysiology base electrodes Support Protocol 2: Building needle electrodes Basic Protocol 2: Rodent anesthesia and surgery for nerve exposure Basic Protocol 3: Compound action potential recording and troubleshooting using WinWCP Basic Protocol 4: Compound action potential data analysis using WinWCP.

Improved post-stroke spontaneous recovery by astrocytic extracellular vesicles

Spontaneous recovery after a stroke accounts for a significant part of the neurological recovery in patients. However limited, the spontaneous recovery is mechanistically driven by axonal restorative processes for which several molecular cues have been previously described. We report the acceleration of spontaneous recovery in a preclinical model of ischemia/reperfusion in rats via a single intracerebroventricular administration of extracellular vesicles released from primary cortical astrocytes. We used magnetic resonance imagingand confocal and multiphoton microscopy to correlate the structural remodeling of the corpus callosum and striatocortical circuits with neurological performance during 21days. We also evaluated the functionality of the corpus callosum by repetitive recordings of compound action potentials to show that the recovery facilitated by astrocytic extracellular vesicles was both anatomical and functional. Our data provide compelling evidence that astrocytes can hasten the basal recovery that naturally occurs post-stroke through the release of cellular mediators contained in extracellular vesicles.