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Abstract
Ion channels and transporters are expressed in every living cell, where they participate in controlling a plethora of biological processes and physiological functions, such as excitation of cells in response to stimulation, electrical activities of cells, excitation-contraction coupling, cellular osmolarity, and even cell growth and death. Alterations of ion channels/transporters can have profound impacts on the cellular physiology associated with these proteins. Expression of ion channels/transporters is tightly regulated and expression deregulation can trigger abnormal processes, leading to pathogenesis, the channelopathies. While transcription factors play a critical role in controlling the transcriptome of ion channels/transporters at the transcriptional level by acting on the 5'-flanking region of the genes, microribonucleic acids (miRNAs), a newly discovered class of regulators in the gene network, are also crucial for expression regulation at the posttranscriptional level through binding to the 3'untranslated region of the genes. These small noncoding RNAs fine tune expression of genes involved in a wide variety of cellular processes. Recent studies revealed the role of miRNAs in regulating expression of ion channels/transporters and the associated physiological functions. miRNAs can target ion channel genes to alter cardiac excitability (conduction, repolarization, and automaticity) and affect arrhythmogenic potential of heart. They can modulate circadian rhythm, pain threshold, neuroadaptation to alcohol, brain edema, etc., through targeting ion channel genes in the neuronal systems. miRNAs can also control cell growth and tumorigenesis by acting on the relevant ion channel genes. Future studies are expected to rapidly increase to unravel a new repertoire of ion channels/transporters for miRNA regulation.
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Affiliation(s)
- Zhiguo Wang
- Harbin Medical University, Harbin, Heilongjiang, People's Republic of China.
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102
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Lin M, Hatcher JT, Wurster RD, Chen QH, Cheng ZJ. Characteristics of single large-conductance Ca2+-activated K+ channels and their regulation of action potentials and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus. Am J Physiol Cell Physiol 2013; 306:C152-66. [PMID: 24196530 DOI: 10.1152/ajpcell.00423.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Large-conductance Ca2(+)-activated K+ channels (BK) regulate action potential (AP) properties and excitability in many central neurons. However, the properties and functional roles of BK channels in parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal 7-9 days. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. Using excised patch single-channel recordings, we identified voltage-gated and Ca(2+)-dependent BK channels in PCMNs. The majority of BK channels exhibited persistent channel opening during voltage holding. These BK channels had a conductance of 237 pS and a 50% opening probability at +27.9 mV, the channel open time constant was 3.37 ms at +20 mV, and dwell time increased exponentially as the membrane potential depolarized. At the +20-mV holding potential, the [Ca2+]50 was 15.2 μM with a P0.5 of 0.4. Occasionally, some BK channels showed a transient channel opening and fast inactivation. Using whole cell voltage clamp, we found that BK channel mediated outward currents and afterhyperpolarization currents (IAHP). Using whole cell current clamp, we found that application of BK channel blocker iberiotoxin (IBTX) increased spike half-width and suppressed fast afterhyperpolarization (fAHP) amplitude following single APs. In addition, IBTX application increased spike half-width and reduced the spike frequency-dependent AP broadening in trains and spike frequency adaption (SFA). Furthermore, BK channel blockade decreased spike frequency. Collectively, these results demonstrate that PCMNs have BK channels that significantly regulate AP repolarization, fAHP, SFA, and spike frequency. We conclude that activation of BK channels underlies one of the mechanisms for facilitation of PCMN excitability.
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Affiliation(s)
- Min Lin
- Biomolecular Science Center, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida
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103
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Książek A, Ladno W, Szulczyk B, Grzelka K, Szulczyk P. Properties of BK-type Ca(+) (+)-dependent K(+) channel currents in medial prefrontal cortex pyramidal neurons in rats of different ages. Front Cell Neurosci 2013; 7:185. [PMID: 24312002 PMCID: PMC3836005 DOI: 10.3389/fncel.2013.00185] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 10/02/2013] [Indexed: 11/13/2022] Open
Abstract
The medial prefrontal cortex (PFC) is involved in cognitive functions, which undergo profound changes during adolescence. This alteration of the PFC function derives from neuron activity, which, in turn, may depend on age-dependent properties and the expression of neuronal ion channels. BK-type channels are involved in controlling both the Ca(+) (+) ion concentration in the cell interior and cell excitability. The purpose of this study was to test the properties of BK currents in the medial PFC pyramidal neurons of young (18- to 22-day-old), adolescent (38- to 42-day-old), and adult (60- to 65-day-old) rats. Whole-cell currents evoked by depolarizing voltage steps were recorded from dispersed medial PFC pyramidal neurons. A selective BK channel blocker - paxilline (10 μM) - irreversibly decreased the non-inactivating K(+) current in neurons that were isolated from the young and adult rats. This current was not significantly affected by paxilline in the neurons obtained from adolescent rats. The properties of single-channel K(+) currents were recorded from the soma of dispersed medial PFC pyramidal neurons in the cell-attached configuration. Of the K(+) channel currents that were recorded, ~90% were BK and leak channel currents. The BK-type channel currents were dependent on the Ca(+) (+) concentration and the voltage and were inhibited by paxilline. The biophysical properties of the BK channel currents did not differ among the pyramidal neurons isolated from young, adolescent, and adult rats. Among all of the recorded K(+) channel currents, 38.9, 12.7, and 21.1% were BK-type channel currents in the neurons isolated from the young, adolescent, and adult rats, respectively. Furthermore, application of paxilline effectively prolonged the half-width of the action potential in pyramidal neurons in slices isolated from young and adult rats but not in neurons isolated from adolescent rats. We conclude that the availability of BK channel currents decreases in medial PFC pyramidal neurons of adolescent rats compared with those in the neurons of young and adult rats while their properties did not change across ages.
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Affiliation(s)
- Aneta Książek
- Department of Physiology and Pathophysiology, Medical University of Warsaw Warsaw, Poland
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104
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Giglio AM, Storm JF. Postnatal development of temporal integration, spike timing and spike threshold regulation by a dendrotoxin-sensitive K+current in rat CA1 hippocampal cells. Eur J Neurosci 2013; 39:12-23. [DOI: 10.1111/ejn.12385] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Revised: 08/30/2013] [Accepted: 09/10/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Anna M. Giglio
- Institute of Basal Medicine; Department of Physiology and Centre of Molecular Biology and Neuroscience; University of Oslo; PB 1104 Blindern, 0317 Oslo Norway
| | - Johan F. Storm
- Institute of Basal Medicine; Department of Physiology and Centre of Molecular Biology and Neuroscience; University of Oslo; PB 1104 Blindern, 0317 Oslo Norway
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105
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Toprani S, Durand DM. Long-lasting hyperpolarization underlies seizure reduction by low frequency deep brain electrical stimulation. J Physiol 2013; 591:5765-90. [PMID: 23981713 DOI: 10.1113/jphysiol.2013.253757] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Mesial temporal lobe epilepsy (MTLE) is a common medically refractory neurological disease. Deep brain electrical stimulation (DBS) of grey matter has been used for MTLE with limited success. However, stimulation of a white matter tract connecting the hippocampi, the ventral hippocampal commissure (VHC), with low frequencies that simulate interictal discharges has shown promising results, with seizure reduction greater than 98% in bilateral hippocampi during stimulation and greater than 50% seizure reduction in bilateral hippocampi after treatment. A major hurdle to the implementation and optimization of this treatment is that the mechanisms of seizure reduction by low frequency electrical stimulation (LFS) are not known. The goal of this study is to understand how commissural fibre tract stimulation reduces bilateral hippocampal epileptic activity in an in vitro slice preparation containing bilateral hippocampi connected by the VHC. It is our hypothesis that electrical stimuli induce hyperpolarization lasting hundreds of milliseconds following each pulse which reduces spontaneous epileptic activity during each inter-stimulus interval (ISI). Stimulus-induced long-lasting-hyperpolarization (LLH) can be mediated by GABA(B) inhibitory post-synaptic potentials (IPSPs) or slow after-hyperpolarization (sAHP). To test the role of LLH in effective bilateral seizure reduction by fibre tract stimulation, we measured stimulus-induced hyperpolarization during LFS of the VHC using electrophysiology techniques. Antagonism of the GABA(B) IPSP and/or sAHP diminished stimulus-induced hyperpolarization concurrently with LFS efficacy (greater than 50% reduction). Blocking both the GABA(B) IPSP and sAHP simultaneously eliminated the effect of electrical stimulation on seizure reduction entirely. These data show that LFS of the VHC is an effective protocol for bilateral hippocampal seizure reduction and that its efficacy relies on the induction of long-lasting hyperpolarization mediated through GABA(B) IPSPs and sAHP. Based on this study, optimization of the timing of LFS and LFS-induced-LLH may lead to improved outcomes from DBS treatments for human epilepsy.
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Affiliation(s)
- Sheela Toprani
- D. M. Durand: Neural Engineering Center, Departments of Biomedical Engineering and Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA.
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106
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What determines the kinetics of the slow afterhyperpolarization (sAHP) in neurons? Biophys J 2013; 104:281-3. [PMID: 23442848 DOI: 10.1016/j.bpj.2012.11.3832] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 11/13/2012] [Accepted: 11/16/2012] [Indexed: 11/20/2022] Open
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107
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Sehgal M, Song C, Ehlers VL, Moyer JR. Learning to learn - intrinsic plasticity as a metaplasticity mechanism for memory formation. Neurobiol Learn Mem 2013; 105:186-99. [PMID: 23871744 DOI: 10.1016/j.nlm.2013.07.008] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 07/09/2013] [Accepted: 07/11/2013] [Indexed: 10/26/2022]
Abstract
"Use it or lose it" is a popular adage often associated with use-dependent enhancement of cognitive abilities. Much research has focused on understanding exactly how the brain changes as a function of experience. Such experience-dependent plasticity involves both structural and functional alterations that contribute to adaptive behaviors, such as learning and memory, as well as maladaptive behaviors, including anxiety disorders, phobias, and posttraumatic stress disorder. With the advancing age of our population, understanding how use-dependent plasticity changes across the lifespan may also help to promote healthy brain aging. A common misconception is that such experience-dependent plasticity (e.g., associative learning) is synonymous with synaptic plasticity. Other forms of plasticity also play a critical role in shaping adaptive changes within the nervous system, including intrinsic plasticity - a change in the intrinsic excitability of a neuron. Intrinsic plasticity can result from a change in the number, distribution or activity of various ion channels located throughout the neuron. Here, we review evidence that intrinsic plasticity is an important and evolutionarily conserved neural correlate of learning. Intrinsic plasticity acts as a metaplasticity mechanism by lowering the threshold for synaptic changes. Thus, learning-related intrinsic changes can facilitate future synaptic plasticity and learning. Such intrinsic changes can impact the allocation of a memory trace within a brain structure, and when compromised, can contribute to cognitive decline during the aging process. This unique role of intrinsic excitability can provide insight into how memories are formed and, more interestingly, how neurons that participate in a memory trace are selected. Most importantly, modulation of intrinsic excitability can allow for regulation of learning ability - this can prevent or provide treatment for cognitive decline not only in patients with clinical disorders but also in the aging population.
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Affiliation(s)
- Megha Sehgal
- Department of Psychology, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
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108
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Ponulak F, Hopfield JJ. Rapid, parallel path planning by propagating wavefronts of spiking neural activity. Front Comput Neurosci 2013; 7:98. [PMID: 23882213 PMCID: PMC3714542 DOI: 10.3389/fncom.2013.00098] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Accepted: 06/26/2013] [Indexed: 12/04/2022] Open
Abstract
Efficient path planning and navigation is critical for animals, robotics, logistics and transportation. We study a model in which spatial navigation problems can rapidly be solved in the brain by parallel mental exploration of alternative routes using propagating waves of neural activity. A wave of spiking activity propagates through a hippocampus-like network, altering the synaptic connectivity. The resulting vector field of synaptic change then guides a simulated animal to the appropriate selected target locations. We demonstrate that the navigation problem can be solved using realistic, local synaptic plasticity rules during a single passage of a wavefront. Our model can find optimal solutions for competing possible targets or learn and navigate in multiple environments. The model provides a hypothesis on the possible computational mechanisms for optimal path planning in the brain, at the same time it is useful for neuromorphic implementations, where the parallelism of information processing proposed here can fully be harnessed in hardware.
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Affiliation(s)
- Filip Ponulak
- Brain Corporation San Diego, CA, USA ; Department of Molecular Biology, Princeton University Princeton, NJ, USA
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109
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Major G, Larkum ME, Schiller J. Active Properties of Neocortical Pyramidal Neuron Dendrites. Annu Rev Neurosci 2013; 36:1-24. [DOI: 10.1146/annurev-neuro-062111-150343] [Citation(s) in RCA: 286] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Guy Major
- School of Biosciences, Cardiff University, Cardiff, CF10 3AX, United Kingdom;
| | - Matthew E. Larkum
- Charité University, Neuroscience Research Center (NWFZ), D-10117 Berlin, Germany;
| | - Jackie Schiller
- Department of Physiology, Technion Medical School, Haifa 31096, Israel;
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110
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Rehak R, Bartoletti TM, Engbers JDT, Berecki G, Turner RW, Zamponi GW. Low voltage activation of KCa1.1 current by Cav3-KCa1.1 complexes. PLoS One 2013; 8:e61844. [PMID: 23626738 PMCID: PMC3633930 DOI: 10.1371/journal.pone.0061844] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 03/14/2013] [Indexed: 02/03/2023] Open
Abstract
Calcium-activated potassium channels of the KCa1.1 class are known to regulate repolarization of action potential discharge through a molecular association with high voltage-activated calcium channels. The current study examined the potential for low voltage-activated Cav3 (T-type) calcium channels to interact with KCa1.1 when expressed in tsA-201 cells and in rat medial vestibular neurons (MVN) in vitro. Expression of the channel α-subunits alone in tsA-201 cells was sufficient to enable Cav3 activation of KCa1.1 current. Cav3 calcium influx induced a 50 mV negative shift in KCa1.1 voltage for activation, an interaction that was blocked by Cav3 or KCa1.1 channel blockers, or high internal EGTA. Cav3 and KCa1.1 channels coimmunoprecipitated from lysates of either tsA-201 cells or rat brain, with Cav3 channels associating with the transmembrane S0 segment of the KCa1.1 N-terminus. KCa1.1 channel activation was closely aligned with Cav3 calcium conductance in that KCa1.1 current shared the same low voltage dependence of Cav3 activation, and was blocked by voltage-dependent inactivation of Cav3 channels or by coexpressing a non calcium-conducting Cav3 channel pore mutant. The Cav3-KCa1.1 interaction was found to function highly effectively in a subset of MVN neurons by activating near –50 mV to contribute to spike repolarization and gain of firing. Modelling data indicate that multiple neighboring Cav3-KCa1.1 complexes must act cooperatively to raise calcium to sufficiently high levels to permit KCa1.1 activation. Together the results identify a novel Cav3-KCa1.1 signaling complex where Cav3-mediated calcium entry enables KCa1.1 activation over a wide range of membrane potentials according to the unique voltage profile of Cav3 calcium channels, greatly extending the roles for KCa1.1 potassium channels in controlling membrane excitability.
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Affiliation(s)
- Renata Rehak
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
| | - Theodore M. Bartoletti
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
| | - Jordan D. T. Engbers
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
| | - Geza Berecki
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
| | - Ray W. Turner
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
| | - Gerald W. Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- * E-mail:
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111
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Abstract
During behavioral quiescence, the neocortex generates spontaneous slow oscillations, which may consist of up-states and down-states. Up-states are short epochs of persistent activity that resemble the activated neocortex during arousal and cognition. Neural activity in neocortical pathways can trigger up-states, but the variables that control their occurrence are poorly understood. We used thalamocortical slices from adult mice to explore the role of thalamocortical and intracortical synaptic cooperativity (the number of coincident afferents) in driving up-states. Cooperativity was adjusted by varying the intensity of electrical or blue-light stimuli in pathways that express channelrhodopsin-2. We found that optogenetics greatly improves the study of thalamocortical pathways in slices because it produces thalamocortical responses that resemble those observed in vivo. The results indicate that more synaptic cooperativity, caused by either thalamocortical or intracortical fast AMPA-receptor excitation, leads to more robust inhibition of up-states because it drives stronger feedforward inhibition. Conversely, during strong synaptic cooperativity that suppresses up-states, blocking fast excitation, and as a result the feedforward inhibition it drives, unmasks up-states entirely mediated by slow NMDA-receptor excitation. Regardless of the pathway's origin, cooperativity mediated by fast excitation is inversely related to the ability of excitatory synaptic pathways to trigger up-states in neocortex.
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112
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Peng BW, Justice JA, He XH, Sanchez RM. Decreased A-currents in hippocampal dentate granule cells after seizure-inducing hypoxia in the immature rat. Epilepsia 2013; 54:1223-31. [PMID: 23815572 DOI: 10.1111/epi.12150] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2013] [Indexed: 11/29/2022]
Abstract
PURPOSE Cerebral hypoxia is a major cause of neonatal seizures, and can lead to epilepsy. Pathologic anatomic and physiologic changes in the dentate gyrus have been associated with epileptogenesis in many experimental models, as this region is widely believed to gate the propagation of limbic seizures. However, the consequences of hypoxia-induced seizures for the immature dentate gyrus have not been extensively examined. METHODS Seizures were induced by global hypoxia (5-7% O2 for 15 min) in rat pups on postnatal day 10. Whole-cell voltage-clamp recordings were used to examine A-type potassium currents (IA ) in dentate granule cells in hippocampal slices obtained 1-17 days after hypoxia treatment. KEY FINDINGS Seizure-inducing hypoxia resulted in decreased maximum IA amplitude in dentate granule cells recorded within the first week but not at later times after hypoxia treatment. The decreased IA amplitude was not associated with changes in the voltage-dependence of activation or inactivation removal, or in sensitivity to inhibition by 4-aminopyridine (4-AP). However, consistent with the role of IA in shaping firing patterns, we observed in the hypoxia group a significantly decreased latency to first spike with depolarizing current injection from hyperpolarized potentials. These differences were not associated with changes in resting membrane potential or input resistance, and were eliminated by application of 10 m 4-AP. SIGNIFICANCE Given the role of IA to slow action potential firing, decreased IA could contribute to long-term hippocampal pathology after neonatal seizure-inducing hypoxia by increasing dentate granule cell excitability during a critical window of activity-dependent hippocampal maturation.
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Affiliation(s)
- Bi-Wen Peng
- Department of Physiology, Wuhan University School of Basic Medical Sciences, Wuhan, Hubei, China
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113
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Bonin RP, Zurek AA, Yu J, Bayliss DA, Orser BA. Hyperpolarization-activated current (In) is reduced in hippocampal neurons from Gabra5-/- mice. PLoS One 2013; 8:e58679. [PMID: 23516534 PMCID: PMC3597723 DOI: 10.1371/journal.pone.0058679] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 02/05/2013] [Indexed: 01/06/2023] Open
Abstract
Changes in the expression of γ-aminobutyric acid type A (GABAA) receptors can either drive or mediate homeostatic alterations in neuronal excitability. A homeostatic relationship between α5 subunit-containing GABAA (α5GABAA) receptors that generate a tonic inhibitory conductance, and HCN channels that generate a hyperpolarization-activated cation current (Ih) was recently described for cortical neurons, where a reduction in Ih was accompanied by a reciprocal increase in the expression of α5GABAA receptors resulting in the preservation of dendritosomatic synaptic function. Here, we report that in mice that lack the α5 subunit gene (Gabra5−/−), cultured embryonic hippocampal pyramidal neurons and ex vivo CA1 hippocampal neurons unexpectedly exhibited a decrease in Ih current density (by 40% and 28%, respectively), compared with neurons from wild-type (WT) mice. The resting membrane potential and membrane hyperpolarization induced by blockade of Ih with ZD-7288 were similar in cultured WT and Gabra5−/− neurons. In contrast, membrane hyperpolarization measured after a train of action potentials was lower in Gabra5−/− neurons than in WT neurons. Also, membrane impedance measured in response to low frequency stimulation was greater in cultured Gabra5−/− neurons. Finally, the expression of HCN1 protein that generates Ih was reduced by 41% in the hippocampus of Gabra5−/− mice. These data indicate that loss of a tonic GABAergic inhibitory conductance was followed by a compensatory reduction in Ih. The results further suggest that the maintenance of resting membrane potential is preferentially maintained in mature and immature hippocampal neurons through the homeostatic co-regulation of structurally and biophysically distinct cation and anion channels.
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Affiliation(s)
- Robert P. Bonin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Agnieszka A. Zurek
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Jieying Yu
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Douglas A. Bayliss
- Department of Pharmacology, University of Virginia Health System, Charlottesville, Virginia, United States of America
| | - Beverley A. Orser
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada
- Department of Anesthesia, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
- * E-mail:
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114
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Castro-Alamancos MA. The motor cortex: a network tuned to 7-14 Hz. Front Neural Circuits 2013; 7:21. [PMID: 23439785 PMCID: PMC3578207 DOI: 10.3389/fncir.2013.00021] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 01/31/2013] [Indexed: 01/13/2023] Open
Abstract
The neocortex or six layer cortex consists of at least 52 cytoarchitectonically distinct areas in humans, and similar areas can be distinguished in rodents. Each of these areas has a defining set of extrinsic connections, identifiable functional roles, a distinct laminar arrangement, etc. Thus, neocortex is extensively subdivided into areas of anatomical and functional specialization, but less is known about the specialization of cellular and network physiology across areas. The motor cortex appears to have a distinct propensity to oscillate in the 7–14 Hz frequency range. Augmenting responses, normal mu and beta oscillations, and abnormal oscillations or after discharges caused by enhancing excitation or suppressing inhibition are all expressed around this frequency range. The substrate for this activity may be an excitatory network that is unique to the motor cortex or that is more strongly suppressed in other areas, such as somatosensory cortex. Interestingly, augmenting responses are dependent on behavioral state. They are abolished during behavioral arousal. Here, I briefly review this evidence.
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115
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Saikosaponin a Enhances Transient Inactivating Potassium Current in Rat Hippocampal CA1 Neurons. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2013; 2013:413092. [PMID: 23554830 PMCID: PMC3608310 DOI: 10.1155/2013/413092] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 01/01/2013] [Indexed: 11/18/2022]
Abstract
Saikosaponin a (SSa), a main constituent of the Chinese herb Bupleurum chinense DC., has been demonstrated to have antiepileptic activity. Recent studies have shown that SSa could inhibit NMDA receptor current and persistent sodium current. However, the effects of SSa on potassium (K+) currents remain unclear. In this study, we tested the effect of SSa on 4AP-induced epileptiform discharges and K+ currents in CA1 neurons of rat hippocampal slices. We found that SSa significantly inhibited epileptiform discharges frequency and duration in hippocampal CA1 neurons in the 4AP seizure model in a dose-dependent manner with an IC50
of 0.7 μM. SSa effectively increased the amplitude of ITotal
and IA, significantly negative-shifted the activation curve, and positive-shifted steady-state curve of IA. However, SSa induced no significant changes in the amplitude and activation curve of IK. In addition, SSa significantly increased the amplitude of 4AP-sensitive K+ current, while there was no significant change in the amplitude of TEA-sensitive K+ current. Together, our data indicate that SSa inhibits epileptiform discharges induced by 4AP in a dose-dependent manner and that SSa exerts selectively enhancing effects on IA. These increases in IA may contribute to the anticonvulsant mechanisms of SSa.
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116
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Song M, Mohamad O, Chen D, Yu SP. Coordinated development of voltage-gated Na+ and K+ currents regulates functional maturation of forebrain neurons derived from human induced pluripotent stem cells. Stem Cells Dev 2013; 22:1551-63. [PMID: 23259973 DOI: 10.1089/scd.2012.0556] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Like embryonic stem (ES) cells, human induced pluripotent stem (hiPS) cells can differentiate into neuronal cells. However, it is unclear how their exquisite neuronal function is electrophysiologically coordinated during differentiation and whether they are functionally identical to human ES cell-derived neurons. In this study, we differentiated hiPS and ES cells into pyramidal-like neurons and conducted electrophysiological characterization over the 4-week terminal differentiation period. The human neuron-like cells express forebrain pyramidal cell markers NeuN, neurofilament, the microtubule-associated protein 2 (MAP2), the paired box protein Pax-6 (PAX6), Tuj1, and the forkhead box protein G1 (FoxG1). The size of developing neurons increased continuously during the 4-week culture, and cell-resting membrane potentials (RMPs) underwent a negative shift from -40 to -70 mV. Expression of the muscarinic receptor-modulated K(+) currents (IM) participated in the development of cell RMPs and controlled excitability. Immature neurons at week 1 could only fire abortive action potentials (APs) and the frequency of AP firing progressively increased with neuronal maturation. Interestingly, the developmental change of voltage-gated Na(+) current (INa) did not correlate with the change in the AP firing frequency. On the other hand, the transient outward K(+) current (IA), but not the delayed rectifier current (IK) contributed to the high frequency firing of APs. Synaptic activities were observed throughout the 4-week development. These morphological and electrophysiological features were almost identical between iPS and ES cell-derived neurons. This is the first systematic investigation showing functional evidence that hiPS cell-derived neurons possess similar neuronal activities as ES cell-derived neurons. These data support that iPS cell-derived neural progenitor cells have the potential for replacing lost neurons in cell-based therapy.
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Affiliation(s)
- Mingke Song
- Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA 30322, USA
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117
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Solntseva EI, Bukanova JV, Skrebitsky VG. Donepezil in low micromolar concentrations modulates voltage-gated potassium currents in pyramidal neurons of rat hippocampus. Biochem Biophys Res Commun 2013; 430:1066-71. [DOI: 10.1016/j.bbrc.2012.12.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 12/08/2012] [Indexed: 02/05/2023]
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Kim KS, Kobayashi M, Takamatsu K, Tzingounis AV. Hippocalcin and KCNQ channels contribute to the kinetics of the slow afterhyperpolarization. Biophys J 2012; 103:2446-54. [PMID: 23260046 DOI: 10.1016/j.bpj.2012.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Revised: 10/25/2012] [Accepted: 11/01/2012] [Indexed: 12/29/2022] Open
Abstract
The calcium-activated slow afterhyperpolarization (sAHP) is a potassium conductance implicated in many physiological functions of the brain including memory, aging, and epilepsy. In large part, the sAHP's importance stems from its exceedingly long-lasting time-course, which integrates action potential-induced calcium signals and allows the sAHP to control neuronal excitability and prevent runaway firing. Despite its role in neuronal physiology, the molecular mechanisms that give rise to its unique kinetics are, to our knowledge, still unknown. Recently, we identified KCNQ channels as a candidate potassium channel family that can contribute to the sAHP. Here, we test whether KCNQ channels shape the sAHP rise and decay kinetics in wild-type mice and mice lacking Hippocalcin, the putative sAHP calcium sensor. Application of retigabine to speed KCNQ channel activation accelerated the rise of the CA3 pyramidal neuron sAHP current in both wild-type and Hippocalcin knockout mice, indicating that the gating of KCNQ channels limits the sAHP activation. Interestingly, we found that the decay of the sAHP was prolonged in Hippocalcin knockout mice, and that the decay was sensitive to retigabine modulation, unlike in wild-type mice. Together, our results demonstrate that sAHP activation in CA3 pyramidal neurons is critically dependent on KCNQ channel kinetics whereas the identity of the sAHP calcium sensor determines whether KCNQ channel kinetics also limit the sAHP decay.
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Affiliation(s)
- Kwang S Kim
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA
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Andrade R, Foehring RC, Tzingounis AV. The calcium-activated slow AHP: cutting through the Gordian knot. Front Cell Neurosci 2012; 6:47. [PMID: 23112761 PMCID: PMC3480710 DOI: 10.3389/fncel.2012.00047] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Accepted: 10/05/2012] [Indexed: 11/13/2022] Open
Abstract
The phenomenon known as the slow afterhyperpolarization (sAHP) was originally described more than 30 years ago in pyramidal cells as a slow, Ca(2+)-dependent afterpotential controlling spike frequency adaptation. Subsequent work showed that similar sAHPs were widely expressed in the brain and were mediated by a Ca(2+)-activated potassium current that was voltage-independent, insensitive to most potassium channel blockers, and strongly modulated by neurotransmitters. However, the molecular basis for this current has remained poorly understood. The sAHP was initially imagined to reflect the activation of a potassium channel directly gated by Ca(2+) but recent studies have begun to question this idea. The sAHP is distinct from the Ca(2+)-dependent fast and medium AHPs in that it appears to sense cytoplasmic [Ca(2+)](i) and recent evidence implicates proteins of the neuronal calcium sensor (NCS) family as diffusible cytoplasmic Ca(2+) sensors for the sAHP. Translocation of Ca(2+)-bound sensor to the plasma membrane would then be an intermediate step between Ca(2+) and the sAHP channels. Parallel studies strongly suggest that the sAHP current is carried by different potassium channel types depending on the cell type. Finally, the sAHP current is dependent on membrane PtdIns(4,5)P(2) and Ca(2+) appears to gate this current by increasing PtdIns(4,5)P(2) levels. Because membrane PtdIns(4,5)P(2) is essential for the activity of many potassium channels, these finding have led us to hypothesize that the sAHP reflects a transient Ca(2+)-induced increase in the local availability of PtdIns(4,5)P(2) which then activates a variety of potassium channels. If this view is correct, the sAHP current would not represent a unitary ionic current but the embodiment of a generalized potassium channel gating mechanism. This model can potentially explain the cardinal features of the sAHP, including its cellular heterogeneity, slow kinetics, dependence on cytoplasmic [Ca(2+)], high temperature-dependence, and modulation.
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Affiliation(s)
- Rodrigo Andrade
- Department of Pharmacology, Wayne State University School of Medicine Detroit, MI, USA
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Heys JG, Hasselmo ME. Neuromodulation of I(h) in layer II medial entorhinal cortex stellate cells: a voltage-clamp study. J Neurosci 2012; 32:9066-72. [PMID: 22745506 PMCID: PMC3462016 DOI: 10.1523/jneurosci.0868-12.2012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 04/19/2012] [Accepted: 05/12/2012] [Indexed: 11/21/2022] Open
Abstract
Stellate cells in layer II of medial entorhinal cortex (mEC) are endowed with a large hyperpolarization-activated cation current [h current (I(h))]. Recent work using in vivo recordings from awake behaving rodents demonstrate that I(h) plays a significant role in regulating the characteristic spatial periodicity of "grid cells" in mEC. A separate, yet related, line of research demonstrates that grid field spacing changes as a function of behavioral context. To understand the neural mechanism or mechanisms that could be underlying these changes in grid spacing, we have conducted voltage-clamp recordings of I(h) in layer II stellate cells. In particular, we have studied I(h) under the influence of several neuromodulators. The results demonstrate that I(h) amplitude can be both upregulated and downregulated through activation of distinct neuromodulators in mEC. Activation of muscarinic acetylcholine receptors produces a significant decrease in the I(h) tail current and a hyperpolarizing shift in the activation, whereas upregulation of cAMP through application of forskolin produces a significant increase in the I(h) amplitude and a depolarizing shift in I(h) activation curve. In addition, there was evidence of differential modulation of I(h) along the dorsal-ventral axis of mEC. Voltage-clamp protocols were also used to determine whether M current is present in stellate cells. In contrast to CA1 pyramidal neurons, which express M current, the data demonstrate that M current is not present in stellate cells. The results from this study provide key insights into a potential mechanism that could be underlying changes seen in grid field spacing during distinct behavioral contexts.
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Affiliation(s)
- James G Heys
- Center for Memory and Brain, Graduate Program for Neuroscience, Department of Psychology, Boston University, Boston, Massachusetts 02215, USA.
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121
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Favero M, Varghese G, Castro-Alamancos MA. The state of somatosensory cortex during neuromodulation. J Neurophysiol 2012; 108:1010-24. [PMID: 22623484 DOI: 10.1152/jn.00256.2012] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During behavioral quiescence, such as slow-wave sleep and anesthesia, the neocortex is in a deactivated state characterized by the presence of slow oscillations. During arousal, slow oscillations are absent and the neocortex is in an activated state that greatly impacts information processing. Neuromodulators acting in neocortex are believed to mediate these state changes, but the mechanisms are poorly understood. We investigated the actions of noradrenergic and cholinergic activation on slow oscillations, cellular excitability, and synaptic inputs in thalamocortical slices of somatosensory cortex. The results show that neuromodulation abolishes slow oscillations, dampens the excitability of principal cells, and rebalances excitatory and inhibitory synaptic inputs in thalamocortical-recipient layers IV-III. Sensory cortex is much more selective about the inputs that can drive it. The source of neuromodulation is critically important in determining this selectivity. Cholinergic activation suppresses the excitatory and inhibitory conductances driven by thalamocortical and intracortical inputs. Noradrenergic activation suppresses the excitatory conductance driven by intracortical inputs but not by thalamocortical inputs and enhances the inhibitory conductance driven by thalamocortical inputs but not by intracortical inputs. Thus noradrenergic activation emphasizes thalamocortical (sensory) inputs relative to intracortical inputs, while cholinergic activation suppresses both.
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Affiliation(s)
- Morgana Favero
- Dept. of Neurobiology and Anatomy, Drexel Univ. College of Medicine, Philadelphia, PA 19129, USA
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122
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Chiang CC, Lin CCK, Ju MS, Durand DM. High frequency stimulation can suppress globally seizures induced by 4-AP in the rat hippocampus: an acute in vivo study. Brain Stimul 2012; 6:180-9. [PMID: 22621942 DOI: 10.1016/j.brs.2012.04.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Revised: 04/02/2012] [Accepted: 04/20/2012] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND High frequency stimulation (HFS) on the hippocampus can locally suppress epileptiform activity in-vitro and decrease seizure frequency in vivo. In-vitro HFS on the ventral commissural tract, a novel target, was shown to block the axonal conduction and suppress activity in the CA1 and CA3 neuron. OBJECTIVE To study the spatial extent of seizure suppression by HFS applied on the tract and focus site in an in vivo experiment. METHODS Five adult Sprague-Dawley rats were used for the study. Six electrodes were placed on the septal, middle, and temporal hippocampus bilaterally to simultaneously record seizure activity in the entire hippocampus. Seizure activity was induced by injecting 4-aminopyridine (4-AP) into the right middle part of the hippocampus. Following induction, HFS (100 Hz) was applied to the tract and the focus site at 100, 300 and 500 μA. RESULTS The induced seizure activity was dominated by two patterns, high frequency spiking and pseudo-periodic spikes. Either tract or focus site stimulation could generate suppression of only the pseudo-periodic spikes. The suppression rates were dependent on stimulation amplitude (P < 0.005, chi square test). However, HFS also caused conversion of the seizure pattern. The conversion rates increased with higher stimulation amplitudes and were higher with focus site stimulation (P < 0.01, Fisher's exact test). CONCLUSIONS The results of this study have two practical implications [1], both tract and focus site stimulation can produce global suppression of hippocampus and [2] the choice of stimulation parameters is critical in order to produce suppression, but not conversion, of seizure pattern.
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Affiliation(s)
- Chia-Chu Chiang
- Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan.
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123
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Molinari F, Cattani A, Mdzomba J, Aniksztejn L. Glutamate transporters control metabotropic glutamate receptors activation to prevent the genesis of paroxysmal burst in the developing hippocampus. Neuroscience 2012; 207:25-36. [DOI: 10.1016/j.neuroscience.2012.01.036] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 12/23/2011] [Accepted: 01/19/2012] [Indexed: 12/26/2022]
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Reduced ictogenic potential of 4-aminopyridine in the hippocampal region in the pilocarpine model of epilepsy. Neurosci Lett 2012; 513:124-8. [PMID: 22342924 DOI: 10.1016/j.neulet.2012.01.071] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 01/25/2012] [Accepted: 01/28/2012] [Indexed: 02/07/2023]
Abstract
It was previously shown that the ictogenic potential of 4-aminopyridine (4-AP) was reduced in the parahippocampal region of kainate treated chronic epileptic rats. In the actual study we investigated the potential of 4-aminopyridine (50 and 100μM) to induce seizure like events (SLEs) in combined entorhinal cortex hippocampal slices from Wistar rats following pilocarpine induced status epilepticus. The potential of 4-AP to induce SLEs in the entorhinal cortex was reduced in the latent period and in slices of chronic epileptic animals with a high seizure incidence in vivo (>2seizures/24h). 4-AP induced SLEs in slices from animals with a low incidence of seizures in vivo (<2seizures/24h) in a similar manner as compared to controls. The hippocampal formation displayed no SLEs, instead short recurrent epileptiform discharges (REDs) were evoked by application of 4-AP in areas CA3 and CA1. The incidence of REDs was largest in slices from control animals. This study shows that the reduced ictogenic potential of 4-AP is not restricted to kainate treated chronic epileptic animals as it can be found in the pilocarpine model as well. The underlying mechanisms may relate to altered expression and editing of voltage gated potassium channels.
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125
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Kernig K, Kirschstein T, Würdemann T, Rohde M, Köhling R. The afterhyperpolarizing potential following a train of action potentials is suppressed in an acute epilepsy model in the rat Cornu Ammonis 1 area. Neuroscience 2012; 201:288-96. [PMID: 22100272 DOI: 10.1016/j.neuroscience.2011.11.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 10/11/2011] [Accepted: 11/02/2011] [Indexed: 11/18/2022]
Abstract
In hippocampal Cornu Ammonis 1 (CA1) neurons, a prolonged depolarization evokes a train of action potentials followed by a prominent afterhyperpolarizing potential (AHP), which critically dampens neuronal excitability. Because it is not known whether epileptiform activity alters the AHP and whether any alteration of the AHP is independent of inhibition, we acutely induced epileptiform activity by bath application of the GABA(A) receptor blocker gabazine (5 μM) in the rat hippocampal slice preparation and studied its impact on the AHP using intracellular recordings. Following 10 min of gabazine wash-in, slices started to develop spontaneous epileptiform discharges. This disinhibition was accompanied by a significant shift of the resting membrane potential of CA1 neurons to more depolarized values. Prolonged depolarizations (600 ms) elicited a train of action potentials, the number of which was not different between baseline and gabazine treatment. However, the AHP following the train of action potentials was significantly reduced after 20 min of gabazine treatment. When the induction of epileptiform activity was prevented by co-application of 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX, 10 μM) and D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5, 50 μM) to block α-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA) and N-methyl-d-aspartate (NMDA) receptors, respectively, the AHP was preserved despite of GABA(A) receptor inhibition suggesting that the epileptiform activity was required to suppress the AHP. Moreover, the AHP was also preserved when the slices were treated with the protein kinase blockers H-9 (100 μM) and H-89 (1 μM). These results demonstrate that the AHP following a train of action potentials is rapidly suppressed by acutely induced epileptiform activity due to a phosphorylation process-presumably involving protein kinase A.
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Affiliation(s)
- K Kernig
- Oscar Langendorff Institute of Physiology, University of Rostock, Gertrudenstrasse 9, 18057 Rostock, Germany
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126
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Schulz R, Kirschstein T, Brehme H, Porath K, Mikkat U, Köhling R. Network excitability in a model of chronic temporal lobe epilepsy critically depends on SK channel-mediated AHP currents. Neurobiol Dis 2012; 45:337-47. [DOI: 10.1016/j.nbd.2011.08.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2011] [Revised: 08/13/2011] [Accepted: 08/18/2011] [Indexed: 11/29/2022] Open
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127
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Hao S, Bao YM, An LJ, Cheng W, Zhao RG, Bi J, Wang HS, Sun CS, Liu JW, Jiang B. Effects of Resibufogenin and Cinobufagin on voltage-gated potassium channels in primary cultures of rat hippocampal neurons. Toxicol In Vitro 2011; 25:1644-53. [DOI: 10.1016/j.tiv.2011.07.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 05/29/2011] [Accepted: 07/04/2011] [Indexed: 10/17/2022]
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128
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Kaczorowski CC. Bidirectional pattern-specific plasticity of the slow afterhyperpolarization in rats: role for high-voltage activated Ca2+ channels and I h. Eur J Neurosci 2011; 34:1756-65. [PMID: 22098477 DOI: 10.1111/j.1460-9568.2011.07899.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A burst of action potentials in hippocampal neurons is followed by a slow afterhyperpolarization (sAHP) that serves to limit subsequent firing. A reduction in the sAHP accompanies acquisition of several types of learning, whereas increases in the sAHP are correlated with cognitive impairment. The present study demonstrates in vitro that activity-dependent bidirectional plasticity of the sAHP does not require synaptic activation, and depends on the pattern of action potential firing. Whole-cell current-clamp recordings from CA1 pyramidal neurons in hippocampal slices from young rats (postnatal days 14-24) were performed in blockers of synaptic transmission. The sAHP was evoked by action potential firing at gamma-related (50 Hz, gamma-AHP) or theta frequencies (5 Hz, theta-AHP), two firing frequencies implicated in attention and memory. Interestingly, when the gamma-AHP and theta-AHP were evoked in the same cell, a gradual potentiation of the gamma-AHP (186 ± 31%) was observed that was blocked using Ca(2+) channel blockers nimodipine (10 μm) or ω-conotoxin MVIIC (1 μm). In experiments that exclusively evoked the sAHP with 50 Hz firing, the gamma-AHP was similarly potentiated (198 ± 44%). However, theta-burst firing pattern alone resulted in a decrease (65 ± 19%) of the sAHP. In these experiments, application of the h-channel blocker ZD7288 (25 μm) selectively prevented enhancement of the gamma-AHP. These data demonstrate that induction requirements for bidirectional AHP plasticity depend on the pattern of action potential firing, and result from distinct mechanisms. The identification of novel mechanisms underlying AHP plasticity in vitro provides additional insight into the dynamic processes that may regulate neuronal excitability during learning in vivo.
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Affiliation(s)
- C C Kaczorowski
- Department of Physiology and Institute for Neuroscience, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
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Acute alterations of somatodendritic action potential dynamics in hippocampal CA1 pyramidal cells after kainate-induced status epilepticus in mice. PLoS One 2011; 6:e26664. [PMID: 22039527 PMCID: PMC3200351 DOI: 10.1371/journal.pone.0026664] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 09/30/2011] [Indexed: 12/20/2022] Open
Abstract
Pathophysiological remodeling processes at an early stage of an acquired epilepsy are critical but not well understood. Therefore, we examined acute changes in action potential (AP) dynamics immediately following status epilepticus (SE) in mice. SE was induced by intraperitoneal (i.p.) injection of kainate, and behavioral manifestation of SE was monitored for 3-4 h. After this time interval CA1 pyramidal cells were studied ex vivo with whole-cell current-clamp and Ca(2+) imaging techniques in a hippocampal slice preparation. Following acute SE both resting potential and firing threshold were modestly depolarized (2-5 mV). No changes were seen in input resistance or membrane time constant, but AP latency was prolonged and AP upstroke velocity reduced following acute SE. All cells showed an increase in AP halfwidth and regular (rather than burst) firing, and in a fraction of cells the notch, typically preceding spike afterdepolarization (ADP), was absent following acute SE. Notably, the typical attenuation of backpropagating action potential (b-AP)-induced Ca(2+) signals along the apical dendrite was strengthened following acute SE. The effects of acute SE on the retrograde spread of excitation were mimicked by applying the Kv4 current potentiating drug NS5806. Our data unveil a reduced somatodendritic excitability in hippocampal CA1 pyramidal cells immediately after acute SE with a possible involvement of both Na(+) and K(+) current components.
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130
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Turner RW, Anderson D, Zamponi GW. Signaling complexes of voltage-gated calcium channels. Channels (Austin) 2011; 5:440-8. [PMID: 21832880 DOI: 10.4161/chan.5.5.16473] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Voltage gated calcium channels are key mediators of depolarization induced calcium entry into electrically excitable cells. There is increasing evidence that voltage gated calcium channels, like many other types of ionic channels, do not operate in isolation, but instead forms signaling complexes with signaling molecules, G protein coupled receptors, and other types of ion channels. Furthermore, there appears to be bidirectional signaling within these protein complexes, thus allowing not only for efficient translation of calcium signals into cellular responses, but also for tight control of calcium entry per se. In this review, we will focus predominantly on signaling complexes between G protein-coupled receptors and high voltage activated calcium channels, and on complexes of voltage-gated calcium channels and members of the potassium channel superfamily.
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Affiliation(s)
- Ray W Turner
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, AB Canada
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131
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Abstract
Excitotoxicity is the major cause of many neurologic disorders including stroke. Potassium currents modulate neuronal excitability and therefore influence the pathological process. A-type potassium current (I(A)) is one of the major voltage-dependent potassium currents, yet its roles in excitotoxic cell death are not well understood. We report that, following ischemic insults, the I(A) increases significantly in large aspiny (LA) neurons but not medium spiny (MS) neurons in the striatum, which correlates with the higher resistance of LA neurons to ischemia. Activation of protein kinase Cα increases I(A) in LA neurons after ischemia. Cultured neurons from transgenic mice lacking both Kv1.4 and Kv4.2 subunits exhibit an increased vulnerability to ischemic insults. Increase of I(A) by recombinant expression of Kv1.4 or Kv4.2 is sufficient in improving the survival of MS neurons against ischemic insults both in vitro and in vivo. These results, taken together, provide compelling evidence for a protective role of I(A) against ischemia.
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132
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Yang G, Zhou MH, Ren Z, Xu JJ, Mei YA. Amoxapine inhibits delayed outward rectifier K(+) currents in cerebellar granule cells via dopamine receptor and protein kinase A activation. Cell Physiol Biochem 2011; 28:163-74. [PMID: 21865859 DOI: 10.1159/000331725] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/14/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Although tricyclic antidepressants amoxapine is proposed to target 5-HT and D2 receptors, very few studies have addressed the effect of amoxapine on molecular and cellular mechanisms via receptor pathways. In this study, we test the effect of amoxapine on rat cerebellar granule neurons (CGNs) to address this possibility. METHODS CGNs cell culture, whole-cell current recording using a patch-clamp technique, western blot and non-radioactive detection analysis of phosphorylated protein kinase A (PKA) were used. RESULTS Amoxapine inhibits delayed rectifier potassium (I(K)) current in a dose-dependent manner and modulates inactivation properties in CGNs. Those effects were not eliminated by preincubation with 5-HT or 5-HT receptor antagonists, but abolished by dopamine and D1/D5 receptor antagonists. Application of GTPγ-S and inhibitor of the Gs signalling cascade abolished the amoxapine-induced effect on I(K). The application of forskolin or dibutyryl-cAMP mimicked the inhibitory effect of amoxapine on I(K). Western blotting for phosphorylated PKA revealed that amoxapine significantly increased the intracellular levels of phosphorylated PKA, a marker of PKA activation. CONCLUSION Amoxapine inhibits I(K) currents in rat CGNs via cAMP/PKA-dependent pathways, as in mouse cortical neurons we reported earlier, but that involves D1-like receptors instead of 5-HT receptors.
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Affiliation(s)
- Guang Yang
- Institutes of Brain Science, School of Life Sciences and State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China
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133
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Galvez R, Nicholson DA, Disterhoft JF. Physiological and anatomical studies of associative learning: Convergence with learning studies of W.T. Greenough. Dev Psychobiol 2011; 53:489-504. [PMID: 21678397 PMCID: PMC3632307 DOI: 10.1002/dev.20554] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The quest to understand how the brain is able to store information for later retrieval has been pursued by many scientists through the years. Although many have made very significant contributions to the field and our current understanding of the process, few have played as pivotal a role in advancing our understanding as William T. Greenough. The current report will utilize associative learning, a training paradigm that has greatly assisted in our understanding of memory consolidation, to demonstrate how findings emerging from the Greenough laboratory helped to not only shape our current understanding of learning induced anatomical plasticity, but to also launch future analyses into the molecular players involved in this process, especially the Fragile X Mental Retardation Protein.
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Affiliation(s)
- Roberto Galvez
- Department of Psychology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, USA
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134
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Moore SJ, Throesch BT, Murphy GG. Of mice and intrinsic excitability: genetic background affects the size of the postburst afterhyperpolarization in CA1 pyramidal neurons. J Neurophysiol 2011; 106:1570-80. [PMID: 21697442 DOI: 10.1152/jn.00257.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
As the use of genetically engineered mice has become increasingly prevalent in neurobiological research, evidence has steadily accumulated that substantial differences exist between strains. Although a number of studies have reported effects of genetic background on behavior, few have focused on differences in neurophysiology. The postburst afterhyperpolarization (AHP) is an important determinant of intrinsic neuronal excitability and has been suggested to play a critical role in the cellular mechanisms underlying learning and memory. Using whole cell current-clamp recordings of CA1 pyramidal neurons, we examined the magnitude of different phases of the AHP (peak, medium, and slow) in two commonly used genetic backgrounds, C57BL/6 (B6) and 129SvEv (129), as well as in an F2 hybrid B6:129 background (F2). We found that neurons from B6 and F2 animals exhibited a significantly larger AHP compared with 129 animals and that this difference was consistent across all phases. Furthermore, our recordings revealed a marked dichotomy in the shape of the AHP waveform, which was independent of genetic background. Approximately 60% of cells exhibited an AHP with a sharp transition between the peak AHP and medium AHP, whereas the remaining 40% exhibited a more gradual transition. Our data add to the growing body of work suggesting that genetic background can affect neuronal function as well as behavior. In addition, these results highlight the innate heterogeneity of CA1 pyramidal neurons, even within a single genetic background. These differences should be taken into consideration during the analysis and comparison of experimental results.
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Affiliation(s)
- Shannon J Moore
- Molecular & Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109-2200, USA
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135
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Guan D, Higgs MH, Horton LR, Spain WJ, Foehring RC. Contributions of Kv7-mediated potassium current to sub- and suprathreshold responses of rat layer II/III neocortical pyramidal neurons. J Neurophysiol 2011; 106:1722-33. [PMID: 21697446 DOI: 10.1152/jn.00211.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
After block of Kv1- and Kv2-mediated K(+) currents in acutely dissociated neocortical pyramidal neurons from layers II/III of rat somatosensory and motor cortex, the remaining current is slowly activating and persistent. We used whole cell voltage clamp to show that the Kv7 blockers linopirdine and XE-991 blocked a current with similar kinetics to the current remaining after combined block of Kv1 and Kv2 channels. This current was sensitive to low doses of linopirdine and activated more slowly and at more negative potentials than Kv1- or Kv2-mediated current. The Kv7-mediated current decreased in amplitude with time in whole cell recordings, but in most cells the current was stable for several minutes. Current in response to a traditional M-current protocol was blocked by muscarine, linopirdine, and XE-991. Whole cell slice recordings revealed that the Q₁₀ for channel deactivation was ∼2.5. Sharp electrode current-clamp recordings from adult pyramidal cells demonstrated that block of Kv7-mediated current with XE-991 reduced rheobase, shortened the latency to firing to near rheobase current, induced more regular firing at low current intensity, and increased the rate of firing to a given current injection. XE-991 did not affect single action potentials or spike frequency adaptation. Application of XE-991 also eliminated subthreshold voltage oscillations and increased gain for low-frequency inputs (<10 Hz) without affecting gain for higher frequency inputs. These data suggest important roles for Kv7 channels in subthreshold regulation of excitability, generation of theta-frequency subthreshold oscillations, regulation of interspike intervals, and biasing selectivity toward higher frequency inputs.
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Affiliation(s)
- D Guan
- Department of Anatomy and Neurobiology, University of Tennessee, Memphis, TN 38163, USA
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Masurkar AV, Chen WR. Potassium currents of olfactory bulb juxtaglomerular cells: characterization, simulation, and implications for plateau potential firing. Neuroscience 2011; 192:247-62. [PMID: 21704678 DOI: 10.1016/j.neuroscience.2011.06.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Revised: 05/06/2011] [Accepted: 06/03/2011] [Indexed: 12/23/2022]
Abstract
Odor identity is encoded by the activity of olfactory bulb glomeruli, which receive primary sensory input and transfer it to projection neurons. Juxtaglomerular cells (JGCs) may influence glomerular processing via firing of long lasting plateau potentials. Though inward currents have been investigated, little is known regarding potassium current contribution to JGC plateau potentials. We pursued study of these currents, with the overarching goal of creating components for a computational model of JGC plateau potential firing. In conditions minimizing calcium-activated potassium current (I(K(Ca))), we used whole cell voltage clamp and in vitro slice preparations to characterize three potassium currents in rat JGCs. The prominent component I(kt1) displayed rapid kinetics (τ(10%-90% rise), 0.6-2 ms; τ(inactivation), 5-10 ms) and was blocked by high concentration 4-aminopyridine (4-AP) (5 mM) and tetramethylammonium (TEA) (40 mM). It had half maximal activation at -10 mV (V(½)max) and little inactivation at rest. I(kt2), with slower kinetics (τ(10%-90% rise), 11-15 ms; τ(inactivation), 100-300 ms), was blocked by low concentration 4-AP (0.5 mM) and TEA (5 mM). The V(½)max was 0 mV and inactivation was also minimal at rest. Sustained current I(kt3) showed sensitivity to low concentration 4-AP and TEA, and had V(½)max of +10 mV. Further experiments, in conditions of physiologic calcium buffering, suggested that I(K(Ca)) contributed to I(kt3) with minimal effect on plateau potential evolution. We transformed these characterizations into Hodgkin-Huxley models that robustly mimicked experimental data. Further simulation demonstrated that I(kt1) would be most efficiently activated by plateau potential waveforms, predicting a critical role in shaping JGC firing. These studies demonstrated that JGCs possess a unique potassium current profile, with delayed rectifier (I(kt3)), atypical A-current (I(kt1)), and D-current (I(kt2)) in accordance with known expression patterns in olfactory bulb (OB) glomeruli. Our simulations also provide an initial framework for more integrative models of JGC plateau potential firing.
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Affiliation(s)
- A V Masurkar
- Department of Neurobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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137
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Abstract
OBJECTIVE To study the safety of 3-4 diaminopyridine (DAP) in patients with motor neuron diseases and to examine its efficacy in reducing muscle fatigue and weakness and in improving objective parameters of muscle function. DESIGN Assessments of safety included a questionnaire of symptoms, clinical examination, blood testing, and electrocardiography at each visit; efficacy was assessed by subjective scores of fatigue and weakness; an Amyotrophic Lateral Sclerosis Functional Rating Scale and functional ability scores, including timed verbal scores; manual muscle testing; grip dynamometry; pulmonary function tests; timed functional tests; and electrophysiological studies. PARTICIPANTS Thirteen subjects with amyotrophic lateral sclerosis and seven subjects with only a lower motor neuron syndrome. MAIN OUTCOMES Assess tolerability of DAP and determine if there was symptomatic improvement of muscle fatigue. SECONDARY OUTCOME: To determine the effects of DAP on objective parameters of muscle function. RESULTS The drug was well tolerated with only four subjects reporting tingling of lips and fingers during the active drug period. The subjective scores for fatigue and weakness showed a mild improvement after 4 weeks on DAP compared with placebo. A significant benefit of DAP was also demonstrated in the timed verbal scores. CONCLUSION 3-4 DAP appeared to be safe and produced subjective benefit in motor neuron diseases. The drug could be added for symptomatic treatment in these diseases. Larger studies are necessary to demonstrate efficacy.
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138
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Gamelli AE, McKinney BC, White JA, Murphy GG. Deletion of the L-type calcium channel Ca(V) 1.3 but not Ca(V) 1.2 results in a diminished sAHP in mouse CA1 pyramidal neurons. Hippocampus 2011; 21:133-41. [PMID: 20014384 DOI: 10.1002/hipo.20728] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Trains of action potentials in CA1 pyramidal neurons are followed by a prolonged calcium-dependent postburst afterhyperpolarization (AHP) that serves to limit further firing to a sustained depolarizing input. A reduction in the AHP accompanies acquisition of several types of learning and increases in the AHP are correlated with age-related cognitive impairment. The AHP develops primarily as the result of activation of outward calcium-activated potassium currents; however, the precise source of calcium for activation of the AHP remains unclear. There is substantial experimental evidence suggesting that calcium influx via voltage-gated L-type calcium channels (L-VGCCs) contributes to the generation of the AHP. Two L-VGCC subtypes are predominately expressed in the hippocampus, Ca(V) 1.2 and Ca(V) 1.3; however, it is not known which L-VGCC subtype is involved in generation of the AHP. This ambiguity is due in large part to the fact that at present there are no subunit-specific agonists or antagonists. Therefore, using mice in which the gene encoding Ca(V) 1.2 or Ca(V) 1.3 was deleted, we sought to determine the impact of alterations in levels of these two L-VCGG subtypes on neuronal excitability. No differences in any AHP measure were seen between neurons from Ca(V) 1.2 knockout mice and controls. However, the total area of the AHP was significantly smaller in neurons from Ca(V) 1.3 knockout mice as compared with neurons from wild-type controls. A significant reduction in the amplitude of the AHP was also seen at the 1 s time point in neurons from Ca(V) 1.3 knockout mice as compared with those from controls. Reductions in both the area and 1 s amplitude suggest the involvement of calcium influx via Ca(V) 1.3 in the slow AHP (sAHP). Thus, the results of our study demonstrate that deletion of Ca(V) 1.3, but not Ca(V) 1.2, significantly impacts the generation of the sAHP.
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Affiliation(s)
- Amy E Gamelli
- Molecular & Behavioral Neuroscience Institute, University of Michigan Medical School, Ann Arbor, Michigan, USA
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139
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Aging redistributes medial prefrontal neuronal excitability and impedes extinction of trace fear conditioning. Neurobiol Aging 2011; 33:1744-57. [PMID: 21531046 DOI: 10.1016/j.neurobiolaging.2011.03.020] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Revised: 03/17/2011] [Accepted: 03/22/2011] [Indexed: 12/21/2022]
Abstract
Cognitive flexibility is critical for survival and reflects the malleability of the central nervous system (CNS) in response to changing environmental demands. Normal aging results in difficulties modifying established behaviors, which may involve medial prefrontal cortex (mPFC) dysfunction. Using extinction of conditioned fear in rats to assay cognitive flexibility, we demonstrate that extinction deficits reminiscent of mPFC dysfunction first appear during middle age, in the absence of hippocampus-dependent context deficits. Emergence of aging-related extinction deficits paralleled a redistribution of neuronal excitability across two critical mPFC regions via two distinct mechanisms. First, excitability decreased in regular spiking neurons of infralimbic-mPFC (IL), a region whose activity is required for extinction. Second, excitability increased in burst spiking neurons of prelimbic-mPFC (PL), a region whose activity hinders extinction. Experiments using synaptic blockers revealed that these aging-related differences were intrinsic. Thus, changes in IL and PL intrinsic excitability may contribute to cognitive flexibility impairments observed during normal aging.
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140
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Sanchez G, Rodriguez MJ, Pomata P, Rela L, Murer MG. Reduction of an afterhyperpolarization current increases excitability in striatal cholinergic interneurons in rat parkinsonism. J Neurosci 2011; 31:6553-64. [PMID: 21525296 PMCID: PMC6622669 DOI: 10.1523/jneurosci.6345-10.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 02/23/2011] [Accepted: 03/08/2011] [Indexed: 01/22/2023] Open
Abstract
Striatal cholinergic interneurons show tonic spiking activity in the intact and sliced brain, which stems from intrinsic mechanisms. Because of it, they are also known as "tonically active neurons" (TANs). Another hallmark of TAN electrophysiology is a pause response to appetitive and aversive events and to environmental cues that have predicted these events during learning. Notably, the pause response is lost after the degeneration of dopaminergic neurons in animal models of Parkinson's disease. Moreover, Parkinson's disease patients are in a hypercholinergic state and find some clinical benefit in anticholinergic drugs. Current theories propose that excitatory thalamic inputs conveying information about salient sensory stimuli trigger an intrinsic hyperpolarizing response in the striatal cholinergic interneurons. Moreover, it has been postulated that the loss of the pause response in Parkinson's disease is related to a diminution of I(sAHP), a slow outward current that mediates an afterhyperpolarization following a train of action potentials. Here we report that I(sAHP) induces a marked spike-frequency adaptation in adult rat striatal cholinergic interneurons, inducing an abrupt end of firing during sustained excitation. Chronic loss of dopaminergic neurons markedly reduces I(sAHP) and spike-frequency adaptation in cholinergic interneurons, allowing them to fire continuously and at higher rates during sustained excitation. These findings provide a plausible explanation for the hypercholinergic state in Parkinson's disease. Moreover, a reduction of I(sAHP) may alter synchronization of cholinergic interneurons with afferent inputs, thus contributing to the loss of the pause response in Parkinson's disease.
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Affiliation(s)
- Gonzalo Sanchez
- Systems Neuroscience Section, Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires C1121ABG, Argentina.
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141
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Calfa G, Hablitz JJ, Pozzo-Miller L. Network hyperexcitability in hippocampal slices from Mecp2 mutant mice revealed by voltage-sensitive dye imaging. J Neurophysiol 2011; 105:1768-84. [PMID: 21307327 PMCID: PMC3075283 DOI: 10.1152/jn.00800.2010] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Accepted: 02/03/2011] [Indexed: 11/22/2022] Open
Abstract
Dysfunctions of neuronal and network excitability have emerged as common features in disorders associated with intellectual disabilities, autism, and seizure activity, all common clinical manifestations of Rett syndrome (RTT), a neurodevelopmental disorder caused by loss-of-function mutations in the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2). Here, we evaluated the consequences of Mecp2 mutation on hippocampal network excitability, as well as synapse structure and function using a combination of imaging and electrophysiological approaches in acute slices. Imaging the amplitude and spatiotemporal spread of neuronal depolarizations with voltage-sensitive dyes (VSD) revealed that the CA1 and CA3 regions of hippocampal slices from symptomatic male Mecp2 mutant mice are highly hyperexcitable. However, only the density of docked synaptic vesicles and the rate of release from the readily releasable pool are impaired in Mecp2 mutant mice, while synapse density and morphology are unaffected. The differences in network excitability were not observed in surgically isolated CA1 minislices, and blockade of GABAergic inhibition enhanced VSD signals to the same extent in Mecp2 mutant and wild-type mice, suggesting that network excitability originates in area CA3. Indeed, extracellular multiunit recordings revealed a higher level of spontaneous firing of CA3 pyramidal neurons in slices from symptomatic Mecp2 mutant mice. The neuromodulator adenosine reduced the amplitude and spatiotemporal spread of VSD signals evoked in CA1 of Mecp2 mutant slices to wild-type levels, suggesting its potential use as an anticonvulsant in RTT individuals. The present results suggest that hyperactive CA3 pyramidal neurons contribute to hippocampal dysfunction and possibly to limbic seizures observed in Mecp2 mutant mice and RTT individuals.
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Affiliation(s)
- Gaston Calfa
- Department of Neurobiology, Civitan International Research Center, The University of Alabama at Birmingham, Birmingham, AL 35294-2182, USA
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142
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Coyne L, Shan M, Przyborski SA, Hirakawa R, Halliwell RF. Neuropharmacological properties of neurons derived from human stem cells. Neurochem Int 2011; 59:404-12. [PMID: 21315124 DOI: 10.1016/j.neuint.2011.01.022] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Accepted: 01/19/2011] [Indexed: 11/29/2022]
Abstract
Human pluripotent stem cells have enormous potential value in neuropharmacology and drug discovery yet there is little data on the major classes and properties of receptors and ion channels expressed by neurons derived from these stem cells. Recent studies in this lab have therefore used conventional patch-clamp electrophysiology to investigate the pharmacological properties of the ligand and voltage-gated ion channels in neurons derived and maintained in vitro from the human stem cell (hSC) line, TERA2.cl.SP12. TERA2.cl.SP12 stem cells were differentiated with retinoic acid and used in electrophysiological experiments 28-50 days after beginning differentiation. HSC-derived neurons generated large whole cell currents with depolarizing voltage steps (-80 to 30 mV) comprised of an inward, rapidly inactivating component and a delayed, slowly deactivating outward component. The fast inward current was blocked by the sodium channel blocker tetrodotoxin (0.1 μM) and the outward currents were significantly reduced by tetraethylammonium ions (TEA, 5 mM) consistent with the presence of functional Na and K ion channels. Application of the inhibitory neurotransmitters, GABA (0.1-1000 μM) or glycine (0.1-1000 μM) evoked concentration dependent currents. The GABA currents were inhibited by the convulsants, picrotoxin (10 μM) and bicuculline (3 μM), potentiated by the NSAID mefenamic acid (10-100 μM), the general anaesthetic pentobarbital (100 μM), the neurosteroid allopregnanolone and the anxiolytics chlordiazepoxide (10 μM) and diazepam (10 μM) all consistent with the expression of GABA(A) receptors. Responses to glycine were reversibly blocked by strychnine (10 μM) consistent with glycine-gated chloride channels. The excitatory agonists, glutamate (1-1000 μM) and NMDA (1-1000 μM) activated concentration-dependent responses from hSC-derived neurons. Glutamate currents were inhibited by kynurenic acid (1 mM) and NMDA responses were blocked by MgCl(2) (2 mM) in a highly voltage-dependent manner. Together, these findings show that neurons derived from human stem cells develop an array of functional receptors and ion channels with a pharmacological profile in keeping with that described for native neurons. This study therefore provides support for the hypothesis that stem cells may provide a powerful source of human neurons for future neuropharmacological studies.
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Affiliation(s)
- Leanne Coyne
- School of Pharmacy, University of the Pacific, Stockton, CA 95211, USA
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143
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Yuan H, Wang WP, Feng N, Wang L, Wang XL. Donepezil attenuated oxygen-glucose deprivation insult by blocking Kv2.1 potassium channels. Eur J Pharmacol 2011; 657:76-83. [PMID: 21300054 DOI: 10.1016/j.ejphar.2011.01.054] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 01/06/2011] [Accepted: 01/25/2011] [Indexed: 10/18/2022]
Abstract
Excessive K(+) efflux via activated voltage-gated K(+) channels (Kv channels) and the consequent intracellular K(+) depletion during and after ischemia/hypoxia induced long-lasting membrane depolarization promotes neuronal apoptosis. Although it has been suggested as an important potassium channel subtype in oxidative stress induced neuron apoptosis, whether Kv2.1 mediates ischemic apoptosis remains undefined. In the present study, the role of Kv2.1 played in hypoxia/anoxia induced cell apoptosis and correlated protective effect of donepezil were evaluated. Kv2.1 transfected HEK293 cell line (Kv2.1/HEK293) was used to study oxygen-glucose deprivation (OGD) induced cell apoptosis. We found Kv2.1 transfection increased the vulnerability of HEK293 cells to OGD insult, blocking Kv2.1 potassium channel by tetraethylammonium (TEA, 10mM) could attenuated OGD induced Kv2.1/HEK293 cell apoptosis significantly. OGD slightly reduced Kv2.1 currents without affecting channel kinetic activity. However, the membrane potential of Kv2.1/HEK293 cells depolarized to around 0mV after OGD treatment, a potential which could activated Kv2.1 persistently. Donepezil blocked Kv2.1 currents in a dose-dependent manner (IC(50)=7.59μM). Under OGD condition, donepezil (30μM) effectively inhibited Kv2.1 currents by accelerating channel inactivation and decreased Kv2.1/HEK293 cell apoptosis rate. In conclusion, our study revealed both the conducting role of Kv2.1 in OGD induced cell apoptosis and the importance of Kv2.1 as a target for neuronal protection. In addition, besides anti-acetylcholinesterase activity, Kv2.1 blockade capability of donepezil may attribute to its neuroprotective effects against ischemic apoptosis.
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Affiliation(s)
- Hui Yuan
- Department of pharmacology, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, No.1 Xiannongtan Street, Xuanwu District,Beijing 100050, China
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144
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Gasparini S. Distance- and activity-dependent modulation of spike back-propagation in layer V pyramidal neurons of the medial entorhinal cortex. J Neurophysiol 2011; 105:1372-9. [PMID: 21209358 DOI: 10.1152/jn.00014.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Layer V principal neurons of the medial entorhinal cortex receive the main hippocampal output and relay processed information to the neocortex. Despite the fundamental role hypothesized for these neurons in memory replay and consolidation, their dendritic features are largely unknown. High-speed confocal and two-photon Ca(2+) imaging coupled with somatic whole cell patch-clamp recordings were used to investigate spike back-propagation in these neurons. The Ca(2+) transient associated with a single back-propagating action potential was considerably smaller at distal dendritic locations (>200 μm from the soma) compared with proximal ones. Perfusion of Ba(2+) (150 μM) or 4-aminopyridine (2 mM) to block A-type K(+) currents significantly increased the amplitude of the distal, but not proximal, Ca(2+) transients, which is strong evidence for an increased density of these channels at distal dendritic locations. In addition, the Ca(2+) transients decreased with each subsequent spike in a 20-Hz train; this activity-dependent decrease was also more prominent at more distal locations and was attenuated by the perfusion of the protein kinase C activator phorbol-di-acetate. These data are consistent with a phosphorylation-dependent control of back-propagation during trains of action potentials, attributable mainly to an increase in the time constant of recovery from voltage-dependent inactivation of dendritic Na(+) channels. In summary, dendritic Na(+) and A-type K(+) channels control spike back-propagation in layer V entorhinal neurons. Because the activity of these channels is highly modulated, the extent of the dendritic Ca(2+) influx is as well, with important functional implications for dendritic integration and associative synaptic plasticity.
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Affiliation(s)
- Sonia Gasparini
- Neuroscience Center, Louisiana State University Health Science Center, 2020 Gravier St., New Orleans, LA 70112, USA.
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145
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Boudkkazi S, Fronzaroli-Molinieres L, Debanne D. Presynaptic action potential waveform determines cortical synaptic latency. J Physiol 2011; 589:1117-31. [PMID: 21224227 DOI: 10.1113/jphysiol.2010.199653] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Synaptic latency at cortical synapses is determined by the presynaptic release probability (Pr). Short- and long-term presynaptic plasticity is associated with modulation of synaptic delay. We show here that the duration and amplitude of the presynaptic action potential also determine synaptic latency at neocortical and hippocampal excitatory synapses. Blockade of voltage-gated potassium (Kv) channels with 4-aminopyridine or dendrotoxin-I, but not tetraethylammonium, induced a 1–2 ms shift in latency at excitatory synaptic connections formed by pairs of neocortical pyramidal neurons. 4-Aminopyridine or dendrotoxin-I, but not tetraethylammonium, increased the duration of the action potential recorded in the axon, suggesting that presynaptic spike duration is controlled by axonal Kv1 potassium channels. Spike width-dependent changes in latency have been identified at the mossy fibre–CA3 cell synapses and contribute to stabilization of synaptic timing during repetitive stimulation. The effects of presynaptic spike amplitude on synaptic latency were also examined. Decreasing the amplitude of the presynaptic action potential with 15–30 nm TTX reduced synaptic latency by ∼0.5 ms. The regulation of synaptic timing by potassium and sodium channel blockers could not be attributed to modulation of axonal conduction. Rather, these effects are compatible with modifications of the kinetics of the presynaptic calcium current. We conclude that synaptic latency at cortical neurons is not constant but dynamically regulated by presynaptic action potential waveform.
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146
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Whyment AD, Coderre E, Wilson JMM, Renaud LP, O'Hare E, Spanswick D. Electrophysiological, pharmacological and molecular profile of the transient outward rectifying conductance in rat sympathetic preganglionic neurons in vitro. Neuroscience 2011; 178:68-81. [PMID: 21211550 DOI: 10.1016/j.neuroscience.2010.12.061] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 12/27/2010] [Accepted: 12/30/2010] [Indexed: 01/13/2023]
Abstract
Transient outward rectifying conductances or A-like conductances in sympathetic preganglionic neurons (SPN) are prolonged, lasting for hundreds of milliseconds to seconds and are thought to play a key role in the regulation of SPN firing frequency. Here, a multidisciplinary electrophysiological, pharmacological and molecular single-cell rt-PCR approach was used to investigate the kinetics, pharmacological profile and putative K+ channel subunits underlying the transient outward rectifying conductance expressed in SPN. SPN expressed a 4-aminopyridine (4-AP) sensitive transient outward rectification with significantly longer decay kinetics than reported for many other central neurons. The conductance and corresponding current in voltage-clamp conditions was also sensitive to the Kv4.2 and Kv4.3 blocker phrixotoxin-2 (1-10 μM) and the blocker of rapidly inactivating Kv channels, pandinotoxin-Kα (50 nM). The conductance and corresponding current was only weakly sensitive to the Kv1 channel blocker tityustoxin-Kα and insensitive to dendrotoxin I (200 nM) and the Kv3.4 channel blocker BDS-II (1 μM). Single-cell RT-PCR revealed mRNA expression for the α-subunits Kv4.1 and Kv4.3 in the majority and Kv1.5 in less than half of SPN. mRNA for accessory β-subunits was detected for Kvβ2 in all SPN with differential expression of mRNA for KChIP1, Kvβ1 and Kvβ3 and the peptidase homologue DPP6. These data together suggest that the transient outwardly rectifying conductance in SPN is mediated by members of the Kv4 subfamily (Kv4.1 and Kv4.3) in association with the β-subunit Kvβ2. Differential expression of the accessory β subunits, which may act to modulate channel density and kinetics in SPN, may underlie the prolonged and variable time-course of this conductance in these neurons.
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Affiliation(s)
- A D Whyment
- Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
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147
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Liao Y, Kristiansen AM, Oksvold CP, Tuvnes FA, Gu N, Rundén-Pran E, Ruth P, Sausbier M, Storm JF. Neuronal Ca2+-activated K+ channels limit brain infarction and promote survival. PLoS One 2010; 5:e15601. [PMID: 21209897 PMCID: PMC3012709 DOI: 10.1371/journal.pone.0015601] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Accepted: 11/16/2010] [Indexed: 11/18/2022] Open
Abstract
Neuronal calcium-activated potassium channels of the BK type are activated by membrane depolarization and intracellular Ca(2+) ions. It has been suggested that these channels may play a key neuroprotective role during and after brain ischemia, but this hypothesis has so far not been tested by selective BK-channel manipulations in vivo. To elucidate the in vivo contribution of neuronal BK channels in acute focal cerebral ischemia, we performed middle cerebral artery occlusion (MCAO) in mice lacking BK channels (homozygous mice lacking the BK channel alpha subunit, BK(-/-)). MCAO was performed in BK(-/-) and WT mice for 90 minutes followed by a 7-hour-reperfusion period. Coronal 1 mm thick sections were stained with 2,3,5-triphenyltetrazolium chloride to reveal the infarction area. We found that transient focal cerebral ischemia by MCAO produced larger infarct volume, more severe neurological deficits, and higher post-ischemic mortality in BK(-/-) mice compared to WT littermates. However, the regional cerebral blood flow was not significantly different between genotypes as measured by Laser Doppler (LD) flowmetry pre-ischemically, intra-ischemically, and post-ischemically, suggesting that the different impact of MCAO in BK(-/-) vs. WT was not due to vascular BK channels. Furthermore, when NMDA was injected intracerebrally in non-ischemic mice, NMDA-induced neurotoxicity was found to be larger in BK(-/-) mice compared to WT. Whole-cell patch clamp recordings from CA1 pyramidal cells in organotypic hippocampal slice cultures revealed that BK channels contribute to rapid action potential repolarization, as previously found in acute slices. When these cultures were exposed to ischemia-like conditions this induced significantly more neuronal death in BK(-/-) than in WT cultures. These results indicate that neuronal BK channels are important for protection against ischemic brain damage.
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Affiliation(s)
- Yiliu Liao
- Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Tübingen, Germany
| | - Ase-Marit Kristiansen
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
| | - Cecilie P. Oksvold
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
| | - Frode A. Tuvnes
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
| | - Ning Gu
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
| | - Elise Rundén-Pran
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
| | - Peter Ruth
- Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Tübingen, Germany
| | - Matthias Sausbier
- Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Tübingen, Germany
- * E-mail: (MS); (JS)
| | - Johan F. Storm
- Centre of Molecular Biology and Neuroscience, and Institute of Basal Medical Sciences, University of Oslo, Oslo, Norway
- * E-mail: (MS); (JS)
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148
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Neural adaptation facilitates oscillatory responses to static inputs in a recurrent network of ON and OFF cells. J Comput Neurosci 2010; 31:73-86. [PMID: 21170577 DOI: 10.1007/s10827-010-0298-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 10/06/2010] [Accepted: 11/26/2010] [Indexed: 10/18/2022]
Abstract
We investigate the role of adaptation in a neural field model, composed of ON and OFF cells, with delayed all-to-all recurrent connections. As external spatially profiled inputs drive the network, ON cells receive inputs directly, while OFF cells receive an inverted image of the original signals. Via global and delayed inhibitory connections, these signals can cause the system to enter states of sustained oscillatory activity. We perform a bifurcation analysis of our model to elucidate how neural adaptation influences the ability of the network to exhibit oscillatory activity. We show that slow adaptation encourages input-induced rhythmic states by decreasing the Andronov-Hopf bifurcation threshold. We further determine how the feedback and adaptation together shape the resonant properties of the ON and OFF cell network and how this affects the response to time-periodic input. By introducing an additional frequency in the system, adaptation alters the resonance frequency by shifting the peaks where the response is maximal. We support these results with numerical experiments of the neural field model. Although developed in the context of the circuitry of the electric sense, these results are applicable to any network of spontaneously firing cells with global inhibitory feedback to themselves, in which a fraction of these cells receive external input directly, while the remaining ones receive an inverted version of this input via feedforward di-synaptic inhibition. Thus the results are relevant beyond the many sensory systems where ON and OFF cells are usually identified, and provide the backbone for understanding dynamical network effects of lateral connections and various forms of ON/OFF responses.
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149
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Alier K, Li Z, Mactavish D, Westaway D, Jhamandas JH. Ionic mechanisms of action of prion protein fragment PrP(106-126) in rat basal forebrain neurons. J Neurosci Res 2010; 88:2217-27. [PMID: 20175205 DOI: 10.1002/jnr.22372] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Prion diseases are neurodegenerative disorders that are characterized by the presence of the misfolded prion protein (PrP). Neurotoxicity in these diseases may result from prion-induced modulation of ion channel function, changes in neuronal excitability, and consequent disruption of cellular homeostasis. We therefore examined PrP effects on a suite of potassium (K(+)) conductances that govern excitability of basal forebrain neurons. Our study examined the effects of a PrP fragment [PrP(106-126), 50 nM] on rat neurons using the patch clamp technique. In this paradigm, PrP(106-126) peptide, but not the "scrambled" sequence of PrP(106-126), evoked a reduction of whole-cell outward currents in a voltage range between -30 and +30 mV. Reduction of whole-cell outward currents was significantly attenuated in Ca(2+)-free external media and also in the presence of iberiotoxin, a blocker of calcium-activated potassium conductance. PrP(106-126) application also evoked a depression of the delayed rectifier (I(K)) and transient outward (I(A)) potassium currents. By using single cell RT-PCR, we identified the presence of two neuronal chemical phenotypes, GABAergic and cholinergic, in cells from which we recorded. Furthermore, cholinergic and GABAergic neurons were shown to express K(v)4.2 channels. Our data establish that the central region of PrP, defined by the PrP(106-126) peptide used at nanomolar concentrations, induces a reduction of specific K(+) channel conductances in basal forebrain neurons. These findings suggest novel links between PrP signalling partners inferred from genetic experiments, K(+) channels, and PrP-mediated neurotoxicity.
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Affiliation(s)
- Kwai Alier
- Department of Medicine (Neurology), University of Alberta, Edmonton, Alberta, Canada
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Lin M, Chen QH, Wurster RD, Hatcher JT, Liu YQ, Li L, Harden SW, Cheng ZJ. Maternal diabetes increases small conductance Ca2+-activated K+ (SK) currents that alter action potential properties and excitability of cardiac motoneurons in the nucleus ambiguus. J Neurophysiol 2010; 104:2125-38. [PMID: 20668269 PMCID: PMC2957455 DOI: 10.1152/jn.00671.2009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Accepted: 07/13/2010] [Indexed: 01/19/2023] Open
Abstract
Parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) play a key role in regulating cardiac functions. In this study, we examined the effects of maternal diabetes on excitability, action potential (AP) properties, and small conductance Ca(2+)-activated K(+) (SK) currents of PCMNs. Neonatal mice from diabetic (OVE26 female, NMDM) and normal (FVB female, control) mothers that had been mated with nondiabetic fathers (FVB male) were used. Tracer XRITC was injected into the pericardial sac at P7-9 to retrogradely label PCMNs. Two days later, XRITC-labeled PCMNs were identified in brain stem slices. The responses of spike frequency, AP repolarization (half-width) and afterhyperpolarization (AHP) of PCMNs to current injections were studied using whole cell current clamp. Outward and afterhyperpolarization currents (I(AHP)) in response to voltage steps were measured using whole cell voltage clamp. In examining the effects of maternal diabetes on excitability and AP properties, we found that in NMDM spike frequency decreased, the half-width and AHP peak amplitude increased, and the peak amplitude of outward transient currents and I(AHP) increased compared with those measured in control. In examining the effects of maternal diabetes on SK channels, we found that after blockage of SK channels with a specific SK channel blocker apamin, maternal diabetes significantly increased apamin-sensitive outward transient currents and I(AHP), and suppressed AHP amplitude in NMDM more than those in control. Further, apamin application increased the firing rate to current injections and completely abolished the difference of the firing rate between control and NMDM. We suggest that the augmented SK-mediated currents may contribute to the increased AHP amplitude and the attenuated excitability of PCMNs in NMDM.
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Affiliation(s)
- Min Lin
- Biomolecular Science Center, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816, USA
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