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The hair cycles in the albino rat.

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THE HAIR, CYCLES I N THE ALBINO R,AT
E B R l i 0. BUTCHER
Biological Laboratory, H a m i l t o n CoZTege, Clinton, LZTew Y o r k
ONE TEXT FIGURE AND T W O PLATES (FIFTEEN FIGURES)
INTRODUCTIOS
For some time an experimental study of the changes in the
hair has been contemplated, since so little is definitely known
as to how various conditions affect the growth and shedding of
this integumentary derivative. It seems extremely unfortunate that our information is so limited ivhen the hair is so
easy of observation and the changes in it are often believed
t o be indicative of metabolic conditioiis in other parts of the
body.
It is well known that the activity of the hair in many mammals is cyclic, that is, the hair has a steady growth until its
ultimate length is reached and then it remains quiescent for
some time until it is finally expelled often through the growth
of a new hair. The quiescent condition and the growth stagc
together, therefore, constitute a cycle. Before experimentation could proceed, it was quite necessary t o know at what
age the normal stages occur in some animal. It would, lilrewise, be advantageous t o find an animal in which the hairs
were in the similar stage of the cycle at the same time. After
considerable examination of several animals, the albino rat
seemed to have a hair coat which was most suitable f o r the
introductory study.
BIATERIALS -4ND METHODS
Despite the fact that the present day tendency is to rely
on gross or external observations of the activity of the hair
5
6
EARL 0. BUTCHER
follicle, it seems that a microscopic stntly of the cells which
are responsible f o r the growth of the hair is very important
a i d should be made simultaneously with the external
observations.
I n order to study the normal hair cycles, rats from the
same litter were used and they were fed t o insure against
aiiy dietary insnffieieiicy. Areas of skin were taken from the
clorsum a i d the venter. They were placed on filter paper,
and then fixed in Bouiii’s fluid. Before embedding iii paraffin,
the pieces were trimmed and oriented in such a manner that
the desired plane of the follicles would result on cutting.
General histological procedure followed, seetioris being cut
10 p in thickness and stained in hematosylin and eosin. Later,
after considerable study had been made and tlie conditions
of the skin were better known, it was found that thin scctions
could be cut free liaiid after a few hours’ fixing, and the stage
of the hair follicle ascertained under the binocular. This
proved to be a great advantage, since large strips from
various parts of the body could be quickly analyzed both as
to surface conditions and the stage of the follicle. Histological examinations were made also to confirm aiiy doubtful
observations made under the binocular.
THE HAIR CYCLER I N THE AIA13190 RAT
Information concerning the growth of the liair in the
alhino rat, as in other mammals, is greatly limited. Fraser
(’28) studied the development of the skin of the back of the
white rat until the eruption of the first hairs, which occurred
on the second day of postnatal life.
Observations made by me oii 1- and 2-day rats confirm the
work of Fraser. The present study, therefore, begins with a
description of tlie hair coat in a M a y rat. At this age various
stages in the growth of the follicles map he observed (fig. 1).
Some of the epithelial down-growths still have a cylindrical
form with few indications of much differentiation, while in
many of them are seen a definite hair shaft with iiiiier and
outer root sheaths. Some follicles have even advanced t o the
H A I R CYCLES, RAT
7
ext eat that tlie hair lias erupted and grown considerably above
tlie surface. Likewise, the depth of the follicles is quite variable, some bending on reaching tlie paiinicuhis carriosus in
order t o complete their growth.
When 7 days old, besides finding that most hairs h a w
erupted and that the parts of the hair are more distinct, oiie
also observes that many of the folIicles have elongated and
straightened.
thicker coriuin and a more fattp subcutaneous layer undoubtedly make longer aiid straighter follicles
possible.
N o new epithelial buds from the epidermis are ohscrrcd in
the skin on the tenth day (fig. 2). Tlie greatest activity is
occurring in the bulb where mitosis is resulting in longer
hairs. Two types of follicles may be found. Some are very
large and contain the longer and coarser hairs of tlie rat's
coat, while the smaller follicles are more numeroi~sand have
shorter and finer hairs. The elongation of follicles and thickening of the dermis and subcutaneous layer after the fifth day
is enormous, as may be seen on comparing figures 1 aiid 2.
The end of the growth period of the hair seenis t o be reached
Jvhen the rats are about 17 days old (fig. 3). No further
elongatioii of follicles and thickening of the corium take place.
Xitotic figures a r e disappearing in the bulb and the stage
of quiescence is approaching.
At 20 days, no evidence of growth is seen in any of the
hair bulbs arid the latter arc transforming into cornified
structures (fig. 4). Many have already started t o move npward. Inactivity in the follicles is completed by 22 days
(fig. 5 ) , and the root of the hair exists as a club-shaped
strnctnre securely lodged in a resting follicle at the level of
the sebaceous gland.
It is interesting that the stage of quiescence occurs in so
many of the hair follicles at the same time and within thc
short interval of a few days (18 to 22). This would seem to
indicate the possibility that a growth stimulus had been present until about the seventeenth clay, or tlie tissue was receptive only until about the seventeenth day. The author ('27)
8
EARL 0. BUTCHER
found similar conditions in the ovary of the rat. Ovarian
follicles enlarged until the seventcenth day and then a great
degeneration occurred between the eighteenth and the twentysecond days. That the inactivity shonld correlate so closely
in both cases furnishes excellent material for speculation
and further experimentation. The fact that there is established such inactivity in the ovary around 18 to 22 days
suggests a possible explanation f o r the varied ovarian response (Davy, '34) to gonad stimulating materials at this
time.
Cross sections of the follicles in the skin of a %-day rat
(fig. 13) show that each contains a single hair and that composite follicles (more than one hair) are not present in the
first coat. Sections of follicles above the sebaceous glands
are found only at this time as the hair is in the quiescent stage.
Direct inspection externally shows that the puppy hairs of
the first coat are smaller than those that grow in the adult
rat, and that they are, likewise, divisable into a long, stiff,
and quite straight type, and a group in which the hairs are
more numerous, finer, and shorter. The last group contains
hairs variable in length. I n all probability the length is dependent on the interval of growth of the follicle, although
this assumption is extremely di6eult to establish.
The quiescent condition that begins in most follicles a t 22
days persists until about 32 days. At this time (fig. 6) the
fatty content of the subcutaneous layer is scanty and the hair
follicles are short and inactive, and contain adhering puppy
hairs. At the bottom of the follicles, however, some epithelial appendages or buds are seen which are the forerunners
of the next growth of hair.
When the rat is 35 days old (fig. 7), the epithelial cords
are greatly elongating through mitosis. Differentiation has
begun in some and the hair bulb has appeared. In a 38-day
rat (fig, 8) it is evident that the core of the column has separated from the peripheral cells; the latter become the outer
sheath of the hair. The hair core, as in the puppy hairs, has
already started its differentiation into the inner sheath and
HAIR CYCLES, RAT
9
the shaft of the hair. Puppy hairs persist, the corium appears
thicker, and the subcutaneous layer has more fat than in
younger rats.
Between 40 and 45 days, the follicle usually reaches its
maximum depth. In figures 9 and 10 are seen some of the
roots of the smaller hairs and one large follicle. The hairs
of the white rat occur in groups, and a large hair, when
present, is found centrally located within the group (Fraser,
'31). Many of the hairs on reaching the panniculus carnosus
have turned in order t o coniplete their growth. The hair
and its sheaths are well formed, and many of them in the
second coat hax-e erupted and grown t o a considerable length.
The great growth of the hair bulb does not continue long.
Apparently multiplication of the cells slows down and gradually stops as the time of sexual maturity, which occurs in the
females of our colony on about tlic fiftieth day, approaches.
I n a 51-day rat (fig. 11) the bulbs are transforming into
cornified structures, and have started to move upward. The
skin of a 53-day rat (fig. 12) shows that the cells, which
covered the papilla, have transformed into coriiified spindles
and the r o o t of the hair has become a club-shaped, slightly
thickened structure. Below the hair is seen an epithelial
strand which is the remains of the empty outer epithelial
sheath. A resting condition is again being established.
So f a r n o description of the venter has been given. The
growth and quiescent stages in this region are quite similar
to those in the dorsum, with the exception that the comparable
condition in the venter is 4 o r 5 days in advance of the similar
stage in the dorsum. I n other words, growth begins first
in the venter and spreads dorsally. Likewise, quiescence
in the venter would be observed 4 or 5 days before there was
any evidence of it in the dorsum. The corium and subcutaneous layers are also thinner. The hair is somewhat shorter on
the venter, but the larger and smaller types may be distingui shed.
Transections of follicles of a %day rat (fig. 14) show that
many of them now contain two hairs, a new and an old,
10
EARL 0. BUTCHER
resulting in a composite follicle. This would then indicate that
a composite follicle is due to the persistence of hairs from
successive cycles. h study of sections shows that the new
hair does not push out the old hair in many iiistaiiees, but
grows beside it. As successive cycles occur, the number of
hairs in a follicle should, therefore, increase and this is
exactly what happens. This explains why the molting process
in the white rat is not so conspicuous and only a few hairs are
lost at the time of the outgrowth of others.
The follicle containing a large hair, when present, is usually
centrally located in a group, and is not as often composite
as the surrounding follicles. When it is composite, it contains
two hairs, one usually smaller than the other. The smaller,
however, is larger than any hairs of the surrounding follicles.
In the latter where two hairs occur, that of the second growth
is slightly larger and longer. This may he due t o the different
of the various
metabolic conditions during the g r a ~ t periods
h
hairs.
The growth of hair which has just been described and began
usually about 32 days and ceased at 50 days is often referred
to as the first adult hair. Lightbody and Lewis ('as),in their
studies on the growth of hair in the white rat, have also found
that the actual weight of the hair in relation t o body weight
of 6- t o 7-week rats is double that of 30 days. The increased
weight is the result of the second growth and the formation
of composite follicles. From different angles, our observations agree. I have found no account, however, of a description of the cycles.
The diagram enables one to follow the cycles in the prepubertal rat easily. The thickness of the skin when the hair
follicles are at their maximum length is outstanding. It is
amazing that inactivity occurs so quickly. While the cycles
in rats of different strains may vary slightly in the time elcment from this diagram, it is believed that the conditions
will be as illustrated for those maturing arouiid 50 days.
It is interesting to note that the growth of the hair in
prepubertal rats parallels the activity in the ovary. For
HAIR CYCLES, RAT
11
instance, according to 1m;v work and that of Hargitt (’30),
ovarian follicles reach a maximal size about the sixteenth day
only t o begin degeneration in great numbers around the
twentieth day. This correlates closely with the growth of the
puppy hair. &“ail1 between 36 and 45 days, when the first adult
hair occurs, IIargitt finds another period of formation of
graafian follicles, their maturation and degeneration. Does
this mean that orarian activity is respoizsible f o r hair grox7tli?
It evidently does not, since the second coat and the resting con-
Diagram showing t h e depth and the condition of hair folliclrs in the dorsum
at various ages, based on histological scctions. ___- , indicates level of
surface epithelium. ------, represents depth of actively growing follicles.
, . . . . . ., shows depth of follielcs in rcsting or quiescent condition.
dition occur exactly in ovariectomized females ( ovariectomimd when 18 days old) a s it does in litter mates. There
may be a common stimulus for the hair and the ovary, but
apparently the gonad has little effect on hair growth in the
rat. The cycles in the prepubertal male are quite like those
of the female, with the exception that the resting condition is
usually established a few days later iii the male than it is in
the female litter mate.
The hair follicles remain in the quiescent stage which is
established ahout the fiftieth day for 15 t o 20 clays. New
epithelial anlagen then appear at the base of the follicles
12
EL4RL 0. BUTCHER
about the seventieth day and the hair coat begins its third
cycle. A resting condition starts usually between 85 and 90
days. Thereafter the cycles have not been closely followed.
It is, therefore, apparent that the hair cycles in the rat have
the duration of approximately 35 days.
Since three growths have occurred in 85 days, follicles contain as many as three different hairs, but never more than this
number (fig. 15). A great many have only two, and this is
either due to the fact that one was pushed out by a new hair,
or accidentally pulled out, or possibly there was no growth in
the third cycle. It is believed, however, that growth usually
occurs.
Apparently hairs will grow o r rest regardless of the fatty
content of the skin (figs. 7 and 12). I am inclined to think that
the growth is slightly faster if there is some subcutaneous fat
in which they can elongate and straighten. Myers ('21) has
found that subcutaneous f a t provides a maximum place f o r
the proliferation of mammary ducts. A s seen in figures
5 and 6, the resting condition is established in the hair, and
this is followed by thinning of the dermis and a reduction
in the fatty content of the subcutaneous layer. In most cases,
the fat reduction is possibly not as great as that seen in figure
6, but there seems t o be some decrease el-en in the best fed
animals (28 days--85 gm.). Rice and Jackson ('34) have
observed a thinner dermis at 9 weeks, yet have given it no
great consideration. In the human scalps that have been examined, it has been found that after the hair is lost, there
follows a decrease in the fatty deposition. According t o
O'Donovan ('30), this is quite true in most cases of presenile
baldness. In these respects, that is, . . . . the establishment
of inactivity of the hair bulb, and then the disappearance of
the fat of the subcutaneous layer and the thinning of the
dermis, the hair coat of man and of the rat are quite alike.
Further investigation is being conducted f o r the cause of these
phenomena in the rat.
HAIR CYCLES, RAT
13
SUMMARY
From the previous descriptions, it is evident that hair
growth in the young albino rat is cyclic. These cycles occur
approximately every 35 days, the resting period and the growi n g stage each being about 17 days in length. The elongated
follicles of the growth period in the first cycle in the dorsum
last from birth until the sixteenth or seventeenth day of life.
Quiescence, during which the follicles are inactive and short,
then continues unt,il the thirty-second to thirty-fourth day
when active growth and lengthening begin again. It is remarkable that practically all the follicles are in the same stage
at the same time, and that the resting condition is established within a very short interval.
The hair cycles in the prepubertal rat parallel the growth
activity in the ovary. The growth of the puppy hair closely
correlates with the growth and formation of the first ovarian
follicles. The latter continue to develop until about tlie sixteenth day and then the same follicles begin to degenerate in
great numbers about the twcnt,icth day. Again between 36
and 45 d;tys, when the first adult hair occurs, another period
of growth of germ cells into the graafian follicles, their
maturation and degeneration take place. The gonad, however,
is not responsible for this hair growth, since the hair cycles
occur in ovariectomized animals as in normal rats. Whether
or not the stimulus for ovarian and hair activity are from a
common source has not been asccrtained.
In the rat new hairs in their growth do not normally push
out tlie old hairs. Of course, this results in an additional
hair in the follicle with each new growth. Finally, a follicle
with several hairs, a composite follicle, is established.
Since the hair cycles occur so definitely and are so easily
analyzed under the binocular, the hair coat presents exceptional material for further experimentation. Especially
the cause of these cycles, and the effect of diet and hormones
on them should be further investigated. Knowledge of the
hair cycles and their control will undoubtedly give needed
insight into many complicated growth processes of other
body structures which are not at present well understood.
14
EART, 0. BUTCHER
LITERATUHE CITlrXl
BUTCHER,
EARL0. 1927 The origin of the definitive ova in the white r a t ( X u s
riorvegicus albinus). Anat. Rcc., vol. 37, pp. 13-31.
DAYY,LEITA 1934 CoInplete recaovrry of gonadotropic substances from urine
of pregnant women. Endocrin., vol. l&, pp. 1-18.
FRASER,
DORISil. 1928 The development of the ski11 of thc back of the albino
r a t until the eruption of the first hairs. Anat. Rec. vol. 38, pp. 203-223.
- 1931 The winter pelage of thc adult albino rat. Am. J. Anat., vol.
47, pp. 35-87.
HARGITT,GEO. T. 1930 The formation of thc sex glands and germ cells of
mammals. 111. The history of the fcinale germ cells in the albino
rat to the time of sexual maturity. J. Morph. and Phgsiol. vol. 49,
pp. 277-331.
LIGHTBODY,
H. D., AKD H. B. LEWIS 1929 The metabolism of sulphur. XV.
The relation of thc protein and cystine content of the diet t o the
growth of the hair in the white rat. J. Riol. Chem., vol. 88, pp. 485-497.
MYERS,J. A . , AND F. J. MYEES 1 9 2 1 Studies on the mammary gland. VII.
The distribution of subcutaneous f a t and its relation to the developing
mammary glands iu male and female albino rats f r o m birth to ten
weeks of age. Anat. Rec., vol. 22, pp. 353-362.
O’DONOVAN,
W. J. 1930 The Hair. p. 130. P. Blakiston’s Son & Co., h e . ,
Philadelphia.
RICE, H. G., A N D C. &I. J a c r r s o ~ 1934 The histological distribution of f a t s
i n the liver, kidney, trachea, lung and skin of the r a t at various
postnatal stages. Anat. Rec., vol. 59, pp. 135-151.
PLATES
15
PLATE 1
EXPLANATION O F FIUURES
Fixation for all sections was Bouin’s; all sections were stained in hematoxyliu
and eosin, and were taken from the dorsum
1 Five-day rat, showing the extent of hair growth. X GO.
2 Skin of a 10-day rat, showing the elongated follicles and increased fatty
content. X 60.
3 Seventeen-day rat, showing the follicles a t the end of the growth period.
X 60.
4 Follielcs in the skin of a 20-day rat P-hich have ceased activity and are
moving upward. X 60.
5 The resting condition as seen in the follicles of a 22-day rat. X GO.
6 Skin of a 32-day rat, showing the resting follicles of the puppy coat, and
the epithelial buds of second coat (e.b.). X 70.
16
HAIR CYCLES, R h T
EARL 0.BU'ICHEIL
17
T H E ANATOMlCAI. ILECORD, T O L . 6 1 , NO. 1
PLATE 2
EXPLANATION 01’ I’ICTJRER
7
Thirty-five-day rat, showing the growing buds of the second hair coat. X 60.
Large and small hair follicles differentiating in thc skin of 38 day rat. X 60.
9 k’nrty-two-day rat, showing the elongated follicles of the second hair coat.
X 60.
1 0 Forty-five-dag rat, showing largc and small follicles actively growing. X 60,
11 The beginning of the quiescent pcriod as seen in a 51-dag rat. X 60.
12 Fifty-three-day rat, showing the follieles in the quiescent condition. x 60.
13 Transections of follicles in the skin of a. 26-day rat, showing trnly one hair
in each follicle. X 107.
14 Fifty-six-day rat, showing that, ninny follicles contain two hairs after the
growth period of the second cgcle. X 1 O i .
15 Transectjons of follicles in the skin of an 84-dav-rat with a third h a i r
as thc result of a growth in the third egcle. X 1 0 i .
8
18
PJATE 2
HAIR CYCLES, RAT
EARL 0. BUTCHEFr
19
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