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.

Parkinson-like early autonomic dysfunction induced by vagal application of DOPAL in rats

AIM

To understand why autonomic failures, a common non-motor symptom of Parkinson's disease (PD), occur earlier than typical motor disorders.

METHODS

Vagal application of DOPAL (3,4-dihydroxyphenylacetaldehyde) to simulate PD-like autonomic dysfunction and understand the connection between PD and cardiovascular dysfunction. Molecular and morphological approaches were employed to test the time-dependent alternation of α-synuclein aggregation and the ultrastructure changes in the heart and nodose (NG)/nucleus tractus solitarius (NTS).

RESULTS

Blood pressure (BP) and baroreflex sensitivity of DOPAL-treated rats were significantly reduced accompanied with a time-dependent change in orthostatic BP, consistent with altered echocardiography and cardiomyocyte mitochondrial ultrastructure. Notably, time-dependent and collaborated changes in Mon-/Tri-α-synuclein were paralleled with morphological alternation in the NG and NTS.

CONCLUSION

These all demonstrate that early autonomic dysfunction mediated by vagal application of DOPAL highly suggests the plausible etiology of PD initiated from peripheral, rather than central site. It will provide a scientific basis for the prevention and early diagnosis of PD.

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

AIM

To study the dominant role of parasympathetic inputs at cellular level of baroreflex afferent pathway and underlying mechanism in neurocontrol of blood pressure regulation.

METHODS

Whole-cell patch-clamp and animal study were conducted.

RESULTS

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.

CONCLUSION

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

AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

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

Background

Molecular and cellular mechanisms of neuropeptide-Y (NPY)-mediated gender-difference in blood pressure (BP) regulation are largely unknown.

Methods

Baroreceptor 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.

Results

The 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 I_Ca 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.

Conclusions

Sex- and afferent-specific expression of Neuropeptide-Y receptors in baroreflex afferent pathway may contribute to sexual-dimorphic neurocontrol of BP regulation.

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

Background

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.

Methods

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.

Results

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 2^nd-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).

Conclusions

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.

Sumoylation of the Tumor Suppressor Promyelocytic Leukemia Protein Regulates Arsenic Trioxide-Induced Collagen Synthesis in Osteoblasts

Background/Aims: Promyelocytic leukemia (PML) protein is a tumor suppressor that fuses with retinoic acid receptor-α (PML-RARα) to contribute to the initiation of acute promyelocytic leukemia (APL). Arsenic trioxide (ATO) upregulates expression of TGF-β1, promoting collagen synthesis in osteoblasts, and ATO binds directly to PML to induce oligomerization, sumoylation, and ubiquitination. However, how ATO upregulates TGF-β1 expression is uncertain. Thus, we suggested that PML sumoylation is responsible for regulation of TGF-β1 protein expression. Methods: Kunming mice were treated with ATO, and osteoblasts were counted under scanning electron microscopy. Masson's staining was used to quantify collagen content. hFOB1.19 cells were transfected with siRNA against UBC9 or RNF4, and then treated with ATO or FBS. TGF-β1, PML expression, and sumoylation were quantified with Western blot, and collagen quantified via immunocytochemistry. Results: ATO enhanced osteoblast accumulation, collagen synthesis, and PML-NB formation in vivo. Knocking down UBC9 in hFOB1.19 cells inhibited ATO- and FBS-induced PML sumoylation, TGF-β1 expression, and collagen synthesis. Conversely, knocking down RNF4 enhanced ATO- and FBS-induced PML sumoylation, TGF-β1 expression, and collagen synthesis. Conclusion: These data suggest that PML sumoylation is required for ATO-induced collagen synthesis in osteoblasts.

Sex- and afferent-specific differences in histamine receptor expression in vagal afferents of rats: A potential mechanism for sexual dimorphism in prevalence and severity of asthma

The incidence of asthma is more common in boys than in girls during the childhood, and more common in premenopausal female than age-matched males. Our previous study demonstrated a gender difference in histamine-mediated neuroexcitability in nodose ganglia neurons (NGNs), highlighting a possibility of histamine-mediated gender difference in asthma via visceral afferent function. In the present study, we aimed to explore the gender difference in expression profiles of histamine receptors (HRs) in nodose ganglia (NG) and individual identified NGNs to provide deeper insights into the mechanisms involved in sexual dimorphism of asthma. Western-blot and SYBR green RT-PCR showed that H2R and H3R were highly expressed in NG of females compared with males and downregulated in ovariectomized females. H1R was equally expressed in NG of both sexes and not altered by ovariectomy. Furthermore, this highly expressive H2R and H3R were distributed in both myelinated and unmyelinated NGNs isolated from adult female rats by immunofluorescence and single-cell RT-PCR. H3R widely distributed in all tested neuron subtypes and its expression did not show significant difference among neuron subtypes. H2R was widely and highly expressed in low-threshold and sex-specific subpopulation of myelinated Ah-types compared with myelinated A- and unmyelinated C-type NGNs. Unexpectedly, weak expression of H1R was detected in both myelinated and unmyelinated NGNs by immunofluorescence, which was further confirmed by single-cell RT-PCR. Our results suggest that the sexual dimorphism in the expression of H2R and H3R in vagal afferents very likely contributes, at least partially, to the gender difference in prevalence and severity of asthma.

Arsenic trioxide exerts a double effect on osteoblast growth in vitro

Arsenic trioxide (ATO) is a promising antitumor agent used to treat acute promyelocytic leukemia (APL) and, recently solid tumor. The present study was designed to evaluate the effect of ATO proliferation of osteoblast that plays very important roles in maintaining the structure integrity and function of bone. Cell survives, apoptosis, collagen, and molecular targets were identified by multiple detecting techniques, including MTT assay, electron microscopy, collagen detecting kit, TUNEL kit, and western blot in hFOB1.19 human osteoblasts cell line. The results showed that low dose of ATO (0.25, 0.5, and 1μM) remarkably enhanced the viability of cultured osteoblasts in a concentration- and time-dependent manner. Intriguingly, a dual effect of high dose of ATO (5, 10, and 20μM) was also observed showing significant reduction in viability of culture osteoblasts at concentration- and time-dependent fashion. Moreover, low dose of ATO promoted secretion and synthesis of collagen, whereas high dose of ATO induced typical morphological characteristics of apoptosis in osteoblasts. Mechanically, western blot results demonstrated that low dose of ATO dramatically up-regulated TGF-β1 protein and activated p-AKT proliferative signaling. And, high dose of ATO increased Bax/Bcl-2 ratio in a time-dependent fashion and activated caspase-3 apoptotic signaling. These results demonstrate at the first time that ATO exerts a double effect on osteoblast function depending upon the concentration and provide a clue to rationally use ATO for clinicians to pay more attention to protect bone from the adverse effects of therapeutic dose of ATO during tumor therapy.

Localization of human mesenchymal stem cells from umbilical cord blood and their role in repair of diabetic foot ulcers in rats

The aim of this study is to explore the localization of human mesenchymal stem cells from umbilical cord matrix (hMSCs-UC) and the role of these cells in the repair of foot ulcerate tissue in diabetic foot ulcers in rats. A diabetic rat model was established by administering Streptozotocin. Diabetic foot ulceration was defined as non-healing or delayed-healing of empyrosis on the dorsal hind foot after 14 weeks. hMSCs-UC were delivered through the left femoral artery. We evaluated the localization of hMSCs-UC and their role in tissue repair in diabetic foot ulcers by histological analysis, PCR, and immunohistochemical staining. A model for diabetes was established in 54 out of 60 rats (90% success rate) and 27 of these rats were treated with hMSCs-UC. The area of ulceration was significantly and progressively reduced at 7 and 14 days following treatment with hMSCs-UC. This gross observation was strongly supported by the histological changes, including newly developed blood vessels and proliferation of inflammatory cells at 3 days post-treatment, significant increase in granulation tissue at 7 days post-treatment and squamous epithelium or stratified squamous epithelium at 14 days post-treatment. Importantly, human leukocyte antigen type-I (HLA-1) was confirmed in ulcerated tissue by RT-PCR. The expression of cytokeratin 19 was significantly increased in diabetic model rats, with no detectable change in cytokeratin 10. Additionally, both collagens I and III increased in model rats treated with hMSCs-UC, but the ratio of collagen I/III was less significant in treated rats compared with control rats. These results suggest that hMSCs-UC specifically localize to the target ulcerated tissue and may promote the epithelialization of ulcerated tissue by stimulating the release of cytokeratin 19 from keratinocytes and extracellular matrix formation.

Gender differences in histamine-induced depolarization and inward currents in vagal ganglion neurons in rats

Evidence has shown gender differences regarding the critical roles of histamine in the prevalence of asthma, anaphylaxis, and angina pectoris. Histamine depolarizes unmyelinated C-type neurons without any effects on myelinated A-type vagal ganglion neurons (VGNs) in male rats. However, little is known if VGNs from females react to histamine in a similar manner. Membrane depolarization and inward currents were tested in VGNs isolated from adult rats using a whole-cell patch technique. Results from males were consistent with the literature. Surprisingly, histamine-induced depolarization and inward currents were observed in both unmyelinated C-type and myelinated A- and Ah-type VGNs from female rats. In Ah-type neurons, responses to 1.0 μM histamine were stronger in intact females than in males and significantly reduced in ovariectomized (OVX) females. In C-type neurons, histamine-induced events were significantly smaller (pA/pF) in intact females compared with males and this histamine-induced activity was dramatically increased by OVX. Female A-types responded to histamine, which was further increased following ovariectomy. Histamine at 300 nM depolarized Ah-types in females, but not Ah-types in OVX females. In contrast, the sensitivity of A- and C-types to histamine was upregulated by OVX. These data demonstrate gender differences in VGN chemosensitivity to histamine for the first time. Myelinated Ah-types showed the highest sensitivity to histamine across female populations, which was changed by OVX. These novel findings improve the understanding of gender differences in the prevalence of asthma, anaphylaxis, and pain. Changes in sensitivity to histamine by OVX may explain alterations in the prevalence of certain pathophysiological conditions when women reach a postmenopausal age.

Increase in neuroexcitability of unmyelinated C-type vagal ganglion neurons during initial postnatal development of visceral afferent reflex functions

BACKGROUND

Baroreflex gain increase up closely to adult level during initial postnatal weeks, and any interruption within this period will increase the risk of cardiovascular problems in later of life span. We hypothesize that this short period after birth might be critical for postnatal development of vagal ganglion neurons (VGNs).

METHODS

To evaluate neuroexcitability evidenced by discharge profiles and coordinate changes, ion currents were collected from identified A- and C-type VGNs at different developmental stages using whole-cell patch clamping.

RESULTS

C-type VGNs underwent significant age-dependent transition from single action potential (AP) to repetitive discharge. The coordinate changes between TTX-S and TTX-R Na(+) currents were also confirmed and well simulated by computer modeling. Although 4-AP or iberiotoxin age dependently increased firing frequency, AP duration was prolonged in an opposite fashion, which paralleled well with postnatal changes in 4-AP- and iberiotoxin-sensitive K(+) current activity, whereas less developmental changes were verified in A-types.

CONCLUSION

These data demonstrate for the first time that the neuroexcitability of C-type VGNs increases significantly compared with A-types within initial postnatal weeks evidenced by AP discharge profiles and coordinate ion channel changes, which explain, at least in part, that initial postnatal weeks may be crucial for ontogenesis in visceral afferent reflex function.

Remodeling of hyperpolarization-activated current, Ih, in Ah-type visceral ganglion neurons following ovariectomy in adult rats

Hyperpolarization-activated currents (I_h) mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels modulate excitability of myelinated A− and Ah-type visceral ganglion neurons (VGN). Whether alterations in I_h underlie the previously reported reduction of excitability of myelinated Ah-type VGNs following ovariectomy (OVX) has remained unclear. Here we used the intact nodose ganglion preparation in conjunction with electrophysiological approaches to examine the role of I_h remodeling in altering Ah-type neuron excitability following ovariectomy in adult rats. Ah-type neurons were identified based on their afferent conduction velocity. Ah-type neurons in nodose ganglia from non-OVX rats exhibited a voltage ‘sag’ as well as ‘rebound’ action potentials immediately following hyperpolarizing current injections, which both were suppressed by the I_h blocker ZD7288. Repetitive spike activity induced afterhyperpolarizations lasting several hundreds of milliseconds (termed post-excitatory membrane hyperpolarizations, PEMHs), which were significantly reduced by ZD7288, suggesting that they resulted from transient deactivation of I_h during the preceding spike trains. Ovariectomy reduced whole-cell I_h density, caused a hyperpolarizing shift of the voltage-dependence of I_h activation, and slowed I_h activation. OVX-induced I_h remodeling was accompanied by a flattening of the stimulus frequency/response curve and loss of PEMHs. Also, HCN1 mRNA levels were reduced by ∼30% in nodose ganglia from OVX rats compared with their non-OVX counterparts. Acute exposure of nodose ganglia to 17beta-estradiol partly restored I_h density and accelerated I_h activation in Ah-type cells. In conclusion, I_h plays a significant role in modulating the excitability of myelinated Ah-type VGNs in adult female rats.

Subtype identification in acutely dissociated rat nodose ganglion neurons based on morphologic parameters

Nodose ganglia are composed of A-, Ah- and C-type neurons. Despite their important roles in regulating visceral afferent function, including cardiovascular, pulmonary, and gastrointestinal homeostasis, information about subtype-specific expression, molecular identity, and function of individual ion transporting proteins is scarce. Although experiments utilizing the sliced ganglion preparation have provided valuable insights into the electrophysiological properties of nodose ganglion neuron subtypes, detailed characterization of their electrical phenotypes will require measurements in isolated cells. One major unresolved problem, however, is the difficulty to unambiguously identify the subtype of isolated nodose ganglion neurons without current-clamp recording, because the magnitude of conduction velocity in the corresponding afferent fiber, a reliable marker to discriminate subtypes in situ, can no longer be determined. Here, we present data supporting the notion that application of an algorithm regarding to microscopic structural characteristics, such as neuron shape evaluated by the ratio between shortest and longest axis, neuron surface characteristics, like membrane roughness, and axon attachment, enables specific and sensitive subtype identification of acutely dissociated rat nodose ganglion neurons, by which the accuracy of identification is further validated by electrophysiological markers and overall positive predictive rates is 89.26% (90.04%, 76.47%, and 98.21% for A-, Ah, and C-type, respectively). This approach should aid in gaining insight into the molecular correlates underlying phenotypic heterogeneity of nodose ganglia. Additionally, several critical points that help for neuron identification and afferent conduction calibration are also discussed.

Protective effect of the daming capsule on impaired baroreflexes in STZ-induced diabetic rats with hyperlipoidemia

Background

The Daming capsule (DMC) is a traditional Chinese medicine used to treat hyperlipoidemia. Both clinic trials and studies on animal models have demonstrated that DMC is beneficial against diabetic symptoms. Impairment of the baroreflex can cause life-threatening arrhythmias and sudden cardiac death in patients with diabetes mellitus (DM). This study was designed to elucidate the effects of DMC on baroreflexes in streptozocin (STZ)-induced diabetic rats with hyperlipoidemia.

Methods

Wistar rats were randomly divided into three groups: untreated controls, rats pretreated STZ and high lipids (a diabetes model or DM rats), and DM rats treated with DMC. The baroreflex sensitivity was examined during intravenous injection of phenylephrine (PE) or sodium nitroprusside (SNP) and quantified by the change in heart rate over the change in mean arterial blood pressure (ΔHR/ΔMABP). Morphological remodeling of baroreceptors was analyzed by transmission electron microscopy (TEM). The mRNA levels and expression of GluR2 and a GABA_A receptor subunit were measured by quantitative RT-PCR and Western blotting.

Results

Compared to untreated DM rats, DMC significantly elevated the ratio of ΔHR/ΔMABP by enhancing the compensatory reduction in HR (-ΔHR) in response to PE-induced hypertension (+ΔMABP) (P < 0.05). In the presence of SNP, DMC increased the ΔMABP (P < 0.05). In addition, DMC markedly shortened the duration of blood pressure changes elicited by PE or SNP in DM rats compared to the untreated DM group (P < 0.05). Electron microscopy revealed disrupted myelin sheaths, swollen ER, and lysed mitochondria in the nucleus ambiguous (NAm) DM rats. These signs of neuropathology were largely prevented by treatment with DMC for 30 days. Treatment with DMC elevated both mRNA and protein level of GluR2 in the NAm of DM rats, but had no effect on GABA_A receptor expression.

Conclusion

The Daming capsule partially reversed the parasympathetic baroreflex impairment observed in STZ-induced diabetic rats with hyperlipoidemia. Treatment with DMC also prevented the degeneration of neurons and myelinated axons in the brain stem NAm and reversed the down-regulation of GluR2 mRNA. Rescue of NAm function may contribute to the medicinal properties of DMC in diabetic rats.

Functional impact of the hyperpolarization-activated current on the excitability of myelinated A-type vagal afferent neurons in the rat

1. The hyperpolarization-induced, cation-selective current I(h) is widely observed in peripheral sensory neurons of the vagal and dorsal root ganglia, but the peak magnitude and voltage- and time-dependent properties of this current vary widely across afferent fibre type. 2. Using patch clamp investigations of rat isolated vagal ganglion neurons (VGN) identified as myelinated A-type afferents, we established a compendium of functional correlates between changes in membrane potential and the dynamic discharge properties of these sensory neurons as a result of the controlled recruitment of I(h) using the current clamp technique. 3. Two robust responses were observed in response to hyperpolarizing step currents: (i) upon initiation of the negative step current, there was a rapid hyperpolarization of membrane potential followed by a depolarizing voltage sag (DVS) towards a plateau in membrane potential as a result of steady state recruitment of I(h); and (ii) upon termination of the negative step current, there was a rapid return to the pretest resting membrane potential that often led to spontaneous action potential discharge. These data were strongly correlated (r(2) > 0.9) with a broad compendium of dynamic discharge characteristics in these A-type VGN. 4. In response to depolarizing step currents of increasing magnitude, the discharge frequency of the A-type VGN responded with increases in the rate of sustained repetitive discharge. Upon termination of the depolarizing step current, there was a post-excitatory membrane hyperpolarization of a magnitude that was strongly correlated with action potential discharge rate (r(2) > 0.9). 5. Application of the selective hyperpolarization-activated cyclic nucleotide gated (HCN) channel blockers ZD7288 (10 micromol/L) or CsCl (1.0 mmol/L) abolished I(h) and all of the aforementioned functional correlates. In addition to reducing the excitability of the A-type VGN to step depolarizing currents. 6. Because there is increasing evidence that the HCN channel current may represent a valid target for pharmacological intervention, the quantitative relationships described in the present study could potentially help guide the molecular and/or chemical modification of HCN channel gating properties to effect a particular outcome in VGN discharge properties, ideally well beyond merely selective blockade of a particular HCN channel subtype.

17Beta-estradiol restores excitability of a sexually dimorphic subset of myelinated vagal afferents in ovariectomized rats

We recently identified a myelinated vagal afferent subpopulation (Ah type) far more prevalent in female than male rats and showed that this difference extends to functionally specific visceral sensory afferents, baroreceptors of the aortic arch. Excitability of myelinated Ah-type afferents is markedly reduced after ovariectomy (OVX). Here we tested the hypothesis that 17beta-estradiol can selectively restore excitability of these sex-specific vagal afferents. Acutely isolated vagal afferent neurons (VGN) from intact and OVX adult female rats were used with patch-clamp technique and current-clamp protocols to assess the effect of acute application of 17beta-estradiol on neuronal excitability. At over physiologically relevant 17beta-estradiol concentrations for rat (1-10 nM) excitability of myelinated Ah-type vagal afferents is restored to discharge frequencies comparable to those in intact females, albeit with some interesting differences related to burst and sustained patterns of neuronal discharge. Restoration of excitability occurs within 3 min of hormone application and is stereo specific, because 1,000 nM 17alpha-estradiol fails to alter excitability. Furthermore, activation of G protein-coupled estrogen receptor GPR30 with highly selective agonist G-1 similarly restores excitability of Ah-type afferents. The effectiveness of 17beta-estradiol and G-1 is completely eliminated by application of high-affinity estrogen receptor ligand ICI-182,780. 17beta-Estradiol conjugated with BSA is approximately 70% as effective as 17beta-estradiol alone in restoring Ah-type VGN excitability. These data support our conclusions that the cellular mechanisms leading to rapid restoration of neuronal excitability of myelinated Ah-type VGN after OVX occur, at least in part, via membrane-bound estrogen receptors. We contend that recovery of high-frequency discharge at physiologically relevant 17beta-estradiol concentrations implies that this unique subtype of low-threshold myelinated vagal afferent may account for some of the sex-related differences in visceral organ system function. Sex differences in cardiovascular and gastrointestinal function and the potential role of GPR30 in modulation of sex-specific myelinated Ah-type vagal afferents are discussed.

Characterization of persistent TTX-R Na+ currents in physiological concentration of sodium in rat visceral afferents

Persistent tetrodotoxin-resistant (TTX-R) Na⁺ (Na_v1.9/SCN11A) currents are not normally recorded in vagal afferent neurons (VANs) with 50 mM of extracellular Na⁺ although the functional expression of this current was observed in the presence of PGE₂ or forskolin. However, it is uncertain whether this current can be seen under physiological condition (150 mM Na⁺). Using the whole-cell patch-clamp technique, we showed that persistent TTX-R Na⁺ currents were expressed in 9 out of 38 VANs bathed in 150 mM Na⁺. The current density, but not the whole-cell capacitance, was significantly enhanced in the VANs expressing Nav1.9. Persistent TTX-R Na⁺ channels were activated at a more hyperpolarized membrane potential near -60 mV, compared with TTX-sensitive (TTX-S at -40 mV) and TTX-R Na⁺ channels (at -20 mV). This indicates that persistent TTX-R Na⁺ channels provide a wider activation window than TTX-S and TTX-R Na channels to up-regulate neuronal excitability. These results suggest that the persistent TTX-R Na⁺ currents may be involved in the neuronal excitability by setting a lower pressure-discharge threshold and higher discharge frequency of VANs, especially the unique subset and gender-specific distribution of myelinated Ah-type VANs, including Ah-type aortic baroreceptor neurons, identified in our previous study.

Electrophysiological and neuroanatomical evidence of sexual dimorphism in aortic baroreceptor and vagal afferents in rat

Evidence for sexual dimorphism in autonomic control of cardiovascular function is both compelling and confounding. Across healthy and disease populations sex-associated differences in neurocirculatory hemodynamics are far too complex to be entirely related to sex hormones. As an initial step toward identifying additional physiological mechanisms, we investigated whether there is a sex bias in the relative expression of low-threshold-myelinated and high-threshold-unmyelinated aortic baroreceptor afferents in rats. These two types of afferent fibers have markedly different reflexogenic effects upon heart rate and blood pressure and thus the potential impact upon baroreflex dynamics could be substantial. Our results, using a combination of a patch-clamp study of fluorescently identified aortic baroreceptor neurons (ABN) and morphometric analysis of aortic baroreceptor nerve fibers, demonstrate that females exhibit a greater percentage of myelinated baroreceptor fibers (24.8% vs. 18.7% of total baroreceptor fiber population, P < 0.01) and express a functional subtype of myelinated ABN rarely found in age-matched males (11% vs. 2.3%, n = 107, P < 0.01). Interestingly, this neuronal phenotype is more prevalent in the general population of female vagal afferent neurons (17.7% vs. 3.8%, n = 169, P < 0.01), and ovariectomy does not alter its expression but does lessen neuronal excitability. These data suggest there are fundamental neuroanatomical and electrophysiological differences between aortic baroreceptor afferents of female and male rats. Possible explanations are presented as to how such a greater prevalence of low-threshold myelinated afferents could be a contributing factor to the altered baroreflex sensitivity and vagal tone of females compared with males.

GM1 ganglioside contributes to retain the neuronal conduction and neuronal excitability in visceral and baroreceptor afferents

GM1 ganglioside has a great impact on the function of nodes of Ranvier on myelinated fiber, suggesting its potential role to maintain the electrical and neuronal excitability of neurons. Here we first demonstrate that visceral afferent conduction velocity of myelinated and unmyelinated fibers are reduced significantly by tetrodotoxin (TTX) or cholera toxin-B subunits (CTX-B), and only the effects mediated by CTX-B are prevented by GM1 pre-treatment. At soma of myelinated A and unmyelinated C-type nodose ganglion neurons (NGNs), the action potential spike frequency reduced by CTX-B is also prevented by GM1. Additionally, the current density of both TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na(+) channels were significantly decreased by CTX-B without changing the voltage-dependent property. These data confirm that endogenous GM1 may play a dominant role in maintaining the electrical and neuronal excitability via modulation of sodium (Na(+)) channel around nodes and soma as well, especially TTX-S Na(+) channel, which is also confirmed by the reduction of spike amplitude and depolarization. Similar data are also extended to fluorescently identified and electrophysiologically characterized aortic baroreceptor neurons. These findings suggest that GM1 plays an important role in the neural modulation of electric and neuronal excitability in visceral afferent system.

Homocysteine inhibits potassium channels in human atrial myocytes

1. A large body of evidence indicates that elevated homocysteine (Hcy) levels portend an increased risk for atrial fibrillation. However, little is known about the electrophysiological effects of Hcy on atrial myocytes. The present study was conducted to investigate the direct effects of Hcy on ion channels in human atria. 2. Whole-cell patch-clamp techniques were used to record potassium currents in human atrial cells. 3. In human atrial myocytes, transient outward potassium currents were significantly decreased by 24.8 +/- 5.9 and 38.4 +/- 10.4% in the presence of 50 and 500 micromol/L Hcy, respectively. The ultrarapid delayed rectifier potassium currents were decreased by approximately 30% when exposed to 500 micromol/L Hcy. The inward rectifier potassium currents were increased by approximately 40% in the presence of 500 micromol/L Hcy. 4. The results of the present study indicate that Hcy, an important risk factor for atrial fibrillation, could cause electrophysiological disturbances of potassium currents in human atrial myocytes.

Increasing Intracellular Calcium of Guinea Pig Ventricular Myocytes Induced by Platelet Activating Factor through IP3 Pathway

We used Fluo-3/AM to examine the effect of platelet-activating factor on the intracellular Ca2+([Ca2+]i) levels in isolated myocytes of guinea pig ventricle. Myocytes were isolated with Langendorff perfusion technique and were challenged with platelet-activating factor. Addition of platelet-activating factor (1 pM to 10 nM) significantly increased the [Ca2+]i in the presence and absence of extracellular Ca2+. The notion that increases in intracellular Ca2+ induced by platelet-activating factor is the result of stimulation of intracellular Ca2+ pool rather than increasing Ca2+ influx was further supported by the whole cell patch-clamp experiments in which the platelet-activating factor did not alter the activity of L-type of Ca2+ channels (I(Ca-L)). Treatment of myocytes with ryanodine failed to abolish the stimulatory effect of platelet-activating factor on [Ca2+]i. In contrast, inhibition of IP3-sensitive Ca2+ release pool with 2-aminoethoxydiphenyl borate (2-APB) blocked the effect of platelet-activating factor. We conclude that the platelet-activating factor-induced increase in intracellular Ca2+ is mediated by stimulation of IP3 receptor but not by stimulation of I(Ca-L) and ryanodine-sensitive receptor.

Effects of artemisinin on action potentials from C-type nodose ganglion neurons

AIM

To investigate the effects of artemisinin (Art) on the action potentials (AP) recorded from identified C-type nodose neurons and study its anti-arrhythmic and anesthetic mechanisms.

METHODS

Neonatal and adult rats were selected for the preparation of isolated nodose ganglia neurons (NGN) and nodose ganglion-vagus slice preparation. Somatic AP were recorded from both isolated and slice NGN using whole-cell patch technique. Conduction velocity (CV) was measured using slice preparation. The effects of Art on AP were evaluated with the reference to ketamine.

RESULTS

Effects of Art on AP were that: (1) AP depolarizing profiles were inhibited without changing resting membrane potential (RMP). The peak of AP (AP(peak)) and upstroke velocity (UV(APD50) and UV(max)) decreased markedly (P<0.01). (2) The duration of AP at the point of half repolarization (APD(50)) was obviously prolonged (P<0.01). (3) Art also slowed down AP repolarization profiles (downstroke velocity, DV(APD50), and DV(max)) and the peak of after-hyperpolarization (AHP(peak)) was less negative. (4) Total inward and outward currents over the course of AP were significantly reduced in the presence of Art. (5) CV did not changed by Art. (6) The effects of Art on AP were concentration-dependent and resembled with those of ketamine except for CV.

CONCLUSION

Art inhibited both depolarization and repolarization of AP, suggesting that the effects of Art were probably, due to the blockade of Na+ and K+ ion channels.

Effects of berbamine on ATP-induced [Ca2+]i mobilization in cultured vascular smooth muscle cells and cardiomyocytes

AIM

To study the effects of berbamine (Ber) on [Ca2+]i homeostasis induced by adenosine triphosphate (ATP) in vascular smooth muscle cells (VSMC) of rabbits and cardiomyocytes of rats.

METHODS

Both cell types were cultured and loaded with Fura 3-AM. [Ca2+]i was measured by fluorescent intensity (FI) in each cell with confocal microscopy.

RESULTS

(1) ATP 30 mumol.L-1 elevated [Ca2+]i in VSMC and cardiomyocytes, FI values reached 660 +/- 258 and 1058 +/- 252 from 250 +/- 84 and 218 +/- 76 at 19 s +/- 5 s and 11.8 s +/- 2.4 s, but FI in nucleus was not changed in VSMC. (2) Ber 30 mumol.L-1 did not affect the resting FI in both cell types, but prolonged the time to peak (P < 0.01) and reduced the FI elevated by ATP (P < 0.01), but not completely inhibited even at 100 mumol.L-1. (3) In D-Hanks' solution or in the presence of egtazic acid (EGTA) 3 mmol.L-1, the inhibitory effect of Ber was not seen (P > 0.05). (4) All effects of Ber on ATP-induced [Ca2+]i mobilization were similar to those of Ver 10 mumol.L-1.

CONCLUSION

In VSMC and cardiomyocytes, ATP-induced CA2+ influx was inhibited by Ber and Ver, while the Ca2+ release was not.

Effects of MK-447 on platelet shape change, aggregation, and ATP release by collagen, ADP, and stable analogue of thromboxane A2 in rabbit platelets

AIM

To investigate the effects of MK-447 on platelet shape change, aggregation, and ATP release by collagen (Col), ADP, and stable analogue of thromboxane A2 (STA2) in rabbits.

METHODS

Platelet shape change and aggregation were quantified in light transmission by turbidimetric method and release reaction was assessed by the amount of ATP in platelet-rich plasma (PRP).

RESULTS

(1) MK-447 100-700 mumol.L-1 caused only the shape change, which was not inhibited by indometacin 3 mumol.L-1. Platelet shape changes by Col, ADP, and STA2 were reduced (P < 0.01) after the addition of MK-447. The lag phase was prolonged (P < 0.01) in Col and shortened (P < 0.01) in ADP. (2) MK-447 reduced the aggregation by Col 5 mg.L-1 (P < 0.01), and enhanced that by ADP 0.3-10 mumol.L-1 and STA2 0.1-3 mumol.L-1 (P < 0.01). (3) The release reaction by STA2 1-3 mumol.L-1 was also increased (P < 0.01). The effects of MK-447 on STA2 were not inhibited by S-145.

CONCLUSION

MK-447 induced the platelet shape change, and showed the dual effects, inhibition or enhancement, on the actions by different aggregating agents.

Cytosolic-Ca2+ and coxsackievirus B3-induced apoptosis in cultured cardiomyocytes of rats

AIM

To explore the role of cytosolic free calcium ([Ca2+]i) in apoptosis induced by coxsackievirus B3 (CVB3) in cultured cardiomyocytes of rats.

METHODS

Primary cultured cardiomyocyte was prepared from Wistar rats ages 2-3 d. The apoptosis in cardiomyocyte was determined by terminated deoxynucleotide transferase directed d-UTP nick and end labeling (TUNEL) method, and the apoptosis was observed under a transmission electron microscope. [Ca2+]i in single cardiomyocyte loaded with Fluo 3-AM was measured by confocal microsorope.

RESULTS

(1) The concentration of CVB3 in the medium reached the peak at 24 h after CVB3 infection. (2) The apoptotic cells were not found in CVB3-infected cardiomyocyte in first 10 h, but amounted to 5% at 17 h, 60% at 24 h, and 90% at 36 h. (3) The peak value of [Ca2+]i elevation reached at 17 h after CVB3 infection (P < 0.01). (4) The characteristics of apoptosis was also seen by transmission electron microscope.

CONCLUSION

CVB3 induced the apoptosis in cultured cardiomyocyte, and [Ca2+]i mobilization was involved in the signal transduction process in apoptosis cells, and played an important role especially in the early stage of apoptosis induced by CVB3.

Antagonistic effects of berbamine on [Ca2+]i mobilization by KCl, norepinephrine, and caffeine in newborn rat cardiomyocytes

AIM

To study the effects of berbamine (Ber) on intracellular calcium concentration ([Ca2+]i) mobilized by KCl depolarization, norepinephrine (NE), and caffeine.

METHODS

[Ca2+]i was measured with fluorescent intensity (FI) by confocal microscope in single cultured cardiomyocytes of newborn rats loaded with Fluo 3-AM 2 mumol.L-1.

RESULTS

FI value of [Ca2+]i in control level was 248 +/- 70 in the presence of extracellular calcium 1.5 mmol.L-1 and was not changed by Ber 3-30 mumol.L-1. KCl (60 mmol.L-1)- and NE (30 mumol.L-1)-induced [Ca2+]i mobilizations were inhibited (P < 0.01) by Ber 30 mumol.L-1, similar to that of verapamil (Ver). The inhibitory effect of Ber on [Ca2+]i induced by KCl was further increased (P < 0.05) in the presence of egtazic acid 3 mmol.L-1, but that on [Ca2+]i induced by NE was not changed. The [Ca2+]i mobilized by caffeine 80 and 160 mumol.L-1 in D-Hanks' solution was not affected (P > 0.05) by Ber and Ver.

CONCLUSION

Ber possessed the antagonistic effects on [Ca2+]i increases via voltage-dependent Ca2+ channel and receptor-operated Ca2+ channel in newborn rat cardiomyocytes, but without effect on intracellular Ca2+ release.

Inhibitory effects of ONO-3708 and S-145 on shape change and aggregation of rabbit platelets induced by STA2

AIM

To study the mode of inhibition of ONO-3708 and S-145, 2 antagonists of thromboxane A2 (TXA2) receptors, against the rabbit platelet shape change and aggregation induced by stable analogue of TXA2 (STA2).

METHODS

The platelet shape change and aggregation were quantified by the light transmission through platelet-rich plasma (PRP) and the intracellular calcium concentration ([Ca2+]i) was measured by fluorescence and imaging.

RESULTS

(1) In PRP, STA2 (3 mumol.L-1)-induced aggregation was inhibited by egtazic acid 3 mmol.L-1, ONO-3708 300 mumol.L-1, and S-145 1 mumol.L-1 (P < 0.01), but not by indometacin (Ind) 3 mumol.L-1. The shape change induced by STA2 was inhibited only by S-145 in a concentration-dependent manner. S-145 1 and 3 mumol.L-1 were required to inhibit the shape change and aggregation. (2) The inhibitory effect of S-145, but not ONO-3708, was increased along with the prolongation of preincubation. (3) ONO-3708 lost the inhibitory effect on STA2-induced aggregation after washing, while the inhibitory effect of S-145 was enhanced by prolongation of preincubation and remained after washing. (4) STA2 3 mumol.L-1-induced [Ca2+]i mobilization was unaffected by Ind, partially reduced by ONO-3708 and egtazic acid 3 mmol.L-1 (P < 0.01), but completely inhibited by S-145 (P < 0.01).

CONCLUSION

S-145 and ONO-3708 were bound to a different site of the TXA2 receptor.