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de Souza JGV, de Souza DP, da Silva CAA, Martins Sá RW, Paton JFR, da Silva MP, Moraes DJA. Electrophysiological Properties and Morphology of Cardiac and Pulmonary Motoneurons within the Dorsal Motor Nucleus of the Vagus of Rats. Neuroscience 2024; 551:153-165. [PMID: 38821242 DOI: 10.1016/j.neuroscience.2024.05.038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Revised: 05/24/2024] [Accepted: 05/27/2024] [Indexed: 06/02/2024]
Abstract
The dorsal motor nucleus of the vagus (DMV) contains parasympathetic motoneurons that project to the heart and lungs. These motoneurons control ventricular excitability/contractility and airways secretions/blood flow, respectively. However, their electrophysiological properties, morphology and synaptic input activity remain unknown. One important ionic current described in DMV motoneurons controlling their electrophysiological behaviour is the A-type mediated by voltage-dependent K+ (Kv) channels. Thus, we compared the electrophysiological properties, synaptic activity, morphology, A-type current density, and single cell expression of Kv subunits, that contribute to macroscopic A-type currents, between DMV motoneurons projecting to either the heart or lungs of adult male rats. Using retrograde labelling, we visualized distinct DMV motoneurons projecting to the heart or lungs in acutely prepared medullary slices. Subsequently, whole cell recordings, morphological reconstruction and single motoneuron qRT-PCR studies were performed. DMV pulmonary motoneurons were more depolarized, electrically excitable, presented higher membrane resistance, broader action potentials and received greater excitatory synaptic inputs compared to cardiac DMV motoneurons. These differences were in part due to highly branched dendritic complexity and lower magnitude of A-type K+ currents. By evaluating expression of channels that mediate A-type currents from single motoneurons, we demonstrated a lower level of Kv4.2 in pulmonary versus cardiac motoneurons, whereas Kv4.3 and Kv1.4 levels were similar. Thus, with the distinct electrical, morphological, and molecular properties of DMV cardiac and pulmonary motoneurons, we surmise that these cells offer a new vista of opportunities for genetic manipulation providing improvement of parasympathetic function in cardiorespiratory diseases such heart failure and asthma.
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Affiliation(s)
- Júlia G V de Souza
- School of Medicine of Ribeirão Preto, Department of Physiology, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Daniel P de Souza
- School of Medicine of Ribeirão Preto, Department of Physiology, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Carlos A A da Silva
- School of Medicine of Ribeirão Preto, Department of Physiology, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Renato W Martins Sá
- School of Medicine of Ribeirão Preto, Department of Physiology, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Julian F R Paton
- Manaaki Manawa - The Centre for Heart Research, Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Melina P da Silva
- Department of Biophysics, Paulista School of Medicine, Federal University of São Paulo, São Paulo, SP, Brazil.
| | - Davi J A Moraes
- Department of Physiology and Biophysics, Biomedical Science Institute, University of São Paulo, São Paulo, SP, Brazil.
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2
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Li Y, Wang JZ, Deng YM, Wang K, Yang L, Long C. Amyloid-β Protein Precursor Regulates Electrophysiological Properties in the Hippocampus via Altered Kv1.4 Expression and Function in Mice. J Alzheimers Dis 2023; 92:1241-1256. [PMID: 36872774 DOI: 10.3233/jad-220606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
Abstract
BACKGROUND Amyloid-β protein precursor (AβPP) is enriched in neurons. However, the mechanism underlying AβPP regulation of neuronal activity is poorly understood. Potassium channels are critically involved in neuronal excitability. In hippocampus, A-type potassium channels are highly expressed and involved in determining neuronal spiking. OBJECTIVE We explored hippocampal local field potential (LFP) and spiking in the presence and absence of AβPP, and the potential involvement of an A-type potassium channel. METHODS We used in vivo extracellular recording and whole-cell patch-clamp recording to determine neuronal activity, current density of A-type potassium currents, and western blot to detect changes in related protein levels. RESULTS Abnormal LFP was observed in AβPP-/- mice, including reduced beta and gamma power, and increased epsilon and ripple power. The firing rate of glutamatergic neurons reduced significantly, in line with an increased action potential rheobase. Given that A-type potassium channels regulate neuronal firing, we measured the protein levels and function of two major A-type potassium channels and found that the post-transcriptional level of Kv1.4, but not Kv4.2, was significantly increased in the AβPP-/- mice. This resulted in a marked increase in the peak time of A-type transient outward potassium currents in both glutamatergic and gamma-aminobutyric acid-ergic (GABAergic) neurons. Furthermore, a mechanistic experiment using human embryonic kidney 293 (HEK293) cells revealed that the AβPP deficiency-induced increase in Kv1.4 may not involve protein-protein interaction between AβPP and Kv1.4. CONCLUSION This study suggests that AβPP modulates neuronal firing and oscillatory activity in the hippocampus, and Kv1.4 may be involved in mediating the modulation.
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Affiliation(s)
- Yi Li
- South China Normal University-Panyu Central Hospital Joint Laboratory of Translational Medical Research, Panyu Central Hospital, Guangzhou, China
- School of Life Sciences, South China Normal University, Guangzhou, China
| | - Jin-Zhao Wang
- School of Life Sciences, South China Normal University, Guangzhou, China
| | - Yue-Ming Deng
- School of Life Sciences, South China Normal University, Guangzhou, China
| | - Kun Wang
- School of Life Sciences, South China Normal University, Guangzhou, China
| | - Li Yang
- School of Life Sciences, Guangzhou University, Guangzhou, China
| | - Cheng Long
- South China Normal University-Panyu Central Hospital Joint Laboratory of Translational Medical Research, Panyu Central Hospital, Guangzhou, China
- School of Life Sciences, South China Normal University, Guangzhou, China
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3
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Menelaou E, Kishore S, McLean DL. Mixed synapses reconcile violations of the size principle in zebrafish spinal cord. eLife 2022; 11:64063. [PMID: 36166290 PMCID: PMC9514842 DOI: 10.7554/elife.64063] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Accepted: 09/12/2022] [Indexed: 11/24/2022] Open
Abstract
Mixed electrical-chemical synapses potentially complicate electrophysiological interpretations of neuronal excitability and connectivity. Here, we disentangle the impact of mixed synapses within the spinal locomotor circuitry of larval zebrafish. We demonstrate that soma size is not linked to input resistance for interneurons, contrary to the biophysical predictions of the ‘size principle’ for motor neurons. Next, we show that time constants are faster, excitatory currents stronger, and mixed potentials larger in lower resistance neurons, linking mixed synapse density to resting excitability. Using a computational model, we verify the impact of weighted electrical synapses on membrane properties, synaptic integration and the low-pass filtering and distribution of coupling potentials. We conclude differences in mixed synapse density can contribute to excitability underestimations and connectivity overestimations. The contribution of mixed synaptic inputs to resting excitability helps explain ‘violations’ of the size principle, where neuron size, resistance and recruitment order are unrelated.
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Affiliation(s)
- Evdokia Menelaou
- Department of Neurobiology, Northwestern University, Evanston, United States
| | - Sandeep Kishore
- Department of Neurobiology, Northwestern University, Evanston, United States
| | - David L McLean
- Department of Neurobiology, Northwestern University, Evanston, United States
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4
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Malloy C, Ahern M, Lin L, Hoffman DA. Neuronal Roles of the Multifunctional Protein Dipeptidyl Peptidase-like 6 (DPP6). Int J Mol Sci 2022; 23:ijms23169184. [PMID: 36012450 PMCID: PMC9409431 DOI: 10.3390/ijms23169184] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 08/09/2022] [Accepted: 08/12/2022] [Indexed: 11/16/2022] Open
Abstract
The concerted action of voltage-gated ion channels in the brain is fundamental in controlling neuronal physiology and circuit function. Ion channels often associate in multi-protein complexes together with auxiliary subunits, which can strongly influence channel expression and function and, therefore, neuronal computation. One such auxiliary subunit that displays prominent expression in multiple brain regions is the Dipeptidyl aminopeptidase-like protein 6 (DPP6). This protein associates with A-type K+ channels to control their cellular distribution and gating properties. Intriguingly, DPP6 has been found to be multifunctional with an additional, independent role in synapse formation and maintenance. Here, we feature the role of DPP6 in regulating neuronal function in the context of its modulation of A-type K+ channels as well as its independent involvement in synaptic development. The prevalence of DPP6 in these processes underscores its importance in brain function, and recent work has identified that its dysfunction is associated with host of neurological disorders. We provide a brief overview of these and discuss research directions currently underway to advance our understanding of the contribution of DPP6 to their etiology.
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5
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Glycogen Synthase Kinase 3: Ion Channels, Plasticity, and Diseases. Int J Mol Sci 2022; 23:ijms23084413. [PMID: 35457230 PMCID: PMC9028019 DOI: 10.3390/ijms23084413] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 04/13/2022] [Accepted: 04/14/2022] [Indexed: 12/15/2022] Open
Abstract
Glycogen synthase kinase 3β (GSK3) is a multifaceted serine/threonine (S/T) kinase expressed in all eukaryotic cells. GSK3β is highly enriched in neurons in the central nervous system where it acts as a central hub for intracellular signaling downstream of receptors critical for neuronal function. Unlike other kinases, GSK3β is constitutively active, and its modulation mainly involves inhibition via upstream regulatory pathways rather than increased activation. Through an intricate converging signaling system, a fine-tuned balance of active and inactive GSK3β acts as a central point for the phosphorylation of numerous primed and unprimed substrates. Although the full range of molecular targets is still unknown, recent results show that voltage-gated ion channels are among the downstream targets of GSK3β. Here, we discuss the direct and indirect mechanisms by which GSK3β phosphorylates voltage-gated Na+ channels (Nav1.2 and Nav1.6) and voltage-gated K+ channels (Kv4 and Kv7) and their physiological effects on intrinsic excitability, neuronal plasticity, and behavior. We also present evidence for how unbalanced GSK3β activity can lead to maladaptive plasticity that ultimately renders neuronal circuitry more vulnerable, increasing the risk for developing neuropsychiatric disorders. In conclusion, GSK3β-dependent modulation of voltage-gated ion channels may serve as an important pharmacological target for neurotherapeutic development.
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6
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Aceto G, Nardella L, Nanni S, Pecci V, Bertozzi A, Colussi C, D'Ascenzo M, Grassi C. Activation of histamine type 2 receptors enhances intrinsic excitability of medium spiny neurons in the nucleus accumbens. J Physiol 2022; 600:2225-2243. [PMID: 35343587 PMCID: PMC9325548 DOI: 10.1113/jp282962] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 03/21/2022] [Indexed: 11/14/2022] Open
Abstract
Abstract Histaminergic neurons are exclusively located in the hypothalamic tuberomammillary nucleus, from where they project to many brain areas including the nucleus accumbens (NAc), a brain area that integrates diverse monoaminergic inputs to coordinate motivated behaviours. While the NAc expresses various histamine receptor subtypes, the mechanisms by which histamine modulates NAc activity are still poorly understood. Using whole‐cell patch‐clamp recordings, we found that pharmacological activation of histamine 2 (H2) receptors elevates the excitability of NAc medium spiny neurons (MSNs), while activation of H1 receptors failed to significantly affect MSN excitability. The evoked firing of MSNs increased after seconds of local H2 agonist administration and remained elevated for minutes. H2 receptor (H2R) activation accelerated subthreshold depolarization in response to current injection, reduced the latency to fire, diminished action potential afterhyperpolarization and increased the action potential half‐width. The increased excitability was protein kinase A‐dependent and associated with decreased A‐type K+ currents. In addition, selective pharmacological inhibition of the Kv4.2 channel, the main molecular determinant of A‐type K+ currents in MSNs, mimicked and occluded the increased excitability induced by H2R activation. Our results indicate that histaminergic transmission in the NAc increases MSN intrinsic excitability through H2R‐dependent modulation of Kv4.2 channels. Activation of H2R will significantly alter spike firing in MSNs in vivo, and this effect could be an important mechanism by which these receptors mediate certain aspects of goal‐induced behaviours. Key points Histamine is synthesized and released by hypothalamic neurons of the tuberomammillary nucleus and serves as a general modulator for whole‐brain activity including the nucleus accumbens. Histamine receptors type 2 (HR2), which are expressed in the nucleus accumbens, couple to Gαs/off proteins which elevate cyclic adenosine monophosphate levels and activate protein kinase A. Whole‐cell patch‐clamp recordings revealed that H2R activation increased the evoked firing in medium spiny neurons of the nucleus accumbens via protein kinase A‐dependent mechanisms. HR2 activation accelerated subthreshold depolarization in response to current injection, reduced the latency to fire, diminished action potential medium after‐hyperpolarization and increased the action potential half‐width. HR2 activation also reduced A‐type potassium current. Selective pharmacological inhibition of the Kv4.2 channel mimicked and occluded the increased excitability induced by H2R activation.
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Affiliation(s)
- Giuseppe Aceto
- Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Roma, Italia.,Department of Neuroscience, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Luca Nardella
- Department of Neuroscience, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Simona Nanni
- Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Roma, Italia.,Department of Translational Medicine and Surgery, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Valeria Pecci
- Department of Translational Medicine and Surgery, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Alessia Bertozzi
- Istituto di Analisi dei Sistemi ed Informatica "Antonio Ruberti", National Research Council, Rome, Italy
| | - Claudia Colussi
- Istituto di Analisi dei Sistemi ed Informatica "Antonio Ruberti", National Research Council, Rome, Italy
| | - Marcello D'Ascenzo
- Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Roma, Italia.,Department of Neuroscience, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Claudio Grassi
- Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Roma, Italia.,Department of Neuroscience, Università Cattolica del Sacro Cuore, Rome, Italy
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7
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Xiao ZC, Lin KK, Young LS. A data-informed mean-field approach to mapping of cortical parameter landscapes. PLoS Comput Biol 2021; 17:e1009718. [PMID: 34941863 PMCID: PMC8741023 DOI: 10.1371/journal.pcbi.1009718] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 01/07/2022] [Accepted: 12/02/2021] [Indexed: 11/19/2022] Open
Abstract
Constraining the many biological parameters that govern cortical dynamics is computationally and conceptually difficult because of the curse of dimensionality. This paper addresses these challenges by proposing (1) a novel data-informed mean-field (MF) approach to efficiently map the parameter space of network models; and (2) an organizing principle for studying parameter space that enables the extraction biologically meaningful relations from this high-dimensional data. We illustrate these ideas using a large-scale network model of the Macaque primary visual cortex. Of the 10-20 model parameters, we identify 7 that are especially poorly constrained, and use the MF algorithm in (1) to discover the firing rate contours in this 7D parameter cube. Defining a "biologically plausible" region to consist of parameters that exhibit spontaneous Excitatory and Inhibitory firing rates compatible with experimental values, we find that this region is a slightly thickened codimension-1 submanifold. An implication of this finding is that while plausible regimes depend sensitively on parameters, they are also robust and flexible provided one compensates appropriately when parameters are varied. Our organizing principle for conceptualizing parameter dependence is to focus on certain 2D parameter planes that govern lateral inhibition: Intersecting these planes with the biologically plausible region leads to very simple geometric structures which, when suitably scaled, have a universal character independent of where the intersections are taken. In addition to elucidating the geometry of the plausible region, this invariance suggests useful approximate scaling relations. Our study offers, for the first time, a complete characterization of the set of all biologically plausible parameters for a detailed cortical model, which has been out of reach due to the high dimensionality of parameter space.
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Affiliation(s)
- Zhuo-Cheng Xiao
- Courant Institute of Mathematical Sciences, New York University, New York, New York, United States of America
| | - Kevin K. Lin
- Department of Mathematics, University of Arizona, Tucson, Arizona, United States of America
| | - Lai-Sang Young
- Courant Institute of Mathematical Sciences, New York University, New York, New York, United States of America
- Institute for Advanced Study, Princeton, New Jersey, United States of America
- * E-mail:
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8
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Fujimoto H, Notsu E, Yamamoto R, Ono M, Hioki H, Takahashi M, Ito T. Kv4.2-Positive Domains on Dendrites in the Mouse Medial Geniculate Body Receive Ascending Excitatory and Inhibitory Inputs Preferentially From the Inferior Colliculus. Front Neurosci 2021; 15:740378. [PMID: 34658777 PMCID: PMC8511456 DOI: 10.3389/fnins.2021.740378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 08/31/2021] [Indexed: 11/13/2022] Open
Abstract
The medial geniculate body (MGB) is the thalamic center of the auditory lemniscal pathway. The ventral division of MGB (MGV) receives excitatory and inhibitory inputs from the inferior colliculus (IC). MGV is involved in auditory attention by processing descending excitatory and inhibitory inputs from the auditory cortex (AC) and reticular thalamic nucleus (RTN), respectively. However, detailed mechanisms of the integration of different inputs in a single MGV neuron remain unclear. Kv4.2 is one of the isoforms of the Shal-related subfamily of potassium voltage-gated channels that are expressed in MGB. Since potassium channel is important for shaping synaptic current and spike waveforms, subcellular distribution of Kv4.2 is likely important for integration of various inputs. Here, we aimed to examine the detailed distribution of Kv4.2, in MGV neurons to understand its specific role in auditory attention. We found that Kv4.2 mRNA was expressed in most MGV neurons. At the protein level, Kv4.2-immunopositive patches were sparsely distributed in both the dendrites and the soma of neurons. The postsynaptic distribution of Kv4.2 protein was confirmed using electron microscopy (EM). The frequency of contact with Kv4.2-immunopositive puncta was higher in vesicular glutamate transporter 2 (VGluT2)-positive excitatory axon terminals, which are supposed to be extending from the IC, than in VGluT1-immunopositive terminals, which are expected to be originating from the AC. VGluT2-immunopositive terminals were significantly larger than VGluT1-immunopositive terminals. Furthermore, EM showed that the terminals forming asymmetric synapses with Kv4.2-immunopositive MGV dendritic domains were significantly larger than those forming synapses with Kv4.2-negative MGV dendritic domains. In inhibitory axons either from the IC or from the RTN, the frequency of terminals that were in contact with Kv4.2-positive puncta was higher in IC than in RTN. In summary, our study demonstrated that the Kv4.2-immunopositive domains of the MGV dendrites received excitatory and inhibitory ascending auditory inputs preferentially from the IC, and not from the RTN or cortex. Our findings imply that time course of synaptic current and spike waveforms elicited by IC inputs is modified in the Kv4.2 domains.
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Affiliation(s)
- Hisataka Fujimoto
- Department of Anatomy, Kawasaki Medical School, Kurashiki, Japan.,Department of Ophthalmology, Kawasaki Medical School, Kurashiki, Japan
| | - Eiji Notsu
- Department of Anatomy, Kawasaki Medical School, Kurashiki, Japan
| | - Ryo Yamamoto
- Department of Physiology, Kanazawa Medical University, Uchinada, Japan
| | - Munenori Ono
- Department of Physiology, Kanazawa Medical University, Uchinada, Japan
| | - Hiroyuki Hioki
- Department of Neuroanatomy, Juntendo University Graduate School of Medicine, Tokyo, Japan
| | - Megumu Takahashi
- Department of Neuroanatomy, Juntendo University Graduate School of Medicine, Tokyo, Japan.,Department of Neuroscience, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Tetsufumi Ito
- Research and Education Program for Life Science, University of Fukui, Fukui, Japan.,Department of Anatomy, Kanazawa Medical University, Uchinada, Japan.,Department of Systems Function and Morphology, Graduate School of Innovative Life Science, University of Toyama, Toyama, Japan
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9
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Abstract
The response to contrast is one of the most important functions of the macaque primary visual cortex, V1, but up to now there has not been an adequate theory for it. To fill this gap in our understanding of cortical function, we built and analyzed a new large-scale, biologically constrained model of the input layer, 4Cα, of macaque V1. We called the new model CSY2. We challenged CSY2 with a three-parameter family of visual stimuli that varied in contrast, orientation, and spatial frequency. CSY2 accurately simulated experimental data and made many new predictions. It accounted for 1) the shapes of firing-rate-versus-contrast functions, 2) orientation and spatial frequency tuning versus contrast, and 3) the approximate contrast-invariance of cortical activity maps. Post-analysis revealed that the mechanisms that were needed to produce the successful simulations of contrast response included strong recurrent excitation and inhibition that find dynamic equilibria across the cortical surface, dynamic feedback between L6 and L4, and synaptic dynamics like inhibitory synaptic depression.
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10
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Chen Z, Boxwell A, Conte C, Haas T, Harley A, Terman DH, Travers SP, Travers JB. Kv4 channel expression and kinetics in GABAergic and non-GABAergic rNST neurons. J Neurophysiol 2020; 124:1727-1742. [PMID: 32997557 DOI: 10.1152/jn.00396.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The rostral nucleus of the solitary tract (rNST) serves as the first central relay in the gustatory system. In addition to synaptic interactions, central processing is also influenced by the ion channel composition of individual neurons. For example, voltage-gated K+ channels such as outward K+ current (IA) can modify the integrative properties of neurons. IA currents are prevalent in rNST projection cells but are also found to a lesser extent in GABAergic interneurons. However, characterization of the kinetic properties of IA, the molecular basis of these currents, as well as the consequences of IA on spiking properties of identified rNST cells is lacking. Here, we show that IA in rNST GABAergic (G+) and non-GABAergic (G-) neurons share a common molecular basis. In both cell types, there was a reduction in IA following treatment with the specific Kv4 channel blocker AmmTx3. However, the kinetics of activation and inactivation of IA in the two cell types were different with G- neurons having significantly more negative half-maximal activation and inactivation values. Likewise, under current clamp, G- cells had significantly longer delays to spike initiation in response to a depolarizing stimulus preceded by a hyperpolarizing prepulse. Computational modeling and dynamic clamp suggest that differences in the activation half-maximum may account for the differences in delay. We further observed evidence for a window current under both voltage clamp and current clamp protocols. We speculate that the location of Kv4.3 channels on dendrites, together with a window current for IA at rest, serves to regulate excitatory afferent inputs.NEW & NOTEWORTHY Here, we demonstrate that the transient outward K+ current IA occurs in both GABAergic and non-GABAergic neurons via Kv4.3 channels in the rostral (gustatory) solitary nucleus. Although found in both cell types, IA is more prevalent in non-GABAergic cells; a larger conductance at more negative potentials leads to a greater impact on spike initiation compared with GABAergic neurons. An IA window current further suggests that IA can regulate excitatory afferent input to the nucleus.
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Affiliation(s)
- Z Chen
- Division of Biosciences, Ohio State University, Columbus, Ohio
| | - A Boxwell
- College of Medicine, Ohio State University, Columbus, Ohio
| | - C Conte
- Department of Statistics, Ohio State University, Columbus, Ohio
| | - T Haas
- Division of Biosciences, Ohio State University, Columbus, Ohio
| | - A Harley
- Division of Biosciences, Ohio State University, Columbus, Ohio
| | - D H Terman
- Department of Mathematics, Ohio State University, Columbus, Ohio
| | - S P Travers
- Division of Biosciences, Ohio State University, Columbus, Ohio
| | - J B Travers
- Division of Biosciences, Ohio State University, Columbus, Ohio
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11
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Aceto G, Re A, Mattera A, Leone L, Colussi C, Rinaudo M, Scala F, Gironi K, Barbati SA, Fusco S, Green T, Laezza F, D'Ascenzo M, Grassi C. GSK3β Modulates Timing-Dependent Long-Term Depression Through Direct Phosphorylation of Kv4.2 Channels. Cereb Cortex 2020; 29:1851-1865. [PMID: 29790931 DOI: 10.1093/cercor/bhy042] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 01/15/2018] [Accepted: 02/07/2018] [Indexed: 12/31/2022] Open
Abstract
Spike timing-dependent plasticity (STDP) is a form of activity-dependent remodeling of synaptic strength that underlies memory formation. Despite its key role in dictating learning rules in the brain circuits, the molecular mechanisms mediating STDP are still poorly understood. Here, we show that spike timing-dependent long-term depression (tLTD) and A-type K+ currents are modulated by pharmacological agents affecting the levels of active glycogen-synthase kinase 3 (GSK3) and by GSK3β knockdown in layer 2/3 of the mouse somatosensory cortex. Moreover, the blockade of A-type K+ currents mimics the effects of GSK3 up-regulation on tLTD and occludes further changes in synaptic strength. Pharmacological, immunohistochemical and biochemical experiments revealed that GSK3β influence over tLTD induction is mediated by direct phosphorylation at Ser-616 of the Kv4.2 subunit, a molecular determinant of A-type K+ currents. Collectively, these results identify the functional interaction between GSK3β and Kv4.2 channel as a novel mechanism for tLTD modulation providing exciting insight into the understanding of GSK3β role in synaptic plasticity.
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Affiliation(s)
- Giuseppe Aceto
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Agnese Re
- Institute of Cell Biology and Neurobiology, National Research Council, Rome, Italy
| | - Andrea Mattera
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Lucia Leone
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy.,Fondazione Policlinico Universitario A Gemelli, IRCCS, Rome, Italy
| | - Claudia Colussi
- Institute of Cell Biology and Neurobiology, National Research Council, Rome, Italy
| | - Marco Rinaudo
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Federico Scala
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Katia Gironi
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy
| | | | - Salvatore Fusco
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy.,Fondazione Policlinico Universitario A Gemelli, IRCCS, Rome, Italy
| | - Thomas Green
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Fernanda Laezza
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA
| | - Marcello D'Ascenzo
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy.,Fondazione Policlinico Universitario A Gemelli, IRCCS, Rome, Italy
| | - Claudio Grassi
- Institute of Human Physiology, Università Cattolica del Sacro Cuore, Rome, Italy.,Fondazione Policlinico Universitario A Gemelli, IRCCS, Rome, Italy
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12
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Mitf Links Neuronal Activity and Long-Term Homeostatic Intrinsic Plasticity. eNeuro 2020; 7:ENEURO.0412-19.2020. [PMID: 32193365 PMCID: PMC7174873 DOI: 10.1523/eneuro.0412-19.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 02/07/2020] [Accepted: 03/02/2020] [Indexed: 12/25/2022] Open
Abstract
Neuroplasticity forms the basis for neuronal circuit complexity and differences between otherwise similar circuits. We show that the microphthalmia-associated transcription factor (Mitf) plays a central role in intrinsic plasticity of olfactory bulb (OB) projection neurons. Mitral and tufted (M/T) neurons from Mitf mutant mice are hyperexcitable, have a reduced A-type potassium current (IA) and exhibit reduced expression of Kcnd3, which encodes a potassium voltage-gated channel subunit (Kv4.3) important for generating the IA Furthermore, expression of the Mitf and Kcnd3 genes is activity dependent in OB projection neurons and the MITF protein activates expression from Kcnd3 regulatory elements. Moreover, Mitf mutant mice have changes in olfactory habituation and have increased habituation for an odorant following long-term exposure, indicating that regulation of Kcnd3 is pivotal for long-term olfactory adaptation. Our findings show that Mitf acts as a direct regulator of intrinsic homeostatic feedback and links neuronal activity, transcriptional changes and neuronal function.
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Su ZJ, Wang XY, Zhou C, Chai Z. Down-regulation of miR-3068-3p enhances kcnip4-regulated A-type potassium current to protect against glutamate-induced excitotoxicity. J Neurochem 2019; 153:617-630. [PMID: 31792968 DOI: 10.1111/jnc.14932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 11/26/2019] [Accepted: 11/27/2019] [Indexed: 11/30/2022]
Abstract
The main cause of excitotoxic neuronal death in ischemic stroke is the massive release of glutamate. Recently, microRNAs (miRNAs) have been found to play an essential role in stroke pathology, although the molecular mechanisms remain to be investigated. Here, to identify potential candidate miRNAs involved in excitotoxicity, we treated rat primary cortical neurons with glutamate and found that miR-3068-3p, a novel miRNA, was up-regulated. We hypothesized that restoring miR-3068-3p expression might influence the neuronal injury outcomes. The inhibition of miR-3068-3p, using tough decoy lentiviruses, significantly attenuated the effects of glutamate on neuronal viability and intracellular calcium overload. To unravel the mechanisms, we employed bioinformatics analysis and RNA sequencing to identify downstream target genes. Additional luciferase assays and western blots validated kcnip4, a Kv4-mediated A-type potassium current (IA ) regulator, as a direct target of miR-3068-3p. The inhibition of miR-3068-3p increased kcnip4 expression and vice versa. In addition, the knockdown of kcnip4 by shRNA abolished the protective effect of miR-3068-3p, and over-expressing kcnip4 alone was sufficient to play a neuroprotective role in excitotoxicity. Moreover the inhibition of miR-3068-3p enhanced the IA density, and the pharmacological inhibition of IA abrogated the protective role of miR-3068-3p inhibition and kcnip4 over-expression. Therefore, we conclude that inhibition of miR-3068-3p protects against excitotoxicity via its target gene, kcnip4, and kcnip4-regulated IA . Our data suggest that the miR-3068-3p/kcnip4 axis may serve as a novel target for the treatment of ischemic stroke.
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Affiliation(s)
- Zi-Jun Su
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Xu-Yi Wang
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Chen Zhou
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Zhen Chai
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
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14
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Gonzalez S, Villa E, Rodriguez M, Ramirez M, Zavala J, Armas R, Dassori A, Contreras J, Raventós H, Flores D, Jerez A, Ontiveros A, Nicolini H, Escamilla M. Fine-mapping scan of bipolar disorder susceptibility loci in Latino pedigrees. Am J Med Genet B Neuropsychiatr Genet 2019; 180:213-222. [PMID: 30779416 DOI: 10.1002/ajmg.b.32715] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 12/27/2018] [Accepted: 01/28/2019] [Indexed: 11/11/2022]
Abstract
We previously identified bipolar disorder (BD) susceptibility loci on 8q24, 14q32, and 2q12-14 in a genome-wide nonparametric linkage screen in a Latino cohort. We now perform a fine mapping analysis using a dense map of additional SNPs to identify BD susceptibility genes within these regions. One thousand nine hundred and thirty-eight individuals with Latino ancestry (880 individuals with BD Type I or Schizoaffective, Bipolar Type) from 416 Latino pedigrees from the United States, Mexico, Costa Rica, and Guatemala were genotyped with 3,074 SNPs to provide dense coverage of the 8q24 (11.5 cM), 14q32 (7.5 cM), and 2q12-14 (6.5 cM) chromosomal loci. Single-marker association tests in the presence of linkage were performed using the LAMP software. The top linkage peak (rs7834818; LOD = 5.08, p = 3.30E - 5) and associated single marker (rs2280915, p = 2.70E - 12) were located within FBXO32 on 8q24. On chromosome 2, the top linkage peak (rs6750326; LOD = 5.06, p = 3.50E - 5) and associated single marker (rs11887088, p = 2.90E - 6) were located in intragenic regions near ACTR3 and DPP10. None of the additional markers in the region around chromosome 14q32 met significance levels for linkage or association. We identified six SNPs on 2q12-q14 and one SNP in FBXO32 on 8q24 that were significantly associated with BD in this Latino cohort.
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Affiliation(s)
- Suzanne Gonzalez
- Center of Emphasis in Neurosciences, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas.,Departments of Psychiatry and Pharmacology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Erika Villa
- Department of Bioinformatics, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Marco Rodriguez
- Center of Emphasis in Neurosciences, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas
| | - Mercedes Ramirez
- Center of Emphasis in Neurosciences, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas.,Department of Psychiatry, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas
| | - Juan Zavala
- Center of Emphasis in Neurosciences, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas.,Department of Psychiatry, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas
| | - Regina Armas
- Langley Porter Psychiatric Institute, University of California at San Francisco, San Francisco, California
| | - Albana Dassori
- Department of Psychiatry, University of Texas Health Science Center at San Antonio, San Antonio, Texas.,Department of Psychiatry, South Texas Veterans Health Care System, San Antonio, Texas
| | - Javier Contreras
- Centro de Investigación en Biología Celular y Molecular y Escuela de Biologia, Universidad de Costa Rica, San Jose, Costa Rica
| | - Henriette Raventós
- Centro de Investigación en Biología Celular y Molecular y Escuela de Biologia, Universidad de Costa Rica, San Jose, Costa Rica
| | - Deborah Flores
- Los Angeles Biomedical Research Center at Harbor, University of California Los Angeles Medical Center, Torrance, California
| | - Alvaro Jerez
- Centro Internacional de Trastornos Afectivos y de la Conducta Adictiva, Guatemala City, Guatemala
| | - Alfonso Ontiveros
- Departamento de Psiquiatria, Hospital Universitario UANL, Monterrey, Nuevo Leon, Mexico
| | - Humberto Nicolini
- Grupo de Estudios Médicos y Familiares Carracci S.C., México, Distrito Federal, Mexico.,Laboratorio de Enfermedades Psychiatricas y Neurodegenerativas, Instituto Nacional de Medicina Genómica, México, Distrito Federal, Mexico
| | - Michael Escamilla
- Center of Emphasis in Neurosciences, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas.,Department of Psychiatry, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas
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15
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Myers TL, Gonzalez OC, Stein JB, Bazhenov M. Characterizing Concentration-Dependent Neural Dynamics of 4-Aminopyridine-Induced Epileptiform Activity. ACTA ACUST UNITED AC 2018; 4. [PMID: 30450487 PMCID: PMC6234984 DOI: 10.4172/2472-0895.1000128] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Epilepsy remains one of the most common neurological disorders. In patients, it is characterized by unprovoked, spontaneous, and recurrent seizures or ictal events. Typically, inter-ictal events or large bouts of population level activity can be measured between seizures and are generally asymptomatic. Decades of research have focused on understanding the mechanisms leading to the development of seizure-like activity using various pro-convulsive pharmacological agents, including 4-aimnopyridine (4AP). However, the lack of consistency in the concentrations used for studying 4AP-induced epileptiform activity in animal models may give rise to differences in results and interpretation thereof. Indeed, the range of 4AP concentration in both in vivo and in vitro studies varies from 3 μM to 40 mM. Here, we explored the effects of various 4AP concentrations on the development and characteristics of hippocampal epileptiform activity in acute mouse brain slices of either sex. Using multi-electrode array recordings, we show that 4AP induces hippocampal epileptiform activity for a broad range of concentrations. The frequency component and the spatiotemporal patterns of the epileptiform activity revealed a dose-dependent response. Finally, in the presence of 4AP, reduction of KCC2 co-transporter activity by KCC2 antagonist VU0240551 prevented the manifestation of the frequency component differences between different concentrations of 4AP. Overall, the study predicts that different concentrations of 4AP can result in the different mechanisms behind hippocampal epileptiform activity, of which some are dependent on the KCC2 co-transporter function.
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Affiliation(s)
- Timothy L Myers
- Neuroscience Graduate Program, University of California, Riverside, California, United States of America.,Department of Cell Biology and Neuroscience, University of California, Riverside, California, United States of America
| | - Oscar C Gonzalez
- Department of Medicine, University of California, San Diego, California, United States of America.,Neuroscience Graduate Program, University of California, San Diego, California, United States of America
| | - Jacob B Stein
- Department of Cell Biology and Neuroscience, University of California, Riverside, California, United States of America
| | - Maxim Bazhenov
- Department of Medicine, University of California, San Diego, California, United States of America
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16
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Suryanarayana SM, Robertson B, Wallén P, Grillner S. The Lamprey Pallium Provides a Blueprint of the Mammalian Layered Cortex. Curr Biol 2017; 27:3264-3277.e5. [PMID: 29056451 DOI: 10.1016/j.cub.2017.09.034] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 09/14/2017] [Accepted: 09/15/2017] [Indexed: 12/26/2022]
Abstract
The basic architecture of the mammalian neocortex is remarkably similar across species. Pallial structures in the reptilian brain are considered amniote precursors of mammalian neocortex, whereas pallia of anamniotes ("lower" vertebrates) have been deemed largely insignificant with respect to homology. Here, we examine the cytoarchitecture of the lateral pallium in the lamprey, the phylogenetically oldest group of extant vertebrates. We reveal a three-layered structure with similar excitatory cell types as in the mammalian cortex and GABAergic interneurons. The ventral parts are sensory areas receiving monosynaptic thalamic input that can be activated from the optic nerve, whereas the dorsal parts contain motor areas with efferent projections to the brainstem, receiving oligosynaptic thalamic input. Both regions receive monosynaptic olfactory input. This three-layered "primordial" lamprey lateral pallium has evolved most features of the three-layered reptilian cortices and is thereby a precursor of the six-layered "neo" cortex with a long-standing evolutionary precedent (some 500 million years ago).
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Affiliation(s)
| | - Brita Robertson
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Peter Wallén
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Sten Grillner
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
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17
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Kim EZ, Vienne J, Rosbash M, Griffith LC. Nonreciprocal homeostatic compensation in Drosophila potassium channel mutants. J Neurophysiol 2017; 117:2125-2136. [PMID: 28298298 DOI: 10.1152/jn.00002.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 03/06/2017] [Accepted: 03/11/2017] [Indexed: 01/30/2023] Open
Abstract
Homeostatic control of intrinsic excitability is important for long-term regulation of neuronal activity. In conjunction with many other forms of plasticity, intrinsic homeostasis helps neurons maintain stable activity regimes in the face of external input variability and destabilizing genetic mutations. In this study, we report a mechanism by which Drosophila melanogaster larval motor neurons stabilize hyperactivity induced by the loss of the delayed rectifying K+ channel Shaker cognate B (Shab), by upregulating the Ca2+-dependent K+ channel encoded by the slowpoke (slo) gene. We also show that loss of SLO does not trigger a reciprocal compensatory upregulation of SHAB, implying that homeostatic signaling pathways utilize compensatory pathways unique to the channel that was mutated. SLO upregulation due to loss of SHAB involves nuclear Ca2+ signaling and dCREB, suggesting that the slo homeostatic response is transcriptionally mediated. Examination of the changes in gene expression induced by these mutations suggests that there is not a generic transcriptional response to increased excitability in motor neurons, but that homeostatic compensations are influenced by the identity of the lost conductance.NEW & NOTEWORTHY The idea that activity-dependent homeostatic plasticity is driven solely by firing has wide credence. In this report we show that homeostatic compensation after loss of an ion channel conductance is tailored to identity of the channel lost, not its properties.
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Affiliation(s)
- Eugene Z Kim
- Department of Biology, Volen Center for Complex Systems, and National Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts; and
| | - Julie Vienne
- Department of Biology, Volen Center for Complex Systems, and National Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts; and
| | - Michael Rosbash
- Department of Biology, Volen Center for Complex Systems, and National Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts; and.,Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts
| | - Leslie C Griffith
- Department of Biology, Volen Center for Complex Systems, and National Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts; and
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18
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Fremont R, Tewari A, Angueyra C, Khodakhah K. A role for cerebellum in the hereditary dystonia DYT1. eLife 2017; 6. [PMID: 28198698 PMCID: PMC5340526 DOI: 10.7554/elife.22775] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 02/14/2017] [Indexed: 02/06/2023] Open
Abstract
DYT1 is a debilitating movement disorder caused by loss-of-function mutations in torsinA. How these mutations cause dystonia remains unknown. Mouse models which have embryonically targeted torsinA have failed to recapitulate the dystonia seen in patients, possibly due to differential developmental compensation between rodents and humans. To address this issue, torsinA was acutely knocked down in select brain regions of adult mice using shRNAs. TorsinA knockdown in the cerebellum, but not in the basal ganglia, was sufficient to induce dystonia. In agreement with a potential developmental compensation for loss of torsinA in rodents, torsinA knockdown in the immature cerebellum failed to produce dystonia. Abnormal motor symptoms in knockdown animals were associated with irregular cerebellar output caused by changes in the intrinsic activity of both Purkinje cells and neurons of the deep cerebellar nuclei. These data identify the cerebellum as the main site of dysfunction in DYT1, and offer new therapeutic targets. DOI:http://dx.doi.org/10.7554/eLife.22775.001 Dystonia is the third most common type of movement disorder after Parkinson’s disease and tremor. Patients with dystonia experience prolonged involuntary contractions of their muscles, often causing uncontrollable postures or repetitive movements. Almost thirty years ago, genetic studies revealed that a mutation in the gene that encodes a protein called torsinA causes the most common type of dystonia, called DYT1. Exactly how mutations that affect the torsinA protein give rise to DYT1 remains unclear, and there are still no effective treatments for the disorder. Part of the problem is that we do not fully understand how torsinA works, or which of its many proposed functions is relevant to dystonia. Moreover, attempts to study DYT1 using genetically modified mice have proved largely unsuccessful. This is because mice that simply express the same genetic mutations that cause dystonia in humans do not show the overt symptoms of dystonia. Fremont, Tewari et al. have now generated a mouse ‘model’ that does show symptoms of dystonia, and used these model mice to investigate the role of torsinA in the disorder. Acutely reducing the amount of torsinA protein in a region of the brain called the cerebellum induced the symptoms of dystonia in the mice. Conversely, reducing the amount of torsinA in a different brain area known as the basal ganglia had no such effect, even though both the cerebellum and the basal ganglia contribute to movement. Furthermore, neither manipulation had any effect in juvenile mice, which suggests that, in contrast to humans, young mice can compensate for the loss of torsinA. Fremont, Tewari et al. also found that the loss of torsinA causes the cerebellum to generate incorrect output signals, which in turn trigger the abnormal movements seen in dystonia. In the future, further studies of the model mice could identify the exact changes that occur in neurons following the loss of torsinA from the cerebellum. Understanding these changes could potentially pave the way for developing effective treatments for DYT1 and other dystonias. DOI:http://dx.doi.org/10.7554/eLife.22775.002
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Affiliation(s)
- Rachel Fremont
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
| | - Ambika Tewari
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
| | - Chantal Angueyra
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
| | - Kamran Khodakhah
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
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Hypocretin/Orexin Peptides Alter Spike Encoding by Serotonergic Dorsal Raphe Neurons through Two Distinct Mechanisms That Increase the Late Afterhyperpolarization. J Neurosci 2016; 36:10097-115. [PMID: 27683906 DOI: 10.1523/jneurosci.0635-16.2016] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 08/11/2016] [Indexed: 01/02/2023] Open
Abstract
UNLABELLED Orexins (hypocretins) are neuropeptides that regulate multiple homeostatic processes, including reward and arousal, in part by exciting serotonergic dorsal raphe neurons, the major source of forebrain serotonin. Here, using mouse brain slices, we found that, instead of simply depolarizing these neurons, orexin-A altered the spike encoding process by increasing the postspike afterhyperpolarization (AHP) via two distinct mechanisms. This orexin-enhanced AHP (oeAHP) was mediated by both OX1 and OX2 receptors, required Ca(2+) influx, reversed near EK, and decayed with two components, the faster of which resulted from enhanced SK channel activation, whereas the slower component decayed like a slow AHP (sAHP), but was not blocked by UCL2077, an antagonist of sAHPs in some neurons. Intracellular phospholipase C inhibition (U73122) blocked the entire oeAHP, but neither component was sensitive to PKC inhibition or altered PKA signaling, unlike classical sAHPs. The enhanced SK current did not depend on IP3-mediated Ca(2+) release but resulted from A-current inhibition and the resultant spike broadening, which increased Ca(2+) influx and Ca(2+)-induced-Ca(2+) release, whereas the slower component was insensitive to these factors. Functionally, the oeAHP slowed and stabilized orexin-induced firing compared with firing produced by a virtual orexin conductance lacking the oeAHP. The oeAHP also reduced steady-state firing rate and firing fidelity in response to stimulation, without affecting the initial rate or fidelity. Collectively, these findings reveal a new orexin action in serotonergic raphe neurons and suggest that, when orexin is released during arousal and reward, it enhances the spike encoding of phasic over tonic inputs, such as those related to sensory, motor, and reward events. SIGNIFICANCE STATEMENT Orexin peptides are known to excite neurons via slow postsynaptic depolarizations. Here we elucidate a significant new orexin action that increases and prolongs the postspike afterhyperpolarization (AHP) in 5-HT dorsal raphe neurons and other arousal-system neurons. Our mechanistic studies establish involvement of two distinct Ca(2+)-dependent AHP currents dependent on phospholipase C signaling but independent of IP3 or PKC. Our functional studies establish that this action preserves responsiveness to phasic inputs while attenuating responsiveness to tonic inputs. Thus, our findings bring new insight into the actions of an important neuropeptide and indicate that, in addition to producing excitation, orexins can tune postsynaptic excitability to better encode the phasic sensory, motor, and reward signals expected during aroused states.
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Kida H, Tsuda Y, Ito N, Yamamoto Y, Owada Y, Kamiya Y, Mitsushima D. Motor Training Promotes Both Synaptic and Intrinsic Plasticity of Layer II/III Pyramidal Neurons in the Primary Motor Cortex. Cereb Cortex 2016; 26:3494-507. [PMID: 27193420 PMCID: PMC4961021 DOI: 10.1093/cercor/bhw134] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Motor skill training induces structural plasticity at dendritic spines in the primary motor cortex (M1). To further analyze both synaptic and intrinsic plasticity in the layer II/III area of M1, we subjected rats to a rotor rod test and then prepared acute brain slices. Motor skill consistently improved within 2 days of training. Voltage clamp analysis showed significantly higher α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/N-methyl-d-aspartate (AMPA/NMDA) ratios and miniature EPSC amplitudes in 1-day trained rats compared with untrained rats, suggesting increased postsynaptic AMPA receptors in the early phase of motor learning. Compared with untrained controls, 2-days trained rats showed significantly higher miniature EPSC amplitude and frequency. Paired-pulse analysis further demonstrated lower rates in 2-days trained rats, suggesting increased presynaptic glutamate release during the late phase of learning. One-day trained rats showed decreased miniature IPSC frequency and increased paired-pulse analysis of evoked IPSC, suggesting a transient decrease in presynaptic γ-aminobutyric acid (GABA) release. Moreover, current clamp analysis revealed lower resting membrane potential, higher spike threshold, and deeper afterhyperpolarization in 1-day trained rats—while 2-days trained rats showed higher membrane potential, suggesting dynamic changes in intrinsic properties. Our present results indicate dynamic changes in glutamatergic, GABAergic, and intrinsic plasticity in M1 layer II/III neurons after the motor training.
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Affiliation(s)
| | | | | | - Yui Yamamoto
- Department of Organ Anatomy, Yamaguchi University Graduate School of Medicine, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan
| | - Yuji Owada
- Department of Organ Anatomy, Yamaguchi University Graduate School of Medicine, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan
| | - Yoshinori Kamiya
- Uonuma Institute of Community Medicine, Niigata University Medical and Dental Hospital, 4132 Urasa, Minami-uonuma, Niigata 949-7302, Japan
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Pathak D, Guan D, Foehring RC. Roles of specific Kv channel types in repolarization of the action potential in genetically identified subclasses of pyramidal neurons in mouse neocortex. J Neurophysiol 2016; 115:2317-29. [PMID: 26864770 DOI: 10.1152/jn.01028.2015] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 02/09/2016] [Indexed: 01/07/2023] Open
Abstract
The action potential (AP) is a fundamental feature of excitable cells that serves as the basis for long-distance signaling in the nervous system. There is considerable diversity in the appearance of APs and the underlying repolarization mechanisms in different neuronal types (reviewed in Bean BP. Nat Rev Neurosci 8: 451-465, 2007), including among pyramidal cell subtypes. In the present work, we used specific pharmacological blockers to test for contributions of Kv1, Kv2, or Kv4 channels to repolarization of single APs in two genetically defined subpopulations of pyramidal cells in layer 5 of mouse somatosensory cortex (etv1 and glt) as well as pyramidal cells from layer 2/3. These three subtypes differ in AP properties (Groh A, Meyer HS, Schmidt EF, Heintz N, Sakmann B, Krieger P. Cereb Cortex 20: 826-836, 2010; Guan D, Armstrong WE, Foehring RC. J Neurophysiol 113: 2014-2032, 2015) as well as laminar position, morphology, and projection targets. We asked what the roles of Kv1, Kv2, and Kv4 channels are in AP repolarization and whether the underlying mechanisms are pyramidal cell subtype dependent. We found that Kv4 channels are critically involved in repolarizing neocortical pyramidal cells. There are also pyramidal cell subtype-specific differences in the role for Kv1 channels. Only Kv4 channels were involved in repolarizing the narrow APs of glt cells. In contrast, in etv1 cells and layer 2/3 cells, the broader APs are partially repolarized by Kv1 channels in addition to Kv4 channels. Consistent with their activation in the subthreshold range, Kv1 channels also regulate AP voltage threshold in all pyramidal cell subtypes.
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Affiliation(s)
- Dhruba Pathak
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, Tennessee
| | - Dongxu Guan
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, Tennessee
| | - Robert C Foehring
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, Tennessee
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22
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Abstract
Many neural circuits show fast reconfiguration following altered sensory or modulatory inputs to generate stereotyped outputs. In the motor circuit of Xenopus tadpoles, I study how certain voltage-dependent ionic currents affect firing thresholds and contribute to circuit reconfiguration to generate two distinct motor patterns, swimming and struggling. Firing thresholds of excitatory interneurons [i.e., descending interneurons (dINs)] in the swimming central pattern generator are raised by depolarization due to the inactivation of Na(+) currents. In contrast, the thresholds of other types of neurons active in swimming or struggling are raised by hyperpolarization from the activation of fast transient K(+) currents. The firing thresholds are then compared with the excitatory synaptic drives, which are revealed by blocking action potentials intracellularly using QX314 during swimming and struggling. During swimming, transient K(+) currents lower neuronal excitability and gate out neurons with weak excitation, whereas their inactivation by strong excitation in other neurons increases excitability and enables fast synaptic potentials to drive reliable firing. During struggling, continuous sensory inputs lead to high levels of network excitation. This allows the inactivation of Na(+) currents and suppression of dIN activity while inactivating transient K(+) currents, recruiting neurons that are not active in swimming. Therefore, differential expression of these currents between neuron types can explain why synaptic strength does not predict firing reliability/intensity during swimming and struggling. These data show that intrinsic properties can override fast synaptic potentials, mediate circuit reconfiguration, and contribute to motor-pattern switching.
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Involvement of Potassium and Cation Channels in Hippocampal Abnormalities of Embryonic Ts65Dn and Tc1 Trisomic Mice. EBioMedicine 2015; 2:1048-62. [PMID: 26501103 PMCID: PMC4588457 DOI: 10.1016/j.ebiom.2015.07.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Revised: 07/24/2015] [Accepted: 07/28/2015] [Indexed: 01/09/2023] Open
Abstract
Down syndrome (DS) mouse models exhibit cognitive deficits, and are used for studying the neuronal basis of DS pathology. To understand the differences in the physiology of DS model neurons, we used dissociated neuronal cultures from the hippocampi of Ts65Dn and Tc1 DS mice. Imaging of [Ca2+]i and whole cell patch clamp recordings were used to analyze network activity and single neuron properties, respectively. We found a decrease of ~ 30% in both fast (A-type) and slow (delayed rectifier) outward potassium currents. Depolarization of Ts65Dn and Tc1 cells produced fewer spikes than diploid cells. Their network bursts were smaller and slower than diploids, displaying a 40% reduction in Δf / f0 of the calcium signals, and a 30% reduction in propagation velocity. Additionally, Ts65Dn and Tc1 neurons exhibited changes in the action potential shape compared to diploid neurons, with an increase in the amplitude of the action potential, a lower threshold for spiking, and a sharp decrease of about 65% in the after-hyperpolarization amplitude. Numerical simulations reproduced the DS measured phenotype by variations in the conductance of the delayed rectifier and A-type, but necessitated also changes in inward rectifying and M-type potassium channels and in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. We therefore conducted whole cell patch clamp measurements of M-type potassium currents, which showed a ~ 90% decrease in Ts65Dn neurons, while HCN measurements displayed an increase of ~ 65% in Ts65Dn cells. Quantitative real-time PCR analysis indicates overexpression of 40% of KCNJ15, an inward rectifying potassium channel, contributing to the increased inhibition. We thus find that changes in several types of potassium channels dominate the observed DS model phenotype. Down syndrome model neurons display altered action potential shape, are less excitable and have decreased potassium currents. The data is accurately described by a numerical simulation that changes conductance of four potassium and the HCN currents. Measurements of the currents related to these four channels, and RT-pcr for a fifth (KCNJ15), confirm the numerical model.
In Down syndrome (DS) cognitive function is impaired, leading us to use cultured hippocampal neuronal networks to investigate the cellular basis of its pathology. DS mouse model neurons are less excitable, produce fewer spikes and generate less network activity. Alterations in several types of potassium currents were detected in these neurons. Numerical simulation of a DS neuron successfully reproduced the experimental results. Beyond extending our understanding of neuronal function and pathology, the alterations in channel conductance can now be targeted with specific drugs so as to point to new directions in therapy of cognitive disabilities of DS.
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Key Words
- 1D, one-dimensional
- 2D, two-dimensional
- DC, direct current
- DS, Down syndrome
- Down syndrome
- EPSC, excitatory post synaptic current
- GABA, gamma-aminobutyric acid
- GIRK, G protein-coupled inwardly-rectifying potassium channels
- HCN, hyperpolarization-activated cyclic nucleotide-gated
- Hippocampus
- Inward rectifiers
- Potassium channels
- Potassium currents
- ROI, region of interest
- RT-PCR, real time polymerase chain reaction
- Reduced excitability
- SEM, standard error of mean
- TTX, tetrodotoxin
- Tc1
- Ts65Dn
- WT, wild type
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Tau-dependent Kv4.2 depletion and dendritic hyperexcitability in a mouse model of Alzheimer's disease. J Neurosci 2015; 35:6221-30. [PMID: 25878292 DOI: 10.1523/jneurosci.2552-14.2015] [Citation(s) in RCA: 115] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Neuronal hyperexcitability occurs early in the pathogenesis of Alzheimer's disease (AD) and contributes to network dysfunction in AD patients. In other disorders with neuronal hyperexcitability, dysfunction in the dendrites often contributes, but dendritic excitability has not been directly examined in AD models. We used dendritic patch-clamp recordings to measure dendritic excitability in the CA1 region of the hippocampus. We found that dendrites, more so than somata, of hippocampal neurons were hyperexcitable in mice overexpressing Aβ. This dendritic hyperexcitability was associated with depletion of Kv4.2, a dendritic potassium channel important for regulating dendritic excitability and synaptic plasticity. The antiepileptic drug, levetiracetam, blocked Kv4.2 depletion. Tau was required, as crossing with tau knock-out mice also prevented both Kv4.2 depletion and dendritic hyperexcitability. Dendritic hyperexcitability induced by Kv4.2 deficiency exacerbated behavioral deficits and increased epileptiform activity in hAPP mice. We conclude that increased dendritic excitability, associated with changes in dendritic ion channels including Kv4.2, may contribute to neuronal dysfunction in early stages AD.
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Yu H, Zou B, Wang X, Li M. Effect of tyrphostin AG879 on Kv 4.2 and Kv 4.3 potassium channels. Br J Pharmacol 2015; 172:3370-82. [PMID: 25752739 DOI: 10.1111/bph.13127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 02/25/2015] [Accepted: 03/02/2015] [Indexed: 10/23/2022] Open
Abstract
BACKGROUND AND PURPOSE A-type potassium channels (IA) are important proteins for modulating neuronal membrane excitability. The expression and activity of Kv 4.2 channels are critical for neurological functions and pharmacological inhibitors of Kv 4.2 channels may have therapeutic potential for Fragile X syndrome. While screening various compounds, we identified tyrphostin AG879, a tyrosine kinase inhibitor, as a Kv 4.2 inhibitor from. In the present study we characterized the effect of AG879 on cloned Kv 4.2/Kv channel-interacting protein 2 (KChIP2) channels. EXPERIMENTAL APPROACH To screen the library of pharmacologically active compounds, the thallium flux assay was performed on HEK-293 cells transiently-transfected with Kv 4.2 cDNA using the Maxcyte transfection system. The effects of AG879 were further examined on CHO-K1 cells expressing Kv 4.2/KChIP2 channels using a whole-cell patch-clamp technique. KEY RESULTS Tyrphostin AG879 selectively and dose-dependently inhibited Kv 4.2 and Kv 4.3 channels. In Kv 4.2/KChIP2 channels, AG879 induced prominent acceleration of the inactivation rate, use-dependent block and slowed the recovery from inactivation. AG879 induced a hyperpolarizing shift in the voltage-dependence of the steady-state inactivation of Kv 4.2 channels without apparent effect on the V1/2 of the voltage-dependent activation. The blocking effect of AG879 was enhanced as channel inactivation increased. Furthermore, AG879 significantly inhibited the A-type potassium currents in the cultured hippocampus neurons. CONCLUSION AND IMPLICATIONS AG879 was identified as a selective and potent inhibitor the Kv 4.2 channel. AG879 inhibited Kv 4.2 channels by preferentially interacting with the open state and further accelerating their inactivation.
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Affiliation(s)
- Haibo Yu
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.,The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA
| | - Beiyan Zou
- The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA
| | - Xiaoliang Wang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Min Li
- The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA
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Williams SB, Hablitz JJ. Differential modulation of repetitive firing and synchronous network activity in neocortical interneurons by inhibition of A-type K(+) channels and Ih. Front Cell Neurosci 2015; 9:89. [PMID: 25852481 PMCID: PMC4364302 DOI: 10.3389/fncel.2015.00089] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 02/26/2015] [Indexed: 12/04/2022] Open
Abstract
GABAergic interneurons provide the main source of inhibition in the neocortex and are important in regulating neocortical network activity. In the presence 4-aminopyridine (4-AP), CNQX, and D-APV, large amplitude GABAA-receptor mediated depolarizing responses were observed in the neocortex. GABAergic networks are comprised of several types of interneurons, each with its own protein expression pattern, firing properties, and inhibitory role in network activity. Voltage-gated ion channels, especially A-type K(+) channels, differentially regulate passive membrane properties, action potential (AP) waveform, and repetitive firing properties in interneurons depending on their composition and localization. HCN channels are known modulators of pyramidal cell intrinsic excitability and excitatory network activity. Little information is available regarding how HCN channels functionally modulate excitability of individual interneurons and inhibitory networks. In this study, we examined the effect of 4-AP on intrinsic excitability of fast-spiking basket cells (FS-BCs) and Martinotti cells (MCs). 4-AP increased the duration of APs in both FS-BCs and MCs. The repetitive firing properties of MCs were differentially affected compared to FS-BCs. We also examined the effect of Ih inhibition on synchronous GABAergic depolarizations and synaptic integration of depolarizing IPSPs. ZD 7288 enhanced the amplitude and area of evoked GABAergic responses in both cell types. Similarly, the frequency and area of spontaneous GABAergic depolarizations in both FS-BCs and MCs were increased in presence of ZD 7288. Synaptic integration of IPSPs in MCs was significantly enhanced, but remained unaltered in FS-BCs. These results indicate that 4-AP differentially alters the firing properties of interneurons, suggesting MCs and FS-BCs may have unique roles in GABAergic network synchronization. Enhancement of GABAergic network synchronization by ZD 7288 suggests that HCN channels attenuate inhibitory network activity.
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Affiliation(s)
| | - John J. Hablitz
- Department of Neurobiology, Civitan International Research Center and Evelyn F. McKnight Brain Institute, University of Alabama at Birmingham, Birmingham, ALUSA
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The expression pattern of a Cav3-Kv4 complex differentially regulates spike output in cerebellar granule cells. J Neurosci 2014; 34:8800-12. [PMID: 24966380 DOI: 10.1523/jneurosci.0981-14.2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The cerebellum receives sensory information by mossy fiber input from a multitude of sources that require differential signal processing. A compartmentalization of function begins with the segregation of mossy fibers across 10 distinct lobules over the rostrocaudal axis, with tactile receptor afferents prevalent in anterior lobules and vestibular input in caudal lobules. However, it is unclear how these unique signals might be differentially processed at the circuit level across the cerebellum. As granule cells receive mossy fiber input, they represent a key stage at which postsynaptic mechanisms could influence signal processing. Granule cells express an A-type current mediated by Kv4 potassium channels that modify the latency and frequency of spike output. The current study examined the potential for a Cav3 calcium-Kv4 channel complex to regulate the response of granule cells to mossy fiber input in lobules 2 and 9 of the rat cerebellum. Similar A-type currents were recorded in both regions, but the Cav3 calcium current was expressed at a substantially higher density in lobule 9 cells, acting to increase A-type current availability through its influence on Kv4 voltage for inactivation. The difference in excitability imparted by Cav3-Kv4 interactions proves to allow lobule 2 granule cells to respond more effectively to tactile stimulus-like burst input and lobule 9 cells to slow shifts in input frequency characteristic of vestibular input. The expression pattern of Cav3 channels and its control of Kv4 availability thus provides a novel means of processing widely different forms of sensory input across cerebellar lobules.
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Leijon S, Magnusson AK. Physiological characterization of vestibular efferent brainstem neurons using a transgenic mouse model. PLoS One 2014; 9:e98277. [PMID: 24867596 PMCID: PMC4035287 DOI: 10.1371/journal.pone.0098277] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 04/30/2014] [Indexed: 01/31/2023] Open
Abstract
The functional role of efferent innervation of the vestibular end-organs in the inner ear remains elusive. This study provides the first physiological characterization of the cholinergic vestibular efferent (VE) neurons in the brainstem by utilizing a transgenic mouse model, expressing eGFP under a choline-acetyltransferase (ChAT)-locus spanning promoter in combination with targeted patch clamp recordings. The intrinsic electrical properties of the eGFP-positive VE neurons were compared to the properties of the lateral olivocochlear (LOC) brainstem neurons, which gives rise to efferent innervation of the cochlea. Both VE and the LOC neurons were marked by their negative resting membrane potential <-75 mV and their passive responses in the hyperpolarizing range. In contrast, the response properties of VE and LOC neurons differed significantly in the depolarizing range. When injected with positive currents, VE neurons fired action potentials faithfully to the onset of depolarization followed by sparse firing with long inter-spike intervals. This response gave rise to a low response gain. The LOC neurons, conversely, responded with a characteristic delayed tonic firing upon depolarizing stimuli, giving rise to higher response gain than the VE neurons. Depolarization triggered large TEA insensitive outward currents with fast inactivation kinetics, indicating A-type potassium currents, in both the inner ear-projecting neuronal types. Immunohistochemistry confirmed expression of Kv4.3 and 4.2 ion channel subunits in both the VE and LOC neurons. The difference in spiking responses to depolarization is related to a two-fold impact of these transient outward currents on somatic integration in the LOC neurons compared to in VE neurons. It is speculated that the physiological properties of the VE neurons might be compatible with a wide-spread control over motion and gravity sensation in the inner ear, providing likewise feed-back amplification of abrupt and strong phasic signals from the semi-circular canals and of tonic signals from the gravito-sensitive macular organs.
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Affiliation(s)
- Sara Leijon
- Center for Hearing and Communication Research, Karolinska Institutet, Stockholm, Sweden
- Department of Clinical Science, Intervention and Technology, Unit of Audiology, Karolinska University Hospital, Stockholm, Sweden
| | - Anna K. Magnusson
- Center for Hearing and Communication Research, Karolinska Institutet, Stockholm, Sweden
- Department of Clinical Science, Intervention and Technology, Unit of Audiology, Karolinska University Hospital, Stockholm, Sweden
- * E-mail:
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Razavinasab M, Moazzami K, Shabani M. Maternal mobile phone exposure alters intrinsic electrophysiological properties of CA1 pyramidal neurons in rat offspring. Toxicol Ind Health 2014; 32:968-79. [PMID: 24604340 DOI: 10.1177/0748233714525497] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Some studies have shown that exposure to electromagnetic field (EMF) may result in structural damage to neurons. In this study, we have elucidated the alteration in the hippocampal function of offspring Wistar rats (n = 8 rats in each group) that were chronically exposed to mobile phones during their gestational period by applying behavioral, histological, and electrophysiological tests. Rats in the EMF group were exposed to 900 MHz pulsed-EMF irradiation for 6 h/day. Whole cell recordings in hippocampal pyramidal cells in the mobile phone groups did show a decrease in neuronal excitability. Mobile phone exposure was mostly associated with a decrease in the number of action potentials fired in spontaneous activity and in response to current injection in both male and female groups. There was an increase in the amplitude of the afterhyperpolarization (AHP) in mobile phone rats compared with the control. The results of the passive avoidance and Morris water maze assessment of learning and memory performance showed that phone exposure significantly altered learning acquisition and memory retention in male and female rats compared with the control rats. Light microscopy study of brain sections of the control and mobile phone-exposed rats showed normal morphology.Our results suggest that exposure to mobile phones adversely affects the cognitive performance of both female and male offspring rats using behavioral and electrophysiological techniques.
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Affiliation(s)
- Moazamehosadat Razavinasab
- Kerman Neuroscience Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Islamic Republic of Iran
| | - Kasra Moazzami
- Cardiovascular Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Mohammad Shabani
- Kerman Neuroscience Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Islamic Republic of Iran
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Hermanstyne TO, Subedi K, Le WW, Hoffman GE, Meredith AL, Mong JA, Misonou H. Kv2.2: a novel molecular target to study the role of basal forebrain GABAergic neurons in the sleep-wake cycle. Sleep 2013; 36:1839-48. [PMID: 24293758 DOI: 10.5665/sleep.3212] [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] [Indexed: 11/03/2022] Open
Abstract
STUDY OBJECTIVES The basal forebrain (BF) has been implicated as an important brain region that regulates the sleep-wake cycle of animals. Gamma-aminobutyric acidergic (GABAergic) neurons are the most predominant neuronal population within this region. However, due to the lack of specific molecular tools, the roles of the BF GABAergic neurons have not been fully elucidated. Previously, we have found high expression levels of the Kv2.2 voltage-gated potassium channel on approximately 60% of GABAergic neurons in the magnocellular preoptic area and horizontal limb of the diagonal band of Broca of the BF and therefore proposed it as a potential molecular target to study this neuronal population. In this study, we sought to determine the functional roles of the Kv2.2-expressing neurons in the regulation of the sleep-wake cycle. DESIGN Sleep analysis between two genotypes and within each genotype before and after sleep deprivation. SETTING Animal sleep research laboratory. PARTICIPANTS Adult mice. Wild-type and Kv2.2 knockout mice with C57/BL6 background. INTERVENTIONS EEG/EMG recordings from the basal state and after sleep-deprivation which was induced by mild agitation for 6 h. RESULTS Immunostaining of a marker of neuronal activity indicates that these Kv2.2-expressing neurons appear to be preferentially active during the wake state. Therefore, we tested whether Kv2.2-expressing neurons in the BF are involved in arousal using Kv2.2-deficient mice. BF GABAergic neurons exhibited augmented expression of c-Fos. These knockout mice exhibited longer consolidated wake bouts than wild-type littermates, and that phenotype was further exacerbated by sleep deprivation. Moreover, in-depth analyses of their cortical electroencephalogram revealed a significant decrease in the delta-frequency activity during the nonrapid eye movement sleep state. CONCLUSIONS These results revealed the significance of Kv2.2-expressing neurons in the regulation of the sleep-wake cycle.
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Affiliation(s)
- Tracey O Hermanstyne
- Department of Neural and Pain Sciences ; Program in Neurosciences ; Department of Developmental Biology, Washington University, St. Louis, MO
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Abstract
In many peripheral and central neurons, A-type K(+) currents, IA, have been identified and shown to be key determinants in shaping action potential waveforms and repetitive firing properties, as well as in the regulation of synaptic transmission and synaptic plasticity. The functional properties and physiological roles of native neuronal IA, however, have been shown to be quite diverse in different types of neurons. Accumulating evidence suggests that this functional diversity is generated by multiple mechanisms, including the expression and subcellular distributions of IA channels encoded by different voltage-gated K(+) (Kv) channel pore-forming (α) subunits, interactions of Kv α subunits with cytosolic and/or transmembrane accessory subunits and regulatory proteins and post-translational modifications of channel subunits. Several recent reports further suggest that local protein translation in the dendrites of neurons and interactions between IA channels with other types of voltage-gated ion channels further expands the functional diversity of native neuronal IA channels. Here, we review the diverse molecular mechanisms that have been shown or proposed to underlie the functional diversity of native neuronal IA channels.
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Affiliation(s)
- Yarimar Carrasquillo
- 1Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO, USA
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Haghani M, Shabani M, Moazzami K. Maternal mobile phone exposure adversely affects the electrophysiological properties of Purkinje neurons in rat offspring. Neuroscience 2013; 250:588-98. [PMID: 23906636 DOI: 10.1016/j.neuroscience.2013.07.049] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 06/25/2013] [Accepted: 07/22/2013] [Indexed: 11/30/2022]
Abstract
Electromagnetic field (EMF) radiations emitted from mobile phones may cause structural damage to neurons. With the increased usage of mobile phones worldwide, concerns about their possible effects on the nervous system are rising. In the present study, we aimed to elucidate the possible effects of prenatal EMF exposure on the cerebellum of offspring Wistar rats. Rats in the EMF group were exposed to 900-MHz pulse-EMF irradiation for 6h per day during all gestation period. Ten offspring per each group were evaluated for behavioral and electrophysiological evaluations. Cerebellum-related behavioral dysfunctions were analyzed using motor learning and cerebellum-dependent functional tasks (Accelerated Rotarod, Hanging and Open field tests). Whole-cell patch clamp recordings were used for electrophysiological evaluations. The results of the present study failed to show any behavioral abnormalities in rats exposed to chronic EMF radiation. However, whole-cell patch clamp recordings revealed decreased neuronal excitability of Purkinje cells in rats exposed to EMF. The most prominent changes included afterhyperpolarization amplitude, spike frequency, half width and first spike latency. In conclusion, the results of the present study show that prenatal EMF exposure results in altered electrophysiological properties of Purkinje neurons. However, these changes may not be severe enough to alter the cerebellum-dependent functional tasks.
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Affiliation(s)
- M Haghani
- Department of Physiology, Shiraz University of Medical Sciences, Shiraz, Iran.
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Guan D, Armstrong WE, Foehring RC. Kv2 channels regulate firing rate in pyramidal neurons from rat sensorimotor cortex. J Physiol 2013; 591:4807-25. [PMID: 23878373 DOI: 10.1113/jphysiol.2013.257253] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The largest outward potassium current in the soma of neocortical pyramidal neurons is due to channels containing Kv2.1 α subunits. These channels have been implicated in cellular responses to seizures and ischaemia, mechanisms for intrinsic plasticity and cell death, and responsiveness to anaesthetic agents. Despite their abundance, knowledge of the function of these delayed rectifier channels has been limited by the lack of specific pharmacological agents. To test for functional roles of Kv2 channels in pyramidal cells from somatosensory or motor cortex of rats (layers 2/3 or 5), we transfected cortical neurons with DNA for a Kv2.1 pore mutant (Kv2.1W365C/Y380T: Kv2.1 DN) in an organotypic culture model to manipulate channel expression. Slices were obtained from rats at postnatal days (P7-P14) and maintained in organotypic culture. We used biolistic methods to transfect neurons with gold 'bullets' coated with DNA for the Kv2.1 DN and green fluorescent protein (GFP), GFP alone, or wild type (WT) Kv2.1 plus GFP. Cells that fluoresced green, contained a bullet and responded to positive or negative pressure from the recording pipette were considered to be transfected cells. In each slice, we recorded from a transfected cell and a control non-transfected cell from the same layer and area. Whole-cell voltage-clamp recordings obtained after 3-7 days in culture showed that cells transfected with the Kv2.1 DN had a significant reduction in outward current (∼45% decrease in the total current density measured 200 ms after onset of a voltage step from -78 to -2 mV). Transfection with GFP alone did not affect current amplitude and overexpression of the Kv2.1 WT resulted in greatly increased currents. Current-clamp experiments were used to assess the functional consequences of manipulation of Kv2.1 expression. The results suggest roles for Kv2 channels in controlling membrane potential during the interspike interval (ISI), firing rate, spike frequency adaptation (SFA) and the steady-state gain of firing. Specifically, firing rate and gain were reduced in the Kv2.1 DN cells. The most parsimonious explanation for the effects on firing is that in the absence of Kv2 channels, the membrane remains depolarized during the ISIs, preventing recovery of Na(+) channels from inactivation. Depolarization and the number of inactivated Na(+) channels would build with successive spikes, resulting in slower firing and enhanced spike frequency adaptation in the Kv2.1 DN cells.
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Affiliation(s)
- Dongxu Guan
- R. C. Foehring: Department of Anatomy & Neurobiology, University of Tennessee Health Science Center, 855 Monroe Avenue, Memphis, TN 38163, USA.
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Yang J, Ye M, Tian C, Yang M, Wang Y, Shu Y. Dopaminergic modulation of axonal potassium channels and action potential waveform in pyramidal neurons of prefrontal cortex. J Physiol 2013; 591:3233-51. [PMID: 23568892 DOI: 10.1113/jphysiol.2013.251058] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Voltage-gated K(+) (KV) channels play critical roles in shaping neuronal signals. KV channels distributed in the perisomatic regions and thick dendrites of cortical pyramidal neurons have been extensively studied. However, the properties and regulation of KV channels distributed in the thin axons remain unknown. In this study, by performing somatic and axonal patch-clamp recordings from layer 5 pyramidal neurons of prefrontal cortical slices, we showed that the rapidly inactivating A-currents mediated the transient K(+) currents evoked by action potential (AP) waveform command (KAP) at the soma, whereas the rapidly activating but slowly inactivating KV1-mediated D-currents dominated the KAP at the axon. In addition, activation of D1-like receptors for dopamine decreased the axonal K(+) currents, as a result of an increase in the activity of cAMP-PKA pathway. In contrast, activation of D2-like receptors showed an opposite effect on the axonal K(+) currents. Further experiments demonstrated that functional D1-like receptors were expressed at the main axon trunk and their activation could broaden the waveforms of axonal APs. Together, these results show that axonal KV channels were subjected to dopamine modulation, and this modulation could regulate the waveforms of propagating APs at the axon, suggesting an important role of dopaminergic modulation of axonal KV channels in regulating neuronal signalling.
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Affiliation(s)
- Jing Yang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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MicroRNA-301a mediated regulation of Kv4.2 in diabetes: identification of key modulators. PLoS One 2013; 8:e60545. [PMID: 23573265 PMCID: PMC3616003 DOI: 10.1371/journal.pone.0060545] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 02/27/2013] [Indexed: 12/27/2022] Open
Abstract
Diabetes is a metabolic disorder that ultimately results in major pathophysiological complications in the cardiovascular system. Diabetics are predisposed to higher incidences of sudden cardiac deaths (SCD). Several studies have associated diabetes as a major underlying risk for heart diseases and its complications. The diabetic heart undergoes remodeling to cope up with the underlying changes, however ultimately fails. In the present study we investigated the changes associated with a key ion channel and transcriptional factors in a diabetic heart model. In the mouse db/db model, we identified key transcriptional regulators and mediators that play important roles in the regulation of ion channel expression. Voltage-gated potassium channel (Kv4.2) is modulated in diabetes and is down regulated. We hypothesized that Kv4.2 expression is altered by potassium channel interacting protein-2 (KChIP2) which is regulated upstream by NFkB and miR-301a. We utilized qRT-PCR analysis and identified the genes that are affected in diabetes in a regional specific manner in the heart. At protein level we identified and validated differential expression of Kv4.2 and KChIP2 along with NFkB in both ventricles of diabetic hearts. In addition, we identified up-regulation of miR-301a in diabetic ventricles. We utilized loss and gain of function approaches to identify and validate the role of miR-301a in regulating Kv4.2. Based on in vivo and in vitro studies we conclude that miR-301a may be a central regulator for the expression of Kv4.2 in diabetes. This miR-301 mediated regulation of Kv4.2 is independent of NFkB and Irx5 and modulates Kv4.2 by direct binding on Kv4.2 3′untranslated region (3′-UTR). Therefore targeting miR-301a may offer new potential for developing therapeutic approaches.
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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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I(A) channels encoded by Kv1.4 and Kv4.2 regulate neuronal firing in the suprachiasmatic nucleus and circadian rhythms in locomotor activity. J Neurosci 2012; 32:10045-52. [PMID: 22815518 DOI: 10.1523/jneurosci.0174-12.2012] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Neurons in the suprachiasmatic nucleus (SCN) display coordinated circadian changes in electrical activity that are critical for daily rhythms in physiology, metabolism, and behavior. SCN neurons depolarize spontaneously and fire repetitively during the day and hyperpolarize, drastically reducing firing rates, at night. To explore the hypothesis that rapidly activating and inactivating A-type (I(A)) voltage-gated K(+) (Kv) channels, which are also active at subthreshold membrane potentials, are critical regulators of the excitability of SCN neurons, we examined locomotor activity and SCN firing in mice lacking Kv1.4 (Kv1.4(-/-)), Kv4.2 (Kv4.2(-/-)), or Kv4.3 (Kv4.3(-/-)), the pore-forming (α) subunits of I(A) channels. Mice lacking either Kv1.4 or Kv4.2 α subunits have markedly shorter (0.5 h) periods of locomotor activity than wild-type (WT) mice. In vitro extracellular multi-electrode recordings revealed that Kv1.4(-/-) and Kv4.2(-/-) SCN neurons display circadian rhythms in repetitive firing, but with shorter periods (0.5 h) than WT cells. In contrast, the periods of wheel-running activity in Kv4.3(-/-) mice and firing in Kv4.3(-/-) SCN neurons were indistinguishable from WT animals and neurons. Quantitative real-time PCR revealed that the transcripts encoding all three Kv channel α subunits, Kv1.4, Kv4.2, and Kv4.3, are expressed constitutively throughout the day and night in the SCN. Together, these results demonstrate that Kv1.4- and Kv4.2-encoded I(A) channels regulate the intrinsic excitability of SCN neurons during the day and night and determine the period and amplitude of circadian rhythms in SCN neuron firing and locomotor behavior.
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Affiliation(s)
- Robert C Foehring
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, 855 Monroe Avenue, Memphis, TN 38163, USA.
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40
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The sodium channel accessory subunit Navβ1 regulates neuronal excitability through modulation of repolarizing voltage-gated K⁺ channels. J Neurosci 2012; 32:5716-27. [PMID: 22539834 DOI: 10.1523/jneurosci.6450-11.2012] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The channel pore-forming α subunit Kv4.2 is a major constituent of A-type (I(A)) potassium currents and a key regulator of neuronal membrane excitability. Multiple mechanisms regulate the properties, subcellular targeting, and cell-surface expression of Kv4.2-encoded channels. In the present study, shotgun proteomic analyses of immunoprecipitated mouse brain Kv4.2 channel complexes unexpectedly identified the voltage-gated Na⁺ channel accessory subunit Navβ1. Voltage-clamp and current-clamp recordings revealed that knockdown of Navβ1 decreases I(A) densities in isolated cortical neurons and that action potential waveforms are prolonged and repetitive firing is increased in Scn1b-null cortical pyramidal neurons lacking Navβ1. Biochemical and voltage-clamp experiments further demonstrated that Navβ1 interacts with and increases the stability of the heterologously expressed Kv4.2 protein, resulting in greater total and cell-surface Kv4.2 protein expression and in larger Kv4.2-encoded current densities. Together, the results presented here identify Navβ1 as a component of native neuronal Kv4.2-encoded I(A) channel complexes and a novel regulator of I(A) channel densities and neuronal excitability.
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Carrasquillo Y, Burkhalter A, Nerbonne JM. A-type K+ channels encoded by Kv4.2, Kv4.3 and Kv1.4 differentially regulate intrinsic excitability of cortical pyramidal neurons. J Physiol 2012; 590:3877-90. [PMID: 22615428 DOI: 10.1113/jphysiol.2012.229013] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Rapidly activating and rapidly inactivating voltage-gated A-type K+ currents, IA, are key determinants of neuronal excitability and several studies suggest a critical role for the Kv4.2 pore-forming α subunit in the generation of IA channels in hippocampal and cortical pyramidal neurons. The experiments here demonstrate that Kv4.2, Kv4.3 and Kv1.4 all contribute to the generation of IA channels in mature cortical pyramidal (CP) neurons and that Kv4.2-, Kv4.3- and Kv1.4-encoded IA channels play distinct roles in regulating the intrinsic excitability and the firing properties of mature CP neurons. In vivo loss of Kv4.2, for example, alters the input resistances, current thresholds for action potential generation and action potential repolarization of mature CP neurons. Elimination of Kv4.3 also prolongs action potential duration, whereas the input resistances and the current thresholds for action potential generation in Kv4.3−/− and WT CP neurons are indistinguishable. In addition, although increased repetitive firing was observed in both Kv4.2−/− and Kv4.3−/− CP neurons, the increases in Kv4.2−/− CP neurons were observed in response to small, but not large, amplitude depolarizing current injections, whereas firing rates were higher in Kv4.3−/− CP neurons only with large amplitude current injections. In vivo loss of Kv1.4, in contrast, had minimal effects on the intrinsic excitability and the firing properties of mature CP neurons. Comparison of the effects of pharmacological blockade of Kv4-encoded currents in Kv1.4−/− and WT CP neurons, however, revealed that Kv1.4-encoded IA channels do contribute to controlling resting membrane potentials, the regulation of current thresholds for action potential generation and repetitive firing rates in mature CP neurons.
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Affiliation(s)
- Yarimar Carrasquillo
- Department of Developmental Biology, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8103, St Louis, MO 63110, USA
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Foeger NC, Norris AJ, Wren LM, Nerbonne JM. Augmentation of Kv4.2-encoded currents by accessory dipeptidyl peptidase 6 and 10 subunits reflects selective cell surface Kv4.2 protein stabilization. J Biol Chem 2012; 287:9640-50. [PMID: 22311982 DOI: 10.1074/jbc.m111.324574] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Rapidly activating and inactivating somatodendritic voltage-gated K(+) (Kv) currents, I(A), play critical roles in the regulation of neuronal excitability. Considerable evidence suggests that native neuronal I(A) channels function in macromolecular protein complexes comprising pore-forming (α) subunits of the Kv4 subfamily together with cytosolic, K(+) channel interacting proteins (KChIPs) and transmembrane, dipeptidyl peptidase 6 and 10 (DPP6/10) accessory subunits, as well as other accessory and regulatory proteins. Several recent studies have demonstrated a critical role for the KChIP subunits in the generation of native Kv4.2-encoded channels and that Kv4.2-KChIP complex formation results in mutual (Kv4.2-KChIP) protein stabilization. The results of the experiments here, however, demonstrate that expression of DPP6 in the mouse cortex is unaffected by the targeted deletion of Kv4.2 and/or Kv4.3. Further experiments revealed that heterologously expressed DPP6 and DPP10 localize to the cell surface in the absence of Kv4.2, and that co-expression with Kv4.2 does not affect total or cell surface DPP6 or DPP10 protein levels. In the presence of DPP6 or DPP10, however, cell surface Kv4.2 protein expression is selectively increased. Further addition of KChIP3 in the presence of DPP10 markedly increases total and cell surface Kv4.2 protein levels, compared with cells expressing only Kv4.2 and DPP10. Taken together, the results presented here demonstrate that the expression and localization of the DPP accessory subunits are independent of Kv4 α subunits and further that the DPP6/10 and KChIP accessory subunits independently stabilize the surface expression of Kv4.2.
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Affiliation(s)
- Nicholas C Foeger
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Sethi J, Sanchez-Alavez M, Tabarean IV. Kv4.2 mediates histamine modulation of preoptic neuron activity and body temperature. PLoS One 2011; 6:e29134. [PMID: 22220205 PMCID: PMC3248414 DOI: 10.1371/journal.pone.0029134] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Accepted: 11/21/2011] [Indexed: 11/28/2022] Open
Abstract
Histamine regulates arousal, circadian rhythms, and thermoregulation. Activation of H3 histamine receptors expressed by preoptic GABAergic neurons results in a decrease of their firing rate and hyperthermia. Here we report that an increase in the A-type K+ current in preoptic GABAergic neurons in response to activation of H3 histamine receptors results in decreased firing rate and hyperthermia in mice. The Kv4.2 subunit is required for these actions in spite of the fact that Kv4.2−/− preoptic GABAergic neurons display A-type currents and firing characteristics similar to those of wild-type neurons. This electrical remodeling is achieved by robust upregulation of the expression of the Kv4.1 subunit and of a delayed rectifier current. Dynamic clamp experiments indicate that enhancement of the A-type current by a similar amount to that induced by histamine is sufficient to mimic its robust effect on firing rates. These data indicate a central role played by the Kv4.2 subunit in histamine regulation of body temperature and its interaction with pERK1/2 downstream of the H3 receptor. We also reveal that this pathway provides a mechanism for selective modulation of body temperature at the beginning of the active phase of the circadian cycle.
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Affiliation(s)
- Jasmine Sethi
- The Department of Molecular and Integrative Neurosciences, The Scripps Research Institute, La Jolla, California, United States of America
| | - Manuel Sanchez-Alavez
- The Department of Molecular and Integrative Neurosciences, The Scripps Research Institute, La Jolla, California, United States of America
| | - Iustin V. Tabarean
- The Department of Molecular and Integrative Neurosciences, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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Guan D, Horton LR, Armstrong WE, Foehring RC. Postnatal development of A-type and Kv1- and Kv2-mediated potassium channel currents in neocortical pyramidal neurons. J Neurophysiol 2011; 105:2976-88. [PMID: 21451062 DOI: 10.1152/jn.00758.2010] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Potassium channels regulate numerous aspects of neuronal excitability, and several voltage-gated K(+) channel subunits have been identified in pyramidal neurons of rat neocortex. Previous studies have either considered the development of outward current as a whole or divided currents into transient, A-type and persistent, delayed rectifier components but did not differentiate between current components defined by α-subunit type. To facilitate comparisons of studies reporting K(+) currents from animals of different ages and to understand the functional roles of specific current components, we characterized the postnatal development of identified Kv channel-mediated currents in pyramidal neurons from layers II/III from rat somatosensory cortex. Both the persistent/slowly inactivating and transient components of the total K(+) current increased in density with postnatal age. We used specific pharmacological agents to test the relative contributions of putative Kv1- and Kv2-mediated currents (100 nM α-dendrotoxin and 600 nM stromatoxin, respectively). A combination of voltage protocol, pharmacology, and curve fitting was used to isolate the rapidly inactivating A-type current. We found that the density of all identified current components increased with postnatal age, approaching a plateau at 3-5 wk. We found no significant changes in the relative proportions or kinetics of any component between postnatal weeks 1 and 5, except that the activation time constant for A-type current was longer at 1 wk. The putative Kv2-mediated component was the largest at all ages. Immunocytochemistry indicated that protein expression for Kv4.2, Kv4.3, Kv1.4, and Kv2.1 increased between 1 wk and 4-5 wk of age.
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Affiliation(s)
- Dongxu Guan
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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Ping Y, Waro G, Licursi A, Smith S, Vo-Ba DA, Tsunoda S. Shal/K(v)4 channels are required for maintaining excitability during repetitive firing and normal locomotion in Drosophila. PLoS One 2011; 6:e16043. [PMID: 21264215 PMCID: PMC3022017 DOI: 10.1371/journal.pone.0016043] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2010] [Accepted: 12/03/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Rhythmic behaviors, such as walking and breathing, involve the coordinated activity of central pattern generators in the CNS, sensory feedback from the PNS, to motoneuron output to muscles. Unraveling the intrinsic electrical properties of these cellular components is essential to understanding this coordinated activity. Here, we examine the significance of the transient A-type K(+) current (I(A)), encoded by the highly conserved Shal/K(v)4 gene, in neuronal firing patterns and repetitive behaviors. While I(A) is present in nearly all neurons across species, elimination of I(A) has been complicated in mammals because of multiple genes underlying I(A), and/or electrical remodeling that occurs in response to affecting one gene. METHODOLOGY/PRINCIPAL FINDINGS In Drosophila, the single Shal/K(v)4 gene encodes the predominant I(A) current in many neuronal cell bodies. Using a transgenically expressed dominant-negative subunit (DNK(v)4), we show that I(A) is completely eliminated from cell bodies, with no effect on other currents. Most notably, DNK(v)4 neurons display multiple defects during prolonged stimuli. DNK(v)4 neurons display shortened latency to firing, a lower threshold for repetitive firing, and a progressive decrement in AP amplitude to an adapted state. We record from identified motoneurons and show that Shal/K(v)4 channels are similarly required for maintaining excitability during repetitive firing. We then examine larval crawling, and adult climbing and grooming, all behaviors that rely on repetitive firing. We show that all are defective in the absence of Shal/K(v)4 function. Further, knock-out of Shal/K(v)4 function specifically in motoneurons significantly affects the locomotion behaviors tested. CONCLUSIONS/SIGNIFICANCE Based on our results, Shal/K(v)4 channels regulate the initiation of firing, enable neurons to continuously fire throughout a prolonged stimulus, and also influence firing frequency. This study shows that Shal/K(v)4 channels play a key role in repetitively firing neurons during prolonged input/output, and suggests that their function and regulation are important for rhythmic behaviors.
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Affiliation(s)
- Yong Ping
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Girma Waro
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Ashley Licursi
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Sarah Smith
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Dai-An Vo-Ba
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Susan Tsunoda
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
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Bourdeau ML, Laplante I, Laurent CE, Lacaille JC. KChIP1 modulation of Kv4.3-mediated A-type K(+) currents and repetitive firing in hippocampal interneurons. Neuroscience 2010; 176:173-87. [PMID: 21129448 DOI: 10.1016/j.neuroscience.2010.11.051] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 11/20/2010] [Accepted: 11/23/2010] [Indexed: 11/18/2022]
Abstract
Neuronal A-type K(+) channels regulate action potential waveform, back-propagation and firing frequency. In hippocampal CA1 interneurons located at the stratum lacunosum-moleculare/radiatum junction (LM/RAD), Kv4.3 mediates A-type K(+) currents and a Kv4 β-subunit of the Kv channel interacting protein (KChIP) family, KChIP1, appears specifically expressed in these cells. However, the functional role of this accessory subunit in A-type K(+) currents and interneuron excitability remains largely unknown. Thus, first we studied KChIP1 and Kv4.3 channel interactions in human embryonic kidney 293 (HEK293) cells and determined that KChIP1 coexpression modulated the biophysical properties of Kv4.3 A-type currents (faster recovery from inactivation, leftward shift of activation curve, faster rise time and slower decay) and this modulation was selectively prevented by KChIP1 short interfering RNA (siRNA) knockdown. Next, we evaluated the effects of KChIP1 down-regulation by siRNA on A-type K(+) currents in LM/RAD interneurons in slice cultures. Recovery from inactivation of A-type K(+) currents was slower after KChIP1 down-regulation but other properties were unchanged. In addition, down-regulation of KChIP1 levels did not affect action potential waveform and firing, but increased firing frequency during suprathreshold depolarizations, indicating that KChIP1 regulates interneuron excitability. The effects of KChIP1 down-regulation were cell-specific since CA1 pyramidal cells that do not express KChIP1 were unaffected. Overall, our findings suggest that KChIP1 interacts with Kv4.3 in LM/RAD interneurons, enabling faster recovery from inactivation of A-type currents and thus promoting stronger inhibitory control of firing during sustained activity.
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Affiliation(s)
- M L Bourdeau
- Département de Physiologie, Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
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Interdependent roles for accessory KChIP2, KChIP3, and KChIP4 subunits in the generation of Kv4-encoded IA channels in cortical pyramidal neurons. J Neurosci 2010; 30:13644-55. [PMID: 20943905 DOI: 10.1523/jneurosci.2487-10.2010] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The rapidly activating and inactivating voltage-dependent outward K(+) (Kv) current, I(A), is widely expressed in central and peripheral neurons. I(A) has long been recognized to play important roles in determining neuronal firing properties and regulating neuronal excitability. Previous work demonstrated that Kv4.2 and Kv4.3 α-subunits are the primary determinants of I(A) in mouse cortical pyramidal neurons. Accumulating evidence indicates that native neuronal Kv4 channels function in macromolecular protein complexes that contain accessory subunits and other regulatory molecules. The K(+) channel interacting proteins (KChIPs) are among the identified Kv4 channel accessory subunits and are thought to be important for the formation and functioning of neuronal Kv4 channel complexes. Molecular genetic, biochemical, and electrophysiological approaches were exploited in the experiments described here to examine directly the roles of KChIPs in the generation of functional Kv4-encoded I(A) channels. These combined experiments revealed that KChIP2, KChIP3, and KChIP4 are robustly expressed in adult mouse posterior (visual) cortex and that all three proteins coimmunoprecipitate with Kv4.2. In addition, in cortical pyramidal neurons from mice lacking KChIP3 (KChIP3(-/-)), mean I(A) densities were reduced modestly, whereas in mean I(A) densities in KChIP2(-/-) and WT neurons were not significantly different. Interestingly, in both KChIP3(-/-) and KChIP2(-/-) cortices, the expression levels of the other KChIPs (KChIP2 and 4 or KChIP3 and 4, respectively) were increased. In neurons expressing constructs to mediate simultaneous RNA interference-induced reductions in the expression of KChIP2, 3, and 4, I(A) densities were markedly reduced and Kv current remodeling was evident.
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Shabani M, Hosseinmardi N, Haghani M, Shaibani V, Janahmadi M. Maternal exposure to the CB1 cannabinoid agonist WIN 55212-2 produces robust changes in motor function and intrinsic electrophysiological properties of cerebellar Purkinje neurons in rat offspring. Neuroscience 2010; 172:139-52. [PMID: 20969930 DOI: 10.1016/j.neuroscience.2010.10.031] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Revised: 10/07/2010] [Accepted: 10/09/2010] [Indexed: 01/18/2023]
Abstract
The cerebellum, which controls coordinated and rapid movements, is a potential target for the deleterious effects of drugs of abuse including cannabis (i.e. marijuana, cannabinoids). Prenatal exposure to cannabinoids has been documented to cause abnormalities in motor and cognitive development, but the exact mechanism of this effect at the cellular level has not been fully elucidated. Previous studies indicate that cannabinoids are capable of modulating synaptic neurotransmission. In addition to altering synaptic activity, cannabinoid exposure may also change intrinsic neuronal properties. In the present study several different approaches including behavioral assays, extracellular field potential recordings and whole-cell patch clamp recordings, were used to address whether maternal exposure to the CB1 cannabinoid receptor agonist WIN 55-212-2 (WIN) affects the intrinsic electrophysiological properties of Purkinje neurons. WIN treatment of pregnant rats produced a significant decrease in the rearing frequency, total distance moved and mobility of the offspring, but significantly increased the time of the righting reflex, the grooming frequency and immobility. Neuromotor function, as assessed in the grip test and balance beam test, was also significantly impaired in prenatally WIN-treated group. Prenatal exposure to WIN increased the amplitude of population spikes (PS) recorded from the cerebellar Purkinje cell layer of offspring following synaptic blockage. WIN treatment of pregnant rats also profoundly affected the intrinsic properties of Purkinje neurons in offspring. This treatment increased the firing regularity, firing frequency, amplitude of afterhyperpolarization (AHP), the peak amplitude of action potential and the first spike latency, but decreased significantly the time to peak and duration of action potentials, the instantaneous firing frequency, the rate of rebound action potential and the voltage "sag" ratio. These results raise the possibility that maternal exposure to cannabinoids may profoundly affect the intrinsic membrane properties of cerebellar Purkinje neurons of offspring by altering the membrane excitability through modulation of intrinsic ion channels.
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Affiliation(s)
- M Shabani
- Neuroscience Research Centre and Department of Physiology, Medical School, Shahid Beheshti University of Medical Sciences, Evin, Tehran, Islamic Republic of Iran
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Marionneau C, Townsend RR, Nerbonne JM. Proteomic analysis highlights the molecular complexities of native Kv4 channel macromolecular complexes. Semin Cell Dev Biol 2010; 22:145-52. [PMID: 20959143 DOI: 10.1016/j.semcdb.2010.10.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2010] [Revised: 10/07/2010] [Accepted: 10/08/2010] [Indexed: 01/24/2023]
Abstract
Voltage-gated K(+) (Kv) channels are key determinants of membrane excitability in the nervous and cardiovascular systems, functioning to control resting membrane potentials, shape action potential waveforms and influence the responses to neurotransmitters and neurohormones. Consistent with this functional diversity, multiple types of Kv currents, with distinct biophysical properties and cellular/subcellular distributions, have been identified. Rapidly activating and inactivating Kv currents, typically referred to as I(A) (A-type) in neurons, for example, regulate repetitive firing rates, action potential back-propagation (into dendrites) and modulate synaptic responses. Currents with similar properties, referred to as I(to,f) (fast transient outward), expressed in cardiomyocytes, control the early phase of myocardial action potential repolarization. A number of studies have demonstrated critical roles for pore-forming (α) subunits of the Kv4 subfamily in the generation of native neuronal I(A) and cardiac I(to,f) channels. Studies in heterologous cells have also suggested important roles for a number of Kv channel accessory and regulatory proteins in the generation of functional I(A) and I(to,f) channels. Quantitative mass spectrometry-based proteomic analysis is increasingly recognized as a rapid and, importantly, unbiased, approach to identify the components of native macromolecular protein complexes. The recent application of proteomic approaches to identify the components of native neuronal (and cardiac) Kv4 channel complexes has revealed even greater complexity than anticipated. The continued emphasis on development of improved biochemical and analytical proteomic methods seems certain to accelerate progress and to provide important new insights into the molecular determinants of native ion channel protein complexes.
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Affiliation(s)
- Céline Marionneau
- L'Institut du Thorax, INSERM UMR-915, Institut de Recherche Thérapeutique-Université de Nantes, Nantes, France
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Song Z, Gomes DA, Stevens W, Sladek CD. Multiple alpha1-adrenergic receptor subtypes support synergistic stimulation of vasopressin and oxytocin release by ATP and phenylephrine. Am J Physiol Regul Integr Comp Physiol 2010; 299:R1529-37. [PMID: 20881098 DOI: 10.1152/ajpregu.00532.2010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Simultaneous exposure of explants of the hypothalamo-neurohypophyseal system (HNS) to ATP and the α(1)-adrenergic receptor (α(1)-R) agonist, phenylephrine (ATP+PE) induces a synergistic stimulation of vasopressin and oxytocin (VP/OT) release that is sustained for hours. The current studies confirm that the synergism is dependent upon activation of α(1)-R by demonstrating that an α(1)-R antagonist prevents the response. The role of the α(1)A, B, and D-adrenergic receptor subtypes in the synergistic effect of ATP+PE on intracellular calcium ([Ca(2+)](i)) in supraoptic nucleus (SON) neurons and VP/OT release from neural lobe was evaluated. The increase in [Ca(2+)](i) induced by PE in SON predominantly reflects release from intracellular stores and is mediated by activation of the α(1)A adrenergic receptor subtype. The α(1)A subtype is also required for the sustained elevation in [Ca(2+)](i) induced by ATP+PE. In contrast, although synergistic stimulation of VP/OT release was eliminated by removal of PE and was blunted by benoxathian, an α(1)-R antagonist that is not subtype selective, no single α(1)-R subtype selective antagonist prevented sustained stimulation of VP/OT release by ATP+PE. Thus, sustained activation of α(1)-R is essential for the synergistic VP and OT response to ATP+PE, but multiple α(1)-R subtypes can support the response. Redundancy amongst the α(1)-R subunits in supporting this response is consistent with the predicted importance of the response for sustaining the elevated VP release required to prevent cardiovascular collapse during hemorrhage and sepsis.
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Affiliation(s)
- Zhilin Song
- Dept. of Physiology and Biophysics, Univ. of Colorado, School of Medicine, 12800 E. 19 Ave, Aurora, CO 80045, USA
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