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Irvine KA, Shi XY, Ferguson AR, Clark JD. Designer Receptor Exclusively Activated by Designer Drug (DREADD)-Mediated Activation of the Periaqueductal Gray Restores Nociceptive Descending Inhibition After Traumatic Brain Injury in Rats. J Neurotrauma 2024; 41:e1761-e1779. [PMID: 38588130 DOI: 10.1089/neu.2024.0031] [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] [Indexed: 04/10/2024] Open
Abstract
Traumatic brain injury (TBI) patients frequently experience chronic pain that can enhance their suffering and significantly impair rehabilitative efforts. Clinical studies suggest that damage to the periaqueductal gray matter (PAG) following TBI, a principal center involved in endogenous pain control, may underlie the development of chronic pain. We hypothesized that TBI would diminish the usual pain control functions of the PAG, but that directly stimulating this center using a chemogenetic approach would restore descending pain modulation. We used a well-characterized lateral fluid percussion model (1.3 ± 0.1 atm) of TBI in male rats (n = 271) and measured hindpaw mechanical nociceptive withdrawal thresholds using von Frey filaments. To investigate the role of the PAG in pain both before and after TBI, we activated the neurons of the PAG using a Designer Receptor Exclusively Activated by Designer Drug (DREADD) viral construct. Immunohistochemical analysis of brain tissue was used to assess the location and confirm the appropriate expression of the viral constructs in the PAG. Activation of the PAG DREADD using clozapine N-oxide (CNO) caused hindpaw analgesia that could be blocked using opioid receptor antagonist, naloxone, in uninjured but not TBI rats. Due to the importance of descending serotonergic signaling in modulating nociception, we ablated spinal serotonin signaling using 5,7-DHT. This treatment strongly reduced CNO-mediated anti-nociceptive effects in TBI but not uninjured rats. To define the serotonergic receptor(s) required for the CNO-stimulated effects in TBI rats, we administered 5-HT7 (SB-269970) and 5-HT1A (WAY-100635) receptor antagonists but observed no effects. The selective 5-HT2A receptor antagonist ketanserin, however, blocked CNO's effects in the DREADD expressing TBI but not DREADD expressing sham TBI animals. Blockade of alpha-1 adrenergic receptors with prazosin also had no effect after TBI. Descending pain control originating in the PAG is mediated through opioid receptors in uninjured rats. TBI, however, fundamentally alters the descending nociceptive control circuitry such that serotonergic influences predominate, and those are mediated by the 5-HT2A receptor. These results provide further evidence that the PAG is a key target for anti-nociception after TBI.
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Affiliation(s)
- Karen-Amanda Irvine
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California, USA
- Anesthesiology Service Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Xiao-You Shi
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California, USA
- Anesthesiology Service Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Adam R Ferguson
- Brain and Spinal Injury Center, Department of Neurosurgery, Weill Institute for Neurosciences, University of California San Francisco, San Francisco, California, USA
- San Francisco Veterans Affairs Healthcare System, San Francisco, California, USA
| | - J David Clark
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California, USA
- Anesthesiology Service Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
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Xu H, Wang Z, Wang Z, Zhou H, Guo J, Li W, Zhou Y. Cerebral Mechanism of Tuina on the Descending Pain Inhibitory System in Knee Osteoarthritis: Protocol for a Randomized Controlled Trial. JMIR Res Protoc 2024; 13:e52820. [PMID: 38238645 PMCID: PMC10897796 DOI: 10.2196/52820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Revised: 12/17/2023] [Accepted: 01/17/2024] [Indexed: 02/13/2024] Open
Abstract
BACKGROUND Knee osteoarthritis (KOA) is reputedly the most common musculoskeletal disease of the lower limbs and the main cause of pain and disability among older individuals. Pain is the most significant and widespread symptom of KOA. The descending pain inhibitory system has a cardinal role in normal pain consciousness, and its malfunction may be one of the pathophysiological mechanisms in KOA. Crucially, the rostral ventromedial medulla (RVM) and periaqueductal gray (PAG), as important components of the descending pain inhibitory system, directly modulate the activity of the spinal neurons involved in pain transmission. Tuina, a manual therapy, is effective and safe for reducing clinical symptoms of KOA; however, the mechanism that influences pain through the descending pain inhibitory system in KOA is unclear. OBJECTIVE This study aims to investigate the modulatory implications of Tuina on the RVM and PAG, which have critical roles in the descending pain inhibitory system in patients with KOA. METHODS This randomized controlled parallel trial will be conducted at the Tuina Clinic of the Third Affiliated Hospital of Henan University of Chinese Medicine (Zhengzhou, China). Patients with KOA will be randomly assigned (1:1) to 6 weeks of health education or Tuina. All patients in both groups will accept a resting-state functional magnetic resonance scan at the beginning and end of the experiment, and the resting-state functional connectivity and the voxel-based morphometry analysis will be performed to detect the RVM and PAG function and structure changes. The clinical outcome assessments will be (1) the pressure pain thresholds, (2) the Numerical Rating Scale, (3) the Hamilton Depression Scale (HAMD), and (4) the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Considering that this trial is a study of resting-state functional magnetic resonance imaging technology, resting-state functional connectivity and voxel-based morphometry are the primary outcomes, and clinical outcome assessments are secondary outcomes. Adverse events will be documented and assessed throughout. All main analyses will be carried out on the basis of the intention-to-treat principle. The outcome evaluators and data statisticians will be masked to the treatment group assignment to reduce the risk of bias. RESULTS This trial was approved by the ethics committee of the Third Affiliated Hospital of Henan University of Chinese Medicine. Enrollment began in December 2023, and the results of this trial are expected to be submitted for publication in May 2025. CONCLUSIONS This trial will identify a possible relationship between function and structure changes of RVM and PAG and the improvement of clinical variables, elucidating the effect of Tuina on the descending pain inhibitory system of patients with KOA. This trial will provide much-needed knowledge for Tuina for patients with KOA. TRIAL REGISTRATION Chinese Clinical Trial Registry ChiCTR2300070289; https://www.chictr.org.cn/showproj.html?proj=182570. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID) PRR1-10.2196/52820.
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Affiliation(s)
- Hui Xu
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Zheng Wang
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Zhen Wang
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Hang Zhou
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Juan Guo
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Wanyu Li
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
| | - Yunfeng Zhou
- School of Acupuncture-moxibustion and Tuina, Henan University of Chinese Medicine, Zhengzhou, China
- Tuina Department, The Third Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, China
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Nguyen E, Chiang MC, Nguyen C, Ross SE. Brainstem Modulation of Nociception by Periaqueductal Gray Neurons Expressing the μ-Opioid Receptor in Mice. Anesthesiology 2023; 139:462-475. [PMID: 37364291 PMCID: PMC10870981 DOI: 10.1097/aln.0000000000004668] [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] [Indexed: 06/28/2023]
Abstract
BACKGROUND Pharmacologic manipulations directed at the periaqueductal gray have demonstrated the importance of the μ-opioid receptor in modulating reflexive responses to nociception. The authors hypothesized that a supraspinal pathway centered on neurons in the periaqueductal gray containing the μ-opioid receptor could modulate nociceptive and itch behaviors. METHODS The study used anatomical, optogenetic, and chemogenetic approaches in male and female mice to manipulate μ-opioid receptor neurons in the periaqueductal gray. Behavioral assays including von Frey, Hargreaves, cold plantar, chloroquine-induced itch, hotplate, formalin-induced injury, capsaicin-induced injury, and open field tests were used. In separate experiments, naloxone was administered in a postsurgical model of latent sensitization. RESULTS Activation of μ-opioid receptor neurons in the periaqueductal gray increased jumping (least-squares mean difference of -3.30 s; 95% CI, -6.17 to -0.44; P = 0.023; n = 7 or 8 mice per group), reduced itch responses (least-squares mean difference of 70 scratching bouts; 95% CI, 35 to 105; P < 0.001; n = 8 mice), and elicited modestly antinociceptive effects (least-squares mean difference of -0.7 g on mechanical and -10.24 s on thermal testing; 95% CI, -1.3 to -0.2 and 95% CI, -13.77 to -6.70, and P = 0.005 and P < 0.001, respectively; n = 8 mice). Last, the study uncovered the role of the periaqueductal gray in suppressing hyperalgesia after a postsurgical state of latent sensitization (least-squares mean difference comparing saline and naloxone of -12 jumps; 95% CI, -17 to -7; P < 0.001 for controls; and -2 jumps; 95% CI, -7 to 4; P = 0.706 after optogenetic stimulation; n = 7 to 9 mice per group). CONCLUSIONS μ-Opioid receptor neurons in the periaqueductal gray modulate distinct nocifensive behaviors: their activation reduced responses to mechanical and thermal testing, and attenuated scratching behaviors, but facilitated escape responses. The findings emphasize the role of the periaqueductal gray in the behavioral expression of nociception using reflexive and noxious paradigms. EDITOR’S PERSPECTIVE
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Affiliation(s)
- Eileen Nguyen
- University of Pittsburgh School of Medicine, Department of Anesthesiology, Pittsburgh, PA, USA
- University of Pittsburgh, Department of Neurobiology, Pittsburgh, PA, USA
- University of California, Los Angeles, Department of Anesthesiology, Los Angeles, CA, USA
| | - Michael C. Chiang
- University of Pittsburgh School of Medicine, Department of Anesthesiology, Pittsburgh, PA, USA
- University of Pittsburgh, Department of Neurobiology, Pittsburgh, PA, USA
| | - Catherine Nguyen
- University of Pittsburgh School of Medicine, Department of Anesthesiology, Pittsburgh, PA, USA
- University of Pittsburgh, Department of Neurobiology, Pittsburgh, PA, USA
| | - Sarah E. Ross
- University of Pittsburgh School of Medicine, Department of Anesthesiology, Pittsburgh, PA, USA
- University of Pittsburgh, Department of Neurobiology, Pittsburgh, PA, USA
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Nguyen E, Grajales-Reyes JG, Gereau RW, Ross SE. Cell type-specific dissection of sensory pathways involved in descending modulation. Trends Neurosci 2023; 46:539-550. [PMID: 37164868 PMCID: PMC10836406 DOI: 10.1016/j.tins.2023.04.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 03/22/2023] [Accepted: 04/07/2023] [Indexed: 05/12/2023]
Abstract
Decades of research have suggested that stimulation of supraspinal structures, such as the periaqueductal gray (PAG) and rostral ventromedial medulla (RVM), inhibits nocifensive responses to noxious stimulation through a process known as descending modulation. Electrical stimulation and pharmacologic manipulations of the PAG and RVM identified transmitters and neuronal firing patterns that represented distinct cell types. Advances in mouse genetics, in vivo imaging, and circuit tracing methods, in addition to chemogenetic and optogenetic approaches, allowed the characterization of the cells and circuits involved in descending modulation in further detail. Recent work has revealed the importance of PAG and RVM neuronal cell types in the descending modulation of pruriceptive as well as nociceptive behaviors, underscoring their roles in coordinating complex behavioral responses to sensory input. This review summarizes how new technical advances that enable cell type-specific manipulation and recording of neuronal activity have supported, as well as expanded, long-standing views on descending modulation.
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Affiliation(s)
- Eileen Nguyen
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Jose G Grajales-Reyes
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine in St Louis, St Louis, MO 63110, USA
| | - Robert W Gereau
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine in St Louis, St Louis, MO 63110, USA
| | - Sarah E Ross
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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Alam MJ, Chen JDZ. Electrophysiology as a Tool to Decipher the Network Mechanism of Visceral Pain in Functional Gastrointestinal Disorders. Diagnostics (Basel) 2023; 13:627. [PMID: 36832115 PMCID: PMC9955347 DOI: 10.3390/diagnostics13040627] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 01/27/2023] [Accepted: 02/07/2023] [Indexed: 02/11/2023] Open
Abstract
Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient's life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs.
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Affiliation(s)
- Md Jahangir Alam
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jiande D. Z. Chen
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA
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Manning CE, Fritz M, Kauer JA. Function of Excitatory Periaqueductal Gray Synapses in the Ventral Tegmental Area following Inflammatory Injury. eNeuro 2022; 9:ENEURO.0324-22.2022. [PMID: 36635253 PMCID: PMC9797208 DOI: 10.1523/eneuro.0324-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Revised: 10/26/2022] [Accepted: 11/28/2022] [Indexed: 12/12/2022] Open
Abstract
Manipulating the activity of ventral tegmental area (VTA) dopamine (DA) neurons can drive nocifensive reflexes, and their firing rates are reduced following noxious stimuli. However, the pain-relevant inputs to the VTA remain incompletely understood. In this study, we used male and female mice in combination with identified dopamine and GABA neurons in the VTA that receive excitatory inputs from the periaqueductal gray (PAG), a nexus of ascending pain information. We tested whether PAG-VTA synapses undergo functional plasticity in response to a pain model using optical stimulation in conjunction with slice electrophysiology. We found that acute carrageenan inflammation does not significantly affect the strength of excitatory PAG synapses onto VTA DA neurons. However, at the PAG synapses on VTA GABA neurons, the subunit composition of NMDA receptors is altered; the complement of NR2D subunits at synaptic sites appears to be lost. Thus, our data support a model in which injury initially alters synapses on VTA GABA neurons. Over time, these alterations may increase tonic inhibition of VTA DA neurons leading to their reduced firing.
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Affiliation(s)
- Claire Elena Manning
- Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, California 94305-5101
| | - Michael Fritz
- Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, California 94305-5101
| | - Julie Ann Kauer
- Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, California 94305-5101
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Mills EP, Keay KA, Henderson LA. Brainstem Pain-Modulation Circuitry and Its Plasticity in Neuropathic Pain: Insights From Human Brain Imaging Investigations. FRONTIERS IN PAIN RESEARCH 2021; 2:705345. [PMID: 35295481 PMCID: PMC8915745 DOI: 10.3389/fpain.2021.705345] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 06/23/2021] [Indexed: 11/17/2022] Open
Abstract
Acute pain serves as a protective mechanism that alerts us to potential tissue damage and drives a behavioural response that removes us from danger. The neural circuitry critical for mounting this behavioural response is situated within the brainstem and is also crucial for producing analgesic and hyperalgesic responses. In particular, the periaqueductal grey, rostral ventromedial medulla, locus coeruleus and subnucleus reticularis dorsalis are important structures that directly or indirectly modulate nociceptive transmission at the primary nociceptive synapse. Substantial evidence from experimental animal studies suggests that plasticity within this system contributes to the initiation and/or maintenance of chronic neuropathic pain, and may even predispose individuals to developing chronic pain. Indeed, overwhelming evidence indicates that plasticity within this circuitry favours pro-nociception at the primary synapse in neuropathic pain conditions, a process that ultimately contributes to a hyperalgesic state. Although experimental animal investigations have been crucial in our understanding of the anatomy and function of the brainstem pain-modulation circuitry, it is vital to understand this system in acute and chronic pain states in humans so that more effective treatments can be developed. Recent functional MRI studies have identified a key role of this system during various analgesic and hyperalgesic responses including placebo analgesia, offset analgesia, attentional analgesia, conditioned pain modulation, central sensitisation and temporal summation. Moreover, recent MRI investigations have begun to explore brainstem pain-modulation circuitry plasticity in chronic neuropathic pain conditions and have identified altered grey matter volumes and functioning throughout the circuitry. Considering the findings from animal investigations, it is likely that these changes reflect a shift towards pro-nociception that ultimately contributes to the maintenance of neuropathic pain. The purpose of this review is to provide an overview of the human brain imaging investigations that have improved our understanding of the pain-modulation system in acute pain states and in neuropathic conditions. Our interpretation of the findings from these studies is often guided by the existing body of experimental animal literature, in addition to evidence from psychophysical investigations. Overall, understanding the plasticity of this system in human neuropathic pain conditions alongside the existing experimental animal literature will ultimately improve treatment options.
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Guo Y, Wang D, Yang X, Jiang P, Xu J, Zhang G. Effects of different sufentanil target concentrations on the MAC BAR of sevoflurane in patients with carbon dioxide pneumoperitoneum stimulus. BMC Anesthesiol 2020; 20:239. [PMID: 32957929 PMCID: PMC7504852 DOI: 10.1186/s12871-020-01160-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Accepted: 09/15/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND This study aims to observe the effects of different target controlled plasma sufentanil concentrations on the minimum alveolar concentration (MAC) of sevoflurane for blocking adrenergic response (BAR) in patients undergoing laparoscopic cholecystectomy with carbon dioxide pneumoperitoneum stimulation. METHODS Eighty-five patients undergoing laparoscopic cholecystectomy, aged 30-65 years, with American Society of Anesthesiologists physical status I-II, were enrolled in this study. All the patients were randomly divided into 5 groups (S0, S1, S2, S3, S4) with different sufentanil plasma target concentration (0.0, 0.1, 0.3, 0.5, 0.7 ng ml- 1). Anesthesia was induced by inhalation of 8% sevoflurane in 100% oxygen, and 0.6 mg kg- 1 of rocuronium was intravenously injected to facilitate the insertion of a laryngeal mask airway. The end-tidal sevoflurane concentration and sufentanil plasma target concentration were adjusted according to respective preset value in each group. The hemodynamic response to pneumoperitoneum stimulus was observed after the end-tidal sevoflurane concentration had been maintained stable at least for 15 min. The MACBAR of sevoflurane was measured by a sequential method. Meanwhile, epinephrine (E) and norepinephrine (NE) concentrations in the blood were also determined before and after pneumoperitoneum stimulus in each group. RESULTS When the method of independent paired reversals was used, the MACBAR of sevoflurane in groups S0, S1, S2, S3, S4 was 5.333% (confidence interval [CI] 95%: 5.197-5.469%), 4.533% (95% CI: 4.451-4.616%), 2.861% (95% CI: 2.752-2.981%), 2.233% (95% CI: 2.142-2.324%) and 2.139% (95% CI: 2.057-2.219%), respectively. Meanwhile, when the isotonic regression analysis was used, the MACBAR of sevoflurane in groups S0, S1, S2, S3, S4 was 5.329% (95% CI: 5.321-5.343%), 4.557% (95% CI: 4.552-4.568%), 2.900% (95% CI: 2.894-2.911%), 2.216% (95% CI: 2.173-2.223%) and 2.171% (95% CI: 2.165-2.183%), respectively. The MACBAR was not significantly different between groups S3 and S4 when using 0.5 and 0.7 ng ml- 1 of sufentanil plasma target concentrations. No significant difference was found in the change of E or NE concentration between before and after pneumoperitoneum stimulation in each group. CONCLUSIONS The MACBAR of sevoflurane can be decreased with increasing sufentanil plasma target concentrations. A ceiling effect of the decrease occurred at a sufentanil plasma target concentration of 0.5 ng ml- 1. When the sympathetic adrenergic response was inhibited in half of the patients to pneumoperitoneum stimulation in each group, the changes of E and NE concentrations showed no significant differences. TRIAL REGISTRATION The study was registered at http://www.chictr.org.cn ( ChiCTR1800015819 , 23, April, 2018).
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Affiliation(s)
- Yanxia Guo
- Department of Anaesthesiology, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China
| | - Dan Wang
- Department of Anaesthesiology, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China
| | - Xiaolin Yang
- Department of Anaesthesiology, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China.
| | - Pingping Jiang
- Department of Anaesthesiology, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China
| | - Juan Xu
- Department of Anaesthesiology, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China
| | - Guoyuan Zhang
- Department of Clinical Laboratory, Affiliated Hospital of North Sichuan Medical College, Nanchong, 637000, Sichuan, China
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St Laurent R, Martinez Damonte V, Tsuda AC, Kauer JA. Periaqueductal Gray and Rostromedial Tegmental Inhibitory Afferents to VTA Have Distinct Synaptic Plasticity and Opiate Sensitivity. Neuron 2020; 106:624-636.e4. [PMID: 32191871 DOI: 10.1016/j.neuron.2020.02.029] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 10/01/2019] [Accepted: 02/25/2020] [Indexed: 12/16/2022]
Abstract
The ventral tegmental area (VTA) is a major target of addictive drugs and receives multiple GABAergic projections originating outside the VTA. We describe differences in synaptic plasticity and behavior when optogenetically driving two opiate-sensitive GABAergic inputs to the VTA, the rostromedial tegmental nucleus (RMTg), and the periaqueductal gray (PAG). Activation of GABAergic RMTg terminals in the VTA in vivo is aversive, and low-frequency stimulation induces long-term depression in vitro. Low-frequency stimulation of PAG afferents in vitro unexpectedly causes long-term potentiation. Opioid receptor activation profoundly depresses PAG and RMTg inhibitory synapses but prevents synaptic plasticity only at PAG synapses. Activation of the GABAergic PAG terminals in the VTA promotes immobility, and optogenetically-driven immobility is blocked by morphine. Our data reveal the PAG as a source of highly opioid-sensitive GABAergic afferents and support the idea that different GABAergic pathways to the VTA control distinct behaviors.
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Affiliation(s)
- Robyn St Laurent
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94035, USA
| | - Valentina Martinez Damonte
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94035, USA
| | - Ayumi C Tsuda
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, RI 02912, USA
| | - Julie A Kauer
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94035, USA.
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μ-Opioid receptors in primary sensory neurons are involved in supraspinal opioid analgesia. Brain Res 2019; 1729:146623. [PMID: 31881186 DOI: 10.1016/j.brainres.2019.146623] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 11/20/2019] [Accepted: 12/23/2019] [Indexed: 11/21/2022]
Abstract
Both inhibiting ascending nociceptive transmission and activating descending inhibition are involved in the opioid analgesic effect. The spinal dorsal horn is a critical site for modulating nociceptive transmission by descending pathways elicited by opioids in the brain. μ-Opioid receptors (MORs, encoded by Oprm1) are highly expressed in primary sensory neurons and their central terminals in the spinal cord. In the present study, we tested the hypothesis that MORs expressed in primary sensory neurons contribute to the descending inhibition and supraspinal analgesic effect induced by centrally administered opioids. We generated Oprm1 conditional knockout (Oprm1-cKO) mice by crossing AdvillinCre/+ mice with Oprm1flox/flox mice. Immunocytochemical labeling in Oprm1-cKO mice showed that MORs are completely ablated from primary sensory neurons and are profoundly reduced in the superficial spinal dorsal horn. Intracerebroventricular injection of morphine or fentanyl produced a potent analgesic effect in wild-type mice, but such an effect was significantly attenuated in Oprm1-cKO mice. Furthermore, the analgesic effect produced by morphine or fentanyl microinjected into the periaqueductal gray was significantly greater in wild-type mice than in Oprm1-cKO mice. Blocking MORs at the spinal cord level diminished the analgesic effect of morphine and fentanyl microinjected into the periaqueductal gray in both groups of mice. Our findings indicate that MORs expressed at primary afferent terminals in the spinal cord contribute to the supraspinal opioid analgesic effect. These presynaptic MORs in the spinal cord may serve as an interface between ascending inhibition and descending modulation that are involved in opioid analgesia.
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Zhang Y, Qu M, Yi X, Zhuo P, Tang J, Chen X, Zhou G, Hu P, Qiu T, Xing W, Mao Y, Chen BT, Wu J, Zhang Y, Liao W. Sensorimotor and pain-related alterations of the gray matter and white matter in Type 2 diabetic patients with peripheral neuropathy. Hum Brain Mapp 2019; 41:710-725. [PMID: 31663232 PMCID: PMC7268085 DOI: 10.1002/hbm.24834] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 08/18/2019] [Accepted: 10/09/2019] [Indexed: 12/13/2022] Open
Abstract
Although diabetic peripheral neuropathy (DPN) has long been considered a disease of the peripheral nervous system, recent neuroimaging studies have shown that alterations in the central nervous system may play a crucial role in its pathogenesis. Here, we used surface‐based morphometry (SBM) and tract‐based spatial statistics (TBSS) to investigate gray matter (GM) and white matter (WM) differences between patients with DPN (n = 67, 44 painless and 23 painful) and healthy controls (HCs; n = 88). Compared with HCs, patients with DPN exhibited GM abnormalities in the pre‐ and postcentral gyrus and in several deep GM nuclei (caudate, putamen, medial pallidum, thalamus, and ventral nuclear). They also exhibited altered WM tracts (corticospinal tract, spinothalamic tract, and thalamocortical projecting fibers). These findings suggest impaired motor and somatosensory pathways in DPN. Further, patients with DPN (particularly painful DPN) exhibited morphological differences in the cingulate, insula, prefrontal cortex, and thalamus, as well as impaired WM integrity in periaqueductal WM and internal and external capsules. This suggests pain‐perception/modulation pathways are altered in painful DPN. Intermodal correlation analyses found that the morphological indices of the brain regions identified by the SBM analysis were significantly correlated with the fractional anisotropy of brain regions identified by the TBSS analysis, suggesting that the GM and WM alterations were tightly coupled. Overall, our study showed sensorimotor and pain‐related GM and WM alterations in patients with DPN, which might be involved in the development of DPN.
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Affiliation(s)
- Youming Zhang
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Minli Qu
- Department of Endocrinology, Xiangya Hospital, Central South University, Changsha, China
| | - Xiaoping Yi
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China.,Postdoctoral Research Workstation of Pathology and Pathophysiology, Basic Medical Sciences, Xiangya Hospital, Central South University, Changsha, China
| | - Pei Zhuo
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Jingyi Tang
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Xin Chen
- Department of Endocrinology, Xiangya Hospital, Central South University, Changsha, China
| | - Gaofeng Zhou
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Ping Hu
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Ting Qiu
- Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, China
| | - Wu Xing
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Yitao Mao
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China
| | - Bihong T Chen
- Department of Diagnostic Radiology, City of Hope National Medical Center, Duarte, California
| | - Jing Wu
- Department of Endocrinology, Xiangya Hospital, Central South University, Changsha, China
| | - Yuanchao Zhang
- Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, China
| | - Weihua Liao
- Department of Radiology, Xiangya Hospital, Central South University, Changsha, China.,National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
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12
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Nasser SA, Afify EA. Sex differences in pain and opioid mediated antinociception: Modulatory role of gonadal hormones. Life Sci 2019; 237:116926. [PMID: 31614148 DOI: 10.1016/j.lfs.2019.116926] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 09/18/2019] [Accepted: 09/30/2019] [Indexed: 12/14/2022]
Abstract
Sex-related differences in pain and opioids has been the focus of many researches. It is demonstrated that women experience greater clinical pain, lower pain threshold and tolerance, more sensitivity and distress to experimentally induced pain compared to men. Sex differences in response to opioid treatment revealed inconsistent results. However, the etiology of these disparities is not fully elucidated. It is, therefore, conceivable now that this literature merits to be revisited comprehensively. Possible multifaceted factors seem to be associated. These include neuroanatomical, hormonal, neuroimmunological, psychological, social and cultural aspects and comorbidities. This review aims at providing an overview of the substantial literature documenting the sex differences in pain and analgesic response to opioids from animal and human studies within the context of the modulatory effects of the aforementioned factors. A detailed and critical discussion of the cellular and molecular signaling pathways underlying the modulatory actions of gonadal hormones in the sexual dimorphism in pain processing and opioid analgesia is extensively presented. It is indicated that sexual dimorphic activation of certain brain regions contributes to differential pain sensitivity between females and males. Plausible crosstalk between sex hormones and neuroimmunological signaling pertinent to toll-like and purinergic receptors is uncovered as causal cues underlying sexually dimorphic pain and opioid analgesia. Conceivably, a thorough understanding of these factors may aid in sex-related advancement in pain therapeutic management.
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Affiliation(s)
- Suzanne A Nasser
- Department of Pharmacology and Therapeutics, Faculty of Pharmacy, Beirut Arab University, Beirut, Lebanon
| | - Elham A Afify
- Department of Pharmacology and Toxicology, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt.
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13
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Eidson LN, Murphy AZ. Inflammatory mediators of opioid tolerance: Implications for dependency and addiction. Peptides 2019; 115:51-58. [PMID: 30890355 PMCID: PMC6863079 DOI: 10.1016/j.peptides.2019.01.003] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 01/24/2019] [Accepted: 01/30/2019] [Indexed: 12/27/2022]
Abstract
Each year, over 50 million Americans suffer from persistent pain, including debilitating headaches, joint pain, and severe back pain. Although morphine is amongst the most effective analgesics available for the management of severe pain, prolonged morphine treatment results in decreased analgesic efficacy (i.e., tolerance). Despite significant headway in the field, the mechanisms underlying the development of morphine tolerance are not well understood. The midbrain ventrolateral periaqueductal gray (vlPAG) is a primary neural substrate for the analgesic effects of morphine, as well as for the development of morphine tolerance. A growing body of literature indicates that activated glia (i.e., microglia and astrocytes) facilitate pain transmission and oppose morphine analgesia, making these cells important potential targets in the treatment of chronic pain. Morphine affects glia by binding to the innate immune receptor toll-like receptor 4 (TLR4), leading to the release of proinflammatory cytokines and opposition of morphine analgesia. Despite the established role of the vlPAG as an integral locus for the development of morphine tolerance, most studies have examined the role of glia activation within the spinal cord. Additionally, the role of TLR4 in the development of tolerance has not been elucidated. This review attempts to summarize what is known regarding the role of vlPAG glia and TLR4 in the development of morphine tolerance. These data, together, provide information about the mechanism by which central nervous system glia regulate morphine tolerance, and identify a potential therapeutic target for the enhancement of analgesic efficacy in the clinical treatment of chronic pain.
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Affiliation(s)
- Lori N Eidson
- Department of Physiology, Emory University, Atlanta, GA, 30322, United States
| | - Anne Z Murphy
- Neuroscience Institute, Georgia State University, Atlanta, GA, 30308, United States.
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Yin-and-yang bifurcation of opioidergic circuits for descending analgesia at the midbrain of the mouse. Proc Natl Acad Sci U S A 2018; 115:11078-11083. [PMID: 30297409 DOI: 10.1073/pnas.1806082115] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the descending analgesia pathway, opioids are known to disinhibit the projections from the periaqueductal gray (PAG) to the rostral ventromedial medulla (RVM), leading to suppression of pain signals at the spinal cord level. The locus coeruleus (LC) has been proposed to engage in the descending pathway through noradrenergic inputs to the spinal cord. Nevertheless, how the LC is integrated in the descending analgesia circuit has remained unknown. Here, we show that the opioidergic analgesia pathway is bifurcated in structure and function at the PAG. A knockout as well as a PAG-specific knockdown of phospholipase C β4 (PLCβ4), a signaling molecule for G protein-coupled receptors, enhanced swim stress-induced and morphine-induced analgesia in mice. Immunostaining after simultaneous retrograde labeling from the RVM and the LC revealed two mutually exclusive neuronal populations at the PAG, each projecting either to the LC or the RVM, with PLCβ4 expression only in the PAG-LC projecting cells that provide a direct synaptic input to LC-spinal cord (SC) projection neurons. The PAG-LC projection neurons in wild-type mice turned quiescent in response to opiates, but remained active in the PLCβ4 mutant, suggesting a possibility that an increased adrenergic function induced by the persistent PAG-LC activity underlies the enhanced opioid analgesia in the mutant. Indeed, the enhanced analgesia in the mutant was reversed by blocking α2-noradrenergic receptors. These findings indicate that opioids suppress descending analgesia through the PAG-LC pathway, while enhancing it through the PAG-RVM pathway, i.e., two distinct pathways with opposing effects on opioid analgesia. These results point to a therapeutic target in pain control.
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Sasaki K, Hall FS, Uhl GR, Sora I. Larger Numbers of Glial and Neuronal Cells in the Periaqueductal Gray Matter of μ-Opioid Receptor Knockout Mice. Front Psychiatry 2018; 9:441. [PMID: 30283366 PMCID: PMC6156378 DOI: 10.3389/fpsyt.2018.00441] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 08/28/2018] [Indexed: 12/23/2022] Open
Abstract
Background: μ-opioid receptor knockout (MOP-KO) mice display baseline hyperalgesia. We have recently identified changes in tissue volume in the periaqueductal gray matter (PAG) using magnetic resonance imaging voxel-based morphometry. Changes in the structure and connectivity of this region might account for some behavior phenotypes in MOP-KO mice, including hyperalgesia. Methods: Adult male MOP-KO and wild-type (WT) mice were studied. Immunohistochemistry was performed to detect microglia, astrocytes, and neurons in the PAG using specific markers: ionized calcium-binding adaptor molecule 1 (Iba-1) for microglia, glial fibrillary acidic protein (GFAP) for astrocytes, and the neuronal nuclei antigen (NeuN; product of the Rbfox3 gene) for neurons, respectively. Cell counting was performed in the four parallel longitudinal columns of the PAG (dorsomedial, dorsolateral, lateral, and ventrolateral) at three different locations from bregma (-3.5, -4.0, and -4.5 mm). Results: The quantitative analysis showed larger numbers of well-distributed Iba1-IR cells (microglia), NeuN-IR cells (neurons), and GFAP-IR areas (astrocytes) at all the anatomically distinct regions examined, namely, the dorsomedial (DM) PAG, dorsolateral (DL) PAG, lateral (L) PAG, and ventrolateral (VL) PAG, in MOP-KO mice than in control mice. Conclusions: The cellular changes in the PAG identified in this paper may underlie aspects of the behavioral alterations produced by MOP receptor deletion, and suggest that alterations in the cellular structure of the PAG may contribute to hyperalgesic states.
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Affiliation(s)
- Kazumasu Sasaki
- Department of Preclinical Evaluation, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan
| | - Frank Scott Hall
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, The University of Toledo, Toledo, OH, United States
| | - George R Uhl
- Raymond G Murphy VA Medical Center, Albuquerque, NM, United States
| | - Ichiro Sora
- Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan
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Schafer SM, Geuter S, Wager TD. Mechanisms of placebo analgesia: A dual-process model informed by insights from cross-species comparisons. Prog Neurobiol 2018; 160:101-122. [PMID: 29108801 PMCID: PMC5747994 DOI: 10.1016/j.pneurobio.2017.10.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 10/24/2017] [Accepted: 10/28/2017] [Indexed: 12/19/2022]
Abstract
Placebo treatments are pharmacologically inert, but are known to alleviate symptoms across a variety of clinical conditions. Associative learning and cognitive expectations both play important roles in placebo responses, however we are just beginning to understand how interactions between these processes lead to powerful effects. Here, we review the psychological principles underlying placebo effects and our current understanding of their brain bases, focusing on studies demonstrating both the importance of cognitive expectations and those that demonstrate expectancy-independent associative learning. To account for both forms of placebo analgesia, we propose a dual-process model in which flexible, contextually driven cognitive schemas and attributions guide associative learning processes that produce stable, long-term placebo effects. According to this model, the placebo-induction paradigms with the most powerful effects are those that combine reinforcement (e.g., the experience of reduced pain after placebo treatment) with suggestions and context cues that disambiguate learning by attributing perceived benefit to the placebo. Using this model as a conceptual scaffold, we review and compare neurobiological systems identified in both human studies of placebo analgesia and behavioral pain modulation in rodents. We identify substantial overlap between the circuits involved in human placebo analgesia and those that mediate multiple forms of context-based modulation of pain behavior in rodents, including forebrain-brainstem pathways and opioid and cannabinoid systems in particular. This overlap suggests that placebo effects are part of a set of adaptive mechanisms for shaping nociceptive signaling based on its information value and anticipated optimal response in a given behavioral context.
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Affiliation(s)
- Scott M Schafer
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA
| | - Stephan Geuter
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA; Institute of Cognitive Science, University of Colorado Boulder, 344 UCB, Boulder, CO 80309, USA; Department of Biostatistics, Johns Hopkins University, 615 N Wolfe St, Baltimore, MD 21205, USA
| | - Tor D Wager
- Department of Psychology and Neuroscience, University of Colorado, 345 UCB, Boulder, CO 80309, USA; Institute of Cognitive Science, University of Colorado Boulder, 344 UCB, Boulder, CO 80309, USA.
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El Bitar N, Pollin B, Karroum E, Pincedé I, Le Bars D. Entanglement between thermoregulation and nociception in the rat: the case of morphine. J Neurophysiol 2016; 116:2473-2496. [PMID: 27605533 PMCID: PMC5133307 DOI: 10.1152/jn.00482.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 09/03/2016] [Indexed: 11/22/2022] Open
Abstract
In thermoneutral conditions, rats display cyclic variations of the vasomotion of the tail and paws, the most widely used target organs in current acute or chronic animal models of pain. Systemic morphine elicits their vasoconstriction followed by hyperthermia in a naloxone-reversible and dose-dependent fashion. The dose-response curves were steep with ED50 in the 0.5-1 mg/kg range. Given the pivotal functional role of the rostral ventromedial medulla (RVM) in nociception and the rostral medullary raphe (rMR) in thermoregulation, two largely overlapping brain regions, the RVM/rMR was blocked by muscimol: it suppressed the effects of morphine. "On-" and "off-" neurons recorded in the RVM/rMR are activated and inhibited by thermal nociceptive stimuli, respectively. They are also implicated in regulating the cyclic variations of the vasomotion of the tail and paws seen in thermoneutral conditions. Morphine elicited abrupt inhibition and activation of the firing of on- and off-cells recorded in the RVM/rMR. By using a model that takes into account the power of the radiant heat source, initial skin temperature, core body temperature, and peripheral nerve conduction distance, one can argue that the morphine-induced increase of reaction time is mainly related to the morphine-induced vasoconstriction. This statement was confirmed by analyzing in psychophysical terms the tail-flick response to random variations of noxious radiant heat. Although the increase of a reaction time to radiant heat is generally interpreted in terms of analgesia, the present data question the validity of using such an approach to build a pain index.
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Affiliation(s)
- Nabil El Bitar
- Sorbonne Universités, Université Pierre et Marie Curie, Faculté de Médecine, Paris, France; and
- Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France
| | - Bernard Pollin
- Sorbonne Universités, Université Pierre et Marie Curie, Faculté de Médecine, Paris, France; and
- Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France
| | - Elias Karroum
- Sorbonne Universités, Université Pierre et Marie Curie, Faculté de Médecine, Paris, France; and
- Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France
| | - Ivanne Pincedé
- Sorbonne Universités, Université Pierre et Marie Curie, Faculté de Médecine, Paris, France; and
- Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France
| | - Daniel Le Bars
- Sorbonne Universités, Université Pierre et Marie Curie, Faculté de Médecine, Paris, France; and
- Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France
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Esmaeili M, Reisi Z, Ezzatpanah S, Haghparast A. Functional interaction between orexin-1 and CB1 receptors in the periaqueductal gray matter during antinociception induced by chemical stimulation of the lateral hypothalamus in rats. Eur J Pain 2016; 20:1753-1762. [DOI: 10.1002/ejp.899] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/13/2016] [Indexed: 11/11/2022]
Affiliation(s)
- M.H. Esmaeili
- Cellular and Molecular Research Center & Department of Physiology; Qazvin University of Medical Sciences; Qazvin Iran
| | - Z. Reisi
- Neuroscience Research Center; School of Medicine; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - S. Ezzatpanah
- Neuroscience Research Center; School of Medicine; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - A. Haghparast
- Neuroscience Research Center; School of Medicine; Shahid Beheshti University of Medical Sciences; Tehran Iran
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19
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Abstract
UNLABELLED The nociceptin/orphanin FQ (NOP) receptor, the fourth member of the opioid receptor family, is involved in many processes common to the opioid receptors including pain and drug abuse. To better characterize receptor location and trafficking, knock-in mice were created by inserting the gene encoding enhanced green fluorescent protein (eGFP) into the NOP receptor gene (Oprl1) and producing mice expressing a functional NOP-eGFP C-terminal fusion in place of the native NOP receptor. The NOP-eGFP receptor was present in brain of homozygous knock-in animals in concentrations somewhat higher than in wild-type mice and was functional when tested for stimulation of [(35)S]GTPγS binding in vitro and in patch-clamp electrophysiology in dorsal root ganglia (DRG) neurons and hippocampal slices. Inhibition of morphine analgesia was equivalent when tested in knock-in and wild-type mice. Imaging revealed detailed neuroanatomy in brain, spinal cord, and DRG and was generally consistent with in vitro autoradiographic imaging of receptor location. Multicolor immunohistochemistry identified cells coexpressing various spinal cord and DRG cellular markers, as well as coexpression with μ-opioid receptors in DRG and brain regions. Both in tissue slices and primary cultures, the NOP-eGFP receptors appear throughout the cell body and in processes. These knock-in mice have NOP receptors that function both in vitro and in vivo and appear to be an exceptional tool to study receptor neuroanatomy and correlate with NOP receptor function. SIGNIFICANCE STATEMENT The NOP receptor, the fourth member of the opioid receptor family, is involved in pain, drug abuse, and a number of other CNS processes. The regional and cellular distribution has been difficult to determine due to lack of validated antibodies for immunohistochemical analysis. To provide a new tool for the investigation of receptor localization, we have produced knock-in mice with a fluorescent-tagged NOP receptor in place of the native NOP receptor. These knock-in mice have NOP receptors that function both in vitro and in vivo and have provided a detailed characterization of NOP receptors in brain, spinal cord, and DRG neurons. They appear to be an exceptional tool to study receptor neuroanatomy and correlate with NOP receptor function.
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20
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Spinal and supraspinal N-methyl-d-aspartate and melanocortin-1 receptors contribute to a qualitative sex difference in morphine-induced hyperalgesia. Physiol Behav 2015; 147:364-72. [DOI: 10.1016/j.physbeh.2015.05.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 05/01/2015] [Accepted: 05/04/2015] [Indexed: 12/27/2022]
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Hu SSJ, Ho YC, Chiou LC. No more pain upon Gq-protein-coupled receptor activation: role of endocannabinoids. Eur J Neurosci 2014; 39:467-84. [PMID: 24494686 DOI: 10.1111/ejn.12475] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Revised: 12/02/2013] [Accepted: 12/05/2013] [Indexed: 01/24/2023]
Abstract
Marijuana has been used to relieve pain for centuries. The analgesic mechanism of its constituents, the cannabinoids, was only revealed after the discovery of cannabinoid receptors (CB1 and CB2) two decades ago. The subsequent identification of the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), and their biosynthetic and degradation enzymes discloses the therapeutic potential of compounds targeting the endocannabinoid system for pain control. Inhibitors of the anandamide and 2-AG degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase, respectively, may be superior to direct cannabinoid receptor ligands as endocannabinoids are synthesized on demand and rapidly degraded, focusing action at generating sites. Recently, a promising strategy for pain relief was revealed in the periaqueductal gray (PAG). It is initiated by Gq-protein-coupled receptor (Gq PCR) activation of the phospholipase C-diacylglycerol lipase enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. Here, we introduce the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, particularly in the PAG. We also review recent studies disclosing the Gq PCR-phospholipase C-diacylglycerol lipase-2-AG retrograde disinhibition mechanism in the PAG, induced by activating several Gq PCRs, including metabotropic glutamatergic (type 5 metabotropic glutamate receptor), muscarinic acetylcholine (M1/M3), and orexin 1 receptors. Disinhibition mediated by type 5 metabotropic glutamate receptor can be initiated by glutamate transporter inhibitors or indirectly by substance P, neurotensin, cholecystokinin and capsaicin. Finally, the putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is discussed.
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Affiliation(s)
- Sherry Shu-Jung Hu
- Department of Psychology, National Cheng Kung University, Tainan, Taiwan
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22
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Sasaki K, Sumiyoshi A, Nonaka H, Kasahara Y, Ikeda K, Hall FS, Uhl GR, Watanabe M, Kawashima R, Sora I. Specific regions display altered grey matter volume in μ-opioid receptor knockout mice: MRI voxel-based morphometry. Br J Pharmacol 2014; 172:654-67. [PMID: 24913308 DOI: 10.1111/bph.12807] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 05/09/2014] [Accepted: 05/24/2014] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND AND PURPOSE μ Opioid receptor knockout (MOP-KO) mice display several behavioural differences from wild-type (WT) littermates including differential responses to nociceptive stimuli. Brain structural changes have been tied to behavioural alterations noted in transgenic mice with targeting of different genes. Hence, we assess the brain structure of MOP-KO mice. EXPERIMENTAL APPROACH Magnetic resonance imaging (MRI) voxel-based morphometry (VBM) and histological methods were used to identify structural differences between extensively backcrossed MOP-KO mice and WT mice. KEY RESULTS MOP-KO mice displayed robust increases in regional grey matter volume in olfactory bulb, several hypothalamic nuclei, periaqueductal grey (PAG) and several cerebellar areas, most confirmed by VBM analysis. The largest increases in grey matter volume were detected in the glomerular layer of the olfactory bulb, arcuate nucleus of hypothalamus, ventrolateral PAG (VLPAG) and cerebellar regions including paramedian and cerebellar lobules. Histological analyses confirm several of these results, with increased VLPAG cell numbers and increased thickness of the olfactory bulb granule cell layer and cerebellar molecular and granular cell layers. CONCLUSIONS AND IMPLICATIONS MOP deletion causes previously undescribed structural changes in specific brain regions, but not in all regions with high MOP receptor densities (e.g. thalamus, nucleus accumbens) or that exhibit adult neurogenesis (e.g. hippocampus). Volume differences in hypothalamus and PAG may reflect behavioural changes including hyperalgesia. Although the precise relationship between volume change and MOP receptor deletion was not determined from this study alone, these findings suggest that levels of MOP receptor expression may influence a broader range of neural structure and function in humans than previously supposed. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.
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Affiliation(s)
- Kazumasu Sasaki
- Department of Biological Psychiatry, Tohoku University Graduate School of Medicine, Sendai, Japan; Department of Functional Brain Imaging, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan
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Abstract
PURPOSE OF REVIEW Chronic pain is an important public health problem that negatively impacts quality of life of affected individuals and exacts an enormous socio-economic cost. Currently available therapeutics provide inadequate management of pain in many patients. Acute pain states generally resolve in most patients. However, for reasons that are poorly understood, in some individuals, acute pain can transform to a chronic state. Our understanding of the risk factors that underlie the development of chronic pain is limited. Recent studies have suggested an important contribution of dysfunction in descending pain modulatory circuits to pain 'chronification'. Human studies provide insights into possible endogenous and exogenous factors that may promote the conversion of pain into a chronic condition. RECENT FINDINGS Descending pain modulatory systems have been studied and characterized in animal models. Human brain imaging techniques, deep brain stimulation and the mechanisms of action of drugs that are effective in the treatment of pain confirm the clinical relevance of top-down pain modulatory circuits. Growing evidence supports the concept that chronic pain is associated with a dysregulation in descending pain modulation. Disruption of the balance of descending modulatory circuits to favour facilitation may promote and maintain chronic pain. Recent findings suggest that diminished descending inhibition is likely to be an important element in determining whether pain may become chronic. This view is consistent with the clinical success of drugs that enhance spinal noradrenergic activity, such as serotonin/norepinephrine reuptake inhibitors (SNRIs), in the treatment of chronic pain states. Consistent with this concept, a robust descending inhibitory system may be normally engaged to protect against the development of chronic pain. Imaging studies show that higher cortical and subcortical centres that govern emotional, motivational and cognitive processes communicate directly with descending pain modulatory circuits providing a mechanistic basis to explain how exogenous factors can influence the expression of chronic pain in a susceptible individual. SUMMARY Preclinical studies coupled with clinical pharmacologic and neuroimaging investigations have advanced our understanding of brain circuits that modulate pain. Descending pain facilitatory and inhibitory circuits arising ultimately in the brainstem provide mechanisms that can be engaged to promote or protect against pain 'chronification'. These systems interact with higher centres, thus providing a means through which exogenous factors can influence the risk of pain chronification. A greater understanding of the role of descending pain modulation can lead to novel therapeutic directions aimed at normalizing aberrant processes that can lead to chronic pain.
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Affiliation(s)
- Michael H Ossipov
- Department of Pharmacology, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona, USA
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Arout CA, Caldwell M, McCloskey DP, Kest B. C-Fos activation in the periaqueductal gray following acute morphine-3β-d-glucuronide or morphine administration. Physiol Behav 2014; 130:28-33. [DOI: 10.1016/j.physbeh.2014.02.056] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 02/28/2014] [Indexed: 10/25/2022]
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Sawynok J, Liu J. Contributions of peripheral, spinal, and supraspinal actions to analgesia. Eur J Pharmacol 2014; 734:114-21. [PMID: 24731877 DOI: 10.1016/j.ejphar.2014.04.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Revised: 04/02/2014] [Accepted: 04/03/2014] [Indexed: 02/08/2023]
Abstract
Pain signaling involves several main compartments that can be considered as potential sites for analgesic drug actions. When drugs are given systemically, they can act at spinal, supraspinal and peripheral sites, and several methods have been developed for identifying where they act. These include (1) localized delivery of drugs to specific sites (via intracerebral, intrathecal, and intraplantar injections), (2) systemic delivery of drugs with localized delivery of antagonists for the receptor on which the drug acts or for a system recruited by the drug, (3) use of peripherally restricted analogs, and (4) use of conditional knockout technology to selectively deplete receptors on nociceptors. Delivery of drugs simultaneously to several sites (spinal/supraspinal, peripheral/spinal, and peripheral/supraspinal) reveals "self-synergy" between sites for some agents. Knowledge of peripheral contributions to drug actions is important because of the potential to develop peripherally restricted analgesics (with a diminished side effect profile due to not entering the central nervous system), the potential to deliver drugs peripherally (e.g. topically) to act on sensory nerve endings and adjacent tissue (with a diminished side effect profile due to limited systemic absorption), and the potential to use combinations of topical and oral drug regimens to obtain improved pain relief (without increasing the side effect burden). This review considers methods used for compartmental analysis, and results of such site analysis for several major classes of analgesic drugs that are in current use.
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Affiliation(s)
- Jana Sawynok
- Department of Pharmacology, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax, Nova Scotia, Canada B3H 4R2.
| | - Jean Liu
- Department of Pharmacology, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax, Nova Scotia, Canada B3H 4R2
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Victoria NC, Inoue K, Young LJ, Murphy AZ. Long-term dysregulation of brain corticotrophin and glucocorticoid receptors and stress reactivity by single early-life pain experience in male and female rats. Psychoneuroendocrinology 2013; 38:3015-28. [PMID: 24094874 DOI: 10.1016/j.psyneuen.2013.08.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 08/29/2013] [Accepted: 08/29/2013] [Indexed: 11/28/2022]
Abstract
Inflammatory pain experienced on the day of birth (postnatal day 0: PD0) significantly dampens behavioral responses to stress- and anxiety-provoking stimuli in adult rats. However, to date, the mechanisms by which early life pain permanently alters adult stress responses remain unknown. The present studies examined the impact of inflammatory pain, experienced on the day of birth, on adult expression of receptors or proteins implicated in the activation and termination of the stress response, including corticotrophin releasing factor receptors (CRFR1 and CRFR2) and glucocorticoid receptor (GR). Using competitive receptor autoradiography, we show that Sprague Dawley male and female rat pups administered 1% carrageenan into the intraplantar surface of the hindpaw on the day of birth have significantly decreased CRFR1 binding in the basolateral amygdala and midbrain periaqueductal gray in adulthood. In contrast, CRFR2 binding, which is associated with stress termination, was significantly increased in the lateral septum and cortical amygdala. GR expression, measured with in situ hybridization and immunohistochemistry, was significantly increased in the paraventricular nucleus of the hypothalamus and significantly decreased in the hippocampus of neonatally injured adults. In parallel, acute stress-induced corticosterone release was significantly attenuated and returned to baseline more rapidly in adults injured on PD0 in comparison to controls. Collectively, these data show that early life pain alters neural circuits that regulate responses to and neuroendocrine recovery from stress, and suggest that pain experienced by infants in the Neonatal Intensive Care Unit may permanently alter future responses to anxiety- and stress-provoking stimuli.
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Affiliation(s)
- Nicole C Victoria
- Neuroscience Institute, Georgia State University, 100 Piedmont Avenue, Room 880, Atlanta, GA 30303, United States; Center for Behavioral Neuroscience, Georgia State University, 100 Piedmont Avenue, Room 880, Atlanta, GA 30303, United States
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Llewelyn MB, Azami J, Roberts MH. Effects of 5-hydroxytryptamine applied into nucleus raphe magnus on nociceptive thresholds and neuronal firing rate. Brain Res 2013; 258:59-68. [PMID: 24010164 DOI: 10.1016/0006-8993(83)91226-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effect of iontophoretically applied 5-hydroxytryptamine on neurones in nucleus raphe magnus, and the effect of microinjection of 5-hydroxytryptamine into nucleus raphe magnus on nociceptive thresholds were examined in the rat. Iontophoretically applied 5-hydroxytryptamine excited 66% and inhibited 6% of the neurones encountered in the nucleus raphe magnus. The excitatory response to 5-hydroxytryptamine was reduced by the putative serotonergic antagonist cinanserin in 21 of 24 cases. In 12 of these neurones the responses to iontophoretically applied glutamate were also examined. In 11 of the 12 studies the responses to glutamate were reduced by cinanserin. Microinjection of 5 microg of 5-hydroxytryptamine into the nucleus raphe magnus produced analgesia as assessed by the tail-flick response to noxious heat stimulation, but no analgesia as assessed by the paw withdrawal response to pressure. Microinjection of 5 microg of 5-hydroxytryptamine into the adjacent nucleus reticularis paragigantocellularis had no analgesic effect in either test. These results indicate that 5-hydroxytryptamine mainly excites neurones in nucleus raphe magnus and that 5-hydroxytryptamine has an action on neurones in nucleus raphe magnus which modulate the nociceptive threshold.
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Affiliation(s)
- M B Llewelyn
- Department of Physiology, University College, Cardiff CF1 JXL, UK
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Victoria NC, Karom MC, Eichenbaum H, Murphy AZ. Neonatal injury rapidly alters markers of pain and stress in rat pups. Dev Neurobiol 2013; 74:42-51. [PMID: 24022912 DOI: 10.1002/dneu.22129] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Revised: 08/15/2013] [Accepted: 09/02/2013] [Indexed: 01/17/2023]
Abstract
Less than 60% of infants undergoing invasive procedures in the neonatal intensive care unit receive analgesic therapy. These infants show long-term decreases in pain sensitivity and cortisol reactivity. In rats, we have previously shown that inflammatory pain experienced on the day of birth significantly decreases adult somatosensory thresholds and responses to anxiety- and stress-provoking stimuli. These long-term changes in pain and stress responsiveness are accompanied by two-fold increases in central met-enkephalin and β-endorphin expression. However, the time course over which these changes in central opioid peptide expression occur, relative to the time of injury, are not known. The present studies were conducted to determine whether the observed changes in adult opioid peptide expression were present within the first postnatal week following injury. The impact of neonatal inflammation on plasma corticosterone, a marker for stress reactivity, was also determined. Brain, spinal cord, and trunk blood were harvested at 24 h, 48 h, and 7 d following intraplantar administration of the inflammatory agent carrageenan on the day of birth. Radioimmunoassay was used to determine plasma corticosterone and met-enkephalin and β-endorphin levels within the forebrain, cortex, midbrain, and spinal cord. Within 24 h of injury, met-enkephalin levels were significantly increased in the midbrain, but decreased in the spinal cord and cortex; forebrain β-endorphin levels were significantly increased as a result of early life pain. Corticosterone levels were also significantly increased. At 7 d post-injury, opioid peptides remained elevated relative to controls, suggesting a time point by which injury-induced changes become programmed and permanent.
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Affiliation(s)
- Nicole C Victoria
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia, 30303
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29
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Lee SH, Lee BC. Use of acupuncture as a treatment method for chronic prostatitis/chronic pelvic pain syndromes. Curr Urol Rep 2011; 12:288-96. [PMID: 21472420 DOI: 10.1007/s11934-011-0186-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is the most common category of clinical prostatitis. The etiologic factors of CP/CPPS still remain unknown, and standard therapies often fail to achieve sustainable amelioration of symptoms; therefore, various treatment therapies have been approached. Recently, there is increasing evidence that acupuncture could be a safe and effective treatment in managing CP/CPPS. However, acupuncture therapy still is ranked as low-priority treatment, which results from the fact that the studies, mostly reported in nontraditional medical journals, had not employed standard definitions of the condition or validated-outcome parameters, and that the mechanism of acupuncture effects on CP/CPPS remains to be elucidated. In this article, we review the recent clinical research using acupuncture to reveal its clinical utility for CP/CPPS and the possible mechanisms of action. This article could encourage health care providers and urologists to apply acupuncture for managing pains of CP/CPPS with standard treatment.
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Affiliation(s)
- Sang-Hun Lee
- Department of Internal Medicine, Integrative Cancer Center, East-West Neo Medical Center, Kyung Hee University, Sangil-dong, Gangdong-Ku, Seoul, Republic of Korea
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Mehta AK, Halder S, Khanna N, Tandon OP, Sharma KK. Antagonism of stimulation-produced analgesia by naloxone and N-methyl-D-aspartate: role of opioid and N-methyl-D-aspartate receptors. Hum Exp Toxicol 2011; 31:51-6. [PMID: 21803783 DOI: 10.1177/0960327111417908] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The present study aims to investigate the influence of electrical stimulation of periaqueductal gray (PAG) following peripheral nerve injury and its modulation by naloxone and N-methyl-D-aspartate (NMDA). Chronic neuropathic pain was induced by chronic constriction injury of the sciatic nerve, and subsequently a cannula was implanted in the PAG area for the purpose of electrical stimulation and intra-PAG drug administration. Intra-PAG administration of morphine, ketamine, and their combination were found to elicit antinociceptive response on hot-plate test. Electrical stimulation of PAG was also observed to demonstrate decreased pain response on hot-plate test, and this effect was reversed by the administration of naloxone, NMDA, and their combination, when injected into the PAG area. These findings suggest that apart from the opioid receptors, probably NMDA receptors also have a role to play in stimulation-produced analgesia.
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Affiliation(s)
- A K Mehta
- Department of Physiology, University College of Medical Sciences, Delhi, India
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Intra-Periaqueductal Gray Matter Microinjection of Orexin-A Decreases Formalin-Induced Nociceptive Behaviors in Adult Male Rats. THE JOURNAL OF PAIN 2011; 12:280-7. [DOI: 10.1016/j.jpain.2010.09.006] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2010] [Revised: 07/21/2010] [Accepted: 09/17/2010] [Indexed: 11/23/2022]
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Ossipov MH, Dussor GO, Porreca F. Central modulation of pain. J Clin Invest 2010; 120:3779-87. [PMID: 21041960 DOI: 10.1172/jci43766] [Citation(s) in RCA: 718] [Impact Index Per Article: 51.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
It has long been appreciated that the experience of pain is highly variable between individuals. Pain results from activation of sensory receptors specialized to detect actual or impending tissue damage (i.e., nociceptors). However, a direct correlation between activation of nociceptors and the sensory experience of pain is not always apparent. Even in cases in which the severity of injury appears similar, individual pain experiences may vary dramatically. Emotional state, degree of anxiety, attention and distraction, past experiences, memories, and many other factors can either enhance or diminish the pain experience. Here, we review evidence for "top-down" modulatory circuits that profoundly change the sensory experience of pain.
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Affiliation(s)
- Michael H Ossipov
- Department of Pharmacology, University of Arizona, Tucson, Arizona 85724, USA
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35
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T-type channels control the opioidergic descending analgesia at the low threshold-spiking GABAergic neurons in the periaqueductal gray. Proc Natl Acad Sci U S A 2010; 107:14857-62. [PMID: 20682748 DOI: 10.1073/pnas.1009532107] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Endogenous opioids generate analgesic signals in the periaqueductal gray (PAG). However, because cell types in the PAG are difficult to identify, its neuronal mechanism has remained poorly understood. To address this issue, we characterized PAG neurons by their electrical properties using differentially labeled GABAergic and output neurons in the PAG. We found that GABAergic neurons were mostly fast-spiking cells and could be further divided into two distinct classes: with or without low-threshold spikes (LTS) driven by T-type channels. In contrast, the PAG output neurons lacked LTS and showed heterogeneous firing patterns. To reveal the function of the LTS, we examined the mutant mice lacking the alpha1G T-type channels (alpha1G(-/-)). The mutant mice lacked LTS in the fast-spiking GABAergic neurons of the PAG and unexpectedly showed impaired opioid-dependent analgesia; a similar phenotype was reproduced in PAG-specific alpha1G-knockdown mice. Electrophysiological analyses revealed functional expression of mu-opioid receptors in the low threshold-spiking GABAergic neurons. These neurons in the mutant lacking LTS showed markedly enhanced discharge activities, which led to an augmented inhibition of output neurons. Furthermore, the impaired analgesia observed in alpha1G(-/-) mice was reversed by blocking local GABA(A) receptors. These results indicate that alpha1G T-type channels are critical for the opioidergic descending analgesia system in the PAG.
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The role of the periaqueductal gray in the modulation of pain in males and females: are the anatomy and physiology really that different? Neural Plast 2009; 2009:462879. [PMID: 19197373 PMCID: PMC2633449 DOI: 10.1155/2009/462879] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 10/17/2008] [Indexed: 01/11/2023] Open
Abstract
Anatomical and physiological studies conducted in the 1960s identified the periaqueductal gray (PAG) and its descending projections to the rostral ventromedial medulla (RVM) and spinal cord dorsal horn, as a primary anatomical pathway mediating opioid-based analgesia. Since these initial studies, the PAG-RVM-spinal cord pathway has been characterized anatomically and physiologically in a wide range of vertebrate species. Remarkably, the majority of these studies were conducted exclusively in males with the implicit assumption that the anatomy and physiology of this circuit were the same in females; however, this is not the case. It is well established that morphine administration produces greater antinociception in males compared to females. Recent studies indicate that the PAG-RVM pathway contributes to the sexually dimorphic actions of morphine. This manuscript will review our anatomical, physiological, and behavioral data identifying sex differences in the PAG-RVM pathway, focusing on its role in pain modulation and morphine analgesia.
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Nociceptive behavior in animal models for peripheral neuropathy: spinal and supraspinal mechanisms. Prog Neurobiol 2008; 86:22-47. [PMID: 18602968 DOI: 10.1016/j.pneurobio.2008.06.002] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2007] [Revised: 04/08/2008] [Accepted: 06/11/2008] [Indexed: 02/01/2023]
Abstract
Since the initial description by Wall [Wall, P.D., 1967. The laminar organization of dorsal horn and effects of descending impulses. J. Neurophysiol. 188, 403-423] of tonic descending inhibitory control of dorsal horn neurons, several studies have aimed to characterize the role of various brain centers in the control of nociceptive input to the spinal cord. The role of brainstem centers in pain inhibition has been well documented over the past four decades. Lesion to peripheral nerves results in hypersensitivity to mild tactile or cold stimuli (allodynia) and exaggerated response to nociceptive stimuli (hyperalgesia), both considered as cardinal signs of neuropathic pain. The increased interest in animal models for peripheral neuropathy has raised several questions concerning the rostral conduction of the neuropathic manifestations and the role of supraspinal centers, especially brainstem, in the inhibitory control or in the abnormal contribution to the maintenance and facilitation of neuropathic-like behavior. This review aims to summarize the data on the ascending and descending modulation of neuropathic manifestations and discusses the recent experimental data on the role of supraspinal centers in the control of neuropathic pain. In particular, the review emphasizes the importance of the reciprocal interconnections between the analgesic areas of the brainstem and the pain-related areas of the forebrain. The latter includes the cerebral limbic areas, the prefrontal cortex, the intralaminar thalamus and the hypothalamus and play a critical role in the control of pain considered as part of an integrated behavior related to emotions and various homeostatic regulations. We finally speculate that neuropathic pain, like extrapyramidal motor syndromes, reflects a disorder in the processing of somatosensory information.
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Emmanouil DE, Quock RM. Advances in understanding the actions of nitrous oxide. Anesth Prog 2007; 54:9-18. [PMID: 17352529 PMCID: PMC1821130 DOI: 10.2344/0003-3006(2007)54[9:aiutao]2.0.co;2] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 09/09/2006] [Indexed: 02/07/2023] Open
Abstract
Nitrous oxide (N(2)O) has been used for well over 150 years in clinical dentistry for its analgesic and anxiolytic properties. This small and simple inorganic chemical molecule has indisputable effects of analgesia, anxiolysis, and anesthesia that are of great clinical interest. Recent studies have helped to clarify the analgesic mechanisms of N(2)O, but the mechanisms involved in its anxiolytic and anesthetic actions remain less clear. Findings to date indicate that the analgesic effect of N(2)O is opioid in nature, and, like morphine, may involve a myriad of neuromodulators in the spinal cord. The anxiolytic effect of N(2)O, on the other hand, resembles that of benzodiazepines and may be initiated at selected subunits of the gamma-aminobutyric acid type A (GABA(A)) receptor. Similarly, the anesthetic effect of N(2)O may involve actions at GABA(A) receptors and possibly at N-methyl-D-aspartate receptors as well. This article reviews the latest information on the proposed modes of action for these clinical effects of N(2)O.
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Affiliation(s)
- Dimitris E Emmanouil
- Department of Pediatric Dentistry, School of Dentistry, Athens University, Athens, Greece.
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Chen X, Geller EB, Rogers TJ, Adler MW. Rapid heterologous desensitization of antinociceptive activity between mu or delta opioid receptors and chemokine receptors in rats. Drug Alcohol Depend 2007; 88:36-41. [PMID: 17049756 PMCID: PMC1880888 DOI: 10.1016/j.drugalcdep.2006.09.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Revised: 09/06/2006] [Accepted: 09/15/2006] [Indexed: 11/19/2022]
Abstract
Previous studies have shown pretreatment with chemokines CCL5/RANTES (100 ng) or CXCL12/SDF-1alpha (100 ng) injected into the periaqueductal grey (PAG) region of the brain, 30 min before the mu opioid agonist DAMGO (400 ng), blocked the antinociception induced by DAMGO in the in vivo cold water tail-flick (CWT) antinociceptive test in rats. In the present experiments, we tested whether the action of other agonists at mu and delta opioid receptors is blocked when CCL5/RANTES or CXCL12/SDF-1alpha is administered into the PAG 30 min before, or co-administered with, opioid agonists in the CWT assay. The results showed that: (1) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), given 30 min before the opioid agonist morphine, or selective delta opioid receptor agonist DPDPE, blocked the antinociceptive effect of these drugs; (2) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), injected at the same time as DAMGO or DPDPE, significantly reduced the antinociceptive effect induced by these drugs. These results demonstrate that the heterologous desensitization is rapid between the mu or delta opioid receptors and either CCL5/RANTES receptor CCR5 or CXCL12/SDF-1alpha receptor CXCR4 in vivo, but the effect is greater if the chemokine is administered before the opioid.
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Affiliation(s)
- Xiaohong Chen
- Center for Substance Abuse Research, Temple University School of Medicine, 3400 N. Broad Street, Philadelphia, PA 19140, USA.
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Bernal SA, Morgan MM, Craft RM. PAG mu opioid receptor activation underlies sex differences in morphine antinociception. Behav Brain Res 2007; 177:126-33. [PMID: 17118467 PMCID: PMC1868665 DOI: 10.1016/j.bbr.2006.10.028] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2006] [Revised: 10/13/2006] [Accepted: 10/28/2006] [Indexed: 01/03/2023]
Abstract
Given the findings that (1) systemic opioid antinociception varies by estrous stage in females and (2) the magnitude of sex differences in opioid antinociception is negatively correlated with opioid agonist efficacy, we hypothesized that sex differences in the function of the descending pain modulatory system are likely influenced by estrous stage in females and by the number of available opioid receptors therein. The present study tested these hypotheses by (1) comparing antinociception produced by morphine microinjection to the ventral periaqueductal gray (vPAG) in females at different stages of the estrous cycle and (2) examining systemic morphine antinociception in males versus females under conditions of reduced vPAG mu opioid receptor availability. When estrous stage of females was not controlled for (Experiment 1), there was no significant sex difference in tail withdrawal antinociception following morphine microinjection (0.3-10microg), although morphine was more potent in males than females in producing immobility. Experiment 2 showed that intra-vPAG morphine produced less antinociception and immobility in estrus than in diestrus females; that is, only estrus females' response to morphine was lower than that of males. Experiment 3 showed that microinjection of the irreversible mu opioid antagonist beta-funaltrexamine (beta-FNA) into the vPAG shifted the systemic morphine dose-effect curve farther to the right in females than in males. That is, a reduction in available vPAG mu opioid receptors had a greater impact on opioid antinociception in females than in males, suggesting that females have fewer vPAG mu opioid receptors than males. Overall, these data suggest that ovarian hormones and PAG mu opioid receptor density contribute to sex differences in antinociception produced by morphine.
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Affiliation(s)
- Scott A Bernal
- Department of Psychology, Washington State University, Pullman, WA 99164-4820, United States
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Krivsky JA, Stoffel EC, Sumner JE, Inman BC, Craft RM. Role of ventral tegmental area, periaqueductal gray and parabrachial nucleus in the discriminative stimulus effects of morphine in the rat. Behav Pharmacol 2006; 17:259-70. [PMID: 16572004 DOI: 10.1097/00008877-200605000-00007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Previous studies have produced mixed results about the role of the ventral tegmental area, periaqueductal gray and parabrachial nucleus in morphine discriminations, perhaps owing to the considerably different methodologies used. The purpose of the present study was to compare the roles of these three brain areas using the same food-reinforced discrimination protocol, to determine whether the schedule of reinforcement influenced maximal substitution produced by site-specific morphine administration and to determine whether the time course of substitution differed by site of morphine administration. Rats were trained to discriminate 3.0 mg/kg subcutaneous morphine from saline under variable interval 15-s or fixed ratio 10 schedules of food reinforcement. Rats were then implanted with one cannula aimed at the lateral ventricle (intracerebroventricular) and one aimed at the ventral tegmental area, periaqueductal gray or parabrachial nucleus. Morphine discrimination curves were obtained by subcutaneous, intracerebroventricular and intrasite routes. When administered subcutaneously, morphine was equipotent in variable interval-trained and fixed ratio-trained rats, although it was more potent in fixed ratio-trained females than fixed ratio-trained males. When administered intracerebroventricularly, morphine (0.3-10 microg) engendered a maximum average of 63% drug-appropriate responding in both variable interval-trained and fixed ratio-trained rats; females showed significantly greater drug-appropriate responding than males, again under the fixed ratio but not under the variable interval schedule. In variable interval-trained rats, intrasite infusions of morphine (0.3-10 microg) produced maximal drug-appropriate responding of approximately 57% (ventral tegmental area), 56% (periaqueductal gray) and 41% (parabrachial nucleus); mean maximal substitution was slightly (< or = 17%) greater in fixed ratio-trained rats. When injected into the ventral tegmental area or periaqueductal gray, but not the parabrachial nucleus, naloxone methiodide (2 microg) significantly decreased drug-appropriate responding following 3.0 mg/kg subcutaneous morphine, in both variable interval-trained and fixed ratio-trained rats. The time course of the discriminative stimulus effects of morphine differed among the three brain sites: intraventral tegmental area morphine produced peak drug-appropriate responding by 15 min after injection, whereas the discriminative stimulus effects of intraperiaqueductal gray and intraparabrachial nucleus morphine peaked at approximately 60 min after injection. Taken together, these results indicate that ventral tegmental area, periaqueductal gray and parabrachial nucleus each play a role in the ability of morphine to function as a discriminative stimulus, regardless of the sex of the subject or the schedule under which the subjects are responding. Ventral tegmental area and periaqueductal gray, however, appear to be more critical than parabrachial nucleus in mediating the discriminative effects of systemic morphine in rats responding under a food reinforcement procedure. The pretreatment time and, to a lesser extent, the schedule of reinforcement are additional variables that should be considered when comparing the relative roles of different brain areas in drug discrimination.
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Affiliation(s)
- Julie A Krivsky
- Department of Psychology, Washington State University, Pullman, Washington 99164-4820, USA
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Shah YB, Haynes L, Prior MJW, Marsden CA, Morris PG, Chapman V. Functional magnetic resonance imaging studies of opioid receptor-mediated modulation of noxious-evoked BOLD contrast in rats. Psychopharmacology (Berl) 2005; 180:761-73. [PMID: 15778889 DOI: 10.1007/s00213-005-2214-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2004] [Accepted: 02/11/2005] [Indexed: 01/29/2023]
Abstract
RATIONALE Functional magnetic resonance imaging (fMRI) in rats can non-invasively identify brain regions activated by physiological stimuli and the effects of pharmacological intervention on these responses. OBJECTIVES This study was conducted to investigate the effects of systemic administration of the mu-opioid receptor agonist morphine on whole brain functional signal intensity in anaesthetised rats; to investigate whether pre-treatment with the opioid receptor antagonist naloxone blocks the effects of morphine; to determine whether pre-treatment with morphine attenuates noxious-evoked changes in whole brain functional signal intensity. METHODS Continuous whole brain fMRI scanning was used to study brain signal intensity prior to, and following, systemic administration of morphine (5 mg/kg, n=7), systemic administration of naloxone (1 mg/kg) and morphine (n=8). Effects of pre-treatment with saline (n=5) or morphine (5 mg/kg, n=5) on formalin (5%, intraplantar)-evoked changes in signal intensity were determined. Data were processed using SMP99 with fixed-effects analysis (p<0.05). RESULTS Morphine produced significant positive bilateral increases in signal intensity in the cingulate cortex, amygdala, thalamus, hypothalamus and PAG (p<0.05), and these effects were blocked by naloxone. Intraplantar injection of formalin produced a significant positive increase in signal intensity in the cingulate cortex, somatosensory cortex, amygdala, thalamus, hypothalamus and PAG (p<0.05). Morphine attenuated formalin-evoked increases in signal intensity in the PAG, amygdala, hypothalamus and cingulate cortex. CONCLUSION Our data demonstrate that morphine modulates noxious-evoked changes in signal intensity in discrete brain regions. fMRI studies in rats are able to identify specific brain regions involved in the pharmacological modification of physiologically evoked changes in regional brain activation.
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Affiliation(s)
- Y B Shah
- E. Floor Medical School, School of Biomedical Sciences, Sir Peter Mansfield Centre of Magnetic Resonance, University of Nottingham, Nottingham, NG72UH, UK
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Lane DA, Tortorici V, Morgan MM. Behavioral and electrophysiological evidence for tolerance to continuous morphine administration into the ventrolateral periaqueductal gray. Neuroscience 2004; 125:63-9. [PMID: 15051146 DOI: 10.1016/j.neuroscience.2004.01.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/13/2004] [Indexed: 11/26/2022]
Abstract
Repeated microinjections of morphine into the ventrolateral periaqueductal gray (vPAG) produce tolerance to the antinociceptive effect of morphine [Behav Neurosci 113 (1999) 833]. These results may be a direct effect of morphine on cells within the vPAG or be caused by cues linked to the microinjection procedure (i.e. associative tolerance). The objective of this paper was to determine whether continuous administration of morphine into the vPAG (i.e. no cues) would produce tolerance. Tolerance was assessed by measuring changes in behavior and changes in the activity of neurons in the rostral ventromedial medulla (RVM), the primary output target of the PAG. Rats were implanted with an osmotic minipump that released morphine (2.5 or 5 microg/h) or saline into the vPAG continuously. Continuous administration of morphine produced an increase in hotplate latency when measured 6 h after initiation of treatment. Tolerance to this antinociception was evident within 24 h. After 3 days, rats were anesthetized and the activity of RVM neurons was assessed. Although acute morphine administration into the RVM inhibits the activity of RVM on-cells and enhances the activity of off-cells, these neurons appeared normal following 3 days of continuous morphine administration. Systemic naloxone administration produced hyperalgesia that was associated with a marked increase in on-cell activity and a complete cessation of off-cell activity. The loss of morphine inhibition of nociception, measured behaviorally and electrophysiologically, demonstrates that tolerance is caused by a direct action of morphine on vPAG neurons.
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Affiliation(s)
- D A Lane
- Washington State University Vancouver, 14204 Northeast Salmon Creek Avenue, Vancouver, WA 98686, USA
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Ossipov MH, Lai J, King T, Vanderah TW, Malan TP, Hruby VJ, Porreca F. Antinociceptive and nociceptive actions of opioids. ACTA ACUST UNITED AC 2004; 61:126-48. [PMID: 15362157 DOI: 10.1002/neu.20091] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Although the opioids are the principal treatment options for moderate to severe pain, their use is also associated with the development of tolerance, defined as the progressive need for higher doses to achieve a constant analgesic effect. The mechanisms which underlie this phenomenon remain unclear. Recent studies revealed that cholecystokinin (CCK) is upregulated in the rostral ventromedial medulla (RVM) during persistent opioid exposure. CCK is both antiopioid and pronociceptive, and activates descending pain facilitation mechanisms from the RVM enhancing nociceptive transmission at the spinal cord and promoting hyperalgesia. The neuroplastic changes elicited by opioid exposure reflect adaptive changes to promote increased pain transmission and consequent diminished antinociception (i.e., tolerance).
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Affiliation(s)
- Michael H Ossipov
- Departments of Pharmacology, Anesthesiology and Chemistry, University of Arizona, Tucson, Arizona 85724, USA
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Carlsson C. Acupuncture mechanisms for clinically relevant long-term effects--reconsideration and a hypothesis. Acupunct Med 2002; 20:82-99. [PMID: 12216606 DOI: 10.1136/aim.20.2-3.82] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
From the author's direct involvement in clinical research, the conclusion has been drawn that clinically relevant long-term pain relieving effects of acupuncture (>6 months) can be seen in a proportion of patients with nociceptive pain. The mechanisms behind such effects are considered in this paper. From the existing experimental data some important conclusions can be drawn: 1. Much of the animal research only represents short-term hypoalgesia probably induced by the mechanisms behind stress-induced analgesia (SIA) and the activation of diffuse noxious inhibitory control (DNIC). 2. Almost all experimental acupuncture research has been performed with electro-acupuncture (EA) even though therapeutic acupuncture is mostly gentle manual acupuncture (MA). 3. Most of the experimental human acupuncture pain threshold (PT) research shows only fast and very short-term hypoalgesia, and, importantly, PT elevation in humans does not predict the clinical outcome. 4. The effects of acupuncture may be divided into two main components--acupuncture analgesia and therapeutic acupuncture. A hypothesis on the mechanisms of therapeutic acupuncture will include: 1. Peripheral events that might improve tissue healing and give rise to local pain relief through axon reflexes, the release of neuropeptides with trophic effects, dichotomising nerve fibres and local endorphins. 2. Spinal mechanisms, for example, gate-control, long-term depression, propriospinal inhibition and the balance between long-term depression and long-term potentiation. 3. Supraspinal mechanisms through the descending pain inhibitory system, DNIC, the sympathetic nervous system and the HPA-axis. Is oxytocin also involved in the long-term effects? 4. Cortical, psychological, "placebo" mechanisms from counselling, reassurance and anxiety reduction.
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Zhuo M, Sengupta JN, Gebhart GF. Biphasic modulation of spinal visceral nociceptive transmission from the rostroventral medial medulla in the rat. J Neurophysiol 2002; 87:2225-36. [PMID: 11976363 DOI: 10.1152/jn.2002.87.5.2225] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Descending inhibitory and facilitatory influences from the rostroventral medulla (RVM) on responses of lumbosacral spinal neurons to noxious colorectal distension (CRD, 80 mmHg, 20 s) were studied. At 25 sites in the RVM, electrical stimulation produced biphasic effects, facilitating responses of spinal neurons to CRD at lesser intensities of stimulation (5-25 microA) and inhibiting responses of the same neurons at greater intensities of stimulation (50-100 microA). At 38 other sites in the RVM, electrical stimulation produced only intensity-dependent inhibition of neuron responses to CRD. At another 13 sites in the RVM, electrical stimulation (5-100 microA) produced only facilitatory effects on responses to CRD. Descending modulatory effects were selective for distension-evoked activity; spontaneous activities of the same spinal neurons were not significantly affected by electrical stimulation that either facilitated or inhibited neuron responses to CRD. Neuron responses to graded CRD (20-100 mmHg) were positively accelerating functions that were shifted leftward or rightward, respectively, by lesser, facilitatory intensities or greater, inhibitory intensities of RVM stimulation. L-glutamate microinjection into the RVM replicated the effects of electrical stimulation, producing similar biphasic modulatory effects as produced by electrical stimulation. Microinjection of glutamate into the RVM at a low dose (5 nmoles) facilitated responses of spinal neurons to CRD and inhibited responses of the same neurons at a greater dose (50 nmoles). In some experiments, microinjection of lidocaine (0.5 microl of 4% solution) or the neurotoxin ibotenic acid (0.5 microl, 10 microg) into the RVM produced reversible or long-lasting, respectively, decreases in spontaneous activity and responses of spinal neurons to CRD. These results reveal that spinal visceral nociceptive transmission is subject to a tonic descending excitatory influence from the RVM and that descending modulatory effects from the RVM on visceral nociceptive transmission are qualitatively similar to modulation of cutaneous nociceptive transmission.
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Affiliation(s)
- M Zhuo
- Department of Pharmacology, College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA
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Affiliation(s)
- S L Ingram
- Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
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Zubrzycka M, Janecka A. Effect of cerebral ventricles perfusion with naloxone on trigemino-hypoglossal reflex in rats. REGULATORY PEPTIDES 2001; 97:7-13. [PMID: 11166401 DOI: 10.1016/s0167-0115(00)00187-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The goal of this study was to determine whether opioid receptor antagonist naloxone abolishes the influence of periaqueductal central gray (PAG) on nociceptive evoked tongue jerks (ETJ) -- a trigemino-hypoglossal reflex induced by tooth pulp stimulation. In rats under chloralose anesthesia three series of experiments were performed. In the first two groups perfusions of lateral ventricles-cerebellomedullary cistern with McIlwain-Rodnight's solution and naloxone were carried out. In group 3 naloxone was infused through a catheter through the jugular vein. The amplitudes of tongue jerks induced by tooth pulp stimulation were recorded during subsequent 10 min perfusions. Mean amplitude of tongue movements induced by tooth pulp stimulation was regarded as the indicator of the magnitude of trigemino-hypoglossal reflex. We observed that perfusion of the cerebral ventricles with naloxone (100 nmol/ml) increased the trigemino-hypoglossal reflex up to 143%. The amplitude of ETJ was significantly reduced during PAG stimulation with a train of electrical impulses. After obtaining a significant -- 93% -- inhibition of ETJ (7% of the control), naloxone (100 nmol/ml) was added to the perfusion fluid. This led to a significant increase of the reflex up to 68%. Infusion of naloxone through the jugular vein did not affect the reflex. The above results suggest that the inhibition of ETJ due to PAG stimulation is partially reversed by naloxone and mediated via interactions with endogenous opioid systems involved in modulation of nociception.
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Affiliation(s)
- M Zubrzycka
- Department of Physiology, Institute of Physiology and Biochemistry, Medical University of Lodz, ul.Lindleya 6, 90-131 Lodz, Poland
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Abstract
Neuropathic pain is associated with abnormal tactile and thermal responses that may be extraterritorial to the injured nerve. Importantly, tactile allodynia and thermal hyperalgesia may involve separate pathways, since complete and partial spinal cord lesions have blocked allodynia, but not hyperalgesia, after spinal nerve ligation (SNL). Furthermore, lesions of the dorsal column, and lidocaine microinjected into dorsal column nuclei block only tactile allodynia. Conversely, thermal hyperalgesia, but not tactile allodynia was blocked by desensitization of C-fibers with resiniferotoxin. Therefore, it seems that tactile allodynia is likely to be mediated by large diameter A beta fibers, and not susceptible to modulation by spinal opioids, whereas hyperalgesia is mediated by unmyelinated C-fibers, and is sensitive to blockade by spinal opioids. Additionally, abnormal, spontaneous afferent drive in neuropathic pain may contribute to NMDA-mediated central sensitization by glutamate and by non-opioid actions of spinal dynorphin. Correspondingly, SNL elicited elevation in spinal dynorphin content in spinal segments at and adjacent to the zone of entry of the injured nerve along with signs of neuropathic pain. Antiserum to dynorphin A(1-17) or MK-801 given spinally blocked thermal hyperalgesia, but not tactile allodynia, after SNL, and also restored diminished morphine antinociception. Finally, afferent drive may induce descending facilitation from the rostroventromedial medulla (RVM). Blocking afferent drive with bupivicaine also restored lost potency of PAG morphine, as did CCK antagonists in the RVM. This observation is consistent with afferent drive activating descending facilitation from the RVM, and thus diminishing opioid activity, and may underlie the clinical observation of limited responsiveness of neuropathic pain to opioids.
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Affiliation(s)
- M H Ossipov
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724, USA
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Borszcz GS, Streltsov NG. Amygdaloid-thalamic interactions mediate the antinociceptive action of morphine microinjected into the periaqueductal gray. Behav Neurosci 2000; 114:574-84. [PMID: 10883807 DOI: 10.1037/0735-7044.114.3.574] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The bilateral administration of the serotonin receptor antagonist methysergide (2.5 microg, 5 microg, and 10 microg) into either the central nucleus of the amygdala (ACe) or nucleus parafascicularis thalami (nPf) produced dose-dependent inhibition of the antinociceptive action of ventrolateral periaqueductal gray (vPAG)-administered morphine. Unilateral administration of these doses of methysergide into either the ACe or nPf had no effect on morphine-induced antinociception. However, the combined unilateral administration of these doses of methysergide into the ACe and nPf produced dose-dependent inhibition of morphine antinociception that was identical to that observed after its bilateral administration into either site. This latter finding is interpreted as evidence that a functional interaction between the ACe and nPf supports the antinociceptive action of morphine administered into the vPAG.
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Affiliation(s)
- G S Borszcz
- Department of Psychology, Wayne State Unviersity, Detroit, Michigan 48202, USA.
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