Spinal Functions of B-Type Natriuretic Peptide Gastrin-ReleasingPeptide and Their Cognate Receptors for Regulating Itch in Mice

摘要

B-type natriuretic peptide (BNP)–natriuretic peptide receptor A (NPRA) and gastrin-releasing peptide (GRP)–GRP receptor (GRPR) systems contribute to spinal processing of itch. However, pharmacological and anatomic evidence of these two spinal ligand-receptor systems are still not clear. The aim of this study was to determine the spinal functions of BNP-NPRA and GRP-GRPR systems for regulating scratching activities in mice by using pharmacological and immunohistochemical approaches. Our results showed that intrathecal administration of BNP (0.3–3 nmol) dose dependently elicited scratching responses, which could be blocked by the NPRA antagonist (Arg6,β-cyclohexyl-Ala8,D-Tic16,Arg17,Cys18)-atrial natriuretic factor(6-18) amide (). However, had no effect on intrathecal GRP-induced scratching. In contrast, pretreatment with a GRPR antagonist (D-Tpi6,Leu13ψ(CH2-NH)-Leu14)bombesin(6-14) (RC-3095) inhibited BNP-induced scratching. Immunostaining revealed that NPRA proteins colocalize with GRP, but not GRPR, in the superficial area of dorsal horn, whereas BNP proteins do not colocalize with either GRP or GRPR in the dorsal horn. Intradermal administration of ligands including endothelin-1, U-46619, bovine adrenalmedulla 8-22, and Ser-Leu-Ile-Gly-Arg-Leu-NH2 (SLIGRL) increasedscratching bouts at different levels of magnitude. Pretreatment with intrathecal did not affect scratching responses elicited by all four pruritogens, whereaspretreatment with RC-3095 only inhibited SLIGRL-induced scratching. Interestingly,immunostaining showed that RC-3095, but not , inhibited SLIGRL-elicited c-Fosactivation in the spinal dorsal horn, which was in line with behavioral outcomes.These findings demonstrate that: 1) BNP-NPRA system may function upstream of theGRP-GRPR system to regulate itch in the mouse spinal cord, and 2) both NPRA and GRPRantagonists may have antipruritic efficacy against centrally, but not peripherally,elicited itch.