Presence of itch qualities in mice

In our clinical study, we found that itching had many different expressions (or qualities), including ‘ muzumuzu ’ (creepy-crawly itching, somewhat like tickling) and ‘itch like mosquito bites’. Therefore, we investigated whether there were behavioral differences in response to different pruritogens in mice. In addition, we compared the behavioral characteristics of spontaneous scratching in mice with atopic-like dermatitis. In this study, we used six pruritogens histamine, 5-hydroxytryptamine (5-HT), substance P, α-melanocyte-stimulating hormone (α-MSH), protease-activated receptor 2 agonist Ser-Leu-Ile-Gly-Arg-Leu-NH2 (SLIGRL), and chloroquine. Pruritogen was intradermally injected into the rostral back skin of institute of cancer research (ICR) mice. Nishiki-nezumi Cinnamon/Nagoya (NC/Nga) mice infected with mites were used as animal model of atopic dermatitis (dermatitis NC/Nga mice). Their behavior was recorded using a digital video camera. The number of scratching behaviors was divided according to the presence or absence of precursor behaviors, such as shivering and body grooming-like behavior with the forelimbs, to scratching behaviors. Intradermal injection of histamine and substance P induced scratching without precursor behavior. On the other hand, intradermal injection of 5-HT and α-MSH-induced scratching after precursor behaviors. SLIGRL elicited scratching both with and without precursor behavior. In dermatitis NC/Nga mice, spontaneous scratching was induced mainly following precursor behaviors. These results suggest that itch-related behavior in mice is also characterized by the type of itching. Itching in atopic dermatitis is resistant to antihistamines. In this study, we demonstrated that the characteristics of histamine-induced scratching and dermatitis-induced spontaneous itching are different. This suggests that behavioral analyses may be useful for developing drugs to treat itching caused by diseases.