Excitable neurons are intrinsically capable of firing action potentials (AP), yet a state of hyperexcitability is prevented in the central nervous system by powerful GABAergic inhibition. For this inhibition to be effective, it must occur before excitatory signals can initiate runaway activity, implying the existence of a proactive control system. To test for such proactive inhibition, we used Ca2+ imaging and patch-clamp recording to measure how hippocampal neurons respond to depolarization and glutamatergic agonists. In mature hippocampal cultures (14 days in vitro (DIV)) and acute brain slices from two-month-old rats, neurons exhibited non-simultaneous responses to various excitatory stimuli, including KCl, NH4Cl, forskolin, domoic acid, and glutamate. We observed that the Ca2+ rise occurred significantly earlier in GABAergic neurons than in glutamatergic neurons. This delay in glutamatergic neurons was abolished by GABA(A) receptor inhibitors, suggesting a mechanism of preliminary γ-aminobutyric acid (GABA) release. We further found that these early-responding GABAergic neurons express calcium-permeable kainate and AMPA receptors (CP-KARs and CP-AMPARs). Application of domoic acid induced an immediate Ca2+ increase in neurons expressing these receptors, but a delayed response in others. Crucially, when domoic acid was applied in the presence of the AMPA receptor inhibitors NBQX or GYKI-52466, the response delay in glutamatergic neurons was significantly prolonged. This confirms that CP-KARs on GABAergic neurons are responsible for the delayed excitation of glutamatergic neurons. In hippocampal slices from two-month-old rats, depolarization with 50 mM KCl revealed two distinct neuronal populations based on their calcium dynamics: a majority group (presumably glutamatergic) exhibited fluctuating Ca2+ signals, while a minority (presumably GABAergic) showed a steady, advancing increase in [Ca2+]i. This distinction was reinforced by the application of domoic acid. The “advancing-response” neurons reacted to domoic acid with a similar prompt increase, whereas the “fluctuating-response” neurons displayed an even more delayed and fluctuating reaction (80 s delay). Therefore, we identify a subgroup of hippocampal neurons—in both slices and cultures—that respond to depolarization and domoic acid with an early [Ca2+]i signal. Consistent with our data from cultures, we conclude these early-responding neurons are GABAergic. Their early GABA release directly explains the delayed Ca2+ response observed in glutamatergic neurons. We propose that this proactive mechanism, mediated by CP-KARs on GABAergic neurons, is a primary means of protecting the network from hyperexcitation. Furthermore, the activity of these CP-KAR-expressing neurons is itself regulated by GABAergic neurons containing CP-AMPARs.

Introduction: Paroxysmal depolarization shifts (PDSs), correlated with interictal epileptiform discharges, involve significant membrane potential changes and action potentials. While synchronicity is crucial in paroxysmal activity, the precise function of PDSs and their propagation mechanisms, especially non-synaptic pathways like ephaptic coupling, remains poorly understood. This study investigates the role of ephaptic coupling in PDS propagation in hippocampal cultures, focusing on voltage-gated calcium channel (VGCC) subtypes. Methods: PDSs were induced in hippocampal neurone-glial cultures using bicuculline. The outside-out patch-clamp technique was used to record PDS activity at varying distances from the neuronal network. The effects of L-type (nifedipine) and T-type (ML-218) VGCC inhibitors on PDS amplitude and frequency were assessed. Membrane capacitance and resistance were monitored to verify the outside-out configuration. Results: PDSs could be recorded up to 16 µm from the network, with amplitude decreasing exponentially with distance. PDS frequency remained constant. Blocking L-type VGCCs completely abolished PDS activity at a distance, while T-type VGCC inhibition significantly reduced PDS amplitude. The transition from whole-cell to outside-out configuration was confirmed by a significant decrease in membrane capacitance. Discussion: The findings suggest that ephaptic coupling contributes to PDS propagation in vitro, with L-type VGCCs playing a critical role in field-mediated signal transmission. Constant PDS frequency with varying amplitude at a distance highlights a potential synchronization mechanism during epileptiform activity. Further research should investigate the interplay between ion channels and the extracellular environment during ephaptic coupling, paving the way for brain stimulation-based therapies. Conclusion: Research demonstrates that ephaptic coupling can propagate PDSs in hippocampal neurone-glial cultures, highlighting a promising mechanism for understanding epileptiform foci. This finding is critical for comprehending how these foci form and expand, and it also opens avenues for developing brain stimulation-based therapies.

Using in vitro models of hypoxia, episodes of short-term hypoxia/reoxygenation, and ischemia-like conditions, we were able to establish different sensitivities of hippocampal neurons to their damaging factors. Using a combination of fluorescence microscopy and immunocytochemistry methods, it was possible to show that GABAergic neurons are the most vulnerable to the damaging effects of hypoxia and ischemia-like conditions, as they have a special metabolism, which is characterized by increased production of reactive oxygen species and nitric oxide. It was shown that long-term hypoxia causes the death of GABAergic neurons due to the induction of a global [Ca2+]i increase, whereas pyramidal neurons are resistant to 30-min hypoxia. Episodes of short-term hypoxia/reoxygenation activate the phenomenon of hypoxic preconditioning in glutamatergic neurons, while this endogenous protective mechanism is absent in GABAergic neurons. Selective activation of PI3K and PKG, combined with NOS inhibition, potentiates the preconditioning effect of hypoxia/reoxygenation in glutamatergic neurons and partially activates this neuroprotective mechanism in GABAergic neurons, as indicated by diminished post-hypoxic NMDA-induced Ca2+ transients. These findings suggest that pharmacological intervention can protect GABAergic neuronal populations. The expression of parvalbumin, calbindin, or calretinin in the cytosol of GABAergic neurons contributes to the suppression of the global [Ca2+]i increase during hypoxia/reoxygenation episodes, which correlates with their survival even in the absence of the hypoxic preconditioning phenomenon. Additionally, all three studied calcium-binding proteins showed potential high efficiency in maintaining the bioenergetics of GABAergic neurons during ischemia-like conditions, limiting ROS production by mitochondria and in the cytosol, and reducing nitric oxide formation. In this case, parvalbumin showed the greatest efficiency.

Serotonin (5-HT) is a neurotransmitter that also plays an important role in the regulation of vascular tone and angiogenesis. This review focuses on the involvement of the 5-HT system in pathological processes leading to the development of Alzheimer’s disease (AD). There is evidence that damage or dysfunction of the 5-HT system contributes to the development of AD, and different subtypes of 5-HT receptors are a potential target for the treatment of AD. A link has been established between AD, depression, stress, and 5-HT deficiency in the brain. There are new data on the role of circadian rhythms in modulating stress, depression, and the 5-HT system; amyloid β (Aβ) plaque clearance; and AD progression. Circadian disruption inhibits Aβ plaque clearance and modulates AD progression. The properties and functions of 5-HT, its receptors, and serotonergic neurons are presented. Special attention is paid to the central role of 5-HT in brain development, including neurite outgrowth, regulation of somatic morphology, motility, synaptogenesis, control of dendritic spine shape and density, neuronal plasticity determining its role in network regeneration, and changes in innervation after brain damage. The results of different studies indicate that the interaction of amyloid β oligomers (AβO) with mitochondria is a sufficient trigger for AD-related neurodegeneration. The action of 5-HT leads to an improvement in mitochondrial quality and the restoration of brain areas after traumatic brain injury, chronic stress, or developmental disorders in AD. The role of a healthy lifestyle and drugs acting on serotonin receptors in the prevention and treatment of AD is discussed.

Calcium-permeable AMPA receptors (CP-AMPARs) and kainate receptors (CP-KARs) play crucial roles in synaptic plasticity and are implicated in various neurological processes. Current methods for identifying neurons expressing these receptors, such as electrophysiological recordings and immunostaining, have limitations in throughput or inability to distinguish functional receptors. This protocol describes a novel approach for the vital identification of neurons containing CP-AMPARs and CP-KARs using calcium imaging. The method involves loading neurons with Fura-2 AM, a calcium- sensitive fluorescent probe, KCl application to identify all neurons, and further addition of specific AMPAR agonists (e.g., 5-fluorowillardiine) in the presence of voltage-gated calcium channel blockers and NMDAR/KAR antagonists to identify CP-AMPAR-containing neurons. CP-KAR-containing neurons are identified using domoic acid applications in the presence and absence of NASPM (a CP-AMPAR antagonist). This technique offers several advantages over existing methods, including the ability to assess large neuronal populations simultaneously, distinguish between different receptor types, and provide functional information about CP-AMPAR and CP-KAR expression in living neurons, making it a valuable tool for studying synaptic plasticity and neurological disorders.

Introduction 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.Methods 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.Results and discussion 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.

Glutamate excitotoxicity accompanies numerous brain pathologies, including traumatic brain injury, ischemic stroke, and epilepsy. Disturbances of the ion homeostasis, mitochondria dysfunction, and further cell death are considered the main detrimental consequences of excitotoxicity. It is well known that neurons demonstrate different vulnerability to pathological exposures. In this regard, neurons containing calcium-permeable AMPA receptors (CP-AMPARs) may show higher susceptibility to excitotoxicity due to an additional pathway of Ca2+ influx. Here, we demonstrate that neurons containing CP-AMPARs are characterized by the higher amplitude of the glutamate-induced elevation of intracellular Ca2+ concentration ([Ca2+]i) and slower restoration of [Ca2+]i level compared to non-CP-AMPA neurons. Moreover, we have found that NASPM, an antagonist of CP-AMPARs, significantly decreases the amplitude of the [Ca2+]i elevation induced by glutamate or selective AMPARs agonist, 5-fluorowillardiine. In contrast, the antagonists of NMDARs or KARs affect insignificantly. We have also described some peculiarities of Na+, K+, and H+ intracellular dynamics in neurons containing CP-AMPARs. In particular, the amplitude of [Na+]i elevation was lower compared to non-CP-AMPA neurons, whereas the amplitude of [K+]i decrease was higher. We have shown the significant inverse correlation between [K+]i and [Ca2+]i and between intracellular pH and [Na+]i in CP-AMPARs-containing and non-CP-AMPA neurons upon glutamate excitotoxicity. Our data indicate that CP-AMPARs-mediated Ca2+ influx and slow removal of Ca2+ from the cytosol may underlie the vulnerability of the CP-AMPARs-containing neurons to glutamate excitotoxicity. Further studies of the mechanisms mediating the disturbances in ion homeostasis are crucial for developing new approaches for protecting these neurons at brain pathologies.

Gi-coupled receptors, particularly cannabinoid receptors (CBRs), are considered perspective targets for treating brain pathologies, including epilepsy. However, the precise mechanism of the anticonvulsant effect of the CBR agonists remains unknown. We have found that WIN 55,212-2 (a CBR agonist) suppresses the synchronous oscillations of the intracellular concentration of Ca2+ ions (epileptiform activity) induced in the neurons of rat hippocampal neuron-glial cultures by bicuculline or NH4Cl. As we have demonstrated, the WIN 55,212-2 effect is mediated by CB1R receptors. The agonist suppresses Ca2+ inflow mediated by the voltage-gated calcium channels but does not alter the inflow mediated by NMDA, AMPA, and kainate receptors. We have also found that phospholipase C (PLC), protein kinase C (PKC), and G-protein-coupled inwardly rectifying K+ channels (GIRK channels) are involved in the molecular mechanism underlying the inhibitory action of CB1R activation against epileptiform activity. Thus, our results demonstrate that the antiepileptic action of CB1R agonists is mediated by different intracellular signaling cascades, including non-canonical PLC/PKC-associated pathways.

Calcium-permeable kainate and AMPA receptors (CP-KARs and CP-AMPARs), as well as NMDARs, play a pivotal role in plasticity and in regulating neurotransmitter release. Here we visualized in the mature hippocampal neuroglial cultures the neurons expressing CP-AMPARs and CP-KARs. These neurons were visualized by a characteristic fast sustained [Ca2+]i increase in response to the agonist of these receptors, domoic acid (DoA), and a selective agonist of GluK1-containing KARs, ATPA. Neurons from both subpopulations are GABAergic. The subpopulation of neurons expressing CP-AMPARs includes a larger percentage of calbindin-positive neurons (39.4 ± 6.0%) than the subpopulation of neurons expressing CP-KARs (14.2 ± 7.5% of CB+ neurons). In addition, we have shown for the first time that NH4Cl-induced depolarization faster induces an [Ca2+]i elevation in GABAergic neurons expressing CP-KARs and CP-AMPARs than in most glutamatergic neurons. CP-AMPARs antagonist, NASPM, increased the amplitude of the DoA-induced Ca2+ response in GABAergic neurons expressing CP-KARs, indicating that neurons expressing CP-AMPARs innervate GABAergic neurons expressing CP-KARs. We assume that CP-KARs in inhibitory neurons are involved in the mechanism of outstripping GABA release upon hyperexcitation.

The mechanisms underlying the antiarrhythmic action of compound trihydrochloride N1-(2,3,4-trimethoxy)-N2-{2-[(2,3,4-trimethoxybenzyl)amino]ethyl}-1,2-ethane-diamine (code ALM-802) were studied in vitro. The experiments were performed on a culture of rat hippocampal neurons. The electrical activity of neurons was recorded by the patch-clamp method in the whole cell configuration. It is shown that the compound ALM-802 effectively blocks potential-dependent Na+ and K+ channels and does not affect the activity of potential-dependent Ca2+ channels. The inhibition of currents through these channels is dose-dependent; the IC50 of Na+ and K+ channels were 94±4 and 67±3 μM, respectively. These findings indicate that compound ALM-802 combines the properties of class I and class III antiarrhythmic agents according to the Vaughan—Williams classification.

Cannabinoid receptors (CBRs) play a key role in various physiological processes, including neurogenesis, synaptic plasticity, immune modulation, cell apoptosis, metabolism regulation, cardiovascular and reproductive systems activity. Since activation of CBRs suppresses hyperexcitation and protect cells from death, their modulation may have therapeutic prospects in the treatment of such pathologies of the nervous system as mental disorders, epilepsy, Parkinson’s and Huntington’s disease, multiple sclerosis, spinal cord and brain injuries. This paper presents experimental data on the effects of the cannabinoid receptor agonist WIN 55,212-2 on the induced oscillations of intracellular Ca2+ concentration ([Ca2+]i) in two in vitro models of epileptiform activity. To study the neuroprotective properties of WIN 55,212-2, hyperexcitation was induced by the application of a GABA(A) receptor antagonist, bicuculline, or depolarizing doses of ammonium chloride. As experiments have shown, WIN 55,212-2 at a concentration of 100 nM and above significantly suppresses the [Ca2+]i oscillation frequency and reduces the basal [Ca2+]i level. At the same time, the amplitude of calcium oscillations also decreased in the presence of the agonist. WIN 55,212-2 at a concentration of 5 μM suppressed NH4Cl-induced [Ca2+]i oscillations in all neurons but caused a transient biphasic increase in the basal [Ca2+]i level in 20% of astrocytes. Thus, in this work, using various models of hyperexcitation of neuronal networks, we have demonstrated the potential antiepileptic effect of the cannabinoid receptor agonist WIN 55,212-2.

Calcium-permeable AMPA receptors (CP-AMPARs) play a pivotal role in brain functioning in health and disease. They are involved in synaptic plasticity, synaptogenesis, and neuronal circuits development. However, the functions of neurons expressing CP-AMPARs and their role in the modulation of network activity remain elusive since reliable and accurate visualization methods are absent. Here we developed an approach allowing the vital identification of neurons containing CP-AMPARs. The proposed method relies on evaluating Ca2+ influx in neurons during activation of AMPARs in the presence of NMDAR and KAR antagonists, and blockers of voltage-gated Ca2+ channels. Using this method, we studied the properties of CP-AMPARs-containing neurons. We showed that the overwhelming majority of neurons containing CP-AMPARs are GABAergic, and they are distinguished by higher amplitudes of the calcium responses to applications of the agonists. Furthermore, about 30% of CP-AMPARs-containing neurons demonstrate the presence of GluK1-containing KARs. Although CP-AMPARs-containing neurons are characterized by more significant Ca2+ influx during the activation of AMPARs than other neurons, AMPAR-mediated Na+ influx is similar in these two groups. We revealed that neurons containing CP-AMPARs demonstrate weak GABA(A)R-mediated inhibition because of the low percentage of GABAergic synapses on the soma of these cells. However, our data show that weak GABA(A)R-mediated inhibition is inherent to all GABAergic neurons in the culture and cannot be considered a unique feature of CP-AMPARs-containing neurons. We believe that the suggested approach will help to understand the role of CP-AMPARs in the mammalian nervous system in more detail.

Abnormal depolarization of neuronal membranes called paroxysmal depolarization shift (PDS) represents a cellular correlate of interictal spikes. The mechanisms underlying the generation of PDSs or PDS clusters remain obscure. This study aimed to investigate the role of ionotropic glutamate receptors (iGluRs) in the generation of PDS and dependence of the PDS pattern on neuronal membrane potential. We have shown that significant depolarization or hyperpolarization (by more than ±50 mV) of a single neuron does not change the number of individual PDSs in the cluster, indicating the involvement of an external stimulus in PDS induction. Based on this data, we have suggested reliable protocols for stimulating single PDS or PDS clusters. Furthermore, we have found that AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors are necessary for PDS generation since AMPAR antagonist NBQX completely suppresses bicuculline-induced paroxysmal activity. In turn, antagonists of NMDA (N-methyl-D-aspartate) and kainate receptors (D-AP5 and UBP310, respectively) caused a decrease in the amplitude of the first action potential in PDSs and in the amplitude of the oscillations of intracellular Ca2+ concentration occurring alongside the PDS cluster generation. The effects of the NMDAR (NMDA receptor) and KAR (kainate receptor) antagonists indicate that these receptors are involved only in the modulation of paroxysmal activity. We have also shown that agonists of some Gi-coupled receptors, such as A1 adenosine (A1Rs) or cannabinoid receptors (CBRs) (N6-cyclohexyladenosine and WIN 55,212-2, respectively), completely suppressed PDS generation, while the A1R agonist even prevented it. We hypothesized that the dynamics of extracellular glutamate concentration govern paroxysmal activity. Fine-tuning of neuronal activity via action on Gi-coupled receptors or iGluRs paves the way for the development of new approaches for epilepsy pharmacotherapy.

Introduction. Cardiovascular diseases (CVD) remain one of the leading causes of death worldwide, claiming over 17 million lives annually. This highlights the urgent need to develop innovative drugs to combat CVD. One potential target for such drugs is type 2 ryanodine receptors (RyR2), as they play an important role in maintaining ion homeostasis in cardiomyocytes, and their abnormal activity plays a key role in the genesis of cardiac arrhythmias. Research objective is to study the mechanisms underlying the antiarrhythmic action of ALM-802. Methods . In the first stage, in vivo experiments were performed using models of aconitine, calcium chloride, barium chloride arrhythmia, and reperfusion arrhythmias to evaluate the antiarrhythmic effect of the compound ALM-802. The second stage of the study involved electrophysiological experiments performed on hippocampal cells of newborn rats to evaluate the effect of the compound on voltage-gated transmembrane Na+, K+, and Ca2+ ion channels, as well as its effect on intracellular ion concentration of Ca2+. Experiments performed on an isolated myocardial strip evaluated the effect of the compound ALM-802 on the activity of RyR2. Results. In in vivo experiments, the compound ALM-802 (2 mg/kg, iv) exhibits significant antiarrhythmic activity comparable/superior to that shown by the reference drugs procainamide, verapamil, and amiodarone on the models mentioned above. In in vitro experiments, it was shown that ALM-802 (69.8 µM) initiates the inactivation of K+ and Na+ ion channels and does not affect the activity of Ca2+ ion channels. The compound ALM-802 effectively prevents the increase of Ca2+ ion concentration in the cytosol during depolarization of contraction. In addition, experiments on isolated myocardial strips showed that the compound ALM-802 (5x10-5 M) blocks RyR2. Conclusion . Thus, based on the spectrum of its antiarrhythmic activity, the compound ALM-802 combines the properties of antiarrhythmic drugs of class IA or IC and class III according to the E.M. Vaughan Williams classification. In addition, the ALM-802 compound exhibits antagonistic activity towards RyR2. The latter is also considered significant, as it is known that under conditions of myocardial pathology, abnormal activity of RyR2 initiates diastolic leakage of Ca2+ ions from the sarcoplasmic reticulum cysterns, which leads to a decrease in the inotropic function of the left ventricle of the heart and significantly increases the risk of developing malignant cardiac arrhythmias.

An increasing number of the population all around the world suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD). This disorder presents different signs of genetic, epigenetic and environmental origin, and molecular, cellular and intracellular dysfunction. At the molecular level, α-synuclein (αSyn) was identified as the principal molecule constituting the Lewy bodies (LB). The gut microbiota participates in the pathogenesis of PD and may contribute to the loss of dopaminergic neurons through mitochondrial dysfunction. The most important pathogenetic link is an imbalance of Ca2+ ions, which is associated with redox imbalance in the cells and increased generation of reactive oxygen species (ROS). In this review, genetic, epigenetic and environmental factors that cause these disorders and their cause-and-effect relationships are considered. As a constituent of environmental factors, the example of organophosphates (OPs) is also reviewed. The role of endothelial damage in the pathogenesis of PD is discussed, and a 'triple hit hypothesis' is proposed as a modification of Braak's dual hit one. In the absence of effective therapies for neurodegenerative diseases, more and more evidence is emerging about the positive impact of nutritional structure and healthy lifestyle on the state of blood vessels and the risk of developing these diseases.

In in vitro experiments on isolated rat hippocampal neurons, we studied the electrophysiological mechanisms of the antiarrhythmic effects of N-deacetyllappaconitine monochlorhydrate (DALCh), active metabolite of lappaconitine hydrobromide (allapinin). Electrical activity of neurons was recorded by the patch-clamp method in the whole cell configuration. It was shown that DALCh increased the duration of both slow and fast depolarization phases and decreased the amplitude of the action potential. DALCh effectively inhibited transmembrane currents of Na + ions and partially K + ions through the corresponding transmembrane voltage-gated ion channels. Thus, DALCh, in contrast to lappaconitine hydrobromide, belongs not to 1C, but to the 1A class of antiarrhythmics according to the Vaughan-Williams classification.