Renal Sympathetic Nerve Activity Research Articles

Effects of intrarenal pelvic infusion of tumour necrosis factor-α and interleukin 1-β on reno-renal reflexes in anaesthetised rats.

Reno-renal reflexes are disturbed in cardiovascular and hypertensive conditions when elevated levels of pro-inflammatory mediators/cytokines are present within the kidney. We hypothesised that exogenously administered inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interleukin (IL)-1β modulate the renal sympatho-excitatory response to chemical stimulation of renal pelvic sensory nerves. In anaesthetised rats, intrarenal pelvic infusions of vehicle [0.9% sodium chloride (NaCl)], TNF-α (500 and 1000 ng/kg) and IL-1β (1000 ng/kg) were maintained for 30 min before chemical activation of renal pelvic sensory receptors was performed using randomized intrarenal pelvic infusions of hypertonic NaCl, potassium chloride (KCl), bradykinin, adenosine and capsaicin. The increase in renal sympathetic nerve activity (RSNA) in response to intrarenal pelvic hypertonic NaCl was enhanced during intrapelvic TNF-α (1000 ng/kg) and IL-1β infusions by almost 800% above vehicle with minimal changes in mean arterial pressure (MAP) and heart rate (HR). Similarly, the RSNA response to intrarenal pelvic adenosine in the presence of TNF-α (500 ng/kg), but not IL-1β, was almost 200% above vehicle but neither MAP nor HR were changed. There was a blunted sympatho-excitatory response to intrapelvic bradykinin in the presence of TNF-α (1000 ng/kg), but not IL-1β, by almost 80% below vehicle, again without effect on either MAP or HR. The renal sympatho-excitatory response to renal pelvic chemoreceptor stimulation is modulated by exogenous TNF-α and IL-1β. This suggests that inflammatory mediators within the kidney can play a significant role in modulating the renal afferent nerve-mediated sympatho-excitatory response.

Adipocyte-Specific Disruption of the BBSome Causes Metabolic and Autonomic Dysfunction.

Obesity is a major public health issue due to its association with type 2 diabetes, hypertension, and other cardiovascular risks. The BBSome, a complex of 8 conserved Bardet-Biedl Syndrome (BBS) proteins, has emerged as a key regulator of energy and glucose homeostasis as well as cardiovascular function. However, the importance of adipocyte BBSome in controlling these physiological processes is not clear. Here, we show that adipocyte-specific constitutive disruption of the BBSome through selective deletion of the Bbs1 gene (AdipoCre/Bbs1fl/fl mice) does not affect body weight under normal chow or high fat & high sucrose diet (HFHSD). However, constitutive BBSome defiency caused impairment in glucose tolerance and insulin sensitivity. Similar phenotypes were observed after inducible adipocyte-specific constitutive disruption of the BBSome (AdipoCreERT2/Bbs1fl/fl mice). Interestingly, a significant increase in renal sympathetic nerve activity, measured using multifiber recording in the conscious state, was observed in AdipoCre/Bbs1fl/fl mice on both chow and HFHSD. A significant increase in tail-cuff arterial pressure was also observed in chow-fed AdipoCre/Bbs1fl/fl mice, but this was not reproduced when arterial pressure was measured by radiotelemetry. Moreover, AdipoCre/Bbs1fl/fl mice had no significant alterations in vascular reactivity. On the other hand, AdipoCre/Bbs1fl/fl mice displayed impaired baroreceptor reflex sensitivity when fed HFHSD, but not on normal chow. Taken together, these data highlight the relevance of the adipocyte BBSome for the regulation of glucose homeostasis, sympathetic traffic. The BBSome also contribute to baroreflex sensitivity under HFHSD, but not normal chow.

PAG Masked Protective Physical Exercise-Induced High H2S Levels in 5/6 Nephrectomized Rats

Background: To investigate the mechanisms of exercise therapeutics in preclinical animal models of chronic kidney disease (CKD), PAG (D, L-propargylglycine), an inhibitor of hydrogen sulfide production, was used to examine the protective effects of physical activity on oxidative stress and inflammation levels during CKD. Methods: Male Wistar rats with CKD, induced by the 5/6 nephrectomy procedure and subjected to 8 weeks of exercise training, received injections of PAG, a cystathionine γ-lyase (CSE) inhibitor, at a dose of 19 mg/kg, i.p., twice a week during those 8 weeks. The systolic blood pressure (BP) and renal sympathetic nerve activity (RSNA) were assessed. Additionally, plasma creatinine, BUN, renal hydrogen sulfide (H2S) levels, oxidative stress, and inflammatory markers were evaluated. Results: In the PAG group, inhibition of H2S production significantly reversed the improvements in plasma creatinine, BUN, renal malondialdehyde (MDA) level, superoxide dismutase (SOD) activity, TNF-α, and IL-6 that were achieved by exercise. Additionally, high RSNA and high BP, which were also reversed in the PAG group, compared to the CKD group subjected to exercise training. Conclusions: The results suggest that the improvement in BP, oxidative stress, and inflammation status by exercise in CKD may be at least partially due to CSE/H2S signaling.

A descending pathway from the lateral/ventrolateral PAG to the rostroventral medulla mediating the vasomotor response evoked by social defeat stress in rats.

The stress-induced cardiovascular response is based upon the defensive reaction in mammals. It has been shown that the sympathetic vasomotor pathway of acute psychological stress is indirectly mediated via neurons in the rostroventral medulla (RVM) from the hypothalamic stress center. In this study, direct projections to the RVM and distribution of neuroexcitatory marker, c-Fos expressed neurons were investigated during social defeat stress (SDS) in conscious rats. The experimental rat that was injected with a neural tracer, FluoroGold (FG) into the unilateral RVM, was exposed to the SDS. Double positive neurons of both c-Fos and FG were locally distributed in the lateral/ventrolateral periaqueductal grey matter (l/vl PAG) in the midbrain. These results suggest that the neurons in the l/vl PAG contribute to the defensive reaction evoked by acute psychological stress, such as the SDS. During the SDS period, arterial pressure (AP) and heart rate (HR) showed sustained increases in the rat. Therefore, we performed chemical stimulation by excitatory amino acid microinjection within the l/vl PAG and measured cardiovascular response and sympathetic nerve activity in some anesthetized rats. The chemical stimulation of neurons in the l/vl PAG caused significant increases in arterial pressure and renal sympathetic nerve activity. Taken together, our results suggest that neurons in the l/vl PAG are a possible candidate for the cardiovascular descending pathway that modulates sympathetic vascular resistance evoked by acute psychological stress, like the SDS.

Vagal nerve and sympathetic nerve activity in response to glucagon-like peptide-1 (GLP-1) receptor stimulation in conscious rats

GLP-1 (Glucagon-Like Peptide-1) is a type of gastrointestinal hormone that plays an integral role in regulating glucose homeostasis and appetite control. GLP-1 receptors are expressed throughout the body, and it has been suggested that GLP-1 can be detected by vagal afferent nerve activity, leading to changes in sympathetic nerve activity. However, the details of the effects of GLP-1 receptor stimulation on autonomic nerve activity have not been reported. Therefore, this study investigated the effects of different sites of GLP-1 receptor stimulation on autonomic nerve activity by administering GLP-1 receptor agonists via three routes: intravenous (IV), intraportal vein (iport), and intraperitoneal (iperi). Male Wistar rats were chronically implanted with electrodes, catheters for measuring cervical vagal activity, renal and lumbar sympathetic nerve activity, electroencephalogram, electromyogram, electrocardiogram, arterial pressure, sensors for tissue fluid glucose concentration, and catheters for drug administration in the vein, portal vein, and abdominal cavity. Exendin-4, a GLP-1 receptor agonist, was administered to conscious rats via one of the following routes: intravenous, intra-portal vein, or intra-abdominal. Cervical vagal activity was increased in all routes of Exendin-4 administration. Renal sympathetic nerve activity was rapidly decreased by Exendin-4 administration and gradually recovered to pre-administration levels. There were no significant differences in renal sympathetic nerve activity among the different routes of Exendin-4 administration. On the other hand, lumbar sympathetic nerve activity increased slowly after Exendin-4 administration through the iperi and iport routes, while it decreased initially, then gradually increased following administration through the IV route. These results demonstrate that stimulation of GLP-1 receptors by Exendin-4 increases vagal nerve activity, decreases renal sympathetic nerve activity, and produces regionally different responses in lumbar sympathetic nerve activity depending on the site of stimulation. JST (JPMJMS2023). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Renal Afferent Nerve Activity and Association with Neurohumoral Dysregulation in a Model of Autosomal Recessive Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a rare, genetic kidney disease characterized by cyst growth that leads to kidney failure. Renal nerves play an important role in the development and maintenance of hypertension and other renal diseases. Afferent (sensory) nerves convey information to the central nervous system in response to intrarenal stimuli. Our laboratory demonstrated that afferent renal nerve activity (ARNA) is elevated in 10-week-old PCK rats compared to non-cystic, age-matched Sprague-Dawley (SD) controls. Furthermore, ARNA positively correlated with cystic index (CI; a measure of cyst growth). To further elucidate the relationship between renal nerve activity, age, and cyst progression, we aimed to quantify both ARNA and renal sympathetic nerve activity (RSNA) in PCK and SD rats. We hypothesized that ARNA and RSNA would be greater in PCK than SD. Furthermore, arginine vasopressin (AVP) is elevated in PKD and increases cyst growth. There is evidence that activation of the afferent renal nerves can contribute to secretion of AVP. Thus, we propose that elevated ARNA increases AVP secretion, thereby increasing cyst growth. We also hypothesized that ARNA would positively correlate with age, CI, and copeptin (an indirect marker of AVP) in young PCK rats. To test our first hypothesis, we conducted direct renal nerve recordings in 10- to 12-week-old PCK (n=16;11M/5F) and 10-week-old SD (n=9;7M/2F) rats. For our second hypothesis, we conducted nerve recordings in 4- to 10-week-old PCK rats to evaluate the correlation of nerve activity with age, cystic index, and copeptin in animals ages 4- to 12-weeks-old (n=28;21M/7F). Multiunit nerve recording was performed under inactin anesthesia. As we previously published, a renal nerve bundle is isolated, placed on an iridium bipolar electrode, and encased in silicone. Resting RSNA was recorded following 10-minute stabilization period, then the nerve bundle was severed proximal to the electrode to isolate ARNA. ARNA recordings were normalized to maximal ARNA evoked by intrarenal 50 μM capsaicin. Comparisons between PCK and SD were analyzed by Student’s t-test (p<.05). Linear regression analyses were used to assess variable correlation (p<.05). Data presented as mean ± SEM. In contrast to our first hypothesis, RSNA did not differ between 10- to 12-week-old SD and PCK rats, whether measured via burst frequency (SD 6.92 ± 0.82; PCK *6.97 ± 0.34 Hz) or bursts/heart beat (SD 1.36±0.16; PCK 1.28 ± 0.06). ARNA was calculated as a percentage of maximal ARNA using either integrated ARNA (ARNAInt) or spikes/s (ARNASpikes). Baseline ARNAInt was greater in PCK rats (29.14±3.35%) than SD (13.46±2.08%, n=4), whereas PCK ARNASpikes trended (p=.06) higher than SD controls (SD 5.57±2.21; PCK 13.90±2.21%). In correlative analysis, RSNA trended (p=.05) to correlate with age in the PCK rat. However, there was no relationship between RSNA and (1) CI (p=0.29) or (2) copeptin (p=0.15). Similarly, there was no correlation detected between ARNA and age (ARNAInt: p=0.41; ARNASpikes: p=0.16) or serum copeptin (ARNAInt: p=0.96; ARNASpikes: p=0.20). ARNAInt trended (p=.07) to correlate with CI, but ARNASpikes did not correlate with CI (p=0.48). Overall, these data partially support our hypotheses. RSNA did not differ between SD and PCK rats, but ARNAInt was increased in PCK rats vs. SD. We failed to detect a correlation between either ARNA or RSNA and age, CI, or copeptin in PCK rats though, ARNAInt trended to correlate with CI. As ARNA does not appear to be correlated with serum copeptin, further studies are required to uncover the relationship between afferent renal nerves and cystogenesis in this model of PKD. PKD Foundation Research Award 1022534 (CB) NIDDK/PKD RRC Pilot and Feasibility Award U24DK126110 (CB) AHA 21PRE0000216068 (MG). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Exercise Pressor Reflex Function Is Exacerbated in Decerebrate Adenine-Induced Chronic Kidney Disease Rats

Cardiovascular disease is the leading cause of death in chronic kidney disease (CKD). While the underlying mechanisms are not completely understood, elevated sympathetic nerve activity (SNA) and exercise intolerance are thought to play an important role. In normal physiological conditions, sympathetic modulation of the cardiovascular system during physical activity is largely governed by a peripheral neural reflex originating in contracting skeletal muscle, known as the exercise pressor reflex (EPR). Pioneering work by Park et al. demonstrated that CKD patients exhibited abnormal SNA and blood pressure (BP) elevations during both static and rhythmic handgrip exercise, suggesting an overactive EPR. However, due to experimental design constraints inherent to humans, the contribution of the EPR to the augmented SNA and BP responses to exercise could not be fully addressed. Therefore, the purpose of this study was to specifically test EPR function in CKD using a reduced animal model. Sprague-Dawley rats were randomly assigned to receive either a powdered chow diet containing adenine (0.25%w/w in feed) to induce CKD or a powdered chow diet alone (control group) for 12 weeks. Subsequently, in decerbrate animals, we measured mean arterial pressure (MAP) and renal SNA (RSNA) in response to isolated EPR activation during hindlimb muscle contraction (i.e., simulated exercise). We further assessed cardiovascular and sympathetic responses to passive muscle stretch to stimulate the mechanoreflex (i.e., activation of the mechanically-sesnsitive component of the EPR), and intra-arterial capsaicin administratration to activate the metaboflex (i.e., stimulation of the metabolically-sensitive component of the EPR). After completion of the diet, levels of plasma creatinine were significantly increased in adenine-fed rats compared to control rats (2.57±1.05 vs. 0.34±0.05 mg/dL, P<0.01), suggesting impaired renal function (i.e., adenine-induced CKD). We found that CKD animals exhibited augmentations in RSNA (Δ=153±75 vs. 61±50 %, P<0.05) and MAP (Δ=35±18 vs. 17±8 mmHg, P<0.05) in response to muscle contraction when compared to control animals. Importantly, the muscle tension developed during contraction was similar between the two groups (Δ=0.9±0.2 vs. 1.0±0.3 kg, P>0.1, CKD vs. control). During stimulation of the mechanoreflex, CKD rats also exhibited significantly greater RSNA (Δ=100±54 vs. 32±26 %, P<0.05) and MAP responses (Δ=25±14 vs. 10±7 mmHg, P<0.05) than control rats. The developed muscle tension during passive stretch was similar between the two groups (Δ=0.9±0.2 vs. 1.0±0.4 kg, P>0.1, CKD vs. control). There was a tendency for the responses to metaboreflex activation to be heightened in the CKD group compared with the control group, but the difference did not reach statistical significance (ΔRSNA=212±68 vs. 107±105 %, P=0.06, ΔMAP=67±12 vs. 48±21 mmHg, P=0.06, CKD vs. control, respectively). Our findings suggest that EPR function, particularly muscle mechanoreflex function, is exaggerated in CKD, leading to sympathetic activation and hypertensive responses during exercise. P30 DK079307 Subaward to H.K. and R01HL-133179 to W.V. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dysfunction of M channels in the insular cortex is involved in pathogenesis of primary hypertension

Heightened sympathetic nerve activity is critically involved in the pathogenesis of primary hypertension. However, the sources driving increased sympathetic vasomotor tone remain unclear. The posterior insular cortex (PIC) is a brain region involved in regulating blood pressure and sympathetic tone. Neurons in the PIC project to the rostral ventrolateral medulla (RVLM), a key brain stem region in regulating sympathetic nerve activity and blood pressure. The non-inactivating voltage-dependent K+ channels, M channels (Kv7/KCNQ channel family) encoded by KCNQ2/3 genes, play a unique role in stabilizing the neuronal membrane potential and regulating neuronal excitability. Here, we determined if the M channel activity of neurons in the PIC is altered in a primary hypertension. Compared with Wistar-Kyoto (WKY) rats, the mRNA and protein expression levels of Kv7.2/Kv7.3 in the PIC tissue were significantly reduced in spontaneously hypertensive rats (SHRs). Microinjection of M channel blocker 10, 10-bis (4-pyridinylmethyl)-9(10H)-anthracnose (XE-991) into the PIC increased arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) in anesthetized WKY rats, while induced minimal changes of ABP and RSNA in SHRs. M currents recorded from PIC neurons in brain slices labeled by retrograde tracer, Fluospheres, injected into the RVLM were significantly smaller in SHRs than in WKY rats. Furthermore, bath application of specific M channel blocker XE-991 increased the firing rate of PIC-RVLM output neurons in WKY rats while caused a minimal increase in firing rate of PIC-RVLM output neurons in SHRs. In addition, M currents recorded from PIC-RVLM output neurons in SHRs were significantly smaller than those recorded from WKY rats. These data suggest that M channel activity is diminished in PIC-RVLM output neurons in SHRs, and the diminished Kv7 channel activity contributes to elevated sympathetic outflow in primary hypertension. This novel information provides new a mechanistic insight into the pathogenesis of neurogenic hypertension. Supported by grants from National Institutes of Health (HL139523, HL142133, and HL159157 to DPL). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Inhibition and potentiation of the mechanoreflex following pharmacological modulation of TRPC6 in male rats

We determined the role played by the transient receptor potential canonical 6 (TRPC6) in evoking the mechanical component of the exercise pressor reflex in male decerebrated Sprague-Dawley rats. Quadruple-labelled immunohistochemistry were used in dorsal root ganglion cells to identify the cells that innervate the triceps surae muscles (DiI), the cells that express TRPC6 and the cells that are (Nf200) or are not myelinated (peripherin) (n=4). In addition, static contraction of triceps surae muscles was evoked by electrically stimulating the left tibial nerve before and after injecting into the superficial epigastric artery the TRPC6 antagonists, BI-749327 (n = 11; 12μg.kg−1) or SAR7334 (n = 11; 7μg.kg−1), or the TRPC6 positive modulator, C20 (n = 11; 18μg.kg−1). Similar experiments were conducted while the triceps surae muscles were passively stretched (n = 8 to 12), a maneuver that isolates the mechanical component of the reflex. Blood pressure, tension, renal sympathetic nerve activity (RSNA) and blood flow were recorded throughout the experiments. The neurons innervating the triceps-surae muscles were positive to TRPC6 antigen and co-expressed the neurofilament 200kDa. These cells were not positive for peripherin. While the TRPC6 blockers decreased the pressor response to static contraction (-32 to -42%; P < 0.05) and passive stretch (-35 to 52%; P < 0.05), the positive modulator increased both of these responses (55 to 65%; P < 0.05). In addition, BI-749327 decreased the peak and integrated RSNA responses to both static contraction (-39 to -43%; P < 0.05) and passive stretch (-56 to -62%; P < 0.05) whereas C20 increased these responses to stretch only (55 to 235%; P < 0.05). All of these results were not replicated when the drugs were injected intravenously or when the vehicle of the drug was injected into the superficial epigastric artery. Collectively, our results showed that TRPC6 play a key role in evoking the mechanical component of the exercise pressor reflex in male rats. Supported by NIH grants HL 161160, HL 156594 and HL 156513. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

On the Regulation of Arterial Blood Pressure by an Intracranial Baroreceptor

Introduction: There is significant evidence for the existence of an intracranial baroreceptor mechanism(s) capable of sensing physiological changes in cerebral blood flow (Marina et al., 2020). However, little is known about the sensitivity of this mechanism to changes in brain perfusion and its interaction with inputs from the peripheral (arterial) baroreceptors. The aim of this study was to characterise the cardiovascular responses to physiological changes in cerebral perfusion induced by experimental manipulations of intracranial pressure (ICP). Methods: The experiments were performed in adult Sprague-Dawley rats (250–300 g), anesthetized with urethane (induction: 1.3 g kg−1, i.p.; maintenance: 10–25 mg kg−1 h−1, i.v.). The femoral artery and vein were cannulated for measurement of arterial blood pressure (ABP) and administration of anaesthetic. The trachea was cannulated, and the animal was mechanically ventilated. The lateral cerebral ventricles were cannulated and connected via saline-filled catheters to a pressure transducer to record ICP and to a “water column” to allow controlled manipulation of ICP. The experiments included the denervation of the arterial baroceptors, stimulation of the aortic depressor nerve and recording of renal sympathetic nerve activity. Results: The resting ICP in rats anesthetized with urethane was 6.2 ± 0.7 mmHg (n=8). Following a small craniotomy that reduced ICP to 0 mmHg, ABP decreased by 11.2 mmHg (n=6) within 30 min. Restoring the integrity of the intracranial space increased ABP to the baseline level. Progressive increases in ABP were observed in response to experimentally-induced increases in ICP by 5, 10, 15 and 20 mmHg, revealing a linear relationship between ICP and systemic arterial pressure within the physiological range of ICP changes. In the absence of inputs from the arterial baroceptors (bilateral sino-aortic denervation and vagotomy) the ABP responses to ICP increases were preserved. Analysis of the ABP and heart rate responses to the electrical stimulation of the aortic depressor nerve suggested baroreflex re-setting at raised ICP. Renal nerve recordings demonstrated increased sympathetic activity at raised ICP (172 ± 34.91 % at 20 mmHg ICP (p=0.003; n=7) with markedly enhanced bursts of activity during the inspiratory phase of the respiratory cycle. Conclusion: These data demonstrate that the intracranial baroceptor mechanism is highly sensitive to changes in cerebral perfusion within the physiological range and suggest that cerebral blood flow is an important determinant of systemic ABP. The data suggest that at raised ICP the baroreflex control of sympathetic vasomotor activity is reset and provides effective control of arterial blood pressure at a higher level required to compensate for reduced brain perfusion. Marina, N., Christie, I.N., Korsak, A., Doronin, M., Brazhe, A., Hosford, P.S., Wells, J.A., Sheikhbahaei, S., Humoud, I., Paton, J.F. and Lythgoe, M.F., 2020. Astrocytes monitor cerebral perfusion and control systemic circulation to maintain brain blood flow. Nature Communications, 11(1), 131. This PhD Studentship is funded by the British Heart Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Lactate and hydrogen ions play a predominant role in evoking the exercise pressor reflex during ischaemic contractions but not during freely perfused contractions.

We investigated the role played by lactate and hydrogen in evoking the exercise pressor reflex (EPR) in decerebrated rats whose hindlimb muscles were either freely perfused or ischaemic. Production of lactate and hydrogen by the contracting hindlimb muscles was manipulated by knocking out the myophosphorylase gene (pygm). In knockout rats (pygm-/-; n=13) or wild-type rats (pygm+/+; n=13), the EPR was evoked by isometrically contracting the triceps surae muscles. Blood pressure, tension, blood flow, renal sympathetic nerve activity and blood lactate concentrations were measured. Intramuscular metabolites and pH changes induced by the contractions were quantified by 31P-magnetic resonance spectroscopy (n=5). In a subset of pygm-/- rats (n=5), contractions were evoked with prior infusion of lactate (pH 6.0) in an attempt to restore the effect of lactate and hydrogen ions. Contraction of freely perfused muscles increased blood lactate and decreased muscle pH in pygm+/+ rats only. Despite these differences, the reflex pressor and sympathetic responses to freely perfused contraction did not differ between groups (P=0.992). During ischaemia, contraction increased muscle lactate and hydrogen ion production in pygm+/+ rats (P<0.0134), whereas it had no effect in pygm-/- rats (P>0.783). Likewise, ischaemia exaggerated the reflex pressor, and sympathetic responses to contraction in pygm+/+ but not in pygm-/- rats. This exaggeration was restored when a solution of lactate (pH 6.0) was infused prior to the contraction in pygm-/- rats. We conclude that lactate and hydrogen accumulation in contracting myocytes play a key role in evoking the metabolic component of the EPR during ischaemic but not during freely perfused contractions. KEY POINTS: Conflicting results exist about the role played by lactate and hydrogen ions in evoking the exercise pressor reflex. Using CRISP-Cas9, we rendered the myophosphorylase gene non-functional to block the production of lactate and hydrogen ions. The exercise pressor reflex was evoked in decerebrated rats by statically contracting the triceps surae muscles with or without muscle ischaemia. Static contraction elevated the concentration of lactate and hydrogen ions in pygm+/+ but not in pygm-/- rats. Despite these differences, the exercise pressor reflex was not different between groups. Acute muscle ischaemia exaggerated the concentration of lactate and hydrogen ions in pygm+/+ but not in pygm-/- rats. Likewise, acute muscle ischaemia exaggerated the exercise pressor reflex in pygm+/+ but not in pygm-/- rats. We conclude that lactate and hydrogen play a key role in evoking the exercise pressor reflex during ischaemic but not during freely perfused contractions.

The Effects of Volatile Anesthetics on Renal Sympathetic and Phrenic Nerve Activity during Acute Intermittent Hypoxia in Rats.

Coordinated activation of sympathetic and respiratory nervous systems is crucial in responses to noxious stimuli such as intermittent hypoxia. Acute intermittent hypoxia (AIH) is a valuable model for studying obstructive sleep apnea (OSA) pathophysiology, and stimulation of breathing during AIH is known to elicit long-term changes in respiratory and sympathetic functions. The aim of this study was to record the renal sympathetic nerve activity (RSNA) and phrenic nerve activity (PNA) during the AIH protocol in rats exposed to monoanesthesia with sevoflurane or isoflurane. Adult male Sprague-Dawley rats (n = 24; weight: 280-360 g) were selected and randomly divided into three groups: two experimental groups (sevoflurane group, n = 6; isoflurane group, n = 6) and a control group (urethane group, n = 12). The AIH protocol was identical in all studied groups and consisted in delivering five 3 min-long hypoxic episodes (fraction of inspired oxygen, FiO2 = 0.09), separated by 3 min recovery intervals at FiO2 = 0.5. Volatile anesthetics, isoflurane and sevoflurane, blunted the RSNA response to AIH in comparison to urethane anesthesia. Additionally, the PNA response to acute intermittent hypoxia was preserved, indicating that the respiratory system might be more robust than the sympathetic system response during exposure to acute intermittent hypoxia.

GLP-1 in the Hypothalamic Paraventricular Nucleus Promotes Sympathetic Activation and Hypertension.

Glucagon-like peptide-1 (GLP-1) and its analogs are widely used for diabetes treatment. The paraventricular nucleus (PVN) is crucial for regulating cardiovascular activity. This study aims to determine the roles of GLP-1 and its receptors (GLP-1R) in the PVN in regulating sympathetic outflow and blood pressure. Experiments were carried out in male normotensive rats and spontaneously hypertensive rats (SHR). Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. GLP-1 and GLP-1R expressions were present in the PVN. PVN microinjection of GLP-1R agonist recombinant human GLP-1 (rhGLP-1) or EX-4 increased RSNA and MAP, which were prevented by GLP-1R antagonist exendin 9-39 (EX9-39) or GLP-1R antagonist 1, superoxide scavenger tempol, antioxidant N-acetylcysteine, NADPH oxidase (NOX) inhibitor apocynin, adenylyl cyclase (AC) inhibitor SQ22536 or protein kinase A (PKA) inhibitor H89. PVN microinjection of rhGLP-1 increased superoxide production, NADPH oxidase activity, cAMP level, AC, and PKA activity, which were prevented by SQ22536 or H89. GLP-1 and GLP-1R were upregulated in the PVN of SHR. PVN microinjection of GLP-1 agonist increased RSNA and MAP in both WKY and SHR, but GLP-1 antagonists caused greater effects in reducing RSNA and MAP in SHR than in WKY. The increased superoxide production and NADPH oxidase activity in the PVN of SHR were augmented by GLP-1R agonists but attenuated by GLP-1R antagonists. These results indicate that activation of GLP-1R in the PVN increased sympathetic outflow and blood pressure via cAMP-PKA-mediated NADPH oxidase activation and subsequent superoxide production. GLP-1 and GLP-1R upregulation in the PVN partially contributes to sympathetic overactivity and hypertension.

LncTCONS_00058568 is involved in the pathophysiologic processes mediated by P2X7R in the lower thoracic spinal cord after acute kidney injury.

Acute kidney injury (AKI), a prevalent clinical syndrome, involves the participation of the nervous system in neuroimmune regulation. However, the intricate molecular mechanism that governs renal function regulation by the central nervous system (CNS) is complex and remains incompletely understood. In the present study, we found that the upregulated expression of lncTCONS_00058568 in lower thoracic spinal cord significantly ameliorated AKI-induced renal tissue injury, kidney morphology, inflammation and apoptosis, and suppressed renal sympathetic nerve activity. Mechanistically, the purinergic ionotropic P2X7 receptor (P2X7R) was overexpressed in AKI rats, whereas lncTCONS_00058568 was able to suppress the upregulation of P2X7R. In addition, RNA sequencing data revealed differentially expressed genes associated with nervous system inflammatory responses after lncTCONS_00058568 was overexpressed in AKI rats. Finally, the overexpression of lncTCONS_00058568 inhibited the activation of PI3K/Akt and NF-κB signaling pathways in spinal cord. Taken together, the results from the present study show that lncTCONS_00058568 overexpression prevented renal injury probably by inhibiting sympathetic nerve activity mediated by P2X7R in the lower spinal cord subsequent to I/R-AKI.

Early Renal Denervation Attenuates Cardiac Dysfunction in Heart Failure With Preserved Ejection Fraction.

The renal sympathetic nervous system modulates systemic blood pressure, cardiac performance, and renal function. Pathological increases in renal sympathetic nerve activity contribute to the pathogenesis of heart failure with preserved ejection fraction (HFpEF). We investigated the effects of renal sympathetic denervation performed at early or late stages of HFpEF progression. Male ZSF1 obese rats were subjected to radiofrequency renal denervation (RF-RDN) or sham procedure at either 8 weeks or 20 weeks of age and assessed for cardiovascular function, exercise capacity, and cardiorenal fibrosis. Renal norepinephrine and renal nerve tyrosine hydroxylase staining were performed to quantify denervation following RF-RDN. In addition, renal injury, oxidative stress, inflammation, and profibrotic biomarkers were evaluated to determine pathways associated with RDN. RF-RDN significantly reduced renal norepinephrine and tyrosine hydroxylase content in both study cohorts. RF-RDN therapy performed at 8 weeks of age attenuated cardiac dysfunction, reduced cardiorenal fibrosis, and improved endothelial-dependent vascular reactivity. These improvements were associated with reductions in renal injury markers, expression of renal NLR family pyrin domain containing 3/interleukin 1β, and expression of profibrotic mediators. RF-RDN failed to exert beneficial effects when administered in the 20-week-old HFpEF cohort. Our data demonstrate that early RF-RDN therapy protects against HFpEF disease progression in part due to the attenuation of renal fibrosis and inflammation. In contrast, the renoprotective and left ventricular functional improvements were lost when RF-RDN was performed in later HFpEF progression. These results suggest that RDN may be a viable treatment option for HFpEF during the early stages of this systemic inflammatory disease.

Inhibition and potentiation of the exercise pressor reflex by pharmacological modulation of TRPC6 in male rats.

We determined the role played by the transient receptor potential canonical 6 (TRPC6) channel in evoking the mechanical component of the exercise pressor reflex in male decerebrated Sprague-Dawley rats. TRPC6 channels were identified by quadruple-labelled (DiI, TRPC6, neurofilament-200 and peripherin) immunohistochemistry in dorsal root ganglion (DRG) cells innervating the triceps surae muscles (n=12). The exercise pressor reflex was evoked by statically contracting the triceps surae muscles before and after injection of the TRPC6 antagonist BI-749327 (n=11; 12μgkg-1 ) or SAR7334 (n=11; 7μgkg-1 ) or the TRPC6 positive modulator C20 (n=11; 18μgkg-1 ). Similar experiments were conducted while the muscles were passively stretched (n=8-12), a manoeuvre that isolated the mechanical component of the reflex. Blood pressure, tension, renal sympathetic nerve activity (RSNA) and blood flow were recorded. Of the DRG cells innervating the triceps surae muscles, 85% stained positive for the TRPC6 antigen, and 45% of those cells co-expressed neurofilament-200. Both TRPC6 antagonists decreased the reflex pressor responses to static contraction (-32 to -42%; P < 0.05) and to passive stretch (-35 to -52%; P < 0.05), whereas C20 increased these responses (55-65%; P < 0.05). In addition, BI-749327 decreased the peak and integrated RSNA responses to both static contraction (-39 to -43%; P < 0.05) and passive stretch (-56 to -62%; P < 0.05), whereas C20 increased the RSNA to passive stretch only. The onset latency of the decrease or increase in RSNA occurred within 2s of the onset of the manoeuvres (P < 0.05). Collectively, our results show that TRPC6 plays a key role in evoking the mechanical component of the exercise pressor reflex. KEY POINTS: The exercise pressor reflex plays a key role in the sympathetic and haemodynamic responses to exercise. This reflex is composed of two components, namely the mechanoreflex and the metaboreflex. The receptors responsible for evoking the mechanoreflex are poorly documented. A good candidate for this function is the transient receptor potential canonical 6 (TRPC6) channel, which is activated by mechanical stimuli and expressed in dorsal root ganglia of rats. Using two TRPC6 antagonists and one positive modulator, we investigated the role played by TRPC6 in evoking the mechanoreflex in decerebrated rats. Blocking TRPC6 decreased the renal sympathetic and the pressor responses to both contraction and stretch, the latter being a manoeuvre that isolates the mechanoreflex. In contrast, the positive modulator increased the pressor reflex to contraction and stretch, in addition to the sympathetic response to stretch. Our results provide strong support for a role played by the TRPC6 channel in evoking the mechanoreflex.

Chronic Intermittent Hypobaric Hypoxia Reduces Hypothalamic N-Methyl-d-Aspartate Receptor Activity and Sympathetic Outflow in Spontaneously Hypertensive Rats.

Guo, Xinqi, Hongyu Ma, Ziye Cui, Qiyue Zhao, Ying Zhang, Lu Jia, Liping Zhang, Hui Guo, Xiangjian Zhang, Yi Zhang, Yue Guan, and Huijie Ma. Chronic intermittent hypobaric hypoxia reduces hypothalamic N-Methyl-d-Aspartate Receptor activity and sympathetic outflow in spontaneously hypertensive rats. High Alt Med Biol. 25:77-88, 2024. Objective: This study aims to determine the role of hypothalamic renin-angiotensin system (RAS) in the antihypertensive effect of chronic intermittent hypobaric hypoxia (CIHH). Methods: Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) received 35 days of hypobaric hypoxia simulating an altitude of 4,000 m, 5 h/day. The levels of RAS, blood pressure, and N-methyl-d-aspartate receptor (NMDAR) activities of hypothalamic paraventricular nucleus (PVN) presympathetic neurons from each group of rats were determined. Results: The systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure (MAP) of SHRs significantly decreased from the third week of CIHH treatment. This blood pressure reduction effect could be maintained for at least 2 weeks after stopping the CIHH treatment. CIHH treatment also attenuated the decrease in MAP and renal sympathetic nerve activity induced by hexamethonium administration in SHRs, but not in WKY rats. Furthermore, CIHH reversed the increase in serum angiotensin (Ang)II concentration and the expression of PVN angiotensin-converting enzyme (ACE) and AngII type 1 (AT1) receptors, as well as the decrease in serum Ang1-7 concentration and the expression of PVN ACE2 and Mas receptors in SHRs. In addition, the administration of CIHH resulted in a reduction in the frequency of miniature excitatory postsynaptic currents and amplitude of NMDAR current in PVN presympathetic neurons of SHRs, which means that CIHH decreased the pre- and postsynaptic NMDAR activity of PVN presympathetic neurons in SHRs. However, pretreatment with A779 (a Mas receptor blocker) or AngII abrogated the above effects. Meanwhile, Ang1-7 pretreatment mimicked the CIHH effect on pre- and postsynaptic NMDAR activity of presympathetic neurons in SHRs. Conclusions: Our data indicate that CIHH reduces pre- and postsynaptic NMDAR activity of PVN presympathetic neurons, sympathetic outflow, and blood pressure by decreasing the activity of the ACE/AngII/AT1 axis and increasing the activity of ACE2/Ang1-7/Mas axis in the hypothalamus in hypertension.

Dynamic changes in renal sodium handling during sympathetic stimulation in healthy human males

The temporal response of changes in renal sodium reabsorption during increased renal sympathetic nerve activity has not been investigated. Central hypovolemia by application of lower-body negative-pressure (LBNP) elicits baroreceptor mediated sympathetic reflexes to maintain arterial blood pressure. We hypothesized, that during 90 min LBNP, the renal sodium retention would increase rapidly, remain increased during intervention, and return to baseline immediately after end of intervention. Methods30 young, healthy, sodium loaded, non-obese males were exposed to −15 mmHg LBNP, −30 mmHg LBNP, −15 mmHg LBNP + renin blockade or time-control (0 mmHg LBNP) for 90 min. Urine was collected every 15 min during 90 min of intervention and 60 min of recovery to identify a possible relation between time of intervention and renal response. ResultsAll intervention groups exhibited a comparable reduction in distal sodium excretion at the end of the intervention (P = 0.46 between groups; −15 mmHg: −3.1 ± 0.9 %, −30 mmHg: −2.9 ± 0.6 %, −15 mmHg + aslikiren: −1.8 ± 0.6 %). −15 mmHg+Aliskiren resulted in a slower onset, but all groups exhibited a continued reduction in sodium excretion after 1 h of recovery despite return to baseline of renin, aldosterone, diuresis and cardiovascular parameters. ConclusionSympathetic stimulation for 90 min via LBNP at −30 mmHg LBNP compared to −15 mmHg did not result in a greater response in fractional Na+ excretion, suggesting that additional baroreceptor unloading did not cause further increases in renal sodium reabsorption. Changes in distal Na+ excretion were linear with respect to time (dose) of intervention, but seem to exhibit a saturation-like effect at a level around 4 %. The lack of recovery after 1 h is also a new finding that warrants further investigation.

A Novel Method for the Analysis of Renal Sympathetic Nerve Activity (RSNA) from Multi-Fiber Nerve Recordings

A Novel Method for the Analysis of Renal Sympathetic Nerve Activity (RSNA) from Multi-Fiber Nerve Recordings

M6A methyltransferase METTL3 contributes to sympathetic hyperactivity post-MI via promoting TRAF6-dependent mitochondrial ROS production

ObjectivesN6-methyladenosine (m6A) is the most prevalent post-translational modification in eukaryotic mRNA. Recently, m6A editing modified by methyltransferase-like enzyme 3 (METTL3), the core m6A methyltransferase, has been demonstrated to be involved in cardiac sympathetic hyperactivity. This study aimed to clarify the effects and underlying mechanisms of METTL3 in the paraventricular nucleus (PVN) in mediating sympathetic activity following myocardial infarction (MI). MethodsWe established rat MI models by left anterior descending coronary artery ligation. m6A quantification was performed.The expression of METTL3 and its downstream gene, tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), were determined. The functional role of METTL3 in sympathetic hyperactivity and electrical conduction stability were verified by assessing renal sympathetic nerve activity (RSNA), norepinephrine (NE) levels, and programmed electrical stimulation. Rescue experiments were also conducted. The mechanism by which m6A is involved in mitochondrial reactive oxygen species (mROS) production, mediated by TRAF6/ECSIT pathway, was explored in lipopolysaccharide (LPS) treated primary microglial cells. ResultsMETTL3 was predominantly localized in the microglia and significantly increased within the PVN at 3 days post-MI. Inhibition of METTL3 decreased m6A levels, TRAF6 expression, and mROS production; downregulated sympathoexcitation, indicated by attenuated NE concentration and RSNA; decreased the incidence of ventricular tachycardia or fibrillation; and improved cardiac function. Mechanistically, downregulation of METTL3 prevented TRAF6 translocation to the mitochondria in the microglia and subsequent TRAF6/ECSIT pathway activation, resulting in decreased mROS production. ConclusionsThis study demonstrates that METTL3-mediated m6A modification promotes sympathetic hyperactivity through TRAF6/ECSIT pathway and mitochondrial oxidative stress in the PVN, thereby leading to ventricular arrhythmias post-MI.