Comparison of rat itch model induced by different pruritogens

Abstract

Objective To compare and analyze the effectiveness of different pruritogens on the itch model in rats. Methods A total of 240 healthy male SD rats aged 3 to 4 months were selected and divided into 3 groups: histamine-dependent pruritogens group (histamine phosphate, compound 48/80), non-histamine-dependent pruritogens group (5-HT, chloroquine and endothelin-1) and normal saline control group. The neck and cheek were selected as the itching area to compare the itching effects of different doses (low, medium and high concentrations) of pruritogens within 30 min after intradermal injection. The difference in the frequency of hind limb scratching was recorded by using the hind limb magnetic ring combined with behavior recording box system. The changes of sensory nerve endings evoked potential in the skin and the mast cells in subcutaneous tissue were observed and analyzed by means of multi-channel physiological signal acquisition and processing system and toluidine blue staining. Results In the histamine-dependent pruritogens group, only compound 48/80 at medium and high concentrations induced the increment of times of neck and cheek scratching, which was significantly different from the control group (P < 0.05); increases in frequency and amplitude of sensory nerve endings evoked potential (P < 0.05); and elevated number of mast cells near the blood vessels in the subcutaneous tissue (P < 0.05). And, increased times of scratching in neck and cheek were observed in the phosphohistamine group after injection of the 3 concentrations (P < 0.05). High concentration enhanced the frequency of subcutaneous evoked potential and increased the number of mast cells between the control group and the histamine phosphate group (both P < 0.05). Conclusion The best itch effectiveness is induced by 5-HT in rats, even with low concentration. While, histamine-dependent pruritogens compound 48/80 and non-histamine-dependent pruritogens chloroquine and endothelin-1 are only effective at medium to high concentrations. Histamine fails to induce scratching behaviors, and is difficult to induce the model.

Keywords

• itch
• rats
• pruritogens
• scratching behavior
• mast cells
• sensory nerve endings evoked potential