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The influence of sex and breeding on skeletal ageing of mice.

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T H E INFLUENCE OF S E X AND BREEDING ON
SKELETAL AGEING OF MICE1
MARTIN SILBERBERG AND RUTH SILBEBBERG
Department of Pathology, New Pork Univereity, College of Medicine, New Pork
TWO PLATES (SIX FIQUBES)
Skeletal growth proceeds at different rates in different strains of
mice. Moreover, in strain C57 the bones of females develop more quickly
than those of males, and the osseous tissues of breeding females more
rapidly than those of virgins. (Silberberg and Silberberg, '41 a). It
was, therefore, thought possible that sex and breeding might influence
skeletal development and ageing in other strains also. I n order to obtain more definite data on this problem, we examined the age changes
in the bones of non breeding and breeding females of various strains.
We compared them with one another and with those seen in males of
corresponding strain and age.
MATERIAL AND METHODS
One hundred forty-seben mice over 4 months of age and belonging to
the closely inbred strains C57, Old Buffalo, CBA, New Buffalo, A, C3H
and D were arranged in groups, each containing as many males, virgins
and breeding females of the same strain and age as were available. Details are given in table 1.
At necropsy, the upper part of the tibia and the lower part of the
femur together with the kneejoints were removed as a whole. The
specimens were prepared for histological study according to the method
described previously ( SiIberberg and Silberberg, '41a ) ,
HISTOLOGICAL EXAMINATION
Before stating the findings in the various groups, we may summarize
some general observations on skeletal ageing: Ageing of cartilage is
indicated by decreased proliferation of the cartilage cells and by increased degenerative processes, affecting cells as well as matrix. The
The material for this investigation was collected in the Laboratory of Research Pathology,
Washington University, Saint Louis, Missouri.
We wish to express our appreciation to Dr. Leo Loeb for his interst and many helpful suggestions in this series of investigations.
89
THE ANATOMIC& RECORD, VOL. 91, NO. 2
FEBRUARY, 1345
90
MASTIN SILBERBERG A N D R U T H SILBERRERG
cells undergo gradual atrophy or break down more rapidly, and finally
they disappear. I n the intercellular ground substance, regression manifests itself in either swelling or hyalinization and calcification. Hyalinization is usually spread diffusely throughout the epiphyseal disk, or it
may cause the formation of small hyaline wedges between the cartilage
cell rows. These hpaline areas show a tendency to metaplastic ossification. Bone thus formed seems to be markedly resistant to perforation
by bone marrow, and the osseous plate remains therefore intact well
into the second year of life. However, it undergoes progressive thinning,
and if the animal lives long enough, the thin bone may yet be resorbed,
and complete epiphyseo-diaphyseal union may ensue.
The second mode of regression of cartilage is characterized by a
rapid but localized destruction of cells leading to the appearance of
“plugs ’’ of degenerated cartilage. This amorphous material becomes
calcified and shows many cracks. Eventually, the plugs may ossify or
become incorporated in the bone that has replaced the growth zones.
At the time, when the resorptive processes begin to predominate, these
plugs often become the site of localized perforations of the epiphyseal
plate by bone marrow. I n some instances, these perforations widen
with advancing age ; in others, they remain stationary for many months
or even for life.
I n a number of ageing mice, the articular cartilage undergoes changes
which vary in degree from slight hyperplasia and hypertrophy to lesions
comparable to osteoarthritis.
A. Ch,anges in the growth zones
1. Strain C57 (ageing at a slow rate). Five groups of animals 7, 10,
15, and 20 to 25 months old were examined.
At the age of 7 months, the epiphyseal disks of the males contained
more and better preserved cartilage than those of the female breeder,
whose growth zones were already markedly hyalinized.
Towards the end of the first year of life, moderate amounts of calcified
cartilage were still present in both males and females. Few and small
plugs of disintegrated cartilage were noted in the male, whereas in the
female these areas of degeneration were larger and more numerous.
One breeding female even showed a perforation of the epiphyseal disk.
At 15 months of age, degeneration of cartilage had made progress in
all mice, but in the males more than in the females. Thus, conditions
in both sexes resembled each other more closely than at the earlier
stages. The growth zones had been broken through in both virgin and
SEX AND BREEDING O N SKELETON IN MICE
91
breeding females, whereas in the male, the epiphyseal plate was still
intact.
I n the oldest age group, there were only traces of cartilage left in
the male, and wide communications connected the epiphyseal and diaphyseal marrow cavities I n the corresponding female on the other
hand, more cartilage was found, and the perforations in the plate were
smaller than in the male.
II. S t r a i n Old B u f f a l o (slowly ageing w i t h marked bone-forming
telzdency). Three groups of animals 10, 14, and 18 to 21 months old
were examined.
In the 10-month-old virgin, the growth zones revealed considerable
amounts of cartilage. The cells were atrophic, and the areas of degeneration were limited in size and showed only little ossification. I n the
male on the other hand, there was less cartilage remaining, and it contained many large calcified and ossified plugs of degenerated tissue.
The growth zones failed to show perforations in either the male or the
virgin female.
At 14 months of age, the greater part of the growth zones had been
resorbed in the male. By contrast, in the epiphyseal disks of virgin females the cartilage cells were more abundant and better preserved;
there were only a few small areas of degeneration, and the resorptive
processes had just begun to predominate. The breeding female on the
other hand, had more extensive degeneration and ossification of the
cartilage than the virgin female, but perforations of the epiphyseal
plate could not be detected in the breeder.
At the age of 18 months and over (plate l ) , all males presented an
advanced degree of epiphyseo-diaphyseal union with only traces of
cartilage left (fig. 1). I n the breeding female the cartilage had undergone further degeneration and calcification as compared with the earlier
stages, and perforations were now noted in the growth zone (fig. 2). The
latter were, however, not as wide as in the male of corresponding age.
The bones of the virgins (fig. 3) had aged only slightly in comparison
with those in the preceding stage, and no breakthrough of the plate
had occurred.
I I I . S t r a i n CBA (slowly ageing). Four groups of animals 12, 15 to
16,19 to 20, and 23 to 30 months old were studied.
At the end of the first pear of life, there was still much cartilage
present in both sexes. However, the male showed more hyalinization of
the matrix, whereas in the corrmponding breeding female calcification
was more pronounced and a perforation of the plate was being initiated.
92
MARTIN SILBERBERG A N D RUTH SILBERBERG
The ageing processes in the latter were, therefore, somewhat more advanced than in the male.
At the age of 15 to 16 months, the growth zones of both virgin and
breeding females were broken through, whereas in the male they were
ossified, but still intact.
At the age of 19 months, almost all cartilage had disappeared in the
male, and epiphyseo-diaphyseal union had occurred. In the females, on
the other hand, some cartilage was still seen; the virgin female now
had wide perforations of the growth zone, whereas in the breeding female these were lacking.
The oldest group consisted only of males; in two of them the epiphyseal disk was perforated, and only traces of cartilage were left.
ZV. S t r a i n N e w B u f f a l o (with a moderately slow rate o f ageing).
Four groups of animals 10, 12, 14 to 16, and 19 to 24 months old were
examined.
I n 10-month-old males, the epiphyseal cartilage cells were more
numerous and better preserved than in breeding females. I n the latter,
almost the entire cartilage had been converted into calcified, amorphous
material, and in one animal a perforation had already occurred. Conditions in the growth zone of the virgin female were intermediate between
those of the males and the least advanced breeding females.
I n the 12-month-old virgin and breeding females, the histological
structure of the cartilage was similar to that seen at the age of 10
months. I n the males, however, the age changes had made further
progress so that the sex differences were now less conspicuous than at
the earlier age. Still, there were no perforations in the epiphyseal
disk in males, whereas advanced resorption was found in two of three
breeding females. Very little change took place in either sex during the
next few months, but at 14 months of age, the histological findings were
similar in breeding and virgin females and males.
I n contrast to the previous stage, resorption of the epiphyseal plate
had advanced markedly in all males 19 months of age and older ; however, epiphyseo-diaphyseal union had not made further progress in
the corresponding breeding females.
V . S t r a i n A (rnodera,tely rapid rate of ageing, marked bone-forming
tendency). Six groups of animals 6, 7, 9 to 11, 12, 13, and 16 to 20
months old were examined.
At 6 months of age, the growth zones were composed of large amounts
in inactive cartilage in both the male and female. I n the male, regressive
changes in the cartilage were not very marked ; but considerable hpalinization and large areas of degeneration were noted in the female.
SEX A N D BREEDING ON SKELETON IN MICE
93
Seven-month-old virgin females still failed to show plugs of degenerated cartilage, whereas such areas were observed in both the males
and breeding females. In the latter, however, they were more numerous
and of larger size than in the former.
I n 9- to 11-month-old mice, the number of cartilage cells had further
decreased in the breeding female, whereas in the male and virgin female the amount of cartilage had remained unchanged as compared
with the earlier age. Regressive changes had made progress in all
groups. This was true particularly in the virgin females whose epiphyseal disks resembled now more closely those of the breeding females
than before. However, in the breeding female the ageing of the cartilage was further advanced than in the virgin females and males.
During the next 2 and 3 months, at 12 to 13 months of age, the breeding females and males showed comparatively little alteration of the
epiphyseal plates.
I n the 14-month-old mice, ageing of the epiphyseal zone proceeded
more slowly in the virgin female than in either the males or breeding
females. The males showed still more and better preserved cartilage
than the breeding females; in the latter, many large plugs of disintegrated cartilage had replaced most of the epiphyseal disk; such cartilage as remained, had undergone marked hyalinization ; one of the
breeders showed beginning perforations of the growth zones. But on
the whole, perforations in this strain were rare even in very old mice,
irrespective of sex and breeding activity.
From the age of 16 months on, there was scarcely any difference in
the structure of the epiphyseal plates of virgin or breeding females
and males. I n other words, the age changes in the males and virgin
females were now similar to those of the breeding females and reached
a stage, where no further progress was made. Even a group of three
males, 22 months old, failed to show any progressive changes as compared with the cdnditions in the preceding stage.
V I . Strain C,H (rapidly ageing with a marked tendency t o boneformatiolz). Five groups of animals 4 , s to 9,13,15, and 19 months and
older were studied.
Up to the age of 9 months, the epiphyseal plates of the males (fig. 4)
and virgin females (fig. 6) were much better preserved, and they
showed fewer and smaller areas of degeneration than those of the
breeding females (fig.5).
At the beginning of the second year of life, these differences became
less sharp. The amount of cartilage present and its state of regression
were similar in all three groups of mice. After 15 months of age, the
94
MARTIN SILBERBERG .4ND RUTH SILBERRERC)
remaining cartilage was gradually ossified. Perforations were seen only
in one breeding female and in three males among the ten mice that had
lived beyond the age of 3 year.
V I I . h'train D (rapidly ageing). Four groups of animals 6 to 7, 8 to
9,12,14, and 19 to 20 months old were examined.
This strain ages so rapidly that as early as the age of 6 months, there
was scarcely any difference between males and breeding and virgin
females as to the amount of cartilage present and its state of preservation. However, in breeding females the growth zones had already been
broken through, whereas in the males and virgin females there was at
most merely a suggestion of perforations.
I n the animals 8 to 9 months old, the age changes had made only very
little progress in the virgin and breeding females as compared with
those in the earlier stage. I n the males, on the other hand, the epiphyseal cartilage had begun to age more rapidly. This was indicated
by an increased ossification and by the progress of resorptive processes
leading t o perforations of the epiphyseal plate. Thus, conditions in
males and females resembled each other more closely than before.
During the second pear of life, scarcely any difference was noticeable
in the growth zones of males, and virgin and breeding females. There
was little cartilage present, and it was in an advanced stage of regression. In the one male and the one virgin female living more than
13 years no further age changes had taken place.
B. Conditions in the joiizts
With advancing age, the articular cartilage underwent changes of
varying degree. As in previous investigations, the following gradations
of the joint lesions were made: Grade I showing slight proliferation
and hypertrophy of the cartilage, grade I1 characterized by a moderate
degree of both regressive and growth processes, and grade I11 showing marked degeneration and hyperplasia of the cartilage comparable
t o osteoarthritis.
The findings in the various strains of mice are shown in tables 2 and 3.
Table 2 gives the incidence of joint lesions in each strain and their
distribution in males (m) and virgin (v) and breeding (b) females. I n
each strain, the joints of virgin females were less affected than those
of males or breeding females. Virgin females revealed the highest
percentage of normal joints (col. 5 ) and the lowest incidence of the
more severe lesions (col. 7. 8). I n males and breeding females, there
was little difference in the incidence of grade I1 and I11 changes. Such
differences as did exist, might have been due to variations in the age of
95
SEX 9 N D BREEDIKG ON SKELETON IN MICE
the mice : I n strain CBA, for instance, grade I1 and I11 changes in males
amounted to 86% (col. 7, 8), whereas in females they were only 67%.
However, as seen from table 1, six of seven or 86% of the males were
older than 1 year, whereas of three breeding females only two or 67%
were of corresponding age.
TABLE 1
Showing the distribution of the aninale according to strain, age and sex.
n
16m.
m v b
CBA
12AN.
N.B.
24AN.
A
37AN.
m v b
m v b
m v b
m v b
17AN.
m v b
TOTAL
m v b
4 1 3
1 1 0
1 0 1
2 1 3
3 4 7
4 2 4
3 3 4
52
3 3 2
3 4 3
1 1 1
4 2 6
7 2 6
4 2 2
2 2 1
61
18-30mos.
1 3 2
3 0 0
5 1 1
4 0 2
6 1 1
2 0 0
1 1 0
34
Total
8 7 7
7 5 5
7 2 3
10311
16714
1046
6 6 5
147
c57
22AN.
AGE QBOWP
A
6-12mos.
O.B.
CsH
20Ab.
R
12 - 1 8 1 p 0 ~ .
C
m
-Males:
64 animals.
v -Virgins:
34 animals.
b - Breeding females: 49 animals.
'Age group A of this strain contained one set of animals 4 months of age ( 1 male, 1 virgin
and 1 breeding female).
Table 2 also gives some indication as to the susceptibility to joint
lesions of the various strains: Strain Old Buffalo was resistant, since
the percentage of normal joints and of grade I lesions was high in
males as well as in virgin and breeding females (col. 5, 6). Likewise in
strain C57, the incidence of the normal joints and of grade I changes
was higher than that of the more severe alterations of grades I1 and 111.
Strain CBA was actually more resistant than would appear at first
sight. No normal joints were found in the males ; but this is probably
due to the fact that the males used were very old (table 1). Conversely
strains C,H and D were more prone to develop articular changes than
appears from the table. According to table 1, one-half of these mice
was under 1year of age, and in strain C,H there was included one set
of very young animals of only 4 months of age.
INCIDENCE OF ARTICULAR CHANGES I N THE THREE AGE GROUPS
Table 3 shows the incidence and severity of joint changes in males
(m) and virgin (v) and breeding (b) females, and their distribution in
the three age groups without regard to the strain. As seen from table
96
MARTIN SILBERBERG AND R U T H SILBERBERO.
TABLE 2
Showing the incidence of joint h s w n s in each strain and their distribution in males, and virgin
and breeding females.
STRAII
NO. O F
ANIMAL
c 57
22
O.B.
15
CBA
12
DISTRIBUTION
I N PERCENT
SEX
25
0
29
0
14
14
m
46.7
33.3
20.0
42
80
67
29
20
33
0
0
0
29
0
0
58.3
16.7
25.0
0
100
33
14
0
0
28
0
0
58
0
67
41.7
12.5
45.8
20
34
18
30
33
36
30
33
46
20
0
0
43.2
18.9
37.9
19
57
28
31
29
14
38
0
36
19
14
22
50.0
20.0
30.0
30
75
17
20
25
33
10
0
17
40
0
33
35.3
35.3
29.4
17
33
20
50
50
40
33
0
40
0
17
0
m
V
b
m
v
b
m
C,H
20
V
b
m
D
17
I11
63
43
28
V
37
I1
12
43
29
b
A
I
36.4
31.8
31.8
v
b
24
0
m
v
b
m
N.B.
CHANGES IN PERCENT
GRADE
B
b
TABLE 3
Showing the incidence and severity of joint changes in males and virgin and breeding females
and their distribution in the three age groups.
NO. O F
ANIXAL
Males
64
AGE
GROUP
0
I
I1
I11
28.0
3T.5
34.5
28
17
18
39
29
32
28
25
23
5
29
27
C
35.4
47.0
17.6
7
44
50
A
B
C
44.9
42.9
12.2
18
29
66
A
B
C
Virgins
Breeding
females
34
49
CHANGES I N PERCENT
GRADE
PERCENT
O F TOTAL
A
B
5
56
17
8
0
0
8
9
0
33
36
19
17
32
33
17
19
0
14
SEX AND BREEDING ON SKELETON IN MICE
97
1, age group A comprises animals 6 to 12 months old, group B those 12
to 18 months of age, and group C those over 18 months of age.
I n age group A, virgin females had more normal joints (75%) than
either males (28%) or breeding females (18%). Severe lesions (col. 7,
8) were somewhat more frequent in the breeding females (46%) than in
the males (33%);they were distinctly rarer in the virgin females (17%).
I n age group B, virgin females again showed the highest number of
normal joints (44%) as compared with 29% in breeding females and
17% in males. The incidence of grade I1 and I11 changes was about the
same in males (54%) and breeding females (52%). However, in the
male, there was a marked tendency to grade I11 lesions (29%); in
breeding females, their incidence was 19% only. I n virgin females on
the other hand, there were no lesions of either grade I1 or 111.
I n age group C, the breeding females presented a large number of
negative cases (66%), whereas normal joints were less numerous in
virgin females (50%) and even fewer in males (18%). The incidence
of severe changes (col. 7 , s ) was highest in males (50%) ; it was lower
in virgin (33%) and lowest in breeding females (17%).
Males had the lowest incidence of joint changes in age group A, normal joints and grade I alterations amounting to 67%, grade I1 and
grade I11 lesions to 33% (col. 7) ; in age groups B and C, conditions in
the joints were about equal: I n group B, there were 46% normal joints
and grade I changes and 54% lesions of grades I1 and 111; the corresponding figures in age group C were both 50%. This means that articular changes became conspicuous in middle life, but did not increase
in frequency or severity in old age.
Virgin females showed a low incidence of joint changes in all age
groups: I n age group A, the negative and grade I cases amounted to
83%, in group B to 100%and in age group C to 67%. The highest percentage of severe lesions (33%) was found in age group C. This would
indicate that the factors responsible for the articular changes acted
more slowly in the virgin female than in the male and became effective
only in old age.
Breeding females revealed a 54% incidence of normal joints and
grade I changes in age group A as compared with 48% in group B and
83% in age group C. But, there were fewer negative and grade I cases
than in virgin females or males of correspondipg age, this in spite of
the fact that more breeders (44.9) were in the younger age group than
either virgin females (35.4%) or males (28%). Severe lesions on the
other hand, had an incidence of 46% in age group A and of 52% in age
group B, whereas their incidence was only 17% in age group C (col. 7,8).
98
MARTIN SILBERBERG AND R U T H SILBERBERG
COMMENT
The present investigation confirms and supplements our previous
findings as to sex differences in skeletal ageing of mice (Silberberg
and Silberberg, '41 a). The results obtained are also in agreement with
gross observations on skeletal development in humans (Pryor, '23 ;
Greulich, '42), rats (Spark and Dawson, '28) and chickens (Latimer,
'27). These investigators found skeletal maturation accelerated in the
females as compared with the males.
During the first year of life, the epiphyseal cartilage of breeding female mice showed more pronounced and further advanced regressive
changes than that of males of the same age. Subsequently, ageing
proceeded more rapidly in males than in females ; thus between the age
of 12 and 15 months, in most strains examined, the males reached an
advanced degree of epiphyseo-diaphyseal union. I n the female on the
other hand, the age changes remained a t this time of life stationary or
made only slight progress.
But there were in addition some differences noticeable among the
females, the cartilage of virgin females in general being better preserved than that of breeders. This was conspicuous already in a series
of 4 months old mice of strain C,H. The cartilage of the breeding female had undergone more widespread and more extensive destruction
than that of the virgin. Moreover in the breeder, marked resorption of
degenerated cartilage suggested an impending perforation, a rather
unusual occurrence in this strain. This very young breeder had probably one but certainly not more than two pregnancies. Breeding, thus,
apparently exerts a potent ageing effect on the cartilage, and correspondingly the cartilage of very young mice may be very sensitive to
the modifying action of pregnancy. This response is somewhat analogous to findings in virgin females and male mice treated with hormones (Silberberg and Silberberg, '43) : The cartilage of young animals was found to react more intensely to hormonal stimulation than
that of older ones. A single pregnancy occurring in early life may thus
exert a more pronounced ageing effect on the cartilage than several
pregnancies occurring later in life. The rapid degeneration of the
epiphyseal cartilage during pregnancy may be due primarily to the influence of estrogen, but anterior hypophyseal hormones may likewise
play a part. The role of estrogen may also be indicated by the relatively
slow progress of epiphyseo-diaphyseal union in breeders as compared
with that of males and virgin females. I n growing mice, estrogen besides accelerating the ageing of the cartilage inhibits resorption and
thus delays the progress of epiphyseo-diaphyseal union. I n males on
SEX AND BREEDING O N SKELETON IN MICE
99
the other hand, the inhibition by estrogen is lacking, and the inhibition
of resorption exerted by androgen is less marked: Thus, epiphyseodiaphyseal union may proceed with greater intensity toward the limit
set by the genetic constitution of the strain. Conditions may be similar
in virgin females, who are likewise exposed to lesser amounts of estrogenic hormones than breeders and, therefore, may show wider perforations and a more advanced degree of epiphyseo-diaphyseal union
than breeders. However, even in the breeder, the effect of hormonal
stimulation may interact with the genetic determination of age changes.
Thus, in strains C57 and CBA old breeders may eventually develop
epiphyseo-diaphyseal union; in strains A and C,H on the other hand,
the marked bone formation (genetic factor) and the inhibition of resorption (hormonal factor) cooperate in making perforations of the
epiphyseal disk a rare occurrence.
As compared with males, the progress of skeletal ageing of virgin
females varied: In the slowly ageing strains C57 and CBA, the early
age changes in males were retarded as compared with those of the
virgin females; on the other hand, in the mory rapidly ageing strains
A, C,H and D, these differences were less accentuated and disappeared
at an earlier age than in the slowly ageing strains.
As to the joint changes, a certain trend seems to be discernible despite the fact that the number of animals in the individual groups is
limited. It is planned t o extend these investigations at a future date.
Our present observations may be summarized as follows: Virgin females of all strains and ages were distinctly less affected than corresponding males or breeding females; but even virgin females did develop severe lesions in old age. Therefore, in virgin females the factors
responsible for these changes probably develop only late in life or they
require more time to accumulate in sufficient strength to cause these
lesions. I n males, on the other hand, the joint changes did not increase
in severity or frequency in old age, while in breeding females the articular lesions were even slightly more numerous than in males and they
were somewhat more severe during the first year of life: During the
first half of the second year of life, males and female breeders were
about equally affected; but at later periods, the incidence and severity
of articular changes dropped sharply in the breeding female.
Thus it appears that (1)the factors leading to joint lesions become
active earlier in the life of breeding females than in either males or
virgin females ; (2) that these factors do not increase in potency in old
age. The smaller number of joint changes in old breeding females may
he attributable to the fact that among the breeders only very resistant
100
M A R T I N SILBRRBERG AND RUTH SILBERBERG
individuals reach the higher age groups (Loeb, '19; Little, Murray and
Cloudman, '39). The low susceptibility of such animals to articular
changes may then be only another symptom of their general resistance
to disease.
Only tentative explanations can be ventured as to the nature of the
factors causing the articular lesions : Their late appearance in virgins
might indicate that they are partly due to old age changes in the cartilage. In males, their aggravation during the first half of the second
year of life and the decline of the sexual function at this time may be a
coincidence, but there is a possibility that it may be connected with the
imbalance of sex life characteristic of this period. Administration of
anterior hypophyseal hormone or transplantation of anterior hypophyseal glands increase the incidence and severity of such joint lesions
and hasten their onset (Silberberg and Silberberg, '41 b). The excess
of anterior hypophyseal hormones released after cessation of the testicular function might play a part either in initiating the joint changes
o r in intensifying abnormal conditions in cartilage that begins to age.
Fundamentally, conditions might be similar in breeding females, even
though they develop articular lesions at an earlier age than males. I n
breeding females, the activity of anterior hypophyseal hormone or of
anterior hypophysis-like hormones is greatly enhanced during pregnancy. An increased output of anterior hypophyseal o r chorionic hormones might affect the articular cartilage and promote the age changes
in it. Estrogen has probably no active role in the causation of the joint
lesions, since it produces sclerosis and atrophy but no growth stimulation of the cartilage.
SUMMARY
I n mice, breeding accelerates skeletal ageing : Onset and progress of
the age changes in virgin females are delayed as compared with conditions in breeding females and males. I n males, skeletal ageing takes
at first a slower course than it does in females, but subsequently the
age changes proceed more rapidly in males than in either the virgin or
breeding females.
I n virgin females, articular age changes are rarer and less severe
than in either males or breeding females. Joint lesions appear earlier
in breeding females and they are in a first stage more severe than in
males. However, in old males, the joints may be more frequently and
more severely affected than in breeding females.
SEX AWD BREEDING ON SKELETON IN MICE
101
LITERATURE CITED
GREULICH,
W. W. 1912 Genic and endocrine determination of skeletal development. Endocrinology, vol. 30, p.8. 1023.
LATIMER,
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PLATE 1
EXPLANAgION OF FIQURES
Sections through the epiphyseal dbks of the upper tibiae of mice of strain Old Buffalo, 18
months of age. Magnification 93 X
.
1 Male: Advanced degree of epiphyseo-diaphyseal union with only traces of cartilage left.
2 Breeding female: Some inactive cartilage left; center of growth zone converted into a
thin bony scar; no perforation of the epiphyseal disk.
3 Virgin female: Cartilage better preserved than in either male (fig. 1) or breeding female (fig. 2), but inactive and markedly calcified; no perforation of the growth zone.
SEX AND BREEDIX’G O X SKELETOK Ili MICE
PLATE 1
M A R T l N SILBERBEBG AND R G T H SILBXRBERC:
103
PLATE 2
EXPLANATION OF FIGURES
Sections through the epiphyseal disks of the upper tibiae of mice of strain C,H, 4 months of
age. Magnification 93 X.
4 Male : Cartilage calcified, small hyaline wedges between the cartilage columns and small
plugs of degenerated cartilage beginning to form.
5 Breeding female: Two plugs of degenerated cartilage in the growth zone.
6 Virgin female : Cartilage better preserved showing some hyalinization of the ground substance, but no “plugs”.
104
PLATE 2
S E X AND B R E E D I N G ON SKELETON I N MICE
MARTIN SILBERBERG AND RUTH S.ILBERBIR0
105
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