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N Barden

Publications and source records attributed to N Barden.

At least 37 records · Page 2Linked to original sources
PubMed1999

Regulation of corticosteroid receptor gene expression in depression and antidepressant action.

OBJECTIVE: Major alterations of the hypothalamic-pituitary-adrenocortical (HPA) system are often seen in patients with depression, and can be reversed by successful antidepressant therapy. Persuasive evidence points to the involvement of a dysfunctional glucocorticoid receptor system in these changes. The authors developed a transgenic mouse to determine the mechanism for these changes. DESIGN: In vivo and in vitro animal experiments. ANIMALS: Transgenic mice expressing glucocorticoid receptor antisense RNA and control mice. INTERVENTIONS: In vivo: hormone assays and dexamethasone suppression tests; in vitro: cell transfection, chloramphenicol acetyl transferase assay, Northern blot analysis, binding assays of cytosolic receptor. OUTCOME MEASURES: Indicators of depressive disorder in transgenic mice, effect of antidepressant therapy on dexamethasone binding in transgenic mouse hippocampus, mouse behaviour, and glucocorticoid receptor activity. RESULTS: Transgenic mice showed no suppression of corticosterone with a dose of 2 mg per 100 g body weight dexamethasone. Treatment with amitriptyline reduced levels of corticotropin and corticosterone, increased glucocorticoid receptor mRNA concentrations and glucocorticoid binding capacity of several brain areas, and reversed behavioural changes. In vitro experiments also showed that desipramine increased glucocorticoid receptor mRNA. CONCLUSION: These transgenic mice have numerous neuroendocrine characteristics of human depression as well as altered behaviour. Many of these neuroendocrinologic and behavioural characteristics are reversed by antidepressants. The antidepressant-induced increase in glucocorticoid receptor activity may render the HPA axis more sensitive to glucocorticoid feedback. This new insight into antidepressant drug action suggests a novel approach to the development of new antidepressant drugs.

Amitriptyline↗
PubMed1998

Age- and stimulus-dependent changes in anxiety-related behaviour of transgenic mice with GR dysfunction.

Transgenic mice expressing antisense directed against glucocorticoid receptor (GR) mRNA were used for a longitudinal study on the effects of hypothalamic-pituitary-adrenocortical dysfunction on anxiety-related behaviour and locomotor activity. Compared with age-matched controls and 5-week-old transgenic animals, 13- and 36-week-old transgenic mice made significantly more entries into and spent significantly more time on the open arms of the elevated plus-maze thereby indicating reduced basal anxiety. In contrast, time spent in the central area of the open field was significantly reduced in transgenic animals indicating an enhanced anxiety under conditions of increased stress. Locomotor activity did not differ between transgenic and control animals. Our results indicate that behavioural changes in transgenic mice differ according to the age of the animals and the behavioural paradigm used. Transgenic animals with an impaired GR function may be of help in studying the interaction of ageing, GR function and the development of behavioural abnormalities.

Aging↗
PubMed1998

Reduced activity of hypothalamic corticotropin-releasing hormone neurons in transgenic mice with impaired glucocorticoid receptor function.

Loss of central glucocorticoid receptor (GR) function is thought to be involved in the development of neuroendocrine and psychiatric disorders associated with corticotropin-releasing hormone (CRH) hyperactivity. The possible causal relationship between defective GR function and altered activity of CRH neurons was studied in transgenic mice (TG) expressing antisense RNA against GR. Immunocytochemical studies showed significant reductions in CRH immunoreactive neurons in the paraventricular nucleus (PVN) and in CRH and vasopressin (AVP) stores in the external zone of the median eminence. Concomitantly, stimulus-evoked CRH secretion from mediobasal hypothalami of TG mice in vitro was reduced significantly. However, CRH mRNA levels in the PVN of TG mice were marginally lower than those in wild-type (WT) mice. 125I-CRH binding autoradiography revealed no differences between WT and TG animals in any of the brain regions that were studied. Basal plasma corticosterone (cort) levels and 125I-CRH binding, CRH-R1 mRNA, POMC mRNA, and POMC hnRNA levels in the anterior pituitary gland were similar in WT and TG mice. Intraperitoneal injection of interleukin-1beta (IL-1beta) increased plasma cort levels, CRH mRNA in the PVN, and anterior pituitary POMC hnRNA similarly in WT and TG mice. The injection of saline significantly reduced anterior pituitary CRH-R1 mRNA levels in WT mice, but not in TG mice, whereas IL-1beta produced a decrease in these mRNA levels in both strains. The data show that long-term GR dysfunction can be associated with reduced activity of CRH neurons in the PVN and decreased sensitivity of pituitary CRH-R1 mRNA to stimulus-induced downregulation. Moreover, the hypothalamic changes observed in this model suggest that impaired GR function, at least if present since early embryonic life, does not necessarily result in CRH hyperexpression characteristics of disorders such as major depression.

Animals↗
PubMed1998

Enhanced morphine-induced behavioural effects and dopamine release in the nucleus accumbens in a transgenic mouse model of impaired glucocorticoid (type II) receptor function: influence of long-term treatment with the antidepressant moclobemide.

In vivo microdialysis experiments were conducted in transgenic mice with impaired glucocorticoid receptor function resulting from expression of antisense directed against glucocorticoid receptor messenger RNA. Basal corticosterone and serotonin levels in the nucleus accumbens of untreated transgenic mice were enhanced compared to control mice (B6C3F1). Following a systemic morphine injection (15 mg/kg) mesolimbic dopamine and serotonin release was markedly increased in transgenic mice compared to control mice and in parallel enhanced behavioural stimulation was observed in these animals. After pretreatment with the antidepressant moclobemide over a time period of eight weeks (15 mg/kg/day) elevated basal levels of both corticosterone and serotonin were normalized in transgenic mice. Furthermore, morphine-induced dopamine and serotonin release as well as behavioral stimulation were suppressed in transgenic mice and similar to that in control mice. The results indicate that impaired glucocorticoid receptor function influences the basal release of serotonin in the nucleus accumbens. This alteration has no effect on basal but on morphine-stimulated release of dopamine in the mesolimbic system. An enhanced sensitivity to the effects of morphine is apparently related to elevated brain corticosterone and serotonin levels and can be normalized by long-term antidepressant treatment.

Animals↗
PubMed1997

Spatial memory in transgenic mice with impaired glucocorticoid receptor function.

Spatial learning and memory function of transgenic mice with impaired glucocorticoid receptor function was assessed in the Morris water maze and the radial arm maze. Transgenic mice took longer to find a submerged and a visual platform in the water maze task than did mice from the parent strain (B6C/3F1), although performance was improved in the visible platform condition relative to the submerged platform task. In the radial arm maze, transgenic mice made significantly more errors than B6C/3F1 mice. In both tasks, the behavioural strategies adopted by transgenic mice were non-optimal for correct performance. It is suggested that the impaired performance displayed by transgenic mice in both tests is largely attributable to these altered behavioural strategies.

Animals↗
PubMed1997

Corticotropin-releasing factor and glucocorticoid receptor (GR) gene expression in the paraventricular nucleus of immune-challenged transgenic mice expressing type II GR antisense ribonucleic acid.

The purpose of this study was to investigate the effect of the immune activator lipopolysaccharide (LPS) on the expression of corticotropin-releasing factor (CRF) and glucocorticoid receptor (GR) mRNA in the paraventricular nucleus (PVN) of transgenic mice with impaired GR function caused by endogenous expression of GR antisense RNA. At 3 and 8 wk of age, control and transgenic mice were sacrificed 4.5 h after a single ip administration of LPS (100 micrograms/100 g of body wt) or vehicle. Frozen brains were mounted on a microtome and cut in 20-microns sections. mRNAs encoding CRF and GR were assayed by in situ hybridization histochemistry using 35S-labeled riboprobes, and localization of Fos-immunoreactive (Fos-ir) nuclei was determined by immunocytochemistry. Basal expression of CRF mRNA in the PVN, central nucleus of the amygdala (CeA), and geniculate complex (GN) was similar in the control and transgenic mice. LPS induced a comparable neuronal activation in the PVN of control and transgenic mice as revealed by the number of Fos-ir neurons. Moreover, the endotoxin caused a significant increase in the CRF mRNA levels within the PVN and CeA, an effect observed in both animal models. The endotoxin did not notably modulate CRF expression in other regions, such as GN. Although GR mRNA was expressed in the PVN of control mice under basal conditions, this transcript was not detected in this hypothalamic structure in LPS-treated and transgenic animals. This indicated that endogenous Type II GR mRNA is decreased in the PVN of mice expressing Type II GR antisense RNA and that gene is downregulated by LPS. Hybridization signal for CRF and GR transcripts was not notably altered by the age of mice. These results provide evidence that the basal expression of CRF and the increase of neuroendocrine CRF transcription in response to immunogenic challenges are not significantly affected by impairment of the Type II GR function.

Animals↗
PubMed1997

Behavioral reactivity to aversive stimuli in a transgenic mouse model of impaired glucocorticoid (type II) receptor function: effects of diazepam and FG-7142.

Transgenic mice with impaired type II-glucocorticoid receptor mediated feedback inhibition of hypthalamic-pituitary-adrenal activity were assessed in three different tests assessing behavioral reactivity to aversive stimuli, the elevated plus maze, the Thatcher-Britton novelty-conflict paradigm, and the startle paradigm. Transgenic mice more frequently entered and spent more time in the open arms of the elevated plus in comparison to B6C/3F1 mice. Transgenic mice took significantly longer to begin eating in the Thatcher-Britton novelty conflict paradigm, and displayed increased reactivity in the startle paradigm. Administration of 1 or 2 mg/kg diazepam reversed the behavioral effects observed in all three tests. Administration of the benzodiazepine receptor inverse agonist N-methyl-beta-carboline-3 carboxamide (FG-7142, 10 mg/kg) reduced the ratio of open to total arm entries and the time spent in the open arms of the plus maze in transgenic, but not B6C/3F1, mice. This dose of FG-7142 did not influence performance of either strain in the Thatcher-Britton or startle paradigms. These results are discussed in terms of the hypothesis that the transgenic mice are more sensitive to the aversive properties of novel stimuli, and that they may have difficulty discriminating between signals of relative safety and danger.

Animals↗
PubMed1997

Endocrine profile and neuroendocrine challenge tests in transgenic mice expressing antisense RNA against the glucocorticoid receptor.

A transgene expressing antisense RNA complementary to a fragment of the glucocorticoid receptor cDNA was incorporated into the mouse genome and resulted in a transgenic animal that has decreased glucocorticoid receptor function. The transgenic mice showed basal plasma ACTH and corticosterone levels similar to those of the normal control animals. We have further investigated changes in HPA axis regulation by use of different neuroendocrine challenge tests including a dexamethasone suppression test (DST). In comparison to normal mice, a tenfold higher dose of dexamethasone (i.e. 20 micrograms/100 g body weight) was required to suppress the basal corticosterone levels of transgenic mice. Dexamethasone (2 micrograms/100 g body weight) produced a long-lasting suppression of plasma ACTH and corticosterone levels in control mice, whereas in transgenic animals only a short-lasting decrease in ACTH levels was apparent. Corticotropin-releasing hormone (CRH) administration resulted in an enhanced response in plasma ACTH levels in transgenic mice, whereas the corticosterone response was markedly reduced. The discrepancy between ACTH and corresponding corticosterone secretions in transgenic mice could be attributed, in part, to a reduced sensitivity of the adrenal gland to stimulation by ACTH. Pituitaries of transgenic mice contained about 50% less proopiomelanocortin (POMC) mRNA than those of control animals. No significant differences were noted in the ACTH or protein contents of normal and transgenic mice pituitary glands although a slight increase in protein content of the transgenic mouse adrenal gland was apparent. In conclusion, transgenic mice with impaired GR function show major disturbances in HPA axis regulation which seem to be caused by the primary defect in conjunction with secondary modifications in, amongst others, pituitary CRH receptor system(s), sympathetic output and adrenal development. This mouse is therefore a useful model to study the consequences of life-long defective GR function and HPA axis regulation in general.

Adrenal Glands↗
PubMed1997

Hypothalamic-pituitary-adrenocortical axis changes in a transgenic mouse with impaired glucocorticoid receptor function.

Recently, a transgenic mouse with impaired glucocorticoid receptor (GR) function was created to serve as an animal model for the study of neuroendocrine changes occurring in stress-related disorders, such as major depression. Here, we investigated the hypothalamic-pituitary-adrenocortical (HPA) axis changes in these transgenic mice. There were no significant differences between basal early morning plasma ACTH and corticosterone levels in normal and transgenic mice. When animals were exposed to a mild stressor, an enhanced response in plasma ACTH was observed in the transgenic mice, whereas plasma corticosterone responses were not different. In view of these differences in plasma ACTH and corticosterone responses, we directed our studies toward the regulation of ACTH secretion on the hypothalamic-hypophyseal level in vitro. Therefore, an in vitro model, the pituitary-hypothalamic complex (PHc) was developed and its ACTH release profile was compared with that of the pituitary (PI) alone. The basal ACTH release by PHc and PI from normal and transgenic mice was similar. Regardless of the strain under study, the basal ACTH release by PI was significantly lower than the release by PHc. Stimulation of tissues with either high K+ (56 mM) or CRH (10 or 20 nM) produced an enhanced ACTH release from both PHc and PI, whereas the response in PI was larger than that in PHC. Moreover, the responses to these stimuli were markedly enhanced in tissues from transgenic mice. In tissues of normal mice, corticosterone inhibited both basal and CRH-stimulated ACTH release more potently in PHc than in PI. Furthermore, the feedback capacity of corticosterone to restrain both basal and CRH-stimulated ACTH release was highly impaired in tissues of transgenic mice, whereas the feedback in PHc appeared to be more affected than that in the PI of these animals. In conclusion, the in vitro data on PHc and PI revealed intrahypothalamic mechanisms operating 1) to fine-tune stimulus-evoked ACTH responses; and 2) to facilitate the negative feedback action of glucocorticoids. Moreover, in the transgenic tissues, the impaired GR function was found to cause augmented stimulus-evoked ACTH responses and an impaired glucocorticoid feedback efficacy which appeared to be mainly defective at the hypothalamic level. Thus, in the transgenic mice with life-long central GR dysfunction we found impaired negative feedback combined with "normal" (i.e. noncompensated) in vivo plasma corticosterone responses. This is a condition with potentially grave pathophysiological consequences and, therefore, this transgenic animal may be regarded as a valuable model for the study of functional glucocorticoid insufficiency at the central nervous system level.

Adrenocorticotropic Hormone↗
PubMed1996

Modulation of glucocorticoid receptor gene expression by antidepressant drugs.

Through expression of a glucocorticoid receptor (GR) antisense RNA in brain, we have produced transgenic mice with an hyperactive hypothalamic-pituitary-adrenocortical (HPA) system similar to that seen in depressed patients. This model supports the hypothesis that disturbed corticosteroid receptor regulation could be the primary factor responsible for both the CRH/AVP hyperdrive that leads to increased activity of the HPA system, and the premature escape from the cortisol suppressant action of dexamethasone seen in affective disorders. Although normalisation of the hyperactive HPA system occurs during successful antidepressant therapy of depressive illness, these improvements do not correlate with changes in monoaminergic neurotransmitter systems, suggesting that unknown mechanisms of action may be operative. Work from my laboratory was the first to show that different types of antidepressants increased glucocorticoid receptor (GR) mRNA. We found increased GR mRNA levels irrespective of the preferential inhibitory action of antidepressant on the monoamine neurotransmitter re-uptake and showed increased GR gene transcription in antidepressant-treated mouse fibroblast cells that do not possess monoamine re-uptake mechanisms. We measured changes in glucocorticoid response in cells transfected with a glucocorticoid-sensitive reporter plasmid (MMTV-CAT) and observed increased glucocorticoid-stimulated CAT activity when the cells were treated with antidepressant. A different chimaeric gene construct consisting of a fragment of the GR gene promoter region fused to the CAT gene allowed more direct measurement of antidepressant action and increased CAT activity was also seen when cells transfected with this construct were treated with antidepressant. Finally, GR mRNA concentration and glucocorticoid binding activity were increased in brain tissues of animals chronically treated with antidepressant. The time course of antidepressant actions on corticosteroid receptors coincides with their long-term actions on HPA system activity and follows closely that of clinical improvement of depression. This suggests that antidepressant-induced changes in brain corticosteroid receptors may underlie the observed simultaneous decrease in circulating ACTH and corticosterone levels and the decreased adrenal size. Some of these effects may be mediated through CRH since, in antidepressant-treated transgenic mice hypothalamic CRH mRNA levels were decreased. From this work we have formulated the hypothesis that a primary action of antidepressants could be the stimulation of corticosteroid receptor gene expression that renders the HPA system more susceptible to feedback inhibition by cortisol. The resultant decrease in HPA system activity could induce secondary changes in glucocorticoid-sensitive gene expression and lead to redressment of neurotransmitter imbalance. This work opens up a completely new insight into antidepressant drug action and suggests a line of approach to the development of new drugs by focusing on this action.

Adrenal Cortex Hormones↗
PubMed1996

Morphine-induced locomotor and neurochemical stimulation is enhanced in transgenic mice with impaired glucocorticoid receptor function.

It has been suggested that the hypothalamic-pituitary-adrenocortical (HPA) system contributes to individual differences in sensitivity towards drug abuse. Therefore, we studied the effects of the prototypic drug morphine in transgenic mice with impaired glucocorticoid receptor function. This mouse model has a profoundly dysfunctional HPA feedback. Since morphine-induced locomotor stimulation is positively correlated with the rewarding effects of morphine, we examined morphine-induced locomotor activity of transgenic mice and control mice (B6C3F1). Because morphine-induced locomotor activity depends on an intact mesolimbic system, dopaminergic (DAergic) neuronal activity was also estimated within the mesolimbic system. Results indicated that the activity after vehicle injection do not differ between these two mouse lines. Compared to vehicle injections, morphine (7.5 and 15 mg/kg; i.p.) dose-dependently increased motor activity for 3 h in control and transgenic mice. However, morphine-induced locomotion was significantly more pronounced in transgenic mice. Further, morphine-induced mesolimbic DAergic activity was enhanced in transgenic animals as compared to control animals. These results parallel endocrine data that show that the plasma ACTH level of transgenic mice reach higher levels compared to those levels observed in control mice after morphine injections. Altogether, this transgenic mouse line shows an enhanced locomotor-stimulant effect to morphine, a response that is reflected by an enhanced DAergic activity within the mesolimbic system and is also associated with increased HPA activity. We submit that the dysregulation of the HPA system in these transgenic mice influences the enhanced vulnerability to drug-seeking behavior.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1995

Do antidepressants stabilize mood through actions on the hypothalamic-pituitary-adrenocortical system?

Patients suffering from severe depression often show an increased activity of the hypothalamic-pituitary-adrenocortical (HPA) system, a premature escape from the cortisol suppressant action of dexamethasone, and a number of other neuroendocrine changes. This might be explained by defective glucocorticoid feedback inhibition. Normalization of the hyperactive HPA system occurs during successful antidepressant pharmacotherapy of depressive illness, and this could be achieved by antidepressant-induced increases in the cellular corticosteroid receptors, rendering the HPA system more susceptible to feedback inhibition by cortisol. Both mineralocorticoid- and glucocorticoid-receptor mRNA levels and hormone-binding activities are found to be increased following treatment of different cell lines or animals with antidepressants. Since the timecourse of antidepressant actions on corticosteroid receptors follows more closely that of clinical improvement of depression, antidepressants might elevate mood in depressives through their long-term effects on HPA regulation.

Affect↗
PubMed1995

Long-term antidepressant treatment reduces behavioural deficits in transgenic mice with impaired glucocorticoid receptor function.

Impaired cognitive function and enhanced activity of the hypothalamic-pituitary-adrenocortical system are among the cardinal symptoms of major depression in humans that resolve after successful antidepressant treatment. We used a transgenic mouse model expressing antisense RNA complementary to that of glucocorticoid receptor (GR) mRNA to test the hypothesis that reduced GR function can cause these clinical disturbances. The transgenic mice show profound behavioural changes in a number of animal tests that are indicative of cognitive impairment. These mice also have elevated plasma corticotropin concentrations in response to stress. After long-term treatment with moclobemide, a reversible inhibitor of monoamine oxidase type A that acts clinically as an antidepressant, both the behavioural deficits and the hormonal alterations disappeared. These observations suggest that a transgenic mouse with GR dysfunction may be a useful model for investigation of drug effects on the cognitive and neuroendocrine aspects of depression.

Animals↗
PubMed1995

Disruption of hypothalamic-pituitary-adrenocortical system in transgenic mice expressing type II glucocorticoid receptor antisense ribonucleic acid permanently impairs T cell function: effects on T cell trafficking and T cell responsiveness during postnatal development.

We used transgenic mice with impaired corticosteroid receptor function, caused by expression of type II glucocorticoid receptor (GR) antisense RNA, to study the role of glucocorticoid feedback during the developmental maturation of hypothalamus-pituitary-adrenal-immune functions. These mice have increased plasma concentrations of ACTH and corticosterone as well as reduced GR binding capacity. In control mice, a strong sex dimorphism in the development of GR gene expression is apparent, and in males between postnatal days 9-36, the GR gene transcript concentration is approximately twice that in female mice. Endogenous GR messenger RNA levels were markedly reduced in transgenic mice, and the sex dimorphism was abolished. An abnormal developmental pattern of adrenal secretory activity accompanied the postnatal maturation of the hypothalamic-pituitary-adrenocortical system of the transgenic mice, and high plasma corticosterone levels were measured at early postnatal ages through adulthood. Inefficient glucocorticoid inhibitory action on the immune axis was supported by both the inability of high circulating levels of corticosterone to reduce thymus weight and the failure of dexamethasone to influence in vitro thymocyte and splenocyte cell proliferation. Alterations in thymocyte trafficking/migration in transgenic mice was supported by flow cytometric analysis of the distribution of phenotypically distinct lymphocyte subsets accompanying the postnatal maturation of the thymus. A marked increase in CD4+CD8+ double positive cells and a 2-fold increase in the CD4/CD8 (helper/suppressor) ratio caused by a 40-60% increase in the CD4+CD8- (T helper) subset and a decrease in the CD4-CD8+ (T suppressor) subset, was seen. Moreover, in transgenic mice, an absence of sexual dimorphism and a significantly increased immune reactivity were observed. The present study shows that disruption of the hypothalamic-pituitary-adrenocortical system has both developmental and permanent effects on T cell function characterized by a shifting of the T cell balance toward the CD4+CD8- helper-inducer phenotype coupled with hyperresponsiveness of the T (helper) cell compartment. These findings point to the GR as a major factor in the counterregulatory feedback loop controlling autoaggressive immune responses and underline the potential modulatory role of sex steroids in this feedback regulation and in the pathogenesis of autoimmune diseases.

Adrenocorticotropic Hormone↗