bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localization of [125I]IGF‐I Binding on the Ovine Pars Tuberalis
Authors: Williams Lynda M. , Kelly Denise , Hannah Lisa‐T. , Morgan Peter J. 
Published: September 2006

AbstractIn the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin‐stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF‐I receptor has been identified in the pars tuberalis using in situ hybridization. In order to define whether IGF‐I may influence the function of the ovine pars tuberalis the presence of receptors for IGF‐I has been investigated. Using in vitro autoradiography specific [125I]IGF‐I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [125I]IGF‐I with a mean dissociation constant (Kd) of 0.5 ± 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF‐I>IGF‐II> > >insulin, in displacing [125I]IGF‐I binding, indicative of a mixed population of IGF‐I and IGF‐II/rnannose‐6‐phosphate receptors and insulin‐like growth factor binding proteins (IGFBPs). Cross‐linking of [125I]IGF‐I to pars tuberalis membrane homogenates and analysis by SDS‐PAGE under reducing conditions confirmed the presence of both IGF‐I receptors and binding proteins. Autophosphorylation of a 97 kDa substrate, compatible with the β‐sub‐unit of the IGF‐I receptor, was increased in the presence of IGF‐I, indicating the existence of functional IGF‐I receptors on the ovine pars tuberalis. In contrast in the rat [125I]IGF‐I binding was restricted to the median eminence region of the brain and was not detectable over the pars tuberalis.
The Effects of Centrally Administered Porcine Relaxin on Drinking Behaviour in Male and Female Rats
Authors: Thornton Simon N. , Fitzsimons James T. 
Published: September 2006

AbstractOf the reproductive hormones it has been suggested that relaxin may play an important role in the increased sodium appetite of pregnancy. ICV injection of porcine relaxin caused water‐replete male and female Wistar rats with access to water and 0.9% or 2.7% NaCl to drink on average about 3 to 8 ml of water within 1 h of injection. By 24 h the cumulative intake of water was no different from the control intake. The amounts of water drunk were similar after doses of 50, 100, 250 and 500 ng of relaxin. A dose of 5 ng was ineffective. Male rats generally drank more water than female rats after ICV injection of angiotensin or relaxin. Male SH rats which drink more water than male WKY rats in response to ICV angiotensin also drank more after ICV relaxin. Intakes of 0.9% or 2.7% NaCl were unaffected for up to 24 h after injection of relaxin, whereas angiotensin‐injected rats showed a significant increase in 0.9% NaCl 1 h after injection though this difference was no longer evident in the 24 h cumulative intake. Relaxin did not cause any increase in NaCl intake in SH rats. Insulin, which is similar in structure and molecular weight to relaxin, was without effect on drinking when doses comparable to dipsogenically effective doses of relaxin were injected ICV. In male Wistar rats treated with DOCA for 5–15 days, relaxin retained its weak stimulatory action on water intake but did not affect NaCl intake despite the increased baseline NaCl intake during DOCA. These results indicate that relaxin is a dipsogen in the rat but that it seems to have little short‐term effect on sodium appetite.
The Ovine Pars Tuberalis does not Appear to be Targeted by Melatonin to Modulate Luteinizing Hormone Secretion, but may be Important for Prolactin Release
Authors: Malpaux Benoît , Skinner Donal C. , Maurice Françoise 
Published: September 2006

AbstractThe pineal hormone, melatonin, transduces photoperiodic information to the neuroendocrine axis of seasonally breeding mammals to regulate reproduction. It is not known where or how melatonin achieves this effect, but the recent identification of the pars tuberalis (PT) as the area with the highest density of melatonin binding sites suggests that this pituitary subdivision may be an important target for the actions of this indoleamine on luteinizing hormone (LH) and prolactin release. The present study was designed to test this hypothesis. Ovariectomized oestradiol‐implanted ewes were exposed to inhibitory long days for 85 days and then received melatonin micro‐implants (Day 0) in the mediobasal hypothalamus (MBH; n = 7) or PT (Melatonin‐PT; n = 5). The effect of these micro‐implants was compared to ewes receiving empty micro‐implants in the PT (Sham‐PT; n = 5). For LH, bi‐weekly jugular blood samples were collected and for prolactin, samples were collected every 20 min for 5 h, with the first hour discarded, on Days ‐4, 26 and 69. Melatonin implanted in the MBH stimulated LH secretion in 3 ewes by Day 46±0 after implantation, and one ewe by Day 67 after implantation. In contrast, no Melatonin‐PT or Sham‐PT ewes exhibited an increase in LH secretion by the end of the study (Day 70). A subsequent experiment, in which the Sham‐PT ewes were implanted with melatonin both subcutaneously and in the PT showed that the micro‐implants did not impair the ability of the ovine reproductive neuroendocrine axis to respond to melatonin. For prolactin, both the Melatonin‐PT ewes and MBH ewes (which had displayed an increase in LH secretion) exhibited a significant decrease in prolactin secretion by Day 26 and this decrease persisted until the end of the study. This result suggests that melatonin may have two sites of action on prolactin secretion; the MBH and PT, or, if melatonin diffused from the MBH to the PT, or vice versa, that only one of these sites is important. In contrast, these data suggest that the PT is not an important target for the action of melatonin on LH secretion.
Effects of Monoclonal Antibodies to Specific Epitopes of Rat Interleukin‐1 Beta (IL‐Iβ) on IL‐1β‐Induced ACTH, Corticosterone and IL‐6 Responses in Rats
Authors: Schotanus Karel , Meloen Rob H. , Puijk Wouter C. , Berkenbosch Frank , Binnekade Rob , Tilders Fred J. H. 
Published: September 2006

AbstractRecently, we developed a panel of monoclonal antibodies (MoAbs) to rat IL‐1β and found that MoAbs binding to the aminoacid sequences 66–85 and 123–143 of mature rIL‐1β inhibited the binding of rIL‐1β to murine EL4 cells. Here we study whether MoAbs to these and other domains of IL‐1 interfere with the biological effects of rIL‐1β in adult male rats in vivo. Administration of rIL‐1β (1 or 5 μg/kg i.v.) enhanced the plasma concentrations of ACTH, corticosterone (CORT) and of IL‐6 in a time‐ (0.5–4 h) and dose‐dependent manner. Because 2 h after 5μg/kg i.v., all three parameters were consistently elevated, this dose and time interval was used for further studies. Prior to injection, rIL‐1β was incubated alone or in the presence of a MoAb (10 mg/kg) for 30 min at 37°C or at 4°C. Plasma ACTH, CORT and IL‐6 responses to these mixtures are compared to those obtained after preincubation of rIL‐1β with a non‐IL‐1 binding MoAb (PEN7). SILK 3, a MoAb that binds to the 66–85 domain of rIL‐1β, reduced the ACTH and IL‐6 responses by 48 and 45% respectively. In contrast, a MoAb to the 123–143 domain (SILK 5) and SILK 16, which binds to the 106–124 domain did not affect any of the IL‐1 induced responses, whereas a MoAb directed to domain 78–97 of rIL‐1β (SILK 20) enhanced the ACTH and CORT responses by 51 and 41% respectively, but not the IL‐6 response.These observations lead us to conclude that the domain 66–85, harbours sequences that are important for receptor binding and for the biological actions of rIL‐1β in the rat and that this biologically active domain is located at the ‘closed side’ rather than at the ‘open side’ of the IL‐1β molecule where domains involved in receptor binding and biological activity are considered to be located.
Neuropeptide Y (NPY) May Integrate Responses of Hypothalamic Feeding Systems and the Hypothalamo‐Pituitary‐Adrenal Axis
Authors: Hanson E. Simon , Dallman Mary F. 
Published: September 2006

AbstractNeuropeptide Y (NPY) is a powerful stimulus to food intake in the rat. Exogenous NPY given into the third ventricle or into the paraventricular nucleus (PVN) of the hypothalamus stimulates both food consumption as well as the hypothalamus‐pituitary‐adrenal (HPA) axis. Presumably NPY activates the adrenocortical system through direct stimulation of CRF containing cells in the PVN. Food intake is also a major regulator of adrenocortical activation. Rhythms in HPA axis activity follow rhythms in food consumption, and rats that have been food deprived overnight have inhibited HPA axis responses to restraint stress and corticosteroid feedback the following morning. To investigate the interaction of NPY with both feeding and HPA axis activation three sets of experiments were performed: Animals fed ad lib were injected icv with NPY (2.5 μg) and allowed access to food or not post injection; animals were fasted overnight prior to NPY injection; finally, dose response experiments were performed to examine the relative sensitivities of feeding and HPA axis activation to exogenous NPY. Ad lib fed animals allowed access to food after NPY injection had slightly greater ACTH responses to NPY while glucocorticoid and insulin responses were not significantly different from ad lib fed animals not allowed access to food post injection. Animals allowed to eat post injection had significantly decreased food consumption the night following injection, however, total 24 h food consumption was not different between these animals and those given food 8 h post NPY injection. In overnight fasted animals NPY injections produced ACTH responses of equal magnitude to those in ad lib fed animals. Insulin responses to NPY were significantly elevated compared to CSF controls in overnight fasted animals. Dose response studies revealed that the adrenocortical system responds to icv NPY with at least as great sensitivity as feeding systems. NPY is discussed as a potential integrator of feeding and responsiveness in the HPA axis.
Evidence that Hypothalamic Neuropeptide Y Gene Expression Increases Before the Onset of the Preovulatory LH Surge*
Authors: Sahu Abhiram , Crowley William R. , Kalra Satya P. 
Published: September 2006

AbstractNeuropeptide Y (NPY), a 36 amino acid residue peptide, is involved in stimulation of LHRH and LH surges on proestrus and those induced by ovarian steroids in ovariectomized (ovx) rats. Recently, we observed that NPY gene expression in the medial basal hypothalamus (MBH) was increased before the onset of the LH surge in the ovarian steroid‐primed ovx rats. Since the ovarian steroidal milieu during the estrous cycle is markedly different from that prevailing after ovarian steroid injections in ovx rats, we evaluated in cycling rats the temporal relationship between MBH preproNPY mRNA levels and the preovulatory LH surge on the day of proestrus and compared that with diestrus II, concomitant with basal LH levels. PreproNPY mRNA levels in the MBH were measured by solution hybridization/RNAse protection assay, using a cRNA probe. On the day of diestrus II, preproNPY mRNA levels changed little between 1000 and 1800 h. Quite unexpectedly, preproNPY mRNA levels at 1000 h on proestrus were similar to diestrus II levels, despite additional exposure to ovarian steroids during this interval. However, from these low levels at 1000 h, the preproNPY mRNA profile displayed a biphasic rise. During the first phase, preproNPY mRNA rose significantly at 1200 h and remained elevated at 1300 and 1400 h concomitant with basal serum LH levels. Thereafter, a second rise in preproNPY mRNA began at 1500 h, peaked rapidly at 1600 h and declined significantly at 1800 h. This secondary activation of NPY gene expression occurred with a slow, two‐fold increase in serum LH at 1500 h, followed by a rapid ascension to peak levels at 1800 h and was associated with an increase at 1400 h of serum progesterone levels which reached their peak at 1800 h. These results demonstrate that a dynamic, biphasic augmentation in hypothalamic NPY gene expression occurs selectively on proestrus, and that the first incremental response is observed some time before the onset of preovulatory LH hypersecretion. Because preproNPY mRNA levels at 1000 h on proestrus were similar to the low levels seen on the preceding diestrous II phase, a neural timing mechanism, and not changes in ovarian hormone levels during this phase may be responsible for the increase in NPY gene expression after 1000 h of proestrus. Because of our previous observations that progesterone can rapidly augment preproNPY mRNA in the MBH and because a rise in serum progesterone occurs hours before the onset of the LH surge, we suggest that the secondary rise in preproNPY mRNA is facilitated by this antecedent increase in serum progesterone. Cumulatively, these results are in accord with the thesis that activation of hypothalamic NPY gene expression is one of the key early neural events initiated by the neural clock that times the preovulatory LHRH and LH surges.
Neuropeptide‐E‐1 Antagonizes the Action of Melanin‐Concentrating Hormone on Stress‐Induced Release of Adrenocorticotropin in the Rat
Authors: Bluet‐Pajot Marie‐Thérèse , Presse Françoise , Voko Zoltan , Hoeger Carl , Mounier Françoise , Epelbaum Jacques , Nahon Jean‐Louis 
Published: September 2006

AbstractThe physiological role of melanin‐concentrating hormone (MCH) in mammals is still very elusive, but this peptide might participate in the central control of the hypothalamopituitary adrenal (HPA) axis during adaptation to stress. Cloning and sequencing of the rat MCH (rMCH) cDNA revealed the existence of additional peptides encoded into the MCH precursor. Among these peptides, neuropeptide (N) glutamic acid (E) isoleucine (I) arnide (NEI) is co‐processed and secreted with MCH in rat hypothalamus. In the present work we examined: (1) The pattern of rMCH mRNA expression during the light and dark conditions in the rat hypothalamus and (2) The effect of intracerebroventricular (ICV) injections of rMCH and NEI in the control of basal or ether stress‐modified release of corticotropin (ACTH), prolactin (PRL) and growth hormone (GH) secretion in vivo in light‐on and light‐off conditions. Our data indicate that rMCH mRNA levels do not change during the light‐on period, but increase after the onset of darkness. Either alone or co‐administered, rMCH and NEI do not modify basal secretion of GH and PRL at any time tested nor do they alter ether stress‐induced changes in these two hormonal secretions. At the end of the light on period corresponding to the peak of the circadian rhythm in ACTH, administration of rMCH but not NEI leads to a decrease in ACTH levels while MCH is not effective during the light off period of the cycle (i.e. when basal ACTH levels are already low). Using a moderate ether induced stress, ACTH levels are only stimulated during the dark phase of the cycle. rMCH (63 or 210 nmoles) prevents the rise in ACTH release while NEI alone does not modify the stress response. Co‐administration of both peptides before stress results in an abolition of the rMCH induced inhibition of ACTH plasma levels. Taken together, these data indicate that rMCH may act as a central corticotropin inhibitory factor involved in the circadian rhythmicity of plasma ACTH levels and that NEI antagonizes its action.
Hypothalamic Mediation of Reduced GH Secretion in Diabetic Rats: Evidence for Reduced Cholinergic Inhibition of Somatostatin Release
Authors: Ismail Ikram , Lewis Mary , Peters John R. , Scanlon Maurice F. 
Published: September 2006

AbstractThe Goto‐Kakizaki (GK) rat is a new model of diabetes mellitus and in this study we have characterized the diabetic and growth hormone (GH) secretory status of male GK rats at 6 and 16 weeks of age. We have also investigated the role of endogenous somatostatin (SS) and cholinergic manipulation on the GH responses to GH‐releasing hormone (GHRH). GK rats were non‐obese with significant fasting hyperglycaemia, hyperinsulinaemia and absent insulin responses to IV glucose. The GH response to GHRH was reduced at 16 weeks compared with normal, age‐matched Wistar rats but no differences were observed at 6 weeks. Pretreatment of older rats (16 weeks) with anti‐somatostatin antibodies (SS‐Ab) significantly increased GH responses to GHRH in both normal and GK groups. Cholinergic augmentation with pyridostigmine (PD) reversed the blunted GH responses to GHRH in older GK rats but had no effect in the normal or young (6 weeks) GK rats. These results indicate that SS release mediates the blunted GH response to GHRH in GK rats and that reduced hypothalamic cholinergic signalling to the somatostatinergic neurone may mediate the increase in SS release. This view is supported by the results from in vitro studies in which cholinergic muscarinic blockade with pirenzepine (PIR) caused dose‐related stimulation of SS release from normal rat hypothalami but was without effect on GK rat hypothalami. The cause of this alteration in hypothalamic function is, at present, unknown.
Circadian Rhythms: Peering into the Molecular Clockwork
Authors: Hastings Michael 
Published: September 2006

AbstractRecent developments in our understanding of the molecular basis of circadian rhythms look set to provide one of the most elegant demonstrations of the relationship between the activity of individual genes and the execution of biologically relevant and complex patterns of behaviour. At the same time the lid is being opened on one of the classic ‘black boxes’ of biology, the circadian clock.
Effect of Lactation on Hypothalamic Preproenkephalin Gene Expression
Authors: Ottinger M. A. , Rosewell K. L. , Weiland N. G. , Margaretten K. T. , Wise P. M. 
Published: September 2006

AbstractEnkephalin appears to modulate several aspects of reproductive function in female rats. The purpose of this study was to determine if lactation influences preproenkephalin gene expression in one or more hypothalamic nuclei known to be involved in maternal or reproductive behavior and prolactin secretion. Lactating rats were killed on day 3 (LAC 3) or day 10 (LAC 10) of lactation. Controls consisted of regular 4‐day cycling rats that were killed on diestrous day 1, with 9 to 12 females per group. We used in situ hybridization histochemistry to assess preproenkephalin gene expression in individual cells in the medial preoptic nucleus, anterior, medial and posterior arcuate nucleus, magnocellular and parvocellular aspects of paraventricular nucleus, and ventromedial nucleus. Preproenkephalin mRNA in the anterior arcuate nucleus increased to reach significance (P < 0.05) at day 10 of lactation. Levels in the medial arcuate nucleus increased significantly (P < 0.001) by day 3 of lactation (LAC 3) and remained elevated on day 10 (LAC 10). No significant differences between lactating and control rats were detected in preproenkephalin mRNA levels in the posterior arcuate nucleus, medial preoptic nucleus or in the ventromedial nucleus. Substantial levels of preproenkephalin mRNA were found in the paraventricular nucleus, particularly in a limited region of the magnocellular portion. However, these levels did not change with lactation. These data provide evidence for differential regulation of the preproenkephalin gene during lactation. This change may contribute to. lactational hyperprolactinemia and suppressed GnRH secretion, leading to reproductive acyclicity.
Melatonin Receptors Couple Through a Cholera Toxin‐Sensitive Mechanism to Inhibit Cyclic AMP in the Ovine Pituitary
Authors: Morgan Peter J. , Barrett Perry , Hazlerigg David , Milligan Graeme , Lawson Wilfred , MacLean Alison , Davidson Gary 
Published: September 2006

AbstractThe nature of melatonin receptor‐G‐protein coupling in ovine pars tuberalis (PT) cells of the pituitary was addressed using cholera (CTX) and pertussis (PTX) toxins. ADP‐ribosylation of ovine PT membrane proteins using 32P‐NAD in the presence of CTX radiolabelled several substrates including 44, 51, and 60 kD proteins. Each were clearly distinct from the 40 kD substrate radiolabelled in the presence of PTX. Acute incubation of PT membranes with either toxin reduced the number of high affinity binding sites for 125I‐MEL, although the magnitude of the inhibition was much greater for CTX (56%) than for PTX (20%). A CTX‐sensitive component also mediates the inhibition of forskolin‐stimulated cyclic AMP accumulation as pre‐treatment of PT cells with CTX (5μg/ml) for 16 h blocked this response.Gsα is a major substrate for ADP‐ribosylation by CTX, and 16 h pre‐treatment of PT cells with CTX (5μg/ml) caused a down‐regulation of Gsα. Northern analysis showed only one major transcript of Gsα of about 2 kb, which would encompass all of the known splice variants of the Gs gene. Screening of a cDNA library from ovine PT for Gs‐related genes and sequencing of clones, combined with RT‐PCR of PT mRNA, revealed no novel products. On this basis it is concluded that the CTX substrate is unlikely to be a novel splice variant or related gene product of the Gs class of G‐protein. These results indicate that a distinct CTX‐sensitive mechanism mediates the inhibition of cyclic AMP by the melatonin receptor, which involves either a novel a‐sub‐unit of a heterotrimeric G‐protein or a protein which associates and functionally modulates the activity of the melatonin receptor/G‐protein complex.
Increased Fos Expression in Preoptic Calcitonin Gene‐Related Peptide (CGRP) Neurones following Mating but not the Luteinizing Hormone Surge in Female Rats
Authors: Herbison Allan E. , King Ian S. , Tan Keith K. C. , Dye Sandra 
Published: September 2006

AbstractThe functional relationship between sexually dimorphic neural populations and sex differences in reproductive functioning is unclear. The present study has investigated the function of the sexually dimorphic, estrogen‐receptive, calcitonin gene‐related peptide (CGRP) neurones in the female preoptic area by examining patterns of Fos immunoreactivity within these cells in relation to the luteinizing hormone surge and lordosis behaviour. In the first experiment, ovariectomized rats were treated with estradiol alone or estradiol plus progesterone to induce the luteinizing hormone surge. The percentage of CGRP neurones with Fos‐positive nuclei was not different in estradiol alone (18 ± 4%) and estradiol/progesterone‐treated (24 ± 3%) rats although the number of Fos‐immunoreactive cells in the medial preoptic nucleus was increased 2‐fold (P<0.01) in estrogen/progesterone‐treated rats and 40 ± 5% of luteinizing hormone‐releasing hormone neurones were found to express Fos in this group. In the second experiment, ovariectomized rats were treated with estradiol and progesterone and either, mated with a single male or placed in an empty cage, for 30 min. The number of Fos‐immunoreactive cells in the medial preoptic nucleus was increased 4‐fold in mated rats (P<0.01) and the percentage of CGRP neurones with Fos‐positive nuclei increased from 24 ± 3% to 38 ± 2% (P<0.01) in mated animals. No differences were detected in the number of luteinizing hormone‐releasing hormone neurones with Fos‐positive nuclei in mated and non‐mated animals.These results suggest that a sub‐population of CGRP neurones in the medial preoptic nucleus may express Fos on a constitutive basis in steroid‐treated animals and that, while not altered in relation to the luteinizing hormone surge, Fos expression by these cells is increased following mating. Although the precise role of these CGRP neurones has yet to be ascertained, the present experiments provide direct evidence of a functional relationship between a specific sexually dimorphic neural population and a component of sexually differentiated reproductive functioning.