Glucocorticoid Receptors In Rats Research Articles

Histone deacetylase inhibition attenuates hepatic steatosis in rats with experimental Cushing's syndrome.

Cushing's syndrome (CS) is a collection of symptoms caused by prolonged exposure to excess cortisol. Chronically elevated glucocorticoid (GC) levels contribute to hepatic steatosis. We hypothesized that histone deacetylase inhibitors (HDACi) could attenuate hepatic steatosis through glucocorticoid receptor (GR) acetylation in experimental CS. To induce CS, we administered adrenocorticotropic hormone (ACTH; 40 ng/kg/day) to Sprague-Dawley rats by subcutaneous infusion with osmotic mini-pumps. We administered the HDACi, sodium valproate (VPA; 0.71% w/v), in the drinking water. Treatment with the HDACi decreased steatosis and the expression of lipogenic genes in the livers of CS rats. The enrichment of GR at the promoters of the lipogenic genes, such as acetyl-CoA carboxylase (Acc), fatty acid synthase (Fasn), and sterol regulatory element binding protein 1c (Srebp1c), was markedly decreased by VPA. Pan-HDACi and an HDAC class I-specific inhibitor, but not an HDAC class II a-specific inhibitor, attenuated dexamethasone (DEX)-induced lipogenesis in HepG2 cells. The transcriptional activity of Fasn was decreased by pretreatment with VPA. In addition, pretreatment with VPA decreased DEX-induced binding of GR to the glucocorticoid response element (GRE). Treatment with VPA increased the acetylation of GR in ACTH-infused rats and DEX-induced HepG2 cells. Taken together, these results indicate that HDAC inhibition attenuates hepatic steatosis hrough GR acetylation in experimental CS.

The regulative effects of Aspergillus fumigatus on expression of glucocorticoid receptor in asthmatic rats

Objective: To study the regulative effects of Aspergillus fumigatus (A.fumigatus) on expression of glucocorticoid receptor (GCR) in asthmatic rats. Methods: Wistar rats were randomly divided into 4 groups: a normal control group (UC), a normal control with A. fumigatus group (UC+ AF), an OVA group (OVA), and an OVA with A. fumigatus group (OVA+ AF). OVA and OVA+ AF groups were sensitized and challenged with OVA to establish asthmatic models. UC and UC+ AF groups were given normal saline as controls. After the last challenge, OVA+ AF and UC+ AF groups were given A. fumigatus spores intranasally. Airway hyper-responsiveness, eosinophil percentage (Eos%) and serum IgE level were measured to confirm the establishment of asthmatic models. Sections of pulmonary tissue were stained with hematoxylin-eosin (HE) and the expression of GCR mRNA and protein in lung tissues were measured by qRT-PCR and Western blot. Lung tissues and blood were plated on the potato dextrose agar(PDA)medium and cultured for 24 h to measure the number of colony. Results: The Penh value, Eos% in BALF and serum IgE level in UC+ AF group were slightly higher than those in the UC group (all the P>0.05). The Penh value, Eos% in BALF and serum IgE level in OVA group were significantly higher than those in the UC group (all the P<0.05). The Penh value in OVA+ AF group was significantly increased compared with the OVA group at the concentration of 25 g/L and 50 g/L of methacholine (all the P>0.05). Pulmonary histology revealed that both OVA group and OVA+ AF group showed high levels of inflammatory cell infiltration of bronchus and lung vessels, interstitial edema and smooth muscle thickening, while the UC and UC + AF groups were normal. Compared with the UC group, the expressions of GCR mRNA and protein in UC+ AF group and OVA group were decreased significantly (GCR mRNA in UC, UC+ AF and OVA group were 0.93±0.15, 0.65±0.10, 0.72±0.22, respectively, F=10.744, P<0.01; GCR protein in UC, UC+ AF and OVA group were 100±0, 89±8, 82±15, respectively, F=18.939, P<0.01). The expressions of GCR mRNA and protein in OVA+ AF group were further decreased than those in OVA group (GCR mRNA: OVA group: 0.72±0.22 vs OVA+ AF group: 0.52±0.08, t=2.462, P<0.05; GCR protein: OVA group: 81.88±15.41 vs OVA+ AF group: 59.09±7.60, t=2.997, P<0.05). The ratio of A. fumigatus colonization in lung tissues in OVA+ AF group (4/8) was higher than the UC+ AF group (0/8). Conclusion:A. fumigatus exposure can down-regulate the expression of GCR in the lung, which maybe an important mechanism of steroid-resistant asthma.

Etomidate inhibits nuclear factor-κB through decreased expression of glucocorticoid receptor in septic rats.

The present study aimed to investigate the effect of etomidate administered prior to or following cecal ligation and puncture (CLP) on the expression of glucocorticoid receptor (GR) and lymphocyte apoptosis in septic rats. Right jugular vein catheterization was performed on female Sprague‑Dawley rats under isoflurane anesthesia, and CLP surgery was performed to induce sepsis 3days following catheterization. The rats were randomly divided into five groups. All groups were infused with 2ml of either etomidate or 5‰ dimethyl sulfoxide (DMSO) at 1ml/h for 2h from 6h post‑surgery. The sham group received abdominal sham surgery and infusion with DMSO; the CLP control group received infusion with DMSO. Treatment groupA received infusion with 2mg/kg etomidate; group B received 0.6mg/kg etomidate following CLP and an infusion of 2mg/kg etomidate. Group C received 0.6mg/kg etomidate 24h prior to CLP and post‑surgical etomidate infusion. The 10‑day survival rates of the rats in the CLP, A, B and C groups were 60, 50, 55 and 40%, respectively. The serum mRNA expression levels of tumor necrosis factor‑α, GR and glucocorticoid‑induced leucine zipper were detected by reverse transcription‑quantitative polymerase chain reaction, the abundance of inhibitor of nuclear factor (NF)-κB‑α was measured by western blotting, and the apoptotic rates of the splenic lymphocytes were determined using flow cytometry. The results suggested that etomidate inhibited NF‑κB by decreasing the expression of GR in the septic rats. The increased apoptosis of lymphocytes induced by etomidate may lead to a poor outcome during sepsis.

Nesfatin‐1/NUCB2 in the amygdala influences visceral sensitivity via glucocorticoid and mineralocorticoid receptors in male maternal separation rats

Nesfatin-1, a recently identified satiety molecule derived from nucleobindin 2 (NUCB2), is associated with visceral hypersensitivity in rats and is expressed in the amygdala. We tested the hypothesis that nesfatin-1 expression in the amygdala is involved in the pathogenesis of irritable bowel syndrome (IBS) visceral hypersensitivity. An animal model of IBS-like visceral hypersensitivity was established using maternal separation (MS) during postnatal days 2-16. The role of nesfatin-1 in the amygdala on visceral sensitivity was evaluated. Rats subjected to MS showed a significantly increased mean abdominal withdrawal reflex (AWR) score and electromyographic (EMG) activity at 40, 60, and 80 mmHg colorectal distension. Plasma concentrations of nesfatin-1 and corticosterone were significantly higher than in non-handled (NH) rats. mRNA and protein expression of nesfatin-1/NUCB2 in the amygdala were increased in MS rats, but not in NH rats. In MS rats, AWR scores and EMG activity were significantly decreased after anti-nesfatin-1/NUCB2 injection. In normal rats, mean AWR score, EMG activity, and corticosterone expression were significantly increased after nesfatin-1 injection into the amygdala. Nesfatin-1-induced visceral hypersensitivity was abolished following application of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) antagonists. Elevated expression of nesfatin-1/NUCB2 in the amygdala in MS rats suggests a potential role in the pathogenesis of visceral hypersensitivity, which could potentially take place via activation of GR and MR signaling pathways.

Effect of moxibustion at Shenshu (BL 23) on the ethology, corticosterone and glucocorticoid receptor in aging rats

Objective To observe the effect of moxibustion on learning and memory abilities, corticosterone and glucocorticoid receptor (GR) in subacute aging rats.

Sex, folic acid and programming of the hepatic glucocorticoid receptor in rats

Sex, folic acid and programming of the hepatic glucocorticoid receptor in rats

Sex differences in the single prolonged stress model

Post traumatic stress disorder (PTSD) is a debilitating anxiety disorder resulting from traumatic stress exposure. Females are more likely to develop PTSD than males, but neurobiological mechanisms underlying female susceptibility are lacking. This can be addressed by using nonhuman animal models. Single prolonged stress (SPS), a nonhuman animal model of PTSD, results in cued fear extinction retention deficits and hippocampal glucocorticoid receptor (GR) upregulation in male rats. These effects appear linked in the SPS model, as well as in PTSD. However, the effects of SPS on cued fear extinction retention and hippocampal GRs in female rats remain unknown. Thus, we examined sex differences in SPS-induced cued fear extinction retention deficits and hippocampal GR upregulation. SPS induced cued fear extinction retention deficits in male rats but not female rats. SPS enhanced GR levels in the dorsal hippocampus of female rats, but not male rats. SPS had no effects on ventral hippocampal GR levels, but ventral hippocampal GR levels were attenuated in female rats relative to males. These results suggest that female rats are more resilient to the effects of SPS. The results also suggest that GR upregulation and cued fear extinction retention deficits can be dissociated in the SPS model.

Acute sleep deprivation enhances avoidance learning and spatial memory and induces delayed alterations in neurochemical expression of GR, TH, DRD1, pCREB and Ki67 in rats

The current study investigated the effects of acute versus repeated periods of sleep deprivation on avoidance learning and spatial memory and on the expression of discrete biochemical brain signals involved in stress regulation, motivation and brain plasticity. Male Long–Evans rats were sleep deprived using the platform-over-water method for a single 4h period (ASD) or for daily 4h RSD period on five consecutive days (CSD). The Y maze passive avoidance task (YM-PAT) and the Morris water maze (MWM) were used to determine learning and memory 1h following the last SD period. Region-specific changes in glucocorticoid receptors (GR), tyrosine hydroxylase (TH), dopamine 1 receptors (DRD1), phospho-CREB (pCREB) and Ki-67 expression were assessed in the hippocampal formation, hypothalamus and mesolimbic regions 72h following RSD. Behaviorally, our findings revealed increased latency to re-enter the aversive arm in the YM-PAT and reduced distance traveled and latency to reach the platform in the MWM in ASD rats compared to all other groups, indicative of improved avoidance learning and spatial memory, respectively. Acute SD enhanced TH expression in the ventral tegmental area, nucleus accumbens and A11 neurons of the hypothalamus and DRD1 expression in the lateral hypothalamus. Cell proliferation in the subventricular zone and pCREB expression in the dentate gyrus and CA3 regions was also enhanced following acute SD. In contrast, repeated SD significantly elevated GR-ir at the hypothalamic paraventricular nucleus and CA1 and CA3 layers of the hippocampus compared to all other groups. Our study supports that a brief 4h sleep deprivation period is sufficient to induce delayed neurochemical changes.

Behavioral testing-related changes in the expression of Synapsin I and glucocorticoid receptors in standard and enriched aged Wistar rats

Our aim was to assess the changes in the Synapsin I and glucocorticoid receptor (GR) expression induced by behavioral testing in the dorsal and ventral hippocampi of standard and enriched aged Wistar rats. The environmental enrichment (EE) was carried out 3h/day over a period of two months and then, the rats were tested in the elevated zero-maze (EZM) and radial-arm water maze (RAWM). Behavioral results showed that, even at an advanced age, EE was able to reduce anxiety-related behaviors and improve the performance in the RAWM. Regarding the neurobiological data, Synapsin I expression in the dorsal CA3, but not in the ventral, was enhanced both in enriched and standard rats when they performed the behavioral testing. Interestingly, the EE exposure was enough to increase Synapsin I in the ventral CA3. The analysis of GR in the dorsal hippocampus showed an increase of this receptor in the dDG both in enriched and standard rats when they performed the behavioral testing, whereas in the dCA1 and dCA3, the effect of the testing depended on the previous housing condition. In the ventral region, we found that the effects of EE were higher because on the one hand, the GR expression induced by the behavioral testing was enhanced in the dSUB, vCA1 and vCA3 when the rats were previously enriched and on the other hand, EE, regardless of the behavioral testing, increased the GR expression in the vDG and vSUB. Therefore, our results suggest that the effect of the behavioral testing on the neurobiological mechanisms studied is different depending on the previous housing condition of aged rats.

Expression of amygdala mineralocorticoid receptor and glucocorticoid receptor in the single-prolonged stress rats.

BackgroundPost-traumatic stress disorder (PTSD) is an anxious disorder associated with low levels of corticosterone and enhanced negative feedback of the hypothalamic–pituitary–adrenal (HPA) axis. Previous studies showed that the amygdala not only has an excitatory effect on the HPA axis but also plays a key role in fear-related behaviors. Coticosterone exert actions through binding to the mineralocorticoid (MR) and glucocorticoid receptor (GR), which are abundant in the amygdala. In our previous study, down-regulation of MR and GR in the hippocampus of PTSD rats was found. But the roles of MR and GR in the amygdala of PTSD rats is incompletely understood.Resultswistar rats were divided into 1 d, 7 d, 14 d groups after single prolonged stress (SPS) and control group. SPS is a reliable animal model of PTSD. Open field test (OF) and elevated plus maze tests (EPM) were performed to examine fear-related behaviors. Morphological changes of the ultrastructure of the amygdala neurons were assessed by transmission electron microscopy (TEM). Dual-immunofluorescence histochemistry was used to determined subcellular distribution and colocalization of MR- and GR-ir. Protein and mRNA of MR and GR was examined by western blotting and RT-PCR. OF and EPM showed enhanced fear in SPS rats. Abnormal neuronal morphology was discovered in the amygdala of SPS rats. The expression of MR- and GR-ir intensity, mRNA and protein within the amygdala decreased after SPS at 1 day, and then gradually recovered by 14 days, although the degree of decrease and recovery were different amongst techniques. We found no change in the MR/GR ratio at 3 levels of the amygdala. But more cytoplasmic distribution and decreased colocalization of MR- and GR-ir were observed in the amygdala after 7 days of SPS.ConclusionThese data suggest that change of MR and GR in the amygdala are involved in the mechanisms of fear in PTSD.

Lose dose genistein inhibits glucocorticoid receptor and ischemic brain injury in female rats

Although acute bolus of genistein treatment has been shown to protect against neuronal damage in experimental brain injury animal models, chronic continuous low dose treatment of genistein on ischemic brain injury has not been well elucidated. In the present study, female rats were received either pure genistein (0.1mg/kg/day via osmotic minipumps) or placebo at the time of ovariectomy, and transient forebrain ischemia was induced 7days later. Results demonstrated that genistein treatment for 14days significantly improved ischemic neuronal survival in hippocampal CA1 region of ovariectomized rats. Glucocorticoid receptor (GR) is a member of the adrenal steroid hormone receptor, which is highly expressed in the rat hippocampus. Activation of the GR plays a critical role in the neuronal stress responses, including ischemic brain damage. This study therefore examined the potential mechanisms by which genistein regulates GR signaling, including the protein distribution and receptor activation in hippocampus following ischemic reperfusion (I/R). Results showed that GR expression in the ovariectomized rats was excessively increased both in neurons (I/R 6h) and activated microglial cells (I/R 7d) in hippocampal CA1 region. Genistein treatment significantly attenuated GR induction and the enhanced GR nuclear translocation and DNA-binding capacity. The effects of genistein on the GR levels was accompanied with decreased blood plasma levels of corticosterone (primary glucocorticoid in rodents) and coupled to an E3 ubiquitin ligase Mdm2 targeted proteasomal degradation of GR, because genistein treatment could enhance the GR–Mdm2 interaction and the ubiquitination level of GR protein. In addition, our results indicated that genistein markedly prevented the excessive activation of microglia in CA1 sector. These results demonstrate the neuroprotective action of chronic low dose genistein replacement against ischemic brain damage, and a potential mechanism associated with the inhibition of both neuronal and microglial GR signaling following ischemic stress.

Expression of locus coeruleus mineralocorticoid receptor and glucocorticoid receptor in rats under single-prolonged stress

The pathogenesis of the post-traumatic stress disorder (PTSD) may involve dysfunction of several brain structures, such as the amygdala, locus coeruleus, hippocampus, noradrenergic system as well as the hypothalamic-pituitary-adrenal (HPA) axis. The cortisol and locus coeruleus dysfunction may affect the secretion of corticosterone. The present study was designed to examine the expression of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in the locus coeruleus in the rats treated with single-prolonged stress (SPS). The results showed that the expression of MR had a sharp decline on day 1, but gradually increased on days 4, 7, 14, and 28. The expression of GR gradually increased on days 1, 4, and 7, but decreased on days 14 and 28, respectively.MR and GR in the locus coeruleus may have a role in the development of long-term persistent neuropsychological sequelae in PTSD.

Neonatal intramuscular injection of plasmid encoding glucagon-like peptide-1 affects anxiety behaviour and expression of the hippocampal glucocorticoid receptor in adolescent rats

Early-life endocrine intervention may programme hippocampal glucocorticoid receptor (GR) expression and cause psychiatric disorders in later life. Glucagon-like peptide-1 (GLP-1) has been implicated in the regulation of neuroendocrine and behavioural responses, but it is yet to be determined whether and how neonatal GLP-1 overexpression may modify hippocampal GR expression and thus programme adolescent behaviour in rats. Two-day old pups were injected intramuscularly with vacant plasmid (VP) or plasmid DNA encoding secretory GLP-1 (GP). Anxiety-related behaviour was assessed in the elevated plus maze (EPM) test at 8 weeks of age. Plasma corticosterone levels were measured with enzyme immunoassay (EIA). Protein and mRNA levels were determined by western blot and real-time polymerase chain reaction (PCR), respectively. The DNA methylation status of the GR exon 1(7) promoter was determined by bisulphate sequencing PCR (BSP). GP rats exhibited anxiolytic behaviour compared with their VP counterparts. Hippocampal GLP-1 receptor (GLP-1R) and GR mRNA expression were significantly elevated in GP rats without a significant difference in plasma corticosterone. Significant reduction in DNA methyltransferase 1 (DNMT1) expression was observed in GP rats disconnected with alterations in DNA methylation of the GR exon 1(7) promoter. Nevertheless, mRNA expression of nerve growth factor-inducible protein A (NGFI-A) was significantly elevated in GP rats. These results suggest that neonatal intramuscular injection of plasmid DNA encoding GLP-1 affects anxiety behaviour in adolescent rats, probably through NGFI-A-activated upregulation of hippocampal GR expression.

The Year In Neuroendocrinology

At the "Year In Neuroendocrinology" session during the 2009 meeting of The Endocrine Society, I highlighted recent progress in three main areas of neuroendocrinology: neural mechanisms of action of estradiol, GnRH regulation, and epigenetics. In the area of neural mechanisms of action of estradiol, we have seen the list of estrogen receptors continue to expand and that neurosteroid synthesis is rapidly regulated by the social environment; that brain sexual differentiation can occur via the action of estradiol in upstream neurons without the need of estrogen receptors in affected neurons; and that a particular xenoestrogen can block the effects of estradiol and testosterone in brain synapses. In the area of GnRH regulation, kisspeptin continues to be a major player in reproductive endocrinology; neurokinin B should be added to the growing list of critical peptides involved in puberty and reproduction; and RFamide-related peptides have a direct role in regulation of gonadotropin-releasing neurons as a gonadotropin-inhibiting hormone. Finally, in the epigenetics field, we learned that the same principles of importance of parental care in epigenetic regulation in hippocampal glucocorticoid receptors in rats applies to humans and may explain some long-term effects of childhood abuse on the hypothalamic-pituitary-adrenal axis. It is difficult, if not impossible, to predict which findings will have an enduring impact on the field. It will be interesting to look back, 10 yr from now, to see whether the papers that were chosen were in fact well cited and whether they were influential in driving additional research in neuroendocrinology.

Effects of a formula of components from Shengmai Powder on glucocorticoid receptor in rats after thermal injury

To investigate the effects of a formula of components from Shengmai Powder, a compound traditional Chinese herbal medicine, on glucocorticoid receptor (GR) in rats after thermal injury. A total of 32 male SD rats were randomly assigned into normal control group, untreated group, ginsenosides group and components group, with 8 rats in each group. Rats in the normal control group were intragastrically administered with normal saline (NS) at room temperature once daily. Rats in the untreated group were treated with NS before thermal injury, and rats in the components group and ginsenosides group were once daily treated with a mixture of aqueous extracts of Ophiopogonis Japoni, Fructus schizandrae Chinensis and ginsenosides and ginsenosides respectively. Rats were administered for one week. After the last administration, rats in the untreated group and treated groups underwent thermal injury for one hour, and then were sacrificed immediately by decapitation. Blood serum was collected, and the serum corticosterone (CS) and adrenocorticotropic hormone (ACTH) levels were determined with enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA) respectively. The liver, lung and kidney homogenates were used to determine the GR binding capacity by radioligand receptor binding assay. The results were analyzed by one point analysis. GR binding capacities in liver, lung and kidney cytosols in the untreated group were obviously lower than those in the normal control group (P<0.01). The GR binding capacities in the liver and lung cytosols in the components group and the ginsenosides group were significantly higher than those in the untreated group (P<0.01), but no significant difference was found in kidney cytosol. Compared with the ginsenosides group, GR binding capacity in liver cytosol in the components group was increased (P<0.01), but there were no noticeable differences when compared with the GR binding capacities in lung and kidney cytosols. Serum CS and ACTH levels of the normal rats were (66+/-16)microg/L and (59+/-18) ng/L respectively. There were significant differences in CS and ACTH levels between the normal control group and the other groups (P<0.01), in which the serum CS and ACTH levels were (113+/-33)microg/L and (125+/-20) ng/L, (123+/-26) microg/L and (110+/-30) ng/L and (118+/-17) microg/L and (115+/-35) ng/L respectively. But there was no significant difference between the untreated group and the other treated groups. The formula of components from Shengmai Powder can enhance the effect of ginsenosides in up-regulating GR in rats after thermal injury.

Modeling receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase dynamics in rats: dual regulation by endogenous and exogenous corticosteroids

Receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase (TAT) were evaluated in normal rats. A group of normal male Wistar rats were injected with 50 mg/kg methylprednisolone (MPL) intramuscularly at the nadir of their plasma corticosterone (CST) rhythm (early light cycle) and sacrificed at various time points up to 96 h post-treatment. Blood and livers were collected to measure plasma MPL, CST, hepatic glucocorticoid receptor (GR) mRNA, cytosolic GR density, TAT mRNA, and TAT activity. The pharmacokinetics of MPL showed bi-exponential disposition with two first-order absorption components from the injection site and bioavailability was 21%. Plasma CST was reduced after MPL dosing, but resumed its daily circadian pattern within 36 h. Cytosolic receptor density was significantly suppressed (90%) and returned to baseline by 72 h resuming its biphasic pattern. Hepatic GR mRNA follows a circadian pattern which was disrupted by MPL and did not return during the study. MPL caused significant down-regulation (50%) in GR mRNA which was followed by a delayed rebound phase (60-70 h). Hepatic TAT mRNA and activity showed up-regulation as a consequence of MPL, and returned to their circadian baseline within 72 and 24 h of treatment. A mechanistic receptor/gene-mediated pharmacokinetic/pharmacodynamic model was able to satisfactorily describe the complex interplay of exogenous and endogenous corticosteroid effects on hepatic GR mRNA, cytosolic free GR, TAT mRNA, and TAT activity in normal rats.

Individual differences in the effects of chronic prazosin hydrochloride treatment on hippocampal mineralocorticoid and glucocorticoid receptors

The aim of this study was to investigate the noradrenergic regulation of mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) in high responder (HR) and low responder (LR) male rats, an animal model of individual differences in hypothalamo-pituitary-adrenal axis activity and vulnerability to drugs of abuse. The effects of a chronic treatment with the noradrenergic alpha(1) antagonist (1-[4-amino-6,7-dimethoxy-2-quinazolinyl]-4-[2-furanylcarbonyl] piperazine) hydrochloride (prazosin) (0.5 mg/kg, i.p., 35 days) were assessed on stress-induced corticosterone (CORT) secretion and on hippocampal MRs and GRs in adrenally intact rats. In order to ascertain whether the effects of chronic prazosin treatment on hippocampal MRs and GRs were direct or indirect, through prazosin-induced CORT secretion, we also assessed the effects of the same treatment on adrenalectomized rats with CORT substitutive therapy. When compared with LR rats, HR rats exhibited a delayed return to the basal level of CORT following acute restraint stress; this was associated with a lower binding of MRs and GRs in HR rats than in LR rats. Chronic prazosin treatment had no effect in HR animals but markedly reduced hippocampal MRs and GRs, and increased stress-induced CORT secretion in LR rats. In LR adrenalectomized rats, prazosin reduced hipppocampal MRs but did not change GRs. Our results provide evidence of a differential regulation by noradrenaline of hippocampal MRs and GRs in HR and LR rats. These data could have clinical implications in terms of individual differences in the resistance to antidepressant treatments and individual differences in drug abuse.

Morphine exposure prevents up-regulation of MR and GR binding sites in the brain of adult male and female rats due to prenatal stress

Our previous work demonstrated that the hormone response to stress and the negative feedback inhibition to these hormones are sex-dependently altered by prenatal morphine exposure in adult rats. An alteration in the glucocorticoid negative feedback inhibition is mediated by glucocorticoid receptors (GR) that are distributed throughout the brain, and mineralocorticoid receptors (MR) localized mainly in the hippocampus and involved in a tonic influence of brain functions. Therefore, the present study examined the binding characteristics of MR and GR in young adult male and female rats exposed prenatally (E11–E18) to morphine (10mg/kg/2×/day), saline or no treatment at all (controls). At 60–90 days of age, animals were adrenalectomized (ADX) 24h prior to decapitation. The hippocampus and hypothalamus were dissected for saturation binding assays. The data demonstrate that prenatal stress due to maternal saline injections up-regulates MR and GR binding in the hippocampus of adult male rats and this effect is prevented by prenatal morphine exposure. There is no effect of prenatal morphine exposure on GR binding in the hypothalamus of males. In female rats, prenatal morphine exposure does not affect the binding of MR and GR in the hippocampus or GR in the hypothalamus relative to controls; however, they are affected by ovarian hormone fluctuation. Moreover, prenatal stress decreases MR binding in the hippocampus of diestrous females and GR binding in the hypothalamus of estrous females. Both decreases are prevented by prenatal morphine exposure. Thus, the present study demonstrates that: (1) prenatal stress due to maternal saline injections alters MR and GR binding of adult male and female rats and is prevented by prenatal morphine exposure; (2) the MR and GR binding in adult female rats are affected by ovarian hormone fluctuations.

Downregulation of spinal glutamate transporter EAAC1 followingnerve injury is regulated by central glucocorticoid receptors in rats

Previous studies have shown that glucocorticoid receptors (GR) were upregulated, whereas glutamate transporters were downregulated, within the spinal cord dorsal horn after peripheral nerve injury. However, the relationship between the expression of spinal GR and glutamate transporter after nerve injury remains unknown. In the present study, we examined the hypothesis that central GR would regulate the expression of spinal glutamate transporter EAAC1 following chronic constriction nerve injury (CCI) in rats. CCI induced a significant downregulation of EAAC1 expression primarily within the ipsilateral spinal cord dorsal horn when examined on postoperative day 7 using both Western blot and immunohistochemistry. The downregulation of EAAC1 was significantly diminished after either the GR antagonist RU38486 (4>2=0.5 μg=vehicle) or a GR antisense oligonucleotide was administered intrathecally twice daily for postoperative day 1–6. Moreover, CCI induced a significant downregulation of nuclear factor κB (NF-κB) within the ipsilateral spinal cord dorsal horn, which also was attenuated by either RU38486 (4>2=0.5 μg=vehicle) or a GR antisense oligonucleotide. The immunohistochemical data indicated a pattern of colocalization between GR and EAAC1 as well as GR and NF-κB within the spinal cord dorsal horn. Since, NF-κB has been shown to regulate the expression of those cellular elements linked to inflammation and tissue injury and its activity can be negatively regulated by GR activation, these results suggest that spinal GR through NF-κB may play a significant role in the regulation of EAAC1 expression after peripheral nerve injury, a cellular pathway that may contribute to the development of neuropathic pain behaviors in rats.

Uteroplacental insufficiency alters hepatic expression, phosphorylation, and activity of the glucocorticoid receptor in fetal IUGR rats

Uteroplacental insufficiency (UPI) induces persistent changes in hepatic gene expression secondary to altered chromatin dynamics in the intrauterine growth- restricted (IUGR) rat liver. The glucocorticoid receptor (GR) is a transcription factor that when activated can induce changes in chromatin structure. To begin the process of identifying pathways by which IUGR affects chromatin structure, we hypothesized that UPI in the rat induces a significant increase in endogenous glucocorticoids (corticosterone) and increases GR expression and activation. To prove our hypothesis, we induced IUGR through bilateral uterine artery ligation of the pregnant rat. At day 1, UPI significantly increased corticosterone levels and was associated with increased total GR mRNA and protein levels in the liver, as well as increased hepatic phosphorylation of GR serine 211. Moreover, cyclin-dependent kinase 2 (CDK2) cyclinA/CDK2 protein levels, which selectively phosphorylate GR serine 211, were also significantly increased. To assess activity of the GR, we measured protein levels of the transcription factor p53 whose levels are downregulated, at least in part, by active GR. In this study, UPI decreased p53 protein and its downstream target Bax mRNA levels. We conclude that UPI in rats affects GR expression and activity in the liver. We speculate that these alterations early in life may contribute to the changes in chromatin structure and gene expression previously described in the IUGR liver.