Morphometric studies of the epidermal-dermal junction in the rat ear: some effects of experimental friction on epidermis and anchoring fibrils.

The aim of this investigation was to determine whether, following the application of experimental friction to the skin, qualitative an quantitative differences could be induced in the epidermis and in anchoring fibrils. The skin of rat ears was subjected to repeated mild fractional stimulation with a rotating bristle brush moistened with saline thrice weekly for three weeks, untreated ears being used as controls. A stratified random sampling design was followed for the morphometric analysis of interfollicular epidermis. With the light microscope, the lengths of the granular cell/keratin (BGK) and epithelial-connective tissue (BEC) junctions were measured using an image analyser, as was the epithelial thickness (T). The ratio BEC/BGK provides an index of the degree of irregularity of the epithelial-connective tissue junction. Using electron microscopy, the numbers of anchoring fibrils per unit length of lamina densa (NB) were determined using stereological intersection counting. There are no significant differences in BEC/BGK or T between control and experimental groups, but anchoring fibril frequency NB increased from 10.29 micrometers in control epidermis to 18.9 micrometers in friction-treated epidermis. It is concluded that a mild frictional stimulus which fails to produce significant alterations in epidermal thickness can produce a marked increase in anchoring fibril frequency. This response may reflect a functional alteration associated with increased mechanical loading, in which epidermal-dermal adherence is augmented by either synthesis of anchoring fibrils or their insertion into the lamina densa.