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Rossi GC, Bodnar RJ. Interactive Mechanisms of Supraspinal Sites of Opioid Analgesic Action: A Festschrift to Dr. Gavril W. Pasternak. Cell Mol Neurobiol 2021; 41:863-897. [PMID: 32970288 DOI: 10.1007/s10571-020-00961-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 09/03/2020] [Indexed: 12/30/2022]
Abstract
Almost a half century of research has elaborated the discoveries of the central mechanisms governing the analgesic responses of opiates, including their receptors, endogenous peptides, genes and their putative spinal and supraspinal sites of action. One of the central tenets of "gate-control theories of pain" was the activation of descending supraspinal sites by opiate drugs and opioid peptides thereby controlling further noxious input. This review in the Special Issue dedicated to the research of Dr. Gavril Pasternak indicates his contributions to the understanding of supraspinal mediation of opioid analgesic action within the context of the large body of work over this period. This review will examine (a) the relevant supraspinal sites mediating opioid analgesia, (b) the opioid receptor subtypes and opioid peptides involved, (c) supraspinal site analgesic interactions and their underlying neurophysiology, (d) molecular (particularly AS) tools identifying opioid receptor actions, and (e) relevant physiological variables affecting site-specific opioid analgesia. This review will build on classic initial studies, specify the contributions that Gavril Pasternak and his colleagues did in this specific area, and follow through with studies up to the present.
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Affiliation(s)
- Grace C Rossi
- Department of Psychology, C.W. Post College, Long Island University, Post Campus, Brookville, NY, USA.
| | - Richard J Bodnar
- Department of Psychology, Queens College of the City University of New York, Flushing, NY, USA
- CUNY Neuroscience Collaborative, Graduate Center, CUNY, New York, NY, USA
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Lesnak J, Sluka KA. Chronic non-inflammatory muscle pain: central and peripheral mediators. CURRENT OPINION IN PHYSIOLOGY 2019; 11:67-74. [PMID: 31998857 PMCID: PMC6988739 DOI: 10.1016/j.cophys.2019.06.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Conditions with chronic widespread non-inflammatory muscle pain, such as fibromyalgia, have complex etiologies with numerous proposed mechanisms for their pathophysiology of underlying chronic pain. Advancements in neuroimaging have allowed for the study of brain function and connectivity in humans with these conditions, while development of animal models have allowed for the study of both peripheral and central factors that lead to chronic pain. This article reviews the current literature surrounding the pathophysiology of chronic widespread non-inflammatory muscle pain focusing on both peripheral and central nervous system, as well as immune system, contributions to the development and maintenance of pain. A better understanding of the mechanisms underlying these conditions can allow for improvements in patient education, treatment and outcomes.
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Affiliation(s)
- Joseph Lesnak
- Department of Physical Therapy and Rehabilitation Science, Pain Research Program, 1-242 MEB, University of Iowa, Iowa City, IA 52252, USA
| | - Kathleen A. Sluka
- Department of Physical Therapy and Rehabilitation Science, Pain Research Program, 1-242 MEB, University of Iowa, Iowa City, IA 52252, USA
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Lima LV, DeSantana JM, Rasmussen LA, Sluka KA. Short-duration physical activity prevents the development of activity-induced hyperalgesia through opioid and serotoninergic mechanisms. Pain 2017; 158:1697-1710. [PMID: 28621702 PMCID: PMC5561491 DOI: 10.1097/j.pain.0000000000000967] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Regular physical activity prevents the development of chronic muscle pain through the modulation of central mechanisms that involve rostral ventromedial medulla (RVM). We tested if pharmacological blockade or genetic deletion of mu-opioid receptors in physically active mice modulates excitatory and inhibitory systems in the RVM in an activity-induced hyperalgesia model. We examined response frequency to mechanical stimulation of the paw, muscle withdrawal thresholds, and expression of phosphorylation of the NR1 subunit of the N-methyl-D-aspartate receptor (p-NR1) and serotonin transporter (SERT) in the RVM. Mice that had performed 5 days of voluntary wheel running prior to the induction of the model were compared with sedentary mice. Sedentary mice showed significant increases in mechanical paw withdrawal frequency and a reduction in muscle withdrawal threshold; wheel running prevented the increase in paw withdrawal frequency. Naloxone-treated and MOR mice had increases in withdrawal frequency that were significantly greater than that in physically active control mice and similar to sedentary mice. Immunohistochemistry in the RVM showed increases in p-NR1 and SERT expression in sedentary mice 24 hours after the induction of the model. Wheel running prevented the increase in SERT, but not p-NR1. Physically active, naloxone-treated, and MOR mice showed significant increases in SERT immunoreactivity when compared with wild-type physically active control mice. Blockade of SERT in the RVM in sedentary mice reversed the activity-induced hyperalgesia of the paw and muscle. These results suggest that analgesia induced by 5 days of wheel running is mediated by mu-opioid receptors through the modulation of SERT, but not p-NR1, in RVM.
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MESH Headings
- Animals
- Disease Models, Animal
- Female
- Gene Expression Regulation/physiology
- Hyperalgesia/etiology
- Hyperalgesia/prevention & control
- Male
- Medulla Oblongata/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Nerve Tissue Proteins/metabolism
- Pain Measurement
- Pain Threshold/physiology
- Physical Conditioning, Animal/methods
- Physical Stimulation/adverse effects
- Receptors, N-Methyl-D-Aspartate/metabolism
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
- Serotonin Plasma Membrane Transport Proteins/metabolism
- Statistics, Nonparametric
- Time Factors
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Affiliation(s)
- Lucas V Lima
- Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
- Graduate Program in Health Sciences, Federal University of Sergipe, Aracaju/Se, Brazil
| | - Josimari M DeSantana
- Graduate Program in Health Sciences, Federal University of Sergipe, Aracaju/Se, Brazil
- Department of Physical Therapy, Federal University of Sergipe, Aracaju/Se, Brazil
| | - Lynn A Rasmussen
- Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
| | - Kathleen A Sluka
- Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
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5
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Regular physical activity prevents development of chronic muscle pain through modulation of supraspinal opioid and serotonergic mechanisms. Pain Rep 2017; 2:e618. [PMID: 29392233 PMCID: PMC5777681 DOI: 10.1097/pr9.0000000000000618] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 07/06/2017] [Accepted: 07/07/2017] [Indexed: 11/26/2022] Open
Abstract
The current study shows that blockade of opioid receptors systemically in the periaqueductal gray and the rostral ventromedial medulla prevents analgesia by 8 weeks of wheel running in a chronic muscle pain model. We further show increases in serotonin transporter expression and reversal of hyperalgesia with a selective reuptake inhibitor in the rostral ventromedial medulla in the chronic muscle pain model, and exercise normalizes serotonin transporter expression. Introduction: It is generally believed that exercise produces its effects by activating central opioid receptors; there are little data that support this claim. The periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) are key nuclei in opioid-induced analgesia, and opioids interact with serotonin to produce analgesia. Objectives: The purpose was to examine central inhibitory mechanisms involved in analgesia produced by wheel running. Methods: C57/Black6 mice were given access to running wheels in their home cages before induction of chronic muscle hyperalgesia and compared with those without running wheels. Systemic, intra-PAG, and intra-RVM naloxone tested the role of central opioid receptors in the antinociceptive effects of wheel running in animals with muscle insult. Immunohistochemistry for the serotonin transporter (SERT) in the spinal cord and RVM, and pharmacological blockade of SERT, tested whether the serotonin system was modulated by muscle insult and wheel running. Results: Wheel running prevented the development of muscle hyperalgesia. Systemic naloxone, intra-PAG naloxone, and intra-RVM naloxone reversed the antinociceptive effect of wheel running in animals that had received muscle insult. Induction of chronic muscle hyperalgesia increased SERT in the RVM, and blockade of SERT reversed the hyperalgesia in sedentary animals. Wheel running reduced SERT expression in animals with muscle insult. The serotonin transporter in the superficial dorsal horn of the spinal cord was unchanged after muscle insult, but increased after wheel running. Conclusion: These data support the hypothesis that wheel running produced analgesia through central inhibitory mechanisms involving opioidergic and serotonergic systems.
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Cai YQ, Wang W, Hou YY, Pan ZZ. Optogenetic activation of brainstem serotonergic neurons induces persistent pain sensitization. Mol Pain 2014; 10:70. [PMID: 25410898 PMCID: PMC4247651 DOI: 10.1186/1744-8069-10-70] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 06/18/2014] [Indexed: 02/07/2023] Open
Abstract
Background The rostral ventromedial medulla (RVM) is a key brainstem structure that conveys powerful descending influence of the central pain-modulating system on spinal pain transmission and processing. Serotonergic (5-HT) neurons are a major component in the heterogeneous populations of RVM neurons and in the descending pathways from RVM. However, the descending influence of RVM 5-HT neurons on pain behaviors remains unclear. Results In this study using optogenetic stimulation in tryptophan hydroxylase 2 (TPH2)- Channelrhodopsin 2 (ChR2) transgenic mice, we determined the behavioral effects of selective activation of RVM 5-HT neurons on mechanical and thermal pain behaviors in vivo. We found that ChR2-EYFP-positive neurons strongly co-localized with TPH2-positive (5-HT) neurons in RVM. Optogenetic stimulation significantly increased c-fos expression in 5-HT cells in the RVM of TPH2-ChR2 mice, but not in wild type mice. Behaviorally, the optogenetic stimulation decreased both mechanical and thermal pain threshold in an intensity-dependent manner, with repeated stimulation producing sensitized pain behavior for up to two weeks. Conclusions These results suggest that selective activation of RVM 5-HT neurons exerts a predominant effect of pain facilitation under control conditions.
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Affiliation(s)
| | | | | | - Zhizhong Z Pan
- Department of Anesthesiology and Pain Medicine, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.
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Taylor BK, Basbaum AI. Systemic morphine-induced release of serotonin in the rostroventral medulla is not mimicked by morphine microinjection into the periaqueductal gray. J Neurochem 2003; 86:1129-41. [PMID: 12911621 DOI: 10.1046/j.1471-4159.2003.01907.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used in vivo microdialysis in awake rats to test the hypothesis that intravenous morphine increases serotonin (5-HT) release within the rostral ventromedial medulla (RVM). We also injected morphine into various sites along the rostrocaudal extent of the periaqueductal gray (PAG), and examined the extent of its diffusion to the RVM. Intravenous morphine (3.0 mg/kg) produced thermal antinociception and increased RVM dialysate 5-HT, 5-hydroxyindole acetic acid (5-HIAA), and homovanillic acid (HVA) in a naloxone-reversible manner. As neither PAG microinjection of morphine (5 micro g/0.5 micro L) nor RVM administration of fentanyl or d-Ala(2),NMePhe(4),Gly-ol(5)]enkephalin (DAMGO) increased RVM 5-HT, we were unable to determine the precise site of action of morphine. Surprisingly, peak morphine levels in the RVM were higher after microinjection into the caudal PAG as compared to either intravenous injection or microinjection into more rostral sites within the PAG. Naloxone-precipitated withdrawal in morphine-tolerant rats not only increased extracellular 5-HT in the RVM, but also dopamine (DA) and HVA. We conclude that substantial amounts of morphine diffuse from the PAG to the RVM, and speculate that opioid receptor interactions at multiple brain sites mediate the analgesic effects of PAG morphine. Further studies will be required to elucidate the contribution of 5-HT and DA release in the RVM to opioid analgesia and opioid withdrawal.
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Affiliation(s)
- Bradley K Taylor
- Department of Pharmacology SL83, Health Sciences Center, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70118, USA.
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Hentall ID, Kurle PJ, White TR. Correlations between serotonin level and single-cell firing in the rat's nucleus raphe magnus. Neuroscience 2000; 95:1081-8. [PMID: 10682715 DOI: 10.1016/s0306-4522(99)00516-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The relation between serotonin release and electrical activity was examined in the nucleus raphe magnus of rats anesthetized with pentobarbital. Serotonin levels were monitored through a carbon-fiber microelectrode by fast cyclic voltammetry (usually at 1 Hz). Single-cell firing was recorded through the same microelectrode, except during the voltammetry waveform and associated electrical artifact (totaling about 30 ms). Multi-barrel micropipettes incorporating the voltammetry electrode were used for iontophoresis of drugs. Cells were inhibited, excited or unaffected by noxious mechanical skin stimulation. These were respectively designated as off(M) cells, on(M) cells and neutral(M) cells, M denoting mechanical. During 3 min of pinching, serotonin slowly rose near seven of 14 on(M) cells and 26 of 46 off(M) cells; it fell near two off(M) cells; it was unchanged near all other cells, including six neutral(M) cells. On a finer spatiotemporal scale, near four of seven on(M) cells, 10 of 14 off(M) cells and 0 of four neutral(M) cells, average serotonin levels fell significantly within +/- 100 ms of spontaneous spikes. Lower serotonin may have caused the higher spike probability; the converse is theoretically unlikely, since delays between release and detection are estimated to exceed 100 ms. Increased serotonin and decreased firing were always seen following iontophoresis or intravenous injection (1 mg/kg) of the serotonin re-uptake inhibitor clomipramine (n = 7). Iontophoresis of +/- propranolol, whose serotonergic actions include antagonism and partial agonism at 5-HT1 receptors, also increased serotonin and decreased firing (n=4). Methiothepin (intravenous, 1 mg/kg), whose serotonergic actions include 5-HT1 and 5-HT2 antagonism, typically raised serotonin levels (four of five cells) and always blocked inhibition by clomipramine (n = 3). Iontophoresis of glutamate always lowered serotonin and increased firing (n = 4). Since serotonin levels and firing were usually inversely correlated, except near on(M) cells during pinch, we propose that serotonin is released from terminals of incoming nociceptive afferents. Prior neuroanatomical knowledge favors a midbrain origin for these afferents, while some of the drug findings suggest that their terminals possess inhibitory serotonergic autoreceptors, possibly of 5-HT1b subtype. The released serotonin could contribute to the inhibition of off(M) cells and excitation of on(M) cells by noxious stimulation, since inhibitory 5-HT1a receptors and excitatory 5-HT2 receptors, respectively, have previously been shown to dominate their serotonergic responses.
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Affiliation(s)
- I D Hentall
- University of Illinois College of Medicine, Rockford 61107-1897, USA
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9
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Xiao DQ, Tang JS, Yuan B, Jia H. Inhibitory effects of 5-hydroxytryptamine microinjection into thalamic nucleus submedius on rat tail flick reflex are mediated by 5-HT2 receptors. Neurosci Lett 1999; 260:85-8. [PMID: 10025705 DOI: 10.1016/s0304-3940(98)00955-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Our previous findings indicated that electrical or chemical activation of the thalamic nucleus submedius (Sm) produced significant antinociceptive effects and that these effect were blocked by lesion or depression of the ventrolateral orbital cortex (VLO) or the periaqueductal gray (PAG) suggesting a role of the Sm in modulation of nociception. To further investigate the neurotransmitter mechanism involved in this nociceptive modulatory pathway, we tested the effects of microinjection of 5-hydroxytryptamine (5-HT, 50 mM, 0.5 microl) into Sm on the tail flick (TF) reflex. The results show that a unilateral microinjection of 5-HT into Sm significantly depresses the TF reflex; and that this effect is repeatable and dose-dependent. Furthermore, microinjection of 5-HT2 receptor antagonist cyproheptadine (CPT, 0.3 mM, 0.5 microl) into the same Sm site reverses this 5-HT-evoked inhibition of TF reflex. These results suggest that 5-HT application to the Sm may activate Sm neurons through the 5-HT2 receptors leading to activation of the brainstem descending inhibitory system via the VLO and depression of the nociceptive information at the spinal level.
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Affiliation(s)
- D Q Xiao
- Department of Physiology, Xi'an Medical University, Shaanxi, People's Republic of China
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10
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Abstract
The serotonergic system, because of very diffuse projections throughout the central nervous system, has been implicated in numerous functions including nociception, analgesia, sleep-wakefulness and autonomic regulation. Despite an abundant literature indicating the presence of neurotensin-containing (neurotensinergic) neurons, fibres and terminals in most areas containing serotonergic neurons, little is known about the possible relationship between serotonergic and neurotensinergic systems. The purpose of this review is (i) to summarize current knowledge on the anatomical relation between neurotensinergic and serotonergic system, (ii) to summarize current knowledge on the action of neurotensin on serotonergic neurons and (iii) to discuss the possible physiological relevance of this action. Neurotensin-containing cell bodies can be found in the most rostral raphe nuclei. There are neurotensin-containing fibres and terminals in all raphe nuclei. Raphe nuclei have also been shown to contain neurotensin-receptor binding sites. In the dorsal raphe nucleus, neurotensin induces a concentration-dependent increase in the firing rate of a subpopulation of serotonergic neurons. The neurotensin-induced excitation, which is selectively blocked by the non-peptide neurotensin receptor antagonist SR 48692, is observed mainly in the ventral part of the nucleus. Most serotonergic neurons show marked desensitization to neurotensin, even at low concentrations. In intracellular experiments, neurotensin induces an inward current, associated in some cases with a decrease in apparent input conductance, which is occluded by supramaximal concentrations of the alpha 1-adrenoceptor agonist phenylephrine. In rare cases, neurotensin induces an excitation of GABAergic or glutamatergic neurons. Since the neurotensinergic system has also been implicated in nociception, analgesia, sleep-wakefulness, and autonomic regulation, the review discusses the possibility that part of this regulation could involve the activation of the serotonergic system.
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Affiliation(s)
- T Jolas
- Department of Psychiatry, Yale University School of Medicine, Connecticut Mental Health Center, New Haven 06508, USA
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Roychowdhury SM, Heinricher MM. Effects of iontophoretically applied serotonin on three classes of physiologically characterized putative pain modulating neurons in the rostral ventromedial medulla of lightly anesthetized rats. Neurosci Lett 1997; 226:136-8. [PMID: 9159508 DOI: 10.1016/s0304-3940(97)00270-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The importance of the rostral ventromedial medulla (RVM) in nociceptive modulation is well documented, and several lines of evidence point to a role for serotonin (5HT) in regulating the activity of pain modulating neurons in this region. The aim of the present study was to examine the effect of iontophoretically applied 5HT upon the firing of three physiologically defined classes of RVM neurons with distinct roles in pain modulation. The predominant effect across all classes was a facilitation of ongoing or evoked activity. A minority of cells within each class were inhibited by 5HT itself, but agonists at 5HT1 receptor types inhibited the majority of cells tested. The results thus indicate that the behavioral effects of manipulating 5HT within the RVM cannot be attributed to a selective influence on a particular cell class.
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Affiliation(s)
- S M Roychowdhury
- Department of Neurology, University of California, San Francisco 94143, USA
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Abstract
The use of the recently released anticonvulsant, gabapentin (Neurontin), in the treatment of severe and refractory reflex sympathetic dystrophy (RSD) pain in six patients ranging in age from 42 to 68 years is reported. Satisfactory pain relief obtained in all six patients suggests that this medication is an effective treatment for RSD pain. In addition to pain control, early evidence of disease reversal in these patients is suggested. Patient 6 is the first documented case of successful treatment and cure of the RSD pain syndrome using gabapentin alone. Specifically, reduced hyperpathia, allodynia, hyperalgesia, and early reversal of skin and soft tissue manifestations were noted. Gabapentin was chosen because it has properties similar to other anticonvulsant drugs and because previous studies have shown that it is well tolerated and appears to have a benign efficacy-to-toxicity ratio. It was considered an acceptable and compassionate therapeutic choice because previous medical and surgical approaches had been ineffective for these patients, who represent the first case series documenting the use of gabapentin for pain management. Presently, the mechanism of pain relief in these patients is unknown. In this article, the pathophysiology of RSD is discussed, and a mechanism by which gabapentin provides pain relief is proposed. In view of encouraging results in these and other RSD patients, further scientific investigation is needed to delineate the role of gabapentin in the treatment of reflex sympathetic dystrophy.
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Affiliation(s)
- G A Mellick
- American Pain Specialists, Inc., Elyria, OH 44035, USA
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Pan ZZ, Wessendorf MW, Williams JT. Modulation by serotonin of the neurons in rat nucleus raphe magnus in vitro. Neuroscience 1993; 54:421-9. [PMID: 8101640 DOI: 10.1016/0306-4522(93)90263-f] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Nucleus raphe magnus contains a large population of raphe-spinal serotonergic neurons that are thought to be involved in descending control of pain transmission and the modulation of opioid analgesia. Intracellular recordings were made from nucleus raphe magnus neurons in the slice preparation. Cells were divided into two groups, primary and secondary cells, based on the action potential waveform and response to opioids, as reported previously. In some experiments, cells were filled with biocytin and 5-hydroxytryptamine-containing cells were identified immunohistochemically. Of the primary cells that were filled with biocytin, 93% stained for 5-hydroxytryptamine; 90% of biocytin-filled secondary cells were unlabeled for 5-hydroxytryptamine. Previous studies have shown that primary cells are disinhibited by opioids; the finding that most primary cells are serotonergic suggests that at least some 5-hydroxytryptamine-containing neurons in the nucleus raphe magnus are excited by opioid analgesics. 5-Hydroxytryptamine hyperpolarized cells in both primary and secondary cell groups. The 5-hydroxytryptamine agonists (+/-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene hydrobromide and 5-carboxamidotryptamine mimicked this action of 5-hydroxytryptamine, indicating that the 5-hydroxytryptamine 1A-subtype mediated this hyperpolarization. The hyperpolarization was mediated by an increase in potassium conductance that rectified inwardly. Local electrical stimulation of afferents evoked an inhibitory postsynaptic potential in primary cells. The inhibitory postsynaptic potential reversed polarity at the potassium equilibrium potential and was blocked by 5-hydroxytryptamine 1A receptor antagonists. It is proposed that the 5-hydroxytrypamine1A receptor on serotonergic primary cells may function as an autoreceptor to regulate the activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- Z Z Pan
- Vollum Institute, Oregon Health Science University, Portland 97201
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14
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Hentall ID, Andresen MJ, Taguchi K. Serotonergic, cholinergic and nociceptive inhibition or excitation of raphe magnus neurons in barbiturate-anesthetized rats. Neuroscience 1993; 52:303-10. [PMID: 8450948 DOI: 10.1016/0306-4522(93)90158-c] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Neurons in the nucleus raphe magnus were recorded extracellularly from barbiturate-anesthetized rats, and were classified by their responses to noxious mechanical stimulation as either pinch-excited, pinch-inhibited or biphasic (inhibited then excited). They were then subjected to iontophoresis of serotonin, some serotonergic agonists and antagonists, acetylcholine, and gamma-amino-n-butyric acid. Serotonin reduced the spontaneous firing of most pinch-inhibited cells (79%). Significantly fewer (P < 0.05) pinch-excited and biphasic cells were inhibited by serotonin (40% and 45%, respectively); in these two cell classes, the observed response was often excitation (30% and 14%), or inhibition for 10-30s followed by excitation for the next 1-2 min (25% and 36%). Acetylcholine showed a similar, statistically significant distribution of effects (P < 0.05), inhibiting all pinch-inhibited neurons (n = 10) but fewer pinch-excited (53%, n = 17) and biphasic neurons (20%, n = 10). Excitation, or excitation then inhibition, was again found frequently among the remaining pinch-excited and biphasic cells. The effect of gamma-amino-n-butyric acid was only inhibitory. In all three nociceptive classes, the serotonin-1A agonist buspirone (n = 15) was inhibitory (87%) and the serotonin-1C/2 antagonist ketanserin (n = 20) was excitatory (35%). The mixed serotonin-1/2 antagonist methysergide (n = 10) was inhibitory (50%) or excitatory (40%). 8-Hydroxy-dipropylaminotetralin (n = 3) was found to increase spontaneous activity (possibly because of partial serotonin-1A agonsim), and +/- propranolol (n = 4) to reduce it (possibly through beta-adrenoceptor antagonism, not serotonin-1A antagonism).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- I D Hentall
- University of Illinois College of Medicine, Rockford 61107-1897
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15
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Kiefel JM, Cooper ML, Bodnar RJ. Serotonin receptor subtype antagonists in the medial ventral medulla inhibit mesencephalic opiate analgesia. Brain Res 1992; 597:331-8. [PMID: 1473004 DOI: 10.1016/0006-8993(92)91490-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Supraspinal opioid analgesia is mediated in part by connections between the midbrain periaqueductal gray (PAG) and the ventral-medial medulla, including the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis (NRGC). A serotonergic synapse appears to participate in this pathway since methysergide microinjected into the NRM-NRGC significantly reduced morphine analgesia elicited from the PAG. The present study evaluated the role of specific serotonin receptor subtypes by pretreating rats with microinjections of either the 5HT2 antagonist, ritanserin or the 5HT3 antagonist, ICS205930, into the NRM-NRGC and examining their effects upon morphine (2.5 micrograms) analgesia elicited from the PAG. Mesencephalic morphine analgesia was significantly reduced following pretreatment with both ritanserin (0.25-2.5 micrograms) on the tail-flick (81%) and jump (65%) tests and ICS205930 (0.25-5 micrograms) on the tail-flick (91%) and jump (63%) tests. Neither ritanserin nor ICS205930 altered basal nociceptive thresholds. Medullary placements ventral or lateral to the NRM/NRGC failed to support these antagonistic effects. These data indicate that ventro-medial medullary 5HT2 and 5HT3 serotonergic receptors modulate the transmission of opioid pain-inhibitory signals from the PAG.
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Affiliation(s)
- J M Kiefel
- Department of Psychology, Queens College, City University of New York, Flushing 11367
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Sawynok J, Reid A. Noradrenergic mediation of spinal antinociception by 5-hydroxytryptamine: characterization of receptor subtypes. Eur J Pharmacol 1992; 223:49-56. [PMID: 1362158 DOI: 10.1016/0014-2999(92)90817-n] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The present study examined the involvement of spinal noradrenergic mechanisms in spinal antinociception by the 5-hydroxy-tryptamine (5-HT) receptor-selective agonists CGS 12066B (5-HT1B; 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]quinoxaline), TFMPP (5-HT1C; M-trifluoromethylphenyl-piperazine) and DOI (5-HT2; 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) using the rat hot plate test. Effects of alpha-adrenoreceptor antagonists (phentolamine, yohimbine), the adrenergic neurotoxin 6-hydroxydopamine, and the selective noradrenergic uptake blocker desipramine were determined. CGS 12066B, TFMPP and DOI produced dose-related antinociception. The antinociceptive effect of each agent was reduced by pretreatment with both phentolamine and yohimbine (15-60 micrograms). Pretreatment with 6-hydroxydopamine (100 micrograms, intrathecal) for 7-10 days, which reduced spinal cord levels of noradrenaline by 87%, inhibited the action of TFMPP (and 5-HT), but not CGS 12066B or DOI. Pretreatment with desipramine (25 mg/kg, systemic) potentiated the action of TFMPP but not CGS 12066B or DOI (or 2-methyl-5-HT). These results suggest that antinociception by TFMPP is dependent on release of endogenous noradrenaline from the spinal cord, while that produced by CGS 12066B and DOI is not. As TFMPP exhibits a close similarity to 5-HT in these experiments, the 5-HT receptor subtype being activated to induce noradrenaline release may either be a 5-HT1C or a 5-HT1S subtype. Other mechanisms account for the observed blockade of the action of CGS 12066B and DOI by alpha-adrenoreceptor antagonists.
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Affiliation(s)
- J Sawynok
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
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17
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Kiefel JM, Cooper ML, Bodnar RJ. Inhibition of mesencephalic morphine analgesia by methysergide in the medial ventral medulla of rats. Physiol Behav 1992; 51:201-5. [PMID: 1311108 DOI: 10.1016/0031-9384(92)90224-p] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The neural substrates of endogenous supraspinal opioid pain inhibition are mediated in part by connections between the midbrain periaqueductal gray (PAG) and the ventral-medial medulla, including the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis (NRGC). To ascertain whether a serotonergic synapse participated in this pathway, the present study determined whether microinjections of methysergide into the NRM or NRGC would alter analgesia elicited by morphine microinjections into the PAG. Morphine (2.5 micrograms) in the PAG and immediately adjacent areas produced significant analgesia on the tail-flick and jump tests in rats. Pretreatment with the serotonin receptor antagonist methysergide (0.5-5 micrograms) in either the NRM or NRGC significantly reduced morphine analgesia elicited from the PAG by 69% on the tail-flick and by 50% on the jump tests without altering basal nociceptive thresholds. Medullary placements ventral or lateral to the NRM/NRGC failed to support this antagonistic effect. These data indicate that a ventro-medial medullary serotonergic synapse participates in the transmission of opioid pain-inhibitory signals from the PAG.
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Affiliation(s)
- J M Kiefel
- Department of Psychology and Neuropsychology, Queens College, City University of New York, Flushing 11367
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18
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Zeng SL, Li YQ, Rao ZR, Shi JW. Projections from serotonin- and substance P-like immunoreactive neurons in the midbrain periaqueductal gray onto the nucleus reticularis gigantocellularis pars alpha in the rat. Neurosci Lett 1991; 131:205-9. [PMID: 1722297 DOI: 10.1016/0304-3940(91)90614-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Serotonin- and substance P-like immunoreactive (5HT-LI and SP-LI) neurons in the midbrain periaqueductal gray (PAG) of the rat were observed to send their axons to the nucleus reticularis gigantocellularis pars alpha (Rgc alpha) by the retrograde horseradish peroxidase (HRP)-tracing method combined with the 5HT- or SP-immunohistochemical technique. These 5HT- or SP-LI PAG neurons were distributed mainly in the ventrolateral subdivision and ventral portion of the medial subdivision at the middle and caudal levels of the PAG, and additionally in the nucleus raphe dorsalis (DR).
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Affiliation(s)
- S L Zeng
- Department of Anatomy, Nanjing Railway Medical College, People's Republic of China
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19
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Yu XM, Hua M, Mense S. The effects of intracerebroventricular injection of naloxone, phentolamine and methysergide on the transmission of nociceptive signals in rat dorsal horn neurons with convergent cutaneous-deep input. Neuroscience 1991; 44:715-23. [PMID: 1661386 DOI: 10.1016/0306-4522(91)90090-b] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In anaesthetized rats, recordings were made from nociceptive dorsal horn neurons with convergent input from the skin and deep somatic tissues. The results of a previous study have shown that in these neurons the input from deep nociceptors is subjected to a much stronger tonic descending inhibition than is the input from cutaneous nociceptors. The aim of the present study was to find out whether at supraspinal levels opioidergic, adrenergic, or serotoninergic transmitters are involved in this quite specific inhibition of deep nociception. Injections of naloxone, phentolamine, and methysergide into the third ventricle showed that only naloxone is capable of abolishing the tonic inhibition of the deep nociceptive input to spinal neurons. The input from cutaneous nociceptors to the same cells was largely unaffected by naloxone. Thus the effects of intracerebroventricular injection of naloxone resembled those obtained with a spinal cold block in a previous study; with the exception that the increase in background activity--which is prominent during cold block--was missing after the injection of naloxone. The present results demonstrate that the tonic descending inhibition of the deep nociception operates with opioidergic synapses at the supraspinal level. In contrast, supraspinal adrenergic and serotoninergic mechanisms do not appear to contribute to the tonic inhibition. The data confirm and extend previous results which suggested that a particular portion of the descending antinociceptive system may act mainly on the input from deep nociceptors. Pharmacologically, this particular portion seems to be opioidergic in nature.
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Affiliation(s)
- X M Yu
- Institut für Anatomie und Zellbiologie, Universität Heidelberg, F.R.G
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20
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Affiliation(s)
- B P Richardson
- Preclinical Research Department, Sandoz Pharma Ltd., Basel, Switzerland
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21
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Abstract
The selective serotonin type-2 (S2) receptor blocker pirenperone (0.24 mg/kg, SC) attenuates morphine-produced tail-flick antinociception in intact rats, but not in rats with transected spinal cords. These results suggest that S2 receptor blockade does not affect intraspinal opioid antinociception. Together with evidence that there are virtually no S2 receptors in the dorsal spinal cord, supraspinal S2 receptors are implicated in the mediation of morphine-produced antinociception.
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Affiliation(s)
- D Paul
- Department of Psychology, University of British Columbia, Vancouver, Canada
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22
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Barber A, Harting J, Wolf HP. Antinociceptive effects of the 5-HT2 antagonist ritanserin in rats: evidence for an activation of descending monoaminergic pathways in the spinal cord. Neurosci Lett 1989; 99:234-8. [PMID: 2501718 DOI: 10.1016/0304-3940(89)90296-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The antinociceptive properties of the 5-HT2 antagonist ritanserin have been investigated in the writhing test using rats implanted with chronic lumbar catheters. The antinociceptive action of 15 mg/kg ritanserin applied subcutaneously (s.c.) was powerfully inhibited by the intrathecal (i.t.) application of ritanserin (50 nmol), methysergide (15 nmol), yohimbine (20 nmol), alpha-flupenthixol (20 nmol) or naloxone (15 nmol), but not atropine (30 nmol), at doses which themselves produced no change in nociceptive threshold. It is concluded that ritanserin acts supraspinally to activate pain-modulating descending serotonergic, noradrenergic, dopaminergic and possibly opioidergic pathways, while spinopetal cholinergic pathways do not seem to be involved. Hyperalgesic effects of s.c. ritanserin following the i.t. application of methysergide or yohimbine were interpreted in terms of the co-release of an excitatory transmitter, possibly substance P, from descending serotonergic and noradrenergic nerve fibres. The supraspinal mechanism by which ritanserin activates spinopetal pathways and its dependence on 5-HT2 receptors have not yet been established.
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Affiliation(s)
- A Barber
- Department of Pharmacology, E. Merck, Darmstadt, F.R.G
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23
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Heinricher MM, Barbaro NM, Fields HL. Putative nociceptive modulating neurons in the rostral ventromedial medulla of the rat: firing of on- and off-cells is related to nociceptive responsiveness. Somatosens Mot Res 1989; 6:427-39. [PMID: 2547275 DOI: 10.3109/08990228909144685] [Citation(s) in RCA: 134] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In the unstimulated, lightly anesthetized rat, both on- and off-cells exhibit alternating periods of silence and activity lasting from several seconds to a few minutes. In the preceding paper, we showed that the active periods of all cells of the same class are always in phase, whereas the firing of cells of different classes is invariably out of phase. Thus, the pattern of firing of any single on- or off-cell provides a useful indication of the excitability of all on- and off-cells in the rostral ventromedial medulla (RVM). In this study, we measured the latency of the tail flick response (TF) at set intervals while recording from TF-related neurons in RVM, and were able to demonstrate a significant relationship between the spontaneous firing of both on- and off-cells and the latency of the TF response. If noxious heat is applied at a time when an off-cell is spontaneously active (or an on-cell is silent), the TF latency is longer than if the TF trial falls during a period in which the off-cell is silent (or the on-cell is active). This correlation between on- and off-cell firing and changes in TF latency is consistent with a nociceptive modulatory role for either or both cell classes. These findings support the hypothesis that off-cells inhibit and on-cells facilitate spinal nociceptive transmission and reflexes.
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Affiliation(s)
- M M Heinricher
- Department of Neurology, University of California, San Francisco 94143
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24
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Paul D, Mana MJ, Pfaus JG, Pinel JP. Attenuation of morphine analgesia by the S2 antagonists, pirenperone and ketanserin. Pharmacol Biochem Behav 1988; 31:641-7. [PMID: 3251248 DOI: 10.1016/0091-3057(88)90243-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The involvement of serotonin type-2 (S2) receptors in morphine-induced analgesia was assessed by challenging the effect of 10 mg/kg of morphine sulphate (IP) with the S2 receptor blockers, pirenperone and ketanserin. Tail-flick latencies were assessed at 0, 30, 60, 90 and 120 min after injections by measuring the time that it took each rat to remove its tail from a 52 degrees C water bath. Pirenperone, at 0.08, 0.16, and 0.24 mg/kg (SC) attenuated morphine-induced antinociception. In contrast, only the high 10 mg/kg (SC) dose of ketanserin attenuated the effect of morphine. Because pirenperone easily enters the central nervous system whereas ketanserin does not, these results indicate the involvement of central S2 receptors in morphine-induced antinociception. The 10 mg/kg dose of ketanserin, however, did not attenuate the antinociception produced by 100 mg/kg of ketamine. Thus, the antianalgesic effect of S2 receptor blockers may be specific to opioid-mediated analgesia.
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Affiliation(s)
- D Paul
- Department of Psychology, University of British Columbia, Vancouver, Canada
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25
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Davie M, Wilkinson LS, Roberts MH. Evidence for excitatory 5-HT2-receptors on rat brainstem neurones. Br J Pharmacol 1988; 94:483-91. [PMID: 3395786 PMCID: PMC1853996 DOI: 10.1111/j.1476-5381.1988.tb11551.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
1. The technique of microiontophoresis was used to investigate the identity of the receptor mediating the excitatory effects of 5-hydroxytryptamine (5-HT) upon neurones in the midline of the medullary brainstem of the rat in vivo. 2. The 5-HT1-like receptor agonists 5-carboxamidotryptamine (5-CT) and 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) failed to excite the majority of neurones excited by 5-HT. The mobilities of 5-CT and 8-OH-DPAT when tested in vitro were found not to differ significantly from that of 5-HT, suggesting that the lack of effect of these agonists was not due to a lower rate of release from the microelectrodes. 3. The excitatory responses to 5-HT were attenuated by the 5-HT 2-receptor antagonists ketanserin and methysergide when applied microiontophoretically or administered intravenously (0.3 and 1 mg kg-1 respectively). Excitatory responses to glutamate and noradrenaline were not reduced. 4. The 5-HT3-receptor antagonist MDL 72222 failed to attenuate selectively the excitatory response to 5-HT when applied either by microiontophoresis or administered intravenously (1 mg kg-1). 5. Microiontophoretic application of the alpha 1-adrenoceptor antagonist prazosin did not attenuate excitatory responses to either 5-HT or noradrenaline. Intravenously administered prazosin (0.8 mg kg-1) also failed to attenuate excitatory responses to 5-HT, but did block excitatory responses to noradrenaline. 6. These results suggest that 5-HT2-receptors, but not 5-HT1-like receptors, 5-HT3-receptors or alpha 1-adrenoceptors, are involved in the excitatory response of midline medullary neurones to 5-HT.
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Affiliation(s)
- M Davie
- Department of Physiology, University College Cardiff
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26
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Drower EJ, Hammond DL. GABAergic modulation of nociceptive threshold: effects of THIP and bicuculline microinjected in the ventral medulla of the rat. Brain Res 1988; 450:316-24. [PMID: 3401715 DOI: 10.1016/0006-8993(88)91570-3] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Neurons of the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis pars alpha (NGCp alpha) have been implicated in the regulation of nociceptive threshold and production of antinociception. Previous studies have shown that the activity of these neurons is modulated by noradrenergic, cholinergic and serotonergic afferents. The present study examined whether these neurons are additionally subject to regulation by a GABAergic input. Microinjection of the GABAA receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; 0.3 or 1.0 microgram) in the NRM or NGCp alpha significantly decreased tail flick latency (TFL) and increased responsiveness to noxious pinch. Hot plate latency (HPL) was not affected by microinjection of 0.3 microgram THIP. Although HPL was increased after microinjection of 1.0 microgram THIP, this effect may reflect motoric disturbances. In contrast to the hyperalgesia produced by THIP, microinjection of the GABAA receptor antagonist bicuculline methiodide (0.04 or 0.1 microgram) produced a small, but significant increase in TFL. Responsiveness to noxious pinch and HPL were not affected by either dose. These findings indicate that neurons of the NRM or NGCp alpha involved in the regulation of nociceptive threshold are subject to an inhibitory GABAergic input mediated by a GABAA receptor. However, in contrast to previously described inhibitory inputs, the GABAergic influence does not appear to be tonically active to a substantial extent in the unanesthetized rat.
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Affiliation(s)
- E J Drower
- Central Nervous System Diseases Research, G.D. Searle & Company, Skokie, IL 60077
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27
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Lakos S, Basbaum AI. An ultrastructural study of the projections from the midbrain periaqueductal gray to spinally projecting, serotonin-immunoreactive neurons of the medullary nucleus raphe magnus in the rat. Brain Res 1988; 443:383-8. [PMID: 3282614 DOI: 10.1016/0006-8993(88)91638-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In this triple-label, electron microscopic study in the rat, a lesion of the midbrain periaqueductal gray (PAG) was made so that the distribution and targets of degenerating PAG terminals could be identified in the medullary nucleus raphe magnus (NRM). Spinally projecting NRM neurons were identified by the retrograde transport of wheat germ agglutinin-horseradish peroxidase from the cervical cord. We also used immunocytochemistry to define the subpopulation of NRM neurons which were serotonin-immunoreactive. We report that both serotonergic and non-serotonergic neurons of the medulla, which project to the spinal cord, receive monosynaptic inputs from the PAG.
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Affiliation(s)
- S Lakos
- Department of Anatomy, University of California at San Francisco 94143
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28
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Chapter 24 Pharmacology of putative neurotransmitters and receptors: 5–hydroxytryptamine. PROGRESS IN BRAIN RESEARCH 1988. [DOI: 10.1016/s0079-6123(08)62799-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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29
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Rees H, Prado WA, Rawlings S, Roberts MH. The effects of intraperitoneal administration of antagonists and development of morphine tolerance on the antinociception induced by stimulating the anterior pretectal nucleus of the rat. Br J Pharmacol 1987; 92:769-79. [PMID: 2892554 PMCID: PMC1853703 DOI: 10.1111/j.1476-5381.1987.tb11380.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
1 The effects of intraperitoneal administration of antagonists to morphine, 5-hydroxytryptamine (5-HT), noradrenaline and dopamine have been studied on the antinociceptive effects of electrical stimulation of the anterior pretectal nucleus (APtN) of the rat. 2 A 15 s period of 35 microA sine wave stimulation of APtN significantly increased the latency of the tail flick reflex to noxious heat for periods up to 1 h. 3 Naloxone (0.25-1.0 mg kg-1) attenuated the effects of APtN stimulation in a dose-dependent manner. In rats made tolerant to morphine by daily administration of morphine, the antinociceptive effects of APtN stimulation were significantly reduced. 4 The 5-HT receptor antagonists methysergide (5 mg kg-1) and ketanserin (1 mg kg-1), the dopamine receptor antagonist haloperidol (1 mg kg-1) and the beta-adrenoceptor antagonist propranolol (1 mg kg-1) had little effect on the antinociceptive effects of stimulating the APtN. 5 alpha-Adrenoceptor antagonists caused a dose-dependent antagonism of the response. The order of potency was; idazoxan greater than prazosin greater than phenoxybenzamine, the respective ED50 for each drug being 0.08: 0.45: 1.5 mg kg-1. 6 It is concluded that antagonism at opioid receptors and alpha-adrenoceptors but not beta-adrenoceptors, dopamine or 5-HT receptors reduces the antinociceptive effects of APtN stimulation. This differs from the reported effects of these antagonists on the antinociception caused by stimulating other sites in the brain.
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Affiliation(s)
- H Rees
- Department of Physiology, University College Cardiff
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30
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Inase M, Nakahama H, Otsuki T, Fang JZ. Analgesic effects of serotonin microinjection into nucleus raphe magnus and nucleus raphe dorsalis evaluated by the monosodium urate (MSU) tonic pain model in the rat. Brain Res 1987; 426:205-11. [PMID: 3690323 DOI: 10.1016/0006-8993(87)90874-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The effects of 5-hydroxytryptamine (5-HT) microinjection into the nucleus raphe magnus (NRM) and the nucleus raphe dorsalis (NRD) on tonic pain were studied using the monosodium urate (MSU) tonic pain model in the rat. For the NRM, 5-HT microinjection produced significant analgesic effects, which were antagonized by systemic naloxone administration and also by subsequent microinjection of naloxone into the NRM. For the NRD, systemic naloxone administration did not antagonize these analgesic effects, although 5-HT microinjection produced significant analgesic effects. Therefore, as far as tonic pain is concerned, it was suggested that neural transmission mediated by 5-HT in the NRM and NRD plays an antinociceptive action, but via different neural mechanisms.
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Affiliation(s)
- M Inase
- Division of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan
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31
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Dickenson AH, Goldsmith G. Evidence for a role of 5-hydroxytryptamine in the responses of rat raphe magnus neurones to peripheral noxious stimuli. Neuropharmacology 1986; 25:863-8. [PMID: 3022179 DOI: 10.1016/0028-3908(86)90012-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The role of serotoninergic mechanisms in the responses of neurones in the nucleus raphe magnus to peripheral noxious stimuli was investigated in rats anaesthetized with halothane. In normal animals a large proportion of neurones responded to peripheral noxious stimuli with excitation or inhibition, the direction of the response being dependent on the spontaneous activity of the neurone. Pretreatment with p-chlorophenylalanine (pCPA; 300 mg/kg X 3 days) led to a marked reduction in the number of cells responding to peripheral stimuli. Similarly, the injection of metergoline (5 mg/kg, i.v.) in normal animals caused a reduction in the magnitude of the neuronal responses to noxious stimuli. The results are discussed with regard to the role of serotoninergic mechanisms in the control of nociceptive transmission by this nucleus.
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32
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Romandini S, Esposito E, Samanin R. Studies on the separate roles of forebrain and spinal serotonin in morphine analgesia. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1986; 332:208-12. [PMID: 3713867 DOI: 10.1007/bf00504855] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
5,7-Dihydroxytryptamine (5,7-DHT) injections in the ventromedial tegmentum (VMT) at the level of nucleus interpeduncularis or in the ventral raphe area (VR) of the medulla oblongata were used to study the separate roles of forebrain and spinal 5-HT in the antinociceptive effect of morphine in rats. 5,7-DHT injections in the VMT, which caused marked, selective depletion of forebrain 5-HT, did not modify the effect of morphine in the hot plate and tail immersion tests. Direct injection of 5,7-DHT into the nucleus raphe medianus also failed to modify the effect of morphine in the two tests used to measure nociceptive responses. The effect of morphine was significantly reduced 30 min after injection to rats depleted of spinal 5-HT by 5,7-DHT injected in the VR but the areas under the curves between vehicle and 5,7-DHT treated animals were not significantly different. The data show that the integrity of 5-HT neurons in the forebrain is not necessary for the antinociceptive effect of morphine and a substantial amount of this effect is still present in rats with marked depletion of spinal 5-HT.
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34
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Wester P, Hardy JA, Marcusson J, Nyberg P, Winblad B. Serotonin concentrations in normal aging human brains: relation to serotonin receptors. Neurobiol Aging 1984; 5:199-203. [PMID: 6083463 DOI: 10.1016/0197-4580(84)90063-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Concentrations of serotonin (5-HT) and its deaminated metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in 7 regions of normal human brains and, in some of the regions, were compared to the number of serotonin receptors (S1 and S2). Neither 5-HT nor 5-HIAA concentrations correlated significantly with increasing age (from 17-100 years) in any of the regions investigated. Positive correlations between 5-HT and 5-HIAA were found in all regions studied, significantly (p less than 0.05) so in 5 of the areas. When comparing 5-HT transmitter and metabolite concentrations to the number of S1 and S2 receptors, no significant correlations were found either within any brain area of between different brain regions. These data confirm that 5-HT transmitter concentrations are not altered by increasing age, support the ideas that S1 and S2 receptors are not presynaptic and also that 5-HT transmitter concentrations and receptor densities are separately controlled.
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35
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Llewelyn MB, Azami J, Roberts MH. The effect of modification of 5-hydroxytryptamine function in nucleus raphe magnus on nociceptive threshold. Brain Res 1984; 306:165-70. [PMID: 6235891 DOI: 10.1016/0006-8993(84)90365-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Thresholds to noxious heat stimulation were increased following microinjection of zimelidine, an inhibitor of 5-hydroxytryptamine (5-HT) re-uptake, into the nucleus raphe magnus (NRM) of rats. Pretreatment with intraperitoneally given cinanserin reduced this effect but pretreatment with intraperitoneally given phenoxybenzamine did not. Fenfluramine, which causes the release of 5-HT from synaptic terminals also elevated nociceptive thresholds following microinjection into NRM. Subanalgesic doses of morphine or zimelidine elevated nociceptive thresholds when microinjected together into NRM. The elevation of nociceptive threshold produced by microinjection of morphine into NRM was reduced by simultaneous microinjection of cinanserin into NRM. Cinanserin alone had no effect when microinjected into NRM. These findings suggest that inhibition of the re-uptake of 5-HT in NRM can elevate nociceptive thresholds and that there may be an interaction between the effects of morphine and 5-HT in NRM.
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36
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Todd AJ, Millar J. Receptive fields and responses to ionophoretically applied noradrenaline and 5-hydroxytryptamine of units recorded in laminae I-III of cat dorsal horn. Brain Res 1983; 288:159-67. [PMID: 6661615 DOI: 10.1016/0006-8993(83)90090-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Recordings were made with carbon fibre microelectrodes from 87 units in laminae I, II and III of the spinal cord in anaesthetized cats, and responses of the units to ionophoretically applied noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were observed. Units with low threshold receptive fields were situated in laminae II and III, while those with high threshold or wide dynamic range fields were mainly restricted to laminae I and II. NA excited nearly half of the units in laminae I and II but had no effect on most units in lamina III. 5-HT excited 68% of the units and these were distributed throughout all 3 laminae. Excitations, particularly by 5-HT, could be very prolonged. NA and 5-HT excited units in all 3 receptive field classes. A few units in lamina I were inhibited. It is suggested that the cells recorded from in the present experiments may be inhibitory interneurones which act on large dorsal horn cells or on their primary afferent inputs.
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Abstract
Non-serotonergic bulbospinal neurons were identified by conduction velocities greater than 6 m/s. These units were found to fire at rates from 0 to 22 Hz, to respond to sensory stimuli with either excitation or inhibition, and to have unremarkable spike shapes. In iontophoretic experiments, both excitation and inhibition were observed in response to acetylcholine, norepinephrine and serotonin. Serotonergic bulbospinal neurons were identified by their conduction velocities below 6 m/s. These neurons, (which have been shown to be destroyed by 5,7-dihydroxytryptamine), exist as two groups: a a slower-conducting group with conduction velocities below 1.2 m/s, and a faster-conducting group with conduction velocities between 2 and 6 m/s. The neurons of the faster-conducting group were found to be similar to the non-serotonergic group in their firing, spike shapes and responses to sensory stimuli; while the units of the slower-conducting group were consistently found to fire between 0.03 and 6 Hz, to respond to sensory stimuli only with excitation, and to have distinctive spike shapes. Despite these differences, both groups of serotonergic units were found to be consistently inhibited by ACh, NE and 5-HT. In contrast to reports of serotonergic neurons in the midbrain, these units were not generally found to be inhibited by i.v. LSD. It is concluded that the serotonergic neurons of the medullary raphe are distinct both from the non-serotonergic neurons, and from serotonergic neurons in other parts of the brain.
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Clark SL, Edeson RO, Ryall RW. The relative significance of spinal and supraspinal actions in the antinociceptive effect of morphine in the dorsal horn: an evaluation of the microinjection technique. Br J Pharmacol 1983; 79:807-18. [PMID: 6652357 PMCID: PMC2044908 DOI: 10.1111/j.1476-5381.1983.tb10019.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Large quantities of morphine injected directly into the brainstem of spinal anaesthetized cats inhibited the noxious heat-evoked excitation of dorsal horn neurones. The amounts required were similar to those that were required intravenously in cats with the spinal cord intact or transected. When the spinal cord was intact the amount of morphine microinjected into the brainstem required to inhibit the excitation of dorsal horn neurones was about ten fold less than it was in spinal animals. It is concluded that large, but not small doses of morphine microinjected into the brainstem can exert effects on the spinal cord after first entering the circulation. The effects of small doses are attributed to a local action in the brainstem which causes inhibition of spinal neurones either by activating descending inhibitory neuronal systems or by liberating endogenous substances which reach the spinal cord via the cerebro-spinal fluid. The concentrations of morphine achieved at various distances from the site of injection by the microinjection of microgram quantities and the time courses of the concentration changes were calculated from diffusion equations, assuming diffusion coefficients of 3 or 5 X 10(6) cm2 s-1. The curves obtained closely approximated those obtained experimentally. The concentrations achieved at distances up to 2 mm from the site of injection of 10 micrograms of morphine were calculated to exceed 10(-4)M and the time-courses of these concentration changes were compatible with the time course of inhibition of spinal neurones, or the production of analgesia after microinjection. Such concentrations are vastly in excess of those achieved in the brain after the systemic administration of morphine in analgesic doses. It is concluded that the local effects in the brainstem produced by the microinjection of microgram quantities of morphine have no relevance to the mechanism of analgesia produced by systemic administration.
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