Histological studies of whisker regeneration in the hooded rat.

It has been shown that generations of rat vibrissae of normal or nearly normal length are produced after the removal of dermal papillae from vibrissa follicles and that even after removal of lengths of the lower end of the follicle (' root ends') regeneration of shorter than normal whiskers may occur. There seemed to be a certain maximal length, approximately one-third of the follicle, which could be removed before complete cessation of whisker production ensued (Oliver, 1966). The destruction or inactivation of the dermal papilla, following the action of carcinogenic hydrocarbons and X-rays, has been said to be the cause of permanent epilation in pelage hair follicles (Wolbach, 1951; Geary, 1952). Nevertheless, there have been reports (e.g. Breedis, 1954; Billingham, 1958) that after the complete destruction or removal of populations of hair follicles in adult mammals, hair neogenesis may occur as it does normally during the seasonal growth of the deer antler. However, Straile (1959) has presented evidence that there is an inward migration of hair follicles from the wound margin and considers that this could account for the reappearance of hair follicles after injury. This study was undertaken to determine whether dermal papillae are reestablished in those follicles which regenerate vibrissae after the removal of dermal papillae and root ends and to investigate histologically the changes which take place during this process.