Predestinating Role of Cardiac Ganglia on Heart Life Expectancy in Rabbits After Brain Death Following Subarachnoid Hemorrhage: An Experimental Study

BACKGROUND

Cardiac ganglia are rechargeable batteries of the heart. The essential role of cardiac ganglia on cardiac life expectancy has not been examined following brain death. The aim of this study was to determine cardiac ganglia numbers and neuron density following subarachnoid hemorrhage (SAH).

METHODS

Twenty-five hybrid rabbits were grouped as control (n = 5), sham (n = 5), and SAH (n = 15). The SAH groups' animals were subjected to injections of lethal dose of 2.00 cc autologous blood into their cisterna magna until linear EEG was obtained. The hearts of all animals were extracted following intracardiac formalin injection and examined. Cardiac ganglia and normal/degenerated neuron densities of cardiac neurons were recorded.

RESULTS

The mean volume of normal neuron density of ganglia was 6.980 ± 830/mm³, and the degenerated neuron density of ganglia was 3 ± 1/mm³ in the control group, 6134 ± 712/mm³; 23 ± 9/mm³ in the sham group, 3456 ± 589; 1161 ± 72/mm³ in the surviving group; and 1734 ± 341/mm³, 4259 ± 865/mm³ in the dead animals in the SAH group. The algebraic results of heart work capacity (Wh) were estimated as 1375 ± 210 Wh in the control group, 1036 ± 225 in the sham group, 800 ± 110 Wh in the surviving group, and < 100 ± 20 in the dead animals in the SAH group. Degenerated cardiac neuron density/Wh correlation is statistically meaningful between the dead in the SAH group versus the SAH-surviving, sham, and control groups (P < .0005).

CONCLUSIONS

Normal cardiac ganglia numbers and/or cardiac ganglia neuron density may be related to cardiac survival following brain death after subarachnoid hemorrhage.

Force regulation and electrical properties of motor units in overloaded muscle

INTRODUCTION

The influence of long-term muscle overload on force regulation and electrical properties of motor units (MUs) was investigated in rats.

METHODS

Compensatory overload of the medial gastrocnemius was induced by tenotomy of its synergists. Electrophysiological experiments were performed on functionally isolated MUs 3 months after the surgery.

RESULTS

Force-frequency curves for overloaded MUs were shifted rightward compared with control, thus MUs developed the same relative tetanic forces at higher frequencies. Higher force increase was achieved in response to an increase in stimulation frequency in overloaded fast MUs compared with control. The optimal tetanic contraction, characterized by the highest force-time area per pulse, was evoked at higher stimulation frequencies for all overloaded MUs except FF. Only minor adaptive changes in MU action potentials occurred.

CONCLUSIONS

Compensatory muscle overload leads to substantial modifications in MU force development mechanisms, which are MU-type-specific and influence whole muscle force regulation.

Adaptations of motoneuron properties to chronic compensatory muscle overload

The aim of the study was to determine whether chronic muscle overload has measurable effect on electrophysiological properties of motoneurons (MNs), and whether duration of this overload influences intensity of adaptations. The compensatory overload was induced in the rat medial gastrocnemius (MG) by bilateral tenotomy of its synergists (lateral gastrocnemius, soleus, and plantaris); as a result, only the MG was able to evoke the foot plantar flexion. To assure regular activation of the MG muscle, rats were placed in wheel-equipped cages and subjected to a low-level treadmill exercise. The intracellular recordings from MG motoneurons were made after 5 or 12 wk of the overload, and in a control group of intact rats. Some of the passive and threshold membrane properties as well as rhythmic firing properties were considerably modified in fast-type MNs, while remaining unaltered in slow-type MNs. The significant changes included a shortening of the spike duration and the spike rise time, an increase of the afterhyperpolarization amplitude, an increase of the input resistance, a decrease of the rheobase, and a decrease of the minimum current necessary to evoke steady-state firing. The data suggest higher excitability of fast-type MNs innervating the overloaded muscle, and a shift towards electrophysiological properties of slow-type MNs. All of the adaptations could be observed after 5 wk of the compensatory overload with no further changes occurring after 12 wk. This indicates that the response to an increased level of chronic activation of MNs is relatively quick and stable.

Allometry of left ventricular myocardial innervation

Body mass (BM) of terrestrial mammalian species ranges from a few grams in the case of the Etruscan shrew to a few tonnes for an elephant. The mass-specific metabolic rate, as well as heart rate, decrease with increasing BM, whereas heart mass is proportional to BM. In the present study, we investigated the scaling behaviour of several compartments of the left ventricular myocardium, notably its innervation, capillaries and cardiomyocytes. Myocardial samples were taken from 10 mammalian species with BM between approximately 2 g and 900 kg. Samples were analysed by design-based stereology and electron microscopy and the resulting data were subjected to linear regression and correlation analyses. The total length of nerve fibres (axons) in the left ventricle increased from 0.017 km (0.020 km) in the shrew to 7237 km (13,938 km) in the horse. The innervation density was similar among species but the mean number of axons per nerve fibre profile increased with rising BM. The total length of capillaries increased from 0.119 km (shrew) to 10,897 km (horse). The volume of cardiomyocytes was 0.017 cm(3) in the shrew and 1818 cm(3) in the horse. Scaling of the data against BM indicated a higher degree of complexity of the axon tree in larger animals and an allometric relationship between total length of nerve fibres/axons and BM. In contrast, the density of nerve fibres is independent of BM. It seems that the structural components of the autonomic nervous system in the heart are related to BM and heart mass rather than to functional parameters such as metabolic rate.

Extracardiac neural remodeling in humans with cardiomyopathy

BACKGROUND

Intramyocardial nerve sprouting after myocardial infarction is associated with ventricular arrhythmias. Whether human stellate ganglia remodel in association with cardiac pathology is unknown. The purpose of this study was to determine whether cardiac pathology is associated with remodeling of the stellate ganglia in humans.

METHODS AND RESULTS

Left stellate ganglia were collected from patients undergoing sympathetic denervation for intractable ventricular arrhythmias and from cadavers, along with intact hearts. Clinical data on patients and cadaveric subjects were reviewed. We classified ganglia from normal, scarred, and nonischemic cardiomyopathic hearts without scar as NL (n=3), SCAR (n=24), and NICM (n=7), respectively. Within left stellate ganglia, neuronal size, density, fibrosis, synaptic density, and nerve sprouting were determined. Nerve density and sprouting were also quantified in cadaveric hearts. Mean neuronal size in normal, scarred, and nonischemic cardiomyopathic hearts without scar groups were 320 ± 4 μm(2), 372 ± 10 μm(2), and 435 ± 10 μm(2) (P=0.002), respectively. No significant differences in neuronal density and fibrosis were present between the groups. Synaptic density in ganglia from SCAR and NICM groups were 57.8 ± 11.2 μm(2)/mm(2) (P=0.084) and 44.5 ± 7.9 μm(2)/mm(2) (P=0.039), respectively, compared with the normal group, 17.8 ± 7 μm(2)/mm(2) (overall P=0.162). There were no significant differences in left stellate ganglia nerve sprouting or myocardial nerve density between the groups.

CONCLUSIONS

Neuronal hypertrophy within left stellate ganglia is associated with chronic cardiomyopathy in humans. Ganglionic and myocardial nerve sprouting and nerve density were not significantly different. These changes may be related to increased cardiac sympathetic signaling and ventricular arrhythmias. Further studies are needed to determine the electrophysiological consequences of extracardiac neuronal remodeling in humans.

The influence of exercise on morphological and neurochemical properties of neurons in rat nodose ganglia

Physical exercise can induce immunohistochemical changes and cell proliferation in the hippocampus. One of the main effects of prolonged exercise is resting bradycardia, most probably caused by enhanced vagal activity. To investigate whether physical exercise can cause neurochemical and morphological changes in vagal afferent neurons, we performed immunohistochemical studies of nodose neurons using isolectin B4 (IB4), 200-kDa neurofilament protein (N52) and calretinin in adult female rats. To distinguish subpopulations of neurons projecting to the left ventricle, we applied a Fast Blue patch to the epicardial surface of the left ventricle. Treadmill running for 8 weeks significantly increased the size of N52-positive cardiac projecting neurons. Furthermore, the proportion of IB4-positive neurons among all nodose ganglia neurons was significantly higher in trained animals. These data indicate that exercise leads to plastic changes in nodose ganglia neurons that may initiate changes of vagal activity caused by prolonged exercise.

Controlling dispersion of axonal regeneration using a multichannel collagen nerve conduit

Single channel conduits are used clinically in nerve repair as an alternative to the autologous nerve graft. Axons regenerating across single channel tubes, however, may disperse resulting in inappropriate target reinnervation. This dispersion may be limited by multichannel nerve conduits as they resemble the structure of nerve multiple basal lamina tubes. In this study, we investigated the influence of channel number on the axonal regeneration using a series of 1-, 2-, 4-, and 7-channel collagen conduits and commercial (NeuraGen) single channel conduits. Nerve conduits were implanted in rats with a 1 cm gap of sciatic nerve. After four months, quantitative results of regeneration were evaluated with nerve morphometry and the accuracy of regeneration was assessed using retrograde tracing: two tracers being applied simultaneously to tibial and peroneal nerves to determine the percentage of motor neurons with double projections. Recovery of function was investigated with compound muscle action potential recordings and ankle motion analysis. We showed that the fabricated 1-channel and 4-channel conduits are superior to other types of conduits in axonal regeneration. Simultaneous tracing showed a significantly lower percentage of motor neurons with double projections after 2- and 4-channel compared with 1-channel conduit repair. This study shows the potential influence of multichannel guidance on limiting dispersion without decreasing quantitative results of regeneration.

Targeted ablation of cardiac sympathetic neurons reduces the susceptibility to ischemia-induced sustained ventricular tachycardia in conscious rats

The Cardiac Arrhythmia Suppression Trial demonstrated that antiarrhythmic drugs not only fail to prevent sudden cardiac death, but actually increase overall mortality. These findings have been confirmed in additional trials. The "proarrhythmic" effects of most currently available antiarrhythmic drugs makes it essential that we investigate novel strategies for the prevention of sudden cardiac death. Targeted ablation of cardiac sympathetic neurons may become a therapeutic option by reducing sympathetic activity. Thus cholera toxin B subunit (CTB) conjugated to saporin (a ribosomal inactivating protein that binds to and inactivates ribosomes; CTB-SAP) was injected into both stellate ganglia to test the hypothesis that targeted ablation of cardiac sympathetic neurons reduces the susceptibility to ischemia-induced, sustained ventricular tachycardia in conscious rats. Rats were randomly divided into three groups: 1) control (no injection); 2) bilateral stellate ganglia injection of CTB; and 3) bilateral stellate ganglia injection of CTB-SAP. CTB-SAP rats had a reduced susceptibility to ischemia-induced, sustained ventricular tachycardia. Associated with the reduced susceptibility to ventricular arrhythmias were a reduced number of stained neurons in the stellate ganglia and spinal cord (segments T(1)-T(4)), as well as a reduced left ventricular norepinephrine content and sympathetic innervation density. Thus CTB-SAP retrogradely transported from the stellate ganglia is effective at ablating cardiac sympathetic neurons and reducing the susceptibility to ventricular arrhythmias.

Psychosocial stress-related changes in gene expression of norepinephrine biosynthetic enzymes in stellate ganglia of adult rats

In this study we investigated the changes in norepinephrine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) gene expression in the stellate ganglia of naive controls and long-term socially isolated (12 weeks) adult rats and the response of these animals to additional immobilization stress. Psychosocial stress produced a significant increase of both TH mRNA and DBH mRNA levels in stellate ganglia. Additional immobilization of long-term psychosocially stressed rats expressed no effect on gene expression of these enzymes. The results presented here suggest that psychosocial stress-induced increase in gene expression of norepinephrine biosynthetic enzymes in stellate ganglia may be connected to the increased risk of cardiovascular disease.