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Polyovular follicles and multinucleate ova in the ovaries of young mice.

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Polyovular Follicles and Multinucleate Ova in
the Ovaries of Young Mice
HARRY A. KENT, JR.
Zoology Department, University o f Georgia, Athens, Georgia'
Polyovular follicles and multinucleate and the arithmetic means calculated for
ova have been observed in the immature each age group, the information is as premembers of numerous species (Hartman, sented in figures 1 and 2.
'26; Lane, '38; Davis and Hall, '50 and
DISCUSSION
Dawson, '51 ). Most of the research studies
The Swiss mouse reaches maturity, as
and conclusions drawn from studies in this
area have dealt with the possibility of a based on successful litter production, by
sequential relationship between the two the 7th week of age. Follicle counts, as
types of juvenile ovarian structures. Kent presented in table 1, indicate an early
('59) has presented evidence of low estro- production of corpora lutea at approxigen level as a primary cause for the pres- mately the 6th week with a steady increase
ence of polyovular follicles and multinu- in numbers through the last analysis pecleate ova in the immature hamster. As a riod, the 10th week. On the basis of proresult of Kent's study it has become ap- portion of total follicles, the level of corparent that a survey of the common labora- pora lutea reaches a peak by the 7th week
tory animals, with regard to establishing (fig. 1) . These figures may be presumed to
the levels and types of ovarian structures indicate establishment of a static level of
at various ages, should be undertaken so follicle maturation by the 7th week.
Production of primary follicles, as preas to complete the picture of immature patterns and to provide a more substantial sented in table 1, presents a picture of inbackground for further experimental stud- creasing numbers throughout the analytiies. The present work initiates the project cal period, while secondary follicles reach
with a timed age survey of the Swiss a maximum at approximately the 6th
week. On the basis of proportions of primouse.
mary and secondary follicles (fig. l ) , an
MATERIALS AND METHODS
anomalous situation is established in which
Forty female Swiss mice, of the strain there is an apparent interacting cyclic bemaintained at the Worcester Foundation havior of the primary and secondary
for Experimental Biology, were used. Five follicle levels.
The reverse curves (fig. 1) are due to
animals were sacrificed at each week of
age, from the third to the 10th week. Ovar- an early increase in proportion of secondies were removed, fixed in Carnoy's fluid, ary follicles which reaches a plateau by
imbedded in paraffin, sectioned serially at the 6th to 7th week, followed by a contin8
and stained with hematoxylin and ued increase in proportion of primary foleosin. All follicles were counted and class- licles continuing through the 9th week at
ified following criteria established by Kent which time the secondary follicles regain
their earlier proportionate value.
('59).
The three curves of figure 1 are of interRESULTS AND OBSERVATIONS
est primarily as a key to the onset of maThe results of the study are presented in turation processes in the ovary. On the
table 1. The count data are further ex- basis of corpora lutea production, luteinizpressed in terms of per cent in order to ing hormone (LH) becomes available in
provide statements of the proportions of
This work was conducted at the Worcester
each type of structure per total number of Foundation for Experimental Biology under the
follicles. When this is done for each ovary auspices of the American Physiological Society.
52 1
HARRY A. KENT, JR.
quantity somewhere during the 5th to 6th
week, while the increasing numbers of
secondary follicles would indicate perhaps
an earlier date for the onset of LH production. Increasing numbers of primary
follicles throughout the analysis period
suggest an increasing estrogen level in the
ovary (Payne, '56) with a preceding elevation in amount of available follicle stimulating hormone (FSH).
Numerous investigators have approached
the problem of immature mammalian ovarian structures with the attitude that the
multinucleate condition precedes the polyovulate. Such an assumption appears to
be substantiated by the present study (table 1 and fig. 2) although the actual number of multinucleate ova is inadequate to
serve as precursors to the more extensive
polyovular follicles. Atretic follicles were
not included in the counts of this study,
since they represent anomalous structures
not directly correlated with the production
of fertilizable ova. It is conceivable that
atretic follicles may provide an explanation of the above statements in that only
a certain proportion of multinucleate ova
may survive to undergo further development.
As an indication of possible approaches
to a solution of causative factors in the development of multinucleate and polyovulate conditions, certain tentative conclusions may be based on the present study.
It is apparent that FSH is dominant during
the third to 4th week with increasing levels
of LH after that time (Fevold, '41). The
increasing numbers of primary and secondary follicles may be assumed to indicate
an accordant increase in estrogen level in
the ovary (Hisaw, '47). It must be
doubted that progesterone is available in
any quantity before the 6th week.
On the basis of these assumptions it
would appear that a low level of FSH permits development of multinucleate structures, and that a subsequent rise in FSH
level limits production of the same structures. Increasing levels of LH presage
development of polyovulate follicles and
attainment of the adult FSH/LH balance
limits further development of either multinucleate ova or polyovular follicles
These statements are, of course, only
suppositional, indicating what course fur-
523
OVARIAN ABNORMALITIES IN THE MOUSE
100 '
90.
80
70.
60
t-
z
W
50.
a
w
a
4 0-
SECONDARY FOLLICLES
30.
2 0.
10CORPORA LUTEA
+-*+
-+
-,
-t
21
28
35
42
49
56
63
70
AGE IN DAYS
Fig. 1 Relative number of monovular and uninucleate primary and secondary follicles
and corpora lutea in the ovaries of mice. One standard error is indicated.
ther studies may take. The purpose of this
work is to establish the normal condition
of the immature mouse ovary with respect
primarily to multinucleate ova and POlYovular follicles.
SUMMARY
The number of monovular, uninucleate,
multiovular and multinucleate follicles in
Swiss mice from the third to 10th week of
age were counted. Polynuclear ova were
most numerous in 4-week-old mice. Poly-
ovular follicles reached a peak at 6 weeks
and decreased in frequency from that
point on. Secondary follicles reached a
maximum value at the 7th week and held a
level while primary follicles continued to
increase throughout the duration of the
study. The data are explained on the basis
that estrogen level affects the incidence
of polyovular and polynuclear follicles and
that both estrogen production and primary
and secondary follicle development may be
correlated with FSH and LH levels.
524
HARRY A. KENT, JR.
PO LY OVU L A R F 0 LLIC L E S
1.
I-
z
BIOVATE
A
W
u
II:
W
CL
21
I
L
A'+YATE
/
+
21
/*--
12.
28
42
35
I
*'-+-*-+
49
$6
63
70
POLYNUCLEAR OVA
10.
1
AGE
IN
DAYS
Fig. 2 Relative number of multinucleate ova and polyovular follicles in the ovaries of
mice. One standard error i s indicated.
LITERATURE CITED
Adams, C. E. 1953 Some aspects of ovulation,
recovery and transplantation of ova i n the immature rabbit. Ciba Found. Symp. On Mammalian Germ Cells, up. 198-211.
Davis, D. E. 1950 Polyovuly and anovular follicles in the wild Norway Rat. Anat. Rec., 107:
187-192.
Dawson, A. B. 1951 Histogenetic interrelationships of oocytes and follicle cells. A possible
explanation of the mode of origin of certain
polyovular follicles in the immature rat. Ibid.,
110: 181-197.
Fevold, H. L. 1941 Synergism of the follicle
stimulating and luteinizing hormones in pro-
ducing estrogen secretion. Endocrinology, 28:
33-36.
Hartmann, G . G. 1926 Polynuclear ova and
polyovular follicles i n the opossum and other
mammals, with special reference to the problem
of fecundity. Am. J. Anat., 37: 1-51.
Hisaw, F. L. 1947 Development of the graafian
follicle and ovulation. Physiol. Rev., 27: 95119.
Kent, H. A., Jr. 1959 Reduction of polyovular
follicles and polynuclear ova by estradiol monobenzoate. Anat. Rec., 134: 455462.
Lane, C. E. 1938 Aberrant follicles in the immature rat. Ibid., 71: 243-247.
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young, ova, multinucleate, mice, follicle, ovaries, polyovular
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