Mouse CA1 Hippocampal Neurons Research Articles

Tau induces inflammasome activation and microgliosis through acetylating NLRP3.

Alzheimer's disease (AD) and related Tauopathies are characterised by the pathologically hyperphosphorylated and aggregated microtubule-associated protein Tau, which is accompanied by neuroinflammation mediated by activated microglia. However, the role of Tau pathology in microglia activation or their causal relationship remains largely elusive. The levels of nucleotide-binding oligomerisation domain(NOD)-like receptor pyrin domain containing 3(NLRP3) acetylation and inflammasome activation in multiple cell models with Tau proteins treatment, transgenic mice with Tauopathy, and AD patients were measured by Western blotting and enzyme-linked immunosorbent assay. In addition, the acetyltransferase activity of Tau and NLRP3 acetylation sites were confirmed using the test-tube acetylation assay, co-immunoprecipitation, immunofluorescence (IF) staining, mass spectrometry and molecular docking. The Tau-overexpressing mouse model was established by overexpression of human Tau proteins in mouse hippocampal CA1 neurons through the adeno-associated virus injection. The cognitive functions of Tau-overexpressing mice were assessed in various behavioural tests, and microglia activation was analysed by Iba-1 IF staining and [18F]-DPA-714 positron emission tomography/computed tomography imaging. A peptide that blocks the interaction between Tau and NLRP3 was synthesised to determine the in vitro and in vivo effects of Tau-NLRP3 interaction blockade on NLRP3 acetylation, inflammasome activation, microglia activation and cognitive function. Excessively elevated NLRP3 acetylation and inflammasome activation were observed in 3xTg-AD mice, microtubule-associated protein Tau P301S (PS19) mice and AD patients. It was further confirmed that mimics of 'early' phosphorylated-Tau proteins which increase at the initial stage of diseases with Tauopathy, including TauT181E, TauS199E, TauT217E and TauS262E, significantly promoted Tau-K18 domain acetyltransferase activity-dependent NLRP3 acetylation and inflammasome activation in HEK293T and BV-2 microglial cells. In addition, Tau protein could directly acetylate NLRP3 at the K21, K22 and K24 sites at its PYD domain and thereby induce inflammasome activation in vitro. Overexpression of human Tau proteins in mouse hippocampal CA1 neurons resulted in impaired cognitive function, Tau transmission to microglia and microgliosis with NLRP3 acetylation and inflammasome activation. As a targeted intervention, competitive binding of a designed Tau-NLRP3-binding blocking (TNB) peptide to block the interaction of Tau protein with NLRP3 inhibited the NLRP3 acetylation and downstream inflammasome activation in microglia, thereby alleviating microglia activation and cognitive impairment in mice. In conclusion, our findings provide evidence for a novel role of Tau in the regulation of microglia activation through acetylating NLRP3, which has potential implications for early intervention and personalised treatment of AD and related Tauopathies.

Enhancing GluN2A-type NMDA receptors impairs long-term synaptic plasticity and learning and memory.

N-methyl-D-aspartic acid type glutamate receptors (NMDARs) play critical roles in synaptic transmission and plasticity, the dysregulation of which leads to cognitive defects. Here, we identified a rare variant in the NMDAR subunit GluN2A (K879R) in a patient with intellectual disability. The K879R mutation enhanced receptor expression on the cell surface by disrupting a KKK motif that we demonstrated to be an endoplasmic reticulum retention signal. Expression of GluN2A_K879R in mouse hippocampal CA1 neurons enhanced the excitatory postsynaptic currents mediated by GluN2A-NMDAR but suppressed those mediated by GluN2B-NMDAR and the AMPA receptor. GluN2A_K879R knock-in mice showed similar defects in synaptic transmission and exhibited impaired learning and memory. Furthermore, both LTP and LTD were severely impaired in the KI mice, likely explaining their learning and memory defects. Therefore, our study reveals a new mechanism by which elevated synaptic GluN2A-NMDAR impairs long-term synaptic plasticity as well as learning and memory.

Sodium sensitivity of KNa channels in mouse CA1 neurons.

Potassium channels play an important role regulating transmembrane electrical activity in essentially all cell types. We were especially interested in those that determine the intrinsic electrical properties of mammalian central neurons. Over 30 different potassium channels have been molecularly identified in brain neurons, but there often is not a clear distinction between molecular structure and the function of a particular channel in the cell. Using patch-clamp methods to search for single potassium channels in excised inside-out (ISO) somatic patches with symmetrical potassium, we found that nearly all patches contained non-voltage-inactivating channels with a single-channel conductance of 100-200 pS. This conductance range is consistent with the family of sodium-activated potassium channels (Slo2.1, Slo2.2, or collectively, KNa). The activity of these channels was positively correlated with a low cytoplasmic Na+ concentration (2-20 mM). Cell-attached recordings from intact neurons, however, showed little or no activity of this K+ channel. Attempts to increase channel activity by increasing intracellular sodium concentration ([Na+]i) with bursts of action potentials or direct perfusion of Na+ through a whole cell pipette had little effect on KNa channel activity. Furthermore, excised outside-out (OSO) patches across a range of intracellular [Na+] showed less channel activity than we had seen with excised ISO patches. Blocking the Na+/K+ pump with ouabain increased the activity of the KNa channels in excised OSO patches to levels comparable with ISO-excised patches. Our results suggest that despite their apparent high levels of expression, the activity of somatic KNa channels is tightly regulated by the activity of the Na+/K+ pump.NEW & NOTEWORTHY We studied KNa channels in mouse hippocampal CA1 neurons. Excised inside-out patches showed the channels to be prevalent and active in most patches in the presence of Na+. Cell-attached recordings from intact neurons, however, showed little channel activity. Increasing cytoplasmic sodium in intact cells showed a small effect on channel activity compared with that seen in inside-out excised patches. Blockade of the Na+/K+ pump with ouabain, however, restored the activity of the channels to that seen in inside-out patches.

An aspherical microlens assembly for deep brain fluorescence microendoscopy

Fluorescence microendoscopy is becoming a standard technique in neuroscience for visualizing neuronal activity in the deep brain. Gradient refractive index (GRIN) lenses are increasingly used for fluorescence microendoscopy; however, they inherently suffer from strong aberrations and distortion. Aspherical lenses change their radius of curvature with distance from the optical axis and can effectively eliminate spherical aberrations. The use of these lenses has not been fully explored in deep brain fluorescence microendoscopy due to technical difficulties in manufacturing miniature aspherical lenses. In this study, we fabricated a novel microendoscope lens assembly comprised two nested pairs of aspherical microlenses made by precision glass molding. This assembly, which was 0.6 mm in diameter and 7.06 mm in length, was assembled in a stainless steel tube of 0.7 mm outer diameter. This assembly exhibited marked improvements in monochromatic and chromatic aberrations compared with a conventional GRIN lens, and is useful for deep brain fluorescence microendoscopy, as demonstrated by two-photon microendoscopic calcium imaging of R-CaMP1.07-labeled mouse hippocampal CA1 neurons. Our aspherical-lens-based approach offers a non-GRIN-lens alternative for fabrication of microendoscopic lenses.

Input-Specific Synaptic Location and Function of the α5 GABAA Receptor Subunit in the Mouse CA1 Hippocampal Neurons.

Hippocampus-dependent learning processes are coordinated via a large diversity of GABAergic inhibitory mechanisms. The α5 subunit-containing GABAA receptor (α5-GABAAR) is abundantly expressed in the hippocampus populating primarily the extrasynaptic domain of CA1 pyramidal cells, where it mediates tonic inhibitory conductance and may cause functional deficits in synaptic plasticity and hippocampus-dependent memory. However, little is known about synaptic expression of the α5-GABAAR and, accordingly, its location site-specific function. We examined the cell- and synapse-specific distribution of the α5-GABAAR in the CA1 stratum oriens/alveus (O/A) using a combination of immunohistochemistry, whole-cell patch-clamp recordings and optogenetic stimulation in hippocampal slices obtained from mice of either sex. In addition, the input-specific role of the α5-GABAAR in spatial learning and anxiety-related behavior was studied using behavioral testing and chemogenetic manipulations. We demonstrate that α5-GABAAR is preferentially targeted to the inhibitory synapses made by the vasoactive intestinal peptide (VIP)- and calretinin-positive terminals onto dendrites of somatostatin-expressing interneurons. In contrast, synapses made by the parvalbumin-positive inhibitory inputs to O/A interneurons showed no or little α5-GABAAR. Inhibiting the α5-GABAAR in control mice in vivo improved spatial learning but also induced anxiety-like behavior. Inhibiting the α5-GABAAR in mice with inactivated CA1 VIP input could still improve spatial learning and was not associated with anxiety. Together, these data indicate that the α5-GABAAR-mediated phasic inhibition via VIP input to interneurons plays a predominant role in the regulation of anxiety while the α5-GABAAR tonic inhibition via this subunit may control spatial learning.SIGNIFICANCE STATEMENT The α5-GABAAR subunit exhibits high expression in the hippocampus, and regulates the induction of synaptic plasticity and the hippocampus-dependent mnemonic processes. In CA1 principal cells, this subunit occupies mostly extrasynaptic sites and mediates tonic inhibition. Here, we provide evidence that, in CA1 somatostatin-expressing interneurons, the α5-GABAAR subunit is targeted to synapses formed by the VIP- and calretinin-expressing inputs, and plays a specific role in the regulation of anxiety-like behavior.

Memory enhancement by ferulic acid ester across species.

Cognitive impairments can be devastating for quality of life, and thus, preventing or counteracting them is of great value. To this end, the present study exploits the potential of the plant Rhodiola rosea and identifies the constituent ferulic acid eicosyl ester [icosyl-(2E)-3-(4-hydroxy-3-methoxyphenyl)-prop-2-enoate (FAE-20)] as a memory enhancer. We show that food supplementation with dried root material from R. rosea dose-dependently improves odor-taste reward associative memory scores in larval Drosophila and prevents the age-related decline of this appetitive memory in adult flies. Task-relevant sensorimotor faculties remain unaltered. From a parallel approach, a list of candidate compounds has been derived, including R. rosea-derived FAE-20. Here, we show that both R. rosea-derived FAE-20 and synthetic FAE-20 are effective as memory enhancers in larval Drosophila. Synthetic FAE-20 also partially compensates for age-related memory decline in adult flies, as well as genetically induced early-onset loss of memory function in young flies. Furthermore, it increases excitability in mouse hippocampal CA1 neurons, leads to more stable context-shock aversive associative memory in young adult (3-month-old) mice, and increases memory scores in old (>2-year-old) mice. Given these effects, and given the utility of R. rosea-the plant from which we discovered FAE-20-as a memory enhancer, these results may hold potential for clinical applications.

ΔFosB Decreases Excitability of Dorsal Hippocampal CA1 Neurons.

Both the function of hippocampal neurons and hippocampus-dependent behaviors are dependent on changes in gene expression, but the specific mechanisms that regulate gene expression in hippocampus are not yet fully understood. The stable, activity-dependent transcription factor ΔFosB plays a role in various forms of hippocampal-dependent learning and in the structural plasticity of synapses onto CA1 neurons. The authors examined the consequences of viral-mediated overexpression or inhibition of ΔFosB on the function of adult mouse hippocampal CA1 neurons using ex vivo slice whole-cell physiology. We found that the overexpression of ΔFosB decreased the excitability of CA1 pyramidal neurons, while inhibition increased excitability. Interestingly, these manipulations did not affect resting membrane potential or spike frequency adaptation, but ΔFosB overexpression reduced hyperpolarization-activated current. Both ΔFosB overexpression and inhibition decreased spontaneous excitatory postsynaptic currents, while only ΔFosB inhibition affected the AMPA/NMDA ratio, which was mediated by decreased NMDA receptor current, suggesting complex effects on synaptic inputs to CA1 that may be driven by homeostatic cell-autonomous or network-driven adaptations to the changes in CA1 cell excitability. Because ΔFosB is induced in hippocampus by drugs of abuse, stress, or antidepressant treatment, these results suggest that ΔFosB-driven changes in hippocampal cell excitability may be critical for learning and, in maladaptive states, are key drivers of aberrant hippocampal function in diseases such as addiction and depression.

Distinct stages of synapse elimination are induced by burst firing of CA1 neurons and differentially require MEF2A/D.

Experience and activity refine cortical circuits through synapse elimination, but little is known about the activity patterns and downstream molecular mechanisms that mediate this process. We used optogenetics to drive individual mouse CA1 hippocampal neurons to fire in theta frequency bursts to understand how cell autonomous, postsynaptic activity leads to synapse elimination. Brief (1 hr) periods of postsynaptic bursting selectively depressed AMPA receptor (R) synaptic transmission, or silenced excitatory synapses, whereas more prolonged (24 hr) firing depressed both AMPAR and NMDAR EPSCs and eliminated spines, indicative of a synapse elimination. Both synapse silencing and elimination required de novo transcription, but only silencing required the activity-dependent transcription factors MEF2A/D. Burst firing induced MEF2A/D-dependent induction of the target gene Arc which contributed to synapse silencing and elimination. This work reveals new and distinct forms of activity and transcription-dependent synapse depression and suggests that these processes can occur independently.

Selective inhibition of extra-synaptic α5-GABAA receptors by S44819, a new therapeutic agent

In the mammalian central nervous system (CNS) GABAA receptors (GABAARs) mediate neuronal inhibition and are important therapeutic targets. GABAARs are composed of 5 subunits, drawn from 19 proteins, underpinning expression of 20–30 GABAAR subtypes. In the CNS these isoforms are heterogeneously expressed and exhibit distinct physiological and pharmacological properties. We report the discovery of S44819, a novel tricyclic oxazolo-2,3-benzodiazepine-derivative, that selectively inhibits α5-subunit-containing GABAARs (α5-GABAARs). Current α5-GABAAR inhibitors bind to the “benzodiazepine site”. However, in HEK293 cells expressing recombinant α5-GABAARs, S44819 had no effect on 3H-flumazenil binding, but displaced the GABAAR agonist 3H-muscimol and competitively inhibited the GABA-induced responses. Importantly, we reveal that the α5-subunit selectivity is uniquely governed by amino acid residues within the α-subunit F-loop, a region associated with GABA binding. In mouse hippocampal CA1 neurons, S44819 enhanced long-term potentiation (LTP), blocked a tonic current mediated by extrasynaptic α5-GABAARs, but had no effect on synaptic GABAARs. In mouse thalamic neurons, S44819 had no effect on the tonic current mediated by δ-GABAARs, or on synaptic (α1β2γ2) GABAARs. In rats, S44819 enhanced object recognition memory and reversed scopolamine-induced impairment of working memory in the eight-arm radial maze. In conclusion, S44819 is a first in class compound that uniquely acts as a potent, competitive, selective antagonist of recombinant and native α5-GABAARs. Consequently, S44819 enhances hippocampal synaptic plasticity and exhibits pro-cognitive efficacy. Given this profile, S44819 may improve cognitive function in neurodegenerative disorders and facilitate post-stroke recovery.

Engineering Pak1 Allosteric Switches.

P21-activated kinases (PAKs) are important regulators of cell motility and morphology. It has been challenging to interrogate their functions because cells adapt to genetic manipulation of PAK, and because inhibitors act on multiple PAK isoforms. Here we describe genetically encoded PAK1 analogues that can be selectively activated by the membrane-permeable small molecule rapamycin. An engineered domain inserted away from the active site responds to rapamycin to allosterically control activity of the PAK1 isoform. To examine the mechanism of rapamycin-induced PAK1 activation, we used molecular dynamics with graph theory to predict amino acids involved in allosteric communication with the active site. This analysis revealed allosteric pathways that were exploited to generate kinase switches. Activation of PAK1 resulted in transient cell spreading in metastatic breast cancer cells, and long-term dendritic spine enlargement in mouse hippocampal CA1 neurons.

Ischemic Preconditioning Mediates Neuroprotection against Ischemia in Mouse Hippocampal CA1 Neurons by Inducing Autophagy.

The hippocampal CA1 region is sensitive to hypoxic and ischemic injury but can be protected by ischemic preconditioning (IPC). However, the mechanism through which IPC protects hippocampal CA1 neurons is still under investigation. Additionally, the role of autophagy in determining the fate of hippocampal neurons is unclear. Here, we examined whether IPC induced autophagy to alleviate hippocampal CA1 neuronal death in vitro and in vivo with oxygen glucose deprivation (OGD) and bilateral carotid artery occlusion (BCCAO) models. Survival of hippocampal neurons increased from 51.5% ± 6.3% in the non-IPC group (55 min of OGD) to 77.3% ± 7.9% in the IPC group (15 min of OGD, followed by 55 min of OGD 24 h later). The number of hippocampal CA1 layer neurons increased from 182 ± 26 cells/mm2 in the non-IPC group (20 min of BCCAO) to 278 ± 55 cells/mm2 in the IPC group (1 min × 3 BCCAO, followed by 20 min of BCCAO 24 h later). Akt phosphorylation and microtubule-associated protein light chain 3 (LC3)-II/LC3-I expression were increased in the preconditioning group. Moreover, the protective effects of IPC were abolished only by inhibiting the activity of autophagy, but not by blocking the activation of Akt in vitro. Using in vivo experiments, we found that LC3 expression was upregulated, accompanied by an increase in neuronal survival in hippocampal CA1 neurons in the preconditioning group. The neuroprotective effects of IPC on hippocampal CA1 neurons were completely inhibited by treatment with 3-MA. In contrast, hippocampal CA3 neurons did not show changes in autophagic activity or beneficial effects of IPC. These data suggested that IPC may attenuate ischemic injury in hippocampal CA1 neurons through induction of Akt-independent autophagy.

Long-delayed expression of the immediate early gene Arc/Arg3.1 refines neuronal circuits to perpetuate fear memory.

Fear memories typically persist for long time periods, and persistent fear memories contribute to post-traumatic stress disorder. However, little is known about the cellular and synaptic mechanisms that perpetuate long-term memories. Here, we find that mouse hippocampal CA1 neurons exhibit biphasic Arc (also known as Arg3.1) elevations after fear experience and that the late Arc expression regulates the perpetuation of fear memoires. An early Arc increase returned to the baseline after 6 h, followed by a second Arc increase after 12 h in the same neuronal subpopulation; these elevations occurred via distinct mechanisms. Antisense-induced blockade of late Arc expression disrupted memory persistence but not formation. Moreover, prolonged fear memories were associated with the delayed, specific elimination of dendritic spines and the reactivation of neuronal ensembles formed during fear experience, both of which required late Arc expression. We propose that late Arc expression refines functional circuits in a delayed fashion to prolong fear memory.

Impairment of hippocampal long-term potentiation and failure of learning in mice treated with d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol

Gangliosides (sialic acid-containing glycosphingolipids) play important roles in many physiological functions, including synaptic plasticity in the hippocampus, which has been suggested as the basal cellular process of learning and memory in the brain. In the present study, long-term potentiation (LTP) and long-term depression (LTD) in CA1 hippocampal neurons and learning behavior were examined in mice treated with (D)-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol ((D)-PDMP), an inhibitor of ganglioside biosynthesis. Mice treated with (D)-PDMP, but not those treated with (L)-PDMP, showed impairment of LTP induction in hippocampal CA1 neurons without any significant change in LTD formation and also showed a failure of learning in the 4-pellet taking test. These results indicate that de novo synthesis of gangliosides in the brain is involved in synaptic plasticity of LTP in mouse hippocampal CA1 neurons and plays important roles in learning and memory.

Role of P2X4 receptors in synaptic strengthening in mouse CA1 hippocampal neurons

P2X4 receptors are calcium-permeable cation channels gated by extracellular ATP. They are found close to subsynaptic sites on hippocampal CA1 neurons. We compared features of synaptic strengthening between wild-type and P2X4 knockout mice (21–26 days old). Potentiation evoked by a tetanic presynaptic stimulus (100 Hz, 1 s) paired with postsynaptic depolarization was less in P2X4−/− mice than in wild-type mice (230 vs. 50% potentiation). Paired-pulse ratios and the amplitude and frequency of spontaneous excitatory postsynaptic currents (EPSCs) were not different between wild-type and knockout mice. Prior hyperpolarization (ten 3 s pulses to −120 mV at 0.17 Hz) potentiated the amplitude of spontaneous EPSCs in wild-type mice, but not in P2X4−/− mice; this potentiation was not affected by nifedipine, but was abolished by 10 mm 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid (BAPTA) in the recording pipette. The amplitude of N-methyl-d-aspartate EPSCs (in 6-cyano-7-nitroquinoxaline-2,3-dione, 10 or 30 μm, at −100 mV) facilitated during 20 min recording in magnesium-free solution. In wild-type mice, this facilitation of the N-methyl-d-aspartate EPSC was reduced by about 50% by intracellular BAPTA (10 mm), ifenprodil (3 μm) or 4-(4-fluorophenyl)-2-(4-methylsulphinylphenyl)-5-(4-pyridyl)1H-imidazole (5 μm). In P2X4−/− mice, the facilitation was much less, and was unaffected by intracellular BAPTA, ifenprodil (3 μm) or mitogen-activated protein (MAP) kinase inhibitor 4-(4-fluorophenyl)-2-(4-methylsulphinylphenyl)-5-(4-pyridyl)1H-imidazole (5 μm). This suggests that the absence of P2X4 receptors limits the incorporation of NR2B subunits into synaptic N-methyl-d-aspartate receptors.

Calcium-Sensitive Translocation of Calmodulin and Neurogranin between Soma and Dendrites of Mouse Hippocampal CA1 Neurons

Calmodulin (CaM) and neurogranin (Ng) are two abundant neuronal proteins whose interactions are implicated in the regulation of synaptic responses and plasticity. We employed the “low-calcium” model of epilepsy in hippocampal slices to investigate the mobilization of these two proteins in CA1 pyramidal neurons. Perfusion of mouse hippocampal slices with Ca2+-free artificial CSF (ACSF) caused a suppression of synaptic transmission and generation of epileptic activity; these responses could be reversed by normal Ca2+-containing ACSF. Fluorescence immunochemical staining of control hippocampal slices bathed in normal ACSF revealed that CaM and Ng were more concentrated in soma than in dendrites; especially for CaM, it was concentrated in the nucleus. Perfusion of hippocampal slices with Ca2+-free ACSF caused translocation of these two proteins from soma to dendrites, and this trafficking was also reversed by Ca2+-containing buffer. A reduction of ∼15 and 40 nM intracellular Ca2+, [Ca2+]i, caused half-maximum translocation of Ng and CaM, respectively. Hippocampal CA1 pyramidal neurons were the most responsive to this Ca2+-sensitive translocation as compared to those from other areas of the hippocampus. These results illustrated the unique feature of hippocampal CA1 pyramidal neurons in sequestering high concentrations of CaM and Ng in soma and releasing them to distal dendrites at reducing level of [Ca2+]i.

Scutellarin Blocks Sodium Current in Freshly Isolated Mouse Hippocampal CA1 Neurons

Scutellarin (Scu), the main bioactive component of Erilgeron breviscapus, protects the brain against ischemic damages. To explore the therapeutic mechanism of Scu, we investigated the impact of Scu on sodium current (I(Na)) of freshly isolated mouse hippocampal CA1 neurons using the whole-cell patch clamp technique. Results showed that Scu inhibited I(Na) in concentration- and holding potential-dependent manners. At 50 μM, Scu markedly shifted the steady state inactivation curve of I (Na) towards a more negative potential, slowed down the recovery of I(Na) from inactivation state, and elicited a frequency-dependent block of I (Na). The shape of the current-voltage (I-V) curve and the steady state activation curve of I(Na) were unaffected by Scu treatment. These findings suggest that Scu is capable of inhibiting I(Na) in neurons through predominantly affecting the inactivated state of I(Na). Inhibition of Na(+) channels provides a novel pharmacological basis for the anti-ischemic application of Scu.

CX 3CL1-induced modulation at CA1 synapses reveals multiple mechanisms of EPSC modulation involving adenosine receptor subtypes

We characterized the role of adenosine receptor (AR) subtypes in the modulation of glutamatergic neurotransmission by the chemokine fractalkine (CX 3CL1) in mouse hippocampal CA1 neurons. CX 3CL1 causes a reversible depression of excitatory postsynaptic current (EPSC), which is abolished by the A 3R antagonist MRS1523, but not by A 1R (DPCPX) or A 2AR (SCH58261) antagonists. Consistently, CX 3CL1-induced EPSC depression is absent in slices from A 3R −/− but not A 1R −/− or A 2AR −/− mice. Further, A 3R stimulation causes similar EPSC depression. In cultured neurons, CX 3CL1-induced depression of AMPA current shows A 1R–A 3R pharmacology. We conclude that glutamatergic depression induced by released adenosine requires the stimulation of different ARs.

Hyperpolarized Views on the Roles of the Hyperpolarization-Activated Channels in Neuronal Excitability

Upregulated H-Current in Hyperexcitable CA1 Dendrites after Febrile Seizures. Dyhrfjeld-Johnsen J, Morgan RJ, Csaba Foldy, Soltesz I., Front Cell Neurosci. 2008;2:2. doi:10.3389/neuro.03.002.2008. Somatic recordings from CA1 pyramidal cells indicated a persistent upregulation of the h-current ( Ih) after experimental febrile seizures. Here, we examined febrile seizure-induced long-term changes in Ih and neuronal excitability in CA1 dendrites. Cell-attached recordings showed that dendritic Ih was significantly upregulated, with a depolarized half-activation potential and increased maximal current. Although enhanced Ih is typically thought to be associated with decreased dendritic excitability, whole-cell dendritic recordings revealed a robust increase in action potential firing after febrile seizures. We turned to computational simulations to understand how the experimentally observed changes in Ih influence dendritic excitability. Unexpectedly, the simulations, performed in three previously published CA1 pyramidal cell models, showed that the experimentally observed increases in Ih resulted in a general enhancement of dendritic excitability, primarily due to the increased Ih-induced depolarization of the resting membrane potential overcoming the excitability-depressing effects of decreased dendritic input resistance. Taken together, these experimental and modeling results reveal that, contrary to the exclusively anti-convulsive role often attributed to increased Ih in epilepsy, the enhanced Ih can co-exist with, and possibly even contribute to, persistent dendritic hyperexcitability following febrile seizures in the developing hippocampus. HCN Hyperpolarization-Activated Cation Channels Inhibit EPSPs by Interactions with M-type K+ Channels. George MS, Abbott LF, Siegelbaum SA. Nat Neurosci 2009;12(5):577–584. The processing of synaptic potentials by neuronal dendrites depends on both their passive cable properties and active voltage-gated channels, which can generate complex effects as a result of their nonlinear properties. We characterized the actions of HCN (hyperpolarization-activated cyclic nucleotide-gated cation) channels on dendritic processing of subthreshold excitatory postsynaptic potentials (EPSPs) in mouse CA1 hippocampal neurons. The HCN channels generated an excitatory inward current ( Ih) that exerted a direct depolarizing effect on the peak voltage of weak EPSPs, but produced a paradoxical hyperpolarizing effect on the peak voltage of stronger, but still subthreshold, EPSPs. Using a combined modeling and experimental approach, we found that the inhibitory action of Ih was caused by its interaction with the delayed-rectifier M-type K+ current. In this manner, Ih can enhance spike firing in response to an EPSP when spike threshold is low and can inhibit firing when spike threshold is high.

HCN hyperpolarization-activated cation channels inhibit EPSPs by interactions with M-type K+ channels

The processing of synaptic potentials by neuronal dendrites depends on both their passive cable properties and active voltage-gated channels, which can generate complex effects due to their nonlinear properties. In this study, we characterized the actions of the hyperpolarization-activated cation current (Ih) on dendritic processing of subthreshold excitatory postsynaptic potentials (EPSPs) in mouse CA1 hippocampal neurons. Although Ih generates an excitatory inward current that exerted a direct depolarizing effect on the peak voltage of weak EPSPs, it produced a paradoxical hyperpolarizing effect on the peak voltage of stronger but still subthreshold EPSPs. Using a combined modeling and experimental approach, we found that the inhibitory action of Ih is caused by its interaction with the delayed rectifier M-type K+ current. In this manner, Ih can enhance spike firing in response to an EPSP when spike threshold is low but inhibit firing when spike threshold is high.

Backpropagating action potential induces endocannabinoid-dependent suppression of inhibitory postsynaptic responses in mouse hippocampal CA1 neurons.

Backpropagating action potential induces endocannabinoid-dependent suppression of inhibitory postsynaptic responses in mouse hippocampal CA1 neurons.