Cyclical changes in rat vibrissa follicles maintained in vitro

In mammals hair growth is cyclical; however, the factors that regulate the hair growth cycle are still poorly understood. The recent development of me thods for culturing hair follicles in vitro has proved an important tool to investigate many aspects of the regulation of hair follicle growth. At pre sent, however, these models are based on the culture of anagen hair follicl es and have only partially been used to address the cyclical nature of hair growth. In this study we have made use of the fact that in rodents the hai r growth cycle is synchronized, well characterized, and relatively short. W e have isolated vibrissa follicles from 12 d old rats and confirmed by hist ology that these follicles are in the anagen stage of their first hair grow th cycle. We have then maintained these follicles in vitro, on Gelfoam supp orts, for up to 23 d (35 d of age) and compared their histology with in viv o follicles from equivalent age littermates. We observed that 12 d old foll icles maintained in vitro for up to 23 d show changes in morphology that su ggest that cultured rat vibrissa follicles retain cyclical activity in vitr o. Cyclical changes in hair follicle morphology were only seen in follicles maintained on gelfoam supports and moreover, hair follicle size appears to be a key feature in determining the ability of the follicle to cycle in vi tro. All follicles that showed cyclical changes in vitro, however, appeared to remain blocked in pro-anagen. These data suggest that the vibrissa foll icle is a in vitro good model system with which to investigate hair cycle c ontrol.