bluuebunny/crossref_metadata_2025 huggingface dataset:
Afferent Stimulation Regulates Oxytocin Messenger Ribonucleic Acid During Early Lactation in Rats
Authors: Spinolo L. H. , Raghow R. , Crowley W. R.
Published: September 2006

The physiological factors that regulate the levels of oxytocin (OT) mRNA in the rat hypothalamo‐neurohypophyseal system during lactation are unknown. The major objective of the present studies was to test whether afferent stimuli provided by the offspring influence the level of OT mRNA in the magnocellular nuclei of the hypothalamus, i.e. the paraventricular nucleus (PVN), supraoptic nucleus (SON) and anterior commissural nucleus (ACN), during lactation. In addition, these studies provide a detailed description of the changes that occur in OT mRNA levels in these nuclei during pregnancy and lactation. Levels of OT mRNA were determined in the total RNA extracted from pooled PVN/SON/ACN, which were microdissected from pregnant and lactating Holtzman rats, by slot‐blot hybridization. RNA blots were hybridized sequentially with a [32P]5’end‐labeled, 25‐base oligonucleotide probe complementary to bases 912–936 of the OT gene and with a random primer‐labeled cDNA complementary to α‐tubulin mRNA, which was used for normalization. Autoradiographs were quantitated by scanning laser densitometry. Compared to the levels on day 1 of pregnancy (the day of mated estrus) the relative levels of OT mRNA were decreased on pregnancy days 7 and 14, and then returned to the mated estrus value on days 16 to 20. The level of OT mRNA again declined prior to parturition on day 23, although it was restored to the estrus value the day after parturition and generally remained at this level throughout lactation. To assess the influence of stimuli provided by the offspring for the regulation of OT mRNA levels during lactation, lactating females were separated from their litters immediately after parturition or on lactation day 8. As compared to nonseparated, time‐matched controls, removal of the litters immediately after parturition resulted in a statistically significant reduction of approximately 25% in the levels of OT mRNA 24 and 48 h later, which returned to control levels by 72 h. In contrast, removal of the litters on lactation day 8 did not significantly alter the level of OT mRNA in the PVN/SON/ACN over the next 3 days. These findings suggest that the level of OT mRNA in hypothalamic magnocellular nuclei is influenced to some extent by afferent stimuli provided by the offspring during an early period of lactation but, thereafter, becomes unresponsive to removal of this influence. Afferent suckling stimuli may be one component of a multifactorial regulation responsible for the maintenance of OT mRNA expression during lactation.
Functionally and Anatomically Distinct Populations of Vasopressinergic Magnocellular Neurons in the Female Golden Hamster
Authors: Ferris Craig F. , Pilapil Carmencita G. , Hayden‐Hixson Diane , Wiley Ronald G. , Koh Edward T.
Published: September 2006

The present study was done to determine whether the vasopressinergic neurons in the hypothalamus controlling flank marking behavior are distinct from the magnocellular neurons comprising the hypothalamo‐neurohypophysial system. Animals were either hypophysectomized or injected with a suicide transport lectin, volkensin, into the neurohypophysis. Both procedures resulted in a pronounced loss of vasopressin‐immunoreactive perikarya throughout the hypothalamus concomitant with increases in water intake and urine output and decreases in circulating levels of vasopressin. The loss of the hypothalamo‐neurohypophysial system was most pronounced in volkensin‐treated animals that presented with frank diabetes insipidus and exceedingly low levels of plasma vasopressin. However, the vasopressinergic fibers and magnocellular neurons in and around the anterior hypothalamus implicated in the control of flank marking survived the volkensin treatment. Volkensin‐treated animals exhibited levels of flank marking typical of untreated animals. These data suggest the presence of anatomically and functionally distinct populations of vasopressinergic magnocellular neurons in the hypothalamus of the golden hamster.
Cerebral Metabolic and Vasopressin and Oxytocin Responses During Osmotic Stimulation in Conscious Rats
Authors: Kadekaro Massako , Summy‐Long Joan Y. , Harris Jennifer S. , Terrell Mary Lee , Freeman Sondra , Eisenberg Howard M.
Published: September 2006

Intravenous infusion of hypertonic saline increased plasma [Na +] and osmolality and induced a short‐latency drinking response. These changes were associated with increased glucose utilization in the supraoptic and paraventricular nuclei and neural lobe, and decreases in the medial septum and nucleus ambiguus. The increases in glucose utilization were more accentuated in the supraoptic nuclei than in paraventricular nuclei, indicating that they are more sensitive to osmotic stimulation than the paraventricular nuclei. In association with enhanced activity in the hypothalamo‐neurohypophysial system, plasma vasopressin and oxytocin concentrations increased, with a preferential increase of oxytocin over vasopressin. The hormonal contents in the neural lobe were not depleted by the osmotic stimulus despite the large increases of their concentrations in the plasma.
Inhibition of Luteinizing Hormone Secretion in the Ewe by Progesterone: Associated Changes in the Release of Gamma‐Aminobutyric Acid and Noradrenaline in the Preoptic Area as Measured by Intracranial Microdialysis
Authors: Robinson Jane E. , Kendrick Keith M.
Published: September 2006

Progesterone inhibits the pulsatile release of luteinizing hormone (LH) in sheep by an action in the brain to suppress the release of LH‐releasing hormone (LHRH). In addition, progesterone blocks the preovulatory surge of LH in this species. The neural basis of this inhibitory action is unknown, but as LHRH cells do not appear to contain progestin receptors other neural systems must mediate the action of this ovarian steroid on LH release. This study focuses on a possible role for the inhibitory amino‐acid GABA and the monoamines (noradrenaline, adrenaline, dopamine and serotonin). The technique of microdialysis was used to monitor changes in these substances in the vicinity of the LHRH cell bodies (in the preoptic area) both before and following the administration of progesterone. Levels of this steroid, similar to those measured during the mid‐luteal phase of the oestrous cycle, inhibited LH release and this was associated with significant alterations in the release of GABA and noradrenaline (but not adrenaline, dopamine or serotonin). Specifically, progesterone augmented GABA while noradrenaline release was depressed. Whether steroid actions on these neurotransmitters were mediated by opioids was also investigated. This possibility arises because of the reported involvement of opioids in progesterone negative feedback in the ewe. The long‐acting opioid antagonist, naltrexone, was administered and GABA and noradrenaline release monitored for a further period both in the presence and absence of progesterone. Naltrexone significantly depressed GABA release in steroid‐treated (but not untreated) ewes suggesting that the actions of progesterone on GABA are mediated by the endogenous opioid peptides. However, noradrenaline release was unaltered. In an earlier study we demonstrated that GABA release fell prior to the LH surge while noradrenaline release increased. These data, in conjunction with those from the present study, suggest that the mechanism by which progesterone is able to inhibit the preovulatory surge of LH in the ewe is by enhancing GABA and depressing noradrenaline release in the vicinity of the LHRH cell bodies. As opioid tone is also reported to fall prior to the surge, the interaction between opiate and GABAergic systems in the regulation of gonadotrophin secretion warrants further investigation.
A Rat Pituitary Tumour K+ Channel Expressed in Frog Oocytes Induces a Transient K+ Current Indistinguishable from that Recorded in Native Cells
Authors: Meyerhof Wolfgang , Schwarz Jürgen R. , Bauer Christiane K. , Hübel Andreas , Richter Dietmar
Published: September 2006

A voltage‐gated K+ channel protein has been cloned from a cDNA library derived from poly(A)+ RNA of the rat pituitary tumour cell line GH3/B6 by the polymerase chain reaction technique. The clone referred to as RGHK9 encodes a protein sequence very similar to a recently cloned K+ channel protein from rat brain and heart, with deviations in a few amino‐acid positions. In situ hybridization experiments show that RGHK9 mRNA is also present in the anterior pituitary as well as in other brain regions and that it is particularly abundant in the hippocampus. After injection of cRNA transcribed from the RGHK9 cDNA clone into Xenopus oocytes, the expressed protein induces a transient K+ current. Except for the activation kinetics the properties of this current are indistinguishable from that of the native transient K+ current measured in GH3/B6 cells, e.g. both K+ currents are blocked by 4‐aminopyridine and show the same voltage dependence and slope of steady state activation and inactivation as well as identical time constants of, and slow recovery from, inactivation. Taken together, these data show that the outward‐rectifying voltage‐gated K+ channel protein encoded by the RGHK9 cDNA correlates well in its functional properties with that of a very similar, if not identical, K+ channel present in GH3/B6 cells.
Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle
Authors: Heiliwell Rachel J. A. , Williams Lynda M.
Published: September 2006

The distribution of putative melatonin receptors in the sheep has been investigated using in vitro autoradiography and the high affinity, high specific activity ligand 2‐[125l]iodomelatonin. A wide distribution of specific labelling was found in both the ovine brain and pituitary gland as previously reported. Several novel areas of binding were also identified in the present study, including a fine layer of labelling at the medial edge of the diagonal band of Broca, the trigeminal nucleus, laminae II and III of the substantia gelatinosa, the molecular layer of the cerebellum as well as a scattered labelling in the pars distalis of the pituitary. There was no evidence of specific labelling in any of the peripheral tissues examined.

Characterization studies performed on both neuronal and pituitary melatonin binding sites revealed that binding was time‐ and temperature‐dependent and reversible on addition of 1 μM melatonin. The binding of 2‐[125l]iodomelatonin was also competitively inhibited by increasing concentrations of 2‐iodomelatonin and melatonin. The inhibition constants (Ki) estimated for each of these substances were similar for both neuronal and pituitary sites. Saturation studies also revealed similarities between neuronal and pituitary tissues with 2‐[125l]iodomelatonin binding specifically to a single class of high affinity binding sites. Values for equilibrium constants (Kd) were within a range of 28 to 48 pM, and values were found to be not significantly different amongst the four regions of the brain investigated and the pars tuberalis of the pituitary. In contrast, the concentration of 2‐[125l]iodomelatonin binding sites (Bmax) ranged from 3 to 218fmol/mg protein and were maximal for the pars tuberalis.

Saturation studies on brain and pituitary tissues taken from ewes killed either on the day of oestrus or during the luteal phase of the oestrous cycle, indicated that no differences exist in the affinity or concentration of 2‐[125l]iodomelatonin binding in any region between the two times of the cycle investigated.
Ibotenate Lesions of the Diagonal Band of Broca Attenuate Baroreceptor Sensitivity of Rat Supraoptic Vasopressin Neurons
Authors: Cunningham J. Thomas , Nissen Ralph , Renaud Leo P.
Published: September 2006

Previous electrophysiological studies in the rat suggest that neurons in the diagonal band of Broca participate in baroreceptor‐induced suppression of the spontaneous activity of vasopressin‐secreting neurons in the hypothalamic supraoptic nucleus. In order to test this hypothesis, extracellular recordings were obtained from phasically‐active vasopressin neurons in the supraoptic nucleus of anesthetized rats injected at least 3 days previously with ibotenic acid (1.25 μg/250 nl) in the diagonal band of Broca, the medial and lateral septum, or the median preoptic nucleus. In normal rats, brief increases in blood pressure produced by injections of metaraminol (10 μg/10 μl iv) that were sufficient to activate peripheral baroreceptors, suppressed the activity of a majority (21 tested, 19 suppressed) of phasically‐active vasopressin‐secreting neurons. In rats with ibotenic acid lesions of the diagonal band of Broca, the number of phasically‐active neurons that were baroreceptor‐sensitive was significantly reduced (21 tested, 8 suppressed) while lesions of the medial and lateral septum (17 tested, 16 suppressed) or the median preoptic nucleus (21 tested, 20 suppressed) had no effect. The results support the hypothesis that diagonal band of Broca neurons participate in a central pathway mediating the inhibitory effects of peripheral baroreceptor stimulation on the activity of vasopressin‐secreting neurons in the rat supraoptic nucleus.
Hypothalamic Effects of C‐Type Natriuretic Peptide on Luteinizing Hormone Secretion
Authors: Huang Fong‐Lee S. , Skala Karl D. , Samson Willis K.
Published: September 2006

Previous studies have demonstrated hypothalamic sites of action of A‐type natriuretic peptide (ANP) in the inhibition of luteinizing hormone (LH) secretion, acting at least in part, via an opiatergic mechanism. C‐type natriuretic peptide (CNP) was identified recently and is thought to be the predominant brain form of the family of natriuretic peptides. Third cerebroventricular injection of CNP in doses of either 0.1, 1.0 or 2.0 nmole significantly inhibited, in a dose‐related fashion, plasma LH levels when compared to levels present in saline‐injected controls. When compared to the LH‐inhibiting action of ANP, CNP appeared more potent (effective at lower doses) and efficacious (longer duration of action for the maximum effective doses). The LH‐inhibiting effect of CNP was blocked by prior treatment with the δ‐opioid receptor antagonist naltrindole (50 μg), suggesting an enkephalinergic mechanism of action. CNP in log doses ranging from 0.01 to 1,000 nM did not significantly alter LH release from dispersed pituitary cells harvested from random cycle female rats, either under static or dynamic (perifusion) incubation conditions. These results indicate that CNP, like ANP, acts at the hypothalamic level to alter LH secretion and suggest that CNP may be the preferential neuroactive members of this family of peptides.
Pineal Photoreceptor Cells: Photoperiodic Control of Melatonin Production After Cell Dissociation and Culture
Authors: Bégay Valérie , Falcón Jacky , Thibault Christèle , Ravault Jean‐Paul , Collin Jean‐Pierre
Published: September 2006

Trout pineal cells were dissociated using a trypsin‐DNase digestion technique. An enriched population of photoreceptor cells was selected from a Percoll gradient centrifugation. The ability of cultured photoreceptor cells (selected or not on a Percoll gradient) to produce melatonin rhythmically was investigated during seven 24 h light/dark cycles. During each cycle, trout pineal photoreceptor cells released low amounts of melatonin during daytime and high amounts during night‐time. Under continuous darkness, melatonin release was continually high. The profile of its rhythm and that of the activity of the hydroxyindole‐O‐methyltransferase—the last enzyme of the melatonin biosynthetic pathway—depended on the substrates and on the culture media used. Some of them appear suitable for short‐ or long‐term culture of photoreceptor cells permitting the study of their neuroendocrine properties.
Developmental Aspect of Differences in Hypothalamic Preproneuropeptide Y Messenger Ribonucleic Acid Content in Lean and Genetically Obese Zucker Rats
Authors: Sanacora Gerard , Finkelstein Judith A. , Whitet Jeffrey D.
Published: September 2006

The genetically obese Zucker rat is a well characterized model of early onset human obesity. Many of the endocrine and metabolic abnormalities of obese animals are common to other strains of genetically obese animals as well as morbidly obese humans. Neuropeptide Y (NPY), a potent orexigenic agent, was recently found to be elevated in adult obese animals compared to their lean littermates. In this study we first examined hypothalamic expression of preproNPY mRNA, using solution hybridization/ nuclease protection analysis, in phenotypically‐matched, i.e. lean or obese, immature (5‐week‐old) and mature (33‐week‐old) animals. Although changes were not statistically different, a trend toward decreased hypothalamic preproNPY mRNA levels was detected in both lean and obese mature animals. We next compared hypothalamic preproNPY mRNA levels between age‐matched lean and obese animals at 5, 14 and 33 weeks of age and found elevated preproNPY mRNA levels in obese rats at all three ages. These data suggest that increased levels of hypothalamic NPY are an early manifestation of the obese phenotype and may, therefore, contribute to hyperphagia and increased weight gain in obese Zucker rats.
Regulation of Prolactin Messenger Ribonucleic Acid Levels by Estradiol and Dihydrotestosterone as Evaluated by in situ Hybridization Performed on Implanted Pituitary Glands and Anterior Pituitary Cells in Culture in the Male Rat
Authors: Tong Yiai , Veilleux Raymonde , Pelletier Georges
Published: September 2006

We have recently demonstrated that 17ß‐estradiol (E2) administration increases protactin (PRL) mRNA levels in the male rat anterior pituitary gland and that this stimulatory effect is partially inhibited by concomitant administration of dihydrotestosterone. In order to gain more information about the site(s) of action of E2 and dihydrotestosterone on PRL gene expression, we have studied the effects of these two hormones in pituitaries implanted under the kidney capsule as well as in anterior pituitary cells in culture. In implanted pituitaries, PRL mRNA levels were increased by 90% as compared to values obtained in the stalk‐connected pituitaries from the same animals. Administration of E2 induced a further increase of PRL mRNA levels in implanted pituitaries, while dihydrotestosterone did not produce any change in animals which had been treated or not with E2. In anterior pituitary cells in culture, addition of E2 to the culture medium resulted in a 60% increase of PRL mRNA levels over control values. Supplementation with dihydrotestosterone did not induce any variation in the concentration of PRL mRNA in cells which were treated or not with E2. These results indicate that E2 exerts a direct action on PRL cells at the pituitary level and strongly support the key role of the hypothalamus in the inhibitory effect of androgens on estrogen‐induced stimulation of PRL mRNA in the male rat pituitary.
Simultaneous Display of Sexual and Ingestive Behaviour by Rats
Authors: Kaplan J. M. , Bednar I. , Södersten P.
Published: September 2006

Intraoral infusion of sucrose activates consummatory ingestive behaviour in rats selectively, i.e. the rat only emits the responses used to ingest food. Activation of consummatory ingestive behaviour in this way had no effect on the subsequent display of sexual behaviour by male or female rats and vice versa. Rats infused intraorally with sucrose and presented with a sexual partner showed ingestive and sexual behaviour simultaneously. Pretreatment with cholecystokinin octapeptide inhibited the ingestion of sucrose in both males and females but had no effect on the simultaneous display of sexual behaviour. Ingestion of sucrose from a drinking spout, a test in which the rat has to emit responses to obtain food, i.e. show appetitive ingestive behaviour, was inhibited by the presentation of a sexual partner in rats of both sexes. These results show that the mechanisms controlling consummatory sexual and ingestive behaviour operate independently and that the presentation of a sexual partner inhibits appetitive ingestive behaviour.

Daily intraoral infusion of sucrose reduced pellet intake in ovariectomized rats while the rats maintained their body weight. Implantation of an oestradiol‐filled implant reduced body weight and inhibited daily intake of pellets but had no effect on the intake of intraorally administered sucrose. Subsequent removal of the oestradiol implant increased sucrose intake and body weight but did not have a marked effect on pellet intake. Thus, rats respond to a lowering of the set point for body weight by decreasing their intake of the least preferable kind of food and increase their intake of the most preferable kind of food in response to an elevation of the set point for body weight. Ovariectomized rats infused intraorally once daily with a highly nutritive milk diet in the absence of food pellets ingested very large amounts and reduced their intake in response to oestradiol implantation. Thus, although oestradiol can inhibit consummatory ingestive behaviour, its suppressive effect on ingestion cannot be described in terms of selective effects on appetitive and/or consummatory aspects of the behaviour nor in terms of an alteration in the preference for a sweet solution.

Inhibition of ingestive behaviour occurred within 24 h after oestrogen treatment as opposed to stimulation of sexual behaviour which had a longer latency, suggesting that oestradiol affects ingestive and sexual behaviour via different mechanisms. While the mechanisms controlling consummatory ingestive and sexual behaviour must be different, there is evidence for a common mechanism mediating the incentive motivation and reward aspects of these behaviours. The mechanisms which enable rats to select between two, possibly equally rewarding courses of action, i.e. display of sexual or ingestive responses, however, are unknown.
Steroid Regulation and Sex Differences in [3H]Muscimol Binding in Hippocampus, Hypothalamus and Midbrain in Rats
Authors: McCarthy M. M. , Coirini H. , Schumacher M. , Johnson A. E. , Pfaff D. W. , Schwartz‐Giblin S. , McEwen B. S.
Published: September 2006

The gonadal steroids estradiol and progesterone have previously been shown to modulate the specific binding of the GABAA agonist, [3H]muscimol, in the CA1 region of the hippocampus, the ventromedial nucleus of the hypothalamus and the midbrain central gray of ovariectomized female rats. In this report we show a sex difference in the level of binding in the very caudal ventromedial nucleus of the hypothalamus. In contrast to females, there is no steroid modulation of [3H]muscimol binding in the ventromedial nucleus of the hypothalamus and midbrain central gray of males. These effects may be functionally related to GABAergic control of female sexual behavior. In contrast, steroid modulation of [3H]muscimol binding in the CA1 region of the hippocampus occurred to the same degree in males and females, and there was no difference in the level of binding in any region of the hippocampus between gonadectomized males and females.

Incubation of brain slices with progesterone or its metabolite 5α‐3α‐pregnanolone dissolved in ethanol, produced a significant increase in [3H]muscimol binding in most brain regions as compared to control brain slices treated with ethanol alone. Moreover, there was also a marked increase in [3H]muscimol binding in all brain areas in the control condition which contained 100 mM ethanol, as compared to brain slices not preincubated with ethanol. The increase in binding after in vitro treatment with either progesterone or 5α‐3α‐pregnanolone is notably different from that seen after progesterone given in vivo 4 h prior to assay in that it is not site‐specific, does not depend on prior treatment with estradiol and shows no sex difference. These results suggest different mechanisms for progesterone effects on the GABAA receptor when administered in vivo as compared to in vitro.
Reproductive History Affects the Synaptology of the Ageing Gonadotropin‐Releasing Hormone System in the Male Rat
Authors: Witkin Joan W.
Published: September 2006

This study is an examination of the density of synaptic input to gonadotropin‐releasing hormone (GnRH) neurons in young adult and aged retired breeder male rats. In earlier experiments on aged virgin male rats we observed an increase in synaptic input to this specific neuronal population, ascribable in part to synapses containing flattened vesicles, suggesting GABAergic input. The present study utilized retired breeders in order to dissect the effects of ageing from those associated with reproductive behavioral history. Tissue from the preoptic area was treated for the simultaneous electron microscopic immunocytochemical demonstration of GnRH with tetramethylbenzidine and glutamic acid decarboxylase (the essential enzyme in the production of GABA) using 3,3′‐diaminobenzidine. Estimates of the density of synaptic input to the soma of GnRH neurons were made by calculating the percentage of perikaryal membrane with postsynaptic modification. Five GnRH neurons per animal were measured using computerized morpho‐metrics and differences in the percent of membrane with synaptic modification between experimental groups were tested using the Mann‐Whitney U non‐parametric statistic. There was no difference in the total density of synaptic input to GnRH neurons in the young and old animals, or in the proportion of this input that was immunoreactive for glutamic acid decarboxylase. Similar measurements were made on random, non‐identified neurons in the same region and a significant decrease with ageing in total synaptic input was found, though the glutamic acid decarboxylase component was unchanged. The present results are in contrast to our earlier findings on virgin males and suggest that reproductive behavioral experience affects the connectivity of GnRH neurons.
Brain Angiotensin II Receptor Subtypes and the Control of Luteinizing Hormone and Prolactin Secretion in Female Rats
Authors: Stephenson K. N. , Steele M. K.
Published: September 2006

The present experiments examined the role of the two recently identified angiotensin II (Ang II) receptor subtypes, AT, and AT2, in the central nervous system regulation of luteinizing hormone (LH) and prolactin secretion in estrogen‐ and progesterone‐treated ovariectomized rats. In this animal model, intracerebroventricular (icv) injection of Ang II stimulates LH and inhibits prolactin release. The specific Ang II receptor subtype antagonists losartan (AT1) or PD123177 (AT2) were administered (icv) in various doses (10 ng to 1,000 ng) 10 min prior to icv injection of Ang II (100 ng). Control animals were pretreated with artificial cerebrospinal fluid prior to Ang II administration. Blood samples for LH and prolactin determinations were taken from conscious, freely‐moving rats prior to and following injection of the antagonists and Ang II. Water intake was measured.

Ang ll‐induced water intake was attenuated 62% by 1,000 ng losartan; water intake was not affected by lower doses of losartan or by any dose of PD123177. Ang ll‐induced stimulation of LH release was abolished by the 1,000 ng doses of losartan and PD123177 and attenuated by the 500 ng doses of both drugs. Lower doses did not affect Ang ll‐induced LH secretion. Ang ll‐induced inhibition of prolactin release was significantly reduced by the 1,000 ng doses of both losartan and PD123177. Lower doses of either drug did not affect the Ang II inhibition of prolactin release.

Previous studies had shown that Ang II administration into the anterior hypothalamus‐medial preoptic (AHPO) area stimulated LH release. This brain area contains AT1 receptors. To investigate the potential brain site where the AT2 receptor may influence LH release, Ang II was injected into the locus ceruleus, a brain nucleus which contains predominately the AT2 receptor subtype. Ang II administration into the locus ceruleus was paired with an injection of artificial cerebrospinal fluid or Ang II into the AHPO area.

Injection of Ang II into the AHPO area stimulated LH release. Injection into the locus ceruleus did not affect LH secretion, nor did it modify the rise in LH elicited by administration of Ang II into the AHPO area. Plasma levels of prolactin were not altered by any of these injections.

Taken together, these data demonstrate that, in estrogen‐ and progesterone‐treated female rats, icv Ang ll‐induced water intake is mediated by the AT, receptor subtype, while Ang ll‐induced changes in LH and prolactin secretion appear to be mediated by both the AT2 and AT2 receptor subtypes. The latter observations are one of the first suggesting a potential function for the AT2 subtype in vivo, although the physiological relevance of this observation, as well as the site of action for the effects on LH and prolactin, remain to be established.
Dopaminergic Regulation of Galanin Gene Expression in the Rat Anterior Pituitary Gland
Authors: Hyde James F. , Keller Brian K. , Howard Georgette
Published: September 2006

Estrogen dramatically increases galanin mRNA and peptide levels in the rat anterior pituitary gland. We recently reported that galanin secretion in vitro from estrogen‐exposed anterior pituitary cells is regulated by hypothalamic factors; dopamine and somatostatin inhibit galanin secretion, and thyrotrophin‐releasing hormone stimulates galanin release. To determine whether galanin is regulated by a dopaminergic mechanism in vivo, we used ovariectomized Fischer 344 rats treated with 17ß‐estradiol‐containing or empty Silastic capsules. Rats were also administered bromocriptine, a dopamine receptor agonist, haloperidol, a dopamine receptor antagonist, or placebo for 2 weeks. Galanin peptide levels were measured in the anterior pituitary, neurointermediate lobe, medial basal hypothalamus, and plasma by radioimmunoassay. Plasma and pituitary prolactin levels were also determined. Bromocriptine decreased gaianin peptide levels in the anterior pituitary gland of ovariectomized rats by 30%, but had no effect on galanin in the neurointermediate lobe or medial basal hypothalamus. In contrast, haloperidol had no effect on galanin in the anterior pituitary or medial basal hypothalamus of ovariectomized rats, but decreased galanin peptide levels in the neurointermediate lobe. In the anterior pituitary gland of estrogen‐treated rats, bromocriptine increased and haloperidol decreased both galanin and prolactin levels. Galanin mRNA levels were quantified in the anterior pituitary gland by solution hybridization. Bromocriptine increased galanin mRNA levels 3‐fold in the anterior pituitary, whereas haloperidol had no effect. Galanin mRNA levels in the anterior pituitary were elevated 10‐fold by estrogen. Bromocriptine reduced galanin mRNA levels in the pituitary by 50% in estrogen‐treated rats, where again haloperidol had no effect. Estrogen increased plasma galanin levels 4‐fold compared to ovariectomized rats and this effect was reduced 60% by bromocriptine and increased 20% by haloperidol.

We conclude 1) galanin synthesis and release from the estrogen‐exposed anterior pituitary gland is inhibited by a dopaminergic mechanism in vivo, 2) dopamine regulates galanin gene expression in the ovariectomized rat, 3) the changes in galanin peptide levels in the anterior pituitary of rats treated with estrogen and dopamine receptor ligands are primarily due to alterations in peptide secretion, and 4) galanin release from the neurointermediate lobe may also be regulated by a dopaminergic mechanism in vivo. These data, in conjunction with previous studies, provide evidence for the co‐regulation of galanin and prolactin in estrogen‐treated rats, and further discriminate between the regulation of galanin in the hypothalamus and pituitary gland.
Central Amygdaloid Involvement in Neuroendocrine Correlates of Conditioned Stress Responses
Authors: Roozendaal B. , Koolhaas J. M. , Bohus B.
Published: September 2006

The purpose of this study was to examine the effects of bilateral electrolytic lesions of the central nucleus of the amygdala (CEA) in comparison with sham lesions on neuroendocrine responses during conditioned emotional stress in male Wistar rats. Lesions in the CEA, made either before or after the single learning trial of inescapable footshock, failed to affect the conditioned response of plasma epinephrine levels. Plasma levels of norepinephrine showed neither a conditioned stress effect nor were influenced by lesioning. Pre‐training CEA lesions, but not post‐training intervention, abolished the conditioned elevations of circulating plasma corticosterone and prolactin. These results suggest that the CEA is involved in the conditioning rather than the retention of neuroendocrine stress responses. The effects of pre‐training lesioning of the CEA can possibly be explained by a reduced feedback of all these neuroendocrine factors during or shortly after acquisition. In addition, there is a remarkable differentiation between various hormonal correlates of conditioned stress following CEA lesioning. Only corticosterone and prolactin, that appear to be correlates of a passive behavioural stress response, were abolished. The lesions failed to affect the sympatho‐active stress parameters (epinephrine and norepinephrine). Relations between coping strategy—active and passive behaviour—and physiology in connection with CEA functioning are discussed.
The Chicken Vasotocin Gene
Authors: Hamann Danja , Hunt Nicholas , Ivell Richard
Published: September 2006

cDNA clones corresponding to the vasotocin precursor polypeptide were isolated from a chicken hypothalamic library and sequenced. The derived amino‐acid sequence indicates a precursor of comparable structural organization to that described for members of the vasotocin/vasopressin gene family from other species. Unlike in mammals the C‐terminal glycopeptide moiety appears not be cleaved off from the neurophysin. Subsequent screening of a chicken genomic library permitted an analysis also of the vasotocin gene structure and exonic composition. The 5’region upstream of the first exon was sequenced and revealed an unusual pattern of 49 repetitive ‐YYCYCYAAAYY‐ motifs, together with a polyadenyl region supporting a bend in the DNA, and a long pyrimidine‐rich sequence. Three AP2‐like elements, identified in the mammalian vasopressin gene, were also observed in the immediate upstream region. There was no obvious homology to the promoter regions of the known oxytocin genes, nor to any other sequence deposited in available databases, nor to other known cis‐elements.
Tyrosine Hydroxylase Messenger Ribonucleic Acid Levels Increase in A1 but not Locus Ceruleus Noradrenergic Neurons in Proestrous Rats but not in Diestrous or Androgen‐Sterilized Animals
Authors: Liaw Jiin‐Jia , He Ju‐Ren , Barraclough Charles A.
Published: September 2006

Norepinephrine (NE) turnovers (an index of secretion) increase in the hypothalamus of proestrous rats concomitant with luteinizing hormone surges, whereas, neither of these events are observed in diestrous nor in androgen‐sterilized rats. Increased hypothalamic NE release may occur as a consequence of the withdrawal of local inhibitory γ‐aminobutyric acid and opiate controls on specific presynaptic NE terminals and/or as a result of an increase in activity within noradrenergic neurons. Tyrosine hydroxylase (TH) is the rate‐limiting enzyme for the synthesis of NE and our earlier studies revealed that increases in TH mRNA in A1 and locus ceruleus (LC) neurons can serve as an index of increased activity within these cells. In the present study, we evaluated whether TH message levels change in A1 and LC neurons prior to and during the hours when luteinizing hormone surges and increased NE turnovers are observed. As controls, TH mRNA levels in A1 and LC neurons were evaluated at the same hours of day in diestrous day 2 and in androgen‐sterilized rats. In situ hybridization histochemistry and quantitative image analysis methods were used to measure changes in TH mRNA levels.

Luteinizing hormone surges in proestrous rats began at 1500 h, peaked between 1600 and 1700 h and declined, thereafter, to 2000 h. In contrast, plasma luteinizing hormone remained basal throughout the day in diestrous and androgen‐sterilized rats. While A1 neuronal TH mRNA levels did not differ in the three groups of rats during the morning (0930 to 1030 h), these message levels were significantly elevated in proestrous rats during the afternoon (1645 to 1715 h) and remained high at 2000 to 2030 h. In contrast, no changes in TH mRNA levels were observed in A1 neurons throughout the afternoon in diestrous animals or androgen‐sterilized rats. TH mRNA levels in the LC did not differ in the three groups of rats and they remained unchanged throughout the afternoon hours we examined. From these observations we conclude that concomitant with afternoon proestrous luteinizing hormone surges and the accompanying increase in hypothalamic NE secretion, there is an increase in activity within A1 but not LC neurons. These data suggest that the proestrous increase in hypothalamic NE turnover we previously observed is not due solely to withdrawal of local inhibitory controls of presynaptic NE release but it also involves an increase in activity within A1 but not LC neurons.
Regulation of Corticotropin‐Releasing Hormone Receptors and Hypothalamic Pituitary Adrenal Axis Responsiveness During Cold Stress
Authors: Hauger Richard L. , Aguilera Greti
Published: September 2006

The relationship between pituitary corticotropin‐releasing hormone (CRH) receptor changes and corticotrope responsiveness was studied during chronic cold stress. Exposure of rats to 4°C caused a gradual increase in plasma adrenocorticotropic hormone (ACTH), reaching 3‐fold over the basal levels by 6 h (P< 0.005), followed by a reduction to levels only 1.3‐fold over basal by 60 h. Plasma corticosterone was significantly increased after 1 h (P<0.005) and remained elevated for up to the 60 h cold exposure (P < 0.005). No significant changes in plasma thyroid‐stimulating hormone, prolactin, growth hormone or vasopressin were observed at 60 h of cold exposure. CRH receptor concentration in the anterior pituitary was unchanged after 18 or 60 h cold stress, whereas in neurointermediate lobe membranes was markedly elevated. Autoradiographic analysis of pituitary CRH receptors confirmed that the increase in CRH binding was confined to the intermediate pituitary. CRH receptor levels in membranes from two brain areas, frontal cortex and amygdala, were unchanged following 60 h cold stress. The areas under the curve for the plasma ACTH and corticosterone levels following an injection of 10μg/kg ovine CRH in conscious rats, were of similar magnitude in control and 60 h cold exposed rats. Plasma ACTH responses to ether stress were significantly higher in rats exposed to cold for 60 h than in controls. In the intermediate pituitary, basal ß‐endorphin/lipotropin release from isolated intermediate pituitary cells was significantly lower in cold stressed rats, and despite the increase in CRH receptors CRH‐stimulated values were not higher than in controls. Following 60 h cold exposure, immunoreactive CRH content was decreased in neurointermediate pituitary extracts, while it was slightly increased in the median eminence. Exposure to ether for 5 min resulted in a significant decrease in immunoreactive CRH in the median eminence of cold stressed rats, but not in the controls. The data show a lack of correlation between changes in CRH receptor levels and responsiveness of the corticotrope in the anterior and intermediate pituitary lobes. This suggests that postreceptor events and interaction of CRH with other regulators of ACTH secretion are more likely to account for the changes in pituitary responsiveness during chronic stress.
Removal of 3’Untranslated Sequences Dramatically Enhances Transient Expression of Ovine Follicle‐Stimulating Hormone Beta Gene Messenger Ribonucleic Acid
Authors: Mountford Peter S. , Brandon Malcolm R. , Adams Timothy E.
Published: September 2006

The influence of the 3’untranslated (3′‐UT) region of the ovine follicle‐stimulating hormone (FSH) β mRNA on the level of transcript expression was studied. Only very low levels of FSH β mRNA were detected following transient transfection of COS cells with a eukaryotic expression vector containing a full‐length ovine FSH β cDNA that includes 1.1 kilobases (kb) of 3′‐UT. In contrast, deletion of all but 135 basepairs (bp) of the 3′‐UT resulted in a striking increase in FSH β mRNA expression following transfection of the truncated cDNA construct. These observations suggest that sequences within the 3′‐UT of the ovine FSH β mRNA may play a significant role in the post‐transcriptional regulation of FSH β expression.
Thyrotropin‐Releasing Hormone Mediates Growth Hormone Release Induced by Milk and Nursing in Neonatal Rats
Authors: Kacsóh Bálint , Tóth Béla E. , Grosvenor Clark E.
Published: September 2006

Previous evidence from this laboratory suggested that growth hormone (GH) release induced by milk in vitro and by nursing in vivo from neonatal rat pituitary glands is mediated by an alternative GH‐releasing factor(s) (GRF) distinct from GH‐releasing hormone (GHRH1–43). In the present experiments we tested whether thyrotropin‐releasing hormone (TRH) could fulfil the criteria of this alternative GRF in neonatal rats. The water‐soluble fraction of rat milk (infranatant, prepared by ultracentrifugation) and its methanol/acetic acid extract (milk‐borne peptides) stimulated GH release from perifused pituitary glands obtained from 2‐day‐old rats. Dialysis of the infranatant (mol wt cut‐off: 2,000) against 500 volumes of culture medium at 4°C eliminated its GH‐releasing activity in the perifusion system, while the infranatant retained its full GRF‐like activity when incubated at 4°C without dialysis. The milk‐borne GRF eluted as a single peak and coeluted with TRH in a combined gel permeation chromatography (Sephadex G‐10) and perifusion set‐up. Prolactin secretion was also stimulated simultaneously with the release of GH induced either by milk or by TRH. In a stepwise C18 reversed‐phase chromatography, milk‐borne GRF was highly hydrophilic and coeluted with synthetic TRH. The in vitro GH‐releasing bioactivities of synthetic TRH and a milk extract purified in C18 reversed‐phase chromatography were abolished by proline‐specific endopeptidase. Thus, TRH and milk‐borne GRF displayed similar molecular weights, hydropathic characteristics and proteolytic enzyme resistance. In vivo, nursing (which has been reported as a potent stimulus of GH secretion even in the absence of milk‐intake) increased serum GH levels in 2‐day‐old pups. A supramaximal dose of TRH (10 ng/g intraperitoneally) stimulated GH release in 2‐day‐old pups separated from their mothers for 6 h to a similar extent as nursing. Nursing‐induced levels of serum GH were not further elevated by TRH. This failure of TRH to further increase serum GH levels was not due to a maximal GH output by the neonatal pituitary gland, since the GH release induced by the serotonin precursor 5‐hydroxy‐L‐tryptophan was augmented either by TRH or by nursing. These data provide evidence that the milk‐borne GRF‐like activity in vitro is indistinguishable from TRH, and suggest that TRH (probably of hypothalamic origin) might be the mediator of the nursing‐induced release of GH in vivo as a physiological GRF in neonatal rats.
The Biosynthesis of Melanin‐Concentrating Hormone in Trout Kept Under Different Conditions of Background Colour and Stress, as Determined by an in vitro Method
Authors: Baker Bridget I. , Bird David J.
Published: September 2006

The aim of this study was to develop a method to monitor the synthetic activity of neurons which secrete the neurohypophysial melanin‐concentrating hormone (MCH), a hormone implicated in two separate physiological roles in fish—pigmentary regulation and the response to stress. Trout hypothalamic fragments, containing the MCH neuronal cell bodies, were incubated in vitro in a medium including [35S]methionine. Labelled MCH‐related products were separated by immunoprecipitation. Gel electrophoresis showed that radioactive methionine was incorporated into MCH precursors and into mature MCH, much as in vivo. Thus, de novo hormone synthesis continues in vitro. Trout reared at a fish‐farm and adapted to black or white tanks for 39 days displayed nearly a 2‐fold difference in their rate of methionine incorporation. Transferring fish from a black to a white background also doubled the rate of incorporation within 7 days and this rate increased only very slightly during the following 3 weeks. The rate of methionine incorporation by tissue from trout reared in black tanks was very depressed, and 4‐fold lower than that of fish reared in white tanks, suggesting that very long‐term adaptation to one or other background has increasingly marked effects on the activity and perhaps the number of synthetically active neurons.

Stress also influenced the rate of methionine incorporation: a mild daily stress was stimulatory but more frequent stress had an inhibitory effect in many cases. The effects of daily dexamethasone administration were inconclusive.

It is suggested that these differences in methionine incorporation reflect the relative rates of MCH synthesis in vivo, and that the method is useful to investigate conditions which modulate the biosynthesis of MCH in the trout.
Changes in Vasoactive Intestinal Peptide Binding Site Densities in the Female Rat Central Nervous System and Pituitary During Lactation
Authors: Viau Victor , Montagne Marie‐Noelle , Sarrieau Alain , Meaney Michael J. , Rostène William
Published: September 2006

Using quantitative autoradiography, vasoactive intestinal peptide (VIP) binding site densities were investigated in the female rat during lactation. Plasma prolactin levels were significantly (P<0.01) elevated on days 3 and 10 of lactation. In the brain, there was a significant (P<0.05) increase in VIP binding sites during lactation in the striatum, thalamus, anterior portion of the paraventricular nucleus of the hypothalamus, and several cortical areas compared to virgin female diestrous rats. VIP binding density in the anterior pituitary was significantly higher (P<0.01) when measured on day 3 of lactation, and decreased to diestrous levels by day 10. Pup removal resulted in a significant reversal of the lactation‐induced increase in VIP binding density in the thalamus, parietal and insular cortices, and the anterior portion of the paraventricular nucleus. Taken together, modifications in VIP binding site density in the pituitary and in several central areas are associated with changes in the level of prolactin secretion. Moreover, the pattern of VIP receptor induction during lactation suggests a role for VIP in the brain that extends beyond the regulation of prolactin secretion.