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Belghazi M, Iborra C, Toutendji O, Lasserre M, Debanne D, Goaillard JM, Marquèze-Pouey B. High-Resolution Proteomics Unravel a Native Functional Complex of Cav1.3, SK3, and Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels in Midbrain Dopaminergic Neurons. Cells 2024; 13:944. [PMID: 38891076 PMCID: PMC11172389 DOI: 10.3390/cells13110944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 05/21/2024] [Accepted: 05/26/2024] [Indexed: 06/21/2024] Open
Abstract
Pacemaking activity in substantia nigra dopaminergic neurons is generated by the coordinated activity of a variety of distinct somatodendritic voltage- and calcium-gated ion channels. We investigated whether these functional interactions could arise from a common localization in macromolecular complexes where physical proximity would allow for efficient interaction and co-regulations. For that purpose, we immunopurified six ion channel proteins involved in substantia nigra neuron autonomous firing to identify their molecular interactions. The ion channels chosen as bait were Cav1.2, Cav1.3, HCN2, HCN4, Kv4.3, and SK3 channel proteins, and the methods chosen to determine interactions were co-immunoprecipitation analyzed through immunoblot and mass spectrometry as well as proximity ligation assay. A macromolecular complex composed of Cav1.3, HCN, and SK3 channels was unraveled. In addition, novel potential interactions between SK3 channels and sclerosis tuberous complex (Tsc) proteins, inhibitors of mTOR, and between HCN4 channels and the pro-degenerative protein Sarm1 were uncovered. In order to demonstrate the presence of these molecular interactions in situ, we used proximity ligation assay (PLA) imaging on midbrain slices containing the substantia nigra, and we could ascertain the presence of these protein complexes specifically in substantia nigra dopaminergic neurons. Based on the complementary functional role of the ion channels in the macromolecular complex identified, these results suggest that such tight interactions could partly underly the robustness of pacemaking in dopaminergic neurons.
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Affiliation(s)
- Maya Belghazi
- CRN2M Centre de Recherche Neurobiologie-Neurophysiologie, CNRS, UMR7286, Aix-Marseille Université, 13015 Marseille, France;
- Institut de Microbiologie de la Méditerranée (IMM), CNRS, Aix-Marseille Université, 13009 Marseille, France
| | - Cécile Iborra
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
| | - Ophélie Toutendji
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
| | - Manon Lasserre
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
| | - Dominique Debanne
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
| | - Jean-Marc Goaillard
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
- Institut de Neurosciences de la Timone, CNRS, Aix-Marseille Université, 13005 Marseille, France
| | - Béatrice Marquèze-Pouey
- Ion Channel and Synaptic Neurobiology, INSERM, UMR1072, Aix-Marseille Université, 13015 Marseille, France; (C.I.); (O.T.); (M.L.); (D.D.); (J.-M.G.)
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Zahra A, Liu R, Han W, Meng H, Wang Q, Wang Y, Campbell SL, Wu J. K Ca-Related Neurological Disorders: Phenotypic Spectrum and Therapeutic Indications. Curr Neuropharmacol 2023; 21:1504-1518. [PMID: 36503451 PMCID: PMC10472807 DOI: 10.2174/1570159x21666221208091805] [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: 04/21/2022] [Revised: 07/21/2022] [Accepted: 07/23/2022] [Indexed: 12/14/2022] Open
Abstract
Although potassium channelopathies have been linked to a wide range of neurological conditions, the underlying pathogenic mechanism is not always clear, and a systematic summary of clinical manifestation is absent. Several neurological disorders have been associated with alterations of calcium-activated potassium channels (KCa channels), such as loss- or gain-of-function mutations, post-transcriptional modification, etc. Here, we outlined the current understanding of the molecular and cellular properties of three subtypes of KCa channels, including big conductance KCa channels (BK), small conductance KCa channels (SK), and the intermediate conductance KCa channels (IK). Next, we comprehensively reviewed the loss- or gain-of-function mutations of each KCa channel and described the corresponding mutation sites in specific diseases to broaden the phenotypic-genotypic spectrum of KCa-related neurological disorders. Moreover, we reviewed the current pharmaceutical strategies targeting KCa channels in KCa-related neurological disorders to provide new directions for drug discovery in anti-seizure medication.
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Affiliation(s)
- Aqeela Zahra
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
- Department of Zoology, University of Sialkot, Sialkot 51310, Pakistan
| | - Ru Liu
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
| | - Wenzhe Han
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Hui Meng
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Qun Wang
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
| | - YunFu Wang
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Susan L. Campbell
- Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
| | - Jianping Wu
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
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Qi ZX, Shen KL, Peng JY, Fan XJ, Huang HW, Jiang JL, Lu JH, Wang XQ, Fang XX, Chen L, Zhuang QX. Histamine bidirectionally regulates the intrinsic excitability of parvalbumin-positive neurons in the lateral globus pallidus and promotes motor behaviour. Br J Pharmacol 2022; 180:1379-1407. [PMID: 36512485 DOI: 10.1111/bph.16010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Revised: 12/06/2022] [Accepted: 12/08/2022] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND AND PURPOSE Parvalbumin (PV)-positive neurons are a type of neuron in the lateral globus pallidus (LGP) which plays an important role in motor control. The present study investigated the effect of histamine on LGPPV neurons and motor behaviour. EXPERIMENTAL APPROACH Histamine levels in LGP as well as its histaminergic innervation were determined through brain stimulation, microdialysis, anterograde tracing and immunostaining. Mechanisms of histamine action were detected by immunostaining, single-cell qPCR, whole-cell patch-clamp recording, optogenetic stimulation and CRISPR/Cas9 gene-editing techniques. The effect of histamine on motor behaviour was detected by animal behavioural tests. KEY RESULTS A direct histaminergic innervation in LGP from the tuberomammillary nucleus (TMN) and a histamine-induced increase in the intrinsic excitability of LGPPV neurons were determined by pharmacological blockade or by genetic knockout of the histamine H1 receptor (H1 R)-coupled TWIK-related potassium channel-1 (TREK-1) and the small-conductance calcium-activated potassium channel (SK3), as well as by activation or overexpression of the histamine H2 receptor (H2 R)-coupled hyperpolarization-activated cyclic nucleotide-gated channel (HCN2). Histamine negatively regulated the STN → LGPGlu transmission in LGPPV neurons via the histamine H3 receptor (H3 R), whereas blockage or knockout of H3 R increased the intrinsic excitability of LGPPV neurons. CONCLUSIONS AND IMPLICATIONS Our results indicated that the endogenous histaminergic innervation in the LGP can bidirectionally promote motor control by increasing the intrinsic excitability of LGPPV neurons through postsynaptic H1 R and H2 R, albeit its action was negatively regulated by the presynaptic H3 R, thereby suggesting possible role of histamine in motor deficits manifested in Parkinson's disease (PD).
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Affiliation(s)
- Zeng-Xin Qi
- Department of Neurosurgery, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,National Center for Neurological Disorders, Shanghai, China.,Shanghai Key Laboratory of Brain Function Restoration and Neural Regeneration, Shanghai, China
| | - Kang-Li Shen
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Jian-Ya Peng
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Xiu-Juan Fan
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Hui-Wei Huang
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Jian-Lan Jiang
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Jian-Hua Lu
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Xiao-Qin Wang
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Xiao-Xia Fang
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - Liang Chen
- Department of Neurosurgery, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,National Center for Neurological Disorders, Shanghai, China.,Shanghai Key Laboratory of Brain Function Restoration and Neural Regeneration, Shanghai, China.,State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, School of Basic Medical Sciences and Institutes of Brain Science, Fudan University, Shanghai, China
| | - Qian-Xing Zhuang
- Department of Physiology, School of Medicine, and Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
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Hunker AC, Soden ME, Krayushkina D, Heymann G, Awatramani R, Zweifel LS. Conditional Single Vector CRISPR/SaCas9 Viruses for Efficient Mutagenesis in the Adult Mouse Nervous System. Cell Rep 2021; 30:4303-4316.e6. [PMID: 32209486 PMCID: PMC7212805 DOI: 10.1016/j.celrep.2020.02.092] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 01/27/2020] [Accepted: 02/25/2020] [Indexed: 11/22/2022] Open
Abstract
Mice engineered for conditional, cell type-specific gene inactivation have dominated the field of mouse genetics because of the high efficiency of Cre-loxP-mediated recombination. Recent advances in CRISPR/Cas9 technologies have provided alternatives for rapid gene mutagenesis for loss-of-function (LOF) analysis. Whether these strategies can be streamlined for rapid genetic analysis with the efficiencies comparable with those of conventional genetic approaches has yet to be established. We show that a single adeno-associated viral (AAV) vector containing a recombinase-dependent Staphylococcus aureus Cas9 (SaCas9) and a single guide RNA (sgRNA) are as efficient as conventional conditional gene knockout and can be adapted for use in either Cre- or Flp-driver mouse lines. The efficacy of this approach is demonstrated for the analysis of GABAergic, glutamatergic, and monoaminergic neurotransmission. Using this strategy, we reveal insight into the role of GABAergic regulation of midbrain GABA-producing neurons in psychomotor activation. Hunker et al. generate single adeno-associated viral vectors for conditional gene mutagenesis in the adult mouse nervous system with efficiencies equivalent to those of conventional gene inactivation strategies. On the basis of this efficacy, they provide a resource of Cre- and Flp-dependent constructs for targeting catecholamine, glutamate, and GABA neurotransmission.
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Affiliation(s)
- Avery C Hunker
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA; Department of Pharmacology, University of Washington, Seattle, WA 98195, USA
| | - Marta E Soden
- Department of Pharmacology, University of Washington, Seattle, WA 98195, USA
| | - Dasha Krayushkina
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA
| | - Gabriel Heymann
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA
| | | | - Larry S Zweifel
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA; Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
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Maqoud F, Scala R, Hoxha M, Zappacosta B, Tricarico D. ATP-sensitive potassium channel subunits in the neuroinflammation: novel drug targets in neurodegenerative disorders. CNS & NEUROLOGICAL DISORDERS-DRUG TARGETS 2021; 21:130-149. [PMID: 33463481 DOI: 10.2174/1871527320666210119095626] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 08/07/2020] [Accepted: 08/28/2020] [Indexed: 11/22/2022]
Abstract
Arachidonic acids and its metabolites modulate plenty of ligand-gated, voltage-dependent ion channels, and metabolically regulated potassium channels including ATP-sensitive potassium channels (KATP). KATP channels are hetero-multimeric complexes of sulfonylureas receptors (SUR1, SUR2A or SUR2B) and the pore-forming subunits (Kir6.1 and Kir6.2) likewise expressed in the pre-post synapsis of neurons and inflammatory cells, thereby affecting their proliferation and activity. KATP channels are involved in amyloid-β (Aβ)-induced pathology, therefore emerging as therapeutic targets against Alzheimer's and related diseases. The modulation of these channels can represent an innovative strategy for the treatment of neurodegenerative disorders; nevertheless, the currently available drugs are not selective for brain KATP channels and show contrasting effects. This phenomenon can be a consequence of the multiple physiological roles of the different varieties of KATP channels. Openings of cardiac and muscular KATP channel subunits, is protective against caspase-dependent atrophy in these tissues and some neurodegenerative disorders, whereas in some neuroinflammatory diseases benefits can be obtained through the inhibition of neuronal KATP channel subunits. For example, glibenclamide exerts an anti-inflammatory effect in respiratory, digestive, urological, and central nervous system (CNS) diseases, as well as in ischemia-reperfusion injury associated with abnormal SUR1-Trpm4/TNF-α or SUR1-Trpm4/ Nos2/ROS signaling. Despite this strategy is promising, glibenclamide may have limited clinical efficacy due to its unselective blocking action of SUR2A/B subunits also expressed in cardiovascular apparatus with pro-arrhythmic effects and SUR1 expressed in pancreatic beta cells with hypoglycemic risk. Alternatively, neuronal selective dual modulators showing agonist/antagonist actions on KATP channels can be an option.
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Affiliation(s)
- Fatima Maqoud
- Department of Pharmacy-Pharmaceutical Science, University of Bari Aldo Moro, via Orabona 4, 70125-I. Italy
| | - Rosa Scala
- Department of Pharmacy-Pharmaceutical Science, University of Bari Aldo Moro, via Orabona 4, 70125-I. Italy
| | - Malvina Hoxha
- Department of Chemical-Toxicological and Pharmacological Evaluation of Drugs, Faculty of Pharmacy, "Catholic University Our Lady of Good Counsel", Tirana. Albania
| | - Bruno Zappacosta
- Department of Chemical-Toxicological and Pharmacological Evaluation of Drugs, Faculty of Pharmacy, "Catholic University Our Lady of Good Counsel", Tirana. Albania
| | - Domenico Tricarico
- Department of Pharmacy-Pharmaceutical Science, University of Bari Aldo Moro, via Orabona 4, 70125-I. Italy
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Maldonado O, Jenkins A, Belalcazar HM, Hernandez-Cuervo H, Hyman KM, Ladaga G, Padilla L, de Erausquin GA. Age-dependent neuroprotective effect of an SK3 channel agonist on excitotoxity to dopaminergic neurons in organotypic culture. PLoS One 2020; 15:e0223633. [PMID: 32701951 PMCID: PMC7377472 DOI: 10.1371/journal.pone.0223633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 07/06/2020] [Indexed: 11/19/2022] Open
Abstract
Background Small conductance, calcium-activated (SK3) potassium channels control the intrinsic excitability of dopaminergic neurons (DN) in the midbrain and modulate their susceptibility to toxic insults during development. Methods We evaluated the age-dependency of the neuroprotective effect of an SK3 agonist, 1-Ethyl-1,3-dihydro-2H-benzimidazol-2-one (1-EBIO), on Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) excitotoxicity to DN in ventral mesencephalon (VM) organotypic cultures. Results Most tyrosine hydroxylase (TH)+ neurons were also SK3+; SK3+/TH- cells (DN+) were common at each developmental stage but more prominently at day in vitro (DIV) 8. Young DN+ neurons were small bipolar and fusiform, whereas mature ones were large and multipolar. Exposure of organotypic cultures to AMPA (100 μm, 16 h) had no effect on the survival of DN+ at DIV 8, but caused significant toxicity at DIV 15 (n = 15, p = 0.005) and DIV 22 (n = 15, p<0.001). These results indicate that susceptibility of DN to AMPA excitotoxicity is developmental stage-dependent in embryonic VM organotypic cultures. Immature DN+ (small, bipolar) were increased after AMPA (100 μm, 16 h) at DIV 8, at the expense of the number of differentiated (large, multipolar) DN+ (p = 0.039). This effect was larger at DIV 15 (p<<<0.0001) and at DIV 22 (p<<<0.0001). At DIV 8, 30 μM 1-EBIO resulted in a large increase in DN+. At DIV 15, AMPA toxicity was prevented by exposure to 30 μM, but not 100 μM 1-EBIO. At DIV 22, excitotoxicity was unaffected by 30 μM 1-EBIO, and partially reduced by 100 μM 1-EBIO. Conclusion The effects of the SK3 channel agonist 1-EBIO on the survival of SK3-expressing dopaminergic neurons were concentration-dependent and influenced by neuronal developmental stage.
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Affiliation(s)
- Oscar Maldonado
- Laboratory of Brain Development, and Repair, Biggs Institute for Alzheimer and Neurodegenerative Diseases, University of Texas Health San Antonio, San Antonio, Texas, United States of America
| | - Alexandra Jenkins
- Department of Molecular Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Helen M. Belalcazar
- Department of Genetics, Albert Einstein College of Medicine, New York City, New York, United States of America
| | - Helena Hernandez-Cuervo
- Department of Molecular Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Katelynn M. Hyman
- Department of Molecular Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Giannina Ladaga
- Laboratory of Brain Development, and Repair, Biggs Institute for Alzheimer and Neurodegenerative Diseases, University of Texas Health San Antonio, San Antonio, Texas, United States of America
| | - Lucia Padilla
- Laboratory of Brain Development, and Repair, Biggs Institute for Alzheimer and Neurodegenerative Diseases, University of Texas Health San Antonio, San Antonio, Texas, United States of America
| | - Gabriel A. de Erausquin
- Laboratory of Brain Development, and Repair, Biggs Institute for Alzheimer and Neurodegenerative Diseases, University of Texas Health San Antonio, San Antonio, Texas, United States of America
- * E-mail:
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Namba H, Nawa H. Post-pubertal Difference in Nigral Dopaminergic Cells Firing in the Schizophrenia Model Prepared by Perinatal Challenges of a Cytokine, EGF. Neuroscience 2020; 441:22-32. [PMID: 32531471 DOI: 10.1016/j.neuroscience.2020.06.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 06/01/2020] [Accepted: 06/02/2020] [Indexed: 12/21/2022]
Abstract
Schizophrenia in humans typically develops during and after adolescence; however, the biological underpinning for the specificity of this onset time window remains to be determined. In the present study, we investigated this knowledge gap using our own animal model for schizophrenia. Rodents and monkeys challenged with a cytokine, epidermal growth factor (EGF), as neonates are known to exhibit various behavioral and cognitive abnormalities at the post-pubertal stage. We used the EGF-challenged mice as an animal model for schizophrenia to evaluate the electrophysiological impact of this modeling on nigral dopamine neurons before and after puberty. In vivo single unit recording revealed that the burst firing of putative dopamine neurons in substantia nigra pars compacta was significantly higher in the post-pubertal stage of the EGF model than in that of control mice; in contrast, this difference was not observed in the pre-pubertal stage. The increase in burst firing was accompanied by a decline in Ca2+-activated K+ (ISK) currents, which influence the firing pattern of dopamine neurons. In vivo local application of the SK channel blocker apamin (80 μM) to the substantia nigra was less effective at increasing burst firing in the EGF model than in control mice, suggesting the pathologic role of the ISK decrease in this model. Thus, these results suggest that the aberrant post-pubertal hyperactivity of midbrain dopaminergic neurons is associated with the temporal specificity of the behavioral deficit of this model, and support the hypothesis that this dopaminergic aberration could be implicated in the adolescent onset of schizophrenia.
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Affiliation(s)
- Hisaaki Namba
- Department of Molecular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan.
| | - Hiroyuki Nawa
- Department of Molecular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan.
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Gain-of-Function Mutations in KCNN3 Encoding the Small-Conductance Ca 2+-Activated K + Channel SK3 Cause Zimmermann-Laband Syndrome. Am J Hum Genet 2019; 104:1139-1157. [PMID: 31155282 DOI: 10.1016/j.ajhg.2019.04.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 04/15/2019] [Indexed: 01/16/2023] Open
Abstract
Zimmermann-Laband syndrome (ZLS) is characterized by coarse facial features with gingival enlargement, intellectual disability (ID), hypertrichosis, and hypoplasia or aplasia of nails and terminal phalanges. De novo missense mutations in KCNH1 and KCNK4, encoding K+ channels, have been identified in subjects with ZLS and ZLS-like phenotype, respectively. We report de novo missense variants in KCNN3 in three individuals with typical clinical features of ZLS. KCNN3 (SK3/KCa2.3) constitutes one of three members of the small-conductance Ca2+-activated K+ (SK) channels that are part of a multiprotein complex consisting of the pore-forming channel subunits, the constitutively bound Ca2+ sensor calmodulin, protein kinase CK2, and protein phosphatase 2A. CK2 modulates Ca2+ sensitivity of the channels by phosphorylating SK-bound calmodulin. Patch-clamp whole-cell recordings of KCNN3 channel-expressing CHO cells demonstrated that disease-associated mutations result in gain of function of the mutant channels, characterized by increased Ca2+ sensitivity leading to faster and more complete activation of KCNN3 mutant channels. Pretreatment of cells with the CK2 inhibitor 4,5,6,7-tetrabromobenzotriazole revealed basal inhibition of wild-type and mutant KCNN3 channels by CK2. Analogous experiments with the KCNN3 p.Val450Leu mutant previously identified in a family with portal hypertension indicated basal constitutive channel activity and thus a different gain-of-function mechanism compared to the ZLS-associated mutant channels. With the report on de novo KCNK4 mutations in subjects with facial dysmorphism, hypertrichosis, epilepsy, ID, and gingival overgrowth, we propose to combine the phenotypes caused by mutations in KCNH1, KCNK4, and KCNN3 in a group of neurological potassium channelopathies caused by an increase in K+ conductance.
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Bambico FR, Li Z, Oliveira C, McNeill S, Diwan M, Raymond R, Nobrega JN. Rostrocaudal subregions of the ventral tegmental area are differentially impacted by chronic stress. Psychopharmacology (Berl) 2019; 236:1917-1929. [PMID: 30796492 DOI: 10.1007/s00213-019-5177-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 01/21/2019] [Indexed: 01/17/2023]
Abstract
RATIONALE The ventral tegmental area (VTA) is implicated in the pathophysiology of depression and addictive disorders and is subject to the detrimental effects of stress. Chronic stress may differentially alter the activity pattern of its different subregions along the rostrocaudal and dorsoventral axes, which may relate to the variable behavioral sensitivity to stress mediated by these subregions. OBJECTIVES Here, chronic stress-exposed rats were tested for depressive-like reactivity. In situ hybridization for zif268 as a marker of neuronal activation was combined with in vivo single-unit recording of dopaminergic neurons to assess modifications in the activity of the rostral VTA (rVTA) and caudal VTA (cVTA). Changes in the expression of stress-responsive glucocorticoid receptors (GR) and brain-derived neurotrophic factor (BDNF) were also assessed. RESULTS Stress-induced anhedonia-like, hyper-anxious, and passive-like responding were associated with reductions in dopaminergic burst activity in the cVTA and an increase in local GABAergic activity, particularly in GABAA receptor sensitivity. On the other hand, stress increased single-spiking activity, burst activity, and zif268 mRNA levels in the rVTA, which were associated with increased glutamatergic tonus and enhanced GR and AMPA receptor (AMPAR) expression. rVTA and cVTA activity differentially correlated with sucrose preference and passivity measures. CONCLUSIONS These data demonstrate that the rVTA and cVTA respond differently to stress and suggest that while cVTA activity may be related to passivity-like states, the activity of both subregions appears to be related to anhedonia and the processing of incentive value. These region-dependent abnormalities indicate the multi-modular composition of the VTA, which could provide multiple substrates for different symptom features.
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Affiliation(s)
- Francis Rodriguez Bambico
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada. .,Department of Psychology, Memorial University of Newfoundland, St John's, NL, A1B 3X9, Canada.
| | - Zhuoliang Li
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
| | - Caio Oliveira
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
| | - Sean McNeill
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
| | - Mustansir Diwan
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
| | - Roger Raymond
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
| | - José N Nobrega
- Behavioural Neurobiology Laboratory, Campbell Family Mental Health Research Institute and Research Imaging Center, Centre for Addiction and Mental Health, Toronto, Ontario, M5T 1R82, Canada
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Hypobaric Hypoxia-Induced Learning and Memory Impairment: Elucidating the Role of Small Conductance Ca2+-Activated K+ Channels. Neuroscience 2018; 388:418-429. [DOI: 10.1016/j.neuroscience.2018.07.026] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 07/11/2018] [Accepted: 07/13/2018] [Indexed: 11/19/2022]
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Chen X, Xue B, Wang J, Liu H, Shi L, Xie J. Potassium Channels: A Potential Therapeutic Target for Parkinson's Disease. Neurosci Bull 2017; 34:341-348. [PMID: 28884460 DOI: 10.1007/s12264-017-0177-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 06/22/2017] [Indexed: 12/21/2022] Open
Abstract
The pathogenesis of the second major neurodegenerative disorder, Parkinson's disease (PD), is closely associated with the dysfunction of potassium (K+) channels. Therefore, PD is also considered to be an ion channel disease or neuronal channelopathy. Mounting evidence has shown that K+ channels play crucial roles in the regulations of neurotransmitter release, neuronal excitability, and cell volume. Inhibition of K+ channels enhances the spontaneous firing frequency of nigral dopamine (DA) neurons, induces a transition from tonic firing to burst discharge, and promotes the release of DA in the striatum. Recently, three K+ channels have been identified to protect DA neurons and to improve the motor and non-motor symptoms in PD animal models: small conductance (SK) channels, A-type K+ channels, and KV7/KCNQ channels. In this review, we summarize the physiological and pharmacological effects of the three K+ channels. We also describe in detail the laboratory investigations regarding K+ channels as a potential therapeutic target for PD.
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Affiliation(s)
- Xiaoyan Chen
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China
| | - Bao Xue
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China
| | - Jun Wang
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China
| | - Haixia Liu
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China
| | - Limin Shi
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China.
| | - Junxia Xie
- Collaborative Innovation Center for Brain Science, Department of Physiology, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders, Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Medical College of Qingdao University, Qingdao, 266071, China.
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Chuhma N, Mingote S, Kalmbach A, Yetnikoff L, Rayport S. Heterogeneity in Dopamine Neuron Synaptic Actions Across the Striatum and Its Relevance for Schizophrenia. Biol Psychiatry 2017; 81:43-51. [PMID: 27692238 PMCID: PMC5121049 DOI: 10.1016/j.biopsych.2016.07.002] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 07/03/2016] [Accepted: 07/07/2016] [Indexed: 02/06/2023]
Abstract
Brain imaging has revealed alterations in dopamine uptake, release, and receptor levels in patients with schizophrenia that have been resolved on the scale of striatal subregions. However, the underlying synaptic mechanisms are on a finer scale. Dopamine neuron synaptic actions vary across the striatum, involving variations not only in dopamine release but also in dopamine neuron connectivity, cotransmission, modulation, and activity. Optogenetic studies have revealed that dopamine neurons release dopamine in a synaptic signal mode, and that the neurons also release glutamate and gamma-aminobutyric acid as cotransmitters, with striking regional variation. Fast glutamate and gamma-aminobutyric acid cotransmission convey discrete patterns of dopamine neuron activity to striatal neurons. Glutamate may function not only in a signaling role at a subset of dopamine neuron synapses, but also in mediating vesicular synergy, contributing to regional differences in loading of dopamine into synaptic vesicles. Regional differences in dopamine neuron signaling are likely to be differentially involved in the schizophrenia disease process and likely determine the subregional specificity of the action of psychostimulants that exacerbate the disorder, and antipsychotics that ameliorate the disorder. Elucidating dopamine neuron synaptic signaling offers the potential for achieving greater pharmacological specificity through intersectional pharmacological actions targeting subsets of dopamine neuron synapses.
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Affiliation(s)
- Nao Chuhma
- Department of Psychiatry, Columbia University, New York, New York; Department of Molecular Therapeutics, NYS Psychiatric Institute, New York, New York
| | - Susana Mingote
- Department of Psychiatry, Columbia University, New York, New York; Department of Molecular Therapeutics, NYS Psychiatric Institute, New York, New York
| | - Abigail Kalmbach
- Department of Psychiatry, Columbia University, New York, New York; Department of Molecular Therapeutics, NYS Psychiatric Institute, New York, New York
| | - Leora Yetnikoff
- Department of Psychiatry, Columbia University, New York, New York; Department of Molecular Therapeutics, NYS Psychiatric Institute, New York, New York
| | - Stephen Rayport
- Department of Psychiatry, Columbia University, New York, New York; Department of Molecular Therapeutics, NYS Psychiatric Institute, New York, New York.
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13
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Martin S, Lazzarini M, Dullin C, Balakrishnan S, Gomes FV, Ninkovic M, El Hady A, Pardo LA, Stühmer W, Del-Bel E. SK3 Channel Overexpression in Mice Causes Hippocampal Shrinkage Associated with Cognitive Impairments. Mol Neurobiol 2016; 54:1078-1091. [PMID: 26803493 PMCID: PMC5310555 DOI: 10.1007/s12035-015-9680-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 12/23/2015] [Indexed: 12/11/2022]
Abstract
The dysfunction of the small-conductance calcium-activated K+ channel SK3 has been described as one of the factors responsible for the progress of psychoneurological diseases, but the molecular basis of this is largely unknown. This report reveals through use of immunohistochemistry and computational tomography that long-term increased expression of the SK3 small-conductance calcium-activated potassium channel (SK3-T/T) in mice induces a notable bilateral reduction of the hippocampal area (more than 50 %). Histological analysis showed that SK3-T/T mice have cellular disarrangements and neuron discontinuities in the hippocampal formation CA1 and CA3 neuronal layer. SK3 overexpression resulted in cognitive loss as determined by the object recognition test. Electrophysiological examination of hippocampal slices revealed that SK3 channel overexpression induced deficiency of long-term potentiation in hippocampal microcircuits. In association with these results, there were changes at the mRNA levels of some genes involved in Alzheimer’s disease and/or linked to schizophrenia, epilepsy, and autism. Taken together, these features suggest that augmenting the function of SK3 ion channel in mice may present a unique opportunity to investigate the neural basis of central nervous system dysfunctions associated with schizophrenia, Alzheimer’s disease, or other neuropsychiatric/neurodegenerative disorders in this model system. As a more detailed understanding of the role of the SK3 channel in brain disorders is limited by the lack of specific SK3 antagonists and agonists, the results observed in this study are of significant interest; they suggest a new approach for the development of neuroprotective strategies in neuropsychiatric/neurodegenerative diseases with SK3 representing a potential drug target.
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Affiliation(s)
- Sabine Martin
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075, Göttingen, Germany
- Center Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), Göttingen, Germany
| | - Marcio Lazzarini
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075, Göttingen, Germany
| | - Christian Dullin
- Department of Diagnostic and Interventional Radiology, Georg-August University Medical Center, 37075, Göttingen, Germany
| | - Saju Balakrishnan
- Center Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), Göttingen, Germany
- Department of Neuro- and Sensory Physiology, Georg-August University Medical Center, 37073, Göttingen, Germany
| | - Felipe V Gomes
- Department of Pharmacology, Medical School of Ribeirão Preto, University of São Paulo, 14040-900, Ribeirão Preto, Brazil
| | - Milena Ninkovic
- Department of Neurosurgery, Georg-August University Medical Center, 37075, Göttingen, Germany
| | - Ahmed El Hady
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075, Göttingen, Germany
- Bernstein Focus for Neurotechnology and Bernstein Center for Computational Neuroscience, Göttingen, Germany
- Theoretical Neurophysics, Department of Non-linear Dynamics, Max Planck Institute for Dynamics and Self-Organization, 37077, Göttingen, Germany
- The Interdisciplinary Collaborative Research Center 889 "Cellular Mechanisms of Sensory Processing", Göttingen, Germany
| | - Luis A Pardo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, 37075, Göttingen, Germany
| | - Walter Stühmer
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075, Göttingen, Germany.
- Center Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), Göttingen, Germany.
- Bernstein Focus for Neurotechnology and Bernstein Center for Computational Neuroscience, Göttingen, Germany.
| | - Elaine Del-Bel
- Department of Morphology, Physiology and Pathology, CNPQ Research 1B (Biophysics, Biochemistry, Pharmacology and Neuroscience), University of São Paulo Dental School of Ribeirão Preto, Avenida do Café 3400, 14040-904, Ribeirão Preto, Brazil.
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14
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Maurice N, Deltheil T, Melon C, Degos B, Mourre C, Amalric M, Kerkerian-Le Goff L. Bee Venom Alleviates Motor Deficits and Modulates the Transfer of Cortical Information through the Basal Ganglia in Rat Models of Parkinson's Disease. PLoS One 2015; 10:e0142838. [PMID: 26571268 PMCID: PMC4646345 DOI: 10.1371/journal.pone.0142838] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 10/27/2015] [Indexed: 11/19/2022] Open
Abstract
Recent evidence points to a neuroprotective action of bee venom on nigral dopamine neurons in animal models of Parkinson’s disease (PD). Here we examined whether bee venom also displays a symptomatic action by acting on the pathological functioning of the basal ganglia in rat PD models. Bee venom effects were assessed by combining motor behavior analyses and in vivo electrophysiological recordings in the substantia nigra pars reticulata (SNr, basal ganglia output structure) in pharmacological (neuroleptic treatment) and lesional (unilateral intranigral 6-hydroxydopamine injection) PD models. In the hemi-parkinsonian 6-hydroxydopamine lesion model, subchronic bee venom treatment significantly alleviates contralateral forelimb akinesia and apomorphine-induced rotations. Moreover, a single injection of bee venom reverses haloperidol-induced catalepsy, a pharmacological model reminiscent of parkinsonian akinetic deficit. This effect is mimicked by apamin, a blocker of small conductance Ca2+-activated K+ (SK) channels, and blocked by CyPPA, a positive modulator of these channels, suggesting the involvement of SK channels in the bee venom antiparkinsonian action. In vivo electrophysiological recordings in the substantia nigra pars reticulata (basal ganglia output structure) showed no significant effect of BV on the mean neuronal discharge frequency or pathological bursting activity. In contrast, analyses of the neuronal responses evoked by motor cortex stimulation show that bee venom reverses the 6-OHDA- and neuroleptic-induced biases in the influence exerted by the direct inhibitory and indirect excitatory striatonigral circuits. These data provide the first evidence for a beneficial action of bee venom on the pathological functioning of the cortico-basal ganglia circuits underlying motor PD symptoms with potential relevance to the symptomatic treatment of this disease.
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Affiliation(s)
- Nicolas Maurice
- Aix Marseille Université, CNRS, IBDM UMR 7288, Marseille, France
- * E-mail:
| | | | - Christophe Melon
- Aix Marseille Université, CNRS, IBDM UMR 7288, Marseille, France
| | - Bertrand Degos
- INSERM, CNRS, Collège de France, CIRB UMR 7241 U-1050, Paris, France
- APHP, Département des Maladies du Système Nerveux, Centre Expert Inter-Régional Ile de France de la Maladie de Parkinson, Hôpital Pitié-Salpêtrière, Paris, France
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15
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Anderegg A, Poulin JF, Awatramani R. Molecular heterogeneity of midbrain dopaminergic neurons--Moving toward single cell resolution. FEBS Lett 2015; 589:3714-26. [PMID: 26505674 DOI: 10.1016/j.febslet.2015.10.022] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 10/19/2015] [Accepted: 10/19/2015] [Indexed: 12/31/2022]
Abstract
Since their discovery, midbrain dopamine (DA) neurons have been researched extensively, in part because of their diverse functions and involvement in various neuropsychiatric disorders. Over the last few decades, reports have emerged that midbrain DA neurons were not a homogeneous group, but that DA neurons located in distinct anatomical locations within the midbrain had distinctive properties in terms of physiology, function, and vulnerability. Accordingly, several studies focused on identifying heterogeneous gene expression across DA neuron clusters. Here we review the importance of understanding DA neuron heterogeneity at the molecular level, previous studies detailing heterogeneous gene expression in DA neurons, and finally recent work which brings together previous heterogeneous gene expression profiles in a coordinated manner, at single cell resolution.
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Affiliation(s)
- Angela Anderegg
- Department of Neurology and Center for Genetic Medicine, Northwestern University, Chicago, IL 60611, United States
| | - Jean-Francois Poulin
- Department of Neurology and Center for Genetic Medicine, Northwestern University, Chicago, IL 60611, United States
| | - Rajeshwar Awatramani
- Department of Neurology and Center for Genetic Medicine, Northwestern University, Chicago, IL 60611, United States
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16
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Dufour MA, Woodhouse A, Goaillard JM. Somatodendritic ion channel expression in substantia nigra pars compacta dopaminergic neurons across postnatal development. J Neurosci Res 2014; 92:981-99. [PMID: 24723263 DOI: 10.1002/jnr.23382] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 02/14/2014] [Accepted: 02/14/2014] [Indexed: 01/12/2023]
Abstract
Dopaminergic neurons of the substantia nigra pars compacta (SNc) are involved in the control of movement, sleep, reward, learning, and nervous system disorders and disease. To date, a thorough characterization of the ion channel phenotype of this important neuronal population is lacking. Using immunohistochemistry, we analyzed the somatodendritic expression of voltage-gated ion channel subunits that are involved in pacemaking activity in SNc dopaminergic neurons in 6-, 21-, and 40-day-old rats. Our results demonstrate that the same complement of somatodendritic ion channels is present in SNc dopaminergic neurons from P6 to P40. The major developmental changes were an increase in the dendritic range of the immunolabeling for the HCN, T-type calcium, Kv4.3, delayed rectifier, and SK channels. Our study sheds light on the ion channel subunits that contribute to the somatodendritic delayed rectifier (Kv1.3, Kv2.1, Kv3.2, Kv3.3), A-type (Kv4.3) and calcium-activated SK (SK1, SK2, SK3) potassium currents, IH (mainly HCN2, HCN4), and the L- (Cav1.2, Cav1.3) and T-type (mainly Cav3.1, Cav3.3) calcium currents in SNc dopaminergic neurons. Finally, no robust differences in voltage-gated ion channel immunolabeling were observed across the population of SNc dopaminergic neurons for each age examined, suggesting that differing levels of individual ion channels are unlikely to distinguish between specific subpopulations of SNc dopaminergic neurons. This is significant in light of previous studies suggesting that age- or region-associated variations in the expression profile of voltage-gated ion channels in SNc dopaminergic neurons may underlie their vulnerability to dysfunction and disease.
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Affiliation(s)
- Martial A Dufour
- INSERM, UMR_S 1072, 13015, Marseille, France; Aix-Marseille Université, UNIS, 13015, Marseille, France
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17
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Ballesteros-Merino C, Watanabe M, Shigemoto R, Fukazawa Y, Adelman JP, Luján R. Differential subcellular localization of SK3-containing channels in the hippocampus. Eur J Neurosci 2014; 39:883-892. [PMID: 24405447 DOI: 10.1111/ejn.12474] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 12/03/2013] [Accepted: 12/03/2013] [Indexed: 12/22/2022]
Abstract
Small-conductance, Ca(2+) -activated K(+) (SK) channels are expressed in the hippocampus where they regulate synaptic responses, plasticity, and learning and memory. To investigate the expression of SK3 (KCNN3) subunits, we determined the developmental profile and subcellular distribution of SK3 in the developing mouse hippocampus using western blots, immunohistochemistry and high-resolution immunoelectron microscopy. The results showed that SK3 expression increased during postnatal development, and that the localization of SK3 changed from being mainly associated with the endoplasmic reticulum and intracellular sites during the first postnatal week to being progressively concentrated in dendritic spines during later stages. In the adult, SK3 was localized mainly in postsynaptic compartments, both at extrasynaptic sites and along the postsynaptic density of excitatory synapses. Double labelling showed that SK3 co-localized with SK2 (KCNN2) and with N-methyl-D-aspartate receptors. Finally, quantitative analysis of SK3 density revealed two subcellular distribution patterns in different hippocampal layers, with SK3 being unevenly distributed in CA1 region of the hippocampus pyramidal cells and homogeneously distributed in dentate gyrus granule cells. Our results revealed a complex cell surface distribution of SK3-containing channels and a distinct developmental program that may influence different hippocampal functions.
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Affiliation(s)
- Carmen Ballesteros-Merino
- Instituto de Investigación en Discapacidades Neurológicas (IDINE), Departamento de Ciencias Médicas, Facultad de Medicina, Universidad Castilla-La Mancha, Campus Biosanitario, Albacete, Spain
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18
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Soden ME, Jones GL, Sanford CA, Chung AS, Güler AD, Chavkin C, Luján R, Zweifel LS. Disruption of dopamine neuron activity pattern regulation through selective expression of a human KCNN3 mutation. Neuron 2013; 80:997-1009. [PMID: 24206670 DOI: 10.1016/j.neuron.2013.07.044] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/25/2013] [Indexed: 11/19/2022]
Abstract
The calcium-activated small conductance potassium channel SK3 plays an essential role in the regulation of dopamine neuron activity patterns. Here we demonstrate that expression of a human disease-related SK3 mutation (hSK3Δ) in dopamine neurons of mice disrupts the balance between tonic and phasic dopamine neuron activity. Expression of hSK3Δ suppressed endogenous SK currents, reducing coupling between SK channels and NMDA receptors (NMDARs) and increasing permissiveness for burst firing. Consistent with enhanced excitability of dopamine neurons, hSK3Δ increased evoked calcium signals in dopamine neurons in vivo and potentiated evoked dopamine release. Specific expression of hSK3Δ led to deficits in attention and sensory gating and heightened sensitivity to a psychomimetic drug. Sensory-motor alterations and psychomimetic sensitivity were recapitulated in a mouse model of transient, reversible dopamine neuron activation. These results demonstrate the cell-autonomous effects of a human ion channel mutation on dopamine neuron physiology and the impact of activity pattern disruption on behavior.
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Affiliation(s)
- Marta E Soden
- Department of Pharmacology, University of Washington, Seattle, WA 98195, USA; Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA
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Lam J, Coleman N, Garing ALA, Wulff H. The therapeutic potential of small-conductance KCa2 channels in neurodegenerative and psychiatric diseases. Expert Opin Ther Targets 2013; 17:1203-20. [PMID: 23883298 DOI: 10.1517/14728222.2013.823161] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION KCa2 or small-conductance Ca(2+)-activated K(+) channels (SK) are expressed in many areas of the central nervous system where they participate in the regulation of neuronal afterhyperpolarization and excitability, and also serve as negative feedback regulators on the glutamate-NMDA pathway. AREAS COVERED This review focuses on the role of KCa2 channels in learning and memory and their potential as therapeutic targets for Alzheimer's and Parkinson's disease, ataxia, schizophrenia and alcohol dependence. EXPERT OPINION There currently exists relatively solid evidence supporting the use of KCa2 activators for ataxia. Genetic KCa2 channel suppression in deep cerebellar neurons induces ataxia, while KCa2 activators like 1-EBIO, SKA-31 and NS13001 improve motor deficits in mouse models of episodic ataxia (EA) and spinal cerebellar ataxia (SCA). Use of KCa2 activators for ataxia is further supported by a report that riluzole improves ataxia in a small clinical trial. Based on accumulating literature evidence, KCa2 activators further appear attractive for the treatment of alcohol dependence and withdrawal. Regarding Alzheimer's disease, Parkinson's disease and schizophrenia, further research, including long-term studies in disease relevant animal models, will be needed to determine whether KCa2 channels constitute valid targets and whether activators or inhibitors would be needed to positively affect disease outcomes.
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Affiliation(s)
- Jenny Lam
- University of California, Davis, Department of Pharmacology , 451 Health Sciences Drive, Genome and Biomedical Sciences Facility Room 3502, Davis, CA 95616 , USA +1 530 754 6135 ; +1 530 752 7710 ;
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Endothelial small-conductance and intermediate-conductance KCa channels: an update on their pharmacology and usefulness as cardiovascular targets. J Cardiovasc Pharmacol 2013; 61:102-12. [PMID: 23107876 DOI: 10.1097/fjc.0b013e318279ba20] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Most cardiovascular researchers are familiar with intermediate-conductance KCa3.1 and small-conductance KCa2.3 channels because of their contribution to endothelium-derived hyperpolarization. However, to immunologists and neuroscientists, these channels are primarily known for their role in lymphocyte activation and neuronal excitability. KCa3.1 is involved in the proliferation and migration of T cells, B cells, mast cells, macrophages, fibroblasts, and dedifferentiated vascular smooth muscle cells and is, therefore, being pursued as a potential target for use in asthma, immunosuppression, and fibroproliferative disorders. In contrast, the 3 KCa2 channels (KCa2.1, KCa2.2, and KCa2.3) contribute to the neuronal medium afterhyperpolarization and, depending on the type of neuron, are involved in determining firing rates and frequencies or in regulating bursting. KCa2 activators are accordingly being studied as potential therapeutics for ataxia and epilepsy, whereas KCa2 channel inhibitors like apamin have long been known to improve learning and memory in rodents. Given this background, we review the recent discoveries of novel KCa3.1 and KCa2.3 modulators and critically assess the potential of KCa activators for the treatment of diabetes and cardiovascular diseases by improving endothelium-derived hyperpolarizations.
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21
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Abstract
New concepts on potassium channel function in neuroinflammation suggest that they regulate mechanisms of microglial activation, including intracellular calcium homeostasis, morphological alterations, pro-inflammatory cytokine release, antigen presentation, and phagocytosis. Although little is known about voltage independent potassium channels in microglia, special attention emerges on small (SK/KCNN1-3/K(Ca)2) and intermediate (IK/KCNN4/K(Ca)3.1)-conductance calcium-activated potassium channels as regulators of microglial activation in the field of research on neuroinflammation and neurodegeneration. In particular, recent findings suggested that SK/K(Ca)2 channels, by regulating calcium homeostasis, may elicit a dual mechanism of action with protective properties in neurons and inhibition of inflammatory responses in microglia. Thus, modulating SK/K(Ca)2 channels and calcium signaling may provide novel therapeutic strategies in neurological disorders, where neuronal cell death and inflammatory responses concomitantly contribute to disease progression. Here, we review the particular role of SK/K(Ca)2 channels for [Ca(2+)](i) regulation in microglia and neurons, and we discuss the potential impact for further experimental approaches addressing novel therapeutic strategies in neurological diseases, where neuronal cell death and neuroinflammatory processes are prominent.
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Affiliation(s)
- Amalia M Dolga
- Institute of Pharmacology and Clinical Pharmacy, University of Marburg Marburg, Germany
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22
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McCutcheon JE, Conrad KL, Carr SB, Ford KA, McGehee DS, Marinelli M. Dopamine neurons in the ventral tegmental area fire faster in adolescent rats than in adults. J Neurophysiol 2012; 108:1620-30. [PMID: 22723669 DOI: 10.1152/jn.00077.2012] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Adolescence may be a period of vulnerability to drug addiction. In rats, elevated firing activity of ventral tegmental area (VTA) dopamine neurons predicts enhanced addiction liability. Our aim was to determine if dopamine neurons are more active in adolescents than in adults and to examine mechanisms underlying any age-related difference. VTA dopamine neurons fired faster in adolescents than in adults as measured with in vivo extracellular recordings. Dopamine neuron firing can be divided into nonbursting (single spikes) and bursting activity (clusters of high-frequency spikes). Nonbursting activity was higher in adolescents compared with adults. Frequency of burst events did not differ between ages, but bursts were longer in adolescents than in adults. Elevated dopamine neuron firing in adolescent rats was also observed in cell-attached recordings in ex vivo brain slices. Using whole cell recordings, we found that passive and active membrane properties were similar across ages. Hyperpolarization-activated cation currents and small-conductance calcium-activated potassium channel currents were also comparable across ages. We found no difference in dopamine D2-class autoreceptor function across ages, although the high baseline firing in adolescents resulted in autoreceptor activation being less effective at silencing neurons. Finally, AMPA receptor-mediated spontaneous excitatory postsynaptic currents occurred at lower frequency in adolescents; GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents occurred at both lower frequency and smaller amplitude in adolescents. In conclusion, VTA dopamine neurons fire faster in adolescence, potentially because GABA tone increases as rats reach adulthood. This elevation of firing rate during adolescence is consistent with it representing a vulnerable period for developing drug addiction.
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Affiliation(s)
- James E McCutcheon
- Department of Cellular and Molecular Pharmacology, Rosalind Franklin University, North Chicago, Illinois, USA.
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23
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Herrik KF, Redrobe JP, Holst D, Hougaard C, Sandager-Nielsen K, Nielsen AN, Ji H, Holst NM, Rasmussen HB, Nielsen EØ, Strøbæk D, Shepard PD, Christophersen P. CyPPA, a Positive SK3/SK2 Modulator, Reduces Activity of Dopaminergic Neurons, Inhibits Dopamine Release, and Counteracts Hyperdopaminergic Behaviors Induced by Methylphenidate. Front Pharmacol 2012; 3:11. [PMID: 22347859 PMCID: PMC3278045 DOI: 10.3389/fphar.2012.00011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 01/19/2012] [Indexed: 11/29/2022] Open
Abstract
Dopamine (DA) containing midbrain neurons play critical roles in several psychiatric and neurological diseases, including schizophrenia and attention deficit hyperactivity disorder, and the substantia nigra pars compacta neurons selectively degenerate in Parkinson’s disease. Pharmacological modulation of DA receptors and transporters are well established approaches for treatment of DA-related disorders. Direct modulation of the DA system by influencing the discharge pattern of these autonomously firing neurons has yet to be exploited as a potential therapeutic strategy. Small conductance Ca2+-activated K+ channels (SK channels), in particular the SK3 subtype, are important in the physiology of DA neurons, and agents modifying SK channel activity could potentially affect DA signaling and DA-related behaviors. Here we show that cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA), a subtype-selective positive modulator of SK channels (SK3 > SK2 > > > SK1, IK), decreased spontaneous firing rate, increased the duration of the apamin-sensitive afterhyperpolarization, and caused an activity-dependent inhibition of current-evoked action potentials in DA neurons from both mouse and rat midbrain slices. Using an immunocytochemically and pharmacologically validated DA release assay employing cultured DA neurons from rats, we show that CyPPA repressed DA release in a concentration-dependent manner with a maximal effect equal to the D2 receptor agonist quinpirole. In vivo studies revealed that systemic administration of CyPPA attenuated methylphenidate-induced hyperactivity and stereotypic behaviors in mice. Taken together, the data accentuate the important role played by SK3 channels in the physiology of DA neurons, and indicate that their facilitation by CyPPA profoundly influences physiological as well as pharmacologically induced hyperdopaminergic behavior.
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Tateno T, Robinson HPC. The mechanism of ethanol action on midbrain dopaminergic neuron firing: a dynamic-clamp study of the role of I(h) and GABAergic synaptic integration. J Neurophysiol 2011; 106:1901-22. [PMID: 21697445 DOI: 10.1152/jn.00162.2011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels are expressed in dopaminergic (DA) neurons of the ventral tegmental area (VTA) as well as in DA and GABAergic neurons of the substantia nigra (SN). The excitation of DA neurons induced by ethanol has been proposed to result from its enhancing HCN channel current, I(h). Using perforated patch-clamp recordings in rat midbrain slices, we isolated I(h) in these neurons by voltage clamp. We showed that ethanol reversibly increased the amplitude and accelerated the activation kinetics of I(h) and caused a depolarizing shift in its voltage dependence. Using dynamic-clamp conductance injection, we injected artificial I(h) and fluctuating GABAergic synaptic conductance inputs into neurons following block of intrinsic I(h). This demonstrated directly a major role of I(h) in promoting rebound spiking following phasic inhibition, which was enhanced as the kinetics and amplitude of I(h) were changed in the manner induced by ethanol. Similar effects of ethanol were observed on I(h) and firing rate in non-DA, putatively GABAergic interneurons, indicating that in addition to its direct effects on firing, ethanol will produce large changes in the inhibition and disinhibition (via GABAergic interneurons) converging on DA neurons. Thus the overall effects of ethanol on firing of DA cells of the VTA and SN in vivo, and hence on phasic dopamine release in the striatum, appear to be determined substantially by its action on I(h) in both DA cells and GABAergic interneurons.
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Affiliation(s)
- Takashi Tateno
- Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
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Liebau S, Steinestel J, Linta L, Kleger A, Storch A, Schoen M, Steinestel K, Proepper C, Bockmann J, Schmeisser MJ, Boeckers TM. An SK3 channel/nWASP/Abi-1 complex is involved in early neurogenesis. PLoS One 2011; 6:e18148. [PMID: 21464958 PMCID: PMC3064656 DOI: 10.1371/journal.pone.0018148] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 02/27/2011] [Indexed: 12/12/2022] Open
Abstract
Background The stabilization or regulated reorganization of the actin cytoskeleton is essential for cellular structure and function. Recently, we could show that the activation of the SK3-channel that represents the predominant SK-channel in neural stem cells, leads to a rapid local outgrowth of long filopodial processes. This observation indicates that the rearrangement of the actin based cytoskeleton via membrane bound SK3-channels might selectively be controlled in defined micro compartments of the cell. Principal Findings We found two important proteins for cytoskeletal rearrangement, the Abelson interacting protein 1, Abi-1 and the neural Wiskott Aldrich Syndrome Protein, nWASP, to be in complex with SK3- channels in neural stem cells (NSCs). Moreover, this interaction is also found in spines and postsynaptic compartments of developing primary hippocampal neurons and regulates neurite outgrowth during early phases of differentiation. Overexpression of the proteins or pharmacological activation of SK3 channels induces obvious structural changes in NSCs and hippocampal neurons. In both neuronal cell systems SK3 channels and nWASP act synergistic by strongly inducing filopodial outgrowth while Abi-1 behaves antagonistic to its interaction partners. Conclusions Our results give good evidence for a functional interplay of a trimeric complex that transforms incoming signals via SK3-channel activation into the local rearrangement of the cytoskeleton in early steps of neuronal differentiation involving nWASP and Abi-1 actin binding proteins.
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Affiliation(s)
- Stefan Liebau
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Julie Steinestel
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Leonhard Linta
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Alexander Kleger
- Department of Internal Medicine I, Ulm University, Ulm, Germany
- Institute of Molecular Medicine and Max-Planck-Research Group on Stem Cell Aging, Ulm, Germany
| | - Alexander Storch
- Department of Neurology and Center for Regenerative Therapies Dresden (CRTD), Dresden University of Technology, Dresden, Germany
| | - Michael Schoen
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Konrad Steinestel
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | | | - Juergen Bockmann
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | | | - Tobias M. Boeckers
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
- * E-mail:
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Grube S, Gerchen MF, Adamcio B, Pardo LA, Martin S, Malzahn D, Papiol S, Begemann M, Ribbe K, Friedrichs H, Radyushkin KA, Müller M, Benseler F, Riggert J, Falkai P, Bickeböller H, Nave KA, Brose N, Stühmer W, Ehrenreich H. A CAG repeat polymorphism of KCNN3 predicts SK3 channel function and cognitive performance in schizophrenia. EMBO Mol Med 2011; 3:309-19. [PMID: 21433290 PMCID: PMC3377084 DOI: 10.1002/emmm.201100135] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 02/24/2011] [Accepted: 02/25/2011] [Indexed: 12/11/2022] Open
Abstract
KCNN3, encoding the small conductance calcium-activated potassium channel SK3, harbours a polymorphic CAG repeat in the amino-terminal coding region with yet unproven function. Hypothesizing that KCNN3 genotypes do not influence susceptibility to schizophrenia but modify its phenotype, we explored their contribution to specific schizophrenic symptoms. Using the Göttingen Research Association for Schizophrenia (GRAS) data collection of schizophrenic patients (n = 1074), we performed a phenotype-based genetic association study (PGAS) of KCNN3. We show that long CAG repeats in the schizophrenic sample are specifically associated with better performance in higher cognitive tasks, comprising the capacity to discriminate, select and execute (p < 0.0001). Long repeats reduce SK3 channel function, as we demonstrate by patch-clamping of transfected HEK293 cells. In contrast, modelling the opposite in mice, i.e. KCNN3 overexpression/channel hyperfunction, leads to selective deficits in higher brain functions comparable to those influenced by SK3 conductance in humans. To conclude, KCNN3 genotypes modify cognitive performance, shown here in a large sample of schizophrenic patients. Reduction of SK3 function may constitute a pharmacological target to improve cognition in schizophrenia and other conditions with cognitive impairment.
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Affiliation(s)
- Sabrina Grube
- Divison of Clinical Neuroscience, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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Functional reduction of SK3-mediated currents precedes AMPA-receptor-mediated excitotoxicity in dopaminergic neurons. Neuropharmacology 2010; 60:1176-86. [PMID: 21044638 DOI: 10.1016/j.neuropharm.2010.10.024] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2010] [Revised: 09/28/2010] [Accepted: 10/26/2010] [Indexed: 11/21/2022]
Abstract
In primary cultures of mesencephalon small-conductance calcium-activated potassium channels (SK) are expressed in dopaminergic neurons. We characterized SK-mediated currents (I(SK)) in this system and evaluated their role on homeostasis against excitotoxicity. I(SK) amplitude was reduced by the glutamatergic agonist AMPA through a reduction in SK channel number in the membrane. Blockade of I(SK) for 12 h with apamin or NS8593 reduced the number of dopaminergic neurons in a concentration-dependent manner. The effect of apamin was not additive to AMPA toxicity. On the other hand, two I(SK) agonists, 1-EBIO and CyPPA, caused a significant reduction of spontaneous loss of dopaminergic neurons. 1-EBIO reversed the effects of both AMPA and apamin as well. Thus, I(SK) influences survival and differentiation of dopaminergic neurons in vitro, and is part of protective homeostatic responses, participating in a rapidly acting negative feedback loop coupling calcium levels, neuron excitability and cellular defenses. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.
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A small-conductance Ca2+-dependent K+ current regulates dopamine neuron activity: a combined approach of dynamic current clamping and intracellular imaging of calcium signals. Neuroreport 2010; 21:667-74. [PMID: 20508546 DOI: 10.1097/wnr.0b013e32833add56] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
To analyze the small-conductance calcium-dependent K current observed in dopaminergic neurons of the rat midbrain, we have developed a new dynamic current clamping method that incorporates recording of intracellular Ca levels. As reported earlier, blocking the small-conductance current with apamin shifted the firing modes of dopaminergic neurons and changed the firing rate and spike afterhyperpolarization. We modeled the kinetic properties of the current and assessed the model in a real-time computational system. Here, we show that the spike afterhyperpolarization is regulated by the small-conductance current, an effect that is observed in dopaminergic neurons. Thus, this current can effectively shape the autonomous firing patterns of dopaminergic neurons.
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29
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Mpari B, Sreng L, Manrique C, Mourre C. KCa2 channels transiently downregulated during spatial learning and memory in rats. Hippocampus 2010; 20:352-63. [PMID: 19437421 DOI: 10.1002/hipo.20622] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Small-conductance calcium-activated potassium channels (K(Ca)2) are essential components involved in the modulation of neuronal excitability, underlying learning and memory. Recent evidence suggests that K(Ca)2 channel activity reduces synaptic transmission in a postsynaptic NMDA receptor-dependent manner and is modulated by long-term potentiation. We used radioactive in situ hybridization and apamin binding to investigate the amount of K(Ca)2 subunit mRNA and K(Ca)2 proteins in brain structures involved in learning and memory at different stages of a radial-arm maze task in naive, pseudoconditioned, and conditioned rats. We observed significant differences in K(Ca)2.2 and K(Ca)2.3, but not K(Ca)2.1 mRNA levels, between conditioned and pseudoconditioned rats. K(Ca)2.2 levels were transiently reduced in the dorsal CA fields of the hippocampus, whereas K(Ca)2.3 mRNA levels were reduced in the dorsal and ventral CA fields of the hippocampus, entorhinal cortex, and basolateral amygdaloid nucleus in conditioned rats, during early stages of learning. Levels of apamin-binding sites displayed a similar pattern to K(Ca)2 mRNA levels during learning. Spatial learning performance was positively correlated with levels of apamin-binding sites and K(Ca)2.3 mRNA in the dorsal CA1 field and negatively correlated in the dorsal CA3 field. These findings suggest that K(Ca)2 channels are transiently downregulated in the early stages of learning and that regulation of K(Ca)2 channel levels is involved in the modification of neuronal substrates underlying new information acquisition.
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Affiliation(s)
- Bedel Mpari
- Laboratoire de Neurobiologie Intégrative et Adaptative, Neurobiologie des Processus Mnésiques, UMR 6149, Aix-Marseille Université, CNRS, Centre St Charles, 3 Place Victor Hugo, 13331 Marseille Cedex 03, France
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30
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Functions and modulation of neuronal SK channels. Cell Biochem Biophys 2009; 55:127-39. [PMID: 19655101 DOI: 10.1007/s12013-009-9062-7] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
Small conductance (SK) channels are calcium-activated potassium channels that, when cloned in 1996, were thought solely to contribute to the afterhyperpolarisation that follows action potentials, and to control repetitive firing patterns of neurons. However, discoveries over the past few years have identified novel roles for SK channels in controlling dendritic excitability, synaptic transmission and synaptic plasticity. More recently, modulation of SK channel calcium sensitivity by casein kinase 2, and of SK channel trafficking by protein kinase A, have been demonstrated. This article will discuss recent findings regarding the function and modulation of SK channels in central neurons.
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31
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Ji H, Hougaard C, Herrik KF, Strøbaek D, Christophersen P, Shepard PD. Tuning the excitability of midbrain dopamine neurons by modulating the Ca2+ sensitivity of SK channels. Eur J Neurosci 2009; 29:1883-95. [PMID: 19473240 DOI: 10.1111/j.1460-9568.2009.06735.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Small conductance Ca(2+) -activated K(+) (SK) channels play a prominent role in modulating the spontaneous activity of dopamine (DA) neurons as well as their response to synaptically-released glutamate. SK channel gating is dependent on Ca(2+) binding to constitutively bound calmodulin, which itself is subject to endogenous and exogenous modulation. In the present study, patch-clamp recording techniques were used to examine the relationship between the apparent Ca(2+) affinity of cloned SK3 channels expressed in cultured human embryonic kidney 293 cells and the excitability of DA neurons in slices from rat substantia nigra using the positive and negative SK channel modulators, 6,7-dichloro-1H-indole-2,3-dione-3-oxime and R-N-(benzimidazol-2-yl)-1,2,3,4-tetrohydro-1-naphtylamine. Increasing the apparent Ca(2+) affinity of SK channels decreased the responsiveness of DA neurons to depolarizing current pulses, enhanced spike frequency adaptation and slowed spontaneous firing, effects attributable to an increase in the amplitude and duration of an apamin-sensitive afterhyperpolarization. In contrast, decreasing the apparent Ca(2+) affinity of SK channels enhanced DA neuronal excitability and changed the firing pattern from a pacemaker to an irregular or bursting discharge. Both the reduction in apparent Ca(2+) affinity and the bursting associated with negative SK channel modulation were gradually surmounted by co-application of the positive SK channel modulator. These results underscore the importance of SK channels in 'tuning' the excitability of DA neurons and demonstrate that gating modulation, in a manner analogous to physiological regulation of SK channels in vivo, represents a means of altering the response of DA neurons to membrane depolarization.
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Affiliation(s)
- Huifang Ji
- Department of Psychiatry, Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD 21228, USA
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32
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Electrophysiological characteristics of dopamine neurons: a 35-year update. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 2009:103-19. [PMID: 20411771 DOI: 10.1007/978-3-211-92660-4_8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
This chapter consists of four sections. The first section provides a general description of the electrophysiological characteristics of dopamine (DA) neurons in both the substantia nigra and ventral tegmental area. Emphasis is placed on the differences between DA and neighboring non-DA neurons. The second section discusses the ionic mechanisms underlying the generation of action potential in DA cells. Evidence is provided to suggest that these mechanisms differ not only between DA and non-DA neurons but also between DA cells located in different areas, with different projection sites and at different developmental stages. Some of the differences may play a critical role in the vulnerability of a DA neuron to cell death. The third section describes the firing patterns of DA cells. Data are presented to show that the current "80/160 ms" criteria for burst identification need to be revised and that the burst firing, originally described by Bunney et al., can be described as slow oscillations in firing rate. In the ventral tegmental area, the slow oscillations are, at least partially, derived from the prefrontal cortex and part of prefrontal information is transferred to DA cells indirectly through inhibitory neurons. The final section focuses on the feedback regulation of DA cells. New evidence suggests that DA autoreceptors are coupled to multiple effectors, and both D1 and D2-like receptors are involved in long-loop feedback control of DA neurons. Because of the presence of multiple feedback and nonfeedback pathways, the effect of a drug on a DA neuron can be far more complex than an inhibition or excitation. A better understanding of the intrinsic properties of DA neurons and their regulation by afferent input will, in time, help to point to the way to more effective and safer treatments for disorders including schizophrenia, drug addiction, and Parkinson's disease.
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Molecular and cellular basis of small--and intermediate-conductance, calcium-activated potassium channel function in the brain. Cell Mol Life Sci 2008; 65:3196-217. [PMID: 18597044 PMCID: PMC2798969 DOI: 10.1007/s00018-008-8216-x] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Small conductance calcium-activated potassium (SK or KCa2) channels link intracellular calcium transients to membrane potential changes. SK channel subtypes present different pharmacology and distribution in the nervous system. The selective blocker apamin, SK enhancers and mice lacking specific SK channel subunits have revealed multifaceted functions of these channels in neurons, glia and cerebral blood vessels. SK channels regulate neuronal firing by contributing to the afterhyperpolarization following action potentials and mediating IAHP, and partake in a calcium-mediated feedback loop with NMDA receptors, controlling the threshold for induction of hippocampal long-term potentiation. The function of distinct SK channel subtypes in different neurons often results from their specific coupling to different calcium sources. The prominent role of SK channels in the modulation of excitability and synaptic function of limbic, dopaminergic and cerebellar neurons hints at their possible involvement in neuronal dysfunction, either as part of the causal mechanism or as potential therapeutic targets.
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SK channel function regulates the dopamine phenotype of neurons in the substantia nigra pars compacta. Exp Neurol 2008; 213:419-30. [PMID: 18680743 DOI: 10.1016/j.expneurol.2008.07.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Revised: 07/02/2008] [Accepted: 07/05/2008] [Indexed: 11/24/2022]
Abstract
Parkinson's disease (PD) is characterized by loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). It is widely believed that replacing lost SNc DA neurons is a key to longer-term effective treatment of PD motor symptoms, but generating new SNc DA neurons in PD patients has proven difficult. Following loss of tyrosine hydroxylase-positive (TH+) SNc neurons in the rodent 6-hydroxy-DA (6-OHDA) model of PD, the number of TH+ neurons partially recovers and there is evidence this occurs via phenotype "shift" from TH- to TH+ cells. Understanding how this putative phenotype shift occurs may help increase SNc DAergic neurons in PD patients. In this study we characterize the electrophysiology of SNc TH- and TH+ cells during recovery from 6-OHDA in mice. Three distinct phenotypes were observed: (1) TH- were fast discharging with a short duration action potential (AP), short afterhyperpolarization (AHP) and no small conductance Ca(2+)-activated K(+) (SK) current; (2) TH+ were slow discharging with a long AP, long AHP and prominent SK current; and (3) cells with features "intermediate" between these TH- and TH+ phenotypes. The same 3 phenotypes were present also in the normal and D2 DA receptor knock-out SNc suggesting they are more closely related to the biology of TH expression than recovery from 6-OHDA. Acute inhibition of SK channel function shifted the electrophysiological phenotype of TH+ neurons toward TH- and chronic (2 weeks) inhibition of SK channel function in normal mice shifted the neurochemical phenotype of SNc from TH+ to TH- (i.e. decreased TH+ and increased TH- cell numbers). Importantly, chronic facilitation of SK channel function shifted the neurochemical phenotype of SNc from TH- to TH+ (i.e. increased TH+ and decreased TH- cell numbers). We conclude that SK channel function bidirectionally regulates the DA phenotype of SNc cells and facilitation of SK channels may be a novel way to increase the number of SNc DAergic neurons in PD patients.
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35
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Segev D, Korngreen A. Kinetics of two voltage-gated K+ conductances in substantia nigra dopaminergic neurons. Brain Res 2007; 1173:27-35. [PMID: 17826751 DOI: 10.1016/j.brainres.2007.08.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Revised: 08/01/2007] [Accepted: 08/02/2007] [Indexed: 10/23/2022]
Abstract
The substantia nigra (SN) is part of the basal ganglia which is a section in the movement circuit in the brain. Dopaminergic neurons (DA) constitute the bulk of substantia nigra neurons and are related to diseases such as Parkinson's disease. Aiming at describing the mechanism of action potential firing in these cells, the current research examined the biophysical characteristics of voltage-gated K+ conductances in the dopaminergic neurons of the SN. The outside-out configuration of the patch-clamp technique was used to measure from dopaminergic neurons in acute brain slices. Two types of K+ voltage-gated conductances, a fast-inactivating A-type-like K+ conductance (K(fast)) and a slow-inactivating delayed rectifier-like K+ conductance (K(slow)), were isolated in these neurons using kinetic separation protocols. The data suggested that a fast-inactivating conductance was due to 69% of the total voltage-gated K+ conductances, while the remainder of the voltage-gated K+ conductance was due to the activation of a slow-inactivating K+ conductance. The two voltage-gated K+ conductances were analyzed assuming a Hodgkin-Huxley model with two activation and one inactivation gate. The kinetic models obtained from this analysis were used in a numerical simulation of the action potential. This simulation suggested that K(fast) may be involved in the modulation of the height and width of action potentials initiated at different resting membrane potentials while K(slow) may participate in action potential repolarization. This mechanism may indicate that SN dopaminergic neurons may perform analog coding by modulation of action potential shape.
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Affiliation(s)
- Dekel Segev
- The Mina & Everard Goodman Faculty of Life Sciences and the Susan & Leslie Gonda Multidiciplinary Brain Research Center, Bar-Ilan University, Ramat-Gan, Israel
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36
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Yanovsky Y, Velte S, Misgeld U. Ca2+ release-dependent hyperpolarizations modulate the firing pattern of juvenile GABA neurons in mouse substantia nigra pars reticulata in vitro. J Physiol 2006; 577:879-90. [PMID: 17053035 PMCID: PMC1890382 DOI: 10.1113/jphysiol.2006.117622] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
A phasic activation of small-conductance Ca(2+)-dependent K(+) channels (SK channels) underlies spike-afterhyperpolarizations and spike-independent, transient hyperpolarizations in juvenile substantia nigra neurons. Outward current pulses that cause the spike-independent hyperpolarizations result from ryanodine receptor-mediated Ca(2+) release from intracellular stores. To study the modulation of excitability by the outward current pulses, we recorded from GABAergic pars reticulata neurons of mice at postnatal days 12-16. We induced a prolongation of SK channel open states by 1-ethyl-2-benzimidazolinone (1-EBIO). In addition to a prolongation of spike-afterhyperpolarizations, 1-EBIO (200 microm) potentiated outward current pulses by increasing their duration. Neurons were manipulated by current injection to display continuous or discontinuous discharge. Despite the prolongation of the outward current pulses by 1-EBIO, continuous action potential discharge became more regular, although its frequency declined. Durations of silent periods (periods of >2x average interspike interval) increased. Caffeine (1 mm) further increased the duration of such silent periods. Caffeine, however, had no effect at short interspike intervals (<600 ms). Cyclopiazonic acid (10 microm) silenced discharge in 1-EBIO, but discharge reappeared with the depletion of Ca(2+) stores. We conclude that the modulation of excitability by an activation of SK channels through ryanodine receptor-mediated release of Ca(2+) critically depends on the frequency of discharge. Outward current pulses occur only if interspike intervals exceed the duration of spike-afterhyperpolarizations. In this instance, the phasic, spike-independent activation of SK channels supports pauses to interrupt autonomous discharge in juvenile GABAergic pars reticulata neurons.
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Affiliation(s)
- Yevgenij Yanovsky
- Institut für Physiologie und Pathophysiologie, Universität Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
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37
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Gargus JJ. Ion channel functional candidate genes in multigenic neuropsychiatric disease. Biol Psychiatry 2006; 60:177-85. [PMID: 16497276 DOI: 10.1016/j.biopsych.2005.12.008] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 11/15/2005] [Accepted: 12/15/2005] [Indexed: 10/25/2022]
Abstract
Scores of monogenic Mendelian ion channel diseases serve to anchor the pathophysiology of the channelopathies, but there are also now clear examples of environmental, pharmacogenetic, and acquired channelopathy mechanisms. The cardinal feature of heritable ion channel disease is a periodic disturbance of rhythmic function in constitutionally hyperexcitable tissue. While the complexity of neuroanatomy obscures functional analysis of mutations causing monogenic seizure, ataxia, or migraine syndromes, extrapolation from the cardiac (Long QT [LQT]) and muscle (Periodic Paralysis) channelopathy syndromes provides a simplified predictive framework of molecular pathology: electrically stabilizing potassium ion (K(+)) and chloride ion (Cl(-)) channels, likely having lesions that diminish their current, and excitatory Na(+) channels, likely having gain-of-function lesions. The voltage-gated calcium channel gene family that contains CACNA1C, the newest LQT locus, causing Timothy Syndrome with a phenotype including autism, has proven to be particularly informative for its members' ability to tie the various central nervous system (CNS) phenotypes together in an interpretable fashion, now including direct extension to the classically multigenic neuropsychiatric phenotypes. Features of a promising ion channel candidate gene arise from its broad locus, gene family, nature of alleles, physiology and pharmacology, tissue expression profile, and phenotype in model organisms. KCNN3 is explored as a paradigm to consider.
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Affiliation(s)
- J Jay Gargus
- Department of Physiology, Section of Human Genetics, University of California, Irvine, California 92697-4034, USA.
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Ji H, Shepard PD. SK Ca2+-activated K+ channel ligands alter the firing pattern of dopamine-containing neurons in vivo. Neuroscience 2006; 140:623-33. [PMID: 16564639 DOI: 10.1016/j.neuroscience.2006.02.020] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Revised: 02/01/2006] [Accepted: 02/08/2006] [Indexed: 11/24/2022]
Abstract
Apamin-sensitive, SK channels play an important role in generating the rhythmic firing patterns exhibited by midbrain dopamine neurons in vitro. However, their contribution to the firing properties of these cells in intact animals has yet to be determined. In the present series of experiments, extracellular single unit recording techniques were used to assess the central effects of prototypical SK channel ligands on the firing pattern of dopamine neurons in the substantia nigra of the chloral hydrate anesthetized rat. I.v. administration of the SK channel blocker apamin (0.4 mg/kg), increased bursting activity in approximately 50% of the dopamine neurons tested without altering average firing rate. The majority of these cells responded slowly to the effects of apamin, gradually transitioning from an irregular single spike to a phasic discharge composed of the same relative proportion of long (>or=three spike) and short (two spike) bursts as "natural" bursting activity recorded in drug naive animals. Local administration of apamin increased bursting activity in all cells tested. Systemic administration of the SK channel opener, 1-ethyl-2-benzimidazolinone (5-25 mg/kg) also had no effect on average firing rate but suppressed bursting activity and increased the precision of firing. The effects of 1-ethyl-2-benzimidazolinon on firing pattern were abolished when recording electrodes contained apamin (125 microM). These results suggest that SK channels actively contribute to the spontaneous firing patterns exhibited by dopamine neurons in vivo and provide additional support for the proposition that this channel could serve as a useful target for modifying their activity.
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Affiliation(s)
- H Ji
- Maryland Psychiatric Research Center and the University of Maryland School of Medicine, Department of Psychiatry, P.O. Box 21247, Baltimore, MD 21228, USA
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Atherton JF, Bevan MD. Ionic mechanisms underlying autonomous action potential generation in the somata and dendrites of GABAergic substantia nigra pars reticulata neurons in vitro. J Neurosci 2006; 25:8272-81. [PMID: 16148235 PMCID: PMC6725542 DOI: 10.1523/jneurosci.1475-05.2005] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Through their repetitive discharge, GABAergic neurons of the substantia nigra pars reticulata (SNr) tonically inhibit the target nuclei of the basal ganglia and the dopamine neurons of the midbrain. As the repetitive firing of SNr neurons persists in vitro, perforated, whole-cell and cell-attached patch-clamp recordings were made from rat brain slices to determine the mechanisms underlying this activity. The spontaneous activity of SNr neurons was not perturbed by the blockade of fast synaptic transmission, demonstrating that it was autonomous in nature. A subthreshold, slowly inactivating, voltage-dependent, tetrodotoxin (TTX)-sensitive Na+ current and a TTX-insensitive inward current that was mediated in part by Na+ were responsible for depolarization to action potential (AP) threshold. An apamin-sensitive spike afterhyperpolarization mediated by small-conductance Ca2+-dependent K+ (SK) channels was critical for the precision of autonomous activity. SK channels were activated, in part, by Ca(2+) flowing throughomega-conotoxin GVIA-sensitive, class 2.2 voltage-dependent Ca2+ channels. Although Cs+/ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride)-sensitive hyperpolarization-activated currents were also observed in SNr neurons, they were activated at voltages that were in general more hyperpolarized than those associated with autonomous activity. Simultaneous somatic and dendritic recordings revealed that autonomously generated APs were observed first at the soma before propagating into dendrites up to 120 microm from the somatic recording site. Backpropagation of autonomously generated APs was reliable with no observable incidence of failure. Together, these data suggest that the resting inhibitory output of the basal ganglia relies, in large part, on the intrinsic firing properties of the neurons that convey this signal.
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Affiliation(s)
- Jeremy F Atherton
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA
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Waroux O, Massotte L, Alleva L, Graulich A, Thomas E, Liégeois JF, Scuvée-Moreau J, Seutin V. SK channels control the firing pattern of midbrain dopaminergic neurons in vivo. Eur J Neurosci 2006; 22:3111-21. [PMID: 16367777 DOI: 10.1111/j.1460-9568.2005.04484.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
A vast body of experimental in vitro work and modelling studies suggests that the firing pattern and/or rate of a majority of midbrain dopaminergic neurons may be controlled in part by Ca2+-activated K+ channels of the SK type. However, due to the lack of suitable tools, in vivo evidence is lacking. We have taken advantage of the development of the water-soluble, medium potency SK blocker N-methyl-laudanosine (CH3-L) to test this hypothesis in anaesthetized rats. In the lateral ventral tegmental area, CH3-L iontophoresis onto dopaminergic neurons significantly increased the coefficient of variation of their interspike intervals and the percentage of spikes generated in bursts as compared to the control condition. The effect of CH3-L persisted in the presence of a specific GABA(A) antagonist, suggesting a direct effect. It was robust and reversible, and was also observed in the substantia nigra. Control experiments demonstrated that the effect of CH3-L could be entirely ascribed to its blockade of SK channels. On the other hand, the firing pattern of noradrenergic neurons was much less affected by CH3-L. We provide here the first demonstration of a major role of SK channels in the control of the switch between tonic and burst firing of dopaminergic neurons in physiological conditions. This study also suggests a new strategy to develop modulators of the dopaminergic (DA) system, which could be of interest in the treatment of Parkinson's disease, and perhaps other diseases in which DA pathways are dysfunctional.
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Affiliation(s)
- Olivier Waroux
- Research Center for Cellular and Molecular Neurobiology and Laboratory of Pharmacology, University of Liège, B-4000 Liège, Belgium
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Koyama S, Kanemitsu Y, Weight FF. Spontaneous activity and properties of two types of principal neurons from the ventral tegmental area of rat. J Neurophysiol 2005; 93:3282-93. [PMID: 15659533 DOI: 10.1152/jn.00776.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the spontaneous activity and properties of freshly isolated ventral tegmental area (VTA) principal neurons by whole cell recording and single-cell RT-PCR. The VTA principal neurons, which were tyrosine hydroxylase-positive and glutamic acid decarboxylase (GAD67)-negative, exhibited low firing frequency and a long action potential (AP) duration. The VTA principal neurons exhibited a calretinin-positive and parvalbumin-negative Ca2+-binding protein mRNA expression pattern. The VTA principal neurons were classified into two subpopulations based on their firing frequency coefficient of variation (CV) at room temperature (21-23 degrees C): irregular-type neurons with a large CV and tonic-type neurons with a small CV. These two firing patterns were also recorded at the temperature of 34 degrees C and in nystatin-perforated patch recording. In VTA principal neurons, the AP afterhyperpolarization (AHP) amplitude contributed to the firing regularity and AHP decay slope contributed to the firing frequency. The AHP amplitude in the irregular-type VTA principal neurons was smaller than that in the tonic-type VTA principal neurons. There was no significant difference in the AHP decay slope between the two-types of VTA principal neurons. Apamin-sensitive small-conductance Ca2+-activated K+ (SK) channels contributed to the AHP and the regular firing of the tonic-type neurons but contributed little to the AHP and firing of the irregular-type neurons. In voltage-clamp tail-current analysis, in both conventional and nystatin-perforated whole cell recording, the apamin-sensitive AHP current density of the tonic-type neurons was significantly larger than that of the irregular-type neurons. We suggest that apamin-sensitive SK current contributes to intrinsic firing differences between the two subpopulations of VTA principal neurons.
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Affiliation(s)
- Susumu Koyama
- Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, USA.
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Yanovsky Y, Zhang W, Misgeld U. Two pathways for the activation of small-conductance potassium channels in neurons of substantia nigra pars reticulata. Neuroscience 2005; 136:1027-36. [PMID: 16203104 DOI: 10.1016/j.neuroscience.2005.08.026] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Revised: 08/11/2005] [Accepted: 08/11/2005] [Indexed: 10/25/2022]
Abstract
Neurons in substantia nigra pars reticulata express the messenger RNA for SK2 but not for SK3 subunits that form small-conductance, Ca2+-dependent K+ channels in dopamine neurons. To determine pathways for the activation of small-conductance, Ca2+-dependent K+ channels in substantia nigra pars reticulata neurons of rats and mice, we studied effects of the selective blocker of small-conductance, Ca2+-dependent K+ channels, apamin (0.01 or 0.3 microM). Apamin diminished the afterhyperpolarization following each action potential and induced burst discharges in substantia nigra pars reticulata neurons. Apamin had a robust effect already at a low (10 nM) concentration consistent with the expression of the SK2 subunit. Afterhyperpolarizations were also reduced by the Ca2+ channel blockers Ni2+ (100 microM) and omega-conotoxin GVIA (1 microM). Depletion of intracellular Ca2+ stores did not change the afterhyperpolarization. However, we observed outward current pulses that occurred independently from action potentials and were abrogated by apamin. Apart from a faster time course, they shared all properties with spontaneous hyperpolarizations or outward currents that ryanodine receptor-mediated Ca2+ release from intracellular stores induces in juvenile dopamine neurons. Sensitization of ryanodine receptors by caffeine silenced substantia nigra pars reticulata neurons. This effect was abolished by the depletion of intracellular Ca2+ stores. We conclude that SK2 channels in substantia nigra pars reticulata neurons are activated by Ca2+ influx through at least two types of Ca2+ channels in the membrane and by ryanodine receptor-mediated Ca2+ release from intracellular stores. Ryanodine receptors do not amplify small-conductance, Ca2+-dependent K+ channel activation by the Ca2+ influx during a single spike. Yet, ryanodine receptor-mediated Ca2+ release and, thereby, an activation of small-conductance, Ca2+-dependent K+ channels by intracellular Ca2+ are available for excitability modulation in these output neurons of the basal ganglia system.
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Affiliation(s)
- Y Yanovsky
- Institut für Physiologie und Pathophysiologie, Universität Heidelberg und Interdisziplinäres Zentrum für Neurowissenschaften, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
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