Spinal functions of b-type natriuretic peptide, gastrin-releasing peptide, and their cognate receptors for regulating itch in mice

Abstract

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 ligandreceptor 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 (A71915). However, A71915 had no effect on intrathecalGRP-induced scratching. In contrast, pretreatment with a GRPR antagonist (D-Tpi6,Leu13Φ (CH2-NH)-Leu14)bombesin(6-14) (RC-3095) inhibited BNPinduced scratching. Immunostaining revealed that NPRA proteins colocalize withGRP, but notGRPR, 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 adrenal medulla 8-22, and Ser-Leu-Ile-Gly-Arg-Leu-NH2 (SLIGRL) increased scratching bouts at different levels of magnitude. Pretreatment with intrathecal A71915 did not affect scratching responses elicited by all four pruritogens, whereas pretreatment with RC-3095 only inhibited SLIGRL-induced scratching. Interestingly, immunostaining showed that RC-3095, but not A71915, inhibited SLIGRLelicited c-Fos activation in the spinal dorsal horn, which was in line with behavioral outcomes. These findings demonstrate that: 1) BNP-NPRA system may function upstream of the GRP-GRPR systemto regulate itch in themouse spinal cord, and 2) bothNPRA and GRPR antagonists may have antipruritic efficacy against centrally, but not peripherally, elicited itch.