Changes in hair growth (1)

Changes in hair growth (1)


INTRODUCTION

Much of the experimental work on hair growth has involved direct or indirect
interference with normal follicle activity. Where severe destructive agents have
been employed on adult follicles (e.g. carcinogenic hydrocarbons, Wolbach,
1951; X-irradiation, Geary, 1952), recovery of fibre production appears to have
depended on the degree of damage to the dermal papilla, and more recently it
has been shown that the papilla can prove resistant to high doses of X-irradiation
(Ibrahim & Wright, 1977).
Direct evidence of the necessity for a dermal papilla for growth and maintenance
of adult follicles was first demonstrated in a series of experiments by
Lillie & Wang (1941,1944) and Wang (1943). They discovered that removal of
the dermal papilla from feather follicles resulted in the permanent termination
of feather production. However, reimplantation of a new papilla resulted in
restoration of feather growth. Following the excision of rat pelage hair follicle
bulbs, Butcher (1965) reported subsequent growth of fragile hairs in the absence
of a dermal papilla. This conflicted with the findings of Oliver (1966a,b) who,
using operational procedures pioneered by Cohen (1961), established that fibre
production in the vibrissa follicle was terminated by removal of the dermal
papilla, and was only restored after papilla regeneration from surrounding lower
follicular mesenchymal cells which are continuous with the base of the papilla.
Furthermore, it was discovered that a papilla could be reformed after removal
of short lengths of follicle root, a finding confirmed by Ibrahim & Wright (1982).
Similarly, the regrowth of human axillary hair following the removal of the bulb
and follicle up to the level of the sebaceous gland has also been described (Inaba,
Anthony & McKinstry, 1979).
One of the advantages of using vibrissa follicles, particularly for quantitative
studies, is the ease with which individual fibres can be measured. Normal growth
characteristics of vibrissae on the upper lip of the rat are therefore well documented
(Oliver, 1965; Ibrahim & Wright, 1975; Young, 1977). In addition, each
follicle has an exact counterpart on the opposite side which produces a fibre of
similar length. This inbuilt 'control' system was exploited by Oliver (1966a, 1967)
who looked at alterations in whisker length brought about by various microsurgical
manipulations.

In the present study a comprehensive examination of the effects of wounding
the lower region of vibrissa follicles with a tungsten needle was undertaken.