bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Neurohypophyseal Vasopressin Release is Associated with Increased Opioid Inhibition of Oxytocin Release
Authors: van de Heijning Bert J. M. , den Herik Ineke Koekkoek‐van , Rots Nynke Y. , Greidanus Tjeerd B. van Wimersma
Published: September 2006

We tested the hypothesis of a cross‐inhibition of oxytocin (OT) release by endogenous opioid peptides co‐released with vasopressin (VP). This opioid cross‐inhibition resulted in a selective block of OT release and hence in preferential release of VP.

The effects of the opiate receptor antagonist naloxone were tested on neurohypophyseal VP release during dehydration, ethanol administration and sulphated cholecystokinin octapeptide (CCK‐8S) application, assuming that the inhibition of pituitary OT release by endogenous opioids increases as neurohypophyseal VP output increases.

A high VP output was found to coincide with increased inhibition of OT release: Subcutaneous injection of graded doses of naloxone (30 min prior to decapitation), augmented OT plasma levels significantly more in 24 h water‐deprived male rats than in normally hydrated rats. Naloxone had no effect on VP release.

Ethanol (10% in saline) administered intragastrically 50 min prior to decapitation and 20 min before subcutaneous naloxone (5 mg/kg) resulted in the inhibition of VP output. The ethanol treatment resulted in a rise in plasma OT levels that was additional to the effect of naloxone. These features were present in normally hydrated as well as in 24 h water‐deprived animals, but were more pronounced in the latter group.

Peripheral CCK‐8S administration induces an abrupt and selective secretion of OT. Blocking the opioid inhibition of OT release with naloxone resulted in a significant rise of OT compared to that with CCK‐8S alone. The magnitude of the opioid inhibition coincided with the activity of the VP system, and a higher dose of naloxone was needed to potentiate the CCK‐8S effect on OT release in the water‐deprived group than in euhydrated rats. No effect of CCK‐8S and/or naloxone was found on VP plasma levels.

The data indicate that opioid peptides co‐released with VP (like dynorphin) may be responsible for cross‐inhibition of OT release during dehydration. This suggests that dynorphin acts in a paracrine way, making it a strong candidate for this role.
Adrenocorticotropin Hyperresponsiveness in Myotonic Dystrophy Following Oral Fenfluramine Administration
Authors: Grice Jeffrey E. , Jackson Jane , Penfold Paula J. , Jackson Richard V.
Published: September 2006

The plasma immunoreactive adrenocorticotropin and cortisol responses to oral fenfluramine hydrochloride (1.5mg/kg body wt) or placebo were examined in 11 patients with myotonic dystrophy, 4 controls with facioscapulohumeral dystrophy, a similarly debilitating muscle wasting disease, and 14 normal controls in single‐blind studies performed in mid‐afternoon.

Mean areas under the adrenocorticotropin response versus time curve were significantly greater in myotonics (2573 + 429 pmol.min/L) than in facioscapulohumeral dystrophy controls (696 + 279 pmol.min/L, P<0.02) and normals (560±61 pmol.min/L, P<0.0001). Corresponding cortisol responses were significantly greater in myotonics (35757 + 3949 nmol.min/L) than in normals (21828±1669 nmol.min/L, P < 0.001), but not significantly greater than those in facioscapulohumeral dystrophy controls (22830 + 6140 nmol.min/L, P = 0.055). No stressful side‐effects which could affect hormone responses, and no significant changes in blood pressure or heart rate were noted.

Fenfluramine activates central serotonergic and/or noradrenergic pathways initiating secretion of corticotropin‐releasing hormone and possibly arginine vasopressin. We postulate that these fenfluramine‐activated pathways are hyperstimulated in myotonics, leading to adrenocorticotropin and cortisol hypersecretion. This may be a manifestation of a general cell membrane defect in myotonic dystrophy. We found a lack of correlation of age (and severity of disease) with adrenocorticotropin response in myotonics, and therefore, the hyperresponse may serve as a useful marker for the disease before development of other overt signs.
Acute Action of Oestrogen on Medial Preoptic Gamma‐Aminobutyric Acid Neurons: Correlation with Oestrogen Negative Feedback on Luteinizing Hormone Secretion
Authors: Herbison Allan E. , Heavens Robert P. , Dye Sandra , Dyer Richard G.
Published: September 2006

The acute effects of oestrogen on the medial preoptic area (MPOA) γ‐aminobutyric acid (GABA) system were examined by delivering an intravenous bolus of 17β‐oestradiol (5 μg/100 g body wt) to conscious ovariectomized rats implanted with microdialysis probes. Fifteen‐min blood samples were taken to determine the time‐course of negative feedback effects of oestrogen on luteinizing hormone (LH) secretion. Two h after administration of 17β‐oestradiol, GABA release from the MPOA was significantly elevated compared with vehicle‐treated controls (P<0.05). The rise in GABA levels continued until the end of the experiment, 4 h after 17β‐ oestradiol, at which time it was over 50% higher than controls (P<0.01). The pulsatile pattern of LH secretion was significantly depressed 2 and 3 h after administration of 17β‐oestradiol compared with controls (P<0.05). To determine the effects of the 17β‐oestradiol treatment on pituitary responsiveness to LH‐releasing hormone (LHRH), a further group of rats were given exogenous LHRH (50ng/100g body wt, intravenously) before and 3 h after vehicle or 17β‐oestradiol treatment and blood samples taken to determine the effect on LH secretion. The maximal LH response to LHRH in 17β‐oestradiol‐treated rats was approximately 50% that of control‐treated values. This study demonstrates the acute and potent action of 17β‐oestradiol on GABA release in the MPOA and lends support to a genomic site of action for oestrogen in modulating neural elements regulating GABA release from the MPOA. These results, showing a parallel decrease in LH secretion with increased GABA levels in the MPOA, suggest a role for GABA elements within the MPOA as a site of oestrogen negative feedback on LH secretion.
Effect of Chronic Nicotine Treatment and its Withdrawal on the Vasopressinergic System in Rats
Authors: Zbuzek Vlasta K. , Zbuzek Vratislav
Published: September 2006

We have studied the effect of chronic nicotine treatment and its withdrawal on the hypothalamo‐neurohypophyseal Vasopressinergic system in male Sprague‐Dawley rats. They were subcutaneously infused with low and high doses of nicotine, free base (0.6 and 6.0 mg/kg/day, respectively) for 28 days, via Alzet osmotic pumps. The studies were carried out immediately after the period of infusion and 1, 7, 14 and 28 (the latter in high dose only) days later. Basal, high K+‐stimulated and total vasopressin release from the superfused neural lobes, the residual vasopressin content in the neural lobes, and hypothalamus and plasma vasopressin concentration were measured by radioimmunoassay.

Treatment with the high dose of chronic nicotine alone decreased vasopressin content in and release from the neural lobe and its plasma concentration, but it did not change significantly the vasopressin content in the hypothalamus. A similar pattern of changes in vasopressin release and plasma concentration, though less pronounced, was observed in the rats infused with the low dose of nicotine.

The withdrawal of the high dose of chronic nicotine gradually returned the decreased plasma vasopressin concentration, and its content in and release from the neural lobe to control values within 2 weeks. However, vasopressin content in the hypothalamus started to decline 1 week after nicotine withdrawal and persisted to decline for at least 3 subsequent weeks. The withdrawal of the high dose was associated with a marked suppression of high K+‐stimulated vasopressin release from the neural lobe for a period of 4 weeks. The withdrawal of the low dose of nicotine exhibited a significant decline in plasma vasopressin concentration for up to 2 weeks only following chronic nicotine withdrawal, tending to return subsequently to control levels.
Effects of Beta‐Endorphin on Pulsatile Luteinizing Hormone and Prolactin Secretion During the Follicular Phase in the Ewe
Authors: Curlewis J. D. , Naylor A. M. , Rhind S. M. , McNeilly A. S.
Published: September 2006

The present study was undertaken to determine the effects of the endogenous opioid ligandβ‐endorphin on pulsatile luteinizing hormone (LH) secretion and plasma prolactin concentrations during the follicular phase of the ewe. Oestrous cycles were synchronized by injection of prostaglandin analogue and, commencing 13 h later, saline or β‐endorphin (2, 10 or 50 μg) was injected intracerebroventricularly at hourly intervals for 3 h. Treatment with β‐endorphin was followed by a significant reduction in LH pulse frequency at all doses due to almost complete cessation of pulses. There were no significant changes in LH pulse amplitude or mean LH concentrations. At the lowest dose ofβ‐endorphin, LH pulses recommenced within 3 h of the last injection in all animals and pulse frequency was not significantly different from the saline‐injected controls during the 3 h post‐treatment period. Following treatment with 10 or 50 μg β‐endorphin, LH pulse frequency remained suppressed during the 3 h post‐treatment period but was not different from saline‐treated controls on the following day. The time to the onset of the LH surge was not affected by intracerebroventricularβ‐endorphin. Plasma prolactin concentrations were significantly increased following intracereb‐roventricular injection of 10 or 50 μg β‐endorphin, declining to control values soon after treatments stopped. Intravenous administration of 50 μg β‐endorphin had no effect on LH but was accompanied by a small increase in prolactin concentrations.

While these results indicate that hypothalamicβ‐endorphin may be involved in the central control of LH and prolactin secretion, they provide no evidence for subtle modulation of LH pulse frequency by this neuropeptide.
Porcine Relaxin Affects the Release of Luteinizing Hormone in Rats
Authors: Summerlee A. J. S. , Mumford A. D. , Smith M. S.
Published: September 2006

The effects of intravenous injection of porcine relaxin on the pulsatile secretion of luteinizing hormone (LH) were investigated in conscious rats. In untreated, ovariectomized animals, relaxin at doses 2.5 to 10/μg/rat caused a dose‐dependent suppression of pulsatile release of LH. At 5μg relaxin, pulses were suppressed for approximately 60 min and there was a significant (P<0.05) fall in mean plasma LH levels. Pulses returned with the same frequency as the pretreatment period but amplitude and nadir of these pulses were significantly (P<0.05) reduced at doses >2.5μg/rat. In ovariectomized rats pretreated with either estradiol or progesterone alone, relaxin did not alter plasma LH levels. In contrast, injection of 5μg relaxin in rats primed with a combination of estradiol and progesterone caused a 90% increase in circulating LH levels. Intracerebroventricular infusion of a specific angiotensin II antagonist blocked the inhibitory effect of relaxin on LH release in untreated, ovariectomized rats and negated the stimulatory effect of relaxin on LH release in estradiol‐progesterone‐primed, ovariectomized rats. The results demonstrate that acute injections of porcine relaxin in ovariectomized rats suppress the pulsatile release of LH. This effect is blocked when the central angiotensinergic system is compromised suggesting that relaxin might act through the central angiotensin system. The findings are in agreement with other studies that indicate relaxin activates the central angiotensin system. It is also possible that relaxin may act at the level of the adenohypophysis to alter secretion of LH but data in the present study suggest that this may not be a significant site of relaxin action.
Identification of a Single Melanin‐Concentrating Hormone Messenger Ribonucleic Acid in Coho Salmon: Structural Relatedness with 7SL Ribonucleic Acid
Authors: Nahon Jean‐Louis , Presset Francoise , Schoepfer Ralf , Vale Wylie
Published: September 2006

Melanin‐concentrating hormone (MCH) is a cyclic neuropeptide possessing antagonistic function to α‐melanocyte‐stimulating hormone and corticotropin‐releasing factor in the control of melanosome dispersion within melanophores and adrenocorticotropin release in fish. We have isolated and characterized MCH cDNAs from coho salmon (Oncorhyncus kisutch). The precursor protein predicted by the longest cDNA consists of 132 amino‐acids with a characteristic signal peptide at the N‐terminus and the biologically active salmon MCH (sMCH) peptide at the C‐terminus. The coho sMCH mRNA and protein sequences are very similar but not identical to the previously reported chum or chinook salmon counterparts, suggesting the existence of species polymorphism. Sequence similarities were revealed between α‐melanocyte‐stimulating hormone and part of the C‐terminal domain of sMCH precursor. Two sMCH genes were found in coho salmon. By contrast to other salmon species, only one major sMCH mRNA was detected in coho species suggesting that differential MCH gene expression might occur in salmon. In addition, under low stringency oligoprobes complementary to the sMCH RNA recognize a 0.3 kb RNA which was identified as the 7SL RNA. The regions conserved between those RNAs fold in a similar secondary structure. These similarities might reflect common ancestry which may have functional significance.
Further Evidence that the Septum is not part of the Main Pathway of the Milk Ejection Reflex in the Rat
Authors: Boudaba Cherif , Poulain Dominique A.
Published: September 2006

The possible role of the medial septum in the control of oxytocin release and of the milk ejection reflex induced by suckling was investigated in lactating rats by using electrical stimulations and lesions. In anaesthetized animals, brief electrical stimulation of the medial septum at 5 to 50 Hz elicited a single brief milk ejection similar to natural reflex milk ejections, whereas prolonged low frequency stimulations (5 to 10 Hz) induced a prolonged inhibition of the reflex. In acute experiments under anaesthesia, lesions of the medial septum did not impair the amplitude and pattern of reflex milk ejections. In chronic experiments, lesions of the medial septum resulted first in a loss of body weight of the mothers and a parallel reduction in growth of the litters. After a few days, the litters gained weight normally, and the pattern of milk ejections was normal. Thus, the pathways which pass through or originate from the medial septum and which are excitatory for oxytocin release appear not to be involved in the regulation of the milk ejection reflex. In view of these results and those from our previous study on the lateral septum, we conclude that the whole septum is not essential to the milk ejection reflex. However, the effects of septal stimulation suggest that the medial and lateral septum may be involved in a secondary neural circuitry that can inhibit the reflex.
Inhibition of Hypothalamic Aromatase Activity by 5 Beta‐Dihydrotestosterone
Authors: Schumacher M. , Hutchison R. E. , Hutchison J. B.
Published: September 2006

A variable amount of circulating testosterone that reaches brain cells is converted to biologically inactive 5β‐reduced metabolites, namely, 5β‐dihydrotestosterone (5β‐DHT) and 5β‐androstane‐3α,17β‐diol (5β,3α‐diol). In avian species, the production of inactive 5β‐DHT and 5β,3α‐diol is highest during embryonic and post‐hatching life. In the present study, we have investigated the possibility that 5β‐reduction may not only correspond to a steroid inactivation pathway, but that 5β‐reduced metabolites of testosterone may exert direct inhibitory effects on enzymatic pathways producing biologically active steroids. When added to hypothalamic homogen‐ates prepared from adult male doves, 5β‐DHT but not 5β,3α‐diol inhibits the activity of the aromatase enzyme, which converts testosterone to 17β‐oestradiol. During the first days after hatching, when the production of 5β‐reduced metabolites is high, the hypothalamic aromatase is also inhibited by 5β‐DHT. We conclude that a high 5β‐reductase activity during sensitive periods for sexual differentiation may protect the avian brain from the differentiating effects of circulating androgens by inhibiting the production of oestrogen.
The Secretory Granule Protein 7B2 is Secreted in Parallel with Proopiomelanocortin and its End‐Products by the Mouse Corticotroph Tumour Cells AtT‐20
Authors: Vieau D. , Tougard C. , Rosenbaum E. , Lenne F. , Bertagna X.
Published: September 2006

First isolated in porcine pituitary glands the protein 7B2 subsequently proved to be a specific biochemical marker of the secretory granules. Likewise 7B2 was detected in almost all normal and tumoral endocrine tissues. Unexpectedly, several authors failed to demonstrate its presence in rat and human adrenocorticotrophin (ACTH)‐secreting cells. In order to definitely establish whether this cell type also produces 7B2 we chose the mouse pituitary corticotroph tumour cell line AtT‐20 as a model. Serial dilutions of the mouse culture medium generated displacement curves parallel to that of the standard in a specific 7B2 RIA directed against the human 7B223–39 fragment. Under basal secretory conditions immunoreactive 7B2 accumulated in the culture medium in parallel with proopiomelanocortin (POMC) and its fragments N‐terminal‐joining peptide (NT‐JP), joining peptide (JP), β‐lipotropin (β‐LPH), and β‐endorphin (β‐end), although at a much lower (approximately 100‐fold) molar concentration. As expected mouse corticotroph cells responded to the stimulatory action of cyclic AMP (3.5 mM) with a preferential increase in the release of POMC end‐products, JP and β‐end, which was accompanied by a parallel increase in immunoreactive 7B2 release.
Simultaneous Monitoring of Cytosolic Free Calcium and Exocytosis at the Single Cell Level
Authors: Chiavaroli Carlo , Vacher Pierre , Vecsey Alice , Mons Nicole , Letari Ornella , Pralong William , Lagnaux Yvan , Whelan Rosemary , Schlegel Werner
Published: September 2006

Quinacrine, a fluorescent basic molecule, accumulates in secretory granules of pituitary cells, as was revealed by its colocalization with immunoreactive prolactin. Thus quinacrine fluorescence may be used to monitor secretory activity at the single cell level. Rat pituitary cells in primary culture were loaded with quinacrine and stimulated with physiological secretagogues, such as thyrotrophin‐releasing hormone or bradykinin, which induced a multiphasic lowering of fluorescence, corresponding to the loss of quinacrine contained in exocytosed granules. Quinacrine was further used in combination with the fluorescent calcium probe fura‐2, in order to monitor simultaneously exocytosis and variations in the cytosolic free calcium concentration, [Ca2+]i. With an appropriate selection of the excitation wavelengths, in dual excitation microfluorimetry experiments, it was possible to distinguish between fluorescence changes due to altered [Ca2+]i versus quinacrine exocytosis. Transient elevations of [Ca2+]i were provoked in individual pituitary cells by enhancing calcium influx through voltage gated channels. In part of the cells an initial increase in [Ca2+]i coincided with stimulated quinacrine release. The approach was also applied to cells of the neuroblastoma line NCB20, where stimulation with bradykinin caused a transient rise in [Ca2+]i, concomitantly with enhanced exocytosis. No increase in exocytosis was ever detected without an elevation of [Ca2+]i, suggesting that in both cellular systems, an increase in [Ca2+]i, is absolutely necessary, but not sufficient to induce secretion.
Production of the Neurosteroid 3alpha‐Hydroxy‐5alpha‐pregnan‐20‐one in Man
Authors: Hiemke Christoph , Banger Markus , Knuppen Rudolf , Haupt Otto , Jussofie Astrid
Published: September 2006

The narcotically active progesterone metabolite 3α‐hydroxy‐5α‐pregnan‐20‐one (HPO) modulates γ‐aminobutyric acid (GABA) neurotransmission by direct actions on the GABAA‐receptor complex. In the present investigation, the formation of HPO was quantified in man. Twenty‐four h urine samples were collected during the night (2300 to 0700 h) and day (0700 to 2300 h) from 11 healthy subjects (31 ± 5 years) for two consecutive days. The concentration of HPO was measured after enzymatic hydrolysis of conjugated HPO and multiple chromatographic separation steps by gas chromatography‐mass spectrometry. The mean excretion rates of HPO were 14.8 ± 11.8 μg/24 h with high inter‐individual variations. There were no significant differences in the production of HPO during the night and day. It seemed unlikely that HPO was primarily formed in the adrenals or gonads since the excretion rates of HPO poorly correlated with the formation of 17‐ketosteroids or 17‐hydroxycorticosteroids that are widely used as indices of adrenal and gonadal steroid production. The data showed for the first time that HPO is produced in male subjects in concentrations similar to that of classical steroid hormones.
Possible Role of Neurokinin A in the Control of Prolactin Secretion in Rats and Hamsters
Authors: Pisera D. , Debeljuk L. , Seilicovich A. , Afione S. , Duvilanski B. , Diaz M. C. , Lasaga M. , Traktemberg R. , Bartke A.
Published: September 2006

The possible role of neurokinin A (NKA) in the control of prolactin secretion was studied in vivo, by injecting anti‐NKA serum to ovariectomized rats treated with estrogens and to proestrous rats and hamsters. Injections of an anti‐NKA serum to ovariectomized rats treated with two doses of 80 μg 17ß‐estradiol 24 h apart, or treated chronically with estradiol implants induced a significant decrease of serum prolactin levels as compared with those of similarly treated rats injected with normal rabbit serum. In proestrous rats, the anti‐NKA serum did not modify the afternoon surge of prolactin or luteinizing hormone, but when the antiserum was injected the day before, on diestrus II, it significantly reduced the prolactin surge during the afternoon of proestrus.

As in these results obtained in the rat, injections of anti‐NKA serum to golden hamsters on diestrus II also significantly decreased the prolactin surge in the afternoon of proestrus.

These results suggest a possible physiological role of NKA on prolactin secretion, exerting a stimulatory influence on the release of this hormone.
Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram
Authors: Lincoln G. A. , Wu F. C. W.
Published: September 2006

Aspartate and glutamate represent a major class of excitatory amino‐acid neurotransmitters in the vertebrate brain, and stimulation of gtutaminergic receptors by the specific agonist N‐methyl‐D, L‐aspartate (NMDA) induces luteinizing hormone‐releasing hormone (LHRH) and LH secretion. In this study, we used NMDA as a probe to investigate the hypothalamic regulation of LH secretion at different stages of a reproductive cycle in Soay rams induced by exposure to alternating 16‐week periods of long and short days. NMDA (20 mg/kg) injected intravenously caused an acute increase in blood plasma concentrations of LH, with a significant increase within 2 to 4 min, and peak levels within 20 min. The magnitude of the response changed markedly during the cycle; it was greatest in the sexually inactive phase under long days (with a linear dose‐response over the range 1 to 20 mg/kg NMDA) and least in the sexually active phase under short days (only 20 mg/kg NMDA produced a small response). Pituitary responsiveness to a standard dose of LHRH (5.3 ng/kg iv) varied only slightly at the different stages and could not account for the observed changes in the LH response to NMDA. There were the expected changes in the endogenous pattern of LH secretion during the cycle, with high frequency LH pulses occurring during the sexually active phase. There was an inverse relationship between the frequency of LH pulses and the LH response to NMDA. Pretreatment of rams with an LHRH antagonist (36 μg/kg iv; Syntex, RS18286) totally blocked the LH response to both NMDA and LHRH, while in a separate study, treatment with dexamethasone (synthetic glucocorticoid, 133.4 μg/kg iv) partially blocked the LH responses. The overall results indicate that NMDA stimulates LHRH secretion in the ram and the response is independent of the activation of the hypothalamo‐pituitary‐adrenal axis. The variation in the LH response during the reproductive cycle may reflect changes in the releasable stores of LHRH in the median eminence. These appear to be depleted in the sexually active phase, when LHRH is secreted in pulses at high frequency. The variation in the response to NMDA may also reflect changes in release of endogenous excitatory amino‐acids, which act via NMDA receptors to form part of the physiological regulation of the reproductive cycle in the ram.
Circadian Variation of Plasma Calcitonin Gene‐Related Peptide in Man
Authors: Wimalawansa Sunil J.
Published: September 2006

Calcitonin gene‐related peptide (CGRP) is one of the most potent endogenous vasodilator peptides known so far. Almost all clinical studies using or measuring CGRP are conducted during the day, and hence this study was carried out to see any variations of CGRP levels in the circulation during this period. Three separate studies were conducted. In the first study, following an overnight fast, sequential samples of blood were taken from six healthy volunteers between 0900 and 2100 h and were assayed for CGRP using a highly sensitive and specific radioreceptor assay. A diurnal variation of CGRP in the circulation (P<0.0001) was demonstrated. No difference in the diurnal pattern of CGRP in plasma was seen between males and females. The range of plasma receptor‐active CGRP was 2.8 to 13.0 pmol/l (mean ±SEM, 7.03±0.28 pmol/l). Two peaks of CGRP were observed in the circulation (increases of ∼100% from the basal levels obtained at 0900 h), one around midday (P<0.0001) and the other in the late afternoon (P< 0.005). To assess the contribution of CGRP released from the gut following food, a second study was carried out in which the protocol of the first study was repeated in three volunteers but avoiding any food during the day. Although a similar diurnal variation of receptor‐recognized CGRP was seen in this study (P<0.01), the changes observed were significantly lower than those observed in the first study, suggesting that the effect of a meal exaggerates the response of diurnal variation of plasma CGRP. In a third study, circadian variation of receptor‐recognized CGRP was examined in three volunteers over a 24 h period. In addition to the diurnal pattern seen with the first study, the plasma CGRP levels continued to decrease up to early morning. The lowest levels of CGRP were detected between 0300 and 0600 h. After this time the levels gradually rose towards midday.

It is well accepted that the incidence of cardiovascular episodes is high during the early hours of the morning. Separate studies are necessary to determine if these low levels of ‘biologically‐active CGRP’ in the early hours of the morning are a coincidence, or whether they play a role (e.g. relative deficiency of CGRP) in contributing to the occlusion of already diseased arteries. Furthermore, the diurnal variations of monomeric CGRP demonstrated here imply that, with any experiments relying on the measurement or infusion of CGRP, timing of blood sampling and relationship to meals are important and should be strictly adhered to in most physiological studies with CGRP. This is the first study which demonstrates the circadian variation in plasma concentrations of CGRP.
Fine Structural Changes in Explants of the Neural Lobe of the Rat Hypophysis
Authors: Dellmann H.‐Dieter , Gabrion Jacqueline , Privat Alain
Published: September 2006

To obtain a purified population of pituicytes, pieces of rat neural lobes were dissected free of the pars intermedia, incubated in a variety of media, and fixed at regular intervals between 7 and 56 days of incubation. Many neurosecretory axons survived for up to 21 days without any apparent signs of degeneration. Most axons, however, degenerated and were progressively phagocytosed and subsequently eliminated by pituicytes and microglial cells. Lysed axons that were not eliminated, persisted as dense bodies or paracrystalline inclusions. After 30 days of culture, cluster‐forming pituicytes predominated the explants. Pituicytes underwent morphologic changes such as medium‐dependent decrease or increase of lipid inclusions, Golgi activation, process extension and interdigitation, formation of gap junctions and bundles of intermediate filaments. At the explant surface in contact with the culture medium, pituicytes differentiated into an epithelial layer of ciliated and microvilli‐bearing cells linked by junctional complexes. Long‐term neural lobe explants are a relatively pure source of viable pituicytes and should be useful for further studies on the functional significance of these cells.
Differential Use of 3’Poly(A) Addition Sites in Vasoactive Intestinal Peptide Messenger Ribonucleic Acid of the Rat Anterior Pituitary Gland
Authors: Chew Li‐Jin , Murphy David , Carter David A
Published: September 2006

The description of vasoactive intestinal peptide (VIP) immunoreactivity in the rat anterior pituitary gland has stimulated much interest in possible autocrine and/or paracrine roles as well as in the regulation of its biosynthesis (1–6). The detection of two VIP transcripts in this tissue, together with the knowledge of the rat VIP cDNA sequence (7), has led us to speculate that they are products of the same gene but as a result of differential transcriptional termination, differ in the length of the 3’untranslated region. In this study, we present evidence for the differential utilization of poly(A) addition sites which accounts for the generation of two distinct VIP RNA species.
A Daily Prolactin Rhythm Persists in the Ewe, Foetus and Newborn Lamb After Maternal Pinealectomy in Late Gestation
Authors: McMillen I. C. , Walker D. W. , Young I. R. , Nowak R.
Published: September 2006

We have investigated the effect of maternal pinealectomy between 104 and 120 days gestation on the daily rhythm in plasma prolactin concentrations in the ewe, foetus and newborn lamb. There was a 24 h prolactin rhythm present in both the intact (n = 4) and pinealectomized (n = 4) ewes. Plasma prolactin concentrations were highest at 2100 h (i.e. 2 h after lights off) and a daily prolactin rhythm was present until at least 24 h before delivery. The mean 24 h foetal plasma concentration of prolactin was significantly higher (P<0.001) in the pinealectomized (35.3 + 1.9 μg/1) than in the intact group (6.9 ± 0.6 μg/1). There was a significant 24 h rhythm in foetal prolactin concentrations and the timing of the daily peak (2100 h) was the same in the foetuses of intact and pinealectomized ewes. During the first 10 weeks after birth there was a significant effect of time of day on prolactin concentrations but the 24 h prolactin profile was significantly different in the lambs delivered to pinealectomized ewes than in the lambs delivered to intact ewes. In the lambs delivered after maternal pinealectomy, plasma prolactin concentrations were higher between 1900 and 2300 h than between 0700 and 1100 h, whereas in lambs delivered to intact ewes, prolactin concentrations were higher at 0100 h than between 1500 and 1700 h. We conclude that the ontogenesis of the daily rhythm in foetal and newborn lamb plasma prolactin concentrations is not dependent on a daily melatonin signal from the ewe.
Interaction of Forskolin and Melatonin on Cyclic AMP Generation in Pars Tuberalis Cells of Ovine Pituitary
Authors: Morgan Peter J. , Lawson Wilfred , Davidson Gary
Published: September 2006

The pineal indoleamine, melatonin, acts on specific secretory cells of the pars tuberalis of the sheep pituitary. Using pars tuberalis cells in primary culture melatonin inhibited forskolin‐stimulated cyclic AMP production in both a time ‐ and dose‐dependent manner, but the nature of the melatonin response was critically dependent upon the stimulatory concentration of forskolin used. Forskolin alone stimulated dose‐dependent cyclic AMP accumulation, which reached an equilibrium state after 15 min. This was maintained for up to 3 h, indicating a lack of desensitization to forskolin. Melatonin (1 μM) inhibited this response by greater than 80% at all doses. However, 100 μM forskolin reduced both the affinity and the number of the melatonin receptors, relative to untreated controls. Consistent with this, melatonin was 100 times less potent at inhibiting forskolin‐stimulated cyclic AMP production, when titrated against 100 μM forskolin as compared to 1 μM forskolin. The response to 1 μM forskolin could be potentiated by 10 μM phorbol 12,13 myristate acetate, but not by calcium ionophore (A23187). This provides evidence for the interaction of the phosphatidylinositol pathway with the cyclic AMP system in these cells. Nevertheless melatonin can inhibit both the potentiated and non‐potentiated response with equal effect.
Functional N‐Methyl‐D‐Aspartate and Non‐N‐Methyl‐D‐Aspartate Receptors are Expressed by Rat Supraoptic Neurosecretory Cells in vitro
Authors: Hu Bin , Bourque Charles W.
Published: September 2006

A considerable amount of evidence has accumulated to support a role for excitatory glutamatergic transmission in the regulation of the hypothalamo‐neurohypophysial system. Glutamate immunoreactivity has been found in axon terminals forming asymmetric synapses on to magnocellular neurosecretory cells and kynurenic acid, a broad spectrum glutamate receptor antagonist inhibits 1) spontaneous electrical activity in vivo, 2) excitatory postsynaptic potentials in hypothalamic slices, and 3) osmotically‐evoked vasopressin release from hypothalamic explants. While this provides strong evidence for glutamatergic regulation of hypothalamic magnocellular neurosecretory cells, the subtypes of glutamate receptors expressed by these cells have not been defined. We have, therefore, obtained current and voltage clamp recordings from supraoptic magnocellular neurosecretory cells in vitro to investigate the functional and pharmacological properties of their glutamate receptors. Application of micromolar concentrations of L‐glutamate, or of the agonists kainate, quisqualate and N‐methyl‐D‐aspartate (NMDA), produced reversible and dose‐dependent depolarizations in all cells tested. These responses were mediated by postsynaptic receptors since they persisted during chemical synaptic blockade with Ca2 + ‐free or tetrodotoxin‐containing solutions. The inward current induced by NMDA showed a marked Mg2+‐sensitive voltage dependence, and was blocked by D, L‐2‐amino‐5‐phosphonovalerate. In contrast, currents induced by kainate and quisqualate showed linear current‐voltage properties and were antagonized by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione. We conclude that both NMDA and non‐NMDA receptors are expressed by magnocellular neurosecretory cells of the rat supraoptic nucleus.
Effects of Estrous Cycle and of in vivo Unilateral or Bilateral Adrenal Demedullation on the Distribution of Norepinephrine and Epinephrine Between Different Zones of the Adrenal
Authors: Bernet François , Maubert Eric , Deloof Sylvie , Bernard Jacqueline , Montel Valerie , Dupouy Jean‐Paul
Published: September 2006

The distribution of norepinephrine (NE) and epinephrine (E) between the capsule/glomerular zone and the remainder of the adrenal was studied in the adult female rat. Both catecholamines were present in these two parts of the gland. The concentration of E was higher than that of NE. In the capsule/glomerular zone the catecholamine concentrations were more than twenty to thirty times lower than in the inner part of the gland. The circulating levels of catecholamines were always very low. The present data also support very weak or no changes in catecholamine concentrations in both parts of the adrenal during the different stages of the estrous cycle.

The plasma levels of both aldosterone and corticosterone, like those of catecholamines, did not vary significantly throughout the estrous cycle. One week after unilateral or bilateral demedullation, both E content and concentration were reduced in the whole capsule/glomerular zone of the adrenal although the NE content did not change. The reduction of NE concentration could be related to the drastic weight increase of this part of the gland on the operated side. Moreover, unilateral demedullation was unable to significantly modify the plasma levels of both E and NE. In contrast bilateral demedullation suppressed circulating E and induced a significant reduction (about 50%) of NE plasma level. The present data suggest: 1) an extra‐adrenal origin for the NE innervation of the capsule/glomerular zone of the adrenal cortex, and 2) a dual origin for E in the capsule/glomerular zone; part of E could arise from the adrenal medulla and part from an extra‐adrenal site.
Oxytocin Excites Neurons Located in the Ventromedial Nucleus of the Guinea‐Pig Hypothalamus
Authors: Inenaga K. , Karman H. , Yamashita H. , Tribollet Eliane , Raggenbass M. , Dreifuss J. J.
Published: September 2006

The area of the ventromedial nucleus of the hypothalamus in the guinea‐pig was shown in autoradiographs to contain high affinity binding sites for oxytocin. In order to ascertain whether these sites may represent neuronal receptors, single‐cell extracellular recordings were obtained from ventromedial neurons in coronal slices of the hypothalamus of adult guinea‐pigs. Oxytocin applied in the nanomolar range excited about half of the neurons tested; none were inhibited. The response to the peptide was reversible and concentration‐dependent. It was exerted directly since it persisted under the condition of synaptic isolation. Moreover, the effect was specific since it could be mimicked by a selective oxytocin agonist and since vasopressin was usually at least 10‐fold weaker than oxytocin. These findings suggest that the binding sites for oxytocin detected by light microscopic autoradiography in the guinea‐pig hypothalamic ventromedial nucleus represent functional receptors.
Haloperidol Inhibits Maternal Retrieval and Licking, but Enhances Nursing Behavior and Litter Weight Gains in Lactating Rats
Authors: Stern Judith M. , Taylor Lisa A.
Published: September 2006

To determine whether the motorically‐active and ‐inactive components of maternal behavior in rats are differentially affected by dopamine, we administered haloperidol, a dopamine receptor antagonist, to lactating rats on day 7 (±1) post‐partum, 3 h after dam‐litter separation and 1 h before their reunion. Compared to treatment with saline or domperidone, a peripherally‐active dopamine antagonist, haloperidol treatment inhibited retrieval and licking of pups in a dose‐dependent manner and hastened the onset of nursing behavior, but impaired the high crouch posture at the highest doses (8 and 10 mg/kg). Also, litters of dams treated with 0.2, 0.4, or 1.0 mg/kg haloperidol gained almost twice as much weight as litters of controls or of dams treated with 5 to 10 mg/ kg haloperidol. To determine whether the milk ejection pattern accounts for differential litter weight gain after moderate and high doses of haloperidol, milk ejections were assessed by pup stretch and nipple‐switching responses for 30 min after the onset of crouching following a 4 h dam‐litter separation on day 12 or 13 post‐partum. The litters of dams treated with 1 or 3 mg/kg haloperidol had substantially greater litter weight gains than litters of control dams or of dams treated with 5 mg/kg haloperidol. The smaller litter weight gain of 5 mg/kg haloperidol litters was due to a retardation of milk ejections in their dams, while the smaller gain of control litters was due, at least in part, to greater behavioral activation by their dams. Non‐dopaminergic effects of large doses of haloperidol (≥5 mg/kg) may have reduced the display of the high crouching posture during nursing and contributed to the retardation of milk ejections. Thus, dopamine is necessary for the motorically‐active components of maternal behavior, but its inhibition may be necessary for the assumption of the immobile nursing postures and for maximal litter weight gains. We hypothesize that extra‐hypothalamic as well as tuberoinfundibular dopaminergic systems are inactivated by the suckling stimulus.
Ultrastructural Characteristics of Estrogen Receptor‐Containing Neurons of the Ventrolateral Nucleus of the Guinea‐Pig Hypothalamus
Authors: Silverman Ann‐Judith , DonCarlos Lydia L. , Morrell Joan I.
Published: September 2006

The ventrolateral nucleus of the hypothalamus (VL) of the guinea‐pig is a key cell group in the neural circuitry underlying the estrogen‐dependent lordosis reflex. The extent to which neurons in the VL are responsive to estrogen or to synaptic inputs depends in part on the presence of specific estrogen and neurotransmitter receptors within the target cells. It also depends on the number, type and location of synaptic inputs. In addition, both sensitivity to circulating hormones and transmitter responsiveness show estrogen‐inducible alterations in the VL. To understand more about the cell types that are directly modulated by estrogens via the nuclear steroid binding protein and the synaptic connectivity of these neurons, we have carried out an ultrastructural study of estrogen receptor‐containing cells in the VL of the female guinea‐pig.

Estrogen receptor was localized for both light and electron microscopy using a specific monoclonal antibody, H‐222, directed against the human estrogen receptor. Numerous immunoreactive neurons were found in the VL. These cells had simple, relatively smooth dendritic processes that were generally unbranched. Reaction product was most intense in the nucleus; lighter deposits were seen in some but not all somata and proximal dendrites. No cell was observed with only cytoplasmic staining. At the ultrastructural level, this distribution of reaction product within cells was confirmed. Gold deposits were associated with euchromatin and excluded from the nucleolus, nucleolar‐associated heterochromatin and Barr body. In the cytoplasm, the small aggregates of gold particles were randomly distributed. Two types of cytologically distinct immunoreactive neurons were characterized. The most numerous category was of large cells with extensive rough endoplasmic reticulum, frequently organized as whorls or ribbons, several stacks of Golgi cisterna, numerous mitochondria and multivesicular bodies. A smaller population, representing approximately 5% of the total, was of much smaller cells which had only a thin rim of cytoplasm around the nucleus, scattered elements of the rough endoplasmic reticulum and a single small Golgi saccule. Based on size, we suggest that the larger neurons are projection neurons and that the smaller ones form local circuits. The larger cells received a dense axo‐somatic and axo‐dendritic innervation. Most of the presynaptic terminals contained small, clear round vesicles; synaptic densities on either pre‐ or postsyn‐ aptic side were absent though a well defined synaptic cleft was evident. Very few synapses were found on the small cells even when serial sections were examined. It is clear that the larger, estrogen receptor‐containing neurons are in a position to integrate both hormonal and neuronal signals and to transmit this information to other regions of the central nervous system involved in the outflow of reproductive behaviors.
In vivo Regulation of Prolactin Gene Expression in the Male Rat: Role of Sex Steroids and Dopamine
Authors: Tong Yiai , Pelletier Georges
Published: September 2006

The influence of sex steroids and the dopaminergic system on the in vivo modulation of prolactin (PRL) mRNA levels was investigated by quantitative in situ hybridization in the male rat anterior pituitary gland. In situ hybridization was performed using a [35S]‐labeled cDNA probe encoding PRL. Orchiectomy performed 14 days earlier did not modify PRL mRNA levels. In orchiectomized rats treatment with the dopaminergic agonist bromocriptine for 14 days decreased PRL mRNA levels by 30%, while in intact animals the same treatment did not induce any changes in PRL mRNA levels. Administration of the dopamine D2 receptor antagonist haloperidol in both intact and orchiectomized rats induced a 4‐fold increase in mRNA levels. Administration of dihydrotestosterone to orchiectomized animals which had been treated or not with haloperidol or bromocriptine did not modify PRL mRNA levels. In orchiectomized animals administration of 17ß‐estradiol (0.25 μg twice daily) for 14 days caused a 4‐fold increase in amounts of PRL mRNA. Administration of bromocriptine to 17ß‐estradiol‐treated animals induced a 15% decrease of PRL mRNA levels compared to those obtained by 17ß‐estradiol administered alone. The concomitant administration of 17ß‐estradiol and haloperidol resulted in a 50% increase in PRL mRNA levels compared to those measured in animals treated with haloperidol alone. The present results clearly demonstrate that in vivo estrogen as well as dopamine‐mediated mechanisms play a regulatory role in PRL mRNA levels in the male rat.
Adrenocorticotropin Release Induced by N‐Methyl‐D‐Aspartate or Stress: Mediation by the Area Postrema
Authors: Ježová Daniela , Opršalová Zdena
Published: September 2006

N‐methyl‐D‐aspartic acid (NMDA) is known to stimulate adrenocorticotropin (ACTH) release after peripheral administration in spite of its inability to readily cross the blood‐brain barrier (BBB). The importance of the area postrema, the hindbrain circumventricular organ which lacks a BBB, for NMDA action and ACTH release during stress was evaluated in this study. ACTH response to NMDA injection (4 mg/kg ip) was significantly reduced in rats with ablation of the area postrema compared to sham‐operated animals. Integrity of the area postrema was also found to be required for full ACTH release in response to two stress stimuli (immobilization, handling). The data show that the area postrema is a brain region involved in the control of the hypothalamic‐pituitary‐adrenocortical (HPA) axis mediating, at least partially, the stimulatory action of NMDA and of stress stimuli on ACTH release.
Fos‐Like Immunoreactivity in the Brainstem of the Rat Following Peripheral Administration of Cholecystokinin
Authors: Luckman S. M.
Published: September 2006

Ninety min after intraperitoneal (ip) injection of Cholecystokinin (CCK, 50 μg/kg body wt) Fos‐like protein was expressed in cells throughout the nucleus of the tractus solitarii (NTS) and area postrema, and also in scattered cells in the lateral reticular area of the brainstem. Using dual fluorescent immunocytochemistry for Fos‐like protein and tyrosine hydroxylase (TH), catecholaminergic cells in the A2 region of the NTS and the A1 region of the lateral reticular area were shown to be activated.