[Relationship between acupoint sensitization and changes in dorsal root ganglion neuron excitability in myocardial ischemia mice].

OBJECTIVE: To investigate the relationship between the sensitization state of acupoints on the surface of the myocardial ischemia (MI) model mice and the changes in the electrophysiological properties of the dorsal root ganglion (DRG) neurons in the corresponding spinal cord segment, and its underlying mechanism. METHODS: Sixty-eight male C57BL/6J mice were randomly divided into control and model groups (34 mice in each group). The model group received an intraperitoneal injection of 160 mg/kg isoproterenol (ISO) to establish the MI model, and the control group received an injection of the same dose of normal saline as the model group. After modeling for about 6 days, MI proportion was measured by HE staining to verify the pathological changes in the heart tissue. Evans blue (EB) dye was injected into the tail vein of mice to reflect the size, location, distribution, and number of exudates on the body surface. Then, whole-cell membrane currents, intrinsic excitability and membrane properties of different types of DRG neurons were evaluated by electrophysiological experiment in vitro. RESULTS: Compared with the control group, the heart size was larger, with pathological outcomes showing enlarged myocardial hypertrophy, destroyed structure of cardiomyocytes, with mononuclear cell infiltration among the cardiomyocytes in the model group. Compared with the control group, the number of EB exudation points was significantly increased (P<0.01), which were mainly concentrated in the epidermis near the T1-T5 segment of the spinal cord, "Feishu" (BL13), "Jueyinshu" (BL14) and "Xinshu" (BL15) in the model group. Compared with the control group, the rheobase and action potential amplitude (APA) of DRG medium-sized neurons were obviously decreased (P<0.01, P<0.05), while the whole-cell membrane currents, the spike numbers, the average instantaneous frequency, and the average discharge frequency were markedly increased (P<0.01). There were no significant alterations in the membrane properties and intrinsic excitability induced by depolarized currents of small-sized neurons between groups. Compared with the control group, the whole-cell membrane currents, spike numbers, and the average instantaneous frequency were significantly increased in the model group(P<0.05, P<0.01) while rheobase was significantly decreased (P<0.05) in DRG medium-sized neurons labeled with biotin and CGRP. CONCLUSION: After the mice were modeled by ISO, the DRG medium-size neurons in the T1-T5 segment of the spinal cord may mediate the sensitization of acupoints on the body surface through their different neuronal membrane properties and intrinsic excitabilities.

[Research on mechanisms of acupoint sensitization in gastric ulcer mice from perspective of dorsal root ganglion neuronal excitability].

OBJECTIVE: To investigate the relationship between acupoint sensitization on the body surface and neuronal intrinsic excitability of the medium- and small-size dorsal root ganglion (DRG) neurons from the perspective of ion channel kinetics in mice with gastric ulcer. METHODS: Male C57BL/6J mice were randomly divided into control (n=32) and model groups (n=34). The gastric ulcer model was established by injection of 60% glacial acetic acid (0.2 mL/100 g) into the gastric wall muscle layer and submucosa near the pylorus in the minor curvature of the stomach. In contrast, the same dose of normal saline was injected in the same way in the control group. Six days after modeling, Evans blue (EB) solution was injected into the mouse's tail vein for observing the number and distribution of the exudation blue spots on the body surface. Histopathological changes of the gastric tissue were observed by H.E. staining. Then, whole-cell membrane currents and intrinsic excitability of medium- and small-size neurons in the spinal T9-T11 DRGs were measured by in vitro electrophysiology combining with biocytin-ABC method. RESULTS: In the control group, EB exudation blue spots were not obvious, while in the model group, the blue spots on the body surface were densely distributed in the area of spinal T9-T11 segments, the epigastric region, and the skin around "Zhongwan" (CV12) and "Huaroumen" (ST24) regions, and near the surgical incision region. Compared with the control group, the model group had a high level of eosinophilic infiltrates in the submucosa of gastric tissues, severe gastric fossa structure damage, gastric fundus gland dilation and other pathological manifestations. The number of exudation blue spots was proportional to the degree of inflammatory reaction in the stomach. In comparison with the control group, the spike discharges of type II of medium-size DRG neurons in T9-T11 segments were decreased, and the current of whole-cell membrane was increased, basic intensity was decreased (P<0.05), discharge frequency and discharge number were increased (P<0.01,P<0.000 1); while the discharges of type I small-size DRG neurons were decreased, those of type II neurons increased, the whole-cell membrane current was decreased, and discharge frequency and discharge number were decreased (P<0.01, P<0.000 1). CONCLUSION: Both the medium- and small-size DRG neurons from the spinal T9-T11 segments involve in gastric ulcer-induced acupoint sensitization via their different spike discharge activities. And intrinsic excitability of these DRG neurons can not only dynamically encode the plasticity of acupoint sensitization, but also can help us understand the neural mechanism of acupoint sensitization induced by visceral injury.

Silica Nanoparticles Disturb Ion Channels and Transmembrane Potentials of Cardiomyocytes and Induce Lethal Arrhythmias in Mice.

BACKGROUND: The toxicity of silica nanoparticles (SiNPs) on cardiac electrophysiology has seldom been evaluated. METHODS: Patch-clamp was used to investigate the acute effects of SiNP-100 (100 nm) and SiNP-20 (20 nm) on the transmembrane potentials (TMPs) and ion channels in cultured neonatal mouse ventricular myocytes. Calcium mobilization in vitro, cardiomyocyte ROS generation, and LDH leakage after exposure to SiNPs in vitro and in vivo were measured using a microplate reader. Surface electrocardiograms were recorded in adult mice to evaluate the arrhythmogenic effects of SiNPs in vivo. SiNP endocytosis was observed using transmission electron microscopy. RESULTS: Within 30 min, both SiNPs (10-8-10-6 g/mL) did not affect the resting potential and IK1 channels. SiNP-100 increased the action potential amplitude (APA) and the INa current density, but SiNP-20 decreased APA and INa density. SiNP-100 prolonged the action potential duration (APD) and decreased the Ito current density, while SiNP-20 prolonged or shortened the APD, depending on exposure concentrations and increased Ito density. Both SiNPs (10-6 g/mL) induced calcium mobilization but did not increase ROS and LDH levels and were not endocytosed within 10 min in cardiomyocytes in vitro. In vivo, SiNP-100 (4-10 mg/kg) and SiNP-20 (4-30 mg/kg) did not elevate myocardial ROS but increased LDH levels depending on dose and exposure time. The same higher dose of SiNPs (intravenously injected) induced tachyarrhythmias and lethal bradyarrhythmias within 90 min in adult mice. CONCLUSION: SiNPs (i) exert rapid toxic effects on the TMPs of cardiomyocytes in vitro largely owing to their direct interfering effects on the INa and Ito channels and Ca2+ homeostasis but not IK1 channels and ROS levels, and (ii) induce tachyarrhythmias and lethal bradyarrhythmias in vivo. SiNP-100 is more toxic than SiNP-20 on cardiac electrophysiology, and the toxicity mechanism is likely more complicated in vivo.

Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice.

It is recognized that stress can induce cardiac dysfunction, but the underlying mechanisms are not well understood. The present study aimed to test the hypothesis that chronic negative stress leads to alterations in DNA methylation of certain cardiac genes, which in turn contribute to pathologic remodeling of the heart. We found that mice that were exposed to chronic restraint stress (CRS) for 4 wk exhibited cardiac remodeling toward heart failure, as characterized by ventricular chamber dilatation, wall thinning, and decreased contractility. CRS also induced cardiac arrhythmias, including intermittent sinus tachycardia and bradycardia, frequent premature ventricular contraction, and sporadic atrioventricular conduction block. Circulating levels of stress hormones were elevated, and the cardiac expression of tyrosine hydroxylase, a marker of sympathetic innervation, was increased in CRS mice. Using reduced representation bisulfite sequencing, we found that although CRS did not lead to global changes in DNA methylation in the murine heart, it nevertheless altered methylation at specific genes that are associated with the dilated cardiomyopathy (DCM) (e.g., desmin) and adrenergic signaling of cardiomyocytes (ASPC) (e.g., adrenergic receptor-α1) pathways. We conclude that CRS induces cardiac remodeling and arrhythmias, potentially through altered methylation of myocardial genes associated with the DCM and ASPC pathways.-Zhang, P., Li, T., Liu, Y.-Q., Zhang, H., Xue, S.-M., Li, G., Cheng, H.-Y.M., Cao, J.-M. Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice.