Histological studies of whisker regeneration in the hooded rat

Abstract

ABSTRACT A histological study has been made of the follicular changes which occur in vibrissa follicles both after the removal of the dermal papilla alone and the removal of various lengths of follicle root (‘root ends’). The dermal papilla of the vibrissa follicle is not always a discrete and permanent entity, as it has been suggested to be in the feather follicle, since it can be regenerated. No whisker is produced from a follicle or follicle remnant unless a dermal papilla is first regenerated. Dermal papillae regenerate by tissue reorganization at, or just above, the puncture in the base of, or the cut across, the capsule. After removal of the dermal papilla alone, a new papilla of apparently normal size is regenerated, but dermal papillae which regenerate after removal of root ends are smaller than normal. Examination of follicles after the removal of root ends demonstrates that the regeneration of dermal papillae and then whiskers occurs only within the lower third of the vibrissa follicle; there is little or no permanent lengthening, or shortening, of the follicle remnant—whether whiskers are regenerated or not. However, lengths of follicle remaining after removing root ends from within the upper two-thirds of the follicle persist—even though dermal papillae do not regenerate and no fibre production occurs. The histological evidence strongly suggests that cells from the mesenchymal layer contribute to and possibly become the new dermal papilla. After removal of the dermal papilla or root end the outer root sheath cells coalesce to form a column or rod. Basophilia arises within the proximal end of this rod, over which the mesenchymal cells aggregate. These cells form the dermal papilla, first as a small indentation which then increases in size whilst acquiring a strongly basophilic ectodermal matrix.