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Biomedical subjects

Mary F Dallman

Publications and source records attributed to Mary F Dallman.

At least 37 records · Page 2Linked to original sources
PubMed2004

Long double-stranded RNA-mediated RNA interference as a tool to achieve site-specific silencing of hypothalamic neuropeptides.

RNA interference (RNAi) has become a popular tool to silence gene expression in a variety of in vitro and in vivo systems. However, it has met with limited success in inhibiting gene expression in adult mammals. Here we demonstrate that long double-stranded RNA (dsRNA) can be used to create a "site-specific", transient knockdown of genes in a fashion that is phenotypically akin to genetically manipulated organisms. Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) that regulate a variety of physiological processes including the hypothalamic-pituitary-adrenal axis (HPA axis), energy and water homeostasis were used as model systems. Stereotaxic injections of dsRNA against CRF and AVP in the PVN specifically abolished the expression of these genes in the PVN leaving expression in other loci intact. Control dsRNA did not affect CRF or AVP expression in any brain region, suggesting that dsRNA did not shut down global protein synthesis. ANOVA showed significant main effects of silencing of CRF on dampening of the stress-activated release of adrenocorticotrophin hormone (ACTH) (F(2,7)=4.87; p<0.047). Silencing of AVP resulted in increased water consumption, increased urine output and decreased urine osmolality as compared to control dsRNA-treated rats. Furthermore, dsRNA had no obvious deleterious effects on body weight or food consumption, variables considered essential in ruling out adverse physiologic effects in animal models. Thus, using long dsRNA, we were able to ascertain site-specific roles of CRF and AVP in adult rats without any developmental compensation and in a wild-type background.

Adrenocorticotropic Hormone↗
PubMed2004

Changes in anxiety-related behaviors and hypothalamic-pituitary-adrenal activity in mice lacking the 5-HT-3A receptor.

The serotonin-3 (5-HT-3A) receptor has been localized in limbic and brainstem structures that regulate anxiety-related behavior and hypothalamic-pituitary-adrenal (HPA) activity, but its role in regulating anxiety-related behaviors is equivocal, and evidence for its role in regulating HPA activity is limited. Therefore, we used 5-HT-3A receptor knockout (KO) mice to further study these issues. Behavior in the elevated plus maze, open field, light-dark box and after Pavlovian fear conditioning was examined in addition to HPA activity under basal and acute stress conditions. Compared to age-matched adult male wild-type (WT) controls, adult male KO mice exhibited increased distance traveled in the open arms of the elevated plus maze, consistent with decreased measures of anxiety. There were no differences between the two genotypes in exploratory behavior in the open field or light-dark test. KO mice displayed enhanced fear conditioning indexed by fear-induced freezing behavior. KO mice displayed lower adrenocorticotropin (ACTH) responses to restraint or lipopolysaccharide (LPS). In addition, lower vasopressin mRNA in the paraventricular nucleus of the hypothalamus (PVN) and higher corticotropin-releasing hormone (CRH) mRNA in the central amygdala were observed in KO compared to WT mice. Therefore, deletion of the 5-HT-3A receptor revealed an important role for this receptor in regulating HPA responses to acute stress and a potential interaction between the 5-HT-3A receptor and CRH in the amygdala. Together, these data suggest that the 5-HT-3A receptor does not have a unitary role in the regulation of anxiety- and fear-related behaviors but has a potentially substantial role in the regulation of HPA activity.

Amygdala↗
PubMed2003

Androgen-sensitive changes in regulation of restraint-induced adrenocorticotropin secretion between early and late puberty in male rats.

Regulation of ACTH secretion changes between early (40 d) and late (60 d) puberty in male rats. We tested whether this occurs because of activating effects of testosterone on the brain. We measured testosterone and ACTH responses to repeated restraint in adrenalectomized, corticosterone-replaced rats entering and leaving puberty with or without treatment with flutamide, a nonsteroidal androgen-receptor antagonist. Flutamide increased testosterone. ACTH responses were high and suppressed by flutamide at 40 d. At 60 d, ACTH responses were low and increased by flutamide. On d 4, basal arginine vasopressin (AVP) mRNA was increased by restraint, but not age, in the medial parvicellular paraventricular nucleus (mpPVN) and medial amygdala and increased with age in the bed nucleus of the stria terminalis. We counted numbers of AVP-immunoreactive (AVP-ir) and corticotropin-releasing factor (CRF)-ir neurons. In medial amygdala, there was no change in AVP+ cells. With restraint, CRF+ cells in the central nucleus decreased at 40 d and increased at 60 d. Flutamide did not affect the response at 40 d but blocked restraint-induced increases at 60 d. After restraint, the bed nucleus of the stria terminalis AVP-ir correlated negatively with mpPVN CRF-ir at 40 d and with mpPVN AVP-ir at 60 d. In PVN, there were no effects on CRF+ cells. However, AVP+ cells increased only with restraint plus flutamide at 40 d and tended to increase with restraint and decrease with restraint plus flutamide at 60 d. We conclude that during puberty testosterone induces marked changes in regulation of neuropeptides in pathways known to determine autonomic, neuroendocrine, and behavioral responses to chronic stress.

Adrenalectomy↗
PubMed2003

Chronic stress and obesity: a new view of "comfort food".

The effects of adrenal corticosteroids on subsequent adrenocorticotropin secretion are complex. Acutely (within hours), glucocorticoids (GCs) directly inhibit further activity in the hypothalamo-pituitary-adrenal axis, but the chronic actions (across days) of these steroids on brain are directly excitatory. Chronically high concentrations of GCs act in three ways that are functionally congruent. (i) GCs increase the expression of corticotropin-releasing factor (CRF) mRNA in the central nucleus of the amygdala, a critical node in the emotional brain. CRF enables recruitment of a chronic stress-response network. (ii) GCs increase the salience of pleasurable or compulsive activities (ingesting sucrose, fat, and drugs, or wheel-running). This motivates ingestion of "comfort food." (iii) GCs act systemically to increase abdominal fat depots. This allows an increased signal of abdominal energy stores to inhibit catecholamines in the brainstem and CRF expression in hypothalamic neurons regulating adrenocorticotropin. Chronic stress, together with high GC concentrations, usually decreases body weight gain in rats; by contrast, in stressed or depressed humans chronic stress induces either increased comfort food intake and body weight gain or decreased intake and body weight loss. Comfort food ingestion that produces abdominal obesity, decreases CRF mRNA in the hypothalamus of rats. Depressed people who overeat have decreased cerebrospinal CRF, catecholamine concentrations, and hypothalamo-pituitary-adrenal activity. We propose that people eat comfort food in an attempt to reduce the activity in the chronic stress-response network with its attendant anxiety. These mechanisms, determined in rats, may explain some of the epidemic of obesity occurring in our society.

Adrenal Glands↗
PubMed2003

Filling the interstices: ghrelin neurons plug several holes in regulation of energy balance.

Of several circulating hormones that act on hypothalamus to affect body energy balance, only ghrelin is also expressed in hypothalamic neurons. From the studies of Horvath and colleagues appearing in this issue of Neuron, it appears that neuronal ghrelin acts presynaptically to stimulate release of the orexigenic peptide, neuropeptide Y, and other neurotransmitters, thus defining a new and subtle modulatory circuit.

Animals↗
PubMed2003

Fast glucocorticoid feedback favors 'the munchies'.

In a recent paper, Tasker and colleagues show that glucocorticoids (GCs) act rapidly, probably through membrane receptors, on corticotropin-releasing factor (CRF)-synthesizing cells to release endocannabinoids. These act locally at presynaptic axons via cannabinoid CB-1 receptors to reduce excitatory glutaminergic input, and therefore induce fast feedback inhibition of CRF by GCs. Similar findings in other hypothalamic neurons suggest that this action of GCs might be common in the brain, and could, in part, explain rapid GC effects on food intake.

Appetite↗
PubMed2003

Compulsive behavior in the 5-HT2C receptor knockout mouse.

The efficacy of serotonergic pharmacotherapy indicates that serotonin (5-HT) plays a role in the treatment, if not the etiology, of obsessive-compulsive disorder (OCD). While some clinical evidence implicates 5-HT(2C) receptors in this disorder, a definitive function has yet to be validated. We hypothesized that 5-HT(2C) receptor knockout (KO) mice may display compulsive-like behavior. This paper describes characterization of several distinct, highly organized behaviors in mice lacking functional 5-HT(2C) receptors, which supports a compulsive-like syndrome.Compulsive-like behavior was assessed in male 5-HT(2C) receptor KO and wildtype (WT) mice. Chewing of non-nutritive clay, chewing patterns on plastic-mesh screens, and the frequency of head dipping were measured. 5-HT(2C) receptor KO mice chewed more clay, produced a distinct pattern of "neat" chewing of plastic screens and exhibited reduced habituation of head dipping activity compared to WT mice. We conclude that the 5-HT(2C) receptor null mutant mouse provides a promising model of compulsive behavior and a means to further explore the role of 5-HT in OCD.

Animals↗
PubMed2003

Repeated stress in young and old 5-HT(2C) receptor knockout mice.

Serotonin (5-HT)(2C) receptor null mutant (knockout, KO) mice develop hyperphagia and midlife obesity. Based upon previous observations indicating altered responsiveness to stressful environmental conditions in these mice, we hypothesized that this KO mouse was hyperresponsive to repeated stress. To test this, we examined the effect of two intensities of repeated stress on food intake and body weight in 5-HT(2C) receptor KO and wild-type (WT) mice. The stressors involved daily cage change (including handling) for 3 days then daily restraint for 4 days. On the final day, mice were immediately decapitated after restraint to assess levels of plasma hormones. Two ages were used: young (12 weeks) and old (32-34 weeks). Basally, young KO were prehyperphagic and weighed the same as WT. In the old mice, KO were frankly hyperphagic and heavier than WT. In response to repeated cage change alone, the genotype-specific difference in food intake in the young group was enhanced, whereas in the old group it was diminished. This stressor did not significantly affect body weight change or caloric efficiency with respect to age or genotype. Repeated restraint had little effect on the young mice. However, in the old mice, KO had decreases in relative body weight and caloric efficiency compared with WT. In the old KO mice, adrenocorticotrophic hormone (ACTH), corticosterone and insulin were increased compared with WT mice. Together, these findings indicate that 5-HT(2C) receptor KO mice are hyperresponsive to repeated stress and this effect is influenced by stressor intensity and initial metabolic state of the mouse.

Adrenocorticotropic Hormone↗
PubMed2003

A spoonful of sugar: feedback signals of energy stores and corticosterone regulate responses to chronic stress.

To begin to understand the effects of chronic stress on food intake and energy stores, the effects of increased activity in the hypothalamo-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) on the body and brain must first be understood. We propose two major systems that are both GC sensitive: a metabolic feedback that is inhibitory and a direct central GC drive. Under basal conditions, the metabolic feedback signal to brain is dominant, although infusion of GC into a lateral brain ventricle blocks the effects of the metabolic feedback. Chronic stress activates GC secretion and brain nuclear GC receptor occupancy, markedly changing the normal relationships between these two major corticosteroid-activated systems. The stressor-induced switch in the relative strengths of these signals determines subsequent brain regulation of stress responses (behavioral, neuroendocrine and autonomic outflows). The metabolic feedback effects of GCs are mimicked by voluntary sucrose ingestion in adrenalectomized rats, and experiments suggest that the metabolic feedback also inhibits the stressor-induced direct GC drive on brain. We speculate that the interaction between peripheral and central GC-sensitive signaling systems may be coupled through the inhibitory actions of endogenous opiatergic inputs on corticotropin-releasing factor (CRF) neurons.

Adrenalectomy↗
PubMed2003

Intermittent morphine administration induces dependence and is a chronic stressor in rats.

Although constant treatment with morphine (implanted pellets) does not activate the hypothalamic-pituitary-adrenal (HPA) axis, intermittent injections of morphine may constitute a chronic stressor in rats. To test this hypothesis, we compared the effects of morphine in escalating doses (10-40 mg/kg, s.c.) or saline injected twice daily for 4 days on energy balance, hormones, HPA responses to novel restraint and central corticotropin-releasing factor (CRF) mRNA 12 h and 8 days after the last morphine injection in adult male Sprague-Dawley rats. Weight gain stopped at the onset of morphine, weight loss was marked 36 h postmorphine; thereafter, body weight gain paralleled saline controls. At 12 h, insulin, leptin, and testosterone concentrations were reduced but normalized by 8 days. Restraint and tail nicks caused facilitated ACTH responses at 12 h, under-responsiveness at 8 days. CRF mRNA, measured only at 12 h, was increased in the paraventricular (PVN) and Barrington's nuclei (BAR), decreased in the bed nuclei of the stria terminalis (BNST) and unchanged in the amygdala (CeA) in morphine-treated rats. After stress, CRF mRNA increased in PVN in both groups, increased in BAR and decreased in BNST in saline but not morphine groups, and was unchanged in CeA in both groups. Results from all variables characterize intermittent morphine injections as a chronic stressor. In contrast to constant treatment, injected morphine probably allows some withdrawal during each 12 h interval, causing repeated stress. Drug addicts treat themselves intermittently, and stress causes relapse after withdrawal. Thus, intermittent morphine, itself, may promote relapse.

Animals↗
PubMed2003

Repeated, non-habituating stress suppresses inflammatory plasma extravasation by a novel, sympathoadrenal dependent mechanism.

The mechanism by which chronic stress affects the course of inflammatory diseases is still not well understood. We have evaluated the effect of two types of nonhabituating stress on a major component of the inflammatory response, synovial plasma extravasation, induced by perfusion of the potent inflammatory mediator, bradykinin and evaluated the underlying neuroendocrine mechanism in the rat. Chronic intermittent noise or ether stress induced profound inhibition of bradykinin-induced plasma extravasation, which is associated with increased adjuvant-arthritis severity. This inhibition, however, took 24 h to fully develop after the last exposure to stress and persisted for at least 48 h. The inhibition could be reversed by an additional exposure to the stressor, just prior to measuring the inflammatory response, suggesting that the delay is due to stress-induced release of a factor that acutely masks the inhibition of the inflammatory response. This novel, unexpected feature of the effect of nonhabituating stress on inflammation may help explain variability in effects of stress in patients with inflammatory disease. The effect of nonhabituating stress on inflammation was dependent on the sympathoadrenal axis with no detectable contribution by the hypothalamic-pituitary-adrenal axis.

Adrenal Medulla↗
PubMed2003

International Union of Pharmacology. XXXVI. Current status of the nomenclature for receptors for corticotropin-releasing factor and their ligands.

Receptors for corticotropin-releasing factor (CRF) are members of a family of G protein-coupled receptors ("Family B") that respond to a variety of structurally dissimilar releasing factors, neuropeptides, and hormones (including secretin, growth hormone-releasing factor, calcitonin, parathyroid hormone, pituitary adenylate cyclase-activating polypeptide, and vasoactive intestinal polypeptide) and signal through the cyclic AMP and/or calcium pathways. To date, three genes encoding additional CRF-like peptides (urocortins) have been identified in mammals. The urocortins and CRF bind with differential ligand selectivity at the two mammalian CRF receptors. This report was prepared by the International Union of Pharmacology Subcommittee on CRF Receptors, to summarize the current state of CRF receptor biology and to propose changes in the classification and nomenclature of CRF ligands and receptors.

Amino Acid Sequence↗
PubMed2003

The hepatic vagus mediates fat-induced inhibition of diabetic hyperphagia.

Diabetic rats both overeat high-carbohydrate diet and have altered hypothalamic neuropeptide Y (NPY) and corticotropin-releasing factor (CRF). In contrast, a high-fat diet reduces caloric intake of diabetics to normal, reflected by normal hypothalamic NPY and CRF content. How the brain senses these changes in diet is unknown. To date, no hormonal changes explain these diet-induced changes in caloric intake. We tested whether the common branch of the hepatic vagus mediates the fat signal. We presented fat in two ways. First, diabetic and vehicle-treated rats were offered a cup of lard in addition to their normal high-carbohydrate diet. Second, we switched diabetic rats from high-carbohydrate diet to high-fat diet, without choice. In streptozotocin-treated rats, both methods resulted in fat-induced inhibition of caloric intake and normalization of hypothalamic neuropeptides to nondiabetic levels. Strikingly, common branch hepatic vagotomy (unlike gastroduodenal vagotomy) entirely blocked these fat-induced changes. Although a shift in hepatic energy status did not explain the lard-induced changes in diabetic rats, the data suggested that common hepatic branch vagotomy does not interfere with hepatic energy status. Furthermore, common branch hepatic vagotomy without diabetes induced indexes of obesity. Abnormal function of the hepatic vagus, as occurs in diabetic neuropathy, may contribute to diabetic obesity.

Adenosine Triphosphate↗
PubMed2002

Corticosterone infused intracerebroventricularly inhibits energy storage and stimulates the hypothalamo-pituitary axis in adrenalectomized rats drinking sucrose.

When allowed to drink sucrose, bilaterally adrenalectomized (ADX) rats exhibit normal weight gain, food intake, sympathetic neural activity, and ACTH compared with sham-ADX rats. Furthermore, ADX rats drinking sucrose have normal corticotropin-releasing factor (CRF) mRNA throughout brain. In ADX rats without sucrose, all of these variables are abnormal. Systemic corticosterone (B) replacement also restores these variables in ADX rats to normal. To test whether B acts centrally, we infused B or saline intracerebroventricularly into ADX rats under basal conditions and after repeated restraint. Rats were exposed to no stress or 3 h/d restraint for 3 d. Body weights and food and fluid intakes were measured. Brains were analyzed using immunocytochemistry against glucocorticoid receptors (GR) and CRF. Intracerebroventricular B blocked the positive effects of sucrose on metabolism, increased basal ACTH concentrations, and augmented ACTH responses to restraint on d 3. B-infused rats exhibited nuclear GR staining in perirhinal cortex, hippocampus, and hypothalamic paraventricular nuclei, showing that infused B spreads effectively. CRF staining in the paraventricular nucleus of the hypothalamus was higher in B- than in saline-infused rats. We conclude that under basal conditions B acts systemically, but not in the brain, to restore metabolism and neuropeptides after adrenalectomy. By contrast, tonic GR occupancy in brain initiates metabolic and ACTH responses characteristic of stress.

Adrenalectomy↗
PubMed2002

Marked regulatory shifts in gonadal, adrenal, and metabolic system responses to repeated restraint stress occur within a 3-week period in pubertal male rats.

We compared testosterone (T), corticotropin (ACTH), corticosterone (B), and leptin responses to three daily 3-h bouts of restraint and blood sampling as well as energy balance of male rats in early (40 d of age) and late (60 d of age) puberty. Rats either remained intact or were adrenalectomized and replaced with B clamped at basal mean values (ADX+B). Hormones, weight gain, food intake, and fat depot weight were measured during or after the days of stress. The major effects of restraint on T, ACTH, and energetic responses were age dependent, but clamped B affected the effects of restraint seen in intact rats at each age. T secretion was inhibited in 40-d-old and was stimulated in 60-d-old rats after restraint. ACTH responses were high, but diminished with repetition of stress in intact, but not ADX+B, 40-d-old rats. ACTH responses were lower, but constant across days, in both intact and ADX+B 60-d-old rats. Younger rats gained weight during the period of stress, whereas older rats stopped gaining weight. We conclude that the central regulation of stress responses shifts markedly between early and late puberty, although stress-induced B responses are important at both ages. In early puberty, priority is placed on maintaining normal ponderal growth, whereas in late puberty, priority is placed on maintaining reproductive capability.

Adipose Tissue↗
PubMed2002

Glucocorticoids prolong Ca(2+) transients in hippocampal-derived H19-7 neurons by repressing the plasma membrane Ca(2+)-ATPase-1.

Calcium ions (Ca(2+)) play an important role in mediating an array of structural and functional responses in cells. In hippocampal neurons, elevated glucocorticoid (GC) levels, as seen during stress, perturb calcium homeostasis and result in altered neuronal excitability and viability. Ligand- and voltage-gated calcium channels have been the presumed targets of hormonal regulation; however, circumstantial evidence has suggested the possibility that calcium extrusion might be an important target of GC regulation. Here we demonstrate that GC-induced repression of the plasma membrane Ca(2+)-ATPase-1 (PMCA1) is an essential determinant of intracellular Ca(2+) levels ([Ca(2+)](i)) in cultured hippocampal H19-7 cells. In particular, GC treatment caused a prolongation of agonist-evoked elevation of [Ca(2+)](i) that was prevented by the expression of exogenous PMCA1. Furthermore, selective inhibition of PMCA1 using the RNA interference technique caused prolongation of Ca(2+) transients in the absence of GC treatment. Taken together, these observations suggest that GC-mediated repression of PMCA1 is both necessary and sufficient to increase agonist-evoked Ca(2+) transients by down-regulating Ca(2+) extrusion mechanisms in the absence of effects on calcium channels. Prolonged exposure to GCs, resulting in concomitant accumulation of [Ca(2+)](i), is likely to compromise neuronal function and viability.

Calcium Signaling↗