Spontaneous Electrical Activity Research Articles

Mama and papa of the early spontaneous electrical activity of the embryo sinoatrial node

In adult mammalian hearts the spontaneous diastolic depolarization of the sinoatrial node (SAN) cells is generated by two interacting systems, a so‐called “membrane‐clock” and “calcium‐clock”. Hyperpolarization‐activated pacemaker current (If) plays a key role in the “membrane‐clock”, while the “calcium‐clock” is based on rhythmic spontaneous Ca2+ release from sarcoplasmic reticulum via ryanodine receptors (RyRs). These complementing systems provide regular pacemaking even in case of damage of one of them. The aim of this study was to evaluate a role of If current and ryanodine receptors in the electrical activity of the developing mouse SAN.MethodsWe used embryos of mice, aged of E9.5, E12.5 and newborn to perform our experiments. After release from the amniotic membrane, the embryos were transferred with a pipette to a clean Petri dish with oxygenated physiological solution containing (in mM/L) 140 NaCl, 5.4 KCl, 0.1 CaCl2, 0.33 NaH2PO4, 1 MgCl2, 10 HEPES, 10 Glucose, (pH 7.38) at room temperature. To record spontaneous action potential (AP) we used conventional microelectodes technique at 37◦C. Differences were considered significant at p < 0.05ResultsMicroelectrode mapping at E9.5 revealed that the SAN cells are located in the inflow tract of the venous pole. At E12 the SAN cells are located in the cavo‐auricular junction. In neonatal mice, SAN cells were detected at intercaval area near to the crista terminalis. At E9.5, in 6 experiments, on 25‐ 30 minute exposure of 3 mkM ivabradine (Iva) an irregularity in AP generation by SAN cells was occurred. The same effects were obtained in 4 experiments on 20‐30 minutes exposure of 3 mkM ryanodine. At E12.5 exposure of Iva 3 mkM for 30 minutes reduced the pacemaker firing rate by 34% (p < 0.05) but did not break the rhythmic generation. In contrast, the exposure of 3 mkM ryanodine for 30 minutes, in 4 experiments, still caused an irregularity in AP generation by SAN cells. In neonatal isolated SAN preparations, exposure of Iva 3 mkM and 3 mkM ryanodine for 30 minutes reduced the pacemaker firing rate equally (on 32%; p < 0.05). However, co‐application of Iva and ryanodine induced an irregularity in AP generation by SAN cells (Figure).Numerical experiments within the framework of mouse SANC model (Kharche, AJP, 11) adopted for embryonic cells (Markov, IEEE, 21) have shown the decrease in the frequency of the AP generation with decreasing of the “funny” currents permeability caused by Iva action.The supposed complete RyRs opening, caused by a relatively low ryanodine concentration, led to a decrease of the AP generation frequency, but not to the rhythm disturbances. However a decrease in RyRs permeability by an order of magnitude led to the appearance of “bursts‐like” irregularity in AP generation.ConclusionThus, the membrane‐clock and the Ca2+‐clock mechanisms is critical for spontaneous electrical activity E9.5 mouse embryos, whereas the Ca2+‐clock mechanisms is critical for increase rate AP generation in development SAN cells.

PO-620-01 PERFORMANCE OF CARDIAC IMPLANTABLE ELECTRONIC DEVICES IN DETECTING PREMATURE VENTRICULAR CONTRACTION BURDEN

Frequent premature ventricular contractions (PVCs) can cause or exacerbate cardiomyopathy. At-risk patients often have pacemakers or implantable cardioverter defibrillators (ICDs), collectively known as cardiac implantable electronic devices (CIEDs), for treatment of bradycardia or ventricular arrhythmias. In addition to these functions, many modern CIEDs collect objective data about spontaneous cardiac electrical activity - including the presence and burden of PVCs. However, the performance of CIEDs for quantifying PVC burden remains unclear.

Updated review on overview of dry needling

Dry needling is a therapeutic method that involves inserting a filiform needle into a target area. Osteoarthritis is a degenerative joint disease that affects the articular cartilage, causes discomfort, and changes the biomechanics. ling is a component of conservative or comprehensive physiotherapeutic management. Increased blood flow, metabolic changes, spontaneous electrical activity, pain gating, and other mechanisms of action of dry needling may generate therapeutic advantages in osteoarthritis. The history of dry needling is extensively discussed. Needling can be defined as superficial or deep needling depending on the depth of the needle insertion, and it can also be classified as trigger point dry needling, fascial needling, scar tissue needling, and so on. The mechanism of Dry Needling is explained by a variety of ideas. The local effects of dry needling were also explored in this review, as well as the mechanism of analgesic effects. The needles can be utilized to provide therapeutic current to the tissues in a variety of ways. It can be done with PENS (Percutaneous Electrical Nerve Stimulation) or ETOIMS (Electro Transcutaneous Electrical Nerve Stimulation) (Electrical Twitch Obtaining Intramuscular Stimulation).

Upscaling biological complexity to boost neuronal and oligodendroglia maturation and improve in vitro developmental neurotoxicity (DNT) evaluation

Human induced pluripotent stem cell (iPSC)-derived neuronal and glial cell models are suitable to assess the effects of environmental chemicals on the developing brain. Such test systems can recapitulate several key neurodevelopmental features, such as neural stem cell formation and differentiation towards different neuronal subtypes and astrocytes, neurite outgrowth, synapse formation and neuronal network formation and function, which are crucial for brain development. While monolayer, two-dimensional (2D) cultures of human iPSC-neuronal or glial derivatives are generally suited for high-throughput testing, they also show some limitations. In particular, differentiation towards myelinating oligodendrocytes can only be achieved after extended periods in differentiation. In recent years, the implementation of three-dimensional (3D) neuronal and glial models obtained from human iPSCs has been shown to compensate for such limitations, enabling robust differentiation towards both neuronal and glial cell populations, myelination and formation of more mature neuronal network activity. Here we compared the differentiation capacity of human iPSC-derived neural stem cells cultured either as 2D monolayer or as 3D neurospheres, and assessed chlorpyrifos (CPF) effects. Data indicate that 3D neurospheres differentiate towards neurons and oligodendroglia more rapidly than 2D cultures; however, the 2D model is more suitable to assess neuronal functionality by analysis of spontaneous electrical activity using multielectrode array. Moreover, 2D and 3D test systems are diversely susceptible to CPF treatment. In conclusion, the selection of the most suitable in vitro test system (either 2D or 3D) should take into account the context of use and intended research goals (‘fit for purpose’ principle).

The Role of Interstitial Fluid Pressure in Cerebral Porous Biomaterial Integration.

Recent advances in biomaterials offer new possibilities for brain tissue reconstruction. Biocompatibility, provision of cell adhesion motives and mechanical properties are among the present main design criteria. We here propose a radically new and potentially major element determining biointegration of porous biomaterials: the favorable effect of interstitial fluid pressure (IFP). The force applied by the lymphatic system through the interstitial fluid pressure on biomaterial integration has mostly been neglected so far. We hypothesize it has the potential to force 3D biointegration of porous biomaterials. In this study, we develop a capillary hydrostatic device to apply controlled in vitro interstitial fluid pressure and study its effect during 3D tissue culture. We find that the IFP is a key player in porous biomaterial tissue integration, at physiological IFP levels, surpassing the known effect of cell adhesion motives. Spontaneous electrical activity indicates that the culture conditions are not harmful for the cells. Our work identifies interstitial fluid pressure at physiological negative values as a potential main driver for tissue integration into porous biomaterials. We anticipate that controlling the IFP level could narrow the gap between in vivo and in vitro and therefore decrease the need for animal screening in biomaterial design.

Tonic serotonergic input increases the burst firing mode and diminishes the firing rate of reticular thalamic nucleus neurons through 5-HT1A receptors activation in anesthetized rats.

The reticular thalamic nucleus (RTn) is a thin shell of GABAergic neurons that covers the dorsal thalamus that regulate the global activity of all thalamic nuclei. RTn controls the flow of information between thalamus and cerebral cortex since it receives glutamatergic information from collaterals of thalamo-cortical (TCs) and cortico-thalamic neurons. It also receives aminergic information from several brain stem nuclei, including serotonergic fibers originated in the dorsal raphe nucleus. RTn neurons express serotonergic receptors including the 5-HT1A subtype, however, the role of this receptor in the RTn electrical activity has been scarcely analyzed. In this work, we recorded in vivo the unitary spontaneous electrical activity of RTn neurons in anesthetized rats; our study aimed to obtain information about the effects of 5-HT1A receptors in RTn neurons. Local application of fluoxetine (a serotonin reuptake inhibitor) increases burst firing index accompanied by a decrease in the basal spiking rate. Local application of different doses of serotonin and 8-OH-DPAT (a specific 5-HT1A receptor agonist) causes a similar response to fluoxetine effects. Local 5-HT1A receptors blockade produces opposite effects and suppresses the effect by 8-OH-DPAT. Our findings indicate the presence of a serotonergic tonic discharge in the RTn that increases the burst firing index and simultaneously decreases the basal spiking frequency through 5-HT1A receptors activation.

Automaticity in ventricular myocyte cell pairs with ephaptic and gap junction coupling.

Spontaneous electrical activity, or automaticity, in the heart is required for normal physiological function. However, irregular automaticity, in particular, originating from the ventricles, can trigger life-threatening cardiac arrhythmias. Thus, understanding mechanisms of automaticity and synchronization is critical. Recent work has proposed that excitable cells coupled via a shared narrow extracellular cleft can mediate coupling, i.e., ephaptic coupling, that promotes automaticity in cell pairs. However, the dynamics of these coupled cells incorporating both ephaptic and gap junction coupling has not been explored. Here, we show that automaticity and synchronization robustly emerges via a Hopf bifurcation from either (i) increasing the fraction of inward rectifying potassium channels (carrying the IK1 current) at the junctional membrane or (ii) by decreasing the cleft volume. Furthermore, we explore how heterogeneity in the fraction of potassium channels between coupled cells can produce automaticity of both cells or neither cell, or more rarely in only one cell (i.e., automaticity without synchronization). Interestingly, gap junction coupling generally has minor effects, with only slight changes in regions of parameter space of automaticity. This work provides insight into potentially new mechanisms that promote spontaneous activity and, thus, triggers for arrhythmias in ventricular tissue.

A Rhythmic Electrocardiographic Pattern in an Older Adult With Chest Pain.

Scenario: An 87-year-old woman with a history of atrial fibrillation, hypertension, and hyperlipidemia came to the emergency department with substernal chest pain that was not relieved with nitroglycerin. She was found to be in atrial fibrillation with rapid ventricular response and had dynamic troponin levels that were concerning for myocardial infarction. Left-sided cardiac catheterization revealed severe coronary disease with about 80% occlusion of the left main and left anterior descending coronary arteries; however, percutaneous coronary intervention (PCI) was not done because of the patient’s hemodynamic instability. After the catheterization, she continued to have substernal chest pain for 2 days and was taken back for emergent PCI with temporary mechanical ventricular support. Two drug-eluting stents were placed. Her bedside electrocardiography (ECG) strip after the emergent PCI is shown here.Atrial bigeminy with a sinus rate of 35 beats per minute and right bundle branch block (RBBB).This patient exhibited multiple deficits in conduction due to acute occlusion of the left main and left anterior descending (LAD) coronary arteries leading to infarction of the surrounding myocardium. The left main coronary artery arises from the aorta, passes between the pulmonary trunk and the left atrial appendage, and bifurcates into the LAD and the left circumflex coronary artery. The LAD, of interest in this example, supplies oxygenated blood to the interventricular septum and left ventricle. Occlusion of both the left main and LAD coronary arteries likely led to the atrial bigeminy and RBBB seen here.Occlusion of the left main coronary artery can induce ischemia in the left atrium and left atrial appendage, propogating atrial bigeminy, a regularly irregular rhythm where a premature atrial contraction (PAC) follows each normal sinus beat (N). Ischemia propagates spontaneous electrical activity such as PACs and disrupts normal conduction. When another region of the atria depolarizes before the sinoatrial node, PACs occur; the PACs may be sporadic or patterned (eg, bigeminy, trigeminy). On an ECG, PACs may show a P wave morphology different from the sinus beat or no P wave preceding the QRS complex. If the P wave preceding the QRS complex is not visible, the P wave is most likely embedded in the preceding T wave. Both PACs and sinus beats travel down the same conduction pathway to the ventricle, producing a morphologically similar QRS complex; this feature differentiates PACs from premature ventricular contractions, which have grossly different morphologies, unless there is an existing BBB (as here), which makes distinguishing PACs from premature ventricular contractions challenging.The wide QRS complexes with slurred qRs morphology in lead V1 and the discordant T waves are due to RBBB, most likely caused by the occlusion of the LAD. In about 90% of patients, the proximal LAD septal perforators perfuse the right bundle branch and the anterior fascicle of the left bundle branch. Thus, occlusion of the LAD may have caused subsequent ischemia in the intraventricular septum, slowing conduction through the bundle branches and inducing an RBBB in this patient. Importantly, an RBBB does not preclude assessment of ST-segment elevation indicative of transmural ischemia due to coronary occlusion, but since it is unknown if the RBBB was preexisting, it is best to review a previous ECG tracing.After emergent PCI, the patient developed atrial bigeminy and remained in the irregular rhythm for 6 hours. She did not develop new ischemic symptoms and did not require more interventions. She remained clinically unstable with a bradycardic sinus rate in atrial bigeminy, but no signs or symptoms of hypoperfusion were noted. The bedside nurse closely monitored the patient and the ECG because atrial bigeminy can progress to atrial fibrillation. Optimal guideline-based therapies for acute coronary syndrome, including dual antiplatelet therapy, are indicated to maintain stent patency. Careful monitoring of the ST segments for ischemia is indicated.

The ischemic model of chronic muscle spasm and pain.

This article was not intended to be a complete review of the electromyography of pathological muscle states, but it was written to illustrate how the “Coletti Method of EMG ChemoDenervation” (CMECD©) protocol for the treatment of chronic pain resulting from chronic muscle spasm was developed and established. That process led to an unexpected understanding of the underlying pathophysiology of chronic muscle spasm, which represents a paradigm shift in our understanding and ultimately in our treatment of muscle spasm-induced chronic pain. Other investigators had brought to light the presence of spontaneous electrical activity (SEA) in states of muscle spasm. Those findings were all but ignored by standard EMG/Nerve conduction studies in clinical practice. Starting with a simple EMG device I experimented with various medications to treat patients with chronic pain associated with chronic muscle spasm. Suppression of SEA with long-acting medications resolved both the chronic spasm and chronic pain. A successful protocol using phenoxybenzamine was established and clinical outcomes were followed. More than 200 patients were successfully treated during last 12 years. Correlating known exercise muscle physiology with the development of the pathological state of chronic muscle spasm as seen by electromyography led to the postulation of the ischemic model of chronic muscle spasm. Light microscopy pathophysiologic supportive findings are presented and discussed. Predictions from this model to various aspects of treatment were supportive. Implications regarding treatment by the CMECD© procedure, as well as other standard therapies, are discussed. Application of the ischemic model to other pain conditions was explored with implications of therapeutic modification. Recommendations for changes in rehabilitation therapy are discussed.

Accelerated Aging Characterizes the Early Stage of Alzheimer's Disease.

For Alzheimer’s disease (AD), aging is the main risk factor, but whether cognitive impairments due to aging resemble early AD deficits is not yet defined. When working with mouse models of AD, the situation is just as complicated, because only a few studies track the progression of the disease at different ages, and most ignore how the aging process affects control mice. In this work, we addressed this problem by comparing the aging process of PS2APP (AD) and wild-type (WT) mice at the level of spontaneous brain electrical activity under anesthesia. Using local field potential recordings, obtained with a linear probe that traverses the posterior parietal cortex and the entire hippocampus, we analyzed how multiple electrical parameters are modified by aging in AD and WT mice. With this approach, we highlighted AD specific features that appear in young AD mice prior to plaque deposition or that are delayed at 12 and 16 months of age. Furthermore, we identified aging characteristics present in WT mice but also occurring prematurely in young AD mice. In short, we found that reduction in the relative power of slow oscillations (SO) and Low/High power imbalance are linked to an AD phenotype at its onset. The loss of SO connectivity and cortico-hippocampal coupling between SO and higher frequencies as well as the increase in UP-state and burst durations are found in young AD and old WT mice. We show evidence that the aging process is accelerated by the mutant PS2 itself and discuss such changes in relation to amyloidosis and gliosis.

SK Current, Expressed During the Development and Regeneration of Chick Hair Cells, Contributes to the Patterning of Spontaneous Action Potentials.

Chick hair cells display calcium (Ca2+)-sensitive spontaneous action potentials during development and regeneration. The role of this activity is unclear but thought to be involved in establishing proper synaptic connections and tonotopic maps, both of which are instrumental to normal hearing. Using an electrophysiological approach, this work investigated the functional expression of Ca2+-sensitive potassium [IK(Ca)] currents and their role in spontaneous electrical activity in the developing and regenerating hair cells (HCs) in the chick basilar papilla. The main IK(Ca) in developing and regenerating chick HCs is an SK current, based on its sensitivity to apamin. Analysis of the functional expression of SK current showed that most dramatic changes occurred between E8 and E16. Specifically, there is a developmental downregulation of the SK current after E16. The SK current gating was very sensitive to the availability of intracellular Ca2+ but showed very little sensitivity to T-type voltage-gated Ca2+ channels, which are one of the hallmarks of developing and regenerating hair cells. Additionally, apamin reduced the frequency of spontaneous electrical activity in HCs, suggesting that SK current participates in patterning the spontaneous electrical activity of HCs.

Stem cells and cardiac arrhythmias.

Recent discoveries in the physiology and pathology of myocardial progenitor cells have allowed researchers to better understand a variety of cardiac pathologies and look at the pathophysiology of arrhythmias from a different perspective. Since the myocardium is composed of a syncytium of electrically interconnected cells, the process of incorporation of newly formed or imported cells into its structure is particularly important. Progenitor cells are stimulated by spontaneous electrical activity, a lengthy action potential, and easily induced triggering activity. All these can lead to arrhythmias development via the three classical mechanisms (reentrancy, automatism, or triggering activity). Transplanted stem cells can influence the electrophysiological properties of cardiomyocytes, thus creating a proarrhythmic substrate. The islets of unbound cells can form an anatomical block, causing unidirectional blockages and recurrent arrhythmias. Similarly, stem cells are capable of establishing heterotopic excitation foci with cardiac stimulatory activity. Finally, the paracrine factors produced by stem cells can also cause proarrhythmic effects. The review examines the factors that influence the proarrhythmic properties of administered stem cells and the mechanisms of arrhythmia development. The results indicate that further research should be carried out to establish the possible impact of stem cells on the development of arrhythmias.

Geometric Analysis of the Spontaneous Electrical Activity in Anterior Pituitary Corticotrophs

Geometric Analysis of the Spontaneous Electrical Activity in Anterior Pituitary Corticotrophs

Lipidomics Reveals Dysregulated Glycerophospholipid Metabolism in the Corpus Striatum of Mice Treated with Cefepime.

Cefepime exhibits a broad spectrum of antimicrobial activity and thus is a widely used treatment for severe bacterial infections. Adverse effects on the central nervous system (CNS) have been reported in patients treated with cefepime. Current explanation for the adverse neurobehavioral effect of cefepime is mainly attributed to its ability to cross the blood-brain barrier and competitively bind to the GABAergic receptor; however, the underlying mechanism is largely unknown. In this study, mice were intraperitoneally administered 80 mg/kg cefepime for different periods, followed by neurobehavioral tests and a brain lipidomic analysis. LC/MS-MS-based metabolomics was used to investigate the effect of cefepime on the brain lipidomic profile and metabolic pathways. Repeated cefepime treatment time-dependently caused anxiety-like behaviors, which were accompanied by reduced locomotor activity in the open field test. Cefepime profoundly altered the lipid profile, acyl chain length, and unsaturation of fatty acids in the corpus striatum, and glycerophospholipids accounted for a large proportion of those significantly modified lipids. In addition, cefepime treatment caused obvious alteration in the lipid-enriched membrane structure, neurites, mitochondria, and synaptic vesicles of primary cultured striatal neurons; moreover, the spontaneous electrical activity of striatal neurons was significantly reduced. Collectively, cefepime reprograms glycerophospholipid metabolism in the corpus striatum, which may interfere with neuronal structure and activity, eventually leading to aberrant neurobehaviors in mice.

A Study on Electroencephalography Findings of Patients Visiting the Psychiatric Clinic: An Experience at A Tertiary Care Center in Western Nepal

Introduction: The electroencephalography (EEG) is the recording of brain’s spontaneous electrical activity over a period of time (20-40 minutes) recorded from multiple electrodes placed on the scalp. It is used in seizure disorder, organicity, and psychiatric conditions. There is a paucity of literature with regard to the application of EEG in various conditions in our setting. Methods: This was a cross-sectional study, where data of the patients who visited the EEG section of psychiatric clinic from September 15, 2019 to July 14, 2020 were collected retrospectively. The demographic details, EEG details, and the clinical details were recorded and analyzed. Results: A total of 110 patients underwent EEG during the study period. Of them, 61 (55.45%) had normal EEG. Among the patients with normal EEG, 60 (98.36%) had clinical history suggestive of seizure disorder. Of the rest 49 (44.55%) patients with abnormal EEG, 48 (97.96%) had history of seizure. Majority patients referred for EEG fell in the prime of their life (1-30yrs). Almost all (98.2%) patients with the history of seizure were taking anti-epileptic drugs. Conclusion: EEG is a common investigation done in psychiatric clinic. Nearly half of the patients with seizure disorders will have an abnormal EEG.

PDE4B and PDE4D differentially regulate cardiac pacemaker activity

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Agence Nationale de la Recherche (ANR) Background Heart rate (HR) is generated by spontaneous electrical activity in the sinoatrial node (SAN) and is modulated by the autonomic nervous system. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) increases cAMP levels, leading to positive chronotropic effect. Among the 6 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during β-stimulation in atrial and ventricular myocytes. PDE4 may also be important for automaticity. 3 genes encode for PDE4 in the heart (pde4a, 4b, 4d). We propose to investigate their respective contribution to the regulation of pacemaker activity. Methods Total PDE activity in mouse SAN was determined as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue from wild-type (WT) and PDE4KO mice. Images were obtained using confocal microscopy. Telemetry EKG was recorded in conscious mice in control (CTRL) conditions, after pharmacological denervation with atropine (1 mg/kg) and propranolol (2 mg/kg) and after β-stimulation with isoproterenol (ISO, 1.5 mg/kg). HR variability was evaluated by calculating the SDNN (standard deviation of RR intervals) parameter. Results Ro-20-1724 (10 µM) increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of total cAMP-PDE activity in SAN. PDE4A, 4B and 4D isoforms were found to be expressed in mouse SAN. In PDE4BKO SAN, the effect of ISO on SAN beating rate was higher than in WT. Ablation of PDE4D induced decreased beating rate in CTRL and ISO conditions and increased Ca2+ spark frequency compared to WT SAN. In vivo, PDE4BKO and PDE4DKO mice displayed increased resting HR during day and night. HR variability was decreased in PDE4BKO, but not in PDE4DKO mice during the day, and decreased in both genotypes at night compared to WT mice. After atropine + propranolol denervation, the rhythmic phenotype was only maintained in PDE4BKO but not in PDE4DKO mice. The response to β-AR stimulation with ISO was higher in PDE4BKO than in PDE4DKO. In addition, under ISO we observed an increased number of premature beats and atrioventricular blocks in PDE4DKO, but not in PDE4BKO mice. Conclusion PDE4B and PDE4D differentially regulate cardiac pacemaker activity. While PDE4B clearly controls intrinsic SAN automaticity, PDE4D might be important for ANS-mediated regulation of HR and conduction.

Autonomous initiation of pacemaking by L-type Cav1.3 calcium channels in mouse sino-atrial myocytes

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Ecole doctorale Background Cardiac pacemaking relies on the spontaneous electrical activity in the right atrium of sino-atrial myocytes (SANCs). Automaticity in SANCs results from a robust interplay of membrane ion channels activity and intracellular calcium dynamics. However, only a fraction of isolated SANCs exhibit rhythmic firing, whereas most SANCs show irregular (dysrhythmic) firing or remain dormant. Purpose To study the capability of L-type Cav1.3 calcium channels to initiate automaticity in dormant SANCs under β-adrenergic stimulation, we used a knock-in mouse strain in which the sensitivity of Cav1.2 α1 subunits to dihydropyridines (DHP) was inactivated (Cav1.2DHP-/-). Methods We performed current and voltage-clamp recordings on isolated SANCs under isoprenaline (ISO, 100 nM) and in the absence or presence of the DHP blocker Nifedipine (Nife, 3 µM). Results Nife significantly reduced the spontaneous firing under ISO perfusion in all rhythmic SANCs (ISO: 447 ± 12, ISO + Nife: 233 ± 25 bpm) and 60% of dysrhythmic SANCs (ISO: 386 ± 12, ISO + Nife: 188 ± 47 bpm) whereas it completely stopped it in the remaining 40% (295 ± 29 bpm to 0). On 25 dormant SANCs, 50% started firing after ISO perfusion (0 to 320 ± 46 bpm). Strikingly, in 75% of them, Nife totally blocked this ISO-induced firing. Interestingly, these cells exhibited a significantly slower rate and a slower slope of the diastolic depolarization under ISO perfusion compared to the remaining 25% dormant SANCs in which Nife only reduced the ISO-induced firing. Moreover, dormant SANCs showed a statistically significant increase in action potential (AP) threshold under ISO compared to dysrhythmic and rhythmic SANCs (dormant: -30.1 ± 2.5, dysrhythmic: -43.3 ± 2.3, rhythmic: -41.2 ± 2.1 mV). No significant difference was observed in the other AP parameters between dormant, dysrhythmic and rhythmic SANCs under ISO. Conclusion Our results seem to point at a difference of expression in ionic channels (Cav1.3, HCN4) within isolated SANCs. Preliminary results on If density support this hypothesis with a lesser density in dormant SANCs compared to dysrhythmic SANCs. These results also tend to indicate that Cav1.3 channels can generate pacemaker activity autonomously, at least in a particular subpopulation of SANCs.

Design and Demonstration In Vitro of a Mouse-Specific Transcranial Magnetic Stimulation Coil

Transcranial magnetic stimulation (TMS) is a technique used to treat different neurological disorders non-invasively. A pulsed current to a coil generates a magnetic field ( $B$ -field) which induces an electric field ( $E$ -field). Underlying biophysical effects of TMS are unclear. Therefore, animal experiments are needed; however, making small TMS coils suitable for mice is difficult and their field strengths are typically much lower than for human sized coils. Objectives/Hypothesis . We aimed to design and demonstrate a mouse-specific coil that can generate high and focused $E$ -field. Methods . We designed a tapered TMS coil of 50 turns of 0.2 mm diameter copper wire around a 5 mm diameter tapered powdered iron core and discharged a $220~\mu \text{F}$ capacitor at 50 V through it. We measured $B$ -field with a Hall probe and induced $E$ -field with a wire loop. We measured temperature rise with a thermocouple. We applied 1200 pulses of continuous theta burst stimulation (cTBS) and intermittent theta burst stimulation (iTBS) to mouse brain slices and analyzed how spontaneous electrical activity changed. Results . The coil gave maximum $B$ -field of 685 mT at the base of the coil and 340 mT at 2 mm below the coil, and maximum $E$ -field 2 mm below the coil of approximately 10 V/m, at 50 V power supply, with a temperature increase of 20 °C after 1200 pulses of cTBS. We observed no changes in $B$ -field with heating. cTBS reduced frequency of spontaneous population events in mouse brain slices up to 20 min after stimulation and iTBS increased frequency up to 20 min after stimulation. No frequency changes occurred after 20 min. No changes in amplitude of spontaneous events were found. Conclusion . The design generated fields strong enough to modulate brain activity in vitro .

L-type Cav1.3 calcium channels are key actors in beta-adrenergic triggered automaticity in dormant mouse sino-atrial myocytes

Cardiac pacemaking relies on the spontaneous electrical activity of sino-atrial myocytes (SANCs) in the right atrium arising from a robust interplay of membrane ion channels activity (membrane clock) and intracellular calcium dynamics (calcium clock). Strikingly, most of isolated SANCs exhibit a dormant state (no apparent spontaneous activity) whereas only a small fraction shows regular firing. It has recently been shown that these non-firing SANCs are also present in intact SAN and can switch into a firing mode under beta-adrenergic stimulation. However, their functional relevance in vivo is unknown. To study the role of L-type Ca v 1.3 calcium channels in dormant SANCs using a knock-in mouse strain in which the sensitivity of Ca v 1.2 α1 subunits to dihydropyridines (DHP) was inactivated (Ca v 1.2 DHP−/− ). We performed voltage and current-clamp recordings and confocal live imaging on isolated SANCs under isoprenaline (ISO, 100 nM) in the absence or presence of the DHP blocker Nifedipine (Nife, 3 μM). Preliminary results seem to show less L-type calcium current I Ca,L in dormant SANCs (D) compared to rhythmic SANCs (R) (D: −6.3 ± 1.2, R: −15.6 pA/pF). Dormant SANCs also have less diastolic calcium (D: 96.9 ± 12, R: 218 ± 51.2 a.u, P = 0.14) but significant higher sarcoplasmic reticulum calcium load (D: 6.3 ± 0.6, R: 3.1 ± 0.3 a.u, P = 0.004). Interestingly, ISO perfusion could only switch half of dormant SANCs into a firing mode in both action potential (AP) and calcium transients (CT) recordings whereas the others remained dormant. Further Nife perfusion completely stopped this ISO-induced firing switching the cells back into a dormant state for the vast majority of them (75% in AP-recorded SANCs and 100% in CT-recorded SANCs). Taken together, these results indicate that Cav1.3 channels play a key role in sustaining the coupling of membrane and calcium clock in dormant SANCs under beta-adrenergic stimulation.

Characterization of Developmental Changes in Spontaneous Electrical Activity of Medial Superior Olivary Neurons Before Hearing Onset With a Combination of Injectable and Volatile Anesthesia.

In this work the impact of two widely used anesthetics on the electrical activity of auditory brainstem neurons was studied during postnatal development. Spontaneous electrical activity in neonate rats of either sex was analyzed through a ventral craniotomy in mechanically ventilated pups to carry out patch clamp and multi-electrode electrophysiology recordings in the medial region of the superior olivary complex (SOC) between birth (postnatal day 0, P0) and P12. Recordings were obtained in pups anesthetized with the injectable mix of ketamine/xylazine (K/X mix), with the volatile anesthetic isoflurane (ISO), or in pups anesthetized with K/X mix that were also exposed to ISO. The results of patch clamp recordings demonstrate for the first time that olivary and periolivary neurons in the medial region of the SOC fire bursts of action potentials. The results of multielectrode recordings suggest that the firing pattern of single units recorded in K/X mix is similar to that recorded in ISO anesthetized rat pups. Taken together, the results of this study provide a framework to use injectable and volatile anesthetics for future studies to obtain functional information on the activity of medial superior olivary neurons in vivo.