Role of Angiotensin II Type 1A Receptors in Cardiovascular Reactivity and Neuronal Activation After Aversive Stress in Mice

The medial amygdala's neural circuitry: Insights into social processing and sex differences

The amygdala, a critical part of the limbic system, is essential for processing social stimuli and regulating stress responses. Among its various neuronal nuclei, the medial amygdala (MeA) remains one of the least studied in humans. The MeA plays a key role in receiving inputs from the olfactory system through pheromones, as well as from crucial areas such as the hypothalamus, hippocampus, and reward system. This allows the MeA to integrate external stimuli with the organism's internal state, finetuning social interactions, endocrine responses, and innate behaviors. Recent advances in neuroscience have highlighted the sex differences of the MeA and how they influence behavior and environmental perception. Understanding these sexspecific variations in brain structures, like the MeA in rodents, is vital for applying this knowledge to humans and could help bridge gaps in our understanding and treatment of mental health disorders, which often differ between sexes in both prevalence and presentation.

Angiotensinergic neurotransmission in the bed nucleus of the stria terminalis is involved in cardiovascular responses to acute restraint stress in rats

The brain angiotensin II acting via AT₁ receptors is a prominent mechanism involved in physiological and behavioral responses during aversive situations. The AT₂ receptor has also been implicated in stress responses, but its role was less explored. Despite these pieces of evidence, the brain sites related to control of the changes during aversive threats by the brain renin-angiotensin system (RAS) are poorly understood. The bed nucleus of the stria terminalis (BNST) is a limbic structure related to the cardiovascular responses by stress, and components of the RAS system were identified in this forebrain region. Therefore, we investigated the role of angiotensinergic neurotransmission present within the BNST acting via local AT₁ and AT₂ receptors in cardiovascular responses evoked by an acute session of restraint stress in rats. For this, rats were subjected to bilateral microinjection of either the angiotensin-converting enzyme inhibitor captopril, the selective AT₁ receptor antagonist losartan, or the selective AT₂ receptor antagonist PD123319 before they underwent the restraint stress session. We observed that BNST treatment with captopril reduced the decrease in tail skin temperature evoked by restraint stress, without affecting the pressor and tachycardic responses. Local AT₂ receptor antagonism within the BNST reduced both the tachycardia and the drop in tail skin temperature during restraint. Bilateral microinjection of losartan into the BNST did not affect the restraint-evoked cardiovascular changes. Taken together, these data indicate an involvement of BNST angiotensinergic neurotransmission acting via local AT₂ receptors in cardiovascular responses during stressful situations.

Involvement of the Renin-Angiotensin System in Stress: State of the Art and Research Perspectives

BACKGROUND

Along with other canonical systems, the renin-angiotensin system (RAS) has shown important roles in stress. This system is a complex regulatory proteolytic cascade composed of various enzymes, peptides, and receptors. Besides the classical (ACE/Ang II/AT1 receptor) and the counter-regulatory (ACE2/Ang-(1-7)/Mas receptor) RAS axes, evidence indicates that nonclassical components, including Ang III, Ang IV, AT₂ and AT₄, can also be involved in stress.

OBJECTIVE AND METHODS

This comprehensive review summarizes the current knowledge on the participation of RAS components in different adverse environmental stimuli stressors, including air jet stress, cage switch stress, restraint stress, chronic unpredictable stress, neonatal isolation stress, and post-traumatic stress disorder.

RESULTS AND CONCLUSION

In general, activation of the classical RAS axis potentiates stress-related cardiovascular, endocrine, and behavioral responses, while the stimulation of the counter-regulatory axis attenuates these effects. Pharmacological modulation in both axes is optimistic, offering promising perspectives for stress-related disorders treatment. In this regard, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are potential candidates already available since they block the classical axis, activate the counter-regulatory axis, and are safe and efficient drugs.

Angiotensinergic receptors in the medial amygdaloid nucleus differently modulate behavioral responses in the elevated plus-maze and forced swimming test in rats

The brain renin-angiotensin system (RAS) has been implicated in anxiety and depression disorders, but the specific brain sites involved are poorly understood. The medial amygdaloid nucleus (MeA) is involved in expression of behavioral responses. However, despite evidence of the presence of all angiotensinergic receptors in this amygdaloid nucleus, regulation of anxiety- and depressive-like behaviors by angiotensinergic neurotransmissions within the MeA has never been reported. Thus, the present study aimed to investigate the role angiotensin II (AT₁ and AT₂ receptors) and angiotensin-(1-7) (Mas receptor) receptors present within the MeA in behavioral responses in the elevated plus-maze (EPM) and forced swimming test (FST). For this, male Wistar rats had cannula-guide bilaterally implanted into the MeA, and independent sets of animals received bilateral microinjections of either the selective AT₁ receptor antagonist losartan, the selective AT₂ receptor antagonist PD123319, the selective Mas receptor antagonist A-779 or vehicle into the MeA before the EPM and FST. Treatment of the MeA with either PD123319 or A-779 decreased the EPM open arms exploration, while losartan did not affect behavioral responses in this apparatus. However, intra-MeA microinjection of losartan decreased immobility in the FST. Administration of either PD123319 or A-779 into the MeA did not affect the immobility during the FST, but changed the pattern of the active behaviors swimming and climbing. Altogether, these results indicate the presence of different angiotensinergic mechanisms within the MeA controlling behavioral responses in the FST and EPM.

Influence of sex on heightened vasoconstrictor mechanisms in the non-Hispanic black population

Cardiovascular disease (CVD) affects individuals of all races and ethnicities; however, its prevalence is highest in non-Hispanic black individuals (BL) relative to other populations. While previous research has provided valuable insight into elevated CVD risk in the BL population, this work has been almost exclusively conducted in men. This is alarming given that BL women suffer from CVD at an equivalent rate to BL men and each has a greater prevalence when compared to all other ethnicities, regardless of sex. The importance of investigating sex differences in mechanisms of cardiovascular function is highlighted by the National Institute of Health requiring sex to be considered as a biological variable in research studies to better our "understanding of key sex influences on health processes and outcomes." The mechanism(s) responsible for the elevated CVD risk in BL women remains unclear and is likely multifactorial. Limited studies in BL women suggest that, while impaired vasodilator capacity is involved, heightened vasoconstrictor tone and/or responsiveness may also contribute. Within this mini-review, we will discuss potential mechanisms of elevated rates of hypertension and other CVDs in BL individuals with a particular focus on young, otherwise healthy, college-aged women. To stimulate academic thought and future research, we will also discuss potential mechanisms for impaired vascular function in BL women, as well as possible divergent mechanisms between BL men and women based on either preliminary data or plausible speculation extending from findings in the existing literature. Last, we will conclude with potential future research directions aimed at better understanding the elevated risk for hypertension and CVD in BL women.

Angiotensin involvement in trauma processing-exploring candidate neurocognitive mechanisms of preventing post-traumatic stress symptoms

The angiotensin-II antagonist losartan is a promising candidate that has enhanced extinction in a post-traumatic stress disorder (PTSD) animal model and was related to reducing PTSD symptom development in humans. Here, we investigate the neurocognitive mechanisms underlying these results, testing the effect of losartan on data-driven and contextual processing of traumatic material, mechanisms proposed to be relevant for PTSD development. In a double-blind between-subject design, 40 healthy participants were randomised to a single oral dose of losartan (50 mg) or placebo, 1 h before being exposed to distressing films as a trauma analogue while heart rate (HR) was measured. Peritraumatic processing was investigated using blurry picture stimuli from the films, which transformed into clear images. Data-driven processing was measured by the level of blurriness at which contents were recognised. Contextual processing was measured as the amount of context information retrieved when describing the pictures' contents. Negative-matched control images were used to test perceptual processing of peripheral trauma-cues. Post-traumatic stress symptoms were assessed via self-report questionnaires after analogue trauma and an intrusion diary completed over 4 days following the experiment. Compared to placebo, losartan facilitated contextual processing and enhanced detail perception in the negative-match pictures. During the films, the losartan group recorded lower HR and higher HR variability, reflecting lower autonomic stress responses. We discuss potential mechanisms of losartan in preventing PTSD symptomatology, including the role of reduced arousal and increased contextual processing during trauma exposure, as well as increased threat-safety differentiation when encountering peripheral trauma-cues in the aftermaths of traumatic events.

The effect of angiotensin AT1A inactivation on innate and learned fear responses in mice and its relationship to blood pressure

Angiotensin AT₁ receptors are implicated in behavioral and physiological processes associated with fear and stress. However, the precise role of AT₁ receptors in modulating fear-related behavior and its relation to their physiological effects remains unclear. Here, we examined innate and learned fear responses and their relationship to cardiovascular arousal in AT_1A receptor knockout (AT_1A^-/-) mice. Using synchronized video and blood pressure telemetry, we found that, in a novel test environment, AT_1A^-/- mice showed reduced neophobia but a similar rise in blood pressure, as compared to AT_1A^+/+ mice. In response to a discrete threat, footshock, both flight behavior and cardiovascular arousal were decreased in AT_1A^-/- mice. Reduced flight behavior was also observed in AT_1A^-/- mice in the elevated T-maze test. During fear conditioning, the immediate freezing response to the first shock, but not the rate of freezing acquisition was decreased in AT_1A^-/- mice. Likewise, AT_1A^-/- mice showed reduced freezing and pressor responses to the first re-exposure, but normal rate of freezing extinction over subsequent trials. Similarly, in the elevated T-maze, the rates of avoidance acquisition and escape learning remained unchanged in AT_1A^-/- mice. Finally, after re-exposure, AT_1A^-/- mice displayed altered c-Fos expression, compared to AT_1A^+/+ mice, in the hypothalamus and periaqueductal gray but not in fear-related limbic-cortical areas, nor in medullary nuclei that convey visceral afferent information. We conclude that AT_1A receptor knockout reduces innate fear responses, without affecting learning efficiency in mice. These effects are dissociable from cardiovascular effects and likely reflect altered neurotransmission in hypothalamic-midbrain defense regions.

Cardiovascular reactivity to emotional stress: The hidden challenge for pets in the urbanized environment

Emotional stress is currently considered an important risk factor for cardiovascular diseases. Experimental evidence clearly shows robust autonomic cardiovascular effects in animals exposed to stress stimuli. Considering the remarkable variability of stressors, the urban environment can pose a severe challenge to cardiovascular control. Interestingly, pet ownership is indicated as an efficient non-pharmacological therapy to attenuate stress effects that can reduce the risk of cardiovascular disease. However, the risk of cardiovascular diseases in pets themselves living in urban environment has not received attention it deserves. Here, we review the central mechanisms involved in the autonomic cardiovascular response to emotional stress. Next, we discuss experimental evidence showing the cardiovascular effects produced by emotional stressors in animals, aiming to establish a parallel with common urban stressors. Association of additional risk factors such as sedentarism, obesity and ambient temperature are also considered. Our aim is to identify and raise awareness of the risk of cardiovascular disease in pets exposed to quotidian emotional stressors present in the urban environment.

Angiotensin II receptor blocker attenuates stress pressor response in young adult African Americans

African Americans (AAs) are susceptible to hypertension (HTN) and its associated organ damage leading to adverse cardiovascular (CV) outcomes. Psychological stress is proposed to contribute to the development of HTN; however, the potential role of the renin-angiotensin system (RAS) in stress-related HTN in AAs is largely unknown. In this study, we tested the hypothesis that activation of RAS is a potential contributing factor for altered CV responses to stress, and suppression of angiotensin II (Ang II) activity will improve hemodynamic responses to a prolonged mental stressor in healthy young AAs. Utilizing a double-blind, randomized, crossover study design, 132 normotensive AAs (25 ± 7 years) were treated with either a placebo (PLC) or 150 mg/d irbesartan (an Ang II type 1 receptor blocker; ARB) for 1 week. On the final day of each treatment, hemodynamic measures and urinary sodium excretion (UNaV) were collected before, during and after a 45 minute-mental stress. The magnitude of stress-induced increase in blood pressure with ARB was blunted and delayed compared to PLC. Systolic blood pressure at the end of recovery on ARB was significantly lower compared to either PLC (110 ± 13 vs 117 ± 12 mm Hg respectively; P < 0.001) or the prestress level on ARB (P = 0.02). ARB treatment reduced overall vasoconstriction and improved poststress UNaV. ARB attenuated blood pressure responses to mental stress and improved the poststress BP recovery process which were partly linked to reduced overall vasoconstriction and improved stress-induced UNaV in young adult AAs prior to the development of disease conditions. These results suggest that treatment approaches that inhibit RAS action could have significant relevance to potentially lower susceptibility to stress responses and eventually the premature development of HTN in AAs.

Acute Pressor Response to Psychosocial Stress Is Dependent on Endothelium-Derived Endothelin-1

Background

Acute psychosocial stress provokes increases in circulating endothelin‐1 (ET‐1) levels in humans and animal models. However, key questions about the physiological function and cellular source of stress‐induced ET‐1 remain unanswered. We hypothesized that endothelium‐derived ET‐1 contributes to the acute pressor response to stress via activation of the endothelin A receptor.

Methods and Results

Adult male vascular endothelium‐specific ET‐1 knockout mice and control mice that were homozygous for the floxed allele were exposed to acute psychosocial stress in the form of cage switch stress (CSS), with blood pressure measured by telemetry. An acute pressor response was elicited by CSS in both genotypes; however, this response was significantly blunted in vascular endothelium‐specific ET‐1 knockout mice compared with control mice that were homozygous for the floxed allele. In mice pretreated for 3 days with the endothelin A antagonist, ABT‐627, or the dual endothelin A/B receptor antagonist, A‐182086, the pressor response to CSS was similar between genotypes. CSS significantly increased plasma ET‐1 levels in control mice that were homozygous for the floxed allele. CSS failed to elicit an increase in plasma ET‐1 in vascular endothelium‐specific ET‐1 knockout mice. Telemetry frequency domain analyses suggested similar autonomic responses to stress between genotypes, and isolated resistance arteries demonstrated similar sensitivity to α₁‐adrenergic receptor‐mediated vasoconstriction.

Conclusions

These findings specify that acute stress‐induced activation of endothelium‐derived ET‐1 and subsequent endothelin A receptor activation is a novel mediator of the blood pressure response to acute psychosocial stress.

The genetics of anxiety-related negative valence system traits

NIMH's Research Domain Criteria (RDoC) domain of negative valence systems (NVS) captures constructs of negative affect such as fear and distress traditionally subsumed under the various internalizing disorders. Through its aims to capture dimensional measures that cut across diagnostic categories and are linked to underlying neurobiological systems, a large number of phenotypic constructs have been proposed as potential research targets. Since "genes" represent a central "unit of analysis" in the RDoC matrix, it is important for studies going forward to apply what is known about the genetics of these phenotypes as well as fill in the gaps of existing knowledge. This article reviews the extant genetic epidemiological data (twin studies, heritability) and molecular genetic association findings for a broad range of putative NVS phenotypic measures. We find that scant genetic epidemiological data is available for experimentally derived measures such as attentional bias, peripheral physiology, or brain-based measures of threat response. The molecular genetic basis of NVS phenotypes is in its infancy, since most studies have focused on a small number of candidate genes selected for putative association to anxiety disorders (ADs). Thus, more research is required to provide a firm understanding of the genetic aspects of anxiety-related NVS constructs. © 2016 Wiley Periodicals, Inc.

Chronic overexpression of angiotensin-(1-7) in rats reduces cardiac reactivity to acute stress and dampens anxious behavior

Angiotensin II (Ang II) acts as a pro-stress hormone, while other evidence indicates that angiotensin-(1-7) [Ang-(1-7)] attenuates physiological responses to emotional stress. To further test this hypothesis, in groups of 5-6 rats we evaluated autonomic, cardiovascular and behavioral parameters in male Sprague-Dawley (SD) and transgenic TGR(A1-7)3292 (TG) rats chronically overexpressing Ang-(1-7). Compared to SD rats, TG rats showed reduced baseline heart rate (HR; SD 380 ± 16 versus TG 329 ± 9 beats per minute (bpm), mean ± standard error of mean, p < .05) and renal sympathetic discharge (SD 138 ± 4 versus TG 117 ± 5 spikes/second, p < .05). TG rats had an attenuated tachycardic response to acute air-puff stress (ΔHR: SD 51 ± 20 versus TG 1 ± 3 bpm; p < .05), which was reversed by intracerebroventricular injection of the Mas receptor antagonist, A-779 (ΔHR: SD 51 ± 20 versus TG 63 ± 15 bpm). TG rats showed less anxious behavior on the elevated plus maze, as revealed by more entries into open arms (SD 2 ± 2 versus TG 47 ± 5% relative to total entries; p < .05), and more time spent in the open arms (SD 5 ± 4 versus TG 53 ± 9% relative to total time, p < .05). By contrast with SD rats, diazepam (1.5 mg/kg, intraperitoneally) did not further reduce anxious behavior in TG rats, indicating a ceiling anxiolytic effect of Ang-(1-7) overexpression. Ang-(1-7) concentrations in hypothalamus and plasma, measured by mass spectrometry were two- and three-fold greater, respectively, in TG rats than in SD rats. Hence, increased endogenous Ang-(1-7) levels in TG rats diminishes renal sympathetic outflow and attenuates cardiac reactivity to emotional stress, which may be via central Mas receptors, and reduces anxious behavior. Lay summaryWe used a genetically modified rat model that produces above normal amounts of a peptide hormone called angiotensin-(1-7) to test whether this peptide can reduce some of the effects of stress. We found that angiotensin-(1-7), acting in the brain, can reduce anxiety and reduce the increase in heart rate associated with emotional stress. These findings may provide a lead for design of new drugs to reduce stress.

Effects of estrogen replacement on stress-induced cardiovascular responses via renin-angiotensin system in ovariectomized rats

The purpose of this study was to determine whether chronic estrogen replacement in ovariectomized rats inhibits the pressor response to psychological stress by attenuating the activation of the renin-angiotensin system. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, the rats were randomly assigned to be implanted subcutaneously with pellets containing either 17β-estradiol (E2) or placebo (Pla). After 4 wk of treatment, the rats underwent cage-switch stress and, in a separate experiment, a subset received an infusion of angiotensin II. The cage-switch stress rapidly elevated blood pressure (BP) and heart rate (HR) as measured by radiotelemetry in both groups. However, the BP and HR responses to the stress were significantly attenuated in the E2 group compared with the Pla group. An angiotensin II type 1 receptor blocker, losartan, given in drinking water, abolished the difference in the pressor response to stress between the two groups. Moreover, the stress-induced elevation in plasma renin activity and angiotensin II concentration was significant in the Pla group, but not in the E2 group. In addition, the expression of renin mRNA in the kidney was lower in the E2 group relative to the Pla group. Finally, we found that intravenous angiotensin II infusion increased BP and decreased HR to a similar degree in both groups. These results suggest that the inhibitory effects of estrogen on psychological stress-induced activation of the renin-angiotensin system could be at least partially responsible for the suppression of the pressor responses to psychological stress seen in estrogen-replaced ovariectomized rats.

Brain angiotensin-(1-7)/Mas axis: A new target to reduce the cardiovascular risk to emotional stress

Emotional stress is now considered a risk factor for several diseases including cardiac arrhythmias and hypertension. It is well known that the activation of neuroendocrine and autonomic mechanisms features the response to emotional stress. However, its link to cardiovascular diseases and the regulatory mechanisms involved remain to be further comprehended. The renin-angiotensin system (RAS) plays an important role in homeostasis on all body systems. Specifically in the brain, the RAS regulates a number of physiological aspects. Recent data indicate that the activation of angiotensin-converting enzyme/angiotensin II/AT1 receptor axis facilitates the emotional stress responses. On the other hand, growing evidence indicates that its counterregulatory axis, the angiotensin-converting enzyme 2 (ACE2)/(Ang)iotensin-(1-7)/Mas axis, reduces anxiety and attenuates the physiological responses to emotional stress. The present review focuses on angiotensin-(1-7)/Mas axis as a promising target to attenuate the physiological response to emotional stress reducing the risk of cardiovascular diseases.

Contribution of Orexin to the Neurogenic Hypertension in BPH/2J Mice

BPH/2J mice are a genetic model of hypertension associated with an overactive sympathetic nervous system. Orexin is a neuropeptide which influences sympathetic activity and blood pressure. Orexin precursor mRNA expression is greater in hypothalamic tissue of BPH/2J compared with normotensive BPN/3J mice. To determine whether enhanced orexinergic signaling contributes to the hypertension, BPH/2J and BPN/3J mice were preimplanted with radiotelemetry probes to compare blood pressure 1 hour before and 5 hours after administration of almorexant, an orexin receptor antagonist. Mid frequency mean arterial pressure power and the depressor response to ganglion blockade were also used as indicators of sympathetic nervous system activity. Administration of almorexant at 100 (IP) and 300 mg/kg (oral) in BPH/2J mice during the dark-active period (2 hours after lights off) markedly reduced blood pressure (-16.1 ± 1.6 and -11.0 ± 1.1 mm Hg, respectively;P<0.001 compared with vehicle). However, when almorexant (100 mg/kg, IP) was administered during the light-inactive period (5 hours before lights off) no reduction from baseline was observed (P=0.64). The same dose of almorexant in BPN/3J mice had no effect on blood pressure during the dark (P=0.79) or light periods (P=0.24). Almorexant attenuated the depressor response to ganglion blockade (P=0.018) and reduced the mid frequency mean arterial pressure power in BPH/2J mice (P<0.001), but not BPN/3J mice (P=0.70). Immunohistochemical labeling revealed that BPH/2J mice have 29% more orexin neurons than BPN/3J mice which are preferentially located in the lateral hypothalamus. The results suggest that enhanced orexinergic signaling contributes to sympathetic overactivity and hypertension during the dark period in BPH/2J mice.

BDNF acting in the hypothalamus induces acute pressor responses under permissive control of angiotensin II

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) during hypertensive stimuli including stress and hyperosmolarity, but its role in PVN cardiovascular regulatory mechanisms is unclear. Chronic BDNF overexpression in the PVN has been shown to elevate sympathetic tone and blood pressure in part by modulating central angiotensin (Ang) II mechanisms. However, the cardiovascular effects of short-term increases in PVN levels of BDNF and the mechanisms governing them are unknown. Therefore, we investigated whether acute BDNF microinjections into the PVN of conscious and anesthetized Sprague-Dawley rats induce blood pressure elevations and whether Ang II signaling is involved in these hypertensive responses. In conscious rats, unilateral BDNF (12.5ng) microinjections into the PVN increased mean arterial pressure (MAP) by 27±1mmHg (P<0.001 vs vehicle), which was significantly attenuated by intracerebroventricular infusion of the Ang II-type-1 receptor (AT1R) antagonist losartan and by ganglionic blockade with intravenous hexamethonium infusion. In anesthetized rats, unilateral PVN microinjection of BDNF increased MAP by 31±4mmHg (P<0.001 vs vehicle), which was prevented by PVN microinjection pretreatments with the high-affinity BDNF receptor TrkB antagonist ANA-12, losartan, the angiotensin converting enzyme inhibitor lisinopril, or by intravenous hexamethonium. Additional experiments in hypothalamic samples including the PVN revealed that BDNF-induced TrkB receptor phosphorylation was prevented by ANA-12 and losartan pretreatments. Collectively, these data indicate that BDNF acting within the PVN acutely raises blood pressure under permissive control of Ang II-AT1R mechanisms and therefore may play an important role in mediating acute pressor responses to hypertensive stimuli.

Novel mechanism within the paraventricular nucleus reduces both blood pressure and hypothalamic pituitary-adrenal axis responses to acute stress

Macrophage migration inhibitory factor (MIF) counteracts pressor effects of angiotensin II (ANG II) in the paraventricular nucleus of the hypothalamus (PVN) in normotensive rats, but this mechanism is absent in spontaneously hypertensive rats (SHRs) due to a lack of MIF in PVN neurons. Since endogenous ANG II in the PVN modulates stress reactivity, we tested the hypothesis that replacement of MIF in PVN neurons would reduce baseline blood pressure and inhibit stress-induced increases in blood pressure and plasma corticosterone in adult male SHRs. Radiotelemetry transmitters were implanted to measure blood pressure, and then an adeno-associated viral vector expressing either enhanced green fluorescent protein (GFP) or MIF was injected bilaterally into the PVN. Cardiovascular responses to a 15-min water stress (1-cm deep, 25°C) and a 60-min restraint stress were evaluated 3-4 wk later. MIF treatment in the PVN attenuated average restraint-induced increases in blood pressure (37.4 ± 2.0 and 27.6 ± 3.5 mmHg in GFP and MIF groups, respectively, P < 0.05) and corticosterone (42 ± 2 and 36 ± 3 μg/dl in GFP and MIF groups, respectively, P < 0.05). MIF treatment in the PVN also reduced stress-induced elevations in the number of c-Fos-positive cells in the rostral ventrolateral medulla (71 ± 5 in GFP and 47 ± 5 in MIF SHRs, P < 0.01) and corticotropin-releasing factor mRNA expression in the PVN. However, MIF had no significant effects on the cardiovascular responses to water stress in SHRs or to either stress in Sprague-Dawley rats. Therefore, viral vector-mediated restoration of MIF in PVN neurons of SHRs attenuates blood pressure and hypothalamic pituitary adrenal axis responses to stress.

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.

Neuropeptides in the posterodorsal medial amygdala modulate central cardiovascular reflex responses in awake male rats

The rat posterodorsal medial amygdala (MePD) links emotionally charged sensory stimuli to social behavior, and is part of the supramedullary control of the cardiovascular system. We studied the effects of microinjections of neuroactive peptides markedly found in the MePD, namely oxytocin (OT, 10 ng and 25 pg; n=6/group), somatostatin (SST, 1 and 0.05 μM; n=8 and 5, respectively), and angiotensin II (Ang II, 50 pmol and 50 fmol; n=7/group), on basal cardiovascular activity and on baroreflex- and chemoreflex-mediated responses in awake adult male rats. Power spectral and symbolic analyses were applied to pulse interval and systolic arterial pressure series to identify centrally mediated sympathetic/parasympathetic components in the heart rate variability (HRV) and arterial pressure variability (APV). No microinjected substance affected basal parameters. On the other hand, compared with the control data (saline, 0.3 µL; n=7), OT (10 ng) decreased mean AP (MAP50) after baroreflex stimulation and increased both the mean AP response after chemoreflex activation and the high-frequency component of the HRV. OT (25 pg) increased overall HRV but did not affect any parameter of the symbolic analysis. SST (1 μM) decreased MAP50, and SST (0.05 μM) enhanced the sympathovagal cardiac index. Both doses of SST increased HRV and its low-frequency component. Ang II (50 pmol) increased HRV and reduced the two unlike variations pattern of the symbolic analysis (P<0.05 in all cases). These results demonstrate neuropeptidergic actions in the MePD for both the increase in the range of the cardiovascular reflex responses and the involvement of the central sympathetic and parasympathetic systems on HRV and APV.

Cardiovascular effect of angiotensin-(1-12) in the caudal ventrolateral medullary depressor area of the rat

Angiotensin (ANG)-(1-12) excites neurons via ANG II type 1 receptors (AT1Rs), which are present in the caudal ventrolateral medullary depressor area (CVLM). We hypothesized that microinjections of ANG-(1-12) into the CVLM may elicit decreases in mean arterial pressure (MAP), heart rate (HR), and sympathetic nerve activity. This hypothesis was tested in urethane-anesthetized adult male Wistar rats. Microinjections of ANG-(1-12) into the CVLM elicited decreases in MAP, HR, and greater splanchnic nerve activity (GSNA). ANG-(1-12)-induced responses consisted of initial (first 1-8 min) and delayed (8-24 min) phases. Prior microinjections of losartan, A-779, and captopril into the CVLM blocked initial, delayed, and both phases of ANG-(1-12) responses, respectively. Blockade of GABA receptors in the rostral ventrolateral medullary pressor area (RVLM) attenuated cardiovascular responses elicited by microinjections of ANG-(1-12) into the ipsilateral CVLM. Microinjections of ANG-(1-12) into the CVLM potentiated the reflex decreases and attenuated the reflex increases in GSNA elicited by intravenous injections of phenylephrine and sodium nitroprusside, respectively. These results indicate that microinjections of ANG-(1-12) into the CVLM elicit decreases in MAP, HR, and GSNA. Initial and delayed phases of these responses are mediated via ANG II and ANG-(1-7), respectively; the effects of ANG II and ANG-(1-7) are mediated via AT1Rs and Mas receptors, respectively. Captopril blocked both phases of ANG-(1-12) responses, indicating that angiotensin-converting enzyme is important in mediating these responses. GABA receptors in the RVLM partly mediate the cardiovascular responses to microinjections of ANG-(1-12) into the CVLM. Microinjections of ANG-(1-12) into the CVLM modulate baroreflex responses.

Baroreceptor reflex control of heart rate in angiotensin type 1A receptor knockout mice

The baroreceptor reflex dampens the short-term fluctuations in blood pressure by feedback modulation of heart rate (HR) and vascular resistance. Impairment of this reflex has been observed in hypertension and heart failure. Angiotensin II, a blood borne hormone, acts via its type 1A receptor to attenuate the baroreceptor reflex and this reflex is reported to be dramatically altered in angiotensin type 1A receptor knockout mice. This study sought to further investigate changes in the arterial and cardiopulmonary baroreceptor reflex control of HR in angiotensin II type 1A receptor knocked out mice. In artificially ventilated, isoflurane anesthetized mice, the arterial and cardiopulmonary baroreceptor reflexes were activated via injection or slow infusions, respectively, of phenylephrine and sodium nitroprusside through the jugular vein. We observed no impairment of either the arterial or cardiopulmonary baroreceptor reflex control of HR in angiotensin type 1A receptor knockout mice.

Activation of angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas axis attenuates the cardiac reactivity to acute emotional stress

Recent data indicate the brain angiotensin-converting enzyme/ANG II/AT1 receptor axis enhances emotional stress responses. In this study, we investigated whether its counterregulatory axis, the angiotensin-converting enzyme 2 (ACE2)/ANG-(1-7)/Mas axis, attenuate the cardiovascular responses to acute emotional stress. In conscious male Wistar rats, the tachycardia induced by acute stress (air jet 10 l/min) was attenuated by intravenous injection of ANG-(1-7) [Δ heart rate (HR): saline 136 ± 22 vs. ANG-(1-7) 61 ± 25 beats/min; P < 0.05]. Peripheral injection of the ACE2 activator compound, XNT, abolished the tachycardia induced by acute stress. We found a similar effect after intracerebroventricular injections of either ANG-(1-7) or XNT. Under urethane anesthesia, the tachycardia evoked by the beta-adrenergic agonist was markedly reduced by ANG-(1-7) [ΔHR: saline 100 ± 16 vs. ANG-(1-7) 18 ± 15 beats/min; P < 0.05]. The increase in renal sympathetic nerve activity (RSNA) evoked by isoproterenol was also abolished after the treatment with ANG-(1-7) [ΔRSNA: saline 39% vs. ANG-(1-7) -23%; P < 0.05]. The tachycardia evoked by disinhibition of dorsomedial hypothalamus neurons, a key nucleus for the cardiovascular response to emotional stress, was reduced by ∼45% after intravenous injection of ANG-(1-7). In cardiomyocyte, the incubation with ANG-(1-7) (1 μM) markedly attenuated the increases in beating rate induced by isoproterenol. Our data show that activation of the ACE2/ANG-(1-7)/Mas axis attenuates stress-induced tachycardia. This effect might be either via the central nervous system reducing anxiety level and/or interfering with the positive chronotropy mediated by activation of cardiac β adrenergic receptors. Therefore, ANG-(1-7) might contribute to reduce the sympathetic load to the heart during situations of emotional stress, reducing the cardiovascular risk.

Chronic angiotensin-II treatment potentiates HR slowing in Sprague-Dawley rat during acute behavioral stress

This study examined the effect of 2-week infusion of angiotensin-II (Ang-II; 175 ng/kg/min) via minipump in rats (n=7) upon the mean arterial blood pressure (mBP) and heart rate (HR) response to an acute stress as compared to rats infused with saline (n=7). The acute stress was produced by a classical aversive conditioning paradigm: a 15s tone (CS+) followed by a half second tail shock. Baseline mBP in Ang-II infused rats (167.7±21.3 mm Hg; mean±SD) significantly exceeded that of controls (127.6±13.5 mm Hg). Conversely, baseline HR in the Ang-II infused rats (348±33) was significantly lower than controls (384±19 bpm). The magnitude of the mBP increase during CS+ did not differ between groups, but the HR slowing during CS+ in the Ang-II infused rats (-13.2±8.9 bpm) was significantly greater than that seen in controls (-4.2±5.5 bpm). This augmented bradycardia may be inferentially attributed to an accentuated increase in cardiac parasympathetic activity during CS+ in the Ang-II infused rats. The mBP increased above baseline immediately post-shock delivery in controls, but fell in the Ang-II infused rats, perhaps because of a 'ceiling effect' in total vascular resistance. This classical conditioning model of 'acute stress' differs from most stress paradigms in rats in yielding a HR slowing concomitant with a pressor response, and this slowing is potentiated by Ang-II.

The brain renin-angiotensin system and cardiovascular responses to stress: insights from transgenic rats with low brain angiotensinogen

The renin-angiotensin system (RAS) has been identified as an attractive target for the treatment of stress-induced cardiovascular disorders. The effects of angiotensin (ANG) peptides during stress responses likely result from an integration of actions by circulating peptides and brain peptides derived from neuronal and glial sources. The present review focuses on the contribution of endogenous brain ANG peptides to pathways involved in cardiovascular responses to stressors. During a variety of forms of stress, neuronal pathways in forebrain areas containing ANG II or ANG-(1-7) are activated to stimulate descending angiotensinergic pathways that increase sympathetic outflow to increase blood pressure. We provide evidence that glia-derived ANG peptides influence brain AT(1) receptors. This appears to result in modulation of the responsiveness of the neuronal pathways activated during stressors that elevate circulating ANG peptides to activate brain pathways involving descending hypothalamic projections. It is well established that increased cardiovascular reactivity to stress is a significant predictor of hypertension and other cardiovascular diseases. This review highlights the importance of understanding the impact of RAS components from the circulation, neurons, and glia on the integration of cardiovascular responses to stressors.

Stress-dependent hypertension and the role of T lymphocytes

Hypertension is a significant global health burden that is associated with an increased risk of stroke, atherosclerosis and other cardiovascular diseases. Several risk factors, including high dietary salt, obesity, genetics and race, as well as behavioural and psychological factors, contribute to development of this complex disease. Various hypertensive stimuli enhance sympathetic drive and promote autonomic dysfunction leading to elevated blood pressure. As our understanding of the pathogenesis and end-organ damage associated with hypertension increases, mounting evidence also highlights the role of inflammation in this process and, in particular, the role of the adaptive immune system and T cells. This review discusses recent findings regarding the role of the central nervous system, T lymphocytes and the impact of cardiovascular risk factors, such as psychological stress, in hypertension.

Neurocardiac dysregulation and neurogenic arrhythmias in a transgenic mouse model of Huntington's disease

Huntington's disease (HD) is a heritable neurodegenerative disorder, with heart disease implicated as one major cause of death. While the responsible mechanism remains unknown, autonomic nervous system (ANS) dysfunction may play a role. We studied the cardiac phenotype in R6/1 transgenic mice at early (3 months old) and advanced (7 months old) stages of HD. While exhibiting a modest reduction in cardiomyocyte diameter, R6/1 mice had preserved baseline cardiac function. Conscious ECG telemetry revealed the absence of 24-h variation of heart rate (HR), and higher HR levels than wild-type littermates in young but not older R6/1 mice. Older R6/1 mice had increased plasma level of noradrenaline (NA), which was associated with reduced cardiac NA content. R6/1 mice also had unstable R-R intervals that were reversed following atropine treatment, suggesting parasympathetic nervous activation, and developed brady- and tachyarrhythmias, including paroxysmal atrial fibrillation and sudden death. c-Fos immunohistochemistry revealed greater numbers of active neurons in ANS-regulatory regions of R6/1 brains. Collectively, R6/1 mice exhibit profound ANS-cardiac dysfunction involving both sympathetic and parasympathetic limbs, that may be related to altered central autonomic pathways and lead to cardiac arrhythmias and sudden death.

Angiotensin 1A receptors transfected into caudal ventrolateral medulla inhibit baroreflex gain and stress responses

AIMS

The caudal ventrolateral medulla (CVLM) is important for autonomic regulation and is rich in angiotensin II type 1A receptors (AT(1A)R). To determine their function, we examined whether the expression of AT(1A)R in the CVLM of mice lacking AT(1A)R (AT(1A)(-/-)) alters baroreflex sensitivity and cardiovascular responses to stress.

METHODS AND RESULTS

Bilateral microinjections into the CVLM of AT(1A)(-/-) mice of lentivirus with the phox-2 selective promoter (PRSx8) were made to express either AT(1A)R (Lv-PRSx8-AT(1A)) or green fluorescent protein (Lv-PRSx8-GFP) as a control. Radiotelemetry was used to record mean arterial pressure (MAP), heart rate (HR), and locomotor activity. Following injection of Lv-PRSx8-GFP, robust neuronal expression of GFP was observed with ∼60% of the GFP-positive cells also expressing the catecholamine-synthetic enzyme tyrosine hydroxylase. After 5 weeks, there were no differences in MAP or HR between groups, but the Lv-PRSx8-AT(1A)- injected mice showed reduced baroreflex sensitivity (-25%, P = 0.003) and attenuated pressor responses to cage-switch and restraint stress compared with the Lv-PRSx8-GFP-injected mice. Reduced MAP mid-frequency power during cage-switch stress reflected attenuated sympathetic activation (Pgroup × stress = 0.04). Fos-immunohistochemistry indicated greater activation of forebrain and hypothalamic neurons in the Lv-PRSx8-AT(1A) mice compared with the control.

CONCLUSION

The expression of AT(1A)R in CVLM neurons, including A1 neurons, while having little influence on the basal blood pressure or HR, may play a tonic role in inhibiting cardiac vagal baroreflex sensitivity. However, they strongly facilitate the forebrain response to aversive stress, yet reduce the pressor response presumably through greater sympatho-inhibition. These findings outline novel and specific roles for angiotensin II in the CVLM in autonomic regulation.

T lymphocytes and vascular inflammation contribute to stress-dependent hypertension

BACKGROUND

Psychological stress is a significant risk factor for hypertension and also directly affects the immune system. We have previously reported that T lymphocytes are essential for development of hypertension and that the central nervous system contributes to peripheral T-lymphocyte activation and vascular inflammation in this disease; however, the role of T-cell activation in stress-related hypertension remains unclear.

METHODS

Wild-type and T-cell-deficient (RAG-1(-/-)) mice were subjected to daily episodes of stress and blood pressure was measured. Circulating T-cell activation markers and vascular infiltration of immune cells were analyzed, as were stress hormone levels and gene expression changes in the brain. The effects angiotensin II infusion in the presence of chronic stress was also studied.

RESULTS

Repeated daily stress contributed to acute elevations in blood pressure that were associated with increased activation of circulating T cells and increased vascular infiltration of T cells. Repeated stress increased blood pressure in wild-type but not RAG-1(-/-) mice. Adoptive transfer of T cells to RAG-1(-/-) mice restored blood pressure elevation in response to stress. Stress-related hypertension and vascular infiltration of T cells was markedly enhanced by angiotensin II. Moreover, angiotensin II-infused mice exposed to chronic stress exhibited greater blood pressure reactivity to an episode of acute stress.

CONCLUSIONS

These data demonstrate that stress-dependent hypertension triggers an inflammatory response that raises blood pressure at baseline and augments the hypertension caused by angiotensin II. These data provide insight as to how psychological stress contributes to hypertension.

Angiotensin type 1A receptors in C1 neurons of the rostral ventrolateral medulla modulate the pressor response to aversive stress

The rise in blood pressure during an acute aversive stress has been suggested to involve activation of angiotensin type 1A receptors (AT(1A)Rs) at various sites within the brain, including the rostral ventrolateral medulla. In this study we examine the involvement of AT(1A)Rs associated with a subclass of sympathetic premotor neurons of the rostral ventrolateral medulla, the C1 neurons. The distribution of putative AT(1A)R-expressing cells was mapped throughout the brains of three transgenic mice with a bacterial artificial chromosome-expressing green fluorescent protein under the control of the AT(1A)R promoter. The overall distribution correlated with that of the AT(1A)Rs mapped by other methods and demonstrated that the majority of C1 neurons express the AT(1A)R. Cre-recombinase expression in C1 neurons of AT(1A)R-floxed mice enabled demonstration that the pressor response to microinjection of angiotensin II into the rostral ventrolateral medulla is dependent upon expression of the AT(1A)R in these neurons. Lentiviral-induced expression of wild-type AT(1A)Rs in C1 neurons of global AT(1A)R knock-out mice, implanted with radiotelemeter devices for recording blood pressure, modulated the pressor response to aversive stress. During prolonged cage-switch stress, expression of AT(1A)Rs in C1 neurons induced a greater sustained pressor response when compared to the control viral-injected group (22 ± 4 mmHg for AT(1A)R vs 10 ± 1 mmHg for GFP; p < 0.001), which was restored toward that of the wild-type group (28 ± 2 mmHg). This study demonstrates that AT(1A)R expression by C1 neurons is essential for the pressor response to angiotensin II and that this pathway plays an important role in the pressor response to aversive stress.

Renin-angiotensin and sympathetic nervous system contribution to high blood pressure in Schlager mice

OBJECTIVE

Schlager hypertensive (BPH/2J) mice have been suggested to have high blood pressure (BP) due to an overactive sympathetic nervous system (SNS), but the contribution of the renin-angiotensin system (RAS) is unclear. In the present study, we examined the cardiovascular effects of chronically blocking the RAS in BPH/2J mice.

METHODS

Schlager normotensive (BPN/3J, n = 6) and BPH/2J mice (n = 8) received the angiotensin AT 1A-receptor antagonist losartan (150 mg/kg per day) in drinking water for 2 weeks. Pre-implanted telemetry devices were used to record mean arterial pressure (MAP), heart rate (HR) and locomotor activity.

RESULTS

MAP was reduced by losartan treatment in BPN/3J (-23 mmHg, P < 0.01) and in BPH/2J mice (-25 mmHg, P < 0.001), whereas HR was increased. Losartan had little effect on initial pressor responses to feeding or to stress, but did attenuate the sustained pressor response to cage-switch stress. During the active period, the hypotension to sympathetic blockade with pentolinium was greater in BPH/2J than BPN/3J (suggesting neurogenic hypertension), but was not affected by losartan. During the inactive period, a greater depressor response to pentolinium was observed in losartan-treated animals.

CONCLUSION

The hypotensive actions of losartan suggest that although the RAS provides an important contribution to BP, it contributes little, if at all, to the hypertension-induced or the greater stress-induced pressor responses in Schlager mice. The effects of pentolinium suggest that the SNS is mainly responsible for hypertension in BPH/2J mice. However, the RAS inhibits sympathetic vasomotor tone during inactivity and prolongs sympathetic activation during periods of adverse stress, indicating an important sympatho-modulatory role.

Blood-borne angiotensin II acts in the brain to influence behavioral and endocrine responses to psychogenic stress

This study elucidates the neural circuits by which circulating angiotensin II (ANGII) acts in the brain to influence humoral and behavioral responses to psychological stressors. To test the hypothesis that systemic ANGII mediates stress responding via the subfornical organ (SFO), we first found that the timing of increased systemic ANGII in response to 60 min restraint coincides with increased c-fos mRNA expression in the SFO. Next, we administered an anterograde neuronal tract tracer into the SFO and found that fibers originating there make appositions onto neurons in the paraventricular nucleus of the hypothalamus that are also c-fos positive following restraint stress. To determine whether circulating ANGII stimulates the release of stress hormones via activation of angiotensin type 1 receptors (AT1R) within the SFO, we delivered lentivirus to knockdown AT1R expression locally in the SFO. Inhibition of AT1R specifically within the SFO blunted the release of adrenocorticotrophin-releasing hormone and corticosterone in response to restraint stress and caused rats to spend more time in the open arms of an elevated-plus maze than controls, indicating that inhibition of AT1R within the SFO is anxiolytic. Collectively, these results suggest that circulating ANGII acts on AT1R in the SFO to influence responding to psychological stressors.

Brain angiotensin AT1 receptors as specific regulators of cardiovascular reactivity to acute psychoemotional stress

1. Cardiovascular reactivity, an abrupt rise in blood pressure (BP) and heart rate in response to psychoemotional stress, is a risk factor for heart disease. Pharmacological and molecular genetic studies suggest that brain angiotensin (Ang) II and AT(1) receptors are required for the normal expression of sympathetic cardiovascular responses to various psychological stressors. Moreover, overactivity of the brain AngII system may contribute to enhanced cardiovascular reactivity in hypertension. 2. Conversely, brain AT(1) receptors appear to be less important for the regulation of sympathetic cardiovascular responses to a range of stressors involving an immediate physiological threat (physical stressors) in animal models. 3. Apart from threatening events, appetitive stimuli can induce a distinct, central nervous system-mediated rise in BP. However, evidence indicates that brain AT(1) receptors are not essential for the regulation of cardiovascular arousal associated with positively motivated behaviour, such as anticipation and the consumption of palatable food. The role of central AT(1) receptors in regulating cardiovascular activation elicited by other types of appetitive stimuli remains to be determined. 4. Emerging evidence also indicates that brain AT(1) receptors play a limited role in the regulation of cardiovascular responses to non-emotional natural daily activities, sleep and exercise. 5. Collectively, these findings suggest that, with respect to cardiovascular arousal, central AT(1) receptors may be involved primarily in the regulation of the defence response. Therefore, these receptors could be a potential therapeutic target for selective attenuation of BP hyperreactivity to aversive stressors, without altering physiologically important cardiovascular adjustments to normal daily activities, sleep and exercise.

Hydration state controls stress responsiveness and social behavior

Life stress frequently occurs within the context of homeostatic challenge, requiring integration of physiological and psychological need into appropriate hormonal, cardiovascular, and behavioral responses. To test neural mechanisms underlying stress integration within the context of homeostatic adversity, we evaluated the impact of a pronounced physiological (hypernatremia) challenge on hypothalamic-pituitary-adrenal (HPA), cardiovascular, and behavioral responses to an acute psychogenic stress. Relative to normonatremic controls, rats rendered mildly hypernatremic had decreased HPA activation in response to physical restraint, a commonly used rodent model of psychogenic stress. In addition, acute hypernatremia attenuated the cardiovascular response to restraint and promoted faster recovery to prestress levels. Subsequent to restraint, hypernatremic rats had significantly more c-Fos expression in oxytocin- and vasopressin-containing neurons within the supraoptic and paraventricular nuclei of the hypothalamus. Hypernatremia also completely eliminated the increased plasma renin activity that accompanied restraint in controls, but greatly elevated circulating levels of oxytocin. The endocrine and cardiovascular profile of hypernatremic rats was predictive of decreased anxiety-like behavior in the social interaction test. Collectively, the results indicate that acute hypernatremia is a potent inhibitor of the HPA, cardiovascular, and behavioral limbs of the stress response. The implications are that the compensatory responses that promote renal-sodium excretion when faced with hypernatremia also act on the nervous system to decrease reactivity to psychogenic stressors and facilitate social behavior, which may suppress the anxiety associated with approaching a communal water source and support the social interactions that may be encountered when engaging in drinking behavior.

Cardiovascular responses to aversive and nonaversive stressors in Schlager genetically hypertensive mice

BACKGROUND

Schlager inbred hypertensive mice (BPH/2J) have been suggested to have high blood pressure (BP) due to an overactive sympathetic nervous system (SNS). The brain nuclei associated with the hypertension are also those involved in the integration of the cardiovascular responses to stress. Therefore, in the present study, we hypothesize that an increased contribution of the SNS in BPH/2J mice may culminate in a greater pressor response to stressful stimuli in these hypertensive mice than normotensive (BPN/3J) mice.

METHODS

Male hypertensive BPH/2J and normotensive BPN/3J mice were implanted with telemetry devices and exposed to a series of behavioral "stress" tests including aversive stress (shaker, clean cage switch, and restraint) and nonaversive stress (feeding).

RESULTS

Aversive stress caused a 67-88% greater pressor response in BPH/2J compared with BPN/3J mice. By contrast, the feeding-induced pressor response was not different between groups. All stressors induced tachycardia that was less in BPH/2J mice (feeding and restraint) and others were not different between groups (clean cage switch and shaker).

CONCLUSIONS

These findings indicate that hypertension in BPH/2J mice is associated with greater pressor responsiveness to aversive stress but not to appetitive arousal. Thus, BPH/2J hypertensive mice may be a particularly relevant model for human hypertensive patients that overrespond to daily stressors.

Acute daily psychological stress causes increased atrophic gene expression and myostatin-dependent muscle atrophy

Psychological stress is known to attenuate body size and lean body mass. We tested the effects of 1, 3, or 7 days of two different models of psychological stress, 1 h of daily restraint stress (RS) or daily cage-switching stress (CS), on skeletal muscle size and atrophy-associated gene expression in mice. Thymus weights decreased in both RS and CS mice compared with unstressed controls, suggesting that both models activated the hypothalamic-pituitary-adrenal axis. Body mass was significantly decreased at all time points for both models of stress but was greater for RS than CS. Mass of the tibialis anterior (TA) and soleus (SOL) muscles was significantly decreased after 3 and 7 days of RS, but CS only significantly decreased SOL mass after 7 days. TA mRNA levels of the atrophy-associated genes myostatin (MSTN), atrogin-1, and the phosphatidylinositol 3-kinase inhibitory subunit p85alpha were all significantly increased relative to unstressed mice after 1 and 3 days of RS, and expression of MSTN and p85alpha mRNA remained elevated after 7 days of RS. Expression of muscle ring finger 1 was increased after 1 day of RS but returned to baseline at 3 and 7 days of RS. MSTN, atrogin-1, and p85alpha mRNA levels also significantly increased after 1 and 3 days of CS but atrogen-1 mRNA levels had resolved back to normal levels by 3 days and p85alpha with 7 days of CS. p21CIP mRNA levels were significantly decreased by 3 days of CS or RS. Finally, body mass was minimally affected, and muscle mass was completely unaffected by 3 days of RS in mice null for the MSTN gene, and MSTN inactivation attenuated the increase in atrogin-1 mRNA levels with 4 days of RS compared with wild-type mice. Together these data suggest that acute daily psychological stress induces atrophic gene expression and loss of muscle mass that appears to be MSTN dependent.

Differences in emotion processing in patients with essential and secondary hypertension

BACKGROUND

An impaired ability to experience and express emotions, known as alexithymia, has previously been associated with hypertension. Alexithymia and related emotion-processing variables, however, have never been examined as a function of the type of hypertension, essential (EH) or secondary (SH).

METHODS

Our working hypothesis was that if dysregulated emotional processes play a key neurobiological role in EH, they would be less present in hypertension due to specific medical causes or SH. A total of 98 consecutive hypertensive patients (73 EH, 25 SH) with similar blood pressure levels completed two complementary measures of emotion processing: the 20-item Toronto Alexithymia Scale (TAS-20) and the Levels of Emotional Awareness Scale (LEAS).

RESULTS

After controlling for confounding variables, LEAS score was lower in EH than SH (estimated means: 46.4 vs. 52.0; P = 0.028; effect size 0.52). TAS-20 scores did not differentiate EH from SH, but the differences were in the expected direction, with an effect size of 0.34 for TAS-20 total score. Neither psychometric measure was associated with the duration of hypertension or the presence of cardiovascular (CV) complications.

CONCLUSIONS

These results are consistent with a contribution of an emotional or psychosomatic component in EH and may have practical implications for the nonpharmacological management of hypertension. They also demonstrate the utility of complementary measures of emotion processing in medically ill patients.