An automated method for registering and quantifying scratching activity in mice: use for drug evaluation

A method, which allows the automated registration of the scratching activity of the hind legs of a mouse for periods longer than 24 h, has been developed and validated. Aluminium rings are placed around the hind limbs of mice just above the ankle. Mice are housed individually in cages placed on the scratch detection unit (SDU), which contains ferrite rods fitted with copper coils. The movement of the metal rings in the field generated by the coils elicits a signal that can be transformed into peaks of different frequencies. Scratching was defined as a regular waveform with a frequency of > 15 Hz and with an amplitude of < 200 mV. Quantification of spontaneous scratching by chronic proliferative dermatitis mice or histamine and Compound 48/80-treated C57BL/Ka mice was performed visually (using a video recording showing both the mice and the computer-generated signal) and using the pruritus detection system (PDS = SDU plus computer program). The correlation between visual and automatic quantification of spontaneous cpdm mouse scratching was 81.7+/-2.5% (mean +/- S.E.M.). For histamine, the correlation was 85.6+/-3.6% (mean +/- S.E.M.) and for Compound 48/80, 85.8+/-3.1% (mean +/- S.E.M.). The PDS routinely detected less than 5% false-positive signals.