Extracellular Field Potential Recordings Research Articles

Alarin potentiates ongoing epileptiform activity in rat brain slices: an in vitro electrophysiological study.

Alarin is a newly discovered neuropeptide that belongs to the galanin peptide family with a wide range of bioactivity in the nervous system. Its function in the brain's autonomic areas has been studied, and it has been reported that alarin is involved in the regulation of excitability in hypothalamic neurons. Its role in the regulation of excitability in the hippocampus, however, is unknown. In this study, we investigated if alarin induced any synchronous discharges or epileptiform activity, and if it had any effect on already initiated epileptiform discharges. We used thick acute horizontal hippocampal slices obtained from 30‑ to 35‑day‑old rats. Extracellular field potential recordings were evaluated in the CA1 region of the hippocampus. Our data demonstrated that, alarin application did not result in any epileptiform activity or abnormal discharges. 4‑aminopyridine was applied to induce epileptiform activity in the slices. We found that alarin increased the frequency of interictal‑like events and the mean power of local field potentials in the CA1 region of the hippocampus, which was induced by 4‑aminopyridine. These results demonstrated for the first time that alarin has a modulatory effect on synchronized neuronal discharges and showed the contribution of the neuropeptide alarin to epilepsy‑like conditions.

Spontaneous slow wave oscillations in extracellular field potential recordings reflect the alternating dominance of excitation and inhibition.

In the resting state, cortical neurons can fire action potentials spontaneously but synchronously (Up state), followed by a quiescent period (Down state) before the cycle repeats. Extracellular recordings in the infragranular layer of cortex with a micro-electrode display a negative deflection (depth-negative) during Up states and a positive deflection (depth-positive) during Down states. The resulting slow wave oscillation (SWO) has been studied extensively during sleep and under anaesthesia. However, recent research on the balanced nature of synaptic excitation and inhibition has highlighted our limited understanding of its genesis. Specifically, are excitation and inhibition balanced during SWOs? We analyse spontaneous local field potentials (LFPs) during SWOs recorded from anaesthetised rats via a multi-channel laminar micro-electrode and show that the Down state consists of two distinct synaptic states: a Dynamic Down state associated with depth-positive LFPs and a prominent dipole in the extracellular field, and a Static Down state with negligible ( ) LFPs and a lack of dipoles extracellularly. We demonstrate that depth-negative and -positive LFPs are generated by a shift in the balance of synaptic excitation and inhibition from excitation dominance (depth-negative) to inhibition dominance (depth-positive) in the infragranular layer neurons. Thus, although excitation and inhibition co-tune overall, differences in their timing lead to an alternation of dominance, manifesting as SWOs. We further show that Up state initiation is significantly faster if the preceding Down state is dynamic rather than static. Our findings provide a coherent picture of the dependence of SWOs on synaptic activity. KEY POINTS: Cortical neurons can exhibit repeated cycles of spontaneous activity interleaved with periods of relative silence, a phenomenon known as 'slow wave oscillation' (SWO). During SWOs, recordings of local field potentials (LFPs) in the neocortex show depth-negative deflection during the active period (Up state) and depth-positive deflection during the silent period (Down state). Here we further classified the Down state into a dynamic phase and a static phase based on a novel method of classification and revealed non-random, stereotypical sequences of the three states occurring with significantly different transitional kinetics. Our results suggest that the positive and negative deflections in the LFP reflect the shift of the instantaneous balance between excitatory and inhibitory synaptic activity of the local cortical neurons. The differences in transitional kinetics may imply distinct synaptic mechanisms for Up state initiation. The study may provide a new approach for investigating spontaneous brain rhythms.

Step-by-step approach: Stereotaxic surgery for in vivo extracellular field potential recording at the rat Schaffer collateral-CA1 synapse using the eLab system

In vivo extracellular field potential recording is a commonly used technique in modern neuroscience research. The success of long-term electrophysiological recordings often depends on the quality of the implantation surgery. However, there is limited use of visually guided stereotaxic neurosurgery and the application of the eLab/ePulse electrophysiology system in rodent models. This study presents a practical and functional manual guide for surgical electrode implantation in rodent models using the eLab/ePulse electrophysiology system for recording and stimulation purposes to assess neuronal functionality and synaptic plasticity. The evaluation parameters included the input/output function (IO), paired-pulse facilitation or depression (PPF/PPD), long-term potentiation (LTP), and long-term depression (LTD).•Provides a detailed picture-guided procedure for conducting in vivo stereotaxic neurosurgery.•Specifically covers the insertion of hippocampal electrodes and the recording of evoked extracellular field potentials.

Female TgF344‐AD hippocampal plasticity after estrogen deprivation

AbstractBackgroundAlzheimer’s Disease (AD) is the seventh leading cause of death worldwide, disproportionately affecting women, with two‐thirds of individuals with AD being female. A decrease in circulating ovarian estrogen during menopause is believed to be a contributing factor to this discrepancy in disease prevalence. AD pathology is known to impact synaptic transmission in the hippocampus, resulting in memory deficits, a hallmark symptom of AD. This study investigates the effect of estrogen deprivation in the dentate gyrus (DG) and CA1 region, areas affected early on in the disease and crucial for memory. As the disease progresses, deficits are seen in the dentate gyrus prior to CA1 region supporting the anatomical spread of the pathology.MethodSynaptic signaling was assessed in DG and CA1 hippocampal subregions of 9 month old TgF344‐AD female rats who underwent long‐term (from ages 3 to 9 months) ovarian hormone deprivation. Extracellular dendritic field potential recordings were conducted in the DG by stimulating the medial perforant path onto dentate granule cells, and in the CA1 region by stimulating Schaffer collateral axons. Input/output relationship, paired pulse ratio, and long term potentiation were assessed, analyzed, and statistically compared between TgF344‐AD rats and non‐transgenic hormone deprived littermates.ResultIt was found that AD females were able to maintain synaptic transmission as there were no significant differences found in the input/output relationship, paired pulse ratio, or long term potentiation between AD animals and their controls.ConclusionThese results show that at this early stage in the disease, ovarian estrogen deprivation does not accelerate synaptic impairment. These results also suggest the possibility that a compensatory mechanism exists at these synapses to maintain function.

Glutamatergic synaptic deficits in the prefrontal cortex of the Ts65Dn mouse model for Down syndrome.

Down syndrome (DS), the most prevalent cause of intellectual disability, stems from a chromosomal anomaly resulting in an entire or partial extra copy of chromosome 21. This leads to intellectual disability and a range of associated symptoms. While there has been considerable research focused on the Ts65Dn mouse model of DS, particularly in the context of the hippocampus, the synaptic underpinnings of prefrontal cortex (PFC) dysfunction in DS, including deficits in working memory, remain largely uncharted territory. In a previous study featuring mBACtgDyrk1a mice, which manifest overexpression of the Dyrk1a gene, a known candidate gene linked to intellectual disability and microcephaly in DS, we documented adverse effects on spine density, alterations in the molecular composition of synapses, and the presence of synaptic plasticity deficits within the PFC. The current study aimed to enrich our understanding of the roles of different genes in DS by studying Ts65Dn mice, which overexpress several genes including Dyrk1a, to compare with our previous work on mBACtgDyrk1a mice. Through ex-vivo electrophysiological experiments, including patch-clamp and extracellular field potential recordings, we identified alterations in the intrinsic properties of PFC layer V/VI pyramidal neurons in Ts65Dn male mice. Additionally, we observed changes in the synaptic plasticity range. Notably, long-term depression was absent in Ts65Dn mice, while synaptic or pharmacological long-term potentiation remained fully expressed in these mice. These findings provide valuable insights into the intricate synaptic mechanisms contributing to PFC dysfunction in DS, shedding light on potential therapeutic avenues for addressing the neurocognitive symptoms associated with this condition.

Flexible 3D printed microwires and 3D microelectrodes for heart-on-a-chip engineering

We developed a heart-on-a-chip platform that integrates highly flexible, vertical, 3D micropillar electrodes for electrophysiological recording and elastic microwires for the tissue’s contractile force assessment. The high aspect ratio microelectrodes were 3D-printed into the device using a conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). A pair of flexible, quantum dots/thermoplastic elastomer nanocomposite microwires were 3D printed to anchor the tissue and enable continuous contractile force assessment. The 3D microelectrodes and flexible microwires enabled unobstructed human iPSC-based cardiac tissue formation and contraction, suspended above the device surface, under both spontaneous beating and upon pacing with a separate set of integrated carbon electrodes. Recording of extracellular field potentials using the PEDOT:PSS micropillars was demonstrated with and without epinephrine as a model drug, non-invasively, along with in situ monitoring of tissue contractile properties and calcium transients. Uniquely, the platform provides integrated profiling of electrical and contractile tissue properties, which is critical for proper evaluation of complex, mechanically and electrically active tissues, such as the heart muscle under both physiological and pathological conditions.

Intermittent systemic exposure to lipopolysaccharide-induced inflammation disrupts hippocampal long-term potentiation and impairs cognition in aging male mice

Age-related cognitive decline, a common component of the brain aging process, is associated with significant impairment in daily functioning and quality of life among geriatric adults. While the complexity of mechanisms underlying cognitive aging are still being elucidated, microbial exposure and the multifactorial inflammatory cascades associated with systemic infections are emerging as potential drivers of neurological senescence. The negative cognitive and neurobiological consequences of a single pathogen-associated inflammatory experience, such as that modeled through treatment with lipopolysaccharide (LPS), are well documented. Yet, the brain aging impacts of repeated, intermittent inflammatory challenges are less well studied. To extend the emerging literature assessing the impact of infection burden on cognitive function among normally aging mice, here, we repeatedly exposed adult mice to intermittent LPS challenges during the aging period. Male 10-month-old C57BL6 mice were systemically administered escalating doses of LPS once every two weeks for 2.5 months. We evaluated cognitive consequences using the non-spatial step-through inhibitory avoidance task, and both spatial working and reference memory versions of the Morris water maze. We also probed several potential mechanisms, including cortical and hippocampal cytokine/chemokine gene expression, as well as hippocampal neuronal function via extracellular field potential recordings. Though there was limited evidence for an ongoing inflammatory state in cortex and hippocampus, we observed impaired learning and memory and a disruption of hippocampal long-term potentiation. These data suggest that a history of intermittent exposure to LPS-induced inflammation is associated with subtle but significantly impaired cognition among normally aging mice. The broader impact of these findings may have important implications for standard of care involving infections in aging individuals or populations at-risk for dementia.

Activation of androgen receptors alters hippocampal synaptic plasticity and memory retention through modulation of L-type calcium channels

AimsIt has been revealed that membrane androgen receptor activation modulates avoidance memory and synaptic plasticity. In a previous study, we showed that Calcineurin, a calcium dependent phosphatase, could be a potential mediator of these AR effects. Also, it is reported that AR activation leads to L-type calcium channel activation. The aim of the current study is to test whether L-type calcium channels are downstream of AR and whether this signal pathway mediates the impairment effect of androgenic steroids on passive avoidance memory and synaptic plasticity. Materials and methodsWe measured the effect of Nandrolone Decanoate (AR agonist), AR antagonist (Nilutamide) plus ND or L-type calcium channel inhibitor (Nifedipine) plus ND on passive avoidance performance of adolescent male rats. For extracellular field potential recordings hippocampal slices were perfused with ND, Nilutamide-ND or Nifedipine-ND. Key findingsOur results clarified that AR activation by ND could impair avoidance behavior as step through latency decreased in ND-treated group while application of both Nilutamide and Nifedipine reestablished normal avoidance behavior. Also, LTP induction in the CA1 area of hippocampus was diminished by ND perfusion and both AR antagonist and L-type calcium channel inhibitor application lead to normal LTP. These findings support our hypothesis that activation of L-type calcium channels are involved in ARs mechanism effects on both avoidance behavior and hippocampal synaptic plasticity. SignificanceUnderstanding the biological effects of AR agonists on cognitive processes and its cellular mechanism may be a new/supplementary way to treating fear-related disorders.

Interaction effects of intracerebroventricular injection of crocin with the α2-adrenoceptors on memory deficit and hippocampal synaptic plasticity following chronic pain in rat

Patients with chronic pain exhibit anxiety and deficits in memory. Additionally, α2-adrenoceptors that are wildly expressed in the brain have an important role in modulating both pain and memory formation. In the present study, we investigated the interaction effects of crocin with central α2-adrenoceptors on pain comorbidity and hippocampal synaptic plasticity changes following chronic constriction injury (CCI) of the sciatic nerve in rats. All the drugs (crocin, an antagonist (yohimbine) and agonist (clonidine) of α2-adrenergic receptors) were injected (via intracerebroventricular injection) from the day of CCI operation (day 0) and continued daily (once per day) until the 14th day post-CCI. The effects of drugs on the cold allodynia (using acetone test) and anxiety-like behaviors (using elevated plus maze, EPM and open field tests) were assessed. Spatial memory (using Barnes maze) was assessed on day 14 post-CCI operation. Hippocampal synaptic plasticity (using in-vivo extracellular field potential recording) was performed on day 14 post-CCI operation. We observed that crocin induced analgesic, anxiolytic and memory enhancer action following CCI surgery. Furthermore, crocin significantly increased long-term potentiation (LTP) (increased fEPSP slope and population spike amplitude). Furthermore, the co-injection of yohimbine effectively decreased analgesic, anxiolytic and enhancer action of crocin on the LTP parameters (fEPSP slope and population spike amplitude). Our study provided information that protective effects of crocin on pain/anxiety responses and synaptic plasticity were possibly mediated by central α2-adrenoceptor in the rats with chronic pain.

FV 16 Long-term potentiation of synaptic plasticity in the temporal cortex of epilepsy patients – in search of a mechanism for memory impairment

Question: Modification of synaptic strength by neuronal activity underlies memory formation. Thus, long-term potentiation (LTP) of synaptic plasticity by electrical stimulation is an efficient model for studying memory at the neurophysiological level. Patients suffering from chronic epilepsy often present with memory deficits. We were therefore interested whether memory impairment was reflected in impacted LTP of synaptic plasticity in the human cortex of epileptic patients. Methods: We prepared acute human temporal cortex slices from resection specimens obtained during surgery for drug-resistant temporal lobe epilepsy. Extracellular field potential recordings were used to assess the induction of long-term potentiation by a standardized theta-burst stimulation protocol. Results: In the human temporal cortex, LTP was impaired and could only be induced sporadically. In some slices, theta-burst stimulation led to paradoxical induction of long-term depression of synaptic plasticity. By contrast, LTP was enhanced in the presence of a glucocorticoid receptor blocker. Conclusions: LTP induction in acute slices presents an opportunity to study the mechanisms underlying memory impairment in the human cortex. This model is a valuable complement to data from non-invasive recording modalities and stereo EEG, as it offers the unique possibility of pharmacological manipulation of synapses.

In vivo electrophysiological study of the targeting of 5-HT3 receptor-expressing cortical interneurons by the multimodal antidepressant, vortioxetine.

The antidepressant vortioxetine has high affinity for the ionotropic 5‐HT3 receptor (5‐HT3R) as well as other targets including the 5‐HT transporter. The procognitive effects of vortioxetine have been linked to altered excitatory:inhibitory balance in cortex. Thus, vortioxetine purportedly inhibits cortical 5‐HT3R‐expressing interneurons (5‐HT3R‐INs) to disinhibit excitatory pyramidal neurons. The current study determined for the first time the effect of vortioxetine on the in vivo firing of putative 5‐HT3R‐INs whilst simultaneously recording pyramidal neuron activity using cortical slow‐wave oscillations as a readout. Extracellular single unit and local field potential recordings were made in superficial layers of the prefrontal cortex of urethane‐anaesthetised rats. 5‐HT3R‐INs were identified by a short‐latency excitation evoked by electrical stimulation of the dorsal raphe nucleus (DRN). Juxtacellular‐labelling found such neurons had the morphological and immunohistochemical properties of 5‐HT3R‐INs: basket cell or bipolar cell morphology, expression of 5‐HT3R‐IN markers and parvalbumin‐immunonegative. Vortioxetine inhibited the short‐latency DRN‐evoked excitation of 5‐HT3R‐INs and simultaneously decreased cortical slow wave oscillations, indicative of pyramidal neuron activation. Likewise, the 5‐HT3R antagonist ondansetron inhibited the short‐latency DRN‐evoked excitation of 5‐HT3R‐INs. However unlike vortioxetine, ondansetron did not decrease cortical slow‐wave oscillations, suggesting a dissociation between this effect and inhibition of 5‐HT3R‐INs. The 5‐HT reuptake inhibitor escitalopram had no consistent effect on any electrophysiological parameter measured. Overall, the current findings suggest that vortioxetine simultaneously inhibits (DRN‐evoked) 5‐HT3R‐INs and excites pyramidal neurons, thereby changing the excitatory:inhibitory balance in cortex. However, under the current experimental conditions, these two effects were dissociable with only the former likely involving a 5‐HT3R‐mediated mechanism.

Pathological Human Tau Induces Alterations in the Brain Insulin Signaling Cascade.

The process of neurodegeneration in Alzheimer’s disease has been associated with a disruption of insulin signaling cascade in neurons, and to insulin resistance. T2DM correlates with Alzheimer’s disease, but mechanisms of interaction are unknown. We have developed a mouse model of tau induced neurodegeneration expressing pseudo-phosphorylated tau [Pathological Human Tau (PH-Tau)] in neurons. This model (PH-Tau-Tg) recapitulated cognitive decline and neurodegeneration observed in AD. In this study we examined if expression of PH-Tau could affect neuronal excitability and insulin receptor signaling. Neuronal excitability was investigated using intracerebral recordings of extracellular field potentials from prefrontal cortex after insulin and kainic acid (KA) injection. Analysis of baseline recordings indicated an increased excitability of PH-Tau-Tg as evidenced by higher spectrum densities (PSDs) of high frequencies brain waves. Injection of insulin (1IU, s.c) led to a decrease of fast ripples PSDs, more pronounced in PH-Tau-Tg mice than controls. Subsequent injection of kainic acid (KA, 5 mg/kg, s.c) led to significant increase in firing rate, amplitude of extracellular field potentials and PSDs of high frequency brain waves in control mice only. To further investigate the role of insulin in PH-Tau-Tg mice, we subjected mice to a glucose tolerance test. We found that PH-Tau-Tg mice were significantly hyperglycemic prior to glucose injection. Interestingly, the PH-Tau-Tg mice showed a moderate increase at 30 min due to the higher baseline, indicating a low sensitivity of insulin receptor in these mice. This is consistent with increased levels of activated insulin receptors in the brain and the inhibitory effect of insulin on ictal activity post KA injection in PH-Tau-Tg mice. We suggest that these mice have reduced insulin sensitivity (hyperglycemia) and as a compensatory mechanism there is overactivation/expression of insulin receptor in the brain rendering neuronal circuits resistant to seizure induction after injection of insulin. These data indicate that insulin signal transduction pathway is altered in PH-Tau-Tg mice, and that injection of exogenous insulin reduces hypersynchronous bursting activity of field potentials recorded from cortical neuronal circuits. We propose that the appearance of abnormal tau might potentiate the toxic environment by interfering with the insulin signaling cascade in the brain of patients with Alzheimer’s disease.

Abstract WP239: Sexually Dimorphic Amygdala Dysfunction In A Mouse Model Of Global Ischemia

Introduction: Advances in modern medicine have greatly increased chances of survival following traumatic events such as cardiac arrest, stroke, or heart attack. With more people able to recover from these ischemic insults, it is becoming apparent that survivors experience long-term effects as it relates to brain function. Despite clinical and animal model evidence of emotional dysfunctions following global ischemia, no study has attempted to identify amygdala dysfunction after Cardiac Arrest and subsequent Cardiopulmonary Resuscitation (CA/CPR). Utilizing a mouse model of CA/CPR-induced global ischemia, we have identified amygdala dysfunctions that are dependent on biological sex. We hypothesize that global ischemia results in deficits in amygdala-dependent learning tasks and circuit specific deficits of LTP in the basolateral amygdala (BLA). Methods: Seven days post CA-induced global ischemia, male and female adult C57BL/6 mice underwent amygdala dependent delay fear conditioning. In a separate cohort of animals acute-transverse slices were prepared seven days post global ischemia and extracellular field potential recordings were collected from the BLA. Results: We have revealed a sexually dimorphic deficit in amygdala dependent fear learning and memory. Both male and female mice display a previously reported contextual fear deficit (Male: 78.6 ± 2.6% sham freezing vs. 51.2±8.7% CA/CPR freezing, n=7; Female 70±5.1% sham freezing vs. 50.2±8.5% CA/CPR freezing, n=9), however, only male mice display a diminished freezing response to cued fear (56.4 ± 7.2% sham freezing vs. 31 ± 6.7% in CA/CPR, n=7). Similarly, plasticity involving cortical inputs to the basolateral amygdala is also disrupted in a sexually dimorphic manner, with only males displaying diminished LTP relative to sham controls (153.4 ± 8.1% of BL in controls, n=4 vs. 102.4 ± 3% of BL in CA/CPR, n=7). Conclusion: These results support the role of the amygdala in cognitive-affective impairments after CA-induced global ischemia and provide new insights into the role that biological sex plays in mediating brain dysfunction following CA. In the future, we will continue to unravel the mechanisms by which this sexually dimorphic impairment occurs and identify therapeutic targets.

Properties of the epileptiform activity in the cingulate cortex of a mouse model of LIS1 dysfunction

Dysfunction of the LIS1 gene causes lissencephaly, a drastic neurological disorder characterized by a deep disruption of the cortical structure. We aim to uncover alterations of the cortical neuronal networks related with the propagation of epileptiform activity in the Lis1/sLis1 mouse, a model lacking the LisH domain in heterozygosis. We did extracellular field-potential and intracellular recordings in brain slices of the anterior cingulate cortex (ACC) or the retrosplenial cortex (RSC) to study epileptiform activity evoked in the presence of bicuculline (10 µM), a blocker of GABAA receptors. The sensitivity to bicuculline of the generation of epileptiform discharges was similar in wild type (WT) and Lis1/sLis1 cortex (EC50 1.99 and 2.24 µM, respectively). In the Lis1/sLis1 cortex, we observed a decreased frequency of the oscillatory post-discharges of the epileptiform events; also, the propagation of epileptiform events along layer 2/3 was slower in the Lis1/sLis1 cortex (WT 47.69 ± 2.16 mm/s, n = 25; Lis1/sLis1 37.34 ± 2.43 mm/s, n = 15; p = 0.004). The intrinsic electrophysiological properties of layer 2/3 pyramidal neurons were similar in WT and Lis1/sLis1 cortex, but the frequency of the spontaneous EPSCs was lower and their peak amplitude higher in Lis1/sLis1 pyramidal neurons. Finally, the propagation of epileptiform activity was differently affected by AMPA receptor blockers: CNQX had a larger effect in both ACC and RSC while GYKI53655 had a larger effect only in the ACC in the WT and Lis1/sLis1 cortex. All these changes indicate that the dysfunction of the LIS1 gene causes abnormalities in the properties of epileptiform discharges and in their propagation along the layer 2/3 in the anterior cingulate cortex and in the restrosplenial cortex.

Assessing the Feasibility of Developing in vivo Neuroprobes for Parallel Intracellular Recording and Stimulation: A Perspective.

Developing novel neuroprobes that enable parallel multisite, long-term intracellular recording and stimulation of neurons in freely behaving animals is a neuroscientist’s dream. When fulfilled, it is expected to significantly enhance brain research at fundamental mechanistic levels including that of subthreshold signaling and computations. Here we assess the feasibility of merging the advantages of in vitro vertical nanopillar technologies that support intracellular recordings with contemporary concepts of in vivo extracellular field potential recordings to generate the dream neuroprobes that read the entire electrophysiological signaling repertoire.

Abstract 11267: Ibrutinib Treatment Results in Arrhythmia in Atrial-Specific Human Ipsc-Derived Cardiomyocytes

Introduction: Cardiovascular sequelae of targeted cancer therapies may provide novel insights into cardiovascular biology and disease pathogenesis, including atrial fibrillation (AF). The Bruton tyrosine kinase (BTK) inhibitor ibrutinib has revolutionized treatment for B-cell malignancies but increases the incidence of AF compared with conventional chemotherapy. Recent data in mouse models have shown that ibrutinib mediated-AF likely results not from inhibition of BTK (“on target” effect), but from off-target inhibition of a different kinase, C-terminal Src kinase (CSK). The signaling pathway by which CSK inhibition results in AF remains unknown and thus may represent a novel mechanism for AF molecular pathogenesis. Methods: To study how CSK inhibition results in AF in a human derived model, we created atrial specific cardiomyocytes from human induced pluripotent stem cells (hiPSC-aCMs) from a healthy control. We studied cellular monolayers of hiPSC-aCMs using extracellular field potential (EFP) recordings obtained by the Nanion CardioExcyte 96 system after 24 hour exposure to vehicle, ibrutinib, or the second generation BTK inhibitor acalabrutinib. Results: Chamber specificity of hiPSC-aCMs was confirmed by Western blot analysis of subtype-specific markers. Treatment with ibrutinib for 24 hours resulted in striking increase in beat-to-beat variability in spontaneous contraction, an in vitro correlate of arrhythmogenic behavior (mean coefficient-of-variance/second following treatment 0.835 for ibrutinib vs. 0.198 for acalabrutinib vs. 0.165 for DMSO vehicle control, p<0.001). Arrhythmogenic behavior was not seen with acalabrutinib, which does not appear to increase the incidence of AF in clinical trials. Conclusion: These experiments provide a novel method of screening for arrhythmogenic potential of targeted cancer therapies and validate atrial-specific hiPSC-CMs as a model system for the study of CSK mediated AF.

Nonhomogeneous volume conduction effects affecting needle electromyography: an analytical and simulation study

Objective. Needle electromyography (EMG) is used to study the electrical behavior of myofiber properties in patients with neuromuscular disorders. However, due to the complexity of electrical potential spatial propagation in nonhomogeneous diseased muscle, a comprehensive understanding of volume conduction effects remains elusive. Here, we develop a framework to study the conduction effect of extracellular abnormalities and electrode positioning on extracellular local field potential (LFP) recordings. Methods. The framework describes the macroscopic conduction of electrical potential in an isotropic, nonhomogeneous (i.e. two tissue) model. Numerical and finite element model simulations are provided to study the conduction effect in prototypical monopolar EMG measurements. Results. LFPs recorded are influenced in amplitude, phase and duration by the electrode position in regards to the vicinity of tissue with different electrical properties. Conclusion. The framework reveals the influence of multiple mechanisms affecting LFPs including changes in the distance between the source–electrode and tissue electrical properties. Clinical significance. Our modeled predictions may lead to new ways for interpreting volume conduction effects on recorded EMG activity, for example in neuromuscular diseases that cause structural and compositional changes in muscle tissue. These change will manifest itself by changing the electric properties of the conductor media and will impact recorded potentials in the area of affected tissue.

An organic transistor matrix for multipoint intracellular action potential recording

Electrode arrays are widely used for multipoint recording of electrophysiological activities, and organic electronics have been utilized to achieve both high performance and biocompatibility. However, extracellular electrode arrays record the field potential instead of the membrane potential itself, resulting in the loss of information and signal amplitude. Although much effort has been dedicated to developing intracellular access methods, their three-dimensional structures and advanced protocols prohibited implementation with organic electronics. Here, we show an organic electrochemical transistor (OECT) matrix for the intracellular action potential recording. The driving voltage of sensor matrix simultaneously causes electroporation so that intracellular action potentials are recorded with simple equipment. The amplitude of the recorded peaks was larger than that of an extracellular field potential recording, and it was further enhanced by tuning the driving voltage and geometry of OECTs. The capability of miniaturization and multiplexed recording was demonstrated through a 4 × 4 action potential mapping using a matrix of 5- × 5-μm2 OECTs. Those features are realized using a mild fabrication process and a simple circuit without limiting the potential applications of functional organic electronics.

ProBDNF Dependence of LTD and Fear Extinction Learning in the Amygdala of Adult Mice.

Neurotrophins are secreted proteins that control survival, differentiation, and synaptic plasticity. While mature neurotrophins regulate these functions via tyrosine kinase signaling (Trk), uncleaved pro-neurotrophins bind preferentially to the p75 neurotrophin receptor (p75NTR) and often exert opposite effects to those of mature neurotrophins. In the amygdala, brain-derived neurotrophic factor (BDNF) enables long-term potentiation as well as fear and fear extinction learning. In the present study, we focused on the impact of mature BDNF and proBDNF signaling on long-term depression (LTD) in the lateral amygdala (LA). Hence, we conducted extracellular field potential recordings in an in vitro slice preparation and recorded LTD in cortical and thalamic afferents to the LA. LTD was unchanged by acute block of BDNF/TrkB signaling. In contrast, LTD was inhibited by blocking p75NTR signaling, by disinhibition of the proteolytic cleavage of proBDNF into mature BDNF, and by preincubation with a function-blocking anti-proBDNF antibody. Since LTD-like processes in the amygdala are supposed to be related to fear extinction learning, we locally inhibited p75NTR signaling in the amygdala during or after fear extinction training, resulting in impaired fear extinction memory. Overall, these results suggest that in the amygdala proBDNF/p75NTR signaling plays a pivotal role in LTD and fear extinction learning.

Phoenixin-14 reduces the frequency of interictal-like events in mice brain slices

Phoenixin-14 (PNX-14) has a wide bioactivity in the central nervous system. Its role in the hypothalamus has been investigated, and it has been reported that it is involved in the regulation of excitability in hypothalamic neurons. However, its role in the regulation of excitability in entorhinal cortex and the hippocampus is unknown. In this study, we investigated whether i. PNX-14 induces any synchronous discharges or epileptiform activity and ii. PNX-14 has any effect on already initiated epileptiform discharges. We used 350 µm thick acute horizontal hippocampal-entorhinal cortex slices obtained from 30- to 35-day-old mice. Extracellular field potential recordings were evaluated in the entorhinal cortex and hippocampus CA1 region. Bath application of PNX-14 did not initiate any epileptiform activity or abnormal discharges. 4-Aminopyridine was applied to induce epileptiform activity in the slices. We found that 200nM PNX-14 reduced the frequency of interictal-like events in both the entorhinal cortex and hippocampus CA1 region which was induced by 4-aminopyridine. Furthermore, PNX-14 led to a similar suppression in the total power of local field potentials of 1-120Hz. The frequency or the duration of the ictal events was not affected. These results exhibited for the first time that PNX-14 has a modulatory effect on synchronized neuronal discharges which should be considered in future therapeutic approaches.