bluuebunny/crossref_metadata_2025_split huggingface dataset:
Immunohistochemical Localization of GnRH in the Crested Newt (Triturus carnifex) Brain and Terminal Nerve: a Developmental Study
Authors: D'Aniello B. , Masucci M. , di Meglio M. , Lela L , Rastogi R. K. 
Published: September 2006

AbstractLocalization of GnRH‐immunoreactive neuronal system was studied by immunohistochemistry in the nasal‐brain area of the crested newt, Triturus carnifex. Besides adults, developmental stages were those from hatchlings up to complete metamorphosis. Neurons containing immunoreactive GnRH were first detected in the nasal area of larvae with yet undifferentiated gonads. Subsequently, in prometamorphic stages, GnRH‐immunoreactive cell bodies and fibers were detected in the proximal part of the terminal nerve as well as along the ventromedial surface of the olfactory bulbs. In older larvae with sexually differentiated gonads and up to the metamorphic climax GnRH‐neurons were detected, as a rostral to caudal continuum, along the ventromedial surface of the olfactory bulbs and midtelencephalon. This is exactly the route followed by the terminal nerve. In the adult brain, besides the presence of occasional GnRH‐neurons and fibers in the terminal nerve proximal to olfactory bulbs, olfactory bulbs and the mid‐basal telencephalon, another aggregate of immunoreactive neurons was present in the anterior preoptic area, and a greater number of fibers in the habenular area as well as in the infundibular floor, median eminence and pars nervosa. These data suggest the nasal area to forebrain migration (along the course of the terminal nerve) of GnRH‐neurons during development in the crested newt.
Calcium Waves and Dynamics Visualized by Confocal Microscopy in Xenopus Oocytes Expressing Cloned TRH Receptors
Authors: Eidne Karin A. , Zabavnik Jelka , Allan W. T. Gordon , Trewavas Anthony J. , Read Nick D. , Anderson Lorraine 
Published: September 2006

AbstractLaser scanning confocal microscopy was used to analyse changes in free cytosolic calcium ([Ca2+]i) in Xenopus laevis oocytes expressing the cloned rat TRH receptor in response to TRH. In oocytes expressing TRH receptors, TRH invariably evoked a dose‐dependent, biphasic calcium response. This response consisted of an initial transient planar wave of calcium propagating just below the surface of the membrane followed by a slower, secondary calcium phase. The TRH antagonist, chlordiazepoxide, markedly inhibited this calcium wave. The origins of calcium involved in this biphasic response were investigated using a variety of intra‐ and extra‐cellular calcium antagonists. The intracellular calcium antagonists thapsigargin and TMB‐8 reduced the initial and to a lesser extent the secondary phase of the planar calcium wave. In contrast, EGTA and the calcium channel blocker nifedipine produced a profound inhibition of the secondary phase while the initial phase was only slightly reduced. These results indicate that the release of intracellular calcium is predominantly responsible for the initial phase of the calcium wave while the influx of extracellular calcium is mainly involved in the secondary phase. Qualitative changes in the patterns of calcium release induced by TRH were observed following pretreatment with intracellular calcium antagonists. Following pretreatment with these compounds, TRH induced spiral or regenerative calcium waves. Addition of EGTA to the extracellular medium did not alter these responses confirming the importance of intracellular calcium in the generation of these spiral calcium waves. This study demonstrates the nature and multiplicity of regulating mechanisms of [Ca2+]i following activation of TRH receptors expressed in Xenopus oocytes.
Oxytocin Administered Centrally Facilitates Formation of a Partner Preference in Female Prairie Voles (Microtus ochrogaster)
Authors: Williams Jessie R. , Insel Thomas R. , Harbaugh Carroll R. , Carter C. Sue 
Published: September 2006

AbstractPrairie voles (Microtus ochrogaster) are monogamous mammals that form male‐female pair bonds. Partner preference formation, one component of the pair bond in prairie voles, occurs following male‐female cohabitation and is facilitated by mating. The peptide hormone oxytocin is released during physical contact and particularly following vaginal stimulation. Oxytocin has been implicated in mother‐infant bond formation. The present study tested the hypothesis that oxytocin participates in the partner preference component of pair bond formation in adult prairie voles. Ovariectomized female prairie voles were implanted with osmotic mini‐pumps releasing oxytocin (1–100 ng/h) or artificial cerebrospinal fluid (CSF). Pumps were implanted intracerebroventricularly or subcutaneously and females then were housed for 6 h with a male partner, followed by a preference test in which females could elect to spend time with either the partner or an unfamiliar male. Females in groups that received centrally‐administered oxytocin (10 or 100 ng/h), but not CSF, exhibited a significant preference for the partner present during infusion. The induction of a partner preference after oxytocin administration appeared specific for central oxytocin pathways as peripheral oxytocin administration was ineffective. Moreover, central administration of a selective oxytocin receptor antagonist inhibited the behavioral effect of exogenous oxytocin. These results suggest that oxytocin may be one factor contributing to the development of partner preferences in this monogamous rodent.
Luteinizing Hormone‐Releasing Hormone Receptor Messenger Ribonucleic Acid Expression in the Rat Pituitary during Lactation and the Estrous Cycle
Authors: Funabashi Toshiya , Brooks Philip J. , Weesner Gary D. , Pfaff Donald W. 
Published: September 2006

AbstractTo study mechanisms underlying the modulation of luteinizing hormone‐releasing hormone receptor (LHRH‐R) during lactation and the estrous cycle, we used a reverse transcriptase‐polymerase chain reaction (RT‐PCR) procedure to generate a probe for rat LHRH‐R messenger RNA (mRNA). Using primers based on the mouse sequence, we amplified an approximately 300 bp fragment from rat pituitary complementary DNA. This PCR product was shown to be part of LHRH‐R cDNA by direct sequencing and by comparing to the rat LHRH‐R cDNA reported recently. Then, this PCR fragment was used as a probe for northern blotting analysis.The level of LHRH‐R mRNA in the pituitary was significantly decreased during lactation, by approximately 80%, compared to that of ovariectomized and intact (diestrous and metestrous cycling) rats while no statistical difference in glyceraldehyde‐3‐phosphate‐dehydrogenase (GAPDH) mRNA level was observed between groups. During the estrous cycle, the level of LHRH‐R mRNA in the pituitary was about two‐fold higher on diestrous day 2 and the morning of proestrus than that on diestrous day 1 and quickly returned toward control level by noon of proestrus. In addition, we found that GAPDH mRNA levels from a so‐called housekeeping gene often thought to be unchanged under different conditions, were significantly higher on proestrus while levels of 18S rRNA were not significantly changed.The large decrease in LHRH‐R mRNA during lactation could account for the changes in LHRH binding previously reported.
A Critical Period for Glutamate Receptor‐Mediated Induction of Precocious Puberty in Female Rats
Authors: Smyth Catherine , Wilkinson M. 
Published: September 2006

AbstractThe excitatory amino acid glutamate and especially its NMDA subtype receptor are important components of the neural system that regulates sexual maturation. It is known that multiple daily injections of immature rats and monkeys with NMDA will induce precocious puberty. We have previously reported that a single daily injection of NMDA administered from 27 days of age to the day of vaginal opening (VO) is sufficient to synchronize and slightly accelerate (1–2 days) first ovulation in female rats. We have now optimized this treatment schedule and show that a higher dose of NMDA (20 mg/kg), or the racemic mixture N‐methyl‐D,L‐aspartate (NMA; 30 mg/kg), initiated earlier in development (24 days to VO) significantly advances first ovulation (4 days). Rats induced to ovulate prematurely had normal estrous cycles. We also report that the same degree of precocity can be obtained when injections are discontinued well before first ovulation occurs. For example, NMA administered from day 21 to 25 or from day 24 to 28 accelerates sexual maturation to the same degree as if injections were continued until VO was observed. It is clear that the hypothalamic‐pituitary‐ovarian (H‐P‐0) axis is stimulated by daily NMDA treatment as shown by the dose‐related luteinizing hormone (LH) release and by an estrogen‐dependent rise in uterine weight. However, stimulation of the P‐O axis with daily injections of GnRH (5 ng/100 g), which elicits an LH response slightly greater than NMDA (20 mg/kg), does not advance puberty. This suggests that NMDA induces some change in hypothalamic control which is not directly related to LH secretion. Interestingly, there also seems to be a critical period of NMDA effectiveness because daily injections of NMA (30 mg/kg) from day 16 to 20 do not induce precocious puberty. Since the ovaries respond with increased estrogen production (increased uterine weight) to gonadotrophin stimulation at this early age (16 days) we conclude that the hypothalamus may be relatively unresponsive to stimulation with NMDA.Paradoxically the hypothalamus is also hyporesponsive to NMDA in the period preceding spontaneous first ovulation. We now show that an LH dose‐response curve for NMDA at age 28 days demonstrates that in NMDA‐treated rats the LH response to NMDA is less than in the control group. Further, the hyporesponsiveness is not due to pituitary desensitization since an LH dose‐response curve for GnRH at age 28 days is identical in the NMDA‐treated and control groups.In conclusion we have determined that precocious ovulation can be induced by single, daily injections of NMDA beginning no earlier than postnatal day 21. In the peripubertal period the LH response to NMDA is severely attenuated in both treated and control rats. The evidence therefore suggests that contrary to the prevailing view, the H‐P‐O axis becomes less sensitive with the approach of puberty even though NMDA can induce premature ovulation.
Osmotic Inhibition of Prolactin Secretion in Rats
Authors: Dohanics Janos , Smith M. Susan , Blackburn Ruth E. , Verbalis Joseph G. 
Published: September 2006

AbstractChronic hyponatremia is known to cause inhibition of pituitary vasopressin (AVP) and oxytocin (OT) secretion in response to most physiological stimuli, as well as a marked inhibition of synthesis of these peptides. Because many studies have implicated neurohypophyseal peptides in the regulation of pituitary prolactin (PRL) secretion, we investigated the effects of chronic hyponatremia on basal and stimulus‐induced PRL secretion in rats. Hyponatremia was induced by subcutaneous infusion of 1‐deamino‐[8‐D‐arginine]‐vasopressin (dDAVP) (5ng/h) to rats fed a nutritionally balanced liquid diet, and plasma [Na+] was maintained ≤115 mmol/l for 10–12 days. After this period, hyponatremic rats and normonatremic controls fed the same diet without dDAVP were subjected to one of the following stimuli known to stimulate PRL release in rats: 3 min exposure to ether, hemorrhage (20 ml/kg), intravenous injection of 5‐hydroxytryptophane (5‐HTP, 10 mg/kg), or intravenous injection of estradiol (5 μg/kg). A baseline blood sample was collected before each stimulus, and 3–6 additional blood samples were collected at selected intervals after the stimulus. Baseline levels of plasma PRL were not different between normonatremic and hyponatremic rats. However, PRL responses induced by ether or estradiol, but not those induced by hemorrhage or 5‐HTP, were very significantly blunted in the chronically hyponatremic rats. Plasma AVP and OT responses were measured as an index of magnocellular secretion, but did not correlate with the PRL responses for any of the stimuli tested. Our results therefore demonstrate that ether‐ and estradiol‐induced PRL release can be osmotically inhibited, but the mechanisms underlying this inhibition appear to be relatively independent of effects on magnocellular AVP and OT secretion. This allows the possibility that either some parvocellular systems regulating PRL secretion are osmosensitive, or alternatively that other substances released from the neural lobe may selectively modulate pituitary PRL release in response to some, but not all, stimuli.
Somatostatin‐lmmunoreactive Neurones in the Hypothalamic Ventromedial Nucleus Possess Oestrogen Receptors in the Male and Female Rat
Authors: Herbison Allan E. 
Published: September 2006

AbstractNeurones containing oestrogen receptors (ERs) in the ventrolateral division of the hypothalamic ventromedial nucleus (VMNvl) are believed to play an important role in mediating oestrogen's regulatory influence on reproductive behaviour. As somatostatin (SOM)‐immunoreactive neurones are found exclusively within the ventrolateral division of VMM, this study has used double‐labelling immunocytochemistry techniques to evaluate whether ER‐immunoreactive cells in the VMNvl synthesize SOM in both the male and female rat. Rats gonadecto‐mized 1 week earlier were perfused and brain sections through the mediobasal hypothalamus processed for ER and SOM immunoreactivity using the H222 monoclonal rat ER antibody and a polyclonal rabbit SOM antiserum. Within the VMN, cells immunoreactive for SOM were found predominantly in the rostral portion of the VMNvl while ER‐immunoreactive cells were distributed throughout the VMNvl. Sequential double‐labelling studies revealed that many ER‐containing cells in the rostral VMNvl were also immunoreactive for SOM. A semi‐quantitative analysis of double‐labelled cells in the rostral VMNvl of male and female rats, respectively, estimated that 52 ± 2% and 55 ±8% of SOM‐IR cells possess ERs while 35 ± 1% and 28 ±3% of ER‐IR cells synthesise SOM in the rostral VMNvl. No sex differences were detected at this level. These results show that approximately half of the SOM‐synthesizing neurones in the rostral VMN possess ERs and indicate that SOM should now be considered alongside enkephalin and Substance P as a putative mediator of oestrogen's regulatory influence on reproduction through the VMN of the rat.
Oestrogen Receptors in the Preoptico‐Hypothalamic Continuum: Immunohistochemical Study of the Distribution and Cell Density During Induced Oestrous Cycle in Ovariectomized Ewe
Authors: Blache D. , Batailler M. , Fabre‐Nys C. 
Published: September 2006

AbstractOestrogen plays a key role in the regulation of the endocrine and behavioural events associated with the oestrous cycle. It is important, therefore, to know the location of neurones receptive to this steroid and to know whether their distribution varies with the oestrous cycle. We have undertaken experiments to identify the location of oestrogen receptors (ER) within the preoptico‐hypothalamic continuum of ovariectomized ewes submitted to a variety of different hormone replacement regimes which mimic the different stages of the oestrous cycle. We used a monoclonal antibody to ER and detected receptors with immunohistological methods in the non‐vascular part of the organum vasculosum of the lamina terminalis, the lateral septum, the medial preoptic area, the supraoptic, suprachiasmatic and arcuate (ARC) nuclei, the ventromedial hypothalamus (HVM) and in the region close to the mamillari recess. ER neurones were scarce or absent from the anterior hypothalamus and the paraventricular nucleus. The density of ER staining in the HVM, but in no other localization, was found to be higher, and in a more lateral position, during the induced luteal phase (progesterone treatment) than during the follicular phase (7 days of progesterone treatment followed by oestradiol) or in the ovariectomized female. In all areas studied, except for the ARC, the apparent surface area of the nucleus in ER immunoreactive cells varied with hormonal treatment. These data, and especially those in the HVM, contribute towards our understanding of how steroids may act in the ovine to control sexual behaviour.
Expression and Down‐Regulation by Retinoic Acid of IGF Binding Protein‐2 and ‐4 in Medium from Human Neuroblastoma Cells
Authors: Bernardini Sergio , Cianfarani Stefano , Spagnoli Anna , Annicchiarico‐Petruzzelli Margherita , Melino Gerry , Massoud Renato , Boscherini Brunetto , Finazzi‐Agró Alessandro , Rosenfeld Ron G. , Federici Giorgio 
Published: September 2006

AbstractInsulin‐like growth factors (IGFs) regulate the autocrine/paracrine growth of neuroblastomas. The IGFs bind to specific binding proteins (IGFBPs) which modulate their biological activity. We investigated, by Western ligand blotting (WLB), the presence of IGFBPs and their possible modulation by retinoic acid (RA), IGF‐I, IGF‐II and truncated Des(1‐3)IGF‐l in conditioned medium (CM) of the human neuroblastoma SK‐N‐BE(2) cell line. We demonstrated the presence of two IGFBPs, with MW 37 kDa and 25 kDa. Following immunoprecipitation, they turned out to be IGFBP‐2 and ‐4, respectively. The RA‐induced differentiation in SK‐N‐BE(2) cells was accompanied by a marked reduction of the intensity of both IGFBP bands after 48 h (32% and 24% of control, respectively) and 72 h (2% and 0% of control, respectively) incubation. The addition of exogenous IGFs, which did not induce cell differentiation, did not change the IGFBP pattern significantly, except for the truncated form of IGF‐I, which induced a marked decrease in both the 37 kDa and 25kDa bands after 72 h incubation (45% and 18% of control, respectively). These findings suggest that IGFBPs have a role in RA‐induced differentiation in human neuroblastoma cells.
[Arg8]Vasotocin Excites Neurones in the Dorsal Vagal Complex in vitro: Evidence for an Action through Novel Class(es) of CNS Receptors
Authors: Ingram C. D. , Tolchard S. 
Published: September 2006

AbstractUsing extracellular recordings from brainstem slices in vitro, it was demonstrated that a high proportion (38/56) of neurones in the dorsal vagal complex of dioestrus, virgin female rats exhibit an excitatory response to [Arg8]‐vasotocin (AVT). Pharmacological characterization suggests that these responses cannot be entirely explained by interaction with either of the currently known classes of central receptors for oxytocin (OT) and vasopressin (V1a). Comparison of the responses with those to the OT receptor‐specific agonist [Thr4,Gly7]‐OT (TGOT), showed that not all neurones that responded to TGOT also responded to AVT (3/27). Furthermore, while the effects of 10−7 M TGOT could be blocked either by the broad‐spectrum antagonist d(CH2)5[d‐Tyr(OEt)2,Val4,Cit8]‐vasopressin or by the selective OT receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr‐NH29]‐vasotocin, these peptides did not completely block the responses to AVT, indicating that AVT is unlikely to act through the central OT receptor. The responses to AVT and [Arg8]‐vasopressin (AVP) indicated the presence of at least 2 classes of receptor with which these agonists could act. Of 42 neurones tested with both AVP and AVT, none responded to AVP in the absence of a response to AVT, while 7/42 responded to AVT without a response to AVP. This might be explained by AVP acting through only the V1 receptor, while AVT acts through both the V1 and its own novel class of receptor. This was substantiated by the fact that two OT/V1 receptor antagonists, d(CH2)5[d‐Tyr(OEt)2,Val4,Cit8]‐VP and d(CH2)5|Tyr(Me)2,Tyr‐NH29]‐AVP, were unable to block completely all the responses to AVT at a dose which suppressed responses to both AVP and TGOT. These data suggest that, in addition to activation by OT and AVP, neurones in the mammalian central nervous system are able to be excited by AVT, possibly involving its own distinct class of receptor.
Cellular Distribution of G Protein Goa in Pituitary Lactotrophs: Effects of Dopamine
Authors: Painson Jean‐Claude , Wenger Tibor , Lagacé Ginette , Masson Nicole D. , Collu Robert 
Published: September 2006

AbstractMembrane‐bound GTP‐binding (G) proteins mediate signal transduction in a variety of cell systems. The exact mechanisms of G proteins action are still under investigation but they appear to involve effectors located in the plasma membrane as well as in other parts of the cell. With this study, we investigated the cellular and ultrastructural localization of G protein subunits, and particularly of Goa, in normal rat anterior pituitaries and in estrone‐induced rat adenomatous lactotrophs. We also evaluated the effects of Goα cellular redistribution in rat adenomatous lactotrophs following short‐term exposure to dopamine (DA). Using the Protein A‐gold (PAG) methodology, Goα was found to be present in the cysternae of the endoplasmic reticulum of normal pituitary cells and of adenomatous lactotrophs. In the latter, Goα could be co‐localized with prolactin (PRL). By immunoblots, using specific antisera, significant amounts of Goα and Gs42α, together with smaller amounts of Giα, Gs47α and Gβ were found to be present in the uncontaminated supernatant fraction of adenomatous lactotrophs. Unexpectedly, exposure of the cells to DA induced a rapid and short‐lived decrease in the cytosolic fraction of Goα and Gβ associated with a decrease of PRL release. Since cytosolic Goα can be ADP‐ribosylated by pertussis toxin (PT) and is therefore in a heterotrimeric form, our data suggest that the soluble Go protein may play a role during lactotrophs' exposure to an inhibitor of PRL release, perhaps through its relocalization after being internalized with the D2 receptor or by being used for interaction with intracellular and/or membrane‐bound effectors.
Neuroactive Steroids Modulate GABAA Receptors in Peptidergic Nerve Terminals
Authors: Zhang Shuanglin J. , Jackson Meyer B. 
Published: September 2006

AbstractNeuroactive steroid modulation of GABAA receptors was investigated in the peptidergic nerve terminals of the posterior pituitary using patch clamp techniques. In common with GABAA receptors in cell bodies, the nerve terminal GABAA receptor was potentiated by the synthetic steroid alphaxalone and by physiological concentrations of the progesterone metabolite allopregnanolone. Both of these agents enhanced Cl− currents elicited by GABA. Estradiol‐17β had a weak inhibitory effect on GABA responses of nerve terminals, but only at high concentrations. The potentiating action was manifest as an increase in the probability of channel opening, with no effect on the rate of desensitization of the GABAA receptor. Neuroactive steroids enhanced GABA‐gated Cl∼ channel activity in cell‐free membrane patches, thus demonstrating a membrane delimited response. These results indicated that with regard to allosteric modulation by neuroactive steroids, the nerve terminal GABAA receptor is similar to the GABAA receptors of nerve cell bodies and endocrine cells. Neuroactive steroids are thus capable of altering the chemosensitivity of nerve terminal membranes by enhancing GABA inhibition at this location. The neuroactive steroid sensitivity of nerve terminal GABAA receptors provides a pathway by which gonadal steroid derivatives could regulate peptide secretion from neurosecretory neurons. Such a pathway could participate in the coordination of neuropeptide secretion during complex neuroendocrine functions. With specific regard to the neurohypophysis, neuroactive steroid‐induced changes in the sensitivity of nerve terminal GABAA receptors could play a role in the initiation of oxytocin secretion during the transition between pregnancy and parturition.