Alterations of calcium channels and cell excitability in intracardiac ganglion neurons from type 2 diabetic rats

Cellular and Molecular Mechanisms Underlying Altered Excitability of Cardiac Efferent Neurons in Cirrhotic Rats

Patients with cirrhosis often exhibit cardiac autonomic dysfunction (CAD), characterized by enhanced cardiac sympathetic activity and diminished cardiac vagal tone, leading to increased morbidity and mortality. This study delineates the cellular and molecular mechanisms associated with altered neuronal activities causing cirrhosis-induced CAD. Biliary and nonbiliary cirrhotic rats were produced by common bile duct ligation (CBDL) and intraperitoneal injections of thioacetamide (TAA), respectively. Three weeks after CBDL or TAA injection, the assessment of heart rate variability revealed autonomic imbalance in cirrhotic rats. We observed increased excitability in stellate ganglion (SG) neurons and decreased excitability in intracardiac ganglion (ICG) neurons in cirrhotic rats compared to sham-operated controls. Additionally, threshold, rheobase, and action potential duration exhibited opposite alterations in SG and ICG neurons, along with changes in afterhyperpolarization duration. A- and M-type K⁺ channels were significantly downregulated in SG neurons, while M-type K⁺ channels were upregulated, with downregulation of the N- and L-type Ca2⁺ channels in the ICG neurons of cirrhotic rats, both in transcript expression and functional activity. Collectively, these findings suggest that cirrhosis induces an imbalance between cardiac sympathetic and parasympathetic neuronal activities via the differential regulation of K+ and Ca2+ channels. Thus, cirrhosis-induced CAD may be associated with impaired autonomic efferent functions within the homeostatic reflex arc that regulates cardiac functions.

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

Hydrogen Peroxide Scavenging Restores N-Type Calcium Channels in Cardiac Vagal Postganglionic Neurons and Mitigates Myocardial Infarction-Evoked Ventricular Arrhythmias in Type 2 Diabetes Mellitus

Objective

Withdrawal of cardiac vagal activity is associated with ventricular arrhythmia-related high mortality in patients with type 2 diabetes mellitus (T2DM). Our recent study found that reduced cell excitability of cardiac vagal postganglionic (CVP) neurons is involved in cardiac vagal dysfunction and further exacerbates myocardial infarction (MI)-evoked ventricular arrhythmias and mortality in T2DM. However, the mechanisms responsible for T2DM-impaired cell excitability of CVP neurons remain unclear. This study tested if and how elevation of hydrogen peroxide (H2O2) inactivates CVP neurons and contributes to cardiac vagal dysfunction and ventricular arrhythmogenesis in T2DM.

Methods and Results

Rat T2DM was induced by a high-fat diet plus streptozotocin injection. Local in vivo transfection of adenoviral catalase gene (Ad.CAT) successfully induced overexpression of catalase and subsequently reduced cytosolic H2O2 levels in CVP neurons in T2DM rats. Ad.CAT restored protein expression and ion currents of N-type Ca2+ channels and increased cell excitability of CVP neurons in T2DM. Ad.CAT normalized T2DM-impaired cardiac vagal activation, vagal control of ventricular function, and heterogeneity of ventricular electrical activity. Additionally, Ad.CAT not only reduced the susceptibility to ventricular arrhythmias, but also suppressed MI-evoked lethal ventricular arrhythmias such as VT/VF in T2DM.

Conclusions

We concluded that endogenous H2O2 elevation inhibited protein expression and activation of N-type Ca2+ channels and reduced cell excitability of CVP neurons, which further contributed to the withdrawal of cardiac vagal activity and ventricular arrhythmogenesis in T2DM. Our current study suggests that the H2O2-N-type Ca2+ channel signaling axis might be an effective therapeutic target to suppress ventricular arrhythmias in T2DM patients with MI.

Effects of long-term consumption of sucralose associated with high-fat diet in male mice

Sucralose is a widely consumed non-nutritive sweetener (NNS). Studies have shown that some NNS can favor weight gain by altering the intestinal microbiota, satiety hormone production, or aspects related to glucose homeostasis. In this study, we investigated the effects of ad libitum sucralose consumption in mice fed with normal or high-fat diet (HFD) for an extended period (16 weeks). Weight gain, final body composition, energy expenditure, intestinal and pancreatic hormone production, and endotoxemia during a voracity test, as well as liver and skeletal muscles were evaluated after 16 weeks. We observed that sucralose supplementation reduced weight gain in HFD-fed mice but did not change weight gain in mice fed with normal diet. The evaluation of HFD mice showed that sucralose supplementation resulted in improvements in glycemic homeostasis, hepatic steatosis, and increased energy expenditure. Our results suggest that sucralose consumption promotes different outcomes in relation to weight gain when combined with different diets, which may explain the controversial data in previous studies, and can be considered in future clinical research aimed at clarifying the impact of NNS consumption on human health.

Reduced Cell Excitability of Cardiac Postganglionic Parasympathetic Neurons Correlates With Myocardial Infarction-Induced Fatal Ventricular Arrhythmias in Type 2 Diabetes Mellitus

Objective

Withdrawal of cardiac vagal activity is considered as one of the important triggers for acute myocardial infarction (MI)-induced ventricular arrhythmias in type 2 diabetes mellitus (T2DM). Our previous study demonstrated that cell excitability of cardiac parasympathetic postganglionic (CPP) neurons was reduced in T2DM rats. This study investigated whether cell excitability of CPP neurons is associated with cardiac vagal activity and MI-induced ventricular arrhythmias in T2DM rats.

Methods

Rat T2DM was induced by a high-fat diet plus streptozotocin injection. MI-evoked ventricular arrhythmia was achieved by surgical ligation of the left anterior descending coronary artery. Twenty-four-hour, continuous ECG recording was used to quantify ventricular arrhythmic events and heart rate variability (HRV) in conscious rats. The power spectral analysis of HRV was used to evaluate autonomic function. Cell excitability of CPP neurons was measured by the whole-cell patch-clamp technique.

Results

Twenty-four-hour ECG data demonstrated that MI-evoked fatal ventricular arrhythmias are more severe in T2DM rats than that in sham rats. In addition, the Kaplan-Meier analysis demonstrated that the survival rate over 2 weeks after MI is significantly lower in T2DM rats (15% in T2DM+MI) compared to sham rats (75% in sham+MI). The susceptibility to ventricular tachyarrhythmia elicited by programmed electrical stimulation was higher in anesthetized T2DM+MI rats than that in rats with MI or T2DM alone (7.0 ± 0.58 in T2DM+MI group vs. 3.5 ± 0.76 in sham+MI). Moreover, as an index for vagal control of ventricular function, changes of left ventricular systolic pressure (LVSP) and the maximum rate of increase of left ventricular pressure (LV dP/dt_max) in response to vagal efferent nerve stimulation were blunted in T2DM rats. Furthermore, T2DM increased heterogeneity of ventricular electrical activities and reduced cardiac parasympathetic activity and cell excitability of CPP neurons (current threshold-inducing action potentials being 62 ± 3.3 pA in T2DM rats without MI vs. 27 ± 1.9 pA in sham rats without MI). However, MI did not alter vagal control of the ventricular function and CPP neuronal excitability, although it also induced cardiac autonomic dysfunction and enhanced heterogeneity of ventricular electrical activities.

Conclusion

The reduction of CPP neuron excitability is involved in decreased cardiac vagal function, including cardiac parasympathetic activity and vagal control of ventricular function, which is associated with MI-induced high mortality and malignant ventricular arrhythmias in T2DM.

Effect of type II diabetes-induced osteoarthritis on articular cartilage aging in rats: A study in vivo and in vitro

OBJECTIVES

Some evidence suggests that type II diabetes mellitus (T2DM) and osteoarthritis (OA) usually occur together clinically, and the symptoms are more obvious compared with non-diabetic patients with OA. We aimed to explore the effects in cartilage degradation, damage, and aging after T2DM combined with OA.

METHODS

Thirty male Sprague-Dawley (SD) rats were randomly divided into the young-control group (YCG, n = 10), old-control group (OCG, n = 10), and old T2DM-induced OA group (OTOG, n = 10) after the pre-experiment. T2DM model was established using a high-fat diet and streptozotocin. In vivo, all rats were evaluated by behavior, histology, immunohistochemistry, and enzyme-linked immunosorbent assay (ELISA). In vitro, chondrocytes of 17-day-old SD rats were cultured to obtain the passage 1 (P1) and passage 5 (P5) chondrocytes. The effects of different concentrations glucose on chondrocyte senescence were evaluated by chondrocyte staining, immunofluorescence, western blotting, and ROS analysis.

RESULTS

The results of histology (hematoxylin-eosin staining, safranin O-fast green staining, alizarin red S staining, and Mankin score), immunohistochemistry (COL-II, MMP-13, and p21), ELISA (IL-6 and IL-8), western blotting (COL-II, MMP-13, p21, p53, and p16), immunofluorescence, and ROS analysis indicated that the degeneration and aging in the articular cartilage of OTOG were more serious than other groups. Moreover, high concentration glucose can accelerated the degradation and aging degree of cartilage. The changes in P5 are more obvious than in P1 cells.

CONCLUSION

T2DM-induced OA can aggravate the aging of articular cartilage in aging individuals. High concentration glucose can cause a certain degree of damage, degradation, and aging of chondrocytes.

Functional plasticity of cardiac efferent neurons contributes to traumatic brain injury-induced cardiac autonomic dysfunction

Traumatic brain injury (TBI) frequently causes cardiac autonomic dysfunction (CAD), irrespective of its severity, which is associated with an increased morbidity and mortality in patients. Despite the significance of probing the cellular mechanism underlying TBI-induced CAD, animal studies on this mechanism are lacking. In the current study, we tested whether TBI-induced CAD is associated with functional plasticity in cardiac efferent neurons. In this regard, TBI was induced by a controlled cortical impact in rats. Assessment of heart rate variability and baroreflex sensitivity indicated that CAD was developed in the sub-acute period after moderate and severe TBI. The cell excitability was increased in the stellate ganglion (SG) neurons and decreased in the intracardiac ganglion (ICG) neurons in TBI rats, compared with the sham-operated rats. The transient A-type K+ (KA) currents, but not the delayed rectifying K+ currents were significantly decreased in SG neurons in TBI rats, compared with sham-operated rats. Consistent with these electrophysiological data, the transcripts encoding the Kv4 α subunits were significantly downregulated in SG neurons in TBI rats, compared with sham-operated rats. TBI causes downregulation and upregulation of M-type K+ (KM) currents and the KCNQ2 mRNA transcripts, which may contribute to the hyperexcitability of the SG neurons and the hypoexcitability of the ICG neurons, respectively. In conclusion, the key cellular mechanism underlying the TBI-induced CAD may be the functional plasticity of the cardiac efferent neurons, which is caused by the regulation of the KA and/or KM currents.

The effects of early diabetes on inner retinal neurons

Diabetic retinopathy is now well understood as a neurovascular disease. Significant deficits early in diabetes are found in the inner retina that consists of bipolar cells that receive inputs from rod and cone photoreceptors, ganglion cells that receive inputs from bipolar cells, and amacrine cells that modulate these connections. These functional deficits can be measured in vivo in diabetic humans and animal models using the electroretinogram (ERG) and behavioral visual testing. Early effects of diabetes on both the human and animal model ERGs are changes to the oscillatory potentials that suggest dysfunctional communication between amacrine cells and bipolar cells as well as ERG measures that suggest ganglion cell dysfunction. These are coupled with changes in contrast sensitivity that suggest inner retinal changes. Mechanistic in vitro neuronal studies have suggested that these inner retinal changes are due to decreased inhibition in the retina, potentially due to decreased gamma aminobutyric acid (GABA) release, increased glutamate release, and increased excitation of retinal ganglion cells. Inner retinal deficits in dopamine levels have also been observed that can be reversed to limit inner retinal damage. Inner retinal targets present a promising new avenue for therapies for early-stage diabetic eye disease.

Metformin Regulates the Expression of SK2 and SK3 in the Atria of Rats With Type 2 Diabetes Mellitus Through the NOX4/p38MAPK Signaling Pathway

We previously found that metformin regulates the ion current conducted by the small conductance calcium-activated potassium channels (SK channels) in the atria of rats with type 2 diabetes mellitus (T2DM) as well as the mRNA and protein expression of the SK2 and SK3 subtypes of SK channels. In this study, we hypothesized that the nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4)/p38 mitogen-activated protein kinase (p38MAPK) signaling pathway was involved in the metformin-mediated regulation of SK2 and SK3 expression in the atria of rats with T2DM. We randomly divided Wistar rats into the control group, the untreated T2DM group, the metformin-treated group, the group receiving subcutaneous injections of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) inhibitor diphenyleneiodonium (DPI), and the group receiving tail vein injections of the p38MAPK agonist anisomycin. Real-time polymerase chain reaction, Western blot, and immunohistochemistry were applied to examine the expression levels of SK2, SK3, NOX4, and phospho-p38MAPK (p-p38MAPK) mRNAs and proteins in the atrial tissue of relevant groups. We observed that the expression levels of NOX4 mRNA and protein and p-p38MAPK protein were significantly elevated in the atria of rats with T2DM compared with the control group. In addition, SK2 protein expression was reduced, whereas SK3 protein expression was increased. The 8-week treatment with metformin markedly reduced the expression levels of NOX4 mRNA and protein and p-p38MAPK protein, upregulated the SK2 expression, and downregulated the SK3 expression. Tail vein injection with anisomycin significantly increased the p-p38MAPK expression while further inhibiting the expression of SK2 and enhancing the expression of SK3. Subcutaneous injection with DPI considerably inhibited the expression of NOX4, further enhanced the expression of SK2 and suppressed the expression of SK3. In addition, subcutaneous injection with DPI significantly suppressed the phosphorylation of p38MAPK. In conclusion, the NOX4/p38MAPK signaling pathway mediates the downregulation of SK2 and the upregulation of SK3 in the atria of rats with T2DM. Long-term metformin treatment upregulates SK2 protein expression and downregulates SK3 protein expression by inhibiting the NOX4/p38MAPK signaling pathway.

Exaggerated pressor and sympathetic responses to stimulation of the mesencephalic locomotor region and exercise pressor reflex in type 2 diabetic rats

The cardiovascular responses to exercise are potentiated in patients with type 2 diabetes mellitus (T2DM). However, the underlying mechanisms causing this abnormality remain unknown. Central command (CC) and the exercise pressor reflex (EPR) are known to contribute significantly to cardiovascular control during exercise. Thus these neural signals are viable candidates for the generation of the abnormal circulatory regulation in this disease. We hypothesized that augmentations in CC as well as EPR function contribute to the heightened cardiovascular responses during exercise in T2DM. To test this hypothesis, changes in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in response to electrical stimulation of mesencephalic locomotor region (MLR), a putative component of the central command pathway, and activation of the EPR, evoked by electrically induced hindlimb muscle contraction, were examined in decerebrate animals. Sprague-Dawley rats were given either a normal diet (control) or a high-fat diet (14-16 wk) in combination with two low doses (35 mg/kg week 1, 25 mg/kg week 2) of streptozotocin (T2DM). The changes in MAP and RSNA responses to MLR stimulation were significantly greater in T2DM compared with control (2,739 ± 123 vs. 1,298 ± 371 mmHg/s, 6,326 ± 1,621 vs. 1,390 ± 277%/s, respectively, P < 0.05). Similarly, pressor and sympathetic responses to activation of the EPR in diabetic animals were significantly augmented compared with control animals (436 ± 74 vs. 134 ± 44 mmHg/s, 645 ± 135 vs. 139 ± 65%/s, respectively, P < 0.05). These findings provide the first evidence that CC and the EPR may generate the exaggerated rise in sympathetic activity and blood pressure during exercise in T2DM.

Carnosine Prevents Type 2 Diabetes-Induced Osteoarthritis Through the ROS/NF-κB Pathway

Background: The anti-inflammatory and antioxidant capacity of carnosine (CAR) has been investigated in autoimmune diseases. The aim of this study was to evaluate the potential protective effects of oral CAR supplements to ameliorate type 2 diabetes mellitus (T2DM)-induced osteoarthritis (OA) in rats and its mechanism.

Methods: Seventy male Sprague–Dawley rats were randomly divided into the control group (CG, n = 10) and the T2DM group (n = 60). A rat model of T2DM was established using a high fat diet and streptozotocin (30 mg/kg, i.p.). The 41 rats that developed T2DM were chosen and randomly divided into four groups: T2DM-induced OA group (OAG, n = 11), and the T2DM-induced OA with low, moderate, and high-doses of CAR for 8 weeks group (CAR-L, CAR-M, and CAR-H, n = 10). After 13 weeks, all rats were evaluated by enzyme-linked immunosorbent assay (ELISA), histology, immunohistochemistry, and western blotting. Fibroblast-like synoviocytes (FLSs) were obtained from the knee joints of all rats. The effects of CAR on the inflammatory response in interleukin (IL)-1β-stimulated FLSs under a high glucose environment were evaluated by real-time quantitative polymerase chain reaction, western blotting, flow cytometry, and immunofluorescence.

Results: The results of ELISA (IL-1β and tumor necrosis factor-α), the histological evaluation (Mankin and OARSI score), western blotting [COL2A1, matrix metalloproteinase (MMP)-3, MMP-13, IL-1β, and nuclear factor-kappaB (NF-κB) p65], and immunohistochemistry (COL2A1, MMP-3, and MMP-13) indicated that oral CAR attenuated the development of T2DM-induced OA and suppressed the inflammatory response. Moreover, CAR alleviated MMP-3 and MMP-13 expression levels by decreasing reactive oxygen species content and suppressing nuclear translocation of NF-κB p65 on IL-1β-induced FLSs in a high glucose environment.

Conclusion: These findings indicate that oral CAR had chondroprotective effects on T2DM-induced OA through the reactive oxygen species (ROS)/NF-κB pathway.

Reduced N-Type Ca2+ Channels in Atrioventricular Ganglion Neurons Are Involved in Ventricular Arrhythmogenesis

Background

Attenuated cardiac vagal activity is associated with ventricular arrhythmogenesis and related mortality in patients with chronic heart failure. Our recent study has shown that expression of N‐type Ca²⁺ channel α‐subunits (Ca_v2.2‐α) and N‐type Ca²⁺ currents are reduced in intracardiac ganglion neurons from rats with chronic heart failure. Rat intracardiac ganglia are divided into the atrioventricular ganglion (AVG) and sinoatrial ganglion. Ventricular myocardium receives projection of neuronal terminals only from the AVG. In this study we tested whether a decrease in N‐type Ca²⁺ channels in AVG neurons contributes to ventricular arrhythmogenesis.

Methods and Results

Lentiviral Ca_v2.2‐α shRNA (2 μL, 2×10⁷ pfu/mL) or scrambled shRNA was in vivo transfected into rat AVG neurons. Nontransfected sham rats served as controls. Using real‐time single‐cell polymerase chain reaction and reverse‐phase protein array, we found that in vivo transfection of Ca_v2.2‐α shRNA decreased expression of Ca_v2.2‐α mRNA and protein in rat AVG neurons. Whole‐cell patch‐clamp data showed that Ca_v2.2‐α shRNA reduced N‐type Ca²⁺ currents and cell excitability in AVG neurons. The data from telemetry electrocardiographic recording demonstrated that 83% (5 out of 6) of conscious rats with Ca_v2.2‐α shRNA transfection had premature ventricular contractions (P<0.05 versus 0% of nontransfected sham rats or scrambled shRNA‐transfected rats). Additionally, an index of susceptibility to ventricular arrhythmias, inducibility of ventricular arrhythmias evoked by programmed electrical stimulation, was higher in rats with Ca_v2.2‐α shRNA transfection compared with nontransfected sham rats and scrambled shRNA‐transfected rats.

Conclusions

A decrease in N‐type Ca²⁺ channels in AVG neurons attenuates vagal control of ventricular myocardium, thereby initiating ventricular arrhythmias.

Correlation of Ventricular Arrhythmogenesis with Neuronal Remodeling of Cardiac Postganglionic Parasympathetic Neurons in the Late Stage of Heart Failure after Myocardial Infarction

Introduction: Ventricular arrhythmia is a major cause of sudden cardiac death in patients with chronic heart failure (CHF). Our recent study demonstrates that N-type Ca²⁺ currents in intracardiac ganglionic neurons are reduced in the late stage of CHF rats. Rat intracardiac ganglia are divided into the atrioventricular ganglion (AVG) and sinoatrial ganglion. Only AVG nerve terminals innervate the ventricular myocardium. In this study, we tested the correlation of electrical remodeling in AVG neurons with ventricular arrhythmogenesis in CHF rats. Methods and Results: CHF was induced in male Sprague-Dawley rats by surgical ligation of the left coronary artery. The data from 24-h continuous radiotelemetry ECG recording in conscious rats showed that ventricular tachycardia/fibrillation (VT/VF) occurred in 3 and 14-week CHF rats but not 8-week CHF rats. Additionally, as an index for vagal control of ventricular function, changes of left ventricular systolic pressure (LVSP) and the maximum rate of left ventricular pressure rise (LV dP/dt_max) in response to vagal efferent nerve stimulation were blunted in 14-week CHF rats but not 3 or 8-week CHF rats. Results from whole-cell patch clamp recording demonstrated that N-type Ca²⁺ currents in AVG neurons began to decrease in 8-week CHF rats, and that there was also a significant decrease in 14-week CHF rats. Correlation analysis revealed that N-type Ca²⁺ currents in AVG neurons negatively correlated with the cumulative duration of VT/VF in 14-week CHF rats, whereas there was no correlation between N-type Ca²⁺ currents in AVG neurons and the cumulative duration of VT/VF in 3-week CHF. Conclusion: Malignant ventricular arrhythmias mainly occur in the early and late stages of CHF. Electrical remodeling of AVG neurons highly correlates with the occurrence of ventricular arrhythmias in the late stage of CHF.

The Role of Essential Fatty Acids in Anorexia Nervosa and Obesity

The two basic questions in food intake study are what we eat, and how much do we eat. Most research is directed toward the control of how much is eaten. This is likely the result of the increased number of individuals with eating disorders in the Western world. Feeding behavior is highly complex, and is controlled by many psychological, physiological, biochemical, and immunological factors. The aim of this review is to clarify the involvement of fatty acids in eating disorders such as anorexia and binge eating disorder. The review will describe the modified fatty acid profile observed in individuals with anorexia or binge eating disorder, and discuss on what factors fatty acids can exert beneficial effects. In addition, the differences and similarities between anorexia and binge eating disorder will be discussed. We suggest that beneficial effects of essential fatty acids on both anorexia and binge eating disorder can be explained by the stabilizing effect of those fatty acids on the neuronal membrane fluidity index.

Attenuated dopaminergic tone in the paraventricular nucleus contributing to sympathoexcitation in rats with Type 2 diabetes

The study was conducted to investigate the role for dopamine in the centrally mediated sympathoexcitatory response in rats with Type 2 diabetes (T2D). T2D was induced by a combination of high-fat diet (HFD) and low-dose streptozotocin (STZ). HFD/STZ treatment for 12-14 wk resulted in significant increase in the number of FosB-positive cells in the paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM). In anesthetized rats, administration of exogenous dopamine (dopamine hydrochloride, 20 mM) in the PVN, but not in the RVLM, elicited decreases in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) in control rats and but not in the T2D rats. Blocking the endogenous dopamine with dopamine D1/D5 receptor antagonist SCH39166 (2 mM) in the PVN and RVLM, resulted in increases in RSNA, MAP, and heart rate (HR) in both control and T2D rats. These responses were significantly attenuated in T2D rats compared with control rats (PVN - ΔRSNA: 21 ± 10 vs. 44 ± 2%; ΔMAP: 7 ± 3 vs. 19 ± 6 mmHg, ΔHR: 17 ± 5 vs. 32 ± 4 bpm, P < 0.05). There were no significant increases in response to dopamine D2/D3 receptor antagonist raclopride application in the PVN and RVLM of both control and T2D rats. Furthermore, there were decreased dopamine D1 receptor and D2 receptor expressions in the PVN of T2D rats. Taken together, these data suggest that reduced endogenous dopaminergic tone within the PVN may contribute to the sympathoexcitation in T2D.

Heart failure-induced changes of voltage-gated Ca2+ channels and cell excitability in rat cardiac postganglionic neurons

Chronic heart failure (CHF) is characterized by decreased cardiac parasympathetic and increased cardiac sympathetic nerve activity. This autonomic imbalance increases the risk of arrhythmias and sudden death in patients with CHF. We hypothesized that the molecular and cellular alterations of cardiac postganglionic parasympathetic (CPP) neurons located in the intracardiac ganglia and sympathetic (CPS) neurons located in the stellate ganglia (SG) possibly link to the cardiac autonomic imbalance in CHF. Rat CHF was induced by left coronary artery ligation. Single-cell real-time PCR and immunofluorescent data showed that L (Ca(v)1.2 and Ca(v)1.3), P/Q (Ca(v)2.1), N (Ca(v)2.2), and R (Ca(v)2.3) types of Ca2+ channels were expressed in CPP and CPS neurons, but CHF decreased the mRNA and protein expression of only the N-type Ca2+ channels in CPP neurons, and it did not affect mRNA and protein expression of all Ca2+ channel subtypes in the CPS neurons. Patch-clamp recording confirmed that CHF reduced N-type Ca2+ currents and cell excitability in the CPP neurons and enhanced N-type Ca2+ currents and cell excitability in the CPS neurons. N-type Ca2+ channel blocker (1 μM ω-conotoxin GVIA) lowered Ca2+ currents and cell excitability in the CPP and CPS neurons from sham-operated and CHF rats. These results suggest that CHF reduces the N-type Ca2+ channel currents and cell excitability in the CPP neurons and enhances the N-type Ca2+ currents and cell excitability in the CPS neurons, which may contribute to the cardiac autonomic imbalance in CHF.

Remodelling of the intracardiac ganglia in diabetic Goto-Kakizaki rats: an anatomical study

Background

Although cardiac autonomic neuropathy is one of major complications of diabetes mellitus (DM), anatomical data on cardiac innervation of diabetic animal models is scant and controversial. We performed this study to check whether long-term diabetic state impacts the anatomy of intracardiac ganglia in Goto-Kakizaki (GK) rats, a genetic model of type 2 DM.

Methods

Twelve GK rats (276 ± 17 days of age; mean ± standard error) and 13 metabolically healthy Wistar rats (262 ± 5 days of age) as controls were used for this study. Blood glucose was determined using test strips, plasma insulin by radioimmunoassay. Intrinsic ganglia and nerves were visualized by acetylcholinesterase histochemistry on whole hearts. Ganglion area was measured, and the neuronal number was assessed according to ganglion area.

Results

The GK rats had significantly elevated blood glucose level compared to controls (11.0 ± 0.6 vs. 5.9 ± 0.1 mmol/l, p < 0.001), but concentration of plasma insulin did not differ significantly between the two groups (84.0 ± 9.8 vs. 67.4 ± 10.9 pmol/l, p = 0.17). The GK rats contained significantly fewer intracardiac ganglia, decreased total area of intracardiac ganglia (1.4 ± 0.1 vs. 2.2 ± 0.1 mm², p < 0.001) and smaller somata of ganglionic neurons. Mean total number of intracardiac neurons in GK rats was 1461 ± 62, while this number in control rats was higher by 39% and reached 2395 ± 110 (p < 0.001).

Conclusions

Results of our study demonstrate the decreased number of intracardiac neurons in GK rats compared to metabolically healthy Wistar rats of similar age. It is likely that the observed structural remodelling of intracardiac ganglia in GK rats is caused by a long-term diabetic state.

Voltage-gated sodium channel expression and action potential generation in differentiated NG108-15 cells

Background

The generation of action potential is required for stimulus-evoked neurotransmitter release in most neurons. Although various voltage-gated ion channels are involved in action potential production, the initiation of the action potential is mainly mediated by voltage-gated Na⁺ channels. In the present study, differentiation-induced changes of mRNA and protein expression of Na⁺ channels, Na⁺ currents, and cell membrane excitability were investigated in NG108-15 cells.

Results

Whole-cell patch-clamp results showed that differentiation (9 days) didn’t change cell membrane excitability, compared to undifferentiated state. But differentiation (21 days) induced the action potential generation in 45.5% of NG108-15 cells (25/55 cells). In 9-day-differentiated cells, Na⁺ currents were mildly increased, which was also found in 21-day differentiated cells without action potential. In 21-day differentiated cells with action potential, Na⁺ currents were significantly enhanced. Western blot data showed that the expression of Na⁺ channels was increased with differentiated-time dependent manner. Single-cell real-time PCR data demonstrated that the expression of Na⁺ channel mRNA was increased by 21 days of differentiation in NG108-15 cells. More importantly, the mRNA level of Na⁺ channels in cells with action potential was higher than that in cells without action potential.

Conclusion

Differentiation induces expression of voltage-gated Na⁺ channels and action potential generation in NG108-15 cells. A high level of the Na⁺ channel density is required for differentiation-triggered action potential generation.

Changes of calcium channel mRNA, protein and current in NG108-15 cells after cell differentiation

Based on the characteristics of differentiated NG108-15 cells (cell membrane excitability, acetylcholine release, and activities of choline acetyltransferase and acetylcholinesterase), NG108-15 cells are extensively used to explore neuronal functions as a cholinergic cell line. In the present study, differentiation-induced alterations of voltage-gated Ca(2+) channel mRNA, protein, and current were investigated in the NG108-15 cells. Real-time PCR, Western blot, and whole-cell patch-clamp data showed that differentiation caused mRNA, protein, and ion current changes of all Ca(2+) channel subunits. However, the changes of mRNA, protein, and ion current are inconsistent in all Ca(2+) channel subunits. Especially, P/Q- and R-type Ca(2+) channel proteins do not form the functional P/Q- and R-type Ca(2+) channels even if the mRNA and protein of P/Q- and R-type Ca(2+) channels can be detected in NG108-15 cells. These results indicate that differentiation can modulate gene transcription, protein translation, and post-translation of the Ca(2+) channels to induce the alteration of the Ca(2+) ion currents in NG108-15 cells. From these data, we understand that combining real-time PCR, Western blot, and patch-clamp techniques can comprehensively unveil the modulation of the Ca(2+) channels.