Increase In Membrane Capacitance Research Articles

Chronic Rapamycin Prevents Electrophysiological and Morphological Alterations Produced by Conditional Pten Deletion in Mouse Cortex.

Abnormalities in the mammalian target of the rapamycin (mTOR) pathway have been implicated in numerous developmental brain disorders. While the molecular and histological abnormalities have been described, less is known about alterations in membrane and synaptic excitability with chronic changes in the mTOR pathway. In the present study, we used a conditional mouse model with a deletion of the phosphatase and tensin homologue (Pten-/-, a negative regulator of mTOR) from cortical pyramidal neurons (CPNs). Whole-cell patch clamp recordings in ex vivo slices examined the intrinsic and synaptic membrane properties of layer II/III CPNs in normal mice treated with rapamycin for four weeks, and Pten-/- mice with and without chronic treatment with rapamycin. Compared with control mice, CPNs from Pten-/- mice demonstrated increased membrane capacitance and time constant in association with increased neuronal somatic size, reduced neuronal firing, and decreased frequency of spontaneous and miniature inhibitory postsynaptic currents, consistent with decreased pre-synaptic GABA release. Rapamycin treatment for four weeks prevented these changes in Pten-/- mice. CPNs from normal mice chronically treated with rapamycin, compared with CPNs from naïve mice, showed reduced capacitance and time constant, increased input resistance, and changes in inhibitory synaptic inputs, consistent with increased pre-synaptic GABA release. These results support the concept that Pten deletion results in significant changes in inhibitory inputs onto CPNs, and these alterations can be prevented with chronic rapamycin treatment. In addition, normal mice treated with rapamycin also display altered membrane and synaptic properties. These findings have potential implications for the treatment of neurological disorders associated with mTOR pathway dysfunction, such as epilepsy and autism.

Corticostriatal maldevelopment in the R6/2 mouse model of juvenile Huntington's disease.

There is a growing consensus that brain development in Huntington's disease (HD) is abnormal, leading to the idea that HD is not only a neurodegenerative but also a neurodevelopmental disorder. Indeed, structural and functional abnormalities have been observed during brain development in both humans and animal models of HD. However, a concurrent study of cortical and striatal development in a genetic model of HD is still lacking. Here we report significant alterations of corticostriatal development in the R6/2 mouse model of juvenile HD. We examined wildtype (WT) and R6/2 mice at postnatal (P) days 7, 14, and 21. Morphological examination demonstrated early structural and cellular alterations reminiscent of malformations of cortical development, and ex vivo electrophysiological recordings of cortical pyramidal neurons (CPNs) demonstrated significant age- and genotype-dependent changes of intrinsic membrane and synaptic properties. In general, R6/2 CPNs had reduced cell membrane capacitance and increased input resistance (P7 and P14), along with reduced frequency of spontaneous excitatory and inhibitory synaptic events during early development (P7), suggesting delayed cortical maturation. This was confirmed by increased occurrence of GABAA receptor-mediated giant depolarizing potentials at P7. At P14, the rheobase of CPNs was significantly reduced, along with increased excitability. Altered membrane and synaptic properties of R6/2 CPNs recovered progressively, and by P21 they were similar to WT CPNs. In striatal medium-sized spiny neurons (MSNs), a different picture emerged. Intrinsic membrane properties were relatively normal throughout development, except for a transient increase in membrane capacitance at P14. The first alterations in MSNs synaptic activity were observed at P14 and consisted of significant deficits in GABAergic inputs, however, these also were normalized by P21. In contrast, excitatory inputs began to decrease at this age. We conclude that the developing HD brain is capable of compensating for early developmental abnormalities and that cortical alterations precede and are a main contributor of striatal changes. Addressing cortical maldevelopment could help prevent or delay disease manifestations.

Corticostriatal Maldevelopment in the R6/2 Mouse Model of Juvenile Huntington's Disease.

There is a growing consensus that brain development in Huntington's disease (HD) is abnormal, leading to the idea that HD is not only a neurodegenerative but also a neurodevelopmental disorder. Indeed, structural and functional abnormalities have been observed during brain development in both humans and animal models of HD. However, a concurrent study of cortical and striatal development in a genetic model of HD is still lacking. Here we report significant alterations of corticostriatal development in the R6/2 mouse model of juvenile HD. We examined wildtype (WT) and R6/2 mice at postnatal (P) days 7, 14, and 21. Morphological examination demonstrated early structural and cellular alterations reminiscent of malformations of cortical development, and ex vivo electrophysiological recordings of cortical pyramidal neurons (CPNs) demonstrated significant age- and genotype-dependent changes of intrinsic membrane and synaptic properties. In general, R6/2 CPNs had reduced cell membrane capacitance and increased input resistance (P7 and P14), along with reduced frequency of spontaneous excitatory and inhibitory synaptic events during early development (P7), suggesting delayed cortical maturation. This was confirmed by increased occurrence of GABA A receptor-mediated giant depolarizing potentials at P7. At P14, the rheobase of CPNs was significantly reduced, along with increased excitability. Altered membrane and synaptic properties of R6/2 CPNs recovered progressively, and by P21 they were similar to WT CPNs. In striatal medium-sized spiny neurons (MSNs), a different picture emerged. Intrinsic membrane properties were relatively normal throughout development, except for a transient increase in membrane capacitance at P14. The first alterations in MSNs synaptic activity were observed at P14 and consisted of significant deficits in GABAergic inputs, however, these also were normalized by P21. In contrast, excitatory inputs began to decrease at this age. We conclude that the developing HD brain is capable of compensating for early developmental abnormalities and that cortical alterations precede and are a main contributor of striatal changes. Addressing cortical maldevelopment could help prevent or delay disease manifestations.

Regulation of XOR function of reduced human L2/3 pyramidal neurons.

The apical dendrites of human L2/3 pyramidal neurons are capable of performing XOR computation by modulating the amplitude of dendritic calcium action potentials (dCaAPs) mediated by calcium ions. What influences this particular function? There is still no answer to this question. In this study, we employed a rational and feasible reduction method to successfully derive simplified models of human L2/3 pyramidal neurons while preserving their detailed functional properties. Using a conductance-based model, we manipulated the membrane potential of the apical dendrite in the simplified model. Our findings indicate that an increase in sodium conductance ( ) and membrane capacitance ( ) weakens the XOR function, while regulation of potassium conductance ( ) demonstrates robustness in maintaining the XOR function. Further analysis reveals that when a single pathway is activated, an increase in and leads to decrease in the amplitude of dCaAPs, whereas increasing has a relatively minor impact on dCaAPs amplitude. In conclusion, although calcium ions play a crucial role in enabling apical dendrites of human L2/3 pyramidal neurons to perform XOR computation, other ion channels' conductance and membrane capacitance can also influence this function.

Responses in fast-spiking interneuron firing rates to parameter variations associated with degradation of perineuronal nets

The perineuronal nets (PNNs) are sugar coated protein structures that encapsulate certain neurons in the brain, such as parvalbumin positive (PV) inhibitory neurons. As PNNs are theorized to act as a barrier to ion transport, they may effectively increase the membrane charge-separation distance, thereby affecting the membrane capacitance. Tewari et al. (2018) found that degradation of PNNs induced a 25%-50% increase in membrane capacitance c_text {m} and a reduction in the firing rates of PV-cells. In the current work, we explore how changes in c_text {m} affects the firing rate in a selection of computational neuron models, ranging in complexity from a single compartment Hodgkin-Huxley model to morphologically detailed PV-neuron models. In all models, an increased c_text {m} lead to reduced firing, but the experimentally reported increase in c_text {m} was not alone sufficient to explain the experimentally reported reduction in firing rate. We therefore hypothesized that PNN degradation in the experiments affected not only c_text {m}, but also ionic reversal potentials and ion channel conductances. In simulations, we explored how various model parameters affected the firing rate of the model neurons, and identified which parameter variations in addition to c_text {m} that are most likely candidates for explaining the experimentally reported reduction in firing rate.

Persistent Firing in Hippocampal CA1 Pyramidal Cells in Young and Aged Rats.

Persistent neuronal firing is often observed in working memory and temporal association tasks both in humans and animals, and is believed to retain necessary information in these tasks. We have reported that hippocampal CA1 pyramidal cells are able to support persistent firing through intrinsic mechanisms in the presence of cholinergic agonists. However, it still remains largely unknown how persistent firing is affected by the development of animals and aging. Using in vitro patch-clamp recordings from CA1 pyramidal cells in rat brain slices, we first show that the cellular excitability of these aged rats was significantly lower than the young rats, responding with fewer spikes to current injection. In addition, we found age-dependent modulations of input resistance, membrane capacitance, and spike width. However, persistent firing in aged (~2 years old) rats was as strong as that in young animals, and the properties of persistent firing were very similar among different age groups. In addition, spike after-hyperpolarization potential (AHP), was not increased by aging and did not correlate with the strength of persistent firing. Lastly, we estimated the depolarization current induced by the cholinergic activation. This current was proportional to the increased membrane capacitance of the aged group and was inversely correlated with the intrinsic excitability of cells. These observations indicate that robust persistent firing can be maintained in aged rats despite reduced excitability, due to the increased amount of cholinergically induced positive current.Significant statement:In an aging society, it is crucial to understand neural mechanisms underlying age-dependent cognitive impairments. In recent years, the importance of intrinsic cellular properties in cognitive functions such as memory has increasingly been recognized. However, research examining age-dependent alteration of intrinsic cellular mechanisms of persistent firing, which is believed to support working memory function, has so far been very scarce. In this study, we demonstrate that the ability to support persistent firing is kept intact in neurons from old rats, despite changes in other properties such as intrinsic excitability. These results identify the ability to support persistent firing as one potential cellular mechanism of rescued cognitive functions under cholinergic enhancement used in Alzheimer's disease and other dementias.

Changes in Electrical Capacitance of Cell Membrane Reflect Drug Partitioning-Induced Alterations in Lipid Bilayer

The plasma membrane is a lipid bilayer that establishes the outer boundary of a living cell. The composition of the lipid bilayer influences the membrane's biophysical properties, including fluidity, thickness, permeability, phase behavior, charge, elasticity, and formation of flat sheet or curved structures. Changes in the biophysical properties of the membrane can be occasioned when new entities, such as drug molecules, are partitioned in the bilayer. Therefore, assessing drugs for their effect on the biophysical properties of the lipid bilayer of a cell membrane is critical to understanding specific and non-specific drug action. Previously, we reported a non-invasive technique for real-time characterization of cellular dielectric properties, such as membrane capacitance and cytoplasmic conductivity. In this study, we discuss the potential application of the technique in assessing the biophysical properties of the cell membrane in response to interaction with amiodarone compared to aspirin/acetylsalicylic acid and glucose. Amiodarone is a potent drug used to treat cardiac arrhythmia, but it also exerts various non-specific effects. Compared to aspirin and glucose, we measured a rapid and higher magnitude increase in membrane capacitance on cells under amiodarone treatment. Increased membrane capacitance induced by aspirin and glucose quickly returned to baseline in 15 s, while amiodarone-induced increased capacitance sustained and decreased slowly, approaching baseline or another asymptotic limit in ~2.5 h. Because amiodarone has a strong lipid partitioning property, we reason that drug partitioning alters the lipid bilayer context and subsequently reduces bilayer thickness, leading to an increase in the electrical capacitance of the cell membrane. The presented microfluidic system promises a new approach to assess drug-membrane interactions and delineate specific and non-specific actions of the drug on cells.

Development of a simultaneous electrorotation device with microwells for monitoring the rotation rates of multiple single cells upon chemical stimulation.

Here, we described a unique simultaneous electrorotation (ROT) device for monitoring the rotation rate of Jurkat cells via chemical stimulation without fluorescent labeling and an algorithm for estimating cell rotation rates. The device comprised two pairs of interdigitated array electrodes that were stacked orthogonally through a 20 μm-thick insulating layer with rectangular microwells. Four microelectrodes (two were patterned on the bottom of the microwells and the other two on the insulating layer) were arranged on each side of the rectangular microwells. The cells, which were trapped in the microwells, underwent ROT when AC voltages were applied to the four microelectrodes to generate a rotating electric field. These microwells maintained the cells even in fluid flows. Thereafter, the ROT rates of the trapped cells were estimated and monitored during the stimulation. We demonstrated the feasibility of estimating the chemical efficiency of cells by monitoring the ROT rates of the cells. After introducing a Jurkat cell suspension into the device, the cells were subjected to ROT by applying an AC signal. Further, the rotating cells were chemically stimulated by adding an ionomycin (a calcium ionophore)-containing aliquot. The ROT rate of the ionomycin-stimulated cells decreased gradually to 90% of the initial rate after 30 s. The ROT rate was reduced by an increase in membrane capacitance. Thus, our device enabled the simultaneous chemical stimulation-induced monitoring of the alterations in the membrane capacitances of many cells without fluorescent labeling.

Noradrenaline and ATP regulate adiponectin exocytosis in white adipocytes: Disturbed adrenergic and purinergic signalling in obese and insulin-resistant mice

White adipocyte adiponectin exocytosis is triggered by cAMP and a concomitant increase of cytosolic Ca2+ potentiates its release. White adipose tissue is richly innervated by sympathetic nerves co-releasing noradrenaline (NA) and ATP, which may act on receptors in the adipocyte plasma membrane to increase cAMP via adrenergic receptors and Ca2+ via purinergic receptors. Here we determine the importance of NA and ATP for the regulation of white adipocyte adiponectin exocytosis, at the cellular and molecular level, and we specifically detail the ATP signalling pathway. We demonstrate that tyrosine hydroxylase (enzyme involved in catecholamine synthesis) is dramatically reduced in inguinal white adipose tissue (IWAT) isolated from mice with diet-induced obesity; this is associated with diminished levels of NA in IWAT and with a reduced ratio of high-molecular-weight (HMW) to total adiponectin in serum. Adiponectin exocytosis (measured as an increase in plasma membrane capacitance and as secreted product) is triggered by NA or ATP alone in cultured and primary mouse IWAT adipocytes, and enhanced by a combination of the two secretagogues. The ATP-induced adiponectin exocytosis is largely Ca2+-dependent and activated via purinergic P2Y2 receptors (P2Y2Rs) and the Gq11/PLC pathway. Adiponectin release induced by the nucleotide is abrogated in adipocytes isolated from obese and insulin-resistant mice, and this is associated with ∼70% reduced abundance of P2Y2Rs. The NA-triggered adiponectin exocytosis is likewise abolished in “obese adipocytes”, concomitant with a 50% lower gene expression of beta 3 adrenergic receptors (β3ARs). An increase in intracellular Ca2+ is not required for the NA-stimulated adiponectin secretion. Collectively, our data suggest that sympathetic innervation is a principal regulator of adiponectin exocytosis and that disruptions of this control are associated with the obesity-associated reduction of circulating levels of HMW/total adiponectin.

Therapeutic concentrations of varenicline increases exocytotic release of catecholamines from human and rat adrenal chromaffin cells in the presence of nicotine

Cardiovascular side effects of varenicline and a case report of a hypertensive crisis in a varenicline-prescribed patient with pheochromocytoma have been reported. The goal of the present study was to determine whether such side effects might derive, in part, from increased exocytosis of secretory vesicles and subsequent catecholamine release triggered by varenicline in human chromaffin cells of the adrenal gland. In this study, we performed electrophysiological plasma membrane capacitance and carbon fiber amperometry experiments to evaluate the effect of varenicline on exocytosis and catecholamine release, respectively, at concentrations reached during varenicline therapy (100 nM). Experiments were conducted in the absence or presence of nicotine, at plasma concentrations achieved right after smoking (250 nM) or steady-state concentrations (110 nM), in chromaffin cells of the adrenal gland obtained from human organ donors. Cells were stimulated with short pulses (10 ms) of acetylcholine (ACh; 300 μM) applied at 0.2 Hz, in order to closer mimic the physiological situation at the splanchnic nerve-chromaffin cell synapse. In addition, rat chromaffin cells were used to compare the effects obtained in cells from a more readily available species. Varenicline increased the exocytosis of secretory vesicles in human and rat chromaffin cells in the presence of nicotine, effects that were not due to an increase of plasma membrane capacitance or currents triggered by the nicotinic agonists alone. These results should be considered in nicotine addiction therapies when varenicline is used.

A dark quencher genetically encodable voltage indicator (dqGEVI) exhibits high fidelity and speed

Voltage sensing with genetically expressed optical probes is highly desirable for large-scale recordings of neuronal activity and detection of localized voltage signals in single neurons. Most genetically encodable voltage indicators (GEVI) have drawbacks including slow response, low fluorescence, or excessive bleaching. Here we present a dark quencher GEVI approach (dqGEVI) using a Förster resonance energy transfer pair between a fluorophore glycosylphosphatidylinositol-enhanced green fluorescent protein (GPI-eGFP) on the outer surface of the neuronal membrane and an azo-benzene dye quencher (D3) that rapidly moves in the membrane driven by voltage. In contrast to previous probes, the sensor has a single photon bleaching time constant of ∼40 min, has a high temporal resolution and fidelity for detecting action potential firing at 100 Hz, resolves membrane de- and hyperpolarizations of a few millivolts, and has negligible effects on passive membrane properties or synaptic events. The dqGEVI approach should be a valuable tool for optical recordings of subcellular or population membrane potential changes in nerve cells.

An Approach to Monitor Exocytosis in White Adipocytes.

Exocytosis, the fusion of vesicles with the plasma membrane, can be measured with the patch-clamp technique as increases in membrane capacitance. Here we provide detailed information on how to monitor white adipocyte exocytosis using this method. We describe how to isolate the stromal vascular fraction of cells (SVF) within adipose tissue and how to differentiate SVF and cultured 3T3-L1 cells into adipocytes suitable for patch-clamp studies. We also give detailed protocols of how to record and analyze exocytosis in the differentiated cells.

A survey of pathways for mechano-electric coupling in the atria

Mechano-electric coupling (MEC) in atrial tissue has received sparse investigation to date, despite the well-known association between chronic atrial dilation and atrial fibrillation (AF). Of note, no fewer than six different mechanisms pertaining to stretch-activated channels, cellular capacitance and geometric effects have been identified in the literature as potential players. In this mini review, we briefly survey each of these pathways to MEC. We then perform computational simulations using single cell and tissue models in presence of various stretch regimes and MEC pathways. This allows us to assess the relative significance of each pathway in determining action potential duration, conduction velocity and rotor stability. For chronic atrial stretch, we find that stretch-induced alterations in membrane capacitance decrease conduction velocity and increase action potential duration, in agreement with experimental findings. In the presence of time-dependent passive atrial stretch, stretch-activated channels play the largest role, leading to after-depolarizations and rotor hypermeandering. These findings suggest that physiological atrial stretches, such as passive stretch during the atrial reservoir phase, may play an important part in the mechanisms of atrial arrhythmogenesis.

Neuronal firing modulation by a membrane-targeted photoswitch

Optical technologies allowing modulation of neuronal activity at high spatio-temporal resolution are becoming paramount in neuroscience. In this respect, azobenzene-based photoswitches are promising nanoscale tools for neuronal photostimulation. Here we engineered a light-sensitive azobenzene compound (Ziapin2) that stably partitions into the plasma membrane and causes its thinning through trans-dimerization in the dark, resulting in an increased membrane capacitance at steady state. We demonstrated that in neurons loaded with the compound, millisecond pulses of visible light induce a transient hyperpolarization followed by a delayed depolarization that triggers action potential firing. These effects are persistent and can be evoked in vivo up to 7 days, proving the potential of Ziapin2 for the modulation of membrane capacitance in the millisecond timescale, without directly affecting ion channels or local temperature.

Magnetoencephalographic Correlates of Suicidal Ideation in Major Depression

BackgroundDefining the neurobiological underpinnings of suicidal ideation (SI) is crucial to improving our understanding of suicide. This study used magnetoencephalographic gamma power as a surrogate marker for population-level excitation-inhibition balance to explore the underlying neurobiology of SI and depression. In addition, effects of pharmacological intervention with ketamine, which has been shown to rapidly reduce SI and depression, were assessed. MethodsData were obtained from 29 drug-free patients with major depressive disorder who participated in an experiment comparing subanesthetic ketamine (0.5 mg/kg) with a placebo saline infusion. Magnetoencephalographic recordings were collected at baseline and after ketamine and placebo infusions. During scanning, patients rested with their eyes closed. SI and depression were assessed, and a linear mixed-effects model was used to identify brain regions where gamma power and both SI and depression were associated. Two regions of the salience network (anterior insula, anterior cingulate) were then probed using dynamic causal modeling to test for ketamine effects. ResultsClinically, patients showed significantly reduced SI and depression after ketamine administration. In addition, distinct regions in the anterior insula were found to be associated with SI compared with depression. In modeling of insula–anterior cingulate connectivity, ketamine lowered the membrane capacitance for superficial pyramidal cells. Finally, connectivity between the insula and anterior cingulate was associated with improvements in depression symptoms. ConclusionsThese findings suggest that the anterior insula plays a key role in SI, perhaps via its role in salience detection. In addition, transient changes in superficial pyramidal cell membrane capacitance and subsequent increases in cortical excitability might be a mechanism through which ketamine improves SI.

Characterization of sequentially-staged cancer cells using electrorotation.

The identification and separation of cells from heterogeneous populations is critical to the diagnosis of diseases. Label-free methodologies in particular have been developed to manipulate individual cells using properties such as density and morphology. The electrical properties of malignant cells, including the membrane capacitance and cytoplasmic conductivity, have been demonstrated to be altered compared to non-malignant cells of similar origin. Here, we exploit these changes to characterize individual cells in a sequentially-staged in vitro cancer model using electrorotation (EROT)—the rotation of a cell induced by a rotating electric field. Using a microfabricated device, a dielectrophoretic force to suspend cells while measuring their angular velocity resulting from an EROT force applied at frequencies between 3 kHz to 10 MHz. We experimentally determine the EROT response for cells at three stages of malignancy and analyze the resultant spectra by considering models that include the effect of the cell membrane alone (single-shell model) and the combined effect of the cell membrane and nucleus (double-shell model). We find that the cell membrane is largely responsible for a given cell’s EROT response between 3 kHz and 10 MHz. Our results also indicate that membrane capacitance, membrane conductance, and cytoplasmic conductivity increase with an increasingly malignant phenotype. Our results demonstrate the potential of using electrorotation as a means making of non-invasive measurements to characterize the dielectric properties of cancer cells.

PMP22 Regulates Cholesterol Trafficking and ABCA1-Mediated Cholesterol Efflux.

The absence of functional peripheral myelin protein 22 (PMP22) is associated with shortened lifespan in rodents and severe peripheral nerve myelin abnormalities in several species including humans. Schwann cells and nerves from PMP22 knock-out (KO) mice show deranged cholesterol distribution and aberrant lipid raft morphology, supporting an unrecognized role for PMP22 in cellular lipid metabolism. To examine the mechanisms underlying these abnormalities, we studied Schwann cells and nerves from male and female PMP22 KO mice. Whole-cell current-clamp recordings in cultured Schwann cells revealed increased membrane capacitance and decreased membrane resistance in the absence of PMP22, which was consistent with a reduction in membrane cholesterol. Nerves from PMP22-deficient mice contained abnormal lipid droplets, with both mRNA and protein levels of apolipoprotein E (apoE) and ATP-binding cassette transporter A1 (ABCA1) being highly upregulated. Despite the upregulation of ABCA1 and apoE, the absence of PMP22 resulted in reduced localization of the transporter to the cell membrane and diminished secretion of apoE. The absence of PMP22 also impaired ABCA1-mediated cholesterol efflux capacity. In nerves from ABCA1 KO mice, the expression of PMP22 was significantly elevated and the subcellular processing of the overproduced protein was aberrant. In wild-type samples, double immunolabeling identified overlapping distribution of PMP22 and ABCA1 at the Schwann cell plasma membrane and the two proteins were coimmunoprecipitated from Schwann cell and nerve lysates. Together, these results reveal a novel role for PMP22 in regulating lipid metabolism and cholesterol trafficking through functional interaction with the cholesterol efflux regulatory protein ABCA1.SIGNIFICANCE STATEMENT Understanding the subcellular events that underlie abnormal myelin formation in hereditary neuropathies is critical for advancing therapy development. Peripheral myelin protein 22 (PMP22) is an essential peripheral myelin protein because its genetic abnormalities account for ∼80% of hereditary neuropathies. Here, we demonstrate that in the absence of PMP22, the cellular and electrophysiological properties of the Schwann cells' plasma membrane are altered and cholesterol trafficking and lipid homeostasis are perturbed. The molecular mechanisms for these abnormalities involve a functional interplay among PMP22, cholesterol, apolipoprotein E, and the major cholesterol-efflux transporter protein ATP-binding cassette transporter A1 (ABCA1). These findings establish a critical role for PMP22 in the maintenance of cholesterol homeostasis in Schwann cells.

Fast-Spiking Interneurons Exposed in Tumor-Associated Epilepsy.

Perineuronal Nets Decrease Membrane Capacitance of Peritumoral Fast Spiking Interneurons in a Model of Epilepsy Tewari BP, Chaunsali L, Campbell SL, Patel DC, Goode AE, and Sontheimer H. Nat Commun. 2018;9(1):4724. doi:10.1038/s41467-018-07113-0Patients with brain tumor commonly present with epileptic seizures. We show that tumor-associated seizures are the consequence of impaired GABAergic inhibition due to an overall loss of peritumoral fast-spiking interneurons (FSNs) concomitant with a significantly reduced firing rate of those that remain. The reduced firing is due to the degradation of perineuronal nets (PNNs) that surround FSNs. We show that PNNs decrease specific membrane capacitance of FSNs permitting them to fire action potentials at supraphysiological frequencies. Tumor-released proteolytic enzymes degrade PNNs, resulting in increased membrane capacitance, reduced firing, and hence decreased GABA release. These studies uncovered a hitherto unknown role of PNNs as an electrostatic insulator that reduces specific membrane capacitance, functionally akin to myelin sheaths around axons, thereby permitting FSNs to exceed physiological firing rates. Disruption of PNNs may similarly account for excitation-inhibition imbalances in other forms of epilepsy and PNN protection through proteolytic inhibition may provide therapeutic benefits.

Perineuronal nets decrease membrane capacitance of peritumoral fast spiking interneurons in a model of epilepsy

Brain tumor patients commonly present with epileptic seizures. We show that tumor-associated seizures are the consequence of impaired GABAergic inhibition due to an overall loss of peritumoral fast spiking interneurons (FSNs) concomitant with a significantly reduced firing rate of those that remain. The reduced firing is due to the degradation of perineuronal nets (PNNs) that surround FSNs. We show that PNNs decrease specific membrane capacitance of FSNs permitting them to fire action potentials at supra-physiological frequencies. Tumor-released proteolytic enzymes degrade PNNs, resulting in increased membrane capacitance, reduced firing, and hence decreased GABA release. These studies uncovered a hitherto unknown role of PNNs as an electrostatic insulator that reduces specific membrane capacitance, functionally akin to myelin sheaths around axons, thereby permitting FSNs to exceed physiological firing rates. Disruption of PNNs may similarly account for excitation-inhibition imbalances in other forms of epilepsy and PNN protection through proteolytic inhibition may provide therapeutic benefits.

Cell Surface N-Glycans Influence Electrophysiological Properties and Fate Potential of Neural Stem Cells.

SummaryUnderstanding the cellular properties controlling neural stem and progenitor cell (NSPC) fate choice will improve their therapeutic potential. The electrophysiological measure whole-cell membrane capacitance reflects fate bias in the neural lineage but the cellular properties underlying membrane capacitance are poorly understood. We tested the hypothesis that cell surface carbohydrates contribute to NSPC membrane capacitance and fate. We found NSPCs differing in fate potential express distinct patterns of glycosylation enzymes. Screening several glycosylation pathways revealed that the one forming highly branched N-glycans differs between neurogenic and astrogenic populations of cells in vitro and in vivo. Enhancing highly branched N-glycans on NSPCs significantly increases membrane capacitance and leads to the generation of more astrocytes at the expense of neurons with no effect on cell size, viability, or proliferation. These data identify the N-glycan branching pathway as a significant regulator of membrane capacitance and fate choice in the neural lineage.