摘要:

The mechanisms of action of glucocorticoid hormones are mediated via specific intracellular receptor proteins. The glucocorticoid receptor (GR) regulates expression of specific target genes or gene networks by ligand‐dependent transcriptional activation, i.e. ligand‐dependent activation of the receptor with subsequent dimer formation and DNA binding. There are a number of factors, such as the receptor concentration, receptor associated proteins, receptor alterations and the effects on the gene network including hormonal regulation of transcription, mRNA splicing and translation, that might influence glucocorticoid responsiveness in a normal and healthy population as well as in different diseases. Several categories of glucocorticoid resistance have been described includinginheritedGR resistance which has been explained in terms of specific mutations and offers an important model for genetic and clinical studies of steroid sensitivity, andrelativeglucocorticoid resistance, which occurs naturally in the course of cellular differentiation, cell to cell or tissue to tissue, since all cells possess receptors for glucocorticoids but do not show the same response to them. From a clinical point of view, it is also interesting to considerpreexistinggenetic susceptibility to glucocorticoids,acquiredchanges in the GR gene structure and organization, including alterations of noncoding sequences, and the importance of mutations, deletions and other changes in the GR gene affecting receptor function. Analysis of mutations within the receptor resulting in relative glucocorticoid resistance, both generalized inherited glucocorticoid resistance (GIGR) and directed mutagenesis, has identified two regions of clustered mutations in the proximity of previosuly identified affinity labeled residues directly affecting the steroid binding function. Finally, studies of New Words primates and cell lines derived from hematologic malignancies constitute animal and human models for the molecular basis of glucocorticoid resistance where a number of inherited and aquired mutations in the GR gene have been demonstra

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04781.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Nitric oxide (NO) is produced by the enzyme NO synthase (NOS) and may be involved in the regulation of nutrient and endocrine homeostasis via actions on neurones of the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. The effects of water deprivation or food deprivation for 4 days on the abundance of messenger RNA encoding NOS in these nuclei in rats were examined usingin situhybridization. Water deprivation markedly increased the abundance of NOS mRNA in both the SON and PVN (225±11% of control, P<0.05 and 261±34% of control, P<0.01 respectively). NOS mRNA abundance also appeared to be increased in magnocellular accessory nuclei. Food deprivation decreased NOS mRNA abundance in the SON and PVN (42±6% and 52±7% of control respectively, both P<0.05), while withdrawal of both food and water produced no significant net changes in the abundance of NOS mRNA. Treatment‐induced alterations in NOS mRNA abundance were reflected by changes in NOS activity, as assessed by NADPH‐diaphorase histochemistry, and NADPH‐diaphorase staining was observed in neurones both positive and negative for oxytocin‐like immunoreactivity. These findings suggest that NOS mRNA abundance, NOS enzymatic activity and presumably NO production are modulated in an activity‐dependent manner in hypothalamic (magnocellular and parvocellular) neurones by alterations in fluid and nutrient homeostasis, and support data from other studies suggesting a role for NO in the central regulation of water and food inta

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04682.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Extracellular recordings of the electrical activity of oxytocin neurones were made from the supraoptic nuclei (SON) of lactating rats, and the milk‐ejection bursts and the background activity of oxytocin neurones were investigated during unilateral and bilateral suckling. When application of pups was limited to the nipples on either the same side (ipsilateral suckling) or the side opposite (contralateral suckling) to the oxytocin neurone recorded, the burst amplitude and background firing rate were significantly (P<0.05) lower and the inter‐burst interval was significantly (P<0.05) longer than during bilateral suckling. Furthermore, the burst amplitude was significantly (P<0.05) lower during ipsilateral suckling than during contralateral suckling. The majority of the oxytocin neurones showed a gradual increase in the burst amplitude during bilateral (88.9%) and contralateral (77.3%) suckling, but during ipsilateral suckling only 40% of the neurones did. The inter‐burst interval became shorter with the progress of the milk ejection reflex during any mode of suckling. Three pairs of oxytocin neurones recorded simultaneously from both SON were successfully tested for the effect of bilateral and unilateral suckling on the electrical activity, and the results showed the same direction of change in the burst amplitude, background activity and burst interval as shown in single side recordings. These findings indicate that the burst amplitude mainly depends on the amount of afferent suckling signals arising from the nipples on the side opposite to the recording side, and that there may exist bilateral summation centres coordinating with the synchronization mechanism of milk‐ejection bursts of oxytocin n

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04703.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

In this study we describe modulatory effects exerted byin vivoactivation of corticosteroid receptors on 5HT responsiveness of rat CA1 pyramidal neurons. In the first series of experiments, adrenalectomized (ADX) rats were injected with corticosterone one hour prior to decapitation (1–1000 μg/100 g body weight) after which 5HT1Ainduced hyperpolarizations were determinedin vitroby means of intracellular recordings. It appeared that 5HT responsiveness was dose‐dependently affected by corticosterone injections: 5HT responses were relatively large when no corticosteroid receptors were activated (ADX); similar 5HT responses were observed or when both mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) were occupied by injection of high doses of corticosterone (100–1000 μg/100 g body weight). However, compared to the latter group, 5HT hyperpolarizations were significantly suppressed in slices from rats that received moderate amounts of corticosterone (10–30 μg/100g). Next, we investigated whether physiological variations of plasma corticosterone levels as occurring in intact rats correlated with the transmitter responsiveness. It was found that high plasma levels of corticosterone due to either stress or exogenous application of high doses of corticosterone correlated with large 5HT‐responsesin vitro. Interestingly, the large 5HT responses recorded after stress were clearly suppressed by pretreatment with RU38486, a GR antagonist. Altogether, this study presents further evidence that 5HT transmission in hippocampal CA1 area is modulated by differential steroid receptor activation as may occur under physiological circumstances due to different plasma concentrat

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04724.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Androgen, mineralocorticoid and glucocorticoid receptors (AR, MR and GR, respectively) are ligand‐activated transcription factors that alter gene expression and have a wide variety of effects in the central nervous system. High levels of AR, MR and GR mRNA have been found in the CA1 pyramidal cell region of the rat hippocampus and all 3 of these proteins bind to a similar hormone response element in DNA suggesting the possibility of common receptor function or cross‐talk between these receptors at the level of transcription. To begin to investigate this hypothesis, we examined the regulation of AR, MR and GR mRNA expression in the rat hippocampus following treatment with androgens in combination with gonadectomy and/or adrenalectomy. Three‐month‐old male Sprague‐Dawley rats were either castrated for 3 weeks, castrated and immediately implanted with 2 Silastic capsules filled with the non‐aromatizable androgen, dihydrotestosterone, or left gonadally intact. Four days prior to sacrifice, these animals were either adrenalectomized or sham operated. GR, MR and AR mRNA were measured in the hippocampal subfields usingin situhybridization. In the CA1 region, dihydrotestosterone treatment of castrates decreased GR mRNA levels to 69 percent of levels found in gonadally intact rats and prevented the adrenalectomy‐induced increases in GR mRNA observed in the gonadally intact and castrated animals. No changes in GR mRNA were observed in the CA3 region or dentate gyrus, where AR expression is low or absent. There was no effect of androgen treatment on MR mRNA levels nor did gonadectomy or androgen replacement alter the increases in MR mRNA following adrenalectomy. AR mRNA levels in the CA1 region were unchanged across all treatment groups.In vitrobinding studies revealed almost complete nuclear occupancy of hippocampal AR in dihydrotestosterone‐treated castrates. No appreciable in vitro binding of dihydrotestosterone to hippocampal MR or GR (Ki≈1500 nM) was observed which suggests that androgen regulation of GR mRNA in the hippocampus is occurring through AR binding. These data demonstrate a functional similarity of androgens and glucocorticoids in the regulation of GR mRNA levels in an area where AR and GR are colocalized. Androgen‐mediated downregulation of GR expression may prove to be an important event in the adaptive responses of CA1 pyramidal cell

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04735.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Estradiol treatment for 48 h increases the density ofα1B‐adrenoceptors in the hypothalamus‐preoptic area of ovariectomized female rats by five‐ to six‐fold. Present studies tested the hypothesis that estradiol elevation of hypothalamus‐preoptic areaα1B‐adrenoceptor density is correlated with increased levels of mRNA for this receptor. We developed a semiquantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) protocol for measuring brainα1b‐adrenoceptor mRNA. The primers chosen yielded the predicted 409 base pair PCR product when used to amplify authenticα1b‐adrenoceptor cDNA. The identity of the RT‐PCR products from rat brain was confirmed by restriction digest analysis and sequencing. Moreover, there was a good correlation between the levels ofα1b‐adrenoceptor mRNA measured by RT‐PCR in liver, whole brain and cerebellum with previous measurements using Northern blots and RNAse protection assays. We then performed RT‐PCR on total RNA from hypothalamic‐preoptic area tissue taken from ovariectomized control rats and from ovariectomized rats injected once or twice with 2 μg of estradiol benzoate at 24 or 24 and 48 h before sacrifice. Exposure to estradiol for either 24 or 48 h significantly increased levels ofα1b‐adrenoceptor mRNA by 86–110% in the hypothalamus‐preoptic area of ovariectomized female rats when compared to oil‐treated controls. We also examined whether estradiol regulatesα1b‐adrenoceptor mRNA in the cortex. Corticalα1b‐adrenoceptor mRNA levels were reduced to approximately 20% of control levels when measured 24 h after hormone injection. A similar decrease in corticalα1b‐adrenoceptor mRNA was observed 48 h after estrogen administration. In summary, estradiol treatment significantly increases the level ofα1b‐adrenoceptor mRNA in the hypothalamus‐preoptic area, a brain region involved in the control of reproductive function. In the cortex, a brain region with relatively few estrogen rece

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04716.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The neuropeptides galanin and pituitary adenylate cyclase‐activating peptide (PACAP) have been implicated in the physiological regulation of lactotroph function. Using the 235‐1 clonal lactotroph rat cell line we have studied the signalling pathways mediating the secretory and mitogenic responses to galanin and PACAP. Both peptides stimulated prolactin release to a similar maximal extent. PACAP (100 nM) stimulated an increase in the proliferation rate of 235‐1 cells, but was significantly less effective than 100 nM galanin (161.8±2.3%vs296.1±9.1% of control). PACAP stimulated cAMP accumulation with an ED50of 3.2 nM, and a maximal effect of almost two‐fold at a concentration of 100 nM. Galanin depleted cAMP, by 30% at a concentration of 100 nM. The aminosteroid phospholipase C (PLC) inhibitor U‐73122 virtually abolished maximal peptide stimulated prolactin release. Depletion of inositol phosphates or downregulation of protein kinase C reduced maximal peptide stimulated prolactin release from about 260% to about 160% of unstimulated release. Both peptides at a concentration of 100 nM caused a sustained increase in intracellular calcium when incubated with cells for 30 min. These results demonstrate that both peptides stimulate prolactin release and the proliferation rate of 235‐1 cells. The most important signalling pathway for prolactin release activated by both peptides is via PLC, although they also regulate cAMP levels, which are increased by PACAP and decreased by galanin. Despite maximal peptide stimulated prolactin release being equal, galanin has a greater mitogenic effect on 235‐1 cells than PACAP, raising the possibility that it activates an additional

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04747.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Several neurotransmitters are implicated in the photoperiodic regulation of prolactin and luteinising hormone (LH) secretion in the ewe. This work investigated whether catecholamines,γ‐amino butyric acid (GABA), excitatory amino acids and serotonin diencephalic contents are affected by photoperiod and how such changes relate to the seasonal effects of photoperiod on LH and prolactin secretions. Moreover, to determine whether photoperiod can influence catecholamine biosynthesis, the activity of its rate limiting enzyme, tyrosine hydroxylase (TH) was also investigated. TH activity and the tissue content of the monoamines and their metabolites were measured in stalk‐median eminence (SME), preoptic area (POA) and the mediobasal, mediodorsal and laterobasal aspects of the hypothalamus. Investigation of excitatory amino acids and GABA was limited to the POA and the SME. Ovariectomized ewes were initially maintained in long days (LD) for 70 days. Thereafter half the ewes remained exposed to long days and the other half were transferred onto short days (SD) for 63 to 66 days to induce a stimulation of LH secretion and an inhibition of prolactin secretion. In each photoperiodic regime, half the ewes were treated with a subcutaneous oestradiol implant (+E) and half were not (−E). As expected, short days induced a decrease in prolactin and an increase in pulsatile LH secretion. These neuroendocrine changes were associated with a decrease in the TH activity of the SME in both oestradiol treated and non treated animals (146.5±24.1, 167.6±26.5 U TH/g of tissue in LD‐E and LD+Evs83.5±12.4 and 95.0±30.2 U TH/g of tissue in SD‐E and SD+E animals; P≤0.01). A similar and parallel short day‐induced decrease was observed in the tissue content of dopamine and its metabolite, 3,4‐dihydroxy‐phenylacetic acid (SD level were 55% of LD levels, P<0.05). In POA, a short day‐induced decrease in dopamine (18%; P≤0.05) and GABA (16.4%; P≤0.05) content and an oestradiol‐induced decrease in aspartate (15.6%; P≤0.05) content were found. This study provides the first report of a photoperiodic control of the synthesis activity of catecholaminergic neurones of the SME in the ewe. The photoperiod‐induced changes in dopaminergic activity at the level of the SME were associated with changes in LH and prolactin secretion indicating that TH activity of dopaminergic neurones of the SME could be a critical component of the photoperiodic regulation of LH and/or prolactin secretion. In particular, this finding is in agreement with the hypothesis that photoperiod can control a dopaminergic pathway inhibitory of LH secreti

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04758.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

To examine the effects of glucocorticoid (GC) on growth hormone (GH)‐releasing hormone (GRH) receptor gene expression, a highly‐sensitive and quantitative reverse‐transcribed polymerase chain reaction (RT‐PCR) method was used in this study. Rat anterior pituitary cells were isolated and cultured for 4 days. The cultured cells were treated with dexamethasone for 2, 6, and 24 h. GRH receptor mRNA levels were determined by competitive RT‐PCR using a recombinant RNA as the competitor. Dexamethasone significantly increased GRH receptor mRNA levels at 5 nM after 6‐ and 24 h‐incubations, and the maximal effect was found at 25 nM. The GC receptor‐specific antagonist, RU 38486 completely eliminated the dexamethasone‐induced enhancement of GRH receptor mRNA levels. Dexamethasone did not alter the mRNA levels ofβ‐actin and prolactin at 5 nM for 24 h, whereas GH mRNA levels were significantly increased by the same treatment. The GH response to GRH was significantly enhanced by the 24‐h incubation with 5 nM dexamethasone. These findings suggest that GC stimulates GRH receptor gene expression through the ligand‐activated GC receptors in the rat somatotrophs. The direct effects of GC on the GRH receptor gene could explain the e

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04779.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04782.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY