bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tyrosine Hydroxylase Messenger Ribonucleic Acid Levels Increase in A1 but not Locus Ceruleus Noradrenergic Neurons in Proestrous Rats but not in Diestrous or Androgen‐Sterilized Animals
Authors: Liaw Jiin‐Jia , He Ju‐Ren , Barraclough Charles A. 
Published: September 2006

AbstractNorepinephrine (NE) turnovers (an index of secretion) increase in the hypothalamus of proestrous rats concomitant with luteinizing hormone surges, whereas, neither of these events are observed in diestrous nor in androgen‐sterilized rats. Increased hypothalamic NE release may occur as a consequence of the withdrawal of local inhibitory γ‐aminobutyric acid and opiate controls on specific presynaptic NE terminals and/or as a result of an increase in activity within noradrenergic neurons. Tyrosine hydroxylase (TH) is the rate‐limiting enzyme for the synthesis of NE and our earlier studies revealed that increases in TH mRNA in A1 and locus ceruleus (LC) neurons can serve as an index of increased activity within these cells. In the present study, we evaluated whether TH message levels change in A1 and LC neurons prior to and during the hours when luteinizing hormone surges and increased NE turnovers are observed. As controls, TH mRNA levels in A1 and LC neurons were evaluated at the same hours of day in diestrous day 2 and in androgen‐sterilized rats. In situ hybridization histochemistry and quantitative image analysis methods were used to measure changes in TH mRNA levels.Luteinizing hormone surges in proestrous rats began at 1500 h, peaked between 1600 and 1700 h and declined, thereafter, to 2000 h. In contrast, plasma luteinizing hormone remained basal throughout the day in diestrous and androgen‐sterilized rats. While A1 neuronal TH mRNA levels did not differ in the three groups of rats during the morning (0930 to 1030 h), these message levels were significantly elevated in proestrous rats during the afternoon (1645 to 1715 h) and remained high at 2000 to 2030 h. In contrast, no changes in TH mRNA levels were observed in A1 neurons throughout the afternoon in diestrous animals or androgen‐sterilized rats. TH mRNA levels in the LC did not differ in the three groups of rats and they remained unchanged throughout the afternoon hours we examined. From these observations we conclude that concomitant with afternoon proestrous luteinizing hormone surges and the accompanying increase in hypothalamic NE secretion, there is an increase in activity within A1 but not LC neurons. These data suggest that the proestrous increase in hypothalamic NE turnover we previously observed is not due solely to withdrawal of local inhibitory controls of presynaptic NE release but it also involves an increase in activity within A1 but not LC neurons.
Regulation of Corticotropin‐Releasing Hormone Receptors and Hypothalamic Pituitary Adrenal Axis Responsiveness During Cold Stress
Authors: Hauger Richard L. , Aguilera Greti 
Published: September 2006

AbstractThe relationship between pituitary corticotropin‐releasing hormone (CRH) receptor changes and corticotrope responsiveness was studied during chronic cold stress. Exposure of rats to 4°C caused a gradual increase in plasma adrenocorticotropic hormone (ACTH), reaching 3‐fold over the basal levels by 6 h (P< 0.005), followed by a reduction to levels only 1.3‐fold over basal by 60 h. Plasma corticosterone was significantly increased after 1 h (P<0.005) and remained elevated for up to the 60 h cold exposure (P < 0.005). No significant changes in plasma thyroid‐stimulating hormone, prolactin, growth hormone or vasopressin were observed at 60 h of cold exposure. CRH receptor concentration in the anterior pituitary was unchanged after 18 or 60 h cold stress, whereas in neurointermediate lobe membranes was markedly elevated. Autoradiographic analysis of pituitary CRH receptors confirmed that the increase in CRH binding was confined to the intermediate pituitary. CRH receptor levels in membranes from two brain areas, frontal cortex and amygdala, were unchanged following 60 h cold stress. The areas under the curve for the plasma ACTH and corticosterone levels following an injection of 10μg/kg ovine CRH in conscious rats, were of similar magnitude in control and 60 h cold exposed rats. Plasma ACTH responses to ether stress were significantly higher in rats exposed to cold for 60 h than in controls. In the intermediate pituitary, basal ß‐endorphin/lipotropin release from isolated intermediate pituitary cells was significantly lower in cold stressed rats, and despite the increase in CRH receptors CRH‐stimulated values were not higher than in controls. Following 60 h cold exposure, immunoreactive CRH content was decreased in neurointermediate pituitary extracts, while it was slightly increased in the median eminence. Exposure to ether for 5 min resulted in a significant decrease in immunoreactive CRH in the median eminence of cold stressed rats, but not in the controls. The data show a lack of correlation between changes in CRH receptor levels and responsiveness of the corticotrope in the anterior and intermediate pituitary lobes. This suggests that postreceptor events and interaction of CRH with other regulators of ACTH secretion are more likely to account for the changes in pituitary responsiveness during chronic stress.
Thyrotropin‐Releasing Hormone Mediates Growth Hormone Release Induced by Milk and Nursing in Neonatal Rats
Authors: Kacsóh Bálint , Tóth Béla E. , Grosvenor Clark E. 
Published: September 2006

AbstractPrevious evidence from this laboratory suggested that growth hormone (GH) release induced by milk in vitro and by nursing in vivo from neonatal rat pituitary glands is mediated by an alternative GH‐releasing factor(s) (GRF) distinct from GH‐releasing hormone (GHRH1–43). In the present experiments we tested whether thyrotropin‐releasing hormone (TRH) could fulfil the criteria of this alternative GRF in neonatal rats. The water‐soluble fraction of rat milk (infranatant, prepared by ultracentrifugation) and its methanol/acetic acid extract (milk‐borne peptides) stimulated GH release from perifused pituitary glands obtained from 2‐day‐old rats. Dialysis of the infranatant (mol wt cut‐off: 2,000) against 500 volumes of culture medium at 4°C eliminated its GH‐releasing activity in the perifusion system, while the infranatant retained its full GRF‐like activity when incubated at 4°C without dialysis. The milk‐borne GRF eluted as a single peak and coeluted with TRH in a combined gel permeation chromatography (Sephadex G‐10) and perifusion set‐up. Prolactin secretion was also stimulated simultaneously with the release of GH induced either by milk or by TRH. In a stepwise C18 reversed‐phase chromatography, milk‐borne GRF was highly hydrophilic and coeluted with synthetic TRH. The in vitro GH‐releasing bioactivities of synthetic TRH and a milk extract purified in C18 reversed‐phase chromatography were abolished by proline‐specific endopeptidase. Thus, TRH and milk‐borne GRF displayed similar molecular weights, hydropathic characteristics and proteolytic enzyme resistance. In vivo, nursing (which has been reported as a potent stimulus of GH secretion even in the absence of milk‐intake) increased serum GH levels in 2‐day‐old pups. A supramaximal dose of TRH (10 ng/g intraperitoneally) stimulated GH release in 2‐day‐old pups separated from their mothers for 6 h to a similar extent as nursing. Nursing‐induced levels of serum GH were not further elevated by TRH. This failure of TRH to further increase serum GH levels was not due to a maximal GH output by the neonatal pituitary gland, since the GH release induced by the serotonin precursor 5‐hydroxy‐L‐tryptophan was augmented either by TRH or by nursing. These data provide evidence that the milk‐borne GRF‐like activity in vitro is indistinguishable from TRH, and suggest that TRH (probably of hypothalamic origin) might be the mediator of the nursing‐induced release of GH in vivo as a physiological GRF in neonatal rats.
The Biosynthesis of Melanin‐Concentrating Hormone in Trout Kept Under Different Conditions of Background Colour and Stress, as Determined by an in vitro Method
Authors: Baker Bridget I. , Bird David J. 
Published: September 2006

AbstractThe aim of this study was to develop a method to monitor the synthetic activity of neurons which secrete the neurohypophysial melanin‐concentrating hormone (MCH), a hormone implicated in two separate physiological roles in fish—pigmentary regulation and the response to stress. Trout hypothalamic fragments, containing the MCH neuronal cell bodies, were incubated in vitro in a medium including [35S]methionine. Labelled MCH‐related products were separated by immunoprecipitation. Gel electrophoresis showed that radioactive methionine was incorporated into MCH precursors and into mature MCH, much as in vivo. Thus, de novo hormone synthesis continues in vitro. Trout reared at a fish‐farm and adapted to black or white tanks for 39 days displayed nearly a 2‐fold difference in their rate of methionine incorporation. Transferring fish from a black to a white background also doubled the rate of incorporation within 7 days and this rate increased only very slightly during the following 3 weeks. The rate of methionine incorporation by tissue from trout reared in black tanks was very depressed, and 4‐fold lower than that of fish reared in white tanks, suggesting that very long‐term adaptation to one or other background has increasingly marked effects on the activity and perhaps the number of synthetically active neurons.Stress also influenced the rate of methionine incorporation: a mild daily stress was stimulatory but more frequent stress had an inhibitory effect in many cases. The effects of daily dexamethasone administration were inconclusive.It is suggested that these differences in methionine incorporation reflect the relative rates of MCH synthesis in vivo, and that the method is useful to investigate conditions which modulate the biosynthesis of MCH in the trout.
Changes in Vasoactive Intestinal Peptide Binding Site Densities in the Female Rat Central Nervous System and Pituitary During Lactation
Authors: Viau Victor , Montagne Marie‐Noelle , Sarrieau Alain , Meaney Michael J. , Rostène William 
Published: September 2006

AbstractUsing quantitative autoradiography, vasoactive intestinal peptide (VIP) binding site densities were investigated in the female rat during lactation. Plasma prolactin levels were significantly (P<0.01) elevated on days 3 and 10 of lactation. In the brain, there was a significant (P<0.05) increase in VIP binding sites during lactation in the striatum, thalamus, anterior portion of the paraventricular nucleus of the hypothalamus, and several cortical areas compared to virgin female diestrous rats. VIP binding density in the anterior pituitary was significantly higher (P<0.01) when measured on day 3 of lactation, and decreased to diestrous levels by day 10. Pup removal resulted in a significant reversal of the lactation‐induced increase in VIP binding density in the thalamus, parietal and insular cortices, and the anterior portion of the paraventricular nucleus. Taken together, modifications in VIP binding site density in the pituitary and in several central areas are associated with changes in the level of prolactin secretion. Moreover, the pattern of VIP receptor induction during lactation suggests a role for VIP in the brain that extends beyond the regulation of prolactin secretion.
6‐Hydroxydopamine Lesions of the Locus Coeruleus Induce a Paradoxical Increase in Growth Hormone Secretion in Male Rats
Authors: Bluet‐Pajot M. T. , Mounier F. , Durand D. , Kordon C. , Llorens‐Cortes C. , Videau C. , Epelbaum J. 
Published: September 2006

AbstractWhile the pharmacology of noradrenaline effects on growth hormone (GH) secretion has been extensively studied, the precise localization of noradrenergic neurons involved remains unclear. In the present work, we investigated whether A6 noradrenergic neurons located in the locus coeruleus can play a role in the rhythmic pattern of GH secretion or in the sensitivity of the hormone response to different external challenges. Three weeks after bilateral 6‐hydroxydopamine injections (8μg/3μl) into the locus coeruleus, hypothalamic noradrenaline concentrations were reduced by 60%. Pulsatile GH secretory patterns were observed in unanaesthetized, freely moving control, sham‐operated or locus coeruleus‐lesioned male rats. The amplitude of the pulses and the area under the curves during the 6‐ or 12‐h sampling period were twice as high in locus coeruleus‐lesioned than in control and sham‐operated rats. In contrast, trough levels of GH and intervals between GH peaks were similar in all groups. Prolactin, adrenocorticotrophin, thyroid‐stimulating hormone and luteinizing hormone plasma levels were not affected by the lesion. GH responses to two centrally acting drugs i.e. clonidine (2.5, 5 and 10μg/100g body wt) and morphine (200μg/100g body wt) were also highly amplified in locus coeruleus‐lesioned rats. In contrast, GH responses to two peptides directly acting on somatotrophs i.e. GH‐releasing factor (0.05 and 1.25μg/100g body wt) and vasoactive intestinal peptide (1.5μg/100g body wt) were the same in sham‐operated and lesioned animals.These data suggest that noradrenergic inputs from the locus coeruleus exert a selective inhibitory influence on GH secretion through centrally mediated mechanisms.
The Distribution and Development of Delta Sleep‐Inducing Peptide‐Like Immunoreactivity in Postnatal and Prepubertal Guinea‐Pig Brain
Authors: Pu L‐P. , Dubois P. M. 
Published: September 2006

AbstractThe distribution and development of delta sleep‐inducing peptide (DSIP) in the guinea‐pig brain were studied in 2‐ to 60‐day‐old animals by using the indirect immunofluorescence method. DSIP‐immunoreactive perikarya were observed in the olfactory bulb and tubercle, diagonal band of Broca, septum, preoptic area, anterior and lateral hypothalamus, arcuate nucleus and hippocampus. In addition to the densest innervation of the median eminence, DSIP‐immunoreactive fibres were widely localized from forebrain to mesencephalon. The field of immunoreactive fibre endings appeared to be in close association with either the blood vessels of brain, ventricles, subarachnoid space or immunolabelled perikarya. Furthermore, throughout development the topographic distribution pattern of immunolabelled neuronal elements seemed to be similar. However, a generalized increase in number, immunofluorescence intensity and varicosities of DSIP fibres was displayed with the growth. The present results provide an anatomical basis for understanding multiple actions of DSIP in the central nervous system and future research for DSIP on development.
Effect of Enhancement of Cholinergic Tone on the Growth Hormone Response to Acute Hyperglycaemia or Thyrotropin‐Releasing Hormone in Dogs
Authors: Arce Victor M. , Cella Silvano G. , Locatelli Vittorio , Müller Eugenio E. 
Published: September 2006

AbstractThe effect of enhancement of cholinergic tone by pyridostigmine on the growth hormone (GH) response to thyrotropin‐releasing hormone (TRH) or glucose‐induced acute hyperglycaemia was tested in six adult unanaesthetized beagle dogs. Both TRH (5μg/ kg iv) and glucose (2 g/kg orally) did not significantly alter baseline GH levels but reduced the GH response to GH‐releasing hormone (GHRH) (2 μg/kg iv), although this effect was more clear‐cut with TRH than with glucose. Pretreatment with pyridostigmine (2 mg/kg orally) counteracted the inhibitory effect of hyperglycaemia on the GHRH‐induced GH release, but had no effect on the inhibition induced by TRH. In summary, these results indicate that: 1) acute hyperglycaemia and TRH play an inhibitory role on GHRH‐stimulated GH secretion in dogs; 2) the inhibitory effect of acute hyperglycaemia is mediated via hypothalamic cholinergic neurotransmission, whereas other neurotransmitter pathways would be. involved in the effect of TRH.
Prostaglandins of the E Series Stimulate Cyclic AMP Accumulation and N‐Acetylation of Serotonin in Chick Pineal Cells
Authors: Van Camp Gilles , Voisin Pierre , Sugden David , Dray Fernand , Coilin Jean‐Pierre 
Published: September 2006

AbstractWe investigated the effects of prostaglandins on cyclic AMP (cAMP) levels and on the activity of the rate‐limiting enzyme of melatonin biosynthesis, arylalkylamine‐N‐acetyltransferase (NAT). The study was performed on primary cultures of dispersed chick pineal cells. Prostaglandin E, (PGE,) increased cAMP levels 2‐fold and this stimulation went up to 4‐fold in the presence of a phosphodiesterase inhibitor. The PGE,‐ evoked increase in cAMP levels did not desensitize over 6 h. The potency order of a series of prostaglandins to increase cAMP levels (PGE1 PGE1>PGA2>PGD2≃PGF2α) agreed with the pharmacological profile of the adenylate cyclase‐coupled prostaglandin receptor. Inhibition of endogenous prostaglandin synthesis by two cyclooxygenase inhibitors (indomethacin and aspirin) caused a 30% decrease in cAMP levels. This effect was completely reversed by the addition of exogenous PGE1 or PGE2. Indomethacin and aspirin also caused a 50% decrease in NAT activity. Prostaglandins of the E series increased NAT activity up to 2‐fold above basal level and restored NAT activity after inhibition by indomethacin or aspirin.These results are the first illustration of a role for prostaglandins in chick pineal cells. The correlations observed between cAMP levels and NAT activity suggest that the regulation of NAT activity by prostaglandins of the E series might be mediated by changes in cAMP concentration.
Multiplex Solution Hybridization‐Ribonuclease Protection Assay for Quantitation of Different Ribonucleic Acid Transcripts from Snap‐Frozen Neuroendocrine Tissues of Individual Animals
Authors: Jakubowski Moshe , Roberts James L. 
Published: September 2006

AbstractWe have compiled a protocol for simultaneous quantitation of a variety of gene transcripts in multiple individual brain and pituitary gland dissections for studying pretranslational regulation of neuroendocrine systems in vivo, using experimental designs compatible with meaningful statistical power. To facilitate collection of many samples at a time, the tissue was snap‐frozen in chilled liquid Freon and stored at −80 °C until further processing. In this way, as many as five different brain and pituitary gland dissections per rat could be collected from eight rats in about an hour. The snap‐frozen tissue was suitable for isolation of separate cytoplasmic and nuclear RNA fractions using homogenization in the presence of detergents. To facilitate homogenization of many samples at a time, we devised a method in which the tissue was repeatedly expelled through a 22 gauge hypodermic needle attached to a 1‐ml plastic syringe used as a disposable, ready‐to‐use homogenizer. In order to promote dissolution of lipid membrane structures which are prevalent in the brain, the lysis buffer has been optimized to include the detergent sodium deoxycholate in addition to Nonidet P‐40. Specific RNA transcripts were analyzed using a quantitative solution hybridization‐ribonuclease protection assay coupled with polyacrylamide gel electrophoresis. The value of this highly sensitive assay has been expanded by including several molecular probes against a variety of neuroendocrine mRNA sequences simultaneously (e.g. progonadotropin‐releasing hormone, proopiomelanocortin, tyrosine hydroxylase, dopamine D2 receptor, prolactin), thus increasing the amount of information obtained from each sample in one assay. Furthermore, each sample was routinely co‐assayed for cyclophilin mRNA, an abundant, generally non‐regulated mRNA whose levels reflected the individual variability in sample processing, thus serving as an internal reference. Once stored in hybridization solution, as many as 100 samples could be analyzed simultaneously for several different RNA transcripts in one assay. This protocol provides a powerful tool for studying regulation of neuroendocrine systems at the molecular level in vivo, using sample sizes suitable for applying statistical analysis of meaningful statistical power.
Corticosterone Reduces Synaptic Inhibition in Rat Hippocampal and Neocortical Neurons in vitro
Authors: Zeise Marc L. , Teschemacher A. , Arriagada J. , Zieglgänsberger W. 
Published: September 2006

AbstractWe examined the effect of corticosterone (10‐7 to 10‐5 M) on membrane properties and postsynaptic potentials, by means of intracellular recordings from neocortical and hippocampal CA1 pyramidal neurons of the intact adult rat in vitro. Corticosterone reduced both the early and the late components of the orthodromically‐evoked inhibitory postsynaptic potential in both structures. The glucocorticoid receptor antagonist RU 38486 (10‐6 M) prevented this effect in the hippocampus. In hippocampal, but not in neocortical pyramidal neurons, corticosterone reduced a depolarizing membrane transient evoked by a depolarizing current step and increased the threshold for eliciting action potentials evoked by depolarizing current pulses. Corticosterone did not detectably alter the afterhyperpolarization following repetitive neuronal discharges evoked by current injection, in either the neocortex or in the hippocampus. Excitatory postsynaptic potentials, action potentials, membrane potential and membrane input resistance were also unchanged.The decrease in synaptic inhibition together with the reduction of electrical excitability in the hippocampus, would imply a modulation of response characteristics in pyramidal neurons such that repeated synaptic inputs become more efficient and low frequency input is blunted.