Changes in the number of Merkel cells with the hair cycle in hair discs on rat back skin.

BACKGROUND: Hair discs are known to contain a large number of Merkel cells and are ideal for investigating Merkel cell biology. Hair follicles, which are important elements of hair discs, undergo unique cyclical morphological and biological changes.
OBJECTIVES: To define the relationships between the number and the morphology of Merkel cells within the hair disc in association with the hair cycle on rat back skin.
METHODS: Merkel cells in hair discs were observed three-dimensionally using immunohistochemistry. Epidermal sheets were incubated with monoclonal murine antibody to CK20. As a result, Merkel cells in hair discs were clearly demonstrated as whole shapes and were counted under a light microscope.
RESULTS: Merkel cells in hair discs increased during the early to middle phase of anagen and decreased during the middle phase of anagen to catagen and telogen in perinatal and postnatal rat back skin. We observed the morphological variation of Merkel cells in hair discs of rat back skin, and consequently divided them into two subtypes at the light microscopic level: the oval type and the dendritic type. The number of oval-type Merkel cells was not markedly affected by the hair cycle. In contrast, the number of dendritic-type Merkel cells markedly changed with the hair cycle.
CONCLUSIONS: This difference of the hair cycle dependency between oval and dendritic-type Merkel cells suggests some functional differences, such as a secretory function, related to the hair cycle.