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Spinal Cord Interneurons Expressing the Gastrin-Releasing Peptide Receptor Convey Itch Through VGLUT2-Mediated Signaling
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics. (Sensory Circuits)ORCID iD: 0000-0002-1386-1307
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics. (Sensory Circuits)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics. (Funktionella neuronala nätverk)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics. (Sensory Circuits)
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2017 (English)In: Pain, ISSN 0304-3959, E-ISSN 1872-6623, Vol. 158, no 5, 945-961 p.Article in journal (Refereed) Published
Abstract [en]

Itch is a sensation that promotes the desire to scratch, which can be evoked by mechanical and chemical stimuli. In the spinal cord, neurons expressing the gastrin-releasing peptide receptor (GRPR) have been identified as specific mediators of itch. However, our understanding of the GRPR population in the spinal cord, and thus how these neurons exercise their functions, is limited. For this purpose, we constructed a Cre line designed to target the GRPR population of neurons (Grpr-Cre). Our analysis revealed that Grpr-Cre cells in the spinal cord are predominantly excitatory interneurons that are found in the dorsal lamina, especially in laminae II-IV. Application of the specific agonist gastrin-releasing peptide induced spike responses in 43.3% of the patched Grpr-Cre neurons, where the majority of the cells displayed a tonic firing property. Additionally, our analysis showed that the Grpr-Cre population expresses Vglut2 mRNA, and mice ablated of Vglut2 in Grpr-Cre cells (Vglut2-lox; Grpr-Cre mice) displayed less spontaneous itch and attenuated responses to both histaminergic and nonhistaminergic agents. We could also show that application of the itch-inducing peptide, natriuretic polypeptide B, induces calcium influx in a subpopulation of Grpr-Cre neurons. To summarize, our data indicate that the Grpr-Cre spinal cord neural population is composed of interneurons that use VGLUT2-mediated signaling for transmitting chemical and spontaneous itch stimuli to the next, currently unknown, neurons in the labeled line of itch.

Place, publisher, year, edition, pages
2017. Vol. 158, no 5, 945-961 p.
Keyword [en]
Itch, Gastrin-releasing peptide receptor population, Natriuretic polypeptide B, Spinal cord, Vesicular glutamate transporter 2, Neuronal networks, Labeled line of itch, Electrophysiology, Conditional knockout analysis, Tracing, Calcium imaging, Grpr, VGLUT2
National Category
Medical and Health Sciences
Research subject
Medical Science
Identifiers
URN: urn:nbn:se:uu:diva-284058DOI: 10.1097/j.pain.0000000000000861ISI: 000402430600021PubMedID: 28157737OAI: oai:DiVA.org:uu-284058DiVA: diva2:919693
Funder
Swedish Research CouncilThe Swedish Brain FoundationThe Royal Swedish Academy of SciencesRagnar Söderbergs stiftelseMagnus Bergvall FoundationGunvor och Josef Anérs stiftelse
Note

Title in thesis list of papers: Spinal Cord Interneurons Expressing the Gastrin Releasing Peptide Receptor Convey Itch through VGLUT2-mediated Signaling

Available from: 2016-04-14 Created: 2016-04-14 Last updated: 2017-07-10Bibliographically approved
In thesis
1. Functional Aspects of Peripheral and Spinal Cord Neurons Involved in Itch and Pain
Open this publication in new window or tab >>Functional Aspects of Peripheral and Spinal Cord Neurons Involved in Itch and Pain
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We have investigated the role of the metabotropic glutamate receptor 7 (mGluR7) and the gastrin releasing peptide receptor (Grpr) population that are involved at different levels of itch transmission. We found that mGuR7 deficient mice displayed an anaphylaxis-like behavior when provoked with histamine. Analysis of blood revealed elevated plasma levels of histamine and mouse mast cell protease-1 (mMCP1), two indicators of anaphylaxis, in mGluR7 deficient mice compared with control mice. Inhibition of the neurokinin 1 receptor, by preventing binding of the corresponding ligand substance P (SP), prior to provocation with histamine prevented the development of anaphylaxis in mGluR7 deficient animals. However, blocking GRPR (gastrin releasing peptide receptor) only resulted in decreased itch levels in mGluR7 deficient mice but did not prevent the systemic anaphylaxis-like behavior. Our findings indicate that mGluR7 normally functions as a brake on histaminergic itch that is mediated through GRPR as well as anaphylaxis through Substance P.

Grpr has previously been shown to mediate both histaminergic and non-histaminergic itch but little is known about the GRPR neuronal population. We used a BAC cloning strategy to construct a Grpr-Cre line, which we crossed with the reporter lines tdTomato and Viaat-egfp as well as with Vglut2-lox. We could conclude that Grpr-Cre neurons are mainly excitatory interneurons located in lamina II-IV, that convey itch using VGLUT2-mediated glutamatergic transmission to the next, currently unknown, step in the labeled line of chemical itch.

To eventually deduce the function of the endogenous opioids dynorphin and enkephalin, which are hypothesized to be involved in gating pain and itch in the spinal cord, we constructed two Cre lines using BAC cloning that targeted the precursor proteins preprodynorphin and preproenkephalin, respectively. Preprodynorphin-Cre neurons were mainly located in lamina II-IV and overlapped to 47% with Vglut2 mRNA, while the co-expression with the inhibitory markers Viaat-egfp and PAX2 was 13% and 28% respectively in the spinal cord. Preproenkephalin neurons were more localized to lamina III in the dorsal horn, furthermore single cell analysis showed that they overlapped to 94% with Vglut2 mRNA while 7% and 13% expressed Viaat-egfp and PAX2 respectively.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 48 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1222
Keyword
mGluR7, anaphylaxis, Grpr, Penk, Pdyn, Cre line, BAC cloning, spinal cord, transgenic line
National Category
Medical and Health Sciences
Research subject
Medical Science
Identifiers
urn:nbn:se:uu:diva-284070 (URN)978-91-554-9568-8 (ISBN)
Public defence
2016-06-04, C2:301, Husargatan 3, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2016-05-13 Created: 2016-04-14 Last updated: 2016-06-01

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Aresh, BejanFreitag, Fabio B.Perry, SharnLau, JoeyFranck, Marina C.M.Lagerström, Malin C.

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