bluuebunny/crossref_metadata_2025 huggingface dataset:
Pituitary Binding Sites for Gonadotrophin‐Releasing Hormone in Booroola Merino Ewes which were Non‐Carriers or Homozygotes of the Fecundity Gene F
Authors: Fleming J. S. , Lun S. , Smith P. , McNatty K. P.
Published: September 2006

Pituitary binding sites for gonadotrophin‐releasing hormone (GnRH) were examined in Booroola ewes on Days 4 and 12 of the oestrous cycle and more than 12 months after ovariectomy. No significant differences were observed in the affinity of the binding sites for [125 I]D Ala6, des Gly10 GnRH ethylamide, in non‐carriers (++) or homozygotes of the fecundity gene (FF), in intact or ovariectomized animals (overall Ka= (1.8 ± 0.1) × 109 M−1; mean ± SEM, n = 67). In ++ ewes, the number of GnRH binding sites on Day 4 of the oestrous cycle (0.199 ± 0.025 fmol/mg pituitary, n = 8) was significantly greater (P<0.05) than on Day 12 (0.107 ± 0.012 fmol/mg pituitary, n = 12). In contrast in FF ewes the number of binding sites on Days 4 and 12 were similar (Day 4: 0.119 ± 0.030, n = 8; Day 12: 0.092 ± 0.014, n = 10). On Day 4, but not Day 12, the binding site numbers were significantly higher in ++ compared with FF pituitaries (P<0.05). Likewise on Day 4, but not Day 12, the plasma concentrations of follicle‐stimulating hormone were significantly higher (P<0.005) in FF (1.60 ± 0.15 ng/ml) than ++ ewes (0.96 ± 0.10 ng/ml). After ovariectomy, no gene‐specific differences in binding site numbers were noted despite significantly higher plasma follicle‐stimulating hormone concentrations in FF animals. No gene‐specific differences in plasma luteinizing hormone concentrations were observed in these animals on Days 4 or 12, or after ovariectomy. Moreover, luteal phase plasma progesterone concentrations were also similar between ++ and FF ewes. We conclude that the gene‐specific differences in pituitary responsiveness to GnRH and in pituitary gonadotrophin output are unlikely to be due to differences in GnRH receptor binding affinities.
Estradiol Regulation of Estrogen Receptor Messenger Ribonucleic Acid in Rat Mediobasal Hypothalamus: An in situ Hybridization Study
Authors: Lauber Andrea H. , Romano Gary J. , Mobbs Charles V. , Pfaff Donald W.
Published: September 2006

We have used in situ hybridization to investigate estradiol regulation of estrogen receptor (ER) mRNA in regions of the mediobasal hypothalamus which contain ER and are related to specific neuroendocrine functions. Ovariectomized rats were treated with oil or 10 μg estradiol benzoate for 2, 4, 18 or 24 h. Brains were sectioned and hybridized with a [3 H]single‐stranded DNA probe prepared from the pORF cDNA of the human ER gene and exposed to autoradiographic emulsion for 4 months. Specificity of labeling was determined by counting the number of grains over cells in hypothalamic regions known to bind estradiol, compared to cells in the thalamus and cortex, and by comparing with sections pretreated with ribonuclease or hybridized with a [3 H]single‐stranded message‐sense (control) probe. Labeling for ER mRNA was distributed differently than glucocorticoid and thyroid hormone receptor mRNAs, and was regulated by estrogen differently than progestin receptor mRNA. These differences indicated specific hybridization for ER mRNA. ER‐expressing cells constituted 11.5% of the cells in the dorsomedial nucleus, 30% of the cells in the arcuate nucleus and 43% in the ventromedial nucleus, in close accordance with previous studies of ER autoradiography and binding. Quantitative analysis showed that the highest level of ER mRNA was present in the ovariectomized controls. ER mRNA levels fell 42% (ventromedial), 64% (arcuate), or remained unchanged (dorsomedial) 18 h following estradiol benzoate treatment. The pattern of decrease was similar for cells in the ventromedial nucleus and arcuate nucleus. These data show that estrogen regulation of ER mRNA in brain parallels that reported for MCF‐7 cells and rat uterus. These results also demonstrate that in situ hybridization can be used to detect and measure the relative level of a low abundance mRNA in a heterogeneous tissue in which only 12% to 40% of the cells in limited regions express the message.
Sex Differences and Steroid Control of Testosterone‐Metabolizing Enzyme Activity in the Quail Brain
Authors: Balthazart J. , Schumacher M. , Evrard L.
Published: September 2006

The activity of three testosterone‐metabolizing enzymes (aromatase, 5α‐reductase and 5β‐reductase) was determined in the quail brain using the Palkovits punch technique combined with a very sensitive radioenzyme assay. Sex differences and the effects of gonadectomy and testosterone treatment on the activity of the three enzymes were quantified in eight brain nuclei which are implicated in the control of various aspects of reproductive behavior and physiology. The aromatase was only present in a few brain areas in which its activity was strongly controlled by testosterone. In two brain regions (medial preoptic nucleus and preoptic area in general) the activity of the enzyme was higher in males than in females. These sex differences disappeared in gonadectomized birds and in gonadectomized birds treated with testosterone, suggesting that they might only result from different circulating steroids in both sexes. However, in the posterior part of the medial preoptic nucleus, there was a strong tendency for the induction of aromatase by testosterone to be larger in males than in females. This supports our earlier finding that in the preoptic area, the aromatase activity is sexually differentiated. This difference probably has a restricted neuroanatomical localization and could only be demonstrated by more precise anatomical methods such as immunocytochemistry. The two testosterone reductases (5α and 5β) showed a more homogeneous distribution in the brain. They were not affected by the hormonal treatments or the sex of the birds except for the 5β‐reductase which was significantly more active in three brain nuclei of the females (ventromedial nucleus of the hypothalamus, area hypothalamica lateralis and tuber) by comparison with the males. These sex differences were maintained irrespective of the hormonal status of the birds suggesting that they might be organizational in nature. The relation of these enzymes and their regulation to the control of reproduction is discussed and the usefulness of this approach combining punch technique and radioenzyme assay is evaluated.
Beta‐Adrenergic Stimulation Decreases Glial and Increases Neural Contact with the Basal Lamina in Rat Neurointermediate Lobes Incubated in vitro
Authors: Smithson K. G. , Suarez I. , Hatton G. I.
Published: September 2006

Physiological stimuli such as dehydration and lactation/suckling of the young have been found to induce reversible changes in the relationships of neural and glial elements with the basal lamina of the neurohypophysis. Such stimulation is associated with a decline in the extent of basal lamina occupied by glial processes and an increase in nerve terminals abutting the lamina. One possible mechanism playing a role in these changes is the activation of beta‐adrenergic receptors on the neurohypophysial glia (the pituicytes), since such cells in primary culture from adult rats undergo dramatic morphological transformation when stimulated with beta‐adrenergic agonists. We sought to determine if changes similar to those seen in vivo and predicted from the responses of cultured cells would occur with beta‐adrenergic stimulation of the isolated neurointermediate lobe in vitro. Neurointermediate lobes from adult male rats were incubated in artificial cerebrospinal fluid containing ascorbic acid alone (control) or in the same medium with either 10−8, 10−7 or 10−5 M isoproterenol for 15 min after a 30‐min period of preincubation in control medium. Quantitative ultrastructural analysis revealed significant decreases in pituicyte and, corresponding increases in neural, membrane abutting the basal lamina at the lower two drug concentrations. These results support the findings of other studies suggesting a beta‐adrenergic mediation of pituicyte morphology and a role for beta‐receptors in control of posterior pituitary function.
The Olfactory Bulbs Tonically Inhibit Serum Gonadotropin and Prolactin Levels in Male Hamsters on Long or Short Photoperiod
Authors: Pieper David R. , Lobocki Catherine A. , Thompson Melinda , Subramanian Marappa G.
Published: September 2006

Bilateral removal of the olfactory bulbs (BX) inhibits the testicular regression associated with maintenance of golden hamsters on short photoperiod (10L:14D). The present study was done to examine the reproductive endocrine changes following BX of hamsters, to test whether BX increases gonadotropin secretion by enhancing the rate of metabolism of peripheral testosterone, and to determine whether BX inhibits the response to photoperiod by blocking chemosensory signals from conspecifics.

BX resulted in a marked increase in tonic serum gonadotropin levels in pre‐pubertal (23 days old) and adult hamsters maintained on long photoperiod (14L:10D). Maintenance on 10L14D inhibited gonadotropin secretion in BX hamsters, but this only reduced the previously elevated levels to those of the sham group on stimulatory photoperiod, and the testes therefore remained large.

BX hamsters on 10L:14D had a higher post‐castration increase in serum luteinizing hormone than sham‐operated hamsters. Following testosterone replacement (20 mm Silastic capsules), BX animals had lower serum testosterone and higher serum follicle‐ stimulating hormone levels than the sham group. BX hamsters had a shorter mean half‐time for disappearance of testosterone from serum following removal of the capsule, but some animals in the sham group also metabolized testosterone rapidly.

Isolation in cages receiving air filtered to remove pheromonal type molecules did not affect the rate or degree of testicular regression in response to short days.

We conclude that the olfactory bulbs tonically inhibit gonadotropin release in golden hamsters on long or short photoperiod. The olfactory bulbs may facilitate the negative feedback of testosterone and may inhibit testosterone metabolism, but there were also steroid‐independent effects. The influence of the olfactory bulbs on the hamsters' response to short days is apparently not related to chemosensory information from other hamsters.
The Olfactory Bulbs Enhance Reproductive Hormone Secretion in Male Rats on Long or Short Photoperiod
Authors: Pieper David R. , Lobocki Catherine A. , Thompson Melinda , Subramanian Marappa G.
Published: September 2006

Unlike seasonally breeding species such as the Syrian hamster, Sprague‐Dawley laboratory rats do not normally respond to short photoperiod (6L18D) with reproductive regression. However, removal of the olfactory bulbs (BX) unmasks a photoperiodic response in pre‐pubertal rats so that blinding or short photoperiod results in an inhibition of reproductive hormone secretion and/or a delay in pubertal development. This is apparently mediated by pineal melatonin which inhibits gonadotropin and/or prolactin secretion, but the mechanism by which BX facilitates the response to photoperiod is not clear.

Experiment I was performed to determine serum levels of reproductive hormones at frequent intervals following BX and/or maintenance on short days. Twenty‐three‐day old male rats were BX or underwent sham BX (SH). They were thereafter maintained on a 14L:10D (long photoperiod) or 6L:18D photoperiod for the duration of the study. At 6 weeks following surgery, BX rats on either photoperiod had smaller testes than the SH groups. At week 8, the BX group on 6L:18D had smaller testes than the other three groups. There were transient reductions in serum luteinizing hormone and follicle‐stimulating hormone in the BX rats on short photoperiod, but there were prolonged effects of BX decreasing prolactin levels in rats on long or short photoperiod. In SH rats, testosterone was elevated for weeks 6 through 10 of the study, and BX blocked this increase.

Experiment II was performed to determine whether BX alters testosterone feedback on gonadotropin secretion. Twenty‐three‐day old male rats were BX or underwent SH operation and were then returned to a room on 14L10D. Six to 8 weeks later, all animals were castrated and placed on 6L18D or returned to 14L:10D. Eight weeks following castration, the rats were implanted with Silastic capsules containing 0, 10, 20 or 40mm testosterone. The post‐castration increase in serum luteinizing hormone and follicle‐stimulating hormone was lower in the BX than SH rats. In long photoperiod, serum luteinizing hormone and follicle‐stimulating hormone were often lower in the BX rats receiving no testosterone replacement or lower doses of testosterone than in the SH group receiving similar capsules. Maintenance on short photoperiod increased the responsiveness to testosterone so that even the rats receiving low doses of testosterone had very low luteinizing hormone and follicle‐stimulating hormone levels whether they were SH or BX.

In summary, BX rats on long or short photoperiod had lower serum prolactin and testosterone levels than the comparable SH group and BX inhibited the post‐castration increase in gonadotropin secretion. The data therefore suggest that the olfactory bulbs tonically enhance reproductive hormone secretion (especially around the time of pubertal development).
Autoradiographic Localization of Insulin‐Like Growth Factor I Binding Sites in the Bovine Adrenal Gland and on Cultured Bovine Adrenal Chromaffin Cells
Authors: Marley Philip D. , Haynes Kerry M. , Wertherf George A. , Perlman Robert L.
Published: September 2006

Previous studies have reported the presence of binding sites for insulin‐like growth factor I (IGF‐I) in membranes prepared from isolated bovine adrenal medullary cells, and IGF‐I was found to regulate the secretory function of bovine chromaffin cells. In the present study, binding sites for IGF‐I have been localized in sections of bovine adrenal gland and on cultured bovine adrenal medullary cells, using [125 l][Thr59]‐IGF‐l as the ligand in conjunction with qualitative autoradiographic techniques. Binding sites were present throughout the adrenal gland and were distributed evenly over all cortical cell layers and over both adrenaline and noradrenaline cell types in the medulla. They were also present at lower density over blood vessels and nerve bundles and over the capsule. The binding of radioligand was to a single class of sites with Kd 0.61 nM, and was completely displaced by excess unlabelled [Thr59]‐IGF‐l and by insulin (Actrapid, Kd 1.04μM). Binding sites were also identified on single cells in primary monolayer cultures of bovine adrenal medullary cells. More than 96% of the cells possessed binding sites, although only 85% of such cells were chromaffin cells, as previously determined from dopamine β‐hydroxylase immunohistochemical staining. The results suggest that IGF‐I may affect the maturation, growth or function not only of adrenal chromaffin cells but also of many others cell types in this tissue.
6‐Hydroxydopamine Lesion of Ventral Tegmental Area Dopaminergic Cell Bodies does not Impair Neuroendocrine Responses to Environmental Stimuli
Authors: Rivet Jean‐Michel , Stinus Louis , Le Moal Michel , Mormède Pierre
Published: September 2006

To evaluate the influence of dopamine neurons in neuroendocrine responses to environmental stimulations, rats received bilateral injections of the neurotoxin 6‐hydroxydopamine in the ventral tegmental area. Six weeks after the lesion, forebrain areas lost up to 88% of their dopamine content, and the areas innervated by the noradrenergic bundle, which passes through the ventral tegmental area, were also depleted of noradrenaline. Despite these profound changes of catecholamine content, we show that the responses of major neuroendocrine systems to environmental stimuli were not modified. Basal levels of circulating adrenocorticotropin, corticosterone, prolactin and catecholamines, as well as their increase by novel environment exposure, handling and/or electric footshock, were not modified by the lesion. These results favor the hypothesis that the effect of dopamine depletion is more on behavioral response initiation and/or performance than on the cognitive functions or emotional processes. They also question the importance of the ventral noradrenergic bundle in the activation of the hypothalamo‐pituitary‐adrenal axis by stressful stimuli.
Involvement of Cholecystokinin in Food Intake: II. Lactational Hyperphagia in the Rat
Authors: Lindén A. , Uvnäs‐Moberg K. , Forsberg G. , Bednar I. , Enerotht P. , Södersten P.
Published: September 2006

The role of Cholecystokinin in the hyperphagia of lactation was studied by measuring the concentration of this hormone in plasma and cerebrospinal fluid in relation to food intake in lactating rats. Cholecystokinin was measured by high‐performance liquid chromatography and radioimmunoassay in plasma and by radioimmunoassay in cerebrospinal fluid. Plasma concentrations of Cholecystokinin were increased in freely‐fed lactating rats compared with non‐lactating, regularly cycling rats. However, after 24 h of food deprivation the concentration of plasma Cholecystokinin was markedly decreased in the lactating rats to levels which were lower than those of non‐lactating animals. Furthermore, plasma levels of Cholecystokinin did not increase in response to 1 h of feeding in lactating rats, whereas in non‐lactating rats they did. In contrast, the concentration of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid was the same in freely‐fed lactating and non‐lactating rats. As in plasma, food deprivation markedly decreased the levels of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid of lactating rats but unlike in plasma, the levels were restored by feeding. The levels of cholecystokinin‐like immunoreactivity were not changed under these conditions in the non‐lactating rats. These results show that there is no correlation between the concentration of Cholecystokinin in plasma and cerebrospinal fluid, which supports the suggestion that the cholecystokinin‐like immunoreactivity in the cerebrospinal fluid is derived from the brain. Removal of the litter from lactating rats deprived of food for 24 h reduced food intake and increased the concentration of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid, but not in plasma. The inhibition of food intake caused by an intraperitoneal injection of Cholecystokinin octapeptide increased after litter removal. It is suggested that hunger in the lactating rat is reflected by a decrease in the levels of cholecystokinin‐like immunoreactivity in the cerebrospinal fluid and satiety by the restoration of these levels.
Characterization of Glucocorticoid Binding Capacity in Human Mononuclear Lymphocytes: Increase by Metyrapone is Prevented by Dexamethasone Pretreatment
Authors: Rupprecht Rainer , Kornhuber Johannes , Wodarz Norbert , Göbel Claudia , Lugauer Johannes , Sinzger Christian , Beckmann Helmut , Riederer Peter , Möller Otto Albrecht
Published: September 2006

Autoregulation of receptor systems by their own ligands is a well established biological phenomenon. While down‐regulation of the glucocorticoid binding capacity by glucocorticoids has been shown in animals and humans, data on up‐regulation processes in humans are lacking. To further explore glucocorticoid receptor plasticity in relation to endogenous ligands, glucocorticoid binding parameters were assessed in 15 healthy controls before and after oral administration of 1.5 g metyrapone with and without dexamethasone pretreatment. Administration of metyrapone resulted in blockade of the feedback of the hypothalamic‐pituitary‐adrenal system as shown by the rise in adrenocorticotropin levels, while pretreatment with 1 mg dexamethasone completely suppressed adrenocorticotropin concentrations. Glucocorticoid binding sites per lymphocyte exhibited an increase of 63% following metyrapone administration, which was prevented by dexamethasone pretreatment. Comparison of morning and afternoon glucocorticoid binding sites per cell in 11 healthy volunteers further revealed a diurnal rhythm of glucocorticoid receptor sites. These data suggest that human lymphocyte glucocorticoid receptors are under autoregulatory control.
11Beta‐Hydroxysteroid Dehydrogenase Messenger Ribonucleic Acid Expression, Bioactivity and Immunoreactivity in Rat Cerebellum
Authors: Moisan Marie‐Pierre , Seckl Jonathan R. , Brett Lawrence P. , Monder Carl , Agarwal Anil K. , White Perrin C. , Edwards Christopher R. W.
Published: September 2006

11β‐Hydroxysteroid dehydrogenase (11β‐OHSD) metabolizes corticosterone to inactive 11‐dehydrocorticosterone and thus protects non‐specific mineralocorticoid receptors from exposure to corticosterone in the kidney in vivo. Clearly, 11β‐OHSD might also regulate corticosterone access to glucocorticoid receptors. We have investigated cerebellum, a tissue with high glucocorticoid receptor, but very low mineralocorticoid receptor levels and have shown marked 11β‐OHSD bioactivity with similar co‐substrate requirements and inhibition kinetics to the renal enzyme. 11β‐OHSD messenger ribonucleic acid was expressed in cerebellum and was localized in Purkinje and granule cells. This distribution was confirmed immunohistochemically. Thus, we provide evidence for 11β‐OHSD in cerebellum and suggest that it may regulate the access of corticosterone to glucocorticoid receptors in addition to mineralocorticoid receptors.
Vasopressin Release Following Microinjection of Angiotensin II into the Caudal Ventrolateral Medulla Oblongata in the Anaesthetized Rabbit
Authors: Allen A. M. , Mendelsohn F. A. O. , Gierobat Z. J. , Blessing W. W.
Published: September 2006

Stimulation of the caudal ventrolateral medulla in rats and rabbits elicits secretion of vasopressin from the neurohypophysis. Inhibition of the area attenuates baroreceptor‐initiated vasopressin secretion. Angiotensin II receptor binding sites and angiotensin‐like immunoreactive nerve terminals are localized in the caudal ventrolateral medulla, in the region of the A1 noradrenaline‐synthesizing neurons. To examine the possible functional role of angiotensin II in this region, we have microinjected angiotensin II into the A1 area in the urethane‐anaesthetized rabbit. Microinjection of angiotensin II (0.1 to 100 pmol in 100 nl) stimulated vasopressin secretion (plasma vasopressin concentration increased from 24 ± 8 pg/ml to 104 ± 8 pg/ml following microinjection of 10 pmol angiotensin II) and produced a depressor response with bradycardia. The responsive area was confined to the region of the A1 cell group. AII responses were blocked by prior intramedullary injection of an angiotensin II receptor antagonist, [Sar1, Thr8] angiotensin II (2 nmol in 200 nl), which had no effect on the response to the excitatory amino‐acid N‐methyl‐D‐aspartate. Following spinal blockade of efferent sympathetic activity, microinjections of angiotensin II into the caudal ventrolateral medulla caused a similar increase in plasma vasopressin concentration without a depressor response, demonstrating that the stimulation of vasopressin release by angiotensin II was not secondary to hypotension. Microinjection of [Sar1, Thr8] angiotensin II dramatically attenuated the normal secretion of vasopressin in response to systemic haemorrhage. Following injection of vehicle into the caudal ventrolateral medulla, haemorrhage stimulated an increase in plasma vasopressin concentration from 3 ± 1 pg/ml to 335 ± 75 pg/ ml (n = 5). After microinjection of [Sar1, Thr8] angiotensin II the haemorrhage‐induced change in vasopressin concentration was only 17 ± 6 pg/ml to 35 ± 7 pg/ml (n = 4). Microinjection of the N‐methyl‐D‐aspartate receptor antagonist, DL‐amino‐5‐phosphonovaleric acid (5 nmol, n = 4), did not alter the secretion of vasopressin in response to haemorrhage. These results in the anaesthetized rabbit suggest that angiotensin II in the caudal ventrolateral medulla may have a physiological role in baroreceptor control of vasopressin release.
Corticotrophin‐Releasing Factor‐41 in the Human and Rat—Utility of a Highly Sensitive Enzyme Amplified Immunometric Assay
Authors: Milton N. G. N. , Hillhouse E. W. , Fuller J. Q. , Self C. H.
Published: September 2006

We have developed a highly sensitive and specific immunoassay for human/rat corticotrophin‐releasing factor‐41 (CRF‐41) to enable determination of immunoreactive CRF‐41 levels in biological samples. To achieve high specificity, sensitivity and speed we have used two antisera in a sandwich enzyme immunoassay combined with enzyme amplification. The assay has a sensitivity of 0.08 fmol/well compared with radioimmunoassay sensitivities of 0.5 fmol/tube and is highly specific for the intact CRF‐41 molecule. Measurement of samples is complete within 24 h compared with the 5 days required to obtain sensitive radioimmunoassay measurement. The assay has been used to measure both rat hypothalamic CRF‐41 tissue content and release in vitro with good correlation when compared to radioimmunoassay measurement using antisera rC70 (0.983) or R1 (0.953). The assay only measures immunoreactive CRF‐41 coeluting with human/rat CRF‐41 and its oxidized form Met [O21,38]CRF‐41 in human and rat tissue extracts separated by high‐performance liquid chromatography. The ability to measure immunoreactive CRF‐41 in unextracted plasma allows rapid measurement and eliminates multiple extraction steps.
Effect of Atrial Natriuretic Peptide on the Vasopressin Response to Osmotic and Hemorrhagic Stimuli in Dogs
Authors: Inoue Minoru , Kimura Tokihisa , Ota Kozo , Shoji Masaru , Sato Kazutoshi , Ohta Masahiro , Yamamoto Tadasu , Yoshinaga Kaoru
Published: September 2006

Effect of atrial natriuretic peptide (ANP) on the vasopressin response to osmotic stimulation (Experiment I) as well as to hemorrhage (Experiment II) was investigated in anesthetized dogs. Moreover, cardiovascular function and renal water and electrolyte excretion were studied. In Experiment I, 2.5 M NaCI, containing 0.02 μg.kg 1 of ANP, was infused intravenously at a rate of 0.2 ml.kg−1, min 1 after one bolus injection of 0.75 μg.kg 1 ANP (HSA group). In the control group, 2.5 M NaCI alone (HS group) was infused. The infusion was continued for 75 min. In Experiment II, 0.15 M NaCI, containing the identical dose of ANP to Experiment I (HA group), or 0.15 M NaCI alone (H group) was infused intravenously during bleeding at a rate of 1 ml.kg−1.min −1 for 40 min. In Experiment I, infused ANP suppressed the vasopressin response to a mild osmotic stimulation, but not to a strong osmotic stimulation and attenuated ANP release and a rise in arterial and central venous pressures in response to plasma volume expansion, without the enhanced natriuresis. In Experiment II, infused ANP neither impaired the vasopressin response to bleeding nor potentiated a fall in mean arterial pressure and central venous pressure.

In conclusion, ANP at physiological and/or supraphysiological range may suppress the vasopressin response to a mild osmotic stimulation, but not to a strong osmotic stimulation and to hemorrhage. In addition, ANP given intravenously may attenuate ANP release and a rise in blood pressure without any natriuresis.
Sex‐Related Differences in Dendritic Branching of Cells in the Prefrontal Cortex of Rats
Authors: Kolb Bryan , Stewart Jane
Published: September 2006

Male and female Sprague‐Dawley rats were given either gonadectomies or sham surgery on the day of birth. In adulthood they were sacrificed and prepared for Golgi‐Cox staining. Using a camera lucida technique, layer II/III pyramidal neurons were drawn in the anterior cingulate cortex areas 1 and 3 and the agranular insular cortex and the number of dendritic branches on the apical and basilar dendrites were then summarized. The results showed that the dendritic arbor of prefrontal cortical cells varied as a function of sex and neonatal gonadectomy. In cingulate 3, castrated males had a smaller arbor on the left relative to normal males, whereas, in cingulate 1 the reverse was found. In addition, females had less apical arbor than males in the cingulate areas, whereas, in the agranular insular cortex, females had greater apical arbor than the males. Furthermore, in this region, gonadectomized groups had less arbor than their respective control groups. Finally, in the agranular insular cortex, the dendritic arbor was greater in the left hemisphere.
Somatostatin Depletion by Cysteamine Increases Somatostatin Binding and Growth Hormone‐Releasing Factor Messenger Ribonucleic Acid in the Arcuate Nucleus
Authors: Bertherat J. , Berod A. , Normand E. , Bloch B. , Rostenef W. , Kordon C. , Epelbaum J.
Published: September 2006

We have previously described somatostatin (SRIF) pericellular binding sites in the vicinity of growth hormone‐releasing factor (GRF)‐containing cells in the ventrolateral part of the arcuate nucleus (ARC) of the male rat. To further assess the direct role of SRIF on GRF messenger ribonucleic acid (mRNA) levels in the mediobasal hypothalamus, we depleted endogenous SRIF by cysteamine (CS; 300 mg/kg body wt 6 h prior to sacrifice). In the ventrolateral part of the ARC, there was a 2‐fold increase (P<0.05) in [125I]SRIF specific binding and GRF mRNA‐labelled cell numbers in the CS‐treated group as compared to control animals. Furthermore, there was a positive correlation between [125I]SRIF binding and the number of GRF mRNA‐labelled cells (r = 0.89; P<0.01). In contrast, such effects were not observed along the base of the ventromedial nucleus where pericellular [125I]SRIF binding was not associated with GRF mRNA‐labelled cells. These results provide functional evidence for a direct SRIF inhibition, through specific receptors, of GRF mRNA levels in ARC neurons.
Non‐Adrenocorticotropin Mediated Effects of Endogenous Corticotropin‐Releasing Factor on the Adrenocortical Activity in the Rat
Authors: van Oers Joep W. A. M. , Tilders Fred J. H.
Published: September 2006

Diurnal changes in plasma corticosterone concentrations of rats are supposed to be controlled by low amplitude changes in plasma adrenocorticotropin (ACTH) that run in phase with marked changes in adrenal sensitivity to ACTH (1, 2). These sensitivity changes are probably under neuronal control (3), but the mechanisms remain to be elucidated. By the use of a highly specific monoclonal antibody to rat corticotropin‐releasing factor (CRF) (4), we studied the role of endogenous CR‐ in these processes. Blockade of endogenous CRF prevented the evening rise in plasma ACTH and reduced corticosterone levels to less than 10%. The CRF antibody did not affect morning ACTH concentrations but nevertheless reduced morning corticosterone levels by 40% to 60%. In dexamethasone‐treated rats, immunoneutralization of endogenous CRF caused a similar reduction in the plasma corticosterone response to exogenous ACTH. We conclude that endogenous CRF plays a physiological role in controlling the adrenal sensitivity to ACTH.
Noradrenaline, Dopamine and Serotonin Release in the Paraventricular and Supraoptic Nuclei of the Rat in Response to Intravenous Cholecystokinin Injections
Authors: Kendrick K. , Leng G. , Higuchi T.
Published: September 2006

Microdialysis sampling was used to measure noradrenaline, dopamine and serotonin release in the supraoptic and paraventricular nuclei of urethane‐anaesthetized rats following intravenous injection of 20μg/kg cholecystokinin. This dose of cholecystokinin stimulates oxytocin release from the posterior pituitary, while slightly inhibiting vasopressin release. Dialysis probes were placed in the paraventricular nucleus, and into dorsal or ventral regions of the supraoptic nucleus. Samples were collected at 10‐min intervals in each animal before, during and after two injections of cholecystokinin, and following a control injection of 0.9% NaCI. The injections of cholecystokinin stimulated significant increases in the concentrations of noradrenaline, dopamine and serotonin in the paraventricular nucleus and of noradrenaline and serotonin in the dorsal supraoptic nucleus region. Conversely, in the ventral supraoptic nucleus region a significant reduction in noradrenaline release was observed, but dopamine and serotonin concentrations were not significantly affected. The control injections did not alter noradrenaline, dopamine or serotonin release.
Prolactin Implants in the Hypothalamus Inhibit Prolactin Surges During Pregnancy and Alter Prolactin Release in Response to Dopamine Receptor Blockade
Authors: Vidal Gabriela , Mathiasen Joanne R. , Voogt James L.
Published: September 2006

The purpose of this study was to determine whether prolactin (PRL) could exert a negative feedback on it's own secretion during pregnancy and following ovariectomy, and to determine the possible mechanism by which this feedback acts. Implantation of ovine PRL into the arcuate nucleus‐median eminence area of the hypothalamus completely inhibited the nocturnal PRL surge during pregnancy in the rat, and lowered baseline PRL to almost undetectable levels in the ovariectomized rat. When ovariectomized rats implanted with ovine PRL in the hypothalamus were injected with the dopamine receptor blocker domperidone the PRL response was significantly lower than in control rats implanted with albumin. Pregnancy increased the ability of domperidone to cause PRL release following ovine PRL implantation compared to what occurred in ovariectomized rats. These results suggest that PRL implantation increases the secretion of dopamine from the tuberoinfundibular neurons, resulting in a decrease in PRL secretion.
Neurophysins, rather than Receptors, are Involved in [3H]Oxytocin and [3H]Vasopressin Binding Detected by Autoradiography in the Hypothalamo‐Neurohypophyseal System
Authors: Freund‐Mercier M. J. , Stoeckel M. E. , Waeber C. , Kremarik P. , Palacios J. M. , Richard Ph.
Published: September 2006

The goal of the present experiments was to analyse the binding of oxytocin (OT) and vasopressin (VP) in the hypothalamo‐neurohypophyseal system to determine whether [3H]OT and [3H]VP binding in this system involved interaction with receptor sites or with neurophysins. Using quantitative autoradiography, several experiments were performed to compare [3H]OT‐ and [3H]VP‐binding characteristics in this system and in brain areas containing identified receptor sites. Saturation experiments indicated much lower affinity of [3H]OT and [3H]VP binding in the magnocellular nuclei and neural lobe than on brain receptors. Competition experiments using selective ligands indicated interaction with neurophysins rather than with receptors in the hypothalamo‐neurohypophyseal system. This system was never labelled in the presence of a [125I]OT antagonist, a selective OT receptor ligand. In contrast with receptors elsewhere in the brain, the magnocellular nuclei were labelled by [3H]OT and [3H]VP in the absence of MgCI2. In the pituitary neural lobe, density of binding sites was moreover obviously related to the amount of neurosecretory granules, as seen in acutely dehydrated rats. Taken together, these data strongly suggest that in the hypothalamo‐neurohypophyseal system [3H]OT and [3H]VP bind to neurophysins rather than to specific receptors.
Immunohistochemical Localization of Multiple Forms of Gonadotropin‐Releasing Hormone in the Brain of the Adult Frog
Authors: di Meglio M. , Masucci M. , D'Aniello B. , Lela L. , Rastogi R. K.
Published: September 2006

Immunohistochemical mapping with antibodies against four different types of gonadotropin‐releasing hormone (GnRH)‐like neuro‐peptides has been studied in the brain of adult Rana esculenta. This study confirms the earlier described distribution pattern of the immunoreactive mammaiian GnRH system in the frog brain, as well as revealing that this system of neuronal cell bodies and fibres is immunopositive to antisera for mammalian, chicken‐I, chicken‐II and salmon GnRH‐like molecules. The results also indicate coexistence of the four GnRH variants in the same anatomical areas. The presence of immunoreactive fibre endings in the cerebellum is also described, perhaps for the first time in the vertebrate brain. In addition, it was found that many immunoreactive GnRH fibres arising in the anterior preoptic area and thalamus‐periventricular area project posteriorly to reach the interpeduncular nucleus‐tegmentum area, thus connecting the diencephalon with the rhombencephalon. These data provide further information on the complex GnRH system in the frog brain. What role(s) in vivo the non‐mammalian forms of GnRH‐like peptides may play in amphibian reproduction is briefly discussed, and in the light of paucity of data it is here stressed that more amphibian species should be studied.
In vivo Intracellular Recording of Neurons in the Supraoptic Nucleus of the Rat Hypothalamus
Authors: Dyball R. E. J. , Tasker J‐G. , Wuarin J‐P. , Dudek F. E.
Published: September 2006

Intracellular recordings were made from cells in the hypothalamic supraoptic nucleus in the urethane‐anaesthetized male rat using the ventral surgical approach. Impalements lasted from 5 min to 1 h and recorded cells had an input resistance of 55 to 170 megohms. Spikes of over 50 mV were recorded from 14 cells which could be antidromically activated by stimulation of the neural stalk. The spikes showed a hyperpolarizing afterpotential and the broadening characteristic of rapidly firing magnocellular neurons, which recovered rapidly (<200 ms). When depolarized, the cells showed evidence of a transient potassium current. Recurrent synaptic coupling between the recorded cell and adjacent cells would be expected to alter the hyperpolarizing afterpotential of an antidromic spike as compared with a spontaneous spike; no perceptible difference in the waveforms of the different types of spike could be detected in 11 spontaneously active cells. Application of just subthreshold stimuli to the neural stalk did not evoke depolarizing or hyperpolarizing potentials. Suprathreshold shocks to the neural stalk, when the antidromic spike was prevented by collision, also had no discernible effect on membrane potential. Thus intracellular recordings from magnocellular neurons in vivo revealed electrophysiological properties similar to those seen in vitro. No evidence for synaptic interconnection between magnocellular neurons was found in male rats.
Changes in the Release of Gamma‐Aminobutyric Acid and Catecholamines in the Preoptic/Septal Area Prior to and During the Preovulatory Surge of Luteinizing Hormone in the Ewe
Authors: Robinson Jane E. , Kendrick Keith M. , Lambart Christine E.
Published: September 2006

The technique of intracranial microdialysis was used to monitor changes in the outflow of the catecholamines, noradrenaline, adrenaline and dopamine and the inhibitory amino‐acid γ‐aminobutyric acid (GABA) in the preoptic/septal area of the conscious ewe during an oestradiol‐induced surge of luteinizing hormone (LH). The same animals were sampled twice from an identical brain site, once in the presence of oestradiol and once in its absence, when no surge occurred and LH levels remained low. Changes in the outflow of GABA, noradrenaline and adrenaline (but not dopamine) were related to changes in LH secretion. Specifically, GABA outflow was maximal in the hours following oestradiol administration but began a sustained fall some 10 h before the surge began, to level off just before the first increment in LH secretion. Low GABA concentrations were maintained until after gonadotrophin levels had once more returned to baseline. The release of all three catecholamines was pulsatile. Noradrenergic activity was greater in the presence of oestradiol although activity did not alter over the 20 h of sampling. The pulse frequency of adrenaline was maximal in the hours immediately prior to the LH surge and minimal in the hours following its initiation. These data suggest that a decrease in GABAergic transmission in the vicinity of the LH‐releasing hormone cell bodies is a necessary component of the neural mechanism by which the oestradiol‐induced surge of LH is generated. A general increase in noradrenergic activity coupled with changes in the release of adrenaline at the time of the surge may be additional prerequisites for successful ovulation.
Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength
Authors: Thiery J‐C.
Published: September 2006

In the ewe, plasma luteinizing hormone and prolactin concentrations exhibit seasonal variations. During long days, inhibition of pulsatile luteinizing hormone secretion is mediated by monoamines. In a model of ovariectomized ewes bearing a subcutaneous oestradiol implant, we previously showed that the steroid‐dependent inhibition of luteinizing hormone involves the A15 dopaminergic nucleus of the retrochiasmatic area. In the present work, we compared the aminergic activities of tele‐diencephalic structures in groups of ovariectomized ewes under artificial illumination for short versus long days (8 versus 16 h/day of light, respectively). Half the animals in each group were bearing a subcutaneous oestradiol implant. Using high‐performance liquid chromatography and electrochemical detection, we measured the levels of amines and amine metabolites in ‘punches’ of tissues from regions containing luteinizing hormone‐releasing hormone axon terminals or cell bodies and catecholaminergic structures. Concurrently, we checked the pulsatile luteinizing hormone release and plasma prolactin concentration to assess the ability of our model to mimic seasonal changes in the hormonal status.

As expected, ovariectomized ewes with a subcutaneous oestradiol implant showed an inhibition of the pulsatile luteinizing hormone release under long days. A higher concentration of plasma prolactin was also observed under long days, without any effect of the steroid treatment. Under this light regimen, statistically significant higher contents of dopamine than under short days were found in the stalk‐median eminence. Larger contents of homovanillic acid, a dopamine metabolite, and 4‐hydroxy‐3‐methoxyphenylethyleneglycol (MHPG), a noradrenaline metabolite were observed in the infundibular nucleus, while the catechola‐mines themselves remained unchanged. Furthermore, oestradiol also significantly increased the content of MHPG in the latter structure. During long days, animals without oestradiol treatment exhibited a significant lower content of noradrenaline in the A15 nucleus, without any alteration of the dopamine content. Daylength or oestradiol treatment had no significant effects on the levels of amines or amine metabolites in the preoptic or septal areas. Thus, our results in the ewe underline the role played by the medial basal hypothalamus in the catecholaminergic regulation of seasonal changes in hormone release and suggest modifications in the turnover of the neurotransmitters in some structures.
A Role for Vasopressin in the Stress‐Induced Inhibition of Gonadotrophin Secretion: Studies in the Brattleboro Rat
Authors: Cover P. O. , Laycock J. F. , Gartside I. B. , Buckingham J. C.
Published: September 2006

The effects of stress on the secretion of adrenocorticotrophin, corticosterone and luteinizing hormone (LH) in rats congenially lacking hypothalamic vasopressin (Brattleboro rats) and in normal controls of the parent strain (Long Evans) have been compared in an attempt to examine the role of vasopressin in the stress‐induced depression of gonadotrophin secretion. In the Long Evans rats, stress (0.6 mg/100g histamine, ip) initiated, within 5 and 20 min respectively, significant (P <0.01, Student's t‐test) increases in the plasma adrenocorticotrophin and corticosterone concentrations. It also caused a reduction in the serum LH concentration which was maximal at 5 min. By contrast, in the vasopressin deficient Brattleboro rats, stress had no effect on the serum LH concentration and produced only modest increases in pituitary adrenocortical activity compared with those in Long Evans controls. Pretreatment of both Long Evans and Brattleboro rats with dexamethasone (20μg/100 g ip, daily for 3 days) effectively abolished the pituitary‐adrenal response to stress. The steroid treatment also prevented the stress‐induced suppression of LH in the Long Evans rats; indeed, these animals, unlike the vehicle‐treated controls, exhibited a rise in serum LH concentration within 5 min of exposure to stress. Stress did not affect the serum LH concentrations in steroid‐treated Brattleboro rats. The results confirm previous reports that vasopressin is required for the full expression of the pituitary‐adrenocortical response stress. They also provide novel evidence which suggests that vasopressin released in stress contributes to the impairment of gonadotrophin secretion.
Neurotransmitter‐Mediated Changes in the Electrophysiological Properties of Pituicytes
Authors: Burnard Diane M. , Pittman Quentin J. , MacVicar Brian A.
Published: September 2006

Intracellular recordings were obtained from pituicytes in the neural lobe of the isolated rat pituitary. Like other glia, pituicytes lacked action potentials in response to depolarizing current injection, but they tended to have more positive resting membrane potentials and higher input resistances than astrocytes in other preparations. Dye‐coupling typical of astrocytes was also demonstrated amongst pituicytes, and their morphologies were similar to those of pituicytes stained for glial fibrillary acidic protein. Action potentials, anode‐break spikes or barium spikes were not observed in pituicytes, even under conditions that maximized the elicitation of Ca2+‐dependent responses. This suggests that pituicytes either have no or a very low density of Ca2+ channels or Ca2+ currents that are too small to generate action potentials. Dynorphin A (1–13), a kappa‐opioid agonist, produced long‐lasting increases in pituicyte input resistance with no significant changes in resting membrane potential. Dynorphin's action was concentration‐dependent and was blocked by the opioid antagonist naloxone. This is consistent with previous reports demonstrating kappa‐opioid receptors on pituicytes in the neurohypophysis. The β‐adrenergic agonist isoproterenol (100 μM) reversed the increases in pituicyte input resistance produced by opioid application, with no significant changes in resting membrane potential. The fact that pituicytes responded to neurotransmitters suggests a functional link between pituicytes and neurosecretory nerve fibres.