Chemogenetic activation of central gastrin‐releasing peptide‐expressing neurons elicits itch‐related scratching behavior in male and female mice

Several lines of evidence have clarified that the key transmission pathways of itching sensation travel from the periphery to the central nervous system (CNS). Despite the functional significance of gastrin‐releasing peptide (GRP) and its cognate receptor in the itch processing mechanism in the spinal dorsal horn (SDH), the roles of GRP‐expressing (GRP(+)) neurons in different regions remain unclear. This study aimed to determine whether GRP(+) neurons in the CNS directly modulated itch processing. To specifically activate spinal and supraspinal GRP neurons by the designer receptors exclusively activated by designer drugs (DREADDs) system, CAG‐LSL‐Gq‐DREADD mice were crossed with GRP‐Cre mice, resulting in the development of GRP‐hM3Dq mice. Immunohistochemistry showed that hM3Dq was highly expressed in the SDH and brainstem closely related to sensory processing. The intraperitoneal, intrathecal, or intracerebroventricular administration of clozapine‐N‐oxide, an agonist of hM3Dq, strongly elicited dermatome‐dependent itch‐related scratching behavior, but did not change pain sensitivity. Importantly, GRP‐Gq‐DREADD‐mediated scratching behavior in GRP‐hM3Dq mice was not affected by the ablation of transient receptor potential vanilloid 1(+) sensory C‐fibers, and it was also observed to a similar degree under chronic itch conditions. Furthermore, there were no significant sex differences in the scratching behavior elicited by GRP‐Gq‐DREADD, suggesting that itch‐dominant roles of central GRP(+) neurons might be common in both sexes, at least under normal physiological conditions. These novel findings not only contribute to understanding the functional roles of central GRP(+) neurons further, but also propose the development of future effective therapeutics for intractable itching.