Ultrastructural changes of human cardiac atrial nerve endings in diabetes mellitus

Cardiac innervation in acute myocardial ischaemia/reperfusion injury and cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Effect of Guizhi Decoction ([symbols; see text]) on heart rate variability and regulation of cardiac autonomic nervous imbalance in diabetes mellitus rats

OBJECTIVE

To observe abnormalities in heart rate variability (HRV) in diabetic rats and to explore the effects of treatment with Guizhi Decoction ([symbols; see text]) on cardiac autonomic nervous (CAN) imbalance.

METHODS

A radio-telemetry system for monitoring physiological parameters was implanted into rats to record electrocardiac signals and all indictors of HRV [time domain measures: standard deviation of all RR intervals in 24 h (SDNN), root mean square of successive differences (RMSSD), percentage of differences between adjacent RR intervals greater than 50 ms (PNN50), and standard deviation of the averages of RR intervals (SDANN); frequency domain measures: low frequency (LF), high frequency (HF), total power (TP), and LF/HF ratio]. The normal group was randomly selected, and the remaining rats were used to establish streptozocin (STZ)-induced diabetic model. After 4 weeks, the model rats were divided into the model group, the methycobal group, and the Guizhi Decoction group, 9 rats in each group. Four weeks after intragastric administration of the corresponding drugs, the right atria of the rats were collected for immunohistochemical staining of tyrosine hydroxylase (TH) and choline acetyltransferase (CHAT) to observe the distribution of the sympathetic and vagus nerves in the right atrium. The myocardial homogenate from the interventricular septum and the left ventricle was used for determination of TH, CHAT, growth-associated protein 43 (GAP-43), nerve growth factor (NGF), and ciliary neurotrophic factor (CNTF) levels using an enzyme-linked immunosorbent assay.

RESULTS

(1) STZ rats had elevated blood glucose levels, reduced body weight, and decreased heart rate; there was no difference between the model group and the drug treated groups. (2) Compared with the model group, only RMSSD and TP increased in the methycobal group significantly (P<0.05); SDNN, RMSSD, PNN50, LF, HF, and TP increased, LF/HF decreased (P<0.05), and SDANN just showed a decreasing trend in the Guizhi Decoction group (P>0.05). TH increased, CHAT decreased, and TH/CHAT increased in the myocardial homogenate of the model group (P<0.05). Compared with the model group, left ventricular TH reduced in the methycobal group; and in the Guizhi Decoction group CHAT increased, while TH and TH/CHAT decreased (P<0.05). Compared with the model group, CNTF in the interventricular septum increased in the methycobal group (P<0.05); GAP-43 increased, NGF decreased, and CNTF increased (P<0.05) in the Guizhi Decoction group. There were significant differences in the reduction of NGF and elevation of CNTF between the Guizhi Decoction group and the methycobal group (P<0.05). (3) Immunohistochemical results showed that TH expression significantly increased and CHAT expression significantly decreased in the myocardia of the model group, whereas TH expression decreased and CHAT expression increased in the Guizhi Decoction group (P<0.05).

CONCLUSION

Guizhi Decoction was effective in improving the function of the vagus nerve, and it could alleviate autonomic nerve damage.

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.

Alterations of the ovarian histomorphometry at pre-puberty in rat offspring from diabetic mothers

Purpose

Maternal diabetes leads to increased blood glucose concentration in the mother and consequently in the foetus, causing various neonatal problems. This study was conducted to evaluate the effects of maternal diabetes on foetal ovarian structure.

Methods

Sixteen adult female rats were allocated into two equal groups. Diabetes was induced in one group by alloxan. Both groups became pregnant by natural mating. Thirty days after birth, the female offspring were terminated, the body weight and blood glucose of the animals measured and their ovaries removed. Various histological and cellular parameters were determined using histological and electron microscopy techniques.

Results

Results revealed a significant increase in body weight and blood glucose in the offspring of the diabetic mothers (ODM) compared to that of the controls. The weight, volume and diameter of the ovary and the ovarian capsule thickness were inclined to decrease in ODM compared to that of controls. The number and diameter of primary, pre-antral and antral follicles were decreased in ovaries in the ODM. The electro-micrographs have demonstrated the organelle alterations in oocytes and granulosa cells that suggest the apoptosis progress and oxidative stress.

Conclusions

Maternal hyperglycaemia exhibited deleterious effects on the female reproductive system in the offspring.

Stereological characterization of left ventricular cardiomyocytes, capillaries, and innervation in the nondiabetic, obese mouse

BACKGROUND

Obesity is associated with left ventricular hypertrophy and dysfunction, but little is known about the structural remodeling of cardiomyocytes, capillaries, and nerve fibers in this state. We hypothesized that all three compartments should show quantitative structural alterations.

METHODS

Ten C57Bl6 mice were randomly assigned to a control or obesity group. Lean mice received standard chow, whereas obese mice received a high-fat Western diet. After 28 weeks, the mice were sacrificed, and the hearts were prepared for design-based stereology using light and electron microscopy.

RESULTS

Body mass and left ventricular mass were significantly elevated in obese vs. control mice. The left ventricular hypertrophy was accompanied by a significant increase in cardiomyocyte lipid droplets and total myocyte volume. The volume fractions of myofibrils, free sarcoplasm, and mitochondria did not differ between the groups. The total length of capillaries was significantly enhanced in obese vs. control mice, whereas the total length of axons ramifying between cardiomyocytes was not different.

CONCLUSIONS

Obesity is associated with significant structural alterations in cardiomyocytes and capillaries, whereas no structural changes in the myocardial innervation were observed. The structural characteristics in obese mice do not provide a clear basis for functional changes observed in obesity-related cardiac hypertrophy.

Interstitial Cajal-like cells (ICLC) in atrial myocardium: ultrastructural and immunohistochemical characterization

We have previously reported (Hinescu & Popescu, 2005) the existence of interstitial Cajal-like cells (ICLC), by transmission electron microscopy, in human atrial myocardium. In the present study, ICLC were identified with non-conventional light microscopy (NCLM) on semi-thin sections stained with toluidine blue and immunohistochemistry (IHC) for CD117/c-kit, CD34, vimentin and other additional antigens for differential diagnosis. Quantitatively, on semi-thin sections, ICLC represent about 1-1.5% of the atrial myocardial volume (vs. approximately 45% working myocytes, approximately 2% endothelial cells, 3-4% for other interstitial cells, and the remaining percentage: extracellular matrix). Roughly, there is one ICLC for 8-10 working atrial myocytes in the intercellular space, beneath the epicardium, with a characteristic (pyriform, spindle or triangular) shape. These ICLC usually have 2-3 definitory processes, emerging from cell body, which usually embrace atrial myocytes (260 nm average distance plasmalemma/sarcolemma) or establish close contact with nerve fibers or capillaries (approximately 420 nm average distance to endothelial cells). Cell prolongations are characteristic: very thin (mean thickness = 0.15+/-0.1 microm), very long for a non-nervous cell (several tens of microm) and moniliform (uneven caliber). Stromal synapses between ICLC and other interstitial cells (macrophages) were found (e.g. in a multicontact type synapse, the average synaptic cleft was approximately 65 nm). Naturally, the usual cell organelles (mitochondria, smooth and rough endoplasmic reticulum, intermediate filaments) are relatively well developed. Caveolae were also visible on cell prolongations. No thick filaments were detected. IHC showed that ICLC were slightly and inconsistently positive for CD117/c-kit, variously co-expressed CD34 and EGF receptor, but appeared strongly positive for vimentin, along their prolongations. Some ICLC seemed positive for a-smooth muscle actin and tau protein, but were negative for nestin, desmin, CD13 and S-100. In conclusion, we provide further evidence of the existence of ICLC in human atrial myocardium, supporting the possible ICLC role in pacemaking, secretion (juxta- and/or paracrine), intercellular signaling (neurons and myocytes). For pathology, ICLC might as well be 'players' in arrhythmogenesis and atrial remodeling.

Norepinephrine release is reduced in cardiac tissue of Type 2 diabetic patients

AIMS/HYPOTHESIS

The aim of this study was to assess whether cardiac catecholamine release is affected in patients with Type 2 diabetes mellitus.

METHODS

A trial tissue was obtained from 19 diabetic (Type 2) and 43 non-diabetic patients undergoing coronary surgery. Endogenous norepinephrine release was examined under baseline conditions as well as during electrical field stimulation (effective voltage 5 V, stimulation frequency 4 Hz, pulse width 2 msec) by high performance liquid chromatography and electrochemical detection. Cardiac function and arterial blood pressure was assessed from coronary angiography.

RESULTS

In atrial tissue from diabetic patients, stimulation-induced norepinephrine release was reduced by 25% compared with non-diabetic patients, while baseline norepinephrine release did not differ between both groups. Preoperative plasma glucose and haemoglobin A(1C) concentrations were increased in patients with diabetes, however, no relation was found to catecholamine release. Diabetic and non-diabetic patients did not differ regarding left ventricular ejection fraction and arterial blood pressure.

CONCLUSION/INTERPRETATION

Cardiac norepinephrine release is suppressed in patients with Type 2 diabetes which could contribute to sympathetic neuropathy. The difference of norepinephrine release in diabetic and non-diabetic patients was independent of cardiac function and arterial blood pressure.

Neurogenic inflammation of gingivomucosal tissue in streptozotocin-diabetic rat

Previously it was assumed that nerve fibres are involved in the neurogenic inflammation induced by mechanical or chemical irriations. It has been also suggested that in diabetes mellitus the unmyelinated small diameter fibers are impaired as a result of diabetic neuropathy. Therefore, our aim was to study the alterations of the nerve processes in the gingivomucosal tissue in streptozotocin (STZ)-diabetic rats. Light- and electronmicroscopical examinations were made to analyze the changes in nerve fibres. After one week of steptozotocin treatment, the gingivomucosal tissue had inflammatory cell infiltration and some degenerated nerve fibres were also observed. Dense mitochondria, disorganization of cell organelles, and appearance of myelin-like dense bodies were found in the axons of degenerared nerve fibres. Semiquantitative analysis showed that 14 +/- 4% of the unmyelinated nerve fibres degenerated after one week of STZ treatment. However, degeneration of the myelinated nerve fibers was not observed. Two weeks after STZ treatment, most of the unmyelinated and myelinated nerve fibers showed degeneration (86 +/- 5%) and the placement of the ligature revealed a non-inflammatory connective tissue adjacent to a normal epithelium. The myelin sheath was disrupted and dark axoplasm with cytolysosomes became manifest. These findings demonstrated that both unmyelinated and myelinated nerve fibers are altered and inflammatory reaction exists in the gingivomucosal tissue only in the early stage of diabetes mellitus.