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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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2
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Chen RYT, Evans RC. Comparing tonic and phasic dendritic calcium in cholinergic pedunculopontine neurons and dopaminergic substantia nigra neurons. Eur J Neurosci 2024; 59:1638-1656. [PMID: 38383047 PMCID: PMC10987283 DOI: 10.1111/ejn.16281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Revised: 01/25/2024] [Accepted: 01/30/2024] [Indexed: 02/23/2024]
Abstract
Several brainstem nuclei degenerate in Parkinson's disease (PD). In addition to the well-characterized dopaminergic neurons of the substantia nigra pars compacta (SNc), the cholinergic neurons of the pedunculopontine nucleus (PPN) also degenerate in PD. One leading hypothesis of selective vulnerability is that pacemaking activity and the activation of low-threshold L-type calcium current are major contributors to tonic calcium load and cellular stress in SNc dopaminergic neurons. However, it is not yet clear whether the vulnerable PPN cholinergic neurons share this property. Therefore, we used two-photon dendritic calcium imaging and whole-cell electrophysiology to evaluate the role of L-type calcium channels in tonic and phasic dendritic calcium signals in PPN and SNc neurons. In addition, we investigated N- and P/Q-type calcium channel regulation of firing properties and dendritic calcium in PPN neurons. We found that blocking L-type channels reduces tonic firing rate and dendritic calcium levels in SNc neurons. By contrast, the tonic calcium load in PPN neurons did not depend on L-, N- or P/Q-type channels. However, we found that blocking either L-type (with nifedipine) or N- and P/Q-type (with omega-conotoxin MVIIC) channels reduces phasic calcium influx in PPN dendrites. Together, these findings show that L-type calcium channels play different roles in the activity of SNc and PPN neurons, and suggest that low-threshold L-type channels are not responsible for tonic calcium levels in PPN cholinergic neurons and are therefore not likely to be a source of selective vulnerability in these cells.
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Affiliation(s)
- Rita Yu-Tzu Chen
- Department of Neuroscience, Georgetown University Medical Center, Washington DC
| | - Rebekah C. Evans
- Department of Neuroscience, Georgetown University Medical Center, Washington DC
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3
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Khamis H, Cohen O. Coupled action potential and calcium dynamics underlie robust spontaneous firing in dopaminergic neurons. Phys Biol 2024; 21:026005. [PMID: 38382117 DOI: 10.1088/1478-3975/ad2bd4] [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: 08/16/2023] [Accepted: 02/21/2024] [Indexed: 02/23/2024]
Abstract
Dopaminergic neurons are specialized cells in the substantia nigra, tasked with dopamine secretion. This secretion relies on intracellular calcium signaling coupled to neuronal electrical activity. These neurons are known to display spontaneous calcium oscillationsin-vitroandin-vivo, even in synaptic isolation, controlling the basal dopamine levels. Here we outline a kinetic model for the ion exchange across the neuronal plasma membrane. Crucially, we relax the assumption of constant, cytoplasmic sodium and potassium concentration. We show that sodium-potassium dynamics are strongly coupled to calcium dynamics and are essential for the robustness of spontaneous firing frequency. The model predicts several regimes of electrical activity, including tonic and 'burst' oscillations, and predicts the switch between those in response to perturbations. 'Bursting' correlates with increased calcium amplitudes, while maintaining constant average, allowing for a vast change in the calcium signal responsible for dopamine secretion. All the above traits provide the flexibility to create rich action potential dynamics that are crucial for cellular function.
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Affiliation(s)
- Hadeel Khamis
- Gateway Institute for Brain Research, Fort Lauderdale, FL 33314, United States of America
| | - Ohad Cohen
- Gateway Institute for Brain Research, Fort Lauderdale, FL 33314, United States of America
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Um KB, Kwak S, Cheon SH, Kim J, Hwang SK. AST-001 Improves Social Deficits and Restores Dopamine Neuron Activity in a Mouse Model of Autism. Biomedicines 2023; 11:3283. [PMID: 38137504 PMCID: PMC10741043 DOI: 10.3390/biomedicines11123283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 12/05/2023] [Accepted: 12/08/2023] [Indexed: 12/24/2023] Open
Abstract
Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by impaired social communication and social interaction, restricted and repetitive behavior, and interests. The core symptoms of ASD are associated with deficits in mesocorticolimbic dopamine pathways that project from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC). AST-001 is an investigational product currently in a phase 3 clinical trial for treating the core symptoms of ASD, with L-serine as the API (active pharmaceutical ingredient). Because the causes of ASD are extremely heterogeneous, a single genetic ASD model cannot represent all autism models. In this paper, we used the VPA-exposed model, which is more general and widely used than a single genetic model, but this is also one of the animal models of autism. Herein, we conducted experiments to demonstrate the efficacy of AST-001 as L-Serine that alters the regulation of the firing rate in dopamine neurons by inhibiting small conductance Ca2+-activated K+ channels (SK channels). Through these actions, AST-001 improved sociability and social novelty by rescuing the intrinsic excitabilities of dopamine neurons in VPA-exposed ASD mouse models that showed ASD-related behavioral abnormalities. It is thought that this effect of improving social deficits in VPA-exposed ASD mouse models is due to AST-001 normalizing aberrant SK channel activities that slowed VTA dopamine neuron firing. Overall, these findings suggest that AST-001 may be a potential therapeutic agent for ASD patients, and that its mechanism of action may involve the regulation of dopamine neuron activity and the improvement of social interaction.
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Affiliation(s)
- Ki Bum Um
- Astrogen Inc., 440, Hyeoksin-daero, Dong-gu, Daegu 41072, Republic of Korea; (K.B.U.); (S.K.)
| | - Soyoung Kwak
- Astrogen Inc., 440, Hyeoksin-daero, Dong-gu, Daegu 41072, Republic of Korea; (K.B.U.); (S.K.)
| | - Sun-Ha Cheon
- Astrogen Inc., 440, Hyeoksin-daero, Dong-gu, Daegu 41072, Republic of Korea; (K.B.U.); (S.K.)
| | - JuHyun Kim
- Astrogen Inc., 440, Hyeoksin-daero, Dong-gu, Daegu 41072, Republic of Korea; (K.B.U.); (S.K.)
| | - Su-Kyeong Hwang
- Astrogen Inc., 440, Hyeoksin-daero, Dong-gu, Daegu 41072, Republic of Korea; (K.B.U.); (S.K.)
- Department of Pediatrics, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
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Horvath JD, Casas M, Kutchukian C, Sánchez SC, Pergande MR, Cologna SM, Simó S, Dixon RE, Dickson EJ. α-Synuclein-dependent increases in PIP5K1γ drive inositol signaling to promote neurotoxicity. Cell Rep 2023; 42:113244. [PMID: 37838947 PMCID: PMC11010634 DOI: 10.1016/j.celrep.2023.113244] [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: 01/31/2023] [Revised: 08/09/2023] [Accepted: 09/25/2023] [Indexed: 10/17/2023] Open
Abstract
Anomalous aggregation of α-synuclein (α-Syn) is a pathological hallmark of many degenerative synucleinopathies including Lewy body dementia (LBD) and Parkinson's disease (PD). Despite its strong link to disease, the precise molecular mechanisms that link α-Syn aggregation to neurodegeneration have yet to be elucidated. Here, we find that elevated α-Syn leads to an increase in the plasma membrane (PM) phosphoinositide PI(4,5)P2, which precipitates α-Syn aggregation and drives toxic increases in mitochondrial Ca2+ and reactive oxygen species leading to neuronal death. Upstream of this toxic signaling pathway is PIP5K1γ, whose abundance and localization is enhanced at the PM by α-Syn-dependent increases in ARF6. Selective inhibition of PIP5K1γ or knockout of ARF6 in neurons rescues α-Syn aggregation and cellular phenotypes of toxicity. Collectively, our data suggest that modulation of phosphoinositide metabolism may be a therapeutic target to slow neurodegeneration for PD and other related neurodegenerative disorders.
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Affiliation(s)
- Jonathan D Horvath
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Maria Casas
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Candice Kutchukian
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Sara Creus Sánchez
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | | | | | - Sergi Simó
- Department of Cell Biology and Human Anatomy, University of California, Davis, Davis, CA 95616, USA
| | - Rose E Dixon
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Eamonn J Dickson
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA.
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Brembati V, Faustini G, Longhena F, Bellucci A. Alpha synuclein post translational modifications: potential targets for Parkinson's disease therapy? Front Mol Neurosci 2023; 16:1197853. [PMID: 37305556 PMCID: PMC10248004 DOI: 10.3389/fnmol.2023.1197853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 04/27/2023] [Indexed: 06/13/2023] Open
Abstract
Parkinson's disease (PD) is the most common neurodegenerative disorder with motor symptoms. The neuropathological alterations characterizing the brain of patients with PD include the loss of dopaminergic neurons of the nigrostriatal system and the presence of Lewy bodies (LB), intraneuronal inclusions that are mainly composed of alpha-synuclein (α-Syn) fibrils. The accumulation of α-Syn in insoluble aggregates is a main neuropathological feature in PD and in other neurodegenerative diseases, including LB dementia (LBD) and multiple system atrophy (MSA), which are therefore defined as synucleinopathies. Compelling evidence supports that α-Syn post translational modifications (PTMs) such as phosphorylation, nitration, acetylation, O-GlcNAcylation, glycation, SUMOylation, ubiquitination and C-terminal cleavage, play important roles in the modulation α-Syn aggregation, solubility, turnover and membrane binding. In particular, PTMs can impact on α-Syn conformational state, thus supporting that their modulation can in turn affect α-Syn aggregation and its ability to seed further soluble α-Syn fibrillation. This review focuses on the importance of α-Syn PTMs in PD pathophysiology but also aims at highlighting their general relevance as possible biomarkers and, more importantly, as innovative therapeutic targets for synucleinopathies. In addition, we call attention to the multiple challenges that we still need to face to enable the development of novel therapeutic approaches modulating α-Syn PTMs.
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7
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Li C, Yu T, Li W, Gong L, Shi J, Liu H, Yu J. PINK1 deficiency with Ca 2+ changes in the hippocampus exacerbates septic encephalopathy in mice. Chem Biol Interact 2023; 374:110413. [PMID: 36804394 DOI: 10.1016/j.cbi.2023.110413] [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: 11/04/2022] [Revised: 02/16/2023] [Accepted: 02/17/2023] [Indexed: 02/21/2023]
Abstract
PTEN-induced putative kinase 1 (PINK1) is a mitochondrial kinase that protects against oxidative stress-induced cellular death. PINK1 deletion, on the other hand, disrupts mitochondrial calcium (Ca2+) homeostasis in various brain disorders. This study looked at how PINK1 affects hippocampal intracellular Ca2+ changes in mice with septic encephalopathy. Mice were injected intraperitoneally with lipopolysaccharide (LPS, 5 mg/kg) to induce septic encephalopathy; then, fiber photometry was used to record hippocampal Ca2+ transients during behavioral tests in freely moving mice. Basal cytoplasmic Ca2+ levels were detected under a fluorescent microscope. LPS induced PINK1 expression and neuronal loss in the hippocampus of mice, whereas no difference in neuronal counts was shown between PINK1 knockout LPS mice and WT LPS mice. PINK1 deficiency led to inhibited Ca2+ transients and increased intracellular Ca2+ levels in the hippocampus of mice, thus, significantly aggravating the cognitive dysfunction in septic mice. An analysis of Parkin and PLC-γ1, downstream effectors of PINK1, showed that they are associated with the effects of PINK1. These results demonstrate that PINK1 deficiency disrupts intracellular Ca2+ homeostasis and exacerbates septic encephalopathy. This observation suggests a protective role of PINK1 in septic encephalopathy.
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Affiliation(s)
- Cui Li
- Department of Anesthesiology and Critical Care Medicine, Tianjin NanKai Hospital, Tianjin Medical University, Tianjin, 300100, China
| | - Tianyu Yu
- Tianjin Medical University, Tianjin, 300070, China
| | - Wenxing Li
- Tianjin Medical University, Tianjin, 300070, China
| | - Lirong Gong
- Department of Anesthesiology and Critical Care Medicine, Tianjin NanKai Hospital, Tianjin Medical University, Tianjin, 300100, China
| | - Jia Shi
- Department of Anesthesiology and Critical Care Medicine, Tianjin NanKai Hospital, Tianjin Medical University, Tianjin, 300100, China
| | - Huayang Liu
- Tianjin Medical University, Tianjin, 300070, China
| | - Jianbo Yu
- Department of Anesthesiology and Critical Care Medicine, Tianjin NanKai Hospital, Tianjin Medical University, Tianjin, 300100, China.
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Sohrabi T, Mirzaei-Behbahani B, Zadali R, Pirhaghi M, Morozova-Roche LA, Meratan AA. Common Mechanisms Underlying α-Synuclein-Induced Mitochondrial Dysfunction in Parkinson's Disease. J Mol Biol 2023:167992. [PMID: 36736886 DOI: 10.1016/j.jmb.2023.167992] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/19/2023] [Accepted: 01/24/2023] [Indexed: 02/05/2023]
Abstract
Parkinson's disease (PD) is the most common neurological movement disorder characterized by the selective and irreversible loss of dopaminergic neurons in substantia nigra pars compacta resulting in dopamine deficiency in the striatum. While most cases are sporadic or environmental, about 10% of patients have a positive family history with a genetic cause. The misfolding and aggregation of α-synuclein (α-syn) as a casual factor in the pathogenesis of PD has been supported by a great deal of literature. Extensive studies of mechanisms underpinning degeneration of the dopaminergic neurons induced by α-syn dysfunction suggest a complex process that involves multiple pathways, including mitochondrial dysfunction and increased oxidative stress, impaired calcium homeostasis through membrane permeabilization, synaptic dysfunction, impairment of quality control systems, disruption of microtubule dynamics and axonal transport, endoplasmic reticulum/Golgi dysfunction, nucleus malfunction, and microglia activation leading to neuroinflammation. Among them mitochondrial dysfunction has been considered as the most primary target of α-syn-induced toxicity, leading to neuronal cell death in both sporadic and familial forms of PD. Despite reviewing many aspects of PD pathogenesis related to mitochondrial dysfunction, a systemic study on how α-syn malfunction/aggregation damages mitochondrial functionality and leads to neurodegeneration is missing in the literature. In this review, we give a detailed molecular overview of the proposed mechanisms by which α-syn, directly or indirectly, contributes to mitochondrial dysfunction. This may provide valuable insights for development of new therapeutic approaches in relation to PD. Antioxidant-based therapy as a potential strategy to protect mitochondria against oxidative damage, its challenges, and recent developments in the field are discussed.
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Affiliation(s)
- Tahereh Sohrabi
- Department of Biological Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
| | - Behnaz Mirzaei-Behbahani
- Department of Biological Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
| | - Ramin Zadali
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Mitra Pirhaghi
- Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran
| | | | - Ali Akbar Meratan
- Department of Biological Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran.
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Song J, Lin H, Liu S. Basal ganglia network dynamics and function: Role of direct, indirect and hyper-direct pathways in action selection. NETWORK (BRISTOL, ENGLAND) 2023; 34:84-121. [PMID: 36856435 DOI: 10.1080/0954898x.2023.2173816] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 10/11/2022] [Accepted: 01/23/2023] [Indexed: 06/18/2023]
Abstract
Basal ganglia (BG) are a widely recognized neural basis for action selection, but its decision-making mechanism is still a difficult problem for researchers. Therefore, we constructed a spiking neural network inspired by the BG anatomical data. Simulation experiments were based on the principle of dis-inhibition and our functional hypothesis within the BG: the direct pathway, the indirect pathway, and the hyper-direct pathway of the BG jointly implement the initiation execution and termination of motor programs. Firstly, we studied the dynamic process of action selection with the network, which contained intra-group competition and inter-group competition. Secondly, we focused on the effects of the stimulus intensity and the proportion of excitation and inhibition on the GPi/SNr. The results suggested that inhibition and excitation shape action selection. They also explained why the firing rate of GPi/SNr did not continue to increase in the action-selection experiment. Finally, we discussed the experimental results with the functional hypothesis. Uniquely, this paper summarized the decision-making neural mechanism of action selection based on the direct pathway, the indirect pathway, and the hyper-direct pathway within BG.
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Affiliation(s)
- Jian Song
- School of Mathematics, South China University of Technology, Guangzhou, China
| | - Hui Lin
- Department of Precision Instruments, Tsinghua University, Beijing, China
| | - Shenquan Liu
- School of Mathematics, South China University of Technology, Guangzhou, China
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10
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Hahn S, Um KB, Kim SW, Kim HJ, Park MK. Proximal dendritic localization of NALCN channels underlies tonic and burst firing in nigral dopaminergic neurons. J Physiol 2023; 601:171-193. [PMID: 36398712 DOI: 10.1113/jp283716] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Accepted: 11/14/2022] [Indexed: 11/19/2022] Open
Abstract
In multipolar nigral dopamine (DA) neurons, the highly excitable proximal dendritic compartments (PDCs) and two Na+ -permeable leak channels, TRPC3 and NALCN, play a key role in pacemaking. However, the causal link between them is unknown. Here we report that the proximal dendritic localization of NALCN underlies pacemaking and burst firing in DA neurons. Our morphological analysis of nigral DA neurons reveals that TRPC3 is ubiquitously expressed in the whole somatodendritic compartment, but NALCN is localized within the PDCs. Blocking either TRPC3 or NALCN channels abolished pacemaking. However, only blocking NALCN, not TRPC3, degraded burst discharges. Furthermore, local glutamate uncaging readily induced burst discharges within the PDCs, compared with other parts of the neuron, and NALCN channel inhibition dissipated burst generation, indicating the importance of NALCN to the high excitability of PDCs. Therefore, we conclude that PDCs serve as a common base for tonic and burst firing in nigral DA neurons. KEY POINTS: Midbrain dopamine (DA) neurons are slow pacemakers that can generate tonic and burst firings, and the highly excitable proximal dendritic compartments (PDCs) and two Na+ -permeable leak channels, TRPC3 and NALCN, play a key role in pacemaking. We find that slow tonic firing depends on the basal activity of both the NALCN and TRPC3 channels, but that burst firing does not require TRPC3 channels but relies only on NALCN channels. We find that TRPC3 is ubiquitously expressed in the entire somatodendritic compartment, but that NALCN exists only within the PDCs in nigral DA neurons. We show that NALCN channel localization confers high excitability on PDCs and is essential for burst generation in nigral DA neurons. These results suggest that PDCs serve as a common base for tonic and burst firing in nigral DA neurons.
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Affiliation(s)
- Suyun Hahn
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea
| | - Ki Bum Um
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea
| | - So Woon Kim
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea
| | - Hyun Jin Kim
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea.,Samsung Medical Center, Samsung Biomedical Research Institute, Seoul, Korea
| | - Myoung Kyu Park
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea.,Samsung Medical Center, Samsung Biomedical Research Institute, Seoul, Korea
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11
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Correa BH, Moreira CR, Hildebrand ME, Vieira LB. The Role of Voltage-Gated Calcium Channels in Basal Ganglia Neurodegenerative Disorders. Curr Neuropharmacol 2023; 21:183-201. [PMID: 35339179 PMCID: PMC10190140 DOI: 10.2174/1570159x20666220327211156] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 01/11/2022] [Accepted: 03/14/2022] [Indexed: 11/22/2022] Open
Abstract
Calcium (Ca2+) plays a central role in regulating many cellular processes and influences cell survival. Several mechanisms can disrupt Ca2+ homeostasis to trigger cell death, including oxidative stress, mitochondrial damage, excitotoxicity, neuroinflammation, autophagy, and apoptosis. Voltage-gated Ca2+ channels (VGCCs) act as the main source of Ca2+ entry into electrically excitable cells, such as neurons, and they are also expressed in glial cells such as astrocytes and oligodendrocytes. The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD). PD and HD are progressive neurodegenerative disorders (NDs) of the basal ganglia characterized by motor impairment as well as cognitive and psychiatric dysfunctions. This review will examine the putative role of neuronal VGCCs in the pathogenesis and treatment of central movement disorders, focusing on PD and HD. The link between basal ganglia disorders and VGCC physiology will provide a framework for understanding the neurodegenerative processes that occur in PD and HD, as well as a possible path towards identifying new therapeutic targets for the treatment of these debilitating disorders.
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Affiliation(s)
- Bernardo H.M. Correa
- Department of Pharmacology, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Carlos Roberto Moreira
- Department of Pharmacology, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | | | - Luciene Bruno Vieira
- Department of Pharmacology, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
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12
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Kulkarni AS, Burns MR, Brundin P, Wesson DW. Linking α-synuclein-induced synaptopathy and neural network dysfunction in early Parkinson's disease. Brain Commun 2022; 4:fcac165. [PMID: 35822101 PMCID: PMC9272065 DOI: 10.1093/braincomms/fcac165] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 03/11/2022] [Accepted: 06/20/2022] [Indexed: 01/18/2023] Open
Abstract
The prodromal phase of Parkinson's disease is characterized by aggregation of the misfolded pathogenic protein α-synuclein in select neural centres, co-occurring with non-motor symptoms including sensory and cognitive loss, and emotional disturbances. It is unclear whether neuronal loss is significant during the prodrome. Underlying these symptoms are synaptic impairments and aberrant neural network activity. However, the relationships between synaptic defects and network-level perturbations are not established. In experimental models, pathological α-synuclein not only impacts neurotransmission at the synaptic level, but also leads to changes in brain network-level oscillatory dynamics-both of which likely contribute to non-motor deficits observed in Parkinson's disease. Here we draw upon research from both human subjects and experimental models to propose a 'synapse to network prodrome cascade' wherein before overt cell death, pathological α-synuclein induces synaptic loss and contributes to aberrant network activity, which then gives rise to prodromal symptomology. As the disease progresses, abnormal patterns of neural activity ultimately lead to neuronal loss and clinical progression of disease. Finally, we outline goals and research needed to unravel the basis of functional impairments in Parkinson's disease and other α-synucleinopathies.
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Affiliation(s)
- Aishwarya S Kulkarni
- Department of Pharmacology & Therapeutics, University of Florida, 1200 Newell Dr, Gainesville, FL 32610, USA
| | - Matthew R Burns
- Department of Neurology, University of Florida, 1200 Newell Dr, Gainesville, FL 32610, USA
- Norman Fixel Institute for Neurological Disorders, University of Florida, 1200 Newell Dr, Gainesville, FL 32610, USA
| | - Patrik Brundin
- Pharma Research and Early Development (pRED), F. Hoffman-La Roche, Little Falls, NJ, USA
| | - Daniel W Wesson
- Department of Pharmacology & Therapeutics, University of Florida, 1200 Newell Dr, Gainesville, FL 32610, USA
- Norman Fixel Institute for Neurological Disorders, University of Florida, 1200 Newell Dr, Gainesville, FL 32610, USA
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13
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Pena RFO, Rotstein HG. The voltage and spiking responses of subthreshold resonant neurons to structured and fluctuating inputs: persistence and loss of resonance and variability. BIOLOGICAL CYBERNETICS 2022; 116:163-190. [PMID: 35038010 DOI: 10.1007/s00422-021-00919-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 12/21/2021] [Indexed: 06/14/2023]
Abstract
We systematically investigate the response of neurons to oscillatory currents and synaptic-like inputs and we extend our investigation to non-structured synaptic-like spiking inputs with more realistic distributions of presynaptic spike times. We use two types of chirp-like inputs consisting of (i) a sequence of cycles with discretely increasing frequencies over time, and (ii) a sequence having the same cycles arranged in an arbitrary order. We develop and use a number of frequency-dependent voltage response metrics to capture the different aspects of the voltage response, including the standard impedance (Z) and the peak-to-trough amplitude envelope ([Formula: see text]) profiles. We show that Z-resonant cells (cells that exhibit subthreshold resonance in response to sinusoidal inputs) also show [Formula: see text]-resonance in response to sinusoidal inputs, but generally do not (or do it very mildly) in response to square-wave and synaptic-like inputs. In the latter cases the resonant response using Z is not predictive of the preferred frequencies at which the neurons spike when the input amplitude is increased above subthreshold levels. We also show that responses to conductance-based synaptic-like inputs are attenuated as compared to the response to current-based synaptic-like inputs, thus providing an explanation to previous experimental results. These response patterns were strongly dependent on the intrinsic properties of the participating neurons, in particular whether the unperturbed Z-resonant cells had a stable node or a focus. In addition, we show that variability emerges in response to chirp-like inputs with arbitrarily ordered patterns where all signals (trials) in a given protocol have the same frequency content and the only source of uncertainty is the subset of all possible permutations of cycles chosen for a given protocol. This variability is the result of the multiple different ways in which the autonomous transient dynamics is activated across cycles in each signal (different cycle orderings) and across trials. We extend our results to include high-rate Poisson distributed current- and conductance-based synaptic inputs and compare them with similar results using additive Gaussian white noise. We show that the responses to both Poisson-distributed synaptic inputs are attenuated with respect to the responses to Gaussian white noise. For cells that exhibit oscillatory responses to Gaussian white noise (band-pass filters), the response to conductance-based synaptic inputs are low-pass filters, while the response to current-based synaptic inputs may remain band-pass filters, consistent with experimental findings. Our results shed light on the mechanisms of communication of oscillatory activity among neurons in a network via subthreshold oscillations and resonance and the generation of network resonance.
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Affiliation(s)
- Rodrigo F O Pena
- Federated Department of Biological Sciences, New Jersey Institute of Technology and Rutgers University, Newark, USA
| | - Horacio G Rotstein
- Federated Department of Biological Sciences, New Jersey Institute of Technology and Rutgers University, Newark, USA.
- Corresponding Investigator, CONICET, Buenos Aires, Argentina.
- Graduate Faculty, Behavioral Neurosciences Program, Rutgers University, Newark, USA.
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14
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Ni A, Ernst C. Evidence That Substantia Nigra Pars Compacta Dopaminergic Neurons Are Selectively Vulnerable to Oxidative Stress Because They Are Highly Metabolically Active. Front Cell Neurosci 2022; 16:826193. [PMID: 35308118 PMCID: PMC8931026 DOI: 10.3389/fncel.2022.826193] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 01/28/2022] [Indexed: 12/21/2022] Open
Abstract
There are 400–500 thousand dopaminergic cells within each side of the human substantia nigra pars compacta (SNpc) making them a minuscule portion of total brain mass. These tiny clusters of cells have an outsized impact on motor output and behavior as seen in disorders such as Parkinson’s disease (PD). SNpc dopaminergic neurons are more vulnerable to oxidative stress compared to other brain cell types, but the reasons for this are not precisely known. Here we provide evidence to support the hypothesis that this selective vulnerability is because SNpc neurons sustain high metabolic rates compared to other neurons. A higher baseline requirement for ATP production may lead to a selective vulnerability to impairments in oxidative phosphorylation (OXPHOS) or genetic insults that impair Complex I of the electron transport chain. We suggest that the energy demands of the unique morphological and electrophysiological properties of SNpc neurons may be one reason these cells produce more ATP than other cells. We further provide evidence to support the hypothesis that transcription factors (TFs) required to drive induction, differentiation, and maintenance of midbrain dopaminergic neural progenitor cells which give rise to terminally differentiated SNpc neurons are uniquely involved in both developmental patterning and metabolism, a dual function unlike other TFs that program neurons in other brain regions. The use of these TFs during induction and differentiation may program ventral midbrain progenitor cells metabolically to higher ATP levels, allowing for the development of those specialized cell processes seen in terminally differentiated cells. This paper provides a cellular and developmental framework for understanding the selective vulnerability of SNpc dopaminergic cells to oxidative stress.
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15
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Montero T, Gatica RI, Farassat N, Meza R, González-Cabrera C, Roeper J, Henny P. Dendritic Architecture Predicts in vivo Firing Pattern in Mouse Ventral Tegmental Area and Substantia Nigra Dopaminergic Neurons. Front Neural Circuits 2021; 15:769342. [PMID: 34867214 PMCID: PMC8640462 DOI: 10.3389/fncir.2021.769342] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 10/12/2021] [Indexed: 11/13/2022] Open
Abstract
The firing activity of ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) dopaminergic (DA) neurons is an important factor in shaping DA release and its role in motivated behavior. Dendrites in DA neurons are the main postsynaptic compartment and, along with cell body and axon initial segment, contribute to action potential generation and firing pattern. In this study, the organization of the dendritic domain in individual VTA and SNc DA neurons of adult male mice, and their relationship to in vivo spontaneous firing, are described. In comparison with dorsal VTA DA neurons, ventrally located VTA neurons (as measured by cell body location) possess a shorter total dendritic length and simpler dendritic architecture, and exhibit the most irregular in vivo firing patterns among DA neurons. In contrast, for DA neurons in the SNc, the higher irregularity of firing was related to a smaller dendritic domain, as measured by convex hull volumes. However, firing properties were also related to the specific regional distribution of the dendritic tree. Thus, VTA DA neurons with a larger extension of their dendritic tree within the parabrachial pigmented (PBP) nucleus fired more regularly compared with those with relatively more dendrites extending outside the PBP. For DA neurons in the SNc, enhanced firing irregularity was associated with a smaller proportion of dendrites penetrating the substantia nigra pars reticulata. These results suggest that differences in dendritic morphology contribute to the in vivo firing properties of individual DA neurons, and that the existence of region-specific synaptic connectivity rules that shape firing diversity.
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Affiliation(s)
- Trinidad Montero
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Rafael Ignacio Gatica
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Navid Farassat
- Institute of Neurophysiology, Goethe University, Frankfurt, Germany
| | - Rodrigo Meza
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Cristian González-Cabrera
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Jochen Roeper
- Institute of Neurophysiology, Goethe University, Frankfurt, Germany
| | - Pablo Henny
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
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16
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Habernig L, Broeskamp F, Aufschnaiter A, Diessl J, Peselj C, Urbauer E, Eisenberg T, de Ory A, Büttner S. Ca2+ administration prevents α-synuclein proteotoxicity by stimulating calcineurin-dependent lysosomal proteolysis. PLoS Genet 2021; 17:e1009911. [PMID: 34780474 PMCID: PMC8629384 DOI: 10.1371/journal.pgen.1009911] [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: 05/20/2021] [Revised: 11/29/2021] [Accepted: 10/25/2021] [Indexed: 12/02/2022] Open
Abstract
The capacity of a cell to maintain proteostasis progressively declines during aging. Virtually all age-associated neurodegenerative disorders associated with aggregation of neurotoxic proteins are linked to defects in the cellular proteostasis network, including insufficient lysosomal hydrolysis. Here, we report that proteotoxicity in yeast and Drosophila models for Parkinson's disease can be prevented by increasing the bioavailability of Ca2+, which adjusts intracellular Ca2+ handling and boosts lysosomal proteolysis. Heterologous expression of human α-synuclein (αSyn), a protein critically linked to Parkinson's disease, selectively increases total cellular Ca2+ content, while the levels of manganese and iron remain unchanged. Disrupted Ca2+ homeostasis results in inhibition of the lysosomal protease cathepsin D and triggers premature cellular and organismal death. External administration of Ca2+ reduces αSyn oligomerization, stimulates cathepsin D activity and in consequence restores survival, which critically depends on the Ca2+/calmodulin-dependent phosphatase calcineurin. In flies, increasing the availability of Ca2+ discloses a neuroprotective role of αSyn upon manganese overload. In sum, we establish a molecular interplay between cathepsin D and calcineurin that can be activated by Ca2+ administration to counteract αSyn proteotoxicity.
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Affiliation(s)
- Lukas Habernig
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Filomena Broeskamp
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Andreas Aufschnaiter
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Jutta Diessl
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Carlotta Peselj
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Elisabeth Urbauer
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Tobias Eisenberg
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
- BioTechMed Graz, Graz, Austria
- Field of Excellence BioHealth–University of Graz, Graz, Austria
| | - Ana de Ory
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Sabrina Büttner
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
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17
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Carmichael K, Sullivan B, Lopez E, Sun L, Cai H. Diverse midbrain dopaminergic neuron subtypes and implications for complex clinical symptoms of Parkinson's disease. AGEING AND NEURODEGENERATIVE DISEASES 2021; 1. [PMID: 34532720 PMCID: PMC8442626 DOI: 10.20517/and.2021.07] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Parkinson’s disease (PD), the most common degenerative movement disorder, is clinically manifested with various motor and non-motor symptoms. Degeneration of midbrain substantia nigra pas compacta (SNc) dopaminergic neurons (DANs) is generally attributed to the motor syndrome. The underlying neuronal mechanisms of non-motor syndrome are largely unexplored. Besides SNc, midbrain ventral tegmental area (VTA) DANs also produce and release dopamine and modulate movement, reward, motivation, and memory. Degeneration of VTA DANs also occurs in postmortem brains of PD patients, implying an involvement of VTA DANs in PD-associated non-motor symptoms. However, it remains to be established that there is a distinct segregation of different SNc and VTA DAN subtypes in regulating different motor and non-motor functions, and that different DAN subpopulations are differentially affected by normal ageing or PD. Traditionally, the distinction among different DAN subtypes was mainly based on the location of cell bodies and axon terminals. With the recent advance of single cell RNA sequencing technology, DANs can be readily classified based on unique gene expression profiles. A combination of specific anatomic and molecular markers shows great promise to facilitate the identification of DAN subpopulations corresponding to different behavior modules under normal and disease conditions. In this review, we first summarize the recent progress in characterizing genetically, anatomically, and functionally diverse midbrain DAN subtypes. Then, we provide perspectives on how the preclinical research on the connectivity and functionality of DAN subpopulations improves our current understanding of cell-type and circuit specific mechanisms of the disease, which could be critically informative for designing new mechanistic treatments.
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Affiliation(s)
- Kathleen Carmichael
- Transgenic Section, Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA.,The Graduate Partnership Program of NIH and Brown University, National Institutes of Health, Bethesda, MD 20892, USA
| | - Breanna Sullivan
- Transgenic Section, Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA
| | - Elena Lopez
- Transgenic Section, Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA
| | - Lixin Sun
- Transgenic Section, Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA
| | - Huaibin Cai
- Transgenic Section, Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA
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18
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Knowlton CJ, Ziouziou TI, Hammer N, Roeper J, Canavier CC. Inactivation mode of sodium channels defines the different maximal firing rates of conventional versus atypical midbrain dopamine neurons. PLoS Comput Biol 2021; 17:e1009371. [PMID: 34534209 PMCID: PMC8480832 DOI: 10.1371/journal.pcbi.1009371] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 09/29/2021] [Accepted: 08/23/2021] [Indexed: 12/21/2022] Open
Abstract
Two subpopulations of midbrain dopamine (DA) neurons are known to have different dynamic firing ranges in vitro that correspond to distinct projection targets: the originally identified conventional DA neurons project to the dorsal striatum and the lateral shell of the nucleus accumbens, whereas an atypical DA population with higher maximum firing frequencies projects to prefrontal regions and other limbic regions including the medial shell of nucleus accumbens. Using a computational model, we show that previously identified differences in biophysical properties do not fully account for the larger dynamic range of the atypical population and predict that the major difference is that originally identified conventional cells have larger occupancy of voltage-gated sodium channels in a long-term inactivated state that recovers slowly; stronger sodium and potassium conductances during action potential firing are also predicted for the conventional compared to the atypical DA population. These differences in sodium channel gating imply that longer intervals between spikes are required in the conventional population for full recovery from long-term inactivation induced by the preceding spike, hence the lower maximum frequency. These same differences can also change the bifurcation structure to account for distinct modes of entry into depolarization block: abrupt versus gradual. The model predicted that in cells that have entered depolarization block, it is much more likely that an additional depolarization can evoke an action potential in conventional DA population. New experiments comparing lateral to medial shell projecting neurons confirmed this model prediction, with implications for differential synaptic integration in the two populations. We developed a theoretical and mathematical framework that could explain the major electrophysiological differences between the conventional midbrain dopamine (DA) neurons with a low maximum firing rate, and the more recently identified atypical DA neurons. Testable predictions from this framework were then verified with in vitro patch-clamp recordings from DA neurons with identified phenotypes and projection targets. Since different subpopulations of DA neurons participate in different circuits, and these circuits are likely differentially dysregulated in diseases such as addiction, Parkinson disease, and schizophrenia, it is important to identify the differences of their intrinsic electrophysiological properties as a prelude to developing more precisely targeted therapies.
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Affiliation(s)
- Christopher J. Knowlton
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
| | | | - Niklas Hammer
- Institut für Neurophysiologie, Goethe University, Frankfurt, Germany
| | - Jochen Roeper
- Institut für Neurophysiologie, Goethe University, Frankfurt, Germany
| | - Carmen C. Canavier
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana, United States of America
- * E-mail:
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19
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Um KB, Hahn S, Kim SW, Lee YJ, Birnbaumer L, Kim HJ, Park MK. TRPC3 and NALCN channels drive pacemaking in substantia nigra dopaminergic neurons. eLife 2021; 10:70920. [PMID: 34409942 PMCID: PMC8456572 DOI: 10.7554/elife.70920] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 08/18/2021] [Indexed: 01/16/2023] Open
Abstract
Midbrain dopamine (DA) neurons are slow pacemakers that maintain extracellular DA levels. During the interspike intervals, subthreshold slow depolarization underlies autonomous pacemaking and determines its rate. However, the ion channels that determine slow depolarization are unknown. Here we show that TRPC3 and NALCN channels together form sustained inward currents responsible for the slow depolarization of nigral DA neurons. Specific TRPC3 channel blockade completely blocked DA neuron pacemaking, but the pacemaking activity in TRPC3 knock-out (KO) mice was perfectly normal, suggesting the presence of compensating ion channels. Blocking NALCN channels abolished pacemaking in both TRPC3 KO and wild-type mice. The NALCN current and mRNA and protein expression are increased in TRPC3 KO mice, indicating that NALCN compensates for TRPC3 currents. In normal conditions, TRPC3 and NALCN contribute equally to slow depolarization. Therefore, we conclude that TRPC3 and NALCN are two major leak channels that drive robust pacemaking in nigral DA neurons.
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Affiliation(s)
- Ki Bum Um
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Suyun Hahn
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - So Woon Kim
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Yoon Je Lee
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Lutz Birnbaumer
- Neurobiology Laboratory. National Institute of Environmental Health Sciences, North Carolina 27709, USA; and Institute of Biomedical Research (BIOMED), Catholic University of Argentina, Buenos Aires, Argentina
| | - Hyun Jin Kim
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Samsung Biomedical Research Institute, Samsung Medical Center, Seoul, Republic of Korea
| | - Myoung Kyu Park
- Department of physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Samsung Biomedical Research Institute, Samsung Medical Center, Seoul, Republic of Korea
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20
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Refining the Identity and Role of Kv4 Channels in Mouse Substantia Nigra Dopaminergic Neurons. eNeuro 2021; 8:ENEURO.0207-21.2021. [PMID: 34131060 PMCID: PMC8293280 DOI: 10.1523/eneuro.0207-21.2021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Accepted: 05/17/2021] [Indexed: 11/21/2022] Open
Abstract
Substantia nigra pars compacta (SNc) dopaminergic (DA) neurons display a peculiar electrical phenotype characterized in vitro by a spontaneous tonic regular activity (pacemaking activity), a broad action potential (AP) and a biphasic postinhibitory response. The transient A-type current (IA) is known to play a crucial role in this electrical phenotype, and so far, this current was considered to be carried exclusively by Kv4.3 potassium channels. Using Kv4.3−/− transgenic mice, we demonstrate that the constitutive loss of this channel is associated with increased exploratory behavior and impaired motor learning at the behavioral level. Consistently, it is also associated with a lack of compensatory changes in other ion currents at the cellular level. Using antigen retrieval (AR) immunohistochemistry, we then demonstrate that Kv4.2 potassium channels are also expressed in SNc DA neurons, although their contribution to IA appears significant only in a minority of neurons (∼5–10%). Using correlative analysis on recorded electrophysiological parameters and multicompartment modeling, we then demonstrate that, rather than its conductance level, IA gating kinetics (inactivation time constant) appear as the main biophysical property defining postinhibitory rebound delay and pacemaking frequency. Moreover, we show that the hyperpolarization-activated current (IH) has an opposing and complementary influence on the same firing features.
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21
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Beckstead MJ, Howell RD. Progressive parkinsonism due to mitochondrial impairment: Lessons from the MitoPark mouse model. Exp Neurol 2021; 341:113707. [PMID: 33753138 PMCID: PMC8169575 DOI: 10.1016/j.expneurol.2021.113707] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 03/17/2021] [Accepted: 03/18/2021] [Indexed: 12/21/2022]
Abstract
The cardinal pathophysiological finding of Parkinson's disease (PD) is a chronic, progressive degeneration of dopamine (DA) neurons in the substantia nigra, which is responsible for the motor and some of the non-motor symptomatology. While the primary causes of nigrostriatal degeneration are hotly debated, considerable evidence supports a central role for impaired mitochondrial function. Postmortem analysis of PD patients reveals impaired respiratory chains and increased mutations of mitochondrial DNA (mtDNA), in addition to increased markers of oxidative stress indicative of mitochondrial impairment. Most animal models of PD, both genetic and toxin-based, target some component of mitochondrial function to reproduce aspects of the human disease. One model that continues to gain attention is the MitoPark mouse, created through a cell type-specific knockout of mitochondrial transcription factor A specifically in midbrain DA neurons. This model effectively recapitulates the slowly developing, adult onset motor decline seen in PD due to mass loss of DA neurons. MitoPark mice therefore represent an effective tool for studying the sequence of events that occurs in the early stages of DA neuron degeneration following mitochondrial impairment, as well as for testing the efficacy of potential disease-modifying therapies in a progressive model of neurodegeneration. A targeted review of key findings from MitoPark mice has not been published since the early years following the initial report of the model in 2007. The current review synthesizes findings from several groups that are exploring MitoPark mice and discusses implications for the future identification of disease-modifying treatments for PD.
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Affiliation(s)
- Michael J Beckstead
- Oklahoma Medical Research Foundation, Aging & Metabolism Research Program, USA.
| | - Rebecca D Howell
- Oklahoma Medical Research Foundation, Aging & Metabolism Research Program, USA
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22
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Dynamical Invariant and Exact Mechanical Analyses for the Caldirola-Kanai Model of Dissipative Three Coupled Oscillators. ENTROPY 2021; 23:e23070837. [PMID: 34208801 PMCID: PMC8304947 DOI: 10.3390/e23070837] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Revised: 06/21/2021] [Accepted: 06/26/2021] [Indexed: 11/17/2022]
Abstract
We study the dynamical invariant for dissipative three coupled oscillators mainly from the quantum mechanical point of view. It is known that there are many advantages of the invariant quantity in elucidating mechanical properties of the system. We use such a property of the invariant operator in quantizing the system in this work. To this end, we first transform the invariant operator to a simple one by using a unitary operator in order that we can easily manage it. The invariant operator is further simplified through its diagonalization via three-dimensional rotations parameterized by three Euler angles. The coupling terms in the quantum invariant are eventually eliminated thanks to such a diagonalization. As a consequence, transformed quantum invariant is represented in terms of three independent simple harmonic oscillators which have unit masses. Starting from the wave functions in the transformed system, we have derived the full wave functions in the original system with the help of the unitary operators.
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23
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Fleming W, Jewell S, Engelhard B, Witten DM, Witten IB. Inferring spikes from calcium imaging in dopamine neurons. PLoS One 2021; 16:e0252345. [PMID: 34086726 PMCID: PMC8177503 DOI: 10.1371/journal.pone.0252345] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 05/12/2021] [Indexed: 11/18/2022] Open
Abstract
Calcium imaging has led to discoveries about neural correlates of behavior in subcortical neurons, including dopamine (DA) neurons. However, spike inference methods have not been tested in most populations of subcortical neurons. To address this gap, we simultaneously performed calcium imaging and electrophysiology in DA neurons in brain slices and applied a recently developed spike inference algorithm to the GCaMP fluorescence. This revealed that individual spikes can be inferred accurately in this population. Next, we inferred spikes in vivo from calcium imaging from these neurons during Pavlovian conditioning, as well as during navigation in virtual reality. In both cases, we quantitatively recapitulated previous in vivo electrophysiological observations. Our work provides a validated approach to infer spikes from calcium imaging in DA neurons and implies that aspects of both tonic and phasic spike patterns can be recovered.
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Affiliation(s)
- Weston Fleming
- Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey, United States of America
| | - Sean Jewell
- Department of Statistics & Biostatistics, University of Washington, Seattle, Washington, United States of America
| | - Ben Engelhard
- Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey, United States of America
| | - Daniela M. Witten
- Department of Statistics & Biostatistics, University of Washington, Seattle, Washington, United States of America
| | - Ilana B. Witten
- Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey, United States of America
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24
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Ortner NJ. Voltage-Gated Ca 2+ Channels in Dopaminergic Substantia Nigra Neurons: Therapeutic Targets for Neuroprotection in Parkinson's Disease? Front Synaptic Neurosci 2021; 13:636103. [PMID: 33716705 PMCID: PMC7952618 DOI: 10.3389/fnsyn.2021.636103] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 01/25/2021] [Indexed: 12/21/2022] Open
Abstract
The loss of dopamine (DA)-producing neurons in the substantia nigra pars compacta (SN) underlies the core motor symptoms of the progressive movement disorder Parkinson's disease (PD). To date, no treatment to prevent or slow SN DA neurodegeneration exists; thus, the identification of the underlying factors contributing to the high vulnerability of these neurons represents the basis for the development of novel therapies. Disrupted Ca2+ homeostasis and mitochondrial dysfunction seem to be key players in the pathophysiology of PD. The autonomous pacemaker activity of SN DA neurons, in combination with low cytosolic Ca2+ buffering, leads to large somatodendritic fluctuations of intracellular Ca2+ levels that are linked to elevated mitochondrial oxidant stress. L-type voltage-gated Ca2+ channels (LTCCs) contribute to these Ca2+ oscillations in dendrites, and LTCC inhibition was beneficial in cellular and in vivo animal models of PD. However, in a recently completed phase 3 clinical trial, the dihydropyridine (DHP) LTCC inhibitor isradipine failed to slow disease progression in early PD patients, questioning the feasibility of DHPs for PD therapy. Novel evidence also suggests that R- and T-type Ca2+ channels (RTCCs and TTCCs, respectively) represent potential PD drug targets. This short review aims to (re)evaluate the therapeutic potential of LTCC, RTCC, and TTCC inhibition in light of novel preclinical and clinical data and the feasibility of available Ca2+ channel blockers to modify PD disease progression. I also summarize their cell-specific roles for SN DA neuron function and describe how their gating properties allow activity (and thus their contribution to stressful Ca2+ oscillations) during pacemaking.
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Affiliation(s)
- Nadine J. Ortner
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
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25
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Zampese E, Surmeier DJ. Calcium, Bioenergetics, and Parkinson's Disease. Cells 2020; 9:cells9092045. [PMID: 32911641 PMCID: PMC7564460 DOI: 10.3390/cells9092045] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 09/04/2020] [Accepted: 09/07/2020] [Indexed: 12/12/2022] Open
Abstract
Degeneration of substantia nigra (SN) dopaminergic (DAergic) neurons is responsible for the core motor deficits of Parkinson’s disease (PD). These neurons are autonomous pacemakers that have large cytosolic Ca2+ oscillations that have been linked to basal mitochondrial oxidant stress and turnover. This review explores the origin of Ca2+ oscillations and their role in the control of mitochondrial respiration, bioenergetics, and mitochondrial oxidant stress.
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26
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Tan C, Šarlija M, Kasabov N. Spiking Neural Networks: Background, Recent Development and the NeuCube Architecture. Neural Process Lett 2020. [DOI: 10.1007/s11063-020-10322-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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27
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van der Velden L, Vinck MA, Wadman WJ. Resonance in the Mouse Ventral Tegmental Area Dopaminergic Network Induced by Regular and Poisson Distributed Optogenetic Stimulation in-vitro. Front Comput Neurosci 2020; 14:11. [PMID: 32132914 PMCID: PMC7040182 DOI: 10.3389/fncom.2020.00011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Accepted: 01/28/2020] [Indexed: 11/13/2022] Open
Abstract
Neurons in many brain regions exhibit spontaneous, intrinsic rhythmic firing activity. This rhythmic firing activity may determine the way in which these neurons respond to extrinsic synaptic inputs. We hypothesized that neurons should be most responsive to inputs at the frequency of the intrinsic oscillation frequency. We addressed this question in the ventral tegmental area (VTA), a dopaminergic nucleus in the midbrain. VTA neurons have a unique propensity to exhibit spontaneous intrinsic rhythmic activity in the 1-5 Hz frequency range, which persists in the in-vitro brain slice, and form a network of weakly coupled oscillators. Here, we combine in-vitro simultaneous recording of action potentials from a 60 channel multi-electrode-array with cell-type-specific optogenetic stimulation of the VTA dopamine neurons. We investigated how VTA neurons respond to wide-band stochastic (Poisson input) as well as regular laser pulses. Strong synchrony was induced between the laser input and the spike timing of the neurons, both for regular pulse trains and Poisson pulse trains. For rhythmically pulsed input, the neurons demonstrated resonant behavior with the strongest phase locking at their intrinsic oscillation frequency, but also at half and double the intrinsic oscillation frequency. Stochastic Poisson pulse stimulation provided a more effective stimulation of the entire population, yet we observed resonance at lower frequencies (approximately half the oscillation frequency) than the neurons' intrinsic oscillation frequency. The non-linear filter characteristics of dopamine neurons could allow the VTA to predict precisely timed future rewards based on past sensory inputs, a crucial component of reward prediction error signaling. In addition, these filter characteristics could contribute to a pacemaker role for the VTA in synchronizing activity with other regions like the prefrontal cortex and the hippocampus.
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Affiliation(s)
- Luuk van der Velden
- Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, Netherlands
| | - Martin A Vinck
- Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation With Max Planck Society, Frankfurt am Main, Germany
| | - Wytse J Wadman
- Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, Netherlands
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28
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Yihe L, Timofeeva Y. Exact solutions to cable equations in branching neurons with tapering dendrites. JOURNAL OF MATHEMATICAL NEUROSCIENCE 2020; 10:1. [PMID: 31993756 PMCID: PMC6987294 DOI: 10.1186/s13408-020-0078-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 01/15/2020] [Indexed: 06/10/2023]
Abstract
Neurons are biological cells with uniquely complex dendritic morphologies that are not present in other cell types. Electrical signals in a neuron with branching dendrites can be studied by cable theory which provides a general mathematical modelling framework of spatio-temporal voltage dynamics. Typically such models need to be solved numerically unless the cell membrane is modelled either by passive or quasi-active dynamics, in which cases analytical solutions can be reduced to calculation of the Green's function describing the fundamental input-output relationship in a given morphology. Such analytically tractable models often assume individual dendritic segments to be cylinders. However, it is known that dendritic segments in many types of neurons taper, i.e. their radii decline from proximal to distal ends. Here we consider a generalised form of cable theory which takes into account both branching and tapering structures of dendritic trees. We demonstrate that analytical solutions can be found in compact algebraic forms in an arbitrary branching neuron with a class of tapering dendrites studied earlier in the context of single neuronal cables by Poznanski (Bull. Math. Biol. 53(3):457-467, 1991). We apply this extended framework to a number of simplified neuronal models and contrast their output dynamics in the presence of tapering versus cylindrical segments.
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Affiliation(s)
- Lu Yihe
- School of Psychology, University of Nottingham, Nottingham, UK
| | - Yulia Timofeeva
- Department of Computer Science, University of Warwick, Coventry, UK
- Centre for Complexity Science, University of Warwick, Coventry, UK
- UCL Queen Square Institute of Neurology, University College London, London, UK
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29
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Goaillard JM, Moubarak E, Tapia M, Tell F. Diversity of Axonal and Dendritic Contributions to Neuronal Output. Front Cell Neurosci 2020; 13:570. [PMID: 32038171 PMCID: PMC6987044 DOI: 10.3389/fncel.2019.00570] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 12/09/2019] [Indexed: 11/13/2022] Open
Abstract
Our general understanding of neuronal function is that dendrites receive information that is transmitted to the axon, where action potentials (APs) are initiated and propagated to eventually trigger neurotransmitter release at synaptic terminals. Even though this canonical division of labor is true for a number of neuronal types in the mammalian brain (including neocortical and hippocampal pyramidal neurons or cerebellar Purkinje neurons), many neuronal types do not comply with this classical polarity scheme. In fact, dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. In several interneuron types, all functions are carried out by dendrites as these neurons are devoid of a canonical axon. In this article, we present a few examples of "misbehaving" neurons (with a non-canonical polarity scheme) to highlight the diversity of solutions that are used by mammalian neurons to transmit information. Moreover, we discuss how the contribution of dendrites and axons to neuronal excitability may impose constraints on the morphology of these compartments in specific functional contexts.
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Affiliation(s)
- Jean-Marc Goaillard
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Estelle Moubarak
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Mónica Tapia
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Fabien Tell
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
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30
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Rumbell T, Kozloski J. Dimensions of control for subthreshold oscillations and spontaneous firing in dopamine neurons. PLoS Comput Biol 2019; 15:e1007375. [PMID: 31545787 PMCID: PMC6776370 DOI: 10.1371/journal.pcbi.1007375] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 10/03/2019] [Accepted: 09/04/2019] [Indexed: 11/20/2022] Open
Abstract
Dopaminergic neurons (DAs) of the rodent substantia nigra pars compacta (SNc) display varied electrophysiological properties in vitro. Despite this, projection patterns and functional inputs from DAs to other structures are conserved, so in vivo delivery of consistent, well-timed dopamine modulation to downstream circuits must be coordinated. Here we show robust coordination by linear parameter controllers, discovered through powerful mathematical analyses of data and models, and from which consistent control of DA subthreshold oscillations (STOs) and spontaneous firing emerges. These units of control represent coordinated intracellular variables, sufficient to regulate complex cellular properties with radical simplicity. Using an evolutionary algorithm and dimensionality reduction, we discovered metaparameters, which when regressed against STO features, revealed a 2-dimensional control plane for the neuron’s 22-dimensional parameter space that fully maps the natural range of DA subthreshold electrophysiology. This plane provided a basis for spiking currents to reproduce a large range of the naturally occurring spontaneous firing characteristics of SNc DAs. From it we easily produced a unique population of models, derived using unbiased parameter search, that show good generalization to channel blockade and compensatory intracellular mechanisms. From this population of models, we then discovered low-dimensional controllers for regulating spontaneous firing properties, and gain insight into how currents active in different voltage regimes interact to produce the emergent activity of SNc DAs. Our methods therefore reveal simple regulators of neuronal function lurking in the complexity of combined ion channel dynamics. Electrophysiological activity of the neuronal membrane and concomitant ion channel properties are highly variable within groups of neurons of the same type from the same brain region. Reconciliation of the mechanisms generating neuronal activity is challenging due to the complexity of the interactions between the channel currents involved. Here we present a set of mathematical analyses that uncover the low-dimensional intracellular parameter combinations capable of regulating features of subthreshold oscillations and spontaneous firing in empirically constrained models of nigral dopaminergic neurons. This method generates, from a naive starting point, linear combinations of ion channel properties that are surprisingly capable of reliably controlling a wide variety of emergent electrophysiological activity, thereby predicting drug effects and shedding light on unsuspected compensatory mechanisms that contribute to neuronal function.
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Affiliation(s)
- Timothy Rumbell
- IBM Research, Computational Biology Center, Thomas J. Watson Research Laboratories, Yorktown Heights, New York, United States of America
- * E-mail:
| | - James Kozloski
- IBM Research, Computational Biology Center, Thomas J. Watson Research Laboratories, Yorktown Heights, New York, United States of America
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31
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Mitochondrial Dysfunction in Parkinson's Disease-Cause or Consequence? BIOLOGY 2019; 8:biology8020038. [PMID: 31083583 PMCID: PMC6627981 DOI: 10.3390/biology8020038] [Citation(s) in RCA: 143] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 01/25/2019] [Accepted: 02/05/2019] [Indexed: 12/18/2022]
Abstract
James Parkinson first described the motor symptoms of the disease that took his name over 200 years ago. While our knowledge of many of the changes that occur in this condition has increased, it is still unknown what causes this neurodegeneration and why it only affects some individuals with advancing age. Here we review current literature to discuss whether the mitochondrial dysfunction we have detected in Parkinson’s disease is a pathogenic cause of neuronal loss or whether it is itself a consequence of dysfunction in other pathways. We examine research data from cases of idiopathic Parkinson’s with that from model systems and individuals with familial forms of the disease. Furthermore, we include data from healthy aged individuals to highlight that many of the changes described are also present with advancing age, though not normally in the presence of severe neurodegeneration. While a definitive answer to this question may still be just out of reach, it is clear that mitochondrial dysfunction sits prominently at the centre of the disease pathway that leads to catastrophic neuronal loss in those affected by this disease.
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Robustness to Axon Initial Segment Variation Is Explained by Somatodendritic Excitability in Rat Substantia Nigra Dopaminergic Neurons. J Neurosci 2019; 39:5044-5063. [PMID: 31028116 DOI: 10.1523/jneurosci.2781-18.2019] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 03/27/2019] [Accepted: 03/27/2019] [Indexed: 01/12/2023] Open
Abstract
In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excitability. Interestingly, the axon of rat SNc dopaminergic (DA) neurons displays a highly variable location and most often arises from an axon-bearing dendrite (ABD). We combined current-clamp somatic and dendritic recordings, outside-out recordings of dendritic sodium and potassium currents, morphological reconstructions and multicompartment modeling on male and female rat SNc DA neurons to determine cell-to-cell variations in AIS and ABD geometry, and their influence on neuronal output (spontaneous pacemaking frequency, action potential [AP] shape). Both AIS and ABD geometries were found to be highly variable from neuron to neuron. Surprisingly, we found that AP shape and pacemaking frequency were independent of AIS geometry. Modeling realistic morphological and biophysical variations helped us clarify this result: in SNc DA neurons, the complexity of the ABD combined with its excitability predominantly define pacemaking frequency and AP shape, such that large variations in AIS geometry negligibly affect neuronal output and are tolerated.SIGNIFICANCE STATEMENT In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excitability. In the current study, we describe large cell-to-cell variations in AIS length or distance from the soma in rat substantia nigra pars compacta dopaminergic neurons. Using neuronal reconstruction and electrophysiological recordings, we show that this morphological variability does not seem to affect their electrophysiological output, as neither action potential properties nor pacemaking frequency is correlated with AIS morphology. Realistic multicompartment modeling suggests that this robustness to AIS variation is mainly explained by the complexity and excitability of the somatodendritic compartment.
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33
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Liss B, Striessnig J. The Potential of L-Type Calcium Channels as a Drug Target for Neuroprotective Therapy in Parkinson's Disease. Annu Rev Pharmacol Toxicol 2019; 59:263-289. [PMID: 30625283 DOI: 10.1146/annurev-pharmtox-010818-021214] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The motor symptoms of Parkinson's disease (PD) mainly arise from degeneration of dopamine neurons within the substantia nigra. As no disease-modifying PD therapies are available, and side effects limit long-term benefits of current symptomatic therapies, novel treatment approaches are needed. The ongoing phase III clinical study STEADY-PD is investigating the potential of the dihydropyridine isradipine, an L-type Ca2+ channel (LTCC) blocker, for neuroprotective PD therapy. Here we review the clinical and preclinical rationale for this trial and discuss potential reasons for the ambiguous outcomes of in vivo animal model studies that address PD-protective dihydropyridine effects. We summarize current views about the roles of Cav1.2 and Cav1.3 LTCC isoforms for substantia nigra neuron function, and their high vulnerability to degenerative stressors, and for PD pathophysiology. We discuss different dihydropyridine sensitivities of LTCC isoforms in view of their potential as drug targets for PD neuroprotection, and we conclude by considering how these aspects could guide further drug development.
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Affiliation(s)
- Birgit Liss
- Institut für Angewandte Physiologie, Universität Ulm, 89081 Ulm, Germany;
| | - Jörg Striessnig
- Abteilung Pharmakologie und Toxikologie, Institut für Pharmazie, and Center for Molecular Biosciences Innsbruck, Universität Innsbruck, A-6020 Innsbruck, Austria;
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34
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Vidyadhara DJ, Sasidharan A, Kutty BM, Raju TR, Alladi PA. Admixing MPTP-resistant and MPTP-vulnerable mice enhances striatal field potentials and calbindin-D28K expression to avert motor behaviour deficits. Behav Brain Res 2018; 360:216-227. [PMID: 30529402 DOI: 10.1016/j.bbr.2018.12.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Revised: 12/04/2018] [Accepted: 12/06/2018] [Indexed: 10/27/2022]
Abstract
Asian-Indians are less vulnerable to Parkinson's disease (PD) than the Caucasians. Their admixed populace has even lesser risk. Studying this phenomenon using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-susceptible C57BL/6J, MPTP-resistant CD-1 and their resistant crossbred mice revealed differences in the nigrostriatal cyto-molecular features. Here, we investigated the electrophysiological and behavioural correlates for differential MPTP-susceptibility and their outcome upon admixing. We recorded local field potentials (LFPs) from dorsal striatum and assessed motor co-ordination using rotarod and grip strength measures. Nigral calbindin-D28K expression, a regulator of striatal activity through nigrostriatal projections was evaluated using immunohistochemistry. The crossbreds had significantly higher baseline striatal LFPs. MPTP significantly increased the neuronal activity in delta (0.5-4 Hz) and low beta (12-16 Hz) ranges in C57BL/6J; significant increase across frequency bands till high beta (0.5-30 Hz) in CD-1, and caused no alterations in crossbreds. MPTP further depleted the already low nigral calbindin-D28K expression in C57BL/6J. While in crossbreds, it was further up-regulated. MPTP affected the rotarod and grip strength performance of the C57BL/6J, while the injected CD-1 and crossbreds performed well. The increased striatal β-oscillations are comparable to that in PD patients. Higher power in CD-1 may be compensatory in nature, which were also reported in pre-symptomatic monkeys. Concurrent up-regulation of nigral calbindin-D28K may assist maintenance of striatal activity by buffering calcium overload in nigra. Thus, preserved motor behaviour in PD reminiscent conditions in CD-1 and crossbreds complement compensated/unaffected striatal LFPs. Similar electrophysiological correlates and cytomorphological features are envisaged in human phenomenon of differential PD prevalence, which are modulated upon admixing.
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Affiliation(s)
- D J Vidyadhara
- Department of Neurophysiology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, 560029, India
| | - Arun Sasidharan
- Axxonet Brain Research Laboratory (ABRL), Axxonet System Technologies Pvt. Ltd., Bengaluru, 560029, India
| | - Bindu M Kutty
- Department of Neurophysiology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, 560029, India
| | - T R Raju
- Department of Neurophysiology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, 560029, India
| | - Phalguni Anand Alladi
- Department of Neurophysiology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, 560029, India.
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35
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Lynch WB, Tschumi CW, Sharpe AL, Branch SY, Chen C, Ge G, Li S, Beckstead MJ. Progressively disrupted somatodendritic morphology in dopamine neurons in a mouse Parkinson's model. Mov Disord 2018; 33:1928-1937. [PMID: 30440089 DOI: 10.1002/mds.27541] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 08/10/2018] [Accepted: 09/16/2018] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Parkinson's disease is characterized by the progressive loss of dopamine neurons in the substantia nigra, leading to severe motor deficits. Although the disease likely begins to develop years before observable motor symptoms, the specific morphological and functional alterations involved are poorly understood. OBJECTIVES MitoPark mice lack the gene coding for mitochondrial transcription factor A specifically in dopamine neurons, which over time produces a progressive decline of neuronal function and related behavior that phenotypically mirrors human parkinsonism. Our previous work identified a progressive decrease in cell capacitance in dopamine neurons from MitoPark mice, possibly suggesting reduced membrane surface area. We therefore sought to identify and quantify somatodendritic parameters in this model across age. METHODS We used whole-cell patch clamp and fluorescent labeling to quantify somatodendritic morphology of single, neurobiotin-filled dopamine neurons in acutely isolated brain slices from MitoPark mice. RESULTS We found that MitoPark mice exhibit an adult-onset, age-dependent reduction of neuritic branching and soma size in dopamine neurons. This decline proceeds similarly in MitoPark mice of both sexes, but does not begin until after the age that early decrements in ion channel physiology and behavior have previously been observed. CONCLUSIONS A progressive and severe decline in somatodendritic morphology occurs prior to cell death, but is not responsible for the subtle decrements observable in the earliest stages of neurodegeneration. This work could help identify the ideal time window for specific treatments to halt disease progression and avert debilitating motor deficits in Parkinson's patients. © 2018 International Parkinson and Movement Disorder Society.
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Affiliation(s)
- William B Lynch
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA
| | - Christopher W Tschumi
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA.,Department of Cellular and Integrative Physiology, University of Texas Health, San Antonio, Texas, USA
| | - Amanda L Sharpe
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA.,Department of Pharmaceutical Sciences, University of Oklahoma College of Pharmacy, Oklahoma City, Oklahoma, USA
| | - Sarah Y Branch
- Department of Cellular and Integrative Physiology, University of Texas Health, San Antonio, Texas, USA
| | - Cang Chen
- Department of Medicine, University of Texas Health, San Antonio, Texas, USA
| | - Guo Ge
- Department of Medicine, University of Texas Health, San Antonio, Texas, USA
| | - Senlin Li
- Department of Medicine, University of Texas Health, San Antonio, Texas, USA
| | - Michael J Beckstead
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA.,Department of Cellular and Integrative Physiology, University of Texas Health, San Antonio, Texas, USA
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36
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Betzer C, Jensen PH. Reduced Cytosolic Calcium as an Early Decisive Cellular State in Parkinson's Disease and Synucleinopathies. Front Neurosci 2018; 12:819. [PMID: 30459551 PMCID: PMC6232531 DOI: 10.3389/fnins.2018.00819] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 10/19/2018] [Indexed: 12/26/2022] Open
Abstract
The more than 30-year-old Calcium hypothesis postulates that dysregulation in calcium dependent processes in the aging brain contributes to its increased vulnerability and this concept has been extended to Alzheimer’s disease and Parkinson’s disease. Central to the hypothesis is that increased levels of intracellular calcium develop and contributes to neuronal demise. We have studied the impact on cells encountering a gradual build-up of aggregated α-synuclein, which is a central process to Parkinson’s disease and other synucleinopathies. Surprisingly, we observed a yet unrecognized phase characterized by a reduced cytosolic calcium in cellular and neuronal models of Parkinson’s disease, caused by α-synuclein aggregates activating the endoplasmic calcium ATPase, SERCA. Counteracting the initial phase with low calcium rescues the subsequent degenerative phase with increased calcium and cell death – and demonstrates this early phase initiates decisive degenerative signals. In this review, we discuss our findings in relation to literature on calcium dysregulation in Parkinson’s disease and dementia.
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Affiliation(s)
- Cristine Betzer
- DANDRITE - Danish Research Institute of Translational Neuroscience, Aarhus University, Aarhus, Denmark.,Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Poul Henning Jensen
- DANDRITE - Danish Research Institute of Translational Neuroscience, Aarhus University, Aarhus, Denmark.,Department of Biomedicine, Aarhus University, Aarhus, Denmark
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37
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di Volo M, Morozova EO, Lapish CC, Kuznetsov A, Gutkin B. Dynamical ventral tegmental area circuit mechanisms of alcohol-dependent dopamine release. Eur J Neurosci 2018; 50:2282-2296. [PMID: 30215874 DOI: 10.1111/ejn.14147] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 08/15/2018] [Accepted: 08/24/2018] [Indexed: 11/28/2022]
Abstract
A large body of data has identified numerous molecular targets through which ethanol (EtOH) acts on brain circuits. Yet how these multiple mechanisms interact to result in dysregulated dopamine (DA) release under the influence of alcohol in vivo remains unclear. In this manuscript, we delineate potential circuit-level mechanisms responsible for EtOH-dependent dysregulation of DA release from the ventral tegmental area (VTA) into its projection areas. For this purpose, we constructed a circuit model of the VTA that integrates realistic Glutamatergic (Glu) inputs and reproduces DA release observed experimentally. We modelled the concentration-dependent effects of EtOH on its principal VTA targets. We calibrated the model to reproduce the inverted U-shape dose dependence of DA neuron activity on EtOH concentration. The model suggests a primary role of EtOH-induced boost in the Ih and AMPA currents in the DA firing-rate/bursting increase. This is counteracted by potentiated GABA transmission that decreases DA neuron activity at higher EtOH concentrations. Thus, the model connects well-established in vitro pharmacological EtOH targets with its in vivo influence on neuronal activity. Furthermore, we predict that increases in VTA activity produced by moderate EtOH doses require partial synchrony and relatively low rates of the Glu afferents. We propose that the increased frequency of transient (phasic) DA peaks evoked by EtOH results from synchronous population bursts in VTA DA neurons. Our model predicts that the impact of acute ETOH on dopamine release is critically shaped by the structure of the cortical inputs to the VTA.
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Affiliation(s)
- Matteo di Volo
- Unité de Neurosciences, Information et Complexité, CNRS, Gif-sur-Yvette, France.,Group for Neural Theory, LNC INSERM U960, DEC Ecole Normale Superieure PSL University, Paris, France
| | | | - Christopher C Lapish
- Addiction Neuroscience Program, Indiana University - Purdue University Indianapolis, Indianapolis, IN, USA
| | - Alexey Kuznetsov
- Department of Mathematical Sciences, Indiana University - Purdue University Indianapolis, Indianapolis, IN, USA
| | - Boris Gutkin
- Group for Neural Theory, LNC INSERM U960, DEC Ecole Normale Superieure PSL University, Paris, France.,Center for Cognition and Decision Making, NRU HSE, Moscow, Russia
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38
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Inoue KI, Miyachi S, Nishi K, Okado H, Nagai Y, Minamimoto T, Nambu A, Takada M. Recruitment of calbindin into nigral dopamine neurons protects against MPTP-Induced parkinsonism. Mov Disord 2018; 34:200-209. [PMID: 30161282 DOI: 10.1002/mds.107] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 06/06/2018] [Accepted: 06/29/2018] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Parkinson's disease is caused by dopamine deficiency in the striatum, which is a result of loss of dopamine neurons from the substantia nigra pars compacta. There is a consensus that a subpopulation of nigral dopamine neurons that expresses the calcium-binding protein calbindin is selectively invulnerable to parkinsonian insults. The objective of the present study was to test the hypothesis that dopamine neuron degeneration might be prevented by viral vector-mediated gene delivery of calbindin into the dopamine neurons that do not normally contain it. METHODS A calbindin-expressing adenoviral vector was injected into the striatum of macaque monkeys to be conveyed to cell bodies of nigral dopamine neurons through retrograde axonal transport, or the calbindin-expressing lentiviral vector was injected into the nigra directly because of its predominant uptake from cell bodies and dendrites. The animals in which calbindin was successfully recruited into nigral dopamine neurons were administered systemically with MPTP. RESULTS In the monkeys that had received unilateral vector injections, parkinsonian motor deficits, such as muscular rigidity and akinesia/bradykinesia, appeared predominantly in the limbs corresponding to the non-calbindin-recruited hemisphere after MPTP administration. Data obtained from tyrosine hydroxylase immunostaining and PET imaging for the dopamine transporter revealed that the nigrostriatal dopamine system was preserved better on the calbindin-recruited side. Conversely, on the non-calbindin-recruited control side, many more dopamine neurons expressed α-synuclein. CONCLUSIONS The present results indicate that calbindin recruitment into nigral dopamine neurons protects against the onset of parkinsonian insults, thus providing a novel approach to PD prevention. © 2018 International Parkinson and Movement Disorder Society.
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Affiliation(s)
- Ken-Ichi Inoue
- Systems Neuroscience Section, Department of Neuroscience, Primate Research Institute, Kyoto University, Inuyama, Aichi, Japan.,Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan.,PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
| | - Shigehiro Miyachi
- Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan.,Cognitive Neuroscience Section, Department of Neuroscience, Primate Research Institute, Kyoto University, Inuyama, Aichi, Japan
| | - Katsunori Nishi
- Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan
| | - Haruo Okado
- Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan.,Department of Brain Development and Neural Regeneration, Tokyo Metropolitan Institute of Medical Science, Setagaya-ku, Tokyo, Japan
| | - Yuji Nagai
- Department of Functional Brain Imaging Research, National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
| | - Takafumi Minamimoto
- Department of Functional Brain Imaging Research, National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
| | - Atsushi Nambu
- Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan.,Division of System Neurophysiology, National Institute for Physiological Sciences and Department of Physiological Sciences, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi, Japan
| | - Masahiko Takada
- Systems Neuroscience Section, Department of Neuroscience, Primate Research Institute, Kyoto University, Inuyama, Aichi, Japan.,Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Fuchu, Tokyo, Japan
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Kirchner MK, Foehring RC, Callaway J, Armstrong WE. Specificity in the interaction of high-voltage-activated Ca 2+ channel types with Ca 2+-dependent afterhyperpolarizations in magnocellular supraoptic neurons. J Neurophysiol 2018; 120:1728-1739. [PMID: 30020842 DOI: 10.1152/jn.00285.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Magnocellular oxytocin (OT) and vasopressin (VP) neurons express an afterhyperpolarization (AHP) following spike trains that attenuates firing rate and contributes to burst patterning. This AHP includes contributions from an apamin-sensitive, medium-duration AHP (mAHP) and from an apamin-insensitive, slow-duration AHP (sAHP). These AHPs are Ca2+ dependent and activated by Ca2+ influx through voltage-gated Ca2+ channels. Across central nervous system neurons that generate Ca2+-dependent AHPs, the Ca2+ channels that couple to the mAHP and sAHP differ greatly, but for magnocellular neurosecretory cells this relationship is unknown. Using simultaneous whole cell recording and Ca2+ imaging, we evaluated the effect of specific high-voltage-activated (HVA) Ca2+ channel blockers on the mAHP and sAHP. Block of all HVA channels via 400 μM Cd2+ inhibited almost the entire AHP. We tested nifedipine, conotoxin GVIA, agatoxin IVA, and SNX-482, specific blockers of L-, N-, P/Q-, and R-type channels, respectively. The N-type channel blocker conotoxin GVIA (1 μM) was the only toxin that inhibited the mAHP in either OT or VP neurons although the effect on VP neurons was weaker by comparison. The sAHP was significantly inhibited by N-type block in OT neurons and by R-type block in VP neurons although neither accounted for the entirety of the sAHP. Thus the mAHP appears to be elicited by Ca2+ from mostly N-type channels in both OT and VP neurons, but the contributions of specific Ca2+ channel types to the sAHP in each cell type are different. Alternative sources to HVA channels may contribute Ca2+ for the sAHP. NEW & NOTEWORTHY Despite the importance of afterhyperpolarization (AHP) mechanisms for regulating firing behavior of oxytocin (OT) and vasopressin (VP) neurons of supraoptic nucleus, which types of high-voltage-activated Ca2+ channels elicit AHPs in these cells was unknown. We found that N-type channels couple to the medium AHP in both cell types. For the slow AHP, N-type channels contribute in OT neurons, whereas R-type contribute in VP neurons. No single Ca2+ channel blocker abolished the entire AHP, suggesting that additional Ca2+ sources are involved.
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Affiliation(s)
- Matthew K Kirchner
- University of Tennessee Health Science Center, Department of Anatomy & Neurobiology
| | - Robert C Foehring
- University of Tennessee Health Science Center, Department of Anatomy & Neurobiology
| | - Joseph Callaway
- University of Tennessee Health Science Center, Department of Anatomy & Neurobiology
| | - William E Armstrong
- University of Tennessee Health Science Center, Department of Anatomy & Neurobiology
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40
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Guzman JN, Ilijic E, Yang B, Sanchez-Padilla J, Wokosin D, Galtieri D, Kondapalli J, Schumacker PT, Surmeier DJ. Systemic isradipine treatment diminishes calcium-dependent mitochondrial oxidant stress. J Clin Invest 2018; 128:2266-2280. [PMID: 29708514 PMCID: PMC5983329 DOI: 10.1172/jci95898] [Citation(s) in RCA: 96] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 03/13/2018] [Indexed: 01/04/2023] Open
Abstract
The ability of the Cav1 channel inhibitor isradipine to slow the loss of substantia nigra pars compacta (SNc) dopaminergic (DA) neurons and the progression of Parkinson's disease (PD) is being tested in a phase 3 human clinical trial. But it is unclear whether and how chronic isradipine treatment will benefit SNc DA neurons in vivo. To pursue this question, isradipine was given systemically to mice at doses that achieved low nanomolar concentrations in plasma, near those achieved in patients. This treatment diminished cytosolic Ca2+ oscillations in SNc DA neurons without altering autonomous spiking or expression of Ca2+ channels, an effect mimicked by selectively knocking down expression of Cav1.3 channel subunits. Treatment also lowered mitochondrial oxidant stress, reduced a high basal rate of mitophagy, and normalized mitochondrial mass - demonstrating that Cav1 channels drive mitochondrial oxidant stress and turnover in vivo. Thus, chronic isradipine treatment remodeled SNc DA neurons in a way that should not only diminish their vulnerability to mitochondrial challenges, but to autophagic stress as well.
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Affiliation(s)
| | | | | | | | | | | | | | - Paul T. Schumacker
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
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41
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Franco-Iborra S, Vila M, Perier C. Mitochondrial Quality Control in Neurodegenerative Diseases: Focus on Parkinson's Disease and Huntington's Disease. Front Neurosci 2018; 12:342. [PMID: 29875626 PMCID: PMC5974257 DOI: 10.3389/fnins.2018.00342] [Citation(s) in RCA: 128] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 05/02/2018] [Indexed: 12/15/2022] Open
Abstract
In recent years, several important advances have been made in our understanding of the pathways that lead to cell dysfunction and death in Parkinson's disease (PD) and Huntington's disease (HD). Despite distinct clinical and pathological features, these two neurodegenerative diseases share critical processes, such as the presence of misfolded and/or aggregated proteins, oxidative stress, and mitochondrial anomalies. Even though the mitochondria are commonly regarded as the "powerhouses" of the cell, they are involved in a multitude of cellular events such as heme metabolism, calcium homeostasis, and apoptosis. Disruption of mitochondrial homeostasis and subsequent mitochondrial dysfunction play a key role in the pathophysiology of neurodegenerative diseases, further highlighting the importance of these organelles, especially in neurons. The maintenance of mitochondrial integrity through different surveillance mechanisms is thus critical for neuron survival. Mitochondria display a wide range of quality control mechanisms, from the molecular to the organellar level. Interestingly, many of these lines of defense have been found to be altered in neurodegenerative diseases such as PD and HD. Current knowledge and further elucidation of the novel pathways that protect the cell through mitochondrial quality control may offer unique opportunities for disease therapy in situations where ongoing mitochondrial damage occurs. In this review, we discuss the involvement of mitochondrial dysfunction in neurodegeneration with a special focus on the recent findings regarding mitochondrial quality control pathways, beyond the classical effects of increased production of reactive oxygen species (ROS) and bioenergetic alterations. We also discuss how disturbances in these processes underlie the pathophysiology of neurodegenerative disorders such as PD and HD.
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Affiliation(s)
- Sandra Franco-Iborra
- Vall d'Hebron Research Institute (VHIR)-Center for Networked Biomedical Research in Neurodegenerative Diseases (CIBERNED), Barcelona, Spain
| | - Miquel Vila
- Vall d'Hebron Research Institute (VHIR)-Center for Networked Biomedical Research in Neurodegenerative Diseases (CIBERNED), Barcelona, Spain
- Catalan Institution for Research and Advanced Studies, Barcelona, Spain
- Department of Biochemistry and Molecular Biology, Autonomous University of Barcelona, Barcelona, Spain
| | - Celine Perier
- Vall d'Hebron Research Institute (VHIR)-Center for Networked Biomedical Research in Neurodegenerative Diseases (CIBERNED), Barcelona, Spain
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42
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Gantz SC, Ford CP, Morikawa H, Williams JT. The Evolving Understanding of Dopamine Neurons in the Substantia Nigra and Ventral Tegmental Area. Annu Rev Physiol 2018; 80:219-241. [PMID: 28938084 DOI: 10.1146/annurev-physiol-021317-121615] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In recent years, the population of neurons in the ventral tegmental area (VTA) and substantia nigra (SN) has been examined at multiple levels. The results indicate that the projections, neurochemistry, and receptor and ion channel expression in this cell population vary widely. This review centers on the intrinsic properties and synaptic regulation that control the activity of dopamine neurons. Although all dopamine neurons fire action potentials in a pacemaker pattern in the absence of synaptic input, the intrinsic properties that underlie this activity differ considerably. Likewise, the transition into a burst/pause pattern results from combinations of intrinsic ion conductances, inhibitory and excitatory synaptic inputs that differ among this cell population. Finally, synaptic plasticity is a key regulator of the rate and pattern of activity in different groups of dopamine neurons. Through these fundamental properties, the activity of dopamine neurons is regulated and underlies the wide-ranging functions that have been attributed to dopamine.
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Affiliation(s)
- Stephanie C Gantz
- Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224, USA
| | - Christopher P Ford
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, Colorado 80045, USA
| | - Hitoshi Morikawa
- Department of Neuroscience and Waggoner Center for Alcohol and Addiction Research, University of Texas, Austin, Texas 78712, USA
| | - John T Williams
- Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97239, USA;
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Abstract
The high energy demands of the substantia nigra pars compacta dopaminergic (DASNc) neurons render these neurons vulnerable to degeneration. These energy demands are a function of their long and extensively arborized axons and very large number of transmitter release sites, and are further augmented by their natural pacemaking activity. Pacemaking is driven by the rhythmic entry of Ca2+ into the cell and, while the entry of Ca2+ into the neuron stimulates energy (ATP) production, the extrusion of Ca2+ conversely saps the energy that is generated. DASNc neurons are said to be operating at a delicate equilibrium where any further stress or environmental demand may lead to their decompensation and degeneration. In experimental models of Parkinson’s disease, reducing the energy requirements of these neurons by trimming the size of the neuronal arbor or by impeding the entry of Ca2+ into the cell has been shown to be protective. Increasing the energy supply to these neurons with d-beta-hydroxybutyrate has also been shown to be protective. The use of gammahydroxybutyrate holds great promise as a neuroprotective in Parkinson’s disease because it can act as an energy source for the cell while simultaneously arresting its pacemaking activity and the entry of Ca2+ into the cell. Short clinical trials of gammahydroxybutyrate in Parkinson’s disease have already demonstrated its immediate capacity to significantly reduce daytime fatigue and sleepiness and to improve sleep at night.
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44
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Role of the Axon Initial Segment in the Control of Spontaneous Frequency of Nigral Dopaminergic Neurons In Vivo. J Neurosci 2017; 38:733-744. [PMID: 29217687 DOI: 10.1523/jneurosci.1432-17.2017] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 10/24/2017] [Accepted: 11/20/2017] [Indexed: 11/21/2022] Open
Abstract
The spontaneous tonic discharge activity of nigral dopamine neurons plays a fundamental role in dopaminergic signaling. To investigate the role of neuronal morphology and architecture with respect to spontaneous activity in this population, we visualized the 3D structure of the axon initial segment (AIS) along with the entire somatodendritic domain of adult male mouse dopaminergic neurons, previously recorded in vivo We observed a positive correlation of the firing rate with both proximity and size of the AIS. Computational modeling showed that the size of the AIS, but not its position within the somatodendritic domain, is the major causal determinant of the tonic firing rate in the intact model, by virtue of the higher intrinsic frequency of the isolated AIS. Further mechanistic analysis of the relationship between neuronal morphology and firing rate showed that dopaminergic neurons function as a coupled oscillator whose frequency of discharge results from a compromise between AIS and somatodendritic oscillators. Thus, morphology plays a critical role in setting the basal tonic firing rate, which in turn could control striatal dopaminergic signaling that mediates motivation and movement.SIGNIFICANCE STATEMENT The frequency at which nigral dopamine neurons discharge action potentials sets baseline dopamine levels in the brain, which enables activity in motor, cognitive, and motivational systems. Here, we demonstrate that the size of the axon initial segment, a subcellular compartment responsible for initiating action potentials, is a key determinant of the firing rate in these neurons. The axon initial segment and all the molecular components that underlie its critical function may provide a novel target for the regulation of dopamine levels in the brain.
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45
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Galtieri DJ, Estep CM, Wokosin DL, Traynelis S, Surmeier DJ. Pedunculopontine glutamatergic neurons control spike patterning in substantia nigra dopaminergic neurons. eLife 2017; 6:30352. [PMID: 28980939 PMCID: PMC5643088 DOI: 10.7554/elife.30352] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 10/04/2017] [Indexed: 12/26/2022] Open
Abstract
Burst spiking in substantia nigra pars compacta (SNc) dopaminergic neurons is a key signaling event in the circuitry controlling goal-directed behavior. It is widely believed that this spiking mode depends upon an interaction between synaptic activation of N-methyl-D-aspartate receptors (NMDARs) and intrinsic oscillatory mechanisms. However, the role of specific neural networks in burst generation has not been defined. To begin filling this gap, SNc glutamatergic synapses arising from pedunculopotine nucleus (PPN) neurons were characterized using optical and electrophysiological approaches. These synapses were localized exclusively on the soma and proximal dendrites, placing them in a good location to influence spike generation. Indeed, optogenetic stimulation of PPN axons reliably evoked spiking in SNc dopaminergic neurons. Moreover, burst stimulation of PPN axons was faithfully followed, even in the presence of NMDAR antagonists. Thus, PPN-evoked burst spiking of SNc dopaminergic neurons in vivo may not only be extrinsically triggered, but extrinsically patterned as well.
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Affiliation(s)
- Daniel J Galtieri
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - Chad M Estep
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - David L Wokosin
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - Stephen Traynelis
- Department of Pharmacology, Emory University, Atlanta, United States
| | - D James Surmeier
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States
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46
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Knowlton C, Kutterer S, Roeper J, Canavier CC. Calcium dynamics control K-ATP channel-mediated bursting in substantia nigra dopamine neurons: a combined experimental and modeling study. J Neurophysiol 2017; 119:84-95. [PMID: 28978764 DOI: 10.1152/jn.00351.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Burst firing in medial substantia nigra (mSN) dopamine (DA) neurons has been selectively linked to novelty-induced exploration behavior in mice. Burst firing in mSN DA neurons, in contrast to lateral SN DA neurons, requires functional ATP-sensitive potassium (K-ATP) channels both in vitro and in vivo. However, the precise role of K-ATP channels in promoting burst firing is unknown. We show experimentally that L-type calcium channel activity in mSN DA neurons enhances open probability of K-ATP channels. We then generate a mathematical model to study the role of Ca2+ dynamics driving K-ATP channel function in mSN DA neurons during bursting. In our model, Ca2+ influx leads to local accumulation of ADP due to Ca-ATPase activity, which in turn activates K-ATP channels. If K-ATP channel activation reaches levels sufficient to terminate spiking, rhythmic bursting occurs. The model explains the experimental observation that, in vitro, coapplication of NMDA and a selective K-ATP channel opener, NN414, is required to elicit bursting as follows. Simulated NMDA receptor activation increases the firing rate and the rate of Ca2+ influx, which increases the activation of K-ATP. The model suggests that additional sources of hyperpolarization, such as GABAergic synaptic input, are recruited in vivo for burst termination or rebound burst discharge. The model predicts that NN414 increases the sensitivity of the K-ATP channel to ADP, promoting burst firing in vitro, and that that high levels of Ca2+ buffering, as might be expected in the calbindin-positive SN DA neuron subpopulation, promote rhythmic bursting pattern, consistent with experimental observations in vivo. NEW & NOTEWORTHY Recently identified distinct subpopulations of midbrain dopamine neurons exhibit differences in their two primary activity patterns in vivo: tonic (single spike) firing and phasic bursting. This study elucidates the biophysical basis of bursts specific to dopamine neurons in the medial substantia nigra, enabled by ATP-sensitive K+ channels and necessary for novelty-induced exploration. A better understanding of how dopaminergic signaling differs between subpopulations may lead to therapeutic strategies selectively targeted to specific subpopulations.
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Affiliation(s)
- Christopher Knowlton
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center , New Orleans, Louisiana
| | - Sylvie Kutterer
- Institut für Neurophysiologie, Goethe University , Frankfurt , Germany
| | - Jochen Roeper
- Institut für Neurophysiologie, Goethe University , Frankfurt , Germany
| | - Carmen C Canavier
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center , New Orleans, Louisiana
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47
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Iyer R, Ungless MA, Faisal AA. Calcium-activated SK channels control firing regularity by modulating sodium channel availability in midbrain dopamine neurons. Sci Rep 2017; 7:5248. [PMID: 28701749 PMCID: PMC5507868 DOI: 10.1038/s41598-017-05578-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 05/31/2017] [Indexed: 12/21/2022] Open
Abstract
Dopamine neurons in the substantia nigra pars compacta and ventral tegmental area regulate behaviours such as reward-related learning, and motor control. Dysfunction of these neurons is implicated in Schizophrenia, addiction to drugs, and Parkinson’s disease. While some dopamine neurons fire single spikes at regular intervals, others fire irregular single spikes interspersed with bursts. Pharmacological inhibition of calcium-activated potassium (SK) channels increases the variability in their firing pattern, sometimes also increasing the number of spikes fired in bursts, indicating that SK channels play an important role in maintaining dopamine neuron firing regularity and burst firing. However, the exact mechanisms underlying these effects are still unclear. Here, we develop a biophysical model of a dopamine neuron incorporating ion channel stochasticity that enabled the analysis of availability of ion channels in multiple states during spiking. We find that decreased firing regularity is primarily due to a significant decrease in the AHP that in turn resulted in a reduction in the fraction of available voltage-gated sodium channels due to insufficient recovery from inactivation. Our model further predicts that inhibition of SK channels results in a depolarisation of action potential threshold along with an increase in its variability.
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Affiliation(s)
- Rajeshwari Iyer
- MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital Campus, Du Cane Road, London, W12 0NN, UK.,Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Mark A Ungless
- MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital Campus, Du Cane Road, London, W12 0NN, UK. .,Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, Du Cane Road, London, W12 0NN, UK.
| | - Aldo A Faisal
- MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital Campus, Du Cane Road, London, W12 0NN, UK. .,Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, Du Cane Road, London, W12 0NN, UK. .,Department of Bioengineering, Imperial College London, London, United Kingdom. .,Department of Computing, Imperial College London, London, United Kingdom.
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48
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Kirchner MK, Foehring RC, Wang L, Chandaka GK, Callaway JC, Armstrong WE. Phosphatidylinositol 4,5-bisphosphate (PIP 2 ) modulates afterhyperpolarizations in oxytocin neurons of the supraoptic nucleus. J Physiol 2017; 595:4927-4946. [PMID: 28383826 DOI: 10.1113/jp274219] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 04/04/2017] [Indexed: 01/19/2023] Open
Abstract
KEY POINTS Afterhyperpolarizations (AHPs) generated by repetitive action potentials in supraoptic magnocellular neurons regulate repetitive firing and spike frequency adaptation but relatively little is known about PIP2 's control of these AHPs. We examined how changes in PIP2 levels affected AHPs, somatic [Ca2+ ]i , and whole cell Ca2+ currents. Manipulations of PIP2 levels affected both medium and slow AHP currents in oxytocin (OT) neurons of the supraoptic nucleus. Manipulations of PIP2 levels did not modulate AHPs by influencing Ca2+ release from IP3 -triggered Ca2+ stores, suggesting more direct modulation of channels by PIP2 . PIP2 depletion reduced spike-evoked Ca2+ entry and voltage-gated Ca2+ currents. PIP2 appears to influence AHPs in OT neurons by reducing Ca2+ influx during spiking. ABSTRACT Oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurons of the supraoptic nucleus (SON) display calcium-dependent afterhyperpolarizations (AHPs) following a train of action potentials that are critical to shaping the firing patterns of these cells. Previous work demonstrated that the lipid phosphatidylinositol 4,5-bisphosphate (PIP2 ) enabled the slow AHP component (sAHP) in cortical pyramidal neurons. We investigated whether this phenomenon occurred in OT and VP neurons of the SON. Using whole cell recordings in coronal hypothalamic slices from adult female rats, we demonstrated that inhibition of PIP2 synthesis with wortmannin robustly blocked both the medium and slow AHP currents (ImAHP and IsAHP ) of OT, but not VP neurons with high affinity. We further tested this by introducing a water-soluble PIP2 analogue (diC8 -PIP2 ) into neurons, which in OT neurons not only prevented wortmannin's inhibitory effect, but slowed rundown of the ImAHP and IsAHP . Inhibition of phospholipase C (PLC) with U73122 did not inhibit either ImAHP or IsAHP in OT neurons, consistent with wortmannin's effects not being due to reducing diacylglycerol (DAG) or IP3 availability, i.e. PIP2 modulation of AHPs is not likely to involve downstream Ca2+ release from inositol 1,4,5-trisphosphate (IP3 )-triggered Ca2+ -store release, or channel modulation via DAG and protein kinase C (PKC). We found that wortmannin reduced [Ca2+ ]i increase induced by spike trains in OT neurons, but had no effect on AHPs evoked by uncaging intracellular Ca2+ . Finally, wortmannin selectively reduced whole cell Ca2+ currents in OT neurons while leaving VP neurons unaffected. The results indicate that PIP2 modulates both the ImAHP and IsAHP in OT neurons, most likely by controlling Ca2+ entry through voltage-gated Ca2+ channels opened during spike trains.
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Affiliation(s)
- Matthew K Kirchner
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Robert C Foehring
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Lie Wang
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Giri Kumar Chandaka
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Joseph C Callaway
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - William E Armstrong
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
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Abstract
Across all kingdoms in the tree of life, calcium (Ca2+) is an essential element used by cells to respond and adapt to constantly changing environments. In multicellular organisms, it plays fundamental roles during fertilization, development and adulthood. The inability of cells to regulate Ca2+ can lead to pathological conditions that ultimately culminate in cell death. One such pathological condition is manifested in Parkinson's disease, the second most common neurological disorder in humans, which is characterized by the aggregation of the protein, α-synuclein. This Review discusses current evidence that implicates Ca2+ in the pathogenesis of Parkinson's disease. Understanding the mechanisms by which Ca2+ signaling contributes to the progression of this disease will be crucial for the development of effective therapies to combat this devastating neurological condition.
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Affiliation(s)
- Sofia V Zaichick
- Ken and Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Kaitlyn M McGrath
- Ken and Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Gabriela Caraveo
- Ken and Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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50
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Dougalis AG, Matthews GAC, Liss B, Ungless MA. Ionic currents influencing spontaneous firing and pacemaker frequency in dopamine neurons of the ventrolateral periaqueductal gray and dorsal raphe nucleus (vlPAG/DRN): A voltage-clamp and computational modelling study. J Comput Neurosci 2017; 42:275-305. [PMID: 28367595 PMCID: PMC5403876 DOI: 10.1007/s10827-017-0641-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 10/28/2016] [Accepted: 03/13/2017] [Indexed: 01/31/2023]
Abstract
Dopamine (DA) neurons of the ventrolateral periaqueductal gray (vlPAG) and dorsal raphe nucleus (DRN) fire spontaneous action potentials (APs) at slow, regular patterns in vitro but a detailed account of their intrinsic membrane properties responsible for spontaneous firing is currently lacking. To resolve this, we performed a voltage-clamp electrophysiological study in brain slices to describe their major ionic currents and then constructed a computer model and used simulations to understand the mechanisms behind autorhythmicity in silico. We found that vlPAG/DRN DA neurons exhibit a number of voltage-dependent currents activating in the subthreshold range including, a hyperpolarization-activated cation current (IH), a transient, A-type, potassium current (IA), a background, ‘persistent’ (INaP) sodium current and a transient, low voltage activated (LVA) calcium current (ICaLVA). Brain slice pharmacology, in good agreement with computer simulations, showed that spontaneous firing occurred independently of IH, IA or calcium currents. In contrast, when blocking sodium currents, spontaneous firing ceased and a stable, non-oscillating membrane potential below AP threshold was attained. Using the DA neuron model we further show that calcium currents exhibit little activation (compared to sodium) during the interspike interval (ISI) repolarization while, any individual potassium current alone, whose blockade positively modulated AP firing frequency, is not required for spontaneous firing. Instead, blockade of a number of potassium currents simultaneously is necessary to eliminate autorhythmicity. Repolarization during ISI is mediated initially via the deactivation of the delayed rectifier potassium current, while a sodium background ‘persistent’ current is essentially indispensable for autorhythmicity by driving repolarization towards AP threshold.
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Affiliation(s)
- Antonios G Dougalis
- MRC London Institute of Medical Sciences (LMS), Du Cane Road, London, W12 0NN, UK.,Institute of Clinical Sciences (ICS), Imperial College London, Faculty of Medicine, Du Cane Road, London, W12 0NN, UK.,Institute of Applied Physiology, University of Ulm, Faculty of Medicine, 89073, Ulm, Germany
| | - Gillian A C Matthews
- MRC London Institute of Medical Sciences (LMS), Du Cane Road, London, W12 0NN, UK.,Institute of Clinical Sciences (ICS), Imperial College London, Faculty of Medicine, Du Cane Road, London, W12 0NN, UK.,Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Birgit Liss
- Institute of Applied Physiology, University of Ulm, Faculty of Medicine, 89073, Ulm, Germany
| | - Mark A Ungless
- MRC London Institute of Medical Sciences (LMS), Du Cane Road, London, W12 0NN, UK. .,Institute of Clinical Sciences (ICS), Imperial College London, Faculty of Medicine, Du Cane Road, London, W12 0NN, UK.
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