bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of a Single Intravenous Injection of N‐Methyl‐D,L‐Aspartic Acid on Secretion of Luteinizing Hormone and Growth Hormone in Holstein Bull Calves
Authors: Shahab M. , Nusser K. D. , Griel L. C. , Deaver D. R. 
Published: September 2006

AbstractThe role of N‐methyl‐D‐aspartate (NMDA) receptor activation in the central regulation of luteinizing hormone (LH) and growth hormone (GH) was tested by administering a bolus intravenous dose of N‐methyl‐D,L‐aspartic acid (NMA), a NMDA receptor agonist, to 24‐week‐old intact (n = 5), estradiol‐treated intact (n = 3) and castrated (n = 3) Holstein bull calves. The calves were bled for 12 h pre‐ and 100 min post‐NMA injection (1.75 mg/kgBW) periods at 10min intervals. Concentrations of LH and GH in plasma were measured by specific RlA. Prior to administration of NMA, the average concentration of LH, but not GH, differed significantly among the 3 groups. As expected, administration of estradiol prevented the normal ontogeny of pulsatile LH secretion, while castration resulted in an increased frequency of LH discharges. Injection of NMA resulted in an acute (P<0.001) release of LH in 3 of 5 intact and 3 of 3 estradiol‐treated intact calves with the peak response being observed at 20 min (3.18 ±1.3 and 5.58 ± 1.3 ng/ml, respectively) following the challenge. Treatment with NMA did not alter the release of LH in castrate calves. Concentrations of GH in plasma increased (P<0.001) within 20 to 30 min after administration of NMA in intact, estradiol‐treated intact and castrate calves with a similar response being observed in each group. Based on these findings, we suggest an involvement of glutamatergic neurotransmission in the hypothalamic or supra‐hypothalamic control of LH and GH secretion, and that the excitatory effects of NMDA receptor activation on LH release are overtly influenced by gonadal steroids in bull calves.
Immunocytochemical Localization of Progesterone Receptors in Galanin Neurons in the Guinea Pig Hypothalamus
Authors: Warembourg Maryvonne , Jolivet Andre 
Published: September 2006

AbstractA double‐label immunocytochemical technique was used to determine whether progesterone receptor‐containing neurons in the female guinea‐pig hypothalamus also contained galanin. Adult ovariectomized guinea‐pigs were primed by estradiol to induce progesterone receptors and injected intracerebroventricularly with colchicine to visualize galanin‐immunopositive neurons. A small proportion of progesterone receptor‐containing perikarya in the medial preoptic area and the mediobasal hypothalamus were found to be immunoreactive for galanin. The medial preoptic, periventricular and arcuate nuclei showed the greatest concentration of double‐labelled cells. Galanin varicosities appeared in close proximity to neurons with progesterone receptor‐containing nuclei. These results provide neuroanatomical evidence that a subset of hypothalamic galanin‐immunoreactive neurons is directly regulated by progesterone.
The Effect of Photoperiod on Plasma Levels of Melanin‐Concentrating Hormone in the Trout
Authors: Lyon V. E. , Baker B. I. 
Published: September 2006

AbstractThe neurohypophysial melanin‐concentrating hormone, MCH, plays a role in adaptive colour change in teleost fishes, inducing pallor when the fish is placed in pale‐coloured surroundings. The present study shows that its plasma concentration, measured in groups of white‐adapted fish, is not uniformly high throughout the day but follows a clear diurnal pattern. Over a 24 h cycle, plasma concentrations rise gradually during the morning to reach peak values around the middle of the photophase, after which they decline significantly before night. Lowest concentrations are observed during the dark period. This pattern was observed under a long photoperiod in summer and a short photoperiod in winter. The peak was shifted within a week of changing the onset of either light or dark. When dawn was delayed by 6 h for fish held on a long photoperiod, the usual morning rise in hormone titres was suppressed but, with the advent of light, hormone concentrations rose more rapidly than usual to reach peak values at about the normal time. If the dawn was advanced by 6 h for fish held under short photoperiod conditions, then peak concentrations were attained 6 h precociously. Fish from a long photoperiod placed in constant light showed a pattern of MCH release which approximated to the normal over the first 24 h period but plasma values then became raised and periodicity was no longer discernible. Plasma hormone concentrations were much reduced in trout kept in black coloured tanks in which nocturnal and daytime values differed, but significant differences during the photophase were not demonstrable. The results suggest that an illuminated white background can initiate the early morning release of MCH, and that an endogenous pacemaker underlies the pattern of MCH secretion.
Regulation of Vasopressin (VP) Gene Expression in the Bed Nucleus of the Stria Terminalis: Gonadal Steroid‐Dependent Changes in VP mRNA Accumulation are Associated with Alterations in mRNA Poly (A) Tail Length but are Independent of the Rate of VP Gene Transcription
Authors: Carter David A. , Murphy David 
Published: September 2006

AbstractForebrain vasopressin (VP) neurons of the bed nucleus of the stria terminalis (BNST) contrast with hypothalamic VP neurons in exhibiting nuclear gonadal steroid receptors which may directly effect steroid‐induced changes in VP gene expression observed in BNST cells. A transcription and Northern mRNA analysis has been performed to determine the mechanism through which gonadal steroids regulate VP gene expression in the BNST. In addition to confirming a distinctive, sexually dimorphic pattern of VP mRNA expression in the BNST as compared with the hypothalamic supraoptic nucleus (SON), our results show that the marked decrease in BNST VP mRNA levels observed two weeks after castration is not associated with a change in transcriptional activity of the VP gene. Similarly, VP gene transcription is not increased, relative to castrated animals, in the BNST of castrated rats treated with testosterone which exhibit normal or somewhat elevated levels of VP mRNA in the BNST. A post‐transcriptional mechanism therefore appears to underlie the gonadal steroid‐regulated changes in VP gene expression in the BNST. Since modulation of mRNA size (due to changes in poly (A) tail length) was also observed following castration and testosterone treatment it is apparent that the post‐transcriptional mechanism may involve regulated changes in VP mRNA poly (A) tail length.The present findings contrast with the osmotic up‐regulation of VP mRNA levels in the SON which is primarily a transcriptional response, and provide a demonstration of the potential physiological importance of post‐transcriptional mechanisms of hormonal gene regulation.
Mating‐lnduced FOS‐Like Immunoreactivity in the Rat Forebrain: A Sex Comparison and a Dimorphic Effect of Pelvic Nerve Transection
Authors: Wersinger S. R. , Baum M. J. , Erskine M. S. 
Published: September 2006

AbstractPrevious research has shown that mating induces the expression of the immediate‐early gene, c‐fos, as detected by the increased presence of nuclear FOS‐like immunoreactivity (FOS‐IR), in specific forebrain regions of both male and female rats. In the male both olfactory/vomeronasal (O/V) and genital/somatosensory (G/S) inputs appear to contribute to the neural FOS response to mating whereas in the female G/S input carried by the pelvic nerves appears to mediate the forebrain FOS response. To date, however, no direct sex comparison of the mating‐induced forebrain FOS response has been made in rats maintained under the same steroidal conditions nor has the contribution of afferent sensory input from the pelvic nerves been assessed in males. We first compared the level of FOS‐IR in brain regions of mated and unpaired gonadectomized male and female rats given 5μg/kg estradiol benzoate (EB) for 7 days and 500 μg progesterone (P) 4 h prior to testing. One h after experiencing 1 ejaculation, both sexes showed increased FOS‐IR in the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala, the ventro‐lateral portion of the ventromedial nucleus of the hypothalamus (VMN), and the midbrain central tegmental field (CTF). This increase was significantly greater in the MPOA and medial amygdala of mated females than of males. Bilateral transection of the pelvic nerves significantly attenuated the increase in FOS‐IR after mating in the CTF of male rats and in the MPOA, BNST, VMN, medial amygdala and CTF of females. Thus, following mating there is no sex difference in the brain regions which express c‐fos, but there is a dimorphism in the contribution of afferent information conveyed by the pelvic nerves to the mating‐induced FOS response. The neural FOS response of the female to mating is heavily dependent upon the G/S afferent inputs carried by the pelvic nerves whereas the male's neural c‐fos response may depend on O/V input plus G/S input conveyed via other afferent pathways such as the pudendal nerves.
Short‐Term Regulation of Gonadotropin Subunit mRNA Levels by Estrogen: Studies in the Hypothalamo‐Pituitary Intact and Hypothalamo‐Pituitary Disconnected Ewe
Authors: Mercer Julie E. , Phillips David J. , Clarke Iain J. 
Published: September 2006

AbstractIn this study the levels of mRNA for the pituitary gonadotropin hormone subunits luteinizing hormone β (LHβ), follicle stimulating hormone β (FSHβ) and the common α‐subunit were assessed during the acute feedback stages of estradiol benzoate (EB) action in ovariectomized (OVX) ewes with and without hypothalamo‐pituitary disconnection (HPD).In OVX/HPD ewes maintained on hourly pulses of 250 μg of gonadotropin‐releasing hormone (GnRH) a single i.m. injection of EB in oil caused a biphasic (decrease and then increase) change in plasma LH levels and a monophasic decrease in FSH levels. There was a decrease in pituitary α‐subunit and FSHβ mRNA levels during the acute negative (8 h post EB) and through the positive feedback (20 h post EB) stages of the response. No significant change was seen in LHβ mRNA levels following treatment with EB.In hypothalamic‐pituitary intact OVX ewes the same EB treatment as above caused a biphasic change in LH secretion with the positive feedback component being much greater than in GnRH‐pulsed OVX‐HPD ewes. The levels of mRNA for all three gonadotropin subunits were reduced by 8 h after EB injection and remained low throughout the positive feedback period.These data suggest that the LH surge in this experimental model does not require an increase in LHB mRNA levels. Furthermore, the fall in LHβ subunit mRNA seen after estrogen injection to OVX ewes is most likely due to an effect of estrogen to decrease GnRH secretion, since pulsatile GnRH replacement prevents this effect. These data also show that estrogen feedback can effect rapid alterations in pituitary gonadotropin subunit mRNA levels. Short‐term changes in FSHβ mRNA are reflected in changes in FSH secretion; the same is not true for LH.
Differential Seasonal Regulation of Melatonin Receptor Density in the Pars Tuberalis and the Suprachiasmatic Nuclei: A Study in the Hedgehog (Erinaceus europaeus, L.)
Authors: Gauer François , Masson‐Pévet Mireille , Saboureau Michel , George Denise , Pévet Paul 
Published: September 2006

AbstractUsing quantitative autoradiography, we have studied the seasonal changes of high affinity melatonin receptor density in both the SCN and PT of the hedgehog, a seasonal breeder and an hibernator. Animals in 3 different physiological states were studied: sexually active animals, and sexually inactive animals during the hibernation period, being then either euthermic or hypothermic. In sexually active animals, Bmaax were 75.8 ± 7.1 fmol/mg protein in PT and 9.1 ± 0.5 fmol/mg protein in SCN; and Kd values were: 94 ± 22 pM in the PT and 101 ± 15 pM in the SCN. This specific binding was strongly decreased in the PT of sexually inactive animals. Moreover, this decrease was significantly stronger in hypothermic than in euthermic hedgehogs. Saturation studies and Scatchard analysis revealed that the observed decrease in the PT resulted from change in the Bmax but not in the Kd, Bmax values being respectively 56.4 ± 5.9 and 29.5 ± 1.9 fmol/mg protein in euthermic and hypothermic sexually at rest animals. In none of the different physiological states, did the density of melatonin receptors of the SCN show any changes, Bmaax values being respectively 9.8 ± 0.5 and 9.8 ± 0.4 fmol/mg protein in euthermic and hypothermic sexually at rest animals. This shows for the first time a tissue‐specific regulation of melatonin receptor density occurring in the PT but not in the SCN. Furthermore, this decrease of binding in the PT is correlated with both sexual inactivity and hibernation period. This strongly suggests that the mediation of the photoperiodic effect on seasonal functions like seasonal hypothermia and reproduction involves an effect of melatonin on the PT rather than on the SCN.
Antidopaminergic‐lnduced Hypothalamic LHRH Release and Pituitary Gonadotrophin Secretion in 12 Day‐Old Female and Male Rats
Authors: Lacau‐Mengido Isabel M. , Becú‐Villalobos Damasia , Thyssen Sandra M. , Rey Estela B. , Lux‐Lantos Victoria A. R. , Libertun Carlos 
Published: September 2006

AbstractIn previous studies we have shown that the developing rat provides an interesting physiologic model in which the dopaminergic control of both LH and FSH is well defined in contrast to the controversial results obtained in adult rats. We wished to establish the role of testosterone in antidopaminergic induced gonadotrophins release in 12 day‐old male and female rats, and evaluate the effect of antidopaminergic drugs at the hypothalamic level during this developmental stage.Haloperidol, an antidopaminergic drug, increased both LH and FSH in female 12 day‐old rats but not in male littermates. The effect was blocked by bromocriptine and not by phentolamine indicating that haloperidol acted on the dopaminergic receptor, and that unspecific stimulation of the noradrenergic system was not involved. Haloperidol was ineffective when female rats were previously ovariectomized and injected with testosterone propionate at 9 days of age. If females were treated on the day of birth with testosterone propionate, haloperidol‐induced FSH and LH release was also abolished. In control males haloperidol had no effect on the release of LH or FSH. But if males were orchidectomized at birth or at 9 days of age, haloperidol released both LH and FSH during the infantile period.In an attempt to establish the site of action of antidopaminergic drugs on gonadotrophin release, hypothalami (mediobasal and preoptic‐suprachiasmatic area) from 12 day‐old infant female rats were perfused with either haloperidol or domperidone (2±10−6 M). Both drugs increased LHRH release into the perifusate. Besides haloperidol did not modify the release of LH or FSH from adenohypophyseal cells incubated in vitro.We therefore conclude that antidopaminergic‐induced gonadotrophins release is modulated by serum testosterone concentrations, and that the site of action is probably the LHRH‐secreting neuron of the hypothalamus.
Immunocytochemical Evidence for Oestrogen Receptors within GABA Neurones Located in the Perinuclear Zone of the Supraoptic Nucleus and GABAA Receptor β2/β3 Subunits on Supraoptic Oxytocin Neurones
Authors: Herbison Allan E. 
Published: September 2006

AbstractThe mechanisms by which oestrogen modulates the biosynthetic and secretory activity of magnocellular oxytocin neurones are poorly understood. Using an antibody directed against the oestrogen receptor (ER), the distribution of ER‐immunoreactive (‐IR) cells in relation to the supraoptic nucleus (SON) was examined. Although no ER‐IR cells were detected within the SON, a small population of immunoreactive cells separate from those in the preoptic area was identified in the perinuclear zone of the SON. Double‐labelling experiments with an antibody specific for glutamic acid decarboxylase (GAD), the neuronal enzyme producing gamma aminobutyric acid (GABA), revealed that approximately 60% of perinuclear zone ER‐IR cells contained GAD. A further set of immunocytochemistry experiments using an antibody raised against the β2. and β3 sub‐units of the GABAA receptor revealed immunoreactivity in the SON. Double‐labelling experiments demonstrated that both oxytocin‐IR and non‐oxytocin‐IR neurones in the SON were immunoreactive for β2 and/or β3 sub‐units of the GABAA receptor. These studies have identified ERs within a GABAergic neural population in the perinuclear zone of the SON and shown that magnocellular oxytocin neurones in the SON possess GABAA receptors comprised of β2 and/or β3 sub‐units. In conjunction with previous evidence that the perinuclear zone GABA neurones are an important source of GABA terminals in the SON, these results provide a morphological basis for the hypothesis that perinuclear zone GABA neurones may be part of a steroid‐sensitive neural circuitry transmitting oestrogen input to oxytocin neurones in the SON.
Characterization of the GABA‐lnduced Current in Frog Pituitary Melanotrophs
Authors: Louiset E. , Mei Y. A. , Valentijn J. A. , Vaudry H. , Cazin L. 
Published: September 2006

AbstractThe molecular mechanisms regulating GABAA receptor activity in cultured frog melanotrophs were studied using the patch‐clamp technique. In the whole‐cell configuration, application of GABA evoked a dose‐related increase of inward chloride currents. The ED50 value, estimated from the sigmoidal dose‐response curve was 2 × 10−6 M and the Hill coefficient was 1.55. The amplitude of the GABA‐induced current decayed with time. Kinetics analysis of the desensitization revealed that the time‐course of the current decrement was fitted by one exponential. Graded doses of GABA or association of GABA with the benzodiazepine receptor agonist flunitrazepam accelerated the desensitization process. In contrast, the time‐course of the current did not significantly vary at different holding potentials. In the outside‐out configuration, GABA was found to activate channels which displayed three unitary conductance levels (8, 15 and 30 pS). The channel openings of the more frequent conductance level (30 pS) exhibited short and long lasting open states (1.2 and 28.3ms at ‐60mV). Altogether these data reveal that frog melanotrophs possess a single population of GABAA receptors which interconvert into a higher affinity state in the presence of benzodiazepine receptor agonists. Two GABA molecules must bind to the receptor to trigger long lasting channel openings. In addition, the activity of the GABAA receptor appears to be independent of the accumulation of intracellular chloride ions.
Characterization of Opioid Binding Sites in the Neural and Intermediate Lobe of the Rat Pituitary Gland by Quantitative Receptor Autoradiography
Authors: Boersma C. J. C. , Pool C. W. , Van Heerikhuize J. J. , Van Leeuwen F. W. 
Published: September 2006

AbstractPrevious studies have suggested an involvement of enkephalins in regulation of oxytocin (OXT) and vasopressin (AVP) release, which seems to disagree with the very low affinities of Met‐ and Leu‐enkephalin for the kappa opioid receptor. As opioid receptors in the neural lobe exclusively exist of kappa receptors, we studied the binding characteristics of larger pro‐enkephalin derived peptides for opioid binding sites in the neural lobe by means of light microscopic receptor autoradiography. In addition, the pharmacological characteristics of opioid binding sites in the neural lobe were compared with those in other parts of the pituitary.In the neural as well as the intermediate lobe both high and low affinity 3H‐bremazocine binding sites were present. Binding to these sites was completely displaceable by both naloxone and nor‐binaltorphimine, suggesting that these sites represent kappa opioid receptors. Also with regard to selectivity and affinity characteristics to other ligands, opioid binding sites in the neural and intermediate lobe were quite similar. In the anterior lobe a very low level of bremazocine binding was present, which could not be displaced by nor‐binaltorphimine.Displacement studies with pro‐enkephalin and pro‐dynorphin derived peptides showed that both groups of peptides could bind to opioid binding sites in the neural and intermediate lobe. Especially the relatively large pro‐dynorphin and pro‐enkephalin derived peptides, such as dynorphin 1–17 and BAM22, appeared to be very potent ligands for these opioid binding sites and were much more potent than smaller fragments, such as dynorphin 1–8, and Met‐ and Leu‐enkephalin. These results contradict the existence of a mismatch in the neural (and intermediate) lobe with regard to the local type of opioid peptides and receptors present.
Hypothalamic Dopaminergic Neurons in Prolactin‐Deficient Ames Dwarf Mice: Localization and Quantification of Deficit by Tyrosine Hydroxylase Immunocytochemistry
Authors: Phelps Carol J. , Carlson Susan W. , Vaccarella Myra Y. 
Published: September 2006

AbstractHypothalamic tuberoinfundibular prolactin‐inhibiting neurons show decreased levels and synthesis of dopamine in two types of genetically prolactin‐deficient dwarf mice (Snell, Ames) which arise from separate mutations. A reduction to 2% of normal in this neuronal population has been quantified for Snell dwarfs. The present study was undertaken in order to quantify morphometrically the deficit and its distribution in Ames dwarf mice, including comparisons of sex and adult age. The brains of dwarf (df/df) and normal phenotypic (DF/?) sibling mice of both sexes from 4 to 16 months of age were immunostained for tyrosine hydroxylase, the rate‐limiting enzyme in dopamine synthesis; neuronal perikarya were counted in coronal sections of tuberoinfundibular arcuate nucleus (area A12), medial zona incerta (A13) and anterior periventricular (A14) hypothalamic areas at 180 μm rostral‐to‐caudal intervals. Normal (DF/?) mice exhibited no differences in neuron numbers, with regard to age or sex, in any of the three dopaminergic areas. In dwarf mice, a tendency toward decreased neuron numbers with age was statistically significant for area A14 only, and the size of the neuronal population in A12 was reduced in males compared with females. Total A12 neuron number in dwarfs was 48% of that in normal mice (P< 0.001). Periventricular (A14) perikaryal numbers were reduced slightly (P<0.05) in dwarfs compared with normals. Numbers of A13 neurons were comparable for DF/? and df/df. The morphometric distribution of tyrosine hydroxylase‐immunoreactive neurons in A12 showed that the decrease in neuronal number in dwarfs was distributed throughout the rostral‐to‐caudal length of the nucleus, with significant decrease of total perikarya (P<0.05) at each 180 μm sampling interval. Thus, lifelong absence of prolactin in Ames dwarf mice is accompanied by a significant decrease in hypothalamic tyrosine hydroxylase‐immunoreactive neurons, which is restricted to hypophysiotropic areas, uniformly distributed within A12, and is less severe than the reduction in the phenotypically similar Snell dwarf.