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,b-cyclohexyl-Ala8,D-Tic16, Arg17,Cys18)-atrial natriuretic factor(6-18) amide (A71915). However, A71915 had no effect on intrathecal GRP-induced scratching. In contrast, pretreatment with a GRPR antagonist (D-Tpi6,Leu13c (CH2-NH)-Leu14)bombesin(6-14) (RC-3095) inhibited BNPinduced 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 adrenal medulla 8-22, and Ser-Leu-Ile-Gly-Arg-Leu-NH 2 (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 system to regulate itch in the mouse spinal cord, and 2) both NPRA and GRPR antagonists may have antipruritic efficacy against centrally, but not peripherally, elicited itch.

A central role for R7bp in the regulation of itch sensation

“…4A) [32; 39; 40]. Scratching behavior resulting from the intrathecal administration of Nppb is blocked by pretreatment with a Grpr antagonist [19]. Wild-type and Nppb −/− mice, but not Grpr −/− mice, exhibit scratching behavior in response to the intrathecal administration of GRP [32; 39].…”

Interventions in the B‐type natriuretic peptide signalling pathway as a means of controlling chronic itch

“…They also demonstrated BNP transmitted itch signals to NPRA expressed primarily in lamina I to contribute to spinal processing of itch (Mishra & Hoon, ). The BNP released from peripheral sensory neurons stimulates its receptor in NPRA + ‐spinal cord neurons to release GRP in the spinal cord to activate canonical GRP receptor ( Grpr ) + ‐neurons in order to transmit itch signal to the brain (Hoon, ; Kiguchi et al, ). In addition, Nppb −/− mice, but not Grpr −/− mice, exhibit scratching behaviour upon intrathecal injection of GRP (Mishra & Hoon, ; Sun & Chen, ).…”

“…Initially, Kiguchi et al observed that the onset and magnitude of intrathecal BNP‐induced scratching are slower and smaller than that induced by intrathecal GRP (Kiguchi et al, ), thus raising the hypothesis that BNP initiates itch indirectly through activation of a GRP pathway. They showed that intrathecal administration of BNP antagonist A71915 in mice had no effect on intrathecal GRP‐induced scratching, whereas the GRP antagonist RC‐3095 inhibited BNP‐induced scratching (Kiguchi et al, ), confirming that the BNP‐NPRA system may act upstream of GRP‐GRPR to regulate itch in the mouse spinal cord (Kiguchi et al, ). In their study, A71915 also had little effect on peripherally elicited scratching upon intradermal injection of ET‐1, thromboxane A 2 analogue, BAM8‐22 (activator of MrgprC11), and SLIGRL (a PAR2 agonist) in mice, thus concluding that there was a minimal role for the spinal BNP‐NPRA system in regulating peripheral itch (Kiguchi et al, ).…”

“…Among them, only A71915 has been tested for itch relief in animal models (Solinski, Dranchak, et al, 2019). induced by intrathecal GRP (Kiguchi et al, 2016), thus raising the hypothesis that BNP initiates itch indirectly through activation of a GRP pathway. They showed that intrathecal administration of BNP antagonist A71915 in mice had no effect on intrathecal GRP-induced scratching, whereas the GRP antagonist RC-3095 inhibited BNPinduced scratching (Kiguchi et al, 2016), confirming that the BNP-NPRA system may act upstream of GRP-GRPR to regulate itch in the mouse spinal cord (Kiguchi et al, 2016).…”

“…They showed that intrathecal administration of BNP antagonist A71915 in mice had no effect on intrathecal GRP-induced scratching, whereas the GRP antagonist RC-3095 inhibited BNPinduced scratching (Kiguchi et al, 2016), confirming that the BNP-NPRA system may act upstream of GRP-GRPR to regulate itch in the mouse spinal cord (Kiguchi et al, 2016). In their study, A71915 also had little effect on peripherally elicited scratching upon intradermal injection of ET-1, thromboxane A 2 analogue, BAM8-22 (activator of MrgprC11), and SLIGRL (a PAR2 agonist) in mice, thus concluding that there was a minimal role for the spinal BNP-NPRA system in regulating peripheral itch (Kiguchi et al, 2016). Their finding was later challenged by Mishra & Hoon (2013), who found that elimination of Nppb or the ablation of spinal interneurons expressing NPRA profoundly attenuated scratching response to intradermal administration of histamine, chloroquine, ET-1, 5-HT, SLIGRL, and compound 48/80.…”