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McPherson KB, Ingram SL. Cellular and circuit diversity determines the impact of endogenous opioids in the descending pain modulatory pathway. Front Syst Neurosci 2022; 16:963812. [PMID: 36045708 PMCID: PMC9421147 DOI: 10.3389/fnsys.2022.963812] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Accepted: 07/15/2022] [Indexed: 01/31/2023] Open
Abstract
The descending pain modulatory pathway exerts important bidirectional control of nociceptive inputs to dampen and/or facilitate the perception of pain. The ventrolateral periaqueductal gray (vlPAG) integrates inputs from many regions associated with the processing of nociceptive, cognitive, and affective components of pain perception, and is a key brain area for opioid action. Opioid receptors are expressed on a subset of vlPAG neurons, as well as on both GABAergic and glutamatergic presynaptic terminals that impinge on vlPAG neurons. Microinjection of opioids into the vlPAG produces analgesia and microinjection of the opioid receptor antagonist naloxone blocks stimulation-mediated analgesia, highlighting the role of endogenous opioid release within this region in the modulation of nociception. Endogenous opioid effects within the vlPAG are complex and likely dependent on specific neuronal circuits activated by acute and chronic pain stimuli. This review is focused on the cellular heterogeneity within vlPAG circuits and highlights gaps in our understanding of endogenous opioid regulation of the descending pain modulatory circuits.
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Affiliation(s)
- Kylie B. McPherson
- Division of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Monserrato, Italy,Department of Neurological Surgery, Oregon Health & Science University, Portland, OR, United States
| | - Susan L. Ingram
- Department of Neurological Surgery, Oregon Health & Science University, Portland, OR, United States,*Correspondence: Susan L. Ingram
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Lu YC, Yin JB, Bai Y, Li X, Zhang T, Yang J, Yi XN, Zhang MM, Li YQ. Morphological Features of Endomorphin-2-immunoreactive Ultrastructures in the Dorsal Root Ganglion and Spinal Dorsal Horn of the Rat. J Chem Neuroanat 2022; 125:102142. [DOI: 10.1016/j.jchemneu.2022.102142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 01/24/2023]
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Projections from the lateral parabrachial nucleus to the lateral and ventral lateral periaqueductal gray subregions mediate the itching sensation. Pain 2021; 162:1848-1863. [PMID: 33449512 DOI: 10.1097/j.pain.0000000000002193] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 12/30/2020] [Indexed: 11/25/2022]
Abstract
ABSTRACT Lateral and ventral lateral subregions of the periaqueductal gray (l/vlPAG) have been proved to be pivotal components in descending circuitry of itch processing, and their effects are related to the subclassification of neurons that were meditated. In this study, lateral parabrachial nucleus (LPB), one of the most crucial relay stations in the ascending pathway, was taken as the input nucleus to examine the modulatory effect of l/vlPAG neurons that received LPB projections. Anatomical tracing, chemogenetic, optogenetic, and local pharmacological approaches were used to investigate the participation of the LPB-l/vlPAG pathway in itch and pain sensation in mice. First, morphological evidence for projections from vesicular glutamate transporter-2-containing neurons in the LPB to l/vlPAG involved in itch transmission has been provided. Furthermore, chemogenetic and optogenetic activation of the LPB-l/vlPAG pathway resulted in both antipruritic effect and analgesic effect, whereas pharmacogenetic inhibition strengthened nociceptive perception without affecting spontaneous scratching behavior. Finally, in vivo pharmacology was combined with optogenetics which revealed that AMPA receptor-expressing neurons in l/vlPAG might play a more essential role in pathway modulation. These findings provide a novel insight about the connections between 2 prominent transmit nuclei, LPB and l/vlPAG, in both pruriceptive and nociceptive sensations and deepen the understanding of l/vlPAG modulatory roles in itch sensation by chosen LPB as source of ascending efferent projections.
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Blank JJ, Liu Y, Yin Z, Spofford CM, Ridolfi TJ, Ludwig KA, Otterson MF, Peterson CY. Impact of Auricular Neurostimulation in Patients Undergoing Colorectal Surgery with an Enhanced Recovery Protocol: A Pilot Randomized, Controlled Trial. Dis Colon Rectum 2021; 64:225-233. [PMID: 33417346 DOI: 10.1097/dcr.0000000000001752] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
BACKGROUND Narcotics are the cornerstone of postoperative pain control, but the opioid epidemic and the negative physiological and psychological effects of narcotics implore physicians to utilize nonpharmacological methods of pain control. OBJECTIVE This pilot study investigated a novel neurostimulation device for postoperative analgesia. We hypothesized that active neurostimulation would decrease postoperative narcotic requirements. DESIGN This was a placebo-controlled, double-blinded trial. SETTINGS This trial was conducted at an academic medical center and a Veterans Affairs hospital. PATIENTS This trial included adult patients who underwent elective bowel resection between December 2016 and April 2018. INTERVENTIONS Patients were randomly assigned to receive an active or inactive (sham) device, which was applied to the right ear before surgery and continued for 5 days. MAIN OUTCOME MEASURES The primary outcome was total opioid consumption. The secondary outcomes included pain, nausea, anxiety, return of bowel function, complications, 30-day readmissions, and opioid consumption at 2 weeks and 30 days. RESULTS A total of 57 patients participated and 5 withdrew; 52 patients were included in the analysis. Twenty-eight patients received an active device and 24 received an inactive device. There was no difference in total narcotic consumption between active and inactive devices (90.79 ± 54.93 vs 90.30 ± 43.03 oral morphine equivalents/day). Subgroup analyses demonstrated a benefit for patients after open surgery (p = 0.0278). When patients were stratified by decade, those aged 60 to 70 and >70 years derived a benefit from active devices in comparison with those aged 30 to 40, 40 to 50, and 50 to 60 years old (p = 0.01092). No serious adverse events were related to this study. LIMITATIONS This study was limited by the small sample sizes. CONCLUSIONS No difference in opioid use was found with auricular neurostimulation. However, this pilot study suggests that older patients and those with larger abdominal incisions may benefit from auricular neurostimulation. Further investigation in these high-risk patients is warranted. See Video Abstract at http://links.lww.com/DCR/B452.ClinicalTrials.gov identifier: NCT02892513. IMPACTO DE LA NEUROESTIMULACIN AURICULAR EN PACIENTES SOMETIDOS A CIRUGA COLORRECTAL CON UN PROTOCOLO DE RECUPERACIN MEJORADA UN ENSAYO PILOTO ALEATORIZADO Y CONTROLADO ANTECEDENTES:Los narcóticos son la piedra angular del control del dolor postoperatorio, pero la epidemia de opioides y los efectos fisiológicos y psicológicos negativos de los narcóticos incentivan a los médicos a que utilicen métodos no farmacológicos de control del dolor.OBJETIVO:Este estudio piloto investigó un nuevo dispositivo de neuroestimulación para analgesia postoperatoria. Hipotetizamos que la neuroestimulación activa disminuiría los requerimientos narcóticos postoperatorios.DISEÑO:Este fue un ensayo doble ciego controlado con placebo.ESCENARIO:Esto se llevó a cabo en un centro médico académico y en un hospital de Asuntos de Veteranos (Veterans Affairs hospital).PACIENTES:Este ensayo incluyó pacientes adultos que se sometieron a resección intestinal electiva entre diciembre de 2016 y abril de 2018.INTERVENCIONES:Los pacientes fueron asignados al azar para recibir un dispositivo activo o inactivo (falso), que se aplicó al oído derecho antes de la cirugía y se mantuvo durante 5 días.PRINCIPALES MEDIDAS DE RESULTADO:El resultado primario fue el consumo total de opioides; los resultados secundarios incluyeron dolor, náusea, ansiedad, retorno de la función intestinal, complicaciones, reingresos a 30 días y consumo de opioides a 2 semanas y a 30 días.RESULTADOS:Participaron un total de 57 pacientes y 5 se retiraron; Se incluyeron 52 pacientes en el análisis. Veintiocho pacientes recibieron un dispositivo activo y 24 recibieron un dispositivo inactivo. No hubo diferencias en el consumo total de narcóticos entre los dispositivos activos e inactivos (90.79 ± 54.93 vs 90.30 ± 43.03 equivalentes de morfina oral [OME] / día). Los análisis de subgrupos demostraron un beneficio para los pacientes después de cirugía abierta (p = 0.0278). Cuando los pacientes se estratificaron por década, aquellos de 60-70 y > 70 años obtuvieron un beneficio de los dispositivos activos en comparación con los de 30-40, 40-50 y 50-60 años (p = 0.01092). No hubo eventos adversos graves relacionados con este estudio.LIMITACIONES:Este estudio estuvo limitado por los pequeños tamaños de muestra.CONCLUSIONES:No se encontró diferencia en el uso de opioides con la neuroestimulación auricular. Sin embargo, este estudio piloto sugiere que los pacientes mayores y aquellos con incisiones abdominales más grandes pueden beneficiarse de la neuroestimulación auricular. Está justificada la investigación adicional en estos pacientes de alto riesgo. Consulte Video Resumen en http://links.lww.com/DCR/B452. (Traducción-Dr. Jorge Silva Velazco).
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Affiliation(s)
- Jacqueline J Blank
- Division of Colorectal Surgery, Medical College of Wisconsin, Wauwatosa, Wisconsin
- Clement J Zablocki Veterans Affairs Medical Center, Department of Surgery, Milwaukee, Wisconsin
| | - Ying Liu
- Division of Biostatistics, Medical College of Wisconsin, Wauwatosa, Wisconsin
| | - Ziyan Yin
- Division of Biostatistics, Medical College of Wisconsin, Wauwatosa, Wisconsin
| | - Christina M Spofford
- Department of Anesthesiology, Medical College of Wisconsin, Wauwatosa, Wisconsin
| | - Timothy J Ridolfi
- Division of Colorectal Surgery, Medical College of Wisconsin, Wauwatosa, Wisconsin
- Clement J Zablocki Veterans Affairs Medical Center, Department of Surgery, Milwaukee, Wisconsin
| | - Kirk A Ludwig
- Division of Colorectal Surgery, Medical College of Wisconsin, Wauwatosa, Wisconsin
| | - Mary F Otterson
- Division of Colorectal Surgery, Medical College of Wisconsin, Wauwatosa, Wisconsin
- Clement J Zablocki Veterans Affairs Medical Center, Department of Surgery, Milwaukee, Wisconsin
| | - Carrie Y Peterson
- Division of Colorectal Surgery, Medical College of Wisconsin, Wauwatosa, Wisconsin
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Bagley EE, Ingram SL. Endogenous opioid peptides in the descending pain modulatory circuit. Neuropharmacology 2020; 173:108131. [PMID: 32422213 DOI: 10.1016/j.neuropharm.2020.108131] [Citation(s) in RCA: 70] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 05/01/2020] [Accepted: 05/04/2020] [Indexed: 02/07/2023]
Abstract
The opioid epidemic has led to a serious examination of the use of opioids for the treatment of pain. Opioid drugs are effective due to the expression of opioid receptors throughout the body. These receptors respond to endogenous opioid peptides that are expressed as polypeptide hormones that are processed by proteolytic cleavage. Endogenous opioids are expressed throughout the peripheral and central nervous system and regulate many different neuronal circuits and functions. One of the key functions of endogenous opioid peptides is to modulate our responses to pain. This review will focus on the descending pain modulatory circuit which consists of the ventrolateral periaqueductal gray (PAG) projections to the rostral ventromedial medulla (RVM). RVM projections modulate incoming nociceptive afferents at the level of the spinal cord. Stimulation within either the PAG or RVM results in analgesia and this circuit has been studied in detail in terms of the actions of exogenous opioids, such as morphine and fentanyl. Further emphasis on understanding the complex regulation of endogenous opioids will help to make rational decisions with regard to the use of opioids for pain. We also include a discussion of the actions of endogenous opioids in the amygdala, an upstream brain structure that has reciprocal connections to the PAG that contribute to the brain's response to pain.
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Affiliation(s)
- Elena E Bagley
- Discipline of Pharmacology and Charles Perkins Centre, University of Sydney, NSW, 2006, Australia
| | - Susan L Ingram
- Department of Neurological Surgery, Oregon Health & Science University, Portland, OR, 97239, USA.
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Matus-Ortega ME, Leff Gelman P, Calva-Nieves JC, Flores-Zamora A, Salazar-Juárez A, Torner-Aguilar CA, Gamba G, De Los Heros P, Peng B, Pintar JE, Gompf HS, Allen CN, Antón-Palma B. Mexneurin is a novel precursor of peptides in the central nervous system of rodents. FEBS Lett 2017; 591:1627-1636. [PMID: 28504339 DOI: 10.1002/1873-3468.12679] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/19/2017] [Accepted: 05/10/2017] [Indexed: 12/29/2022]
Abstract
Endomorphins (EMs) have been proposed as the endogenous ligand agonists of the μ-opioid receptor; however, no propeptide precursor protein for EMs has been identified. Here, to identify the presumed precursor of EMs, we designed an immunoscreening assay using specific affinity-purified rabbit antisera raised against synthetic EMs in a whole-mouse brain cDNA library. Following this approach, we identify a DNA sequence encoding a protein precursor, which we name proMexneurin, that contains three different peptide sequences: Mexneurin-1 (an EM-like peptide), Mexneurin-2, and Mexneurin-3, a peptide which appears to be unrelated to EMs. RT-PCR analysis and in situ hybridization reveal a widespread distribution of proMexneurin mRNA throughout the mouse brain. Both Mexneurin-1 and Mexneurin-3 peptides display biological activities in the mouse CNS.
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Affiliation(s)
- Maura E Matus-Ortega
- Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Ciudad de México, México
| | | | - Juan C Calva-Nieves
- Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Ciudad de México, México
| | - Anabel Flores-Zamora
- Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Ciudad de México, México
| | | | | | - Gerardo Gamba
- Molecular Physiology Unit, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán and Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Paola De Los Heros
- Dirección de Investigación, Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Bonnie Peng
- Department of Neuroscience and Cell Biology, Rutgers Biomedical and Health Sciences, Newark, NJ, USA
| | - John E Pintar
- Department of Neuroscience and Cell Biology, Rutgers Biomedical and Health Sciences, Newark, NJ, USA
| | - Heinrich S Gompf
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Charles N Allen
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Benito Antón-Palma
- Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Ciudad de México, México
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7
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Mu and kappa opioid receptors of the periaqueductal gray stimulate and inhibit thermogenesis, respectively, during psychological stress in rats. Pflugers Arch 2017; 469:1151-1161. [DOI: 10.1007/s00424-017-1966-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/20/2017] [Accepted: 03/06/2017] [Indexed: 12/18/2022]
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8
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Chen T, Li J, Feng B, Hui R, Dong YL, Huo FQ, Zhang T, Yin JB, Du JQ, Li YQ. Mechanism Underlying the Analgesic Effect Exerted by Endomorphin-1 in the rat Ventrolateral Periaqueductal Gray. Mol Neurobiol 2015; 53:2036-2053. [DOI: 10.1007/s12035-015-9159-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 03/25/2015] [Indexed: 12/11/2022]
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9
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Chen L, Wang K, Yang T, Wang W, Mei XP, Zhu C, Wang W, Zhang FX, Li YQ. Downregulation of spinal endomorphin-2 correlates with mechanical allodynia in a rat model of tibia cancer. Neuroscience 2014; 286:151-61. [PMID: 25457129 DOI: 10.1016/j.neuroscience.2014.11.049] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 11/18/2014] [Accepted: 11/20/2014] [Indexed: 01/13/2023]
Abstract
The endogenous tetrapeptide endomorphin-2 (EM2) participates in pain modulation by binding to pre- and/or post-synaptic μ opioid receptor (MOR). In the present study, pathological expression and antinociceptive effects of EM2 at the spinal level were investigated in a rat model of bone cancer pain. The model was established by introducing Walker 256 mammary gland carcinoma cells into the tibia medullary cavity. Immunohistochemical staining for EM2 showed a markedly reduced EM2-immunoreactivity in the ipsilateral spinal dorsal horn on days 6, 12 and 18 post Walker 256 inoculation (p < 0.05). Intrathecal injection (i.t.) of EM2 significantly attenuated cancer-induced mechanical allodynia (p < 0.05) which could be blocked by β-funaltrexamine (β-FNA), the μ receptor antagonist (p < 0.05). Furthermore, topical application of EM2 dose-dependently inhibited the electrically evoked C-fiber responses and postdischarge of wide dynamic range (WDR) neurons within the spinal cord (p < 0.05), and pretreatment with β-FNA abolished the hyperactivity of these neurons. Compared with the antinociception of morphine which took effect from 40 min to 100 min post application, the analgesic action of EM2 was characterized by quick onset and short-lived efficacy (p < 0.05), being most potent at 10 min and lasting about 20 min. These findings indicate that the down-regulated spinal EM2 is an important contributor to the neuropathological process of bone cancer pain and enhancing activation of EM2/μ receptor signaling might provide a therapeutic alternative to optimizing the treatment of cancer-induced bone pain.
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Affiliation(s)
- L Chen
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, Fourth Military Medical University, Xi'an 710032, China; Department of Ultrasound, Armed Police Tianjin Corps Hospital, Tianjin 300252,China
| | - K Wang
- Department of Pain Relief, Tianjin Key Laboratory of Cancer Prevention and Treatment, National Clinical Research Center of Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China
| | - T Yang
- Department of Ultrasound, Armed Police Tianjin Corps Hospital, Tianjin 300252,China
| | - W Wang
- Department of Anesthesiology, School of Stomatology, Fourth Military Medical University, Xi'an 710032, China
| | - X-P Mei
- Department of Anesthesiology, School of Stomatology, Fourth Military Medical University, Xi'an 710032, China
| | - C Zhu
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, Fourth Military Medical University, Xi'an 710032, China
| | - W Wang
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, Fourth Military Medical University, Xi'an 710032, China
| | - F-X Zhang
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, Fourth Military Medical University, Xi'an 710032, China.
| | - Y-Q Li
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, Fourth Military Medical University, Xi'an 710032, China.
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Yin JB, Wu HH, Dong YL, Zhang T, Wang J, Zhang Y, Wei YY, Lu YC, Wu SX, Wang W, Li YQ. Neurochemical properties of BDNF-containing neurons projecting to rostral ventromedial medulla in the ventrolateral periaqueductal gray. Front Neural Circuits 2014; 8:137. [PMID: 25477786 PMCID: PMC4238372 DOI: 10.3389/fncir.2014.00137] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Accepted: 10/31/2014] [Indexed: 12/18/2022] Open
Abstract
The periaqueductal gray (PAG) modulates nociception via a descending pathway that relays in the rostral ventromedial medulla (RVM) and terminates in the spinal cord. Previous behavioral pharmacology and electrophysiological evidence suggests that brain-derived neurotrophic factor (BDNF) plays an important role in descending pain modulation, likely through the PAG-RVM pathway. However, detailed information is still lacking on the distribution of BDNF, activation of BDNF-containing neurons projecting to RVM in the condition of pain, and neurochemical properties of these neurons within the PAG. Through fluorescent in situ hybridization (FISH) and immunofluorescent staining, the homogenous distributions of BDNF mRNA and protein were observed in the four subregions of PAG. Both neurons and astrocytes expressed BDNF, but not microglia. By combining retrograde tracing methods and formalin pain model, there were more BDNF-containing neurons projecting to RVM being activated in the ventrolateral subregion of PAG (vlPAG) than other subregions of PAG. The neurochemical properties of BDNF-containing projection neurons in the vlPAG were investigated. BDNF-containing projection neurons expressed the autoreceptor TrkB in addition to serotonin (5-HT), neurotensin (NT), substance P (SP), calcitonin gene related peptide (CGRP), nitric oxide synthase (NOS), and parvalbumin (PV) but not tyrosine decarboxylase (TH). It is speculated that BDNF released from projection neurons in the vlPAG might participate in the descending pain modulation through enhancing the presynaptic release of other neuroactive substances (NSs) in the RVM.
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Affiliation(s)
- Jun-Bin Yin
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Huang-Hui Wu
- Department of Anesthesiology, Fuzhou General Hospital Affiliated to Fujian Medical University Fuzhou, China
| | - Yu-Lin Dong
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Ting Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Jian Wang
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Yong Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Yan-Yan Wei
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Ya-Cheng Lu
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Sheng-Xi Wu
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Wen Wang
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
| | - Yun-Qing Li
- Department of Anatomy and K.K. Leung Brain Research Centre, Preclinical School of Medicine, Fourth Military Medical University Xi'an, China
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Postsynaptic insertion of AMPA receptor onto cortical pyramidal neurons in the anterior cingulate cortex after peripheral nerve injury. Mol Brain 2014; 7:76. [PMID: 25359681 PMCID: PMC4221704 DOI: 10.1186/s13041-014-0076-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Accepted: 10/21/2014] [Indexed: 12/12/2022] Open
Abstract
Long-term potentiation (LTP) is the key cellular mechanism for physiological learning and pathological chronic pain. Postsynaptic accumulation of AMPA receptor (AMPAR) GluA1 plays an important role for injury-related cortical LTP. However, there is no direct evidence for postsynaptic GluA1 insertion or accumulation after peripheral injury. Here we report nerve injury increased the postsynaptic expression of AMPAR GluA1 in pyramidal neurons in the layer V of the anterior cingulate cortex (ACC), including the corticospinal projecting neurons. Electrophysiological recordings show that potentiation of postsynaptic responses was reversed by Ca2+ permeable AMPAR antagonist NASPM. Finally, behavioral studies show that microinjection of NASPM into the ACC inhibited behavioral sensitization caused by nerve injury. Our findings provide direct evidence that peripheral nerve injury induces postsynaptic GluA1 accumulation in cingulate cortical neurons, and inhibits postsynaptic GluA1 accumulation which may serve as a novel target for treating neuropathic pain.
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12
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Chen T, Koga K, Descalzi G, Qiu S, Wang J, Zhang LS, Zhang ZJ, He XB, Qin X, Xu FQ, Hu J, Wei F, Huganir RL, Li YQ, Zhuo M. Postsynaptic potentiation of corticospinal projecting neurons in the anterior cingulate cortex after nerve injury. Mol Pain 2014; 10:33. [PMID: 24890933 PMCID: PMC4060852 DOI: 10.1186/1744-8069-10-33] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 05/13/2014] [Indexed: 12/25/2022] Open
Abstract
Long-term potentiation (LTP) is the key cellular mechanism for physiological learning and pathological chronic pain. In the anterior cingulate cortex (ACC), postsynaptic recruitment or modification of AMPA receptor (AMPAR) GluA1 contribute to the expression of LTP. Here we report that pyramidal cells in the deep layers of the ACC send direct descending projecting terminals to the dorsal horn of the spinal cord (lamina I-III). After peripheral nerve injury, these projection cells are activated, and postsynaptic excitatory responses of these descending projecting neurons were significantly enhanced. Newly recruited AMPARs contribute to the potentiated synaptic transmission of cingulate neurons. PKA-dependent phosphorylation of GluA1 is important, since enhanced synaptic transmission was abolished in GluA1 phosphorylation site serine-845 mutant mice. Our findings provide strong evidence that peripheral nerve injury induce long-term enhancement of cortical-spinal projecting cells in the ACC. Direct top-down projection system provides rapid and profound modulation of spinal sensory transmission, including painful information. Inhibiting cortical top-down descending facilitation may serve as a novel target for treating neuropathic pain.
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Affiliation(s)
- Tao Chen
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi'an, China
- Department of Anatomy, Histology and Embryology and K.K. Leung Brain Research Center, the Fourth Military Medical University, Xi’an 710032, China
- Department of Physiology, Faculty of Medicine, Center for the Study of Pain, University of Toronto, 1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada
| | - Kohei Koga
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi'an, China
- Department of Physiology, Faculty of Medicine, Center for the Study of Pain, University of Toronto, 1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada
| | - Giannina Descalzi
- Department of Physiology, Faculty of Medicine, Center for the Study of Pain, University of Toronto, 1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada
| | - Shuang Qiu
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi'an, China
- Department of Physiology, Faculty of Medicine, Center for the Study of Pain, University of Toronto, 1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada
| | - Jian Wang
- Department of Anatomy, Histology and Embryology and K.K. Leung Brain Research Center, the Fourth Military Medical University, Xi’an 710032, China
| | - Le-Shi Zhang
- Department of Anatomy, Histology and Embryology and K.K. Leung Brain Research Center, the Fourth Military Medical University, Xi’an 710032, China
| | - Zhi-Jian Zhang
- Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, China
- Wuhan National Laboratory for Optoelectronics, Wuhan 430074, China
- College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Xiao-Bin He
- Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xin Qin
- College of Life Science, Wuhan University, Wuhan 430071, China
| | - Fu-Qiang Xu
- Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, China
- Wuhan National Laboratory for Optoelectronics, Wuhan 430074, China
- College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ji Hu
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi'an, China
| | - Feng Wei
- Department of Biomedical Sciences, University of Maryland Dental School, Baltimore, MD 21201, USA
| | - Richard L Huganir
- Department of Neuroscience and Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Yun-Qing Li
- Department of Anatomy, Histology and Embryology and K.K. Leung Brain Research Center, the Fourth Military Medical University, Xi’an 710032, China
| | - Min Zhuo
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi'an, China
- Department of Physiology, Faculty of Medicine, Center for the Study of Pain, University of Toronto, 1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada
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13
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Luo DS, Huang J, Dong YL, Wu ZY, Wei YY, Lu YC, Wang YY, Yanagawa Y, Wu SX, Wang W, Li YQ. Connections between EM2- and SP-containing terminals and GABAergic neurons in the mouse spinal dorsal horn. Neurol Sci 2014; 35:1421-7. [PMID: 24718557 DOI: 10.1007/s10072-014-1774-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Accepted: 03/25/2014] [Indexed: 12/22/2022]
Abstract
Endomorphin-2 (EM2) demonstrates a potent antinociceptive effect in pain modulation. To investigate the potential interactions of EM2- and substance P (SP)-containing primary afferents and γ-amino butyric acid (GABA)-containing interneurons in lamina II in nociceptive transmission, connections between EM2- and SP-containing terminals and GABAergic neurons in the spinal dorsal horn were studied. Double-immunofluorescent labeling showed that approximately 62.3 % of EM2-immunoreactive neurons exhibited SP-immunostaining, and 76.9 % of SP-immunoreactive neurons demonstrated EM2-immunoreactivities in the dorsal root ganglion (DRG). Dense double-labeled EM2- and SP-immunoreactivities were mainly observed in lamina II of the lumbar dorsal horn. Furthermore, triple-immunofluorescent labeling results revealed that EM2 and SP double-labeled terminals overlapped with GABAergic neurons. Immuno-electron microscopy confirmed that the EM2- or SP-immunoreactive terminals formed synapses with GABA-immunoreactive dendrites in lamina II of the lumbar dorsal horn. During noxious information transmission induced by formalin plantar injection, GABAergic neurons expressing FOS in their nuclei were contacted with EM2- or SP-immunoreactive terminals. These results suggest that the interactions between EM2- and SP-containing terminals and GABAergic interneurons in the lamina II influence pain transmission and modulation in the spinal dorsal horn.
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Affiliation(s)
- Dao-Shu Luo
- Department of Anatomy, Histology and Embryology, Basic Medical College, Fujian Medical University, Fuzhou, 350004, China
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14
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Liu J, Ren Y, Li G, Liu ZL, Liu R, Tong Y, Zhang L, Yang K. GABAB receptors resist acute desensitization in both postsynaptic and presynaptic compartments of periaqueductal gray neurons. Neurosci Lett 2013; 543:146-51. [DOI: 10.1016/j.neulet.2013.03.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 03/17/2013] [Accepted: 03/18/2013] [Indexed: 10/27/2022]
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15
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French L, Lane S, Xu L, Siu C, Kwok C, Chen Y, Krebs C, Pavlidis P. Application and evaluation of automated methods to extract neuroanatomical connectivity statements from free text. Bioinformatics 2012; 28:2963-70. [PMID: 22954628 PMCID: PMC3496336 DOI: 10.1093/bioinformatics/bts542] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
MOTIVATION Automated annotation of neuroanatomical connectivity statements from the neuroscience literature would enable accessible and large-scale connectivity resources. Unfortunately, the connectivity findings are not formally encoded and occur as natural language text. This hinders aggregation, indexing, searching and integration of the reports. We annotated a set of 1377 abstracts for connectivity relations to facilitate automated extraction of connectivity relationships from neuroscience literature. We tested several baseline measures based on co-occurrence and lexical rules. We compare results from seven machine learning methods adapted from the protein interaction extraction domain that employ part-of-speech, dependency and syntax features. RESULTS Co-occurrence based methods provided high recall with weak precision. The shallow linguistic kernel recalled 70.1% of the sentence-level connectivity statements at 50.3% precision. Owing to its speed and simplicity, we applied the shallow linguistic kernel to a large set of new abstracts. To evaluate the results, we compared 2688 extracted connections with the Brain Architecture Management System (an existing database of rat connectivity). The extracted connections were connected in the Brain Architecture Management System at a rate of 63.5%, compared with 51.1% for co-occurring brain region pairs. We found that precision increases with the recency and frequency of the extracted relationships. AVAILABILITY AND IMPLEMENTATION The source code, evaluations, documentation and other supplementary materials are available at http://www.chibi.ubc.ca/WhiteText. CONTACT paul@chibi.ubc.ca. SUPPLEMENTARY INFORMATION Supplementary data are available at Bioinformatics Online.
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Affiliation(s)
- Leon French
- Department of Psychiatry, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
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16
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Liu ZL, Ma H, Xu RX, Dai YW, Zhang HT, Yao XQ, Yang K. Potassium channels underlie postsynaptic but not presynaptic GABAB receptor-mediated inhibition on ventrolateral periaqueductal gray neurons. Brain Res Bull 2012; 88:529-33. [DOI: 10.1016/j.brainresbull.2012.05.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Accepted: 05/15/2012] [Indexed: 01/25/2023]
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17
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Sex similarities and differences in pain-related periaqueductal gray connectivity. Pain 2011; 153:444-454. [PMID: 22154332 DOI: 10.1016/j.pain.2011.11.006] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 10/07/2011] [Accepted: 11/03/2011] [Indexed: 01/09/2023]
Abstract
This study investigated sex similarities and differences in pain-related functional connectivity in 60 healthy subjects. We used functional magnetic resonance imaging and psychophysiological interaction analysis to investigate how exposure to low vs high experimental pain modulates the functional connectivity of the periaqueductal gray (PAG). We found no sex differences in pain thresholds, and in both men and women, the PAG was more functionally connected with the somatosensory cortex, the supplemental motor area, cerebellum, and thalamus during high pain, consistent with anatomic predictions. Twenty-six men displayed a pain-induced increase in PAG functional connectivity with the amygdala caudate and putamen that was not observed in women. In an extensive literature search, we found that female animals have been largely overlooked when the connections between the PAG and the amygdala have been described, and that women are systematically understudied with regard to endogenous pain inhibition. Our results emphasize the importance of including both male and female subjects when studying basic mechanisms of pain processing, and point toward a possible sex difference in endogenous pain inhibition.
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18
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Marques-Lopes J, Martins I, Pinho D, Morato M, Wilson SP, Albino-Teixeira A, Tavares I. Decrease in the expression of N-methyl-D-aspartate receptors in the nucleus tractus solitarii induces antinociception and increases blood pressure. J Neurosci Res 2011; 90:356-66. [PMID: 21948527 DOI: 10.1002/jnr.22760] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 07/05/2011] [Accepted: 07/08/2011] [Indexed: 12/18/2022]
Abstract
N-methyl-D-aspartate receptors (NMDAR) have a role in cardiovascular control at the nucleus tractus solitarii (NTS), eliciting increases or decreases in blood pressure (BP), depending on the area injected with the agonists. In spite of the association between cardiovascular control and pain modulation, the effects of manipulating NMDAR in pain responses have never been evaluated. In this study, we decreased the expression of NMDAR in the NTS using gene transfer to target receptor subunits and evaluate long-term effects. Seven days after the injection of lentiviral vectors containing the NR1a subunit cDNA of NMDAR, in antisense orientation, into the intermediate NTS of Wistar rats, BP was measured, and the formalin test of nociception was performed. The antisense vector induced a decrease of NR1 expression in the NTS and elicited BP rises and hypoalgesia. Antisense vectors inhibited formalin-evoked c-Fos expression in the spinal cord, indicating decreased nociceptive activity of spinal neurons. Using a time-course approach, we verified that the onset of both the increases in BP and the hypoalgesia was at 4 days after vector injection into the NTS. The injection of NMDA into the NTS reversed the effects of antisense vectors in pain behavioral responses and spinal neuronal activation and decreased BP and heart rate. The present study shows that the NR1 subunit of the NMDAR at the NTS is critical in the regulation of tonic cardiovascular and nociceptive control and shows an involvement of the nucleus in the modulation of sustained pain.
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Affiliation(s)
- J Marques-Lopes
- Instituto de Farmacologia & Terapêutica, Faculdade de Medicina, Universidade do Porto, Porto, Portugal
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19
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Zhu C, Hui R, Chen T, Zuo ZF, Wang W, Gao CJ, Zhang T, Wang YY, Li H, Wu SX, Li YQ. Origins of endomorphin-2 immunopositive fibers and terminals in the rat medullary dorsal horn. Brain Res 2011; 1410:38-47. [DOI: 10.1016/j.brainres.2011.06.067] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 06/21/2011] [Accepted: 06/30/2011] [Indexed: 01/20/2023]
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20
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Hui R, Wang W, Chen T, Lü BC, Li H, Zhang T, Wu SX, Li YQ. Origins of endomorphin-2 immunopositive fibers and terminals in the spinal dorsal horn of the rat. Neuroscience 2010; 169:422-30. [PMID: 20457220 DOI: 10.1016/j.neuroscience.2010.05.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 05/02/2010] [Accepted: 05/03/2010] [Indexed: 01/06/2023]
Abstract
Endomorphin 2 (EM2) plays essential roles in regulating nociceptive transmission within the spinal dorsal horn, where EM2-immunopositive (EM2-IP) fibers and terminals are densely encountered. However, the origins of these EM2-IP structures are still obscure. Unilateral primary sensory afferents disruption (lumbar 3-6 dorsal roots rhizotomy) significantly decreased the density of EM2-IP fibers and terminals in the superficial laminae (laminae I and II) on the ipsilateral but not contralateral lumbar dorsal horn (LDH). Spinal hemisection at the 7th thoracic (T7) segment down-regulated bilateral EM2 expression, with a higher influence on the ipsilateral side of the LDH. Unilateral L3-6 dorsal roots rhizotomy combined with spinal transection but not with hemisection at T7 level completely obliterated EM2-IP fibers and terminals on the rhizotomized-side of the LDH. Disruption of bilateral (exposure to the primary afferent neurotoxin, capsaicin) primary sensory afferents combined with spinal hemisection at T7 decreased the EM2-IP density bilaterally but could obliterate it on neither side of the LDH. While in capsaicin plus transection rats, EM2 was depleted symmetrically and completely. In the colchicine treated rats, no EM2-IP neuronal cell bodies could be detected in the spinal gray matter. After injecting tetramethyl rhodamine dextran-amine (TMR) into the LDH, some of the TMR retrogradely labeled neurons in the nucleus tractus solitarii (NTS) showed EM2-immunoreactivities. The present results indicate that EM2-IP fibers and terminals in the spinal dorsal horn originate from the ipsilateral primary afferents and bilateral descending fibers from NTS.
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Affiliation(s)
- R Hui
- Department of Anatomy, Histology & Embryology, K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an 710032, PR China
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Topographical distributions of endomorphinergic pathways from nucleus tractus solitarii to periaqueductal gray in the rat. J Chem Neuroanat 2010; 39:166-74. [DOI: 10.1016/j.jchemneu.2009.11.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 10/20/2009] [Accepted: 11/11/2009] [Indexed: 01/09/2023]
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22
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Abstract
This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, 65-30 Kissena Blvd, Flushing, NY 11367, United States.
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23
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Niu L, Chen T, Wang YY, Li YQ. Neurochemical phenotypes of endomorphin-2-containing neurons in vagal nodose neurons of the adult rat. Neurochem Int 2009; 55:542-51. [PMID: 19463881 DOI: 10.1016/j.neuint.2009.05.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Revised: 04/23/2009] [Accepted: 05/11/2009] [Indexed: 12/12/2022]
Abstract
It has been shown that endomorphin-2-like immunoreactive (EM2-LI) neurons in dorsal root ganglion play important roles in regulating somatic information transmission. Although EM2-ergic neurons have been found in nodose ganglion (NG) which is mainly involved in transmitting visceral information into the nucleus tractus solitarii (NTS), the neurochemical phenotypes of EM2-ergic neurons have not yet been investigated. In the present study, immunofluorescent histochemical staining showed that 43.5% of the NG neurons contained EM2 and these neurons were small to medium in size. 15.2%, 27.8%, 74.4% and 25.2% of the EM2-LI NG neurons expressed substance P (SP), calcitonin gene-related peptide (CGRP), nitric oxide synthase (NOS) and vasoactive intestinal peptide (VIP), respectively. In addition, about 90.8% of EM2-LI NG neurons also contained mu-opioid receptor (MOR). EM2/MOR and EM2/SP double-labeled peripheral axons were observed in the vagal trunk. Anterograde tracing combined with immunofluorescent staining showed EM2/MOR and EM2/SP double-labeled vagal afferents in the NTS. EM2/MOR/SP and EM2/MOR/CGRP triple-labeled neurons and axons were observed in the NG. Importantly, at the ultrastructrual level, post-embedding electron microscopy revealed that EM2-LI and SP-LI gold particles coexisted in the same large dense-cored synaptic vesicles in the pre-synaptic button, while MOR-LI gold particles existed on both pre- and post-synaptic membranes in the NTS. These results suggest that EM2 in axon terminals of NG neurons might be involved in visceral information transmission and homeostatic control through modulating the release of other neurotransmitters (such as SP, CGRP, NO, VIP) via pre-synaptic MOR and through post-synaptic mechanisms in the NTS.
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Affiliation(s)
- Le Niu
- Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, P.R. China
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24
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Holden JE, Pizzi JA, Jeong Y. An NK1 receptor antagonist microinjected into the periaqueductal gray blocks lateral hypothalamic-induced antinociception in rats. Neurosci Lett 2009; 453:115-9. [PMID: 19356605 PMCID: PMC3463133 DOI: 10.1016/j.neulet.2009.01.083] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Revised: 01/23/2009] [Accepted: 01/31/2009] [Indexed: 12/22/2022]
Abstract
Substantial data are accumulating that implicate the lateral hypothalamus (LH) as part of the descending pain modulatory system. The LH modifies nociception in the spinal cord dorsal horn partly through connections with the periaqueductal gray (PAG), an area known to play a central role in brainstem modulation of nociception. Early work demonstrated a putative substance P connection between the LH and the PAG, but the connection is not fully defined. To determine whether LH-induced antinociception mediated by the PAG is neurokinin1 (NK1) receptor-dependent, we conducted behavioral experiments in which the cholinergic agonist carbachol (125 nmol) was microinjected into the LH of lightly anesthetized female Sprague-Dawley rats (250-350 g) and antinociception was obtained on the tail flick or foot withdrawal tests. Cobalt chloride (100 nM), which reversibly blocks synaptic activation, blocked LH-induced antinociception. In another set of experiments, the specific NK1 receptor antagonist L-703,606 (5 microg) was microinjected in the PAG following LH stimulation with carbachol abolished LH-induced antinociception as well. Microinjection of cobalt chloride or L-703,606 in the absence of LH stimulation had no effect. These behavioral experiments coupled with earlier work provide converging evidence to support the hypothesis that antinociception produced by activating neurons in the LH is mediated in part by the subsequent activation of neurons in the PAG by NK1 receptors.
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Affiliation(s)
- Janean E Holden
- Division of Acute, Critical and Long-Term Care Programs, School of Nursing, The University of Michigan, Ann Arbor, MI 48109-5482, USA.
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