Stimulation Of Fibers Research Articles

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).

Active Neural Interface Circuits and Systems for Selective Control of Peripheral Nerves: A Review.

Interfaces with peripheral nerves have been widely developed to enable bioelectronic control of neural activity. Peripheral nerve neuromodulation shows great potential in addressing motor dysfunctions, neurological disorders, and psychiatric conditions. The integration of high-density neural electrodes with stimulation and recording circuits poses a challenge in the design of neural interfaces. Recent advances in active electrode strategies have achieved improved reliability and performance by implementing in-situ control, stimulation, and recording of neural fibers. This paper presents an overview of state-of-the-art neural interface systems that comprise a range of neural electrodes, neurostimulators, and bio-amplifier circuits, with a special focus on interfaces for the peripheral nerves. A discussion on the efficacy of active electrode systems and recommendations for future directions conclude this paper.

Association of connexin36 with adherens junctions at mixed synapses and distinguishing electrophysiological features of those at mossy fiber terminals in rat ventral hippocampus.

Granule cells in the hippocampus project axons to hippocampal CA3 pyramidal cells where they form large mossy fiber terminals. We have reported that these terminals contain the gap junction protein connexin36 (Cx36) specifically in the stratum lucidum of rat ventral hippocampus, thus creating morphologically mixed synapses that have the potential for dual chemical/electrical transmission. Here, we used various approaches to characterize molecular and electrophysiological relationships between the Cx36-containing gap junctions at mossy fiber terminals and their postsynaptic elements and to examine molecular relationships at mixed synapses in the brainstem. In rat and human ventral hippocampus, many of these terminals, identified by their selective expression of vesicular zinc transporter-3 (ZnT3), displayed multiple, immunofluorescent Cx36-puncta representing gap junctions, which were absent at mossy fiber terminals in the dorsal hippocampus. In rat, these were found in close proximity to the protein constituents of adherens junctions (i.e., N-cadherin and nectin-1) that are structural hallmarks of mossy fiber terminals, linking these terminals to the dendritic shafts of CA3 pyramidal cells, thus indicating the loci of gap junctions at these contacts. Cx36-puncta were also associated with adherens junctions at mixed synapses in the brainstem, supporting emerging views of the structural organization of the adherens junction-neuronal gap junction complex. Electrophysiologically induced long-term potentiation (LTP) of field responses evoked by mossy fiber stimulation was greater in the ventral than dorsal hippocampus. The electrical component of transmission at mossy fiber terminals may contribute to enhanced LTP responses in the ventral hippocampus.

Effects of tail nerve electrical stimulation on the activation and plasticity of the lumbar locomotor circuits and the prevention of skeletal muscle atrophy after spinal cord transection in rats.

Severe spinal cord injury results in the loss of neurons in the relatively intact spinal cord below the injury area and skeletal muscle atrophy in the paralyzed limbs. These pathological processes are significant obstacles for motor function reconstruction. We performed tail nerve electrical stimulation (TNES) to activate the motor neural circuits below the injury site of the spinal cord to elucidate the regulatory mechanisms of the excitatory afferent neurons in promoting the reconstruction of locomotor function. Eight days after T10 spinal cord transection in rats, TNES was performed for 7 weeks. Behavioral scores were assessed weekly. Electrophysiological tests and double retrograde tracings were performed at week 8. After 7 weeks of TNES treatment, there was restoration in innervation, the number of stem cells, and mitochondrial metabolism in the rats' hindlimb muscles. Double retrograde tracings of the tail nerve and sciatic nerve further confirmed the presence of synaptic connections between the tail nerve and central pattern generator (CPG) neurons in the lumbar spinal cord, as well as motor neurons innervating the hindlimb muscles. The mechanisms of TNES induced by the stimulation of primary afferent nerve fibers involves efficient activation of the motor neural circuits in the lumbosacral segment, alterations of synaptic plasticity, and the improvement of muscle and nerve regeneration, which provides the structural and functional foundation for the future use of cutting-edge biological treatment strategies to restore voluntary movement of paralyzed hindlimbs.

Recovery kinetics of short-term depression of GABAergic and glutamatergic synapses at layer 2/3 pyramidal cells in the mouse barrel cortex.

Short-term synaptic plasticity (STP) is a widespread mechanism underlying activity-dependent modifications of cortical networks. To investigate how STP influences excitatory and inhibitory synapses in layer 2/3 of mouse barrel cortex, we combined whole-cell patch-clamp recordings from visually identified pyramidal neurons (PyrN) and parvalbumin-positive interneurons (PV-IN) of cortical layer 2/3 in acute slices with electrical stimulation of afferent fibers in layer 4 and optogenetic activation of PV-IN. These experiments revealed that electrical burst stimulation (10 pulses at 10 Hz) of layer 4 afferents to layer 2/3 neurons induced comparable short-term depression (STD) of glutamatergic postsynaptic currents (PSCs) in PyrN and in PV-IN, while disynaptic GABAergic PSCs in PyrN showed a stronger depression. Burst-induced depression of glutamatergic PSCs decayed within <4 s, while the decay of GABAergic PSCs required >11 s. Optogenetically-induced GABAergic PSCs in PyrN also demonstrated STD after burst stimulation, with a decay of >11 s. Excitatory postsynaptic potentials (EPSPs) in PyrN were unaffected after electrical burst stimulation, while a selective optogenetic STD of GABAergic synapses caused a transient increase of electrically evoked EPSPs in PyrN. In summary, these results demonstrate substantial short-term plasticity at all synapses investigated and suggest that the prominent STD observed in GABAergic synapses can moderate the functional efficacy of glutamatergic STD after repetitive synaptic stimulations. This mechanism may contribute to a reliable information flow toward the integrative layer 2/3 for complex time-varying sensory stimuli.

Combining Celiac and Hepatic Vagus Nerve Neuromodulation Reverses Glucose Intolerance and Improves Glycemic Control in Pre- and Overt-Type 2 Diabetes Mellitus.

Neurological disorders and type 2 diabetes mellitus (T2DM) are deeply intertwined. For example, autonomic neuropathy contributes to the development of T2DM and continued unmanaged T2DM causes further progression of nerve damage. Increasing glycemic control has been shown to prevent the onset and progression of diabetic autonomic neuropathies. Neuromodulation consisting of combined stimulation of celiac vagal fibers innervating the pancreas with concurrent electrical blockade of neuronal hepatic vagal fibers innervating the liver has been shown to increase glycemic control in animal models of T2DM. The present study demonstrated that the neuromodulation reversed glucose intolerance in alloxan-treated swine in both pre- and overt stages of T2DM. This was demonstrated by improved performance on oral glucose tolerance tests (OGTTs), as assessed by area under the curve (AUC). In prediabetic swine (fasting plasma glucose (FPG) range: 101-119 mg/dL) the median AUC decreased from 31.9 AUs (IQR = 28.6, 35.5) to 15.9 AUs (IQR = 15.1, 18.3) p = 0.004. In diabetic swine (FPG range: 133-207 mg/dL) the median AUC decreased from 54.2 AUs (IQR = 41.5, 56.6) to 16.0 AUs (IQR = 15.4, 21.5) p = 0.003. This neuromodulation technique may offer a new treatment for T2DM and reverse glycemic dysregulation at multiple states of T2DM involved in diabetic neuropathy including at its development and during progression.

Decoupling the effects of varying amplitude and frequency in the electrical stimulation of optic nerve fibers

Abstract Introduction. Computational models of optic nerve stimulation can allow to estimate the neural response of optic nerve fibers electrical stimulation and thus can be exploited to tune stimulation parameters to obtain a specific target perception. In principle, such tuning should be performed in an automatic way, so that the chosen stimulation parameters minimize some given cost function related to the quality of resulting the visual perception, but the use of such automatic methods is still under study and no satisfactory solution is available yet. In the absence of automatic methods, stimulation parameters are customarily set via manual tuning, which can be extremely time-consuming if performed in a non-principled way. Methods. We build biophysically-accurate hybrid models of monopolar and bipolar electrical stimulation of optic nerve fibers to study how the fibers firing rates depend upon the stimulation parameters. Results. In the case of monopolar sinusoidal stimulation of optic nerve fibers, we show that the amplitude of stimulation controls the size of the recruited cluster of fibers, and that the frequency controls their firing rate, independently. Instead, for bipolar stimulation, we show that when cross-talk is non negligible it is very difficult to obtain rules of thumb linking the firing rate of target fibers to stimulation parameters. Conclusion. We show that, if the stimulation amplitude is kept such that neighboring stimulating sites do not produce cross-talk, it is possible to reconstruct visual scenes “pixel-by-pixel” without needing any optimization process. If on the contrary current steering is required and cross-talk is non negligible, then it is very difficult to obtain rules of thumb and the development and use of automatic optimization techniques should be preferable.

Muscarinic Receptor Stimulation Does Not Inhibit Voltage-dependent Ca2+ Channels in Rat Adrenal Medullary Chromaffin Cells.

Adrenal medullary chromaffin (AMC) and sympathetic ganglion cells are derived from the neural crest and show a similar developmental path. Thus, these two cell types have many common properties in membrane excitability and signaling. However, AMC cells function as endocrine cells while sympathetic ganglion cells are neurons. In rat sympathetic ganglion cells, muscarinic M1 and M4 receptors mediate excitation and inhibition via suppression of M-type K+ channels and suppression of voltage-dependent Ca2+ channels, respectively. On the other hand, M1 receptor stimulation in rat AMC cells also produces excitation by suppressing TWIK-related acid sensitive K+ (TASK) channels. However, whether M4 receptors are coupled with voltage-dependent Ca2+ channel suppression is unclear. We explore this issue electrophysiologically and biochemically. Electrical stimulation of nerve fibers in rat adrenal glands trans-synaptically increased the Ca2+ signal in AMC cells. This electrically evoked increased Ca2+ signal was not altered during muscarine-induced increase in Ca2+ signal, whereas it decreased significantly during a GABA-induced increase, due to a shunt effect of increased Cl- conductance. The whole-cell current recordings revealed that voltage-dependent Ca2+ currents in AMC cells were suppressed by adenosine triphosphate, but not by muscarinic agonists. The fractionation analysis and immunocytochemistry indicated that CaV1.2 Ca2+ channels and M4 receptors are located in the raft and non-raft membrane domains, respectively. We concluded that muscarinic stimulation in rat AMC cells does not produce voltage-dependent Ca2+ channel inhibition. This lack of muscarinic inhibition is at least partly due to physical separation of voltage-dependent Ca2+ channels and M4 receptors in the plasma membrane.

Effects of anesthetics on nociceptive sensory evoked potentials by intraepidermal noxious electrical stimulation of A-δ fibers.

Generation of nociceptive sensory evoked potentials (NEPs) by selective stimulation of nociceptive intraepidermal nerve fibers is a simple technique which could be used as intraoperative nociception monitor. We evaluated the effects of remifentanil, propofol and sevoflurane on NEPs by this technique. Patients undergoing general anesthesia were assigned to groups in two studies. A-δ fiber selective NEPs were recorded. Study 1: NEPs were recorded at control, under anesthetics administration: remifentanil at an effect-site concentration (Ce) of 1.0ng/mL (n = 10), propofol at Ce of 0.5µg/mL (n = 10), or sevoflurane at 0.2 minimum alveolar concentration (MAC) (n = 10), and recovery from the anesthetics. Study 2: NEPs were recorded at control and under administration of higher dose anesthetics: propofol at Ce of 0.5 and 1.0µg/mL (n = 10) or sevoflurane at 0.2 and 0.5 MAC (n = 10). A P-value < 0.016 was considered statistically significant in multiple analyses. Study 1: Remifentanil at Ce of 1.0ng/mL significantly suppressed the amplitude of NEPs (mean amplitude (standard deviation) of control vs. remifentanil administration: 16.8µV (3.8) vs. 10.1µV (2.5), P < 0.001). Propofol and sevoflurane did not suppress the amplitude significantly. Study 2: Propofol at Ce of 0.5 and 1.0µg/mL and sevoflurane at 0.2 and 0.5 MAC did not suppress the amplitude significantly. The amplitude of A-δ fiber selective NEPs was suppressed by remifentanil but not propofol or sevoflurane. NEPs with intraepidermal electrical stimulation can assess the analgesic effect of anesthetics. UMIN000038214 REGISTRY URL: https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000043328.

Investigating the electrode-electrolyte interface modelling in cochlear implants

Objective. Proposing a good electrode-electrolyte interface (EEI) model and properly identifying relevant parameters may help designing safer and more optimized auditory nerve fiber stimulation and recording in cochlear implants (CI). However, in literature, EEI model parameter values exhibit large variability. We aim to explain some root causes of this variability using the Cole model and its simpler form, the Basic RC model. Approach. We use temporal and spectral methods and fit the models to stimulation pulse voltage response (SPVR) and electrochemical impedance spectroscopy (EIS) data. Main Results. Temporal fittings show that there are multiple sets of model parameters that provide a good fit to the SPVR data. Therefore, small methodological differences in literature may result in different model fits. While these models share similar characteristics at high frequencies >500 Hz, the SPVR fitting is blind to low frequencies, thus it cannot correctly estimate the Faradaic resistor. Similarly, the polarization capacitor and its fractional order are not estimated robustly (capacitor variations in the nano- to micro-farad range) due to limited observation of mid-range frequencies. EIS provides a good model fit down to ∼3Hz, and thus robust estimation for the polarization capacitor. At lower frequencies charge mechanisms may modify the EEI, requiring multi-compartment Cole model fitting to EIS to improve the estimation of Faradaic characteristics. Our EIS data measurements down to 0.05Hz show that a two-compartment Cole model is sufficient to explain the data. Significance. Our study describes the scope and limitation of SPVR and EIS fitting methods, by which literature variability is explained among CI EEI models. The estimation of mid-to-low-frequency characteristics of the CI EEI is not in the scope of the SPVR method. EIS provides a better fit; however, its results should not be extrapolated to unobserved frequencies where new charge transfer mechanisms may emerge at the EEI.

Evaluation of the Efficacy and Results of Intraoperative Nerve Conduction in Nerve Reconstruction of the Hand

Nerve reconstruction in the hand is a critical aspect of hand surgery, aiming to restore sensory and motor function and improve overall hand functionality. Intraoperative nerve conduction, a neurophysiological technique, plays a pivotal role in nerve reconstruction surgeries. This literature review evaluates the efficacy and results of intraoperative nerve conduction in hand nerve reconstruction. Theoretical Framework: Intraoperative nerve conduction involves electrical stimulation of nerve fibers and the recording of nerve conduction responses in real-time during surgery. The technique aids in nerve identification, assessment, and surgical decision-making. Discussion: Intraoperative nerve conduction has shown efficacy in guiding surgical interventions and predicting postoperative outcomes. It has been particularly useful in complex nerve injuries, providing valuable feedback for optimal surgical planning. Challenges: Despite its benefits, intraoperative nerve conduction has limitations, such as timing issues and the need for skilled neurophysiologists and specialized equipment. Future Implications: Standardizing protocols and conducting larger prospective studies can enhance its reliability and identify specific scenarios where intraoperative nerve conduction provides the greatest benefit. Conclusion: Intraoperative nerve conduction is a valuable tool in hand nerve reconstruction, contributing to improved patient outcomes and the advancement of hand surgery. Continued research and technological advancements hold promise for its further optimization and wider applicability in the field.

ID: 208947 Ultrashort Microscopic Magnetic Vagal Stimulation

Electrical stimulation of the cervical vagus nerve is an emerging treatment field for various central nervous system disorders. Invasive electrical Vagus nerve stimulation (VNS) is an FDA-approved add-on treatment to medication for refractory partial-onset seizures in patients 12 years of age and older. However, only approximately 40-50% of patients experience a marked seizure reduction of 50% or more than seizures before treatment [1]. The effects of VNS on neurotransmitter systems, including the noradrenergic system originating from the locus coeruleus and the serotonergic system from the dorsal raphe nucleus, have been reported in experimental settings. The therapeutic effect of VNS in the brain is linked to the stimulation of large diameter afferent fibers. These large myelinated afferent fibers, terminating in the nucleus tractus solitarius in the brainstem, are assumed to deliver the therapeutic effect through further projections into the other brain areas. Non-selective stimulation results in inadvertent activation of efferent fibers that innervate a wide range of peripheral organs resulting in adverse effects [2] with a rare but severe risk of bradyarrhythmia and asystole.

Tonotopic fitting of the sound processor cochlear implant in normal cochlea anatomy

Introduction. Cochlear implantation is very effective due to the known tonotopic organization of the cochlea. These data are used in the distribution of signals along the channels of the cochlear implant electrode. The more accurate and natural the stimulation of the auditory nerve fibers, the better the perception of speech, sounds and speech intelligibility.The aim of the study was to compare the clinical and anatomical settings of the cochlear implant processor.Materials and methods. The study included 63 patients aged 2 to 60 years using cochlear implantation system, implants with a standard long electrode array (31.5 mm). All participants underwent computed tomography (CT) of the temporal bones with a step of 0.6 mm or less. CT data were processed using Otoplan and Sliser 3D software. The geometric dimensions of the cochlea, the length of the cochlear canal, the angular position and tonotopic frequency of each electrode were calculated, and a 3D reconstruction of the cochlea and electrode was built.Results. The correction of the frequency filters of the electrodes and the anatomical adjustment of the processor were performed according to the data obtained in the Otoplan program. A comparison was made between the clinical and anatomical setting. After the redistribution of frequency filters, patients noted a more natural sound, improved speech intelligibility. Thus, with anatomical adjustment, an exact correspondence is achieved between the central frequency of each electrode channel and the tonotopic frequency of the cochlear zone, individually determined by computed tomography.Conclusions. A new tool has appeared that allows you to significantly improve the quality and provide an individual approach to setting up processors after cochlear implantation.

Rapid, activity-dependent co-release of GABA and glycine in the mouse brainstem

Presympathetic neurons in the ventrolateral and ventromedial medulla (VLM/VMM) control the sympathetic tone, and GABA was identified as a primary mechanism for sympathoinhibition. Intriguingly, there is evidence that both GABA and glycine efficiently inhibit sympathetic tone; however, the mechanism of glycine release is unknown. In this study, we tested the hypothesis that GABA and glycine are co-released in the VLM/VMM. Glycine is recycled by glycine transporter 2 (GlyT2), which is a reliable marker of glycinergic neurons. Therefore, we crossed heterozygous GlyT2Cre mice with floxed channelrhodopsin 2 (ChR2-EYFP) mice to generate GlyT2 reporter mice (GlyT2ChR2/EYFP), which were used to determine the mechanism of glycine release and reveal the location of glycinergic neurons. Whole-cell patch-clamp recordings from presympathetic VLM/VMM neurons revealed that GABA mediates most spontaneous inhibitory postsynaptic currents (sIPSCs); whereas increased activity of inhibitory inputs promotes the release of glycine. Light stimulation of glycinergic fibers expressing ChR2 in GlyT2ChR2/EYFP mice evoked IPSCs (eIPSCs) with glycinergic and GABAergic components. Bath application of GABAA receptors antagonist (bicuculline, 10 μM) decreased the amplitude of eIPSCs, suggesting that approximately 70% of the eIPSCs are generated by glycine. Moreover, blockade of GlyT2 partially diminished the glycinergic component of the light-evoked IPSCs. Using GlyT2ChR2/EYFP mice, we found that glycinergic fibers are abundant throughout the rostral brainstem, and GlyT2-expressing neurons were distributed within the ventral gigantocellular nucleus and medial reticular formation. Immunofluorescence labeling of glycine receptor subunits in the VLM/VMM revealed the expression of two prevalent forms of glycine receptors formed by α1 and α3. In summary, we found that GABA and glycine are co-released in the VLM/VMM, and blockage of GlyT2 decreased the amplitude of light-evoked IPSCs, suggesting that GABA and glycine are likely located in separate vesicles. Our data provide evidence for the co-inhibition of presympathetic neurons in the VLM/VMM by GABA and glycine and suggest that GABA controls the threshold excitability, while glycine is released on demand to increase the strength of inhibition. Supported by: NIDDK122842 and Tulane Brain Institute Marko Spark Innovation Research Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The NEB-P2ry1 lung-brainstem axis and the control of breathing in a mouse model of bronchopulmonary dysplasia

Breathing control problems, like apnea of prematurity, are a common complication in preterm infants with bronchopulmonary dysplasia (BPD), but the underlying factors remain incompletely understood. A subpopulation of pulmonary vagal afferent nerve fibers (P2ry1+) innervate CO2 and O2 sensitive clusters of lung neuroendocrine cells (neuroepithelial bodies (NEBs)) located along conducting airways. P2ry1 fibers provide direct sensory input to the brainstem and inhibit breathing upon stimulation. NEBs are hyperplastic in BPD infants and may increase activity of inhibitory P2ry1 vagal fibers. Herein, we sought to determine if the NEB-P2ry1 lung-brainstem axis is altered in association with breathing control in BPD. BPD in mice was induced by exposure to chronic neonatal (postnatal day (P) 0-14) hyperoxia (Hx; 70% O2; n=20) or normoxia (Nx; n=17). Consistent with human BPD, Hx caused alveolar simplification supported by a reduction in alveolar density (p&lt;0.05) and alveoli (p&lt;0.05) in P22 H&amp;E-stained lung sections. Hx mice spent more time apneic at P14 and P17 (p&lt;0.05) in room air and acute hypoxia. Overall (main effect), room air minute ventilation (VE) was reduced in HX mice (p&lt;0.05). Further, VE was reduced during acute hypoxia at P14 and P17 (not P21) with an overall reduction of breathing in Hx mice (p&lt;0.05). From a subset of mice (n=4-5/group) VCO2, VO2, and heat production at rest were greater in P21 Hx mice during room air, suggesting the Hx mice were hypoventilating. Immunofluorescent staining of CGRP (hallmark NEB marker), Ki67 (proliferation), and SEZ6L2 (new NEB cell-membrane marker) in Hx and Nx lungs were imaged and analyzed by a blinded investigator. Consistent with clinical findings, Hx mice had hyperplastic NEBs (8.6 ± 0.45 vs 10.7 ± 1.3 cells/NEB; p&lt;0.05) while only 2 of 143 NEBs expressed Ki67, suggesting no proliferation at P22. CGRP co-localized with SEZ6L2 in both Nx and Hx lungs. A subset of mice received intratracheal delivery of 1ug SEZ6L2-Saporin toxin to lesion NEBs and assess their function. 4 days after SEZ-Saporin treatment breathing frequency was elevated by 11% ± 5% in room air and by 7% ± 5% during acute hypoxia but not in PBS-treated, adult mice (n=3/group) suggesting NEBs have a mild inhibitory influence under normal conditions. Lastly, wireless optogenetic stimulation of P2ry1 vagal fibers in unanesthetized adult control mice (n=3) increased room air breathing by 20% ± 1% and drive to breathe by 36% ± 19% compared to pre-stim breathing. Together, our data demonstrate that hyperoxia-induced BPD alters the control of breathing which may in part be mediated via a unique lung-brainstem axis comprised of hyperplastic NEBs causing greater inhibition of excitatory P2ry1 vagal fibers. The NEB-P2ry1 axis may serve as a novel target for improving breathing in BPD. GCM: Advancing Healthier Wisconsin REAC Award, AHA 20CDA35310121; MRH: HL122358; JLG: DK133121, HL134850, and HL084207; JLS: DK133121 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Stimulation of non-motor subthalamic nucleus impairs selective response inhibition via prefrontal connectivity.

Given the inconsistent results in the past, there is an ongoing debate whether and how deep brain stimulation in the subthalamic nucleus modifies cognitive control processes like response inhibition in persons with Parkinson's disease. In this study, we examined how the location of the stimulation volume within the subthalamic nucleus affects the performance in an antisaccade task but also how its structural connectivity is related to response inhibition. Antisaccade error rates and latencies were collected in 14 participants on and off deep brain stimulation in a randomized order. Stimulation volumes were computed based on patient-specific lead localizations using preoperative MRI and postoperative CT scans. Structural connectivity of the stimulation volumes with pre-defined cortical oculomotor control regions as well as whole-brain connectivity was estimated using a normative connectome. We showed that the detrimental effect of deep brain stimulation on response inhibition, measured as antisaccade error rate, depended upon the magnitude of the intersection of volumes of activated tissue with the non-motor subregion of the subthalamic nucleus and on its structural connectivity with regions of the prefrontal oculomotor network including bilateral frontal eye fields and right anterior cingulate cortex. Our results corroborate previous recommendations for avoidance of stimulation in the ventromedial non-motor subregion of the subthalamic nucleus which connects to the prefrontal cortex to prevent stimulation-induced impulsivity. Furthermore, antisaccades were initiated faster with deep brain stimulation when the stimulation volume was connected to fibres passing the subthalamic nucleus laterally and projecting onto the prefrontal cortex, indicating that improvement of voluntary saccade generation with deep brain stimulation may be an off-target effect driven by stimulation of corticotectal fibres directly projecting from the frontal and supplementary eye fields onto brainstem gaze control areas. Taken together, these findings could help implement individualized circuit-based deep brain stimulation strategies that avoid impulsive side effects while improving voluntary oculomotor control.

Imaging Voltage Globally and in Isofrequency Lamina in Slices of Mouse Ventral Cochlear Nucleus.

The cochlear nuclei (CNs) receive sensory information from the ear and perform fundamental computations before relaying this information to higher processing centers. These computations are performed by distinct types of neurons interconnected in circuits dedicated to the specialized roles of the auditory system. In the present study, we explored the use of voltage imaging to investigate CN circuitry. We tested two approaches based on fundamentally different voltage sensing technologies. Using a voltage-sensitive dye we recorded glutamate receptor-independent signals arising predominantly from axons. The mean conduction velocity of these fibers of 0.27 m/s was rapid but in range with other unmyelinated axons. We then used a genetically-encoded hybrid voltage sensor (hVOS) to image voltage from a specific population of neurons. Probe expression was controlled using Cre recombinase linked to c-fos activation. This activity-induced gene enabled targeting of neurons that are activated when a mouse hears a pure 15-kHz tone. In CN slices from these animals auditory nerve fiber stimulation elicited a glutamate receptor-dependent depolarization in hVOS probe-labeled neurons. These cells resided within a band corresponding to an isofrequency lamina, and responded with a high degree of synchrony. In contrast to the axonal origin of voltage-sensitive dye signals, hVOS signals represent predominantly postsynaptic responses. The introduction of voltage imaging to the CN creates the opportunity to investigate auditory processing circuitry in populations of neurons targeted on the basis of their genetic identity and their roles in sensory processing.

Titin function in the active sarcomere studied in frog muscle fibers upon inhibition of myosin motors by para-nitro-blebbistatin.

Titin spans the whole half-sarcomere, through the I-band connecting the Z-line to the myosin filament tip, and through the A-band, associated to myosin filament, up to M-line. Titin in the I-band transmits the stress also without attached myosin motors and is responsible for the passive force developed when a skeletal muscle fibre is stretched at rest. However, the passive stiffness in the range of physiological sarcomere lengths (SL, <2.7 µm) is too low to account for a putative role of I-band titin as mechanical link able to sustain mechanosensing in myosin filaments and prevent development of sarcomere inhomogeneity during contraction. Here we define titin mechanics during tetanic stimulation of intact frog muscle fibers using 20 μM para-nitro-blebbistatin (which fully inhibits myosin ATPase in vitro) to suppress the myosin-based mechanical responses. Small-angle X-ray fiber diffraction at the European Synchrotron ESRF demonstrates that the resting structure of thick filament is fully preserved upon tetanic stimulation. Under these conditions we use stepwise changes in force (10-50 pN per half-thick filament, htf) to elicit the lengthening transient that defines titin dynamic stiffness in situ at 2.3–3.0 µm SL. We show that, upon tetanic stimulation titin switches from the OFF-state characterised by a large, SL-dependent, extensibility, to the ON-state in which it opposes stretching with an effective stiffness one-two order of magnitude larger (∼3 pN·nm−1·htf−1) and independent of SL. The results demonstrate that, in the active sarcomere working at physiological lengths, I-band titin is an efficient mechanical link between the Z-line and the myosin filament tip, a condition for playing a role in mechanosensing-based myosin filament activation and for opposing to development of SL inhomogeneity during contraction. Supported by ECRF, University of Florence and MUR (Italy), ESRF (France) and EJP-RD.

Selective stimulation of nociceptive small fibers during intraepidermal electrical stimulation: Experiment and computational analysis.

Electrical stimulation of skin nociceptors is gaining attention in pain research and peripheral neuropathy diagnosis. However, the optimal parameters for selective stimulation are still difficult to determine because they require simultaneous characterization of the electrical response of small fibers (Aδ- and C-fibers). In this study, we measured the in vivo electrical threshold responses of small fibers to train-pulse stimulation in humans for the first time. We also examined selective stimulation via a computational model, which combines electrical analysis, and terminal fiber and synaptic models, including the first cutaneous pain C-fiber model. Selective stimulation of small fibers is performed by injecting train-pulse stimulation via coaxial electrodes with an intraepidermal needle tip at varying pulse counts and frequencies. The activation Aδ- or C-fibers was discriminated from the differences in reaction time. Aδ-fiber elicited a pinpricking sensation with a mean reaction time of 0.522 s, and C-fiber elicited a tingling sensation or slight burning itch with a mean reaction time of 1.243 s. The implemented multiscale electrical model investigates synaptic effects while considering stimulation waveform characteristics. Experimental results showed that perception thresholds decreased with the number of consecutive pulses and frequency up to convergence (five pulses or 70 Hz) during the selective stimulation of Aδ- and C-fibers. Considering the synaptic properties, the optimal stimulus conditions for selective stimulation of Aδ- vs. C-fibers were train of at least four pulses and a frequency of 40-70 Hz at a pulse width of 1 ms. The experimental results were modeled with high fidelity by incorporating temporal synaptic effects into the computational model. Numerical analysis revealed terminal axon thickness to be the most important biophysical factor affecting threshold variability. The computational model can be used to estimate perception thresholds while understanding the mechanisms underlying the selective stimulation of small fibers. The parameters derived here are important in exploring selective stimulation between Aδ- and C-fibers for diagnosing neuropathies.

Differential Regulation of Prelimbic and Thalamic Transmission to the Basolateral Amygdala by Acetylcholine Receptors.

The amygdalar anterior basolateral nucleus (BLa) plays a vital role in emotional behaviors. This region receives dense cholinergic projections from basal forebrain which are critical in regulating neuronal activity in BLa. Cholinergic signaling in BLa has also been shown to modulate afferent glutamatergic inputs to this region. However, these studies, which have used cholinergic agonists or prolonged optogenetic stimulation of cholinergic fibers, may not reflect the effect of physiological acetylcholine release in the BLa. To better understand these effects of acetylcholine, we have used electrophysiology and optogenetics in male and female mouse brain slices to examine cholinergic regulation of afferent BLa input from cortex and midline thalamic nuclei. Phasic ACh release evoked by single pulse stimulation of cholinergic terminals had a biphasic effect on transmission at cortical input, producing rapid nicotinic receptor-mediated facilitation followed by slower mAChR-mediated depression. In contrast, at this same input, sustained ACh elevation through application of the cholinesterase inhibitor physostigmine suppressed glutamatergic transmission through mAChRs only. This suppression was not observed at midline thalamic nuclei inputs to BLa. In agreement with this pathway specificity, the mAChR agonist, muscarine more potently suppressed transmission at inputs from prelimbic cortex than thalamus. Muscarinic inhibition at prelimbic cortex input required presynaptic M4 mAChRs, while at thalamic input it depended on M3 mAChR-mediated stimulation of retrograde endocannabinoid signaling. Muscarinic inhibition at both pathways was frequency-dependent, allowing only high-frequency activity to pass. These findings demonstrate complex cholinergic regulation of afferent input to BLa that is pathway-specific and frequency-dependent.SIGNIFICANCE STATEMENT Cholinergic modulation of the basolateral amygdala regulates formation of emotional memories, but the underlying mechanisms are not well understood. Here, we show, using mouse brain slices, that ACh differentially regulates afferent transmission to the BLa from cortex and midline thalamic nuclei. Fast, phasic ACh release from a single optical stimulation biphasically regulates glutamatergic transmission at cortical inputs through nicotinic and muscarinic receptors, suggesting that cholinergic neuromodulation can serve precise, computational roles in the BLa. In contrast, sustained ACh elevation regulates cortical input through muscarinic receptors only. This muscarinic regulation is pathway-specific with cortical input inhibited more strongly than midline thalamic nuclei input. Specific targeting of these cholinergic receptors may thus provide a therapeutic strategy to bias amygdalar processing and regulate emotional memory.