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Neurosecretory material in the supraoptico-hypophyseal tract of the bat throughout the hibernating and summer periods.

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Neurosecretory Material in the SupraopticoHypophyseal Tract of the Bat Throughout
the Hibernating a n d Summer Periods ’
J. ROBERT TROYER
Department of Anatomy, Temple University School of Medicine,
Philadelphia, Pennsylvania
ABSTRACT
Neurosecretory material in the supraoptico-hypophyseal tract of 151
hibernating and summer bats (Myotis Imifugus Zucifugus) was studied in chromealum-hematoxylin-phloxine-stained
serial sagittal sections. Seasonal variations of neurosecretory content throughout the hibernating period (mid-September through midMay) and “active” summer period (June to mid-September) were observed and the
staining density of the neurosecretory material in the supraoptic nucleus, infundibular
stem and pars nervosa was “quantitated” visually. Cell counts and measurements also
were made to determine if cell number and size changes accompanied seasonal
changes in neurosecretory content.
A signiiicantly greater staining density of neurosecretory material in the supraoptico-hypophyseal tract of the hibernating bats, than in the “active” animals was
observed. These differences were always greater in the infundibular stem than in the
supraoptic nucleus and pars nervosa. Although there was n o correlation between
seasonal activity and the total number of neurosecretory cells in each brain, there
was always a smaller number of dark-staining cells in the “active” bats than in those
that were hibernating. Nucleocytoplasmic ratios of hibernating bats were below those
of the active animals. These resulted from smaller nuclear and larger cytoplasmic
sizes during hibernation than in the summer. Nucleolar sizes, however, were slightly
greater in the hibernating bats than in the active animals. The significance of these
results in terms of seasonal activity is discussed.
Numerous studies have shown that hibernating mammals exhibit extreme variations in autonomic functions during their
annual cycles of activity. Many of these
studies have been ably reviewed by Kayser
(’61) and Lyman and Chatfield (’55).
Since the hypothalamus of mammals is
generally considered to be the highest subcortical center for the regulation of autonomic functions in mammals (Truex and
Carpenter, ’64), it would appear that this
region of the central nervous system might
exhibit anatomic and physiologic changes
that are related to the seasonal activity of
the hibernator. The regulation of water
metabolism by the hypothalamus is one of
the vegetative functions that seems to lend
itself well to such a study in the hibernating bat. It is established that bats properly
hibernate only if there is a high relative
humidity of the atmosphere (Pirlot, ’46)
and if they can awaken and drink during
hibernation (Anciaux, ’48).
Several investigators have shown in nonhibernating mammals that antidiuretic
ANAT. REC.,162: 407-424.
hormone is secreted by cells of the supraoptic nucleus (Thorn, ‘58; Lederis, ’61).
These cells also elaborate a Gomori stainable neurosecretory material that may be
bound to the antidiuretic hormone (Acher,
’58). Even though it is fairly well established that the stainable neurosecretory
material is not antidiuretic hormone (Sawyer, ’63; Scharrer and Scharrer, ’63; De
Robertis, ’64), the close relationship of
these substances is demonstrated by the
disappearance of both after prolonged
water deprivation or hypertonic saline administration (Ortmann, ’51; Leveque, ’53).
In previous studies on hibernating mammals, Azzali (‘53, ’54, ’55) and Barry
(’54) have shown in European bats, and
Suomalainen (’60) in hedgehogs, that
there are seasonable variations of neurosecretory material content in the supraoptico-hypophyseal system. Only in Suomalainen’s paper have these staining differ1 This investigation was supported by research
grant A 5793 from the National Institutes of F f l c
and Metabolic Diseases of the National Institutes of
Health, Public Health Service.
407
408
J. ROBERT TROYER
ences been correlated with the size of the Since previous experience had shown that
cellular constituents of the supraoptic nu- variations in the intensity of staining could
cleus in an attempt to establish an index result from this procedure, two precautions
of cellular activity. Since the present au- were taken. First, sections through the midthor (Troyer, '65) has shown that there is sagittal plane and through the greatest exa well defined Gomori-positive supraoptico- tent of the supraoptic nucleus from anihypophyseal pathway in the bat (Myotis mals representing different monthly groups
lucifugus lucifugus),it was decided to in- were stained together in the same rack.
vestigate the possible seasonal variations Second, the running tap water rinse folin neurosecretory content throughout the lowing stainiing in hematoxylin was reannual cycle of activity of this animal. placed by three tap water rinses which
Since preliminary investigation showed were adjusted to a pH of 8.5 to insure unithat changes were present, cell counts and form staining.
Differences in the stainability of neurocytoplasmic, nuclear and nucleolar measurements were made to determine if cell secretory material in the supraoptic nunumber and size accompanied seasonal cleus, infundibular stem, and pars nervosa
changes in neurosecretory content of the (infundibular process) of the pituitary
gland, between animals representing varisupraoptic nucleus.
ous periods of the year, were "quantitated"
MATERIALS AND METHODS
by an estimation of the darkness of stainThe localization and extent of neuro- ing of the neurosecretory material using a
secretory material (N.S.M.) was studied in ten-point scale. In this procedure a ten
Gomori-stained serial sections of brains rating indicated the darkest staining and
from 151 Myotis lucifugus lucifugus col- most prevalent distribution of neurosecrelected over a 15 month period from Janu- tory material and zero represented the
ary of one year through March of the least. This method is comparable to that
following year. Hibernating bats were described for other histological procedures
taken monthly from mid-September to mid- (Chiquoine, '54). Since the differences in
May and were maintained in the dormant stainability of the supraoptic nucleus could
state at 6"4 1°C for at least 24 hours, but have been the result of a greater number
not longer than one week, before they of CHP-positive cells being present in one
were sacrificed. Summer bats were col- field of one brain than in another, the CHPlected monthly from June to mid-Septem- positive cells of the left half of each brain
ber and were returned in an "active" state were counted by the method used in a
to the laboratory and maintained at room previous paper (Troyer, '65). These cell
temperature (23" 2 3°C) until the follow- counts were carried out in four animals
ing morning when they were sacrificed. from each monthly group. In view of the
Water was available to all animals but no fact that in all brains some very lightfood was offered. Thus, with the exception staining supraoptic cells with small granof temperature exposure, all animals in the ules were observed that might indicate a
study were maintained under similar con- different functional state from the other
ditions. In an attempt to obviate any varia- CHP-positivecells, separate counts of these
tions in results that might be due to dif- cells were made. Due to limitations of the
ferences in the sexual cycle, males were staining density method the actual numused whenever they could be obtained. bers of light-staining cells found during
Consequently, all of the animals from the different perilods of the year is not as valid
hibernating period and half of the bats as the relative numbers that are determined for ealch period of the year.
from the summer colony were males.
The procedure for cell measurements
All animals were sacrificed by chloroform anesthesia followed by perfusion of was similar to that previously described
Zenker-formol (Helly's) fluid. All brains by Troyer ('65). All well-defined neurowere serially sectioned at 10 p in the sagit- secretory cells demonstrating a nucleolus
tal plane and stained by Smith's ('51) in sections through the greatest extent of
modification of Gomori's chrome-alum- the rostral and caudal portions of the suhematoxylin-phloxine (CHP) procedure. praoptic nuclei were measured with an
NEUROSECRETION
ocular drum micrometer. A cell size factor
for each cell, expressed in microns, was
determined by adding the greatest length
of the cell body to the greatest width and
dividing by two. Nuclear size factors expressed in microns were determined by a
similar process. Nucleocytoplasmic ratios
were determined by dividing the nuclear
size factor by the cell size factor for each
cell. Nucleolar sizes expressed in microns
also were obtained with an ocular drum
micrometer. Since the nucleoli of some of
the cells had an elliptical shape nucleolar
size factors also were derived from measurements of the greatest length and width.
RESULTS
The visual observations based on the
stainability of neurosecretory material in
the supraoptico-hypophyseal tract of the
bat are summarized in table 1. It was generally observed that CHP-positive cells
were present in the supraoptic nuclei of
all animals during both the hibernating
and “active” (summer, awake) periods. A
large difference in stainability appeared
between the supraoptic cells of the hibernating bats and those of the active animals
(table 1 and figs. 3-6). The lightness of.
staining of the supraoptic cells of active
bats was due in part to the fact that many
of the cells lacked the large clumps of
dark staining material and appeared to be
comprised primarily of many very small
light staining granules. There appeared to
be little fluctuation in neurosecretory content during the hibernating and active periods. Thus, there was no gradual transition
of neurosecretory content from the hibernating period to the “active” period and
vice versa.
In the infundibular stem and the pars
nervosa, there was noticeably less neuro-
IN THE BAT
409
secretory material in active animals than
in those bats that were hibernating. This
was particularly so in the infundibular
stem where the lowest recorded mean levels of neurosecretory material for any
structure in this system were recorded for
active animals (5.0-5.7) while the levels
for hibernating animals (8.7-9.8) were
fairly high (figs. 7-8). In contrast to this
the staining density of the pars nervosae of
active bats (7.9-8.6) was only slightly less
(9.0-9.8) than that of the hibernating animals (figs. 9-10).
The results of the cell counts are summarized in figure 1. Only CHP-positive
cells of the left supraoptic nucleus were
counted. In addition to the Gomori-positive
cells, there were about an equal number of
cells that were not CHP-positive. This result is consistent with previous h d i n g s in
this animal (Troyer, ’65). The data show
that there is a large variation in the number of CHP-positive cells in the bats used
in this study and that the mean values of
hibernating and active bats is similar.
Thus it would appear that the difference in
stainability of the supraoptic nucleus between hibernating and active bats is not
due to marked differences in the number
of CHP-positive cells.
Counts of light-staining and dark-staining CHP-positive cells showed a marked
seasonal correlation (fig. 1). More darkstaining neurosecretory cells were present
in the hibernating, than in the active bats.
This difference in mean values between the
two groups was statistically very highly
significant ( p = < 0.001). The percentage
of dark-staining cells of the May animals
appears to be intermediate to the April and
June levels. Even though one of the May
animals was observed to be active, its darkstaining cell percentage was not markedly
TABLE 1
Visual observations of neurosecretory materiul i n the bat supraoptico-hypophyseal tract
based on a 0-10 scale of staining density
Activity
state
(months
reuresented)
Hibernating ( September-May)
Number
Supraoptic
of animals
?FtgS
106
9.4
(7-10)
Active (May-September)
35
Infundibular
stem
(range)
9.2
(&lo)
nervola
Pars
hypophysis
(ranee)
9.6
(7-10)
7.4
5.4
8.2
(4-10)
(3-10)
(4-10)
410
J. ROBERT TROYER
NUMBER
TOTAL
-
OF
CELLS
40r
0
3 50
2
30-<’ , <’’ , ‘ ;
x
2 5-
\
P
.
.
1 1 1 1
+ A
i
2 0v)
--
-1
1
w
0
2 7-
-
-
22-
p
1712-
/
$-wY/--//
-
-
OF
NUMBER
- - -
-
)/
/
/O
.
DARK-STAINING
- -
f-w-TqJ
!i
7-
_OF
PERCENT
70-
8
CELLS
DARK-STAINING;
CELLS
0
50
20
HIB.--*
~-HIBERNATING+-.ACTIVE+
1
1
1
1
1
1
1
Sept Oct Nov Dec Jan Feb Mar Air Mby
I
JuAe J i y Aug
Sipt
MONTHS
Fig. 1 Cell counts in the left supraoptic nucleus of the brat. The means presented for
each month were acquired from four animals, except in August when five bats were used
for the cell counts. One bat from the May group and one from the September group were
visibly more active than the other hibernating animals, but were included in the counts.
All ranges are expressed as k 1 standard deviation. The diagonal-hatched areas represent
the standard errors of each of the hibernating and “active” means.
different from that of others in the group
and it’s believed that the May level represents a transition from the hibernating to
the active state. Although there was a significant difference in percentage between
animals fromi the last month of the summer period (,$ugust) to the first month of
the hibernating period (September), it was
not as statistically highly significant as that
which occurred in passing from the end
41 1
NEUROSECRETION IN THE BAT
of the hibernating period (April) to the
active period (June )
The results of the cell body and nuclear
measurements are summarized in figure 2.
The mean nuclear size factor for all of the
.
hibernating bats (7.00 p) was below that
of all active animals (7.54 u). In contrast
to this the mean cell size factor of the hibernating animals (13.58 p ) was greater
than that of the active animals (12.69 p).
NUCLEOCYTOPLASMIC
0.66‘
RATIO
T
0.61-
1.15
N
v)
0.56
1.00
0.51‘
XI
m
r
L
0.46
3
-
<
m
CYTOPLASMIC
SIZE
-I
0
15.
14
/P%.
1.00
‘T
I3
0.93
12
*.
- .*.
I
Q-.
2m
3
-
z
0
I I.
NUCLEAR
SIZE
z
rn
7.5.
,1.08
7.0.
. I .oo
5
6.5.
6.0
-HIBERNATING?-ACTIVEI
1
1
1
1
1
1
1
1
Sept Oct Nov Dec Jan Feb Mar Apr May
I
I
I
I
I
May June July Aug Sept
MONTHS
Fig. 2 Neurosecretory cell diameters in the left supraoptic nucleus of the bat. The nuclear size
and cytoplasmic size were determined by adding the greatest length to the greatest width of the
nucleus and cell, respectively, and dividing by two. The nucleocytoplasmic ratio was determined by
dividing nuclear size by cell size. The means presented for each month were acquired from groups
of four animals, with the exception of August when five bats were used, and M a y and September
when groups of three hibernating bats and one “active” bat were used. A n average of 23 cells were
measured in each of the 49 animals studied. All ranges are expressed as 2 1 standard deviation.
The diagonal-hatched areas represent the standard errors of each of the hibernating and “active”
means. The dotted lines represent the general trends of nuclear and cytoplasmic size throughout the
total annual cycle of activity.
412
J. ROBERT TROYER
As might be expected, therefore, the nucleocytoplasmic ratio of the hibernating
animals (0.516 p) is considerably below
that of the active bats (0.592 p). All of
these differences were highly significant.
The p values for these were: < 0.001 for
nuclear size; < 0.005 for cell size, and
< 0.001 for nucleocytoplasmic ratio. These
differences are more fully appreciated
when sizes relative to the hibernating mean
are studied (fig. 2). There is a 15% increase in the nucleocytoplasmic mean from
hibernation to the active months. If these
sizes were expressed in volume the percentages would be markedly greater. In
the month-to-month examination of the
data, there was an indication that nuclear
and cell sizes were greatest during the
mid-hibernating (January) and mid-active
(July) months with the lowest sizes being
recorded just prior to hibernation (early
September) and summer (May). The
marked increase in nucleocytoplasmic ratios from the end of the hibernating period
(0.515 p) to the beginning of the active
period (0.605 v) and the large decrease
from August (0.596 p) to September
(0.509 p ) are quite abrupt and do not indicate gradual changes in preparation for
arousal or hibernation.
In comparing measurements of lightstaining cells with dark-staining cells in
each animal it was found that the nuclear
size factors and cell size factors of the
light-staining cells were usually significantly smaller than those of the darkstaining cells. Seasonal variations in nucleocytoplasmic ratios of light- and darkstaining cells were seen. In hibernating
animals the nucleocytoplasmic ratio of
light-staining cells was slightly lower than
that for the dark-staining cells, whereas
the reverse was true for the summer bats.
In neither case were the differences statistic ally significant.
A correlation of seasonal activity with
nucleolar size also was observed (table 2).
The mean nucleolar size factor of hibernating bats was far greater than that for
the active animals. This difference which
was statistically highly significant (p =
< 0.001), held true for both light-staining
and dark-staining cells. Even when nucleolar size factors were compared between
active and suimmer bats that had the same
mean nuclear size factors, the nucleoli of
the hibernating bats were larger than those
of the summer animals. During either the
summer or hibernating periods there were
no progressive changes in size in the
month-to-month study. In the hibernating
bats, however, the nucleolar size factor of
the dark-staining cells was significantly
greater than that of the light-staining cells.
DISCUSSION
This study indicates that neurosecretory
material in the supraoptico-hypophyseal
tract of the bat, Myotis lucifugus lucifugus,
varies in amount during different periods
of the year. The general observation of
more CHP-positive material in hibernating
bats than in active summer animals is
similar to that found in European bats
(Azzali, '53, '54, '55; Barry, '54) and in
hedgehogs ( Suomalainen and Nyholm,
'56). The results of the present study contrast sharply, however, with those of earlier
investigations when animals from months
embracing the arousal (post-lethargic) period and the entrance to hibernation (prelethargic) aye critically examined. Azzali
('53) and Suomalainen ('60) describe distinct differences in the stainability and
TABLE 2
Summary of nuckolar sizes of supraoptic neurosecretory cells of the bat
Activity
state of
animals
Neurosecretory
cells
measured
Mean
nucleolar
size factor
fi
.Hibernatingbats
Hibernating bats
Hibernating bats
Total (light and dark)
Light-staining cells
Dark-staining cells
2.91 (S.D. -I- 0.294)
2.79 (S.D. I+ 0.312)
3.03 (S.D. 2 0.230)
Summer active bats
Summer active bats
Summer active bats
Total (light and dark)
Light-staining cells
Dark-staining cells
2.39 (S.D.-I- 0.169)
2.40 (S.D. C 0.189)
2 34 (S.D. i- 0.082)
NEUROSECRETION IN T H E BAT
granule size of neurosecretory material between four periods of the annual cycle : the
lethargic, post-lethargic, summer and prelethargic. In Myotis lucifugus lucifugus the
rise and fall of supraoptico-hypophyseal
neurosecretory material in spring and autumn are very abrupt and do not indicate
a gradual reduction and increase as the
active and lethargic periods are approached. The greater disappearance of
neurosecretory material from the infundibular stem in the active period than from
any of the other regions is similar to that
found in Vesperugo savi by Azzali (‘53).
In addition, the presence of more CHPpositive material in the pars nervosae of
these bats than in other regions corresponds well with the results found in studies on European bats (Azzali, ‘55). It is
worthy of note that in any one section of
all brains studied there was a fairly wide
variation in the content of neurosecretory
material of individual cells (figs. 3-6). In
addition, there were variations in total content of CHP-positive material between animals of the same monthly group. Since
hibernating bats awaken periodically to
drink water, it is likely that these variations
are correlated to different metabolic states
of the animal. Consequently, it would
seem that the use of a large number of
animals in this study more clearly indicates the seasonal fluctuations of neurosecretory material than might be garnered
from a study on fewer animals which
would reflect individual variations as seasonal changes.
The CHP-positive cell count studies support a conclusion that the decline in neurosecretory content of “active” animals, as
compared to hibernating bats, is not due
to the total disappearance of this substance
from cells of the supraoptic nucleus, but
is represented as a diminution of neurosecretory material in many cells of this
nucleus. The resultant light-staining cells
with dusty granules have previously been
described for other hibernators by Azzali
(’53, ’54) and Suomalainen (’60). Their
observations differ from the present study,
however, in the season that the light-staining cells make their appearance, since
they noted these in the pre- and postlethargic periods and saw almost no neurosecretory material in summer animals.
413
This seasonal difference in neurosecretory
content between Myotis lucifugus lucifugus
and the other hibernators might be the result of variations in hydration of the animals imposed by differences in laboratory
maintenance and may not represent intrinsic seasonal differences in neurosecretory
content.
Cell measurements have been used extensively by many authors as indices of
cell activity in reflecting the functional
status of neurosecretory cells (see Ortmann, ’60; Ifft and Berkowitz, ’65). The
larger cytoplasmic size factor in hibernating bats than in summer animals correlates well with the presence of CHPpositive material. Since the dark-staining
cells generally have a larger cytoplasmic
size than the light-staining cells, it appears
that the cell-bodies are larger when they
are engorged with neurosecretory material
than when little of this material is present.
The results of the karyometric studies
showing larger nuclear size factors in active animals than in hibernating animals
is similar to that found in the preoptic
nucleus of hibernating Rana temporariu
(Dierickx and Van Meirvenne, ’61), but is
in sharp contrast to that found in the hibernating hedgehog by Suomalainen (’60).
From the present study it would seem that
supraoptic cells are more actively synthesizing neurosecretory material during the
summer, and that the production of neurosecretory material is reduced during the
hibernating period. If this is true then the
greater cytoplasmic size and stainability
of cells from hibernating bats would indicate that neurosecretory material is being
stored during hibernation and that the demands for its mobilization and utilization
do not appear to be as great as they are
in the summer. Azzali (’53) proposed a
similar conclusion for European bats, but
he did not carry out cellular measurements
in support of this. One of the results in
the present study that does not appear to
support this conclusion that smaller nuclear size represents a storage phase is
that within each monthly group the nuclei
of the light-staining cells have an average
size that is slightly smaller than that of
the dark-staining cells. It should be noted,
however, that the average cytoplasmic size
of the light-staining cells, also, is smaller
414
J. ROBERT TROYER
and that more of the smaller cells, or possibly neuroglial cells, are being included in
the light-cell measurements, than in the
dark-cell determinations.
Nucleolar measurements in the bat, also,
do not support the above conclusion. If
nucleolar size is a true indication of the
synthesis of neurosecretory material as
some authors have indicated (Lea and
Thomsen, ’61; Ifft and Berkowitz, ’65),
then it would appear that there is a greater
protein synthesis taking place in hibernating bats than in summer animals and that
there is greater synthesis in dark cells than
light cells in hibernating bats.
It would appear from the conflicting results of nuclear and nucleolar measurements, that additional studies are needed
to determine if neurosecretory activity
and/or the chemical composition of this
material in the hibernating bat is different
from that of other hibernators and nonhibernators. Suomalainen and Nyholm
( ’ 5 6 ) in nuclear measurements on the hibernating hedgehog found some results
that appear to run counter to some of their
seasonal findings. Although they observed
that nuclear diameters were larger during
hibernation than in the summer, they also
noted that the diameters remained large in
animals kept in a warm environment during hibernation and that diameters were
reduced in animals kept in a cold room
during summer. In view of these observations in a hibernator, and the results of
measurements in the present study, it
would seem that more insight into neurosecretory activity of cells of the supraoptic
nucleus of the bat could be gathered from
future studies on bats subjected to experimental conditions of altered temperatures
and water availability. In addition, histochemical and electron-microscopic studies
of these cells might more clearly depict
their neurosecretory activity during different periods of the year.
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NEUROSECRETION IN THE BAT
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415
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PLATE 1
EXPLANATION OF FIGURES
3 Sagittal section through the caudal portion of the supraoptic nucleus
(CSO) and optic tract (OT) of a hibernating bat. The staining density of the neurosecretory cells (9.5) represents the mean value for
all hibernating bats studied, 10 p thickness. x 190. The insert is a
higher magniikation photomicrograph of neuralsecretory cells from
the same section. x 615.
4
416
Sagittal section through the caudal portion of the supraoptic nucleus
( C S O ) and optic tract (OT)of a bat taken from. the summer colony.
The staining density of the neurosecretory cells was 7.5 and represents the mean value for all of the “active” bats studied, 10 p
thickness. x 190. The insert shows a higher magnification of the
neurosecretory cells from the same section. x 615.
NEUROSECRETION IN THE BAT
J. Robert Troyer
PLATE 1
417
PLATE 2
EXPLANATION OF FIGURES
418
5
Sagittal section through the rostral portion of the supraoptic nucleus
(RSO) and optic tract (OT) of a hibernating bat. The staining density of the neurosecretory cells (9.0) is the same as the mean value
for all of the hibernating bats studied, 10 p thickness. x 190. The
insert shows the same cells a t a higher magnification. x 615.
6
Sagittal section through the rostral portion of thle supraoptic nucleus
(RSO) and optic tract (OT) of a bat taken from the summer colony.
The staining density of the neurosecretory cells (7.0) is the same
as the mean value for all of the “active” bats studied, 10 p thickness. x 190. The insert shows the same cells at a higher magnification. x 615.
NEUROSECRETION IN THE BAT
J. Robert Troyer
PLATE 2
419
PLATE 3
EXPLANATION OF FIGURES
420
7
Sagittal section of the infundibular stem ( I S ) of a hibernating bat.
The staining density of the hypothalamo-hypophyseal tract (HT)
represents the mean value (9.0) for all of the hibernating bats
studied. The pars tuberalis (PT) and pars distalis (PD) also are
shown, 10 ,u thickness. x 190.
8
Sagittal section through the infundibular stem (IS) and pars distalis
(PD) of a bat taken from the summer colony. The staining density
of the hypothalamo-hypophyseal tract (HT) represents the mean
value ( 5 . 5 ) for all of the “active” bats studied, 10 p thickness. x 190.
NEUROSECRETION I N THE BAT
J. Robert Troyer
PLATE 3
421
PLATE 4
EXPLANATION O F FIGURES
422
9
Sagittal section of the pars nervosa of a hibernating bat. The staining
density of 9.5 represents the mean value for a l l hibernating bats
studied, 10 fi thickness. x 190.
10
Sagittal section of the pars nervosa of a bat taken from the summer
colony. The staining density of 8.0 represents the mean value for all
of the “active” bats studied, 10 I.L thickness. x 1910.
NEUROSECRETION IN THE BAT
J. Robert Troyer
PLATE 4
423
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neurosecretory, bat, period, supraoptic, trace, hibernation, hypophyseal, material, summer, throughout
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