Depressor Response Research Articles

Differential contributions of cardiac, coronary and pulmonary artery vagal mechanoreceptors to reflex control of the circulation.

Distinct populations of stretch‐sensitive mechanoreceptors attached to myelinated vagal afferents are found in the heart and adjoining coronary and pulmonary circulations. Receptors at atrio‐venous junctions appear to be involved in control of intravascular volume. These atrial receptors influence sympathetic control of the heart and kidney, but contribute little to reflex control of systemic vascular resistance. Baroreceptors at the origins of the coronary circulation elicit reflex vasodilatation, like feedback control from systemic arterial baroreceptors, as well as having characteristics that could contribute to regulation of mean pressure. In contrast, feedback from baroreceptors in the pulmonary artery and bifurcation is excitatory and elicits a pressor response. Elevation of pulmonary arterial pressure resets the vasomotor limb of the systemic arterial baroreflex, which could be relevant for control of sympathetic vasoconstrictor outflow during exercise and other states associated with elevated pulmonary arterial pressure. Ventricular receptors, situated mainly in the inferior posterior wall of the left ventricle, and attached to unmyelinated vagal afferents, are relatively inactive under basal conditions. However, a change to the biochemical environment of cardiac tissue surrounding these receptors elicits a depressor response. Some ventricular receptors respond, modestly, to mechanical distortion. Probably, ventricular receptors contribute little to tonic feedback control; however, reflex bradycardia and hypotension in response to chemical activation may decrease the work of the heart during myocardial ischaemia. Overall, greater awareness of heterogeneous reflex effects originating from cardiac, coronary and pulmonary artery mechanoreceptors is required for a better understanding of integrated neural control of circulatory function and arterial blood pressure.

Chemogenetic inhibition of Phox2-expressing neurons in the commissural NTS decreases blood pressure in anesthetized spontaneously hypertensive rats

Interruption of the activity of neurons in the commissural portion of the nucleus of the solitary tract (cNTS) decreases blood pressure (BP) in experimental models of hypertension, such as the spontaneously hypertensive (SH) rat. To examine whether PHOX2B expressing cNTS neurons are involved in maintaining the elevated BP, we used replication-deficient viruses with a modified Phox2 binding site promoter to express the inhibitory chemogenetic allatostatin receptor or green fluorescent protein in the cNTS. Following administration of allatostatin, we observed a depressor and bradycardic response in anesthetized SH rats that expressed the allatostatin receptor. Injection of allatostatin did not affect BP or heart rate (HR) in control SH rats expressing green fluorescent protein in the cNTS. Immunohistochemistry showed that the majority of transduced cNTS neurons were PHOX2B-immunoreactive and some also expressed tyrosine hydroxylase. We conclude that in anesthetized SH rat, the Phox2B expressing cNTS neurons maintain elevated BP.

Neurogenic Hypotension and Bradycardia Modulated by Electroacupuncture in Hypothalamic Paraventricular Nucleus.

Electroacupuncture (EA) stimulates somatic median afferents underlying P5-6 acupoints and modulates parasympathoexcitatory reflex responses through central processing in the brainstem. Although decreases in blood pressure and heart rate by the neural-mediated Bezold-Jarisch reflex responses are modulated by EA through opioid actions in the nucleus tractus solitarius and nucleus ambiguus, the role of the hypothalamus is unclear. The hypothalamic paraventricular nucleus (PVN) is activated by sympathetic afferents and regulates sympathetic outflow and sympathoexcitatory cardiovascular responses. In addition, the PVN is activated by vagal afferents, but little is known about its regulation of cardiopulmonary inhibitory hemodynamic responses. We hypothesized that the PVN participates in the Bezold-Jarisch reflex responses and EA inhibits these cardiopulmonary responses through the PVN opioid system. Rats were anesthetized and ventilated, and their heart rate and blood pressures were monitored. Application of phenylbiguanide every 10 min close to the right atrium induced consistent depressor and bradycardia reflex responses. Unilateral microinjection of the depolarization blockade agent kainic acid or glutamate receptor antagonist kynurenic acid in the PVN reduced these reflex responses. In at least 70% of the rats, 30 min of bilateral EA at P5-6 acupoints reduced the depressor and bradycardia responses for at least 60 min. Blockade of the CCK-1 receptors converted the non-responders into EA-responders. Unilateral PVN-microinjection with naloxone reversed the EA inhibition. Vagal-evoked activity of the PVN cardiovascular neurons was reduced by 30 min EA (P5-6) through opioid receptor activation. These data indicate that PVN processes inhibitory cardiopulmonary reflexes and participates in EA-modulation of the neural-mediated vasodepression and bradycardia.

Renal Nerve Activity and Arterial Depressor Responses Induced by Neuromodulation of the Deep Peroneal Nerve in Spontaneously Hypertensive Rats.

Hypertension is a main cause of death in the United States with more than 103 million adults affected. While pharmacological treatments are effective, blood pressure (BP) remains uncontrolled in 50–60% of resistant hypertensive subjects. Using a custom-wired miniature electrode, we previously reported that deep peroneal nerve stimulation (DPNS) elicited acute cardiovascular depressor responses in anesthetized spontaneously hypertensive rats (SHRs). Here, we further study this effect by implementing a wireless system and exploring different stimulation parameters to achieve a maximum depressor response. Our results indicate that DPNS consistently induces a reduction in BP and suggests that renal sympathetic nerve activity (RSNA) is altered by this bioelectronic treatment. To test the acute effect of DPNS in awake animals, we developed a novel miniaturized wireless microchannel electrode (w-μCE), with a Z-shaped microchannel through which the target nerves slide and lock into the recording/stimulation chamber. Animals implanted with w-μCE and BP telemetry systems for 3 weeks showed an average BP of 150 ± 14 mmHg, which was reduced significantly by an active DPNS session to 135 ± 8 mmHg (p < 0.04), but not in sham-treated animals. The depressor response in animals with an active w-μCE was progressively returned to baseline levels 14 min later (164 ± 26 mmHg). This depressor response was confirmed in restrained fully awake animals that received DPNS for 10 days, where tail-cuff BP measurements showed that systolic BP in SHR lowered 10% at 1 h and 16% 2 h after the DPNS when compared to the post-implantation baseline. Together, these results support the use of DPN neuromodulation as a possible strategy to lower BP in drug-resistant hypertension.

Deletion of the Transient Receptor Vanilloid‐1 (TRPV1) Channel in Rats Attenuates 2‐Kidney‐1‐Clip Hypertension

Renal denervation lowers arterial blood pressure (ABP) in both clinical populations and multiple experimental models of hypertension. This therapeutic effect is partly attributed to the removal of overactive renal sensory nerves that increase sympathetic efferent activity and ABP. Renal sensory nerves highly express TRPV1 channels, and administration of the TRPV1 agonist capsaicin increases renal sensory nerve activity. However, the extent by which TRPV1 channels directly contribute to renal nerve dependent models of hypertension has not been tested. To test this hypothesis, we generated a novel Trpv1‐/‐ rat using CRISPR/Cas9 and deletion of exon 3. Male and female Trpv1‐/‐ and wild‐type littermates (8‐12 weeks) were instrumented with telemetry. At 2 weeks later, renovascular hypertension via renal stenosis was produced by placement of a PTFE cuff (0.16 x 0.22 inches, 1mm long) around the right renal artery. Male Trpv1‐/‐ and wild‐type rats had no differences in baseline mean ABP (99±2 vs 98±3 mmHg, respectively; n=7‐9) or heart rate (390±7 vs 400±8 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, mean ABP was significantly lower at Day 28 in male Trpv1‐/‐ versus wild‐type rats (125±8 vs 155±2 mmHg, respectively: P&lt;0.01). Ganglionic blockade with chlorisondamine (2.5mg/kg, sc) at Day 28 produced a smaller fall in mean ABP of male Trpv1‐/‐ versus wild‐type rats (‐53±4 vs ‐86±3 mmHg, respectively; P&lt;0.001). On the other hand, female Trpv1‐/‐ and wild‐type rats had no differences in baseline mean ABP (102±2 vs 104±1 mmHg, respectively; n=6‐9) or heart rate (419±8 vs 410±7 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, there were no differences at Day 28 between female Trpv1‐/‐ versus wild‐type rats (117±8 vs 122±6 mmHg, respectively). Moreover, the increase in mean ABP was smaller in females versus males. The ganglionic blocker chlorisondamine produced similar depressor responses in female Trpv1‐/‐ versus wild‐type rats (‐64±7 vs ‐65±7 mmHg, respectively). These findings illustrate a sex difference in renovascular hypertension in rats, but importantly indicate that Trpv1‐/‐ channels contribute to the established phase of renovascular hypertension in male rats.

Angiotensin II Type 1 Receptor‐Mediated Hypothalamic Paraventricular Nucleus Neuroinflammation And Blood Brain Barrier Disruption Contribute To Age‐Dependent Hypertension In Male, But Not Female, Sprague Dawley Rats

AimAging is a risk factor for the development of hypertension. Recently, neuroinflammation in cardio‐regulatory centers of the brain, specifically the hypothalamic paraventricular nucleus (PVN), has been identified as a potential driver of hypertension via sympathetically‐mediated mechanisms. We hypothesize neuroinflammatory mechanisms contribute to the progression of age‐dependent hypertension.MethodsIn male (M) Sprague Dawley (SD) rats aged 3, 8, and 16 months old (MO) and female (F) SD rats aged 3 and 16 MO femoral artery cannulation was used to measure mean arterial pressure (MAP; mmHg) and assess sympathetic tone to the vasculature (ΔMAP; mmHg) via depressor response to ganglionic blockade (i.v. hexamethonium 30 mg/kg). Global sympathetic tone was assessed as plasma norepinephrine (nmol/L) via ELISA. Blood brain barrier (BBB) dysfunction in the PVN was assessed via PVN FITC extravasation following co‐infusion of FITC‐Dextran (10 kDa) and rhodamine B isothiocyanate‐Dextran (70 kDa). Immunohistochemistry was performed in male rats only for microglia (CD11b/c), astrocytes (GFAP), interleukin 6 (IL‐6) and tumor necrosis factor‐alpha (TNF‐α) in the PVN. MAP, assessments of sympathetic tone, BBB dysfunction, and microglia and astrocyte activity were also measured in 16 MO M rats treated with subcutaneous (s.c.) losartan, an Angiotensin II Type 1 Receptor (AT1R) antagonist, for 21 days (s.c. 3 mg/kg/day; N=6/group).ResultsM, but not F, SD rats develop age‐dependent hypertension (MAP [mmHg] 3 MO M 124±4, 8 MO M 138±5, 16 MO M 153±5, p&lt;0.05; 3 MO F 132±5, 16 MO F 133±4), increased vascular sympathetic tone (ΔMAP to hexamethonium [mmHg] 3 MO M ‐34±7, 8 MO M ‐68±5, 16 MO M ‐60±9, p&lt;0.05; 3 MO F ‐36±8, 16 MO F ‐34±8) and increased global sympathetic tone (Plasma NE [nmol/L] 3 MO M 39±6, 8 MO M 44±8, 16 MO M 58±9, p&lt;0.05; 3 MO F 44±6, 16 MO F 46±7). In M rats only, BBB dysfunction occurs at 8 MO and 16 MO‐ F rats do not exhibit BBB disruption with age (% FITC extravasation [% area] 3 MO M 1.5±1.0, 8 MO M 9.4±1.3, 16 MO M 9.8±2.6, p&lt;0.05; 3 MO F 1.3±0.6, 16 MO F 2.67±1.37). Further, 16 MO M rats exhibit significant neuroinflammation indicated by increased astrocyte reactivity and microglial activation, and increased IL‐6 and TNF‐α expression in the PVN. Following losartan administration in 16 MO M rats, there is a significant decrease in MAP, vascular and global sympathetic tone. BBB disruption is attenuated and neuroinflammation is ameliorated following losartan treatment as shown by a decrease in microglial activation and astrocytic reactivity.ConclusionsAge‐dependent hypertension develops in a sex‐dependent manner in the SD rat, potentially due to a protective effect of female sex steroids. Amelioration of neuroinflammation and reduction of BBB disruption via AT1R antagonism attenuates hypertension, vascular tone and global sympathetic outflow in an age‐dependent manner in male rats. These results indicate that PVN neuroinflammation modulates sympathetic nervous system activity and age‐related control of blood pressure in male rats potentially by an AT1R‐mediated mechanism.

Protein Restriction in the Peri-Pubertal Period Induces Autonomic Dysfunction and Cardiac and Vascular Structural Changes in Adult Rats.

Perturbations to nutrition during critical periods are associated with changes in embryonic, fetal or postnatal developmental patterns that may render the offspring more likely to develop cardiovascular disease in later life. The aim of this study was to evaluate whether autonomic nervous system imbalance underpins in the long-term hypertension induced by dietary protein restriction during peri-pubertal period. Male Wistar rats were assigned to groups fed with a low protein (4% protein, LP) or control diet (20.5% protein; NP) during peri-puberty, from post-natal day (PN) 30 until PN60, and then all were returned to a normal protein diet until evaluation of cardiovascular and autonomic function at PN120. LP rats showed long-term increased mean arterial pressure (p = 0.002) and sympathetic arousal; increased power of the low frequency (LF) band of the arterial pressure spectral (p = 0.080) compared with NP animals. The depressor response to the ganglion blocker hexamethonium was increased in LP compared with control animals (p = 0.006). Pulse interval variability showed an increase in the LF band and LF/HF ratio (p = 0.062 and p = 0.048) in LP animals. The cardiac response to atenolol and/or methylatropine and the baroreflex sensitivity were similar between groups. LP animals showed ventricular hypertrophy (p = 0.044) and increased interstitial fibrosis (p = 0.028) compared with controls. Reduced protein carbonyls (PC) (p = 0.030) and catalase activity (p = 0.001) were observed in hearts from LP animals compared with control. In the brainstem, the levels of PC (p = 0.002) and the activity of superoxide dismutase and catalase (p = 0.044 and p = 0.012) were reduced in LP animals, while the levels of GSH and total glutathione were higher (p = 0.039 and p = 0.038) compared with NP animals. Protein restriction during peri-pubertal period leads to hypertension later in life accompanied by sustained sympathetic arousal, which may be associated with a disorganization of brain and cardiac redox state and structural cardiac alteration.

Ah-type Baroreceptor Neurons Expressing Estrogen Dependent mGluR7 Mediate Descending Inhibition of Cardiac Nociception

Silent myocardial infarction (MI) is critical for clinical practice with increasing risk for women and the cause remains a medical mystery. Upon the discovery of female-specific Ah-type baroreceptor neurons (BRNs), we hypothesize that glutamate mediates depressor response through afferent-specific expression of particular glutamate receptors (mGluRs) leading descending inhibition of cardiac nociception. In vivo, tail-flick reflex and electromyography were assessed to evaluate glutamate-mediated blood pressure regulation, peripheral and cardiac nociception. The results showed that glutamate decreased mean arterial pressure (MAP) and increased peripheral nociception. Interestingly, glutamate-mediated capsaicin-induced cardiac nociception was strongly reduced in female rats compared with males. Furthermore, Nodose (NG) microinjection of mGluR7 agonist significantly increased MAP in males and slightly decreased that in females. Even though mGluR8 direct activation intensified baroreceptor activation, the sensitivity was similar between sexes. In vitro, the expression profiles of mGluRs were investigated using Western blot and identified BRNs using single-cell qRT-PCR under ischemic conditions. Glutamate in serum, NG and nucleus tractus solitary (NTS) was raised significantly in the model rats of both sexes vs. sham-controls. Female-specific expression of mGluR7 in the baroreflex afferent pathway, especially higher expression in Ah-type BRNs, contributes significantly to cardiac analgesia, which may explain that the pathogenesis of silent MI occurs mainly in female patients. Therefore, higher expression of mGluR7 in female-specific subpopulation of Ah-type BRNs plays a critical role in cardiac analgesia and peripheral nociception.

Prostaglandin F 2α evokes vasoconstrictor and vasodepressor activities that are both independent of the F prostanoid receptor

The F prostanoid receptor (FP), which accounts for the therapeutic effect of PGF2α in uterine atony that leads to postpartum hemorrhage and maternal morbidity, could possibly mediate vasoconstrictor effect in small or resistance arteries to elevate blood pressure that limits the clinical use of the agent in patients with cardiovascular disorders. This study aimed to test the above hypothesis with genetically altered mice. Ex vivo and in vivo experiments were performed on control wild-type (WT) mice and mice with deficiencies in FP (FP-/- ) or thromboxane (Tx)-prostanoid receptor (the original receptor of TxA2 ; TP-/- ), and/or those with an additional deficiency in E prostanoid receptor-3 (one of the vasoconstrictor receptors of PGE2 ; EP3-/- ). Here, we show that PGF2α indeed evoked vasoconstrictor responses in the above-mentioned tissues of WT mice, which were however unaltered by FP-/- . Interestingly, such contractile responses were reversed into dilations by TP-/- /EP3-/- . A similar pattern of results was observed with the pressor effect of PGF2α under in vivo conditions. However, TP-/- alone (which could largely remove the contractile responses) did not result in relaxation to PGF2α . Also, either the ex vivo vasodilator effect or the in vivo depressor response of PGF2α obtained after the removal of TP and EP3-mediated actions was unaltered by FP-/- . Therefore, both the ex vivo vasoconstrictor action in small or resistance arteries and the systemic pressor effect of PGF2α can reflect vasoconstrictor activities derived from the non-FP receptors TP and EP3 outweighing a concurrently activated dilator effect, which is again independent of FP.

A Novel Organ-Specific Approach to Selectively Target Sensory Afferents Innervating the Aortic Arch.

The brain maintains cardiovascular homeostasis, in part, via the arterial baroreflex which senses changes in blood pressure (BP) at the level of the aortic arch. Sensory afferents innervating the aortic arch employ baroreceptors to convert stretch exerted on the arterial wall into action potentials carried by the vagus nerve to second order neurons residing within the nucleus of the solitary tract (NTS). Although the baroreflex was described more than 80 years ago, the specific molecular, structural, and functional phenotype of the baroreceptors remain uncharacterized. This is due to the lack of tools that provide the genetic and target organ specificity that is required to selectively characterize baroreceptor afferents. Here, we use a novel approach to selectively target baroreceptors. Male mice on a C57BL/6J background were anesthetized with isoflurane, intubated, and artificially ventilated. Following sternotomy, the aortic arch was exposed, and a retrograde adeno-associated virus was applied to the aortic arch to direct the expression of channelrhoropsin-2 (ChR2) and/or tdTomato (tdTom) to sensory afferents presumably functioning as baroreceptors. Consistent with the structural characteristics of arterial baroreceptors, robust tdTom expression was observed in nerve endings surrounding the aortic arch, within the fibers of the aortic depressor and vagus nerves, cell bodies of the nodose ganglia (NDG), and neural projections to the caudal NTS (cNTS). Additionally, the tdTom labeled cell bodies within the NDG also expressed mRNAs coding for the mechanically gated ion channels, PIEZO-1 and PIEZO-2. In vitro electrophysiology revealed that pulses of blue light evoked excitatory post-synaptic currents in a subset of neurons within the cNTS, suggesting a functional connection between the labeled aortic arch sensory afferents and second order neurons. Finally, the in vivo optogenetic stimulation of the cell bodies of the baroreceptor expressing afferents in the NDG produced robust depressor responses. Together, these results establish a novel approach for selectively targeting sensory neurons innervating the aortic arch. This approach may be used to investigate arterial baroreceptors structurally and functionally, and to assess their role in the etiology or reversal of cardiovascular disease.

Estrogen-dependent depressor response of melatonin via baroreflex afferent function and intensification of PKC-mediated Nav1.9 activation.

Recent studies suggest that melatonin (Mel) plays an important role in the regulation of blood pressure (BP) via the aortic baroreflex pathway. In this study, we investigated the interaction between the baroreflex afferent pathway and Mel-mediated BP regulation in rats under physiological and hypertensive conditions. Mel (0.1, 0.3, and 1.0 mg/mL) was microinjected into the nodose ganglia (NG) of rats. We showed that Mel-induced reduction of mean arterial pressure in female rats was significantly greater than that in male and in ovariectomized rats under physiological condition. Consistently, the expression of Mel receptors (MTNRs) in the NG of female rats was significantly higher than that of males. In L-NAME-induced hypertensive and spontaneously hypertensive rat models, MTNRs were upregulated in males but downregulated in female models. Interestingly, Mel-induced BP reduction was found in male hypertensive models. In whole-cell recording from identified baroreceptor neurons (BRNs) in female rats, we found that Mel (0.1 μM) significantly increased the excitability of a female-specific subpopulation of Ah-type BRNs by increasing the Nav1.9 current density via a PKC-mediated pathway. Similar results were observed in baroreceptive neurons of the nucleus tractus solitarius, showing the facilitation of spontaneous and evoked excitatory post-synaptic currents in Ah-type neurons. Collectively, this study reveals the estrogen-dependent effect of Mel/MTNRs under physiological and hypertensive conditions is mainly mediated by Ah-type BRNs, which may provide new theoretical basis and strategies for the gender-specific anti-hypertensive treatment in clinical practice.

Effect of hyperphosphatemia on impairment of vascular function in adenine-induced renal injury in rats

We reported that vascular function in adenine-induced renal injury rats was impaired mediated by increase in plasma indoxyl sulfate concentration. It is known that hyperphosphatemia leads to calcification and atherosclerosis. In the present study, we examined effect of hyperphosphatemia on vascular dysfunction in adenine-induced renal injury in anesthetized rats. Renal injury was induced by feeding 0.75% adenine diet for 4 weeks. Lanthanum carbonate was treated with gavage after 2 weeks induced adenine. Treatment with lanthanum carbonate significantly decreased in plasma phosphorus concentration in adenine rats. N-nitro-L-arginine (L-NA) potentiated the ACh-induced depressor response in normal-diet. However, L-NA failed to potentiate the response in adenine rats or lanthanum-treated rats. Sodium nitroprusside (SNP)-induced depressor response in adenine rats was significantly smaller than that in normal rats. Lanthanum carbonate tended to recover impairment of SNP-induced depressor responses in adenine rats. These findings suggest that hyperphosphatemia is partially related to impairment of smooth muscle function rather than that of endothelial function in adenine rats.

Bradykinin-mediated estrogen-dependent depressor response by direct activation of female-specific distribution of myelinated Ah-type baroreceptor neurons in rats.

AimTo understand the direct impact of bradykinin in autonomic control of circulation through baroreflex afferent pathway.MethodsThe mean arterial pressure (MAP) was monitored while bradykinin and its agonists were applied via nodose (NG) microinjection, the expression of bradykinin receptors (BRs) in the NG (1st‐order) and nucleus tractus solitarius (NTS, 2nd‐order) were tested in adult male, age‐matched female, and ovariectomized rats under physiological and hypertensive conditions. Additionally, bradykinin‐induced depolarization was also tested in identified baroreceptor and baroreceptive neurons using whole‐cell patch‐clamp technique.ResultsUnder physiological condition, bradykinin‐induced dose‐ and estrogen‐dependent reductions of MAP with lower estimated EC50 in females. B2R agonist mediated more dramatic MAP reduction with long‐lasting effect compared with B1R activation. These functional observations were consistent with the molecular and immunostaining evidences. However, under hypertensive condition, the MAP reduction was significantly less dramatic in N’‐Nitro‐L‐Arginine‐methyl ester (L‐NAME) induced secondary and spontaneous hypertension rats in males compared with female rats. Electrophysiological data showed that bradykinin‐elicited concentration‐dependent membrane depolarization with discharges during initial phase in identified myelinated Ah‐types baroreceptor neurons, not myelinated A‐types; while, higher concentration of bradykinin was required for depolarization of unmyelinated C‐types without initial discharges.ConclusionThese datasets have demonstrated for the first time that bradykinin mediates direct activation of baroreflex afferent function to trigger estrogen‐dependent depressor response, which is due mainly to the direct activation/neuroexcitation of female‐specific myelinated Ah‐type baroreceptor neurons leading to a sexual dimorphism in parasympathetic domination of blood pressure regulation via activation of B2R/B1R expression in baroreflex afferent pathway.

Direct evidence of VEGF-mediated neuroregulation and afferent explanation of blood pressure dysregulation during angiogenic therapy

Abstract Objective Oncocardiology is increasingly hot research field/topic in the clinical management of cancer with anti-angiogenic therapy of vascular endothelial growth factor (VEGF) that may cause cardiovascular toxicity, such as hypertension via vascular dysfunction and attenuation of eNOS/NO signaling in the baroreflex afferent pathway. The aim of the current study was to evaluate the potential roles of VEGF/VEGF receptors (VEGFRs) expressed in the baroreflex afferent pathway in autonomic control of blood pressure (BP) regulation. Methods The distribution and expression of VEGF/VEGFRs were detected in the nodose ganglia (NG) and nucleus of tractus solitary (NTS) using immunostaining and molecular approaches. The direct role of VEGF was tested by NG microinjection under physiological and hypertensive conditions. Results Immunostaining data showed that either VEGF or VEGFR2/VEGFR3 was clearly detected in the NG and NTS of adult male rats. Microinjection of VEGF directly into the NG reduced the mean blood pressure (MBP) dose-dependently, which was less dramatic in renovascular hypertension (RVH) rats, suggesting the VEGF-mediated depressor response by direct activation of the 1st-order baroreceptor neurons in the NG under both normal and disease conditions. Notably, this reduced depressor response in RVH rats was directly caused by the downregulation of VEGFR2, which compensated the up regulation of VEGF/VEGFR3 in the NG during the development of hypertension. Conclusion It demonstrated for the first time that the BP-lowering property of VEGF/VEGFRs signaling via the activation of baroreflex afferent function may be a common target/pathway leading to BP dysregulation in anti-angiogenic therapy.

Dexamethasone attenuates the modulatory effect of the insular cortex on the baroreflex in anesthetized rat.

The arterial baroreflex (BR) is an important neural mechanism for the stabilization of arterial pressure (AP). It is known that the insular cortex (IC) and other parts of the central autonomic network (CAN) are able to modulate the BR arc, altering baroreflex sensitivity (BRS). In addition, the sensitivity of the BR changes under the influence of hormones, in particular glucocorticoids (GCs). It has been suggested that GCs may influence BRS by altering the ability of the IC to modulate the BR. This hypothesis has been tested in experiments on rats anesthetized with urethane. It was found that microelectrostimulation of the visceral area in the left IC causes a short-term drop in AP, which is accompanied by bradycardia and impairs BRS. The synthetic GC dexamethasone (DEX) did not significantly affect the magnitude of depressor responses but increased BRS and impaired the effect of IC stimulation on the BR. The results obtained confirm the hypothesis put forward and suggest that GC can attenuate the inhibitory effects of the IC on the BR arc, thereby enhancing the sensitivity of the BR.

Epididymal Fat-Derived Sympathoexcitatory Signals Exacerbate Neurogenic Hypertension in Obese Male Mice Exposed to Early Life Stress.

[Figure: see text].

Tempol Reverses the Negative Effects of Morphine on Arterial Blood-Gas Chemistry and Tissue Oxygen Saturation in Freely-Moving Rats.

We have reported that pretreatment with the clinically approved superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), blunts the cardiorespiratory depressant responses elicited by a subsequent injection of fentanyl, in halothane-anesthetized rats. The objective of the present study was to determine whether Tempol is able to reverse the effects of morphine on arterial blood-gas (ABG) chemistry in freely-moving Sprague Dawley rats. The intravenous injection of morphine (10 mg/kg) elicited substantial decreases in pH, pO2 and sO2 that were accompanied by substantial increases in pCO2 and Alveolar-arterial gradient, which results in diminished gas-exchange within the lungs. Intravenous injection of a 60 mg/kg dose of Tempol 15 min after the injection of morphine caused minor improvements in pO2 and pCO2 but not in other ABG parameters. In contrast, the 100 mg/kg dose of Tempol caused an immediate and sustained reversal of the negative effects of morphine on arterial blood pH, pCO2, pO2, sO2 and Alveolar-arterial gradient. In other rats, we used pulse oximetry to determine that the 100 mg/kg dose of Tempol, but not the 60 mg/kg dose elicited a rapid and sustained reversal of the negative effects of morphine (10 mg/kg, IV) on tissue O2 saturation (SpO2). The injection of morphine caused a relatively minor fall in mean arterial blood pressure that was somewhat exacerbated by Tempol. These findings demonstrate that Tempol can reverse the negative effects of morphine on ABG chemistry in freely-moving rats paving the way of structure-activity and mechanisms of action studies with the host of Tempol analogues that are commercially available.

A method to evaluate dynamic cerebral pressure-flow relationships in the conscious rat.

The classic dogma of cerebral autoregulation is that cerebral blood flow is steadily maintained across a wide range of perfusion pressures. This has been challenged by recent studies suggesting little to no "autoregulatory plateau" in the relationship between cerebral blood flow and blood pressure (BP). Therefore, the mechanisms underlying the cerebral pressure-flow relationship still require further understanding. Here, we present a novel approach to examine dynamic cerebral autoregulation in conscious Wistar rats (n = 16) instrumented to measure BP and internal carotid blood flow (iCBF), as an indicator of cerebral blood flow. Transient reductions in BP were induced by occluding the vena cava via inflation of a chronically implanted intravascular silicone balloon. Falls in BP were paralleled by progressive decreases in iCBF, with no evidence of a steady-state plateau. No significant changes in internal carotid vascular resistance (iCVR) were observed. In contrast, intravenous infusions of the vasoactive drug sodium nitroprusside (SNP) produced a similar fall in BP but increases in iCBF and decreases in iCVR were observed. These data suggest a considerable confounding influence of vasodilatory drugs such as SNP on cerebrovascular tone in the rat, making them unsuitable to investigate cerebral autoregulation. We demonstrate that our technique of transient vena cava occlusion produced reliable and repeatable depressor responses, highlighting the potential for our approach to permit assessment of the dynamic cerebral pressure-flow relationship over time in conscious rats.NEW & NOTEWORTHY We present a novel technique to overcome the use of vasoactive agents when studying cerebrovascular dynamics in the conscious rat. Our method of vena cava occlusion to reduce BP was associated with decreased iCBF and no change in iCVR. In contrast, comparable BP falls with intravenous SNP increased iCBF and reduced iCVR. Thus, the dynamic cerebral pressure-flow relationship shows a narrower, less level autoregulatory plateau than conventionally thought. We confirm our method allows repeatable assessment of cerebrovascular dynamics in conscious rats.

Abstract MP23: Arterial Depressor Responses Induced By Neuromodulation Of Deep Peroneal Nerve In Spontaneously Hypertensive Rats

Hypertension affects nearly half of the US population but only 43% achieved blood pressure control with medication alone. Medical devices for hypertension include implantable lead electrodes that stimulate the carotid baroreceptors with promising results, albeit with significant adverse complications. To address these limitations, we have proposed the use of deep peroneal nerve stimulation (DPNS), which elicited a depressor response in anesthetized, breathing supported, spontaneously hypertensive rats (SHR). In this study, we further define the electrical stimulation parameters that optimize the DPNS depressor response, and demonstrated that increasing the pulse duration from 0.15 ms to 1ms, of 1.0 mA pulses at 2 Hz for 10 sec, significantly reduced the mean arterial pressure (MAP) by 8±4 mmHg (p&lt;0.005; n=4) in this animal model. DPNS also caused an immediate increase in renal nerve activity (RNA; p&lt; 0.004, n=5), which may represent afferent sensory axons from the kidney, although this possibility needs to be further investigated. In a separate cohort of anesthetized SHR animals, breathing spontaneously, we demonstrated that optimal DPNS stimulation reduced the MAP from 121±3 to 108±4; p=0.02; n=10). To confirm if DPNS is able to evoke a depressor response in fully awake SHR animals, we developed a novel miniaturized wireless microchannel electrode (w-μCE) with a L-shaped microchannel, through which the DPN slides and locks into a recording/stimulation chamber, causing no discomfort to the animal during locomotion. Two weeks after implantation of the w-μCE neural stimulation device, animals were movement-retrained to received wireless DPNS for 10 min daily for 2 weeks. Blood pressure was measured by tail-cuff at baseline, 10 days after device implantation, and 1 and 2-hr 15 days after DPNS. After two weeks of DPNS, the acute neuromodulation treatment reduced the initial systolic BP of 154±20 mmHg to 127±7 and 119±2 mmHg at 1 and 2 hr; respectively (p&lt; 0.001, n=15-19 measurements; n=2 animals). These results provide evidence of the effectiveness and reliability of DPN neuromodulation as a possible treatment for drug-resistant hypertension.

Abstract MP45: Deletion Of The Transient Receptor Vanilloid-1 (TRPV1) Channel In Rats Attenuates 2 Kidney 1 Clip Hypertension

Renal denervation lowers arterial blood pressure (ABP) in both clinical populations and multiple experimental models of hypertension. This therapeutic effect is partly attributed to the removal of overactive renal sensory nerves that increase sympathetic efferent activity and ABP. Renal sensory nerves highly express TRPV1 channels, and administration of the TRPV1 agonist capsaicin increases renal sensory nerve activity. However, the extent by which TRPV1 channels directly contribute to renal nerve dependent models of hypertension has not been tested. To test this hypothesis, we generated a novel TRPV1 -/- rat using CRISPR/Cas9 and deletion of exon 3. Male and female TRPV1 -/- and wild-type littermates (8-12 weeks) were instrumented with telemetry. At 2 weeks later, renovascular hypertension via renal stenosis was produced by placement of a PTFE cuff (0.16 x 0.22 inches, 1mm long) around the right renal artery. Male TRPV1 -/- and wild-type rats had no differences in baseline mean ABP (99±2 vs 98±3 mmHg, respectively; n=7-9) or heart rate (390±7 vs 400±8 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, mean ABP was significantly lower at Day 28 in male TRPV1 -/- versus wild-type rats (125±8 vs 155±2 mmHg, respectively: P&lt;0.01). Ganglionic blockade with chlorisondamine (2.5mg/kg, sc) at Day 28 produced a smaller fall in mean ABP of male TRPV1 -/- versus wild-type rats (-53±4 vs -86±3 mmHg, respectively; P&lt;0.001). On the other hand, female TRPV1 -/- and wild-type rats had no differences in baseline mean ABP (102±2 vs 104±1 mmHg, respectively; n=6-9) or heart rate (419±8 vs 410±7 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, there were no differences at Day 28 between female TRPV1 -/- versus wild-type rats (117±8 vs 122±6 mmHg, respectively). Moreover, the increase in mean ABP was smaller in females versus males. The ganglionic blocker chlorisondamine produced similar depressor responses in female TRPV1 -/- versus wild-type rats (-64±7 vs -65±7 mmHg, respectively). These findings illustrate a sex difference in renovascular hypertension in rats, but importantly indicate that TRPV1 channels contribute to the established phase of renovascular hypertension in male rats.