Neurohumoral regulation in ischemia-induced heart failure. Role of the forebrain

Sexual Functions Following Cardiac Resynchronization Therapy: Evaluation of Male Patients and Their Partners

INTRODUCTION

Sexual functionality, a critical component of health-related quality of life, can decline for various reasons, including heart failure (HF). Our purpose was to prospectively evaluate male patients with HF scheduled for cardiac resynchronization therapy (CRT) in terms of sexual function, erectile function, and alterations in hormonal and biochemical parameters. In addition, we sought to determine the sexual functioning of the partners of these patients.

METHODS

 The study enrolled 103 male patients and their partners. The International Index of Erectile Function-5 (IIEF-5) was administered to all males and the Arizona Sexual Experience Scale (ASEX) questionnaire was completed by all participants, at baseline and three months after CRT.

RESULTS

 The ASEX scores of patients and partners demonstrated significant declines from baseline to post-intervention analysis. The IIEF-5 scores of patients showed a significant increase from baseline to post-intervention (p=0.001 for all).

CONCLUSION

 We conclude that sexual dysfunction is experienced by the partners of male patients with erectile dysfunction before CRT and that reversal of erectile problems with CRT yields improvements in both male and female sexual functions.

Angiotensin II induces apoptosis of cardiac microvascular endothelial cells via regulating PTP1B/PI3K/Akt pathway

Endothelial cell apoptosis and renin-angiotensin-aldosterone system (RAAS) activation are the major pathological mechanisms for cardiovascular disease and heart failure; however, the interaction and mechanism between them remain unclear. Investigating the role of PTP1B in angiotensin II (Ang II)-induced apoptosis of primary cardiac microvascular endothelial cells (CMECs) may provide direct evidence of the link between endothelial cell apoptosis and RAAS. Isolated rat CMECs were treated with different concentrations of Ang II to induce apoptosis, and an Ang II concentration of 4 nM was selected as the effective dose for the subsequent studies. The CMECs were cultured for 48 h with or without Ang II (4 nM) in the absence or presence of the PTP1B inhibitor TCS 401 (8 μM) and the PI3K inhibitor LY294002 (10 μM). The level of CMEC apoptosis was assessed by TUNEL staining and caspase-3 activity. The protein expressions of PTP1B, PI3K, Akt, p-Akt, Bcl-2, Bax, caspase-3, and cleaved caspase-3 were determined by Western blot (WB). The results showed that Ang II increased apoptosis of CMECs, upregulated PTP1B expression, and inhibited the PI3K/Akt pathway. Furthermore, cotreatment with PTP1B inhibitor significantly decreased the number of apoptotic CMECs induced by Ang II, along with increased PI3K expression, phosphorylation of Akt and the ratio of Bcl-2/Bax, decreased caspase-3 activity, and a cleaved caspase-3/caspase-3 ratio, while treatment with LY294002 partly inhibited the anti-apoptotic effect of the PTP1B inhibitor. Ang II induces apoptosis of primary rat CMECs via regulating the PTP1B/PI3K/Akt pathway.

Overexpression of copper/zinc superoxide dismutase in the median preoptic nucleus improves cardiac function after myocardial infarction in the rat

Previous reports indicate that overexpression of copper/zinc superoxide dismutase (CuZnSOD), an intracellular superoxide (O2 (•-) ) scavenging enzyme, in the brain subfornical organ improves cardiac function in a mouse model of heart failure (HF). A downstream hypothalamic site, the MnPO, may act as a relay centre for O2 (•-) to serve as a mediator in the pathophysiology of HF. To test the hypothesis that elevated O2 (•-) in the MnPO contributes to the pathophysiology of HF and decreased cardiac function, we injected adenovirus encoding CuZnSOD (AdCuZnSOD, n=7) or control empty adenovirus vector (AdEmpty, n=7) into the MnPO of normal rats. Subsequently, rats were subjected to coronary artery ligation to create a myocardial infarct (MI) of the left ventricle. Cardiac function was monitored via echocardiography. Upon completion, rat brains were examined for CuZnSOD expression in MnPO via immunofluorescence and histopathological analyses of cardiac infarct size were conducted. Baseline (EF) ejection fractions (%) of AdCuZnSOD and AdEmpty rats were 73 ± 1 and 71 ± 1, respectively. Two weeks after MI, EF was significantly decreased in both groups of rats (AdCuZnSOD: 51 ± 3, AdEmpty: 46 ± 1). In contrast, by 4 weeks post MI, EF had improved to 64 ± 2 in AdCuZnSOD rats, yet was only 52 ± 1 in AdEmpty rats, and this was accompanied by lower plasma noradrenaline levels in AdCuZnSOD rats (0.49 ± 0.19 ng/mL) compared to AdEmpty rats (1.20 ± 0.32 ng/mL). In conclusion, despite decreases in EF early after MI, overexpression of CuZnSOD in the MnPO was related to an improvement in left ventricular function and concomitant decreased plasma noradrenaline levels 4 weeks post MI.

Mesenchymal Stem Cells Improve Heart Rate Variability and Baroreflex Sensitivity in Rats with Chronic Heart Failure

Heart failure induced by myocardial infarct (MI) attenuates the heart rate variability (HRV) and baroreflex sensitivity, which are important risk factors for life-threatening cardiovascular events. Therapies with mesenchymal stem cells (MSCs) have shown promising results after MI. However, the effects of MSCs on hemodynamic (heart rate and arterial pressure) variability and baroreflex sensitivity in chronic heart failure (CHF) following MI have not been evaluated thus far. Male Wistar rats received MSCs or saline solution intravenously 1 week after ligation of the left coronary artery. Control (noninfarcted) rats were also evaluated. MI size was assessed using single-photon emission computed tomography (SPECT). The left ventricular ejection fraction (LVEF) was evaluated using radionuclide ventriculography. Four weeks after MSC injection, the animals were anesthetized and instrumented for chronic ECG recording and catheters were implanted in the femoral artery to record arterial pressure. Arterial pressure and HRVs were determined in time and frequency domain (spectral analysis) while HRV was also examined using nonlinear methods: DFA (detrended fluctuation analysis) and sample entropy. The initial MI size was the same among all infarcted rats but was reduced by MSCs. CHF rats exhibited increased myocardial interstitial collagen and sample entropy combined with the attenuation of the following cardiocirculatory parameters: DFA indices, LVEF, baroreflex sensitivity, and HRV. Nevertheless, MSCs hampered all these alterations, except the LVEF reduction. Therefore, 4 weeks after MSC therapy was applied to CHF rats, MI size and myocardial interstitial fibrosis decreased, while baroreflex sensitivity and HRV improved.

Bidirectional neuro-glial signaling modalities in the hypothalamus: role in neurohumoral regulation

Maintenance of bodily homeostasis requires concerted interactions between the neuroendocrine and the autonomic nervous systems, which generate adaptive neurohumoral outflows in response to a variety of sensory inputs. Moreover, an exacerbated neurohumoral activation is recognized to be a critical component in numerous disease conditions, including hypertension, heart failure, stress, and the metabolic syndrome. Thus, the study of neurohumoral regulation in the brain is of critical physiological and pathological relevance. Most of the work in the field over the last decades has been centered on elucidating neuronal mechanisms and pathways involved in neurohumoral control. More recently however, it has become increasingly clear that non-neuronal cell types, particularly astrocytes and microglial cells, actively participate in information processing in areas of the brain involved in neuroendocrine and autonomic control. Thus, in this work, we review recent advances in our understanding of neuro-glial interactions within the hypothalamic supraoptic and paraventricular nuclei, and their impact on neurohumoral integration in these nuclei. Major topics reviewed include anatomical and functional properties of the neuro-glial microenvironment, neuron-to-astrocyte signaling, gliotransmitters, and astrocyte regulation of signaling molecules in the extracellular space. We aimed in this review to highlight the importance of neuro-glial bidirectional interactions in information processing within major hypothalamic networks involved in neurohumoral integration.

Central regulation of blood pressure by the mineralocorticoid receptor

Addition of mineralocorticoid receptor (MR) antagonists to standard therapy for heart failure, kidney disease, metabolic syndrome, and diabetes is increasing steadily in response to clinical trials demonstrating clear benefits. In addition to blocking deleterious activity of MR within the heart, vessels and kidneys, MR antagonists target MR in hemodynamic regulatory centers in the brain, thereby decreasing excessive sympathetic nervous system drive, vasopressin release, abnormal baroreceptor function, and circulating and tissue pro-inflammatory cytokines. However, brain MR are also involved with cognition, memory, affect and functions yet to be determined. Understanding specific central mechanisms involved in blood pressure regulation by MR is necessary for the development of agents to target downstream events specific to central hemodynamic regulation, not only to avoid the hypokalemia caused by inhibition of renal tubular MR, but also to avoid untoward long term effects of inhibiting brain MR that are not involved in blood pressure control.

SOD1 overexpression in paraventricular nucleus improves post-infarct myocardial remodeling and ventricular function

Excessive sympathetic activation contributes to the progression of chronic heart failure. Reactive oxygen species in paraventricular nucleus (PVN) play an important role in the enhanced sympathetic outflow. This study was designed to determine whether superoxide dismutase 1 (SOD1) overexpression in the PVN attenuated the sympathetic activation and cardiac dysfunction in rats after an episode of myocardial infarction (MI). Adenoviral vectors containing human SOD1 (Ad-SOD) or null adenoviral vectors (Ad-null) were immediately microinjected into the PVN of rats with coronary artery ligation or sham operation. At the eighth week, the SOD1 protein level and activity in the PVN increased while the superoxide anions in the PVN decreased in Ad-SOD rats. The SOD1 overexpression in the PVN prevented the increases in left ventricular end-diastolic pressure and volume, and the decreases in ejection fraction and peak velocities of contraction in MI rats. In addition, there was an attenuation of renal sympathetic nerve activity, cardiac sympathetic afferent reflex and plasma norepinephrine level in MI rats. Furthermore, the SOD1 overexpression in the PVN reduced cardiomyocyte size, collagen deposition and the TUNEL-positive cardiomyocytes in MI rats. These results indicate that the SOD1 overexpression in the PVN attenuates the excessive sympathetic activation, myocardial remodeling, cardiomyocyte apoptosis and ventricular dysfunction in MI rats.

Contribution of central nervous system endothelial nitric oxide synthase to neurohumoral activation in heart failure rats

Neurohumoral activation, a hallmark in heart failure (HF), is linked to the progression and mortality of HF patients. Thus, elucidating its precise underlying mechanisms is of critical importance. Other than its classic peripheral vasodilatory actions, the gas NO is a pivotal neurotransmitter in the central nervous system control of the circulation. While accumulating evidence supports a contribution of blunted NO function to neurohumoral activation in HF, the precise cellular sources, and NO synthase (NOS) isoforms involved, remain unknown. Here, we used a multidisciplinary approach to study the expression, cellular distribution, and functional relevance of the endothelial NOS isoform within the hypothalamic paraventricular nucleus in sham and HF rats. Our results show high expression of endothelial NOS in the paraventricular nucleus (mostly confined to astroglial cells), which contributes to constitutive NO bioavailability, as well as tonic inhibition of presympathetic neuronal activity and sympathoexcitatory outflow from the paraventricular nucleus. A diminished endothelial NOS expression and endothelial NOS-derived NO availability were found in the paraventricular nucleus of HF rats, resulting, in turn, in blunted NO inhibitory actions on neuronal activity and sympathoexcitatory outflow. Taken together, our study supports blunted central nervous system endothelial NOS-derived NO as a pathophysiological mechanism underlying neurohumoral activation in HF.

EP₃ receptors mediate PGE₂-induced hypothalamic paraventricular nucleus excitation and sympathetic activation

Prostaglandin E(2) (PGE(2)), an important mediator of the inflammatory response, acts centrally to elicit sympathetic excitation. PGE(2) acts on at least four E-class prostanoid (EP) receptors known as EP(1), EP(2), EP(3), and EP(4). Since PGE(2) production within the brain is ubiquitous, the different functions of PGE(2) depend on the expression of these prostanoid receptors in specific brain areas. The type(s) and location(s) of the EP receptors that mediate sympathetic responses to central PGE(2) remain unknown. We examined this question using PGE(2), the relatively selective EP receptor agonists misoprostol and sulprostone, and the available selective antagonists for EP(1), EP(3), and EP(4). In urethane-anesthetized rats, intracerebroventricular (ICV) administration of PGE(2), sulprostone or misoprostol increased renal sympathetic nerve activity, blood pressure, and heart rate. These responses were significantly reduced by ICV pretreatment with the EP(3) receptor antagonist; the EP(1) and EP(4) receptor antagonists had little or no effect. ICV PGE(2) or misoprostol increased the discharge of neurons in the hypothalamic paraventricular nucleus (PVN). ICV misoprostol increased the c-Fos immunoreactivity of PVN neurons, an effect that was substantially reduced by the EP(3) receptor antagonist. Real-time PCR detected EP(3) receptor mRNA in PVN, and immunohistochemical studies revealed sparsely distributed EP(3) receptors localized in GABAergic terminals and on a few PVN neurons. Direct bilateral PVN microinjections of PGE(2) or sulprostone elicited sympathoexcitatory responses that were significantly reduced by the EP(3) receptor antagonist. These data suggest that EP(3) receptors mediate the central excitatory effects of PGE(2) on PVN neurons and sympathetic discharge.

Ten questions about systems biology

In this paper we raise 'ten questions' broadly related to 'omics', the term systems biology, and why the new biology has failed to deliver major therapeutic advances for many common diseases, especially diabetes and cardiovascular disease. We argue that a fundamentally narrow and reductionist perspective about the contribution of genes and genetic variants to disease is a key reason 'omics' has failed to deliver the anticipated breakthroughs. We then point out the critical utility of key concepts from physiology like homeostasis, regulated systems and redundancy as major intellectual tools to understand how whole animals adapt to the real world. We argue that a lack of fluency in these concepts is a major stumbling block for what has been narrowly defined as 'systems biology' by some of its leading advocates. We also point out that it is a failure of regulation at multiple levels that causes many common diseases. Finally, we attempt to integrate our critique of reductionism into a broader social framework about so-called translational research in specific and the root causes of common diseases in general. Throughout we offer ideas and suggestions that might be incorporated into the current biomedical environment to advance the understanding of disease through the perspective of physiology in conjunction with epidemiology as opposed to bottom-up reductionism alone.

Centrally administered lipopolysaccharide elicits sympathetic excitation via NAD(P)H oxidase-dependent mitogen-activated protein kinase signaling

OBJECTIVE

The mechanisms by which inflammation activates sympathetic drive in heart failure and hypertension remain ill-defined. In this study, an intracerebroventricular injection of lipopolysaccharide (LPS) was used to induce the expression of cytokines and other inflammatory mediators in the brain, in the absence of other excitatory mediators, and the downstream signaling pathways leading to sympathetic activation were examined using intracerebroventricular injections of blocking or inhibiting agents.

METHODS AND RESULTS

In anesthetized rats, intracerebroventricular injection of LPS (5 microg) increased (P < 0.05) renal sympathetic nerve activity, blood pressure and heart rate. LPS increased (P < 0.05) hypothalamic mRNA for NAD(P)H oxidase subunits p47 and gp91, NAD(P)H oxidase-dependent superoxide generation, hypothalamic mRNA for tumor necrosis factor-alpha, cyclooxygenase-2 and cerebrospinal fluid levels of tumor necrosis factor-alpha and prostaglandin E2. In the paraventricular nucleus of hypothalamus, dihydroethidium staining for superoxide expression and c-Fos activity (indicating neuronal excitation) increased. The superoxide scavenger tempol significantly (P < 0.05) diminished the expression of inflammatory mediators, as well as superoxide expression and neuronal excitation in paraventricular nucleus. SB203580 (p38 mitogen-activated protein kinase inhibitor) also reduced the expression of inflammatory mediators in hypothalamus and cerebrospinal fluid. Tempol, apocynin [NAD(P)H oxidase inhibitor], SB203580 and NS398 (cyclooxygenase-2 inhibitor) all reduced cerebrospinal fluid prostaglandin E2 and the sympathoexcitatory response to LPS. LPS also increased angiotensin II type 1 receptor mRNA, a response blocked by apocynin and tempol but not by SB203580.

CONCLUSION

These findings suggest that central inflammation in pathophysiological conditions activates the sympathetic nervous system via NAD(P)H oxidase and p38 mitogen-activated protein kinase-dependent synthesis of prostaglandin E2.

Enhanced angiotensin-mediated excitation of renal sympathetic nerve activity within the paraventricular nucleus of anesthetized rats with heart failure

Chronic heart failure (HF) is characterized by increased sympathetic drive. Enhanced angiotensin II (ANG II) activity may contribute to the increased sympathoexcitation under HF condition. The present study examined sympathoexcitation by 1) the effects of ANG II in the paraventricular nucleus (PVN) on renal sympathetic nerve activity (RSNA), and 2) the altered ANG II type 1 (AT(1)) receptor expression during HF. Left coronary artery ligation was used to induce HF. In the anesthetized Sprague-Dawley rats, microinjection of ANG II (0.05-1 nmol) into the PVN increased RSNA, mean arterial pressure (MAP), and heart rate (HR) in both sham-operated and HF rats. The responses of RSNA and HR were significantly enhanced in rats with HF compared with sham rats (RSNA: 64 +/- 8% vs. 33 +/- 4%, P < 0.05). Microinjection of AT(1) receptor antagonist losartan into the PVN produced a decrease of RSNA, MAP, and HR in both sham and HF rats. The RSNA and HR responses to losartan in HF rats were significantly greater (RSNA: -25 +/- 4% vs. -13 +/- 1%, P < 0.05). Using RT-PCR and Western blot analysis, we found that there were significant increases in the AT(1) receptor mRNA (Delta186 +/- 39%) and protein levels (Delta88 +/- 20%) in the PVN of rats with HF (P < 0.05). The immunofluorescence of AT(1) receptors was significantly higher in the PVN of rats with HF. These data support the conclusion that an increased angiotensinergic activity on sympathetic regulation, due to the upregulation of ANG II AT(1) receptors within the PVN, may contribute to the elevated sympathoexcitation that is observed during HF.

Excitability of paraventricular nucleus neurones that project to the rostral ventrolateral medulla is regulated by small-conductance Ca2+-activated K+ channels

Whole cell patch-clamp recordings were performed in brain slices to investigate mechanisms regulating the excitability of paraventricular nucleus (PVN) neurones that project directly to the rostral ventrolateral medulla (RVLM) (PVN-RVLM neurones) of rats. In voltage-clamp recordings, step depolarization elicited a calcium-dependent outward tail current that reversed near E(K). The current was nearly abolished by apamin and by UCL1684, suggesting mediation by small-conductance Ca(2+)-activated K(+) (SK) channels. In current-clamp recordings, depolarizing step current injections evoked action potentials that underwent spike-frequency adaptation (SFA). SK channel blockade with apamin or UCL1684 increased the spike frequency without changing the rate of SFA. Upon termination of step current injection, a prominent medium after-hyperpolarization potential (mAHP) was observed. SK channel blockade abolished the mAHP and revealed an after-depolarization potential (ADP). In response to ramp current injections, the rate of sub-threshold depolarization was increased during SK channel blockade, indicating that depolarizing input resistance was increased. Miniature EPSC frequency, amplitude, and decay kinetics were unaltered by bath application of apamin, suggesting that SK channel blockade likely increased excitability by a postsynaptic action. We conclude that although SK channels play little role in generating SFA in PVN-RVLM neurones, their activation nevertheless does dampen excitability. The mechanism appears to involve activation of a mAHP that opposes a prominent ADP that would otherwise facilitate firing.

Stress, depression and cardiovascular dysregulation: a review of neurobiological mechanisms and the integration of research from preclinical disease models

Bidirectional associations between mood disorders and cardiovascular diseases are extensively documented. However, the precise physiological and biochemical mechanisms that underlie such relationships are not well understood. This review focuses on the neurobiological processes and mediators that are common to both mood and cardiovascular disorders. The discussion places an emphasis on the role of exogenous stressors in addition to: (a) neuroendocrine and neurohumoral changes involving dysfunction of the hypothalamic-pituitary-adrenal axis and the activation of the renin-angiotensin-aldosterone system, (b) immune alterations including activation of pro-inflammatory cytokines, (c) autonomic and cardiovascular dysregulation including increased sympathetic drive, withdrawal of parasympathetic tone, cardiac rate and rhythm disturbances, and altered baroreceptor reflex function, (d) central neurotransmitter system dysfunction involving the dopamine, norepinephrine and serotonin systems, and (e) behavioral changes including fatigue and physical inactivity. The review also discusses experimental investigations using preclinical disease models to elucidate the neurobiological mechanisms underlying the link between mood disorders and cardiovascular disease. These include: (a) the chronic mild stress model of depression, (b) a model of congestive heart failure, (c) a model of cardiovascular deconditioning, (d) pharmacological manipulations of body fluid and sodium balance, and (e) pharmacological manipulations of the central serotonergic system. In combination with an extensive human research literature, the investigation of mechanisms underlying mood and cardiovascular regulation using animal models will enhance understanding the association between depression and cardiovascular disease. This will ultimately promote the development of better treatments and interventions for individuals with co-morbid psychological and somatic pathologies.

Central mineralocorticoid receptors and cardiovascular disease

The mineralocorticoid receptor (MR) is expressed in many cell types throughout the body, including specific neurons, and mediates diverse functions, many of which are just now being appreciated. MR that pertain to the central modulation of cardiovascular function and health are addressed herein.

Cardiac damage after lesions of the nucleus tractus solitarii

Humans with central lesions that augment sympathetic nerve activity are predisposed to cardiac arrhythmias, myocardial lesions, and sudden death. Previously, we showed that selectively killing neurons with neurokinin-1 receptors in the nucleus tractus solitarii (NTS) of rats attenuated the baroreflex and, in some animals, led to sudden unexplained death within approximately 2 wk. Interruption of arterial baroreflexes is known to increase sympathetic activity. Here we tested the hypothesis that lesions in the NTS lead to fatal cardiac arrhythmias and myocardial lesions. We studied electrocardiograms, echocardiograms, blood pressure, and heart rate in 14 adult male rats after bilateral microinjection into the NTS of stabilized substance P conjugated to the toxin saporin and compared the variables in five sham control rats and in five animals with toxin injected outside the NTS. Only injection of toxin into the NTS led to increased lability of arterial blood pressure, a sign of baroreflex interruption. Two animals treated with toxin died suddenly. All animals engaged in normal activity until, in two, rapid development of asystole and death over 6-8 min. Cardiac function when examined by echocardiography was normal, but pathologic examination of the heart revealed diffuse microscopic areas of acute coagulation necrosis in the myocardium in five animals, focal subacute necrosis in two animals, and both changes in one animal. This study supports the hypothesis that NTS lesions interrupting the baroreflex may induce cardiac arrhythmias and myocardial changes similar to those seen in humans with central lesions and may lead to sudden cardiac death.

Activation of Rho-kinase in the brainstem enhances sympathetic drive in mice with heart failure

Rho-kinase is involved in the pathogenesis of hypertension and left ventricular remodelling after myocardial infarction (MI). In an earlier study, we had demonstrated that Rho-kinase in the brainstem contributes to hypertensive mechanisms via the sympathetic nervous system; however, it is not known whether Rho-kinase in the brainstem also contributes to sympathetic nerve activation after MI. Male Institute of Cancer Research mice (8-10 weeks old) were used for the study. Two days before coronary artery occlusion (MI group), the left ventricular function was estimated by echocardiography. Following this, Y-27632 (0.5 mM, 0.25 microL/h), a specific Rho-kinase inhibitor, or a vehicle was intracisternally infused in the mice using an osmotic mini-pump. Nine days after coronary artery occlusion, we evaluated the 24-hour urinary norepinephrine excretion (U-NE) as a marker of sympathetic nerve activity. Ten days after coronary artery occlusion, we measured organ weight and evaluated Rho-kinase activity in the brainstem by measuring the amount of phosphorylated ezrin/radixin/moesin proteins, one of the substrates of Rho-kinase. The control group underwent a sham operation. Rho-kinase activity, U-NE, and lungs and liver weight were significantly greater in the MI group compared with the control group. Left ventricular size increased and percent fractional shortening decreased in the MI group compared with the control group. Y-27632 significantly decreased Rho-kinase activity and attenuated the increase in U-NE after MI. These results demonstrate that Rho-kinase is activated in the brainstem after MI and that the activation of this pathway is involved in the resulting enhanced sympathetic drive.

Mechanisms underlying altered mood and cardiovascular dysfunction: the value of neurobiological and behavioral research with animal models

A bidirectional association between mood disorders and cardiovascular diseases has been described in humans, yet the precise neurobiological mechanisms that underlie this association are not fully understood. This article is focused on neurobiological processes and mediators in mood and cardiovascular disorders, with an emphasis on common mechanisms including stressor reactivity, neuroendocrine and neurohumoral changes, immune alterations, autonomic and cardiovascular dysregulation, and central neurotransmitter and neuropeptide dysfunction. A discussion of the utility of experimental investigations with rodent models, including those in rats and prairie voles (Microtus ochrogaster), is presented. Specific studies using these models are reviewed, focusing on the analysis of behavioral, physiological and neural mechanisms underlying depressive disorders and cardiovascular disease. Considered in combination with studies using human samples, the investigation of mechanisms underlying depressive behaviors and cardiovascular regulation using animal models will enhance our understanding of the association of depression and cardiovascular disease, and will promote the development of improved interventions for individuals with these detrimental disorders.

Mechanisms of sympathetic activation in heart failure

1. Heart Failure (HF) is a serious, debilitating condition with poor survival rates and an increasing level of prevalence. A characteristic of HF is a compensatory neurohumoral activation that increases with the severity of the condition. 2. The increase in sympathetic activity may be beneficial initially, providing inotropic support to the heart and peripheral vasoconstriction, but in the longer term it promotes disease progression and worsens prognosis. This is particularly true for the increase in cardiac sympathetic nerve activity, as shown by the strong inverse correlation between cardiac noradrenaline spillover and prognosis and by the beneficial effect of beta-adrenoceptor antagonists. 3. Possible causes for the raised level of sympathetic activity in HF include altered neural reflexes, such as those from baroreceptors and chemoreceptors, raised levels of hormones, such as angiotensin II, acting on circumventricular organs, and changes in central mechanisms that may amplify the responses to these inputs. 4. The control of sympathetic activity to different organs is regionally heterogeneous, as demonstrated by a lack of concordance in burst patterns, different responses to reflexes, opposite responses of cardiac and renal sympathetic nerves to central angiotensin and organ-specific increases in sympathetic activity in HF. These observations indicate that, in HF, it is essential to study the factors causing sympathetic activation in individual outflows, in particular those that powerfully, and perhaps preferentially, increase cardiac sympathetic nerve activity.

Overexpression of eNOS in brain stem reduces enhanced sympathetic drive in mice with myocardial infarction

Reduced nitric oxide (NO) in the brain might contribute to enhanced sympathetic drive in heart failure (HF). The aim of this study was to determine whether increased NO production induced by local overexpression of endothelial NO synthase (eNOS) in the nucleus tractus solitarius (NTS) of the brain stem reduces the enhanced sympathetic drive in mice with HF. Myocardial infarction (MI) was induced in mice by ligating the left coronary artery. MI mice exhibited left ventricular dilatation and a reduced left ventricular ejection fraction. Urinary norepinephrine excretion in MI mice was greater than that in sham-operated mice, indicating that sympathetic drive was enhanced in this model. Thus this model has features that are typical of HF. Western blot analysis and immunohistochemical staining for neuronal NOS (nNOS) indicated that nNOS protein expression was significantly reduced in the brain stem of MI mice. MI mice had a significantly smaller increase in blood pressure evoked by intracisternal injection of N(G)-monomethyl-L-arginine than sham-operated mice. Adenoviral vectors encoding either eNOS (AdeNOS) or beta-galactosidase (Adbeta gal) were transfected into the NTS to examine the effect of increased NO production in the NTS on the enhanced sympathetic drive in HF. After the gene transfer, urinary norepinephrine excretion was reduced in AdeNOS-transfected MI mice but not in Adbeta gal-transfected MI mice. These results indicate that nNOS expression in the brain stem, especially in the NTS, is reduced in the MI mouse model of HF, and increased NO production induced by overexpression of eNOS in the NTS attenuates the enhanced sympathetic drive in this model.

Augmented input from cardiac sympathetic afferents inhibits baroreflex in rats with heart failure

It has been established that the baroreflex is markedly decreased in chronic heart failure (CHF). Our recent study has indicated that activation of the cardiac sympathetic afferent reflex (CSAR) inhibits the baroreflex in normal rats, and in the rats with CHF the CSAR is significantly enhanced, which is related to augmented central angiotensin II (Ang II) mechanism. Therefore, the hypothesis is that the augmented CSAR in the CHF state tonically inhibits the baroreflex via central AT1 receptor. To test the hypothesis, the rats with myocardial infarction-induced CHF or sham surgery were anesthetized with alpha-chloralose and urethane, vagotomized, and recordings were made of the mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). We found: (1) left ventricular epicardial application of capsaicin or electrical stimulation of the central end of the left cardiac sympathetic nerve blunted the baroreflex in both sham and CHF rats; (2) left ventricular epicardial application of lidocaine had no significant effects on the baroreflex in sham rats but improved the baroreflex in CHF rats (maximum slope, 1.7+/-0.3 to 2.9+/-0.2%/mm Hg; P<0.01); and (3) intracerebral ventricular injection of losartan had no significant effect on baroreflex in sham rats but improved the baroreflex in CHF rats (maximum slope 1.9+/-0.2 to 3.1+/-0.2%/mm Hg; P<0.01). These results suggest that tonic cardiac sympathetic afferent input plays an important role in the blunted baroreflex associated with CHF, which is mediated by central AT1 receptors.

ANG II in the paraventricular nucleus potentiates the cardiac sympathetic afferent reflex in rats with heart failure

Chronic heart failure (CHF) is characterized by sympathoexcitation, and the cardiac sympathetic afferent reflex (CSAR) is a sympathoexcitatory reflex. Our previous studies have shown that the CSAR was enhanced in CHF. In addition, central angiotensin II (ANG II) is an important modulator of this reflex. This study was performed to determine whether the CSAR evoked by stimulation of cardiac sympathetic afferent nerves (CSAN) in rats with coronary ligation-induced CHF is enhanced by ANG II in the paraventricular nucleus (PVN). Under alpha-chloralose and urethane anesthesia, renal sympathetic nerve activity (RSNA) was recorded. The RSNA responses to electrical stimulation (5, 10, 20, and 30 Hz) of the CSAN were evaluated. Bilateral microinjection of the AT1-receptor antagonist losartan (50 nmol) into the PVN had no significant effects in the sham group, but it abolished the enhanced RSNA response to stimulation in the CHF group. Unilateral microinjection of three doses of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to stimulation. Although ANG II also potentiated the RSNA response to electrical stimulation in sham rats, the RSNA responses to stimulation after ANG II into the PVN in rats with CHF were much greater than in sham rats. The effects of ANG II were prevented by pretreatment with losartan into the PVN in CHF rats. These results suggest that the central gain of the CSAR is enhanced in rats with coronary ligation-induced CHF and that ANG II in the PVN augments the CSAR evoked by CSAN, which is mediated by the central angiotensin AT1 receptors in rats with CHF.

Brain mineralocorticoid receptors: orchestrators of hypertension and end-organ disease

PURPOSE OF REVIEW

'New' tasks have been discovered for aldosterone and its receptor, the mineralocorticoid receptor, within both epithelial tissues of vectorial ion and water transport, such as the kidney, and non-epithelial organs, including the brain, heart and vessels. Promising results of clinical trials using low doses of mineralocorticoid receptor antagonists to forestall end-organ disease is resulting in an increase in their use, yet the biology of the mineralocorticoid receptor is far from clear.

RECENT FINDINGS

Mineralocorticoid receptors within the kidney, heart and blood vessels mediate direct effects of aldosterone, including tissue inflammation, hypertrophy and fibrosis, that are independent of blood pressure. Activation, by aldosterone, of mineralocorticoid receptors in the brain increases central sympathetic nervous system drive to the periphery, thereby producing hypertension through multiple mechanisms, and increases levels of proinflammatory cytokines in both the circulation and peripheral tissues. Blocking of the mineralocorticoid receptor of the forebrain lowers the levels of peripheral tissue cytokines, including those induced by ischemic injury in the heart. Aldosterone is produced within the heart, blood vessels and brain, potentially liberating regulation of local concentrations of the steroid from peripheral mechanisms of control. A conundrum yet to be explained is the ligand-dependent functional specificity of the mineralocorticoid receptor in some non-epithelial tissues, which may be crucial to our understanding the end-organ pathophysiology of hypertension.

SUMMARY

New technology is rapidly adding layers of complexity to, rather than simplifying, our understanding of the facile terms 'hemodynamic homeostasis' and 'end-organ' disease, but within this new knowledge lies the promise of better, more precise treatment of hypertension and its sequelae.

Modifications to central neural circuitry during heart failure

AIM

During heart failure (HF), excess sodium retention is triggered by increased plasma renin-angiotensin-aldosterone activity and increased basal sympathetic nerve discharge (SND). Enhanced basal SND in the renal nerves plays a role in sodium retention. Therefore, as a hypothetical model for the central sympathetic control pathways that are dysregulated as a consequence of HF, the central neural pathways regulating the sympathetic motor output to the kidney are reviewed in the context of their role during HF.

CONCLUSION

From these findings, a model of the neuroanatomical circuitry that may be affected during HF is constructed.

Biological mechanisms in the relationship between depression and heart disease

Psychological depression is shown to be associated with several aspects of coronary artery disease (CAD), including arrhythmias, myocardial infarction, heart failure and sudden death. The physiological mechanisms accounting for this association are unclear. Hypothalamic-pituitary-adrenal dysregulation, diminished heart rate variability, altered blood platelet function and noncompliance with medial treatments have been proposed as mechanisms underlying depression and cardiovascular disease. Recent evidence also suggests that reduced baroreflex sensitivity, impaired immune function, chronic fatigue and the co-morbidity of depression and anxiety may be involved in the relationship between depression and cardiovascular dysregulation. An experimental strategy using animal models for investigating underlying physiological abnormalities in depression is presented. A key to understanding the bidirectional association between depression and heart disease is to determine whether there are common changes in brain systems that are associated with these conditions. Such approaches may hold promise for advancing our understanding of the interaction between this mood disorder and CAD.