MORPHOLOGICAL AND ULTRASTRUCTURAL ASPECTS OF THE DERMAL PAPILLA DURING THE GROWTH-CYCLE OF THE VIBRISSAL FOLLICLE IN THE RAT

Abstract

The sensory mystacial vibrissal follicles are ideal for hair growth cycle studies. Their large size and prominent disposition elucidate the inductive influence, mediated by the dermal papilla, which is essential for the development and proliferation of the hair follicle. The growth of vibrissae in the rat occurs via a characteristic cycle of developmental events, comparable to that seen in the pelage, but without shortening of the follicle or the formation of a papilla rest during the brief catagen and telogen phases of vibrissal follicles. A high level of synthesis and exchange of materials at the vibrissal papilla during anagen was suggested by light microscopy and EM. At catagen, loss of ground substance and vascular tissue led to the aggregation of papillary fibroblasts. Golgi bodies and RER [rough endoplasmic reticulum], which were extensively developed in these cells during anagen, were replaced by lysosomes and autophagic vacuoles. Maximal diminution of the papilla at telogen coincided with the cessation of mitosis in the epidermal matrix and a thickening of the basal lamina in the hair bulb with dense projections into the regressed papilla.