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Combinations of classical and non-classical voltage dependent potassium channel openers suppress nociceptor discharge and reverse chronic pain signs in a rat model of Gulf War illness. Neurotoxicology 2022; 93:186-199. [PMID: 36216193 DOI: 10.1016/j.neuro.2022.10.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 09/27/2022] [Accepted: 10/05/2022] [Indexed: 11/15/2022]
Abstract
In a companion paper we examined whether combinations of Kv7 channel openers (Retigabine and Diclofenac; RET, DIC) could be effective modifiers of deep tissue nociceptor activity; and whether such combinations could then be optimized for use as safe analgesics for pain-like signs that developed in a rat model of GWI (Gulf War Illness) pain. In the present report, we examined the combinations of Retigabine/Meclofenamate (RET/MEC) and Meclofenamate/Diclofenac (MEC/DIC). Voltage clamp experiments were performed on deep tissue nociceptors isolated from rat DRG (dorsal root ganglion). In voltage clamp studies, a stepped voltage protocol was applied (-55 to -40 mV; Vh=-60 mV; 1500 msec) and Kv7 evoked currents were subsequently isolated by Linopirdine subtraction. MEC greatly enhanced voltage dependent conductance and produced exceptional maximum sustained currents of 6.01 ± 0.26 pA/pF (EC50: 62.2 ± 8.99 μM). Combinations of RET/MEC, and MEC/DIC substantially amplified resting currents at low concentrations. MEC/DIC also greatly improved voltage dependent conductance. In current clamp experiments, a cholinergic challenge test (Oxotremorine-M, 10 μM; OXO), associated with our GWI rat model, produced powerful action potential (AP) bursts (85 APs). Optimized combinations of RET/MEC (5 and 0.5 μM) and MEC/DIC (0.5 and 2.5 μM) significantly reduced AP discharges to 3 and 7 Aps, respectively. Treatment of pain-like ambulatory behavior in our rat model with a RET/MEC combination (5 and 0.5 mg/kg) successfully rescued ambulation deficits, but could not be fully separated from the effect of RET alone. Further development of this approach is recommended.
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Development of KVO treatment strategies for chronic pain in a rat model of Gulf War Illness. Toxicol Appl Pharmacol 2022; 434:115821. [PMID: 34896435 DOI: 10.1016/j.taap.2021.115821] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/01/2021] [Accepted: 12/04/2021] [Indexed: 12/19/2022]
Abstract
We examined whether combinations of Kv7 channel openers could be effective modifiers of deep tissue nociceptor activity; and whether such combinations could then be optimized for use as safe analgesics for pain-like signs that developed in a rat model of GWI (Gulf War Illness) pain. Voltage clamp experiments were performed on subclassified nociceptors isolated from rat DRG (dorsal root ganglion). A stepped voltage protocol was applied (-55 to -40 mV; Vh = -60 mV; 1500 ms) and Kv7 evoked currents were subsequently isolated by linopirdine subtraction. Directly activated and voltage activated K+ currents were characterized in the presence and absence of Retigabine (5-100 μM) and/or Diclofenac (50-140 μM). Retigabine produced substantial voltage dependent effects and a maximal sustained current of 1.14 pA/pF ± 0.15 (ED50: 62.7 ± 3.18 μM). Diclofenac produced weak voltage dependent effects but a similar maximum sustained current of 1.01 ± 0.26 pA/pF (ED50: 93.2 ± 8.99 μM). Combinations of Retigabine and Diclofenac substantially amplified resting currents but had little effect on voltage dependence. Using a cholinergic challenge test (Oxotremorine, 10 μM) associated with our GWI rat model, combinations of Retigabine (5 uM) and Diclofenac (2.5, 20 and 50 μM) substantially reduced or totally abrogated action potential discharge to the cholinergic challenge. When combinations of Retigabine and Diclofenac were used to relieve pain-signs in our rat model of GWI, only those combinations associated with serious subacute side effects could relieve pain-like behaviors.
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Nguyen H, Sahbaie P, Goba L, Sul J, Suzaki A, Clark JD, Huang TT. Exposure to Gulf War Illness-related agents leads to the development of chronic pain and fatigue. Life Sci 2021; 283:119867. [PMID: 34358550 DOI: 10.1016/j.lfs.2021.119867] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 07/13/2021] [Accepted: 07/23/2021] [Indexed: 11/25/2022]
Abstract
AIMS A substantial contingent of veterans from the first Gulf War continues to suffer from a number of Gulf War-related illnesses (GWI) affecting the neurological and musculoskeletal systems; the most common symptoms include chronic pain and fatigue. Although animal models have recapitulated several aspects of cognitive impairments in GWI, the pain and fatigue symptoms have not been well documented to allow examination of potential pathogenic mechanisms. MAIN METHODS We used a mouse model of GWI by exposing mice repeatedly to a combination of Gulf War chemicals (pyridostigmine bromide, permethrin, DEET, and chlorpyrifos) and mild immobilization stress, followed by investigating their pain susceptibilities and fatigue symptoms. To assess whether enhanced antioxidant capacity can counter the effects of GW agents, transgenic mice overexpressing extracellular superoxide dismutase (SOD3OE) were also examined. KEY FINDINGS The mouse model recapitulated several aspects of the human illness, including hyperalgesia, impaired descending inhibition of pain, and increased tonic pain. There is a close association between chronic pain and fatigue in GWI patients. Consistent with this observation, the mouse model showed a significant reduction in physical endurance on the treadmill. Examination of skeletal muscles suggested reduction in mitochondrial functions may have contributed to the fatigue symptoms. Furthermore, the negative impacts of GW agents in pain susceptibilities were largely diminished in SOD3OE mice, suggesting that increased oxidative stress was associated with the emergence of these Gulf War symptoms. SIGNIFICANCE the mouse model will be suitable for delineating specific defects in the pain pathways and mechanisms of fatigue in GWI.
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Affiliation(s)
- Huy Nguyen
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, United States of America; Palo Alto Veterans Institute for Research, VA Palo Alto Health Care System, United States of America; Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, United States of America
| | - Peyman Sahbaie
- Department of Anesthesiology, Stanford University School of Medicine, United States of America; Palo Alto Veterans Institute for Research, VA Palo Alto Health Care System, United States of America; Anesthesiology Service, VA Palo Alto Health Care System, United States of America
| | - Lihle Goba
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, United States of America
| | - Julian Sul
- Palo Alto Veterans Institute for Research, VA Palo Alto Health Care System, United States of America
| | - Aoi Suzaki
- Palo Alto Veterans Institute for Research, VA Palo Alto Health Care System, United States of America
| | - J David Clark
- Department of Anesthesiology, Stanford University School of Medicine, United States of America; Anesthesiology Service, VA Palo Alto Health Care System, United States of America
| | - Ting-Ting Huang
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, United States of America; Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, United States of America.
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Penatzer JA, Miller JV, Prince N, Shaw M, Lynch C, Newman M, Hobbs GR, Boyd JW. Differential phosphoprotein signaling in the cortex in mouse models of Gulf War Illness using corticosterone and acetylcholinesterase inhibitors. Heliyon 2021; 7:e07552. [PMID: 34307952 PMCID: PMC8287240 DOI: 10.1016/j.heliyon.2021.e07552] [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: 04/01/2021] [Revised: 06/16/2021] [Accepted: 07/08/2021] [Indexed: 11/29/2022] Open
Abstract
Aims Veterans from the 1990–91 Gulf War were exposed to acetylcholinesterase inhibitors (AChEIs), and, following service, an estimated one-third began suffering from a medically unexplained, multi-symptom illness termed Gulf War Illness (GWI). Previous research has developed validated rodent models that include exposure to exogenous corticosterone (CORT) and AChEIs to simulate high stress and chemical exposures encountered in theater. This combination of exposures in mice resulted in a marked increase in neuroinflammation, which is a common symptom of veterans suffering from GWI. To further elucidate the mechanisms associated with these mouse models of GWI, an investigation into intracellular responses in the cortex were performed to characterize the early cellular signaling changes associated with this exposure-initiated neuroinflammation. Main methods Adult male C57BL/6J mice were exposed to CORT in the drinking water (200 μg/mL) for 7 days followed by a single intraperitoneal injection of diisopropyl fluorophosphate (DFP; 4.0 mg/kg) or chlorpyrifos oxon (CPO; 8.0 mg/kg), on day 8 and euthanized 0.5, 2, and 24 h post-injection. Eleven post-translationally modified protein targets were measured using a multiplexed ELISA. Key findings Phosphoprotein responses were found to be exposure specific following AChEI insult, with and without CORT. Specifically, CORT + CPO exposure was found to sequentially activate several phosphoproteins involved in mitogen activated protein kinase signaling (p-MEK1/2, p-ERK1/2, and p-JNK). DFP alone similarly increased proteins in this pathway (p-RPS6, and p-JNK), but the addition of CORT ameliorated these affects. Significance The results of this study provide insight into differentially activated pathways depending on AChEI in these GWI models.
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Affiliation(s)
- Julia A Penatzer
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morvantown, WV, USA
| | | | - Nicole Prince
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morvantown, WV, USA
| | - Misa Shaw
- Department of Orthopaedics, West Virginia University School of Medicine, Morgantown, WV, USA.,Clinical and Translational Science Institute, West Virginia University School of Medicine, Morgantown, WV, USA
| | - Cayla Lynch
- Department of Orthopaedics, West Virginia University School of Medicine, Morgantown, WV, USA
| | - Mackenzie Newman
- Department of Orthopaedics, West Virginia University School of Medicine, Morgantown, WV, USA
| | - Gerald R Hobbs
- Department of Statistics, West Virginia University, Morgantown, WV, USA
| | - Jonathan W Boyd
- Department of Orthopaedics, West Virginia University School of Medicine, Morgantown, WV, USA
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Vanneste S, Mohan A, Yoo HB, Huang Y, Luckey AM, McLeod SL, Tabet MN, Souza RR, McIntyre CK, Chapman S, Robertson IH, To WT. The peripheral effect of direct current stimulation on brain circuits involving memory. SCIENCE ADVANCES 2020; 6:6/45/eaax9538. [PMID: 33148657 PMCID: PMC7673706 DOI: 10.1126/sciadv.aax9538] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 08/31/2020] [Indexed: 05/11/2023]
Abstract
An ongoing debate surrounding transcranial direct current stimulation (tDCS) of the scalp is whether it modulates brain activity both directly and in a regionally constrained manner enough to positively affect symptoms in patients with neurological disorders. One alternative explanation is that direct current stimulation affects neural circuits mainly indirectly, i.e., via peripheral nerves. Here, we report that noninvasive direct current stimulation indirectly affects neural circuits via peripheral nerves. In a series of studies, we show that direct current stimulation can cause activation of the greater occipital nerve (ON-tDCS) and augments memory via the ascending fibers of the occipital nerve to the locus coeruleus, promoting noradrenaline release. This noradrenergic pathway plays a key role in driving hippocampal activity by modifying functional connectivity supporting the consolidation of a memory event.
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Affiliation(s)
- Sven Vanneste
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA.
- Center for Brain Health, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
- Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
| | - Anusha Mohan
- Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
| | - Hye Bin Yoo
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
- Department of Neurological Surgery, University of Texas Southwestern, Dallas, TX 75390, USA
| | - Yuefeng Huang
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Alison M Luckey
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
- Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
| | - S Lauren McLeod
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Michel N Tabet
- Neurobiology of Memory Lab, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Rimenez R Souza
- Neurobiology of Memory Lab, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Christa K McIntyre
- Neurobiology of Memory Lab, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Sandra Chapman
- Center for Brain Health, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
| | - Ian H Robertson
- Center for Brain Health, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
- Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
| | - Wing Ting To
- Lab for Clinical and Integrative Neuroscience, School for Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX, USA
- Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
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Michalovicz LT, Kelly KA, Sullivan K, O'Callaghan JP. Acetylcholinesterase inhibitor exposures as an initiating factor in the development of Gulf War Illness, a chronic neuroimmune disorder in deployed veterans. Neuropharmacology 2020; 171:108073. [PMID: 32247728 PMCID: PMC7398580 DOI: 10.1016/j.neuropharm.2020.108073] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 02/26/2020] [Accepted: 03/25/2020] [Indexed: 12/19/2022]
Abstract
Gulf War Illness (GWI) is a chronic multi-symptom disorder, characterized by symptoms such as fatigue, pain, cognitive and memory impairment, respiratory, skin and gastrointestinal problems, that is experienced by approximately one-third of 1991 Gulf War veterans. Over the nearly three decades since the end of the war, investigators have worked to elucidate the initiating factors and underlying causes of GWI. A significant portion of this research has indicated a strong correlation between GWI and exposure to a number of different acetycholinesterase inhibitors (AChEIs) in theater, such as sarin and cyclosarin nerve agents, chlorpyrifos and dichlorvos pesticides, and the anti-nerve agent prophylactic pyridostigmine bromide. Through studying these exposures and their relationship to the symptoms presented by ill veterans, it has become increasingly apparent that GWI is the likely result of an underlying neuroimmune disorder. While evidence indicates that AChEIs are a key exposure in the development of GWI, particularly organophosphate AChEIs, the mechanism(s) by which these chemicals instigate illness appears to be related to "off-target", non-cholinergic effects. In this review, we will discuss the role of AChEI exposure in the development and persistence of GWI; in particular, how these chemicals, combined with other exposures, have led to a chronic neuroimmune disorder. This article is part of the special issue entitled 'Acetylcholinesterase Inhibitors: From Bench to Bedside to Battlefield'.
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Affiliation(s)
- Lindsay T Michalovicz
- Health Effects Laboratory Division, Centers for Disease Control and Prevention - National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | - Kimberly A Kelly
- Health Effects Laboratory Division, Centers for Disease Control and Prevention - National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | | | - James P O'Callaghan
- Health Effects Laboratory Division, Centers for Disease Control and Prevention - National Institute for Occupational Safety and Health, Morgantown, WV, USA.
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Behavioral, cellular and molecular maladaptations covary with exposure to pyridostigmine bromide in a rat model of gulf war illness pain. Toxicol Appl Pharmacol 2018; 352:119-131. [PMID: 29803855 DOI: 10.1016/j.taap.2018.05.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 05/16/2018] [Accepted: 05/20/2018] [Indexed: 12/12/2022]
Abstract
Many veterans of Operation Desert Storm (ODS) struggle with the chronic pain of Gulf War Illness (GWI). Exposure to insecticides and pyridostigmine bromide (PB) have been implicated in the etiology of this multisymptom disease. We examined the influence of 3 (DEET (N,N-diethyl-meta-toluamide), permethrin, chlorpyrifos) or 4 GW agents (DEET, permethrin, chlorpyrifos, pyridostigmine bromide (PB)) on the post-exposure ambulatory and resting behaviors of rats. In three independent studies, rats that were exposed to all 4 agents consistently developed both immediate and delayed ambulatory deficits that persisted at least 16 weeks after exposures had ceased. Rats exposed to a 3 agent protocol (PB excluded) did not develop any ambulatory deficits. Cellular and molecular studies on nociceptors harvested from 16WP (weeks post-exposure) rats indicated that vascular nociceptor Nav1.9 mediated currents were chronically potentiated following the 4 agent protocol but not following the 3 agent protocol. Muscarinic linkages to muscle nociceptor TRPA1 were also potentiated in the 4 agent but not the 3 agent, PB excluded, protocol. Although Kv7 activity changes diverged from the behavioral data, a Kv7 opener, retigabine, transiently reversed ambulation deficits. We concluded that PB played a critical role in the development of pain-like signs in a GWI rat model and that shifts in Nav1.9 and TRPA1 activity were critical to the expression of these pain behaviors.
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Flunker LK, Nutter TJ, Johnson RD, Cooper BY. DEET potentiates the development and persistence of anticholinesterase dependent chronic pain signs in a rat model of Gulf War Illness pain. Toxicol Appl Pharmacol 2016; 316:48-62. [PMID: 28025109 DOI: 10.1016/j.taap.2016.12.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 12/16/2016] [Accepted: 12/20/2016] [Indexed: 12/18/2022]
Abstract
Exposure to DEET (N,N-diethyl-meta-toluamide) may have influenced the pattern of symptoms observed in soldiers with GWI (Gulf War Illness; Haley and Kurt, 1997). We examined how the addition of DEET (400mg/kg; 50% topical) to an exposure protocol of permethrin (2.6mg/kg; topical), chlorpyrifos (CP; 120mg/kg), and pyridostigmine bromide (PB;13mg/kg) altered the emergence and pattern of pain signs in an animal model of GWI pain (Nutter et al., 2015). Rats underwent behavioral testing before, during and after a 4week exposure: 1) hindlimb pressure withdrawal threshold; 2) ambulation (movement distance and rate); and 3) resting duration. Additional studies were conducted to assess the influence of acute DEET (10-100μM) on muscle and vascular nociceptor Kv7, KDR, Nav1.8 and Nav1.9. We report that a 50% concentration of DEET enhanced the development and persistence of pain-signs. Rats exposed to all 4 compounds exhibited ambulation deficits that appeared 5-12weeks post-exposure and persisted through weeks 21-24. Rats exposed to only three agents (CP or PB excluded), did not fully develop ambulation deficits. When PB was excluded, rats also developed rest duration pain signs, in addition to ambulation deficits. There was no evidence that physiological doses of DEET acutely modified nociceptor Kv7, KDR, Nav1.8 or Nav1.9 activities. Nevertheless, DEET augmented protocols decreased the conductance of Kv7 expressed in vascular nociceptors harvested from chronically exposed rats. We concluded that DEET enhanced the development and persistence of pain behaviors, but the anticholinesterases CP and PB played a determinant role.
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Affiliation(s)
- L K Flunker
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
| | - T J Nutter
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
| | - R D Johnson
- Dept. of Physiological Sciences, University of Florida College of Veterinary Science, Gainesville, FL 32610, USA.
| | - B Y Cooper
- Division of Neuroscience, Dept. of Oral and Maxillofacial Surgery, Box 100416, JHMHC, University of Florida College of Dentistry, Gainesville, FL 32610, USA.
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Masson P. Novel approaches in prophylaxis/pretreatment and treatment of organophosphorus poisoning. PHOSPHORUS SULFUR 2016. [DOI: 10.1080/10426507.2016.1211652] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Patrick Masson
- Neuropharmacology Laboratory, Kazan Federal University, Kazan, Russian Federation
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