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Ratté S, Lankarany M, Rho YA, Patterson A, Prescott SA. Subthreshold membrane currents confer distinct tuning properties that enable neurons to encode the integral or derivative of their input. Front Cell Neurosci 2015; 8:452. [PMID: 25620913 PMCID: PMC4288132 DOI: 10.3389/fncel.2014.00452] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Accepted: 12/15/2014] [Indexed: 11/25/2022] Open
Abstract
Neurons rely on action potentials, or spikes, to encode information. But spikes can encode different stimulus features in different neurons. We show here through simulations and experiments how neurons encode the integral or derivative of their input based on the distinct tuning properties conferred upon them by subthreshold currents. Slow-activating subthreshold inward (depolarizing) current mediates positive feedback control of subthreshold voltage, sustaining depolarization and allowing the neuron to spike on the basis of its integrated stimulus waveform. Slow-activating subthreshold outward (hyperpolarizing) current mediates negative feedback control of subthreshold voltage, truncating depolarization and forcing the neuron to spike on the basis of its differentiated stimulus waveform. Depending on its direction, slow-activating subthreshold current cooperates or competes with fast-activating inward current during spike initiation. This explanation predicts that sensitivity to the rate of change of stimulus intensity differs qualitatively between integrators and differentiators. This was confirmed experimentally in spinal sensory neurons that naturally behave as specialized integrators or differentiators. Predicted sensitivity to different stimulus features was confirmed by covariance analysis. Integration and differentiation, which are themselves inverse operations, are thus shown to be implemented by the slow feedback mediated by oppositely directed subthreshold currents expressed in different neurons.
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Affiliation(s)
- Stéphanie Ratté
- Neurosciences and Mental Health, The Hospital for Sick Children Toronto, ON, Canada ; Department of Physiology and Institute of Biomaterials and Biomedical Engineering, University of Toronto Toronto, ON, Canada ; Pittsburgh Center for Pain Research, University of Pittsburgh Pittsburgh, PA, USA
| | - Milad Lankarany
- Neurosciences and Mental Health, The Hospital for Sick Children Toronto, ON, Canada ; Department of Physiology and Institute of Biomaterials and Biomedical Engineering, University of Toronto Toronto, ON, Canada
| | - Young-Ah Rho
- Pittsburgh Center for Pain Research, University of Pittsburgh Pittsburgh, PA, USA
| | - Adam Patterson
- Neurosciences and Mental Health, The Hospital for Sick Children Toronto, ON, Canada
| | - Steven A Prescott
- Neurosciences and Mental Health, The Hospital for Sick Children Toronto, ON, Canada ; Department of Physiology and Institute of Biomaterials and Biomedical Engineering, University of Toronto Toronto, ON, Canada ; Pittsburgh Center for Pain Research, University of Pittsburgh Pittsburgh, PA, USA
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52
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Ilin V, Stevenson IH, Volgushev M. Injection of fully-defined signal mixtures: a novel high-throughput tool to study neuronal encoding and computations. PLoS One 2014; 9:e109928. [PMID: 25335081 PMCID: PMC4204817 DOI: 10.1371/journal.pone.0109928] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Accepted: 09/05/2014] [Indexed: 12/18/2022] Open
Abstract
Understanding of how neurons transform fluctuations of membrane potential, reflecting input activity, into spike responses, which communicate the ultimate results of single-neuron computation, is one of the central challenges for cellular and computational neuroscience. To study this transformation under controlled conditions, previous work has used a signal immersed in noise paradigm where neurons are injected with a current consisting of fluctuating noise that mimics on-going synaptic activity and a systematic signal whose transmission is studied. One limitation of this established paradigm is that it is designed to examine the encoding of only one signal under a specific, repeated condition. As a result, characterizing how encoding depends on neuronal properties, signal parameters, and the interaction of multiple inputs is cumbersome. Here we introduce a novel fully-defined signal mixture paradigm, which allows us to overcome these problems. In this paradigm, current for injection is synthetized as a sum of artificial postsynaptic currents (PSCs) resulting from the activity of a large population of model presynaptic neurons. PSCs from any presynaptic neuron(s) can be now considered as "signal", while the sum of all other inputs is considered as "noise". This allows us to study the encoding of a large number of different signals in a single experiment, thus dramatically increasing the throughput of data acquisition. Using this novel paradigm, we characterize the detection of excitatory and inhibitory PSCs from neuronal spike responses over a wide range of amplitudes and firing-rates. We show, that for moderately-sized neuronal populations the detectability of individual inputs is higher for excitatory than for inhibitory inputs during the 2-5 ms following PSC onset, but becomes comparable after 7-8 ms. This transient imbalance of sensitivity in favor of excitation may enhance propagation of balanced signals through neuronal networks. Finally, we discuss several open questions that this novel high-throughput paradigm may address.
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Affiliation(s)
- Vladimir Ilin
- Department of Psychology, University of Connecticut, Storrs, Connecticut, United States of America
| | - Ian H. Stevenson
- Department of Psychology, University of Connecticut, Storrs, Connecticut, United States of America
| | - Maxim Volgushev
- Department of Psychology, University of Connecticut, Storrs, Connecticut, United States of America
- * E-mail:
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53
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Jones KS, Corbin JG, Huntsman MM. Neonatal NMDA receptor blockade disrupts spike timing and glutamatergic synapses in fast spiking interneurons in a NMDA receptor hypofunction model of schizophrenia. PLoS One 2014; 9:e109303. [PMID: 25290690 PMCID: PMC4188593 DOI: 10.1371/journal.pone.0109303] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 09/10/2014] [Indexed: 01/06/2023] Open
Abstract
The dysfunction of parvalbumin-positive, fast-spiking interneurons (FSI) is considered a primary contributor to the pathophysiology of schizophrenia (SZ), but deficits in FSI physiology have not been explicitly characterized. We show for the first time, that a widely-employed model of schizophrenia minimizes first spike latency and increases GluN2B-mediated current in neocortical FSIs. The reduction in FSI first-spike latency coincides with reduced expression of the Kv1.1 potassium channel subunit which provides a biophysical explanation for the abnormal spiking behavior. Similarly, the increase in NMDA current coincides with enhanced expression of the GluN2B NMDA receptor subunit, specifically in FSIs. In this study mice were treated with the NMDA receptor antagonist, MK-801, during the first week of life. During adolescence, we detected reduced spike latency and increased GluN2B-mediated NMDA current in FSIs, which suggests transient disruption of NMDA signaling during neonatal development exerts lasting changes in the cellular and synaptic physiology of neocortical FSIs. Overall, we propose these physiological disturbances represent a general impairment to the physiological maturation of FSIs which may contribute to schizophrenia-like behaviors produced by this model.
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Affiliation(s)
- Kevin S. Jones
- Biology Department, Howard University, Washington, DC, United States of America
- Center for Neuroscience Research, Children’s National Medical Center, Washington, DC, United States of America
| | - Joshua G. Corbin
- Center for Neuroscience Research, Children’s National Medical Center, Washington, DC, United States of America
| | - Molly M. Huntsman
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, and Department of Pediatrics, School of Medicine, University of Colorado, Anschutz Medical Campus, Aurora, CO, United States of America
- * E-mail:
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54
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Sosanya NM, Brager DH, Wolfe S, Niere F, Raab-Graham KF. Rapamycin reveals an mTOR-independent repression of Kv1.1 expression during epileptogenesis. Neurobiol Dis 2014; 73:96-105. [PMID: 25270294 DOI: 10.1016/j.nbd.2014.09.011] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 08/11/2014] [Accepted: 09/21/2014] [Indexed: 01/12/2023] Open
Abstract
Changes in ion channel expression are implicated in the etiology of epilepsy. However, the molecular leading to long-term aberrant expression of ion channels are not well understood. The mechanistic/mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that mediates activity-dependent protein synthesis in neurons. mTOR is overactive in epilepsy, suggesting that excessive protein synthesis may contribute to the neuronal pathology. In contrast, we found that mTOR activity and the microRNA miR-129-5p reduce the expression of the voltage-gated potassium channel Kv1.1 in an animal model of temporal lobe epilepsy (TLE). When mTOR activity is low, Kv1.1 expression is high and the frequency of behavioral seizures is low. However, as behavioral seizure activity rises, mTOR activity increases and Kv1.1 protein levels drop. In CA1 pyramidal neurons, the reduction in Kv1.1 lowers the threshold for action potential firing. Interestingly, blocking mTOR activity with rapamycin reduces behavioral seizures and temporarily keeps Kv1.1 levels elevated. Overtime, seizure activity increases and Kv1.1 protein decreases in all animals, even those treated with rapamycin. Notably, the concentration of miR-129-5p, the negative regulator of Kv1.1 mRNA translation, increases by 21days post-status epilepticus (SE), sustaining Kv1.1 mRNA translational repression. Our results suggest that following kainic-acid induced status epilepticus there are two phases of Kv1.1 repression: (1) an initial mTOR-dependent repression of Kv1.1 that is followed by (2) a miR-129-5p persistent reduction of Kv1.1.
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Affiliation(s)
- Natasha M Sosanya
- Center for Learning and Memory, Department of Neuroscience, University of Texas at Austin, USA; Institute for Cell and Molecular Biology, University of Texas at Austin, USA
| | - Darrin H Brager
- Center for Learning and Memory, Department of Neuroscience, University of Texas at Austin, USA
| | - Sarah Wolfe
- Institute for Cell and Molecular Biology, University of Texas at Austin, USA; Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin University Station C7000, Austin, TX 78712, USA
| | - Farr Niere
- Center for Learning and Memory, Department of Neuroscience, University of Texas at Austin, USA
| | - Kimberly F Raab-Graham
- Center for Learning and Memory, Department of Neuroscience, University of Texas at Austin, USA; Institute for Cell and Molecular Biology, University of Texas at Austin, USA; Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin University Station C7000, Austin, TX 78712, USA.
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55
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Fontaine B, MacLeod KM, Lubejko ST, Steinberg LJ, Köppl C, Peña JL. Emergence of band-pass filtering through adaptive spiking in the owl's cochlear nucleus. J Neurophysiol 2014; 112:430-45. [PMID: 24790170 DOI: 10.1152/jn.00132.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the visual, auditory, and electrosensory modalities, stimuli are defined by first- and second-order attributes. The fast time-pressure signal of a sound, a first-order attribute, is important, for instance, in sound localization and pitch perception, while its slow amplitude-modulated envelope, a second-order attribute, can be used for sound recognition. Ascending the auditory pathway from ear to midbrain, neurons increasingly show a preference for the envelope and are most sensitive to particular envelope modulation frequencies, a tuning considered important for encoding sound identity. The level at which this tuning property emerges along the pathway varies across species, and the mechanism of how this occurs is a matter of debate. In this paper, we target the transition between auditory nerve fibers and the cochlear nucleus angularis (NA). While the owl's auditory nerve fibers simultaneously encode the fast and slow attributes of a sound, one synapse further, NA neurons encode the envelope more efficiently than the auditory nerve. Using in vivo and in vitro electrophysiology and computational analysis, we show that a single-cell mechanism inducing spike threshold adaptation can explain the difference in neural filtering between the two areas. We show that spike threshold adaptation can explain the increased selectivity to modulation frequency, as input level increases in NA. These results demonstrate that a spike generation nonlinearity can modulate the tuning to second-order stimulus features, without invoking network or synaptic mechanisms.
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Affiliation(s)
- Bertrand Fontaine
- Dominick Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York;
| | - Katrina M MacLeod
- Department of Biology, Neuroscience and Cognitive Science Program, University of Maryland, College Park, Maryland; and
| | - Susan T Lubejko
- Department of Biology, Neuroscience and Cognitive Science Program, University of Maryland, College Park, Maryland; and
| | - Louisa J Steinberg
- Dominick Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Christine Köppl
- Cluster of Excellence "Hearing4all" and Research Center Neurosensory Science and Department of Neuroscience School of Medicine and Health Science, Carl von Ossietzky University, Oldenburg, Germany
| | - Jose L Peña
- Dominick Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
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56
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Fontaine B, Peña JL, Brette R. Spike-threshold adaptation predicted by membrane potential dynamics in vivo. PLoS Comput Biol 2014; 10:e1003560. [PMID: 24722397 PMCID: PMC3983065 DOI: 10.1371/journal.pcbi.1003560] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Accepted: 02/21/2014] [Indexed: 11/18/2022] Open
Abstract
Neurons encode information in sequences of spikes, which are triggered when their membrane potential crosses a threshold. In vivo, the spiking threshold displays large variability suggesting that threshold dynamics have a profound influence on how the combined input of a neuron is encoded in the spiking. Threshold variability could be explained by adaptation to the membrane potential. However, it could also be the case that most threshold variability reflects noise and processes other than threshold adaptation. Here, we investigated threshold variation in auditory neurons responses recorded in vivo in barn owls. We found that spike threshold is quantitatively predicted by a model in which the threshold adapts, tracking the membrane potential at a short timescale. As a result, in these neurons, slow voltage fluctuations do not contribute to spiking because they are filtered by threshold adaptation. More importantly, these neurons can only respond to input spikes arriving together on a millisecond timescale. These results demonstrate that fast adaptation to the membrane potential captures spike threshold variability in vivo. Neurons spike when their membrane potential exceeds a threshold value, but this value has been shown to be variable in the same neuron recorded in vivo. This variability could reflect noise, or deterministic processes that make the threshold vary with the membrane potential. The second alternative would have important functional consequences. Here, we show that threshold variability is a genuine feature of neurons, which reflects adaptation to the membrane potential at a short timescale, with little contribution from noise. This demonstrates that a deterministic model can predict spikes based only on the membrane potential.
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Affiliation(s)
- Bertrand Fontaine
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - José Luis Peña
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Romain Brette
- Laboratoire Psychologie de la Perception, CNRS and Université Paris Descartes, Paris, France
- Département d'Etudes Cognitives, Ecole Normale Supérieure, Paris, France
- Sorbonne Universités, UPMC Univ. Paris 06, UMR_S 968, Institut de la Vision, Paris, France
- INSERM, U968, Paris, France
- CNRS, UMR_7210, Paris, France
- * E-mail:
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57
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Brette R. Sharpness of spike initiation in neurons explained by compartmentalization. PLoS Comput Biol 2013; 9:e1003338. [PMID: 24339755 PMCID: PMC3854010 DOI: 10.1371/journal.pcbi.1003338] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 09/30/2013] [Indexed: 11/23/2022] Open
Abstract
In cortical neurons, spikes are initiated in the axon initial segment. Seen at the soma, they appear surprisingly sharp. A standard explanation is that the current coming from the axon becomes sharp as the spike is actively backpropagated to the soma. However, sharp initiation of spikes is also seen in the input–output properties of neurons, and not only in the somatic shape of spikes; for example, cortical neurons can transmit high frequency signals. An alternative hypothesis is that Na channels cooperate, but it is not currently supported by direct experimental evidence. I propose a simple explanation based on the compartmentalization of spike initiation. When Na channels are placed in the axon, the soma acts as a current sink for the Na current. I show that there is a critical distance to the soma above which an instability occurs, so that Na channels open abruptly rather than gradually as a function of somatic voltage. Spike initiation determines how the combined inputs to a neuron are converted to an output. Since the pioneering work of Hodgkin and Huxley, it is known that spikes are generated by the opening of sodium channels with depolarization. According to this standard theory, these channels should open gradually when the membrane potential increases, but spikes measured at the soma appear to suddenly rise from rest. This apparent contradiction has triggered a controversy about the origin of spike “sharpness.” This study shows with biophysical modelling that if sodium channels are placed in the axon rather than in the soma, they open all at once when the somatic membrane potential exceeds a critical value. This work explains the sharpness of spike initiation and provides another demonstration that morphology plays a critical role in neural function.
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Affiliation(s)
- Romain Brette
- Laboratoire Psychologie de la Perception, CNRS and Université Paris Descartes, Paris, France
- Equipe Audition, Département d'Etudes Cognitives, Ecole Normale Supérieure, Paris, France
- * E-mail:
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58
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Kirchheim F, Tinnes S, Haas CA, Stegen M, Wolfart J. Regulation of action potential delays via voltage-gated potassium Kv1.1 channels in dentate granule cells during hippocampal epilepsy. Front Cell Neurosci 2013; 7:248. [PMID: 24367293 PMCID: PMC3852106 DOI: 10.3389/fncel.2013.00248] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 11/20/2013] [Indexed: 11/13/2022] Open
Abstract
Action potential (AP) responses of dentate gyrus granule (DG) cells have to be tightly regulated to maintain hippocampal function. However, which ion channels control the response delay of DG cells is not known. In some neuron types, spike latency is influenced by a dendrotoxin (DTX)-sensitive delay current (ID) mediated by unidentified combinations of voltage-gated K(+) (Kv) channels of the Kv1 family Kv1.1-6. In DG cells, the ID has not been characterized and its molecular basis is unknown. The response phenotype of mature DG cells is usually considered homogenous but intrinsic plasticity likely occurs in particular in conditions of hyperexcitability, for example during temporal lobe epilepsy (TLE). In this study, we examined response delays of DG cells and underlying ion channel molecules by employing a combination of gramicidin-perforated patch-clamp recordings in acute brain slices and single-cell reverse transcriptase quantitative polymerase chain reaction (SC RT-qPCR) experiments. An in vivo mouse model of TLE consisting of intrahippocampal kainate (KA) injection was used to examine epilepsy-related plasticity. Response delays of DG cells were DTX-sensitive and strongly increased in KA-injected hippocampi; Kv1.1 mRNA was elevated 10-fold, and the response delays correlated with Kv1.1 mRNA abundance on the single cell level. Other Kv1 subunits did not show overt changes in mRNA levels. Kv1.1 immunolabeling was enhanced in KA DG cells. The biophysical properties of ID and a delay heterogeneity within the DG cell population was characterized. Using organotypic hippocampal slice cultures (OHCs), where KA incubation also induced ID upregulation, the homeostatic reversibility and neuroprotective potential for DG cells were tested. In summary, the AP timing of DG cells is effectively controlled via scaling of Kv1.1 subunit transcription. With this antiepileptic mechanism, DG cells delay their responses during hyperexcitation.
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Affiliation(s)
- Florian Kirchheim
- Cellular Neurophysiology, Department of Neurosurgery, University Medical Center Freiburg Freiburg, Germany ; Faculty of Biology, University of Freiburg Freiburg, Germany
| | - Stefanie Tinnes
- Experimental Epilepsy Research, Department of Neurosurgery, University Medical Center Freiburg Freiburg, Germany
| | - Carola A Haas
- Experimental Epilepsy Research, Department of Neurosurgery, University Medical Center Freiburg Freiburg, Germany
| | - Michael Stegen
- Cellular Neurophysiology, Department of Neurosurgery, University Medical Center Freiburg Freiburg, Germany ; Department of Biomedicine, Institute of Physiology, University of Basel Basel, Switzerland
| | - Jakob Wolfart
- Cellular Neurophysiology, Department of Neurosurgery, University Medical Center Freiburg Freiburg, Germany ; Oscar Langendorff Institute of Physiology, University of Rostock Rostock, Germany
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59
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Shah NH, Aizenman E. Voltage-gated potassium channels at the crossroads of neuronal function, ischemic tolerance, and neurodegeneration. Transl Stroke Res 2013; 5:38-58. [PMID: 24323720 DOI: 10.1007/s12975-013-0297-7] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 09/14/2013] [Accepted: 10/14/2013] [Indexed: 11/29/2022]
Abstract
Voltage-gated potassium (Kv) channels are widely expressed in the central and peripheral nervous system and are crucial mediators of neuronal excitability. Importantly, these channels also actively participate in cellular and molecular signaling pathways that regulate the life and death of neurons. Injury-mediated increased K(+) efflux through Kv2.1 channels promotes neuronal apoptosis, contributing to widespread neuronal loss in neurodegenerative disorders such as Alzheimer's disease and stroke. In contrast, some forms of neuronal activity can dramatically alter Kv2.1 channel phosphorylation levels and influence their localization. These changes are normally accompanied by modifications in channel voltage dependence, which may be neuroprotective within the context of ischemic injury. Kv1 and Kv7 channel dysfunction leads to neuronal hyperexcitability that critically contributes to the pathophysiology of human clinical disorders such as episodic ataxia and epilepsy. This review summarizes the neurotoxic, neuroprotective, and neuroregulatory roles of Kv channels and highlights the consequences of Kv channel dysfunction on neuronal physiology. The studies described in this review thus underscore the importance of normal Kv channel function in neurons and emphasize the therapeutic potential of targeting Kv channels in the treatment of a wide range of neurological diseases.
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Affiliation(s)
- Niyathi Hegde Shah
- Department of Neurobiology, University of Pittsburgh School of Medicine, 3500 Terrace Street, E1456 BST, Pittsburgh, PA, 15261, USA,
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60
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Giglio AM, Storm JF. Postnatal development of temporal integration, spike timing and spike threshold regulation by a dendrotoxin-sensitive K+current in rat CA1 hippocampal cells. Eur J Neurosci 2013; 39:12-23. [DOI: 10.1111/ejn.12385] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Revised: 08/30/2013] [Accepted: 09/10/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Anna M. Giglio
- Institute of Basal Medicine; Department of Physiology and Centre of Molecular Biology and Neuroscience; University of Oslo; PB 1104 Blindern, 0317 Oslo Norway
| | - Johan F. Storm
- Institute of Basal Medicine; Department of Physiology and Centre of Molecular Biology and Neuroscience; University of Oslo; PB 1104 Blindern, 0317 Oslo Norway
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61
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Hyun JH, Eom K, Lee KH, Ho WK, Lee SH. Activity-dependent downregulation of D-type K+ channel subunit Kv1.2 in rat hippocampal CA3 pyramidal neurons. J Physiol 2013; 591:5525-40. [PMID: 23981714 DOI: 10.1113/jphysiol.2013.259002] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The intrinsic excitability of neurons plays a critical role in the encoding of memory at Hebbian synapses and in the coupling of synaptic inputs to spike generation. It has not been studied whether somatic firing at a physiologically relevant frequency can induce intrinsic plasticity in hippocampal CA3 pyramidal cells (CA3-PCs). Here, we show that a conditioning train of 20 action potentials (APs) at 10 Hz causes a persistent reduction in the input conductance and an acceleration of the AP onset time in CA3-PCs, but not in CA1-PCs. Induction of such long-term potentiation of intrinsic excitability (LTP-IE) was accompanied by a reduction in the D-type K(+) current, and was abolished by the inhibition of endocytosis or protein tyrosine kinase (PTK). Consistently, the CA3-PCs from Kv1.2 knock-out mice displayed no LTP-IE with the same conditioning. Furthermore, the induction of LTP-IE depended on the back-propagating APs (bAPs) and intact distal apical dendrites. These results indicate that LTP-IE is mediated by the internalization of Kv1.2 channels from the distal regions of apical dendrites, which is triggered by bAP-induced dendritic Ca(2+) signalling and the consequent activation of PTK.
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Affiliation(s)
- Jung Ho Hyun
- S.-H. Lee: Department of Physiology, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul, 110-799, Republic of Korea.
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62
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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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63
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Simeone TA, Simeone KA, Samson KK, Kim DY, Rho JM. Loss of the Kv1.1 potassium channel promotes pathologic sharp waves and high frequency oscillations in in vitro hippocampal slices. Neurobiol Dis 2013; 54:68-81. [PMID: 23466697 DOI: 10.1016/j.nbd.2013.02.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 02/12/2013] [Accepted: 02/22/2013] [Indexed: 01/10/2023] Open
Abstract
In human disease, channelopathies involving functional reduction of the delayed rectifier potassium channel α-subunit Kv1.1 - either by mutation or autoimmune inhibition - result in temporal lobe epilepsy. Kv1.1 is prominently expressed in the axons of the hippocampal tri-synaptic pathway, suggesting its absence will result in widespread effects on normal network oscillatory activity. Here, we performed in vitro extracellular recordings using a multielectrode array to determine the effects of loss of Kv1.1 on spontaneous sharp waves (SPWs) and high frequency oscillations (HFOs). We found that Kcna1-null hippocampi generate SPWs and ripples (80-200Hz bandwidth) with a 50% increased rate of incidence and 50% longer duration, and that epilepsy-associated pathologic HFOs in the fast ripple bandwidth (200-600Hz) are also present. Furthermore, Kcna1-null CA3 has enhanced coupling of excitatory inputs and population spike generation and CA3 principal cells have reduced spike timing reliability. Removing the influence of mossy fiber and perforant path inputs by micro-dissecting the Kcna1-null CA3 region mostly rescued the oscillatory behavior and improved spike timing. We found that Kcna1-null mossy fibers and medial perforant path axons are hyperexcitable and produce greater pre- and post-synaptic responses with reduced paired-pulse ratios suggesting increased neurotransmitter release at these terminals. These findings were recapitulated in wild-type slices exposed to the Kv1.1 inhibitor dendrotoxin-κ. Collectively, these data indicate that loss of Kv1.1 enhances synaptic release in the CA3 region, which reduces spike timing precision of individual neurons leading to disorganization of network oscillatory activity and promotes the emergence of fast ripples.
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Affiliation(s)
- Timothy A Simeone
- Creighton University, Department of Pharmacology, Omaha, NE 68174, USA.
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Campanac E, Gasselin C, Baude A, Rama S, Ankri N, Debanne D. Enhanced Intrinsic Excitability in Basket Cells Maintains Excitatory-Inhibitory Balance in Hippocampal Circuits. Neuron 2013; 77:712-22. [DOI: 10.1016/j.neuron.2012.12.020] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/12/2012] [Indexed: 12/24/2022]
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Wester JC, Contreras D. Biophysical mechanism of spike threshold dependence on the rate of rise of the membrane potential by sodium channel inactivation or subthreshold axonal potassium current. J Comput Neurosci 2013; 35:1-17. [PMID: 23344915 DOI: 10.1007/s10827-012-0436-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 11/21/2012] [Accepted: 12/26/2012] [Indexed: 10/27/2022]
Abstract
Spike threshold filters incoming inputs and thus gates activity flow through neuronal networks. Threshold is variable, and in many types of neurons there is a relationship between the threshold voltage and the rate of rise of the membrane potential (dVm/dt) leading to the spike. In primary sensory cortex this relationship enhances the sensitivity of neurons to a particular stimulus feature. While Na⁺ channel inactivation may contribute to this relationship, recent evidence indicates that K⁺ currents located in the spike initiation zone are crucial. Here we used a simple Hodgkin-Huxley biophysical model to systematically investigate the role of K⁺ and Na⁺ current parameters (activation voltages and kinetics) in regulating spike threshold as a function of dVm/dt. Threshold was determined empirically and not estimated from the shape of the Vm prior to a spike. This allowed us to investigate intrinsic currents and values of gating variables at the precise voltage threshold. We found that Na⁺ nactivation is sufficient to produce the relationship provided it occurs at hyperpolarized voltages combined with slow kinetics. Alternatively, hyperpolarization of the K⁺ current activation voltage, even in the absence of Na⁺ inactivation, is also sufficient to produce the relationship. This hyperpolarized shift of K⁺ activation allows an outward current prior to spike initiation to antagonize the Na⁺ inward current such that it becomes self-sustaining at a more depolarized voltage. Our simulations demonstrate parameter constraints on Na⁺ inactivation and the biophysical mechanism by which an outward current regulates spike threshold as a function of dVm/dt.
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Affiliation(s)
- Jason C Wester
- Department of Neuroscience, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA
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66
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Abstract
In 1948, Hodgkin delineated different classes of axonal firing. This has been mathematically translated allowing insight and understanding to emerge. As such, the terminology of ‘Type I’ and ‘Type II’ neurons is commonplace in the Neuroscience literature today. Theoretical insights have helped us realize that, for example, network synchronization depends on whether neurons are Type I or Type II. Mathematical models are precise with analyses (considering Type I/II aspects), but experimentally, the distinction can be less clear. On the other hand, experiments are becoming more sophisticated in terms of distinguishing and manipulating particular cell types but are limited in terms of being able to consider network aspects simultaneously. Although there is much work going on mathematically and experimentally, in my opinion it is becoming common that models are either superficially linked with experiment or not described in enough detail to appreciate the biological context. Overall, we all suffer in terms of impeding our understanding of brain networks and applying our understanding to neurological disease. I suggest that more modelers become familiar with experimental details and that more experimentalists appreciate modeling assumptions. In other words, we need to move beyond our comfort zones.
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Affiliation(s)
- Frances K Skinner
- Toronto Western Research Institute, University Health Network, Toronto, ONT, Canada ; Departments of Medicine (Neurology) and Physiology, University of Toronto, Toronto, ONT, Canada
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Szücs A, Berton F, Sanna PP, Francesconi W. Excitability of jcBNST neurons is reduced in alcohol-dependent animals during protracted alcohol withdrawal. PLoS One 2012; 7:e42313. [PMID: 22927925 PMCID: PMC3424185 DOI: 10.1371/journal.pone.0042313] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 07/06/2012] [Indexed: 11/18/2022] Open
Abstract
Alcohol dependence and withdrawal has been shown to cause neuroadaptive changes at multiple levels of the nervous system. At the neuron level, adaptations of synaptic connections have been extensively studied in a number of brain areas and accumulating evidence also shows the importance of alcohol dependence-related changes in the intrinsic cellular properties of neurons. At the same time, it is still largely unknown how such neural adaptations impact the firing and integrative properties of neurons. To address these problems, here, we analyze physiological properties of neurons in the bed nucleus of stria terminalis (jcBNST) in animals with a history of alcohol dependence. As a comprehensive approach, first we measure passive and active membrane properties of neurons using conventional current clamp protocols and then analyze their firing responses under the action of simulated synaptic bombardment via dynamic clamp. We find that most physiological properties as measured by DC current injection are barely affected during protracted withdrawal. However, neuronal excitability as measured from firing responses under simulated synaptic inputs with the dynamic clamp is markedly reduced in all 3 types of jcBNST neurons. These results support the importance of studying the effects of alcohol and drugs of abuse on the firing properties of neurons with dynamic clamp protocols designed to bring the neurons into a high conductance state. Since the jcBNST integrates excitatory inputs from the basolateral amygdala (BLA) and cortical inputs from the infralimbic and the insular cortices and in turn is believed to contribute to the inhibitory input to the central nucleus of the amygdala (CeA) the reduced excitability of the jcBNST during protracted withdrawal in alcohol-dependent animals will likely affect ability of the jcBNST to shape the activity and output of the CeA.
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Affiliation(s)
- Attila Szücs
- BioCircuits Institute, University of California San Diego, La Jolla, California, United States of America.
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Farries MA, Wilson CJ. Biophysical basis of the phase response curve of subthalamic neurons with generalization to other cell types. J Neurophysiol 2012; 108:1838-55. [PMID: 22786959 DOI: 10.1152/jn.00054.2012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Experimental evidence indicates that the response of subthalamic neurons to excitatory postsynaptic potentials (EPSPs) is well described by their infinitesimal phase response curves (iPRC). However, the factors controlling the shape of that iPRC, and hence controlling the way subthalamic neurons respond to synaptic input, are unclear. We developed a biophysical model of subthalamic neurons to aid in the understanding of their iPRCs; this model exhibited an iPRC type common to many subthalamic cells. We devised a method for deriving its iPRC from its biophysical properties that clarifies how these different properties interact to shape the iPRC. This method revealed why the response of subthalamic neurons is well approximated by their iPRCs and how that approximation becomes less accurate under strong fluctuating input currents. It also connected iPRC structure to aspects of cellular physiology that could be estimated in simple current-clamp experiments. This allowed us to directly compare the iPRC predicted by our theory with the iPRC estimated from the response to EPSPs or current pulses in individual cells. We found that theoretically predicted iPRCs agreed well with estimates derived from synaptic stimuli, but not with those estimated from the response to somatic current injection. The difference between synaptic currents and those applied experimentally at the soma may arise from differences in the dynamics of charge redistribution on the dendrites and axon. Ultimately, our approach allowed us to identify novel ways in which voltage-dependent conductances interact with AHP conductances to influence synaptic integration that will apply to a wide range of cell types.
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Affiliation(s)
- Michael A Farries
- Department of Biology, University of Texas San Antonio, San Antonio, Texas 78249, USA.
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Farries MA, Wilson CJ. Spike threshold dynamics reshape the phase response curve and increase the degree of synchronization among neurons coupled by excitatory synapses. BMC Neurosci 2012. [PMCID: PMC3403302 DOI: 10.1186/1471-2202-13-s1-p12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Huang M, Volgushev M, Wolf F. A small fraction of strongly cooperative sodium channels boosts neuronal encoding of high frequencies. PLoS One 2012; 7:e37629. [PMID: 22666374 PMCID: PMC3362627 DOI: 10.1371/journal.pone.0037629] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 04/26/2012] [Indexed: 11/24/2022] Open
Abstract
Generation of action potentials (APs) is a crucial step in neuronal information processing. Existing biophysical models for AP generation almost universally assume that individual voltage-gated sodium channels operate statistically independently, and their avalanche-like opening that underlies AP generation is coordinated only through the transmembrane potential. However, biological ion channels of various types can exhibit strongly cooperative gating when clustered. Cooperative gating of sodium channels has been suggested to explain rapid onset dynamics and large threshold variability of APs in cortical neurons. It remains however unknown whether these characteristic properties of cortical APs can be reproduced if only a fraction of channels express cooperativity, and whether the presence of cooperative channels has an impact on encoding properties of neuronal populations. To address these questions we have constructed a conductance-based neuron model in which we continuously varied the size of a fraction [Formula: see text] of sodium channels expressing cooperativity and the strength of coupling between cooperative channels [Formula: see text]. We show that starting at a critical value of the coupling strength [Formula: see text], the activation curve of sodium channels develops a discontinuity at which opening of all coupled channels becomes an all-or-none event, leading to very rapid AP onsets. Models with a small fraction, [Formula: see text], of strongly cooperative channels generate APs with the most rapid onset dynamics. In this regime APs are triggered by simultaneous opening of the cooperative channel fraction and exhibit a pronounced biphasic waveform often observed in cortical neurons. We further show that presence of a small fraction of cooperative Na+ channels significantly improves the ability of neuronal populations to phase-lock their firing to high frequency input fluctuation. We conclude that presence of a small fraction of strongly coupled sodium channels can explain characteristic features of cortical APs and has a functional impact of enhancing the spike encoding of rapidly varying signals.
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Affiliation(s)
- Min Huang
- Max-Planck-Institute for Dynamics and Self-Organization, Bernstein Center for Computational Neuroscience, and Faculty of Physics, Georg August University School of Science (GAUSS), Göttingen, Germany
- State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, Beijing, China
| | - Maxim Volgushev
- Department of Psychology, University of Connecticut, Storrs, Connecticut, United States of America
| | - Fred Wolf
- Max-Planck-Institute for Dynamics and Self-Organization, Bernstein Center for Computational Neuroscience, and Faculty of Physics, Georg August University School of Science (GAUSS), Göttingen, Germany
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