Src Kinases Regulate Glutamatergic Input to Hypothalamic Presympathetic Neurons and Sympathetic Outflow in Hypertension

Targeting the tyrosine kinase Src in endothelium attenuates inflammation and atherogenesis induced by disturbed flow

BACKGROUND AND PURPOSE

Previous studies have shown that Src can regulate inflammation and tumour progression. However, the mechanisms by which Src regulates the inflammatory response of vascular endothelium and atherogenesis are currently poorly understood. This study aimed to investigate the role of Src in endothelial inflammation and atherogenesis, as well as the underlying mechanisms.

EXPERIMENTAL APPROACH

Real-time quantitative PCR was used to measure the mRNA levels of inflammatory genes. The phosphorylation and localization of proteins were examined using western blotting and immunofluorescence, respectively. The level of p-Src Y416 in mouse endothelium was directly determined using en face staining. Endothelial-specific knockdown of Src was achieved by tail vein injection of AAV-sgSrc in ApoE-/-; Cas9LSL/LSL; Cdh5-cre mice. Atherosclerosis was induced by partial ligation of the carotid artery.

KEY RESULTS

Oscillatory shear stress (OSS) promotes the phosphorylation of Src at Y416 in endothelial cells, and Piezo1 is required for this regulatory process. Overexpression of constitutively active Src promotes endothelial inflammation, as well as phosphorylation of Stat3 (at Y705) and its nuclear translocation. Endothelial inflammation induced by OSS was abolished by the Src inhibitor dasatinib or si-Src. Dasatinib, when administered orally, reduced endothelial inflammation and plaque formation in ApoE-/- mice induced by partial carotid artery ligation. Additionally, plaque formation was decreased in the ligated left carotid artery of mice with endothelial-specific Src knockdown.

CONCLUSION AND IMPLICATIONS

Disturbed flow promotes endothelial inflammation and atherogenesis through the Piezo1-Src-Stat3 pathway. Therefore, inhibiting Src in endothelial cells could be a promising therapeutic strategy to treat atherogenesis.

Central administration of AICAR attenuates hypertension via AMPK/Nrf2 pathway in the hypothalamic paraventricular nucleus of hypertensive rats

BACKGROUND

Oxidative stress and inflammatory cytokines in the hypothalamus paraventricular nucleus (PVN) have been implicated in sympathetic nerve activity and the development of hypertension, but the specific mechanisms underlying their production in the PVN remains to be elucidated. Previous studies have demonstrated that activation of nuclear transcription related factor-2 (Nrf2) in the PVN reduced the production of reactive oxygen species (ROS) and inflammatory mediators. Moreover, AMP-activated protein kinase (AMPK), has been observed to decrease ROS and inflammatory cytokine production when activated in the periphery. 5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide (AICAR) is an AMPK agonist. However, little research has been conducted on the role of AMPK in the PVN during hypertension. Therefore, we hypothesized that AICAR in the PVN is involved in regulating AMPK/Nrf2 pathway, affecting ROS and inflammatory cytokine expression, influencing sympathetic nerve activity.

METHODS

Adult male Sprague-Dawley rats were utilized to induce two-kidney, one-clip (2K1C) hypertension via constriction of the right renal artery. Bilateral PVN was microinjected with either artificial cerebrospinal fluid or AICAR once a day for 4 weeks.

RESULTS

Compared to the SHAM group, the PVN of 2K1C hypertensive rats decreased p-AMPK and p-Nrf2 expression, increased Fra-Like, NAD(P)H oxidase (NOX)2, NOX4, tumor necrosis factor-α and interleukin (IL)-1β expression, elevated ROS levels, decreased superoxide dismutase 1 and IL-10 expression, and elevated plasma norepinephrine levels. Bilateral PVN microinjection of AICAR significantly ameliorated these changes.

CONCLUSION

These findings suggest that repeated injection of AICAR in the PVN suppresses ROS and inflammatory cytokine production through the AMPK/Nrf2 pathway, reducing sympathetic nerve activity and improving hypertension.

Calcineurin regulates synaptic Ca2+-permeable AMPA receptors in hypothalamic presympathetic neurons via α2δ-1-mediated GluA1/GluA2 assembly

Hypertension is a major adverse effect of calcineurin inhibitors, such as tacrolimus (FK506) and cyclosporine, used clinically as immunosuppressants. Calcineurin inhibitor-induced hypertension (CIH) is linked to augmented sympathetic output from the hypothalamic paraventricular nucleus (PVN). GluA2-lacking, Ca2+-permeable AMPA receptors (CP-AMPARs) are a key feature of glutamatergic synaptic plasticity, yet their role in CIH remains elusive. Here, we found that systemic administration of FK506 in rats significantly increased serine phosphorylation of GluA1 and GluA2 in PVN synaptosomes. Strikingly, FK506 treatment reduced GluA1/GluA2 heteromers in both synaptosomes and endoplasmic reticulum-enriched fractions from the PVN. Blocking CP-AMPARs with IEM-1460 induced a larger reduction of AMPAR-mediated excitatory postsynaptic current (AMPAR-EPSC) amplitudes in retrogradely labelled, spinally projecting PVN neurons in FK506-treated rats than in vehicle-treated rats. Furthermore, FK506 treatment shifted the current-voltage relationship of AMPAR-EPSCs from linear to inward rectification in labelled PVN neurons. FK506 treatment profoundly enhanced physical interactions of α2δ-1 with GluA1 and GluA2 in the PVN. Inhibiting α2δ-1 with gabapentin, α2δ-1 genetic knockout, or disrupting α2δ-1-AMPAR interactions with an α2δ-1 C terminus peptide restored GluA1/GluA2 heteromers in the PVN and diminished inward rectification of AMPAR-EPSCs in labelled PVN neurons induced by FK506 treatment. Additionally, microinjection of IEM-1460 or α2δ-1 C terminus peptide into the PVN reduced renal sympathetic nerve discharges and arterial blood pressure elevated in FK506-treated rats but not in vehicle-treated rats. Thus, calcineurin in the hypothalamus constitutively regulates AMPAR subunit composition and phenotypes by controlling GluA1/GluA2 interactions with α2δ-1. Synaptic CP-AMPARs in PVN presympathetic neurons contribute to augmented sympathetic outflow in CIH. KEY POINTS: Systemic treatment with the calcineurin inhibitor increases serine phosphorylation of synaptic GluA1 and GluA2 in the PVN. Calcineurin inhibition enhances the prevalence of postsynaptic Ca2+-permeable AMPARs in PVN presympathetic neurons. Calcineurin inhibition potentiates α2δ-1 interactions with GluA1 and GluA2, disrupting intracellular assembly of GluA1/GluA2 heterotetramers in the PVN. Blocking Ca2+-permeable AMPARs or α2δ-1-AMPAR interactions in the PVN attenuates sympathetic outflow augmented by the calcineurin inhibitor.

DNA demethylation in the hypothalamus promotes transcription of Agtr1a and Slc12a2 and hypertension development

Increased expression of angiotensin II AT1A receptor (encoded by Agtr1a) and Na+-K+-Cl- cotransporter-1 (NKCC1, encoded by Slc12a2) in the hypothalamic paraventricular nucleus (PVN) contributes to hypertension development. However, little is known about their transcriptional control in the PVN in hypertension. DNA methylation is a critical epigenetic mechanism that regulates gene expression. Here, we determined whether transcriptional activation of Agtr1a and Slc12a2 results from altered DNA methylation in spontaneously hypertensive rats (SHR). Methylated DNA immunoprecipitation and bisulfite sequencing-PCR showed that CpG methylation at Agtr1a and Slc12a2 promoters in the PVN was progressively diminished in SHR compared with normotensive Wistar-Kyoto rats (WKY). Chromatin immunoprecipitation-quantitative PCR revealed that enrichment of DNA methyltransferases (DNMT1 and DNMT3A) and methyl-CpG binding protein 2, a DNA methylation reader protein, at Agtr1a and Slc12a2 promoters in the PVN was profoundly reduced in SHR compared with WKY. By contrast, the abundance of ten-eleven translocation enzymes (TET1-3) at Agtr1a and Slc12a2 promoters in the PVN was much greater in SHR than in WKY. Furthermore, microinjecting of RG108, a selective DNMT inhibitor, into the PVN of WKY increased arterial blood pressure and correspondingly potentiated Agtr1a and Slc12a2 mRNA levels in the PVN. Conversely, microinjection of C35, a specific TET inhibitor, into the PVN of SHR markedly reduced arterial blood pressure, accompanied by a decrease in Agtr1a and Slc12a2 mRNA levels in the PVN. Collectively, our findings suggest that DNA hypomethylation resulting from the DNMT/TET switch at gene promoters in the PVN promotes transcription of Agtr1a and Slc12a2 and hypertension development.

Inactivation of the paraventricular nucleus attenuates the cardiogenic sympathetic afferent reflex in the spontaneously hypertensive rat

BACKGROUND

Myocardial ischemia causes the release of bradykinin, which stimulates cardiac afferents, causing sympathetic excitation and chest pain. Glutamatergic activation of the paraventricular hypothalamic nucleus (PVN) in the spontaneously hypertensive rat (SHR) drives elevated basal sympathetic activity. Thus, we tested the hypothesis that inactivation of the PVN attenuates the elevated reflex response to epicardial bradykinin in the SHR and that ionotropic PVN glutamate receptors mediate the elevated reflex.

METHODS

We recorded the arterial pressure and renal sympathetic nerve activity (RSNA) response to epicardial bradykinin application in anesthetized SHR and Wistar Kyoto (WKY) rats before and after PVN microinjection of GABA A agonist muscimol or ionotropic glutamate receptor antagonist kynurenic acid.

RESULTS

Muscimol significantly decreased the arterial pressure response to bradykinin from 180.4 ± 5.8 to 119.5 ± 6.9 mmHg in the SHR and from 111.8 ± 7.0 to 84.2 ± 8.3 mmHg in the WKY and the RSNA response from 186.2 ± 7.1 to 142.7 ± 7.3% of baseline in the SHR and from 201.0 ± 11.5 to 160.2 ± 9.3% of baseline in the WKY. Kynurenic acid significantly decreased the arterial pressure response in the SHR from 164.5 ± 5.0 to 126.2 ± 7.7 mmHg and the RSNA response from 189.9 ± 13.7to 168.5 ± 12.7% of baseline but had no effect in the WKY.

CONCLUSION

These results suggest that tonic PVN activity is critical for the full manifestation of the CSAR in both the WKY and SHR. Glutamatergic PVN activity contributes to the augmented CSAR observed in the SHR.

Brain α2δ-1-Bound NMDA Receptors Drive Calcineurin Inhibitor-Induced Hypertension

BACKGROUND

Calcineurin is highly enriched in immune T cells and the nervous system. Calcineurin inhibitors, including cyclosporine and tacrolimus (FK506), are the cornerstone of immunosuppressive regimens for preserving transplanted organs and tissues. However, these drugs often cause persistent hypertension owing to excess sympathetic outflow, which is maintained by N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory input to the hypothalamic paraventricular nucleus (PVN). It is unclear how calcineurin inhibitors increase NMDAR activity in the PVN to augment sympathetic vasomotor activity. α2δ-1 (encoded by the Cacna2d1 gene), known colloquially as a calcium channel subunit, is a newly discovered NMDAR-interacting protein. In this study, we determined whether α2δ-1 plays a role in calcineurin inhibitor-induced synaptic NMDAR hyperactivity in the PVN and hypertension development.

METHODS

Immunoblotting and coimmunoprecipitation assays were used to quantify synaptic protein levels and the physical interaction between GluN1 (the obligatory NMDAR subunit) and α2δ-1. Whole-cell patch-clamp recordings of retrogradely labeled, spinally projecting PVN were conducted in perfused brain slices to measure presynaptic and postsynaptic NMDAR activity. Radio-telemetry was implanted in rodents to continuously record arterial blood pressure in conscious states.

RESULTS

Prolonged treatment with FK506 in rats significantly increased protein levels of α2δ-1, GluN1, and the α2δ-1-GluN1 complex in PVN synaptosomes. These effects were blocked by inhibiting α2δ-1 with gabapentin or interrupting the α2δ-1-NMDAR interaction with an α2δ-1 C-terminus peptide. Treatment with FK506 potentiated the activity of presynaptic and postsynaptic NMDARs in spinally projecting PVN neurons; such effects were abolished by gabapentin, Cacna2d1 knockout, or α2δ-1 C-terminus peptide. Furthermore, microinjection of α2δ-1 C-terminus peptide into the PVN diminished renal sympathetic nerve discharges and arterial blood pressure that had been increased by FK506 treatment. Remarkably, concurrent administration of gabapentin prevented the development of FK506-induced hypertension in rats. Additionally, FK506 treatment induced sustained hypertension in wild-type mice but not in Cacna2d1 knockout mice.

CONCLUSIONS

α2δ-1 is essential for calcineurin inhibitor-induced increases in synaptic NMDAR activity in PVN presympathetic neurons and sympathetic outflow. Thus, α2δ-1 and α2δ-1-bound NMDARs represent new targets for treating calcineurin inhibitor-induced hypertension. Gabapentinoids (gabapentin and pregabalin) could be repurposed for treating calcineurin inhibitor-induced neurogenic hypertension.

The Regulatory Effect of the Paraventricular Nucleus on Hypertension

Hypertension is among the most harmful factors of cardiovascular and cerebrovascular diseases and poses an urgent problem for the development of human society. In addition to previous studies on its pathogenesis focusing on the peripheral sympathetic nervous system, investigating the central causes of high blood pressure involving the neuroendocrine and neuroinflammatory mechanisms of the hypothalamic paraventricular nucleus (PVN) is paramount. This nucleus is considered to regulate the output of neurohormones and sympathetic nerve activity. In this article, we focussed on the neuroendocrine mechanism, primarily exploring the specific contributions and interactions of various neurons and neuroendocrine hormones, including GABAergic and glutamatergic neurons, nitric oxide, arginine vasopressin, oxytocin, and the renin-angiotensin system. Additionally, the neuroinflammatory mechanism in the PVN was discussed, encompassing microglia, reactive oxygen species, inflammatory factors, and pathways, as well as immune connections between the brain and extracerebral organs. Notably, the two central mechanisms involved in the PVN not only exist independently but also communicate with each other, jointly maintaining the hypertensive state of the body. Furthermore, we introduce well-known molecules and signal transduction pathways within the PVN that can play a regulatory role in the two mechanisms to provide a basis and inspire ideas for further research.

Calcineurin Controls Hypothalamic NMDA Receptor Activity and Sympathetic Outflow

Rationale:

Hypertension is a common and serious adverse effect of calcineurin inhibitors, including cyclosporine and tacrolimus (FK506). Although increased sympathetic nerve discharges are associated with calcineurin inhibitor–induced hypertension, the sources of excess sympathetic outflow and underlying mechanisms remain elusive. Calcineurin (protein phosphatase-2B) is broadly expressed in the brain, including the paraventricular nuclear (PVN) of the hypothalamus, which is critically involved in regulating sympathetic vasomotor tone.

Objective:

We determined whether prolonged treatment with the calcineurin inhibitor causes elevated sympathetic output and persistent hypertension by potentiating synaptic N-methyl-D-aspartate (NMDA) receptor activity in the PVN.

Methods and Results:

Telemetry recordings showed that systemic administration of FK506 (3 mg/kg per day) for 14 days caused a gradual and profound increase in arterial blood pressure in rats, which lasted at least 7 days after discontinuing FK506 treatment. Correspondingly, systemic treatment with FK506 markedly reduced calcineurin activity in the PVN and circumventricular organs, but not rostral ventrolateral medulla, and increased the phosphorylation level and synaptic trafficking of NMDA receptors in the PVN. Immunocytochemistry labeling showed that calcineurin was expressed in presympathetic neurons in the PVN. Whole-cell patch-clamp recordings in brain slices revealed that treatment with FK506 increased baseline firing activity of PVN presympathetic neurons; this increase was blocked by the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist. Also, treatment with FK506 markedly increased presynaptic and postsynaptic NMDA receptor activity of PVN presympathetic neurons. Furthermore, microinjection of the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist into the PVN of anesthetized rats preferentially attenuated renal sympathetic nerve discharges and blood pressure elevated by FK506 treatment. In addition, systemic administration of memantine, a clinically used NMDA receptor antagonist, effectively attenuated FK506 treatment–induced hypertension in conscious rats.

Conclusions:

Our findings reveal that normal calcineurin activity in the PVN constitutively restricts sympathetic vasomotor tone via suppressing NMDA receptor activity, which may be targeted for treating calcineurin inhibitor–induced hypertension.

Effects of Nrf1 in Hypothalamic Paraventricular Nucleus on Regulating the Blood Pressure During Hypertension

The incidence rate and mortality of hypertension increase every year. Hypothalamic paraventricular nucleus (PVN) plays a critical role on the pathophysiology of hypertension. It has been demonstrated that the imbalance of neurotransmitters including norepinephrine (NE), glutamate (Glu) and γ-aminobutyric acid (GABA) are closely related to sympathetic overactivity and pathogenesis of hypertension. N-methyl-D-aspartate receptor (NMDAR), consisting of GluN1 and GluN2 subunits, is considered to be a glutamate-gated ion channel, which binds to Glu, and activates neuronal activity. Studies have found that the synthesis of respiratory chain enzyme complex was affected and mitochondrial function was impaired in spontaneously hypertensive rats (SHR), further indicating that mitochondria is associated with hypertension. Nuclear respiratory factor 1 (Nrf1) is a transcription factor that modulates mitochondrial respiratory chain and is related to GluN1, GluN2A, and GluN2B promoters. However, the brain mechanisms underlying PVN Nrf1 modulating sympathoexcitation and blood pressure during the development of hypertension remains unclear. In this study, an adeno-associated virus (AAV) vector carrying the shRNA targeting rat Nrf1 gene (shNrf1) was injected into bilateral PVN of male rats underwent two kidneys and one clip to explore the role of Nrf1 in mediating the development of hypertension and sympathoexcitation. Administration of shNrf1 knocked down the expression of Nrf1 and reduced the expression of excitatory neurotransmitters, increased the expression of inhibitory neurotransmitters, and reduced the production of reactive oxygen species (ROS), and attenuated sympathoexcitation and hypertension. The results indicate that knocking down Nrf1 suppresses sympathoexcitation in hypertension by reducing PVN transcription of NMDAR subunits (GluN1, GluN2A, and GluN2B), rebalancing PVN excitatory and inhibitory neurotransmitters, inhibiting PVN neuronal activity and oxidative stress, and attenuating sympathetic activity.

Chronic Blockade of NMDAR Subunit 2A in the Hypothalamic Paraventricular Nucleus Alleviates Hypertension Through Suppression of MEK/ERK/CREB Pathway

BACKGROUND

N-Methyl-d-aspartate receptor (NMDAR) in the hypothalamic paraventricular nucleus (PVN) plays critical roles in regulating sympathetic outflow. Studies showed that acute application of the antagonists of NMDAR or its subunits would reduce sympathetic nerve discharges. However, little is known about the effect of long-term management of NMDAR in hypertensive animals.

METHODS

PEAQX, the specific antagonist of NMDAR subunit 2A (GluN2A) was injected into both sides of the PVN of two-kidney, one-clip (2K1C) renal hypertensive rats and control (normotensive rats) for 3 weeks.

RESULTS

Three weeks of PEAQX infusion significantly reduced the blood pressure of the 2K1C rats. It managed to resume the balance between excitatory and inhibitory neural transmitters, reduce the level of proinflammatory cytokines and reactive oxygen species in the PVN, and reduce the level of norepinephrine in plasma of the 2K1C rats. PEAQX administration also largely reduced the transcription and translation levels of GluN2A and changed the expression levels of NMDAR subunits 1 and 2B (GluN1 and GluN2B). In addition, NMDAR was known to function through activating the extracellular regulated protein kinases (ERK) or phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathways. In our study, we found that in the PVN of 2K1C rats treated with PEAQX, the phosphorylation levels of mitogen-activated protein kinase kinase (MEK), ERK1/2, and cAMP-response element-binding protein (CREB) significantly reduced, while the phosphorylation level of PI3K did not change significantly.

CONCLUSIONS

Chronic blockade of GluN2A alleviates hypertension through suppression of MEK/ERK/CREB pathway.

α2δ-1-Dependent NMDA Receptor Activity in the Hypothalamus Is an Effector of Genetic-Environment Interactions That Drive Persistent Hypertension

The interplay between genetic and environmental factors is critically involved in hypertension development. The paraventricular nucleus (PVN) of the hypothalamus regulates sympathetic output during stress responses and chronic hypertension. In this study, we determined mechanisms of synaptic plasticity in the PVN in chronic stress-induced persistent hypertension in male borderline hypertensive rats (BHR), the first offspring of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats. In Wistar-Kyoto rats, chronic unpredictable mild stress (CUMS) increased arterial blood pressure (ABP) and heart rate, which quickly returned to baseline after CUMS ended. In contrast, in BHR, CUMS caused persistent elevation in ABP, which lasted at least 2 weeks after CUMS ended. CUMS also increased the mRNA level of α2δ-1 and synaptic protein levels of GluN1, α2δ-1, and α2δ-1-GluN1 complexes in the PVN in BHR. Furthermore, CUMS significantly increased the frequency of miniature EPSCs and the amplitude of NMDAR currents in spinally projecting PVN neurons in BHR; these increases were normalized by blocking NMDARs with AP5, inhibiting α2δ-1 with gabapentin, or disrupting the α2δ-1-NMDAR interaction with α2δ-1Tat peptide. Microinjection of AP5 or α2δ-1Tat peptide into the PVN normalized elevated ABP and renal sympathetic nerve activity in stressed BHR. In addition, systemically administered gabapentin or memantine attenuated higher ABP induced by CUMS in BHR. Our findings indicate that chronic stress-induced persistent hypertension is mediated by augmented sympathetic outflow via α2δ-1-bound NMDARs in the PVN. This new information provides a cellular and molecular basis for how the genetic-environment interactions cause persistent hypertension.SIGNIFICANCE STATEMENT Chronic stress is a major risk factor for hypertension development, especially for individuals with a genetic predisposition to hypertension. Using a rat model of borderline hypertension, we showed that chronic stress induced long-lasting hypertension and sympathetic nerve hyperactivity, which were maintained by NMDAR activation in the hypothalamus. Chronic stress also increased the expression of α2δ-1, previously regarded as a Ca2+ channel subunit, promoting physical interaction with and synaptic trafficking of NMDARs in the hypothalamus. Inhibiting α2δ-1, blocking NMDARs, or disrupting α2δ-1-bound NMDARs reversed chronic stress-induced sympathetic outflow and persistent hypertension. Thus, α2δ-1-dependent NMDAR activity in the hypothalamus is an effector of genetic-environment interactions and may be targeted for treating stress-induced neurogenic hypertension.

Src-family Protein Tyrosine Kinases: A promising target for treating Cardiovascular Diseases

The Src-family protein tyrosine kinases (SFKs), a subfamily of non-receptor tyrosine kinases, are ubiquitously expressed in various cell types. Numerous studies have suggested that SFKs are related to signal transduction in major cardiac physiological and pathological processes, it is the activity of SFKs that is connected with the maintenance of cardiovascular homeostasis. Upon stimulation of various injury factors or stress, the phosphorylation state of SFKs is changed, which has been found to modulate different cardiac pathological conditions, such as hypertension, coronary heart disease, ischemic heart disease, myocardial ischemia-reperfusion injury, arrhythmia and cardiomyopathy via regulating cell growth, differentiation, movement and function, electrophysiologic signals. This review summarizes the basic information about SFKs, updates its role in the different processes underlying the development of multiple cardiovascular diseases (CVDs), and highlights their potential role as disease biomarkers and therapeutic targets, which would help understand the pathophysiology of CVDs and promote the further potential clinical adhibition.

Group III metabotropic glutamate receptors regulate hypothalamic presympathetic neurons through opposing presynaptic and postsynaptic actions in hypertension

The hypothalamic paraventricular nucleus (PVN) plays a major role in generating increased sympathetic output in hypertension. Although group III metabotropic glutamate receptors (mGluRs) are expressed in the hypothalamus, little is known about their contribution to regulating PVN presympathetic neurons in hypertension. Here we show that activating group III mGluRs with L-2-amino-4-phosphonobutyric acid (L-AP4) consistently inhibited the firing activity of spinally projecting PVN neurons in normotensive rats. However, in spontaneously hypertensive rats (SHRs), L-AP4 inhibited 45% of PVN neurons but excited 37%. L-AP4 significantly reduced glutamatergic and GABAergic input to PVN neurons in both groups. Blocking postsynaptic G protein signaling eliminated the excitatory but not the inhibitory effect of L-AP4 on PVN neurons in SHRs. Remarkably, prior activation of group I mGluRs converted the L-AP4 effect from inhibitory to excitatory in PVN neurons, and L-AP4 consistently inhibited PVN neurons when mGluR5 was blocked in SHRs. Furthermore, the expression level of mGluR4 and mGluR6 in the PVN was significantly higher in SHRs than in normotensive rats. Microinjection of L-AP4 into the PVN decreased blood pressure and lumbar sympathetic nerve discharges in normotensive rats and SHRs. Additionally, blocking group I mGluRs in the PVN potentiated L-AP4's sympathoinhibitory effect in SHRs. Therefore, activation of presynaptic group III mGluRs inhibits the excitability of PVN presympathetic neurons to attenuate sympathetic vasomotor activity. Through crosstalk with mGluR5, postsynaptic group III mGluR stimulation paradoxically excites PVN presympathetic neurons in SHRs. Concurrently blocking mGluR5 and activating group III mGluRs in the PVN can effectively reduce sympathetic outflow in hypertension.

Exacerbated pressor and sympathoexcitatory effects of central Elabela in spontaneously hypertensive rats

Elabela (ELA) is a newly discovered peptide that acts as a novel endogenous ligand of angiotensin receptor-like 1 (APJ) receptor. This study was designed to evaluate the effects of ELA-21 in paraventricular nucleus (PVN) on blood pressure and sympathetic nerve activity in spontaneously hypertensive rats (SHR). Experiments were performed in male Wistar-Kyoto rats (WKY) and SHR. ELA expression was upregulated in PVN of SHR. PVN microinjection of ELA-21 increased renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), heart rate (HR), plasma norepinephrine, and arginine vasopressin (AVP) levels in SHR. Intravenous injection of ELA-21 significantly decreased MAP and HR in both WKY and SHR, but only induced a slight decrease in RSNA. APJ antagonist F13A in PVN abolished the effects of ELA-21 on RSNA, MAP and HR. Intravenous infusion of both ganglionic blocker hexamethonium and AVP V1a receptor antagonist SR49059 caused significant reduction in the effects of ELA-21 on RSNA, MAP and HR in SHR, while combined administration of hexamethonium and SR49059 abolished the effects of ELA-21. ELA-21 microinjection stimulated Akt and p85α subunit of phosphatidylinositol 3-kinase (PI3K) phosphorylation in PVN, whereas PI3K inhibitor LY294002 or Akt inhibitor MK-2206 almost abolished the effects of ELA-21 on RSNA, MAP, and HR. Chronic PVN infusion of ELA-21 induced sympathetic activation, hypertension, and AVP release accompanied with cardiovascular remodeling in normotensive WKY. In conclusion, ELA-21 in PVN induces exacerbated pressor and sympathoexcitatory effects in hypertensive rats via PI3K-Akt pathway.NEW & NOTEWORTHY We demonstrated that PVN microinjection of ELA-21 increases sympathetic nerve activity and blood pressure, which can be abolished by pretreatment of APJ antagonist. This is the first demonstration that central ELA can induce hypertension. The pressor effects in PVN are mediated by both sympathetic activation and vasopressin release via PI3K-Akt pathway. Our data confirm that ELA is upregulated in the PVN of SHR and so may be involved in the pressor and sympathoexcitatory effects in hypertension.

Activation of ADAM17 (A Disintegrin and Metalloprotease 17) on Glutamatergic Neurons Selectively Promotes Sympathoexcitation

Chronic activation of the brain renin-angiotensin system contributes to the development of hypertension by altering autonomic balance. Beyond the essential role of Ang II (angiotensin II) type 1 receptors, ADAM17 (A disintegrin and metalloprotease 17) is also found to promote brain renin-angiotensin system overactivation. ADAM17 is robustly expressed in various cell types within the central nervous system. The aim of this study was to determine whether ADAM17 modulates presympathetic neuronal activity to promote autonomic dysregulation in salt-sensitive hypertension. To test our hypothesis, ADAM17 was selectively knocked down in glutamatergic neurons using Cre-loxP technology. In mice lacking ADAM17 in glutamatergic neurons, the blood pressure increase induced by deoxycorticosterone acetate-salt treatment was blunted. Deoxycorticosterone acetate-salt significantly elevated cardiac and vascular sympathetic drive in control mice, while such effects were reduced in mice with ADAM17 knockdown. This blunted sympathoexcitation was extended to the spleen, with a lesser activation of the peripheral immune system, translating into a sequestration of circulating T cells within this organ, compared with controls. Within the paraventricular nucleus, Ang II-induced activation of kidney-related presympathetic glutamatergic neurons was reduced in ADAM17 knockdown mice, with the majority of cells no longer responding to Ang II stimulation, confirming the supportive role of ADAM17 in increasing presympathetic neuronal activity. Overall, our data highlight the pivotal role of neuronal ADAM17 in regulating sympathetic activity and demonstrate that activation of ADAM17 in glutamatergic neurons leads to a selective increase of sympathetic output, but not vagal tone, to specific organs, ultimately contributing to dysautonomia and salt-sensitive hypertension.

Activation of alpha-1 adrenergic receptors increases cytosolic calcium in neurones of the paraventricular nucleus of the hypothalamus

Norepinephrine (NE) activates adrenergic receptors (ARs) in the hypothalamic paraventricular nucleus (PVN) to increase excitatory currents, depolarise neurones and, ultimately, augment neuro-sympathetic and endocrine output. Such cellular events are known to potentiate intracellular calcium ([Ca²⁺ ]_i ); however, the role of NE with respect to modulating [Ca²⁺ ]_i in PVN neurones and the mechanisms by which this may occur remain unclear. We evaluated the effects of NE on [Ca²⁺ ]_i of acutely isolated PVN neurones using Fura-2 imaging. NE induced a slow increase in [Ca²⁺ ]_i compared to artificial cerebrospinal fluid vehicle. NE-induced Ca²⁺ elevations were mimicked by the α₁ -AR agonist phenylephrine (PE) but not by α₂ -AR agonist clonidine (CLON). NE and PE but not CLON also increased the overall number of neurones that increase [Ca²⁺ ]_i (ie, responders). Elimination of extracellular Ca²⁺ or intracellular endoplasmic reticulum Ca²⁺ stores abolished the increase in [Ca²⁺ ]_i and reduced responders. Blockade of voltage-dependent Ca²⁺ channels abolished the α₁ -AR induced increase in [Ca²⁺ ]_i and number of responders, as did inhibition of phospholipase C inhibitor, protein kinase C and inositol triphosphate receptors. Spontaneous phasic Ca²⁺ events, however, were not altered by NE, PE or CLON. Repeated K⁺ -induced membrane depolarisation produced repetitive [Ca²⁺ ]_i elevations. NE and PE increased baseline Ca²⁺ , whereas NE decreased the peak amplitude. CLON also decreased peak amplitude but did not affect baseline [Ca²⁺ ]_i . Taken together, these data suggest receptor-specific influence of α₁ and α₂ receptors on the various modes of calcium entry in PVN neurones. They further suggest Ca²⁺ increase via α₁ -ARs is co-dependent on extracellular Ca²⁺ influx and intracellular Ca²⁺ release, possibly via a phospholipase C inhibitor-mediated signalling cascade.

Endogenous AT1 receptor-protein kinase C activity in the hypothalamus augments glutamatergic input and sympathetic outflow in hypertension

KEY POINTS

The angiotensin AT1 receptor expression and protein kinase C (PKC)-mediated NMDA receptor phosphorylation levels in the hypothalamus are increased in a rat genetic model of hypertension. Blocking AT1 receptors or PKC activity normalizes the increased pre- and postsynaptic NMDA receptor activity of hypothalamic presympathetic neurons in hypertensive animals. Inhibition of AT1 receptor-PKC activity in the hypothalamus reduces arterial blood pressure and sympathetic nerve discharges in hypertensive animals. AT1 receptors in the hypothalamus are endogenously activated to sustain NMDA receptor hyperactivity and elevated sympathetic outflow via PKC in hypertension.

ABSTRACT

Increased synaptic N-methyl-d-aspartate receptor (NMDAR) activity in the hypothalamic paraventricular nucleus (PVN) plays a major role in elevated sympathetic output in hypertension. Although exogenous angiotensin II (AngII) can increase NMDAR activity in the PVN, whether endogenous AT1 receptor-protein kinase C (PKC) activity mediates the augmented NMDAR activity of PVN presympathetic neurons in hypertension is unclear. Here we show that blocking AT1 receptors with losartan or inhibiting PKC with chelerythrine significantly decreased the frequency of NMDAR-mediated miniature excitatory postsynaptic currents (mEPSCs) and the amplitude of puff NMDA currents of retrogradely labelled spinally projecting PVN neurons in spontaneously hypertensive rats (SHRs). Also, treatment with chelerythrine abrogated the potentiating effect of AngII on mEPSCs and puff NMDA currents of labelled PVN neurons in SHRs. In contrast, neither losartan nor chelerythrine had any effect on mEPSCs or puff NMDA currents in labelled PVN neurons in Wistar-Kyoto (WKY) rats. Furthermore, levels of AT1 receptor mRNA and PKC-mediated NMDAR phosphorylation in the PVN were significantly higher in SHRs than in WKY rats. In addition, microinjection of losartan or chelerythrine into the PVN substantially reduced blood pressure and renal sympathetic nerve discharges in SHRs but not in WKY rats. Chelerythrine blocked sympathoexcitatory responses to AngII microinjected into the PVN. Our findings suggest that endogenous AT1 receptor-PKC activity is essential for presynaptic and postsynaptic NMDAR hyperactivity of PVN presympathetic neurons and for the augmented sympathetic outflow in hypertension. This information advances our mechanistic understanding of the interplay between angiotensinergic and glutamatergic excitatory inputs in hypertension.

Impaired Hypothalamic Regulation of Sympathetic Outflow in Primary Hypertension

The hypothalamic paraventricular nucleus (PVN) is a crucial region involved in maintaining homeostasis through the regulation of cardiovascular, neuroendocrine, and other functions. The PVN provides a dominant source of excitatory drive to the sympathetic outflow through innervation of the brainstem and spinal cord in hypertension. We discuss current findings on the role of the PVN in the regulation of sympathetic output in both normotensive and hypertensive conditions. The PVN seems to play a major role in generating the elevated sympathetic vasomotor activity that is characteristic of multiple forms of hypertension, including primary hypertension in humans. Recent studies in the spontaneously hypertensive rat model have revealed an imbalance of inhibitory and excitatory synaptic inputs to PVN pre-sympathetic neurons as indicated by impaired inhibitory and enhanced excitatory synaptic inputs in hypertension. This imbalance of inhibitory and excitatory synaptic inputs in the PVN forms the basis for elevated sympathetic outflow in hypertension. In this review, we discuss the disruption of balance between glutamatergic and GABAergic inputs and the associated cellular and molecular alterations as mechanisms underlying the hyperactivity of PVN pre-sympathetic neurons in hypertension.

Regulation of sympathetic vasomotor activity by the hypothalamic paraventricular nucleus in normotensive and hypertensive states

The hypothalamic paraventricular nucleus (PVN) is a unique and important brain region involved in the control of cardiovascular, neuroendocrine, and other physiological functions pertinent to homeostasis. The PVN is a major source of excitatory drive to the spinal sympathetic outflow via both direct and indirect projections. In this review, we discuss the role of the PVN in the regulation of sympathetic output in normal physiological conditions and in hypertension. In normal healthy animals, the PVN presympathetic neurons do not appear to have a major role in sustaining resting sympathetic vasomotor activity or in regulating sympathetic responses to short-term homeostatic challenges such as acute hypotension or hypoxia. Their role is, however, much more significant during longer-term challenges, such as sustained water deprivation, chronic intermittent hypoxia, and pregnancy. The PVN also appears to have a major role in generating the increased sympathetic vasomotor activity that is characteristic of multiple forms of hypertension. Recent studies in the spontaneously hypertensive rat model have shown that impaired inhibitory and enhanced excitatory synaptic inputs to PVN presympathetic neurons are the basis for the heightened sympathetic outflow in hypertension. We discuss the molecular mechanisms underlying the presynaptic and postsynaptic alterations in GABAergic and glutamatergic inputs to PVN presympathetic neurons in hypertension. In addition, we discuss the ability of exercise training to correct sympathetic hyperactivity by restoring blood-brain barrier integrity, reducing angiotensin II availability, and decreasing oxidative stress and inflammation in the PVN.

Hypoxic Preconditioning Maintains GLT-1 Against Transient Global Cerebral Ischemia Through Upregulating Cx43 and Inhibiting c-Src

Transient global cerebral ischemia (tGCI) causes excessive release of glutamate from neurons. Astrocytic glutamate transporter-1 (GLT-1) and glutamine synthetase (GS) together play a predominant role in maintaining glutamate at normal extracellular concentrations. Though our previous studies reported the alleviation of tGCI-induced neuronal death by hypoxic preconditioning (HPC) in hippocampal Cornu Ammonis 1 (CA1) of adult rats, the underlying mechanism has not yet been fully elaborated. In this study, we aimed to investigate the roles of GLT-1 and GS in the neuroprotection mediated by HPC against tGCI and to ascertain whether these roles can be regulated by connexin 43 (Cx43) and cellular-Src (c-Src) activity. We found that HPC decreased the level of extracellular glutamate in CA1 after tGCI via maintenance of GLT-1 expression and GS activity. Inhibition of GLT-1 expression with dihydrokainate (DHK) or inhibition of GS activity with methionine sulfoximine (MSO) abolished the neuroprotection induced by HPC. Also, HPC markedly upregulated Cx43 and inhibited p-c-Src expression in CA1 after tGCI, whereas inhibition of Cx43 with Gap26 dramatically reversed this effect. Furthermore, inhibition of p-c-Src with 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo (3, 4-d) pyrimidine (PP2) decreased c-Src activity, increased protein levels of GLT-1 and Cx43, enhanced GS activity, and thus reduced extracellular glutamate level in CA1 after tGCI. Collectively, our data demonstrated that reduced extracellular glutamate induced by HPC against tGCI through preventing the reduction of GLT-1 expression and maintaining GS activity in hippocampal CA1, which was mediated by upregulating Cx43 expression and inhibiting c-Src activity.

α2δ-1 couples to NMDA receptors in the hypothalamus to sustain sympathetic vasomotor activity in hypertension

KEY POINTS

α2δ-1 is upregulated, promoting the interaction with NMDA receptors (NMDARs), in the hypothalamus in a rat model of hypertension. The prevalence of α2δ-1-bound NMDARs at synaptic sites in the hypothalamus is increased in hypertensive animals. α2δ-1 is essential for the increased presynaptic and postsynaptic NMDAR activity of hypothalamic neurons in hypertension. α2δ-1-bound NMDARs in the hypothalamus are critically involved in augmented sympathetic outflow in hypertensive animals.

ABSTRACT

Increased glutamate NMDA receptor (NMDAR) activity in the paraventricular nucleus (PVN) of the hypothalamus leads to augmented sympathetic outflow in hypertension. However, the molecular mechanisms underlying this effect remain unclear. α2δ-1, previously considered to be a voltage-activated calcium channel subunit, is a newly discovered powerful regulator of NMDARs. In the present study, we determined the role of α2δ-1 in regulating synaptic NMDAR activity of rostral ventrolateral medulla (RVLM)-projecting PVN neurons in spontaneously hypertensive rats (SHRs). We show that the protein levels of α2δ-1 and NMDARs in synaptosomes and the α2δ-1-NMDAR complexes in the hypothalamus were substantially higher in SHRs than in normotensive control rats. The basal amplitude of evoked NMDAR currents and NMDAR-mediated synaptic glutamate release in RVLM-projecting PVN neurons were significantly increased in SHRs. Strikingly, inhibiting α2δ-1 activity with gabapentin or disrupting the α2δ-1-NMDAR association with an α2δ-1 C-terminus peptide completely normalized the amplitude of evoked NMDAR currents and NMDAR-mediated synaptic glutamate release in RVLM-projecting PVN neurons in SHRs. In addition, microinjection of the α2δ-1 C-terminus peptide into the PVN substantially reduced arterial blood pressure and renal sympathetic nerve discharges in SHRs. Our findings indicate that α2δ-1-bound NMDARs in the PVN are required for the potentiated presynaptic and postsynaptic NMDAR activity of PVN presympathetic neurons and for the elevated sympathetic outflow in hypertension. α2δ-1-bound NMDARs may be an opportune target for treating neurogenic hypertension.

α2δ-1 Is Essential for Sympathetic Output and NMDA Receptor Activity Potentiated by Angiotensin II in the Hypothalamus

Both the sympathetic nervous system and the renin-angiotensin system are critically involved in hypertension development. Although angiotensin II (Ang II) stimulates hypothalamic paraventricular nucleus (PVN) neurons to increase sympathetic vasomotor tone, the molecular mechanism mediating this action remains unclear. The glutamate NMDAR in the PVN controls sympathetic outflow in hypertension. In this study, we determined the interaction between α2δ-1 (encoded by Cacna2d1), commonly known as a Ca²⁺ channel subunit, and NMDARs in the hypothalamus and its role in Ang II-induced synaptic NMDAR activity in PVN presympathetic neurons. Coimmunoprecipitation assays showed that α2δ-1 interacted with the NMDAR in the hypothalamus of male rats and humans (both sexes). Ang II increased the prevalence of synaptic α2δ-1-NMDAR complexes in the hypothalamus. Also, Ang II increased presynaptic and postsynaptic NMDAR activity via AT1 receptors, and such effects were abolished either by treatment with pregabalin, an inhibitory α2δ-1 ligand, or by interrupting the α2δ-1-NMDAR interaction with an α2δ-1 C terminus-interfering peptide. In Cacna2d1 knock-out mice (both sexes), Ang II failed to affect the presynaptic and postsynaptic NMDAR activity of PVN neurons. In addition, the α2δ-1 C terminus-interfering peptide blocked the sympathoexcitatory response to microinjection of Ang II into the PVN. Our findings indicate that Ang II augments sympathetic vasomotor tone and excitatory glutamatergic input to PVN presympathetic neurons by stimulating α2δ-1-bound NMDARs at synapses. This information extends our understanding of the molecular basis for the interaction between the sympathetic nervous and renin-angiotensin systems and suggests new strategies for treating neurogenic hypertension.SIGNIFICANCE STATEMENT Although both the sympathetic nervous system and renin-angiotensin system are closely involved in hypertension development, the molecular mechanisms mediating this involvement remain unclear. We showed that α2δ-1, previously known as a calcium channel subunit, interacts with NMDARs in the hypothalamus of rodents and humans. Angiotensin II (Ang II) increases the synaptic expression level of α2δ-1-NMDAR complexes. Furthermore, inhibiting α2δ-1, interrupting the α2δ-1-NMDAR interaction, or deleting α2δ-1 abolishes the potentiating effects of Ang II on presynaptic and postsynaptic NMDAR activity in the hypothalamus. In addition, the sympathoexcitatory response to Ang II depends on α2δ-1-bound NMDARs. Thus, α2δ-1-NMDAR complexes in the hypothalamus serve as an important molecular substrate for the interaction between the sympathetic nervous system and the renin-angiotensin system. This evidence suggests that α2δ-1 may be a useful target for the treatment neurogenic hypertension.

Enhanced Hypothalamic NMDA Receptor Activity Contributes to Hyperactivity of HPA Axis in Chronic Stress in Male Rats

Chronic stress stimulates corticotrophin-releasing hormone (CRH)-expressing neurons in the paraventricular nucleus (PVN) of the hypothalamus and leads to hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, but the mechanisms underlying this action are unknown. Because chronic stress enhances N-methyl-d-aspartate receptor (NMDAR) activity in various brain regions, we hypothesized that augmented NMDAR activity contributes to the hyperactivity of PVN-CRH neurons and the HPA axis in chronic stress. We performed whole-cell patch-clamp recordings on PVN-CRH neurons expressing CRH promoter-driven enhanced green fluorescent protein in brain slices from rats exposed to chronic unpredictable mild stress (CUMS) and unstressed rats. CUMS rats had significantly higher expression levels of the NMDAR subunits GluN1 in the PVN than unstressed rats. Furthermore, puff NMDA-elicited currents, evoked NMDAR currents, and the baseline frequency of the miniature excitatory postsynaptic currents (mEPSCs) in PVN-CRH neurons were significantly larger in CUMS rats than in unstressed rats. The NMDAR-specific antagonist 2-amino-5-phosphonopentanoic acid (AP5) significantly decreased the frequency of mEPSCs of PVN-CRH neurons in CUMS rats but did not change the frequency or amplitude of mEPSCs in unstressed rats. Bath application of AP5 normalized the elevated firing activity of PVN-CRH neurons in CUMS rats but not in unstressed rats. In addition, microinjection of the NMDAR antagonist memantine into the PVN normalized the elevated corticosterone (CORT) levels in CUMS rats to the levels in unstressed rats, but did not alter CORT levels in unstressed rats. Our findings suggest that synaptic NMDAR activity is enhanced in CUMS rats and contributes to the hyperactivity of PVN-CRN neurons and the HPA axis.

CaMKII Regulates Synaptic NMDA Receptor Activity of Hypothalamic Presympathetic Neurons and Sympathetic Outflow in Hypertension

NMDAR activity in the hypothalamic paraventricular nucleus (PVN) is increased and critically involved in heightened sympathetic vasomotor tone in hypertension. Calcium/calmodulin-dependent protein kinase II (CaMKII) binds to and modulates NMDAR activity. In this study, we determined the role of CaMKII in regulating NMDAR activity of PVN presympathetic neurons in male spontaneously hypertensive rats (SHRs). NMDAR-mediated EPSCs and puff NMDA-elicited currents were recorded in spinally projecting PVN neurons in SHRs and male Wistar-Kyoto (WKY) rats. The basal amplitude of evoked NMDAR-EPSCs and puff NMDA currents in retrogradely labeled PVN neurons were significantly higher in SHRs than in WKY rats. The CaMKII inhibitor autocamtide-2-related inhibitory peptide (AIP) normalized the increased amplitude of NMDAR-EPSCs and puff NMDA currents in labeled PVN neurons in SHRs but had no effect in WKY rats. Treatment with AIP also normalized the higher frequency of NMDAR-mediated miniature EPSCs of PVN neurons in SHRs. CaMKII-mediated phosphorylation level of GluN2B serine 1303 (S1303) in the PVN, but not in the hippocampus and frontal cortex, was significantly higher in SHRs than in WKY rats. Lowering blood pressure with celiac ganglionectomy in SHRs did not alter the increased level of phosphorylated GluN2B S1303 in the PVN. In addition, microinjection of AIP into the PVN significantly reduced arterial blood pressure and lumbar sympathetic nerve discharges in SHRs. Our findings suggest that CaMKII activity is increased in the PVN and contributes to potentiated presynaptic and postsynaptic NMDAR activity to elevate sympathetic vasomotor tone in hypertension.SIGNIFICANCE STATEMENT Heightened sympathetic vasomotor tone is a major contributor to the development of hypertension. Although glutamate NMDA receptor (NMDAR)-mediated excitatory drive in the hypothalamus plays a critical role in increased sympathetic output in hypertension, the molecular mechanism involved in potentiated NMDAR activity of hypothalamic presympathetic neurons remains unclear. Here we show that the activity of calcium/calmodulin-dependent protein kinase II (CaMKII) is increased and plays a key role in the potentiated presynaptic and postsynaptic NMDAR activity of hypothalamic presympathetic neurons in hypertension. Also, the inhibition of CaMKII in the hypothalamus reduces elevated blood pressure and sympathetic nerve discharges in hypertension. This new knowledge extends our understanding of the mechanism of synaptic plasticity in the hypothalamus and suggests new strategies to treat neurogenic hypertension.

Glutamatergic Regulation of Hypothalamic Presympathetic Neurons in Hypertension

Elevated sympathetic vasomotor tone emanating from the brain is a major mechanism involved in the development of hypertension. Increased glutamatergic excitatory input to presympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus leads to increased sympathetic outflow in various animal models of hypertension. Recent studies have revealed molecular and cellular mechanisms underlying enhanced glutamatergic synaptic input to PVN presympathetic neurons in hypertension. In this review article, we summarize recent findings on changes in inotropic and metabotropic glutamate receptors, at both presynaptic and postsynaptic sites, responsible for increased glutamatergic input to PVN presympathetic neurons in hypertension. Particular emphasis is placed on the role of protein kinases and phosphatases in the potentiated activity of synaptic NMDA receptors in the PVN in hypertension. New findings about glutamatergic synaptic plasticity in the PVN not only improve the understanding of molecular mechanisms involved in heightened activity of the sympathetic nervous system but also suggest new therapeutic targets for treating drug-resistant, neurogenic hypertension.