Elevated Noradrenaline Concentrations Research Articles

Dynamics of neuroeffector coupling at cardiac sympathetic synapses.

The present study demonstrates, by in vitro and in vivo analyses, the novel concept that signal transmission between sympathetic neurons and the heart, underlying the physiological regulation of cardiac function, operates in a quasi-synaptic fashion. This is a result of the direct coupling between neurotransmitter releasing sites and effector cardiomyocyte membranes. Cardiac sympathetic neurons (SNs) finely tune the rate and strength of heart contractions to match blood demand, both at rest and during acute stress, through the release of noradrenaline (NE). Junctional sites at the interface between the two cell types have been observed, although whether direct neurocardiac coupling has a role in heart physiology has not been clearly demonstrated to date. We investigated the dynamics of SN/cardiomyocyte intercellular signalling, both by fluorescence resonance energy transfer-based imaging of cAMP in co-cultures, as a readout of cardiac β-adrenergic receptor activation, and in vivo, using optogenetics in transgenic mice with SN-specific expression of Channelrhodopsin-2. We demonstrate that SNs and cardiomyocytes interact at specific sites in the human and rodent heart, as well as in co-cultures. Accordingly, neuronal activation elicited intracellular cAMP increases only in directly contacted myocytes and cell-cell coupling utilized a junctional extracellular signalling domain with an elevated NE concentration. In the living mouse, optogenetic activation of cardiac SNs innervating the sino-atrial node resulted in an instantaneous chronotropic effect, which shortened the heartbeat interval with single beat precision. Remarkably, inhibition of the optogenetically elicited chronotropic responses required a high dose of propranolol (20-50mgkg-1 ), suggesting that sympathetic neurotransmission in the heart occurs at a locally elevated NE concentration. Our in vitro and in vivo data suggest that the control of cardiac function by SNs occurs via direct intercellular coupling as a result of the establishment of a specific junctional site.

P.3.013 - Hypermethylation of the monoamine oxidase A gene – a new epigenetic marker for posttraumatic stress disorder?

Posttraumatic Stress Disorder (PTSD) can develop after experiencing or witnessing any severe traumatic event such as combat. Point prevalence rates in war-affected regions, e.g. Bosnia-Herzegovina and Kosovo, range from 18% to 35%. Noradrenergic dysfunction as represented by e.g. elevated noradrenaline concentrations in the cerebrospinal fluid of PTSD patients is known to play a substantial role in the pathogenesis of PTSD symptoms [1]. Epigenetic regulation (i.e. DNA methylation) is strongly suggested to moderate the interaction between environmental influences and a genetic predisposition. Therefore, differential methylation of genes involved in the noradrenergic system such as the monoamine oxidase A (MAOA) gene might be part of the complex biological underpinnings of a dysregulated noradrenergic system and thereby contribute to PTSD risk. The present study aimed at investigating MAOA gene methylation as a possible epigenetic marker of PTSD status and severity in a sample comprising patients with PTSD and healthy controls recruited from war-affected regions in Bosnia-Herzegovina, Croatia and Kosovo. DNA methylation levels of MAOA (exonI/intronI region) were analyzed in PTSD patients [N=216; m=157, age (mean±s.d.): 50.08±6.74 years], remitted PTSD patients [N=151; m=98, age (mean±s.d.): 49.48±8.20 years] and healthy controls [N=349, m=232, age (mean±s.d.): 48.81±8.50 years] by direct sequencing of sodium bisulfite-treated DNA followed by semi-quantitative analysis of the sequencing results via the Epigenetic Sequencing Methylation software. Severity of PTSD symptoms was assessed by the Clinician-Administered PTSD Scale (CAPS). All participants were assessed for potential confounders of methylation (sex, age, or smoking status). Possible categorical differences were analyzed by (M)ANCOVAs with age and smoking status as covariates. Post-hoc tests (Bonferroni) were performed to test individual differences in methylation across groups. Associations between dimensional measures were analyzed performing partial correlation analyses controlled for age and smoking status. In the male subsample, analyses revealed significant methylation differences at three out of 13 CpG sites between patients with current PTSD, remitted PTSD patients, and healthy controls. Post-hoc tests showed trend-wise significant (padjusted In the female subsample, we failed to observe association of MAOA methylation with either current or remitted PTSD, while there was a positive correlation between MAOA methylation and symptom severity (r=0.294, p=0.033). The results of the present study for the first time suggest MAOA hypermethylation – possibly resulting in an increased noradrenergic tonus – as a disease status and severity marker of PTSD particularly in male patients. Given robust replication, MAOA hypermethylation might thus serve as an epigenetic marker within the complex risk factor constellation of PTSD. Furthermore, applying a personalized pharmaco-therapeutic approach, anti-adrenergic agents might prove to be beneficial in counterbalancing increased noradrenergic signalling specifically in male PTSD patients displaying MAOA hypermethylation.

The noradrenergic locus coeruleus as a chronic pain generator.

Central noradrenergic centers such as the locus coeruleus (LC) are traditionally viewed as pain inhibitory; however, complex interactions among brainstem pathways and their receptors modulate both inhibition and facilitation of pain. In addition to the well-described role of descending pontospinal pathways that inhibit spinal nociceptive transmission, an emerging body of research now indicates that noradrenergic neurons in the LC and their terminals in the dorsal reticular nucleus (DRt), medial prefrontal cortex (mPFC), spinal dorsal horn, and spinal trigeminal nucleus caudalis participate in the development and maintenance of allodynia and hyperalgesia after nerve injury. With time after injury, we argue that the balance of LC function shifts from pain inhibition to pain facilitation. Thus, the pain-inhibitory actions of antidepressant drugs achieved with elevated noradrenaline concentrations in the dorsal horn may be countered or even superseded by simultaneous activation of supraspinal facilitating systems dependent on α1 -adrenoreceptors in the DRt and mPFC as well as α2 -adrenoreceptors in the LC. Indeed, these opposing actions may account in part for the limited treatment efficacy of tricyclic antidepressants and noradrenaline reuptake inhibitors such as duloxetine for the treatment of chronic pain. We propose that the traditional view of the LC as a pain-inhibitory structure be modified to account for its capacity as a pain facilitator. Future studies are needed to determine the neurobiology of ascending and descending pathways and the pharmacology of receptors underlying LC-mediated pain inhibition and facilitation. © 2016 Wiley Periodicals, Inc.

The effect of central cholinergic and noradrenergic denervation on hippocampal sympathetic ingrowth and apoptosis-like reactivity in the rat

In this study, the effect of intraseptal injection of specific cholinotoxin 192-IgG saporin (SAP) ± intraperitoneal injection of N-[chloroethyl]- N-ethyl-2-bromobenzylamine (DSP-4) (noradrenergic fiber neurotoxin) was examined in rat hippocampus. Medial septal lesions resulted not only in selective cholinergic denervation of hippocampus (Medial septal lesion + ganglionectomy; SAP + Gx) but also in hippocampal sympathetic ingrowth (IG) of adrenergic fibers (Medial septal lesion + sham ganglionectomy; SAP + IG). Saporin-induced septal lesions produced a significant reduction in hippocampal choline acetyltransferase activity in all tested groups (SAP + IG ± DSP-4 and SAP + Gx ± DSP-4), and an increase in noradrenaline concentration in the SAP + IG group. Visualization of noradrenergic fibers by histofluorescence revealed a mixture of fine and thick varicosities in the SAP + IG but only fine fibers in control and SAP + Gx animals. SAP + IG + DSP-4 lesions produced significant reduction in noradrenaline concentration in all groups with a concomitant decrease in visualization of central noradrenergic fibers in dorsal and ventral hippocampus. Treatment of SAP + IG animals with DSP-4 left mostly thick fibers, probably derived from peripheral sympathetic ingrowth. No fluorescence was seen in either the control + DSP-4 or SAP + Gx + DSP-4 animals. Apoptotic-like changes, using in situ oligonucleotide ligation techniques, were also assessed. Proapoptotic changes were seen in the SAP + Gx ± DSP-4 group as compared to CON ± DSP-4 groups. SAP + IG regardless of DSP-4 treatment protected hippocampal cells from apoptotic cell death when compared to positive control and SAP + Gx ± DSP-4 groups. In summary, elevated noradrenaline concentration following specific cholinergic denervation probably reflects compensatory hippocampal ingrowth originating from the peripheral sympathetic system which may be responsible for neuroprotective effects, i.e., antiapoptosis-like effect. Since cholinergic and noradrenergic systems are known to be involved in Alzheimer's disease and related cognitive function, knowing how these neurotransmitters work after specific lesions may be of importance as an animal model of Alzheimer's disease and as a potential target for Alzheimer's disease drug therapies.

Elevated Plasma Noradrenaline Concentrations in Patients with Low-Output Cardiac Failure: Dependence on Increased Noradrenaline Secretion Rates

1. Plasma noradrenaline concentrations are elevated in patients with congestive heart failure; however, the pathogenesis of these elevated noradrenaline levels is controversial. 2. Possible mechanisms for elevated noradrenaline concentrations in patients with congestive heart failure include increased noradrenaline secretion, decreased clearance of noradrenaline, and a combination of increased secretion and decreased clearance. 3. In the present study, plasma noradrenaline clearance and apparent secretion rates were determined using a whole-body steady-state radionuclide tracer method in six otherwise healthy patients with moderate degrees of low-output cardiac failure and in six normal control subjects. 4. The venous plasma noradrenaline level was elevated in the patients with congestive heart failure as compared with the control subjects (4.18 +/- 1.34 versus 1.54 +/- 0.16 nmol/l, P less than 0.05). There was no stimulation of the adrenal medulla as evident by normal plasma adrenaline levels in both groups (0.19 +/- 0.04 versus 0.18 +/- 0.02 nmol/l, not significant). The apparent secretion rate of noradrenaline was elevated in the patients with congestive heart failure (4.75 +/- 1.95 versus 1.78 +/- 0.18 nmol min-1 m-2, P less than 0.05), whereas the clearance rate of noradrenaline was similar in the two groups (1.26 +/- 0.27 versus 1.16 +/- 0.02 l min-1 m-2, not significant). 5. We conclude that the high peripheral venous plasma noradrenaline concentrations in patients with mildly decompensated low-output cardiac failure are initially due to increased secretion, rather than to decreased metabolic clearance, perhaps in response to diminished effective arterial blood volume.

Effect of cyclic AMP-dependent protein kinase on insulin receptor tyrosine kinase activity.

To explain the insulin resistance induced by catecholamines, we studied the tyrosine kinase activity of insulin receptors in a state characterized by elevated noradrenaline concentrations in vivo, i.e. cold-acclimation. Insulin receptors were partially purified from brown adipose tissue of 3-week- or 48 h-cold-acclimated mice. Insulin-stimulated receptor autophosphorylation and tyrosine kinase activity of insulin receptors prepared from cold-acclimated mice were decreased. Since the effect of noradrenaline is mediated by cyclic AMP and cyclic AMP-dependent protein kinase, we tested the effect of the purified catalytic subunit of this enzyme on insulin receptors purified by wheat-germ agglutinin chromatography. The catalytic subunit had no effect on basal phosphorylation, but completely inhibited the insulin-stimulated receptor phosphorylation. Similarly, receptor kinase activity towards exogenous substrates such as histone or a tyrosine-containing copolymer was abolished. This inhibitory effect was observed with receptors prepared from brown adipose tissue, isolated hepatocytes and skeletal muscle. The same results were obtained on epidermal-growth-factor receptors. Further, the catalytic subunit exerted a comparable effect on the phosphorylation of highly purified insulin receptors. To explain this inhibition, we were able to rule out the following phenomena: a change in insulin binding, a change in the Km of the enzyme for ATP, activation of a phosphatase activity present in the insulin-receptor preparation, depletion of ATP, and phosphorylation of a serine residue of the receptor. These results suggest that the alteration in the insulin-receptor tyrosine kinase activity induced by cyclic AMP-dependent protein kinase could contribute to the insulin resistance produced by catecholamines.

Differential effects of neonatal 6-hydroxydopamine treatment on the catecholamine content of hypothalamic nuclei and brain stem regions

Following neonatal 6-hydroxydopamine treatment the noradrenaline content of the frontal cortex, the periventricular nucleus, the arcuate nucleus and the median eminence, but not that of the paraventricular nucleus, the supraoptic nucleus and the dorsomedial nucleus, was significantly decreased compared to that of vehicle treated controls 13 weeks after birth. The adrenaline concentration of the periventricular nucleus was slightly lowered. An elevated noradrenaline concentration was observed in the locus coeruleus, the A5 region and the nucleus reticularis medullae oblongatae pars ventralis. In the latter two regions the dopamine levels were increased as well. It is concluded (a) that not all hypothalamic terminal areas of locus coeruleus neurons are equally affected by 6-hydroxydopamine (6-OHDA) and (b) that also noradrenergic projections of brain stem cell body regions other than the locus coeruleus are affected.