An anatomical and histochemical examination of the ... - Tübitak

Turkish Journal of Veterinary and Animal Sciences
http://journals.tubitak.gov.tr/veterinary/
Research Article
Turk J Vet Anim Sci
(2013) 37: 399-403
© TÜBİTAK
doi:10.3906/vet-1108-21
An anatomical and histochemical examination of the pituitary gland of carp (Cyprinus carpio)
Aygül EKİCİ*, Metin TİMUR
Department of Aquaculture, Faculty of Fisheries, İstanbul University, Laleli, İstanbul, Turkey
Received: 24.08.2011 Accepted: 26.12.2012 Published Online: 29.07.2013 Printed: 26.08.2013
Abstract: The present study was carried out for the purpose of studying the anatomical and the histochemical structure of the pituitary
gland of the common carp, Cyprinus carpio. Anatomically, the shape of the gland has been observed to be round-oval, looking like an
acorn. The pituitary gland consists of the adenohypophysis and neurohypophysis parts. Microscopically, the adenohypophysis consists
of anterior (pars distalis) and posterior (pars intermedia) parts. The second lobe of the gland, called the neurohypophysis, is found in
the core of the gland. Histologically, acidophilic prolactin cells stained red or orange and were dispersed in the rostral pars distalis (proadenohypophysis)
of the adenohypophysis. Basophilic thyrotropin cells stained blue and were found in a small number in the same
region. Adrenocorticotropin cells showed a chromophobic character; therefore, they did not get stained by the periodic acid-Schiff
staining techniques. Gonadotropin cells were observed in the proximal pars distalis (meso-adenohypophysis) of the adenohypophysis.
In the examined specimens, the faintly stained, elongated or pyramidal cells in the pars intermedia of the adenohypophysis were covering
the neurohypophysis region. The neurohypophysial lobe was composed of unmyelinated nerve fibers and the pituicyte cells were located
among the nerve fibers. Herring bodies were seen scattered in the neurohypophysis.
Key words: Cyprinus carpio, carp, adenohypophysis, neurohypophysis, pituicyte, Herring bodies
1. Introduction
The pituitary gland of fish is suspended from the
hypothalamus. It is one of the most important endocrine
organs of fish. The histology of the pituitary of teleost fish
has been described by a number of authors (1–3). These
descriptions do not provide details on the histophysiology
and the endocrinology of this gland.
The common carp (Cyprinus carpio) is a seasonal
breeding fish with definite fluctuations in reproductive
function during its annual cycle. It is well known that
this process is controlled by hypophyseal gonadotropin
hormones, which play a decisive role in gonadal
development, ovulation, and spermiation (4).
In all vertebrates, the pituitary gland or hypophysis
consists of 2 parts, separable on the bases of
embryology, structure, and function. These parts are
the neurohypophysis and the adenohypophysis (5). The
function of the adenohypophysis is the synthesis and
storage of several hormones. The neurohypophysis of
teleost fishes secretes 2 kinds of octapeptide hormones,
arginine vasotocin and isotocin (3).
In some studies on teleost fishes, it has been proven that
prolactin-releasing hormone, thyrotrophin-stimulating
hormone (TSH), and adrenocorticotropin (ACTH) are
released from the adenohypophysis (6–11). In these
* Correspondence: aekici@istanbul.edu.tr
studies, it has been observed that the granules of prolactin
cells can be stained red by implementing Masson’s
trichrome technique, but they cannot be stained using
the periodic acid-Schiff (PAS), Alcian blue, or aldehyde
fuchsin techniques.
The cells that release α cells, especially in marine fishes,
are acidophilic cells located in the pars distalis section of
the pituitary gland and these may be inactive prolactin
cells (12). These cells may become visible using the Orange
G staining technique (13,14).
Gonadotropes (β and α cells) in teleost fishes are
usually localized in the proximal pars distalis section
of the pituitary gland (15). It has been proven that the
hormones released by the pituitary gland of vimba
(Vimba vimba), common carp (C. carpio), and zander
(Stizostedion lucioperca) are similar to the hormones
released by mammals. In common carp, in the rostral pars
distalis, which is connected to the proximal pars distalis by
the connective tissue prolactin, TSH and ACTH cells, in
the shape of a plate, are present in the rostral pars distalis
section of the gland (2).
Studies on fish pituitary glands prove that many
physiological functions like growth, reproduction,
reproduction-related behavior, instinct for nidification,
regulation of body electrolyte balance, and gonad
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development are controlled by hormones that are released
from the pituitary gland, in the same way that it functions
in mammals (16,17).
In our study, the anatomical position of the pituitary
gland in the cranium and the cells of this gland that release
these hormones were examined histologically.
2. Materials and methods
This study was conducted at the Sapanca Inland Waters
Research Unit of the İstanbul University Faculty of
Fisheries. A total of 20 common carp (C. carpio) that were
3+ years old and 1400 ± 100 g in weight were used. During
this study, the fish were kept in 3 PVC circular tanks with
a diameter of 3 m and a height of 1.5 m at 18–20 °C. Prior
to each sampling, the fish were anaesthetized with 200
ppm tricaine methanesulfonate (MS222) for 5 min (18). A
cranial incision was performed using a bone saw about 1
cm behind the eyes. A second incision was placed parallel
to and about 3 cm from the first incision. The frontal bone
located between the 2 fractions was carefully removed.
The cranial incision into the scalp was cut into 2
equal parts in a dorsoventral direction in the course of
a median line from dorsal through ventral. After the
hypophysectomy, the pituitary gland in the cavity of the
parasphenoid sella turcica was removed. White matter was
collected from the nerve fibers in this area.
After removal, the fresh pituitary glands were
fixed in 10% neutral buffered formaldehyde or Bouin
solution according to the histochemical method to be
implemented. Fixed samples were then processed for
histopathology (19,20). Paraffin-embedded tissues were
cut into sections 4–5 µm thick using a Leica RM 2125 RT
manual microtome.
For the histological research, the tissue samples
were stained using the hematoxylin and eosin (H&E)
technique. For the histochemical study, the tissue samples
were stained using the PAS, Masson’s trichrome, PAS–
Orange G, Heidenhain’s azan, and orange fuchsin green
(OFG) staining techniques. Stained tissue sections were
examined under a Nikon E-600 computerized binocular
light microscope connected to a Nikon camera.
3. Results
3.1. Anatomical results
After the hypophysectomy operation, we saw loose
connective tissue in the thickness of the gel covering the
brain. When this loose connective tissue was cleared and
the brain was removed, we saw that the brain is located
in a specific cavity named the sella turcica over the
parasphenoid bone (Figure 1).
In the brain tissue, which is cream-white in color, the
same as the pituitary gland, macroscopically distinguishable
telencephalon, optic lobes, cerebellum, and medulla
oblongata sections were located. It was determined that
the pituitary gland, which has a smooth surface, is under
the optic lobes of the brain, morphologically similar to an
acorn or pear, and its size ranges from approximately 1 × 3
mm to 2 × 3 mm (Figure 2).
3.2. Histological results
The adenohypophysis and neurohypophysis sections
of the pituitary gland of the common carp were easily
distinguished when the samples were stained with the
H&E staining technique.
3.2.1. Adenohypophysis
Prolactin cells, ACTH cells, and TSH cells were
observed in the front part of the adenohypophysis (proadenohypophysis)
section of the pituitary gland, which is
formed of hormone-releasing glandular tissues.
It was confirmed that the prolactin cells are distributed
randomly in the hypophysis of common carp while they
are in follicular distribution in salmon and eels (Figure
3). It was observed that these acidophilic cells containing
secretion granules do not get stained well with PAS but
nonetheless can be stained with Heidenhain’s azan stain.
It was seen that adrenocorticotropic cells are lined
up in single or double rows in such a way as to become
neighbors with the neurohypophysis in the upper parts
of the adenohypophysis (Figure 4). In the examination of
these cells after using Heidenhain’s azan staining technique,
it was observed that they contain secreting granules.
TSH cells were seen individually or in groups. These
basophilic cells found in tissue samples that were stained
using the PAS and Heidenhain’s azan staining techniques
revealed a large number of secreting granules (Figure 5).
We noted that gonadotrope (GTH) cells increase in
number in common carp. It was determined that the tissues
stained with PAS are basophilic in character (unpublished
data) and have numerous secreting granules (Figure 6).
3.2.2. Neurohypophysis
In microscopic examinations of the neurohypophysis,
numerous glia (pituicytes) were detected among the nerve
fibers (Figure 7). Herring bodies, which are stainable
secretion granules and are found in nerve fibers, were seen
in large numbers in the tissue samples (Figure 8).
4. Discussion
The pituitary gland in common carp, like in all vertebrates,
is a master internal secretion organ controlling growth
and reproduction, enabling body electrolyte balance and
controlling all other endocrine glands (21).
In the anatomical examination made of the common
carp’s cranium, it was seen that the pituitary gland is
embedded in the sella turcica cavity, which is above the
parasphenoid bone right beneath the brain. The gland is
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Figure 1. The pituitary gland is located in the sella turcica.
Figure 3. Prolactin cells in pro-adenohypophysis, PAS 100×, bar
= 10 µm.
Figure 2. The general appearance of the pituitary gland is similar
to an acorn or pear.
similar to an acorn in shape. However, it has been stated
that this gland is in the shape of a cone in zander and
sunfish, and is round in vimba (V. vimba) (2).
In common carp, like in all vertebrates, it was observed
that the pituitary gland is formed of the adenohypophysis
and the neurohypophysis lobes, while the adenohypophysis
divides into the pars distalis and pars intermedia parts,
and one of these parts, the pars distalis, constitutes the
proximal and the rostral parts. It has been stated that the
pars tuberalis part, which is formed by the extension of the
adenohypophysis through the infundibular stem, does not
exist in common carp (16,22–25).
As in European eels (Anguilla anguilla) and crucian
carp (Carassius carassius), in the rostral pars distalis part
of the pituitary gland of the common carp used in our
research, the presence of TSH and ACTH cells was detected
Figure 4. ACTH cells in pro-adenohypophysis, H&E 100×, bar
= 10 µm.
(23,24). It was seen that the prolactin cells, as stated by
other researchers, are of an acidophilic character, as they
are stained red or orange with the H&E, Heidenhain’s
azan, PAS, PAS–Orange G, and OFG stains (19,20,22), and
these cells are found all around except in the dorsal parts
of the pars distalis in common carp.
It was seen that the cells that release TSH from the
pituitary gland are of basophilic character and are stained
blue with the H&E, Heidenhain’s azan, PAS, PAS–Orange
G, and OFG stains (1–3).
It was determined that the ACTH cells, which are
chromophobic and do not get stained at all, are distributed
all around the pars distalis (19,24,26).
Our previous experimental results showed that
somatotropes, STH cells, were located in the mesoadenohypophysis
part of the common carp (C. carpio)
pituitary gland, and these cells were shown in the samples
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Figure 5. TSH cells in pro-adenohypophysis, Heidenhain’s azan
100×, bar = 10 µm.
Figure 7. Pituicyte cells in neurohypophysis, Heidenhain’s azan
100×, bar = 10 µm.
Figure 6. GTH cells in meso-adenohypophysis, Masson’s
trichrome 100×, bar = 10 µm.
Figure 8. Herring bodies in neurohypophysis, OFG 100×, bar =
10 µm.
stained with the PAS–Orange G and H&E staining
techniques. In the meta-adenohypophysis, melanocytestimulating
hormone (MSH) cells were stained with PAS
stain (27).
Gonadotropic cells, found in the pars distalis part of
the pituitary gland in teleost fishes, were observed to be
basophilic in character and they were stained dark blue
with PAS, Masson’s trichrome, and Heidenhain’s azan
stains (3).
Like in other teleost fishes and tetrapods, it was
determined in this research that the neurohypophysis
nerve fibers and nerve cells are without myelin (pituicytes).
It was observed that the stainable and the secreting granule
containing a specific type (Herring bodies) of these fibers
exist in great numbers in the neurohypophysis (2,3).
In conclusion, it was seen that the pituitary gland of the
common carp is morphologically similar to an acorn. It was
determined that, anatomically, this gland is substantially
similar to the pituitary gland of other vertebrates. As for
histology, the acidophilic, basophilic, and chromophobic
cells described in vertebrates, and characterized in other
teleost fishes, show similar histochemical reactions in
common carp (5).
Acknowledgments
The authors would like to thank Prof Dr Charles Allen
Scarboro for helping with the English grammar. We
would also like to thank Assist Prof Erdoğan Güven and
the Sapanca Inland Water Research Unit workers. This
research project was supported by the İstanbul University
Research Fund (Project Number: 4326).
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