Publications by authors named "Devin M Barry"

24 Publications

  • Page 1 of 1

A spinal neural circuitry for converting touch to itch sensation.

Nat Commun 2020 10 8;11(1):5074. Epub 2020 Oct 8.

Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, St. Louis, MO, 63110, USA.

Touch and itch sensations are crucial for evoking defensive and emotional responses, and light tactile touch may induce unpleasant itch sensations (mechanical itch or alloknesis). The neural substrate for touch-to-itch conversion in the spinal cord remains elusive. We report that spinal interneurons expressing Tachykinin 2-Cre (Tac2) receive direct Aβ low threshold mechanoreceptor (LTMR) input and form monosynaptic connections with GRPR neurons. Ablation or inhibition markedly reduces mechanical but not acute chemical itch nor noxious touch information. Chemogenetic inhibition of Tac2 neurons also displays pronounced deficit in chronic dry skin itch, a type of chemical itch in mice. Consistently, ablation of gastrin-releasing peptide receptor (GRPR) neurons, which are essential for transmitting chemical itch, also abolishes mechanical itch. Together, these results suggest that innocuous touch and chemical itch information converge on GRPR neurons and thus map an exquisite spinal circuitry hard-wired for converting innocuous touch to irritating itch.
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http://dx.doi.org/10.1038/s41467-020-18895-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7545208PMC
October 2020

Exploration of sensory and spinal neurons expressing gastrin-releasing peptide in itch and pain related behaviors.

Nat Commun 2020 03 13;11(1):1397. Epub 2020 Mar 13.

Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, St. Louis, MO, 63110, USA.

Gastrin-releasing peptide (GRP) functions as a neurotransmitter for non-histaminergic itch, but its site of action (sensory neurons vs spinal cord) remains controversial. To determine the role of GRP in sensory neurons, we generated a floxed Grp mouse line. We found that conditional knockout of Grp in sensory neurons results in attenuated non-histaminergic itch, without impairing histamine-induced itch. Using a Grp-Cre knock-in mouse line, we show that the upper epidermis of the skin is exclusively innervated by GRP fibers, whose activation via optogeneics and chemogenetics in the skin evokes itch- but not pain-related scratching or wiping behaviors. In contrast, intersectional genetic ablation of spinal Grp neurons does not affect itch nor pain transmission, demonstrating that spinal Grp neurons are dispensable for itch transmission. These data indicate that GRP is a neuropeptide in sensory neurons for non-histaminergic itch, and GRP sensory neurons are dedicated to itch transmission.
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http://dx.doi.org/10.1038/s41467-020-15230-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7070094PMC
March 2020

Pain Inhibits GRPR Neurons via GABAergic Signaling in the Spinal Cord.

Sci Rep 2019 11 1;9(1):15804. Epub 2019 Nov 1.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, 63110, USA.

It has been known that algogens and cooling could inhibit itch sensation; however, the underlying molecular and neural mechanisms remain poorly understood. Here, we show that the spinal neurons expressing gastrin releasing peptide receptor (GRPR) primarily comprise excitatory interneurons that receive direct and indirect inputs from C and Aδ fibers and form contacts with projection neurons expressing the neurokinin 1 receptor (NK1R). Importantly, we show that noxious or cooling agents inhibit the activity of GRPR neurons via GABAergic signaling. By contrast, capsaicin, which evokes a mix of itch and pain sensations, enhances both excitatory and inhibitory spontaneous synaptic transmission onto GRPR neurons. These data strengthen the role of GRPR neurons as a key circuit for itch transmission and illustrate a spinal mechanism whereby pain inhibits itch by suppressing the function of GRPR neurons.
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http://dx.doi.org/10.1038/s41598-019-52316-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6825123PMC
November 2019

Internode length is reduced during myelination and remyelination by neurofilament medium phosphorylation in motor axons.

Exp Neurol 2018 08 14;306:158-168. Epub 2018 May 14.

Department of Biological Sciences, University of Missouri, Columbia, MO 65211, United States; C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, United States. Electronic address:

The distance between nodes of Ranvier, referred to as internode length, positively correlates with axon diameter, and is optimized during development to ensure maximal neuronal conduction velocity. Following myelin loss, internode length is reestablished through remyelination. However, remyelination results in short internode lengths and reduced conduction rates. We analyzed the potential role of neurofilament phosphorylation in regulating internode length during remyelination and myelination. Following ethidium bromide induced demyelination, levels of neurofilament medium (NF-M) and heavy (NF-H) phosphorylation were unaffected. Preventing NF-M lysine-serine-proline (KSP) repeat phosphorylation increased internode length by 30% after remyelination. To further analyze the role of NF-M phosphorylation in regulating internode length, gene replacement was used to produce mice in which all KSP serine residues were replaced with glutamate to mimic constitutive phosphorylation. Mimicking constitutive KSP phosphorylation reduced internode length by 16% during myelination and motor nerve conduction velocity by ~27% without altering sensory nerve structure or function. Our results suggest that NF-M KSP phosphorylation is part of a cooperative mechanism between axons and Schwann cells that together determine internode length, and suggest motor and sensory axons utilize different mechanisms to establish internode length.
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http://dx.doi.org/10.1016/j.expneurol.2018.05.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5994378PMC
August 2018

Non-canonical Opioid Signaling Inhibits Itch Transmission in the Spinal Cord of Mice.

Cell Rep 2018 Apr;23(3):866-877

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address:

Chronic itch or pruritus is a debilitating disorder that is refractory to conventional anti-histamine treatment. Kappa opioid receptor (KOR) agonists have been used to treat chronic itch, but the underlying mechanism remains elusive. Here, we find that KOR and gastrin-releasing peptide receptor (GRPR) overlap in the spinal cord, and KOR activation attenuated GRPR-mediated histamine-independent acute and chronic itch in mice. Notably, canonical KOR-mediated G signaling is not required for desensitizing GRPR function. In vivo and in vitro studies suggest that KOR activation results in the translocation of Ca-independent protein kinase C (PKC)δ from the cytosol to the plasma membrane, which in turn phosphorylates and inhibits GRPR activity. A blockade of phospholipase C (PLC) in HEK293 cells prevented KOR-agonist-induced PKCδ translocation and GRPR phosphorylation, suggesting a role of PLC signaling in KOR-mediated GRPR desensitization. These data suggest that a KOR-PLC-PKCδ-GRPR signaling pathway in the spinal cord may underlie KOR-agonists-induced anti-pruritus therapies.
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http://dx.doi.org/10.1016/j.celrep.2018.03.087DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5937707PMC
April 2018

Distinct roles of NMB and GRP in itch transmission.

Sci Rep 2017 11 13;7(1):15466. Epub 2017 Nov 13.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, 63110, USA.

A key question in our understanding of itch coding mechanisms is whether itch is relayed by dedicated molecular and neuronal pathways. Previous studies suggested that gastrin-releasing peptide (GRP) is an itch-specific neurotransmitter. Neuromedin B (NMB) is a mammalian member of the bombesin family of peptides closely related to GRP, but its role in itch is unclear. Here, we show that itch deficits in mice lacking NMB or GRP are non-redundant and Nmb/Grp double KO (DKO) mice displayed additive deficits. Furthermore, both Nmb/Grp and Nmbr/Grpr DKO mice responded normally to a wide array of noxious stimuli. Ablation of NMBR neurons partially attenuated peripherally induced itch without compromising nociceptive processing. Importantly, electrophysiological studies suggested that GRPR neurons receive glutamatergic input from NMBR neurons. Thus, we propose that NMB and GRP may transmit discrete itch information and NMBR neurons are an integral part of neural circuits for itch in the spinal cord.
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http://dx.doi.org/10.1038/s41598-017-15756-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5684337PMC
November 2017

Response to Comment on "Molecular and neural basis of contagious itch behavior in mice".

Science 2017 07;357(6347)

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA.

Liljencrantz report the failure of observing contagious itch behavior using mice injected with histamine as the demonstrators. Analysis of their results shows that the histamine model is limited by inadequate frequency and duration of scratching bouts required for contagious itch test. To streamline the contagious itch test, the screen paradigm is highly recommended.
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http://dx.doi.org/10.1126/science.aan5000DOI Listing
July 2017

Spinal Mechanisms of Itch Transmission.

Neurosci Bull 2018 Feb 1;34(1):156-164. Epub 2017 Apr 1.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, 63110, USA.

Peripheral itch stimuli are transmitted by sensory neurons to the spinal cord dorsal horn, which then transmits the information to the brain. The molecular and cellular mechanisms within the dorsal horn for itch transmission have only been investigated and identified during the past ten years. This review covers the progress that has been made in identifying the peptide families in sensory neurons and the receptor families in dorsal horn neurons as putative itch transmitters, with a focus on gastrin-releasing peptide (GRP)-GRP receptor signaling. Also discussed are the signaling mechanisms, including opioids, by which various types of itch are transmitted and modulated, as well as the many conflicting results arising from recent studies.
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http://dx.doi.org/10.1007/s12264-017-0125-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5799115PMC
February 2018

Molecular and neural basis of contagious itch behavior in mice.

Science 2017 03;355(6329):1072-1076

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA.

Socially contagious itch is ubiquitous in human society, but whether it exists in rodents is unclear. Using a behavioral paradigm that does not entail prior training or reward, we found that mice scratched after observing a conspecific scratching. Molecular mapping showed increased neuronal activity in the suprachiasmatic nucleus (SCN) of the hypothalamus of mice that displayed contagious scratching. Ablation of gastrin-releasing peptide receptor (GRPR) or GRPR neurons in the SCN abolished contagious scratching behavior, which was recapitulated by chemogenetic inhibition of SCN GRP neurons. Activation of SCN GRP/GRPR neurons evoked scratching behavior. These data demonstrate that GRP-GRPR signaling is necessary and sufficient for transmitting contagious itch information in the SCN. The findings may have implications for our understanding of neural circuits that control socially contagious behaviors.
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http://dx.doi.org/10.1126/science.aak9748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5502115PMC
March 2017

Ischemic post-conditioning attenuates acute lung injury induced by intestinal ischemia-reperfusion in mice: role of Nrf2.

Lab Invest 2016 10 8;96(10):1087-104. Epub 2016 Aug 8.

Department of Anesthesiology, Renmin Hospital of Wuhan University, Wuhan, China.

Intestinal ischemic post-conditioning (IPo) protects against lung injury induced by intestinal ischemia-reperfusion (IIR) partly through promotion of expression and function of heme oxygenase-1 (HO-1). NF-E2-related factor-2 (Nrf2) is a key transcription factor that interacts with HO-1 and regulates antioxidant defense. However, the role of Nrf2 in IPo protection of IIR-induced pulmonary injury is not completely understood. Here we show that IPo significantly attenuated IIR-induced lung injury and suppressed oxidative stress and systemic inflammatory responses. IPo also increased the expression of both Nrf2 and HO-1. Consistently, the beneficial effects of IPo were abolished by ATRA and Brusatol, potent inhibitors of Nrf2. Moreover, the Nrf2 agonist t-BHQ showed similar activity as IPo. Taken together, our data suggest that Nrf2 activity, along with HO-1, plays an important role in the protective effects of IPo against IIR-induced acute lung injury.
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http://dx.doi.org/10.1038/labinvest.2016.87DOI Listing
October 2016

Facilitation of TRPV4 by TRPV1 is required for itch transmission in some sensory neuron populations.

Sci Signal 2016 07 19;9(437):ra71. Epub 2016 Jul 19.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA. Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA. Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA. Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA.

The transient receptor potential channels (TRPs) respond to chemical irritants and temperature. TRPV1 responds to the itch-inducing endogenous signal histamine, and TRPA1 responds to the itch-inducing chemical chloroquine. We showed that, in sensory neurons, TRPV4 is important for both chloroquine- and histamine-induced itch and that TRPV1 has a role in chloroquine-induced itch. Chloroquine-induced scratching was reduced in mice in which TRPV1 was knocked down or pharmacologically inhibited. Both TRPV4 and TRPV1 were present in some sensory neurons. Pharmacological blockade of either TRPV4 or TRPV1 significantly attenuated the Ca(2+) response of sensory neurons exposed to histamine or chloroquine. Knockout of Trpv1 impaired Ca(2+) responses and reduced scratching behavior evoked by a TRPV4 agonist, whereas knockout of Trpv4 did not alter TRPV1-mediated capsaicin responses. Electrophysiological analysis of human embryonic kidney (HEK) 293 cells coexpressing TRPV4 and TRPV1 revealed that the presence of both channels enhanced the activation kinetics of TRPV4 but not of TRPV1. Biochemical and biophysical studies suggested a close proximity between TRPV4 and TRPV1 in dorsal root ganglion neurons and in cultured cells. Thus, our studies identified TRPV4 as a channel that contributes to both histamine- and chloroquine-induced itch and indicated that the function of TRPV4 in itch signaling involves TRPV1-mediated facilitation. TRP facilitation through the formation of heteromeric complexes could be a prevalent mechanism by which the vast array of somatosensory information is encoded in sensory neurons.
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http://dx.doi.org/10.1126/scisignal.aaf1047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5310287PMC
July 2016

Microinjection of histone deacetylase inhibitor into the ventrolateral orbital cortex potentiates morphine induced behavioral sensitization.

Brain Res 2016 09 14;1646:418-425. Epub 2016 Jun 14.

College of Forensic Medicine, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710061, China; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, China. Electronic address:

Accumulating evidence indicates that epigenetic regulation, such as changes in histone modification in reward-related brain regions, contributes to the memory formation of addiction to opiates and psychostimulants. Our recent results suggested that the ventrolateral orbital cortex (VLO) is involved in the memories of stress and drug addiction. Since addiction and stress memories share some common pathways, the present study was designed to investigate the role of histone deacetylase (HDAC) activity in the VLO during morphine induced-behavioral sensitization. Rats received a single exposure to morphine for establishing the behavioral sensitization model. The effect of HDAC activity in the VLO in morphine induced-behavioral sensitization was examined by microinjection of HDAC inhibitor Trichostatin A (TSA). Furthermore, the protein expression levels of extracellular signal-regulated kinase (ERK) and phosphorylated ERK (p-ERK), histone H3 lysine 9 acetylation (aceH3K9) and brain-derived neurotrophic factor (BDNF) in the VLO in morphine-induced behavioral sensitization were examined. The results showed that the bilateral VLO lesions suppressed the expression phase, but not the developmental phase of morphine-induced behavioral sensitization. Microinjection of TSA into the VLO significantly increased both the development and expression phases. Moreover, the protein levels of p-ERK, aceH3K9 and BDNF except ERK in the VLO were significantly upregulated in morphine-treated rats in the expression phase. These effects were further strengthened by intra-VLO injection of TSA. Our findings suggest that HDAC activity in the VLO could potentiate morphine-induced behavioral sensitization. The upregulated expression of p-ERK, aceH3K9 and BDNF in the VLO might be the underlying mechanism of histone acetylation enhancing the morphine-induced behavioral sensitization.
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http://dx.doi.org/10.1016/j.brainres.2016.06.019DOI Listing
September 2016

Critical evaluation of the expression of gastrin-releasing peptide in dorsal root ganglia and spinal cord.

Mol Pain 2016 11;12. Epub 2016 Apr 11.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, USA Departments of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA Departments of Psychiatry, Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, USA Departments of Developmental Biology, Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO, USA

There are substantial disagreements about the expression of gastrin-releasing peptide (GRP) in sensory neurons and whether GRP antibody cross-reacts with substance P (SP). These concerns necessitate a critical revaluation of GRP expression using additional approaches. Here, we show that a widely used GRP antibody specifically recognizes GRP but not SP. In the spinal cord of mice lacking SP (Tac1KO), the expression of not only GRP but also other peptides, notably neuropeptide Y (NPY), is significantly diminished. We detectedGrpmRNA in dorsal root ganglias using reverse transcription polymerase chain reaction, in situ hybridization and RNA-seq. We demonstrated thatGrpmRNA and protein are upregulated in dorsal root ganglias, but not in the spinal cord, of mice with chronic itch. Few GRP(+)immunostaining signals were detected in spinal sections following dorsal rhizotomy and GRP(+)cell bodies were not detected in dissociated dorsal horn neurons. Ultrastructural analysis further shows that substantially more GRPergic fibers form synaptic contacts with gastrin releasing peptide receptor-positive (GRPR(+)) neurons than SPergic fibers. Our comprehensive study demonstrates that a majority of GRPergic fibers are of primary afferent origin. A number of factors such as low copy number ofGrptranscripts, small percentage of cells expressingGrp, and the use of an eGFP GENSAT transgenic as a surrogate for GRP protein have contributed to the controversy. Optimization of experimental procedures facilitates the specific detection of GRP expression in dorsal root ganglia neurons.
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http://dx.doi.org/10.1177/1744806916643724DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4972254PMC
December 2016

A novel snake venom-derived GPIb antagonist, anfibatide, protects mice from acute experimental ischaemic stroke and reperfusion injury.

Br J Pharmacol 2015 Aug 12;172(15):3904-16. Epub 2015 Jun 12.

Department of Pharmacology, School of Basic Medical Science, Anhui Medical University, Hefei, Anhui, China.

Background And Purpose: Ischaemic stroke is a serious disease with limited therapy options. Glycoprotein (GP)Ib binding to von Willebrand factor (vWF) exposed at vascular injury initiates platelet adhesion and contributes to platelet aggregation. GPIb has been suggested as an effective target for antithrombotic therapy in stroke. Anfibatide is a GPIb antagonist derived from snake venom and we investigated its protective effect on experimental brain ischaemia in mice.

Experimental Approach: Focal cerebral ischaemia was induced by 90 min of transient middle cerebral artery occlusion (MCAO). These mice were then treated with anfibatide (4, 2, 1 μg·kg(-1) ), injected i.v., after 90 min of MCAO, followed by 1 h of reperfusion. Tirofiban, a GPIIb/IIIα antagonist, was used as a positive control.

Key Results: Twenty-four hours after MCAO, anfibatide-treated mice showed significantly improved ischaemic lesions in a dose-dependent manner. The mice had smaller infarct volumes, less severe neurological deficits and histopathology of cerebrum tissues compared with the untreated MCAO mice. Moreover, anfibatide decreased the amount of GPIbα, vWF and accumulation of fibrin(ogen) in the vasculature of the ischaemic hemisphere. Tirofiban had similar effects on infarct size and fibrin(ogen) deposition compared with the MCAO group. Importantly, the anfibatide-treated mice showed a lower incidence of intracerebral haemorrhage and shorter tail bleeding time compared with the tirofiban-treated mice.

Conclusions And Implications: Our data indicate anfibatide is a safe GPIb antagonist that exerts a protective effect on cerebral ischaemia and reperfusion injury. Anfibatide is a promising candidate that could be beneficial for the treatment of ischaemic stroke.
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http://dx.doi.org/10.1111/bph.13178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4523344PMC
August 2015

Descending control of itch transmission by the serotonergic system via 5-HT1A-facilitated GRP-GRPR signaling.

Neuron 2014 Nov 30;84(4):821-34. Epub 2014 Oct 30.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address:

Unlabelled: Central serotonin (5-hydroxytryptophan, 5-HT) modulates somatosensory transduction, but how it achieves sensory modality-specific modulation remains unclear. Here we report that enhancing serotonergic tone via administration of 5-HT potentiates itch sensation, whereas mice lacking 5-HT or serotonergic neurons in the brainstem exhibit markedly reduced scratching behavior. Through pharmacological and behavioral screening, we identified 5-HT1A as a key receptor in facilitating gastrin-releasing peptide (GRP)-dependent scratching behavior. Coactivation of 5-HT1A and GRP receptors (GRPR) greatly potentiates subthreshold, GRP-induced Ca(2+) transients, and action potential firing of GRPR(+) neurons. Immunostaining, biochemical, and biophysical studies suggest that 5-HT1A and GRPR may function as receptor heteromeric complexes. Furthermore, 5-HT1A blockade significantly attenuates, whereas its activation contributes to, long-lasting itch transmission. Thus, our studies demonstrate that the descending 5-HT system facilitates GRP-GRPR signaling via 5-HT1A to augment itch-specific outputs, and a disruption of crosstalk between 5-HT1A and GRPR may be a useful antipruritic strategy.

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http://dx.doi.org/10.1016/j.neuron.2014.10.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4254557PMC
November 2014

Cross-inhibition of NMBR and GRPR signaling maintains normal histaminergic itch transmission.

J Neurosci 2014 Sep;34(37):12402-14

Center for the Study of Itch, and Departments of Anesthesiology, Psychiatry, Developmental Biology,

We previously showed that gastrin-releasing peptide receptor (GRPR) in the spinal cord is important for mediating nonhistaminergic itch. Neuromedin B receptor (NMBR), the second member of the mammalian bombesin receptor family, is expressed in a largely nonoverlapping pattern with GRPR in the superficial spinal cord, and its role in itch transmission remains unclear. Here, we report that Nmbr knock-out (KO) mice exhibited normal scratching behavior in response to intradermal injection of pruritogens. However, mice lacking both Nmbr and Grpr (DKO mice) showed significant deficits in histaminergic itch. In contrast, the chloroquine (CQ)-evoked scratching behavior of DKO mice is not further reduced compared with Grpr KO mice. These results suggest that NMBR and GRPR could compensate for the loss of each other to maintain normal histamine-evoked itch, whereas GRPR is exclusively required for CQ-evoked scratching behavior. Interestingly, GRPR activity is enhanced in Nmbr KO mice despite the lack of upregulation of Grpr expression; so is NMBR in Grpr KO mice. We found that NMB acts exclusively through NMBR for itch transmission, whereas GRP can signal through both receptors, albeit to NMBR to a much lesser extent. Although NMBR and NMBR(+) neurons are dispensable for histaminergic itch, GRPR(+) neurons are likely to act downstream of NMBR(+) neurons to integrate NMB-NMBR-encoded histaminergic itch information in normal physiological conditions. Together, we define the respective function of NMBR and GRPR in itch transmission, and reveal an unexpected relationship not only between the two receptors but also between the two populations of interneurons in itch signaling.
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http://dx.doi.org/10.1523/JNEUROSCI.1709-14.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4160775PMC
September 2014

Axonal transport: how high microtubule density can compensate for boundary effects in small-caliber axons.

Biophys J 2014 Feb;106(4):813-23

Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697. Electronic address:

Long-distance intracellular axonal transport is predominantly microtubule-based, and its impairment is linked to neurodegeneration. In this study, we present theoretical arguments that suggest that near the axon boundaries (walls), the effective viscosity can become large enough to impede cargo transport in small (but not large) caliber axons. Our theoretical analysis suggests that this opposition to motion increases rapidly as the cargo approaches the wall. We find that having parallel microtubules close enough together to enable a cargo to simultaneously engage motors on more than one microtubule dramatically enhances motor activity, and thus minimizes the effects of any opposition to transport. Even if microtubules are randomly placed in axons, we find that the higher density of microtubules found in small-caliber axons increases the probability of having parallel microtubules close enough that they can be used simultaneously by motors on a cargo. The boundary effect is not a factor in transport in large-caliber axons where the microtubule density is lower.
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http://dx.doi.org/10.1016/j.bpj.2013.12.047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944719PMC
February 2014

B-type natriuretic peptide is neither itch-specific nor functions upstream of the GRP-GRPR signaling pathway.

Mol Pain 2014 Jan 18;10. Epub 2014 Jan 18.

Center for the Study of Itch, Washington University School of Medicine Pain Center, St, Louis, MO 63110, USA.

Background: A recent study by Mishra and Hoon identified B-type natriuretic peptide (BNP) as an important peptide for itch transmission and proposed that BNP activates spinal natriuretic peptide receptor-A (NPRA) expressing neurons, which release gastrin releasing peptide (GRP) to activate GRP receptor (GRPR) expressing neurons to relay itch information from the periphery to the brain (Science 340:968-971, 2013). A central premise for the validity of this novel pathway is the absence of GRP in the dorsal root ganglion (DRG) neurons. To this end, they showed that Grp mRNA in DRG neurons is either absent or barely detectable and claimed that BNP but not GRP is a major neurotransmitter for itch in pruriceptors. They showed that NPRA immunostaining is perfectly co-localized with Grp-eGFP in the spinal cord, and a few acute pain behaviors in Nppb-/- mice were tested. They claimed that BNP is an itch-selective peptide that acts as the first station of a dedicated neuronal pathway comprising a GRP-GRPR cascade for itch. However, our studies, along with the others, do not support their claims.

Findings: We were unable to reproduce the immunostaining of BNP and NPRA as shown by Mishra and Hoon. By contrast, we were able to detect Grp mRNA in DRGs using in situ hybridization and real time RT-PCR. We show that the expression pattern of Grp mRNA is comparable to that of GRP protein in DRGs. Pharmacological and genetic blockade of GRP-GRPR signaling does not significantly affect intrathecal BNP-induced scratching behavior. We show that BNP inhibits inflammatory pain and morphine analgesia.

Conclusions: Accumulating evidence demonstrates that GRP is a key neurotransmitter in pruriceptors for mediating histamine-independent itch. BNP-NPRA signaling is involved in both itch and pain and does not function upstream of the GRP-GRPR dedicated neuronal pathway. The site of BNP action in itch and pain and its relationship with GRP remain to be clarified.
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http://dx.doi.org/10.1186/1744-8069-10-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3930899PMC
January 2014

Chronic itch development in sensory neurons requires BRAF signaling pathways.

J Clin Invest 2013 Nov;123(11):4769-80

Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF(Nav1.8) mice). We found that constitutive BRAF pathway activation in BRAF(Nav1.8) mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF(Nav1.8) mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis– or dry skin–elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.
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http://dx.doi.org/10.1172/JCI70528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809799PMC
November 2013

The role of α₂ adrenoceptor in mediating noradrenaline action in the ventrolateral orbital cortex on allodynia following spared nerve injury.

Exp Neurol 2013 Oct 18;248:381-6. Epub 2013 Jul 18.

Department of Physiology and Pathophysiology, Xi'an Jiaotong University College of Medicine, Yanta Road W. 76#, Xi'an, Shaanxi 710061, PR China; Department of Physiology, Xi'an Medical University, Xinwang Road 1#, Xi'an, Shaanxi 710021, PR China.

The present study examined the role of α₂ adrenoceptor in mediating noradrenaline action in the ventrolateral orbital cortex (VLO) on allodynia induced by spared nerve injury (SNI) in the rat. The mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of noradrenaline (1, 2, 4 μg in 0.5 μl) into the VLO, contralateral to the site of nerve injury, reduced allodynia; PWT increased in a dose-dependent manner. Similar to noradrenaline, microinjection of selective α₂ adrenoceptor agonist clonidine into the same VLO site also reduced allodynia, and was blocked by selective α₂ adrenoceptor antagonist yohimbine. Furthermore, administration of γ-aminobutyric acid A (GABAA) receptor antagonist bicuculline or picrotoxin to the VLO significantly enhanced clonidine-induced inhibition of allodynia, while GABAA receptor agonist muscimol or THIP (2,5,6,7-retrahydroisoxazolo(5,4-c)pyridine-3-ol hydrochloride) attenuated clonidine-induced inhibition. These results suggest that noradrenaline acting in the VLO can potentially reduce allodynia induced by SNI, and this effect is mediated by α₂ adrenoceptor. Moreover, GABAergic disinhibition may participate in α₂ receptor mediating effects in neuropathic pain in the central nervous system.
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http://dx.doi.org/10.1016/j.expneurol.2013.07.004DOI Listing
October 2013

Expansion of neurofilament medium C terminus increases axonal diameter independent of increases in conduction velocity or myelin thickness.

J Neurosci 2012 May;32(18):6209-19

Department of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA.

Maturation of the peripheral nervous system requires specification of axonal diameter, which, in turn, has a significant influence on nerve conduction velocity. Radial axonal growth initiates with myelination, and is dependent upon the C terminus of neurofilament medium (NF-M). Molecular phylogenetic analysis in mammals suggested that expanded NF-M C termini correlated with larger-diameter axons. We used gene targeting and computational modeling to test this new hypothesis. Increasing the length of NF-M C terminus in mice increased diameter of motor axons without altering neurofilament subunit stoichiometry. Computational modeling predicted that an expanded NF-M C terminus extended farther from the neurofilament core independent of lysine-serine-proline (KSP) phosphorylation. However, expansion of NF-M C terminus did not affect the distance between adjacent neurofilaments. Increased axonal diameter did not increase conduction velocity, possibly due to a failure to increase myelin thickness by the same proportion. Failure of myelin to compensate for larger axonal diameters suggested a lack of plasticity during the processes of myelination and radial axonal growth.
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http://dx.doi.org/10.1523/JNEUROSCI.0647-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3363292PMC
May 2012

The spinal muscular atrophy mouse model, SMAΔ7, displays altered axonal transport without global neurofilament alterations.

Acta Neuropathol 2011 Sep 17;122(3):331-41. Epub 2011 Jun 17.

Division of Biological Sciences, University of Missouri-Columbia, Columbia, MO 65211, USA.

Spinal muscular atrophy (SMA) is a neurodegenerative disease resulting from decreased levels of survival motor neuron 1 (SMN1) protein. Reduced SMN1 levels are linked to pathology at neuromuscular junctions (NMJs), which includes decreased vesicle density and organization, decreased quantal release, increased endplate potential duration, and neurofilament (NF) accumulations. This work presents a first study towards defining molecular alterations that may lead to the development of NMJ pathology in SMA. Fast, anterograde transport of synaptic vesicle 2 (SV2-c) and synaptotagmin (Syt1) proteins was reduced 2 days prior to the observed decrease in synaptic vesicle density. Moreover, reduced accumulation of SV2-c or Syt1 was not due to reduced protein expression or reduced kinesin activity. Dynein levels were reduced at times that are consistent with NF accumulations at NMJs. Furthermore, NF distribution, from cell body to sciatic nerve, appeared normal in SMA∆7 mice. Taken together, these results suggest that reduced axonal transport may provide a mechanistic explanation for reduced synaptic vesicle density and concomitant synaptic transmission defects, while providing evidence that suggests NF accumulations result from local NMJ alterations to NFs.
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http://dx.doi.org/10.1007/s00401-011-0848-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3286646PMC
September 2011

Muscle pathology without severe nerve pathology in a new mouse model of Charcot-Marie-Tooth disease type 2E.

Hum Mol Genet 2011 Jul 14;20(13):2535-48. Epub 2011 Apr 14.

Department of Biological Sciences, C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA.

Mutations in neurofilament light (NF-L) have been linked to Charcot-Marie-Tooth disease type 2E (CMT2E) in humans. To provide insight into disease pathogenesis, we developed a novel line of CMT2E mice that constitutively express human NF-L (hNF-L) with a glutamic acid to lysine mutation at position 397 (hNF-L(E397K)). This new line of mice developed signs consistent with CMT2E patients. Disease signs were first observed at 4 months in hNF-L(E397K) mice, and consisted of aberrant hind limb posture, digit deformities, reduced voluntary locomotor activity, reduced motor nerve conduction velocities (MNCVs) and muscle atrophy. Reduced voluntary locomotor activity and muscle pathology occurred without significant denervation, and hNF-L(E397K) mice showed relatively mild signs of nerve pathology. Nerve pathology in hNF-L(E397K) mice was characterized by ectopic accumulations of phosphorylated NFs in motor neuron cell bodies as early as 1 month. Moreover, NF organization was altered in motor and sensory roots, with small motor axons being most affected. Peak axonal diameter was reduced for small motor axons prior to and after the onset of overt phenotypes, whereas large motor axons were affected only after onset, which correlated with reduced MNCVs. Additionally, there was a small reduction in the number of sensory axons in symptomatic hNF-L(E397K) mice. hNF-L(E397K) mice are a novel line of CMT2E mice that recapitulate many of the overt phenotypes observed in CMT2E patients and hNF-L(P22S) mice. The cellular pathology observed in hNF-L(E397K) mice differed from that recently reported in hNF-L(P22S) mice, suggesting that overt CMT2E phenotypes may arise through different cellular mechanisms.
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http://dx.doi.org/10.1093/hmg/ddr152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3109999PMC
July 2011

New movements in neurofilament transport, turnover and disease.

Exp Cell Res 2007 Jun 21;313(10):2110-20. Epub 2007 Mar 21.

Division of Biological Sciences, University of Missouri-Columbia, 1201 East Rollins Street, Columbia, MO 65211, USA.

Revealing the mechanisms by which neurofilament transport and turnover are regulated has proven difficult over the years but recent studies have given new insight into these processes. Mature neurofilament fibers may incorporate a fourth functional subunit, alpha-internexin, as new evidence suggests. Recent findings have made the role of phosphorylation in regulating neurofilament transport velocity controversial. Kinesin and dynein may transport neurofilaments in slow axonal transport as they have been found to associate with neurofilaments. Neurofilament transport and turnover rates may be reduced depending on the existing stationary neurofilament network. Finally, mutations in neurofilament light that have been linked to Charcot-Marie-Tooth disease as well as other neurofilament abnormalities in human disease are discussed.
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http://dx.doi.org/10.1016/j.yexcr.2007.03.011DOI Listing
June 2007