title: Primary afferent and spinal cord expression of gastrin-releasing peptide: message, protein, and antibody concerns.
abstract: There is continuing controversy relating to the primary afferent neurotransmitter that conveys itch signals to the spinal cord. Here, we investigated the DRG and spinal cord expression of the putative primary afferent-derived "itch" neurotransmitter, gastrin-releasing peptide (GRP). Using ISH, qPCR, and immunohistochemistry, we conclude that GRP is expressed abundantly in spinal cord, but not in DRG neurons. Titration of the most commonly used GRP antiserum in tissues from wild-type and GRP mutant mice indicates that the antiserum is only selective for GRP at high dilutions. Paralleling these observations, we found that a GRPeGFP transgenic reporter mouse has abundant expression in superficial dorsal horn neurons, but not in the DRG. In contrast to previous studies, neither dorsal rhizotomy nor an intrathecal injection of capsaicin, which completely eliminated spinal cord TRPV1-immunoreactive terminals, altered dorsal horn GRP immunoreactivity. Unexpectedly, however, peripheral nerve injury induced significant GRP expression in a heterogeneous population of DRG neurons. Finally, dual labeling and retrograde tracing studies showed that GRP-expressing neurons of the superficial dorsal horn are predominantly interneurons, that a small number coexpress protein kinase C gamma (PKCγ), but that none coexpress the GRP receptor (GRPR). Our studies support the view that pruritogens engage spinal cord "itch" circuits via excitatory superficial dorsal horn interneurons that express GRP and that likely target GRPR-expressing interneurons. The fact that peripheral nerve injury induced de novo GRP expression in DRG neurons points to a novel contribution of this peptide to pruritoceptive processing in neuropathic itch conditions.
authors.affiliation: Departments of Anatomy.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0003-4624-6711
authors.initials: C
authors.lastname: Solorzano
authors.affiliation: Departments of Anatomy.
authors.forename: David
authors.initials: D
authors.lastname: Villafuerte
authors.affiliation: Departments of Anatomy.
authors.forename: Karuna
authors.initials: K
authors.lastname: Meda
authors.affiliation: Departments of Anatomy, Dermatology, and.
authors.forename: Ferda
authors.initials: F
authors.lastname: Cevikbas
authors.affiliation: Departments of Anatomy.
authors.forename: Joao
authors.identifier: http://orcid.org/0000-0002-5792-1017
authors.initials: J
authors.lastname: Bráz
authors.affiliation: Departments of Anatomy.
authors.forename: Reza
authors.identifier: http://orcid.org/0000-0001-8896-5306
authors.initials: R
authors.lastname: Sharif-Naeini
authors.affiliation: Departments of Anatomy.
authors.forename: Dina
authors.initials: D
authors.lastname: Juarez-Salinas
authors.affiliation: Cardiovascular Medicine, Human Physiology and Centre for Neuroscience, Flinders University, Bedford Park, SA 5042, Australia.
authors.forename: Ida J
authors.initials: IJ
authors.lastname: Llewellyn-Smith
authors.affiliation: Anesthesia and Perioperative Care, University of California San Francisco, San Francisco, California 94158, and.
authors.forename: Zhonghui
authors.initials: Z
authors.lastname: Guan
authors.affiliation: Departments of Anatomy, allan.basbaum@ucsf.edu.
authors.forename: Allan I
authors.initials: AI
authors.lastname: Basbaum
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D019886:Gastrin-Releasing Peptide / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D007120:Immunochemistry / Q000379:methods / Q000592:standards; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009475:Neurons, Afferent / Q000378:metabolism*; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012680:Sensitivity and Specificity; D013116:Spinal Cord / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism
chemical_list: D000906:Antibodies; D012333:RNA, Messenger; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D019886:Gastrin-Releasing Peptide
keywords: DRG; GRP; GRPR; itch; nerve injury; pain