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Hegarty DM, Hermes SM, Largent-Milnes TM, Aicher SA. Capsaicin-responsive corneal afferents do not contain TRPV1 at their central terminals in trigeminal nucleus caudalis in rats. J Chem Neuroanat 2014; 61-62:1-12. [PMID: 24996127 DOI: 10.1016/j.jchemneu.2014.06.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Revised: 06/23/2014] [Accepted: 06/23/2014] [Indexed: 10/25/2022]
Abstract
We examined the substrates for ocular nociception in adult male Sprague-Dawley rats. Capsaicin application to the ocular surface in awake rats evoked nocifensive responses and suppressed spontaneous grooming responses. Thus, peripheral capsaicin was able to activate the central pathways encoding ocular nociception. Our capsaicin stimulus evoked c-Fos expression in a select population of neurons within rostral trigeminal nucleus caudalis in anesthetized rats. These activated neurons also received direct contacts from corneal afferent fibers traced with cholera toxin B from the corneal surface. However, the central terminals of the corneal afferents that contacted capsaicin-activated trigeminal neurons did not contain TRPV1. To determine if TRPV1 expression had been altered by capsaicin stimulation, we examined TRPV1 content of corneal afferents in animals that did not receive capsaicin stimulation. These studies confirmed that while TRPV1 was present in 30% of CTb-labeled corneal afferent neurons within the trigeminal ganglion, TRPV1 was only detected in 2% of the central terminals of these corneal afferents within the trigeminal nucleus caudalis. Other TRP channels were also present in low proportions of central corneal afferent terminals in unstimulated animals (TRPM8, 2%; TRPA1, 10%). These findings indicate that a pathway from the cornea to rostral trigeminal nucleus caudalis is involved in corneal nociceptive transmission, but that central TRP channel expression is unrelated to the type of stimulus transduced by the peripheral nociceptive endings.
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Affiliation(s)
- Deborah M Hegarty
- Department of Physiology and Pharmacology, Oregon Health & Science University, Mail code: L334, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, United States.
| | - Sam M Hermes
- Department of Physiology and Pharmacology, Oregon Health & Science University, Mail code: L334, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, United States.
| | - Tally M Largent-Milnes
- Department of Physiology and Pharmacology, Oregon Health & Science University, Mail code: L334, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, United States.
| | - Sue A Aicher
- Department of Physiology and Pharmacology, Oregon Health & Science University, Mail code: L334, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, United States.
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Nilius B, Szallasi A. Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine. Pharmacol Rev 2014; 66:676-814. [DOI: 10.1124/pr.113.008268] [Citation(s) in RCA: 348] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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Itch elicited by intradermal injection of serotonin, intracisternal injection of morphine, and their synergistic interactions in rats. Neuroscience 2014; 274:119-27. [PMID: 24875173 DOI: 10.1016/j.neuroscience.2014.05.025] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 05/09/2014] [Accepted: 05/13/2014] [Indexed: 12/19/2022]
Abstract
We used the cheek model of itch and pain in rats to determine the dose-response relationships for intradermal injection of serotonin and α methylserotonin on scratching behavior. We also determined the dose-related effects of intracisternally injected morphine on scratching, effects that were greatly reduced by administration of the opiate antagonist naloxone. We then examined the interactions of intradermal injection of serotonin and intracisternal injection of morphine on scratching and found that the two procedures act synergistically to increase itch. These results suggest that morphine applied to the CNS is capable of producing itch and greatly increasing itch originating in the skin (hyperknesis).
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Klein AH, Joe CL, Davoodi A, Takechi K, Carstens MI, Carstens E. Eugenol and carvacrol excite first- and second-order trigeminal neurons and enhance their heat-evoked responses. Neuroscience 2014; 271:45-55. [PMID: 24759772 DOI: 10.1016/j.neuroscience.2014.04.019] [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: 12/06/2013] [Revised: 04/08/2014] [Accepted: 04/09/2014] [Indexed: 12/30/2022]
Abstract
Eugenol and carvacrol from clove and oregano, respectively, are agonists of the warmth-sensitive transient receptor potential channel TRPV3 and the irritant-sensitive transient receptor potential ankyrin (TRPA)-1. Eugenol and carvacrol induce oral irritation that rapidly desensitizes, accompanied by brief enhancement of innocuous warmth and heat pain in humans. We presently investigated if eugenol and carvacrol activate nociceptive primary afferent and higher order trigeminal neurons and enhance their heat-evoked responses, using calcium imaging of cultured trigeminal ganglion (TG) and dorsal root ganglion (DRG) neurons, and in vivo single-unit recordings in trigeminal subnucleus caudalis (Vc) of rats. Eugenol and carvacrol activated 20-30% of TG and 7-20% of DRG cells, the majority of which additionally responded to menthol, mustard oil and/or capsaicin. TG cell responses to innocuous (39°) and noxious (42 °C) heating were enhanced by eugenol and carvacrol. We identified dorsomedial Vc neurons responsive to noxious heating of the tongue in pentobarbital-anesthetized rats. Eugenol and carvacrol dose-dependently elicited desensitizing responses in 55% and 73% of heat-sensitive units, respectively. Responses to noxious heat were briefly enhanced by eugenol and carvacrol. Many eugenol- and carvacrol-responsive units also responded to menthol, cinnamaldehyde and capsaicin. These data support a peripheral site for eugenol and carvacrol to enhance warmth- and noxious heat-evoked responses of trigeminal neurons, and are consistent with the observation that these agonists briefly enhance warmth and heat pain on the human tongue.
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Affiliation(s)
- A H Klein
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA
| | - C L Joe
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA
| | - A Davoodi
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA
| | - K Takechi
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA
| | - M I Carstens
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA
| | - E Carstens
- Department of Neurobiology, Physiology and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
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Moser HR, Giesler GJ. Characterization of pruriceptive trigeminothalamic tract neurons in rats. J Neurophysiol 2014; 111:1574-89. [PMID: 24478156 PMCID: PMC4035772 DOI: 10.1152/jn.00668.2013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 01/22/2014] [Indexed: 11/22/2022] Open
Abstract
Rodent models of facial itch and pain provide a valuable tool for distinguishing between behaviors related to each sensation. In rats, pruritogens applied to the face elicit scratching using the hindlimb while algogens elicit wiping using the forelimb. We wished to determine the role of trigeminothalamic tract (VTT) neurons in carrying information regarding facial itch and pain to the forebrain. We have characterized responses to facially applied pruritogens (serotonin, BAM8-22, chloroquine, histamine, capsaicin, and cowhage) and noxious stimuli in 104 VTT neurons recorded from anesthetized rats. Each VTT neuron had a mechanically sensitive cutaneous receptive field on the ipsilateral face. All pruriceptive VTT neurons also responded to noxious mechanical and/or thermal stimulation. Over half of VTT neurons responsive to noxious stimuli also responded to at least one pruritogen. Each tested pruritogen, with the exception of cowhage, produced an increase in discharge rate in a subset of VTT neurons. The response to each pruritogen was characterized, including maximum discharge rate, response duration, and spike timing dynamics. Pruriceptive VTT neurons were recorded from throughout superficial and deep layers of the spinal trigeminal nucleus and were shown to project via antidromic mapping to the ventroposterior medial nucleus or posterior thalamic nuclei. These results indicate that pruriceptive VTT neurons are a subset of polymodal nociceptive VTT neurons and characterize a system conducive to future experiments regarding the similarities and differences between facial itch and pain.
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Affiliation(s)
- Hannah R Moser
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
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Akiyama T, Nagamine M, Carstens MI, Carstens E. Behavioral model of itch, alloknesis, pain and allodynia in the lower hindlimb and correlative responses of lumbar dorsal horn neurons in the mouse. Neuroscience 2014; 266:38-46. [PMID: 24530451 DOI: 10.1016/j.neuroscience.2014.02.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 02/02/2014] [Accepted: 02/04/2014] [Indexed: 12/01/2022]
Abstract
We have further developed a behavioral model of itch and pain in the lower hindlimb (calf) originally reported by LaMotte et al. (2011) that allows comparisons with responses of lumbar dorsal horn neurons to pruritic and noxious stimuli. Intradermal (id) microinjection of the pruritogens histamine, SLIGRL-NH2 (agonist of PAR-2 and MrgprC11) and chloroquine (agonist of MrgprA3) into the calf of the lower limb elicited significant biting and a small amount of licking directed to the injection site, over a 30-min time course. Following id injection of histamine, low-threshold mechanical stimuli reliably elicited discrete episodes of biting (alloknesis) over a longer time course; significantly less alloknesis was observed following id injection of SLIGRL-NH2. Capsaicin injections elicited licking but little biting. Following id injection of capsaicin, low-threshold mechanical stimuli elicited discrete hindlimb flinches (allodynia) over a prolonged (>2h) time course. In single-unit recordings from superficial lumbar dorsal horn neurons, low-threshold mechanically evoked responses were significantly enhanced, accompanied by receptive field expansion, following id injection of histamine in histamine-responsive neurons. This was not observed in histamine-insensitive neurons, or following id injection of saline or SLIGRL-NH2, regardless of whether the latter activated the neuron or not. These results suggest that itch-responsive neurons are selectively sensitized by histamine but not SLIGRL-NH2 to account for alloknesis. The presently described "calf" model appears to distinguish between itch- and pain-related behavioral responses, and provides a basis to investigate lumbar spinal neural mechanisms underlying itch, alloknesis, pain and allodynia.
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Affiliation(s)
- T Akiyama
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, USA
| | - M Nagamine
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, USA
| | - M I Carstens
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, USA
| | - E Carstens
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, USA.
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Rossbach K, Bäumer W. PCR detects bands consistent with the expression of receptors associated with pruritus in canine dorsal root ganglia. Vet Dermatol 2013; 25:9-e4. [PMID: 24289149 DOI: 10.1111/vde.12093] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/12/2013] [Indexed: 01/17/2023]
Abstract
BACKGROUND Various mediators are involved in the induction of itch, i.e. pruritus; however, the in vivo pharmacology of pruritus seems to be different in distinct species, and little is known about receptors that are involved in the induction of itch in dogs. The species differences in the mediation of pruritus might be explained by species differences in receptor expression in the sensory nerves, including the dorsal root ganglia (DRG). HYPOTHESIS/OBJECTIVES The aim of the study was to analyse the expression of receptors for various mediators of pruritus in canine DRG. METHODS Dorsal root ganglia of 14 dogs, which were euthanized for reasons not related to this study, were analysed. Multiple DRG per dog were dissected and, after homogenization of the DRG tissues, total RNA was isolated, reverse transcribed to complementary DNA and amplified with custom-synthesized primers. RESULTS The following receptors were found in canine DRG: transient receptor potential cation channel subfamily V member 1, tachykinin receptor 1, Toll-like receptor 7, endothelin receptor type A, opioid receptors μ1 and κ1, histamine H1 -H4 receptors and the interleukin-31 receptor complex. CONCLUSIONS AND CLINICAL IMPORTANCE PCR analysis detected bands consistent with the expression of receptors associated with pruritus in canine DRG.
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Affiliation(s)
- Kristine Rossbach
- Institute of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Bünteweg 17, 30559, Hannover, Germany
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58
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Abstract
While considerable effort has been made to investigate the neural mechanisms of pain, much less effort has been devoted to itch, at least until recently. However, itch is now gaining increasing recognition as a widespread and costly medical and socioeconomic issue. This is accompanied by increasing interest in the underlying neural mechanisms of itch, which has become a vibrant and rapidly-advancing field of research. The goal of the present forefront review is to describe the recent progress that has been made in our understanding of itch mechanisms.
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Affiliation(s)
- Tasuku Akiyama
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, United States
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59
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Nishida K, Takechi K, Akiyama T, Carstens MI, Carstens E. Scratching inhibits serotonin-evoked responses of rat dorsal horn neurons in a site- and state-dependent manner. Neuroscience 2013; 250:275-81. [PMID: 23867770 DOI: 10.1016/j.neuroscience.2013.07.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 06/30/2013] [Accepted: 07/04/2013] [Indexed: 10/26/2022]
Abstract
Scratching inhibits pruritogen-evoked responses of neurons in the superficial dorsal horn, implicating a spinal site for scratch inhibition of itch. We investigated if scratching differentially affects neurons depending on whether they are activated by itchy vs. painful stimuli, and if the degree of inhibition depends on the relative location of scratching. We recorded from rat lumbar dorsal horn neurons responsive to intradermal (id) microinjection of serotonin (5-hydroxytryptamine, 5-HT). During the response to 5-HT, scratch stimuli (3mm, 300 mN, 2 Hz, 20s) were delivered at the injection site within the mechanosensitive receptive field (on-site), or 4-30 mm away, outside of the receptive field (off-site). During off-site scratching, 5-HT-evoked firing was significantly attenuated followed by recovery. On-site scratching excited neurons, followed by a significant post-scratch decrease in 5-HT-evoked firing. Most neurons additionally responded to mustard oil (allyl isothiocyanate). Off-site scratching had no effect, while on-site scratching excited the neurons. These results indicate that scratching exerts a state-dependent inhibitory effect on responses of spinal neurons to pruritic but not algesic stimuli. Moreover, on-site scratching first excited neurons followed by inhibition, while off-site scratching immediately evoked the inhibition of pruritogen-evoked activity. This accounts for the suppression of itch by scratching at a distance from the site of the itchy stimulus.
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Affiliation(s)
- K Nishida
- Department of Anesthesiology and Resuscitology, Ehime University School of Medicine, Matsuyama, Japan
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60
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Boucher Y, Felizardo R, Klein AH, Carstens MI, Carstens E. Gustatory modulation of the responses of trigeminal subnucleus caudalis neurons to noxious stimulation of the tongue in rats. Eur J Neurosci 2013; 38:2812-22. [PMID: 23802589 DOI: 10.1111/ejn.12282] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 05/15/2013] [Accepted: 05/22/2013] [Indexed: 11/30/2022]
Abstract
Certain tastants inhibit oral irritation by capsaicin, whereas anesthesia of the chorda tympani (CT) enhances oral capsaicin burn. We tested the hypothesis that tastants activate the CT to suppress responses of trigeminal subnucleus caudalis (Vc) neurons to noxious oral stimuli. In anesthetized rats, we recorded Vc unit responses to noxious electrical, chemical (pentanoic acid, 200 μm) and thermal (55 °C) stimulation of the tongue. Electrically evoked responses were significantly reduced by a tastant mix and individually applied NaCl, monosodium glutamate (MSG), and monopotassium glutamate. Sucrose, citric acid, quinine and water (control) had no effect. Pentanoic acid-evoked responses were similarly attenuated by NaCl and MSG, but not by other tastants. Responses to noxious heat were not affected by any tastant. Transection and/or anesthesia of the CT bilaterally affected neither Vc neuronal responses to electrical or pentanoic acid stimulation, nor the depressant effect of NaCl and MSG on electrically evoked responses. Calcium imaging showed that neither NaCl nor MSG directly excited any trigeminal ganglion cells or affected their responses to pentanoic acid. GABA also had no effect, arguing against peripheral effects of GABA, NaCl or MSG on lingual nocicepive nerve endings. The data also rule out a central mechanism, as the effects of NaCl and MSG were intact following CT transection. We speculate that the effect is mediated peripherally by the release from taste receptor cells (type III) of some mediator(s) other than GABA to indirectly inhibit trigeminal nociceptors. The results also indicate that the CT does not exert a tonic inhibitory effect on nociceptive Vc neurons.
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Affiliation(s)
- Yves Boucher
- UFR Odontologie, Université Diderot Paris, Paris, France
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Itch and analgesia resulting from intrathecal application of morphine: contrasting effects on different populations of trigeminothalamic tract neurons. J Neurosci 2013; 33:6093-101. [PMID: 23554490 DOI: 10.1523/jneurosci.0216-13.2013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Intrathecal application of morphine is among the most powerful methods used to treat severe chronic pain. However, this approach commonly produces itch sufficiently severe that patients are forced to choose between relief of pain or itch. The neuronal populations responsible for processing and transmitting information underlying itch caused by intrathecal application of morphine have not been identified and characterized. We describe two populations of antidromically identified trigeminothalamic tract (VTT) neurons in anesthetized rats that are differentially affected by morphine and explain several aspects of opioid-induced itch and analgesia. We found that intrathecal application of morphine increased ongoing activity of itch-responsive VTT neurons. In addition, intrathecal application of morphine increased responses to pruritogens injected into the skin and greatly heightened responses to innocuous mechanical stimuli. In contrast, the ongoing activity and responses to noxious pinches in nociceptive VTT neurons were frequently inhibited by the same dose of morphine. These results reveal that i.t. application of morphine affects specific subpopulations of VTT neurons in ways that may produce itch, hyperknesis, alloknesis, and analgesia.
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Liu T, Ji RR. New insights into the mechanisms of itch: are pain and itch controlled by distinct mechanisms? Pflugers Arch 2013; 465:1671-85. [PMID: 23636773 DOI: 10.1007/s00424-013-1284-2] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 04/13/2013] [Accepted: 04/14/2013] [Indexed: 12/30/2022]
Abstract
Itch and pain are closely related but distinct sensations. They share largely overlapping mediators and receptors, and itch-responding neurons are also sensitive to pain stimuli. Itch-mediating primary sensory neurons are equipped with distinct receptors and ion channels for itch transduction, including Mas-related G protein-coupled receptors (Mrgprs), protease-activated receptors, histamine receptors, bile acid receptor, toll-like receptors, and transient receptor potential subfamily V1/A1 (TRPV1/A1). Recent progress has indicated the existence of an itch-specific neuronal circuitry. The MrgprA3-expressing primary sensory neurons exclusively innervate the epidermis of skin, and their central axons connect with gastrin-releasing peptide receptor (GRPR)-expressing neurons in the superficial spinal cord. Notably, ablation of MrgprA3-expressing primary sensory neurons or GRPR-expressing spinal cord neurons results in selective reduction in itch but not pain. Chronic itch results from dysfunction of the immune and nervous system and can manifest as neural plasticity despite the fact that chronic itch is often treated by dermatologists. While differences between acute pain and acute itch are striking, chronic itch and chronic pain share many similar mechanisms, including peripheral sensitization (increased responses of primary sensory neurons to itch and pain mediators), central sensitization (hyperactivity of spinal projection neurons and excitatory interneurons), loss of inhibitory control in the spinal cord, and neuro-immune and neuro-glial interactions. Notably, painful stimuli can elicit itch in some chronic conditions (e.g., atopic dermatitis), and some drugs for treating chronic pain are also effective in chronic itch. Thus, itch and pain have more similarities in pathological and chronic conditions.
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Affiliation(s)
- Tong Liu
- Pain Signaling and Plasticity Laboratory, Department of Anesthesiology and Neurobiology, Duke University Medical Center, 595 LaSalle Street, GSRB-I, Room 1027A, DUMC 3094, Durham, NC, 27710, USA,
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Lavinka PC, Dong X. Molecular signaling and targets from itch: lessons for cough. COUGH 2013; 9:8. [PMID: 23497684 PMCID: PMC3630061 DOI: 10.1186/1745-9974-9-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 02/08/2013] [Indexed: 01/05/2023]
Abstract
Itch is described as an unpleasant sensation that elicits the desire to scratch, which results in the removal of the irritant from the skin. The cough reflex also results from irritation, with the purpose of removing said irritant from the airway. Could cough then be similar to itch? Anatomically, both pathways are mediated by small-diameter sensory fibers. These cough and itch sensory fibers release neuropeptides upon activation, which leads to inflammation of the nerves. Both cough and itch also involve mast cells and their mediators, which are released upon degranulation. This common inflammation and interaction with mast cells are involved in the development of chronic conditions of itch and cough. In this review, we examine the anatomy and molecular mechanisms of itch and compare them to known mechanisms for cough. Highlighting the common aspects of itch and cough could lead to new thoughts and perspectives in both fields.
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Affiliation(s)
- Pamela Colleen Lavinka
- The Solomon H, Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, 725 N Wolfe Street, Baltimore, MD, 21205, USA.
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Spradley JM, Davoodi A, Carstens MI, Carstens E. Effects of acute stressors on itch- and pain-related behaviors in rats. Pain 2012; 153:1890-1897. [PMID: 22770638 DOI: 10.1016/j.pain.2012.05.032] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Revised: 05/26/2012] [Accepted: 05/29/2012] [Indexed: 11/18/2022]
Abstract
Many acute stressors reduce pain, a phenomenon called stress-induced antinociception (SIA). Stress also is associated with increased scratching in chronic itch conditions. We investigated effects of acute stressors on facial itch and pain using a recently introduced rat model. Under baseline (no-swim) conditions, intradermal (id) cheek microinjection of the pruritogen serotonin (5-HT) selectively elicited hindlimb scratch bouts, whereas the algogen mustard oil (allyl isothiocyanate [AITC]) selectively elicited ipsilateral forepaw swipes, directed to the cheek injection site. To test effects of swim stress, rats received id cheek microinjection of 5-HT (1%), AITC (10%), or vehicle, and were then subjected to one of the following swim conditions: (1) weak SIA (W-SIA), (2) naltrexone-sensitive SIA (intermediate or I-SIA), or (3) naltrexone-insensitive SIA (strong or S-SIA). After the swim, we recorded the number of hindlimb scratch bouts and forelimb swipes directed to the cheek injection site, as well as facial grooming by both forepaws. Under S-SIA, AITC-evoked swiping and 5-HT-evoked scratching were both reduced. I-SIA reduced AITC-evoked swiping with no effect on 5-HT-evoked scratching. Facial grooming immediately post-swim was suppressed by S-SIA, but not I- or W-SIA. W-SIA tended to equalize scratching and swiping elicited by 5-HT and AITC compared with no-swim controls, suggesting altered itch and pain processing. Exercise (wheel-running), novelty, cold exposure, and fear (shaker table), key components of swim stress, differentially affected tail-flick latencies and 5-HT-evoked swiping and scratching behavior. Thus, itch and pain can be simultaneously suppressed by a combination of acute stress-related factors via an opioid-independent mechanism.
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Affiliation(s)
- Jessica Marie Spradley
- Department of Neurobiology, Physiology and Behavior, University of California-Davis, Davis, CA, USA
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Spradley JM, Davoodi A, Gee LB, Carstens MI, Carstens E. Differences in peripheral endocannabinoid modulation of scratching behavior in facial vs. spinally-innervated skin. Neuropharmacology 2012; 63:743-9. [PMID: 22683515 DOI: 10.1016/j.neuropharm.2012.05.032] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Revised: 05/09/2012] [Accepted: 05/14/2012] [Indexed: 11/29/2022]
Abstract
Cannabinoids suppress nocifensive behaviors in rodents. We presently investigated peripheral endocannabinoid modulation of itch- and pain-related behaviors elicited from facial vs. spinally-innervated skin of rats. Intradermal (id) injection of the pruritogen serotonin (5-HT) elicited significantly more hindlimb scratch bouts, and longer cumulative time scratching, when injected in the rostral back compared to the cheek. Pretreatment of skin with inhibitors of degrading enzymes for the endocannabinoids anandamide (URB597) or 2-arachidonoylglycerol (JZL184) significantly reduced scratching elicited by 5-HT in the rostral back. These effects were prevented by co-treatment with antagonists of the CB₁ (AM251) or CB₂ receptor (AM630), implicating both receptor subtypes in endocannabinoid suppression of scratching in spinally-innervated skin. Conversely, pretreatment with either enzyme inhibitor, or with AM630 alone, increased the number of scratch bouts elicited by id 5-HT injection in the cheek. Moreover, pretreatment with JZL184 also significantly increased pain-related forelimb wipes directed to the cheek following id injection of the algogen, allyl isothiocyanate (AITC; mustard oil). Thus, peripheral endocannabinoids have opposite effects on itch-related scratching behaviors in trigeminally- vs. spinally-innervated skin. These results suggest that increasing peripheral endocannabinoid levels represents a promising therapeutic approach to treat itch arising from the lower body, but caution that such treatment may not relieve, and may even exacerbate, itch and pain arising from trigeminally-innervated skin of the face or scalp.
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Affiliation(s)
- Jessica Marie Spradley
- Department of Neurobiology, Physiology & Behavior, University of California, One Shields Avenue, Davis, CA 95616-8519, USA
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66
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Abstract
Detection of environmental stimuli that provoke an aversive response has been shown to involve many receptors in the periphery. Probably the least-studied of these stimuli are those that induce the perception of itch (pruritus), an often-experienced unpleasant stimulus. This review covers the ligands and their receptors which are known to cause primary sensory neuron activation and initiate itch sensation. Also covered are several itch-inducing substances which may act indirectly by activating other cell types in the periphery which then signal to primary neurons. Finally, progress in identifying candidate neurotransmitters that sensory neurons use to propagate the itch signal is discussed.
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Affiliation(s)
- Benjamin McNeil
- The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Baltimore, Maryland 21205 USA
| | - Xinzhong Dong
- The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Baltimore, Maryland 21205 USA
- Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 USA
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Green BG. Chemesthesis and the chemical senses as components of a "chemofensor complex". Chem Senses 2011; 37:201-6. [PMID: 22210122 DOI: 10.1093/chemse/bjr119] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
An important function of the chemical senses is to warn against dangerous biological and chemical agents in the environment. The discovery in recent years of "taste" receptor cells outside the oral cavity that appear to have protective functions has raised new questions about the nature and scope of the chemical senses in general and of chemesthesis in particular. The present paper briefly reviews these findings within the context of what is currently known about the body's chemically sensitive protective mechanisms, including nonsensory processes that help to expel or neutralize threatening agents once they have been encountered. It is proposed that this array of defense mechanisms constitutes a "chemofensor complex" in which chemesthesis is the most ubiquitous, functionally diverse, and interactive chemosensory component.
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Affiliation(s)
- Barry G Green
- The John B. Pierce Laboratory, New Haven, CT 06519, USA.
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