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1.
Yoshihiro WAKABAYASHI Hiroaki OKAMURA Takashi YAMAMURA 《The Journal of reproduction and development》2021,67(6):352
Kisspeptin neurons in the arcuate nucleus (ARC), which co-express neurokinin B (NKB) and dynorphin A, are termed KNDy neurons. These neurons are candidates for the intrinsic gonadotropin-releasing hormone (GnRH) pulse generator. The central and peripheral administration of NKB or its receptor (NK3R) agonist evokes GnRH pulse generator activity and the subsequent pulsatile GnRH/luteinizing hormone (LH) secretion. However, the mechanism responsible for neural activation of the GnRH pulse generator in goats is unclear. We conducted electrophysiological and histochemical experiments to test the hypothesis that KNDy neurons receive NKB and that the signal is transmitted bilaterally to a population of KNDy neurons. Bilateral electrodes aimed at a cluster of KNDy neurons were inserted into the ovariectomized goat ARC. We observed the GnRH pulse generator activity, represented by characteristic increases in multiple-unit activity (MUA volleys). The unilateral administration of NKB or vehicle in the close vicinity of KNDy neurons under simultaneous MUA recording from both sides revealed that only NKB evoked MUA volley(s) immediately after administration. The timing of the MUA volley(s) evoked on the ipsilateral side was synchronized to that on the contralateral side. The double-labeled ISH for KISS1 and TACR3, which encode kisspeptin and NK3R, respectively, revealed that most KNDy neurons co-expressed TACR3. Therefore, NKB could directly stimulate KNDy neurons, following which the stimulatory signal is immediately transmitted to the entire population of KNDy neurons via connection with their fibers. This mechanism helps synchronize burst activity among KNDy neurons, thereby generating neural signals that govern pulsatile GnRH secretion. 相似文献
2.
Yoshihiro WAKABAYASHI Takashi YAMAMURA Kohei SAKAMOTO Yuji MORI Hiroaki OKAMURA 《The Journal of reproduction and development》2013,59(1):40-48
Neurons in the arcuate nucleus (ARC) that concomitantly express kisspeptin, neurokinin B
(NKB) and dynorphin A are termed KNDy neurons and are likely candidates for the intrinsic
gonadotropin-releasing hormone (GnRH) pulse generator. Our hypothesis is that KNDy neurons
are functionally and anatomically interconnected to generate discrete neural signals that
govern pulsatile GnRH secretion. Our goal was to address this hypothesis using
electrophysiological and anatomical experiments in goats. Bilateral electrodes targeting
KNDy neurons were implanted into ovariectomized goats, and GnRH pulse generator activity,
represented by characteristic increases in multiple-unit activity (MUA volleys), was
measured. Spontaneous and pheromone- or senktide (an NKB receptor agonist)-induced MUA
volleys were simultaneously recorded from both sides of the ARC. An anterograde tracer,
biotinylated dextran amine (BDA), was also injected unilaterally into the ARC of castrated
male goats, and the distribution of fibers containing both BDA and NKB was examined using
dual-labeling histochemistry. The results showed that MUA volleys, regardless of origin
(spontaneous or experimentally induced), occur simultaneously between the right and left
sides of the ARC. Tract tracing indicated that axons projecting from NKB neurons in the
ARC were directly apposed to other NKB neuronal cells located bilaterally in the ARC.
These results demonstrate that GnRH pulse generator activity occurs synchronously between
both sides of the ARC in goats and that KNDy neurons are bilaterally interconnected in the
ARC via NKB-containing fibers. Taken together, the results suggest that KNDy neurons form
a neuronal circuit to synchronize burst activity among KNDy neurons and thereby generate
discrete neural signals that govern pulsatile GnRH secretion. 相似文献
3.
Matsuyama S Ohkura S Ichimaru T Sakurai K Tsukamura H Maeda K Okamura H 《The Journal of reproduction and development》2004,50(6):697-704
The time course of GnRH pulse generator activity and plasma concentrations of energy substrates and insulin were simultaneously observed in female goats during 4-day fasting and subsequent refeeding in the presence or absence of estrogen for a better understanding of the mechanism of energetic control of gonadotropin secretion in ruminants. The GnRH pulse generator activity was electrophysiologically assessed with the intervals of characteristic increases in multiple-unit activity (MUA volleys) in the mediobasal hypothalamus. In estradiol-treated ovariectomized (OVX+E2) goats, the MUA volley intervals increased as fasting progressed. Plasma concentrations of non-esterified fatty acid and ketone body increased, while those of acetic acid and insulin decreased during fasting. The MUA volley intervals and plasma concentrations of those metabolites and insulin were restored to pre-fasting levels after subsequent refeeding. In ovariectomized (OVX) goats, changes in plasma metabolites and insulin concentrations were similar to those in OVX+E2 goats, but the MUA volley intervals were not altered. The present results demonstrated that fasting suppressed GnRH pulse generator activity in an estrogen-dependent manner. Changes in plasma concentrations of energy substrates and insulin during fasting were associated with the GnRH pulse generator activity in the presence of estrogen, but not in the absence of the steroid in female goats. 相似文献
4.
Takashi YAMAMURA Yoshihiro WAKABAYASHI Satoshi OHKURA Victor M. NAVARRO Hiroaki OKAMURA 《The Journal of reproduction and development》2015,61(1):20-29
Recent evidence suggests that neurokinin B (NKB), a member of the neurokinin (tachykinin) peptide family, plays a pivotal role in gonadotropin-releasing hormone (GnRH) pulse generation. Three types of neurokinin receptors (NKRs), NK1R, NK2R and NK3R, are found in the brain. Although NKB preferentially binds to NK3R, other NKRs are possibly also involved in NKB action. The present study examined the effects of intravenous administration of the NKR subtype-selective agonists GR73632 (NK1R), GR64349 (NK2R), and senktide (NK3R) on GnRH pulse generator activity and luteinizing hormone (LH) secretion. Multiple-unit activity (MUA) was monitored in ovariectomized goats (n = 5) implanted with recording electrodes. Characteristic increases in MUA (MUA volleys) were considered GnRH pulse generator activity. Although three NKR agonists dose-dependently induced an MUA volley and an accompanying increase in LH secretion, the efficacy in inducing the volley markedly differed. As
little as 10 nmol of senktide induced an MUA volley in all goats, whereas a dose of 1000 nmol was only effective for the NK1R and NK2R agonists in two and four goats, respectively. When the treatment failed to evoke an MUA volley, no apparent change was observed in the MUA or LH secretion. Similar effects of the NK2R and NK3R agonists were observed in the presence of estradiol. The results demonstrated that NK3R plays a predominant role in GnRH pulse generation and suggested that the contributions of NK1R and NK2R to this mechanism may be few, if any, in goats. 相似文献
5.
Adachi S Yamada S Takatsu Y Matsui H Kinoshita M Takase K Sugiura H Ohtaki T Matsumoto H Uenoyama Y Tsukamura H Inoue K Maeda K 《The Journal of reproduction and development》2007,53(2):367-378
Metastin/kisspeptin, the KiSS-1 gene product, has been identified as an endogenous ligand of GPR54 that reportedly regulates GnRH/LH surges and estrous cyclicity in female rats. The aim of the present study was to determine if metastin/kisspeptin neurons are a target of estrogen positive feedback to induce GnRH/LH surges. We demonstrated that preoptic area (POA) infusion of the anti-rat metastin/kisspeptin monoclonal antibody blocked the estrogen-induced LH surge, indicating that endogenous metastin/kisspeptin released around the POA mediates the estrogen positive feedback effect on GnRH/LH release. Metastin/kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) may be responsible for mediating the feedback effect because the percentage of c-Fos-expressing KiSS-1 mRNA-positive cells to total KiSS-1 mRNA-positive cells was significantly higher in the afternoon than in the morning in the anteroventral periventricular nucleus (AVPV) of high estradiol (E(2))-treated females. The percentage of c-Fos-expressing metastin/kisspeptin neurons was not different between the afternoon and morning in the arcuate nucleus (ARC). Most of the KiSS-1 mRNA expressing cells contain ERalpha immunoreactivity in the AVPV and ARC. In addition, AVPV KiSS-1 mRNA expressions were highest in the proestrous afternoon and lowest in the diestrus 1 in females and were increased by estrogen treatment in ovariectomized animals. On the other hand, the ARC KiSS-1 mRNA expressions were highest at diestrus 2 and lowest at proestrous afternoon and were increased by ovariectomy and decreased by high estrogen treatment. Males lacking the surge mode of GnRH/LH release showed no obvious cluster of metastin/kisspeptin-immunoreactive neurons in the AVPV when compared with high E(2)-treated females, which showed a much greater density of these neurons. Taken together, the present study demonstrates that the AVPV metastin/kisspeptin neurons are a target of estrogen positive feedback to induce GnRH/LH surges in female rats. 相似文献
6.
Mst. Parvin MOSTARI Nahoko IEDA Chikaya DEURA Shiori MINABE Shunji YAMADA Yoshihisa UENOYAMA Kei-ichiro MAEDA Hiroko TSUKAMURA 《The Journal of reproduction and development》2013,59(3):266-272
Accumulating evidence suggests that the arcuate nucleus (ARC) kisspeptin/neurokinin B
(NKB)/dynorphin (KNDy) neurons play a role in estrogen negative feedback action on
pulsatile gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release. The
present study aimed to determine if dynorphin (Dyn) is involved in estrogen negative
feedback on pulsatile GnRH/LH release. The effect of the injection of nor-binaltorphimine
(nor-BNI), a kappa-opioid receptor (KOR) antagonist, into the third cerebroventricle (3V)
on LH pulses was determined in ovariectomized (OVX) adult female rats with/without
replacement of negative feedback levels of estradiol (low E2). The mean LH
concentrations and baseline levels of LH secretion in nor-BNI-injected, low
E2-treated rats were significantly higher compared with vehicle-treated
controls. On the other hand, the nor-BNI treatment failed to affect any LH pulse
parameters in OVX rats without low E2 treatment. These results suggest that Dyn
is involved in the estrogen negative feedback regulation of pulsatile GnRH/LH release. The
low E2 treatment had no significant effect on the numbers of ARC
Pdyn (Dyn gene)-,Kiss1- and
Tac2 (NKB gene)-expressing cells. The treatment also did not affect
mRNA levels of Pdyn and Oprk1 (KOR gene) in the
ARC-median eminence region, but significantly increased the ARC kisspeptin
immunoreactivity. These findings suggest that the negative feedback level of estrogen
suppresses kisspeptin release from the ARC KNDy neurons through an unknown mechanism
without affecting the Dyn and KOR expressions in the ARC. Taken together, the present
result suggests that Dyn-KOR signaling is a part of estrogen negative feedback action on
GnRH/LH pulses by reducing the kisspeptin release in female rats. 相似文献
7.
Tomomi TANAKA Satoshi OHKURA Yoshihiro WAKABAYASHI Takenobu KUROIWA Kiyosuke NAGAI Natsumi ENDO Akira TANAKA Hisanori MATSUI Masami KUSAKA Hiroaki OKAMURA 《The Journal of reproduction and development》2013,59(6):563-568
The aim of the present study was to determine if the estradiol-induced luteinizing
hormone (LH) surge is influenced by the constant exposure to TAK-683, an
investigational metastin/kisspeptin analog, that had been established to depress the
pulsatile gonadotropin-releasing hormone (GnRH) and LH secretion in goats.
Ovariectomized goats subcutaneously received TAK-683 (TAK-683 group, n=6) or vehicle
(control group, n=6) constantly via subcutaneous implantation of an osmotic pump.
Five days after the start of the treatment, estradiol was infused intravenously in
both groups to evaluate the effects on the LH surge. Blood samples were collected at
6-min intervals for 4 h prior to the initiation of either the TAK-683 treatment or
the estradiol infusion, to determine the profiles of pulsatile LH secretion. They
were also collected at 2-h intervals from –4 h to 32 h after the start of estradiol
infusion for analysis of LH surges. The frequency and mean concentrations of LH
pulses in the TAK-683 group were remarkably suppressed 5 days after the start of
TAK-683 treatment compared with those of the control group (P<0.05). On the other
hand, a clear LH surge was observed in all animals of both groups. There were no
significant differences in the LH concentrations for surge peak and the peak time of
the LH surge between the TAK-683 and control groups. These findings suggest that the
effects of continuous exposure to kisspeptin or its analog on the mechanism(s) that
regulates the pulsatile and surge mode secretion of GnRH/LH are different in
goats. 相似文献
8.
Kakuma Y Ichimaru T Yonezawa T Momozawa Y Hashizume C Iwata E Kikusui T Takeuchi Y Ohkura S Okamura H Mori Y 《The Journal of reproduction and development》2007,53(4):829-834
Previously we showed that the primer pheromone responsible for the "male effect" was produced in specific skin regions of castrated male goats by androgen treatments. In the present study, we examined whether androgen can also induce production of the male effect pheromone in female goats. Capsules containing dihydrotestosterone (DHT) or testosterone (T) were subcutaneously implanted into six ovariectomized (OVX) goats for 28 days. Small skin samples were collected from the head and rump regions, and the pheromone activity of their ether extracts was examined using a bioassay that monitors the electrophysiological manifestation of the hypothalamic gonadotropin-releasing hormone pulse generator as multiple-unit activity. Behaviors of OVX goats towards ovary-intact estrous goats were also examined before and at the end of DHT or T treatment. Before androgen treatment, neither the head nor rump skin samples in OVX goats showed pheromone activity. DHT treatment induced pheromone activity in the head skin sample of six OVX goats and in the rump skin sample of two OVX goats. Similar results were obtained by T treatment. In addition, OVX goats treated with T showed masculine-type sexual behaviors such as courtship and mounting behaviors towards the estrous goats. These results demonstrate that androgen is capable of inducing primer pheromone activity in the female and suggest that the synthesis pathway of the male effect pheromone exists in both sexes in the goat. 相似文献
9.
Iwata E Kikusui T Takeuchi Y Mori Y 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2003,65(9):1019-1021
A major constituent of the characteristic "goaty odor" 4-ethyl octanoic acid (4EOA) was previously shown to have no primer pheromone activity. This was also confirmed by our own bioassay system utilizing the recording technique of neural activity of the hypothalamic gonadotropin-releasing hormone pulse generator in goats. However, when the synthetic 4EOA solution was kept at room temperature for several months, primer pheromone activity appeared in the same solution. Headspace gas chromatography/mass spectrometry analysis revealed that there were several newly formed substances in addition to 4EOA samples with primer pheromone activity. These results suggest that 4EOA derived substance(s) but not 4EOA itself is(are) primer pheromone in goats. 相似文献
10.
Smith JT 《Domestic animal endocrinology》2012,43(2):75-84
Sheep are seasonal breeders, experiencing an annual period of reproductive quiescence in response to increased photoperiod during the late-winter into spring and renaissance during the late summer. The nonbreeding (anestrous) season is characterized by a reduction in the pulsatile secretion of GnRH from the brain, in part because of an increase in negative feedback activity of estrogen. Neuronal populations in the hypothalamus that produce kisspeptin and gonadotropin-inhibitory hormone (GnIH) appear to be important for the seasonal shift in reproductive activity, and the former are also mandatory for puberty onset. Kisspeptin cells in the arcuate nucleus (ARC) and preoptic area appear to regulate GnRH neurons and transmit sex-steroid feedback signals to these neurons. Moreover, kisspeptin expression in the ARC is markedly up-regulated at the onset of the breeding season, as too are the number of kisspeptin fibers in close apposition to GnRH neurons. The lower levels of kisspeptin seen during the nonbreeding season can be "corrected" by infusion of kisspeptin, which causes ovulation in seasonally acyclic females. The role of GnIH is less clear, but mounting evidence supports a role for this neuropeptide in the inhibitory regulation of both GnRH secretion and gonadotropin release from the pituitary gland. Contrary to kisspeptin, GnIH expression is markedly reduced at the onset of the breeding season. In addition, the number of GnIH fibers in close apposition to GnRH neurons also decreases during this time. Importantly, exogenous GnIH treatment can block both the pulsatile release of LH and the preovulatory LH surge during the breeding season. In summary, it is most likely the integrated function of both these neuropeptide systems that modulate the annual shift in photoperiod to a physiological change in fertility. 相似文献
11.
Iwata E Wakabayashi Y Matsuse S Kikusui T Takeuchi Y Mori Y 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(3):347-348
Castrated goats were treated with dihydrotestosterone (DHT) for four weeks. Skin samples were collected from the head and the rump regions before and after the DHT treatment. The primer pheromone activities of these samples were assessed neurophysiologically by recording electrophysiological manifestations of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity. Pheromone activity was detected in both the head and rump skin samples following the DHT treatment, although the development of sebaceous glands was limited to the head region. Taken together with our previous finding that testosterone treatment results in the appearance of primer pheromone activity in the skin sample of the head region but not of the rump region. these observations suggests that the regional difference of pheromone production would be ascribed to intrinsic expression levels of 5alpha-reductase, an enzyme converting testosterone to DHT. 相似文献
12.
Hayato SAITO Tatsuru SAWADA Tomoyoshi YAEGASHI Yuki GOTO Jin JIN Ken SAWAI Tsutomu HASHIZUME 《Animal Science Journal》2012,83(6):487-492
The aims of the present study were to clarify the effect of kisspeptin‐10 (Kp10) on the secretion of luteinizing hormone (LH) and testosterone (T) in pre‐pubertal and post‐pubertal male ruminants. Four male goats (Shiba goats) were given an intravenous (i.v.) injection of Kp10 (5 µg/kg body weight (b.w.)), gonadotoropin‐releasing hormone (GnRH, 1 µg/kg b.w.), or 2 mL of saline as a control at the ages of 3 (pre‐pubertal) and 6 (post‐pubertal) months. A single i.v. injection of Kp10 significantly stimulated the release of LH and T in both groups. The area under the response curve (AUC) of LH for a 60‐min period after the i.v. injection of Kp10 was significantly greater in the pre‐pubertal goats (P < 0.05). The AUC of T for a 120 min period post‐injection did not differ between the two age groups. A single i.v. injection of GnRH also significantly stimulated the release of LH and T in both groups (P < 0.05). The secretory pattern of LH and T in response to GnRH resembled that in response to Kp10. These results show that the LH‐releasing response to Kp10 is greater in pre‐pubertal than post‐pubertal male goats. They also show that Kp10, as well as GnRH, is able to stimulate the release of T in male goats. 相似文献
13.
Tatsuo NAKAHARA Yoshihisa UENOYAMA Akira IWASE Shinya OISHI Sho NAKAMURA Shiori MINABE Youki WATANABE Chikaya DEURA Taro NOGUCHI Nobutaka FUJII Fumitaka KIKKAWA Kei-ichiro MAEDA Hiroko TSUKAMURA 《The Journal of reproduction and development》2013,59(5):479-484
Puberty in mammals is timed by an increase in gonadotropin-releasing hormone (GnRH)
secretion. Previous studies have shown involvement of the two neuropeptides,
kisspeptin and neurokinin B (NKB), in controlling puberty onset. Little is known
about the role of the other key neuropeptide, dynorphin, in controlling puberty
onset, although these three neuropeptides colocalize in the arcuate kisspeptin
neurons. The arcuate kisspeptin neuron, which is also referred to as the KNDy neuron,
has recently been considered to play a role as an intrinsic source of the GnRH pulse
generator. The present study aimed to determine if attenuation of inhibitory
dynorphin-kappa-opioid receptor (KOR) signaling triggers the initiation of puberty in
normal developing female rats. The present study also determined if stimulatory
NKB-neurokinin 3 receptor (NK3R) signaling advances puberty onset. Female
Wistar-Imamichi rats were weaned and intraperitoneally implanted with osmotic
minipumps filled with nor-binaltorphimine (nor-BNI), a KOR antagonist, or senktide, a
NK3R agonist, at 20 days of age. Fourteen days of intraperitoneal infusion of nor-BNI
or senktide advanced puberty onset, manifested as vaginal opening and the first
vaginal estrus in female rats. Frequent blood sampling showed that nor-BNI
significantly increased luteinizing hormone (LH) pulse frequency at 29 days of age
compared with vehicle-treated controls. Senktide tended to increase this frequency,
but its effect was not statistically significant. The present results suggest that
the inhibitory input of dynorphin-KOR signaling plays a role in the prepubertal
restraint of GnRH/LH secretion in normal developing female rats and that attenuation
of dynorphin-KOR signaling and increase in NKB-NK3R signaling trigger the onset of
puberty in female rats. 相似文献
14.
Nahoko IEDA Yoshihisa UENOYAMA Yoko TAJIMA Tomoko NAKATA Masatoshi KANO Yousuke NANIWA Youki WATANABE Shiori MINABE Junko TOMIKAWA Naoko INOUE Fuko MATSUDA Satoshi OHKURA Kei-ichiro MAEDA Hiroko TSUKAMURA 《The Journal of reproduction and development》2014,60(4):312-316
Puberty is associated with an increase in gonadotropin secretion as a result of an increase in gonadotropin-releasing hormone
(GnRH) secretion. Kisspeptin is considered to play a key role in puberty onset in many mammalian species, including rodents,
ruminants and primates. The present study aimed to determine if changes in hypothalamic expression of the KISS1
gene, encoding kisspeptin, are associated with the onset of puberty in pigs. The animals (n=4 in each group) were perfused with 4%
paraformaldehyde at 0, 1, 2, 3 and 4 months old, as prepubertal stages, and at 5 months old, as the peripubertal stage, following
each blood sampling. KISS1 gene expressions in coronal sections of brains were visualized by in
situ hybridization. Plasma luteinizing hormone (LH) was measured by radioimmunoassay. KISS1 mRNA
signals were observed in the arcuate nucleus (ARC) at all ages examined without any significant difference in the number of
KISS1-expressing cells, indicating that the KISS1 gene is constantly expressed in the ARC
throughout pubertal development in pigs. The plasma LH concentration was the highest in 0-month-old piglets and significantly
decreased in the 1- and 2 month-old groups (P<0.05), suggesting a developing negative feedback mechanism affecting gonadotropin
release during the prepubertal period. Considering the potent stimulating effect of kisspeptin on gonadotropin release in
prepubertal pigs, kisspeptin secretion rather than kisspeptin synthesis may be responsible for the onset of puberty in pigs. 相似文献
15.
The hypothalamo‐pituitary‐gonadal (HPG) axis is the regulatory system for reproduction in mammals. Because secretion of gonadotropin‐releasing hormone (GnRH) into the portal vessels is the final step at which the brain controls gonadal activities, the GnRH neuronal system had been thought to be central to the HPG axis. A newly discovered neural peptide, kisspeptin, has opened a new era in reproductive neuroendocrinology. As shown in a variety of mammals, kisspeptin is a potent endogenous secretagogue of GnRH, and the kisspeptin neuronal system governs both the pulsatile GnRH secretion that drives folliculogenesis, spermatogenesis and steroidogenesis, and the GnRH surge that triggers ovulation in females. The kisspeptin neuronal system is therefore considered a master player in the central control of mammalian reproduction, and kisspeptin and related substances could therefore be valuable for the development of novel strategies for the management of fertility in farm animals. To this end, the present review aimed to summarize the current research on kisspeptin signaling with a focus on domestic animals such as sheep, goats, cattle, pigs and horses. 相似文献
16.
Yoshihisa UENOYAMA Akira TANAKA Kenji TAKASE Shunji YAMADA Vutha PHENG Naoko INOUE Kei-ichiro MAEDA Hiroko TSUKAMURA 《The Journal of reproduction and development》2015,61(4):351-359
The present study aimed to determine estrogen feedback action sites to mediate prepubertal restraint of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release in female rats. Wistar-Imamichi strain rats were ovariectomized (OVX) and received a local estradiol-17β (estradiol) or cholesterol microimplant in several brain areas, such as the medial preoptic area (mPOA), paraventricular nucleus, ventromedial nucleus and arcuate nucleus (ARC), at 20 or 35 days of age. Six days after receiving the estradiol microimplant, animals were bled to detect LH pulses at 26 or 41 days of age, representing the pre- or postpubertal period, respectively. Estradiol microimplants in the mPOA or ARC, but not in other brain regions, suppressed LH pulses in prepubertal OVX rats. Apparent LH pulses were found in the postpubertal period in all animals bearing estradiol or cholesterol implants. It is unlikely that pubertal changes in responsiveness to estrogen are due to a change in
estrogen receptor (ER) expression, because the number of ERα-immunoreactive cells and mRNA levels of Esr1, Esr2 and Gpr30 in the mPOA and ARC were comparable between the pre- and postpubertal periods. In addition, kisspeptin or GnRH injection overrode estradiol-dependent prepubertal LH suppression, suggesting that estrogen inhibits the kisspeptin-GnRH cascade during the prepubertal period. Thus, estrogen-responsive neurons located in the mPOA and ARC may play key roles in estrogen-dependent prepubertal restraint of GnRH/LH secretion in female rats. 相似文献
17.
Gazal S Kouakou B Amoah EA Barb CR Barrett JB Gelaye S 《Journal of animal science》2002,80(6):1623-1628
Photoperiod modulates reproduction in goats. We tested the hypothesis that the excitatory glutamatergic tone is reduced in the photoinhibited goat. The objectives of this study were to determine the effect of photoperiod and glutamatergic stimulation on LH, GH, and testosterone (T) secretion in goat bucks. Eight mature, intact bucks were used in two simultaneous 4 x 4 Latin square designs. Variables were two photoperiod regimens (short day; SD, 10 h light:14 h dark, n = 4; vs long day; LD, 16 h light:8 h dark, n = 4) and four doses of N-methyl-D-L-aspartate (NMA; 0, 1, 2 and 4 mg/kg BW, i.v.). Venous blood was obtained for 2 h before and after NMA injection, followed by GnRH injection and then a final 1 h of sampling. Injection of NMA increased (P < 0.002) LH secretion within 20 min. This increase was sustained for 120 min, but the response was most pronounced in LD goats. The increase in mean LH was associated with a concomitant dose-dependent increase in pulse frequency (P < 0.006). However, NMA treatment had no effect (P > 0.10) on LH pulse amplitude. The release of LH after injection of GnRH was not affected by photoperiod. Exposure of bucks to LD reduced T secretion relative to that of SD bucks (P < 0.01). However, GH secretion was enhanced in LD bucks (P< 0.001). The response of GH to NMA was dependent on photoperiod history. A highly significant immediate and sustained increase (P < 0.001) was observed in LD but not in SD bucks within 10 min. Overall, a dose-dependent increase (P < 0.01) in T secretion was stimulated by NMA in both LD and SD bucks. These results indicate that NMA receptors may be involved in the regulation of LH, GH, and testosterone secretion in the goat. Furthermore, length of day influences GH secretion in the goat and NMA receptor activation had divergent effects on the secretion of this hormone. 相似文献
18.
This study tested the hypothesis that the effects of the opiate antagonist naloxone on GnRH (and LH) secretion is affected by photoperiod length and testosterone (T) concentrations. The effect of infusing naloxone on GnRH and LH pulse patterns was determined in four groups of orchidectomized sheep: long day (LD) photoperiod treated with T, LD without T (LDC), short day photoperiod (SD) with T, SDC (n = 5-7/group). Hypophyseal-portal and jugular blood samples were collected at 10 min intervals for 4 h before and 4 h during naloxone infusion (1 mg/kg/h). Neither photoperiod nor T affected either mean GnRH or LH whereas naloxone (P < 0.01) increased both. LD photoperiod (P < 0.01), T (P < 0.01) and naloxone (P < 0.01) all increased LH pulse amplitude whereas only naloxone increased GnRH pulse amplitude (P < 0.01). There was an interaction (P < 0.01) between steroid and naloxone on LH, but not GnRH, pulse amplitude. Both LD photoperiod and T increased both LH and GnRH (P < 0.01) interpulse-interval (IPI). Naloxone decreased GnRH IPI (P < 0.01). The LH/GnRH pulse amplitude ratio was (P < 0.02) increased by T--likely a secondary response to the T-induced increase in IPI. These results are interpreted as showing that in the ram the endogenous opiate peptides regulate both GnRH pulse frequency and amplitude, but that their specific role is modulated by photoperiod and T. These results do not support the concept that the opiate peptides are the primary mediators of the negative feedback effects of T. 相似文献
19.
Yousuke NANIWA Keisuke NAKATSUKASA Shohei SETSUDA Shinya OISHI Nobutaka FUJII Fuko MATSUDA Yoshihisa UENOYAMA Hiroko TSUKAMURA Kei-ichiro MAEDA Satoshi OHKURA 《The Journal of reproduction and development》2013,59(6):588-594
Kisspeptin is a key molecule that stimulates gonadotropin secretion via release of
gonadotropin-releasing hormone (GnRH). In the present study, our aim was to
investigate whether kisspeptin has stimulatory effects on follicular development via
GnRH/gonadotropin secretion in cows. Japanese Black beef cows were intravenously
injected with full-length bovine kisspeptin [Kp-53 (0.2 or 2 nmol/kg)] or vehicle 5
days after they exhibited standing estrus (Day 0). In cows injected with Kp-53 at 2
nmol/kg, the follicular sizes of the first dominant follicles increased on Day 6 and
thereafter. Ovulation of the first dominant follicle occurred in 1 out of 4 cows
treated with Kp-53 at 2 nmol/kg. Injection of Kp-53 at 2 nmol/kg increased the
concentration of plasma luteinizing hormone (LH) but not follicle-stimulating
hormone, over a 4-h period following injection in all cows. The present study
suggests that administration of full-length kisspeptin causes LH secretion, which is
sustained for a few hours, and it is capable of stimulating follicular development
and/or ovulation. 相似文献
20.
Gonadotropin‐releasing hormone (GnRH) is a key molecule in the control of reproduction in mammals. It is generally thought that the secretion of GnRH into the pituitary portal vessels is governed by two distinct neural mechanisms: the pulsatile and surge mode centers. The former is called the GnRH pulse generator, and this neural substrate plays a role as the master regulator of the reproductive function. An electrophysiological technique for monitoring the neural activity of the GnRH pulse generator has been established in the Shiba goat. The central actions of several neuropeptides have been assessed using this system. Results suggest that several neuropeptides including neuropeptide Y, cholecystokinin‐octapeptide and melanocortins are involved in the regulation of the GnRH pulse generator activity in the goat. Each input of those neuropeptides likely represents a unique mechanism conveying specific information about changes in the internal and external environments such as olfactory signals, nutrition, stress, and steroidal milieu, to the GnRH pulse generator. Further elucidations of actions of neurotransmitters on the GnRH pulse generator may serve for better understanding of the neuroendocrine control of reproduction in the ruminant. 相似文献