Stimulation Of Α-adrenergic Receptors Research Articles

The Dual Cardiovascular Effect of Centrally Administered Clonidine: A Comparative Study between Pentobarbital- and Ketamine/Xylazine-Anesthetized Rats

The administration of the α2-adrenergic receptor agonist clonidine via intracerebroventricular route produces hypotension in pentobarbital-anesthetized rats and pressor responses in conscious normotensive rats. We explored the impact of different anesthetics on the central nervous system-dependent cardiovascular effects of clonidine. Normotensive male Wistar rats with guide cannulas previously implanted in the cerebroventricular system were anesthetized with pentobarbital or ketamine/xylazine and prepared for blood pressure measurement. The animals received intracerebroventricular injections of 10 μg clonidine or 0.6 μg dexmedetomidine, and the effects on the systolic, diastolic, mean arterial pressure, and heart rate were evaluated. The influence of 5 μg yohimbine, a selective α2-adrenergic receptor antagonist, was also assessed. The i.c.v. microinjection of clonidine decreased all three components of systemic arterial pressure and the heart rate of pentobarbital-anesthetized rats. On the other hand, clonidine increased the blood pressure and generated a less intense reduction in the heart rate of ketamine/xylazine-anesthetized rats. The pressor and bradycardic effects of clonidine in ketamine/xylazine-anesthetized animals were reproduced by dexmedetomidine, a more selective α2-adrenergic receptor agonist. Notably, the previous intracerebroventricular injection of yohimbine significantly inhibited the hypertensive effect of clonidine and dexmedetomidine. This study discloses that while normotensive rats anesthetized with pentobarbital show hypotensive responses, the stimulation of α2-adrenergic receptors increases the blood pressure in rats under ketamine/xylazine-induced anesthesia, reproducing the effects seen in conscious normotensive animals. Recognizing the mechanisms involved in these differences may allow us to understand better the final effects of clonidine and other α2-adrenergic receptor agonists in the central nervous system, contributing to the repurposing of these drugs.

Features of α2-Adrenergic Regulation of Isolated Rat Heart after Hypokinesia.

We studied the effect of the α2-adrenergic receptor agonist clonidine hydrochloride (10-9-10-6 M) on the isolated heart of adult rats after 30-day restriction of motor activity. In hypokinetic rats, in comparison with control animals, clonidine caused a positive inotropic effect; the dynamics of coronary flow was changed after stimulation of α2-adrenergic receptors by clonidine in the minimum and maximum concentrations. Moreover, clonidine in concentrations of 10-8 and 10-7 M reduced coronary flow both in the control group and against the background of hypokinesia. Clonidine (10-8-10-6 M) had a negative chronotropic effect in control and hypokinetic animals, while the dynamics of HR was multidirectional, i.e. either an increase or decrease in the effects was observed depending of the agonist concentration. Overall, the data obtained indicate the participation of α2-adrenergic receptors in adaptive processes after motor activity limitation.

Age-Related Peculiarities of the Effect of Stimulation of α2-Adrenergic Receptors on the Electrical Activity of Rat Cardiomyocytes

Age-Related Peculiarities of the Effect of Stimulation of α2-Adrenergic Receptors on the Electrical Activity of Rat Cardiomyocytes

Response of Isolated Rat Heart to α2-Adrenergic Receptor Stimulation after If Current Blockade in the Late Postinfarction Period.

We studied the effect of α2-adrenoreceptor activation after preliminary If-current blockade on the performance of the Langendorff-isolated rat heart 54 days after modeling myocardial infarction. Stimulation of α2-adrenoreceptors against the background of application of If blocker ZD7288 in concentrations of 10-9 and 10-5 M decreased myocardial inotropy in isolated rat hearts by 50 and 39% (p<0.05) and increased HR by 20 and 15% (p<0.05), respectively. Activation of α2-adrenoreceptors against the background of application of ZD7288 in a concentration of 10-9 and 10-5 M led to a decrease in the coronary flow in the isolated rat heart with the model of myocardial infarction by 21% (p<0.05) and 32% (p<0.05), respectively.

Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levels.

Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.

Effects of α2-adrenoceptor stimulation on luminal alkalinisation and net fluid flux in rat duodenum.

The sympathetic nervous system is highly involved in the regulation of gastrointestinal functions such as luminal alkalinisation and fluid absorption. However, the exact mechanisms are not clear. This study aimed to delineate how α2-adrenergic receptor stimulation reduces duodenal luminal alkalinisation and induces net fluid absorption. This was tested by perfusing the duodenum of anesthetized rats with isotonic solutions devoid of Cl- and/or Na+, in the absence and presence of the α2-adrenoceptor agonist clonidine. The clonidine was also studied in rats treated with dimethylamiloride (a Na+/H+ exchange inhibitor), vasoactive intestinal peptide, and the nicotinic receptor antagonist hexamethonium. Clonidine reduced luminal alkalinisation and induced net fluid absorption. The Cl--free solution decreased luminal alkalinisation and abolished net fluid absorption, but did not prevent clonidine from doing so. Both the Na+-free solution and luminal dimethylamiloride increased luminal alkalinisation and abolished net fluid absorption, effects counteracted by clonidine. The NaCl-free solution (D-mannitol) did not affect luminal alkalinisation, but reduced net fluid absorption. Clonidine reduced luminal alkalinisation and induced net fluid absorption in rats perfused luminally with mannitol. However, clonidine did not affect the vasoactive intestinal peptide-induced increase in luminal alkalinisation or fluid secretion. Pre-treatment with hexamethonium abolished the effects of clonidine on luminal alkalinisation and net fluid flux. In summary, our in vivo experiments showed that clonidine-induced reduction in luminal alkalinisation and induction of net fluid absorption was unrelated to luminal Na+ and Cl-, or to apical Na+/H+ or Cl-/HCO3- exchangers. Instead, clonidine seems to exert its effects via suppression of nicotinic receptor-activated acetylcholine secretomotor neurons.

Is the Pannexin-1 Channel a Mechanism Underlying Hypertension in Humans? a Translational Study of Human Hypertension

In preclinical models, the pannexin-1 channel has been shown to be involved in blood pressure regulation through an effect on peripheral vascular resistance. Pannexin-1 releases ATP, which can activate constrictive purinergic receptors on the smooth muscle cells. Pannexin-1 opening is proposed to be mediated by α-adrenergic receptors to potentiate sympathetic constriction. This positions pannexin-1 as a putative pharmacological target in blood pressure regulation in humans. The aim was to provide the first translational evidence for a role of pannexin-1 in essential hypertension in humans by use of an advanced invasive mechanistic approach. Middle-aged stage-1 hypertensive (n=13; 135.7±6.4 over 83.7±3.7 mm Hg) and normotensive men (n=12; 117.3±5.7 over 72.2±3.5 mm Hg) were included. Blood pressure and leg vascular resistance were determined during femoral arterial infusion of tyramine (α-adrenergic receptor stimulation), sodium nitroprusside, and acetylcholine. Measurements were made during control conditions and with pannexin-1 blockade (3000 mg probenecid). Expression of Pannexin-1, purinergic- and α-adrenergic receptors in skeletal muscle biopsies was determined by Western blot. The changes in leg vascular resistance in response to tyramine (+289% versus +222%), sodium nitroprusside (-82% versus -78%) and acetylcholine (-40% versus -44%) infusion were not different between the 2 groups (P>0.05) and pannexin-1 blockade did not alter these variables (P>0.05). Expression of pannexin-1 and of purinergic- and α-adrenergic receptors was not different between the 2 groups (P>0.05). Contrary to our hypothesis, the data demonstrate that pannexin-1 does not contribute to the elevated blood pressure in essential hypertension, a finding, which also opposes that reported in preclinical models.

Sympathetic regulation of coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in men.

What is the central question of this study? What is the role of β- and α-adrenergic receptors in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans? What is the main finding and its importance? β-Adrenergic receptor, but not α-adrenergic receptor, blockade significantly blunted the increases in coronary blood velocity observed during handgrip. Coronary blood velocity was unchanged from baseline during isolated muscle metaboreflex activation. This highlights the important role of β-adrenergic receptors in the coronary circulation during handgrip in humans, and the more limited involvement of the α-adrenergic receptors. We sought to investigate the role of β- and α-adrenergic receptors in coronary circulation during static handgrip exercise and isolated muscle metaboreflex activation in humans. Seventeen healthy young men underwent two experimental sessions, consisting of 3min of static handgrip exercise at a target force of 40% maximum voluntary force (not achieved for the full 3min), and 3min of metaboreflex activation (post-exercise ischaemia) in two conditions: (1) control and β-blockade (oral propranolol), and (2) control and α-blockade (oral prazosin). In both sessions, coronary blood velocity (CBV, echocardiography) was increased during handgrip (Δ8.0±7.4cms-1 ) but unchanged with metaboreflex activation (Δ2.5±3.2cms-1 ) under control conditions. β-Blockade abolished the increase in CBV during handgrip, while CBV was unchanged from control with α-blockade. Cardiac work, estimated from rate pressure product (RPP; systolic blood pressure multiplied by heart rate), increased during handgrip and metaboreflex in control conditions in both sessions. β-Blockade reduced RPP responses to handgrip and metaboreflex, whereas α-blockade increased RPP, but the responses to handgrip and metaboreflex were unchanged. CBV and RPP were only significantly correlated during handgrip under control (r=0.71, P<0.01) and β-blockade (r=0.54, P=0.03) conditions, and the slope of this relationship was unaltered with β-blockade. Collectively, these findings indicate that β-adrenergic receptors play the primary role to the increase of coronary circulation during handgrip exercise, but CBV is unchanged with metaboreflex activation, while α-adrenergic receptor stimulation seems to exert no effect in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans.

Involvement of noradrenergic and serotonergic systems in risk-based decisions between options of equivalent expected value in rats

Risk perception is an important factor that may mediate risk-based decision-making processes regulated by noradrenergic (NA) and serotonergic (5-HT) systems. Most risk-based decision-making models involve complex factors, such as risk perception or reward value, such that the final decision is the result of the interactions among these factors. However, the contribution of risk perception per se in risk decisions has remained unclear. Therefore, in the present study, we made some modifications to the classical probabilistic discounting task (PDT) to focus on the impact of risk perception and noradrenergic/serotonergic systems on decision-making behavior. Meanwhile, we conducted an elevated plus-maze (EPM) test to detect the correlation between anxiety and choice behavior. In the current study, rats had to choose between a “certain” lever that delivered a certain number of pellets and a “risky” lever that delivered eight pellets in a probabilistic manner (descending: 50%, 25%, 12.5% or ascending 12.5%, 25%, 50% of the time). The long-term rewarding values of the two levers were always identical in each block within each session. According to their baseline performances in choosing the risky lever, rats were divided into the risk-prefer group and risk-averse group. The results showed that there was a significant correlation between open arm time in EPM and risky choice for both descending order and ascending order, indicating that highly anxious rats more often preferred the safe option under risk. Pharmacological stimulation of α2-adrenergic receptors via dexmedetomidine (0.01 mg/kg) decreased the preference of probabilistic rewards in the risk-prefer group, while blocking α2 receptors by atipamezole (0.3 mg/kg) also reduced risky choices. The NA reuptake inhibitor, atomoxetine, increased the preference for risky choices in the risk-prefer group, the effect of which was attained via multiple superimposed doses. Administration of the 5-HT2A receptor agonist, DOI (0.1 mg/kg), increased risk-taking behavior in the risk-prefer group. Taken together, these results suggest that NA may be more inclined to process negative information such as loss or uncertainty in the regulation of risk-related decision making, whereas 5-HT may function primarily to increase risk-taking behavior. Our findings may help to further elucidate how noradrenergic and serotonergic systems differentially affect individuals with different risk preferences in terms of regulating risk perception in risk-related decision making.

Effect of α2-Adrenergic Receptor Stimulation on the Isolated Rat Heart against the Background of If Blockade.

The study examined the effect of α2-adrenoreceptor (α2-AR) activation against the background of preliminary blockage of If on the performance of Langerndorff-isolated rat heart. Stimulation of α2-AR in isolated rat hearts against the background of ZD7288 in concentrations of 10-9 M and 3×10-5 M changed the negative dynamics of myocardial inotropy to positive (by 25 and 38%; p<0.05). Activation of α2-AR produced opposite effects on HR. If blockade abolished tachycardia caused by activation of α2-AR; HR deceleration in response to α2-AR agonist against the background of If blocker in a concentration 10-9 M was 41% (p<0.05). We observed negative dynamics of coronary flow (by 38%; p<0.05) in isolated adult rat hearts after application of α2-AR agonist against the background of If blockade (10-9 M).

Abstract 194: Effects of PEG-20k on Coronary Perfusion Pressure and Post-Resuscitation Myocardial and Cerebral Function in a Rat Model of Cardiac Arrest

Introduction: Epinephrine is the primary drug given during cardiopulmonary resuscitation (CPR), when given early, to reverse cardiac arrest (CA) by stimulation of α-adrenergic receptors in vascular smooth muscle. This increases coronary perfusion pressure (CPP) and increases rate of return of spontaneous circulation (ROSC). However, the use of epinephrine is not associated with a significant difference in long-term survival or favorable neurologic outcome when given late after arrest onset. In the present study, we compared the effects of aortic injection of polyethylene glycol-20k (PEG-20k) vs. epinephrine during CPR on CPP and postresuscitation myocardial and cerebral function in a rat model of CA. Hypothesis: Aortic injection of PEG-20k during CPR will increase CPP to the same extent as epinephrine without adversely affecting post-resuscitation myocardial and cerebral function. Methods: Twenty four male Sprague-Dawley rats weighing between 450-550 g were randomized into four groups: 1) PEG-20k 2) epinephrine 3) saline placebo 4) saline-intra-aorta (IA). Eight minutes of CPR was initiated after 6 minutes of untreated ventricular fibrillation. PEG-20k IA (10% est. total blood volume [1.8ml]), saline IA, saline IV or epinephrine IV (20ug/kg) was given after 4 minutes of CPR by continuous infusion over 3 minutes. CPP was recorded continuously and resuscitation was attempted with 4 Joule defibrillation. Myocardial function was measured at baseline, 2, 4, and 6 hours after ROSC by echocardiography and neurologic deficit scores (NDS) were recorded at 24, 48, and 72 hours after ROSC. Results: In both saline groups, CPP did not change. However, aortic injection of PEG-20k increased CPP significantly to the same extent as epinephrine (Fig 1). Post-resuscitation ejection fraction was significantly greater in PEG-20k compared to epinephrine (64 + 1 vs 45 + 3, p&lt;0.05) and NDS was significantly improved in PEG-20k compared to epinephrine (100 + 50 vs 450 + 50, p&lt;0.05).

Effect of Stimulation of α2-Adrenergic Receptors on Action Potential of Working Cardiomyocytes in Rat Atrium.

The study examined the effect of clonidine hydrochloride (10-9-10-5 М) on electrical activity of working cardiomyocytes in rat right atrium. Stimulation of α2-adrenergic receptor with clonidine changed electrical activity of the heart. All tested concentrations of the agonist lengthened the action potential and decreased the firing rate of cardiomyocytes in a dose-dependent manner. The maximum effects of clonidine were observed at concentration of 10-5 М.

Effect of α2-Adrenoceptor Stimulation on Functional Parameters of Langendorff-Isolated Rat Heart.

We studied the effect of α2-adrenoreceptor agonist clonidine hydrochloride in concentrations of 10-9-10-6 M on inotropy, chronotropy, and coronary flow in Langendorff-isolated heart of adult rats. It was found that α2-adrenoreceptor agonist changed all studied parameters. Left ventricular myocardium contraction force decreased after application of all tested concentrations, the maximum effect was observed at a concentration of 10-6 M. Stimulation of α2-adrenergic receptors in concentrations of 10-8, 10-7, and 10-6 M produced a two-phase effect (initial increase and a subsequent decrease) on the coronary flow. Clonidine hydrochloride in the maximum concentration (10-6 M) caused a decrease in HR in one group and an increase in the other.

Management of an acute catecholamine-induced cardiomyopathy and circulatory collapse: a multidisciplinary approach.

A phaeochromocytoma (PC) is a rare, catecholamine-secreting neuroendocrine tumour arising from the adrenal medulla. Presenting symptoms of this rare tumour are highly variable but life-threatening multiorgan dysfunction can occur secondary to catecholamine-induced hypertension or hypotension and subsequent cardiovascular collapse. High levels of circulating catecholamines can induce an acute stress cardiomyopathy, also known as Takotsubo cardiomyopathy. Recent studies have focused on early diagnosis and estimation of the prevalence of acute stress cardiomyopathy in patients with PC, but very little is reported about management of these complex cases. Here, we report the case of a 38-year-old lady who presented with an acute Takotsubo or stress cardiomyopathy and catecholamine crisis, caused by an occult left-sided 5 cm PC. The initial presenting crisis manifested with symptoms of severe headache and abdominal pain, triggered by a respiratory tract infection. On admission to hospital, the patient rapidly deteriorated, developing respiratory failure, cardiogenic shock and subsequent cardiovascular collapse due to further exacerbation of the catecholamine crisis caused by a combination of opiates and intravenous corticosteroid. An echocardiogram revealed left ventricular apical hypokinesia and ballooning, with an estimated left ventricular ejection fraction of 10–15%. Herein, we outline the early stabilisation period, preoperative optimisation and intraoperative management, providing anecdotal guidance for the management of this rare life-threatening complication of PC.Learning points:A diagnosis of phaeochromocytoma should be considered in patients presenting with acute cardiomyopathy or cardiogenic shock without a clear ischaemic or valvular aetiology.Catecholamine crisis is a life-threatening medical emergency that requires cross-disciplinary expertise and management to ensure the best clinical outcome.After initial resuscitation, treatment of acute catecholamine-induced stress cardiomyopathy requires careful introduction of alpha-blockade followed by beta-blockade if necessary to manage β-receptor-mediated tachycardia.Prolonged α-adrenergic receptor stimulation by high levels of circulating catecholamines precipitates arterial vasoconstriction and intravascular volume contraction, which can further exacerbate hypotension. Invasive pressure monitoring can aid management of intravascular volume in these complex patients.

Noradrenaline Modulates the Membrane Potential and Holding Current of Medial Prefrontal Cortex Pyramidal Neurons via β1-Adrenergic Receptors and HCN Channels.

The medial prefrontal cortex (mPFC) receives dense noradrenergic projections from the locus coeruleus. Adrenergic innervation of mPFC pyramidal neurons plays an essential role in both physiology (control of memory formation, attention, working memory, and cognitive behavior) and pathophysiology (attention deficit hyperactivity disorder, posttraumatic stress disorder, cognitive deterioration after traumatic brain injury, behavioral changes related to addiction, Alzheimer’s disease and depression). The aim of this study was to elucidate the mechanism responsible for adrenergic receptor-mediated control of the resting membrane potential in layer V mPFC pyramidal neurons. The membrane potential or holding current of synaptically isolated layer V mPFC pyramidal neurons was recorded in perforated-patch and classical whole-cell configurations in slices from young rats. Application of noradrenaline (NA), a neurotransmitter with affinity for all types of adrenergic receptors, evoked depolarization or inward current in the tested neurons irrespective of whether the recordings were performed in the perforated-patch or classical whole-cell configuration. The effect of noradrenaline depended on β1- and not α1- or α2-adrenergic receptor stimulation. Activation of β1-adrenergic receptors led to an increase in inward Na+ current through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which carry a mixed Na+/K+ current. The protein kinase A- and C-, glycogen synthase kinase-3β- and tyrosine kinase-linked signaling pathways were not involved in the signal transduction between β1-adrenergic receptors and HCN channels. The transduction system operated in a membrane-delimited fashion and involved the βγ subunit of G-protein. Thus, noradrenaline controls the resting membrane potential and holding current in mPFC pyramidal neurons through β1-adrenergic receptors, which in turn activate HCN channels via a signaling pathway involving the βγ subunit.

Probenecid Inhibits α-Adrenergic Receptor-Mediated Vasoconstriction in the Human Leg Vasculature.

Coordination of vascular smooth muscle cell tone in resistance arteries plays an essential role in the regulation of peripheral resistance and overall blood pressure. Recent observations in animals have provided evidence for a coupling between adrenoceptors and Panx1 (pannexin-1) channels in the regulation of sympathetic nervous control of peripheral vascular resistance and blood pressure; however, evidence for a functional coupling in humans is lacking. We determined Panx1 expression and effects of treatment with the pharmacological Panx1 channel inhibitor probenecid on the vasoconstrictor response to α1- and α2-adrenergic receptor stimulation in the human forearm and leg vasculature of young healthy male subjects (23±3 years). By use of immunolabeling and confocal microscopy, Panx1 channels were found to be expressed in vascular smooth muscle cells of arterioles in human leg skeletal muscle. Probenecid treatment increased (P<0.05) leg vascular conductance at baseline by ≈15% and attenuated (P<0.05) the leg vasoconstrictor response to arterial infusion of tyramine (α1- and α2-adrenergic receptor stimulation) by ≈15%, whereas the response to the α1-agonist phenylephrine was unchanged. Inhibition of α1-adrenoceptors prevented the probenecid-induced increase in baseline leg vascular conductance, but did not alter the effect of probenecid on the vascular response to tyramine. No differences with probenecid treatment were detected in the forearm. These observations provide the first line of evidence in humans for a functional role of Panx1 channels in setting resting tone via α1-adrenoceptors and in the constrictive effect of noradrenaline via α2-adrenoceptors, thereby contributing to the regulation of peripheral vascular resistance and blood pressure in humans.

Noradrenergic regulation of plasticity marker expression in the adult rodent piriform cortex

The adult rodent piriform cortex has been reported to harbor immature neurons that express markers associated with neurodevelopment and plasticity, namely polysialylated neural cell adhesion molecule (PSA-NCAM) and doublecortin (DCX). We characterized the expression of PSA-NCAM and DCX across the rostrocaudal axis of the rat piriform cortex and observed higher numbers of PSA-NCAM and DCX positive cells in the posterior subdivision. As observed in the rat piriform cortex, Nestin-GFP reporter mice also revealed a similar gradient of GFP-positive cells with an increasing rostro-caudal gradient of expression. Given the extensive noradrenergic innervation of the piriform cortex and its role in regulating piriform cortex function and synaptic plasticity, we addressed the influence of norepinephrine (NE) on piriform cortex plasticity marker expression. Depletion of NE by treatment with the noradrenergic neurotoxin DSP-4 significantly increased the number of DCX and PSA-NCAM immunopositive cells in the piriform cortex of adult rats. Similarly, DSP-4 treated Nestin-GFP reporter mice revealed a robust induction of GFP-positive cells within the piriform cortex following NE depletion. Genetic loss of NE in dopamine β-hydroxylase knockout (Dbh −/−) mice phenocopied the effects of DSP-4, with an increase noted in PSA-NCAM and DCX positive cells in the piriform cortex. Further, chronic α2-adrenergic receptor stimulation with the agonist guanabenz increased PSA-NCAM and DCX positive cells in the piriform cortex of adult rats and GFP-positive cells in the piriform cortex of Nestin-GFP mice. By contrast, chronic α2-adrenergic receptor blockade with the antagonist yohimbine reduced PSA-NCAM and DCX positive cells in the piriform cortex of adult rats. Our results provide novel evidence for a role of NE in regulating the expression of plasticity markers, including PSA-NCAM, DCX, and nestin, within the adult mouse and rat piriform cortex.

Effects of dexmedetomidine preconditioning on myocardial expression of high mobility group box-1 protein during myocardial ischemia/reperfusion injury in rats

Objective To investigate the effects of dexmedetomidine(Dex) preconditioning on myocardial expression of high mobility group box-1 protein (HMGB1) during ischemia/reperfusion(I/R) injury in rats. Methods Fifty-two healthy male SD rats, weighing 250-300 g, were randomly divided into 4 groups(n=13): group sham operation(group S), group I/R, group Dex+I/R(group D), group Dex+yohimbine+I/R(group D/Y). In group I/R, group D and group D/Y, myocardial I/R was produced by occlusion of left coronary anterior descending artery for 30 min followed by 120 min reperfusion. Blood samples were taken for detecting the concentration of IL-6 and TNF-α by ELISA at the end of reperfusion. The rats were then killed, and the heart was removed for measuring infarct size and area at risk using 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. Myocardial HMGB1 expressions were measured by Western blot analysis. Results Compared with group S, the levels of IL-6[(336±41) ng/L], TNF-α[(636±25) ng/L] in serum and the IS/AAR ratio were significantly increased, the expression of HMGB1 were also significantly increased in group I/R(P 0.05). Conclusions Dex preconditioning decrease the expression of HMGB1 and alleviate inflammatory response during myocardial ischemia/reperfusion injury(MI/RI) in rats, which might be a result of the α2 adrenergic receptor stimulation. Key words: Dexmedetomidine; Preconditioning; myocardial ischemia/reperfusion injury; High mobility group box-1 protein; Rat

Neuroprotection by α2-Adrenergic Receptor Stimulation after Excitotoxic Retinal Injury: A Study of the Total Population of Retinal Ganglion Cells and Their Distribution in the Chicken Retina.

We have studied the effect of α2-adrenergic receptor stimulation on the total excitotoxically injured chicken retinal ganglion cell population. N-methyl-D-aspartate (NMDA) was intraocularly injected at embryonic day 18 and Brn3a positive retinal ganglion cells (Brn3a+ RGCs) were counted in flat-mounted retinas using automated routines. The number and distribution of the Brn3a+ RGCs were analyzed in series of normal retinas from embryonic day 8 to post-hatch day 11 retinas and in retinas 7 or 14 days post NMDA lesion. The total number of Brn3a+ RGCs in the post-hatch retina was approximately 1.9x106 with a density of approximately 9.2x103 cells/mm2. The isodensity maps of normal retina showed that the density decreased with age as the retinal size increased. In contrast to previous studies, we did not find any specific region with increased RGC density, rather the Brn3a+ RGCs were homogeneously distributed over the central retina with decreasing density in the periphery and in the region of the pecten oculli. Injection of 5–10 μg NMDA caused 30–50% loss of Brn3a+ cells and the loss was more severe in the dorsal than in the ventral retina. Pretreatment with brimonidine reduced the loss of Brn3a+ cells both 7 and 14 days post lesion and the protective effect was higher in the dorsal than in the ventral retina. We conclude that α2-adrenergic receptor stimulation reduced the impact of the excitotoxic injury in chicken similarly to what has been shown in mammals. Furthermore, the data show that the RGCs are evenly distributed over in the retina, which challenges previous results that indicate the presence of specific high RGC-density regions of the chicken retina.

Alpha2-Adrenergic-Agonist Brimonidine Stimulates Negative Feedback and Attenuates Injury-Induced Phospho-ERK and Dedifferentiation of Chicken Müller Cells.

Retinal injury induces Müller cell dedifferentiation by activating extracellular signal-regulated kinase (ERK) signaling. Stimulation of α2-adrenergic receptors protects against injury but also activates ERK in Müller cells. The purpose of this work was to study the effect of α2-adrenergic signaling on injury-induced ERK and Müller cell dedifferentiation. We tested the hypothesis that α2-stimulation triggers negative feedback regulation of the injury-induced ERK pathway that attenuates Müller cell dedifferentiation. Chicken retina injured by N-methyl-D-aspartate and cultured primary Müller cells were stimulated by the α2-adrenergic agonist brimonidine. Immunostaining, quantitative RT-PCR, and Western blot techniques in combination with receptor blockers were used for analysis of the cellular responses. Alpha2-adrenergic receptor stimulation attenuated injury-induced ERK activation and dedifferentiation of Müller cells as seen by decreased phospho-ERK, expression of transitin, and retinal progenitor cell genes. The attenuation was concomitant with a synergistic upregulation of several negative ERK-signal feedback regulators including ERK-phosphatases, Raf1-, and growth factor receptor-binding proteins. The results were also seen in cultures of primary Müller cells. Alpha2-adrenergic signaling on Müller cells elicits an intracellular attenuation of the injury response that comprises negative ERK-signaling feedback leading to attenuated Müller cell dedifferentiation. The implications of this study are that adrenergic stress signals may directly modulate glial function in retina and that α2-adrenergic receptor pharmacology may be used to control glial injury response.