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1.
The present study examined the differential mRNA expression levels of three forms of GnRH (sGnRH, pjGnRH and cGnRH-II) and
two forms of GnRH receptor (pjGnRH-R I and pjGnRH-R II) in the brain, pituitary, and ovaries of pejerrey in relation to the
reproductive status. The analysis revealed the presence of significant amounts of mRNA of the three GnRH forms while the ovaries
showed only two (sGnRH and pjGnRH). The GnRH receptor II was found ubiquitously in the brain, pituitary, and ovaries while
the form I was detected only in the brain. The levels of pjGnRH mRNA in the brain and pjGnRH-R II in the pituitary gland varied
in correlation with the ovarian condition. However, brain sGnRH and pjGnRH-R I mRNA levels reached a maximum during early
stages of ovarian development. In contrast, the brain levels of cGnRH-II mRNA showed no variation. The present study also
shows a good correlation of ovarian sGnRH and pjGnRH-R II mRNA levels with the reproductive condition, suggesting that these
molecules are may be involved in the regulation of pejerrey ovarian function. 相似文献
2.
Ky Xuan Pham Masafumi Amano Noriko Amiya Yutaka Kurita Akio Shimizu Kunio Yamamori 《Fisheries Science》2007,73(5):1113-1122
ABSTRACT: To clarify the possible roles of gonadotropin-releasing hormone (GnRH) in the reproduction of Japanese flounder Paralichthys olivaceus , localization of salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II), and sea bream GnRH (sbGnRH) immunoreactive (ir) cell bodies and fibers in the brain and pituitary were examined together with follicle stimulating hormone (FSH) and luteinizing hormone (LH)-ir cells in the pituitary by immunohistochemistry. sGnRH-ir cell bodies were localized in the ventromedial part of the rostral olfactory bulb and cGnRH-II-ir cell bodies were restricted to the midbrain tegmentum, while sbGnRH-ir cell bodies were evident in the preoptic area. sGnRH-ir fibers were distributed throughout the brain, especially abundant in the forebrain. cGnRH-II-ir fibers were also scattered in many areas of the brain with abundance in the midbrain, but sbGnRH-ir fibers were observed in the preoptic–hypothalamic area and innervated the pituitary. In the pituitary, neither sGnRH-ir fibers nor cGnRH-II-ir fibers were found, but sbGnRH-ir fibers were profuse in the neurohypophysis and invaded the proximal pars distalis, targeting FSH and LH cells. These results suggest that three GnRH systems can play different physiological roles in the brain of Japanese flounder. Among them, sbGnRH is considered to be involved in reproduction by stimulating gonadotropin secretion, while sGnRH and cGnRH-II can function as a neurotransmitter and/or neuromodulator within the brain in this species. 相似文献
3.
Masafumi Amano Kataaki Okubo Takeshi Yamanome Yoshitaka Oka Shoji Kitamura Kazumasa Ikuta Akiyoshi Takahashi Katsumi Aida Kunio Yamamori 《Fish physiology and biochemistry》2003,28(1-4):19-22
Multiple forms of the gonadotropin-releasing hormone (GnRH) exist in teleost fish. A salmonid fish, masu salmon Oncorhynchus masou has salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II). sGnRH neurons were scattered from the olfactory nerve through the ventral telencephalon (VT) and the preoptic area (POA). sGnRH but not cGnRH-II was detected in the pituitary. sGnRH mRNA levels in the VT and the POA increased during gonadal maturation, suggesting that sGnRH neurons in these areas are involved in gonadal maturation. sGnRH neurons were first detected in a cluster near the olfactory epithelium 40 days after fertilization. sGnRH neurons were not detected in the brain by the olfactory epithelia lesion, suggesting that sGnRH neurons are derived from the olfactory epithelium. A pleuronectiform fish, barfin flounder Verasper moseri has sGnRH, cGnRH-II and seabream GnRH (sbGnRH). sGnRH and cGnRH-II-immunoreactive fibers were observed throughout the brain, but not in the pituitary. sbGnRH neurons were located in the POA and sent fibers to the pituitary, indicating that sbGnRH is involved in GTH secretion. Judging from the location of neuronal somata and their projections, it is indicated that three GnRH systems exist in the barfin flounder; the TN-, the MT- and the POA-GnRH system. However, in masu salmon, clear anatomical identification of the TN- and the POA-GnRH system is difficult, because the GnRH neurons located in the ventral forebrain are consecutive and the GnRH form produced in these neurons is the same (sGnRH). Thus, it is suggested in masu salmon that sGnRH neurons are derived from the olfactory epithelium, migrate into the brain and play different roles according to the location in the brain. 相似文献
4.
Masafumi Amano Katsumi Aida Naoto Okumoto Yoshihisa Hasegawa 《Fish physiology and biochemistry》1993,11(1-6):233-240
Levels of two types of gonadotropin-releasing hormone (salmon GnRH and chicken GnRH-II) in the brain and pituitary, and content of gonadotropin (GTHIβ and IIβ) in the pituitary were measured in male masu salmon from hatching to gonadal maturation for three years in order to clarify the involvement of GnRHs in precocious maturation. Underyearling precocious males were distinguishable in summer of year 1 and were marked by an increased GSI. Spermiation was observed among these individuals thereafter every autumn. Pituitary GTHIβ content in both precocious and immature males, and GTHIIβ content in precocious males showed seasonal fluctuations — high in autumn and low in winter. Pituitary GTHIIβ content was low in immature males. Pituitary sGnRH content in precocious males increased from spring to autumn during the three-year period. sGnRH concentrations in discrete brain areas showed seasonal changes — high during autumn to winter and low in summer. Concentrations in the olfactory bulbs and hypothalamus increased significantly in association with testicular maturation during year 3. sGnRH concentrations in the hypothalamus were significantly higher in precocious males than in immature males; this was possibly due to positive feedback of steroid hormones. cGnRH-II was undetectable in the pituitary and no distinct changes were observed in its concentration in the brain in relation to maturation. The phenomenon of underyearling precocious maturation is considered to be triggered before the onset of early summer. It is suggested that males which mature precociously are larger in size and contain much sGnRH in the pituitary before the outward signs of precocity appear; sGnRH may stimulate GTH II synthesis and induce precocious maturation. 相似文献
5.
The distribution of immunoreactive GnRH was studied in the brain and pituitary gland of normal and human chorionic gonadotrophin (hCG) injected silver eels. It was found that the general organization of GnRH systems in this species is similar to that reported in other teleosts. Cell bodies were present in the olfactory bulbs, ventral telencephalon, periventricular hypothalamus and dorsal tegmentum. No positive perikarya could be detected in the preoptic region. Only scarce fibers were observed in the proximal neurohypophysis. Treatment with hCG does not modify the distribution of GnRH but it increases the density of positive structures, in particular at the level of the pituitary. The results are discussed in relation with the present status of knowledge of the mechanisms underlying the blockage of sexual maturation in the European eel at the silver stage. 相似文献
6.
Distribution of three GnRHs in the brain and pituitary of the wild Japanese flounder Paralichthys olivaceus 总被引：1，自引：1，他引：1
Ky Xuan Pham Masafumi Amano Noriko Amiya Yutaka Kurita Kunio Yamamori 《Fisheries Science》2006,72(1):89-94
ABSTRACT: Wild adult maturing and immature female Japanese flounder Paralichthys olivaceus were collected in June 2004 and January 2005, respectively, to clarify a possible role of gonadotropin-releasing hormones (GnRHs) in reproduction. Levels of salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and sea bream GnRH (sbGnRH) in the brain and pituitary were examined by time-resolved fluoroimmunoassay. Three forms of GnRHs were detected in the discrete brain at various levels. In the pituitary of both maturing and immature fish, sbGnRH was abundant together with a pronounced amount of sGnRH, whereas cGnRH-II was almost below the detectable limit. In maturing fish, levels of sbGnRH were high in the telencephalon, hypothalamus and pituitary, while levels of sbGnRH of immature fish were very low in these regions. These results indicate that sbGnRH is mainly responsible for gonadotropin secretion, and that sbGnRH in the anterior part of the brain is associated with gonadal maturation in the Japanese flounder. 相似文献
7.
In this study we examined the endocrine mediation between environmental factors (temperature and photoperiod) and the brain–pituitary–gonadal
axis in females of pejerrey Odontesthes bonariensis. Changes in the expression of brain gonadotropin-releasing hormones (GnRHs) and gonadotropin (GtH) subunit [follicle stimulating-β
(FSH-β), luteinizing hormone-β (LH-β), glycoprotein hormone-α (GPH-α)] genes, plasma gonadal steroids [estradiol (E2) and testosterone (T)], gonadal histology, and gonadosomatic index (GSI) in adult females exposed to combinations of short-day
(8 h) or long-day (16 h) photoperiods and low (12°C) or high (20°C) temperatures after winter conditions (8 h light, 12°C)
were analyzed. Pejerrey females kept under the short photoperiod had low GSIs, and their ovaries contained only previtellogenic
oocytes regardless of the experimental temperature. In contrast, females exposed to the long photoperiod had high GSIs and
ovaries with vitellogenic oocytes at both temperatures. These fish also showed a significantly higher expression of sGnRH,
pjGnRH, cGnRH-II (the three different GnRH variants found to date in the pejerrey brain), FSH-β, LH-β and GPH-α genes and
plasma E2 levels than those at the shorter photoperiod. No significant changes were observed in plasma T levels. Based on these results,
we concluded that the increase in day length but not that of temperature triggers the maturation of pejerrey females after
the winter period of gonadal rest and that this occurs by an integrated stimulation of the various components of the brain–pituitary–gonad
axis. 相似文献
8.
A.D. Montaner L.A. Miranda D. Vizziano A. López K. Okuzawa G.M. Somoza 《Fish physiology and biochemistry》2001,24(3):243-246
Gonadotropin-releasing hormone (GnRH) molecular variants were characterized by gradient reverse phase high performance liquid chromatography (RP)-HPLC) from brain extracts of two perciforms with economic importance for Argentina and Uruguay. RP-HPLC fractions were tested in radioimmunoassays (RIAs) with both poly-specific and specific antisera. Both species showed the presence of the same three molecular forms, immunologically and chromatographically indistinguishable from sbGnRH, cGnRH-II and sGnRH. This study supports the hypothesis that their expression is a common pattern in perciforms. 相似文献
9.
10.
M. Kobayashi M. Amano M.H. Kim Y. Yoshiura Y.C. Sohn H. Suetake K. Aida 《Fish physiology and biochemistry》1997,17(1-6):1-8
Reproductive activities in vertebrates are regulated by an endocrine system, consisting of the brain-pituitary-gonad axis. In teleosts, gonadotropin-releasing hormone (GnRH) in the brain stimulates gonadotropin (GTH) release in the pituitary gland, but because of lack of the portal vessel, it is not known when and how much GnRH is released for the regulation of GTH release. There are multiple molecular types of GnRH in teleosts and several distinct populations of GnRH neurons in the brain. However, we do not know which types and populations of GnRH neurons regulate reproductive activities. Here we summarize our recent studies on GnRH and GTH in masu salmon Oncorhynchus masou and goldfish Carassius auratus. Immunocytochemistry showed the location and molecular types of GnRH neurons. Salmon (sGnRH) and chicken-II GnRH (cGnRH-II) neuronal fibers were widely distributed in the brain of both masu salmon and goldfish. Only sGnRH fibers were observed in the pituitary of masu salmon, whereas both sGnRH and cGnRH-II fibers were observed in the goldfish pituitary, indicating that species specific GnRH profiles are involved in the regulation of pituitary function in teleosts. A series of experiments in masu salmon and goldfish suggest that among GnRH neuron populations GnRH neurons in the ventral telencephalon and the hypothalamus regulate GTH release, and that GnRH of the terminal nerve origin is not essential to gonadal maturation and ovulation. The biological function of other GnRH neurons remains unkown. Two GTHs appear to be characteristic of teleost; however, regulation of reproduction by these GTHs is a question that remains to be elucidated. In salmonid species, it is proposed that GTH I stimulates early gonadal development, whereas GTH II acts in later stages. When GTH expression was examined in goldfish, both GTH I and II mRNA levels in the pituitary gland showed increases in accordance with gonadal development, unlike the sequential expression of GTH subunits in salmonids. The expression of these GTH subunit mRNAs were affected by water temperature, starvation, and steroid hormones in goldfish, but in what manner these two GTHs regulate gonadal development remains to be clarified. 相似文献
11.
Effects of photoperiod on gonadotropin-releasing hormone levels in the brain and pituitary of underyearling male barfin flounder 总被引：2，自引：0，他引：2
Masafumi AMANO Takeshi YAMANOME Hideaki YAMADA Koichi OKUZAWA Kunio YAMAMORI 《Fisheries Science》2004,70(5):812-818
ABSTRACT: A pleuronectiform fish, the barfin flounder Verasper moseri , expresses three gonadotropin-releasing hormone (GnRH) forms in the brain: salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and seabream GnRH (sbGnRH). To clarify the effects of photoperiod on GnRH systems, changes in brain and pituitary GnRH peptide levels were examined using time-resolved fluoroimmunoassays. In experiment 1, 5-month-old male barfin flounder (mean total length 9.0 cm, body weight 11.0 g) were divided into short (8:16 h light : dark [L:D] cycle; lights on 08.00–16.00 hours) and long photoperiod (16:8 h L:D cycle; lights on 04.00–20.00 hours) groups in mid September and maintained until November under natural water temperature (19.3–15.2°C). Brain sGnRH concentrations were significantly higher in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in total length, body weight, plasma testosterone concentration, brain cGnRH-II concentration and pituitary sbGnRH content. In experiment 2, 7-month-old male barfin flounder (mean total length 16.5 cm, body weight 76.8 g) were divided into short and long photoperiod groups in mid December and maintained until February under natural water temperature (12.5–6.6°C). Total length, body weight and condition factor were significantly greater in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in plasma testosterone concentration and GnRH levels in the brain and pituitary. These results indicate that levels of sGnRH in barfin flounder are influenced by photoperiodic treatment dependent on water temperature and/or body size. 相似文献
12.
M.A. Ravaglia F.L. Lo Nostro M.C. Maggese G.A. Guerrero G.M. Somoza 《Fish physiology and biochemistry》1997,16(5):425-436
This paper studies the molecular variants of gonadotropin-releasing hormone (GnRH) present in the brain of the protogynous
swamp eel, Synbranchus marmoratus, and the effects of the administration of salmon GnRH analogue (sGnRH-A) and the dopamine
receptor antagonist, domperidone (DOM) on final maturation and gamete release in this species. Evidence for the presence of
two GnRH variants, sGnRH and cIIGnRH were obtained by reverse phase high-pressure liquid chromatography (RP-HPLC) and radioimmunoassay
with different antisera. The effects of treatment with sGnRH-A+DOM were checked by three ways: oocyte and milt release by
stripping, histological analysis of the gonadal tissue, and androgen serum levels at different times throughout the experiment.
In males, spermiation was induced after three weeks of treatment. In the female group, sGnRH-A+DOM did not induce ovulation
at the end of the experiment. Histological analysis of the gonads from the female group showed evidence of sex reversal. All
the treated fish had elevated androgen serum levels from the third week, with respect to control fish. In all cases, serum
estradiol levels were undetectable. These results suggest that treatment with sGnRH analog and DOM induce sex reversal in
female and spermiation in males.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
H.J.Th. Goos P.T. Bosma J. Bogerd C.P. Tensen C.P. Tensen K.W. Li K.W. Li M.A. Zandbergen R.W. Schulz 《Fish physiology and biochemistry》1997,17(1-6):45-51
Two gonadotropin releasing hormones (GnRHs) were identified in the African catfish: chicken GnRH-II (cGnRH-II) and catfish GnRH (cfGnRH). Immunological screening of HPLC fractions from pituitary extracts indicated a third GnRH which co-eluted with lamprey GnRH-III. However, mass determination and amino acid sequencing identified this material as isotocin. This underlines the risk of identifying multiple forms of GnRH in tissue extracts on the basis of immunoreactivity in HPLC fractions. In vivo and in vitro studies demonstrated that cGnRH-II is an over 100-fold more potent gonadotropin (GTH) secretagogue than cfGnRH. This correlates with the respective receptor affinities. The presence of both GnRHs in the pituitary gland suggests that they may modulate each other's GTH release activity. Sub-threshold or low doses of cGnRH-II partly inhibited cfGnRH-induced GTH II secretion. Conversely, combinations of sub-threshold or low doses of cfGnRH with effective doses of cGnRH-II led to increases in GTH II levels similar to those induced by cGnRH-II alone. Combinations of submaximally effective dose of the 2 peptides resulted in additive effects. Hence, both GnRHs participate in the regulation of GTH II release, and their relative concentrations may determine the overall effect. Immunocytochemistry, using anti-bodies against the respective recombinant GnRH associated peptides (GAPs), as well as in situ hybridization showed that cfGnRH neurones are scattered in the ventral forebrain and project into the pituitary gland, while cGnRH-II neurones are confined to the midbrain tegmentum and without projections to the pituitary gland. Transfection experiments with GnRH receptor cDNA shows ligand activation characteristics similar to those of the native GnRH-R. Autoradiographic studies and hormone release studies indicate that GnRH-Rs in the African catfish pituitary gland are restricted to the gonadotrophs. 相似文献
14.
Ahmad Gharaei Fereidoun Mahboudi Abbas Esmaili-Sari Rozita Edalat Ahmad Adeli Saeed Keyvanshokooh 《Fish physiology and biochemistry》2010,36(3):803-817
Two gonadotropin-releasing hormone (GnRH) isoforms were identified in the beluga (Huso huso) brain by cDNA sequencing: prepro-mammalian GnRH (mGnRH) and prepro-chicken GnRH-II (cGnRH-II). The nucleotide sequences
of the beluga mGnRH and cGnRH-II precursors are 273 and 258 base pairs (bp) long, encoding peptides of 91 and 86 amino acids,
respectively. To investigate the effect of methylmercury (MeHg) on GnRH gene expression, animals were fed with four diets
containing increasing levels of MeHg (0 mg kg−1 [control]; 0.76 mg kg−1 [low]; 7.8 mg kg−1 [medium]; 16.22 mg kg−1 [high]) for 32 days. The effects of MeHg on brain GnRH mRNA levels were evaluated by real-time PCR. A significant decrease
in brain mGnRH and cGnRH-II mRNA levels were detected in fish receiving high dietary MeHg dose compared to controls on day
11 (P < 0.05). On day 18 and 32, all treatment groups had significantly lower brain mGnRH and cGnRH-II mRNA levels compared to
the control group (P < 0.05). These findings demonstrate a disruptive role of MeHg on the level of brain mGnRH and cGnRH-II mRNAs in immature
beluga. 相似文献
15.
H. Chiba M. Amano H. Yamada Y. Fujimoto D. Ojima K. Okuzawa T. Yamanome K. Yamamori M. Iwata 《Fish physiology and biochemistry》2004,30(3-4):267-273
Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro were studied in barfin flounder Verasper moseri, masu salmon Oncorhynchus masou and goldfish Carassius auratus. Seabream GnRH (sbGnRH) at a dose of 200 ng/50 g body weight (BW) significantly increased plasma T4 levels 1 h after the in vivo injection in the barfin flounder, but thereafter the levels normalized. Salmon GnRH (sGnRH) significantly increased plasma
T4 levels l h after the injection with a significant return to initial levels in male masu salmon and male goldfish. In contrast,
sGnRH and cGnRH-II in barfin flounder, and cGnRH-II in male masu salmon and male goldfish were not effective in stimulating
T4 release. To clarify direct involvement of GnRH in T4 release, dissected lower jaw including scattered thyroid follicles was incubated with sbGnRH (1 μg/well) in barfin flounder,
and with two doses (0.1 and 1 μg/well) of sGnRH in masu salmon and goldfish in vitro. T4 concentrations of control were stable during 24 h. Incubation of lower jaw with high dose (1 μg/well) of GnRH significantly
(P<0.05) increased T4 concentrations of incubation medium at 1 h in all experimental fishes. These results indicate that direct stimulation of
T4 secretion by GnRH occurs widely in teleost fish. 相似文献
16.
Minakshi Mazumdar Praful Singru Amul Sakharkar Makrand Deshmukh Nishikant Subhedar 《Fish physiology and biochemistry》2005,31(2-3):173-176
Glucagon-like peptide-1-immunoreactivity (GLP-ir) was seen in several olfactory receptor neurons in the olfactory epithelium
and in the olfactory nerve fascicles that extend caudally to the bulb and innervate the glomerular layer. Thick GLP-ir fascicles
were seen in the medial olfactory tracts (MOT); these probably represent the extrabulbar olfactory projections. GLP-ir fibers
in the MOT penetrate into the telencephalon, swing dorsocaudally into the area ventralis telencephali/pars supracommissuralis
(Vs) just above the anterior commissure. The immunoreactive fascicles continue caudally in the dorsal hypothalamus and are
traceable as far as the lateral recesses. Scattered GLP-ir fibers were seen in the ventral telencephalon and preoptic area.
While several immunoreactive cells were seen in the pars intermedia of the pituitary gland, few were encountered in the rostral
pars distalis and proximal pars distalis. Role for the peptide in the processing of olfactory information and in the regulation
of pituitary gland may be suggested. 相似文献
17.
为了深入了解斑马鱼端脑的微细形态和超微结构,采用光镜和电镜技术对斑马鱼端脑进行观察研究。斑马鱼端脑由左、右嗅球和左、右大脑半球构成。嗅球前方有一对嗅神经,后端伸出嗅茎与大脑半球联系。光镜下,嗅球组织结构从外向内依次为上皮层、神经纤维层、小细胞层和内部细胞层。大脑半球外部覆盖很薄的大脑皮,基部为纹状体,两者之间的腔隙为公共脑室。纹状体由神经核团和神经纤维构成。神经核团分布于纹状体周缘,主要有连前核、背嗅核、侧嗅核、视前核和脚内核等。神经纤维包括横行的前连合,纵行和斜行的中央嗅束和侧嗅束。电镜下,嗅球分层明显,可观察到僧帽细胞、神经胶质细胞和众多突触。大脑半球中可见神经胶质细胞、突触以及血脑屏障系统等。斑马鱼端脑形态结构与大多数硬骨鱼相似,但有个别核团存在差异。实验结果可为斑马鱼神经生物学模型的建立与应用提供有效的理论基础。 相似文献
18.
T. Kitani S. Matsumoto H. Yamada M. Amano M. Iwata H. Ueda 《Fish physiology and biochemistry》2003,28(1-4):269-270
Levels of two moleculer types of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH–II (cGnRH–II) in the various brain regions and pituitary gland of sockeye salmon (Oncorhynchus nerka) and chum salmon (O. keta) during smoltification and spawning migration, respectively, were measured using specific time-resolved fluoroimmunoassay (TR-FIA) systems. Changes in sGnRH levels in different brain regions tended to be specifically synchronized with serum thyroid hormone or pituitary gonadotropin (GTH) levels during smoltification and spawning migration, respectively. In contrast, cGnRH–II levels did not show such synchronized changes. SGnRH and cGnRH–II in various brain regions might have different roles during smoltification and spawning migration of salmonid fishes. 相似文献
19.
P.G. Vissio A.V. Stefano G.M. Somoza M.C. Maggese D.A. Paz 《Fish physiology and biochemistry》1999,21(2):121-127
The purpose of this study was to determine if there is any association between immunoreactive (ir) gonadotropin-releasing hormone (GnRH) fibers with different pituitary endocrine cell types in the pejerrey, Odontesthes bonariensis. Using a monoclonal antibody raised against mammalian GnRH (mGnRH) (LRH13), ir-GnRH fibers were observed passing through the pituitary stalk and reaching the three areas of the pituitary gland: rostral (RPD) and proximal pars distalis (PPD) and pars intermedia (PI). Double labeled immunocytochemistry showed ir-GnRH fibers in close association with prolactin (PRL)-producing cells in the RPD, growth hormone (GH)-producing cells in the PPD, gonadotropin (GtH)-producing cells in the PPD and the external border of the PI, and with somatolactin (SL)-producing cells in the PI. Our results show, direct morphological evidences of a close association of GnRH fibers with GH, PRL, GtH and SL-expressing cells. These results would suggest that GnRH has a broad role in the regulation of the secretion of different pituitary hormones. 相似文献
20.
Pituitary gonadotropin (GTH) secreting cells and brain gonadotropin-releasing hormone (GnRH) secreting neurons are known to be subjected to feedback control by gonadal steroid in teleosts. In masu salmon, Oncorhynchus masou, salmon GnRH (sGnRH) neurons in the ventral telencephalon (VT) and the preoptic area (POA) are involved in the control of GTH cells because sGnRH synthesis in these areas is activated with gonadal maturation. In this study, we attempted to clarify mechanisms of feedback control of sGnRH neurons by gonadal steroids. We examined the effects of 17-methyltestosterone (MT) on sGnRH synthesis in yearling and 2-year-old female fish (which were immature during experimentation in May), and the effects of castration on sGnRH synthesis in underyearling precocious male fish in August. sGnRH synthesis in the POA, but not in the VT, was increased by MT administration in 2-year-old females only, indicating higher sensitivity to MT in the preoptic sGnRH neurons. Castration increased sGnRH synthesis in the VT but not in the POA. These results suggest that sGnRH neurons in the VT and those in the POA are differentially regulated by gonadal steroids. 相似文献