Glucocorticoids act in the dorsal hindbrain to increase arterial pressure

Hindbrain Adrenergic/Noradrenergic Control of Integrated Endocrine and Autonomic Stress Responses

Hindbrain adrenergic/noradrenergic nuclei facilitate endocrine and autonomic responses to physical and psychological challenges. Neurons that synthesize adrenaline and noradrenaline target hypothalamic structures to modulate endocrine responses while descending spinal projections regulate sympathetic function. Furthermore, these neurons respond to diverse stress-related metabolic, autonomic, and psychosocial challenges. Accordingly, adrenergic and noradrenergic nuclei are integrative hubs that promote physiological adaptation to maintain homeostasis. However, the precise mechanisms through which adrenaline- and noradrenaline-synthesizing neurons sense interoceptive and exteroceptive cues to coordinate physiological responses have yet to be fully elucidated. Additionally, the regulatory role of these cells in the context of chronic stress has received limited attention. This mini-review consolidates reports from preclinical rodent studies on the organization and function of brainstem adrenaline and noradrenaline cells to provide a framework for how these nuclei coordinate endocrine and autonomic physiology. This includes identification of hindbrain adrenaline- and noradrenaline-producing cell groups and their role in stress responding through neurosecretory and autonomic engagement. Although temporally and mechanistically distinct, the endocrine and autonomic stress axes are complementary and interconnected. Therefore, the interplay between brainstem adrenergic/noradrenergic nuclei and peripheral physiological systems is necessary for integrated stress responses and organismal survival.

NOX-dependent reactive oxygen species production underlies arrhythmias susceptibility in dexamethasone-treated rats

Dexamethasone is the most clinically used glucocorticoid with an established role in the treatment of a wide spectrum of inflammatory-related diseases. While the therapeutic actions are well known, dexamethasone treatment causes a number of cardiovascular side effects, which are complex, frequent and, in some cases, clinically unnoticeable. Here, we investigated whether a therapeutic regimen of dexamethasone affects cardiac arrhythmogenesis, focusing on the contribution of Nox-derived reactive oxygen species (ROS). Male Wistar rats were treated with dexamethasone (2 mg/kg, i.p.) for 7 days. Afterward, hemodynamic measurements, autonomic modulation, left ventricular function, cardiac fibrosis, reactive oxygen species (ROS) generation, Nox protein expression, superoxide dismutase (SOD) and catalase activities, and arrhythmias incidence were evaluated. Here, we show that dexamethasone increases blood pressure, associated with enhanced cardiac and vascular sympathetic modulation. Moreover, a marked increase in the cardiac ROS generation was observed, whereas the enhanced SOD activity did not prevent the higher levels of lipid peroxidation in the dexamethasone group. On the other hand, increased cardiac Nox 4 expression and hydrogen peroxide decomposition rate was observed in dexamethasone-treated rats, while Nox 2 remained unchanged. Interestingly, although preserved ventricular contractility and β-adrenergic responsiveness, we found that dexamethasone-treated rats displayed greater interstitial and perivascular fibrosis than control. Surprisingly, despite the absence of arrhythmias at basal condition, we demonstrated, by in vivo and ex vivo approaches, that dexamethasone-treated rats are more susceptible to develop harmful forms of ventricular arrhythmias when challenged with pharmacological drugs or burst pacing-induced arrhythmias. Notably, concomitant treatment with apocynin, an inhibitor of NADPH oxidase, prevented these ectopic ventricular events. Together, our results reveal that hearts become arrhythmogenic during dexamethasone treatment, uncovering the pivotal role of ROS-generating NADPH oxidases for arrhythmias vulnerability.

Corticolimbic regulation of cardiovascular responses to stress

Cardiovascular disease, a leading cause of death worldwide, is frequently initiated or exacerbated by stress. In fact, chronic stress exposure and heightened reactions to acute psychological stress are both associated with increased cardiovascular morbidity. This brief review focuses on the mechanisms by which corticolimbic nuclei, critical for stress appraisal and emotional reactivity, regulate heart rate and blood pressure responses to psychological stress. Both human and rodent data are examined with a major emphasis on basic studies investigating prefrontal cortex, amygdala, and hippocampus. A detailed literature review reveals substantial limitations in our understanding of this circuitry, as well as significant opportunities for future investigation that may ultimately reduce the burden of cardiovascular illness.

Hypothalamic-Pituitary--Adrenal Axis-Feedback Control

The hypothalamo-pituitary-adrenal axis (HPA) is responsible for stimulation of adrenal corticosteroids in response to stress. Negative feedback control by corticosteroids limits pituitary secretion of corticotropin, ACTH, and hypothalamic secretion of corticotropin-releasing hormone, CRH, and vasopressin, AVP, resulting in regulation of both basal and stress-induced ACTH secretion. The negative feedback effect of corticosteroids occurs by action of corticosteroids at mineralocorticoid receptors (MR) and/or glucocorticoid receptors (GRs) located in multiple sites in the brain and in the pituitary. The mechanisms of negative feedback vary according to the receptor type and location within the brain-hypothalmo-pituitary axis. A very rapid nongenomic action has been demonstrated for GR action on CRH neurons in the hypothalamus, and somewhat slower nongenomic effects are observed in the pituitary or other brain sites mediated by GR and/or MR. Corticosteroids also have genomic actions, including repression of the pro-opiomelanocortin (POMC) gene in the pituitary and CRH and AVP genes in the hypothalamus. The rapid effect inhibits stimulated secretion, but requires a rapidly rising corticosteroid concentration. The more delayed inhibitory effect on stimulated secretion is dependent on the intensity of the stimulus and the magnitude of the corticosteroid feedback signal, but also the neuroanatomical pathways responsible for activating the HPA. The pathways for activation of some stressors may partially bypass hypothalamic feedback sites at the CRH neuron, whereas others may not involve forebrain sites; therefore, some physiological stressors may override or bypass negative feedback, and other psychological stressors may facilitate responses to subsequent stress.

Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.

Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.

Neurogenic mechanisms underlying the rapid onset of sympathetic responses to intermittent hypoxia

Sleep apnea (SA) leads to metabolic abnormalities and cardiovascular dysfunction. Rodent models of nocturnal intermittent hypoxia (IH) are used to mimic arterial hypoxemias that occur during SA. This mini-review focuses on our work examining central nervous system (CNS) mechanisms whereby nocturnal IH results in increased sympathetic nerve discharge (SND) and hypertension (HTN) that persist throughout the 24-h diurnal period. Within the first 1-2 days of IH, arterial pressure (AP) increases even during non-IH periods of the day. Exposure to IH for 7 days biases nucleus tractus solitarius (NTS) neurons receiving arterial chemoreceptor inputs toward increased discharge, providing a substrate for persistent activation of sympathetic outflow. IH HTN is blunted by manipulations that reduce angiotensin II (ANG II) signaling within the forebrain lamina terminalis suggesting that central ANG II supports persistent IH HTN. Inhibition of the hypothalamic paraventricular nucleus (PVN) reduces ongoing SND and acutely lowers AP in IH-conditioned animals. These findings support a role for the PVN, which integrates information ascending from NTS and descending from the lamina terminalis, in sustaining IH HTN. In summary, our findings indicate that IH rapidly and persistently activates a central circuit that includes the NTS, forebrain lamina terminalis, and the PVN. Our working model holds that NTS neuromodulation increases transmission of arterial chemoreceptor inputs, increasing SND via connections with PVN and rostral ventrolateral medulla. Increased circulating ANG II sensed by the lamina terminalis generates yet another excitatory drive to PVN. Together with adaptations intrinsic to the PVN, these responses to IH support rapid onset neurogenic HTN.

Brain-derived neurotrophic factor modulates angiotensin signaling in the hypothalamus to increase blood pressure in rats

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) in response to hypertensive stimuli including stress and hyperosmolarity. However, it is unclear whether BDNF in the PVN contributes to increases in blood pressure (BP). We tested the hypothesis that increased BDNF levels within the PVN would elevate baseline BP and heart rate (HR) and cardiovascular stress responses by altering central angiotensin signaling. BP was recorded using radiotelemetry in male Sprague-Dawley rats after bilateral PVN injections of adeno-associated viral vectors expressing green fluorescent protein (GFP) or myc epitope-tagged BDNF fusion protein. Cardiovascular responses to acute stress were evaluated 3 to 4 wk after injections. Additional GFP and BDNF-treated animals were equipped with osmotic pumps for intracerebroventricular infusion of saline or the angiotensin type-1 receptor (AT1R) inhibitor losartan (15 μg·0.5 μl(-1)·h(-1)). BDNF treatment significantly increased baseline BP (121 ± 3 mmHg vs. 99 ± 2 mmHg in GFP), HR (394 ± 9 beats/min vs. 314 ± 4 beats/min in GFP), and sympathetic tone indicated by HR- and BP-variability analysis and adrenomedullary tyrosine hydroxylase protein expression. In contrast, body weight and BP elevations to acute stressors decreased. BDNF upregulated AT1R mRNA by ∼80% and downregulated Mas receptor mRNA by ∼50% in the PVN, and losartan infusion partially inhibited weight loss and increases in BP and HR in BDNF-treated animals without any effect in GFP rats. Our results demonstrate that BDNF overexpression in the PVN results in sympathoexcitation, BP and HR elevations, and weight loss that are mediated, at least in part, by modulating angiotensin signaling in the PVN.

Glucocorticoid receptors in the nucleus of the solitary tract (NTS) decrease endocrine and behavioral stress responses

Stress activates the hypothalamo-pituitary-adrenal (HPA) axis, leading to adrenocortical secretion of glucocorticoids. The magnitude and duration of the HPA axis response is mediated in large part by the glucocorticoid receptor (GR). The nucleus of the solitary tract (NTS) abundantly expresses the GR and is a key brain region for processing autonomic and endocrine stress responses. This study tests the hypothesis that GR within the NTS plays an important role in inhibiting stress-induced endocrine and behavioral responses. Cohorts of rats received bilateral micropellet (30 μg) implantations of crystalline corticosterone, mifepristone (a GR antagonist) or cholesterol (control) directed into the region of the NTS, and were subsequently subjected to either acute psychogenic (restraint) stress or chronic variable stress (CVS). We found that NTS GR antagonism increased acute stress-induced corticosterone levels, whereas GR activation within the NTS attenuated this response. Following CVS, basal and 15 min post-restraint plasma corticosterone levels were increased by NTS GR antagonism, which was associated with an increase in Fos immunoreactivity within the PVN. Using the elevated plus maze (EPM) and forced swim test (FST), we assessed the effect of NTS GR inhibition on anxiety- and depression-like behaviors, respectively. GR inhibition within the NTS decreased open arm exploratory behavior in the EPM and increased immobility in the FST relative to controls. Together, the findings reveal a novel role of NTS GR signaling for inhibiting both endocrine and behavioral responses to stress.

Elevated corticosterone in the dorsal hindbrain increases plasma norepinephrine and neuropeptide Y, and recruits a vasopressin response to stress

Repeated stress and chronically elevated glucocorticoids cause exaggerated cardiovascular responses to novel stress, elevations in baseline blood pressure, and increased risk for cardiovascular disease. We hypothesized that elevated corticosterone (Cort) within the dorsal hindbrain (DHB) would: 1) enhance arterial pressure and neuroendocrine responses to novel and repeated restraint stress, 2) increase c-Fos expression in regions of the brain involved in sympathetic stimulation during stress, and 3) recruit a vasopressin-mediated blood pressure response to acute stress. Small pellets made of 10% Cort were implanted on the surface of the DHB in male Sprague-Dawley rats. Blood pressure was measured by radiotelemetry. Cort concentration was increased in the DHB in Cort-treated compared with Sham-treated rats (60 ± 15 vs. 14 ± 2 ng Cort/g of tissue, P < 0.05). DHB Cort significantly increased the integrated arterial pressure response to 60 min of restraint stress on days 6, 13, and 14 following pellet implantation (e.g., 731 ± 170 vs. 1,204 ± 68 mmHg/60 min in Sham- vs. Cort-treated rats, day 6, P < 0.05). Cort also increased baseline blood pressure by day 15 (99 ± 2 vs. 108 ± 3 mmHg for Sham- vs. Cort-treated rats, P < 0.05) and elevated baseline plasma norepinephrine and neuropeptide Y concentrations. Cort significantly enhanced stress-induced c-Fos expression in vasopressin-expressing neurons in the paraventricular nucleus of the hypothalamus, and blockade of peripheral vasopressin V1 receptors attenuated the effect of DHB Cort to enhance the blood pressure response to restraint. These data indicate that glucocorticoids act within the DHB to produce some of the adverse cardiovascular consequences of chronic stress, in part, by a peripheral vasopressin-dependent mechanism.

Glucocorticoid receptor deletion from the dorsal raphé nucleus of mice reduces dysphoria-like behavior and impairs hypothalamic-pituitary-adrenocortical axis feedback inhibition

Glucocorticoids can cause depression and anxiety. Mechanisms for glucocorticoid effects on mood are largely undefined. The dorsal raphé nucleus (DRN) produces the majority of serotonin in the brain, and expresses glucocorticoid receptors (GR). Because we previously showed that antidepressants used to treat depression and anxiety decrease DRN GR expression, we hypothesized that deleting DRN GR would have anxiolytic- and antidepressant-like effects. We also hypothesized that DRN GR deletion would disinhibit activity of the hypothalamic-pituitary-adrenal (HPA) axis. Adeno-associated virus pseudotype AAV2/9 expressing either Cre recombinase (DRNGRKO mice) or GFP (DRN-GFP mice) was injected into the DRN of floxed GR mice to test these hypotheses. Three weeks after injection, mice underwent 21 days of social defeat or control handling and were tested for anxiety-like behavior (open-field test, elevated-plus maze), depression-like behavior [sucrose preference, forced-swim test (FST), tail-suspension test (TST)], social interaction, and circadian and stress-induced HPA activity. DRN GR deletion decreased anxiety-like behavior in control but not in defeated mice. DRN GR deletion decreased FST and tended to decrease TST despair-like behavior in both control and defeated mice, but did not affect sucrose preference. Exploration of social (a novel mouse) as well as neutral (an empty box) targets was increased in DRNGRKO mice, suggesting that DRN GR deletion also promotes active coping. DRN GR deletion increased stress-induced HPA activity without strongly altering circadian HPA activity. We have shown a novel role for DRN GR to mediate anxiety- and despair-like behavior and to regulate HPA negative feedback during acute stress.

Knockdown of tyrosine hydroxylase in the nucleus of the solitary tract reduces elevated blood pressure during chronic intermittent hypoxia

Noradrenergic A2 neurons in nucleus tractus solitarius (NTS) respond to stressors such as hypoxia. We hypothesize that tyrosine hydroxylase (TH) knockdown in NTS reduces cardiovascular responses to chronic intermittent hypoxia (CIH), a model of the arterial hypoxemia observed during sleep apnea in humans. Adult male Sprague-Dawley rats were implanted with radiotelemetry transmitters and adeno-associated viral constructs with green fluorescent protein (GFP) reporter having either short hairpin RNA (shRNA) for TH or scrambled virus (scRNA) were injected into caudal NTS. Virus-injected rats were exposed to 7 days of CIH (alternating periods of 10% O2 and of 21% O2 from 8 AM to 4 PM; from 4 PM to 8 AM rats were exposed to 21% O2). CIH increased mean arterial pressure (MAP) and heart rate (HR) during the day in both the scRNA (n = 14, P < 0.001 MAP and HR) and shRNA (n = 13, P < 0.001 MAP and HR) groups. During the night, MAP and HR remained elevated in the scRNA rats (P < 0.001 MAP and HR) but not in the shRNA group. TH immunoreactivity and protein were reduced in the shRNA group. FosB/ΔFosB immunoreactivity was decreased in paraventricular nucleus (PVN) of shRNA group (P < 0.001). However, the shRNA group did not show any change in the FosB/ΔFosB immunoreactivity in the rostral ventrolateral medulla. Exposure to CIH increased MAP which persisted beyond the period of exposure to CIH. Knockdown of TH in the NTS reduced this CIH-induced persistent increase in MAP and reduced the transcriptional activation of PVN. This indicates that NTS A2 neurons play a role in the cardiovascular responses to CIH.

Dexamethasone rapidly increases GABA release in the dorsal motor nucleus of the vagus via retrograde messenger-mediated enhancement of TRPV1 activity

Glucocorticoids influence vagal parasympathetic output to the viscera via mechanisms that include modulation of neural circuitry in the dorsal vagal complex, a principal autonomic regulatory center. Glucocorticoids can modulate synaptic neurotransmitter release elsewhere in the brain by inducing release of retrograde signalling molecules. We tested the hypothesis that the glucocorticoid agonist dexamethasone (DEX) modulates GABA release in the rat dorsal motor nucleus of the vagus (DMV). Whole-cell patch-clamp recordings revealed that DEX (1-10 µM) rapidly (i.e. within three minutes) increased the frequency of tetrodotoxin-resistant, miniature IPSCs (mIPSCs) in 67% of DMV neurons recorded in acutely prepared slices. Glutamate-mediated mEPSCs were also enhanced by DEX (10 µM), and blockade of ionotropic glutamate receptors reduced the DEX effect on mIPSC frequency. Antagonists of type I or II corticosteroid receptors blocked the effect of DEX on mIPSCs. The effect was mimicked by application of the membrane-impermeant BSA-conjugated DEX, and intracellular blockade of G protein function with GDP _βS in the recorded cell prevented the effect of DEX. The enhancement of GABA release was blocked by the TRPV1 antagonists, 5’-iodoresiniferatoxin or capsazepine, but was not altered by the cannabinoid type 1 receptor antagonist AM251. The DEX effect was prevented by blocking fatty acid amide hydrolysis or by inhibiting anandamide transport, implicating involvement of the endocannabinoid system in the response. These findings indicate that DEX induces an enhancement of GABA release in the DMV, which is mediated by activation of TRPV1 receptors on afferent terminals. The effect is likely induced by anandamide or other ‘endovanilloid’, suggesting activation of a local retrograde signal originating from DMV neurons to enhance synaptic inhibition locally in response to glucocorticoids.

Effect of global and regional sympathetic blockade on arterial pressure during water deprivation in conscious rats

Forty-eight hours of water deprivation (WD) in conscious rats results in a paradoxical increase in mean arterial pressure (MAP). Previous studies suggest this may be due to increased sympathetic nerve activity (SNA). However, this remains to be investigated in conscious, freely behaving animals. The purpose of this study was to determine, in conscious rats, the role of the sympathetic nervous system (SNS) in mediating WD-induced increases in MAP and to identify which vascular beds are targeted by increased SNA. Each rat was chronically instrumented with a radiotelemetry transmitter to measure MAP and heart rate (HR) and an indwelling venous catheter for plasma sampling and/or drug delivery. MAP and HR were continuously measured during a 2-day baseline period followed by 48 h of WD and then a recovery period. By the end of the WD period, MAP increased by ∼15 mmHg in control groups, whereas HR did not change significantly. Chronic blockade of α(1)/β(1)-adrenergic receptors significantly attenuated the WD-induced increase in MAP, suggesting a role for global activation of the SNS. However, the MAP response to WD was unaffected by selective denervations of the hindlimb, renal, or splanchnic vascular beds, or by adrenal demedullation. In contrast, complete adrenalectomy (with corticosterone and aldosterone replaced) significantly attenuated the MAP response to WD in the same time frame as α(1)/β(1)-adrenergic receptor blockade. These results suggest that, in conscious water-deprived rats, the SNS contributes to the MAP response and may be linked to release of adrenocortical hormones. Finally, this sympathetically mediated response is not dependent on increased SNA to one specific vascular bed.

Regulation of the stress response in rats by central actions of glucocorticoids

Chronic stress causes elevations in glucocorticoid secretion and also increases the incidence of hypertension and other manifestations of cardiovascular disease. The extent to which the elevated glucocorticoids mediate the stress-associated increase in cardiovascular disease risk is unknown. Chronically elevated glucocorticoids can cause hypertension by acting in the periphery, but their effects within the brain on blood pressure regulation remain largely unexplored. We developed a method to produce selective chronic increases in the endogenous glucocorticoid corticosterone or the glucocorticoid receptor antagonist mifepristone within the hindbrain region, which includes a key cardiovascular regulatory area, the nucleus of the solitary tract (NTS). Experiments were performed in male Sprague-Dawley, Wistar-Kyoto (WKY) and borderline hypertensive rats (BHR). The results indicate that elevated exogenous corticosterone can act within the hindbrain to enhance the arterial pressure response to novel restraint stress and to reduce the gain and increase the mid-point of the arterial baroreflex. Basal levels of endogenous corticosterone have no effect on the arterial pressure response to stress in normotensive rats but enhance this response in BHR. Chronic stress-induced increases in baseline corticosterone enhance the arterial pressure response to stress in BHR but attenuate the adaptation of the response in WKY rats. Furthermore, an elevated corticosterone concentration within the hindbrain is necessary but not sufficient to cause glucocorticoid-induced hypertension. The effects of corticosterone within the hindbrain on blood pressure regulation are mediated in part by the glucocortiocid receptor, but are also likely to involve mineralocorticoid receptor-mediated effects and NTS catecholaminergic neurons. These data support the hypothesis that elevated glucocorticoids acting within the brain probably contribute to the adverse effects of stress on cardiovascular health in susceptible people.

Chronic blockade of hindbrain glucocorticoid receptors reduces blood pressure responses to novel stress and attenuates adaptation to repeated stress

Exogenous glucocorticoids act within the hindbrain to enhance the arterial pressure response to acute novel stress. Here we tested the hypothesis that endogenous glucocorticoids act at hindbrain glucocorticoid receptors (GR) to augment cardiovascular responses to restraint stress in a model of stress hyperreactivity, the borderline hypertensive rat (BHR). A 3- to 4-mg pellet of the GR antagonist mifepristone (Mif) was implanted over the dorsal hindbrain (DHB) in Wistar-Kyoto (WKY) and BHRs. Control pellets consisted of either sham DHB or subcutaneous Mif pellets. Rats were either subjected to repeated restraint stress (chronic stress) or only handled (acute stress) for 3-4 wk, then all rats were stressed on the final day of the experiment. BHR showed limited adaptation of the arterial pressure response to restraint, and DHB Mif significantly (P Collapse

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MESH Headings

• Adaptation, Physiological/physiology
• Animals
• Blood Pressure/physiology
• Body Weight/physiology
• Corticosterone/blood
• Disease Models, Animal
• Heart Rate/physiology
• Hormone Antagonists/pharmacology
• Hypertension/metabolism
• Hypertension/physiopathology
• Male
• Mifepristone/pharmacology
• Rats
• Rats, Inbred WKY
• Rats, Sprague-Dawley
• Receptors, Glucocorticoid/antagonists & inhibitors
• Receptors, Glucocorticoid/drug effects
• Receptors, Glucocorticoid/metabolism
• Rhombencephalon/metabolism
• Stress, Physiological/physiology

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Grants

• R01-HL-076807 NHLBI NIH HHS

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Affiliation(s)

Andrea G Bechtold Department of Medical Pharmacology, School of Medicine, University of California Davis, Davis, California, USA
Gina Patel
Guenther Hochhaus
Deborah A Scheuer

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Cardiac corticosteroid receptors mediate the enlargement of the ovine fetal heart induced by chronic increases in maternal cortisol

Previous studies have demonstrated that modest, physiologically relevant increases in maternal cortisol in late gestation result in enlargement of the fetal heart. In this study, we investigated the role of mineralocorticoid receptor (MR) or glucocorticoid receptor (GR) in this enlargement. Ewes with single fetuses were randomly assigned at approximately 120 days of gestation to one of four groups: maternal cortisol infusion (1 mg/kg per day, cortisol); maternal cortisol infusion with fetal intrapericardial infusion of the MR antagonist (MRa) potassium canrenoate (600 microg/day; cortisol+MRa); maternal cortisol infusion with fetal intrapericardial infusion of the GR antagonist (GRa) mifepristone (50 microg/day, cortisol+GRa); and maternal saline infusion (control). At approximately 130 days of gestation, fetal heart to body weight ratio and right ventricular (RV) and left ventricular (LV) free wall thicknesses were increased in the cortisol group when compared with control group. Fetal hearts from the cortisol+MRa group weighed significantly less, with thinner LV, RV, and interventricular septum walls, when compared with the cortisol group. Fetal hearts from the cortisol+GRa group had significantly thinner RV walls than the cortisol group. Fetal arterial pressure and heart rate were not different among groups at 130 days. Picrosirius red staining of fetal hearts indicated that the increased size was not accompanied by cardiac fibrosis. These results suggest that physiologic increases in maternal cortisol in late gestation induce fetal cardiac enlargement via MR and, to a lesser extent, by GR, and indicate that the enlargement is not secondary to an increase in fetal blood pressure or an increase in fibrosis within the fetal heart.

Genetic predisposition to hypertension sensitizes borderline hypertensive rats to the hypertensive effects of prenatal glucocorticoid exposure

An adverse intrauterine environment can increase the incidence of hypertension and other cardiovascular disease risk factors. However, in clinical and experimental studies the magnitude of the effect is variable. Possibly, the relative influence of the prenatal environment on cardiovascular disease is determined in part by genetic factors that predispose individuals to the development of environmentally induced hypertension. We tested this hypothesis by comparing the effects of prenatal dexamethasone treatment (Dex, 300 microg kg(-1) i.p. on days 15 and 16 of gestation) in borderline hypertensive rats (BHR) and control Wistar-Kyoto (WKY) rats. Blood pressure, heart rate and plasma corticosterone values were measured at rest during the middle of the day, and during 1 h of restraint stress in the adult offspring using indwelling arterial catheters implanted at least 4 days prior to data collection. Compared with the saline (vehicle) control treatment, prenatal dexamethasone significantly (P < 0.05) increased baseline mean arterial pressure in male (123 +/- 2 versus 131 +/- 3 mmHg, saline versus Dex) and female (121 +/- 2 versus 130 +/- 2 mmHg, saline versus Dex) BHR, but not in male (108 +/- 3 versus 113 +/- 2 mmHg, saline versus Dex) or female (112 +/- 2 versus 110 +/- 2 mmHg, saline versus Dex) WKY rats. Relative to saline treatment, prenatal Dex also significantly increased baseline heart rate (328 +/- 6 versus 356 +/- 5 beats min(-1), saline versus Dex) and plasma corticosterone (5 +/- 2 versus 24 +/- 4 microg dl(-1), saline versus Dex), and prolonged the corticosterone response to acute stress, selectively in female BHR. However, prenatal Dex significantly enhanced the arterial pressure response to acute stress only in female WKY, while Dex augmented the elevation in heart rate during stress only in male rats. We conclude that prenatal dexamethasone increased baseline arterial pressure selectively in BHR, and plasma corticosterone only in female BHR. In contrast, prenatal Dex enhanced cardiovascular reactivity to stress in both BHR and WKY rats.

Differential regulation of parvocellular neuronal activity in the paraventricular nucleus of the hypothalamus following single vs. repeated episodes of water restriction-induced drinking

Acute activation of the hypothalamic-pituitary-adrenal (HPA) axis releases glucocorticoids to maintain homeostasis, whereas prolonged exposure to elevated glucocorticoids has deleterious effects. Due to the potential benefits of limiting stress-induced glucocorticoid secretion, the present study uses drinking in dehydrated rats as a model to delineate mechanisms mobilized to rapidly inhibit HPA activity during stress. Using Fos expression as an indicator of neuronal activation, the effect of a single or repeated episode of dehydration-induced drinking on the activity of magnocellular and parvocellular neurons in the paraventricular nucleus (PVN) of the hypothalamus was examined. Adult male rats underwent a single episode or repeated (six) episodes of water restriction and were sacrificed before or after drinking water in the AM. Plasma osmolality, vasopressin (AVP), adrenocorticotropic hormone (ACTH) and corticosterone were elevated by water restriction and reduced after drinking in both models. Fos expression was elevated in AVP-positive magnocellular PVN neurons and AVP- and corticotropin releasing hormone (CRH)-positive parvocellular PVN neurons after water restriction. Fos expression was reduced in magnocellular AVP neurons after both models of restriction-induced drinking. In contrast, Fos expression did not change in AVP and CRH parvocellular neurons after a single episode of restriction-induced drinking, but was reduced after repeated episodes of restriction-induced drinking. These data indicate that drinking-induced decreases in glucocorticoids in dehydrated rats involve multiple factors including reduction in magnocellular release of vasopressin and reduction in parvocellular neuronal activity. The differential inhibition of PVN parvocellular neurons after repeated rehydration may reflect a conditioned response to repeated stress reduction.

Chronic activation of dorsal hindbrain corticosteroid receptors augments the arterial pressure response to acute stress

Augmented cardiovascular responses to acute stress can predict cardiovascular disease in humans. Chronic systemic increases in glucocorticoids produce enhanced cardiovascular responses to psychological stress; however, the site of action is unknown. Recent evidence indicates that glucocorticoids can act within the dorsal hindbrain to modulate cardiovascular function. Therefore, we tested the hypothesis that the endogenous glucocorticoid corticosterone can act in the dorsal hindbrain to enhance cardiovascular responses to restraint stress in conscious rats. Adrenal-intact animals with indwelling arterial catheters were treated for 4 or 6 days with 3- to 4-mg pellets of corticosterone or silastic (sham pellets) implanted on the dorsal hindbrain surface. Corticosterone pellets were also implanted either on the surface of the dura or subcutaneously to control for the systemic effects of corticosterone (systemic corticosterone). The integrated increase in arterial pressure during 1 hour of restraint stress was significantly (P<0.05) greater in dorsal hindbrain corticosterone (912+/-98 mm Hg per 60 minutes) relative to dorsal hindbrain sham (589+/-57 mm Hg per 60 minutes) or systemic corticosterone (592+/-122 mm Hg per 60 minutes) rats. The plasma glucose response after 10 minutes of stress was also significantly higher in dorsal hindbrain corticosterone-treated rats relative to both other groups. There were no significant between-group differences in the heart rate or corticosterone responses to stress. There were no differences in baseline values for any measured parameters. We conclude that corticosterone can act selectively in the dorsal hindbrain in rats with normal plasma corticosterone levels to augment the arterial pressure response to restraint stress.

Limited brain diffusion of the glucocorticoid receptor agonist RU28362 following i.c.v. administration: implications for i.c.v. drug delivery and glucocorticoid negative feedback in the hypothalamic-pituitary-adrenal axis

The experiments described herein present a method for tracking diffusion of the glucocorticoid receptor agonist RU28362 in brain following i.c.v. drug administration. A useful property of glucocorticoid receptor is that it is primarily cytoplasmic when unbound and rapidly translocates to the nucleus when bound by ligand. Thus, removal of endogenous glucocorticoids by adrenalectomy allows us to identify brain regions with activated glucocorticoid receptor after i.c.v. glucocorticoid receptor agonist treatment by examining the presence or absence of nuclear glucocorticoid receptor immunostaining. We have previously demonstrated that an i.p. injection of 150 microg/kg RU28362 1 h prior to restraint stress is sufficient to suppress stress-induced hypothalamic-pituitary-adrenal axis hormone secretion [Ginsberg AB, Campeau S, Day HE, Spencer RL (2003) Acute glucocorticoid pretreatment suppresses stress-induced hypothalamic-pituitary-adrenal axis hormone secretion and expression of corticotropin-releasing hormone hnRNA but does not affect c-fos mRNA or fos protein expression in the paraventricular nucleus of the hypothalamus. J Neuroendocrinol 15:1075-1083]. We report here, however, that in rats i.c.v. treatment with a high-dose of RU28362 (1 microg) 1 h prior to stressor onset does not suppress stress-induced hypothalamic-pituitary-adrenal axis activity. We then performed a series of experiments to examine the possible differences in glucocorticoid receptor activation patterns in brain and pituitary after i.c.v. or i.p. treatment with RU28362. In a dose-response study we found that 1 h after i.c.v. injection of RU28362 (0.001, 0.1 and 1.0 microg) glucocorticoid receptor nuclear immunoreactivity was only evident in brain tissue immediately adjacent to the lateral or third ventricle, including the medial but not more lateral portion of the medial parvocellular paraventricular nucleus of the hypothalamus. In contrast, i.p. injection of RU28362 produced a uniform predominantly nuclear glucocorticoid receptor immunostaining pattern throughout all brain tissue. I.c.v. injection of the endogenous glucocorticoid receptor agonist, corticosterone (1 microg) also had limited diffusion into brain tissue. Time-course studies indicated that there was not a greater extent of nuclear glucocorticoid receptor immunostaining present in brain after shorter (10 or 30 min) or longer (2 or 3 h) intervals of time after i.c.v. RU28362 injection. Importantly, time-course studies found that i.c.v. RU28362 produced significant increases in nuclear glucocorticoid receptor immunostaining in the anterior pituitary that were evident within 10 min after injection and maximal after 1 h. These studies support an extensive literature indicating that drugs have very limited ability to diffuse out of the ventricles into brain tissue after i.c.v. injection, while at the same time reaching peripheral tissue sites. In addition, these studies indicate that significant occupancy of some glucocorticoid receptor within the paraventricular nucleus of the hypothalamus and pituitary is not necessarily sufficient to suppress stress-induced hypothalamic-pituitary-adrenal axis activity.

Glucocorticoids act in the dorsal hindbrain to modulate baroreflex control of heart rate

Systemic corticosterone (Cort) modulates arterial baroreflex control of both heart rate and renal sympathetic nerve activity. Because baroreceptor afferents terminate in the dorsal hindbrain (DHB), an area with dense corticosteroid receptor expression, we tested the hypothesis that prolonged activation of DHB Cort receptors increases the midpoint and reduces the gain of arterial baroreflex control of heart rate in conscious rats. Small (3-4 mg) pellets of Cort (DHB Cort) or Silastic (DHB Sham) were placed on the surface of the DHB, or Cort was administered systemically by placing a Cort pellet on the surface of the dura (Dura Cort). Baroreflex control of heart rate was determined in conscious male Sprague Dawley rats on each of 4 days after initiation of treatment. Plots of arterial pressure vs. heart rate were analyzed using a four-parameter logistic function. After 3 days of treatment, the arterial pressure midpoint for baroreflex control of heart rate was increased in DHB Cort rats (123 +/- 2 mmHg) relative to both DHB Sham (108 +/- 3 mmHg) and Dura Cort rats (109 +/- 2 mmHg, P < 0.05). On day 4, baseline arterial pressure was greater in DHB Cort (112 +/- 2 mmHg) compared with DHB Sham (105 +/- 2 mmHg) and Dura Cort animals (106 +/- 2 mmHg, P < 0.05), and the arterial pressure midpoint was significantly greater than mean arterial pressure in the DHB Cort group only. Also on day 4, maximum baroreflex gain was reduced in DHB Cort (2.72 +/- 0.12 beats x min(-1) x mmHg(-1)) relative to DHB Sham and Dura Cort rats (3.51 +/- 0.28 and 3.37 +/- 0.27 beats x min(-1) x mmHg(-1), P < 0.05). We conclude that Cort acts in the DHB to increase the midpoint and reduce the gain of the heart rate baroreflex function.