Abstract
Arthropods are the largest group of living organisms, and among them, mosquitoes spread parasites and viruses causing deadly diseases. They can easily spread these pathogens because of their painless skin piercing. Although the lack of pain is mainly due to the thinness of their fascicle, it is possible that mosquito saliva, which is discharged during their piercing, might also contribute to it. If mosquito saliva contains antinociceptive substances, it should act on the sensory neurons innervating the epidermis where there are several ion channels that can detect noxious stimuli, such as the transient receptor potential (TRP) channels. We found that mosquito head homogenates and mouse saliva inhibit TRP vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1) channels, either heterologously expressed in HEK293T cells or endogenously expressed in native mouse sensory neurons. Among the different substances contained in mosquito head homogenates or mouse saliva, we have also identified sialorphin as a candidate antinociceptive peptide because it showed similar inhibition effects on TRPV1 and TRPA1. Finally, we confirmed the antinociceptive effects of mosquito head homogenates, mouse saliva, and sialorphin in vivo by observing decreased pain-related behaviors in mice coinjected with these substances. Similar inhibitory effects of mosquito head homogenates and mouse saliva on TRPV1 and TRPA1 suggest that the antinociceptive effects of saliva are universal, which could explain why many animals including humans often lick their wounds. These findings would lead to the development of novel and safe antinociceptive agents.