TRPA1 Channel is Involved in SLIGRL-Evoked Thermal and Mechanical Hyperalgesia in Mice

Persistent itch (pruritus) accompanying dermatologic and systemic diseases can significantly impair the quality of life. It is well known that itch is broadly categorized as histaminergic (sensitive to antihistamine medications) or non-histaminergic. Sensory neurons expressing Mas-related G-protein-coupled receptors (Mrgprs) mediate histamine-independent itch. These receptors have been shown to bind selective pruritogens in the periphery and mediate non-histaminergic itch. For example, mouse MrgprA3 responds to chloroquine (an anti-malarial drug), and are responsible for relaying chloroquine-induced scratching in mice. Mouse MrgprC11 responds to a different subset of pruritogens including bovine adrenal medulla peptide (BAM8-22) and the peptide Ser-Leu-Ile-Gly-Arg-Leu (SLIGRL). On the other hand, the possibility that itch mediators also influence pain is supported by recent findings that most non-histaminergic itch mediators require the transient receptor potential ankyrin 1 (TRPA1) channel. We have recently found a significant increase of thermal and mechanical hyperalgesia induced by non-histaminergic pruritogens chloroquine and BAM8-22, injected into mice hindpaw, for the first 30-45 min. Pretreatment with TRPA1 channel antagonist HC-030031 did significantly reduce the magnitude of this hyperalgesia, as well as significantly shortened the time-course of hyperalgesia induced by chloroquine and BAM8-22. Here, we report that MrgprC11-mediated itch by their agonist SLIGRL is accompanied by heat and mechanical hyperalgesia via the TRPA1 channel. We measured nociceptive thermal paw withdrawal latencies and mechanical thresholds bilaterally in mice at various time points following intra-plantar injection of SLIGRL producing hyperalgesia. When pretreated with the TRPA1 antagonist HC-030031, we found a significant reduction of thermal and mechanical hyperalgesia.