bluuebunny/crossref_metadata_2025 huggingface dataset:
The Pineal Gland Mediates the Inhibition of Proestrous Luteinizing Hormone Surge and Ovulation in Rats Resulting from Stimulation of the Medial Raphe Nucleus or Injection of 5‐HT into the Third Ventricle
Authors: Morello Héctor , Caligaris Laura , Haymal Beatriz , Taleisnik Samuel
Published: September 2006

In cycling rats, electrochemical stimulation of the medial raphe nucleus or injection of 5‐HT into the third ventricle on the day of proestrus blocked the preovulatory surge of luteinizing hormone and inhibited ovulation. The inhibitory effect of these procedures on gonadotropin secretion failed to occur in rats that had been pinealectomized a few weeks earlier. In contrast, sham‐pinealectomized rats exhibited a response similar to that of intact rats. Luteinizing hormone release and ovulation in pinealectomized rats were not different from that in the controls. The results of the present work indicate that inhibition of gonadotropin secretion induced by activation of the serotonergic system requires the presence of the pineal gland.
Effects of Gonadotrophin‐Releasing Hormone Variants on Reproductive Organs and Plasma Testosterone in the Male Lizard, Podarcis s. sicula
Authors: Ciarcia G. , Paolucci M. , Botte V.
Published: September 2006

The effects of various gonadotrophin‐releasing hormone (GnRH) forms (mammalian GnRH (mGnRH), chicken I GnRH (cGnRH‐I), chicken II GnRH (cGnRH‐II) and salmon GnRH (sGnRH)) on the genital apparatus and plasma testosterone level in the male lizard, Podarcis s. sicula, have been investigated.

In short duration experiments (20 min to 76 h) GnRH forms did not affect testicular and epididymal morphology. A single dose (0.05 μg) of mGnRH, cGnRH‐II and sGnRH, however, induced a rise in plasma testosterone after 20 to 40 min. Variable results were obtained in the animals given GnRH variants every 12 h for 3 days since mGnRH and cGnRH‐I caused a decrease of circulating hormone; cGnRH‐II and sGnRH a slight increase.

Daily peptide administration, for 15 to 30 days, caused severe inhibition of both testicular and epididymal activity and a significant drop of circulating testosterone.

In Podarcis s. sicula, species specificity of pituitary sensitivity to GnRH variants appeared to be low. On the other hand, this gland seemed to show some desensitization after chronic peptide administration.
Naloxone does not Affect the Luteinizing Hormone‐Releasing Hormone‐Induced Inhibition of Luteinizing Hormone Secretion in Sheep
Authors: Naylor A. M. , Porter D. W. F. , Lincoln D. W.
Published: September 2006

Injection of luteinizing hormone‐releasing hormone (21 pmol) into the third cerebral ventricle of long‐term ovariectomized ewes caused a marked inhibition of luteinizing hormone secretion. Mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly when compared with the control responses to saline (50 μl). A notable characteristic of the response was the delayed and sustained nature of the luteinizing hormone‐releasing hormone‐induced inhibition. In the presence of the opioid antagonist naloxone (4 ± 25 mg iv), the central administration of luteinizing hormone‐releasing hormone still produced a marked inhibition of luteinizing hormone secretion. Again, mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly. When naloxone was injected iv, there was a significant rise in mean luteinizing hormone levels as a consequence of an increase in pulse frequency (in four out of five ewes) and a significant increase in luteinizing hormone pulse amplitude.

In conclusion, these data suggest that central opioid pathways sensitive to blockade by naloxone are not involved in the luteinizing hormone‐releasing hormone‐induced inhibition of luteinizing hormone release. Furthermore, in the long‐term ovariectomized ewe, endogenous opioid peptides exert a tonic inhibitory influence on luteinizing hormone‐releasing hormone/luteinizing hormone secretion.
Pulsatile Luteinizing Hormone Secretion in the Rat: Methodological Aspects of Cannulation Route and Sampling Intensity
Authors: Dong Qihan , Handelsman David J.
Published: September 2006

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

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

The mouse neuroblastoma cell line is an excellent model in which to study thyroid hormone action and metabolism, particularly in neural tissue. We therefore undertook the molecular cloning and characterization in these cells of putative thyroid hormone receptors related to c‐erb‐A. Since rat brain tissue contains multiple cell types, and because of possible subtle differences between species (mouse and rat), we therefore screened a new cDNA library constructed from mouse neuroblastoma cell mRNA with synthetic oligonucleotide probes based on the published nucleotide sequence of the c‐erb‐A gene in whole rat brain. Despite the fact that this rat brain cDNA sequence is now recognized to represent a c‐erb‐A α 1 form, the cDNA clones that we isolated were all members of the newly‐recognized c‐erb‐A α 2 form. This identification was made on the basis of nucleotide sequence divergence downstream of the nucleotide corresponding to amino‐acid residue 370 in the predicted coding region. The two longest mouse neuroblastoma cDNA clones, clone 29 (1796 bp) and clone 32 (1410 bp), were 93% to 94% homologous with the c‐erb‐A α 2 and c‐erb‐A α 1 forms in their DNA binding and thyroid hormone binding domains (up to amino‐acid residue 370 in the latter). Both clones 29 and 32 were incomplete in that they terminated at their 3’ends at an internal Eco R1 site. Fortunately this 120 bp (40 derived amino‐acid) truncation was downstream of the reported thyroid hormone binding domain. The 5’untranslated end of clone 29 (446 bp) was of interest because a region of its nucleotide sequence (279 bp) revealed a high degree of homology (87%) with rat brain c‐erb‐A α 1. This highly conserved region in clone 29 appeared to be important in the regulation of translation because only clone 32, in which this region was truncated, efficiently translated protein in a cell‐free system. The protein product of clone 32 did not bind thyroid hormone. Northern blot analysis of mouse neuroblastoma mRNA with site‐specific synthetic oligonucleotides revealed that the c‐erb‐A α 2 species was dominant (major band of 2.4 kb), with a lesser amount of the c‐erb‐A α1 species (major band of 1.8 kb).

In conclusion: 1) We report the molecular cloning of c‐erb‐A variants in a specific neural tissue cell type, namely mouse neuroblastoma cells; 2) The cells contained predominantly the c‐erb‐A α 2 subtype; 3) This c‐erb‐A α 2 form was unique up to bp 167 at its 5’untranslated end, and was then followed, up to the ATG initiation codon, by a highly conserved region common to all c‐erb‐A a species; 4) The 5’untranslated region appeared to play a role in the translational efficiency of this mRNA; 5) The protein product of the c‐erb‐A α 2 mRNA in these cells did not appear to bind thyroid hormone. In view of this finding, the physiological role of the c‐erb‐A α 2 protein remained speculative and may involve a represser function at the thyroid hormone responsive element.
Expression and Post‐Translational Processing of Preprodynorphin in the Rat Anterior Pituitary Cell Line, GH4C1
Authors: Devi Lakshmi , Gupta Prem
Published: September 2006

A recombinant plasmid containing the rat preprodynorphin cDNA was introduced into the rat anterior pituitary cell line, GH4C1. These cells normally express growth hormone and prolactin but not prodynorphin. Stable transformants were isolated and analyzed for the expression and processing of prodynorphin. Chromatographic analyses demonstrated that the prodynorphin was incompletely processed in GH4C1 cells. Analyses of the peptides by specific radioimmunoassays to chemically synthesized peptides showed that the cells have the ability to process both at dibasic and monobasic cleavage sites. The release of prodynorphin‐derived peptides paralleled that of prolactin upon stimulation with thyrotropin‐releasing hormone, forskolin or carbachol suggesting that the prodynorphin‐derived peptides and prolactin are sequestered in similar physiologically responsive compartments. These data suggest that the GH4C1 cells incompletely process prodynorphin. The processing in GH4C1 cells occurs both at monobasic and dibasic cleavage sites.
Stimulation of Maternal Behaviour in Rats with Cholecystokinin Octapeptide
Authors: Lindén A. , Uvnäs‐Moberg K. , Eneroth P. , Sodersten P.
Published: September 2006

Research on the neuroendocrine control of maternal behaviour has concentrated on the role of ovarian and pituitary hormones (1). It is known that the gastrointestinal tract plays an important role in synchronizing mother‐young interactions (2), but the possible contribution of gastrointestinal secretions to maternal behaviour has not been investigated. We show here that treatment with oestradiol benzoate (OB) in combination with cholecystokinin octapeptide (CCK‐8), a duodenal peptide (3), stimulates maternal behaviour within 4 h of exposure to newborn pups in ovariectomized rats. The elevated concentrations of CCK‐8 which are found in the plasma of lactating rats may, therefore, contribute to the development and maintenance of mother‐young interactions during lactation.
Glutamergic Action on Alpha‐Melanocyte‐Stimulating Hormone Release from the Rat Hypothalamus
Authors: Tiligada Ekaterini , Wilson John Fawcett
Published: September 2006

Release of α‐melanocyte‐stimulating hormone (α‐MSH) synthesized in the hypothalamus is regulated by monoaminergic neuronal systems. An endogenous dopaminergic system inhibits α‐MSH release (1, 2) whilst serotoninergic systems exert a biphasic effect on peptide release (3). The toxic effects of neonatal peripheral administration of monosodium glutamate on hypothalamic neurons containing proopiomelanocortin‐ (POMC‐) derived peptides (4, 5) suggest additionally the presence of glutamate receptors on or indirectly influencing the POMC neuron. By comparison of the effect of the excitatory amino‐acid agonists N‐methyl‐D‐aspartate (NMDA), quisqualate and kainate on the release of α‐MSH from superfused slices of rat hypothalamus, we have demonstrated a stimulatory glutamergic action on α‐MSH release mediated through NMDA‐type receptors.
Analysis of the Inhibitory Effect of Oestradiol on Functional GABA/5‐HT Relationship in the Rat Suprachiasmatic Area
Authors: Francois‐Bellan Anne‐Marie , Hery Micheline , Faudon Maxime , Hery Francis
Published: September 2006

The purpose of this study was to test the capacity of oestradiol to modulate the stimulating effect of a‐aminobutyric acid (GABA) on serotonin (5‐HT) metabolism, previously described in the Suprachiasmatic area of the male rat. After an in vivo stimulation of GABA transmission by systemic administration of a GABA‐transaminase inhibitor (amino‐oxyacetic acid) or a GABAB agonist (RS‐baclofen), the 5‐HT metabolism was studied in the Suprachiasmatic area of ovariectomized, and ovariectomized oestradiol‐treated rats.

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

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

We administered a combined dexamethasone‐human corticotrophin‐releasing hormone (hCRH) challenge test to 14 in‐patients with a major depressive episode and to 14 age‐matched controls. After pretreatment with 1.5 mg dexamethasone at 2300 h the day before, 100 μg hCRH was administered iv at 1500 h. Blood samples for cortisol determinations by radioimmunoassay were drawn at 1400 h, 1430 h and 1500 h before infusion of hCRH and thereafter every 15 min until 1700 h. Cortisol secretion after injection of hCRH assessed as area under the curve was significantly increased in patients with depression when compared to controls (14.5 ± 4.3 ng × min × 1,000/ml vs 3.1 ± 2.4 ng × min × 1,000/ml). Multiple regression analysis among patients revealed a significant impact of age and severity of depression upon hCRH‐induced cortisol secretion, whereas in normal controls no significant influence of age on cortisol secretion after hCRH emerged.

Our data show that in depressed patients hCRH evokes an escape from dexamethasone‐induced suppression of the pituitary‐adrenocortical activity, whereas it fails to do so among controls. This finding suggests that at the pituitary level the action of hCRH is enhanced by a factor that is less sensitive to dexamethasone suppression in depression. We postulate that this factor is vasopressin.
Chloroquine Decreases Adrenocorticotrophin‐Secretory Response to Corticotrophin‐Releasing Factor but not to Vasopressin in Rat Pituitary Cells: Further Evidence for Differentially Responsive Subpopulations
Authors: Schwartz Jeffrey , Pham Thao , Funder John W.
Published: September 2006

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

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

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

Normal subjects show a wide range of growth hormone (GH) responses to growth hormone‐releasing hormone (GHRH) stimulation, but it is uncertain whether this variability reflects differences among individuals or whether it would also be observed on repeated tests of the same subject. To clarify this, we tested nine normal men repeatedly with iv bolus doses of 1 μg/kg GHRH(1–44)NH2. Most subjects showed wide variations in their GH responses on repeated testing, and the intra‐individual variability was nearly as great as the inter‐individual variability in responses, accounting for about two‐thirds of the overall variance. A minority of subjects had lower and less variable responses. Ultradian fluctuations in hypothalamic somatostatin secretion may account for this marked intra‐individual variability.
In vitro Effects of 17Beta‐Estradiol on Thyrotropin‐Releasing Hormone‐Induced and Dopamine‐lnhibited Prolactin Release from Adult Male Rat Lactotrophs in Primary Culture
Authors: Zhang Jin , Chen Chen , Kukstas Lucy Anna , Verrier Dany , Vincent Jean‐Didier , Israel Jean Marc
Published: September 2006

Continuous cell perifusion and reverse hemolytic plaque assay have been used to show a regulatory action of 17 β‐estradiol on lactotroph responsiveness to thyrotropin‐releasing hormone (TRH) or dopamine (DA) in vitro. Lactotroph‐enriched cell cultures were obtained from adult male rats after trypsinization and mechanical dissociation followed by separation on a continuous bovine serum albumin gradient at unit gravity. After 7 days in culture, perifusion experiments showed that prolactin was continuously released and this release was increased by TRH and decreased by DA. Both TRH‐induced secretion and DA‐induced inhibition of prolactin release were dose‐dependent with a half maximal effect obtained at 7 × 10−9 M for TRH and at 10−9 M for DA. It was shown by reverse hemolytic plaque assay that about 55% of the cells were plaque‐forming (lysis of red blood cells) and were thus identified as prolactin‐secreting cells. This was similar to a previous result obtained by immunofluorescent staining. Heterogeneity among lactotrophs with regard to the quantity of prolactin released was clearly shown by the varying plaque areas in all preparations. In order to make a quantitative analysis of the effect of 17 β‐estradiol on TRH‐stimulation and DAergic inhibition in these heterogeneous prolactin cells, they were divided into two groups: large plaques (≥ 3 × 103μ m2) constituted about 35% of all plaque‐forming cells, and small plaques (< 3 × 103μ m2), about 65%. Pretreatment with 17β‐estradiol (10−8 M) either for 10 h or 48 h markedly increased TRH‐stimulated prolactin release and decreased the inhibitory effect of DA both in perifusion and reverse hemolytic plaque assay experiments. However, these pretreatments did not change the values of half maximum dose for TRH and DA. TRH transformed about 7% of the small plaques into large plaques and this proportion was increased to 25% after 17β‐estradiol treatment. On the contrary, DA and its more stable analogue bromocriptine increased the percentage of small plaques by 10% to 15% but this effect was decreased after 17β‐estradiol treatment. We conclude that: 1) Normal rat pituitary lactotrophs show heterogeneity with respect to their spontaneous release and responsiveness to TRH and DA; 2) pretreatment with 17β‐estradiol increases the response to TRH and decreases the response to DA without altering the doses at which they have half maximal effect; 3) there is no significant difference between the effect of 17β‐estradiol obtained after 10 h and after 48 h pretreatment.
Immunocytochemical Localization of Angiotensinogen and Angiotensin II in the Rat Pituitary
Authors: Thomas Walter G. , Sernia Conrad
Published: September 2006

The presence and distribution of angiotensinogen and angiotensin II (All) were demonstrated in rat pituitary by immunocytochemical staining with the avidin‐biotin‐peroxidase method, using primary polyclonal antibodies specific for angiotensinogen and All. Silver enhancement of the reaction product was used to intensify lightly stained areas. Attempts were made to identify immunopositive cells by colocalization studies with antisera against luteinizing hormone, prolactin and S‐100, a glial cell protein. In the anterior pituitary, angiotensinogen‐immunoreactivity was observed in cells lining follicle‐like structures. These cells, which were irregularly shaped and had processes extending between the glandular cells, did not colocalize with any of the reference antisera and are therefore of unknown cell type. The follicular endothelium was also immunopositive for angiotensinogen. After silver intensification, dispersed immunoreactive glandular cells were consistently observed in the anterior lobe. A proportion of these costained for luteinizing hormone, but not prolactin or S‐100, indicating their identity as gonadotrophs. In the posterior pituitary, angiotensinogen immunostaining was associated only with the vasculature, while groups of immunopositive cells were observed in the medial region of the intermediate lobe after silver enhancement. All‐immunoreactivity was observed in large cells preferentially located at the poles of the anterior pituitary which also costained for luteinizing hormone. No staining was observed in either the posterior or intermediate lobes. The presence of immunoreactive angiotensinogen in all three lobes of the pituitary suggests that there are sites, in addition to gonadotrophs, at which the intracellular production of All could occur.
Activation of Hypothalamic Gamma‐Aminobutyric Acid Receptors Resets the Pendulum of the Growth Hormone Clock
Authors: Willoughby J. O. , Kapoor R.
Published: September 2006

Plasma levels of growth hormone in male rats exhibit an ultradian rhythm having a periodicity of 3 to 4 h, bursts of growth hormone being separated by troughs when growth hormone secretion ceases. To determine if neurons in the vicinity of somatostatin neurons in the preoptic/anterior hypothalamic area participate in the generation of the rhythm, we temporarily inhibited this region with injections of the γ‐aminobutyric acid agonist, muscimol, in unanaesthetized rats previously prepared with a venous catheter and stereotaxically implanted intracerebral guide tubes. The injection resulted in an immediate burst of growth hormone release, followed by a trough period and another growth hormone burst, 3.4 ± 0.1 h later. The induction of a trough and synchronization of growth hormone bursts was not reproduced by a burst of intravenously injected exogenous growth hormone at least as large as the first burst initiated by muscimol. These findings indicate that, in the short term, the ultradian rhythm is independent of growth hormone feedback and provide the first evidence that structures in the anterior hypothalamus receiving a γ‐aminobutyric acid input are an important component of the neural generator of the ultradian rhythm of growth hormone.
Diverse Effects of Norepinephrine on Vasopressin Release may Reflect Modulation by Hypotonicity
Authors: Sladek Celia D. , Yagil Ghana
Published: September 2006

Previous studies in this laboratory and others have demonstrated both stimulation and inhibition of vasopressin release by norepinephrine. In other regions of the central nervous system, diverse effects of norepinephrine reflect activation of different types of adrenergic receptors and the interaction of norepinephrine with other regulatory signals. In this study, the role of these two mechanisms in the diverse action of norepinephrine on vasopressin release were examined using organ‐cultured explants of the hypothalamo‐neurohypophyseal system. Receptor‐specific adrenergic agonists were found to have different effects on vasopressin release, and their effects were dependent upon whether they were delivered in isotonic saline or distilled water. When delivered in isotonic saline at a concentration of 10−5 M, norepinephrine and phenylephrine, an α1‐adrenergic agonist, increased vasopressin release (P< 0.005 and P< 0.025, respectively); isoproterenol (10−5 M), a β‐adrenergic agonist, did not alter vasopressin release; and clonidine, an α2‐adrenergic agonist, was ineffective at 10−5 M, but stimulated vasopressin release at 10−4 M (P<0.024). However, when these agonists were delivered in 10 μl of distilled water, their effects on vasopressin release were different. This amount of distilled water lowered the osmolality of the culture medium by 3 to 5 mosmol/kg H2O, but did not significantly alter vasopressin release. Vasopressin release was reduced below basal levels when norepinephrine (10−5 M) or clonidine (10−6 M) were delivered in distilled water (P<0.025), but it was not significantly different from basal when phenylephrine or isoproterenol (10−5 M) were delivered in distilled water. These data support the hypothesis that osmotic signals modulate the effect of norepinephrine on vasopressin release, and suggest that, at least in part, this reflects modulation of the type of adrenergic receptor dominating the regulation of vasopressin release.
Positive Feedback of Vasopressin on its Own Release in the Central Nervous System: in vitro Studies
Authors: Ramirez V. D. , Ramirez A. D. , Rodriguez F. , Vincent J. D.
Published: September 2006

In this paper evidence is shown that synthetic arginine vasopressin (AVP) can evoke marked in vitro release of endogenous immunoreactive AVP (I‐AVP) from male rat septal and hypothalamic tissue superfused in vitro. The stimulatory action was dosedependent with a maximal amplification factor of 2.3 when using 14 pg of synthetic AVP as the stimulus. It was highly specific since only AVP was effective and not three closely related substances such as lysine vasopressin, oxytocin and a 4–9 C fragment of AVP. This reproducible effect of AVP required, however, effective concentrations of bacitracin (10−4 to 10−5 M) in the superfusion medium to inhibit aminopeptidase(s) capable of inactivating AVP. Lastly, the stimulatory action of AVP on its own release was not blocked by a V1‐receptor antagonist of AVP but was blocked by a V2‐antagonist. It is proposed that this novel and robust positive feedback of AVP on its own release may be involved in the mechanism of memory consolidation of certain behavioral tasks known to be affected by AVP.
Central Nervous System Sites of Action of an Enkephalin Analogue, (D‐Met2, Pro5)‐Enkephalinamide, and Naloxone on the Secretion of Five Anterior Pituitary Hormones of Male Rats
Authors: Molnár Judith , Marton Jenõ , Halász Béla
Published: September 2006

Central nervous system sites of action of opioid peptides on pituitary hormone secretion were investigated. One nmol of an enkephalin analogue, (D‐Met2, Pro5)‐enkephalinamide, and 10 nmol of the opiate antagonist naloxone were injected into ten different regions of the brain of conscious male rats and their effect on the release of five anterior pituitary hormones tested. The injections were made through a special injection cannula which was inserted into the brain through a guide cannula fixed on the skull and implanted into the brain 5 to 7 days earlier. Both compounds injected into the medial septum, medial preoptic area and hypothalamic paraventricular nucleus affected prolactin, growth hormone and luteinizing hormone (LH) secretion. The enkephalin analogue stimulated prolactin and growth hormone and inhibited LH release. Naloxone induced the opposite effect. Drugs given into the hypothalamic ventromedial nucleus caused changes in plasma prolactin and growth hormone levels. Enkephalinamide increased and naloxone decreased plasma concentrations of both hormones. Administration of the compounds into the dorsal raphe area resulted in alterations of prolactin and LH release, the analogue caused elevation of prolactin and inhibition of LH release, whereas the opiate antagonist resulted in opposite changes. Only an LH response was obtained from the hypothalamic dorsomedial nucleus and a growth hormone response from the central amygdala. Also in these cases the enkephalin analogue decreased LH and elevated growth hormone plasma levels, and naloxone brought about a rise in LH and a diminution of growth hormone concentration. None of the regions were effective in inducing a clear‐cut adrenocorticotrophin or follicle‐stimulating hormone response. The parietal cortex, medial amygdala and the dentate gyrus were entirely ineffective sites. The findings suggest that in the brain there are multiple sites of action of opioids on pituitary trophic hormone secretion and the effective sites are not identical in terms of pituitary hormone response.
Inhibitory Effect of Progesterone on Occupied Estrogen Receptors of Anterior Pituitary and Uterus in Adult Rats
Authors: Fuentes Miguel A. , Muldoon Thomas G. , Mahesh Virendra B.
Published: September 2006

The acute effects of a single progesterone injection on estradiol receptor (E2R) binding in the anterior pituitary and uterus were examined in the mature ovariectomized rat. Adult ovariectomized female rats receiving estradiol were injected with various doses of progesterone followed 1 h later by a final injection of 2 μg of estradiol. All animals were sacrificed 1 h after estradiol and the E2R binding in the nuclei and cytosol was determined. In the anterior pituitary, progesterone decreased total nuclear E2R in a biphasic inhibitory pattern, with maximal effects at 0.8 and 4 mg/kg body wt doses of progesterone and a smaller decrease with the 2 mg/kg body wt dose. This progesterone‐induced decrease of nuclear E2R was due to a decrease in the occupied form of nuclear E2R. The unoccupied nuclear E2R and cytosol E2R binding were not altered by progesterone administration. In the uterus, progesterone caused a dose‐dependent decrease in total nuclear E2R binding. This effect also occurred in the occupied form of E2R. The uterine unoccupied nuclear E2R and cytosol E2R were not altered by progesterone administration.

These studies emphasize differences in the tissue specificity of progesterone action on occupied nuclear E2R which are presumably responsible for the mediation of estradiol action, and provide a biochemical basis for our previous observations of multiphasic effect of progesterone on gonadotropin secretion.
Effects of Timed Melatonin Infusions and Lesions of the Suprachiasmatic Nuclei on Prolactin and Progesterone Secretions in Pregnant or Pseudopregnant Mink (Mustela vison)
Authors: Bonnefond C. , Martinet L. , Monnerie R.
Published: September 2006

To test the hypothesis that the duration of melatonin secretion may be a critical parameter in the transduction of photoperiodic signals on prolactin and progesterone secretions, timed intravenous melatonin infusions were carried out in intact and ganglionectomized pregnant and pseudopregnant mink. To localize the target sites of melatonin, electrolytic lesions of hypothalamic nuclei were performed in females receiving melatonin infusions. As a control, the first experiment was designed to confirm that pineal denervation by bilateral ablation of the superior cervical ganglion rendered the pregnant mink totally unresponsive to the inhibitory effects of short days on progesterone secretion. In the following experiments, timed intravenous melatonin infusions were carried out in intact and ganglionectomized females from Day 12 to 32 of pregnancy or pseudopregnancy. Daily infusions of melatonin for 16 h in intact females or for 11 or 13 h in ganglionectomized females suppressed the rise in plasma prolactin and progesterone levels. In intact as in ganglionectomized females, daily infusions of melatonin for 9 h delayed the rise in plasma prolactin concentrations without affecting the secretion of progesterone. In ganglionectomized females, saline infusions for 13 h or melatonin infusions for 7h did not modify the secretions of prolactin and progesterone. In ganglionectomized females bearing lesions of the Suprachiasmatic nuclei or the retrochiasmatic area, melatonin infusions for 13 h were still able to inhibit prolactin and progesterone secretions. These results are consistent with the hypothesis postulating that the peak duration of melatonin secretion is a critical parameter for transducing photoperiodic responses in pregnant or pseudopregnant mink. Secondly, they suggest that the Suprachiasmatic nuclei and the retrochiasmatic area are not essential for the action of melatonin in the photoperiodic control of prolactin and progesterone secretions during pregnancy or pseudopregnancy in the mink.
Kappa‐Opioid Receptor Involvement in the Regulation of Pulsatile Luteinizing Hormone Release During Early Pregnancy in the Rat
Authors: Gallo Robert V.
Published: September 2006

The object of this study was to gain further insight into endogenous opioid peptide suppression of pulsatile luteinizing hormone (LH) release in early gestation in the rat by examining whether selective blockade of mu ‐, delta ‐, or kappa‐opioid receptor(s) results in stimulation of pulsatile LH secretion at this time. Previous reports demonstrated stimulation of pulsatile LH release during early gestation by intravenous infusions of naloxone, an endogenous opioid peptide receptor antagonist whose binding is not specific to a single class of opioid peptide receptors. In the present study, naloxone infused intraventricularly similarly stimulated an increase in pulsatile LH release on Days 7 to 8 of gestation. Antagonists of specific opioid peptide receptor subtypes were thus given by this route. Administration of nor‐binaltorphimine, an antagonist of kappa‐opioid receptors, but not β‐funaltrexamine or ICI 174, 864, antagonists of mu‐ and delta‐opioid receptors, respectively, exerted a stimulatory action on both LH pulse amplitude and frequency similar to that of naloxone, indicating involvement of this opioid peptide receptor subtype in the endogenous opioid peptide suppression of pulsatile LH release in early gestation in the rat.
Effect of Naloxone on the Pulsatile Secretion of Luteinizing Hormone in Gonadectomized Male and Female Ferrets Before and After Oestradiol Replacement
Authors: Lambert G. M. , Erskine M. S. , Baum M. J.
Published: September 2006

Intravenous infusions of the opioid receptor antagonist, naloxone, caused a significant rise in luteinizing hormone (LH) pulse frequency in male and female ferrets which had been gonadectomized 10 days earlier while in breeding condition; mean LH concentrations and LH pulse amplitudes were not affected. By contrast, naloxone failed to stimulate LH pulse frequency, or other LH parameters in gonadectomized ferrets of either sex which received daily injections of a low dose of oestradiol. Our results for the ferret, in which the female is an induced ovulator, resemble those previously obtained in another induced ovulator, the rabbit. They contrast, however, with the results of numerous studies using spontaneously ovulating species in which sex steroids, if anything, facilitate the ability of naloxone to stimulate LH secretion.
‘Peripheral’ Benzodiazepine Receptor Ligands Stimulate Prolactin Release in the Rat
Authors: Calogerot Aldo E. , Kamilaris Themis C. , Johnson Elizabeth O. , Gold Philip W. , Chrousos George P.
Published: September 2006

High concentrations of ‘peripheral’ benzodiazepine binding sites have been described in the pituitary gland and in several other endocrine glands, such as the adrenal glands and the testes. The role played by these receptors on the regulation of the endocrine system is largely unknown. In this study, we report the effects of two ligands of the ‘peripheral’ benzodiazepine receptor, Ro5–4864 and PK 11195, on prolactin (PRL) release in the adult male rat. Ro5‐4864 stimulated PRL release with half maximal and maximal stimulatory doses of about 0.6 and 1.2 mg/kg, respectively. Pretreatment with the ‘peripheral’ benzodiazepine receptor antagonist PK 11195 did not have any effect on Ro5‐4864‐induced PRL release. Accordingly, PK 11195, given alone, stimulated PRL release in a dose‐dependent fashion. To examine whether the stimulatory effect of Ro5‐4864 and PK 11195 on PRL release was due to a direct effect of these compounds at the pituitary gland, we used primary cultures of anterior pituicytes. Neither Ro5‐4864 nor PK 11195 had an effect on basal PRL release nor were these agents capable of modulating thyrotropin‐releasing hormone‐stimulated or dopamine‐inhibited PRL release.

These findings suggest that administration of agents that interact with the ‘peripheral’ benzodiazepine binding receptor cause PRL release without directly stimulating the pituitary gland. We speculate that Ro5–4864 and PK 11195 increase plasma PRL levels by modulating brain release of neurotransmitters and/or neuropeptides involved in the regulation of PRL release.
Involvement of Cholecystokinin in Food Intake: I. Concentrations of Cholecystokinin‐Like Immunoreactivity in the Cerebrospinal Fluid of Male Rats
Authors: Lindén A. , Uvnäs‐Moberg K. , Forsbergt G. , Bednar I. , Södersten P.
Published: September 2006

To investigate the role of central neural cholecystokinin in food intake the concentration of cholecystokinin‐like immunoreactivity was measured by radioimmunoassay in the cerebrospinal fluid of male rats. Characterization of the molecular forms of Cholecystokinin was made by high‐performance liquid chromatography before radioimmunoassay. Four molecular forms of cholecystokinin corresponding to standards of the tetra‐, penta‐ and sulphated octapeptide and a late eluting peak probably corresponding to cholecystokinin‐58 were found. The concentration of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid decreased in response to 48 h of food deprivation and was restored after 1 h of food intake, the main increase occurring within 30 min after the onset of feeding. Cholecystokinin‐like immunoreactivity increased in the cerebrospinal fluid 10 min after an intraperitoneal injection of 5 μg cholecystokinin octapeptide, a dose which also suppressed the amount of food consumed during 1 h in rats deprived of food for 48 h. Intraperitoneal injection of the peripheral, cholecystokinin A receptor antagonists lorglumide (450 μg) or L‐364. 718 (20 μg) reversed the inhibitory effect of cholecystokinin octapeptide on food intake and prevented the increase of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid. It is suggested that central neural cholecystokinin is involved in the control of food intake and that this is reflected in the alterations in cholecystokinin‐like immunoreactivity in the cerebrospinal fluid which occur in response to food deprivation and food intake. However, a variety of ways of intracerebral administration of Cholecystokinin octapeptide failed to affect food intake in food‐deprived rats. The possibility is raised that Cholecystokinin octapeptide acts in concert with another transmitter in the brain to affect food intake.