The roles of sensitization and neuroplasticity in the long-term regulation of blood pressure and hypertension

Association between anxiety and elevated blood pressure in adolescent patients: a single-center cross-sectional study

OBJECTIVE

Although anxiety is known to be associated with elevated blood pressure and hypertension in adults, this has not been studied in children. The aim of this study was to determine the association between anxiety and elevated blood pressures in adolescents.

METHODS

Adolescents, aged 12-18 years old, referred to the nephrology clinic were eligible to participate. Elevated blood pressure was defined as either SBP or DBP measurement above the 95th percentile for age, height, and sex. Participants were evaluated for anxiety using the validated Screen for Child Anxiety Related Disorders questionnaire filled independently by the child (SCARED-C) and parent (SCARED-P) evaluating the child.

RESULTS

Two hundred adolescents participated in this study. Thirty-one (53%) of SCARED-P-positive participants were found to have elevated blood pressure compared with 27 (19%) of SCARED-P negative, P 0.03. Twenty-five (43%) of SCARED-P positive had elevated DBP compared with 31 (28%) of SCARED-P negative ( P 0.003). In SCARED-P positive, mean DBP (78.4 ± 9.9) was higher compared with SCARED-P negative (74.9 ± 9.2) ( P 0.03). In a subgroup of adolescents (№ 130) not treated with blood pressure medications mean DBP was higher in both SCARED-P (79.0 ± 10.1) and SCARED-C (77.1 ± 10.4) positive groups compared with SCARED-P (73.6 ± 9.3) and SCARED-C (73 ± 8.9) negative, respectively.

CONCLUSION

Our study demonstrates an association between anxiety and elevated DBP in adolescent children. Screening adolescents for anxiety should be a part of the routine evaluation of adolescent children.

Linking Blood Pressure-Associated Emotional Dampening to Trait Empathy

Gradual and sustained increases in resting blood pressure are accompanied by gradual and sustained reductions in the capacity to consciously experience several affective and somatosensory processes. Burgeoning theory suggests that this phenomenon, termed cardiovascular emotional dampening, contributes to heart disease risk by interfering with our ability to effectively respond to environmental demands. Interpersonal relationships are contexts in which this risk cascade likely occurs, but prior researchers have paid little attention to how emotional dampening might influence these relationships. As empathy is a construct used to describe facets of emotion-linked responding that facilitate interpersonal relationships, if emotional dampening influences interpersonal relationships, then we might expect resting blood pressure to covary with measures of empathy as it does with other previously studied aspects of affective responding. We recruited 175 healthy undergraduate college student participants (120 Women; M age = 19.17, SD age = 2.08) to complete a counterbalanced procedure in which we measured resting blood pressure and related it to participants' responses on the Toronto Alexithymia Scale, the Questionnaire of Cognitive and Affective Empathy, and a demographic survey. Bivariate comparisons revealed a significant inverse relationship between average resting systolic blood pressure (SBP) and cognitive empathy, as well as a significant inverse relationship between SBP and affective empathy. Multiple regression analyses revealed that SBP remained a significant predictor of cognitive empathy, but not affective empathy, after controlling for related covariates (i.e., sex, age, and alexithymia). SBP predicted cognitive empathy such that higher SBP was associated with lower cognitive empathy. Thus, people with higher resting blood pressures might experience increased interpersonal distress because of a reduced capacity for empathetic accuracy and perspective-taking. We discuss the implications and future directions of these findings.

Comparative analysis of intracardiac neural structures in the aged rats with essential hypertension

Persistent arterial hypertension initiates cardiac autonomic imbalance and alters cardiac tissues. Previous studies have shown that neural component contributes to arterial hypertension etiology, maintenance, and progression and leads to brain damage, peripheral neuropathy, and remodeling of intrinsic cardiac neural plexus. Recently, significant structural changes of the intracardiac neural plexus were demonstrated in young prehypertensive and adult hypertensive spontaneously hypertensive rats (SHR), yet structural alterations of intracardiac neural plexus that occur in the aged SHR remain undetermined. Thus, we analyzed the impact of uncontrolled arterial hypertension in old (48-52 weeks) SHR and the age-matched Wistar-Kyoto rats (WKY). Intrinsic cardiac neural plexus was examined using a combination of immunofluorescence confocal microscopy and transmission electron microscopy in cardiac sections and whole-mount preparations. Our findings demonstrate that structural changes of intrinsic cardiac neural plexus caused by arterial hypertension are heterogeneous and may support recent physiological implications about cardiac denervation occurring together with the hyperinnervation of the SHR heart. We conclude that arterial hypertension leads to (i) the decrease of the neuronal body area, the thickness of atrial nerves, the number of myelinated nerve fibers, unmyelinated axon area and cumulative axon area in the nerve, and the density of myocardial nerve fibers, and (ii) the increase in myelinated nerve fiber area and density of neuronal bodies within epicardiac ganglia. Despite neuropathic alterations of myelinated fibers were exposed within intracardiac nerves of both groups, SHR and WKY, we consider that the determined significant changes in structure of intrinsic cardiac neural plexus were predisposed by arterial hypertension.

Sensitization of Hypertension: The Impact of Earlier Life Challenges: Excellence Award for Hypertension Research 2021

Hypertension affects over 1 billion individuals worldwide. Because the cause of hypertension is known only in a small fraction of patients, most individuals with high blood pressure are diagnosed as having essential hypertension. Elevated sympathetic nervous system activity has been identified in a large portion of hypertensive patients. However, the root cause for this sympathetic overdrive is unknown. A more complete understanding of the breadth of the functional capabilities of the sympathetic nervous system may lead to new insights into the cause of essential hypertension. By employing a unique experimental paradigm, we have recently discovered that the neural network controlling sympathetic drive is more reactive after rats are exposed to mild challenges (stressors) and that the hypertensive response can be sensitized (ie, hypertensive response sensitization [HTRS]). We have also found that the induction of HTRS involves plasticity in the neural network controlling sympathetic drive. The induction and maintenance of the latent HTRS state also require the functional integrity of the brain renin-angiotensin-aldosterone system and the presence of several central inflammatory factors. In this review, we will discuss the induction and expression of HTRS in adult animals and in the progeny of mothers with prenatal obesity/overnutrition or with maternal gestational hypertension. Also, interventions that reverse the effects of stressor-induced HTRS will be reviewed. Understanding the mechanisms underlying HTRS and identifying the beneficial effects of maternal or offspring early-life interventions that prevent or reverse the sensitized state can provide insights into therapeutic strategies for interrupting the vicious cycle of transgenerational hypertension.

Effects of 3-month CPAP therapy on brain structure in obstructive sleep apnea: A diffusion tensor imaging study

White matter (WM) fiber alterations in patients with obstructive sleep apnea (OSA) is associated with cognitive impairment, which can be alleviated by continuous positive airway pressure (CPAP). In this study, we aimed to investigate the changes in WM in patients with OSA at baseline (pre-CPAP) and 3 months after CPAP adherence treatment (post-CPAP), and to provide a basis for understanding the reversible changes after WM alteration in this disease. Magnetic resonance imaging (MRI) was performed on 20 severely untreated patients with OSA and 20 good sleepers. Tract-based spatial statistics was used to evaluate the fractional anisotropy (FA), mean diffusion coefficient, axial diffusion coefficient, and radial diffusion coefficient (RD) of WM. To assess the efficacy of treatment, 20 patients with pre-CPAP OSA underwent MRI again 3 months later. A correlation analysis was conducted to evaluate the relationship between WM injury and clinical evaluation. Compared with good sleepers, patients with OSA had decreased FA and increased RD in the anterior thalamic radiation, forceps major, inferior fronto-occipital tract, inferior longitudinal tract, and superior longitudinal tract, and decreased FA in the uncinate fasciculus, corticospinal tract, and cingulate gyrus (P < 0.05). No significant change in WM in patients with post-CPAP OSA compared with those with pre-CPAP OSA. Abnormal changes in WM in untreated patients with OSA were associated with oxygen saturation, Montreal cognitive score, and the apnea hypoventilation index. WM fiber was extensively alteration in patients with severe OSA, which is associated with cognitive impairment. Meanwhile, cognitive recovery was not accompanied by reversible changes in WM microstructure after short-term CPAP therapy.

Predator Scent-Induced Sensitization of Hypertension and Anxiety-like Behaviors

Post-traumatic stress disorder (PTSD), an anxiety-related syndrome, is associated with increased risk for cardiovascular diseases. The present study investigated whether predator scent (PS) stress, a model of PTSD, induces sensitization of hypertension and anxiety-like behaviors and underlying mechanisms related to renin-angiotensin systems (RAS) and inflammation. Coyote urine, as a PS stressor, was used to model PTSD. After PS exposures, separate cohorts of rats were studied for hypertensive response sensitization (HTRS), anxiety-like behaviors, and changes in plasma levels and mRNA expression of several components of the RAS and proinflammatory cytokines (PICs) in the lamina terminalis (LT), paraventricular nucleus (PVN), and amygdala (AMY). Rats exposed to PS as compared to control animals exhibited (1) a significantly greater hypertensive response (i.e., HTRS) when challenged with a slow-pressor dose of angiotensin (ANG) II, (2) significant decrease in locomotor activity and increase in time spent in the closed arms of a plus maze as well as general immobility (i.e., behavioral signs of increased anxiety), (3) upregulated plasma levels of ANG II and interleukin-6, and (4) increased expression of message for components of the RAS and PICs in key brain nuclei. All the PS-induced adverse effects were blocked by pretreatment with either an angiotensin-converting enzyme antagonist or a tumor necrosis factor-α inhibitor. The results suggest that PS, used as an experimental model of PTSD, sensitizes ANG II-induced hypertension and produces behavioral signs of anxiety, probably through upregulation of RAS components and inflammatory markers in plasma and brain areas associated with anxiety and blood pressure control.

Voluntary Exercise Prevents Hypertensive Response Sensitization Induced by Angiotensin II

Exercise training has profound effects on the renin-angiotensin system, inflammatory cytokines and oxidative stress, all of which affect autonomic nervous system activity and regulate blood pressure (BP) in both physiological and pathophysiological states. Using the Induction-Delay-Expression paradigm, our previous studies demonstrated that various challenges (stressors) during Induction resulted in hypertensive response sensitization (HTRS) during Expression. The present study tested whether voluntary exercise would protect against subpressor angiotensin (ANG) II-induced HTRS in rats. Adult male rats were given access to either “blocked” (sedentary rats) or functional running (exercise rats) wheels for 12 weeks, and the Induction-Delay-Expression paradigm was applied for the rats during the last 4 weeks. A subpressor dose of ANG II given during Induction produced an enhanced hypertensive response to a pressor dose of ANG II given during Expression in sedentary rats in comparison to sedentary animals that received saline (vehicle control) during Induction. Voluntary exercise did not attenuate the pressor dose of ANG II-induced hypertension but prevented the expression of HTRS seen in sedentary animals. Moreover, voluntary exercise reduced body weight gain and feed efficiency, abolished the augmented BP reduction after ganglionic blockade, reversed the increased mRNA expression of pro-hypertensive components, and upregulated mRNA expression of antihypertensive components in the lamina terminalis and hypothalamic paraventricular nucleus, two key brain nuclei involved in the control of sympathetic activity and BP regulation. These results indicate that exercise training plays a beneficial role in preventing HTRS and that this is associated with shifting the balance of the brain prohypertensive and antihypertensive pathways in favor of attenuated central activity driving sympathetic outflow and reduced BP.

Controlled Hemorrhage Sensitizes Angiotensin II-Elicited Hypertension through Activation of the Brain Renin-Angiotensin System Independently of Endoplasmic Reticulum Stress

Hemorrhagic shock is associated with activation of renin-angiotensin system (RAS) and endoplasmic reticulum stress (ERS). Previous studies demonstrated that central RAS activation produced by various challenges sensitizes angiotensin (Ang) II-elicited hypertension and that ERS contributes to the development of neurogenic hypertension. The present study investigated whether controlled hemorrhage could sensitize Ang II-elicited hypertension and whether the brain RAS and ERS mediate this sensitization. Results showed that hemorrhaged (HEM) rats had a significantly enhanced hypertensive response to a slow-pressor infusion of Ang II when compared to sham HEM rats. Treatment with either angiotensin-converting enzyme (ACE) 1 inhibitor, captopril, or ACE2 activator, diminazene, abolished the HEM-induced sensitization of hypertension. Treatment with the ERS agonist, tunicamycin, in sham HEM rats also sensitized Ang II-elicited hypertension. However, blockade of ERS with 4-phenylbutyric acid in HEM rats did not alter HEM-elicited sensitization of hypertension. Either HEM or ERS activation produced a greater reduction in BP after ganglionic blockade, upregulated mRNA and protein expression of ACE1 in the hypothalamic paraventricular nucleus (PVN), and elevated plasma levels of Ang II but reduced mRNA expression of the Ang-(1-7) receptor, Mas-R, and did not alter plasma levels of Ang-(1-7). Treatment with captopril or diminazene, but not phenylbutyric acid, reversed these changes. No treatments had effects on PVN protein expression of the ERS marker glucose-regulated protein 78. The results indicate that controlled hemorrhage sensitizes Ang II-elicited hypertension by augmenting RAS prohypertensive actions and reducing RAS antihypertensive effects in the brain, which is independent of ERS mechanism.

Association between anxiety and hypertension in adults: A systematic review and meta-analysis

We assessed the association between anxiety and hypertension in adults via a systematic review/meta-analysis. We searched PubMed, Ovid, and PsycINFO through 27 March 2020 with no language or publication type restrictions and systematically contacted study authors for unpublished information/data. We meta-analysed 59 studies including a total of 4,012,775 participants. Study quality was rated with the Newcastle-Ottawa Scale and random-effects analyses were performed. A significant anxiety-hypertension association was found in cross-sectional (OR = 1.37, 95 % CI = 1.21-1.54) and prospective studies (OR = 1.40, 95 % CI = 1.23-1.59). In sensitivity analyses, results were influenced by method of hypertension diagnosis, but not by study quality, method of anxiety diagnosis, study population, and effect size type. In subgroup analyses, study location, in particular country economic status, but not participant age, influenced the results. Longitudinal data and theoretical literature indicate that anxiety may precede hypertension. These findings have important clinical implications for the early detection and treatment of both anxiety and hypertension. Suggestions for future research are discussed.

Sex difference in blood pressure, a combinatorial consequence of the differential in RAAS components, sex hormones and time course

The longitudinal increment of blood pressure (BP) with age is attributed to lifestyle, internal and external environments. It is not limited to systemic brain-derived neurotrophic factor (BDNF), signaling to allow the individuals to better adapt to the developmental and environmental change. This regulation is necessary for all lives, regardless of sex. Basic levels of renin-angiotensin- aldosterone system (RAAS) components in males and females define the fundamental sex difference in BP, which may be set by prenatal programming and profoundly influence BP after birth. The innate sex difference in BP is magnified during puberty growth and further modified by menopause. At the age of 70 or older, blood pressure was similar in men and women. The understanding of the prenatal setup and development of sexual dimorphism in BP may provide preventative therapeutic strategies, including timing and drugs, for individuals with abnormal BP.

Piezo2 channel in nodose ganglia neurons is essential in controlling hypertension in a pathway regulated directly by Nedd4-2

Baroreflex plays a crucial role in regulation of arterial blood pressure (BP). Recently, Piezo1 and Piezo2, the mechanically-activated (MA) ion channels, have been identified as baroreceptors. However, the underlying molecular mechanism for regulating these baroreceptors in hypertension remains unknown. In this study, we used spontaneously hypertensive rats (SHR) and NG-Nitro-l-Arginine (L-NNA)- and Angiotensin II (Ang II)-induced hypertensive model rats to determine the role and mechanism of Piezo1 and Piezo2 in hypertension. We found that Piezo2 was dominantly expressed in baroreceptor nodose ganglia (NG) neurons and aortic nerve endings in Wistar-Kyoto (WKY) rats. The expression of Piezo2 not Piezo1 was significantly downregulated in these regions in SHR and hypertensive model rats. Electrophysiological results showed that the rapidly adapting mechanically-activated (RA-MA) currents and the responsive neuron numbers were significantly reduced in baroreceptor NG neurons in SHR. In WKY rats, the arterial BP was elevated by knocking down the expression of Piezo2 or inhibiting MA channel activity by GsMTx4 in NG. Knockdown of Piezo2 in NG also attenuated the baroreflex and increased serum norepinephrine (NE) concentration in WKY rats. Co-immunoprecipitation experiment suggested that Piezo2 interacted with Neural precursor cell-expressed developmentally downregulated gene 4 type 2 (Nedd4-2, also known as Nedd4L); Electrophysiological results showed that Nedd4-2 inhibited Piezo2 MA currents in co-expressed HEK293T cells. Additionally, Nedd4-2 was upregulated in NG baroreceptor neurons in SHR. Collectively, our results demonstrate that Piezo2 not Piezo1 may act as baroreceptor to regulate arterial BP in rats. Nedd4-2 induced downregulation of Piezo2 in baroreceptor NG neurons leads to hypertension in rats. Our findings provide a novel insight into the molecular mechanism for the regulation of baroreceptor Piezo2 and its critical role in the pathogenesis of hypertension.

Obstructive and Central Sleep Apnea in First Ever Ischemic Stroke are Associated with Different Time Course and Autonomic Activation

INTRODUCTION

Sleep-related breathing disorders are highly prevalent in patients with ischemic stroke. Among sleep-disordered breathing disorders, obstructive sleep apnea is the most represented one, but central sleep apnea, isolated or in the context of a periodic breathing/Cheyne-Stokes respiration, is frequently reported in these patients. Altered baroreflex responses have been reported in the acute phases of a cerebral event.

METHODS

We conducted, in a group of patients with ischemic stroke (n=60), a prospective 3-month follow-up physiological study to describe the breathing pattern during sleep and baroreflex sensitivity in the acute phase and in the recovery phase.

RESULTS

In the acute phase, within 10 days from the onset of symptoms, 22.4% of patients had a normal breathing pattern, 40.3% had an obstructive pattern, 16.4% had a central pattern, and 29.9% showed a mixed pattern. Smaller variations in the Apnea-Hypopnea Index were found in normal breathing and obstructive groups (ΔAHI 2.1±4.1 and -2.8±11.6, respectively) in comparison with central and mixed patterns (ΔAHI -6.9±15.1 and -12.5±13.1, respectively; ANOVA p=0.01). The obstructive pattern became the most frequent pattern, in 38.3% of patients at baseline and 61.7% of patients at follow-up. Modification of baroreflex sensitivity over time was influenced by the site of the lesion and by the sleep disorder pattern in the acute phase (MANOVA p=0.005).

CONCLUSION

We suggest that a down-regulation of autonomic activity, possibly related to reduced vagal modulation, may help the recovery after stroke, or a transitory disconnection from the cortical node that participates in the regulation of sympathetic outflow.

Interactions of the Brain Renin-Angiotensin-System (RAS) and Inflammation in the Sensitization of Hypertension

Mounting evidence indicates that the renin-angiotensin (RAS) and immune systems interact with one another in the central nervous system (CNS) and that they are importantly involved in the pathogenesis of hypertension. Components comprising the classic RAS were first identified in the periphery, and subsequently, similar factors were found to be generated de novo in many different organs including the brain. There is humoral-neural coupling between the systemic and brain RASs, which is important for controlling sympathetic tone and the release of endocrine factors that collectively determine blood pressure (BP). Similar to the interactions between the systemic and brain RASs is the communication between the peripheral and brain immune systems. Systemic inflammation activates the brain’s immune response. Importantly, the RAS and inflammatory factors act synergistically in brain regions involved in the regulation of BP. This review presents evidence of how such interactions between the brain RAS and central immune mechanisms contribute to the pathogenesis of hypertension. Emphasis focuses on the role of these interactions to induce neuroplastic changes in a central neural network resulting in hypertensive response sensitization (HTRS). Neuroplasticity and HTRS can be induced by challenges (stressors) presented earlier in life such as a low-dose of angiotensin II or high fat diet (HFD) feeding in adults. Similarly, the offspring of mothers with gestational hypertension or of mothers ingesting a HFD during pregnancy are reprogrammed and manifest HTRS when exposed to new stressors as adults. Consideration of the actions and interactions of the brain RAS and inflammatory mediators in the context of the induction and expression of HTRS will provide insights into the etiology of high BP that may lead to new strategies for the prevention and treatment of hypertension.

Sympathetic Nervous System Contributions to Hypertension: Updates and Therapeutic Relevance

The sympathetic nervous system plays a pivotal role in the long-term regulation of arterial blood pressure through the ability of the central nervous system to integrate neurohumoral signals and differentially regulate sympathetic neural input to specific end organs. Part 1 of this review will discuss neural mechanisms of salt-sensitive hypertension, obesity-induced hypertension, and the ability of prior experiences to sensitize autonomic networks. Part 2 of this review focuses on new therapeutic advances to treat resistant hypertension including renal denervation and carotid baroactivation. Both advances lower arterial blood pressure by reducing sympathetic outflow. We discuss potential mechanisms and areas of future investigation to target the sympathetic nervous system.

A preliminary study of the effect of a high-salt diet on transcriptome dynamics in rat hypothalamic forebrain and brainstem cardiovascular control centers

BACKGROUND

High dietary salt intake is strongly correlated with cardiovascular (CV) diseases and it is regarded as a major risk factor associated with the pathogenesis of hypertension. The CV control centres in the brainstem (the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM)) and hypothalamic forebrain (the subfornical organ, SFO; the supraoptic nucleus, SON and the paraventricular nucleus, PVN) have critical roles in regulating CV autonomic motor outflows, and thus maintaining blood pressure (BP). Growing evidence has implicated autonomic regulatory networks in salt-sensitive HPN (SSH), but the genetic basis remains to be delineated. We hypothesized that the development and/ or maintenance of SSH is reliant on the change in the expression of genes in brain regions controlling the CV system.

METHODOLOGY

We used RNA-Sequencing (RNA-Seq) to describe the differential expression of genes in SFO, SON, PVN, NTS and RVLM of rats being chronically fed with high-salt (HS) diet. Subsequently, a selection of putatively regulated genes was validated with quantitative reverse transcription polymerase chain reaction (qRT-PCR) in both Spontaneously Hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats.

RESULTS

The findings enabled us to identify number of differentially expressed genes in SFO, SON, PVN, NTS and RVLM; that are either up-regulated in both strains of rats (SON- Caprin2, Sctr), down-regulated in both strains of rats (PVN- Orc, Gkap1), up-regulated only in SHRs (SFO- Apopt1, Lin52, AVP, OXT; SON- AVP, OXT; PVN- Caprin2, Sclt; RVLM- A4galt, Slc29a4, Cmc1) or down-regulated only in SHRs (SON- Ndufaf2, Kcnv1; PVN- Pi4k2a; NTS- Snrpd2l, Ankrd29, St6galnac6, Rnf157, Iglon5, Csrnp3, Rprd1a; RVLM- Ttr, Faim).

CONCLUSIONS

These findings demonstrated the adverse effects of HS diet on BP, which may be mediated via modulating the signaling systems in CV centers in the hypothalamic forebrain and brainstem.

Amphetamine-induced sensitization of hypertension and lamina terminalis neuroinflammation

Psychomotor stimulants are prescribed for many medical conditions, including obesity, sleep disorders, and attention-deficit/hyperactivity disorder. However, despite their acknowledged therapeutic utility, these stimulants are frequently abused, and their use can have both short- and long-term negative consequences. Although stimulants such as amphetamines acutely elevate blood pressure, it is unclear whether they cause any long-term effects on cardiovascular function after use has been discontinued. Previous work in our laboratory has demonstrated that physiological and psychosocial stressors will produce sensitization of the hypertensive response, a heightened pressor response to a hypertensinogenic stimulus delivered after stressor exposure. Here, we tested whether pretreatment with amphetamine for 1 wk can sensitize the hypertensive response in rats. We found that repeated amphetamine administration induced and maintained sensitization of the pressor response to angiotensin II following a 7-day delay after amphetamine injections were terminated. We also found that amphetamine pretreatment altered mRNA expression for molecular markers associated with neuroinflammation and renin-angiotensin-aldosterone system (RAAS) activation in the lamina terminalis, a brain region implicated in the control of sympathetic nervous system tone and blood pressure. The results indicated amphetamine upregulated mRNA expression underlying neuroinflammation and, to a lesser degree, message for components of the RAAS in the lamina terminalis. However, we found no changes in mRNA expression in the paraventricular nucleus. These results suggest that a history of stimulant use may predispose individuals to developing hypertension by promoting neuroinflammation and upregulating activity of the RAAS in the lamina terminalis.

Blockade of angiotensin-converting enzyme or tumor necrosis factor-α reverses maternal high-fat diet-induced sensitization of angiotensin II hypertension in male rat offspring

Maternal high-fat diet (HFD) is associated with metabolic syndrome and cardiovascular diseases in adult offspring. Our previous study demonstrated that maternal HFD enhances pressor responses to ANG II or a proinflammatory cytokine (PIC), which is associated with increased expression of brain renin-angiotensin system (RAS) components and PICs in adult offspring. The present study further investigated whether inhibition of angiotensin-converting enzyme (ACE) or tumor necrosis factor-α (TNF-α) blocks sensitization of ANG II hypertension in offspring of HFD dams. All offspring were bred from dams with normal fat diet (NFD) or HFD starting two weeks before mating and maintained until weaning of the offspring. Then the weaned offspring were treated with an ACE inhibitor (captopril) or a TNF-α inhibitor (pentoxifylline) in the drinking water through the end of testing with a slow-pressor dose of ANG II. RT-PCR analyses of the lamina terminalis and paraventricular nucleus revealed upregulation of mRNA expression of several RAS components and PICs in male offspring of HFD dams when compared with age-matched offspring of NFD dams. The enhanced gene expression was attenuated by blockade of either RAS or PICs. Likewise, ANG II administration produced an augmented pressor response in offspring of HFD dams. This was abolished by either ACE or TNF-α inhibitor. Taken together, this study provides mechanistic evidence and a therapeutic strategy that systemic inhibition of the RAS and PICs can block maternal HFD-induced sensitization of ANG II hypertension, which is associated with attenuation of brain RAS and PIC expression in offspring.

Linking Lifestyle Factors to Complex Pain States: 3 Reasons Why Understanding Epigenetics May Improve the Delivery of Patient-Centered Care

Persistent pain is determined by a diverse and ever-changing combination of biology, psychology, and society. Research suggests a need to embrace a patient-centered, biopsychosocial approach to improve outcomes. Only through in-depth understanding of complex mechanisms and by using mechanism-based reasoning can the clinician tailor interventions-the basic tenet of patient-centered care. Epigenetics is helping to unravel complex underlying mechanisms and might have at least 3 major clinical implications for orthopaedic and sports physical therapists. First, it promotes mechanism-based clinical reasoning by improved understanding of the pathophysiology of many health conditions and the underlying mechanisms of action of commonly used interventions. Second, it might help patient subgrouping, allowing more targeted interventions. Finally, it might be used as a biomarker to monitor the effects of environmental factors and lifestyle interventions on health. For these reasons, the authors urge clinicians and clinical researchers to follow this rapidly growing area of research, as it might be soon contributing to patient assessment. J Orthop Sports Phys Ther 2019;49(10):683-687. doi:10.2519/jospt.2019.0612.

Genetic knockdown of brain-derived neurotrophic factor in the nervous system attenuates angiotensin II-induced hypertension in mice

Introduction:

Brain-derived neurotropic factor (BDNF) is expressed throughout the central nervous system and peripheral organs involved in the regulation of blood pressure, but the systemic effects of BDNF in the control of blood pressure are not well elucidated.

Materials and methods:

We utilized loxP flanked BDNF male mice to cross with nestin-Cre female mice to generate nerve system BDNF knockdown mice, nestin-BDNF (+/–), or injected Cre adenovirus into the subfornical organ to create subfornical organ BDNF knockdown mice. Histochemistry was used to verify injection location. Radiotelemetry was employed to determine baseline blood pressure and pressor response to angiotensin II (1000 ng/kg/min). Real-time polymerase chain reaction was used to measure the expression of renin–angiotensin system components in the laminal terminalis and peripheral organs.

Results:

Nestin-BDNF (+/–) mice had lower renin–angiotensin system expression in the laminal terminalis and peripheral organs including the gonadal fat pad, and a lower basal blood pressure. They exhibited an attenuated hypertensive response and a weak or similar modification of renin–angiotensin system component expression to angiotensin II infusion. Subfornical organ BDNF knockdown was sufficient for the attenuation of angiotensin II-induced hypertension.

Conclusion:

Central BDNF, especially subfornical organ BDNF is involved in the maintenance of basal blood pressure and in augmentation of hypertensive response to angiotensin II through systemic regulation of the expression of renin–angiotensin system molecules.

Nociceptive pulmonary-cardiac reflexes are altered in the spontaneously hypertensive rat

KEY POINTS

We investigated the cardiovascular and respiratory responses of the normotensive Wistar-Kyoto (WKY) rat and the spontaneously hypertensive (SH) rat to inhalation and intravenous injection of the noxious stimuli allyl isothiocyanate (AITC). AITC inhalation evoked atropine-sensitive bradycardia in conscious WKY rats, and evoked atropine-sensitive bradycardia and atenolol-sensitive tachycardia with premature ventricular contractions (PVCs) in conscious SH rats. Intravenous injection of AITC evoked bradycardia but no tachycardia/PVCs in conscious SHs, while inhalation and injection of AITC caused similar bradypnoea in conscious SH and WKY rats. Anaesthesia (inhaled isoflurane) inhibited the cardiac reflexes evoked by inhaled AITC but not injected AITC. Data indicate the presence of a de novo nociceptive pulmonary-cardiac reflex triggering sympathoexcitation in SH rats, and this reflex is dependent on vagal afferents but is not due to steady state blood pressure or due to remodelling of vagal efferent function.

ABSTRACT

Inhalation of noxious irritants/pollutants activates airway nociceptive afferents resulting in reflex bradycardia in healthy animals. Nevertheless, noxious pollutants evoke sympathoexcitation (tachycardia, hypertension) in cardiovascular disease patients. We hypothesize that cardiovascular disease alters nociceptive pulmonary-cardiac reflexes. Here, we studied reflex responses to irritants in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive (SH) rats. Inhaled allyl isothiocyanate (AITC) evoked atropine-sensitive bradycardia with atrial-ventricular (AV) block in conscious WKY rats, thus indicating a parasympathetic reflex. Conversely, inhaled AITC in conscious SH rats evoked complex brady-tachycardia with both AV block and premature ventricular contractions (PVCs). Atropine abolished the bradycardia and AV block, but the atropine-insensitive tachycardia and PVCs were abolished by the β₁ -adrenoceptor antagonist atenolol. The aberrant AITC-evoked reflex in SH rats was not reduced by acute blood pressure reduction by captopril. Surprisingly, intravenous AITC only evoked bradycardia in conscious SH and WKY rats. Furthermore, anaesthesia reduced the cardiac reflexes evoked by inhaled but not injected AITC. Nevertheless, anaesthesia had little effect on AITC-evoked respiratory reflexes. Such data suggest distinct differences in nociceptive reflex pathways dependent on cardiovascular disease, administration route and downstream effector. AITC-evoked tachycardia in decerebrate SH rats was abolished by vagotomy. Finally, there was no difference in the cardiac responses of WKY and SH rats to vagal efferent electrical stimulation. Our data suggest that AITC inhalation in SH rats evokes de novo adrenergic reflexes following vagal afferent activation. This aberrant reflex is independent of steady state hypertension and is not evoked by intravenous AITC. We conclude that pre-existing hypertension aberrantly shifts nociceptive pulmonary-cardiac reflexes towards sympathoexcitation.

AT1 receptors in the subfornical organ modulate arterial pressure and the baroreflex in two-kidney, one-clip hypertensive rats

The subfornical organ (SFO), a forebrain circumventricular organ that lies outside the blood-brain barrier, has been implicated in arterial pressure and baroreflex responses to angiotensin II (ANG II). We tested whether pharmacological inhibition or selective silencing of SFO ANG II type 1 receptors (AT₁R) of two-kidney, one-clip rats with elevated plasma ANG II decreases resting arterial pressure and renal sympathetic nerve activity (RSNA) and/or modulates arterial baroreflex responses of heart rate (HR) and RSNA. Male Sprague-Dawley rats underwent renal artery clipping [2-kidney, 1-clip (2K,1C)] or sham clipping (sham). After 6 wk, conscious rats instrumented with vascular catheters, renal nerve electrodes, and a cannula directed to the SFO were studied. In another set of experiments, rats were instrumented with hemodynamic and nerve radio transmitters and injected with scrambled RNA or silencing RNA targeted against AT₁R. Mean arterial pressure (MAP) was significantly higher in 2K,1C rats. Acute SFO injection with the AT₁R inhibitor losartan did not change MAP in sham or 2K,1C rats. Baroreflex curves of HR and RSNA were shifted rightward in 2K,1C rats. Losartan exerted no effect. SFO AT₁R knockdown did not influence MAP in sham rats but decreased MAP in 2K,1C rats, despite no change in plasma ANG II or resting RSNA. AT₁R knockdown prevented the reduction in maximum gain and slope of baroreflex responses of HR and RSNA; the reduced RSNA response to baroreceptor unloading was partially restored in 2K,1C rats. These findings show that AT₁R activation within the SFO contributes to hypertension and baroreflex dysfunction in 2K,1C rats and highlight the temporal requirement for reversal of these effects.

Central nervous system neuroplasticity and the sensitization of hypertension

The causes of essential hypertension remain an enigma. Interactions between genetic and external factors are generally recognized to act as aetiological mechanisms that trigger the pathogenesis of high blood pressure. However, the questions of which genes and factors are involved, and when and where such interactions occur, remain unresolved. Emerging evidence indicates that the hypertensive response to pressor stimuli, like many other physiological and behavioural adaptations, can become sensitized to particular stimuli. Studies in animal models show that, similarly to other response systems controlled by the brain, hypertensive response sensitization (HTRS) is mediated by neuroplasticity. The brain circuitry involved in HTRS controls the sympathetic nervous system. This Review outlines evidence supporting the phenomenon of HTRS and describes the range of physiological and psychosocial stressors that can produce a sensitized hypertensive state. Also discussed are the cellular and molecular changes in the brain neural network controlling sympathetic tone involved in long-term storage of information relating to stressors, which could serve to maintain a sensitized state. Finally, this Review concludes with a discussion of why a sensitized hypertensive response might previously have been beneficial and increased biological fitness under some environmental conditions and why today it has become a health-related liability.

AT1a influences GABAA-mediated inhibition through regulation of KCC2 expression

The median preoptic nucleus (MnPO) is an integrative site involved in body fluid homeostasis, cardiovascular control, thermoregulation, and sleep homeostasis. Angiotensin II (ANG II), a neuropeptide shown to have excitatory effects on MnPO neurons, is of particular interest with regard to its role in body fluid homeostasis and cardiovascular control. The present study investigated the role of angiotensin type 1a (AT1a) receptor activation on neuronal excitability in the MnPO. Male Sprague-Dawley rats were infused with an adeno-associated virus with an shRNA against the AT1a receptor or a scrambled control. In vitro loose-patch voltage-clamp recordings of spontaneous action potential activity were made from labeled MnPO neurons in response to brief focal application of ANG II or the GABAA receptor agonist muscimol. Additionally, tissue punches from MnPO were taken to asses mRNA and protein expression. AT1a receptor knockdown neurons were insensitive to ANG II and showed a marked reduction in GABAA-mediated inhibition. The reduction in GABAA-mediated inhibition was not associated with reductions in mRNA or protein expression of GABAA β-subunits. Knockdown of the AT1a receptor was associated with a reduction in the potassium-chloride cotransporter KCC2 mRNA as well as a reduction in pS940 KCC2 protein. The impaired GABAA-mediated inhibition in AT1a knockdown neurons was recovered by bath application of phospholipase C and protein kinase C activators. The following study indicates that AT1a receptor activation mediates the excitability of MnPO neurons, in part, through the regulation of KCC2. The regulation of KCC2 influences the intracellular [Cl-] and the subsequent efficacy of GABAA-mediated currents.

A proposed mechanism for the Berecek phenomenon with implications for cardiovascular reprogramming

Berecek et al reported in the 1990s that when spontaneously hypertensive rat (SHR) mating pairs were treated with captopril and the resulting pups were continued on the drug for 2 months followed by drug discontinuation, the pups did not develop full blown hypertension, and the cardiovascular structural changes associated with hypertension in SHR were mitigated. The offspring of the pups also displayed diminished hypertension and structural changes, suggesting that the drug therapy produced a heritable amelioration of the SHR phenotype. This observation is reviewed. The link between cellular renin angiotensin systems and epigenetic histone modification is explored, and a mechanism responsible for the observation is proposed. In any case, the observations of Berecek are sufficiently intriguing and biologically important to merit re-exploration and definitive explanation. Equally important is determining the role of renin angiotensin systems in epigenetic modification.

Maternal high-fat diet acts on the brain to induce baroreflex dysfunction and sensitization of angiotensin II-induced hypertension in adult offspring

Accumulating evidence indicates that maternal high-fat diet (HFD) is associated with metabolic syndrome and cardiovascular disease in adult offspring. The present study tested the hypothesis that maternal HFD modulates the brain renin-angiotensin system (RAS), oxidative stress, and proinflammatory cytokines that alter angiotensin II (ANG II) and TNF-α actions and sensitize the ANG II-elicited hypertensive response in adult offspring. All offspring were cross fostered by dams on the same or opposite diet to yield the following four groups: offspring from normal-fat control diet-fed dams suckled by control diet-fed dams (OCC group) or by HFD-fed dams (OCH group) and offspring from HFD-fed dams fed a HFD suckled by control diet-fed dams (OHC group) or by HFD-fed dams (OHH group). RT-PCR analyses of the lamina terminalis and paraventricular nucleus indicated upregulation of mRNA expression of several RAS components, NADPH oxidase, and proinflammatory cytokines in 10-wk-old male offspring of dams fed a HFD during either pregnancy, lactation, or both (OHC, OCH, and OHH groups). These offspring also showed decreased cardiac baroreflex sensitivity and increased pressor responses to intracerebroventricular microinjection of either ANG II or TNF-α. Furthermore, chronic systemic infusion of ANG II resulted in enhanced upregulation of mRNA expression of RAS components, NADPH oxidase, and proinflammatory cytokines in the lamina terminalis and paraventricular nucleus and an augmented hypertensive response in the OHC, OCH, and OHH groups compared with the OCC group. The results suggest that maternal HFD blunts cardiac baroreflex function and enhances pressor responses to ANG II or proinflammatory cytokines through upregulation of the brain RAS, oxidative stress, and inflammation. NEW & NOTEWORTHY The results of our study indicate that a maternal high-fat diet during either pregnancy or lactation is sufficient for perinatal programming of sensitization for hypertension, which is associated with hyperreactivity of central cardiovascular nuclei that, in all likelihood, involves elevated expression of the renin-angiotensin system, NADPH oxidase, and proinflammatory cytokines. The present study demonstrates, for the first time, the central mechanism underlying maternal high-fat diet sensitization of the hypertensive response in adult offspring.

Differential effects of long-term slow-pressor and subpressor angiotensin II on contractile and relaxant reactivity of resistance versus conductance arteries

Vascular reactivity was evaluated in three separate arteries isolated from rats after angiotensin II (Ang II) was infused chronically in two separate experiments, one using a 14-day high, slow-pressor dose known to produce hypertension and the other using a 7-day low, subpressor but hypertensive-sensitizing dose. There were three new findings. First, there was no evidence of altered vascular reactivity in resistance arteries that might otherwise explain the hypertension due to the high Ang II or the hypertensive-sensitizing effect of the low Ang II dose. Second, the high Ang II dose exerted a novel differential effect on arterial contractile responsiveness to the sympathetic neurotransmitter, norepinephrine, depending on the level of sympathetic innervation. It clearly enhanced that responsiveness in the sparsely innervated aorta but not in small mesenteric resistance arteries or the proximal (conductance) portion of the caudal artery, both of which are densely innervated. This suggests that the increased expression of alpha adrenergic receptors after long-term exposure to Ang II as previously reported for aortic smooth muscle, is prevented in densely innervated arteries, likely due to long-term Ang II-mediated increase in sympathetic neural traffic to those vessels. Third, the same high dose of Ang II impaired aortic relaxation in response to the nitric oxide (NO) donor nitroprusside without impairing aortic endothelium-dependent relaxation. NO is the main relaxing substance released by aortic endothelium. Accordingly, it is possible that this dose of Ang II is also associated with enhanced release of and/or enhanced smooth muscle responsiveness to other endothelial relaxing substances in a compensatory capacity.

Enhanced angiotensin II induced sodium appetite in renovascular hypertensive rats

Renovascular hypertensive 2-kidney, 1-clip (2K1C) rats have an increased activity of the renin-angiotensin system and an initial transitory increase in daily water and NaCl intake. However, the dipsogenic and natriorexigenic responses to angiotensin II (ANG II) have not been tested yet in 2K1C rats. Therefore, in the present study, we evaluated water and 0.3 M NaCl intake induced by water deprivation (WD)-partial rehydration (PR) or intracerebroventricular (icv) ANG II in 2K1C rats. In addition, the cardiovascular changes to these treatments were also evaluated. Male Holtzman rats received a silver clip around the left renal artery to induce 2K1C renovascular hypertension. In the 5th week, a group of animals received a guide cannula in the lateral ventricle for icv injections. Daily water intake increased from the 3rd week after surgery and remained elevated until the 6th week (last recording week), whereas daily 0.3 M NaCl intake transiently increased from the 2nd to the 5th week after surgery. On the 6th week, in spite of comparable daily 0.3 M NaCl intake between 2K1C and sham rats, WD-PR and icv ANG II induced an increased 0.3 M NaCl intake in 2K1C rats. Water intake induced by WD-PR, not by icv ANG II, also increased in 2K1C rats. The increase in arterial pressure to WD-PR or icv ANG II was similar in sham and 2K1C rats. Therefore, these results suggest that 2K1C rats are more responsive to the natriorexigenic effects of ANG II, whereas other responses to ANG II are not modified.

Cortical autonomic network gray matter and sympathetic nerve activity in obstructive sleep apnea

The sympathetic excitation elicited acutely by obstructive apnea during sleep (OSA) carries over into wakefulness. We hypothesized that OSA induces structural changes in the insula and cingulate, key central autonomic network elements with projections to brainstem sympathetic premotor regions. The aims of this study were to (1) apply two distinct but complementary methods (cortical thickness analysis [CTA] and voxel-based morphometry [VBM]) to compare insula and cingulate gray matter thickness in participants without and with OSA; (2) determine whether oxygen desaturation index (ODI) relates to cortical thickness; and (3) determine whether cortical thickness or volume in these regions predicts muscle sympathetic nerve activity (MSNA) burst incidence (BI). Overnight polysomnography, anatomical magnetic resonance imaging, and MSNA data were acquired in 41 participants with no or mild OSA (n = 19; 59 ± 2 years [Mean ± SE]; six females; apnea-hypopnea index [AHI] 7 ± 1 events per hour) or moderate-to-severe OSA (n = 22; 59 ± 2 years; five females; AHI 31 ± 4 events per hour). Between-group CTA analyses identified cortical thinning within the left dorsal posterior insula and thickening within the left mid-cingulate cortex (LMCC), whereas VBM identified thickening within bilateral thalami (all [p < .05]). CTA revealed inverse relationships between ODI and bilateral dpIC and left posterior cingulate cortex (LPCC) or precuneus thickness. Positive correlations between BI and LMCC gray matter thickness or volume were evident with both methods and between BI and left posterior thalamus volume using VBM. In OSA, the magnitude of insular thinning, although a function of hypoxia severity, does not influence MSNA, whereas cingulate and thalamic thickening relate directly to the intensity of sympathetic discharge during wakefulness.

Role of Vasopressin in Rat Models of Salt-Dependent Hypertension

PURPOSE OF REVIEW

Dietary salt intake increases both plasma sodium and osmolality and therefore increases vasopressin (VP) release from the neurohypophysis. Although this effect could increase blood pressure by inducing fluid reabsorption and vasoconstriction, acute activation of arterial baroreceptors inhibits VP neurons via GABA_A receptors to oppose high blood pressure. Here we review recent findings demonstrating that this protective mechanism fails during chronic high salt intake in rats.

RECENT FINDINGS

Two recent studies showed that chronic high sodium intake causes an increase in intracellular chloride concentration in VP neurons. This effect causes GABA_A receptors to become excitatory and leads to the emergence of VP-dependent hypertension. One study showed that the increase in intracellular chloride was provoked by a decrease in the expression of the chloride exporter KCC2 mediated by local secretion of brain-derived neurotrophic factor and activation of TrkB receptors. Prolonged high dietary salt intake can cause pathological plasticity in a central homeostatic circuit that controls VP secretion and thereby contribute to peripheral vasoconstriction and hypertension.

Centrally Mediated Cardiovascular Actions of the Angiotensin II Type 2 Receptor

Sustained increases in the activity of the sympathetic neural pathways that exit the brain and which increase blood pressure (BP) are a major underlying factor in resistant hypertension. Recently available information on the occurrence of angiotensin II type 2 receptors (AT2Rs) within or adjacent to brain cardiovascular control centers is consistent with findings that stimulation of these receptors lowers BP, particularly during hypertension of neurogenic origin. Until recently brain AT2R had not been considered by many to play a role in the central control of BP. Demonstration of these powerful antihypertensive effects of brain AT2R opens the door to reconsideration of their role in BP regulation, and their consideration as a novel therapeutic avenue for resistant hypertension.

A Single Angiotensin II Hypertensive Stimulus Is Associated with Prolonged Neuronal and Immune System Activation in Wistar-Kyoto Rats

Activation of autonomic neural pathways by chronic hypertensive stimuli plays a significant role in pathogenesis of hypertension. Here, we proposed that even a single acute hypertensive stimulus will activate neural and immune pathways that may be important in initiation of memory imprinting seen in chronic hypertension. We investigated the effects of acute angiotensin II (Ang II) administration on blood pressure, neural activation in cardioregulatory brain regions, and central and systemic immune responses, at 1 and 24 h post-injection. Administration of a single bolus intra-peritoneal (I.P.) injection of Ang II (36 μg/kg) resulted in a transient increase in the mean arterial pressure (MAP) (by 22 ± 4 mmHg vs saline), which returned to baseline within 1 h. However, in contrast to MAP, neuronal activity, as measured by manganese-enhanced magnetic resonance (MEMRI), remained elevated in several cardioregulatory brain regions over 24 h. The increase was predominant in autonomic regions, such as the subfornical organ (SFO; ~20%), paraventricular nucleus of the hypothalamus (PVN; ~20%) and rostral ventrolateral medulla (RVLM; ~900%), among others. Similarly, systemic and central immune responses, as evidenced by circulating levels of CD4⁺/IL17⁺ T cells, and increased IL17 levels and activation of microglia in the PVN, respectively, remained elevated at 24 h following Ang II challenge. Elevated Fos expression in the PVN was also present at 24 h (by 73 ± 11%) following Ang II compared to control saline injections, confirming persistent activation of PVN. Thus, even a single Ang II hypertensive stimulus will initiate changes in neuronal and immune cells that play a role in the developing hypertensive phenotype.

Recent Advances in Neurogenic Hypertension: Dietary Salt, Obesity, and Inflammation

Neurally-mediated hypertension results from a dysregulation of sympathetic and/or neuroendocrine mechanisms to increase ABP. Multiple factors may exert multiple central effects to alter neural circuits and produce unique sympathetic signatures and elevate ABP. In this brief review, we have discussed novel observations regarding three contributing factors: dietary salt intake, obesity, and inflammation. However, the interaction among these and other factors is likely much more complex; recent studies suggest a prior exposure to one stimulus may sensitize the response to a subsequent hypertensive stimulus. Insight into the central mechanisms by which these factors selectively alter SNA or cooperatively interact to impact hypertension may represent a platform for novel therapeutic treatment strategies.

Central TrkB blockade attenuates ICV angiotensin II-hypertension and sympathetic nerve activity in male Sprague-Dawley rats

Increased sympathetic nerve activity and the activation of the central renin-angiotensin system are commonly associated with cardiovascular disease states such as hypertension and heart failure, yet the precise mechanisms contributing to the long-term maintenance of this sympatho-excitation are incompletely understood. Due to the established physiological role of neurotrophins contributing toward neuroplasticity and neuronal excitability along with recent evidence linking the renin-angiotensin system and brain-derived neurotrophic factor (BDNF) along with its receptor (TrkB), it is likely the two systems interact to promote sympatho-excitation during cardiovascular disease. However, this interaction has not yet been fully demonstrated, in vivo. Thus, we hypothesized that central angiotensin II (Ang II) treatment will evoke a sympatho-excitatory state mediated through the actions of BDNF/TrkB. We infused Ang II (20ng/min) into the right lateral ventricle of male Sprague-Dawley rats for twelve days with or without the TrkB receptor antagonist, ANA-12 (50ng/h). We found that ICV infusion of Ang II increased mean arterial pressure (+40.4mmHg), increased renal sympathetic nerve activity (+19.4% max activity), and induced baroreflex dysfunction relative to vehicle. Co-infusion of ANA-12 attenuated the increase in blood pressure (-20.6mmHg) and prevented the increase in renal sympathetic nerve activity (-22.2% max) and baroreflex dysfunction relative to Ang II alone. Ang II increased thirst and decreased food consumption, and Ang II+ANA-12 augmented the thirst response while attenuating the decrease in food consumption. We conclude that TrkB signaling is a mediator of the long-term blood pressure and sympathetic nerve activity responses to central Ang II activity. These findings demonstrate the involvement of neurotrophins such as BDNF in promoting Ang II-induced autonomic dysfunction and further implicate TrkB signaling in modulating presympathetic autonomic neurons during cardiovascular disease.

Maternal Gestational Hypertension-Induced Sensitization of Angiotensin II Hypertension Is Reversed by Renal Denervation or Angiotensin-Converting Enzyme Inhibition in Rat Offspring

Numerous findings demonstrate that there is a strong association between maternal health during pregnancy and cardiovascular disease in adult offspring. The purpose of the present study was to test whether maternal gestational hypertension modulates brain renin-angiotensin-aldosterone system (RAAS) and proinflammatory cytokines that sensitizes angiotensin II-elicited hypertensive response in adult offspring. In addition, the role of renal nerves and the RAAS in the sensitization process was investigated. Reverse transcription polymerase chain reaction analyses of structures of the lamina terminalis and paraventricular nucleus indicated upregulation of mRNA expression of several RAAS components and proinflammatory cytokines in 10-week-old male offspring of hypertensive dams. Most of these increases were significantly inhibited by either renal denervation performed at 8 weeks of age or treatment with an angiotensin-converting enzyme inhibitor, captopril, in drinking water starting at weaning. When tested beginning at 10 weeks of age, a pressor dose of angiotensin II resulted in enhanced upregulation of mRNA expression of RAAS components and proinflammatory cytokines in the lamina terminalis and paraventricular nucleus and an augmented pressor response in male offspring of hypertensive dams. The augmented blood pressure change and most of the increases in gene expression in the offspring were abolished by either renal denervation or captopril. The results suggest that maternal hypertension during pregnancy enhances pressor responses to angiotensin II through overactivity of renal nerves and the RAAS in male offspring and that upregulation of the brain RAAS and proinflammatory cytokines in these offspring may contribute to maternal gestational hypertension-induced sensitization of the hypertensive response to angiotensin II.

Arousal From Sleep and Sympathetic Excitation During Wakefulness

Obstructive apnea during sleep elevates the set point for efferent sympathetic outflow during wakefulness. Such resetting is attributed to hypoxia-induced upregulation of peripheral chemoreceptor and brain stem sympathetic function. Whether recurrent arousal from sleep also influences daytime muscle sympathetic nerve activity is unknown. We therefore tested, in a cohort of 48 primarily nonsleepy, middle-aged, male (30) and female (18) volunteers (age: 59±1 years, mean±SE), the hypothesis that the frequency of arousals from sleep (arousal index) would relate to daytime muscle sympathetic burst incidence, independently of the frequency of apnea or its severity. Polysomnography identified 24 as having either no or mild obstructive sleep apnea (apnea–hypopnea index <15 events/h) and 24 with moderate-to-severe obstructive sleep apnea (apnea–hypopnea index >15 events/h). Burst incidence correlated significantly with arousal index ( r =0.53; P <0.001), minimum oxygen saturation ( r =−0.43; P =0.002), apnea–hypopnea index ( r =0.41; P =0.004), age ( r =0.36; P =0.013), and body mass index ( r =0.33; P =0.022) but not with oxygen desaturation index ( r =0.28; P =0.056). Arousal index was the single strongest predictor of muscle sympathetic nerve activity burst incidence, present in all best subsets regression models. The model with the highest adjusted R 2 (0.456) incorporated arousal index, minimum oxygen saturation, age, body mass index, and oxygen desaturation index but not apnea–hypopnea index. An apnea- and hypoxia-independent effect of sleep fragmentation on sympathetic discharge during wakefulness could contribute to intersubject variability, age-related increases in muscle sympathetic nerve activity, associations between sleep deprivation and insulin resistance or insomnia and future cardiovascular events, and residual adrenergic risk with persistence of hypertension should therapy eliminate obstructive apneas but not arousals.

Angiotensin II AT1 receptors mediate neuronal sensitization and sustained blood pressure response induced by a single injection of amphetamine

A single exposure to amphetamine induces neurochemical sensitization in striatal areas. The neuropeptide angiotensin II, through AT₁ receptors (AT₁-R) activation, is involved in these responses. However, amphetamine-induced alterations can be extended to extra-striatal areas involved in blood pressure control and their physiological outcomes. Our aim for the present study was to analyze the possible role for AT₁-R in these events using a two-injection protocol and to further characterize the proposed AT₁-R antagonism protocol. Central effect of orally administered AT₁-R blocker (Candesartan, 3mg/kg p.o.×5days) in male Wistar rats was analyzed by spontaneous activity of neurons within locus coeruleus. In another group of animals pretreated with the AT₁-R blocker or vehicle, sensitization was achieved by a single administration of amphetamine (5mg/kg i.p. - day 6) followed by a 3-week period off drug. On day 27, after receiving an amphetamine challenge (0.5mg/kg i.p.), we evaluated: (1) the sensitized c-Fos expression in locus coeruleus (LC), nucleus of the solitary tract (NTS), caudal ventrolateral medulla (A1) and central amygdala (CeAmy); and (2) the blood pressure response. AT₁-R blockade decreased LC neurons' spontaneous firing rate. Moreover, sensitized c-Fos immunoreactivity in TH+neurons was found in LC and NTS; and both responses were blunted by the AT₁-R blocker pretreatment. Meanwhile, no differences were found neither in CeAmy nor A1. Sensitized blood pressure response was observed as sustained changes in mean arterial pressure and was effectively prevented by AT₁-R blockade. Our results extend AT₁-R role in amphetamine-induced sensitization over noradrenergic nuclei and their cardiovascular output.

Sympathetic overactivity occurs before hypertension in the two-kidney, one-clip model

Our knowledge of mechanisms responsible for both the development and the maintenance of hypertension remains incomplete in the Goldblatt (two-kidney, one-clip; 2K1C) model. We tested the hypothesis that elevated sympathetic nerve activity (SNA) occurs before the onset of hypertension in 2K1C rats, considering the time course of the increase in SNA in relationship to the onset of the hypertension. We used a decorticated in situ working heart-brainstem preparation of three groups of male Wistar rats, namely sham-operated animals (SHAM, n = 7) and animals 3 weeks post-2K1C, of which some were hypertensive (2K1C-H, n = 6) and others normotensive (2K1C-N, n = 9), as determined in vivo a priori. Perfusion pressure was higher in both 2K1C groups (2K1C-H, 76 ± 1 mmHg; 2K1C-N, 74 ± 3 mmHg; versus SHAM, 60 ± 2 mmHg, P < 0.05). The SNA was significantly elevated in both 2K1C groups (2K1C-H, 47.7 ± 6.1 μV; 2K1C-N, 32.8 ± 2.8 μV; versus SHAM, 20.5 ± 2.5 μV, P < 0.05) owing to its increased respiratory modulation; the chemoreflex was augmented and baroreflex depressed. Precollicular transection reduced SNA in all groups (2K1C-H, -32.5 ± 7.5%; 2K1C-NH, -48 ± 6.9%; versus SHAM, -13.2 ± 1%, P < 0.05). Subsequent medullary spinal cord transection abolished SNA in both SHAM and 2K1C-N groups, but decreased it by only 57 ± 5.5% in 2K1C-H preparations. Thus, SNA is raised before the onset of hypertension, by the third week after renal artery clipping, and this originates, in part, from its enhanced respiratory modulation. Spinal circuits contribute to the elevation of SNA in the 2K1C model, but only after hypertension has developed.