Abstract P358: Cardiac Innervation Remodeling And Impaired Brain Derived Neurotrophic Factor (bdnf) Levels In Physiological Aging Vivo Model

Aging is a multifactorial process associated with gradual loss of function and decay involving several neurohormonal systems, such as the autonomic nervous system (ANS). Progressive remodeling of ANS, induces a circulating catecholamines spillover and cardiac autonomic fibers depletion with raising both morbidities and mortality risk. Neurotrophic factors (NF) play a pivotal role in modulating neuronal function and are impaired in cardiovascular disorders. Whether and how physiological aging impacts these neurobiomarkers and cardiac innervation remains still unclear. Therefore, we investigated the impact of aging on neurotrophins (such as BDNF and NGF) production and secretion and its consequences, on cardiac nervous system homeostasis. In vivo, we used young (age: 3 months; n=10) and old (age: 24 months; n=11) male Fisher rats. In vitro, human neuroblastoma cells (SH-SY5Y) were stimulated with serum withdrawn from both experimental groups. Old rats showed a significant reduction in overall ANS fiber density, sympathetic (marked by dopamine β-hydroxylase, dβh) and cholinergic compartment (evidenced by vesicular acetylcholine transporter, VaChT) compared to the young group, assessed by immunohistochemical staining. In addition, we observed a marked downregulation of GAP-43 and BDNF protein levels in left ventricle total lysates via immunoblot analysis, in aged hearts as opposed to young ones. Conversely, no changes were observed in NGF protein expression. To further investigate the autocrine effect of aging on autonomic nerve fibers, we treated SH-SY5Y cells in vitro, with blood serum obtained by young or old rats. Both stimuli induced a remarkable increase in neuronal sprouting, as evidenced via crystal violet assay. Nevertheless, we found a bulky drop in the neuronal function of cells stimulated with old rat serum. Interestingly, this effect was accompanied by a sizeable blunt in GAP-43 and BDNF protein levels, compared to cells treated with young rat serum. Taken together, our data suggest that neuronal function impairment aging-induced associated with significant BDNF impoverishment, might favor maladaptive remodeling of cardiac ANS.

Quality and utility of [123I]I-metaiodobenzylguanidine cardiac SPECT imaging in nondiabetic postinfarction heart failure patients qualified for implantable cardioverter defibrillator

Objective Impaired cardiac adrenergic activity has been demonstrated in heart failure (HF) and in diabetes mellitus (DM). [123I]I-metaiodobenzylguanidine (MIBG) enables assessment of the cardiac adrenergic nervous system. Tomographic imaging of the heart is expected to be superior to planar imaging. This study aimed to determine the quality and utility of MIBG SPECT in the assessment of cardiac innervation in postinfarction HF patients without DM, qualified for implantable cardioverter defibrillator (ICD) in primary prevention of sudden cardiac death. Methods Consecutive patients receiving an ICD on the basis of contemporary guidelines were prospectively included. Planar MIBG studies were followed by SPECT. The essential analysis was based on visual assessment of the quality of SPECT images (“high”, “low” or “unacceptable”). The variables used in the further analysis were late summed defect score for SPECT images and heart-to-mediastinum rate for planar images. MIBG images were assessed independently by two experienced readers. Results Fifty postinfarction nondiabetic HF subjects were enrolled. In 13 patients (26%), the assessment of SPECT studies was impossible. In addition, in 13 of 37 patients who underwent semiquantitative SPECT evaluation, the assessment was equivocal. Altogether, in 26/50 patients (52%, 95% confidence interval 38–65%), the quality of SPECT images was unacceptable or low and was limited by low MIBG cardiac uptake and by comparatively high, interfering MIBG uptake in the neighboring structures (primarily, in the lungs). Conclusions The utility of MIBG SPECT imaging, at least with conventional imaging protocols, in the qualification of postinfarction HF patients for ICD, is limited. In approximately half of the postinfarction HF patients, SPECT assessment of cardiac innervation can be impossible or equivocal, even without additional damage from diabetic cardiac neuropathy. The criteria predisposing the patient to good-quality MIBG SPECT are: high values of LVEF from the range characterizing the patients qualified to ICD (i.e., close to 35%) and left lung uptake intensity in planar images comparable to or lower than heart uptake.

Imaging cardiac innervation

Cardiac autonomic nervous system contributes to maintain haemodynamic and electrophysiological stability to changing demands. Cardiac innervation imaging can be performed by means of planar scintigraphy/SPECT or PET using different radiotracers developed for the assessment of pre- and postsynaptic receptors of the cardiac autonomic nervous system, with sufficient sensitivity to assess a process that takes place at picomolar concentrations. Clinically, cardiac innervation imaging is mainly performed targeting postganglionic presynaptic sympathetic neurons by means of myocardial 123I-metaiodobenzylguanidine (123I-mIBG) planar scintigraphy and SPECT, which has shown to be of value in the assessment of patients with different cardiac disorders, especially in those with heart failure (HF), having an independent prognostic value. This clinically oriented chapter updates the subject with inclusion of new data reinforcing the use of sympathetic cardiac innervation imaging for improving patient management.

REFRACTORY EPILEPSY AND VAGUS NERVE STIMULATION: THE WAY FORWARD

Vagus Nerve Stimulation (VNS) an efficacious neurophysiological modality of treatment for both medically & surgically refractory epilepsy was first implanted in 1988 & later approved by US FDA in 1997. In clinical practice, trains of current are applied intermittently to the left vagus using a pacemaker or AICD like device 'the VNS device'. The device has four components pulse generator, lead, spiral electrodes & a magnet. The pulse generator is implanted beneath left clavicle by a simple surgical method & attached to left vagus nerve via lead & spiral electrodes.[1] The magnet provides an extra edge to control the aura or impending seizure by providing 'On Demand' stimulations. The poor cardiac innervation by left vagus helps to minimize the unwanted or at time dangerous side effects like severe bradycardia, brady arrythmia, or even cardiac asystole.[2]

Effects of Different n6/n3 PUFAs Dietary Ratio on Cardiac Diabetic Neuropathy

We studied the influence of experimentally induced DM1, in combination with different dietary n6:n3 polyunsaturated fatty acid (PUFA) ratios on different types of nerve fibers in rat myocardium, in order to reveal whether protective/unfavorable effects of different PUFAs on myocardial function in diabetic patients could be a (partial) repercussion of their effect on the changes in cardiac innervation. The control group (c) and diabetic group (stz) were fed with an n6/n3 ratio of ≈7; the diet of the stz+n6 group had an n6/n3 ratio ≈60, while the diet for the stz+DHA group contained 2.5% of fish oil (containing 16% eicosapentaenoic acid—EPA and 19% docosahexaenoic acid—DHA), n6/n3 ratio of ≈1. DM1 was induced by i.p. injection of streptozotocin (55 mg/kg) and rats were euthanized 30 days after induction. Immunohistochemistry was used for the detection and quantification of different types of neuronal fibers in the cardiac septum. We found changes in cardiac innervations characteristics for the initial phase of experimental DM1, which manifested as an increase in total number and area density of all neuronal fibers, measured by Pgp9.5 immunoreactivity. By detailed analysis, we found that this increase consisted mostly of heavy myelinated NF200 immunoreactive fibers and TH immunoreactive sympathetic fibers, while the density of ChAT immunoreactive parasympathetic fibers decreased. In the deep (middle) part of the myocardium, where rare fibers (of all studied types) were found, significant differences were not found. Surprisingly, we found a more consistent protective effect of n6 PUFAs, in comparison to n3 PUFAs supplementation. These results may provide a better understanding of the potential impacts of different PUFA ratios in the diet of diabetic patients on cardiac innervation and genesis and outcome of diabetic autonomic cardiomyopathy.