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Gama de Barcellos Filho P, Dantzler HA, Hasser EM, Kline DD. Oxytocin and corticotropin-releasing hormone exaggerate nucleus tractus solitarii neuronal and synaptic activity following chronic intermittent hypoxia. J Physiol 2024. [PMID: 38698722 DOI: 10.1113/jp286069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Accepted: 03/28/2024] [Indexed: 05/05/2024] Open
Abstract
Chronic intermittent hypoxia (CIH) in rodents mimics the hypoxia-induced elevation of blood pressure seen in individuals experiencing episodic breathing. The brainstem nucleus tractus solitarii (nTS) is the first site of visceral sensory afferent integration, and thus is critical for cardiorespiratory homeostasis and its adaptation during a variety of stressors. In addition, the paraventricular nucleus of the hypothalamus (PVN), in part through its nTS projections that contain oxytocin (OT) and/or corticotropin-releasing hormone (CRH), contributes to cardiorespiratory regulation. Within the nTS, these PVN-derived neuropeptides alter nTS activity and the cardiorespiratory response to hypoxia. Nevertheless, their contribution to nTS activity after CIH is not fully understood. We hypothesized that OT and CRH would increase nTS activity to a greater extent following CIH, and co-activation of OT+CRH receptors would further magnify nTS activity. Our data show that compared to their normoxic controls, 10 days' CIH exaggerated nTS discharge, excitatory synaptic currents and Ca2+ influx in response to CRH, which were further enhanced by the addition of OT. CIH increased the tonic functional contribution of CRH receptors, which occurred with elevation of mRNA and protein. Together, our data demonstrate that intermittent hypoxia exaggerates the expression and function of neuropeptides on nTS activity. KEY POINTS: Episodic breathing and chronic intermittent hypoxia (CIH) are associated with autonomic dysregulation, including elevated sympathetic nervous system activity. Altered nucleus tractus solitarii (nTS) activity contributes to this response. Neurons originating in the paraventricular nucleus (PVN), including those containing oxytocin (OT) and corticotropin-releasing hormone (CRH), project to the nTS, and modulate the cardiorespiratory system. Their role in CIH is unknown. In this study, we focused on OT and CRH individually and together on nTS activity from rats exposed to either CIH or normoxia control. We show that after CIH, CRH alone and with OT increased to a greater extent overall nTS discharge, neuronal calcium influx, synaptic transmission to second-order nTS neurons, and OT and CRH receptor expression. These results provide insights into the underlying circuits and mechanisms contributing to autonomic dysfunction during periods of episodic breathing.
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Affiliation(s)
- Procopio Gama de Barcellos Filho
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Heather A Dantzler
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Eileen M Hasser
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
| | - David D Kline
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
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Bernardo EM, Pedroza AADS, Ferreira DJS, de Andrade SC, Rozendo A, Fernandes MSDS, Silva TL, Fernandes MP, Lagranha CJ. The deleterious effects of maternal protein deprivation on the brainstem are minimized with moderate physical activity by offspring during early life. Appl Physiol Nutr Metab 2024; 49:157-166. [PMID: 37816257 DOI: 10.1139/apnm-2023-0122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/12/2023]
Abstract
Maternal protein malnutrition during developmental periods might impair the redox state and the brain's excitatory/inhibitory neural network, increasing central sympathetic tone. Conversely, moderate physical exercise at an early age reduces the risk of chronic diseases. Thus, we hypothesized that a moderate training protocol could reduce the harmful effects of a low-protein maternal diet on the brainstem of young male offspring. We used a rat model of maternal protein restriction during the gestational and lactation period followed by an offspring's continuous treadmill exercise. Pregnant rats were divided into two groups according to the protein content in the diet: normoprotein (NP), receiving 17% of casein, and low protein (LP), receiving 8% of casein until the end of lactation. At 30 days of age, the male offspring were further subdivided into sedentary (NP-Sed and LP-Sed) or exercised (NP-Ex and LP-Ex) groups. Treadmill exercise was performed as follows: 4 weeks, 5 days/week, 60 min/day at 50% of maximal running capacity. The trained animals performed a treadmill exercise at 50% of the maximal running capacity, 60 min/day, 5 days/week, for 4 weeks. Our results indicate that a low-protein diet promotes deficits in the antioxidant system and a likely mitochondrial uncoupling. On the other hand, physical exercise restores the redox balance, which leads to decreased oxidative stress caused by the diet. In addition, it also promotes benefits to GABAergic inhibitory signaling. We conclude that regular moderate physical exercise performed in youthhood protects the brainstem against changes induced by maternal protein restriction.
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Affiliation(s)
| | | | | | - Severina Cassia de Andrade
- Neuropsyquiatry and Behavioral Science Graduate Program, Federal University of Pernambuco (UFPE), Recife, Pernambuco, Brazil
| | - Allifer Rozendo
- Laboratory of Biochemistry and Exercise Biochemistry/CAV, Federal University of Pernambuco, Vitoria de Santo Antao, PE, Brazil
| | | | - Tercya Lucidi Silva
- Neuropsyquiatry and Behavioral Science Graduate Program, Federal University of Pernambuco (UFPE), Recife, Pernambuco, Brazil
| | - Mariana Pinheiro Fernandes
- Laboratory of Biochemistry and Exercise Biochemistry/CAV, Federal University of Pernambuco, Vitoria de Santo Antao, PE, Brazil
| | - Claudia J Lagranha
- Biochemistry and Physiology Graduate Program, Federal University of Pernambuco, Recife, PE, Brazil
- Neuropsyquiatry and Behavioral Science Graduate Program, Federal University of Pernambuco (UFPE), Recife, Pernambuco, Brazil
- Laboratory of Biochemistry and Exercise Biochemistry/CAV, Federal University of Pernambuco, Vitoria de Santo Antao, PE, Brazil
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Jacquemot N, Wersinger E, Brabet P, Cia D. Hydrogen Peroxide Affects the Electroretinogram of Isolated Perfused Rat Retina. Curr Eye Res 2023; 48:1179-1188. [PMID: 37706511 DOI: 10.1080/02713683.2023.2256029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 09/02/2023] [Indexed: 09/15/2023]
Abstract
PURPOSE To evaluate the effects of H2O2 as an oxidant on the electroretinogram (ERG) in isolated rat retina. METHODS Retinas were isolated from rat eyes and perfused with a nutrient solution. ERGs were recorded every 3 min. Once the signal was at a steady state, H2O2 was added to the perfusion solution. RESULTS H2O2 caused instantaneous and transient changes in amplitudes and implicit times of the ERG, followed by changes in retinal survival curves. H2O2 0.2 mM produced a rapid increase in b-wave amplitude, followed by a return to the initial value and a survival curve above the control (without H2O2). A slight increase in a-wave was observed, followed by a decrease and a recovery above the control. The slow PIII decreased and then recovered to the initial value. H2O2 0.6 mM induced a small increase in b-wave amplitude, followed by a rapid decrease without recovery. The a-wave and slow PIII decreased rapidly without recovery. The implicit times of the a-wave and b-wave increased moderately with a low dose of H2O2, whereas they significantly increased with a high dose. Whatever the dose, the slow PIII implicit time increased significantly, followed by a return to the initial value. Barium increased the a-wave and b-wave, and then H2O2 reduced the two waves with a stronger effect on the a-wave. Aspartate and barium isolated the fast PIII, which decreased after H2O2 application. CONCLUSIONS H2O2 affects retinal function as shown by ERGs in isolated rat retina. The response differs with the dose of H2O2, suggesting that mechanisms underlying the action at low doses might be different from those at high doses. Our results also suggest an effect of H2O2 on ionic currents and/or neurotransmitter releases involved in the generation of the ERG and indicate a more pronounced effect on photoreceptors than on postsynaptic cells.
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Affiliation(s)
- Nathalie Jacquemot
- Laboratoire de Biophysique Neurosensorielle, Université Clermont Auvergne, INSERM U1107 NEURO-DOL, Clermont-Ferrand, France
| | - Eric Wersinger
- Laboratoire de Biophysique Neurosensorielle, Université Clermont Auvergne, INSERM U1107 NEURO-DOL, Clermont-Ferrand, France
| | - Philippe Brabet
- Institut des Neurosciences de Montpellier, INSERM U1051, Montpellier, France
| | - David Cia
- Laboratoire de Biophysique Neurosensorielle, Université Clermont Auvergne, INSERM U1107 NEURO-DOL, Clermont-Ferrand, France
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Humphrey CM, Hooker JW, Thapa M, Wilcox MJ, Ostrowski D, Ostrowski TD. Synaptic loss and gliosis in the nucleus tractus solitarii with streptozotocin-induced Alzheimer's disease. Brain Res 2023; 1801:148202. [PMID: 36521513 PMCID: PMC9840699 DOI: 10.1016/j.brainres.2022.148202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/21/2022] [Accepted: 12/09/2022] [Indexed: 12/14/2022]
Abstract
Obstructive sleep apnea is highly prevalent in Alzheimer's disease (AD). However, brainstem centers controlling respiration have received little attention in AD research, and mechanisms behind respiratory dysfunction in AD are not understood. The nucleus tractus solitarii (nTS) is an important brainstem center for respiratory control and chemoreflex function. Alterations of nTS integrity, like those shown in AD patients, likely affect neuronal processing and adequate control of breathing. We used the streptozotocin-induced rat model of AD (STZ-AD) to analyze cellular changes in the nTS that corroborate previously documented respiratory dysfunction. We used 2 common dosages of STZ (2 and 3 mg/kg STZ) for model induction and evaluated the early impact on cell populations in the nTS. The hippocampus served as control region to identify site-specific effects of STZ. There was significant atrophy in the caudal nTS of the 3 mg/kg STZ-AD group only, an area known to integrate chemoafferent information. Also, the hippocampus had significant atrophy with the highest STZ dosage tested. Both STZ-AD groups showed respiratory dysfunction along with multiple indices for astroglial and microglial activation. These changes were primarily located in the caudal and intermediate nTS. While there was no change of astrocytes in the hippocampus, microglial activation was accompanied by a reduction in synaptic density. Together, our data demonstrate that STZ-AD induces site-specific effects on all major cell types, primarily in the caudal/intermediate nTS. Both STZ dosages used in this study produced a similar outcome and can be used for future studies examining the initial symptoms of STZ-AD.
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Affiliation(s)
- Chuma M Humphrey
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University, 800 W. Jefferson St., Kirksville, MO, USA
| | - John W Hooker
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University, 800 W. Jefferson St., Kirksville, MO, USA
| | - Mahima Thapa
- Department of Biology, Truman State University, 100 E. Normal Ave., Kirksville, MO, USA
| | - Mason J Wilcox
- Department of Biology, Truman State University, 100 E. Normal Ave., Kirksville, MO, USA
| | - Daniela Ostrowski
- Department of Biology, Truman State University, 100 E. Normal Ave., Kirksville, MO, USA
| | - Tim D Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University, 800 W. Jefferson St., Kirksville, MO, USA.
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Ehlen JC, Forman CM, Ostrowski D, Ostrowski TD. Autonomic Dysfunction Impairs Baroreflex Function in an Alzheimer's Disease Animal Model. J Alzheimers Dis 2022; 90:1449-1464. [PMID: 36278348 PMCID: PMC9742304 DOI: 10.3233/jad-220496] [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] [Indexed: 12/14/2022]
Abstract
BACKGROUND Alzheimer's disease (AD) patients frequently present with orthostatic hypotension. This inability to reflexively increase blood pressure on standing is a serious health concern and increases the risk of stroke and cardiovascular diseases. OBJECTIVE Since there are no clear mechanisms for orthostatic hypotension in human AD, the present study assessed the autonomic changes that could explain this comorbidity in an AD animal model. METHODS We used the established streptozotocin-induced rat model of AD (STZ-AD), which mimics many hallmark symptoms of sporadic AD in humans. Baroreflex responses were analyzed in anesthetized STZ-AD rats using femoral catheterization for blood pressure and heart rate, and autonomic activity was assessed using specific blockers and splanchnic sympathetic nerve recordings. Expression levels of autonomic receptors at the heart were examined using the western blot technique. RESULTS Baroreflex function in STZ-AD showed a blunted heart rate (HR) response to low blood pressure challenges, and the maximal sympathetic nerve activity was reduced. Conversely, HR responses to high blood pressure were similar to control, indicating no change in parasympathetic nerve activity. Under resting conditions, autonomic blockade demonstrated a baseline shift to increased sympathetic tone in STZ-AD. Protein expression levels of beta-1 adrenergic receptor and muscarinic acetylcholine receptor M2 in the heart were unchanged. CONCLUSION Our study provides the first data on the pathological influence of AD on baroreflex function, which primarily affected the sympathetic nervous system in STZ-AD. These results represent the first mechanisms that may correlate with the orthostatic hypotension in human AD.
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Affiliation(s)
- John C. Ehlen
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA
| | | | | | - Tim D. Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA
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Rijal S, Jang SH, Cho DH, Han SK. Hydrogen peroxide suppresses excitability of gonadotropin-releasing hormone neurons in adult mouse. Front Endocrinol (Lausanne) 2022; 13:939699. [PMID: 36387844 PMCID: PMC9650413 DOI: 10.3389/fendo.2022.939699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 10/14/2022] [Indexed: 11/13/2022] Open
Abstract
It has been reported that reactive oxygen species (ROS) derived from oxygen molecule reduction can interfere with the cross-talk between the hypothalamic-pituitary-gonadal (HPG) axis and other endocrine axes, thus affecting fertility. Furthermore, ROS have been linked to GnRH receptor signaling in gonadotropes involved in gonadotropin release. There has been evidence that ROS can interfere with the HPG axis and gonadotropin release at various levels. However, the direct effect of ROS on gonadotropin-releasing hormone (GnRH) neuron remains unclear. Thus, the objective of this study was to determine the effect of hydrogen peroxide (H2O2), an ROS source, on GnRH neuronal excitabilities in transgenic GnRH-green fluorescent protein-tagged mice using the whole-cell patch-clamp electrophysiology. In adults, H2O2 at high concentrations (mM level) hyperpolarized most GnRH neurons tested, whereas low concentrations (pM to μM) caused slight depolarization. In immature GnRH neurons, H2O2 exposure induced excitation. The sensitivity of GnRH neurons to H2O2 was increased with postnatal development. The effect of H2O2 on adult female GnRH neurons was found to be estrous cycle-dependent. Hyperpolarization mediated by H2O2 persisted in the presence of tetrodotoxin, a voltage-gated Na+ channel blocker, and amino-acids receptor blocking cocktail containing blockers for the ionotropic glutamate receptors, glycine receptors, and GABAA receptors, indicating that H2O2 could act on GnRH neurons directly. Furthermore, glibenclamide, an ATP-sensitive K+ (KATP) channel blocker, completely blocked H2O2-mediated hyperpolarization. Increasing endogenous H2O2 by inhibiting glutathione peroxidase decreased spontaneous activities of most GnRH neurons. We conclude that ROS can act as signaling molecules for regulating GnRH neuron's excitability and that adult GnRH neurons are sensitive to increased ROS concentration. Results of this study demonstrate that ROS have direct modulatory effects on the HPG axis at the hypothalamic level to regulate GnRH neuron's excitabilities.
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Affiliation(s)
- Santosh Rijal
- Department of Oral Physiology, School of Dentistry and Institute of Oral Bioscience, Jeonbuk National University, Jeonju, South Korea
| | - Seon Hui Jang
- Department of Oral Physiology, School of Dentistry and Institute of Oral Bioscience, Jeonbuk National University, Jeonju, South Korea
| | - Dong Hyu Cho
- Department of Obstetrics and Gynecology, Jeonbuk National University Medical School, Institute of Clinical Medicine of Jeonbuk National University-Biomedical Research Institute for Medical Sciences, Jeonbuk National University Hospital, Jeonju, South Korea
- *Correspondence: Dong Hyu Cho, ; Seong Kyu Han,
| | - Seong Kyu Han
- Department of Oral Physiology, School of Dentistry and Institute of Oral Bioscience, Jeonbuk National University, Jeonju, South Korea
- *Correspondence: Dong Hyu Cho, ; Seong Kyu Han,
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Jia Q, Sieburth D. Mitochondrial hydrogen peroxide positively regulates neuropeptide secretion during diet-induced activation of the oxidative stress response. Nat Commun 2021; 12:2304. [PMID: 33863916 PMCID: PMC8052458 DOI: 10.1038/s41467-021-22561-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 03/17/2021] [Indexed: 12/17/2022] Open
Abstract
Mitochondria play a pivotal role in the generation of signals coupling metabolism with neurotransmitter release, but a role for mitochondrial-produced ROS in regulating neurosecretion has not been described. Here we show that endogenously produced hydrogen peroxide originating from axonal mitochondria (mtH2O2) functions as a signaling cue to selectively regulate the secretion of a FMRFamide-related neuropeptide (FLP-1) from a pair of interneurons (AIY) in C. elegans. We show that pharmacological or genetic manipulations that increase mtH2O2 levels lead to increased FLP-1 secretion that is dependent upon ROS dismutation, mitochondrial calcium influx, and cysteine sulfenylation of the calcium-independent PKC family member PKC-1. mtH2O2-induced FLP-1 secretion activates the oxidative stress response transcription factor SKN-1/Nrf2 in distal tissues and protects animals from ROS-mediated toxicity. mtH2O2 levels in AIY neurons, FLP-1 secretion and SKN-1 activity are rapidly and reversibly regulated by exposing animals to different bacterial food sources. These results reveal a previously unreported role for mtH2O2 in linking diet-induced changes in mitochondrial homeostasis with neuropeptide secretion.
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Affiliation(s)
- Qi Jia
- PIBBS program, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Derek Sieburth
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
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Wang G, Yang Q, Zheng C, Li D, Li J, Zhang F. Physiological Concentration of H 2O 2 Supports Dopamine Neuronal Survival via Activation of Nrf2 Signaling in Glial Cells. Cell Mol Neurobiol 2021; 41:163-171. [PMID: 32318898 DOI: 10.1007/s10571-020-00844-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 04/07/2020] [Indexed: 10/24/2022]
Abstract
Traditionally, hydrogen peroxide (H2O2) was formed from cellular oxidative metabolism and often viewed as toxic waste. In fact, H2O2 was a benefit messenger for neuron-glia signaling and synaptic transmission. Thus, H2O2 was a double-edged sword and neuroprotection vs. neurotoxicity produced by H2O2 was difficult to define. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been implicated as an intracellular regulator of neuronal growth. Inactivation of Nrf2 participated in the development of Parkinson's disease (PD). Thus, suitable activation of Nrf2 was essential for the prevention and treatment of PD. This study aimed to explore whether H2O2-conferred neuroprotective effects to support neuronal survival. H2O2 were added into primary neuron-glia, neuron-astroglia and neuron-microglia co-cultures in concentration- and time-dependent manners. H2O2 increased dopamine (DA) neuronal survival in concentration- and time-dependent manners. In addition, glial cells Nrf2 activation involved in H2O2-supported DA neuronal survival with the following phenomenons. First, H2O2 activated Nrf2 signaling pathway. Second, H2O2 generated beneficial neuroprotection in neuron-glia, neuron-astroglia and neuron-microglia co-cultures but not in neuron-enriched cultures. Third, silence of Nrf2 in glial cells abolished H2O2-conferred DA neuronal survival. This study demonstrated that physiological concentration of H2O2-supported DA neuronal survival via activation of Nrf2 signaling in glial cells. Our data permit to re-evaluate the role of H2O2 in the pathogenesis and therapeutic strategies for PD.
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Affiliation(s)
- Guoqing Wang
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China
| | - Qiuyu Yang
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China
| | - Changqing Zheng
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China
| | - Daidi Li
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China
| | - Jingjie Li
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China
| | - Feng Zhang
- Joint International Research Laboratory of Ethnomedicine of Ministry of Education and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical University, Zunyi, Guizhou, China.
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Vicente MC, Humphrey CM, Gargaglioni LH, Ostrowski TD. Decreased excitability of locus coeruleus neurons during hypercapnia is exaggerated in the streptozotocin-model of Alzheimer's disease. Exp Neurol 2020; 328:113250. [PMID: 32088169 DOI: 10.1016/j.expneurol.2020.113250] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 02/04/2020] [Accepted: 02/17/2020] [Indexed: 10/25/2022]
Abstract
The locus coeruleus (LC) is a pontine nucleus important for respiratory control and central chemoreception. It is affected in Alzheimer's disease (AD) and alteration of LC cell function may account for respiratory problems observed in AD patients. In the current study, we tested the electrophysiological properties and CO2/pH sensitivity of LC neurons in a model for AD. Sporadic AD was induced in rats by intracerebroventricular injection of 2 mg/kg streptozotocin (STZ), which induces behavioral and molecular impairments found in AD. LC neurons were recorded using the patch clamp technique and tested for responses to CO2 (10% CO2, pH = 7.0). The majority (~60%) of noradrenergic LC neurons in adult rats were inhibited by CO2 exposure as indicated by a significant decrease in action potential (AP) discharge to step depolarizations. The STZ-AD rat model had a greater sensitivity to CO2 than controls. The increased CO2-sensitivity was demonstrated by a significantly stronger inhibition of activity during hypercapnia that was in part due to hyperpolarization of the resting membrane potential. Reduction of AP discharge in both groups was generally accompanied by lower LC network activity, depolarized AP threshold, increased AP repolarization, and increased current through a subpopulation of voltage-gated K+ channels (KV). The latter was indicated by enhanced transient KV currents particularly in the STZ-AD group. Interestingly, steady-state KV currents were reduced under hypercapnia, a change that would favor enhanced AP discharge. However, the collective response of most LC neurons in adult rats, and particularly those in the STZ-AD group, was inhibited by CO2.
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Affiliation(s)
- Mariane C Vicente
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA; Department of Animal Morphology and Physiology, Sao Paulo State University-UNESP/FCAV at Jaboticabal, SP, Brazil
| | - Chuma M Humphrey
- Department of Biology, Truman State University, Kirksville, MO, USA
| | - Luciane H Gargaglioni
- Department of Animal Morphology and Physiology, Sao Paulo State University-UNESP/FCAV at Jaboticabal, SP, Brazil
| | - Tim D Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA.
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Joksimovic SM, DiGruccio MR, Boscolo A, Jevtovic-Todorovic V, Todorovic SM. The Role of Free Oxygen Radicals in Lasting Hyperexcitability of Rat Subicular Neurons After Exposure to General Anesthesia During Brain Development. Mol Neurobiol 2019; 57:208-216. [PMID: 31493241 DOI: 10.1007/s12035-019-01770-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 08/29/2019] [Indexed: 12/30/2022]
Abstract
A large number of preclinical studies have established that general anesthetics (GAs) may cause neurodevelopmental toxicity in rodents and nonhuman primates, which is followed by long-term cognitive deficits. The subiculum, the main output structure of hippocampal formation, is one of the brain regions most sensitive to exposure to GAs at the peak of synaptogenesis (i.e., postnatal day (PND) 7). We have previously shown that subicular neurons exposed to GAs produce excessive amounts of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), which is a known modulator of neuronal excitability. To further explore the association between GA-mediated increase in ROS levels and long-term functional changes within subicular neurons, we sought to investigate the effects of ROS on excitability of these neurons using patch-clamp electrophysiology in acute rat brain slices. We hypothesized that both acute application of H2O2 and an early exposure (at PND 7) to GA consisting of midazolam (9 mg/kg), 70% nitrous oxide, and 0.75% isoflurane can affect excitability of subicular neurons and that superoxide dismutase and catalase mimetic, EUK-134, may reverse GA-mediated hyperexcitability in the subiculum. Our results using whole-cell recordings demonstrate that acute application of H2O2 has bidirectional effects on neuronal excitability: lower concentrations (0.001%, 0.3 mM) cause an excitatory effect, whereas higher concentrations (0.01%, 3 mM) inhibited neuronal firing. Furthermore, 0.3 mM H2O2 increased the average action potential frequency of subicular neurons by almost twofold, as assessed using cell-attach configuration. Finally, we found that preemptive in vivo administration of EUK-134 reduced GA-induced long-lasting hyperexcitability of subicular neurons ex vivo when studied in neonatal and juvenile rats. This finding suggests that the increase in ROS after GA exposure may play an important role in regulating neuronal excitability, thus making it an attractive therapeutic target for GA-induced neurotoxicity in neonates.
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Affiliation(s)
- Srdjan M Joksimovic
- Department of Anesthesiology, University of Colorado Anschutz Medical Campus, Mail Stop 8130, 12801 E. 17th Avenue, Rm L18-4100, Aurora, CO, 80045, USA
| | - Michael R DiGruccio
- Department of Anesthesiology, University of Colorado Anschutz Medical Campus, Mail Stop 8130, 12801 E. 17th Avenue, Rm L18-4100, Aurora, CO, 80045, USA
| | - Annalisa Boscolo
- UOC Anaesthesia and Intensive Care, Hospital of Padua, Padua, Italy
| | - Vesna Jevtovic-Todorovic
- Department of Anesthesiology, University of Colorado Anschutz Medical Campus, Mail Stop 8130, 12801 E. 17th Avenue, Rm L18-4100, Aurora, CO, 80045, USA
| | - Slobodan M Todorovic
- Department of Anesthesiology, University of Colorado Anschutz Medical Campus, Mail Stop 8130, 12801 E. 17th Avenue, Rm L18-4100, Aurora, CO, 80045, USA. .,Neuroscience Graduate Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA. .,Pharmacology Graduate Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
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Dantzler HA, Matott MP, Martinez D, Kline DD. Hydrogen peroxide inhibits neurons in the paraventricular nucleus of the hypothalamus via potassium channel activation. Am J Physiol Regul Integr Comp Physiol 2019; 317:R121-R133. [PMID: 31042419 DOI: 10.1152/ajpregu.00054.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The paraventricular nucleus (PVN) of the hypothalamus is an important homeostatic and reflex center for neuroendocrine, respiratory, and autonomic regulation, including during hypoxic stressor challenges. Such challenges increase reactive oxygen species (ROS) to modulate synaptic, neuronal, and ion channel activity. Previously, in the nucleus tractus solitarius, another cardiorespiratory nucleus, we showed that the ROS H2O2 induced membrane hyperpolarization and reduced action potential discharge via increased K+ conductance at the resting potential. Here, we sought to determine the homogeneity of influence and mechanism of action of H2O2 on PVN neurons. We recorded PVN neurons in isolation and in an acute slice preparation, which leaves neurons in their semi-intact network. Regardless of preparation, H2O2 hyperpolarized PVN neurons and decreased action potential discharge. In the slice preparation, H2O2 also decreased spontaneous excitatory postsynaptic current frequency, but not amplitude. To examine potential mechanisms, we investigated the influence of the K+ channel blockers Ba2+, Cs+, and glibenclamide on membrane potential, as well as the ionic currents active at resting potential and outward K+ currents (IK) upon depolarization. The H2O2 hyperpolarization was blocked by K+ channel blockers. H2O2 did not alter currents between -50 and -110 mV. However, H2O2 induced an outward IK at -50 mV yet, at potentials more positive to 0 mV H2O2, decreased IK. Elevated intracellular antioxidant catalase eliminated H2O2 effects. These data indicate that H2O2 alters synaptic and neuronal properties of PVN neurons likely via membrane hyperpolarization and alteration of IK, which may ultimately alter cardiorespiratory reflexes.
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Affiliation(s)
- Heather A Dantzler
- Department of Biomedical Sciences, University of Missouri , Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri , Columbia, Missouri
| | - Michael P Matott
- Department of Biomedical Sciences, University of Missouri , Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri , Columbia, Missouri
| | - Diana Martinez
- Department of Biomedical Sciences, University of Missouri , Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri , Columbia, Missouri
| | - David D Kline
- Department of Biomedical Sciences, University of Missouri , Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri , Columbia, Missouri
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12
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Brown AG, Thapa M, Hooker JW, Ostrowski TD. Impaired chemoreflex correlates with decreased c-Fos in respiratory brainstem centers of the streptozotocin-induced Alzheimer's disease rat model. Exp Neurol 2018; 311:285-292. [PMID: 30359566 DOI: 10.1016/j.expneurol.2018.10.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/17/2018] [Accepted: 10/20/2018] [Indexed: 12/29/2022]
Abstract
Besides impairment in cognition and memory, patients with Alzheimer's disease (AD) often exhibit marked dysfunction in respiratory control. Sleep-disordered breathing (SDB) is commonly found in cases of AD, resulting in periods of hypoxia during sleep. Early structural changes in brainstem areas controlling respiratory function may account for SDB in the course of AD. However, to date the underlying mechanisms for these complications are not known. The streptozotocin (STZ)-induced rat model of AD exhibits abnormal responses to hypoxia and increased astrogliosis in a key region for respiratory control. In this study we further defined the pathophysiological respiratory response of STZ-AD rats to 10% O2. In addition, we analyzed hypoxia-induced neuronal activation in respiratory and cardiovascular nuclei of the dorsal and ventral brainstem. Two hours of hypoxia induced a transient increase in tidal volume that was followed by a prolonged increase in respiratory rate. Only respiratory rate was significantly blunted in the STZ-AD model, which continued over the entire duration of the hypoxic episode. Analysis of c-Fos expression as a marker for neuronal activation showed abundant labeling throughout the nTS, nuclei of the ventral respiratory column, and A1/C1 cells of cardiovascular centers in the ventral brainstem. STZ-AD rats showed a significant decrease of c-Fos labeling in the caudal/medial nTS, rostral ventral respiratory group, and Bötzinger complex. c-Fos in other respiratory centers and A1/C1 cells was unaltered when compared to control. The results of this study document a region-specific impact of STZ-induced AD in respiratory brainstem nuclei. This decrease in c-Fos expression correlates with the observed blunting of respiration to hypoxia in the STZ-AD rat model.
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Affiliation(s)
- Andrea G Brown
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA
| | - Mahima Thapa
- Department of Biology, Truman State University, Kirksville, MO, USA
| | - John W Hooker
- Department of Biology, Truman State University, Kirksville, MO, USA
| | - Tim D Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA.
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13
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Pardo-Peña K, Lorea-Hernández JJ, Camacho-Hernández NP, Ordaz B, Villasana-Salazar B, Morales-Villagrán A, Peña-Ortega F. Hydrogen peroxide extracellular concentration in the ventrolateral medulla and its increase in response to hypoxia in vitro: Possible role of microglia. Brain Res 2018; 1692:87-99. [DOI: 10.1016/j.brainres.2018.04.032] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 03/31/2018] [Accepted: 04/25/2018] [Indexed: 12/12/2022]
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14
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Chen Q, Wang Q, Zhu J, Xiao Q, Zhang L. Reactive oxygen species: key regulators in vascular health and diseases. Br J Pharmacol 2017; 175:1279-1292. [PMID: 28430357 DOI: 10.1111/bph.13828] [Citation(s) in RCA: 183] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2017] [Revised: 03/31/2017] [Accepted: 04/11/2017] [Indexed: 12/18/2022] Open
Abstract
ROS are a group of small reactive molecules that play critical roles in the regulation of various cell functions and biological processes. In the vascular system, physiological levels of ROS are essential for normal vascular functions including endothelial homeostasis and smooth muscle cell contraction. In contrast, uncontrolled overproduction of ROS resulting from an imbalance of ROS generation and elimination leads to the development of vascular diseases. Excessive ROS cause vascular cell damage, the recruitment of inflammatory cells, lipid peroxidation, activation of metalloproteinases and deposition of extracellular matrix, collectively leading to vascular remodelling. Evidence from a large number of studies has revealed that ROS and oxidative stress are involved in the initiation and progression of numerous vascular diseases including hypertension, atherosclerosis, restenosis and abdominal aortic aneurysm. Furthermore, considerable research has been implemented to explore antioxidants that can reduce ROS production and oxidative stress in order to ameliorate vascular diseases. In this review, we will discuss the nature and sources of ROS, their roles in vascular homeostasis and specific vascular diseases and various antioxidants as well as some of the pharmacological agents that are capable of reducing ROS and oxidative stress. The aim of this review is to provide information for developing promising clinical strategies targeting ROS to decrease cardiovascular risks. LINKED ARTICLES This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.
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Affiliation(s)
- Qishan Chen
- Department of Cardiology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Qiwen Wang
- Department of Cardiology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Jianhua Zhu
- Department of Cardiology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Qingzhong Xiao
- Centre for Clinical Pharmacology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK
| | - Li Zhang
- Department of Cardiology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
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15
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Ostrowski TD, Dantzler HA, Polo-Parada L, Kline DD. H 2O 2 augments cytosolic calcium in nucleus tractus solitarii neurons via multiple voltage-gated calcium channels. Am J Physiol Cell Physiol 2017; 312:C651-C662. [PMID: 28274920 DOI: 10.1152/ajpcell.00195.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 03/06/2017] [Accepted: 03/08/2017] [Indexed: 12/20/2022]
Abstract
Reactive oxygen species (ROS) play a profound role in cardiorespiratory function under normal physiological conditions and disease states. ROS can influence neuronal activity by altering various ion channels and transporters. Within the nucleus tractus solitarii (nTS), a vital brainstem area for cardiorespiratory control, hydrogen peroxide (H2O2) induces sustained hyperexcitability following an initial depression of neuronal activity. The mechanism(s) associated with the delayed hyperexcitability are unknown. Here we evaluate the effect(s) of H2O2 on cytosolic Ca2+ (via fura-2 imaging) and voltage-dependent calcium currents in dissociated rat nTS neurons. H2O2 perfusion (200 µM; 1 min) induced a delayed, slow, and moderate increase (~27%) in intracellular Ca2+ concentration ([Ca2+]i). The H2O2-mediated increase in [Ca2+]i prevailed during thapsigargin, excluding the endoplasmic reticulum as a Ca2+ source. The effect, however, was abolished by removal of extracellular Ca2+ or the addition of cadmium to the bath solution, suggesting voltage-gated Ca2+ channels (VGCCs) as targets for H2O2 modulation. Recording of the total voltage-dependent Ca2+ current confirmed H2O2 enhanced Ca2+ entry. Blocking VGCC L, N, and P/Q subtypes decreased the number of cells and their calcium currents that respond to H2O2 The number of responder cells to H2O2 also decreased in the presence of dithiothreitol, suggesting the actions of H2O2 were dependent on sulfhydryl oxidation. In summary, here, we have shown that H2O2 increases [Ca2+]i and its Ca2+ currents, which is dependent on multiple VGCCs likely by oxidation of sulfhydryl groups. These processes presumably contribute to the previously observed delayed hyperexcitability of nTS neurons in in vitro brainstem slices.
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Affiliation(s)
- Tim D Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, Missouri.,Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - Heather A Dantzler
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - Luis Polo-Parada
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and
| | - David D Kline
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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16
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Ebel DL, Torkilsen CG, Ostrowski TD. Blunted Respiratory Responses in the Streptozotocin-Induced Alzheimer's Disease Rat Model. J Alzheimers Dis 2017; 56:1197-1211. [PMID: 28106557 DOI: 10.3233/jad-160974] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Alzheimer's disease (AD) is known for the progressive decline of cognition and memory. In addition to these disease-defining symptoms, impairment of respiratory function is frequently observed and often expressed by sleep-disordered breathing or reduced ability to adjust respiration when oxygen demand is elevated. The mechanisms for this are widely unknown. Postmortem analysis from the brainstem of AD patients reveals pathological alterations, including in nuclei responsible for respiratory control. In this study, we analyzed respiratory responses and morphological changes in brainstem nuclei following intracerebroventricular (ICV) injections of streptozotocin (STZ), a rat model commonly used to mimic sporadic AD. ICV-STZ induced significant astrogliosis in the commissural part of the nucleus tractus solitarii, an area highly involved in respiration control. The astrogliosis was identified by a significant increase in S100B-immunofluorescence that is similar to the astrogliosis found in the CA1 region of the hippocampus. Using plethysmography, the control group displayed a typical age-dependent decrease of ventilation that was absent in the STZ rat group. This is indicative of elevated minute ventilation at rest after STZ treatment. Peripheral chemoreflex responses were significantly blunted in STZ rats as seen by a reduced respiratory rate and minute ventilation to hypoxia. Central chemoreflex responses to hypercapnia, on the other hand, only decreased in respiratory rate following STZ treatment. Overall, our results show that ICV-STZ induces respiratory dysfunction at rest and in response to hypoxia. This provides a new tool to study the underlying mechanisms of breathing disorders in clinical AD.
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Abstract
It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.
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Affiliation(s)
- Roxana Loperena
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 2220 Pierce Drive, Room 536 Robinson Research Building, Nashville, TN 37232, USA
| | - David G Harrison
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Vanderbilt University, 2220 Pierce Drive, Room 536 Robinson Research Building, Nashville, TN 37232, USA.
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18
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Hydrogen peroxide modulates neuronal excitability and membrane properties in ventral horn neurons of the rat spinal cord. Neuroscience 2016; 331:206-20. [DOI: 10.1016/j.neuroscience.2016.06.033] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 05/27/2016] [Accepted: 06/17/2016] [Indexed: 01/29/2023]
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19
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Jovanovic ZD, Stanojevic MB, Nedeljkov VB. The neurotoxic effects of hydrogen peroxide and copper in Retzius nerve cells of the leech Haemopis sanguisuga. Biol Open 2016; 5:381-8. [PMID: 26935393 PMCID: PMC4890660 DOI: 10.1242/bio.014936] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Oxidative stress and the generation of reactive oxygen species (ROS) play an important role in cellular damage. Electrophysiological analyses have shown that membrane transport proteins are susceptible to ROS. In the present study, oxidative stress was induced in Retzius nerve cells of the leechHaemopis sanguisugaby bath application of 1 mM of hydrogen peroxide (H2O2) and 0.02 mM of copper (Cu) for 20 min. The H2O2/Cu(II) produced considerable changes in the electrical properties of the Retzius nerve cells. Intracellular recording of the resting membrane potential revealed that the neuronal membrane was depolarized in the presence of H2O2/Cu(II). We found that the amplitude of action potentials decreased, while the duration augmented in a progressive way along the drug exposure time. The combined application of H2O2and Cu(II) caused an initial excitation followed by depression of the spontaneous electrical activity. Voltage-clamp recordings revealed a second effect of the oxidant, a powerful inhibition of the outward potassium channels responsible for the repolarization of action potentials. The neurotoxic effect of H2O2/Cu(II) on the spontaneous spike electrogenesis and outward K(+)current of Retzius nerve cells was reduced in the presence of hydroxyl radical scavengers, dimethylthiourea and dimethyl sulfoxide, but not mannitol. This study provides evidence for the oxidative modification of outward potassium channels in Retzius nerve cells. The oxidative mechanism of the H2O2/Cu(II) system action on the electrical properties of Retzius neurons proposed in this study might have a wider significance, referring not only to leeches but also to mammalian neurons.
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Affiliation(s)
- Zorica D Jovanovic
- Department of Pathological Physiology, Faculty of Medical Sciences, University of Kragujevac, 34000 Kragujevac, Serbia
| | - Marija B Stanojevic
- Institute for Pathological Physiology, School of Medicine, University of Belgrade, 11000 Belgrade, Serbia
| | - Vladimir B Nedeljkov
- Institute for Pathological Physiology, School of Medicine, University of Belgrade, 11000 Belgrade, Serbia
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Oxidative stress induced by cumene hydroperoxide evokes changes in neuronal excitability of rat motor cortex neurons. Neuroscience 2015; 289:85-98. [PMID: 25592424 DOI: 10.1016/j.neuroscience.2014.12.055] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/30/2014] [Accepted: 12/31/2014] [Indexed: 01/12/2023]
Abstract
Oxidative stress and the production of reactive oxygen radicals play a key role in neuronal cell damage. This paper describes an in vitro study that explores the neuronal responses to oxidative stress focusing on changes in neuronal excitability and functional membrane properties. This study was carried out in pyramidal cells of the motor cortex by applying whole-cell patch-clamp techniques on brain slices from young adult rats. Oxygen-derived free radical formation was induced by bath application of 10μM cumene hydroperoxide (CH) for 30min. CH produced marked changes in the electrophysiological properties of neurons (n=30). Resting membrane potential became progressively depolarized, as well as depolarization voltage, with no variations in voltage threshold. Membrane resistance showed a biphasic behavior, increasing after 5min of drug exposure and then it started to decrease, even under control values, after 15 and 30min. At the same time, changes in membrane resistance produced compensatory variations in the rheobase. The amplitude of the action potentials diminished and the duration increased progressively over time. Some of the neurons under study also lost their ability to discharge action potentials in a repetitive way. Most of the neurons, however, kept their repetitive discharge even though their maximum frequency and gain decreased. Furthermore, cancelation of the repetitive firing discharge took place at intensities that decreased with time of exposure to CH, which resulted in a narrower working range. We can conclude that oxidative stress compromises both neuronal excitability and the capability of generating action potentials, and so this type of neuronal functional failure could precede the neuronal death characteristics of many neurodegenerative diseases.
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