Potassium Channels In Neurons Research Articles

EFFICACY AND TOLERABILITY OF FLUPIRTINE MALEATE VERSUS DICLOFENAC IN MECHANICAL LOW BACK PAIN – A PROSPECTIVE COMPARATIVE STUDY

Objective: Low back pain (LBW) is one of the most common reasons for adults visiting orthopedic outpatient clinics in our country. The objective of the study was to compare the safety and efficacy of flupirtine, a selective neuronal potassium channel opener, with diclofenac, a widely used NSAIDs analgesic, in patients with mechanical LBW (MLBP). Methods: This prospective, open-labeled, and randomized comparative clinical study included 100 patients with MLBP for more than 6 weeks. Fifty patients received flupirtine 100 mg, and 50 patients received diclofenac 100 mg for 7 days. Follow-up was done on day 8 and day 30. Assessments of functional improvement by the Oswestry Disability Index (ODI), pain relief by the Visual Analog Scale (VAS), Numerical Rating Scale (NRS), and Pain Relief Rate (PRR) were recorded. Safety and tolerability were also assessed. Data were analyzed using the Chi-square and Paired student t-tests. Results: VAS, NRS, and ODI scores were assessed for each visit (0, 1, and 2), and PRR was assessed on visits 1 and 2. VAS (p<0.05), NRS (p<0.05) scores, and sustained effect after stoppage of the drug were found to be better in the flupirtine group compared to the diclofenac group. Flupirtine was well tolerated. More patients reported adverse events in diclofenac than in the flupirtine group. Conclusion: Flupirtine may have a superior sustained effect compared to diclofenac in MLBP.

Intrinsic and Extrinsic Tongue Muscles are Driven by Physiologically Distinct Motoneuron Pools

The hypoglossal motor nucleus innervates six of the seven tongue muscles responsible for wide-ranging behaviors including speech, breathing, and swallowing. Despite the task-specific nature of tongue movements, neurophysiologic research has historically treated hypoglossal motoneurons as a homogeneous population. Our previous work showed that hypoglossal motoneurons innervating specific tongue muscles had different firing thresholds and resting membrane potential. Here, we extend this work by comparing potassium conductance in motor neurons innervating the superior longitudinalis (SL; intrinsic) and genioglossus (GG; extrinsic), tongue muscles with opposing actions of tongue retraction and tongue protrusion, respectively. Experiments were performed using N=10 neonatal rat pups aged post-natal day 0-5 ( n=5 each of SL and GG). Motoneurons were back-labeled by injection of dextran rhodamine conjugated to Texas Red into either the SL or GG muscle. > 24-hours after injection, animals were anesthetized on ice and decapitated. The brainstem and spinal cord were removed and 250 μm transverse slices of the medulla containing the hypoglossal nucleus were obtained. SL or GG motor neurons were visualized under a fluorescence microscope and resting membrane potential, rheobase current, frequency-current relation and potassium currents were recorded using whole-cell patch clamp. Statistical analysis revealed that SL motoneurons were ~11 mV more depolarized than GG motoneurons (resting membrane potential of -49 vs -60 mV, p<0.05). Rheobase current (the minimal electrical current required to evoke an action potential) was greater in GG motoneurons than SL motoneurons (approximately 300 vs 150 pA, p<0.05). SL motoneurons had a higher firing rate than GG motoneurons in response to current injection ( p<0.05). Evaluation of neuronal potassium channel conductance showed that the magnitude of transient ( p < 0.01) and sustained (p < 0.01) potassium currents were greater in GG than SL motoneurons, consistent with our finding that resting membrane potential was more negative, and firing rate was slower, in GG than SL motoneurons. Finally, additional SL motoneuron recordings were performed to evaluate for potential sex differences in N=12 (6 male) rat pups aged post-natal day 0-5. Preliminary analysis revealed no significant difference in resting membrane potential between male (-49 mV) and female (-52 mV) SL motoneurons, suggesting that the properties of a specific hypoglossal motoneuron pool are consistent across sexes. Overall, these results demonstrate that GG motoneurons are less excitable than SL motoneurons, which supports the idea that intrinsic and extrinsic tongue muscles are driven by physiologically distinct motoneuron pools. This work has potential to guide development of therapeutics for disordered speech, breathing, and swallowing, all of which depend on proper neuromotor control of the tongue. This work was funded by NIH 5R01DC020889-02. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Participation of calcium-permeable AMPA receptors in the regulation of epileptiform activity of hippocampal neurons.

Epileptiform activity is the most striking result of hyperexcitation of a group of neurons that can occur in different brain regions and then spread to other sites. Later it was shown that these rhythms have a cellular correlate in vitro called paroxysmal depolarization shift (PDS). In 13-15 DIV neuron-glial cell culture, inhibition of the GABA(A) receptors induces bursts of action potential in the form of clasters PDS and oscillations of intracellular Ca2+ concentration ([Ca2+]i). We demonstrate that GABAergic neurons expressing calcium-permeable AMPA receptors (CP-AMPARs) as well as Kv7-type potassium channels regulate hippocampal glutamatergic neurons' excitability during epileptiform activity in culture. A combination of whole-cell patch-clamp in current clamp mode and calcium imaging microscopy was used to simultaneously register membrane potential and [Ca2+]i level. To identify GABAergic cell cultures were fixed and stained with antibodies against glutamate decarboxylase GAD 65/67 and neuron-specific enolase (NSE) after vital [Ca2+]i imaging. It was shown that CP-AMPARs are involved in the regulation of the PDS clusters and [Ca2+]i pulses accompanied them. Activation of CP-AMPARs of GABAergic neurons is thought to cause the release of GABA, which activates the GABA(B) receptors of other GABAergic interneurons. It is assumed that activation of these GABA(B) receptors leads to the release of beta-gamma subunits of Gi protein, which activate potassium channels, resulting in hyperpolarization and inhibition of these interneurons. The latter causes disinhibition of glutamatergic neurons, the targets of these interneurons. In turn, the CP-AMPAR antagonist, NASPM, has the opposite effect. Measurement of membrane potential in GABAergic neurons by the patch-clamp method in whole-cell configuration demonstrated that NASPM suppresses hyperpolarization in clusters and individual PDSs. It is believed that Kv7-type potassium channels are involved in the control of hyperpolarization during epileptiform activity. The blocker of Kv7 channels, XE 991, mimicked the effect of the CP-AMPARs antagonist on PDS clusters. Both drugs increased the duration of the PDS cluster. In turn, the Kv7 activator, retigabine, decreased the duration of the PDS cluster and Ca2+ pulse. In addition, retigabine led to deep posthyperpolarization at the end of the PDS cluster. The Kv7 channel is believed to be involved in the formation of PDS, as the channel blocker reduced the rate of hyperpolarization in the PDS almost three times. Thus, GABAergic neurons expressing CP-AMPARs, regulate the membrane potential of innervated glutamatergic neurons by modulating the activity of postsynaptic potassium channels of other GABAergic neurons.

Design of Ultrapotent Genetically Encoded Inhibitors ofKv4.2 for Gating Neural Plasticity.

The Kv4.2 potassium channel plays established roles in neuronal excitability, while also being implicated in plasticity. Current means to study the roles of Kv4.2 are limited, motivating us to design a genetically encoded membrane tethered Heteropodatoxin-2 (MetaPoda). We find that MetaPoda is an ultrapotent and selective gating-modifier of Kv4.2. We narrow its site of contact with the channel to two adjacent residues within the voltage sensitive domain (VSD) and, with docking simulations, suggest that the toxin binds the VSD from within the membrane. We also show that MetaPoda does not require an external linker of the channel for its activity. In neurons (obtained from female and male rat neonates), MetaPoda specifically, and potently, inhibits all Kv4 currents, leaving all other A-type currents unaffected. Inhibition of Kv4 in hippocampal neurons does not promote excessive excitability, as is expected from a simple potassium channel blocker. We do find that MetaPoda's prolonged expression (1 week) increases expression levels of the immediate early gene cFos and prevents potentiation. These findings argue for a major role of Kv4.2 in facilitating plasticity of hippocampal neurons. Lastly, we show that our engineering strategy is suitable for the swift engineering of another potent Kv4.2-selective membrane-tethered toxin, Phrixotoxin-1, denoted MetaPhix. Together, we provide two uniquely potent genetic tools to study Kv4.2 in neuronal excitability and plasticity.

Optogenetic stimulation suppresses ictal activity in a 4-aminopyridine model of epileptic activity <i>in vitro</i>

The WHO estimates that nearly 1% of the population suffers from epilepsy. Despite advances in the development of new antiepileptic drugs, seizures cannot be completely eliminated in nearly one-third of patients. One promising approach to the treatment of epilepsy may be gene therapy. Because epileptic activity is caused by an imbalance between excitation and inhibition, researchers have focused primarily on regulating neuronal excitability. Initially, the main approaches were based on the hyperexpression of inhibitory peptides such as galanin or NPY, or the suppression of neuronal excitability by the hyperexpression of potassium channels in neurons. However, these effects should be well calculated and strictly dosed, as it is difficult to correct the expression later. If the expression is too low, the anticonvulsant effect will not be achieved, and if the expression is too high, the neuronal networks will be impaired due to strong inhibition. For this reason, methodological approaches to treatment in which the effect on the neuronal excitability in the epileptic focus can be controlled are of great interest. Optogenetic methods offer such an advantage. Optogenetics uses light to alter the excitability of specific neuronal populations and can also be used in a biofeedback paradigm in which the light source is activated only at the risk of generating seizure activity. A number of optogenetic tools have now been developed, including light-activated cationic (e.g., ChR2) and anion channels (ACR), metabotropic receptors, pumps (NpHR, Arch), and enzymes. However, the optogenetic approach has a number of technical difficulties in delivering the light source and the risk of developing an immune response to the expression of rhodopsins. This report reviews the experience of practical application of optogenetic tools in the use of 4-aminopyridine in vitro model of epileptiform activity in experiencing slices of the entorhinal cortex. We tested the efficacy of suppressing ictal activity using several variants of optogenetic stimulation: (1) activation of excitatory and inhibitory neurons (in Thy1-ChR2-YFP mice), (2) activation of inhibitory interneurons only (in PV-Cre mice after virus injection with the channelodopsin-2 gene), hyperpolarization of excitatory neurons after expression of (3) archaeodopsin or (4) a light-dependent sodium pump. We found that ictal activity was successfully suppressed when low-frequency optogenetic stimulation induced regular interictal activity. Usually, interictal activity was induced by rhythmic synchronous activation of the principal neurons of the entorhinal cortex. In other cases, the ictal activity was preserved, although its characteristics may have changed. We determined the parameters of optogenetic stimulation that were most effective in suppressing ictal activity. The availability of a wide range of gene therapy approaches for epilepsy that have demonstrated efficacy in preclinical studies suggests that clinical trials of some of these approaches will begin in the next few years.

Modulation of potassium conductances optimizes fidelity of auditory information.

Potassium channels in auditory neurons are rapidly modified by changes in the auditory environment. In response to elevated auditory stimulation, short-term mechanisms such as protein phosphorylation and longer-term mechanisms such as accelerated channel synthesis increase the amplitude of currents that promote high-frequency firing. It has been suggested that this allows neurons to fire at high rates in response to high sound levels. We have carried out simple simulations of the response to postsynaptic neurons to patterns of neurotransmitter release triggered by auditory stimuli. These demonstrate that the amplitudes of potassium currents required for optimal encoding of a low-amplitude auditory signal differ from those for louder sounds. Specifically, the cross-correlation of the output of a neuron with an auditory stimulus is improved by increasing potassium currents as sound amplitude increases. Temporal fidelity for low-frequency stimuli is improved by increasing potassium currents that activate at negative potentials, while that for high-frequency stimuli requires increases in currents that activate at positive membrane potentials. These effects are independent of the firing rate. Moreover, levels of potassium currents that maximize the fidelity of the output of an ensemble of neurons differ from those that maximize fidelity for a single neuron. This suggests that the modulatory mechanisms must coordinate channel activity in groups of neurons or an entire nucleus. The simulations provide an explanation for the modulation of the intrinsic excitability of auditory brainstem neurons by changes in environmental sound levels, and the results may extend to information processing in other neural systems.

Modulation of potassium channels preserves temporal fidelity in auditory network models.

Potassium channels in auditory neurons are rapidly modified by changes in the auditory environment. In response to elevated auditory stimulation, short-term mechanisms such as protein phosphorylation and long-term mechanisms linked to channel synthesis increase the activity of channels that promote high frequency firing. We have now used simple simulations of cochlear hair cells and postsynaptic neurons to demonstrate that the amplitudes of potassium currents in neurons required for optimal encoding of a low-level auditory signal differs substantially from that for louder sounds. Specifically, the cross correlation of the output of a neuron with an auditory stimulus is increased by increasing potassium currents as sound amplitude increases. Although it has been suggested that channel modulation allows neurons to fire at high rates in response to high sound levels, we found that the cross correlation is entirely independent of firing rate and that combinations of currents that maximize firing to a stimulus provide very poor temporal fidelity. We also found that levels of potassium currents that maximize the temporal fidelity of the output of an ensemble of thirty neurons differ from those that maximize temporal fidelity for a single neuron. This suggests that, to maximize preservation of temporal information, modulatory mechanisms must coordinate channel activity in groups of neurons receiving similar synaptic inputs. The simulations provide an explanation for the modulation of the intrinsic excitability of auditory brainstem neurons by changes in environmental sound levels, and the results may extend to information processing in other neural systems.

Ion-tunable antiambipolarity in mixed ion–electron conducting polymers enables biorealistic organic electrochemical neurons

Biointegrated neuromorphic hardware holds promise for new protocols to record/regulate signalling in biological systems. Making such artificial neural circuits successful requires minimal device/circuit complexity and ion-based operating mechanisms akin to those found in biology. Artificial spiking neurons, based on silicon-based complementary metal-oxide semiconductors or negative differential resistance device circuits, can emulate several neural features but are complicated to fabricate, not biocompatible and lack ion-/chemical-based modulation features. Here we report a biorealistic conductance-based organic electrochemical neuron (c-OECN) using a mixed ion–electron conducting ladder-type polymer with stable ion-tunable antiambipolarity. The latter is used to emulate the activation/inactivation of sodium channels and delayed activation of potassium channels of biological neurons. These c-OECNs can spike at bioplausible frequencies nearing 100 Hz, emulate most critical biological neural features, demonstrate stochastic spiking and enable neurotransmitter-/amino acid-/ion-based spiking modulation, which is then used to stimulate biological nerves in vivo. These combined features are impossible to achieve using previous technologies.

Neural Subtype-dependent Cholinergic Modulation of Neural Activities by Activation of Muscarinic 2 Receptors and G Protein-activated Inwardly Rectifying Potassium Channel in Rat Periaqueductal Gray Neurons

Acetylcholine plays a pivotal role in the regulation of functions such as pain and the sleep and wake cycle by modulating neural activities of the ventrolateral periaqueductal gray (vlPAG). Electrophysiological studies have shown that cholinergic effects are inconsistent among recorded neurons, particularly in the depolarization and hyperpolarization of the resting membrane potential (RMP). This discrepancy may be due to the neural subtype-dependent cholinergic modulation of the RMP. To examine this possibility, we performed whole-cell patch-clamp recordings from subtype-identified neurons using vesicular GABA transporter (VGAT)-Venus × ChAT-TdTomato rats and elucidated cellular mechanisms of cholinergic effects on the RMP. The application of carbachol hyperpolarized the RMP of cholinergic neurons in a dose-dependent manner but had much less of an effect on other neural subtypes, including GABAergic/glycinergic and glutamatergic neurons. Cholinergic hyperpolarization was accompanied by a decrease in input resistance. These cholinergic effects were blocked by AF-DX384 or gallamine and were mimicked by arecaidine but-2-ynyl ester tosylate, suggesting that the carbachol-induced hyperpolarization of the RMP in cholinergic neurons is mediated via M2 receptors. Tertiapin suppressed the carbachol-induced G protein-activated inwardly rectifying potassium channel (GIRK) currents and hyperpolarization of the RMP in cholinergic neurons. Intracellular application of GDP-β-S blocked the carbachol-induced hyperpolarization of the RMP. Neostigmine slowly hyperpolarized the RMP in cholinergic neurons. These results suggest that neural firing of vlPAG cholinergic neurons is suppressed by GIRK currents induced via M2 receptor activation, and this negative feedback regulation of cholinergic neuronal activities can be induced by acetylcholine, which is intrinsically released in the vlPAG.

Early life exposure to chronic unpredictable stress induces anxiety-like behaviors and increases the excitability of cerebellar neurons in zebrafish

Anxiety is a common emotional disorder in children. To understand its underlying mechanisms, chronic unpredictable stress (CUS) has been established as a stress model in zebrafish. By using the tall tank test, the stress response reliability could be improved in adult fish which has not been confirmed in larvae. In addition, the increasing evidences have shown that cerebellum plays important roles in anxiety. Whether CUS will affect cerebellar neuronal activity remains unknown. We found that CUS exposure to larvae (from 10 to 17 days post fertilization) induced anxiety-like behaviors and social cohesion impairments within 1–2 d after CUS, including a prolonged freezing time, an increased time spent at the bottom of tank, an increased thigmotaxis index, and an increased interindividual distance. Our results showed that the four behavioral tests were homogeneous, especially the tall tank test either anxiety-like behaviors or the basal locomotion. Furthermore, we found that CUS enhanced the excitability of cerebellar neurons, as the amplitude, frequency, time to peak and half-width of spontaneous firing significantly decreased, as well as the amplitude of excitatory post-synaptic current when compared with the control group. CUS also activated hyperpolarization-activated cyclic nucleotide-gated and potassium channels of cerebellar neurons. Multiple linear regression analysis showed that the total distance in bottom (tall tank test) was correlated positively with outward Na+-K+ currents (r = 0.848, P = 0.016), and the thigmotaxis index (open field test) correlated with action potential amplitude (r = 0.854, P = 0.030). Altogether, early life CUS transiently induced an anxiety-like behavior which could be more accurately assessed by combining the tall tank test with other behavior tests in young zebrafish. CUS increased the excitability of cerebellar neurons might provide new targets to treat emotional diseases such as anxiety.

A-278 Neuropsychological Profile of a Child with KCNQ2

Abstract Objective: The KCNQ2 gene mutations (KCNQ2), a known cause of neuronal potassium channel dysfunction in brain cells, causes susceptibility to seizures beginning within the first days of life. Seizure semiology, severity and cognitive sequela can vary depending on the type of KCNQ2 mutation. Cognitive impact ranges from moderate to severe; no known consistent presentation. KCNQ2 affects approximately 2.8 in 100,000 births: over 3,000 annual cases worldwide. We describe the neuropsychological findings of an 11-year-old female with a monoallelic mutation of the KCNQ2 gene, and history of seizures. EEG indicated generalized epilepsy syndrome with a right occipital focal area of dysfunction. We highlight the importance of neuropsychological evaluation in medical and psychological management of children with KCNQ2. Methods: Medical history includes multifocal seizures beginning at 2 days old and significant anxiety, both managed with medication, language delay, and a diagnosis of KCNQ2 at age 9. A comprehensive neuropsychological evaluation was conducted to assess slower processing speed, behavioral concerns, and anxiety. Results: Evaluation revealed low average overall cognition and average academic performances, with strengths in verbal comprehension, fluid reasoning, and written expression. Cognitive processing speed was atypical, with slow processing speed affecting her performance across multiple domains. Behavior assessment supports Generalized Anxiety Disorder. Conclusion: This case of a girl with KCNQ2 demonstrated an atypical cognitive and behavioral profile, contributing to our limited knowledge of how KCNQ2 presents. The patterns of her performances add to the literature of the KCNQ2 gene mutation and raise important questions regarding the role of KCNQ2 in manifestations of cognitive and behavioral symptoms.

Exanthema after lamotrigine use: A clinical case

Introduction: Lamotrigine is a phenyltriazine compound that inhibits sodium and potassium channels in presynaptic neurons. Maculopapular exanthema is a common side effect of Lamotrigine therapy, occurring most frequently during the first eight weeks of treatment in approximately 3–10% of patients. Case Report: A 74-year-old female had started Lamotrigine 50 mg due to emotional lability and depression. About 8–9 weeks after the introduction of the drug she presented a rash with exanthema, maculopapular in appearance. The attending physician suggested discontinuation of the medication and reevaluation. Complete regression of the clinical picture occurred. No severe skin rashes, including Stevens-Johnson syndrome and toxic epidermal necrolysis were observed. Conclusion: Lamotrigine is effective for a variety of types of conditions involving neuronal excitability, however, such drug exposes the individual to side reactions ranging from mild skin rashes to even those leading to hospitalization. Measures such as adherence to the manufacturer’s dosing guidelines, titration, and intrinsic characteristics of the individual can minimize this effect.

A 4/8 Subtype α-Conotoxin Vt1.27 Inhibits N-Type Calcium Channels With Potent Anti-Allodynic Effect.

A novel 4/8 subtype α-conotoxin, Vt1.27 (NCCMFHTCPIDYSRFNC-NH2), was identified from Conus vitulinus in the South China Sea by RACE methods. The peptide was synthesized and structurally characterized. Similar to other α-conotoxins that target neuronal nicotinic acetylcholine receptor (nAChR) subtypes, Vt1.27 inhibited the rat α3β2 nAChR subtype (IC50 = 1160 nM) and was inactive at voltage-gated sodium and potassium channels in rat sensory neurons. However, Vt1.27 inhibited high voltage-activated N-type (CaV2.2) calcium channels expressed in HEK293T cells with an IC50 of 398 nM. An alanine scan of the peptide showed that residues Phe5, Pro9, Ile10, and Ser13 contribute significantly to the inhibitory activity of Vt1.27. The molecular dockings indicate that Vt1.27 inhibits the transmembrane region of CaV2.2, which is different from that of ω-conotoxins. Furthermore, Vt1.27 exhibited potent anti-allodynic effect in rat partial sciatic nerve injury (PNL) and chronic constriction injury (CCI) pain models at 10 nmol/kg level with the intramuscular injection. The pain threshold elevation of Vt1.27 groups was higher than that of α-conotoxin Vc1.1 in CCI rat models. These findings expand our knowledge of targets of α-conotoxins and potentially provide a potent, anti-allodynic peptide for the treatment of neuropathic pain.

Neuronal KCNQ2/3 channels are recruited to lipid raft microdomains by palmitoylation of BACE1.

β-Secretase 1 (β-site amyloid precursor protein [APP]-cleaving enzyme 1, BACE1) plays a crucial role in the amyloidogenesis of Alzheimer's disease (AD). BACE1 was also discovered to act like an auxiliary subunit to modulate neuronal KCNQ2/3 channels independently of its proteolytic function. BACE1 is palmitoylated at its carboxyl-terminal region, which brings BACE1 to ordered, cholesterol-rich membrane microdomains (lipid rafts). However, the physiological consequences of this specific localization of BACE1 remain elusive. Using spectral Förster resonance energy transfer (FRET), BACE1 and KCNQ2/3 channels were confirmed to form a signaling complex, a phenomenon that was relatively independent of the palmitoylation of BACE1. Nevertheless, palmitoylation of BACE1 was required for recruitment of KCNQ2/3 channels to lipid-raft domains. Two fluorescent probes, designated L10 and S15, were used to label lipid-raft and non-raft domains of the plasma membrane, respectively. Coexpressing BACE1 substantially elevated FRET between L10 and KCNQ2/3, whereas the BACE1-4C/A quadruple mutation failed to produce this effect. In contrast, BACE1 had no significant effect on FRET between S15 probes and KCNQ2/3 channels. A reduction of BACE1-dependent FRET between raft-targeting L10 probes and KCNQ2/3 channels by applying the cholesterol-extracting reagent methyl-β-cyclodextrin (MβCD), raft-disrupting general anesthetics, or pharmacological inhibitors of palmitoylation, all supported the hypothesis of the palmitoylation-dependent and raft-specific localization of KCNQ2/3 channels. Furthermore, mutating the four carboxyl-terminal cysteines (4C/A) of BACE1 abolished the BACE1-dependent increase of FRET between KCNQ2/3 and the lipid raft-specific protein caveolin 1. Taking these data collectively, we propose that the AD-related protein BACE1 underlies the localization of a neuronal potassium channel.

The Molecular Basis for the Calcium-Dependent Slow Afterhyperpolarization in CA1 Hippocampal Pyramidal Neurons.

Neuronal signal transmission depends on the frequency, pattern, and timing of spike output, each of which are shaped by spike afterhyperpolarizations (AHPs). There are classically three post-spike AHPs of increasing duration categorized as fast, medium and slow AHPs that hyperpolarize a cell over a range of 10 ms to 30 s. Intensive early work on CA1 hippocampal pyramidal cells revealed that all three AHPs incorporate activation of calcium-gated potassium channels. The ionic basis for a fAHP was rapidly attributed to the actions of big conductance (BK) and the mAHP to small conductance (SK) or Kv7 potassium channels. In stark contrast, the ionic basis for a prominent slow AHP of up to 30 s duration remained an enigma for over 30 years. Recent advances in pharmacological, molecular, and imaging tools have uncovered the expression of a calcium-gated intermediate conductance potassium channel (IK, KCa3.1) in central neurons that proves to contribute to the slow AHP in CA1 hippocampal pyramidal cells. Together the data show that the sAHP arises in part from a core tripartite complex between Cav1.3 (L-type) calcium channels, ryanodine receptors, and IK channels at endoplasmic reticulum-plasma membrane junctions. Work on the sAHP in CA1 pyramidal neurons has again quickened pace, with identified contributions by both IK channels and the Na-K pump providing answers to several mysteries in the pharmacological properties of the sAHP.

Efficacy of rituximab in autism spectrum disorders associated with hereditary folate malabsorption with signs of antineuronal autoimmunity

Background. One of the key advances in psychiatry is an elucidation of the association of hereditary folate malabsorption (HFM) with autistic spectrum disorders (ASD), the evidence for which is based on the results of 5 meta-analyses of randomized controlled trials. It is shown that in such cases the antineuronal autoimmune reaction is an important mechanism of encephalopathy formation. The purpose of the study was to investigate the efficacy of rituximab in children with HFM-associated ASD who showed serological signs of antineuronal autoimmunity to expand the current arsenal of neuroprotective therapy in immunodependent encephalopathy in such cases. Materials and methods. Medical data of 138 children aged 3 to 8 years with HFM and ASD (97 boys and 41 girls) were analyzed. Parents of 62 of 81 patients with signs of antineuronal autoimmunity agreed to rituximab immunotherapy at a dose of 375 mg/m2 of body surface area per month for 3–9 months (study group, SG). Relatives of the other 19 patients with a similar distribution of antineuronal autoantibodies refused treatment (control group, CG). The dynamics of the mental state of children during immunotherapy was assessed by the ABC scale. For statistical analysis, we calculated the parametric Student’s t-test with the confidence probability p and the non-parametric criterion — the number of signs Z by U.V. Urbach, as well as the odds ratio (OR) and 95% confidence interval (95% CI). Results. Rituximab treatment resulted in a progressive decrease in serum antineuronal autoantibodies concentration in patients with ASD associated with HFM, with a more pronounced effect in the production of autoantibodies to neuronal potassium channels compared to autoantibodies to the GADA with complete elimination of the seropositivity after a 9-month course of immunotherapy in 92 % of cases. The phenomenon of rituximab-induced elimination of serum antineuronal autoantibodies is associated with the effect of neuroprotection, which was confirmed by the normalization of previously elevated serum concentrations of laboratory biomarkers of NSE cerebral damage (OR = 17.875; 95% CI = 4.738–67.436 at Ab to GADA and 41.800; 7.257–240.778 at Ab to potassium channels) and S-100 protein (9.750; 2.707–35.113 and 18.333; 3.462–97.083, respectively). In parallel, there was a progressive improvement in all indicators of the mental status of children with ASD on the ABC scale with a latency period of about 2 months (p < 0.05: Z < Z0.05). Conclusions. Immunotherapy with rituximab by eliminating the serological signs of antineuronal autoimmunity realizes the effect of neuroprotection, reducing the severity of all major clinical signs of ASD in children with HFM.

Hypoxia with inflammation and reperfusion alters membrane resistance by dynamically regulating voltage-gated potassium channels in hippocampal CA1 neurons

Hypoxia typically accompanies acute inflammatory responses in patients and animal models. However, a limited number of studies have examined the effect of hypoxia in combination with inflammation (Hypo-Inf) on neural function. We previously reported that neuronal excitability in hippocampal CA1 neurons decreased during hypoxia and greatly rebounded upon reoxygenation. We attributed this altered excitability mainly to the dynamic regulation of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels and input resistance. However, the molecular mechanisms underlying input resistance changes by Hypo-Inf and reperfusion remained unclear. In the present study, we found that a change in the density of the delayed rectifier potassium current (IDR) can explain the input resistance variability. Furthermore, voltage-dependent inactivation of A-type potassium (IA) channels shifted in the depolarizing direction during Hypo-Inf and reverted to normal upon reperfusion without a significant alteration in the maximum current density. Our results indicate that changes in the input resistance, and consequently excitability, caused by Hypo-Inf and reperfusion are at least partially regulated by the availability and voltage dependence of KV channels. Moreover, these results suggest that selective KV channel modulators can be used as potential neuroprotective drugs to minimize hypoxia- and reperfusion-induced neuronal damage.

TPEN attenuates amyloid-\u03b225\u201335-induced neuronal damage with changes in the electrophysiological properties of voltage-gated sodium and potassium channels

To understand the role of intracellular zinc ion (Zn2+) dysregulation in mediating age-related neurodegenerative changes, particularly neurotoxicity resulting from the generation of excessive neurotoxic amyloid-β (Aβ) peptides, this study aimed to investigate whether N, N, N′, N′-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a Zn2+-specific chelator, could attenuate Aβ25–35-induced neurotoxicity and the underlying electrophysiological mechanism. We used the 3-(4, 5-dimethyl-thiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay to measure the viability of hippocampal neurons and performed single-cell confocal imaging to detect the concentration of Zn2+ in these neurons. Furthermore, we used the whole-cell patch-clamp technique to detect the evoked repetitive action potential (APs), the voltage-gated sodium and potassium (K+) channels of primary hippocampal neurons. The analysis showed that TPEN attenuated Aβ25–35-induced neuronal death, reversed the Aβ25–35-induced increase in intracellular Zn2+ concentration and the frequency of APs, inhibited the increase in the maximum current density of voltage-activated sodium channel currents induced by Aβ25–35, relieved the Aβ25–35-induced decrease in the peak amplitude of transient outward K+ currents (IA) and outward-delayed rectifier K+ currents (IDR) at different membrane potentials, and suppressed the steady-state activation and inactivation curves of IA shifted toward the hyperpolarization direction caused by Aβ25–35. These results suggest that Aβ25–35-induced neuronal damage correlated with Zn2+ dysregulation mediated the electrophysiological changes in the voltage-gated sodium and K+ channels. Moreover, Zn2+-specific chelator-TPEN attenuated Aβ25–35-induced neuronal damage by recovering the intracellular Zn2+ concentration.

Functional analysis of a de novo variant in the neurodevelopment and generalized epilepsy disease gene NBEA

Neurobeachin (NBEA) was initially identified as a candidate gene for autism. Recently, variants in NBEA have been associated with neurodevelopmental delay and childhood epilepsy. Here, we report on a novel NBEA missense variant (c.5899G > A, p.Gly1967Arg) in the Domain of Unknown Function 1088 (DUF1088) identified in a child enrolled in the Undiagnosed Diseases Network (UDN), who presented with neurodevelopmental delay and seizures. Modeling of this variant in the Caenorhabditis elegans NBEA ortholog, sel-2, indicated that the variant was damaging to in vivo function as evidenced by altered cell fate determination and trafficking of potassium channels in neurons. The variant effect was indistinguishable from that of the reference null mutation suggesting that the variant is a strong hypomorph or a complete loss-of-function. Our experimental data provide strong support for the molecular diagnosis and pathogenicity of the NBEA p.Gly1967Arg variant and the importance of the DUF1088 for NBEA function.

Age dependent effects of Retigabine on absence seizure in WAG/Rij rats; an experimental study.

Retigabine (RTG, Ezogabine, DC23129) is the first neuronal potassium channel opener in the treatment of epilepsy and exerts its effects through the activation of neuronal KCNQ2/3 potassium channels; in higher doses, it acts also on sodium and voltage-gated calcium channels. The aim of this study was to investigate possible age-dependent therapeutic effects of RTG on spike-and-wave discharges (SWD) in an animal model of absence epilepsy using WAG/Rij rats. In this study, 6- and 12-month-old WAG/Rij rats were used. For both age categories, three sub-groups that consisted of one control group (n=7) by the administration of 20% DMSO (control) and two study groups by the administration of 5mg/kg (n=7) and 15mg/kg RTG (n=7) were designed. EEG electrodes were placed onto the skull of anaesthetized animals; and baseline EEG was recorded for one hour after a recovery period from surgery. Then, the pre-determined two distinct doses of RTG and 20% DMSO were administered as a solvent via intraperitoneal injections, and EEG was recorded for 3hours. After injection, both doses of RTG increased the total SWD number and duration of SWD in the first and second hours in 12-month-old rats. These parameters were elevated compared to 6-month-old rats. Age-dependent effects of RTG were observed in SWD activity. Pro-epileptic effects in middle-aged WAG/Rij rats were demonstrated in both RTG doses. Differences in the distribution of KCNQ2/3 channels and switch of GABAergic system from inhibitory to excitatory with age might contribute to increased SWD activity in middle-aged rats.