title: A histocytological study of the rat hair follicle--an appraisal of a monocellular layer ("middle root sheath") between inner and outer root sheaths.
abstract: Hair follicles of male Wistar rats in the anagen stage were examined by light and electron microscopy. A distinct monocellular layer was identified between the Henle's layer and the outer root sheath (ORS). In the lower part of the ORS, this cell layer is more closely bound to the inner root sheath (IRS) than to the ORS, while in the upper half the situation is reversed. Electron density and staining property of this layer are gradually changed according to regions of the hair follicle which may indicate the metabolic conditions of the organism. The origin of this layer can be traced back to the germinal matrix directly facing the neck of the hair papilla. Findings are also reported about the gaps formed between the cells of Henle's layer after keratinization and about the contact formed between the cells of Huxley's layer and the cells of this monocellular layer through these gaps. Our observation reported in this study strongly suggests that this layer belongs neither to the IRS nor to the ORS, but that it represents an independent layer of cells. Therefore we propose to name this layer the "middle root sheath." This middle root sheath may serve the following three functions: 1) alleviation of intrinsic friction generated by colliding cell dynamics between the IRS and the ORS, 2) deterrence of keratinization of the ORS after exfoliation of the IRS and 3) secretion and excretion of metabolites.
authors.affiliation: Department of Anatomy, Tokyo Women's Medical College, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Fujisawa
authors.forename: T
authors.initials: T
authors.lastname: Kushida
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D018859:Hair Follicle / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017208:Rats, Wistar