HAIR-FOLLICLES OF YOUNG WISTAR STRAIN HAIRLESS RATS - A HISTOLOGICAL STUDY

The histological changes in hair follicles in hairless rats derived fr om the Wistar strain (hW, hairless Wistar) were examined from birth to maturity and compared with those of age-matched normal Wistar rats. I n the Ist hair cycle, the hair follicles of hW rats were shorter and l ess well developed than those of Wistar rats. In early anagen, eosinop hilic bodies were observed in some hair follicles which showed immatur e histological features. By using Tdt-mediated dUTP nick end labelling (TUNEL) method and electron microscopic examination, these bodies wer e confirmed to be apoptotic bodies. These follicles seemed to disappea r by abnormal regression. In late anagen phase, the follicles in which the apoptosis did not occur showed enlarged hair roots with hypertrop hy of the inner root sheath. Subsequently, when the follicles in norma l Wistar rats synchronously regressed in the catagen phase, most of th e follicles in hW rats similarly entered the catagen phase, but a few follicles did not regress completely and showed aberrant hair root enl argement, Finally, both types of follicle in hW rats formed follicular cysts. These abnormalities in follicle development (abnormal follicul ar regression and follicular cyst formation) appear to be associated w ith the hairlessness in this rat strain.