096 Standardized macroscopic quantification of murine hair follicle regression (catagen) in vivo by dotmetric planimetry

Murat Ünalan and Ralf Paus; Department of Dermatology, University Hospital Eppendorf, University of Hamburg, Hamburg, Germany

The murine hair cycle is an instructive model for identifying catagen-manipulatory agents, and the analysis of catagen-associated changes in back skin pigmentation of C57BL/6 mice has been a particularly attractive study system. However, standardized, sensitive, accurate and quantitative techniques for assessing these skin color changes as indicator of catagen development in vivo remain to be developed. Here we present “dotmetric planimetry” (DMP) as a very simple, new assay system that meets these requirements.To correlate distinct hair cycle stages with the catagen-associated back skin color changes, telogen C57BL/6 mice were anagen-induced by depilation. Spontaneous catagen development was then assessed by photodocumenting the skin color changes, and by planimetric measurement of the percentage of the catagen area, using a transparency and a uniform dot pattern (=dot matrix). Dots were counted and related to the total dot-count of the entire back skin area. On day 18 after depilation, i.e. when back skin displays three different colorgrades (black-grey-pink) and when almost all anagen follicles have entered into catagen, the mice were sacrificed, and color-classified biopsies were subjected to quantitative histomorphometry. On day 18 after depilation, the skin classified as pink occupied 17-27%, grey skin 31-44% and black skin 37-45% of the back skin. By histomorphometry , pink skin corresponded predominantly to catagen stages VI+VII (97%), grey skin to catagen stages III-V (76%), and black skin samples to catagen II+III (88%). DMP allows one to easily correlate the macroscopic skin color with the underlying hair cycle stage, and enables one to record and quantify the effects of any test agent on the wave-like, polarized catagen development from neck to tail in murine back skin - during ongoing in vivo-experimentation, and without the need for histology. DMP may also be used for analyzing a wide range of patterned skin phenomena, including androgenetic alopecia and alopecia areata.