Changes in hair growth (6)

Changes in hair growth (6)

Wounding experiments

Method I
During this procedure it was observed that cellular material was being lost
from the follicle capsule (Jahoda & Oliver, 1984). Omitted data represented
occasions where information was inadequate to satisfy the criteria necessary to
make growth rate estimates.
Following injury, all but one follicle terminated fibre production and lost their
growing hairs. Subsequently, two of the experimental follicles failed to produce
emergent whiskers. Six follicles produced new hairs less than 10 days after being
damaged. Thirty-three vibrissae were visible between 10 and 20 days postoperatively
and a further four new hairs were first seen at 24, 28, 43 and 49 days
after wounding.
Length (Table 1)
Differences of 4 mm and greater between experimental and control vibrissae
were regarded as significant. This value represented a margin of 2 mm above the
differences in terminal length found in over 95 % of the previously described
measurements of undamaged whisker pairs, and lmm above the maximum
difference.
In the first generation following injury (Gl) the majority of follicles produced
whiskers within 4 mm of their controls. However, over 40 % of the postoperative

A margin of 0-1 mm/day was chosen to distinguish differences in follicle
behaviour between the experimental and control sides. While essentially an
arbitrary figure, this represents a club length difference of 5 mm over a 50-day
period of growth, and provides a convenient indication of variation in growth
rate following injury.
In Gl just over half of the wounded follicles produced vibrissae at a growth
rate below that of their controls. The percentage of slower growing hairs was
raised slightly in G2, but fell to below 50 % in G3. Each of the latter two generations
revealed a single faster growing hair.
It is of great interest that the distribution of reduced growth rate was almost
uniform among experimental follicles producing whiskers of equivalent, longer
or shorter length to their controls in Gl. Thus it is clear that the five follicles
which had manufactured longer hairs (at equivalent or reduced rate), had
produced them over a prolonged growing period. Similarly, ten vibrissae which
had not altered in length, had grown at a reduced rate and had been produced
over a longer period of time.
In every case control follicles showed remarkable consistency in both length
and growth rate over successive generations.
In addition to these quantitative observations, method I follicles displayed
a number of abnormal phenomena including the production of multiple fibres;
the abrupt cessation of growth and premature fibre loss; and an increase in the
length of time between termination of hair growth and the emergence of a new whisker.

Method II

Wounding operations were successfully performed on 18 follicles in 10 male
rats. In contrast to method I, there was no loss of follicular material from the

Hair growth changes following vibrissa wounding
capsule. Wounded follicles and their controls were kept under observation for
up to 170 days, by which time the majority of experimental follicles had produced
two complete generations of whiskers.

Following injury all follicles ceased hair production and lost their growing
fibres. Subsequently, two failed to display emergent vibrissae. Of the remaining
sixteen follicles, fourteen produced hairs between 9 and 20 days post-operatively
and two whiskers were first seen at 27 and 44 days respectively.
Terminal length measurements (Table 3) revealed that half of the follicles
which produced vibrissae in Gl had hairs at least 4 mm longer than their controls.
The longest of these (Figs 2, 3) measured 15 mm more, and was therefore 29 %
longer, than its right side counterpart. A further four whiskers were of equivalent
length to their controls, and four were shorter, though one of this latter group was a broken fibre.
More detailed information about the eleven follicles which produced at least
one long hair postoperatively is displayed in Table 4. Five of these manufactured
significantly longer hairs in both Gl and G2. Therefore, although three
follicles switched to producing longer hairs in G2, three others went in the
reverse direction. None of the latter group attained full terminal length, as
one was broken, and the other two biopsied prematurely. Nevertheless, the
mean percentage increase in length for Gl whiskers of 15-6% fell by over 5 % in G2.
There was no increase in rates of growth; over 75 % of the follicles produced
hairs at a reduced rate in both Gl and G2. Increases in whisker length were
therefore associated with extended growing periods.