Roles of mast cells and histamine in mosquito bite-induced allergic itch-associated responses in mice

We investigated itch-associated responses (scratching) to mosquito bites an d the role of histamine and mast cells in mosquito-induced itching in mice. Although the first bites of mosquito Aedes albopictus did not increase scr atching, repeated bites increased scratching. The response was not diminish ed even after an interval of 2 months. Similarly, repeated intradermal (i.d .) injections of salivary gland extract (SGE) from Aedes albopictus increas ed scratching after SGE injection itself and mosquito bites. The scratching peaked within 10 min and almost subsided by 60 min. The opioid antagonist naloxone (1 mg/kg, s.c.) inhibited scratching following SGE injection. Alth ough the non-sedative H-1-histamine-receptor antagonist terfenadine (30 mg/ kg, p.o.) significantly suppressed scratching induced by histamine (100 nmo l/site, i.d.) in either naive or mosquito-sensitized mice, it did not affec t mosquito-induced scratching in mosquito-sensitized mice. Repeated injecti ons of SGE increased scratching in mast cell-deficient (WBB6F1-W/W-v) mice as well as in normal (WBB6F1-+/_) littermates. Repeated exposure to mosquit o bites roughly doubled serum concentrations of total IgE and IgG(1), but n ot IgG(2a). Repeated injections of SGE markedly increased plasma extravasat ion induced by mosquito bites and such an increase was almost completely su ppressed by terfenadine (30 mg/kg,p.o.). The results show the presence of h istamine-mediated and histamine-independent mechanisms in cutaneous itching and suggest that histamine probably released from mast cells does not play an important role in itching in immediate allergic reaction. Our murine mo del of mosquito itching may be useful for studying the mechanisms of immedi ate allergic itching.