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Pickny L, Hindermann M, Ditting T, Hilgers KF, Linz P, Ott C, Schmieder RE, Schiffer M, Amann K, Veelken R, Rodionova K. Myocardial infarction with a preserved ejection fraction-the impaired function of the cardio-renal baroreflex. Front Physiol 2023; 14:1144620. [PMID: 37082237 PMCID: PMC10110856 DOI: 10.3389/fphys.2023.1144620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2023] [Accepted: 03/14/2023] [Indexed: 04/22/2023] Open
Abstract
Introduction: In experimental myocardial infarction with reduced ejection fraction causing overt congestive heart failure, the control of renal sympathetic nerve activity (RSNA) by the cardio-renal baroreflex was impaired. The afferent vagal nerve activity under these experimental conditions had a lower frequency at saturation than that in controls. Hence, by investigating respective first neurons in the nodose ganglion (NG), we wanted to test the hypothesis that after myocardial infarction with still-preserved ejection fraction, the cardiac afferent nerve pathway is also already impaired. Material and methods: A myocardial infarction was induced by coronary artery ligature. After 21 days, nodose ganglion neurons with cardiac afferents from rats with myocardial infarction were cultured. A current clamp was used to characterize neurons as "tonic," i.e., sustained action potential (AP) firing, or "phasic," i.e., <5 APs upon current injection. Cardiac ejection fraction was measured using echocardiography; RSNA was recorded to evaluate the sensitivity of the cardiopulmonary baroreflex. Renal and cardiac histology was studied for inflammation and fibrosis markers. Results: A total of 192 neurons were investigated. In rats, after myocardial infarction, the number of neurons with a tonic response pattern increased compared to that in the controls (infarction vs. control: 78.6% vs. 48.5%; z-test, *p < 0.05), with augmented production of APs (23.7 ± 2.86 vs. 15.5 ± 1.86 APs/600 ms; mean ± SEM, t-test, *p < 0.05). The baseline activity of RSNA was subtly increased, and its control by the cardiopulmonary baroreflex was impaired following myocardial infarction: the fibrosis marker collagen I augmented in the renal interstitium. Discussion: After myocardial infarction with still-preserved ejection fraction, a complex impairment of the afferent limb of the cardio-renal baroreflex caused dysregulation of renal sympathetic nerve activity with signs of renal fibrosis.
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Affiliation(s)
- Lisa Pickny
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Martin Hindermann
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Tilmann Ditting
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
- Department of Internal Medicine 4—Nephrology and Hypertension, Paracelsus Private Medical School Nuremberg, Nuremberg, Germany
| | - Karl F. Hilgers
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Peter Linz
- Department of Radiology, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Christian Ott
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
- Department of Internal Medicine 4—Nephrology and Hypertension, Paracelsus Private Medical School Nuremberg, Nuremberg, Germany
| | - Roland E. Schmieder
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Mario Schiffer
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Kerstin Amann
- Department of Nephropathology, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Roland Veelken
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
- Department of Internal Medicine 4—Nephrology and Hypertension, Paracelsus Private Medical School Nuremberg, Nuremberg, Germany
- *Correspondence: Roland Veelken,
| | - Kristina Rodionova
- Department of Internal Medicine 4—Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
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Li S, Zhao F, Tang Q, Xi C, He J, Wang Y, Zhu MX, Cao Z. Sarco/endoplasmic reticulum Ca 2+ -ATPase 2b mediates oxidation-induced endoplasmic reticulum stress to regulate neuropathic pain. Br J Pharmacol 2021; 179:2016-2036. [PMID: 34811737 DOI: 10.1111/bph.15744] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 09/24/2021] [Accepted: 11/05/2021] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Neuropathic pain is a widespread health problem with limited curative treatment. Decreased sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA) expression has been reported in dorsal root ganglion (DRG) of animals suffering from neuropathic pain. We aimed to establish the relationship between SERCA expression and the pain responses and to elucidate the underlying molecular mechanism. EXPERIMENTAL APPROACH Neuropathic pain was modeled using rat chronic constriction injury (CCI). Ca2+ imaging and current clamp patch-clamp were used to determine cytosolic Ca2+ levels and action potential firing, respectively. Western blots, immunofluorescence staining and RT-PCR were used to quantitatively assess protein and mRNA expression, respectively. H&E staining and coupled enzyme assay were used to evaluate the nerve injury and SERCA2b activity, respectively. KEY RESULTS SERCA2b is the predominant SERCA isoform in rat DRG and its expression is decreased after CCI at mRNA, protein and activity levels. Whereas inhibiting SERCA with thapsigargin causes neuronal hyperexcitation, nerve injury, ER stress, satellite glial cell activation and mechanical allodynia, activating SERCA by CDN1163 or overexpressing SERCA2b in DRG after CCI produces long-term relief of mechanical and thermal allodynia with accompanied morphological and functional restoration through alleviation of ER stress. Furthermore, the downregulation of DRG SERCA2b in CCI rats is caused by increased production of reactive oxygen species (ROS) through Sp1-dependent transcriptional inhibition. CONCLUSION AND IMPLICATIONS Our findings reveal a novel pathway centering around SERCA2b as the key molecule underlying the mechanism of development and maintenance of neuropathic pain, and SERCA2b activators have the potential for therapeutic treatment of neuropathic pain.
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Affiliation(s)
- Shaoheng Li
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Fang Zhao
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Qinglian Tang
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Chuchu Xi
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Jing He
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Yujing Wang
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
| | - Michael X Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, USA
| | - Zhengyu Cao
- State Key Laboratory of Natural Medicines and Jiangsu Provincial Key Laboratory for TCM Evaluation and Translational Development, School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu, China
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3
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Rodionova K, Hilgers KF, Rafii-Tabrizi S, Doellner J, Cordasic N, Linz P, Karl AL, Ott C, Schmieder RE, Schiffer M, Amann K, Veelken R, Ditting T. Responsiveness of afferent renal nerve units in renovascular hypertension in rats. Pflugers Arch 2021; 473:1617-1629. [PMID: 34232378 PMCID: PMC8433106 DOI: 10.1007/s00424-021-02591-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 05/12/2021] [Accepted: 06/03/2021] [Indexed: 12/01/2022]
Abstract
Previous data suggest that renal afferent nerve activity is increased in hypertension exerting sympathoexcitatory effects. Hence, we wanted to test the hypothesis that in renovascular hypertension, the activity of dorsal root ganglion (DRG) neurons with afferent projections from the kidneys is augmented depending on the degree of intrarenal inflammation. For comparison, a nonhypertensive model of mesangioproliferative nephritis was investigated. Renovascular hypertension (2-kidney, 1-clip [2K1C]) was induced by unilateral clipping of the left renal artery and mesangioproliferative glomerulonephritis (anti-Thy1.1) by IV injection of a 1.75-mg/kg BW OX-7 antibody. Neuronal labeling (dicarbocyanine dye [DiI]) in all rats allowed identification of renal afferent dorsal root ganglion (DRG) neurons. A current clamp was used to characterize neurons as tonic (sustained action potential [AP] firing) or phasic (1–4 AP) upon stimulation by current injection. All kidneys were investigated using standard morphological techniques. DRG neurons exhibited less often tonic response if in vivo axonal input from clipped kidneys was received (30.4% vs. 61.2% control, p < 0.05). However, if the nerves to the left clipped kidneys were cut 7 days prior to investigation, the number of tonic renal neurons completely recovered to well above control levels. Interestingly, electrophysiological properties of neurons that had in vivo axons from the right non-clipped kidneys were not distinguishable from controls. Renal DRG neurons from nephritic rats also showed less often tonic activity upon current injection (43.4% vs. 64.8% control, p < 0.05). Putative sympathoexcitatory and impaired sympathoinhibitory renal afferent nerve fibers probably contribute to increased sympathetic activity in 2K1C hypertension.
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Affiliation(s)
- Kristina Rodionova
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Karl F Hilgers
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Salman Rafii-Tabrizi
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Johannes Doellner
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Nada Cordasic
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Peter Linz
- Department of Radiology, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Anna-Lena Karl
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Christian Ott
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany.,Department of Internal Medicine 4 - Nephrology and Hypertension, Paracelsus Private Medical School Nuremberg, Nuremberg, Germany
| | - Roland E Schmieder
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Mario Schiffer
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Kerstin Amann
- Department of Nephropathology, Friedrich-Alexander University Erlangen, Erlangen, Germany
| | - Roland Veelken
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany. .,Department of Radiology, Friedrich-Alexander University Erlangen, Erlangen, Germany.
| | - Tilmann Ditting
- Department of Internal Medicine 4 - Nephrology and Hypertension, Friedrich-Alexander University Erlangen, Erlangen, Germany.,Department of Internal Medicine 4 - Nephrology and Hypertension, Paracelsus Private Medical School Nuremberg, Nuremberg, Germany
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4
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Middleton SJ, Barry AM, Comini M, Li Y, Ray PR, Shiers S, Themistocleous AC, Uhelski ML, Yang X, Dougherty PM, Price TJ, Bennett DL. Studying human nociceptors: from fundamentals to clinic. Brain 2021; 144:1312-1335. [PMID: 34128530 PMCID: PMC8219361 DOI: 10.1093/brain/awab048] [Citation(s) in RCA: 67] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 11/26/2020] [Accepted: 12/08/2020] [Indexed: 12/14/2022] Open
Abstract
Chronic pain affects one in five of the general population and is the third most important cause of disability-adjusted life-years globally. Unfortunately, treatment remains inadequate due to poor efficacy and tolerability. There has been a failure in translating promising preclinical drug targets into clinic use. This reflects challenges across the whole drug development pathway, from preclinical models to trial design. Nociceptors remain an attractive therapeutic target: their sensitization makes an important contribution to many chronic pain states, they are located outside the blood-brain barrier, and they are relatively specific. The past decade has seen significant advances in the techniques available to study human nociceptors, including: the use of corneal confocal microscopy and biopsy samples to observe nociceptor morphology, the culture of human nociceptors (either from surgical or post-mortem tissue or using human induced pluripotent stem cell derived nociceptors), the application of high throughput technologies such as transcriptomics, the in vitro and in vivo electrophysiological characterization through microneurography, and the correlation with pain percepts provided by quantitative sensory testing. Genome editing in human induced pluripotent stem cell-derived nociceptors enables the interrogation of the causal role of genes in the regulation of nociceptor function. Both human and rodent nociceptors are more heterogeneous at a molecular level than previously appreciated, and while we find that there are broad similarities between human and rodent nociceptors there are also important differences involving ion channel function, expression, and cellular excitability. These technological advances have emphasized the maladaptive plastic changes occurring in human nociceptors following injury that contribute to chronic pain. Studying human nociceptors has revealed new therapeutic targets for the suppression of chronic pain and enhanced repair. Cellular models of human nociceptors have enabled the screening of small molecule and gene therapy approaches on nociceptor function, and in some cases have enabled correlation with clinical outcomes. Undoubtedly, challenges remain. Many of these techniques are difficult to implement at scale, current induced pluripotent stem cell differentiation protocols do not generate the full diversity of nociceptor populations, and we still have a relatively poor understanding of inter-individual variation in nociceptors due to factors such as age, sex, or ethnicity. We hope our ability to directly investigate human nociceptors will not only aid our understanding of the fundamental neurobiology underlying acute and chronic pain but also help bridge the translational gap.
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Affiliation(s)
- Steven J Middleton
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK
| | - Allison M Barry
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK
| | - Maddalena Comini
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK
| | - Yan Li
- Department of Anesthesia and Pain Medicine, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Pradipta R Ray
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Stephanie Shiers
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Andreas C Themistocleous
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK.,Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa
| | - Megan L Uhelski
- Department of Anesthesia and Pain Medicine, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Xun Yang
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK
| | - Patrick M Dougherty
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa
| | - Theodore J Price
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX 75080, USA
| | - David L Bennett
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK
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5
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Neurogenic substance P-influences on action potential production in afferent neurons of the kidney? Pflugers Arch 2021; 473:633-646. [PMID: 33786667 PMCID: PMC8049925 DOI: 10.1007/s00424-021-02552-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 03/01/2021] [Accepted: 03/03/2021] [Indexed: 12/23/2022]
Abstract
We recently showed that a substance P (SP)–dependent sympatho-inhibitory mechanism via afferent renal nerves is impaired in mesangioproliferative nephritis. Therefore, we tested the hypothesis that SP released from renal afferents inhibits the action potential (AP) production in their dorsal root ganglion (DRG) neurons. Cultured DRG neurons (Th11-L2) were investigated in current clamp mode to assess AP generation during both TRPV1 stimulation by protons (pH 6) and current injections with and without exposure to SP (0.5 µmol) or CGRP (0.5 µmol). Neurons were classified as tonic (sustained AP generation) or phasic (≤ 4 APs) upon current injection; voltage clamp experiments were performed for the investigation of TRPV1-mediated inward currents due to proton stimulation. Superfusion of renal neurons with protons and SP increased the number of action potentials in tonic neurons (9.6 ± 5 APs/10 s vs. 16.9 ± 6.1 APs/10 s, P < 0.05, mean ± SD, n = 7), while current injections with SP decreased it (15.2 ± 6 APs/600 ms vs. 10.2 ± 8 APs/600 ms, P < 0.05, mean ± SD, n = 29). Addition of SP significantly reduced acid-induced TRPV1-mediated currents in renal tonic neurons (− 518 ± 743 pA due to pH 6 superfusion vs. − 82 ± 50 pA due to pH 6 with SP superfusion). In conclusion, SP increased action potential production via a TRPV1-dependent mechanism in acid-sensitive renal neurons. On the other hand, current injection in the presence of SP led to decreased action potential production. Thus, the peptide SP modulates signaling pathways in renal neurons in an unexpected manner leading to both stimulation and inhibition of renal neuronal activity in different (e.g., acidic) environmental contexts.
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6
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Wen J, Chen Z, Wang S, Zhao M, Wang S, Zhao S, Zhang X. Age-related reductions in the excitability of phasic dorsal root ganglion neurons innervating the urinary bladder in female rats. Brain Res 2021; 1752:147251. [PMID: 33421375 DOI: 10.1016/j.brainres.2020.147251] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Revised: 11/04/2020] [Accepted: 12/15/2020] [Indexed: 11/23/2022]
Abstract
Previous studies have revealed an impairment in bladder sensory transduction in aged animals. To examine the contributions of electrical property changes of bladder primary afferents to this impairment, we compared the electrical properties of dorsal root ganglion (DRG) neurons innervating the bladder among young (3 months), middle-aged (12 months), and old (24 months) female rats. The DRG neurons were labeled using axonal tracing techniques. Whole-cell current-clamp recordings of small and medium-sized neurons were performed to assess their passive and active properties. Two patterns of firing were identified based on responses to super-threshold stimuli (1.5, 2.0, 2.5, and 3.0 × rheobase): tonic neurons fired more action potentials (APs), whereas phasic neurons fired only one AP at the onset of stimulus. Tonic neurons were smaller and had a slower rate of AP rise, longer AP duration, more depolarized voltage threshold, and greater rheobase than phasic neurons. In phasic neurons, there was an age-associated increase in voltage threshold and an increase of rheobase (P < 0.05), suggesting an age-related decrease in excitability. In addition, both middle-aged and old rats had longer AP durations and slower rates of AP rise than young rats (P < 0.05). In tonic neurons, old rats had a greater AP overshoot and greater rate of AP rise, but no age-associated changes were identified in any other electrical properties. Our results suggest that the electrical properties of tonic and phasic bladder afferents are differentially altered with aging. A decrease in excitability may contribute to age-related reductions in bladder sensory function.
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Affiliation(s)
- Jiliang Wen
- Department of Urology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China; Department of Urology, Shandong Provincial Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Zhenghao Chen
- Department of Urology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Si Wang
- Department of Neurology, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Mengmeng Zhao
- Department of Urology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Shaoyong Wang
- Department of Urology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Shengtian Zhao
- Department of Urology, Shandong Provincial Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China
| | - Xiulin Zhang
- Department of Urology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250000, PR China.
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Pastori V, D'Aloia A, Blasa S, Lecchi M. Serum-deprived differentiated neuroblastoma F-11 cells express functional dorsal root ganglion neuron properties. PeerJ 2019; 7:e7951. [PMID: 31687277 PMCID: PMC6825413 DOI: 10.7717/peerj.7951] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 09/25/2019] [Indexed: 11/29/2022] Open
Abstract
The isolation and culture of dorsal root ganglion (DRG) neurons cause adaptive changes in the expression and regulation of ion channels, with consequences on neuronal excitability. Considering that not all neurons survive the isolation and that DRG neurons are heterogeneous, it is difficult to find the cellular subtype of interest. For this reason, researchers opt for DRG-derived immortal cell lines to investigate endogenous properties. The F-11 cell line is a hybridoma of embryonic rat DRG neurons fused with the mouse neuroblastoma line N18TG2. In the proliferative condition, F-11 cells do not display a gene expression profile correspondent with specific subclasses of sensory neurons, but the most significant differences when compared with DRGs are the reduction of voltage-gated sodium, potassium and calcium channels, and the small amounts of TRPV1 transcripts. To investigate if functional properties of mature F-11 cells showed more similarities with those of isolated DRG neurons, we differentiated them by serum deprivation. Potassium and sodium currents significantly increased with differentiation, and biophysical properties of tetrodotoxin (TTX)-sensitive currents were similar to those characterized in small DRG neurons. The analysis of the voltage-dependence of calcium currents demonstrated the lack of low threshold activated components. The exclusive expression of high threshold activated Ca2+ currents and of TTX-sensitive Na+ currents correlated with the generation of a regular tonic electrical activity, which was recorded in the majority of the cells (80%) and was closely related to the activity of afferent TTX-sensitive A fibers of the proximal urethra and the bladder. Responses to capsaicin and substance P were also recorded in ~20% and ~80% of cells, respectively. The percentage of cells responsive to acetylcholine was consistent with the percentage referred for rat DRG primary neurons and cell electrical activity was modified by activation of non-NMDA receptors as for embryonic DRG neurons. These properties and the algesic profile (responses to pH5 and sensitivity to both ATP and capsaicin), proposed in literature to define a sub-classification of acutely dissociated rat DRG neurons, suggest that differentiated F-11 cells express receptors and ion channels that are also present in sensory neurons.
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Affiliation(s)
- Valentina Pastori
- Department of Biotechnology and Biosciences and Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy
| | - Alessia D'Aloia
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Stefania Blasa
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Marzia Lecchi
- Department of Biotechnology and Biosciences and Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy
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Zemel BM, Ritter DM, Covarrubias M, Muqeem T. A-Type K V Channels in Dorsal Root Ganglion Neurons: Diversity, Function, and Dysfunction. Front Mol Neurosci 2018; 11:253. [PMID: 30127716 PMCID: PMC6088260 DOI: 10.3389/fnmol.2018.00253] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Accepted: 07/04/2018] [Indexed: 12/13/2022] Open
Abstract
A-type voltage-gated potassium (Kv) channels are major regulators of neuronal excitability that have been mainly characterized in the central nervous system. By contrast, there is a paucity of knowledge about the molecular physiology of these Kv channels in the peripheral nervous system, including highly specialized and heterogenous dorsal root ganglion (DRG) neurons. Although all A-type Kv channels display pore-forming subunits with similar structural properties and fast inactivation, their voltage-, and time-dependent properties and modulation are significantly different. These differences ultimately determine distinct physiological roles of diverse A-type Kv channels, and how their dysfunction might contribute to neurological disorders. The importance of A-type Kv channels in DRG neurons is highlighted by recent studies that have linked their dysfunction to persistent pain sensitization. Here, we review the molecular neurophysiology of A-type Kv channels with an emphasis on those that have been identified and investigated in DRG nociceptors (Kv1.4, Kv3.4, and Kv4s). Also, we discuss evidence implicating these Kv channels in neuropathic pain resulting from injury, and present a perspective of outstanding challenges that must be tackled in order to discover novel treatments for intractable pain disorders.
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Affiliation(s)
- Benjamin M. Zemel
- Vollum Institute, Oregon Health and Science University, Portland, OR, United States
| | - David M. Ritter
- Division of Neurology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States
| | - Manuel Covarrubias
- Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sidney Kimmel Medical College and Jefferson College of Life Sciences at Thomas Jefferson University, Philadelphia, PA, United States
| | - Tanziyah Muqeem
- Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sidney Kimmel Medical College and Jefferson College of Life Sciences at Thomas Jefferson University, Philadelphia, PA, United States
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9
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de Moraes ER, Kushmerick C, Naves LA. Morphological and functional diversity of first-order somatosensory neurons. Biophys Rev 2017; 9:847-856. [PMID: 28889335 DOI: 10.1007/s12551-017-0321-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2017] [Accepted: 08/24/2017] [Indexed: 01/01/2023] Open
Abstract
First-order somatosensory neurons transduce and convey information about the external or internal environment of the body to the central nervous system. They are pseudo unipolar neurons with cell bodies residing in one of several ganglia located near the central nervous system, with the short branch of the axon connecting to the spinal cord or the brain stem and the long branch extending towards the peripheral organ they innervate. Besides their sensory transducer and conductive role, somatosensory neurons also have trophic functions in the tissue they innervate and participate in local reflexes in the periphery. The cell bodies of these neurons are remarkably diverse in terms of size, molecular constitution, and electrophysiological properties. These parameters have provided criteria for classification that have proved useful to establish and study their functions. In this review, we discuss ways to measure and classify populations of neurons based on their size and action potential firing pattern. We also discuss attempts to relate the different populations to specific sensory modalities.
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Affiliation(s)
- Eder Ricardo de Moraes
- Departamento de Fisiologia, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Sergipe, São Cristóvão, Sergipe, Brazil
| | - Christopher Kushmerick
- Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Lígia Araujo Naves
- Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
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Honda M, Kawamoto B, Morizane S, Hikita K, Muraoka K, Sejima T, Takenaka A. Impact of postoperative phosphodiesterase type 5 inhibitor treatment on lower urinary tract symptoms after robot-assisted radical prostatectomy: a longitudinal study. Scand J Urol 2016; 51:33-37. [PMID: 27841089 DOI: 10.1080/21681805.2016.1250810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVE This study aimed to assess the role of tadalafil, a phosphodiesterase type 5 inhibitor (PDE5-I), in recovery of lower urinary tract symptoms (LUTS) after robot-assisted radical prostatectomy (RARP). MATERIALS AND METHODS All patients treated with RARP between October 2010 and August 2013 were enrolled in this retrospective study on prospectively collected data. Patients were retrospectively divided into groups according to postoperative treatment: patients taking tadalafil twice weekly from 1 month to 6 months after RARP, and patients not taking tadalafil. The International Prostate Symptom Score (IPSS), the Overactive Bladder Symptom Score (OABSS) and urinary continence (UC) were assessed preoperatively (2 days before RARP) and at 1, 3, 6, 9 and 12 months after RARP. RESULTS There was no difference in the overall IPSS score between the groups. At 6 and 9 months, the IPSS storage symptom scores were significantly lower in patients taking tadalafil than in patients not taking tadalafil. In patients with overactive bladder (OAB) before RARP (n = 22), no differences in the total scores of OABSS were seen between patients taking tadalafil and patients not taking tadalafil. On the other hand, in non-OAB patients before RARP (n = 68), at 3, 6 and 9 months, the total scores of OABSS were significantly lower in patients taking tadalafil than in patients not taking tadalafil. No differences in UC rates after surgery were seen between the groups. CONCLUSION Postoperative tadalafil treatment may be temporarily effective for the recovery of the IPSS storage symptom scores and OABSS.
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Affiliation(s)
- Masashi Honda
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Bunya Kawamoto
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Shuichi Morizane
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Katsuya Hikita
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Kuniyasu Muraoka
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Takehiro Sejima
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
| | - Atsushi Takenaka
- a Department of Urology , Tottori University Faculty of Medicine , Yonago , Japan
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Girard B, Peterson A, Malley S, Vizzard MA. Accelerated onset of the vesicovesical reflex in postnatal NGF-OE mice and the role of neuropeptides. Exp Neurol 2016; 285:110-125. [PMID: 27342083 DOI: 10.1016/j.expneurol.2016.06.021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 05/30/2016] [Accepted: 06/20/2016] [Indexed: 12/31/2022]
Abstract
The mechanisms underlying the postnatal maturation of micturition from a somatovesical to a vesicovesical reflex are not known but may involve neuropeptides in the lower urinary tract. A transgenic mouse model with chronic urothelial overexpression (OE) of NGF exhibited increased voiding frequency, increased number of non-voiding contractions, altered morphology and hyperinnervation of the urinary bladder by peptidergic (e.g., Sub P and CGRP) nerve fibers in the adult. In early postnatal and adult NGF-OE mice we have now examined: (1) micturition onset using filter paper void assays and open-outlet, continuous fill, conscious cystometry; (2) innervation and neurochemical coding of the suburothelial plexus of the urinary bladder using immunohistochemistry and semi-quantitative image analyses; (3) neuropeptide protein and transcript expression in urinary bladder of postnatal and adult NGF-OE mice using Q-PCR and ELISAs and (4) the effects of intravesical instillation of a neurokinin (NK)-1 receptor antagonist on bladder function in postnatal and adult NGF-OE mice using conscious cystometry. Postnatal NGF-OE mice exhibit age-dependent (R2=0.996-0.998; p≤0.01) increases in Sub and CGRP expression in the urothelium and significantly (p≤0.01) increased peptidergic hyperinnervation of the suburothelial nerve plexus. By as early as P7, NGF-OE mice exhibit a vesicovesical reflex in response to intravesical instillation of saline whereas littermate WT mice require perigenital stimulation to elicit a micturition reflex until P13 when vesicovesical reflexes are first observed. Intravesical instillation of a NK-1 receptor antagonist, netupitant (0.1μg/ml), significantly (p≤0.01) increased void volume and the interval between micturition events with no effects on bladder pressure (baseline, threshold, peak) in postnatal NGF-OE mice; effects on WT mice were few. NGF-induced pleiotropic effects on neuropeptide (e.g., Sub P) expression in the urinary bladder contribute to the maturation of the micturition reflex and are excitatory to the micturition reflex in postnatal NGF-OE mice. These studies provide insight into the mechanisms that contribute to the postnatal development of the micturition reflex.
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Affiliation(s)
- Beatrice Girard
- University of Vermont College of Medicine, Department of Neurological Sciences, Burlington, VT 05405, USA
| | - Abbey Peterson
- University of Vermont College of Medicine, Department of Neurological Sciences, Burlington, VT 05405, USA
| | - Susan Malley
- University of Vermont College of Medicine, Department of Neurological Sciences, Burlington, VT 05405, USA
| | - Margaret A Vizzard
- University of Vermont College of Medicine, Department of Neurological Sciences, Burlington, VT 05405, USA.
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12
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Ditting T, Freisinger W, Rodionova K, Schatz J, Lale N, Heinlein S, Linz P, Ott C, Schmieder RE, Scrogin KE, Veelken R. Impaired excitability of renal afferent innervation after exposure to the inflammatory chemokine CXCL1. Am J Physiol Renal Physiol 2015; 310:F364-71. [PMID: 26697980 DOI: 10.1152/ajprenal.00189.2015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 12/15/2015] [Indexed: 01/06/2023] Open
Abstract
Recently, we showed that renal afferent neurons exhibit a unique firing pattern, i.e., predominantly sustained firing, upon stimulation. Pathological conditions such as renal inflammation likely alter excitability of renal afferent neurons. Here, we tested whether the proinflammatory chemokine CXCL1 alters the firing pattern of renal afferent neurons. Rat dorsal root ganglion neurons (Th11-L2), retrogradely labeled with dicarbocyanine dye, were incubated with CXCL1 (20 h) or vehicle before patch-clamp recording. The firing pattern of neurons was characterized as tonic, i.e., sustained action potential (AP) firing, or phasic, i.e., <5 APs following current injection. Of the labeled renal afferents treated with vehicle, 58.9% exhibited a tonic firing pattern vs. 7.8%, in unlabeled, nonrenal neurons (P < 0.05). However, after exposure to CXCL1, significantly more phasic neurons were found among labeled renal neurons; hence the occurrence of tonic neurons with sustained firing upon electrical stimulation decreased (35.6 vs. 58.9%, P < 0.05). The firing frequency among tonic neurons was not statistically different between control and CXCL1-treated neurons. However, the lower firing frequency of phasic neurons was even further decreased with CXCL1 exposure [control: 1 AP/600 ms (1-2) vs. CXCL1: 1 AP/600 ms (1-1); P < 0.05; median (25th-75th percentile)]. Hence, CXCL1 shifted the firing pattern of renal afferents from a predominantly tonic to a more phasic firing pattern, suggesting that CXCL1 reduced the sensitivity of renal afferent units upon stimulation.
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Affiliation(s)
- Tilmann Ditting
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Wolfgang Freisinger
- Department of Internal Medicine 1, Nephrology Johannes-Guttenberg University, Mainz, Germany
| | - Kristina Rodionova
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Johannes Schatz
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Nena Lale
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Sonja Heinlein
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Peter Linz
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Christian Ott
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Roland E Schmieder
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany
| | - Karie E Scrogin
- Department of Molecular Pharmacology and Therapeutics, Loyola University Chicago Stritch School of Medicine, Chicago, Illinois
| | - Roland Veelken
- Department of Internal Medicine 4, Nephrology and Hypertension, Friedrich-Alexander University, Erlangen, Germany;
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13
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Characteristics of dorsal root ganglia neurons sensitive to Substance P. Mol Pain 2014; 10:73. [PMID: 25431155 PMCID: PMC4280706 DOI: 10.1186/1744-8069-10-73] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Accepted: 10/20/2014] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND Substance P modulates ion channels and the excitability of sensory neurons in pain pathways. Within the heterogeneous population of Dorsal Root Ganglia (DRG) primary sensory neurons, the properties of cells that are sensitive to Substance P are poorly characterized. To define this population better, dissociated rat DRG neurons were tested for their responsiveness to capsaicin, ATP and acid. Responses to ATP were classified according to the kinetics of current activation and desensitization. The same cells were then tested for modulation of action potential firing by Substance P. RESULTS Acid and capsaicin currents were more frequently encountered in the largest diameter neurons. P2X3-like ATP currents were concentrated in small diameter neurons. Substance P modulated the excitability in 20 of 72 cells tested (28%). Of the Substance P sensitive cells, 10 exhibited an increase in excitability and 10 exhibited a decrease in excitability. There was no significant correlation between sensitivity to capsaicin and to Substance P. Excitatory effects of Substance P were strongly associated with cells that had large diameters, fired APs with large overshoots and slowly decaying after hyperpolarizations, and expressed acid currents at pH 7. No neurons that were excited by Substance P presented P2X3-like currents. In contrast, neurons that exhibited inhibitory effects of Substance P fired action potentials with rapidly decaying after hyperpolarizations. CONCLUSION We conclude that excitatory effects of Substance P are restricted to a specific neuronal subpopulation with limited expression of putative nociceptive markers.
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Yu YQ, Chen XF, Yang Y, Yang F, Chen J. Electrophysiological identification of tonic and phasic neurons in sensory dorsal root ganglion and their distinct implications in inflammatory pain. Physiol Res 2014; 63:793-9. [PMID: 25157654 DOI: 10.33549/physiolres.932708] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
In the mammalian autonomic nervous system, tonic and phasic neurons can be differentiated on firing patterns in response to long depolarizing current pulse. However, the similar firing patterns in the somatic primary sensory neurons and their functional significance are not well investigated. Here, we identified two types of neurons innervating somatic sensory in rat dorsal root ganglia (DRG). Tonic neurons fire action potentials (APs) in an intensity-dependent manner, whereas phasic neurons typically generate only one AP firing at the onset of stimulation regardless of intensity. Combining retrograde labeling of somatic DRG neurons with fluorescent tracer DiI, we further find that these neurons demonstrate distinct changes under inflammatory pain states induced by complete Freund's adjuvant (CFA) or bee venom toxin melittin. In tonic neurons, CFA and melittin treatments significantly decrease rheobase and AP durations (depolarization and repolarization), enhance amplitudes of overshoot and afterhyperpolarization (AHP), and increase the number of evoked action potentials. In phasic neurons, however, the same inflammation treatments cause fewer changes in these electrophysiological parameters except for the increased overshoot and decreased AP durations. In the present study, we find that tonic neurons are more hyperexcitable than phasic neurons after peripheral noxious inflammatory stimulation. The results indicate the distinct contributions of two types of DRG neurons in inflammatory pain.
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Affiliation(s)
- Y-Q Yu
- Institute for Biomedical Sciences of Pain and Institute for Functional Brain Disorders, Fourth Military Medical University, Xi'an, PR China.
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15
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Nicotine enhances excitability of medial habenular neurons via facilitation of neurokinin signaling. J Neurosci 2014; 34:4273-84. [PMID: 24647947 DOI: 10.1523/jneurosci.2736-13.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The medial habenula (MHb) densely expresses nicotinic acetylcholine receptors (nAChRs) and participates in nicotine-related behaviors such as nicotine withdrawal and regulating nicotine intake. Although specific nAChR subunits are identified as being involved in withdrawal behavior, the cellular mechanisms through which nicotine acts to cause this aversive experience is unclear. Here, we demonstrate an interaction between the nicotinic and neurokinin signaling systems that may form the basis for some symptoms experienced during nicotine withdrawal. Using patch-clamp electrophysiology in mouse brain slices, we show that nicotine (1 μm) increases intrinsic excitability in MHb neurons. This nicotine-induced phenomenon requires α5-containing nAChRs and depends on intact neurokinin signaling. The effect is blocked by preincubation with neurokinin 1 (NK1; L-732138, 10 μm) and NK3 (SB222200, 2 μm) antagonists and mimicked by NK1 (substance P, 100 nm) and NK3 (neurokinin B [NKB], 100 nm) agonists. Microinjections (1 μl) of L-732138 (50 nm) and SB222200 (100 nm) into the MHb induces withdrawal behavior in chronic nicotine-treated (8.4 mg/kg/d, 2 weeks) mice. Conversely, withdrawal behavior is absent with analogous microinjections into the lateral habenula of nicotine-treated mice or in mice chronically treated with a vehicle solution. Further, chronic nicotine reduces nicotine's acute modulation of intrinsic excitability while sparing modulation by NKB. Our work elucidates the interplay between two neuromodulatory signaling systems in the brain through which nicotine acts to influence intrinsic excitability. More importantly, we document a neuroadaptation of this mechanism to chronic nicotine exposure and implicate these mechanisms collectively in the emergence of nicotine withdrawal behavior.
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16
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Modulation of peripheral Na+ channels and neuronal firing by n-butyl-p-aminobenzoate. Eur J Pharmacol 2014; 727:158-66. [DOI: 10.1016/j.ejphar.2014.01.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 01/15/2014] [Accepted: 01/22/2014] [Indexed: 11/21/2022]
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17
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Liu C, Liu X, Liu S. Bifurcation analysis of a Morris-Lecar neuron model. BIOLOGICAL CYBERNETICS 2014; 108:75-84. [PMID: 24435761 DOI: 10.1007/s00422-013-0580-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Accepted: 12/10/2013] [Indexed: 06/03/2023]
Abstract
In this paper, we investigate the dynamical behaviors of a Morris-Lecar neuron model. By using bifurcation methods and numerical simulations, we examine the global structure of bifurcations of the model. Results are summarized in various two-parameter bifurcation diagrams with the stimulating current as the abscissa and the other parameter as the ordinate. We also give the one-parameter bifurcation diagrams and pay much attention to the emergence of periodic solutions and bistability. Different membrane excitability is obtained by bifurcation analysis and frequency-current curves. The alteration of the membrane properties of the Morris-Lecar neurons is discussed.
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Affiliation(s)
- Congmin Liu
- Department of Mathematics, South China University of Technology, Guangzhou, 510640, China
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18
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Mechanisms of Pelvic Organ Cross-Talk: 2. Impact of Colorectal Distention on Afferent Nerve Activity of the Rat Bladder. J Urol 2013; 190:1123-30. [DOI: 10.1016/j.juro.2013.03.079] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/21/2013] [Indexed: 12/30/2022]
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19
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Freisinger W, Schatz J, Ditting T, Lampert A, Heinlein S, Lale N, Schmieder R, Veelken R. Sensory renal innervation: a kidney-specific firing activity due to a unique expression pattern of voltage-gated sodium channels? Am J Physiol Renal Physiol 2013; 304:F491-7. [PMID: 23283993 DOI: 10.1152/ajprenal.00011.2012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Sensory neurons with afferent axons from the kidney are extraordinary in their response to electrical stimulation. More than 50% exhibit a tonic firing pattern, i.e., sustained action potential firing throughout depolarizing, pointing to an increased excitability, whereas nonrenal neurons show mainly a phasic response, i.e., less than five action potentials. Here we investigated whether these peculiar firing characteristics of renal afferent neurons are due to differences in the expression of voltage-gated sodium channels (Navs). Dorsal root ganglion (DRG) neurons from rats (Th11-L2) were recorded by the current-clamp technique and distinguished as "tonic" or "phasic." In voltage-clamp recordings, Navs were characterized by their tetrodotoxoxin (TTX) sensitivity, and their molecular identity was revealed by RT-PCR. The firing pattern of 66 DRG neurons (41 renal and 25 nonrenal) was investigated. Renal neurons exhibited more often a tonic firing pattern (56.1 vs. 12%). Tonic neurons showed a more positive threshold (-21.75 ± 1.43 vs.-29.33 ± 1.63 mV; P < 0.05), a higher overshoot (56.74 [53.6-60.96] vs. 46.79 mV [38.63-54.75]; P < 0.05) and longer action potential duration (4.61 [4.15-5.85] vs. 3.35 ms [2.12-5.67]; P < 0.05). These findings point to an increased presence of the TTX-resistant Navs 1.8 and 1.9. Furthermore, tonic neurons exhibited a relatively higher portion of TTX-resistant sodium currents. Interestingly, mRNA expression of TTX-resistant sodium channels was significantly increased in renal, predominantly tonic, DRG neurons. Hence, under physiological conditions, renal sensory neurons exhibit predominantly a firing pattern associated with higher excitability. Our findings support that this is due to an increased expression and activation of TTX-resistant Navs.
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Affiliation(s)
- Wolfgang Freisinger
- Dept. of Medicine 4, Univ. of Erlangen-Nürnberg, Loschgestraβe 8, 91054 Erlangen, Germany.
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20
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Hood B, Andersson KE. Common theme for drugs effective in overactive bladder treatment: inhibition of afferent signaling from the bladder. Int J Urol 2013; 20:21-7. [PMID: 23072271 PMCID: PMC3558796 DOI: 10.1111/j.1442-2042.2012.03196.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 09/19/2012] [Indexed: 12/21/2022]
Abstract
The overactive bladder syndrome and detrusor overactivity are conditions that can have major effects on quality of life and social functioning. Antimuscarinic drugs are still first-line treatment. These drugs often have good initial response rates, but adverse effects and decreasing efficacy cause long-term compliance problems, and alternatives are needed. The recognition of the functional contribution of the urothelium/suburothelium, the autonomous detrusor muscle activity during bladder filling and the diversity of nerve transmitters involved has sparked interest in both peripheral and central modulation of overactive bladder syndrome/detrusor overactivity pathophysiology. Three drugs recently approved for treatment of overactive bladder syndrome/detrusor overactivity (mirabegron, tadalafil and onabotulinum toxin A), representing different pharmacological mechanisms; that is, β-adrenoceptor agonism, phosphodiesterase type 5 inhibition, and inhibition of nerve release of efferent and afferent transmitters, all seem to have one effect in common: inhibition of the afferent nervous activity generated by the bladder during filling. In the present review, the different mechanisms forming the pharmacological basis for the use of these drugs are discussed.
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Affiliation(s)
- Brandy Hood
- Institute for Regenerative Medicine, Wake Forest University School of MedicineWinston-Salem, North Carolina, USA
- Department of Urology, Wake Forest Baptist Medical CenterWinston-Salem, North Carolina, USA
| | - Karl-Erik Andersson
- Institute for Regenerative Medicine, Wake Forest University School of MedicineWinston-Salem, North Carolina, USA
- Department of Urology, Wake Forest Baptist Medical CenterWinston-Salem, North Carolina, USA
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Giuliano F, Ückert S, Maggi M, Birder L, Kissel J, Viktrup L. The mechanism of action of phosphodiesterase type 5 inhibitors in the treatment of lower urinary tract symptoms related to benign prostatic hyperplasia. Eur Urol 2012; 63:506-16. [PMID: 23018163 DOI: 10.1016/j.eururo.2012.09.006] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 09/03/2012] [Indexed: 12/22/2022]
Abstract
CONTEXT Clinical trials of phosphodiesterase type 5 inhibitors (PDE5-Is) have consistently demonstrated a significant reduction in lower urinary tract symptoms (LUTS) and small urinary flow rate changes in men with benign prostatic hyperplasia (BPH). OBJECTIVE This review presents the proposed mechanisms of action of PDE5-Is in the treatment of BPH-LUTS focusing on the localization of PDE5 isoenzymes in the pelvic structures; smooth muscle relaxation in the bladder, prostate, and supporting vasculature; increased blood perfusion of the bladder and prostate; and modulation of sensory impulses from these organs. EVIDENCE ACQUISITION Literature describing in vitro, preclinical, or clinical studies of pathologic processes contributing to LUTS or effects of PDE5 inhibition on the lower urinary tract (LUT) was selected for review. EVIDENCE SYNTHESIS We objectively assessed and summarized the published data focusing on articles published within the past 10 yr. Articles before the time cut-off were included if historically relevant. CONCLUSIONS The PDE5 isoenzymes are highly expressed in the LUT including the bladder, prostate, and their supporting vasculature. In vitro assays have demonstrated PDE5-Is by regulating cyclic guanosine monophosphate (cGMP) degradation and enhancing the nitric oxide/cGMP signaling pathway to relax human smooth muscle strips from the prostate, bladder, and LUT arteries. In animals characterized by ischemia/hypoxia of the genitourinary tract, treatment with PDE5-Is increases bladder and prostate tissue oxygenation. PDE5-Is have been shown to reduce nonvoiding contractions and bladder afferent nerve firing in decerebrate spinal cord-injured rats, and to reduce mechanosensitive afferent activities of both Aδ- and C-fibers in an irritated or overextended bladder model.
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Affiliation(s)
- François Giuliano
- Neuro-Uro-Andrology Department of Physical Medicine and Rehabilitation, Raymond Poincaré Academic Hospital, Garches, Versailles Saint Quentin en Yvelines University, Garches, France.
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Zhang X, Pietra C, Lovati E, de Groat WC. Activation of neurokinin-1 receptors increases the excitability of guinea pig dorsal root ganglion cells. J Pharmacol Exp Ther 2012; 343:44-52. [PMID: 22736506 DOI: 10.1124/jpet.112.196113] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The suppression of overactive bladder symptoms in patients and overactive bladder reflexes in animal models by neurokinin (NK)-1 receptor antagonists raises the possibility that these drugs target sensory neurons. This mechanism was evaluated by examining the interactions between a specific NK-1 agonist, [Sar(9),Met(O(2))(11)]-substance P (Sar-Met-SP), and a potent NK-1 antagonist, netupitant (NTP), on small size (20-30 μm) dissociated L6 and S1 dorsal root ganglion (DRG) neurons from female guinea pigs. Current-clamp recording revealed that Sar-Met-SP (1 μM) elicited membrane depolarization (average 8.05 ± 1.38 mV) in 27% (18 of 65) of DRG neurons. In 74% of the remaining neurons (35 of 47) Sar-Met-SP decreased the rheobase for action potential (AP) generation and increased the response to a suprathreshold stimulus (3 times rheobase) without changing the membrane potential. Sar-Met-SP also induced changes in the action potential (AP) wave form, including 1) an increase in overshoot (average 5 mV, n = 35 neurons), 2) a prolongation of AP duration (from 4.64 to 5.29 ms, n = 34), and 3) a reduction in the maximal rate of AP repolarization. NTP (200 nM) reversed the Sar-Met-SP-induced changes. Ca(2+) imaging showed that application of Sar-Met-SP (1 μM) decreased the tachyphylaxis induced by repeated application of capsaicin (0.5 μM), an effect blocked by pretreatment with NTP (200 nM). These results raise the possibility that activation of NK-1 receptors in primary sensory neurons plays a role in the generation of overactive bladder and that block of NK-1 receptors in these neurons may contribute to efficacy of NK-1 antagonists in the treatment of overactive bladder symptoms.
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Affiliation(s)
- Xiulin Zhang
- Department of Pharmacology and Chemical Biology, University of Pittsburgh Medical School, Pittsburgh, Pennsylvania, USA.
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Reactive oxygen species are second messengers of neurokinin signaling in peripheral sensory neurons. Proc Natl Acad Sci U S A 2012; 109:E1578-86. [PMID: 22586118 DOI: 10.1073/pnas.1201544109] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Substance P (SP) is a prominent neuromodulator, which is produced and released by peripheral damage-sensing (nociceptive) neurons; these neurons also express SP receptors. However, the mechanisms of peripheral SP signaling are poorly understood. We report a signaling pathway of SP in nociceptive neurons: Acting predominantly through NK1 receptors and G(i/o) proteins, SP stimulates increased release of reactive oxygen species from the mitochondrial electron transport chain. Reactive oxygen species, functioning as second messengers, induce oxidative modification and augment M-type potassium channels, thereby suppressing excitability. This signaling cascade requires activation of phospholipase C but is largely uncoupled from the inositol 1,4,5-trisphosphate sensitive Ca(2+) stores. In rats SP causes sensitization of TRPV1 and produces thermal hyperalgesia. However, the lack of coupling between SP signaling and inositol 1,4,5-trisphosphate sensitive Ca(2+) stores, together with the augmenting effect on M channels, renders the SP pathway ineffective to excite nociceptors acutely and produce spontaneous pain. Our study describes a mechanism for neurokinin signaling in sensory neurons and provides evidence that spontaneous pain and hyperalgesia can have distinct underlying mechanisms within a single nociceptive neuron.
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Kanai A, Zabbarova I, Oefelein M, Radziszewski P, Ikeda Y, Andersson KE. Mechanisms of action of botulinum neurotoxins, β3-adrenergic receptor agonists, and PDE5 inhibitors in modulating detrusor function in overactive bladders: ICI-RS 2011. Neurourol Urodyn 2012; 31:300-8. [DOI: 10.1002/nau.21246] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Accepted: 11/07/2011] [Indexed: 01/01/2023]
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25
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An antinociceptive role for substance P in acid-induced chronic muscle pain. Proc Natl Acad Sci U S A 2011; 109:E76-83. [PMID: 22084095 DOI: 10.1073/pnas.1108903108] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Release of substance P (SP) from nociceptive nerve fibers and activation of its receptor neurokinin 1 (NK1) are important effectors in the transmission of pain signals. Nonetheless, the role of SP in muscle pain remains unknown. Here we show that a single i.m. acid injection in mice lacking SP signaling by deletion of the tachykinin precursor 1 (Tac1) gene or coadministration of NK1 receptor antagonists produces long-lasting hyperalgesia rather than the transient hyperalgesia seen in control animals. The inhibitory effect of SP was found exclusively in neurons expressing acid-sensing ion channel 3, where SP enhances M-channel-like potassium currents through the NK1 receptor in a G protein-independent but tyrosine kinase-dependent manner. Furthermore, the SP signaling could alter action potential thresholds and modulate the expression of TTX-resistant sodium currents in medium-sized muscle nociceptors. Thus, i.m. SP mediates an unconventional NK1 receptor signal pathway to inhibit acid activation in muscle nociceptors, resulting in an unexpected antinociceptive effect against chronic mechanical hyperalgesia, here induced by repeated i.m. acid injection.
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Kanai A, Wyndaele JJ, Andersson KE, Fry C, Ikeda Y, Zabbarova I, De Wachter S. Researching bladder afferents-determining the effects of β(3) -adrenergic receptor agonists and botulinum toxin type-A. Neurourol Urodyn 2011; 30:684-91. [PMID: 21661014 DOI: 10.1002/nau.21102] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
A substantial portion of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated, enhanced and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source for drug targets. Established drug therapies such as muscarinic receptor antagonists, and two emerging therapies, β(3) -adrenergic receptor agonists and botulinum toxin type-A, may act partly through afferent mechanisms. This review focuses on these two new principles and new and established methods for determining their sites of action. It also provides brief information on the innervation of the bladder, afferent receptors and transmitters and how these may communicate with the urothelium, interstitial cells and detrusor smooth muscle to regulate micturition. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms and urgency sensations are also covered. This work is the result from 'Think Tank' presentations, and the lengthy discussions that followed, at the 2010 International Consultation on Incontinence Research Society meeting in Bristol, UK.
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Affiliation(s)
- Anthony Kanai
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
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Castillo C, Norcini M, Baquero-Buitrago J, Levacic D, Medina R, Montoya-Gacharna JV, Blanck TJJ, Dubois M, Recio-Pinto E. The N-methyl-D-aspartate-evoked cytoplasmic calcium increase in adult rat dorsal root ganglion neuronal somata was potentiated by substance P pretreatment in a protein kinase C-dependent manner. Neuroscience 2011; 177:308-20. [PMID: 21215796 DOI: 10.1016/j.neuroscience.2010.12.040] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Revised: 12/16/2010] [Accepted: 12/21/2010] [Indexed: 12/27/2022]
Abstract
The involvement of substance P (SP) in neuronal sensitization through the activation of the neurokinin-1-receptor (NK1r) in postsynaptic dorsal horn neurons has been well established. In contrast, the role of SP and NK1r in primary sensory dorsal root ganglion (DRG) neurons, in particular in the soma, is not well understood. In this study, we evaluated whether SP modulated the NMDA-evoked transient increase in cytoplasmic Ca2+ ([Ca2+]cyt) in the soma of dissociated adult DRG neurons. Cultures were treated with nerve growth factor (NGF), prostaglandin E2 (PGE2) or both NGF+PGE2. Treatment with NGF+PGE2 increased the percentage of N-methyl-D-aspartate (NMDA) responsive neurons. There was no correlation between the percentage of NMDA responsive neurons and the level of expression of the NR1 and NR2B subunits of the NMDA receptor or of the NK1r. Pretreatment with SP did not alter the percentage of NMDA responsive neurons; while it potentiated the NMDA-evoked [Ca2+]cyt transient by increasing its magnitude and by prolonging the period during which small- and some medium-sized neurons remained NMDA responsive. The SP-mediated potentiation was blocked by the SP-antagonist ([D-Pro4, D-Trp7,9]-SP (4-11)) and by the protein kinase C (PKC) blocker bisindolylmaleimide I (BIM); and correlated with the phosphorylation of PKCε. The Nk1r agonist [Sar9, Met(O2)11]-SP (SarMet-SP) also potentiated the NMDA-evoked [Ca2+]cyt transient. Exposure to SP or SarMet-SP produced a rapid increase in the labeling of phosphorylated-PKCε. In none of the conditions we detected phosphorylation of the NR2B subunit at Ser-1303. Phosphorylation of the NR2B subunit at Tyr1472 was enhanced to a similar extent in cells exposed to NMDA, SP or NMDA+SP, and that enhancement was blocked by BIM. Our findings suggest that NGF and PGE2 may contribute to the injury-evoked sensitization of DRG neurons in part by enhancing their NMDA-evoked [Ca2+]cyt transient in all sized DRG neurons; and that SP may further contribute to the DRG sensitization by enhancing and prolonging the NMDA-evoked increase in [Ca2+]cyt in small- and medium-sized DRG neurons.
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Affiliation(s)
- C Castillo
- Department of Anesthesiology, New York University (NYU) Langone Medical Center, NY 10016, USA
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Sculptoreanu A, Kullmann FA, Artim DE, Bazley FA, Schopfer F, Woodcock S, Freeman BA, de Groat WC. Nitro-oleic acid inhibits firing and activates TRPV1- and TRPA1-mediated inward currents in dorsal root ganglion neurons from adult male rats. J Pharmacol Exp Ther 2010; 333:883-95. [PMID: 20304940 DOI: 10.1124/jpet.109.163154] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nitro-oleic acid (OA-NO(2)), an electrophilic fatty acid by-product of nitric oxide and nitrite reactions, is present in normal and inflamed mammalian tissues at up to micromolar concentrations and exhibits anti-inflammatory signaling actions. The effects of OA-NO(2) on cultured dorsal root ganglion (DRG) neurons were examined using fura-2 Ca(2+) imaging and patch clamping. OA-NO(2) (3.5-35 microM) elicited Ca(2+) transients in 20 to 40% of DRG neurons, the majority (60-80%) of which also responded to allyl isothiocyanate (AITC; 1-50 microM), a TRPA1 agonist, and to capsaicin (CAPS; 0.5 microM), a TRPV1 agonist. The OA-NO(2)-evoked Ca(2+) transients were reduced by the TRPA1 antagonist 2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4-isopropylphenyl) acetamide (HC-030031; 5-50 microM) and the TRPV1 antagonist capsazepine (10 microM). Patch-clamp recording revealed that OA-NO(2) depolarized and induced inward currents in 62% of neurons. The effects of OA-NO(2) were elicited by concentrations >or=5 nM and were blocked by 10 mM dithiothreitol. Concentrations of OA-NO(2) >or=5 nM reduced action potential (AP) overshoot, increased AP duration, inhibited firing induced by depolarizing current pulses, and inhibited Na(+) currents. The effects of OA-NO(2) were not prevented or reversed by the NO-scavenger carboxy-2-phenyl-4,4,5,5-tetramethylimidazolineoxyl-1-oxyl-3-oxide. A large percentage (46-57%) of OA-NO(2)-responsive neurons also responded to CAPS (0.5 microM) or AITC (0.5 microM). OA-NO(2) currents were reduced by TRPV1 (diarylpiperazine; 5 microM) or TRPA1 (HC-030031; 5 microM) antagonists. These data reveal that endogenous OA-NO(2) generated at sites of inflammation may initially activate transient receptor potential channels on nociceptive afferent nerves, contributing to the initiation of afferent nerve activity, and later suppresses afferent firing.
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Affiliation(s)
- A Sculptoreanu
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh Medical School, Pittsburgh, Pennsylvania 15261, USA.
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Ditting T, Tiegs G, Rodionova K, Reeh PW, Neuhuber W, Freisinger W, Veelken R. Do distinct populations of dorsal root ganglion neurons account for the sensory peptidergic innervation of the kidney? Am J Physiol Renal Physiol 2009; 297:F1427-34. [DOI: 10.1152/ajprenal.90599.2008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Peptidergic afferent renal nerves (PARN) have been linked to kidney damage in hypertension and nephritis. Neither the receptors nor the signals controlling local release of neurokinines [calcitonin gene-related peptide (CGRP) and substance P (SP)] and signal transmission to the brain are well-understood. We tested the hypothesis that PARN, compared with nonrenal afferents (Non-RN), are more sensitive to acidic stimulation via transient receptor potential vanilloid type 1 (TRPV1) channels and exhibit a distinctive firing pattern. PARN were distinguished from Non-RN by fluorescent labeling (DiI) and studied by in vitro patch-clamp techniques in dorsal root ganglion neurons (DRG; T11-L2). Acid-induced currents or firing due to current injection or acidic superfusion were studied in 252 neurons, harvested from 12 Sprague-Dawley rats. PARN showed higher acid-induced currents than Non-RN (transient: 15.9 ± 5.1 vs. 0.4 ± 0.2* pA/pF at pH 6; sustained: 20.0 ± 4.5 vs. 6.2 ± 1.2* pA/pF at pH 5; * P < 0.05). The TRPV1 antagonist capsazepine inhibited sustained, amiloride-transient currents. Forty-eight percent of PARN were classified as tonic neurons (TN = sustained firing during current injection), and 52% were phasic (PN = transient firing). Non-RN were rarely tonic (15%), but more frequently phasic (85%), than PARN ( P < 0.001). TN were more frequently acid-sensitive than PN (50–70 vs. 2–20%, P < 0.01). Furthermore, renal PN were more frequently acid-sensitive than nonrenal PN (20 vs. 2%, P < 0.01). Confocal microscopy revealed innervation of renal vessels, tubules, and glomeruli by CGRP- and partly SP-positive fibers coexpressing TRPV1. Our data show that PARN are represented by a very distinct population of small-to-medium sized DRG neurons exhibiting more frequently tonic firing and TRPV1-mediated acid sensitivity. These very distinct DRG neurons might play a pivotal role in renal physiology and disease.
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Affiliation(s)
- Tilmann Ditting
- Department of Internal Medicine 4, Nephrology, and Hypertension,
| | - Gisa Tiegs
- Division of Experimental Immunology and Hepatology, Center of Internal Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | | | | | | | | | - Roland Veelken
- Department of Internal Medicine 4, Nephrology, and Hypertension,
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Sculptoreanu A, Artim DE, de Groat WC. Neurokinins inhibit low threshold inactivating K+ currents in capsaicin responsive DRG neurons. Exp Neurol 2009; 219:562-73. [PMID: 19631644 DOI: 10.1016/j.expneurol.2009.07.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2009] [Revised: 07/15/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
Neurokinins (NK) released from terminals of dorsal root ganglion (DRG) neurons may control firing of these neurons by an autofeedback mechanism. In this study we used patch clamp recording techniques to determine if NKs alter excitability of rat L4-S3 DRG neurons by modulating K(+) currents. In capsaicin (CAPS)-responsive phasic neurons substance P (SP) lowered action potential (AP) threshold and increased the number of APs elicited by depolarizing current pulses. SP and a selective NK(2) agonist, [betaAla(8)]-neurokinin A (4-10) also inhibited low threshold inactivating K(+) currents isolated by blocking non-inactivating currents with a combination of high TEA, (-) verapamil and nifedipine. Currents recorded under these conditions were heteropodatoxin-sensitive (Kv4 blocker) and alpha-dendrotoxin-insensitive (Kv1.1 and Kv1.2 blocker). SP and NKA elicited a >10 mV positive shift of the voltage dependence of activation of the low threshold currents. This effect was absent in CAPS-unresponsive neurons. The effect of SP or NKA on K(+) currents in CAPS-responsive phasic neurons was fully reversed by an NK(2) receptor antagonist (MEN10376) but only partially reversed by a PKC inhibitor (bisindolylmaleimide). An NK(1) selective agonist ([Sar(9), Met(11)]-substance P) or direct activation of PKC with phorbol 12,13-dibutyrate, did not change firing in CAPS-responsive neurons, but did inhibit various types of K(+) currents that activated over a wide range of voltages. These data suggest that the excitability of CAPS-responsive phasic afferent neurons is increased by activation of NK(2) receptors and that this is due in part to inhibition and a positive voltage shift in the activation of heteropodatoxin-sensitive Kv4 channels.
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Affiliation(s)
- Adrian Sculptoreanu
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA.
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Zagorodnyuk VP, Brookes SJH, Spencer NJ, Gregory S. Mechanotransduction and chemosensitivity of two major classes of bladder afferents with endings in the vicinity to the urothelium. J Physiol 2009; 587:3523-38. [PMID: 19470774 DOI: 10.1113/jphysiol.2009.172577] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The guinea pig bladder is innervated by at least five distinct major classes of extrinsic sensory neurons. In this study, we have examined the mechanisms of mechanotransduction and chemosensitivity of two classes of bladder afferents that have their endings in the vicinity of the urothelium: stretch-sensitive muscle-mucosal mechanoreceptors and stretch-insensitive, mucosal high-responding afferents. The non-selective P2 purinoreceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid did not affect stretch- or stroking-induced firing of these afferents but significantly reduced the excitatory action of alpha,beta-methylene ATP. Blocking synaptic transmission in Ca(2+)-free solution did not affect stretch-evoked firing but slightly reduced stretch-induced tension responses. Stroking-induced firing of both classes of afferents was also not affected in Ca(2+)-free solution. Of blockers of mechano-gated channels, benzamil (100 microM), but not amiloride (100 microM), Gd(3+) (100 microM) or SKF 96365 (50 microM), inhibited stretch- and stroking-induced firing. Serotonin (100 microM) applied directly onto receptive fields predominantly activated muscle-mucosal afferents. Muscarine (100 microM) and substance P (100 microM) in 24% and 36% cases activated only mucosal high-responding units. Bradykinin (10 microM), but not prostaglandin E2 (10 microM), excites predominantly mucosal units. High (80 mM) K(+) solution activated both afferent classes, but responses of mucosal units were 4 times greater. In contrast to muscle-mucosal units, most mucosal high-responding units were activated by hot Krebs solution (45-46 degrees C), low pH (pH 4) and capsaicin (3 microm). TRPV1 antagonist, capsazepine (10 microM) was without effect on mechanotransduction by mucosal high-responding afferents. The results show that mechanotransduction of these two types of afferents are not dependant upon Ca(2+)-dependent exocytotic release of mediators, or ATP, and it is likely that benzamil-sensitive stretch-activated ion channels on their endings are involved in direct mechanotransduction. The chemosensitivity to agonists and noxious stimuli differs significantly between these two major classes of bladder afferents that reflects their different physiological and pathophysiological roles in the bladder.
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Affiliation(s)
- Vladimir P Zagorodnyuk
- Department of Human Physiology, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia.
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Bassi GS, Broiz AC, Gomes MZ, Brandão ML. Evidence for mediation of nociception by injection of the NK-3 receptor agonist, senktide, into the dorsal periaqueductal gray of rats. Psychopharmacology (Berl) 2009; 204:13-24. [PMID: 19093101 DOI: 10.1007/s00213-008-1434-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2008] [Accepted: 12/01/2008] [Indexed: 10/21/2022]
Abstract
RATIONALE Ultrasound vocalizations (USVs) at approximately 22 kHz are usual components of the defensive response of rats. However, depending on the neural substrate that is activated, such as the dorsal periaqueductal gray (dPAG), USV emissions may be reduced. Activation of neurokinin-1 (NK-1)-mediated mechanisms of the dPAG causes analgesia, reduced 22 kHz USVs, and anxiogenic-like effects in rats exposed to the elevated plus maze (EPM). Involvement of other types of neurokinin receptors in this activation has not yet been evaluated. OBJECTIVES The present study examined whether local injections of the selective NK-3 agonist senktide (1-100 pmol/0.2 microL) into the dPAG can (1) cause anxiogenic effects in the EPM, (2) influence novelty-induced 22 kHz USVs, or (3) change nociceptive reactivity in the tail-flick test. RESULTS Senktide elicited a significant increase in exploratory behavior, an effect accompanied by hyperalgesia and an increase in the number of 22 kHz USVs. The nociceptive effects, increased locomotor activity, and USV emissions elicited by local injections of senktide (50 pmol/0.2 microL) were reduced by prior injections of the selective NK-3 receptor antagonist SB222200 (50 pmol/0.2 microL) into the dPAG. CONCLUSIONS These findings show that NK-3 receptors in the dPAG mediate nociceptive responses in this area, contrasting with the known fear-related processes mediated by NK-1 receptors in the dPAG. Both hyperalgesia and fear-related processes are accompanied by emissions of 22 kHz USVs.
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Affiliation(s)
- Gabriel S Bassi
- Instituto de Neurociências & Comportamento-INeC, Ribeirão Preto, SP, Brasil
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Li J, Micevych P, McDonald J, Rapkin A, Chaban V. Inflammation in the uterus induces phosphorylated extracellular signal-regulated kinase and substance P immunoreactivity in dorsal root ganglia neurons innervating both uterus and colon in rats. J Neurosci Res 2009; 86:2746-52. [PMID: 18478547 DOI: 10.1002/jnr.21714] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In women, clinical studies suggest that pain syndromes such as irritable bowel syndrome and interstitial cystitis, which are associated with visceral hyperalgesia, are often comorbid with endometriosis and chronic pelvic pain. One of the possible explanations for this phenomenon is viscerovisceral cross-sensitization, in which increased nociceptive input from an inflamed pelvic organ sensitizes neurons that receive convergent input to the same dorsal root ganglion (DRG) from an unaffected visceral organ. Nociception induces up-regulation of cellular mechanisms such as phosphorylated extracellular signal-regulated kinase (pERK) and substance P (SP), neurotransmitters associated with induced pain sensation. The purpose of this study was to determine, in a rodent model, whether uterine inflammation increased the number of pERK- and SP-positive neurons that received input from both the uterus and the colon. Cell bodies of colonic and uterine DRG were retrogradely labeled with fluorescent tracer dyes microinjected into the colon/rectum and into the uterus. Ganglia were harvested for fluorescent microscopy to identify positively stained neurons. Approximately 6% of neurons were colon specific and 10% uterus specific. Among these uterus- or colon-specific neurons, up to 3-5% of DRG neurons in the lumbosacral neurons (L1-S3 levels) received input from both visceral organs. Uterine inflammation increased the number of pERK- and SP-immunoreactive DRG neurons innervating specifically colon, or innervating specifically uterus, and those innervating both organs. These results suggest that a localized inflammation activates primary visceral afferents, regardless of whether they innervate the affected organ. This visceral sensory integration in the DRG may underlie the observed comorbidity of female pelvic pain syndromes.
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Affiliation(s)
- Jichang Li
- Department of Anesthesiology, Harbor-UCLA Medical Center, Los Angeles, California, USA
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Srinivasan R, Wolfe D, Goss J, Watkins S, de Groat WC, Sculptoreanu A, Glorioso JC. Protein kinase C epsilon contributes to basal and sensitizing responses of TRPV1 to capsaicin in rat dorsal root ganglion neurons. Eur J Neurosci 2009; 28:1241-54. [PMID: 18973552 DOI: 10.1111/j.1460-9568.2008.06438.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Phosphorylation of the vanilloid receptor (TRPV1) by protein kinase C epsilon (PKCepsilon) plays an important role in the development of chronic pain. Here, we employ a highly defective herpes simplex virus vector (vHDNP) that expresses dominant negative PKCepsilon (DNPKCepsilon) as a strategy to demonstrate that PKCepsilon is essential for: (i) maintenance of basal phosphorylation and normal TRPV1 responses to capsaicin (CAPS), a TRPV1 agonist and (ii) enhancement of TRPV1 responses by phorbol esters. Phorbol esters induced translocation of endogenous PKCepsilon to the plasma membrane and thereby enhanced CAPS currents. These results were extended to an in-vivo pain model in which vHDNP delivery to dorsal root ganglion neurons caused analgesia in CAPS-treated, acutely inflamed rat hind paws. These findings support the conclusion that in addition to receptor sensitization, PKCepsilon is essential for normal TRPV1 responses in vitro and in vivo.
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Affiliation(s)
- Rahul Srinivasan
- Department of Microbiology and Molecular Genetics and Biochemistry, University of Pittsburgh, Pittsburgh, PA 15261, USA
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Abstract
The afferent innervation of the urinary bladder consists primarily of small myelinated (Adelta) and unmyelinated (C-fiber) axons that respond to chemical and mechanical stimuli. Immunochemical studies indicate that bladder afferent neurons synthesize several putative neurotransmitters, including neuropeptides, glutamic acid, aspartic acid, and nitric oxide. The afferent neurons also express various types of receptors and ion channels, including transient receptor potential channels, purinergic, muscarinic, endothelin, neurotrophic factor, and estrogen receptors. Patch-clamp recordings in dissociated bladder afferent neurons and recordings of bladder afferent nerve activity have revealed that activation of many of these receptors enhances neuronal excitability. Afferent nerves can respond to chemicals present in urine as well as chemicals released in the bladder wall from nerves, smooth muscle, inflammatory cells, and epithelial cells lining the bladder lumen. Pathological conditions alter the chemical and electrical properties of bladder afferent pathways, leading to urinary urgency, increased voiding frequency, nocturia, urinary incontinence, and pain. Neurotrophic factors have been implicated in the pathophysiological mechanisms underlying the sensitization of bladder afferent nerves. Neurotoxins such as capsaicin, resiniferatoxin, and botulinum neurotoxin that target sensory nerves are useful in treating disorders of the lower urinary tract.
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Affiliation(s)
- William C de Groat
- Department of Pharmacology, University of Pittsburgh School of Medicine, West 1352 Starzl Biomedical Science Tower, Pittsburgh, PA 15261, USA.
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Abstract
Cough is the most common symptom for which individuals seek medical attention and spend health-care dollars. Despite the burden induced by cough, the current treatments for cough are only partially effective. Delineating the sites and mechanisms in the cough central network for changes in the cough reflex could lead to new therapeutic strategies and drug target sites for more effective treatments. The first synaptic target in the CNS for the cough-related sensory input is the second-order neurons in the nucleus tractus solitarius (NTS); these neurons reorganize the primary sensory information into a coherent output. The NTS neurons have been shown to undergo neuroplasticity under a variety of conditions, such as respiratory disorders, stress, and exposures to environmental pollutants. The NTS contains a rich innervation of substance P immunoreactive nerve terminals, suggesting that substance P might be important in altered cough reflex response. This chapter summarizes our current findings on the role of substance P in enhanced cough reflex as well as the potential NTS targets for the action of substance P.
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Affiliation(s)
- C-Y Chen
- Department of Pharmacology, University of California, Davis School of Medicine, 4150 V Street, 1104 PSSB, Sacramento, CA 95817, USA
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Donnerer J, Liebmann I, Schuligoi R. Capsaicin- and Mustard Oil-Induced Extracellular Signal-Regulated Protein Kinase Phosphorylation in Sensory Neuronsin vivo: Effects of Neurokinins 1 and 2 Receptor Antagonists and of a Nitric Oxide Synthase Inhibitor. Basic Clin Pharmacol Toxicol 2009; 104:11-6. [DOI: 10.1111/j.1742-7843.2008.00338.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Abstract
Peptides released in the spinal cord from the central terminals of nociceptors contribute to the persistent hyperalgesia that defines the clinical experience of chronic pain. Using substance P (SP) and calcitonin gene-related peptide (CGRP) as examples, this review addresses the multiple mechanisms through which peptidergic neurotransmission contributes to the development and maintenance of chronic pain. Activation of CGRP receptors on terminals of primary afferent neurons facilitates transmitter release and receptors on spinal neurons increases glutamate activation of AMPA receptors. Both effects are mediated by cAMP-dependent mechanisms. Substance P activates neurokinin receptors (3 subtypes) which couple to phospholipase C and the generation of the intracellular messengers whose downstream effects include depolarizing the membrane and facilitating the function of AMPA and NMDA receptors. Activation of neurokinin-1 receptors also increases the synthesis of prostaglandins whereas activation of neurokinin-3 receptors increases the synthesis of nitric oxide. Both products act as retrograde messengers across synapses and facilitate nociceptive signaling in the spinal cord. Whereas these cellular effects of CGRP and SP at the level of the spinal cord contribute to the development of increased synaptic strength between nociceptors and spinal neurons in the pathway for pain, the different intracellular signaling pathways also activate different transcription factors. The activated transcription factors initiate changes in the expression of genes that contribute to long-term changes in the excitability of spinal and maintain hyperalgesia.
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Affiliation(s)
- V S Seybold
- Department of Neuroscience, University of Minnesota, 6-145 Jackson Hall, 321 Church St., S.E., Minneapolis, MN 55455, USA.
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Biophysical basis for three distinct dynamical mechanisms of action potential initiation. PLoS Comput Biol 2008; 4:e1000198. [PMID: 18846205 PMCID: PMC2551735 DOI: 10.1371/journal.pcbi.1000198] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Accepted: 09/03/2008] [Indexed: 11/19/2022] Open
Abstract
Transduction of graded synaptic input into trains of all-or-none action
potentials (spikes) is a crucial step in neural coding. Hodgkin identified three
classes of neurons with qualitatively different analog-to-digital transduction
properties. Despite widespread use of this classification scheme, a
generalizable explanation of its biophysical basis has not been described. We
recorded from spinal sensory neurons representing each class and reproduced
their transduction properties in a minimal model. With phase plane and
bifurcation analysis, each class of excitability was shown to derive from
distinct spike initiating dynamics. Excitability could be converted between all
three classes by varying single parameters; moreover, several parameters, when
varied one at a time, had functionally equivalent effects on excitability. From
this, we conclude that the spike-initiating dynamics associated with each of
Hodgkin's classes represent different outcomes in a nonlinear
competition between oppositely directed, kinetically mismatched currents. Class
1 excitability occurs through a saddle node on invariant circle bifurcation when
net current at perithreshold potentials is inward (depolarizing) at steady
state. Class 2 excitability occurs through a Hopf bifurcation when, despite net
current being outward (hyperpolarizing) at steady state, spike initiation occurs
because inward current activates faster than outward current. Class 3
excitability occurs through a quasi-separatrix crossing when fast-activating
inward current overpowers slow-activating outward current during a stimulus
transient, although slow-activating outward current dominates during constant
stimulation. Experiments confirmed that different classes of spinal lamina I
neurons express the subthreshold currents predicted by our simulations and,
further, that those currents are necessary for the excitability in each cell
class. Thus, our results demonstrate that all three classes of excitability
arise from a continuum in the direction and magnitude of subthreshold currents.
Through detailed analysis of the spike-initiating process, we have explained a
fundamental link between biophysical properties and qualitative differences in
how neurons encode sensory input. Information is transmitted through the nervous system in the form of action
potentials or spikes. Contrary to popular belief, a spike is not generated
instantaneously when membrane potential crosses some preordained threshold. In
fact, different neurons employ different rules to determine when and why they
spike. These different rules translate into diverse spiking patterns that have
been observed experimentally and replicated time and again in computational
models. In this study, our aim was not simply to replicate different spiking
patterns; instead, we sought to provide deeper insight into the connection
between biophysics and neural coding by relating each to the process of spike
initiation. We show that Hodgkin's three classes of excitability result
from a nonlinear competition between oppositely directed, kinetically mismatched
currents; the outcome of that competition is manifested as dynamically distinct
spike-initiating mechanisms. Our results highlight the benefits of forward
engineering minimal models capable of reproducing phenomena of interest and then
dissecting those models in order to identify general explanations of how those
phenomena arise. Furthermore, understanding nonlinear dynamical processes such
as spike initiation is crucial for definitively explaining how biophysical
properties impact neural coding.
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40
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Sculptoreanu A, Aura Kullmann F, de Groat WC. Neurokinin 2 receptor-mediated activation of protein kinase C modulates capsaicin responses in DRG neurons from adult rats. Eur J Neurosci 2008; 27:3171-81. [PMID: 18598261 DOI: 10.1111/j.1460-9568.2008.06267.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Patch-clamp techniques and Ca2+ imaging were used to examine the interaction between neurokinins (NK) and the capsaicin(CAPS)-evoked transient receptor potential vanilloid receptor 1 (TRPV1) responses in rat dorsal root ganglia neurons. Substance P (SP; 0.2-0.5 microM) prevented the reduction of Ca2+ transients (tachyphylaxis) evoked by repeated brief applications of CAPS (0.5 microM). Currents elicited by CAPS were increased in amplitude and desensitized more slowly after administration of SP or a selective NK2 agonist, [Ala8]-neurokinin A (4-10) (NKA). Neither an NK1-selective agonist, [Sar9, Met11]-SP, nor an NK3-selective agonist, [MePhe7]-NKB, altered the CAPS currents. The effects of SP on CAPS currents were inhibited by a selective NK2 antagonist, MEN10,376, but were unaffected by the NK3 antagonist, SB 235,375. Phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C(PKC), also increased the amplitude and slowed the desensitization of CAPS responses. Phosphatase inhibitors, decamethrin and alpha-naphthyl acid phosphate (NAcPh), also enhanced the currents and slowed desensitization of CAPS currents. Facilitatory effects of SP, NKA and PDBu were reversed by bisindolylmaleimide, a PKC inhibitor, and gradually decreased in magnitude when the agents were administered at increasing intervals after CAPS application. The decrease was partially prevented by prior application of NAcPh. These data suggest that activation of NK2 receptors in afferent neurons leads to PKC-induced phosphorylation of TRPV1, resulting in sensitization of CAPS-evoked currents and slower desensitization. Thus, activation of NK2 autoreceptors by NKs released from the peripheral afferent terminals or by mast cells during inflammatory responses may be a mechanism that sensitizes TRPV1 channels and enhances afferent excitability.
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Affiliation(s)
- Adrian Sculptoreanu
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA.
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41
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Fiber-coupled light-emitting diode for localized photostimulation of neurons expressing channelrhodopsin-2. J Neurosci Methods 2008; 169:27-33. [DOI: 10.1016/j.jneumeth.2007.11.012] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Revised: 10/25/2007] [Accepted: 11/20/2007] [Indexed: 11/17/2022]
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42
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Bassi GS, Nobre MJ, de Araújo JE, Brandão ML. Anxiogenic effects of activation of NK-1 receptors of the dorsal periaqueductal gray as assessed by the elevated plus-maze, ultrasound vocalizations and tail-flick tests. Neuropeptides 2007; 41:365-74. [PMID: 17981325 DOI: 10.1016/j.npep.2007.09.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2007] [Revised: 08/23/2007] [Accepted: 09/15/2007] [Indexed: 11/28/2022]
Abstract
Ultrasound vocalizations (USVs) known as 22kHz are usual components of the defensive responses of rats exposed to threatening conditions. The amount of emission of 22kHz USVs depends on the intensity of the aversive stimuli. While moderate fear causes an anxiolytic-sensitive enhancement of the defensive responses, high fear tended to reduce the defensive performance of the animals to aversive stimuli. The dorsal periaqueductal gray (dPAG) is an important vocal center and a crucial structure for the expression of defensive responses. Substance P (SP) is involved in the modulation of the defensive response at this midbrain level, but the type of neurokinin receptors involved in this action is not completely understood. In this study we examined whether local injections of the selective NK-1 agonist SAR-MET-SP (10-100 pmol/0.2microL) into the dPAG (i) cause anxiogenic effects in the elevated plus-maze (EPM) (Exp. I), (ii) influence the novelty-induced 22kHz USVs recorded within the frequency range of 20-26kHz (Exp. II) and (iii) change the nociceptive reactivity to heat applied to the rat's tail (Exp III). The data obtained showed that SAR-MET-SP elicited significant "anxiety-like" behaviors, as revealed by the decrease in the number of entries into and time spent onto the open arms of the EPM. These anxiogenic effects were accompanied with antinociception and disruption of the novelty-induced increase in the number and duration of 22kHz USVs. These findings are in agreement with the notion that NK-1 receptors of the dPAG may be an important neurochemical target for new selective drugs aimed at the control of pathological anxiety states.
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Affiliation(s)
- Gabriel S Bassi
- Instituto de Neurociências & Comportamento-INeC, Campus USP, 14040-901, Ribeirão Preto, SP, Brazil
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Yamane H, de Groat WC, Sculptoreanu A. Effects of ralfinamide, a Na+ channel blocker, on firing properties of nociceptive dorsal root ganglion neurons of adult rats. Exp Neurol 2007; 208:63-72. [PMID: 17707373 PMCID: PMC2117901 DOI: 10.1016/j.expneurol.2007.07.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 07/08/2007] [Accepted: 07/10/2007] [Indexed: 12/11/2022]
Abstract
Recent studies revealed that ralfinamide, a Na(+) channel blocker, suppressed tetrodotoxin-resistant Na(+) currents in dorsal root ganglion (DRG) neurons and reduced pain reactions in animal models of inflammatory and neuropathic pain. Here, we investigated the effects of ralfinamide on Na(+) currents; firing properties and action potential (AP) parameters in capsaicin-responsive and -unresponsive DRG neurons from adult rats in the presence of TTX (0.5 microM). Ralfinamide inhibited TTX-resistant Na(+) currents in a frequency- and voltage-dependent manner. Small to medium sized neurons exhibited different firing properties during prolonged depolarizing current pulses (600 ms). One group of neurons fired multiple spikes (tonic), while another group fired four or less APs (phasic). In capsaicin-responsive tonic firing neurons, ralfinamide (25 microM) reduced the number of APs from 10.6+/-1.8 to 2.6+/-0.7 APs/600 ms, whereas in capsaicin-unresponsive tonic neurons, the drug did not significantly change firing (8.4+/-0.9 in control to 6.6+/-2.0 APs/600 ms). In capsaicin-responsive phasic neurons, substance P and 4-aminopyridine induced multiple spikes, an effect that was reversed by ralfinamide (25 microM). In addition to effects on firing, ralfinamide increased the threshold, decreased the overshoot, and increased the rate of rise of the AP. To conclude, ralfinamide suppressed afferent hyperexcitability selectively in capsaicin-responsive, presumably nociceptive neurons, but had no measurable effects on firing in CAPS-unresponsive neurons. The action of ralfinamide to selectively inhibit tonic firing in nociceptive neurons very likely contributes to the effectiveness of the drug in reducing inflammatory and neuropathic pain as well as bladder overactivity.
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Affiliation(s)
- Hana Yamane
- Department of Pharmacology, University of Pittsburgh School of Medicine, E1304 Biomedical Science Tower, Pittsburgh, PA 15261, USA
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