bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Pituitary Adenylate Cyclase‐Activating Polypeptide (PACAP) and Vasoactive Intestinal Polypeptide (VIP) on Prolactin, Luteinizing Hormone and Growth Hormone Secretion in the Ewe
Authors: Sawangjaroen K. , Curlewis J. D. 
Published: September 2006

AbstractThis study was undertaken to investigate the roles of PACAP and VIP in the control of pituitary hormone secretion in the ewe. The first experiment was designed to identify any direct effects at the level of the pituitary and was conducted during the luteal phase of a prostaglandin‐synchronized oestrous cycle. PACAP (0.008, 0.04, 0.2 and 1.0 nmol/min) or VIP (0.06, 0.2, 0.6 and 1.8 nmol/min) was infused into the carotid artery over a 10 min period. Blood samples were taken before and after the infusions so that plasma PRL, LH and GH concentrations could be measured. Blood pressure was also monitored to determine if the doses used were biologically active. In no case was an effect on hormone secretion observed. In contrast, the highest dose of each peptide induced an increase in heart rate to almost three‐fold the resting value. Although both peptides are active in vivo, this result suggests that neither peptide has a direct effect on hormone release from the pituitary of prostaglandin‐synchronized ewes. In a second experiment, we investigated whether the peptides had central effects on hormone secretion. Intracerebroventricular (ICV) injection of PACAP or VIP at the dose 10nmol was tested in ovariectomized ewes. After injection, PACAP suppressed PRL and GH secretion so that plasma hormone concentrations from 1–3 h after injection were significantly different from the control (P<0.05 for PRL, P<0.01 for GH). In addition, PACAP significantly reduced mean LH concentration (P<0.05) and LH pulse frequency (P<0.01). A similar suppressive effect on LH secretion was also observed after ICV injection of VIP (P<0.05 for both parameters), although PRL and GH release were not affected. These results suggest a possible role for PACAP in the neuroendocrine control of PRL, GH and LH secretion in sheep. In addition, VIP may be involved in the control of LH secretion. In contrast, there is no evidence to suggest that either peptide is a hypophysiotropic factor for PRL, LH or GH in prostaglandin‐synchronized ewes.
In Situ Hybridization Detection of TSHβ Subunit Gene Expression in the Serum‐Free Primary Culture of the Adult Rat Pituitary
Authors: Koibuchi Noriyuki , Ohtake Hideki , Sakai Mikako , Kato Yukio , Yamaoka Sadao 
Published: September 2006

AbstractThis study was designed to construct the primary culture system to detect the change in TSHβ subunit (TSHβ) gene expression in individual cells. Adult, male Wistar rats were sacrificed by transcardial perfusion of 0.25% trypsin solution under pentobarbital anesthesia (50 mg/kg body weight). Their anterior pituitaries were removed, dispersed and cultured for 1, 2, 3 or 6 days with or without 1 nM triiodothyronine (T3) under the serum‐free condition. In some cultures, TRH was added to a final concentration of 1 μM on 6, 12 or 24 h before fixation. Then the culture media were removed to measure TSH concentration. Cells were fixed with paraformaldehyde and hybridized with 35S‐labeled RNA probe complementary to TSHβ mRNA. Emulsion autoradiography was subsequently performed. T3 treatment markedly suppressed relative cellular levels of TSH4bT mRNA on 2, 3 and 6 days after the onset of culture (day 2, 3 and 6) and suppressed TSH secretion on day 3 and 6. TRH treatment increased TSHβ mRNA on 12 and 24 h after the treatment on day 2 and 3 but did not increase TSHβ mRNA on day 6. TSH concentration in the culture medium was increased by TRH treatment on 6, 12 and 24 h after the treatment on day 2, on 12 h and 24 h on day 3, and 24 h on day 6. On day 2 and 3, although T3 treatment suppressed basal level of TSHβ mRNA, TRH‐induced increase in TSHβ mRNA was not suppressed by T3 treatment. These results show that the thyroid hormone and TRH regulate TSHβ gene expression independently. Our culture system may provide a useful model to examine the action of individual substances on a specific subpopulation of the anterior pituitary cells.
Distribution of Estrogen Receptor‐lmmunoreactive Cells in the Brain of the Rainbow Trout (Oncorhynchus mykiss)
Authors: Anglade Isabelle , Pakdel Farzad , Bailhache Thierry , Petit Fabrice , Salbert Gilles , Jego Patrick , Valotaire Yves , Kah Olivier 
Published: September 2006

AbstractUsing antibodies against the hormone binding domain of the trout estrogen receptor (ER), the distribution of ER‐immunoreactive (ER‐IR) cells was studied in the brain of maturing diploid and triploid female rainbow trout using a streptavidin‐biotin‐peroxidase method followed by a nickel‐intensified diaminobenzidine reaction. This technique resulted in an excellent signal/background ratio allowing unambiguous identification of positive cells. In all animals, ER‐IR cells were consistently located in three brain regions, the ventral telencephalon, the anterior ventral preoptic region, and the mediobasal hypothalamus. About 250 ER‐IR cells were observed in the ventral and dorsal parts of the ventral telencephalon. In the anterior nucleus preopticus periventricularis, about 2400 ER‐IR cells were observed surrounding the preoptic recess. In the posterior hypothalamus, approximately 2700 ER‐IR cells were located in the anterior, posterior and inferior divisions of the nucleus lateralis tuberis and in the nucleus saccus vasculosus. In these regions, cell nuclei exhibiting different densities of staining were observed and absolutely no labeling of cytoplasmic processes was detected. These results are in partial agreement with those obtained either after injection of tritiated‐estradiol in other teleots species or in situ hybridization of ER mRNAs in trout. In particular, no immunoreactivity was observed in the thalamic region nor in the nucleus posterioris periventricularis. These data indicate that target cells for estradiol are essentially located in brain regions involved in the neuroendocrine control of pituitary functions and having direct connections with the hypophysis.
Diurnal Rhythm in Proopiomelanocortin mRNA in the Arcuate Nucleus of the Male Rat
Authors: Steiner Robert A. , Kabigting Emilia , Lent Karin , Clifton Donald K. 
Published: September 2006

AbstractWe tested the hypotheses that in the male rat, expression of proopiomelanocortin (POMC) mRNA in cells of the arcuate nucleus displays a diurnal fluctuation and that expression of this rhythm is dependent upon the secretory products of the testis. To accomplish this, we sacrificed groups of testes‐intact and castrated adult male rats throughout the day and compared levels of POMC mRNA in individual cells of the arcuate nucleus across time and between groups. Adult male rats were housed on a 12–12 L D cycle with lights on a 0600 h and were divided into groups that were either castrated or left intact. Four days later, pairs from these groups were sacrificed at 0600 h, 1200 h, 1800 h, 2400 h, and again at 0600 h (n = 4 per group at each time point). We used in situ hybridization and a computerized image analysis system to measure cellular levels of POMC mRNA, as reflected by the number of autoradiographic grains over individual cells in the rostral quarter of the arcuate nucleus (counting ∼ 30 cells per animal). Using cosinor analysis, we observed that in intact male rats, POMC mRNA levels varied significantly over the 24 h day with a nadir value at 1800 h. In contrast, there was no significant diurnal variation in POMC mRNA levels in castrated animals. POMC mRNA levels were significantly greater in the intact compared with castrated animals at every time point (P<0.01), except at 1800 h, when the groups did not differ significantly from one another. We conclude that adult male rats display at diurnal rhythm in cellular POMC mRNA levels in the arcuate nucleus, and we infer that testosterone or some other secretory product of the testis is a prerequisite for expression of this rhythm.
Differential Dependence of ACTH Secretion Induced by Various Cytokines on the Integrity of the Paraventricular Nucleus
Authors: Kovács Krisztina J. , Elenkovt Ilia J. 
Published: September 2006

AbstractEffect of different cytokines, human recombinant interleukin‐la and fl (IL‐1 a, 1L‐1 j), interleukin‐6 and tumor necrosis factor‐a (TNF) on adrenocorticotropin (ACTH) secretion was compared in sham‐operated rats and those with lesions of the hypothalamic paraventricular nucleus. IL‐1 a was less active than IL‐1 b in stimulating ACTH in sham‐operated rats. Intravenous injection of IL‐1 fl in sham‐operated animals resulted in a rapid elevation of ACTH secretion. Five days after surgical lesion of the paraventricular nucleus, the main hypothalamic source of hypophysiotropic corticotropin‐releasing factor‐41, the response to IL‐1 /I was attenuated but not abolished. This suggests involvement of extra‐paraventricular releasing factors in mediation of ACTH‐releasing activity of IL‐1 P, altered responsiveness of pituitary to CRFs, and/or direct action of IL‐1 j on the corticotrope cells. TNF resulted in a biphasic stimulation of ACTH concentration, with peaks at 15 min and 90 min. In paraventricular‐lesioned, TNF injected rats both of these ACTH peaks disappeared, suggesting that CRFs from the paraventricular origin mediates ACTH‐inducing activity of TNF. IL‐6 elevated ACTH secretion much later than the other intravenously injected cytokines, the peak was at 1 h in sham‐lesioned rats. Paraventricular lesion completely prevented the increase of ACTH plasma levels after IL‐6 injection. These data suggest that: (1) Effect of TNF and IL‐6 on hypothalamo‐pituitary‐adrenal axis is mediated through the hypothalamic paraventricular nucleus and (2) IL‐lB is able to release ACTH even in the absence of hypothalamic drive.
Negative Feedback Regulation following Administration of Chronic Exogenous Corticosterone
Authors: Young Elizabeth A. , Kwak Seung P. , Kottak Juliet 
Published: September 2006

AbstractAdministration of exogenous glucocorticoids is known to suppress the HPA axis and has been reported to occupy brain glucocorticoid receptors, eventually leading to down‐regulation. To determine the effects of chronic corticosterone administration on HPA axis function, corticosterone was administered as both 25% and 50% corticosteronekholesterol pellets. Rats were sacrificed 6 days after corticosterone pellet implantation. The 25% corticosterone pellets produced a small increase in morning corticosterone concentrations but no change in evening ACTH or corticosterone secretion. The 50% corticosterone pellets produced constant corticosterone concentrations of 5–6 pg/dl, with no circadian variation in corticosterone, indicating inhibition of evening ACTH and corticosterone secretion. The 25% corticosterone pellets produced no significant decrease in thymus weight or in adrenal weight; 50% corticosterone pellets produced significant decreases in thymus weight and adrenal weight. Neither 25% nor 50% corticosterone pellets produced significant decreases in GR in hippocampus and cortex. The 50% corticosterone pellets treatment resulted in a decrease in anterior pituitary POMC mRNA levels, a decrease in baseline and oCRH stimulated ACTH release from the anterior pituitary, and a near complete inhibition of the AM and PM response to restraint stress. These results suggest that: 1) the HPA axis was able to adjust to the small increase in glucocorticoids produced by the 25% cort pellets with minimal disturbances in function and 2) 50% corticosterone pellets exert a significant inhibitory effect on stress and diurnal ACTH secretion which appears to be exerted at the pituitary as well as possible inhibitory effects on brain.
Nucleotides as Extracellular Signalling Molecules
Authors: Chen Zhen‐Ping , Levy Andrew , Lightman Stafford L. 
Published: September 2006

AbstractThere is now wide acceptance that ATP and other nucleotides are ubiquitous extracellular chemical messengers. ATP and diadenosine polyphosphates can be released from synaptosomes. They act on a large and diverse family of P2 purinoceptors, four of which have been cloned. This receptor family can be divided into two distinct classes: ligand‐gated ion channels for P2X receptors and G protein‐coupled receptors for P2Y, P2U, P2T and P2D receptors. The P2Y, P2U and P2D receptors have a fairly wide tissue distribution, while the P2X receptor is mainly found in neurons and muscles and the P2T and P2Z receptors confined to platelets and immune cells, respectively. lnositol phosphate and calcium signalling appear to be the predominant mechanisms for transducing the G‐protein linked P2 receptor signals. Multiple P2 receptors are expressed by neurons and glia in the CNS and also in neuroendocrine cells. ATP and other nucleotides may therefore have important roles not only as a neurotransmitter but also as a neuroendocrine regulatory messenger.
Corticosteroid Feedback Resistance in Rats Genetically Selected for Increased Dopamine Responsiveness
Authors: Rots Nynke Y. , Cools Alexander R. , de Jong Jeannette , De Kloet E. Ronald 
Published: September 2006

AbstractPharmacogerietically selected Wistar rat lines were used to investigate the implication of either high or low responsiveness of the dopamine system for the activity of the hypothalamus‐pituitary‐adrenal (HPA) axis. As selection criterion the gnawing response induced by the dopamine agonist apomorphine was used. This criterion allows to distinguish apomorphine susceptible (apo‐sus) rats which show a vigorous gnawing response from apomorphine unsusceptible (apo‐unsus) rats. The present study, using male animals of the 9‐1 2th generation of the two rat lines, revealed the following characteristics of the stress response system: (i) in apo‐sus rats under basal conditions corticotrophin‐releasing hormone (CRH) mRNA level in the paraventricular nucleus (PVN) and plasma adrenocorticotropin (ACTH) concentration were significantly higher; total corticosterone (B) plasma level was similar but free B level was lower; (ii) exposure to a novel environment resulted in a higher and prolonged plasma ACTH and total B response in the apo‐sus rats. Moreover, the elevated free B level was also prolonged; (iii) apo‐sus rats had increased CRH‐induced pituitary ACTH release and B secretion was also increased, but not as prolonged as during novelty. (iv) In dexamethasone‐pretreated rats an intravenous ACTH1–24 injection resulted in a similar plasma B response in rats of both lines; (v) In vitro, ACTH1–24 produced a significantly higher B secretion by adrenocortical cells of apo‐sus rats reflecting the higher in vivo ACTH priming of the adrenal glands in these animals. (vi) apo‐sus rats had higher body and thymic weight.In conclusion, rats genetically selected for increased susceptibility of the dopamine system to apomorphine display subtle adrenocortical hyporesponsiveness and show resistance to corticosteroid hormone feedback action.
Nicotine Acts Directly on Pituitary GH3 Cells to Inhibit Prolactin Promoter Activity
Authors: Coleman Daniel T. , Bancroft Carter 
Published: September 2006

AbstractWe have employed the GH3 rat pituitary cell line to investigate whether nicotine can regulate prolactin (PRL) gene expression. Nicotine strongly inhibited (45%) transient expression of a construct containing the first 187 base‐pairs of the rat PRL promoter cloned upstream of the chloramphenicol acetyl transferase (CAT) gene. This implies that nicotine acts directly on the GH3 cells to inhibit transcription directed by the PRL promoter. Expression of a control reporter construct containing the CAT gene under the control of the RSV promoter was not affected by exposure of the cells to nicotine, demonstrating that the effect of nicotine is promoter‐specific. The inhibition by nicotine of PRL promoter activity was not blocked by hexamethonium, suggesting that this effect of nicotine may be mediated by a novel type of nicotine receptor previously described in frog pituitary cells. Nicotine was also observed to yield a concentration‐dependent inhibition of the stimulation by thyrotrophin‐releasing hormone (TRH) of PRL promoter activity, implying that nicotine can also interfere with hormonal regulation of the PRL gene. These results suggest that the reduced serum PRL levels that result from smoking may originate in part from decreased transcription of the PRL gene resulting from a direct effect of nicotine on pituitary PRL‐secreting cells.
Biosynthesis and Processing of the N‐Terminal Part of Proopiomelanocortin in Xenopus laevis: Characterization of γ‐MSH Peptides
Authors: van Strien Frank J. C. , Devreese Bart , Van Beeurnen Jozef , Roubos Eric W. , Jenks Bruce G. 
Published: September 2006

AbstractThe aim of this study was to determine the terminal products of processing of the N‐terminal part of proopiomelanocortin (POMC) in pituitary melanotrope cells of Xenopus laevis. Biosynthetic in vitro labelling studies showed that POMC is rapidly processed to form N‐terminal peptides with an estimated molecular mass of 18 kDa, 9 kDa and 4 kDa. All peptides were released into the medium, indicating that they are processing end products. An antiserum was raised against the synthetic N‐terminal eight amino acids of the putative Xenopusγ‐MSH which is present in the N‐terminal part of POMC. With immunocytochemistry we demonstrated that γ‐MSH‐immunoreactive material in the pituitary gland is restricted to the pars intermedia. A radioimmunoassay in combination with reversed‐phase HPLC revealed the presence of at least two γ‐MSH‐like peptides. Complete purification followed by electrospray ionization mass spectrometry and amino acid sequence determination showed that these peptides are γ1‐MSH and glycosylated γ3‐MSH. The amounts of these γ‐MSH peptides were low compared to the other POMC‐derived peptides, α‐MSH and β‐endorphin. Only 10% of POMC is processed into γ‐MSH peptides and the 4 kDa peptide, leaving the 18 kDa and 9 kDa peptides as the major end products.
Intraventricular Prolactin Inhibits Hypothalamic Vasoactive‐Intestinal Polypeptide‐Expression in Doves
Authors: Saldanha Colin J. , Silver Rae 
Published: September 2006

AbstractWhile the role of prolactin in promoting the development of the crop‐sac in members of the pigeon family (Columbiformes) is well established, its action in the central nervous system is less well understood. In the present study, prolactin was administered intracerebroventricularily (i.c.v.) in ring doves, and central expression of vasoactive‐intestinal polypeptide (VIP) and gonadotropin‐releasing hormone (GnRH), and the display of sexual behavior was investigated. Ovine‐prolactin (1 μg in 2 μl o‐prl) was injected daily for six days through chronically implanted cannula either prior to a 2‐h period of courtship, or late in incubation. Control subjects were given vehicle injections and were otherwise identical to experimental animals. Prolactin administered prior to courtship resulted in a reduction of sexual behavior, and in a decrease in testicular weight but had no detectable effect on the number of neurons expressing VIP or GnRH. In contrast, i.c.v. prolactin during incubation resulted in a reduced number of infundibular VIP‐positive neurons and decreased crop weight. We conclude that during incubation prolactin regulates its own synthesis and/or release by modulating VIP expression in infundibular neurons.
The Effect of Pentobarbital on the Electrical Activity of LHRH Pulse Generator in the Ovariectomized Rat with or without Estrogen Priming
Authors: Kimura Fukuko , Sano Akane 
Published: September 2006

AbstractEffects of pentobarbital sodium (PB) on the electrical activity of LHRH pulse generator were investigated in the ovariectomized (OVX) rat fitted with chronically implanted electrode arrays in the arcuate‐median eminence region of the hypothalamus. PB was injected intraperitoneally (i.p.) at a dose of 32 mg/kg bw, which has blocked the surge of LH secretion when injected at 13.45 on the day of proestrus, presumably by blocking the activity of the LHRH surge generator. After i.p. injection of PB, the first characteristic increase (volley) in the hypothalamic multiunit activity (MUA), each of which was associated with the initiation of an LH pulse, appeared at the mean interval of 42 min, which was significantly greater than the value, 30 min, in the rat given i.p. injection of saline. The second and third MUA volleys appeared, however, at similar intervals to those in rats given saline. There were no significant changes in the amplitude of LH pulses which followed. In the OVX rat implanted with a silastic tube packed with estradiol‐benzoate (E2) for 1 day, MUA volleys were unclear, mingled with high background activities, but clear volleys appeared after PB injection. The mean interval of LH pulses in the rat given i.p. injection of saline was 51 min, by 24 min longer than the value in the E2‐unimplanted OVX rat. But, after PB injection, the 1st LH pulse appeared at the interval of 37 min, which was by 25 min smaller than that after saline and the overall mean of 3 intervals was 34 min, showing a significant shortage. No PB effect was seen in the LH pulse amplitude in the E2‐implanted OVX rat. The presults show that the LHRH pulse generator is much more resistant to PB than the surge generator in the OVX rat either with or without estrogen priming, and in the rat with estrogen priming, the pulse generator is rather activated by PB.
Evidence for a Regulatory Role of Melatonin on Serotonin Release and Uptake in the Pineal Gland
Authors: Míguez Jesús M. , Simonneaux Valérie , Pévet Paul 
Published: September 2006

AbstractMelatonin has been proposed to exert some regulatory actions within the pineal gland itself. The present study examined the effect of melatonin on the release of serotonin (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) from rat pineal glands by using an in vitro perifusion system. Melatonin induced a concentration‐dependent stimulatory effect on 5‐HT secretion from 10−6 M to 10−3 M. Maximal effects were obtained with melatonin 10−3M and concentrations lower than 10−6 M were without effect. The secretion of 5‐HIAA was inhibited by melatonin 10−3 and 10−4M, but it was increased when pineals were incubated with 10−5 and 10−6 M of melatonin. The indoleamine secretion was also studied on peripherally denervated rat pineal glands. Basal output of 5‐HT from these glands was increased when compared with those from control rats. In contrast, the secretion of 5‐HIAA was strongly reduced after removal of the sympathetic input to the pineal gland. Melatonin 10−3 M failed to stimulate 5‐HT release from denervated pineal glands, although it inhibited 5‐HIAA secretion. In contrast, melatonin 10−5 M enhanced 5‐HT release without altering 5‐HIAA output. Fluoxetine, a 5‐HT uptake inhibitor, produced similar effects than mM concentrations of melatonin on the indoleamine secretion from control pineal glands, but it had no effect on glands taken from peripherally denervated rats. These data suggest that mM concentrations of the pineal hormone are able to stimulate 5‐HT release from the pinealocyte, while mM concentrations of melatonin increase extracellular 5‐HT by inhibiting its reuptake in the adrenergic nerve endings. These findings are discussed in relation to the possible role of melatonin regulating the intra‐ and extracellular availability of 5‐HT in the pineal gland and its significance as an autocrine factor.