bluuebunny/crossref_metadata_2025_split huggingface dataset:
Naloxone does not Affect the Luteinizing Hormone‐Releasing Hormone‐Induced Inhibition of Luteinizing Hormone Secretion in Sheep
Authors: Naylor A. M. , Porter D. W. F. , Lincoln D. W. 
Published: September 2006

AbstractInjection of luteinizing hormone‐releasing hormone (21 pmol) into the third cerebral ventricle of long‐term ovariectomized ewes caused a marked inhibition of luteinizing hormone secretion. Mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly when compared with the control responses to saline (50 μl). A notable characteristic of the response was the delayed and sustained nature of the luteinizing hormone‐releasing hormone‐induced inhibition. In the presence of the opioid antagonist naloxone (4 ± 25 mg iv), the central administration of luteinizing hormone‐releasing hormone still produced a marked inhibition of luteinizing hormone secretion. Again, mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly. When naloxone was injected iv, there was a significant rise in mean luteinizing hormone levels as a consequence of an increase in pulse frequency (in four out of five ewes) and a significant increase in luteinizing hormone pulse amplitude.In conclusion, these data suggest that central opioid pathways sensitive to blockade by naloxone are not involved in the luteinizing hormone‐releasing hormone‐induced inhibition of luteinizing hormone release. Furthermore, in the long‐term ovariectomized ewe, endogenous opioid peptides exert a tonic inhibitory influence on luteinizing hormone‐releasing hormone/luteinizing hormone secretion.
Pulsatile Luteinizing Hormone Secretion in the Rat: Methodological Aspects of Cannulation Route and Sampling Intensity
Authors: Dong Qihan , Handelsman David J. 
Published: September 2006

AbstractWe have investigated some requirements for valid estimates of pulsatile luteinizing hormone (LH) secretion in the castrate male rat. The choice of cannulation route and the minimal sampling intensity required to produce stable, unbiased estimates of parameters of pulsatile LH secretion were examined. Castrate mature male Wistar rats with unilateral ligation of a carotid artery (an inevitable consequence of carotid artery cannulation) had a 47% reduction in mean LH levels (1.8 vs 3.4 ng/ml, P< 0.011) attributable to a 40% reduction in LH pulse frequency (6.2 vs 10.4 peaks/6 h P<0.006) without change in LH pulse amplitude or other parameters of pulsatile LH secretion. In another study, a range of sampling intensities were examined to derive estimates of pulsatile LH secretion. Parameter estimates derived from the most intensive regime (q10 min sampling for 6 h) were compared with estimates of pulsatile LH secretion parameters determined from less intensive derivative sub‐series composed of either fixed sampling frequency, but variable total study duration (i.e. the first 1, 2, 3, 4 and 5 h at 10 min intervals), or a fixed total study duration but variable sampling frequency. LH pulse frequency (or its inverse, interpulse interval) was quite sensitive to sampling intensity whereas pulse amplitude, maximum, minimum and overall mean LH were estimated accurately at even relatively low sampling intensity (q20 min for one h duration). Lower frequency sampling (q20 min) gave marked underestimates of LH pulse frequency (4.9 vs 10.4 peaks/6 h, P<0.05) compared with q10min sampling over a 6h study. These results indicated that for stable and unbiased estimates of pulsatile LH secretion in the castrate mature male rat it is necessary (but may not be sufficient) to (1) avoid carotid artery cannulation and (2) undertake blood sampling at intervals of not more than 10 min for at least 3 h.
Septal and Hippocampal Release of Oxytocin, but not Vasopressin, in the Conscious Lactating Rat During Suckling
Authors: Neumann Inga , Landgraf Rainer 
Published: September 2006

AbstractThe central release of both oxytocin and vasopressin within the septum and dorsal hippocampus in response to suckling was studied in conscious, freely‐behaving lactating rats. Three consecutive 30‐min push‐pull perfusions were carried out before, during and after suckling (suckled group) or without suckling (control group). As compared to control levels, suckling resulted in a significantly increased oxytocin release within both limbic brain areas (septum: to 140%, dorsal hippocampus: to 1,600%). After removal of the suckling pups, the oxytocin concentration in the final perfusates remained at the stimulation level (septum) or tended to return to control values (dorsal hippocampus). In contrast to oxytocin, the vasopressin perfusate levels did not differ significantly between unsuckled and suckled rats.
Molecular Cloning and Characterization of c‐erb‐A mRNA Species in Mouse Neuroblastoma Cells
Authors: Moeller Marie , Rapoport Basil , Gavin Laurence A. 
Published: September 2006

AbstractThe mouse neuroblastoma cell line is an excellent model in which to study thyroid hormone action and metabolism, particularly in neural tissue. We therefore undertook the molecular cloning and characterization in these cells of putative thyroid hormone receptors related to c‐erb‐A. Since rat brain tissue contains multiple cell types, and because of possible subtle differences between species (mouse and rat), we therefore screened a new cDNA library constructed from mouse neuroblastoma cell mRNA with synthetic oligonucleotide probes based on the published nucleotide sequence of the c‐erb‐A gene in whole rat brain. Despite the fact that this rat brain cDNA sequence is now recognized to represent a c‐erb‐A α 1 form, the cDNA clones that we isolated were all members of the newly‐recognized c‐erb‐A α 2 form. This identification was made on the basis of nucleotide sequence divergence downstream of the nucleotide corresponding to amino‐acid residue 370 in the predicted coding region. The two longest mouse neuroblastoma cDNA clones, clone 29 (1796 bp) and clone 32 (1410 bp), were 93% to 94% homologous with the c‐erb‐A α 2 and c‐erb‐A α 1 forms in their DNA binding and thyroid hormone binding domains (up to amino‐acid residue 370 in the latter). Both clones 29 and 32 were incomplete in that they terminated at their 3’ends at an internal Eco R1 site. Fortunately this 120 bp (40 derived amino‐acid) truncation was downstream of the reported thyroid hormone binding domain. The 5’untranslated end of clone 29 (446 bp) was of interest because a region of its nucleotide sequence (279 bp) revealed a high degree of homology (87%) with rat brain c‐erb‐A α 1. This highly conserved region in clone 29 appeared to be important in the regulation of translation because only clone 32, in which this region was truncated, efficiently translated protein in a cell‐free system. The protein product of clone 32 did not bind thyroid hormone. Northern blot analysis of mouse neuroblastoma mRNA with site‐specific synthetic oligonucleotides revealed that the c‐erb‐A α 2 species was dominant (major band of 2.4 kb), with a lesser amount of the c‐erb‐A α1 species (major band of 1.8 kb).In conclusion: 1) We report the molecular cloning of c‐erb‐A variants in a specific neural tissue cell type, namely mouse neuroblastoma cells; 2) The cells contained predominantly the c‐erb‐A α 2 subtype; 3) This c‐erb‐A α 2 form was unique up to bp 167 at its 5’untranslated end, and was then followed, up to the ATG initiation codon, by a highly conserved region common to all c‐erb‐A a species; 4) The 5’untranslated region appeared to play a role in the translational efficiency of this mRNA; 5) The protein product of the c‐erb‐A α 2 mRNA in these cells did not appear to bind thyroid hormone. In view of this finding, the physiological role of the c‐erb‐A α 2 protein remained speculative and may involve a represser function at the thyroid hormone responsive element.
Expression and Post‐Translational Processing of Preprodynorphin in the Rat Anterior Pituitary Cell Line, GH4C1
Authors: Devi Lakshmi , Gupta Prem 
Published: September 2006

AbstractA recombinant plasmid containing the rat preprodynorphin cDNA was introduced into the rat anterior pituitary cell line, GH4C1. These cells normally express growth hormone and prolactin but not prodynorphin. Stable transformants were isolated and analyzed for the expression and processing of prodynorphin. Chromatographic analyses demonstrated that the prodynorphin was incompletely processed in GH4C1 cells. Analyses of the peptides by specific radioimmunoassays to chemically synthesized peptides showed that the cells have the ability to process both at dibasic and monobasic cleavage sites. The release of prodynorphin‐derived peptides paralleled that of prolactin upon stimulation with thyrotropin‐releasing hormone, forskolin or carbachol suggesting that the prodynorphin‐derived peptides and prolactin are sequestered in similar physiologically responsive compartments. These data suggest that the GH4C1 cells incompletely process prodynorphin. The processing in GH4C1 cells occurs both at monobasic and dibasic cleavage sites.
Analysis of the Inhibitory Effect of Oestradiol on Functional GABA/5‐HT Relationship in the Rat Suprachiasmatic Area
Authors: Francois‐Bellan Anne‐Marie , Hery Micheline , Faudon Maxime , Hery Francis 
Published: September 2006

AbstractThe purpose of this study was to test the capacity of oestradiol to modulate the stimulating effect of a‐aminobutyric acid (GABA) on serotonin (5‐HT) metabolism, previously described in the Suprachiasmatic area of the male rat. After an in vivo stimulation of GABA transmission by systemic administration of a GABA‐transaminase inhibitor (amino‐oxyacetic acid) or a GABAB agonist (RS‐baclofen), the 5‐HT metabolism was studied in the Suprachiasmatic area of ovariectomized, and ovariectomized oestradiol‐treated rats.Amino‐oxyacetic acid or RS‐baclofen treatment increased the endogenous content of 5‐HT in the Suprachiasmatic area of males and ovariectomized rats. These two treatments were without effect in ovariectomized oestradiol‐treated rats. GABA transmission stimulation induced by amino‐oxyacetic acid treatment failed to affect the release and synthesis of 5‐HT in ovariectomized oestradiol‐treated rats while it increased these two parameters of 5‐HT metabolism in the Suprachiasmatic area of male and ovariectomized rats. To investigate the main target of oestradiol effect, comparative studies of the serotoninergic and GABAergic metabolism in the Suprachiasmatic area were performed in the three experimental groups. Under our experimental conditions the endogenous 5‐HT metabolism was similar between ovariectomized and ovariectomized oestradiol‐treated rats. Nevertheless, 5‐HT metabolism was higher in the two female groups than in the male group. Neither GABA metabolism nor GABAergic response to GABA‐related drug treatment differed between ovariectomized, and ovariectomized oestradiol‐treated rats. However, the turnover of GABA was higher when compared to the two female groups. It is concluded that the lack of 5‐HT responsiveness to GABA transmission stimulation in ovariectomized oestradiol‐treated rats was not related to an effect of oestradiol on 5‐HT metabolism or to an effect of the steroid on GABA turnover. Furthermore, our results suggest a sex difference in the activity of serotoninergic and GABAergic systems in the Suprachiasmatic area.
Time‐Dependent Effect of Melatonin on Glutamic Acid Decarboxylase Activity and 36CI− Influx in Rat Hypothalamus
Authors: Rosenstein Ruth E. , Estévez Alvaro G. , Cardinali Daniel P. 
Published: September 2006

AbstractThe objective of the first series of experiments was to assess whether melatonin treatment modifies the activity of the y‐aminobutyric acid synthesizing enzyme, glutamic acid decarboxylase, in the preoptic‐medial basal hypotnalamic area, cerebral cortex and cerebellar cortex of rats receiving 25 to 300 μg of melatonin in the early morning and late evening in the diurnal cycle. A significant increase of apparent Vmax and Km of the enzyme was found in the hypothalamus of rats killed at the 12th h of the light phase (i.e. the time when lights were turned off) and receiving 25 to 300 μg/kg of melatonin 3 h earlier. In the early morning, only a 300 μg/kg dose of melatonin (injected in the 1st h of the light phase) was effective to increase Vmax and Km of hypothalamic glutamic acid decarboxylase 3 h later. In cerebral and cerebellar cortices, increases in Vmax and Km of enzyme activity were apparent only in the evening and with the highest melatonin dose employed (300 μg/kg). In a second series of experiments the activity of melatonin to modify in vitro36CI influx by 900 x g pellets of rat preoptic‐medial basal hypothalamic area was studied at the 4th and 12th h of the light phase of daily photoperiod. Melatonin increased 36CI− influx at a minimum concentration of 100 nM (in the morning) or 10 nM (in the evening). The effect of melatonin on 36CI− influx was prevented by co‐incubation with 100 μM picrotoxin. Addition of 10 to 100 μM of y‐aminobutyric acid to the resuspended 900 x g pellets brought about a dose‐dependent increase of 36CI − influx. Preincubation with melatonin at threshold doses of 1 μM (in the morning) or 0.1 μM (in the evening) significantly augmented y‐aminobutyric acid effect on 36CI− uptake. These results indicate that melatonin facilitates pre‐ and postsynaptic activities of y‐aminobutyric acid neurons, particularly in the hypothalamus, through an effect that displays a diurnal sensitivity compatible with the documented activity of the hormone on a number of physiological functions.
Cortisol Response to a Combined Dexamethasone‐Human Corticotrophin‐Releasing Hormone Challenge in Patients with Depression
Authors: von Bardeleben Ulrich , Holsboer Florian 
Published: September 2006

AbstractWe administered a combined dexamethasone‐human corticotrophin‐releasing hormone (hCRH) challenge test to 14 in‐patients with a major depressive episode and to 14 age‐matched controls. After pretreatment with 1.5 mg dexamethasone at 2300 h the day before, 100 μg hCRH was administered iv at 1500 h. Blood samples for cortisol determinations by radioimmunoassay were drawn at 1400 h, 1430 h and 1500 h before infusion of hCRH and thereafter every 15 min until 1700 h. Cortisol secretion after injection of hCRH assessed as area under the curve was significantly increased in patients with depression when compared to controls (14.5 ± 4.3 ng × min × 1,000/ml vs 3.1 ± 2.4 ng × min × 1,000/ml). Multiple regression analysis among patients revealed a significant impact of age and severity of depression upon hCRH‐induced cortisol secretion, whereas in normal controls no significant influence of age on cortisol secretion after hCRH emerged.Our data show that in depressed patients hCRH evokes an escape from dexamethasone‐induced suppression of the pituitary‐adrenocortical activity, whereas it fails to do so among controls. This finding suggests that at the pituitary level the action of hCRH is enhanced by a factor that is less sensitive to dexamethasone suppression in depression. We postulate that this factor is vasopressin.
Chloroquine Decreases Adrenocorticotrophin‐Secretory Response to Corticotrophin‐Releasing Factor but not to Vasopressin in Rat Pituitary Cells: Further Evidence for Differentially Responsive Subpopulations
Authors: Schwartz Jeffrey , Pham Thao , Funder John W. 
Published: September 2006

AbstractThe relationships between adrenocorticotrophin (ACTH) content, basal ACTH secretion and the ACTH‐secretory response to corticotrophin‐releasing factor (CRF) or vasopressin in cultured rat anterior pituitary cells were examined in studies using chloroquine, an agent that diverts nascent ACTH from a storage pathway to direct release from cells. Chloroquine (200 mUM from t=minus 2 h) significantly elevated the basal ACTH secretory rate (by 0.7 ± 0.2 ng over 30 min incubation, 1.1 ± 0.3 ng over 60 min and 2.3 ± 0.6 ng over 120 min). It also decreased the ACTH‐secretory response to CRF (2.9±0.5 vs 4.6 ± 0.5 ng/well over 30 min; 4.3 ± 0.7 vs 8.0 ± 1.4 ng/well over 60 min; 12.4±1.7 vs 20.2 ± 3.6 ng/well over 120 min). In marked contrast, the net responses to vasopressin were unaltered (0.9 ± 0.3 vs 0.9±0.2 ng/well over 30 min; 2.2 ± 0.9 vs 2.1 ±0.3 ng/well over 60 min; 3.8±0.9 vs 3.3 ± 1.0 ng/well over 120 min). These data further support the association of the ACTH‐secretory response to CRF with stored cellular ACTH, and the minimal dependence of the response to vasopressin on stored ACTH.
Characterization of Glucocorticoid Type II Receptors in Neuronal and Glial Cultures from Rat Brain
Authors: Chou Yun‐Chia , Luttge William G. , Sumners Colin 
Published: September 2006

AbstractThe purpose of this study was to characterize and compare the properties of glucocorticoid Type II receptors in neuronal and astrocyte glial cultures prepared from rat brain. Type II receptors in cytosol prepared from cultured cells were labeled with [3 H]dexamethasone (DEX) at 0°C. The binding was saturable and specific, with a complete displacement by unlabeled DEX or RU 28362 (a pure glucocorticoid). Scatchard analysis of [3 H]DEX binding suggested a single class of receptors with a slightly lower dissociation constant (Kd) in neuronal (1.13 nM) versus astrocyte glial (1.64 nM) cytosol. The number of binding sites (Bmax) in astrocyte glial cultures was four times that in neuronal cultures on a per milligram protein basis (120.3 versus 29.3 fmol/mg protein). The presence of Type II receptors in cultured neurons and astrocyte glia was further confirmed by immunofluorescent staining with a monoclonal antibody against this receptor (BuGR‐2). The steroid specificity of Type II receptors was studied by examining the displacement of [3 H]DEX binding to cytosol with unlabeled steroids. For both types of cultures, the potency series for competition was RU 28362> DEX> corticosterone> > aldosterone. Switching cultured cells from serum‐supplemented to serum‐free medium reduced [3 H]DEX binding at low concentrations (0.5 to 5 nM) of the ligand in both types of culture, thus resulting in a decrease in the apparent affinity. This treatment did not, however, have any significant effect on the total number of binding sites. In summary, these results demonstrate that both neuronal and astrocyte glial cells in culture contain specific glucocorticoid Type II receptors, which resemble those seen in the brain and peripheral tissues.
Lack of Correlation Between Immunoreactive Corticotropin‐Releasing Factor Concentration Profiles in Hypophysial‐Portal and Peripheral Plasma
Authors: Plotsky Paul M. , Otto Stefan , Toyama Terry , Sutton Steve 
Published: September 2006

AbstractCorticotropin‐releasing factor (CRF‐41) is the primary mediator of adrenocorticotropin secretion from the adenohypophysis. This 41‐amino‐acid peptide is synthesized in perikarya of the paraventricular nuclei, transported to nerve terminals in the external zone of the median eminence and released into the hypophysial‐portal circulation. It is also synthesized in multiple extrahypothalamic and peripheral sites. In addition, immunoreactive (ir) CRF‐41 is present in the systemic circulation, raising the possibility that systemic measurements might provide a useful index of hypothalamic irCRF‐41 secretion. This hypothesis was tested in several rat models. Neither bilateral destruction of hypothalamic irCRF‐41 producing perikarya, nor infundibular stalk transection altered peripheral plasma irCRF‐41 concentration. Furthermore, central administration of norepinephrine, an agent previously shown to evoke irCRF‐41 secretion into the portal circulation, was without effect on peripheral irCRF‐41 concentration. Finally, while increased irCRF‐41 levels in both the hypophysial‐portal and the peripheral circulation were associated with nitroprusside‐induced hypotension, bilateral paraventricular nuclei lesions blocked irCRF‐41 secretion into the hypophysial‐portal circulation without blunting the rise observed in the peripheral circulation. The source of peripheral irCRF‐41 remains undetermined; however, the adrenals may be excluded as bilateral adrenalectomy failed to alter circulating irCRF‐41 levels. Therefore, our observations do not support the concept that peripheral irCRF‐41 levels provide a useful index of hypothalamic secretion of this peptide into the hypophysial‐portal circulation under the conditions tested.
lntra‐ and Inter‐Individual Variability in Growth Hormone Responses to Growth Hormone‐Releasing Hormone*
Authors: Fornito Maria C. , Calogero Aldo E. , Mongioi Alessandro , Coniglione Francesca , Vicari Enzo , Moncada Maria Luisa , D'Agata Rosario , Merriam George R. 
Published: September 2006

AbstractNormal subjects show a wide range of growth hormone (GH) responses to growth hormone‐releasing hormone (GHRH) stimulation, but it is uncertain whether this variability reflects differences among individuals or whether it would also be observed on repeated tests of the same subject. To clarify this, we tested nine normal men repeatedly with iv bolus doses of 1 μg/kg GHRH(1–44)NH2. Most subjects showed wide variations in their GH responses on repeated testing, and the intra‐individual variability was nearly as great as the inter‐individual variability in responses, accounting for about two‐thirds of the overall variance. A minority of subjects had lower and less variable responses. Ultradian fluctuations in hypothalamic somatostatin secretion may account for this marked intra‐individual variability.