Current Ih Research Articles

Loss of HCN1 subunits causes absence epilepsy in rats

Hyperpolarized-activated cyclic nucleotide-gated (HCN) channels underlie hyperpolarization-activated current (Ih) and are involved in controlling the excitability and electrical responsiveness of neurons. Absence epilepsy is clinically defined by a sudden, brief impairment of consciousness and behavioral arrest. Spike-and-wave discharges (SWDs) on electroencephalograms (EEG) are a diagnostic hallmark of absence epilepsy. In rat models of absence epilepsy, impaired function or expression of HCN1, a subtype of HCN channels, has been found. Here, to evaluate whether HCN1 deficiency causes absence epilepsy in rats, we developed Hcn1-knockout rats by transcription activator-like effector nuclease mutagenesis. The cortical and hippocampal pyramidal neurons of these rats displayed a significant reduction of Ih, a pronounced hyperpolarizing shift of the resting membrane potential, and increased input resistance, which indicated that the Hcn1-knockout rats were deficient in HCN1 function. The Hcn1-knockout rats were also more vulnerable to pentylenetetrazol-induced acute convulsions. More importantly, they exhibited spontaneous SWDs, which were accompanied by behavioral arrest, both of which were suppressed by ethosuximide. These results confirm the involvement of the HCN1 subunit in the regulation of input resistance and provide direct evidence that a deficiency of HCN1 caused absence epilepsy in rats.

The anticonvulsant lamotrigine enhances Ih in layer 2/3 neocortical pyramidal neurons of patients with pharmacoresistant epilepsy

Alterations of the hyperpolarization activated nonselective cation current (Ih) are associated with epileptogenesis. Accordingly, the second-generation antiepileptic drug lamotrigine (LTG) enhances Ih in rodent hippocampus. We directly evaluated here whether LTG fails to enhance Ih in neocortical slices from patients with pharmacoresistant epilepsy. With somatic current clamp recordings we observed that LTG depolarized the membrane potential, decreased the input resistance and increased the “sag” in human layer 2/3 neocortical pyramidal neurons when confounding IKir was blocked. In subsequent voltage clamp recordings we confirmed a LTG induced increase of Ih that was qualitatively similar to the one we found in rat neocortical and hippocampal pyramidal neurons. This increase is sufficient to curtail single excitatory postsynaptic potentials (EPSPs) and reduces their temporal summation in human neocortical pyramidal neurons under physiological conditions, i.e. without blocking any other currents, as estimated by sharp microelectrode recordings.Taken together LTG increases Ih and thereby alters neuronal excitability, even in neurons of pharmacoresistant patients. However, whether this increase fully countervails the deficits of Ih in epileptic patients, remains elusive.

Dynamical ventral tegmental area circuit mechanisms of alcohol-dependent dopamine release.

A large body of data has identified numerous molecular targets through which ethanol (EtOH) acts on brain circuits. Yet how these multiple mechanisms interact to result in dysregulated dopamine (DA) release under the influence of alcohol invivo remains unclear. In this manuscript, we delineate potential circuit-level mechanisms responsible for EtOH-dependent dysregulation of DA release from the ventral tegmental area (VTA) into its projection areas. For this purpose, we constructed a circuit model of the VTA that integrates realistic Glutamatergic (Glu) inputs and reproduces DA release observed experimentally. We modelled the concentration-dependent effects of EtOH on its principal VTA targets. We calibrated the model to reproduce the inverted U-shape dose dependence of DA neuron activity on EtOH concentration. The model suggests a primary role of EtOH-induced boost in the Ih and AMPA currents in the DA firing-rate/bursting increase. This is counteracted by potentiated GABA transmission that decreases DA neuron activity at higher EtOH concentrations. Thus, the model connects well-established invitro pharmacological EtOH targets with its invivo influence on neuronal activity. Furthermore, we predict that increases in VTA activity produced by moderate EtOH doses require partial synchrony and relatively low rates of the Glu afferents. We propose that the increased frequency of transient (phasic) DA peaks evoked by EtOH results from synchronous population bursts in VTA DA neurons. Our model predicts that the impact of acute ETOH on dopamine release is critically shaped by the structure of the cortical inputs to the VTA.

HCN Channels: New Therapeutic Targets for Pain Treatment

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are highly regulated proteins which respond to different cellular stimuli. The HCN currents (Ih) mediated by HCN1 and HCN2 drive the repetitive firing in nociceptive neurons. The role of HCN channels in pain has been widely investigated as targets for the development of new therapeutic drugs, but the comprehensive design of HCN channel modulators has been restricted due to the lack of crystallographic data. The three-dimensional structure of the human HCN1 channel was recently reported, opening new possibilities for the rational design of highly-selective HCN modulators. In this review, we discuss the structural and functional properties of HCN channels, their pharmacological inhibitors, and the potential strategies for designing new drugs to block the HCN channel function associated with pain perception.

Dexmedetomidine relieves neuropathic pain by inhibiting hyperpolarization-activated cyclic nucleotide-gated currents in dorsal root ganglia neurons.

This study was designed to examine the effect and mechanism of dexmedetomidine (Dex) on neuropathic pain (NP). The NP model was established by performing chronic sciatic nerve constriction injury (CCI). Seven days after CCI surgery, the rats were injected intraperitoneally with Dex, ZD7288 (an HCN channel inhibitor), and saline, respectively. The paw withdrawal threshold to mechanical stimulation and the thermal withdrawal latency tests were performed. After administration, the L4, L5 dorsal root ganglia (DRG) neurons of rats were isolated. In addition, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels subtype plasmids were transfected into human embryonic kidney (HEK)293 cells. Whole-cell clamp recordings were used to examine the properties of HCN currents (Ih) expressed in HEK293 cells and DRG neurons. After surgery, the paw withdrawal threshold to mechanical stimulation and thermal withdrawal latency were reduced, the HCN currents (Ih) amplitude of DRG neurons was increased, and the semiactivated voltage (V1/2) value was decreased in CCI rats (P<0.05). CCI rats treated with Dex or ZD7288 had reduced mechanical and thermal hyperalgesia. The Ih amplitude was lower and the V1/2 value was increased in DRG neurons in CCI rats treated with Dex or ZD7288 (P<0.05). In addition, Dex inhibited HCN1 and HCN2 currents in HEK293 cells; caused a decrease in maximal currents, an increase in the inhibition rate of Ih, and a negative shift in V1/2 (P<0.05). Taken together, our finding suggested that Dex alleviates NP and the effect is likely because of the inhibition of HCN currents.

HCN channels in the hippocampus regulate active coping behavior.

Active coping is an adaptive stress response that improves outcomes in medical and neuropsychiatric diseases. To date, most research into coping style has focused on neurotransmitter activity and little is known about the intrinsic excitability of neurons in the associated brain regions that facilitate coping. Previous studies have shown that HCN channels regulate neuronal excitability in pyramidal cells and that HCN channel current (Ih ) in the CA1 area increases with chronic mild stress. Reduction of Ih in the CA1 area leads to antidepressant-like behavior, and this region has been implicated in the regulation of coping style. We hypothesized that the antidepressant-like behavior achieved with CA1 knockdown of Ih is accompanied by increases in active coping. In this report, we found that global loss of TRIP8b, a necessary subunit for proper HCN channel localization in pyramidal cells, led to active coping behavior in numerous assays specific to coping style. We next employed a viral strategy using a dominant negative TRIP8b isoform to alter coping behavior by reducing HCN channel expression. This approach led to a robust reduction in Ih in CA1 pyramidal neurons and an increase in active coping. Together, these results establish that changes in HCN channel function in CA1 influences coping style.

Sex Differences in the Physiological Response to Ethanol of Rat Basolateral Amygdala Neurons Following Single-Prolonged Stress.

Females are more likely to develop post-traumatic stress disorder (PTSD) than males. Also, symptoms of PTSD frequently precede alcohol abuse in females. Stressful, threat-related stimuli are evaluated by the amygdala, which is critical for establishing the emotional salience of environmental stimuli. Ethanol and stress have been shown to modify amygdala excitability, but effects of acute ethanol on neurons of the basolateral amygdala (BLA) in both males and females exposed to stress is unknown. The purpose of this study is to determine stress-induced changes in membrane properties of BLA neurons and to determine how ethanol modulates these changes in male and female rats. Whole-cell recordings were obtained from BLA neurons of both male and female rats exposed to single-prolonged stress (SPS). Neuronal excitability, quantified as the number of action potentials, was determined in current clamp mode by applying a series of depolarizing current steps. Hyperpolarization-activated current (Ih) was elicited in voltage clamp. Excitability and Ih amplitude were determined before and during the superfusion of ethanol (EtOH; 30 mM) in BLA neurons from SPS-treated male and female rats. SPS alone did not alter the firing properties of BLA neurons from either males or females. However, following SPS, BLA neurons from males and females respond differently to ethanol. Superfusion of EtOH (30 mM) inhibited spike firing in BLA neurons from rats exposed to SPS, and EtOH-induced inhibition was greater in females than in males exposed to stress. Also, EtOH (30 mM) selectively decreased Ih amplitude in BLA neurons from SPS-treated male rats from 171 ± 46 pA in (pre-EtOH) control to 53 ± 51 pA in the presence of EtOH (30 mM). EtOH did not reduce Ih in BLA neurons from SPS-treated females. Together, these suggest important sex differences in the physiological responses to EtOH in stress disorders such as PTSD, that have high comorbidity with alcohol use disorders.

PACAP-Induced PAC1 Receptor Internalization and Recruitment of Endosomal Signaling Regulate Cardiac Neuron Excitability.

Pituitary adenylate cyclase-activating polypeptide (PACAP, Adcyap1) activation of PAC1 receptors (Adcyap1r1) significantly increases excitability of guinea pig cardiac neurons. This modulation of excitability is mediated in part by plasma membrane G protein-dependent activation of adenylyl cyclase and downstream signaling cascades, as well as by endosomal signaling mechanisms. PACAP/PAC1 receptor-mediated activation of plasma membrane adenylyl cyclase (AC) and the resulting increase in cellular cAMP enhances a hyperpolarization-induced nonselective cationic current Ih, which contributes to the PACAP-induced increase in cardiac neuron excitability. Further, PACAP-mediated AC/cAMP/PKA downstream signaling also appears to enhance cardiac neuron IT to facilitate the excitatory responses. PACAP activation of PAC1 receptors rapidly stimulates receptor internalization, and reducing ambient temperature or treatments with the clathrin inhibitor Pitstop2 or the dynamin I/II inhibitor dynasore to block endocytic events can suppress PACAP-enhanced neuronal excitability. Thus, endocytosis inhibitors essentially eliminate PACAP-enhanced excitability suggesting that endosomal platforms represent a primary signaling mechanism. Endosomal signaling is associated canonically with ERK activation and in accord, PACAP-enhanced cardiac neuron excitability is reduced by MEK inhibitor pretreatments. PACAP activation of MEK/ERK signaling can enhance currents through voltage-dependent Nav1.7 channels. Hence, PACAP-induced PAC1 receptor internalization/endosomal signaling, recruitment of MEK/ERK signaling, and modulation of Nav1.7 are implicated as key mechanisms contributing to the PACAP-enhanced neuronal excitability. PACAP/PAC1 receptor-mediated endosomal ERK signaling in central circuits can play key roles in development of chronic pain and anxiety-related responses; thus, PAC1 endosomal signaling likely participates in a variety of homeostatic responses within neuronal circuits in the CNS.

Alcohol Consumption during Adolescence in a Mouse Model of Binge Drinking Alters the Intrinsic Excitability and Function of the Prefrontal Cortex through a Reduction in the Hyperpolarization-Activated Cation Current.

Periodic episodes of excessive alcohol consumption ("binge drinking") occur frequently among adolescents, and early binge drinking is associated with an increased risk of alcohol use disorders later in life. The PFC undergoes significant development during adolescence and hence may be especially susceptible to the effects of binge drinking. In humans and in animal models, adolescent alcohol exposure is known to alter PFC neuronal activity and produce deficits in PFC-dependent behaviors, such as decision making, response inhibition, and working memory. Using a voluntary intermittent access to alcohol (IA EtOH) procedure in male mice, we demonstrate that binge-level alcohol consumption during adolescence leads to altered drinking patterns and working memory deficits in young adulthood, two outcomes that suggest medial PFC dysfunction. We recorded from pyramidal neurons (PNs) in the prelimbic subregion of the medial PFC in slices obtained from mice that had IA EtOH and found that they display altered excitability, including a hyperpolarization of the resting membrane potential and reductions in the hyperpolarization-activated cation current (Ih) and in intrinsic persistent activity (a mode of neuronal firing that is dependent on Ih). Many of these effects on intrinsic excitability were sustained following abstinence and observed in mice that showed working memory deficits. In addition, we found that resting membrane potential and the Ih-dependent voltage "sag" in prelimbic PFC PNs are developmentally regulated during adolescence, suggesting that adolescent alcohol exposure may compromise PFC function by arresting the normal developmental trajectory of PN intrinsic excitability.SIGNIFICANCE STATEMENT Binge alcohol drinking during adolescence has negative consequences for the function of the developing PFC. Using a mouse model of voluntary binge drinking during adolescence, we found that this behavior leads to working memory deficits and altered drinking behavior in adulthood. In addition, we found that adolescent drinking is associated with specific changes to the intrinsic excitability of pyramidal neurons in the PFC, reducing the ability of these neurons to generate intrinsic persistent activity, a phenomenon thought to be important for working memory. These findings may help explain why human adolescent binge drinkers show performance deficits on tasks mediated by the PFC.

Long-term high-intensity sound stimulation inhibits h current (Ih ) in CA1 pyramidal neurons.

Afferent neurotransmission to hippocampal pyramidal cells can lead to long-term changes to their intrinsic membrane properties and affect many ion currents. One of the most plastic neuronal currents is the hyperpolarization-activated cationic current (Ih ), which changes in CA1 pyramidal cells in response to many types of physiological and pathological processes, including auditory stimulation. Recently, we demonstrated that long-term potentiation (LTP) in rat hippocampal Schaffer-CA1 synapses is depressed by high-intensity sound stimulation. Here, we investigated whether a long-term high-intensity sound stimulation could affect intrinsic membrane properties of rat CA1 pyramidal neurons. Our results showed that Ih is depressed by long-term high-intensity sound exposure (1min of 110 dB sound, applied two times per day for 10days). This resulted in a decreased resting membrane potential, increased membrane input resistance and time constant, and decreased action potential threshold. In addition, CA1 pyramidal neurons from sound-exposed animals fired more action potentials than neurons from control animals; however, this effect was not caused by a decreased Ih . On the other hand, a single episode (1min) of 110 dB sound stimulation which also inhibits hippocampal LTP did not affect Ih and firing in pyramidal neurons, suggesting that effects on Ih are long-term responses to high-intensity sound exposure. Our results show that prolonged exposure to high-intensity sound affects intrinsic membrane properties of hippocampal pyramidal neurons, mainly by decreasing the amplitude of Ih .

Accelerated Development of the First-Order Central Auditory Neurons With Spontaneous Activity.

In developing sensory systems, elaborate morphological connectivity between peripheral cells and first-order central neurons emerges via genetic programming before the onset of sensory activities. However, how the first-order central neurons acquire the capacity to interface with peripheral cells remains elusive. By making patch-clamp recordings from mouse brainstem slices, we found that a subset of neurons in the cochlear nuclei, the first central station to receive peripheral acoustic impulses, exhibits spontaneous firings (SFs) as early as at birth, and the fraction of such neurons increases during the prehearing period. SFs are reduced but not eliminated by a cocktail of blockers for excitatory and inhibitory synaptic inputs, implicating the involvement of intrinsic pacemaker channels. Furthermore, we demonstrate that these intrinsic firings (IFs) are largely driven by hyperpolarization- and cyclic nucleotide-gated channel (HCN) mediated currents (Ih), as evidenced by their attenuation in the presence of HCN blockers or in neurons from HCN1 knockout mice. Interestingly, genetic deletion of HCN1 cannot be fully compensated by other pacemaker conductances and precludes age-dependent up regulation in the fraction of spontaneous active neurons and their firing rate. Surprisingly, neurons with SFs show accelerated development in excitability, spike waveform and firing pattern as well as synaptic pruning towards mature phenotypes compared to those without SFs. Our results imply that SFs of the first-order central neurons may reciprocally promote their wiring and firing with peripheral inputs, potentially enabling the correlated activity and crosstalk between the developing brain and external environment.

Synaptic transmission and excitability during hypoxia with inflammation and reoxygenation in hippocampal CA1 neurons

Although a number of experimental and clinical studies have shown that hypoxia typically accompanies acute inflammatory responses, the combinatorial effect of the two insults on basic neural function has not been thoroughly investigated. Previous studies have predominantly suggested that hypoxia reduces network activity; however, several studies suggest the opposite effect. Of note, inflammation is known to increase neural activity. In the current study, we examined the effects of limited oxygen in combination with an inflammatory stimulus, as well as the effects of reoxygenation, on synaptic transmission and excitability. We observed a significant reduction of both synaptic transmission and excitability when hypoxia and inflammation occurred in combination, whereas reoxygenation caused hyperexcitability of neurons. Further, we found that the observed reduction in synaptic transmission was due to compromised presynaptic release efficiency based on an adenosine-receptor–dependent increase in synaptic facilitation. Excitability changes in both directions were attributable to dynamic regulation of the hyperpolarization-activated cation current (Ih) and to changes in the input resistance and the voltage difference between resting membrane potential and action potential threshold. We found that zatebradine, an Ih current inhibitor, reduced the fluctuation in excitability, suggesting that it may have potential as a drug to ameliorate reperfusion brain injury.

Cell-Type Specific Development of the Hyperpolarization-Activated Current, Ih, in Prefrontal Cortical Neurons.

H-current, also known as hyperpolarization-activated current (Ih), is an inward current generated by the hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels. Ih plays an essential role in regulating neuronal properties, synaptic integration and plasticity, and synchronous activity in the brain. As these biological factors change across development, the brain undergoes varying levels of vulnerability to disorders like schizophrenia that disrupt prefrontal cortex (PFC)-dependent function. However, developmental changes in Ih in PFC neurons remains untested. Here, we examine Ih in pyramidal neurons vs. gamma-aminobutyric acid (GABA)ergic parvalbumin-expressing (PV+) interneurons in developing mouse PFC. Our findings show that the amplitudes of Ih in these cell types are identical during the juvenile period but differ at later time points. In pyramidal neurons, Ih amplitude significantly increases from juvenile to adolescence and follows a similar trend into adulthood. In contrast, the amplitude of Ih in PV+ interneurons decreases from juvenile to adolescence, and does not change from adolescence to adulthood. Moreover, the kinetics of HCN channels in pyramidal neurons is significantly slower than in PV+ interneurons, with a gradual decrease in pyramidal neurons and a gradual increase in PV+ cells across development. Our study reveals distinct developmental trajectories of Ih in pyramidal neurons and PV+ interneurons. The cell-type specific alteration of Ih during the critical period from juvenile to adolescence reflects the contribution of Ih to the maturation of the PFC and PFC-dependent function. These findings are essential for a better understanding of normal PFC function, and for elucidating Ih’s crucial role in the pathophysiology of neurodevelopmental disorders.

Inhibition of GluR Current in Microvilli of Sensory Neurons via Na+-Microdomain Coupling Among GluR, HCN Channel, and Na+/K+ Pump.

Glutamatergic dendritic EPSPs evoked in cortical pyramidal neurons are depressed by activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels expressed in dendritic spines. This depression has been attributed to shunting effects of HCN current (Ih) on input resistance or Ih deactivation. Primary sensory neurons in the rat mesencephalic trigeminal nucleus (MTN) have the somata covered by spine-like microvilli that express HCN channels. In rat MTN neurons, we demonstrated that Ih enhancement apparently diminished the glutamate receptor (GluR) current (IGluR) evoked by puff application of glutamate/AMPA and enhanced a transient outward current following IGluR (OT-IGluR). This suggests that some outward current opposes inward IGluR. The IGluR inhibition displayed a U-shaped voltage-dependence with a minimal inhibition around the resting membrane potential, suggesting that simple shunting effects or deactivation of Ih cannot explain the U-shaped voltage-dependence. Confocal imaging of Na+ revealed that GluR activation caused an accumulation of Na+ in the microvilli, which can cause a negative shift of the reversal potential for Ih (Eh). Taken together, it was suggested that IGluR evoked in MTN neurons is opposed by a transient decrease or increase in standing inward or outward Ih, respectively, both of which can be caused by negative shifts of Eh, as consistent with the U-shaped voltage-dependence of the IGluR inhibition and the OT-IGluR generation. An electron-microscopic immunohistochemical study revealed the colocalization of HCN channels and glutamatergic synapses in microvilli of MTN neurons, which would provide a morphological basis for the functional interaction between HCN and GluR channels. Mathematical modeling eliminated the possibilities of the involvements of Ih deactivation and/or shunting effect and supported the negative shift of Eh which causes the U-shaped voltage-dependent inhibition of IGluR.

Mirror Neurons Modeled Through Spike-Timing-Dependent Plasticity are Affected by Channelopathies Associated with Autism Spectrum Disorder.

Mirror neurons fire action potentials both when the agent performs a certain behavior and watches someone performing a similar action. Here, we present an original mirror neuron model based on the spike-timing-dependent plasticity (STDP) between two morpho-electrical models of neocortical pyramidal neurons. Both neurons fired spontaneously with basal firing rate that follows a Poisson distribution, and the STDP between them was modeled by the triplet algorithm. Our simulation results demonstrated that STDP is sufficient for the rise of mirror neuron function between the pairs of neocortical neurons. This is a proof of concept that pairs of neocortical neurons associating sensory inputs to motor outputs could operate like mirror neurons. In addition, we used the mirror neuron model to investigate whether channelopathies associated with autism spectrum disorder could impair the modeled mirror function. Our simulation results showed that impaired hyperpolarization-activated cationic currents (Ih) affected the mirror function between the pairs of neocortical neurons coupled by STDP.

Long‐term high‐intensity sound stimulation inhibits Ih in CA1 pyramidal neurons.

Afferent neurotransmission on hippocampal pyramidal cells can change their intrinsic membrane properties and affect many ion currents. One of the most plastic neuronal currents is the hyperpolarization activated cationic current (Ih), which changes in CA1 pyramidal cells in responseto many types of physiological and pathological processes. Several evidences demonstrated that hippocampal CA1 pyramidal neurons are affected by auditory stimulation. Recently we demonstrated that long‐term potentiation (LTP) is depressed by high‐intensity sound stimulation. Here we investigated if a long‐term high‐intensity sound stimulation could affect intrinsic membrane properties of CA1 pyramidal neurons. Our results showed that Ih is depressed by longterm (2 minutes per day, for 10 days) high intensity sound (110 dB) exposure. This resulted in a decreased resting membrane potential, increased membrane input resistance and time constant, and decreased action potential threshold. In contrast, CA1 pyramidal neurons from sound‐exposed animals fired more action potentials than neurons from control animals, but this effect was not caused by a decreased Ih. Interestingly, a single episode (1 minute) of 110 dB sound stimulation which also inhibits hippocampal LTP did not affect Ih and firing in pyramidal neurons, suggesting that these are long‐term responses to high intensity sound exposure. Our results show that prolonged exposure to high‐intensity sound affects intrinsic membrane properties of hippocampal pyramidal neurons mainly by decreasing the amplitude of Ih.Support or Funding InformationFAPESP, CNPQ and CapesThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

MP09-02 DIFFERENTIAL DISTRIBUTION OF HYPERPOLARIZATION-ACTIVATED CHANNELS IN PEPTIDERGIC AND CHOLINERGIC FIBERS OF THE HUMAN BLADDER

You have accessJournal of UrologyBladder & Urethra: Anatomy, Physiology & Pharmacology I1 Apr 2018MP09-02 DIFFERENTIAL DISTRIBUTION OF HYPERPOLARIZATION-ACTIVATED CHANNELS IN PEPTIDERGIC AND CHOLINERGIC FIBERS OF THE HUMAN BLADDER Pradeep Tyagi, Mahendra Kashyap, and Naoki Yoshimura Pradeep TyagiPradeep Tyagi More articles by this author , Mahendra KashyapMahendra Kashyap More articles by this author , and Naoki YoshimuraNaoki Yoshimura More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.328AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Hyperpolarization-activated cyclic nucleotide-gated channels (HCN) have been previously identified by us in the cell bodies of rat bladder afferent neurons, where they carry currents to perform diverse functions, including the hyperpolarization activated Ih current. Recent studies indicate expression of HCN channels in human bladder and suggest their involvement in the modulation of bladder contractility. HCN channels in neurons are responsible for setting the resting membrane potential, regulate discharge patterns and network activity. Present study was conducted to identify and characterize HCN1 and HCN4 immunoreactive (IR) nerve fibers in urothelium, suburothelium and detrusor regions of human bladder by immunocytochemistry. METHODS Human bladders were obtained from 3 deceased organ donors (either male or female between 16 to 82 years old) with full ethical approval. Bladders were surgically separated into urothelium (containing suburothelium) and detrusor section. Tissue regions from trigone region were cryopreserved and sectioned into 10μm thick cryosections. Sections were fixed in chilled acetone and processed for immunohistochemistry using antibodies for either HCN1 and HCN4 primary antibody. Double immunostaining with neuronal markers of calcitonin gene related peptide (CGRP) and choline acetyltransferase (ChAT) was performed. RESULTS The expression of HCN1 was relatively stronger in urothelium, sub urothelium and detrusor, whereas HCN4 expression was strongest in detrusor and suburothelium, while expression in urothelium was minimal. The co-localization of HCN1 and CGRP+ve peptidergic neuron fibers was higher than the co-localization of HCN1 with ChAT +ve cholinergic fibers in suburothelium and detrusor regions. The HCN4 immunoreactivity co-localized with the red immunoreactivity of ChAT much strongly in detrusor than in sub-urothelium. CONCLUSIONS Based on these findings, HCN ion channel mechanisms are postulated to modulate the release of neurotransmitters and initiate action potentials in response to transmitter-evoked depolarization forafferent (HCN1) and efferent ( HCN4) arm of micturition reflex. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e105-e106 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Pradeep Tyagi More articles by this author Mahendra Kashyap More articles by this author Naoki Yoshimura More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Adrenergic Modulation Regulates the Dendritic Excitability of Layer 5 Pyramidal Neurons In Vivo

The excitability of the apical tuft of layer 5 pyramidal neurons is thought to play a crucial role in behavioral performance and synaptic plasticity. We show that the excitability of the apical tuft is sensitive to adrenergic neuromodulation. Using two-photon dendritic Ca2+ imaging and invivo whole-cell and extracellular recordings in awake mice, we show that application of the α2A-adrenoceptor agonist guanfacine increases the probability of dendritic Ca2+ events in the tuft and lowers the threshold for dendritic Ca2+ spikes. We further show that these effects are likely to be mediated by the dendritic current Ih. Modulation of Ih in a realistic compartmental model controlled both the generation and magnitude of dendritic calcium spikes in the apical tuft. These findings suggest that adrenergic neuromodulation may affect cognitive processes such as sensory integration, attention, and working memory by regulating the sensitivity of layer 5 pyramidal neurons to top-down inputs.

MOCVD-derived GdYBCO tapes with smooth surface and low Rs based on a new self-heating technology

The metal organic chemical vapor deposition (MOCVD) method was used to prepare GdYBCO films on LaMnO3/ homo epitaxial-MgO/ ion-beam-assisted-deposition-MgO/ solution-deposition-planarization-Y2O3 buffered Hastelloy tapes. By adopting a simple self-heating technique, the substrates were heated by the joule effect after applying a heating current (Ih) through Hastelloy metal tapes. The effects of substrate temperature and (Gd, Y)/Ba ratio (rc) in the precursor on the biaxial texture, surface morphology and superconducting performance of GdYBCO films were systematically investigated by varying the values of Ih and rc. Needle-like outgrowths formed on the substrate surface were characterized using a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction system. The results show that a high Ih or rc leads to the formation of needle-like outgrowths. Therefore, Ih and rc are crucial process parameters that control the growth of needle-like outgrowths on the surface of GdYBCO films. Three hundred nanometer thick GdYBCO films were prepared at different Ih and rc by the MOCVD process. At an Ih of 27.0 A and an rc of 0.6, the surface of the GdYBCO film was very smooth and dense, which can provide a good template for multiple depositions of GdYBCO films. The critical current density of the deposited 300 nm-thick GdYBCO film was 4.4 MA/cm2 (77 K, 0 T), which is attributed to good biaxial texture and appropriate film composition. Furthermore, the microwave surface resistance (77 K, 10 GHz) of the GdYBCO film was merely 0.581 mΩ.

Inward rectifier potassium current IKir promotes intrinsic pacemaker activity of thalamocortical neurons.

Slow repetitive burst firing by hyperpolarized thalamocortical (TC) neurons correlates with global slow rhythms (<4 Hz), which are the physiological oscillations during non-rapid eye movement sleep or pathological oscillations during idiopathic epilepsy. The pacemaker activity of TC neurons depends on the expression of several subthreshold conductances, which are modulated in a behaviorally dependent manner. Here we show that upregulation of the small and neglected inward rectifier potassium current IKir induces repetitive burst firing at slow and delta frequency bands. We demonstrate this in mouse TC neurons in brain slices by manipulating the Kir maximum conductance with dynamic clamp. We also performed a thorough theoretical analysis that explains how the unique properties of IKir enable this current to induce slow periodic bursting in TC neurons. We describe a new ionic mechanism based on the voltage- and time-dependent interaction of IKir and hyperpolarization-activated cationic current Ih that endows TC neurons with the ability to oscillate spontaneously at very low frequencies, even below 0.5 Hz. Bifurcation analysis of conductance-based models of increasing complexity demonstrates that IKir induces bistability of the membrane potential at the same time that it induces sustained oscillations in combination with Ih and increases the robustness of low threshold-activated calcium current IT-mediated oscillations. NEW & NOTEWORTHY The strong inwardly rectifying potassium current IKir of thalamocortical neurons displays a region of negative slope conductance in the current-voltage relationship that generates potassium currents activated by hyperpolarization. Bifurcation analysis shows that IKir induces bistability of the membrane potential; generates sustained subthreshold oscillations by interacting with the hyperpolarization-activated cationic current Ih; and increases the robustness of oscillations mediated by the low threshold-activated calcium current IT. Upregulation of IKir in thalamocortical neurons induces repetitive burst firing at slow and delta frequency bands (<4 Hz).