Production of acute and chronic itch with histamine and contact sensitizers in the mouse and guinea pig

Itch is a major symptom of skin disease and is poorly understood, in part due to the lack of adequate small animal models. We show, using iontophoresis of histamine and capsaicin, that it is possible to induce scratching behaviour in both guinea pig and mouse. Use of iontophoresis may obviate the problems of induction of pain as well as itch when injection is used. The behavioural response to capsaicin, however, differs from that seen with histamine, raising the possibility that the use of scratch counts as a method of measuring itch severity needs to be set in the context of other responses. Naloxone partly inhibits scratching in mouse and guinea pig due to histamine. We also show that contact sensitization with 2-4 dinitrochlorobenzene DNCB) can be used as a simple assay for chronic itch allowing study of scratching over at least a 15-h period. The characteristics of scratching (but not the time course) induced with DNCB are similar to those seen with histamine.