Neuronal Norepinephrine Release Research Articles

Serum Galanin in Children with Autism Spectrum Disorder.

Recent studies have attempted to measure several biomarkers to understand the complex interactions of the anatomic systems that may be involved in autism spectrum disorder (ASD). In CNS, galanin takes part in a variety of pathological and physiological processes. Prior research has indicated it is involved in several neuropsychiatric disorders and has a role in inhibiting the neuronal firing and release of serotonin, norepinephrine, and acetylcholine. To date, serum galanin levels have not been investigated in the context of ASD. This study aimed, therefore, to compare the serum galanin levels of children with ASD and healthy controls and to reveal any association between galanin level and the severity of ASD, as well as other psychological and demographic parameters. Serum galanin levels were measured by radioimmunoassay in 116 children with ASD and 98 healthy children. We observed significantly increased serum concentrations of galanin in children with ASD relative to healthy children. Moreover, children with severe ASD had significantly higher galanin levels than those with less severe disease. We also confirmed significant positive correlations between galanin and psychiatric parameters in children with ASD. For the first time, we suggest a possible correlation between serum galanin and the degree of ASD severity. Increased galanin levels may play a role in the pathogenesis of ASD.

52-Year-Old Woman With Fever, Diaphoresis, and Abdominal Pain

52-Year-Old Woman With Fever, Diaphoresis, and Abdominal Pain

Abstract 381: Chemogenetic Activation of Satellite Glial Gq-GPCR Signaling Enhances Cardiovascular Function in vivo

The autonomic nervous system (ANS) exerts profound regulatory influence over cardiovascular physiology. The integrated network among autonomic nuclei in the central nervous system (CNS), as well as ganglionic innervation in the peripheral nervous system (PNS) are essential for homeostasis and for coordinating adaptive changes in physiology and behavior. In addition to neurons, the ANS contains large numbers of Glial Fibrillary Acidic Protein (GFAP) - expressing cells (GFAP + glial cells), which serve many functions in assisting neuronal network activity in both the CNS and the PNS. The present study explores the active role of GFAP + glial cells in regulating cardiovascular function in vivo . Using DREADD technology, we selectively activate Gq-GPCR signaling in satellite glial cells (SGCs) within sympathetic ganglia, which led to fast-acting, long-lasting increases in cardiac function and blood pressure in vivo . In addition, ganglionic SGCs likely increase postganglionic neuronal firing and subsequent norepinephrine release via a “local stimulatory effect“ on postganglionic neurons. Ongoing studies ex vivo using superior cervical ganglia cultures focus on identifying the mechanism underlying the interaction between sympathetic SGCs and postganglionic neurons.

Involvement of endothelins in deoxycorticosterone acetate-salt hypertension through the modulation of noradrenergic transmission in the rat posterior hypothalamus.

What is the central question of this study? Does ex vivo administration of endothelin-1 and endothelin-3 regulate noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate-salt hypertensive rats compared with normotensive rats? What is the main finding and its importance? Endothelin-1 and endothelin-3 enhanced diverse mechanisms leading to increased noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate-salt hypertensive rats. Unveiling the role of brain endothelins in hypertension would probably favour the development of new therapeutic targets for the treatment of essential hypertension, which still represents a challenging disease with high mortality. Brain catecholamines participate in diverse biological functions regulated by the hypothalamus. We have previously reported that endothelin-1 and endothelin-3 (ET-1 and ET-3) modulate catecholaminergic activity in the anterior and posterior hypothalamus of normotensive rats. The aim of the present study was to evaluate the interaction between endothelins and noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We assessed the effects of ET-1 and ET-3 on tyrosine hydroxylase activity and expression, neuronal noradrenaline (NA) release, neuronal NA transporter (NAT) activity and expression, monoamine oxidase activity and NA endogenous content and utilization (as a marker of turnover) in the posterior hypothalamus of DOCA-salt hypertensive rats. In addition, levels of ETA and ETB receptors were assayed in normotensive and hypertensive rats. Results showed that tyrosine hydroxylase activity and total and phosphorylated levels, NAT activity and content, NA release, monoamine oxidase activity and NA utilization were increased in DOCA-salt rats. Both ET-1 and ET-3 further enhanced all noradrenergic parameters except for total tyrosine hydroxylase level and NA endogenous content and utilization. The expression of ETA receptors was increased in the posterior hypothalamus of DOCA-salt rats, but ETB receptors showed no changes. These results show that ET-1 and ET-3 upregulate noradrenergic activity in the posterior hypothalamus of DOCA-salt hypertensive rats. Our findings suggest that the interaction between noradrenergic transmission and the endothelinergic system in the posterior hypothalamus may be involved in the development and/or maintenance of hypertension in this animal model.

Effects of long-term fluoxetine treatment on adrenergic plasticity in rat vas deferens

Chronic antidepressant administration increases neurotrophin levels in the central and peripheral nervous system, leading to an increase of neuronal sprouting, reestablishment of neural networks and neurotransmitter levels. Injured peripheral nerves regenerate at very slow rates. However, the recovery of the hypogastric nerve in rodents after injury is significantly improved with neurotrophin administration. Accordingly, our goal was to determine whether treatment with the antidepressant fluoxetine affects catecholamine levels and neuronal function, after surgical denervation of the rat vas deferens. Noradrenaline levels in the denervated vas deferens were higher in fluoxetine-treated animals than in the vehicle-treated group, as measured by high performance liquid chromatography. In functional studies of smooth muscle contraction, the responses induced by phenylephrine or ATP, as well as pre-synaptic α2-adrenoceptor reactivity, were not modified by chronic treatment with the antidepressant. However, the contraction mediated by neuronal release of noradrenaline induced by tyramine was increased on days 7 and 21 after denervation in rats treated with fluoxetine. These data indicate that fluoxetine can improve functional recovery after rat vas deferens denervation.

Dexmedetomidine decreases requirement of thiopentone sodium and pentazocine followed with improved recovery in patients undergoing laparoscopic cholecystectomy.

Background:Pain relief remains the most fundamental and consequential aspect of surgery for patients throughout perioperative period. Dexmedetomidine has created an interest in α2-adrenoceptor agonists in the management of pain and hence the aim of this study was to evaluate the effectiveness of the drug in hilly population of North India.Materials and Methods:Patients, irrespective of gender, were randomly allocated to two groups, control and test, each having 30 patients. Test group received an infusion of dexmedetomidine at a rate of 0.5 μg/kg/h 30 min before induction and 0.6 μg/kg/h after inducing anesthesia. Control patients received a volume-matched infusion of normal saline as placebo. Approximately 2 min before induction, analgesia was provided in the form of pentazocine, 0.5 mg/kg in control and 0.3 mg/kg in the test group. Induction was performed by 2 mg/kg thiopentone sodium supplemented with intravenous boluses of 25 mg thiopentone sodium every 15 s until loss of eyelid reflex (determined every 15 s). Induction dose of thiopentone sodium and total pentazocine dose were recorded. Recovery was assessed on the clinical recovery score (CRS) scale.Results:Infusion of dexmedetomidine decreased the induction dose of thiopentone approximately by 33% and of pentazocine dose by approximately 39% in patients undergoing laparoscopic cholecystectomy. Moreover, incidence of pain was also decreased significantly. Improved CRS from 4.33 to 6.87 was noticed immediately post-operatively in dexmedetomidine group of patients.Conclusion:Infusion of dexmedetomidine during the laparoscopic cholecystectomy decreases the requirement of thiopentone sodium and pentazocine and leads to early recovery of patients.

Enhanced Assymetrical Noradrenergic Transmission in the Olfactory Bulb of Deoxycorticosterone Acetate-Salt Hypertensive Rats

The ablation of olfactory bulb induces critical changes in dopamine, and monoamine oxidase activity in the brain stem. Growing evidence supports the participation of this telencephalic region in the regulation blood pressure and cardiovascular activity but little is known about its contribution to hypertension. We have previously reported that in the olfactory bulb of normotensive rats endothelins enhance noradrenergic activity by increasing tyrosine hydroxylase activity and norepinephrine release. In the present study we sought to establish the status of noradrenergic activity in the olfactory bulb of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Different steps in norepinephrine transmission including tyrosine hydroxylase activity, neuronal norepinephrine release and uptake were assessed in the left and right olfactory bulb of DOCA-salt hypertensive rats. Increased tyrosine hydroxylase activity, and decreased neuronal norepinephrine uptake were observed in the olfactory bulb of DOCA-salt hypertensive rats. Furthermore the expression of tyrosine hydroxylase and its phosphorylated forms were also augmented. Intriguingly, asymmetrical responses between the right and left olfactory bulb of normotensive and hypertensive rats were observed. Neuronal norepinephrine release was increased in the right but not in the left olfactory bulb of DOCA-salt hypertensive rats, whereas non asymmetrical differences were observed in normotensive animals. Present findings indicate that the olfactory bulb of hypertensive rats show an asymmetrical increase in norepinephrine activity. The observed changes in noradrenergic transmission may likely contribute to the onset and/or progression of hypertension in this animal model.

Concentration gradient of endogenous noradrenaline from periphery to centre in the rabbit cornea

AbstractPurpose The source of endogenous catecholamines that activate corneal adrenoceptors is largely unknown. Since the cornea is a densely innervated tissue we hypothesized that the major source would be the neuronal release of noradrenaline (NA) from intrinsic sympathetic nerves rather than circulating or non‐neuronal local production.Methods Three concentric segments (central, intermediate, peripheral) were obtained by double trephination (9.5‐7.25 mm) performed on corneas harvested from 3‐4 month old rabbits, along with aqueous humor and blood samples. Endogenous catecholamines were quantified by HPLC‐EC. Results are means±SEM. ANOVA was used for statistical analysis.Results NA and adrenaline (AD) were identified in all corneal segments (n=15/16) at the following concentrations: 101.3±24.1 pmol/g for NA, 4.8±2.7 pmol/g for AD in the centre; 76.8±18.8 pmol/g for NA, 23.0±11.1 pmol/g for AD in the intermediate segment; 317.0±135.7 pmol/g for NA and11.1±6.1 pmol/g for AD in the periphery. Statistically significant (P<0.05) were the differences between: 1) NA concentrations in peripheral segments and those either in central or intermediate segments; 2) NA and AD concentrations in all segments. In the aqueous humor concentrations of NA were 77.0±9.8 nmol/L (n=6) and no AD was found. Plasma concentrations (n=4) were 28.0±2,5 μmol/L for NA, 36.2±8.5 μmol/L for AD.Conclusion There is a concentration gradient for NA decreasing from the corneal periphery towards the centre. In contrast, no such gradient exists for AD. Moreover, NA is the most abundant of the two catecholamines in all segments, whereas in the plasma AD predominates. Taken together, these results suggest that corneal NA is mostly of neuronal origin.

Chemical phenotypes of P2X2 purinoreceptor immunoreactive cell bodies in the area postrema

Purines such as adenosine 5'-triphosphate (ATP) act as extracellular messengers through specific purinergic receptors. Three different classes of purinergic receptors have been identified and termed P1, P2X, and P2Y. The purinergic receptor subunit P2X2 is a ligand-gated ion channel that is widely expressed by neurons in the CNS. In the brainstem medulla oblongata, the ionotropic P2X2 receptor (P2X2R) is enriched in the area postrema (AP). Two different antisera to P2X2R were used to determine the chemical nature of P2X2R immunoreactive cell bodies in the rat AP, an area lacking a blood-brain barrier. Subcellularly, P2X2R immunoreactivity was located to the periphery of individual cell bodies. The majority of P2X2R-immunoreactive cells were shown to contain tyrosine hydroxylase (TH) (63.5 ± 7.7%) and dopamine β-hydroxylase (61.5 ± 5.1%). Phenylethanolamine N-methyltransferase (PNMT)-containing cells were not detected in the AP, supporting a noradrenergic nature of P2X2R cells in the AP. There were no P2X2R-immunoreactive cells in the AP that contained the GABA-synthesizing enzyme glutamic acid decarboxylase 65. Only single vesicular glutamate transporter 2-immunoreactive cell bodies that were not P2X2R-positive were demonstrated in the AP. Some P2X2R-positive cells in the AP were immunoreactive for the neuropeptides substance P and pituitary adenylate cyclase-activating polypeptide, whereas dynorphin-, enkephalin-, or cholecystokinin-positive cells were not P2X2R-immunoreactive. Presence of P2X2R in a majority of noradrenergic cells of the AP implies that ATP may have a regulatory action on neuronal noradrenaline release from the AP, a circumventricular organ with a strategic position enabling interactions between circulating substances and the central nervous system.

Effects of the α2-Adrenergic Agonist Clonidine on the Pharmacodynamics and Pharmacokinetics of 3,4-Methylenedioxymethamphetamine in Healthy Volunteers

The mechanism of action of 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) involves the carrier-mediated and potentially vesicular release of monoamines. We assessed the effects of the sympatholytic α₂-adrenergic receptor agonist clonidine (150 μg p.o.), which inhibits the neuronal vesicular release of norepinephrine, on the cardiovascular and psychotropic response to MDMA (125 mg p.o.) in 16 healthy subjects. The study used a randomized, double-blind, placebo-controlled crossover design with four experimental sessions. The administration of clonidine 1 h before MDMA reduced the MDMA-induced increases in plasma norepinephrine concentrations and blood pressure but only to the extent that clonidine lowered norepinephrine levels and blood pressure compared with placebo. Thus, no interaction was found between the cardiovascular effects of the two drugs. Clonidine did not affect the psychotropic effects or pharmacokinetics of MDMA. The lack of an interaction of the effects of clonidine and MDMA indicates that vesicular release of norepinephrine, which is inhibited by clonidine, does not critically contribute to the effects of MDMA in humans. Although clonidine may be used in the treatment of stimulant-induced hypertensive reactions, the present findings do not support a role for α₂-adrenergic receptor agonists in the prevention of psychostimulant dependence.

Central Sympatholytic Drugs

• Central sympatholytic drugs reduce blood pressure mainly by stimulating central α(2) -adrenergic receptors in the brainstem centers, thereby reducing sympathetic nerve activity and neuronal release of norepinephrine to the heart and peripheral circulation. • This class of drugs, however, is currently used mainly as fourth-line (or beyond) drug therapy for hypertension because of side effects of drowsiness, fatigue, and dry mouth. • Rebound hypertension is also another major concern in certain drugs with a short half-life, particularly in patients who are nonadherent to the regimen. Therefore, their use on a "PRN" basis for treatment of blood pressure surge in the absence of symptoms or acute target complications should also be avoided.

PTH-receptors regulate norepinephrine release in human heart and kidney

Recent data suggests that chronic renal failure and hyperparathyroidism are associated with sympathetic overactivity. Since peptide hormones are known to modulate norepinephrine (NE) release by activating prejunctional receptors, this study investigates whether parathyroid hormone fragment (1–34) (hPTH(1–34)) increases neuronal NE release in human heart and kidney. Using specific PTH-receptor agonists and antagonists, this study furthermore highlights functional differences between PTH1 and PTH2 receptors.Human atrial and renal tissues were incubated with [3H]-NE and superfused. Three electrical stimulations (5Hz, 1min) induced a stable [3H]-NE release which was taken as an index of endogenous NE release. RT-PCR with specific primers for PTH1- and PTH2-receptor was performed in heart and kidney.hPTH(1–34) (0.01–0.1μmol/L) and a stable analog of its second messenger cAMP (8-bromo-cAMP) increased [3H]-NE release in human atria. This facilitatory effect of PTH was also observed in human renal cortex. The PTH1-receptor antagonist (D-Trp12, Tyr34)-pTH-(7–34) (0.5μmol/L) abolished the effect of hPTH(1–34). This data was verified using isolated perfused mouse kidneys. Tuberoinfundibular peptide of 39 residues (TIP-39) (0.1nmol/L–0.1μmol/L) decreased [3H]-NE release in atria.PTH1- and PTH2-receptor expressions were demonstrated in human heart and kidney. Moreover, a splice variant of the PTH2-receptor was detected in human kidney.In conclusion, PTH is able to facilitate NE release in human atria and renal cortex by activation of PTH1-receptors. The highly increased PTH levels that can be observed in chronic renal failure might be one contributor for the elevated sympathetic nerve activity and the associated cardiovascular mortality in patients with end stage renal disease.

Simultaneous parasympathetic and sympathetic activation reveals altered autonomic control of heart rate, vascular tension, and epinephrine release in anesthetized hypertensive rats

Sympathetic hyperactivity and parasympathetic insufficiency characterize blood pressure (BP) control in genetic hypertension. This shift is difficult to investigate in anesthetized rats. Here we present a pharmacological approach to simultaneously provoke sympathetic and parasympathetic transmitter release, and identify their respective roles in the concomitant cardiovascular response. To stimulate transmitter release in anesthetized normotensive (WKY) and spontaneously hypertensive rats (SHR), we injected intravenously 4-aminopyridine (4-AP), a voltage-sensitive K+ channel (KV) inhibitor. A femoral artery catheter monitored BP, an ascending aorta flow-probe recorded cardiac output and heart rate (HR). Total peripheral vascular resistance (TPVR) was calculated. 4-AP-induced an immediate, atropine (muscarinic antagonist)- and hexamethonium (ganglion blocker)-sensitive bradycardia in WKY, and in both strains, a subsequent, sustained tachycardia, and norepinephrine but not epinephrine release. Reserpine (sympatholytic), nadolol (β-adrenoceptor antagonist) or right vagal nerve stimulation eliminated the late tachycardia, adrenalectomy, scopolamine (central muscarinic antagonist) or hexamethonium did not. 4-AP increased TPVR, transiently in WKY but sustained in SHR. Yohimbine (α2-adrenoceptor antagonist) prevented the TPVR down-regulation in WKY. Reserpine and prazosin (α1-adrenoceptor antagonist) eliminated the late vasoconstriction in SHR. Plasma epinephrine overflow increased in nadolol-treated SHR. Through inhibition of KV, 4-AP activated parasympathetic ganglion transmission and peripheral, neuronal norepinephrine release. The sympathetic component dominated the 4-AP–HR-response in SHR. α2-adrenoceptor-dependent vasodilatation opposed norepinephrine-induced α1-adrenergic vasoconstriction in WKY, but not SHR. A βAR-activated, probably vagal afferent mechanism, hampered epinephrine secretion in SHR. Thus, 4-AP activated the autonomic system and exposed mechanisms relevant to hypertensive disease.

Sleep apnoea and malignant ventricular arrhythmias in heart failure

This editorial refers to ‘Cheyne–Stokes respiration and obstructive sleep apnoea are independent risk factors for malignant ventricular arrhythmias requiring appropriate cardioverter-defibrillator therapies in patients with congestive heart failure’, by T. Bitter et al. doi:10.1093/eurheartj/ehq327 Sleep-related breathing disorders (SRBDs) are present in ∼50% of patients with chronic heart failure (CHF), with fairly equal prevalence of obstructive sleep apnoea (OSA) and central sleep apnoea with Cheyne–Stokes respiration (CSA).1,2 Obstructive apnoeas are characterized by recurring upper airway collapse with ongoing respiratory effort during sleep, causing repetitive surges of negative intra-thoracic pressure. As opposed to OSA, CSA results from a reduction or cessation of output from the central respiratory generator in the brainstem, manifesting as apnoeas or hypopnoeas without accompanying respiratory effort. Common to OSA and CSA are recurrent cycles of apnoea, hypoxia, hypercapnia, and arousal from sleep, each of which acts independently to trigger surges of central sympathetic vasoconstrictor outflow and neuronal noradrenaline release, resulting in a rise, rather than the normal fall, in blood pressure during sleep. Muscle sympathetic nerve activity (MSNA) peaks during the apnoeic phase of OSA but during the hyperpnoeic phase of CSA.3,4 Circadian ventricular metabolic gene expression and metabolic capacity are at their nadir during sleep. Thus, the failing heart of individuals with co-existing sleep apnoea suffers these adverse autonomic, chemical, and haemodynamic burdens at the time of day when it is least able to cope.5 Moreover, the sympathetic activation accompanying these SRBDs does not subside upon waking: daytime MSNA is higher in heart failure patients with than in those without sleep apnoea,6 a finding consistent with the concept that these two stimuli exert independent excitatory effects on central sympathetic outflow.7 In mild heart failure, only cardiac noradrenaline spillover (CNaS) is elevated. Over time, renal and total body noradenaline … *Corresponding author. Fax: +49 551 398918, Email: sandreas{at}lungenfachklinik-immenhausen.de

α2B-Adrenoceptor Deficiency Leads to Postnatal Respiratory Failure in Mice*

α(2)-Adrenoceptors belong to the family of adrenergic receptors, which regulate the neuronal release of norepinephrine as part of a negative feedback loop. Among the α(2)-adrenoceptors, the α(2B)-subtype may also influence developmental signaling pathways involved in angiogenesis of the placenta. Thus, the aim of the present study was to determine whether α(2B)-adrenoceptors are also involved in other developmental processes beyond placental angiogenesis. Ablation of α(2B)-adrenoceptors led to lethality of mutant mice during the first hours after birth. Despite normal breathing and drinking behavior, mutant mice developed cyanosis, which could be traced back to a defect in lung morphology with significantly reduced alveolar volume and thickened interalveolar septi. In α(2B)-deficient lungs and in isolated alveolar type II cells, expression of sonic hedgehog (SHH) was significantly increased, resulting in mesenchymal proliferation. In vitro α(2B)-adrenoreceptor stimulation suppressed expression of sonic hedgehog and the cell cycle genes cyclin D1 and Ki67. In vivo inhibition of enhanced SHH signaling by the smoothened antagonist cyclopamine partially rescued perinatal lethality, lung morphology, and altered gene expression in mutant mice. Thus, α(2B)-adrenoceptors in lung epithelia play an important role in suppressing sonic hedgehog-mediated proliferation of mesenchymal cells and thus prevent respiratory failure.

The Residual Nonadrenergic Contractile Response to Nerve Stimulation of the Mouse Prostate Is Mediated by Acetylcholine but Not ATP in a Comparison with the Mouse Vas Deferens

Neuronal release of noradrenaline is primarily responsible for the contraction of prostatic smooth muscle in all species, and this forms the basis for the use of α(1)-adrenoceptor antagonists as pharmacotherapies for benign prostatic hyperplasia. Previous studies in mice have demonstrated that a residual nonadrenergic component to nerve stimulation remains after α(1)-adrenoceptor antagonism. In the guinea pig and rat prostate and the vas deferens of guinea pigs, rats, and mice, ATP is the mediator of this residual contraction. This study investigates the mediator of residual contraction in the mouse prostate. Whole prostates from wild-type, α(1A)-adrenoceptor, and P2X1-purinoceptor knockout mice were mounted in organ baths, and the isometric force that tissues developed in response to electrical field stimulation or exogenously applied agonists was recorded. Deletion of the P2X1 purinoceptor did not affect nerve-mediated contraction. Furthermore, the P2-purinoceptor antagonist suramin (30 μM) failed to attenuate nerve-mediated contractions in wild-type, α(1A)-adrenoceptor, or P2X1-purinoceptor knockout mice. Atropine (1 μM) attenuated contraction in prostates taken from wild-type mice. In the presence of prazosin (0.3 μM) or guanethidine (10 μM), or in prostates taken from α(1A)-adrenoceptor knockout mice, residual nerve-mediated contraction was abolished by atropine (1 μM), but not suramin (30 μM). Exogenously administered acetylcholine elicited reproducible concentration-dependent contractions of the mouse prostate that were atropine-sensitive (1 μM), but not prazosin-sensitive (0.3 μM). Acetylcholine, but not ATP, mediates the nonadrenergic component of contraction in the mouse prostate. This cholinergic component of prostatic contraction is mediated by activation of muscarinic receptors.

Short-term Effects of Endothelins on Tyrosine Hydroxylase Activity and Expression in the Olfactory Bulb of Normotensive Rats

The olfactory system in rats is part of the limbic region with extensive afferent connections with brain areas involved in the regulation of behaviour and autonomic responses. The existence of the endothelin system and catecholaminergic neurons in the olfactory bulb suggests that endothelins may modulate noradrenergic transmission and diverse olfactory mediated processes. In the present work we studied the effect of endothelin-1 and -3 on neuronal norepinephrine release and the short-term regulation of tyrosine hydroxylase in the olfactory bulb. Results showed that both endothelins increased tyrosine hydroxylase activity through the activation of a non-conventional endothelin G-protein coupled receptor, coupled to the stimulation of protein kinase A and C, as well as Ca(2+)/calmodulin-dependent protein kinase II. On the other hand, neither endothelin-1 nor endothelin-3 modified tyrosine hydroxylase total protein levels, but both peptides increased the phosphorylation of serine residues of the enzyme at sites 19 and 40. Furthermore, endothelins enhanced norepinephrine release in olfactory neurons suggesting that this event may contribute to increased tyrosine hydroxylase activity by reducing the feedback inhibition. Taken together present findings show a clear interaction between the endothelin system, and the catecholaminergic transmission in the olfactory bulb. Additional studies are required to evaluate the physiological functions regulated by endothelins at this brain level.

Norepinephrine Density Is Decreased in Human Failing Myocardium

Background: Norepinephrine (NE) is released from its storage granules when the nerve is stimulated and enters the synaptic cleft to bind to alpha and beta-receptors on the effector cells. Chemical signaling is terminated by a rapid reuptake of neurotransmitter into presynaptic nerve terminals mainly via NE transport systems (NET). Previous studies in animal model of heart failure showed that both increased neuronal release of NE and decreased efficiency of NET contribute to decreased myocardial NE content which correlates directly with decreasing the left ventricular ejection fraction.

β1-Adrenoceptor blockade mitigates excessive norepinephrine release into cardiac interstitium in mitral regurgitation in dog

Mitral regurgitation (MR) is associated with increased neuronal release of norepinephrine (NE) and epinephrine (EP) into myocardial interstitial fluid (ISF) that may be necessary in sustaining left ventricular (LV) function via activation of cardiomyocyte beta-adrenergic receptors (ARs). However, activation of neuronal beta-ARs on cardiac neurons may lead to further catecholamine release, with an attendant risk of functional deterioration. We hypothesize that a beneficial effect of beta-AR blockade may therefore mitigate excessive catecholamine release from cardiac adrenergic neurons in dogs with MR. We measured the effects of chronic beta-receptor blockade (beta-RB) on ISF NE and EP release using in vivo microdialysis in open-chest anesthetized dogs after 4 wk of MR with or without extended release of metoprolol succinate (100 mg/day) as well as in control dogs. Fractional shortening increased by 30% in both MR and MR + beta-RB dogs after 4 wk of MR. In MR + beta-RB dogs, stellate-stimulated heart rate change was attenuated compared with control and MR dogs, whereas peak change of LV pressure over time (+dP/dt) increased equally in all groups. Stellate-stimulated ISF NE increased fivefold over baseline in MR versus twofold in control dogs (< 0.05), but the NE release was significantly attenuated in MR + beta-RB dogs. In contrast, stellate-stimulated increases in ISF EP did not differ in control, MR, and MR + beta-RB dogs. This study demonstrates that beta-RB attenuates ISF NE release from cardiac neurons and that the LV functional response to MR is not dependent on an excess increase in ISF NE. Thus beta1-RB may exert a beneficial effect by attenuating untoward effects of excessive sympathetic efferent neural NE release while sustaining early LV functional adaptation to MR.

Involvement of nitric oxide pathways in short term modulation of tyrosine hydroxylase activity by endothelins 1 and 3 in the rat anterior hypothalamus

The ability of endothelins 1 and 3 (ET-1 and ET-3) to reduce neuronal norepinephrine release through ETB receptor activation involving nitric oxide (NO) pathways in the rat anterior hypothalamus region (AHR) was previously reported. In the present work, we studied the effects of ET-1 and -3 on tyrosine hydroxylase (TH) activity and the possible involvement of NO pathways. Results showed that ET-1 and -3 (10 nM) diminished TH activity in AHR and this effect was blocked by a selective ETB receptor antagonist (100 nM BQ-788), but not by a ET A receptor antagonist (BQ-610). To confirm these results, 1 μM IRL-1620 (ET B agonist) reduced TH activity whereas 300 nM sarafotoxin S6b falled to modify it. N ω-Nitro- l-arginine methyl ester (10 μM), 7-nitroindazole (10 μM), 1 H-[1,2,4]oxadiazolo[4,3- a]quinoxalin-1-ona (10 μM), KT5823 (2 μM), inhibitors of nitric oxide synthase, neuronal nitric oxide synthase, NO-sensitive-guanylyl cyclase, and protein kinase G, respectively, did not modify the reduction of TH activity produced by ETs. In addition, both 100 μM sodium nitroprusside and 50 μM 8-bromoguanosine-3′,5′-cyclic monophosphate (NO donor and guanosine-3′,5′-cyclic monophosphate analog, respectively) diminished TH activity. Present results showed that ET-1 and ET-3 diminished TH activity through the activation of ET B receptors involving the NO/guanosine-3′,5′-cyclic monophosphate/protein kinase G pathway. Taken jointly present and previous results it can be concluded that both ETs play an important role as modulators of norepinephrine neurotransmission in the rat AHR.