title: Itch-associated peptides: RNA-Seq and bioinformatic analysis of natriuretic precursor peptide B and gastrin releasing peptide in dorsal root and trigeminal ganglia, and the spinal cord.
abstract: BACKGROUND
  Three neuropeptides, gastrin releasing peptide (GRP), natriuritic precursor peptide B (NPPB), and neuromedin B (NMB) have been proposed to play roles in itch sensation. However, the tissues in which these peptides are expressed and their positions in the itch circuit has recently become the subject of debate. Here we used next-gen RNA-Seq to examine the expression of transcripts coding for GRP, NPPB, NMB, and other peptides in DRG, trigeminal ganglion, and the spinal cord as well as expression levels for their cognate receptors in these tissues.
  
  
  RESULTS
  RNA-Seq demonstrates that GRP is not transcribed in mouse, rat, or human sensory ganglia. NPPB, which activates natriuretic peptide receptor 1 (NPR1), is well expressed in mouse DRG and less so in rat and human, whereas NPPA, which also acts on the NPR1 receptor, is expressed in all three species. Analysis of transcripts expressed in the spinal cord of mouse, rat, and human reveals no expression of Nppb, but unambiguously detects expression of Grp and the GRP-receptor (Grpr). The transcripts coding for NMB and tachykinin peptides are among the most highly expressed in DRG. Bioinformatics comparisons using the sequence of the peptides used to produce GRP-antibodies with proteome databases revealed that the C-terminal primary sequence of NMB and Substance P can potentially account for results from previous studies which showed GRP-immunostaining in the DRG.
  
  
  CONCLUSIONS
  RNA-Seq corroborates a primary itch afferent role for NPPB in mouse and potentially NPPB and NPPA in rats and humans, but does not support GRP as a primary itch neurotransmitter in mouse, rat, or humans. As such, our results are at odds with the initial proposal of Sun and Chen (2007) that GRP is expressed in DRG. By contrast, our data strongly support an itch pathway where the itch-inducing actions of GRP are exerted through its release from spinal cord neurons.
authors.forename: Samridhi C
authors.initials: SC
authors.lastname: Goswami
authors.forename: Danielle
authors.initials: D
authors.lastname: Thierry-Mieg
authors.forename: Jean
authors.initials: J
authors.lastname: Thierry-Mieg
authors.forename: Santosh
authors.initials: S
authors.lastname: Mishra
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hoon
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Mannes
authors.affiliation: Department of Perioperative Medicine, Building 10, Room 2C401, MSC 1510, Clinical Center, NIH, 10 Center Drive, Bethesda, MD 20892, USA. michael.iadarola@nih.gov.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Iadarola
mesh_terms: D000818:Animals; D001483:Base Sequence; D019295:Computational Biology; D005727:Ganglia, Spinal / Q000378:metabolism*; D019886:Gastrin-Releasing Peptide / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D020097:Natriuretic Peptide, Brain / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D018013:Receptors, Neuropeptide / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D013116:Spinal Cord / Q000166:cytology*; D012668:Trigeminal Ganglion / Q000378:metabolism*
chemical_list: D018013:Receptors, Neuropeptide; D020097:Natriuretic Peptide, Brain; D019886:Gastrin-Releasing Peptide