Baroreflex Afferent Pathway Research Articles

Closed-loop baroreflex model with biophysically detailed afferent pathway.

In this work, we couple a lumped-parameter closed-loop model of the cardiovascular system with a physiologically-detailed mathematical description of the baroreflex afferent pathway. The model features a classical Hodgkin-Huxley current-type model for the baroreflex afferent limb (primary neuron) and for the second-order neuron in the central nervous system. The pulsatile arterial wall distension triggers a frequency-modulated sequence of action potentials at the afferent neuron. This signal is then integrated at the brainstem neuron model. The efferent limb, representing the sympathetic and parasympathetic nervous system, is described as a transfer function acting on heart and blood vessel model parameters in order to control arterial pressure. Three in silico experiments are shown here: a step increase in the aortic pressure to evaluate the functionality of the reflex arch, a hemorrhagic episode and an infusion simulation. Through this model, it is possible to study the biophysical dynamics of the ionic currents proposed for the afferent limb components of the baroreflex during the cardiac cycle, and the way in which currents dynamics affect the cardiovascular function. Moreover, this system can be further developed to study in detail each baroreflex loop component, helping to unveil the mechanisms involved in the cardiovascular afferent information processing.

Piezo1 channel activation facilitates baroreflex afferent neurotransmission with subsequent blood pressure reduction in control and hypertension rats.

Mechanosensitive cation channels such as Piezo1 and Piezo2 are activated by mechanical force like a starched wall of the aorta while blood pressure (BP) rising, which helps to elucidate the underlying mechanism of mechanotransduction of baroreceptor endings. In this study we investigated how Piezo1 channel activation-mediated gender- and afferent-specific BP regulation in rats. We established high-fat diet and fructose drink-induced hypertension model rats (HFD-HTN) and deoxycorticosterone (DOCA)-sensitive hypertension model rats. We showed that the expression levels of Piezo1 and Piezo2 were significantly up-regulated in left ventricle of HFD and DOCA hypertensive rats, whereas the down-regulation of Piezo1 was likely to be compensated by Piezo2 up-regulation in the aorta. Likewise, down-regulated Piezo1 was observed in the nodose ganglion (NG), while up-regulated Piezo2 was found in the nucleus tractus solitarius (NTS), which might synergistically reduce the excitatory neurotransmitter release from the presynaptic membrane. Notably, microinjection of Yoda1 (0.025-2.5 mg/ml) into the NG concentration-dependently reduced BP in both hypertensive rat models as well as in control rats with similar EC50; the effect of Yoda1 was abolished by microinjection of a Piezo1 antagonist GsMTx4 (1.0 μM). Functional analysis in an in vitro aortic arch preparation showed that instantaneous firing frequency of single Ah-fiber of aortic depressor nerve was dramatically increased by Yoda1 (0.03-1.0 μM) and blocked by GsMTx4 (1.0 μM). Moreover, spontaneous synaptic currents recorded from identified 2nd-order Ah-type baroreceptive neurons in the NTS was also facilitated over 100% by Yoda1 (1.0 μM) and completely blocked by GsMTx4 (3.0 μM). These results demonstrate that Piezo1 expressed on Ah-type baroreceptor and baroreceptive neurons in the NG and NTS plays a key role in a sexual-dimorphic BP regulation under physiological and hypertensive condition through facilitation of baroreflex afferent neurotransmission, which is presumably collaborated by Piezo2 expression at different level of baroreflex afferent pathway via compensatory and synergistic mechanisms.

Natriuretic Peptides-New Targets for Neurocontrol of Blood Pressure via Baroreflex Afferent Pathway.

Natriuretic peptides (NPs) induce vasodilation, natriuresis, and diuresis, counteract the renin-angiotensin-aldosterone system and autonomic nervous system, and are key regulators of cardiovascular volume and pressure homeostasis. Baroreflex afferent pathway is an important reflex loop in the neuroregulation of blood pressure (BP), including nodose ganglion (NG) and nucleus tractus solitarius (NTS). Dysfunction of baroreflex would lead to various hypertensions. Here, we carried out functional experiments to explore the effects of NPs on baroreflex afferent function. Under physiological and hypertensive condition (high-fructose drinking-induced hypertension, HFD), BP was reduced by NPs through NG microinjection and baroreflex sensitivity (BRS) was enhanced via acute intravenous NPs injection. These anti-hypertensive effects were more obvious in female rats with the higher expression of NPs and its receptor A/B (NPRA/NPRB) and lower expression of its receptor C (NPRC). However, these effects were not as obvious as those in HFD rats compared with the same gender control group, which is likely to be explained by the abnormal expression of NPs and NPRs in the hypertensive condition. Our data provide additional evidence showing that NPs play a crucial role in neurocontrol of BP regulation via baroreflex afferent function and may be potential targets for clinical management of metabolic-related hypertension.

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.

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.

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.

The baroreflex afferent pathway plays a critical role in H2S-mediated autonomic control of blood pressure regulation under physiological and hypertensive conditions.

Hydrogen sulfide (H2S), which is closely related to various cardiovascular disorders, lowers blood pressure (BP), but whether this action is mediated via the modification of baroreflex afferent function has not been elucidated. Therefore, the current study aimed to investigate the role of the baroreflex afferent pathway in H2S-mediated autonomic control of BP regulation. The results showed that baroreflex sensitivity (BRS) was increased by acute intravenous NaHS (a H2S donor) administration to renovascular hypertensive (RVH) and control rats. Molecular expression data also showed that the expression levels of critical enzymes related to H2S were aberrantly downregulated in the nodose ganglion (NG) and nucleus tractus solitarius (NTS) in RVH rats. A clear reduction in BP by the microinjection of NaHS or L-cysteine into the NG was confirmed in both RVH and control rats, and a less dramatic effect was observed in model rats. Furthermore, the beneficial effects of NaHS administered by chronic intraperitoneal infusion on dysregulated systolic blood pressure (SBP), cardiac parameters, and BRS were verified in RVH rats. Moreover, the increase in BRS was attributed to activation and upregulation of the ATP-sensitive potassium (KATP) channels Kir6.2 and SUR1, which are functionally expressed in the NG and NTS. In summary, H2S plays a crucial role in the autonomic control of BP regulation by improving baroreflex afferent function due at least in part to increased KATP channel expression in the baroreflex afferent pathway under physiological and hypertensive conditions.

Contribution of Baroreflex Afferent Pathway to NPY-Mediated Regulation of Blood Pressure in Rats.

Neuropeptide Y (NPY), a metabolism-related cardiovascular factor, plays a crucial role in blood pressure (BP) regulation via peripheral and central pathways. The expression of NPY receptors (Y1R/Y2R) specific to baroreflex afferents impacts on the sexually dimorphic neural control of circulation. This study was designed to investigate the expression profiles of NPY receptors in the nodose ganglion (NG) and nucleus tractus solitary (NTS) under hypertensive conditions. To this end, rats with hypertension induced by NG-nitro-L-arginine methylester (L-NAME) or high fructose drinking (HFD), and spontaneously hypertensive rats (SHRs) were used to explore the effects/mechanisms of NPY on BP using functional, molecular, and electrophysiological approaches. The data showed that BP was elevated along with baroreceptor sensitivity dysfunction in model rats; Y1R was up- or down-regulated in the NG or NTS of male and female HFD/L-NAME groups, while Y2R was only down-regulated in the HFD groups as well as in the NG of the male L-NAME group. In SHRs, Y1R and Y2R were both down-regulated in the NTS, and not in the NG. In addition to NPY-mediated energy homeostasis, leptin-melanocortin activation may be essential for metabolic disturbance-related hypertension. We found that leptin and α-melanocyte stimulating hormone (α-MSH) receptors were aberrantly down-regulated in HFD rats. In addition, α-MSH concentrations were reduced and NPY concentrations were elevated in the serum and NTS at 60 and 90min after acute leptin infusion. Electrophysiological recordings showed that the decay time-constant and area under the curve of excitatory post-synaptic currents were decreased by Y1R activation in A-types, whereas, both were increased by Y2R activation in Ah- or C-types. These results demonstrate that sex- and afferent-specific NPY receptor expression in the baroreflex afferent pathway is likely to be a novel target for the clinical management of metabolism-related and essential hypertension.

Anti-Hypertensive Action of Fenofibrate via UCP2 Upregulation Mediated by PPAR Activation in Baroreflex Afferent Pathway.

Fenofibrate, an agonist for peroxisome proliferator-activated receptor alpha (PPAR-α), lowers blood pressure, but whether this action is mediated via baroreflex afferents has not been elucidated. In this study, the distribution of PPAR-α and PPAR-γ was assessed in the nodose ganglion (NG) and the nucleus of the solitary tract (NTS). Hypertension induced by drinking high fructose (HFD) was reduced, along with complete restoration of impaired baroreceptor sensitivity, by chronic treatment with fenofibrate. The molecular data also showed that both PPAR-α and PPAR-γ were dramatically up-regulated in the NG and NTS of the HFD group. Expression of the downstream signaling molecule of PPAR-α, the mitochondrial uncoupling protein 2 (UCP2), was up-regulated in the baroreflex afferent pathway under similar experimental conditions, along with amelioration of reduced superoxide dismutase activity and increased superoxide in HFD rats. These results suggest that chronic treatment with fenofibrate plays a crucial role in the neural control of blood pressure by improving baroreflex afferent function due at least partially to PPAR-mediated up-regulation of UCP2 expression and reduction of oxidative stress.

Spontaneous activities in baroreflex afferent pathway contribute dominant role in parasympathetic neurocontrol of blood pressure regulation.

To study the dominant role of parasympathetic inputs at cellular level of baroreflex afferent pathway and underlying mechanism in neurocontrol of blood pressure regulation. Whole-cell patch-clamp and animal study were conducted. For the first time, we demonstrated the spontaneous activities from resting membrane potential in myelinated A- and Ah-type baroreceptor neurons (BRNs, the 1st-order), but not in unmyelinated C-types, using vagus-nodose slice of adult female rats. These data were further supported by the notion that the spontaneous synaptic currents could only be seen in the pharmacologically and electrophysiologically defined myelinated A- and Ah-type baroreceptive neurons (the 2nd-order) of NTS using brainstem slice of adult female rats. The greater frequency and the larger amplitude of the spontaneous excitatory postsynaptic currents (EPSCs) compared with the inhibitory postsynaptic currents (IPSCs) were only observed in Ah-types. The ratio of EPSCs:IPSCs was estimated at 3:1 and higher. These results confirmed that the afferent-specific spontaneous activities were generated from baroreflex afferent pathway in female-specific subpopulation of myelinated Ah-type BRNs in nodose and baroreceptive neurons in NTS, which provided a novel insight into the dominant role of sex-specific baroreflex-evoked parasympathetic drives in retaining a stable and lower blood pressure status in healthy subjects, particularly in females. The data from current investigations establish a new concept for the role of Ah-type baroreceptor/baroreceptive neurons in controlling blood pressure stability and provide a new pathway for pharmacological intervention for hypertension and cardiovascular diseases.

Direct activation of tachykinin receptors within baroreflex afferent pathway and neurocontrol of blood pressure regulation.

Substance P (SP) causes vasodilation and blood pressure (BP) reduction. However, the involvement of tachykinin receptors (NKRs) within baroreflex afferent pathway in SP-mediated BP regulation is largely unknown. Under control and hypertensive condition, NKRs' expressions were evaluated in nodose (NG) and nucleus of tractus solitary (NTS) of male, female, and ovariectomized (OVX) rats; BP was recorded after microinjection of SP and NKRs agonists into NG; Baroreceptor sensitivity (BRS) was tested as well. Immunostaining and immunoblotting data showed that NK1R and NK2R were estrogen-dependently expressed on myelinated and unmyelinated afferents in NG. A functional study showed that BP was reduced dose-dependently by SP microinjection, which was more dramatic in males and can be mimicked by NK1R and NK2R agonists. Notably, further BP elevation and BRS dysfunction were confirmed in desoxycorticosterone acetate (DOCA)-salt model in OVX compared with DOCA-salt model in intact female rats. Additionally, similar changes in NKRs' expression in NG were also detected using DOCA-salt and SHR. Compared with NG, inversed expression profiles of NKRs were also found in NTS with either gender. The estrogen-dependent NKRs' expression in baroreflex afferent pathway participates at least partially in sexual-dimorphic and SP-mediated BP regulation under physiological and hypertensive conditions.

Corrigendum to "KCa1.1 is potential marker for distinguishing Ah-type baroreceptor neurons in NTS and contributes to sex-specific presynaptic neurotransmission in baroreflex afferent pathway" [Neurosci. Lett. 604 (2015) 1-6

Corrigendum to "KCa1.1 is potential marker for distinguishing Ah-type baroreceptor neurons in NTS and contributes to sex-specific presynaptic neurotransmission in baroreflex afferent pathway" [Neurosci. Lett. 604 (2015) 1-6

The Potential Role of Fibroblast Growth Factor 21 in Lipid Metabolism and Hypertension

Fibroblast growth factor (FGF) 21 belongs to the FGF superfamily that is involved in cell proliferation and differentiation, neural development, angiogenesis, and metabolism. FGF21 requires β-Klotho as a co-receptor. Tissues involved in metabolism such as the liver, adipose tissues, skeletal muscle, and pancreas express FGF21. Starvation increases hepatic expression of FGF21, which then acts centrally to increase hepatic gluconeogenesis. FGF21 also increases fatty acid oxidation. This may be relevant in cold exposure, when expression of FGF21 is induced. Chronic treatment with recombinant FGF21 reduces serum and hepatic triglyceride levels and ameliorates fatty liver in obese mice, through the suppression of the lipogenic gene, Srebp-1. FGF21 reduces hepatic cholesterol production by inhibiting Srebp-2, a transactivator of proprotein convertase subtilisin/kexin type 9 (PCSK9). LY2045319, an FGF21 analog, reduces LDL-C and triglycerides and increases HDL-C in obese human subjects with type 2 diabetes. FGF21 does not seem to lower blood pressure acutely. In rats fed with high-fructose water to induce mild hypertension, 4-week treatment with recombinant FGF21 led to normalization of systolic blood pressure and improved serum lipid profile. FGF receptors and β-Klotho are expressed on the nucleus tractus solitarii and nodose ganglion in the baroreflex afferent pathway. Moreover, FGF21 acts on the hypothalamus to release corticosterone and induces in adipocytes the production of adiponectin, an adipokine with antihypertensive activities. Therefore, FGF21 may decrease blood pressure indirectly, through its actions in the liver, brain, and adipose tissues.

Neuropeptide Y-mediated sex- and afferent-specific neurotransmissions contribute to sexual dimorphism of baroreflex afferent function.

BackgroundMolecular and cellular mechanisms of neuropeptide-Y (NPY)-mediated gender-difference in blood pressure (BP) regulation are largely unknown.MethodsBaroreceptor sensitivity (BRS) was evaluated by measuring the response of BP to phenylephrine/nitroprusside. Serum NPY concentration was determined using ELISA. The mRNA and protein expression of NPY receptors were assessed in tissue and single-cell by RT-PCR, immunoblot, and immunohistochemistry. NPY was injected into the nodose while arterial pressure was monitored. Electrophysiological recordings were performed on nodose neurons from rats by patch-clamp technique.ResultsThe BRS was higher in female than male and ovariectomized rats, while serum NPY concentration was similar among groups. The sex-difference was detected in Y1R, not Y2R protein expression, however, both were upregulated upon ovariectomy and canceled by estrogen replacement. Immunostaining confirmed Y1R and Y2R expression in myelinated and unmyelinated afferents. Single-cell PCR demonstrated that Y1R expression/distribution was identical between A- and C-types, whereas, expressed level of Y2R was ∼15 and ∼7 folds higher in Ah- and C-types than A-types despite similar distribution. Activation of Y1R in nodose elevated BP, while activation of Y2R did the opposite. Activation of Y1R did not alter action potential duration (APD) of A-types, but activation of Y2R- and Y1R/Y2R in Ah- and C-types frequency-dependently prolonged APD. N-type ICa was reduced in A-, Ah- and C-types when either Y1R, Y2R, or both were activated. The sex-difference in Y1R expression was also observed in NTS.ConclusionsSex- and afferent-specific expression of Neuropeptide-Y receptors in baroreflex afferent pathway may contribute to sexual-dimorphic neurocontrol of BP regulation.

FGF21 ameliorates the neurocontrol of blood pressure in the high fructose-drinking rats.

Fibroblast growth factor-21 (FGF21) is closely related to various metabolic and cardiovascular disorders. However, the direct targets and mechanisms linking FGF21 to blood pressure control and hypertension are still elusive. Here we demonstrated a novel regulatory function of FGF21 in the baroreflex afferent pathway (the nucleus tractus solitarii, NTS; nodose ganglion, NG). As the critical co-receptor of FGF21, β-klotho (klb) significantly expressed on the NTS and NG. Furthermore, we evaluated the beneficial effects of chronic intraperitoneal infusion of recombinant human FGF21 (rhFGF21) on the dysregulated systolic blood pressure, cardiac parameters, baroreflex sensitivity (BRS) and hyperinsulinemia in the high fructose-drinking (HFD) rats. The BRS up-regulation is associated with Akt-eNOS-NO signaling activation in the NTS and NG induced by acute intravenous rhFGF21 administration in HFD and control rats. Moreover, the expressions of FGF21 receptors were aberrantly down-regulated in HFD rats. In addition, the up-regulated peroxisome proliferator-activated receptor-γ and -α (PPAR-γ/-α) in the NTS and NG in HFD rats were markedly reversed by chronic rhFGF21 infusion. Our study extends the work of the FGF21 actions on the neurocontrol of blood pressure regulations through baroreflex afferent pathway in HFD rats.

Ketamine-mediated afferent-specific presynaptic transmission blocks in low-threshold and sex-specific subpopulation of myelinated Ah-type baroreceptor neurons of rats.

Ketamine enhances autonomic activity, and unmyelinated C-type baroreceptor afferents are more susceptible to be blocked by ketamine than myelinated A-types. However, the presynaptic transmission block in low-threshold and sex-specific myelinated Ah-type baroreceptor neurons (BRNs) is not elucidated. Action potentials (APs) and excitatory post-synaptic currents (EPSCs) were investigated in BRNs/barosensitive neurons identified by conduction velocity (CV), capsaicin-conjugated with Iberiotoxin-sensitivity and fluorescent dye using intact nodose slice and brainstem slice in adult female rats. The expression of mRNA and targeted protein for NMDAR1 was also evaluated. Ketamine time-dependently blocked afferent CV in Ah-types in nodose slice with significant changes in AP discharge. The concentration-dependent inhibition of ketamine on AP discharge profiles were also assessed and observed using isolated Ah-type BRNs with dramatic reduction in neuroexcitability. In brainstem slice, the 2nd-order capsaicin-resistant EPSCs were identified and ~50% of them were blocked by ketamine concentration-dependently with IC50 estimated at 84.4 µM compared with the rest (708.2 µM). Interestingly, the peak, decay time constant, and area under curve of EPSCs were significantly enhanced by 100 nM iberiotoxin in ketamine-more sensitive myelinated NTS neurons (most likely Ah-types), rather than ketamine-less sensitive ones (A-types). These data have demonstrated, for the first time, that low-threshold and sex-specific myelinated Ah-type BRNs in nodose and Ah-type barosensitive neurons in NTS are more susceptible to ketamine and may play crucial roles in not only mean blood pressure regulation but also buffering dynamic changes in pressure, as well as the ketamine-mediated cardiovascular dysfunction through sexual-dimorphic baroreflex afferent pathway.

KCa1.1 is potential marker for distinguishing Ah-type baroreceptor neurons in NTS and contributes to sex-specific presynaptic neurotransmission in baroreflex afferent pathway

Sexual-dimorphic neurocontrol of circulation has been described in baroreflex due largely to the function of myelinated Ah-type baroreceptor neurons (BRNs, 1st-order) in nodose. However, it remains unclear if sex- and afferent-specific neurotransmission could also be observed in the central synapses within nucleus of solitary track (NTS, 2nd-order). According to the principle of no mixed neurotransmission among afferents and differentiation of Ah- and A-types to iberiotoxin (IbTX) observed in nodose, the 2nd-order Ah-type BRNs are highly expected. To test this hypothesis, the excitatory post-synaptic currents (EPSCs) were recorded in identified 2nd-order BRNs before and after IbTX using brain slice and whole-cell patch. These results showed that, in male rats, the dynamics of EPSCs in capsaicin-sensitive C-types were dramatically altered by IbTX, but not in capsaicin-insensitive A-types. Interestingly, near 50% capsaicin-insensitive neurons in females showed similar effects to C-types, suggesting the existence of Ah-types in NTS, which may be the likely reason why the females had lower blood pressure and higher sensitivity to aortic depressor nerve stimulation via KCa1.1-mediated presynaptic glutamate release from Ah-type afferent terminals.