4-Aminopyridine-induced licking response and histamine liberation in mice

4-Aminopyridine (4-AP) 1 mg.kg-1 sc at the scruff induced a licking response in mice. H1 receptor blockaders, such as diphenhydramine HCl (1, 10 mg.kg-1, sc at the scruff or 40 mg.kg-1, i.p.), chlorphenamine maleate (20 mg.kg-1, i.p.), and astemizole (2 mg.kg-1, i.g.), inhibited the licking response caused by 4-AP. Repeated injections of 4-AP (1 mg.kg-1) reduced the times of lick and the histamine content in the skin of injected site. 4-AP also promoted histamine release from incubated mouse peritoneal mast cells (PMC) in a dose-dependent manner. The results indicate that the licking response may originate from the histamine liberation of mast cells.