Α2-adrenoceptor Agonist Research Articles

Effect of Different Doses of Atipamezole on Reversal of Medetomidine-Induced Tear-Flow Decrease in Rats.

It has been reported that α2-adrenoceptor agonists such as medetomidine decrease tear flow in many species, including rats. Few studies have investigated the involvement of α2-adrenoceptor in decreased tear flow; the issue has not been illustrated sufficiently. Therefore, we aimed to investigate the effect of different doses of atipamezole on the reversal of medetomidine-induced tear-flow decrease to reveal the specific involvement of α2-adrenoceptor. Treatment with 400, 800, or 1600 µg/kg atipamezole (or saline as the control) was intramuscularly administered to rats 15 min following intramuscular administration of 200 µg/kg medetomidine. After medetomidine administration, tear flow was measured using a phenol red thread test (PRTT). PRTT values decreased significantly after 200 µg/kg medetomidine administration. The PRTT values after 800 (optimal dose to reverse) and 1600 µg/kg atipamezole administration reached baseline, but never exceeded it significantly. Treatment with 400 µg/kg atipamezole also reversed the decrease in PRTT value but the PRTT remained lower than baseline. The optimal dose and the higher dose of atipamezole fully reversed the medetomidine-induced decrease in tear flow to the baseline level in rats, while the lower dose of atipamezole partially recovered tear flow.

Various Systemic Effects of MK-467, A Peripherally Acting α2-adrenoceptor Antagonist in Different Animal Species: An Overview

Most commonly used α2-adrenoceptor agonist shows adverse cardiovascular effects during anaesthesia. They mainly depress the cardiovascular system by provoking vasoconstriction followed by bradycardia. Although α2-adrenoceptor antagonist like atipamezole can reverse these effects along with that they also reverse the sedation and nociception. Concomitant administration of peripherally acting α2-adrenoceptor antagonist MK-467 can reverse the adverse cardiovascular effect of α2-adrenoceptor agonists without affecting the sedation and nociception. MK-467 has been successfully used in different animals like dogs, cats, sheep, horses along with different α2-adrenoceptor agonist drugs. This review aims to summarize the effects of MK-467 on sedation, cardiopulmonary system, the minimum alveolar concentration of different inhalant anaesthetics, plasma drug concentration, plasma glucose and insulin in different animals.

Dexmedetomidine attenuates sevoflurane‑induced neurocognitive impairment through α2‑adrenoceptors.

It has been reported that sevoflurane induces neurotoxicity in the developing brain. Dexmedetomidine is an α2 adrenoceptor agonist used for the prevention of sevoflurane-induced agitation in children in clinical practice. The aim of the present study was to determine whether dexmedetomidine could prevent sevoflurane-induced neuroapoptosis, neuroinflammation, oxidative stress and neurocognitive impairment. Additionally, the involvement of α2 adrenoceptors in the neuroprotective effect of dexmedetomidine was assessed. Postnatal day (P)6 C57BL/6 male mice were randomly divided into four groups (n=6 in each group). Mice were pretreated with dexmedetomidine, either alone or together with yohimbine, an α2 adrenoceptor inhibitor, then exposed to 3% sevoflurane in 25% oxygen. Control mice either received normal saline alone or with sevoflurane exposure. Following sevoflurane exposure, the expression of cleaved caspase-3 was detected by immunohistochemistry in hippocampal tissue sections. In addition, the levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and malondialdehyde, as well as superoxide dismutase (SOD) activity in the hippocampus were measured. At P35, the learning and memory abilities were assessed in each mouse using a Morris water maze test. Dexmedetomidine significantly decreased the expression of activated caspase-3 following sevoflurane exposure. Moreover, dexmedetomidine significantly decreased the levels of TNF-α, IL-1β and IL-6 in the hippocampus. SOD activity also increased in a dose-dependent manner in dexmedetomidine-treated mice. MDA decreased in a dose-dependent manner in dexmedetomidine-treated mice. Lastly, sevoflurane-induced learning and memory impairment was reversed by dexmedetomidine treatment. By contrast, co-administration of yohimbine significantly attenuated the neuroprotective effects of dexmedetomidine. These findings suggested that dexmedetomidine exerted a neuroprotective effect against sevoflurane-induced apoptosis, inflammation, oxidative stress and neurocognitive impairment, which was mediated, at least in part, by α2 adrenoceptors.

Involvement of G proteins and Rho kinase in α1-adrenoceptor mediated contractions of the rat portal vein.

Contractions of the rat portal vein in response to the α1-adrenoceptor agonist phenylephrine consist of phasic contractions at low concentrations, with tonic contractions superimposed at higher concentrations. The α1D-adrenoceptor antagonist BMY7378 (7.0, -log M) did not affect phasic or tonic contractions to phenylephrine. The relatively nonselective α1-adrenoceptor antagonist prazosin (7.5) shifted equally the potencies of phenylephrine at producing phasic and tonic contractions, with pKB values of 8.85 and 8.83 (-log M), respectively. The α1A-adrenoceptor antagonist RS100329 (8.5) produced a significantly greater shift in phenylephrine potency for phasic (pKB of 10.51) than tonic contractions (pKB of 9.78). Prazosin was less effective than RS100329 at reducing the effects of phenylephrine on frequency of phasic contractions. The Rho kinase inhibitor fasudil (5.0) did not affect phasic contractions to phenylephrine, but significantly reduced tonic contractions. It is concluded that there is no evidence for involvement of α1D-adrenoceptors in responses of the rat portal vein to phenylephrine, but phasic responses involve predominantly α1A-adrenoceptors. Tonic responses may involve predominantly α1B-adrenoceptors and are at least partly mediated by mechanisms involving Rho kinase sensitive to fasudil.

Arterial oxygenation in anesthetized horses placed in a 5-degree reverse Trendelenburg position

Low arterial oxygen is a common complication in anesthetized horses and placing the animal in reverse Trendelenburg (RT) position may treat hypoxemia. The objective of this study was to assess the arterial partial pressure of oxygen (PaO2) in horses placed in a 5-degree RT compared to horizontal (H) position. Client-owned healthy horses (n = 60) undergoing elective surgeries were enrolled in a randomized controlled clinical study. Horses were sedated with butorphanol, an α2-adrenoceptor agonist, ± acepromazine and induced with ketamine combined with a benzodiazepine, propofol, or guaifenesin. Anesthesia was maintained with isoflurane in oxygen with mechanical ventilation. Each group (RT and H) included 30 horses, 10 in each recumbency (dorsal, right and left lateral). Arterial blood gas analyses (aBG) were performed following arterial catheter placement then hourly. Time first-to-last aBG, changes in PaO2, dynamic compliance (Cdyn), estimated pulmonary shunt fraction (F-shunt), and alveolar dead space to tidal volume ratio (VD/VT) were evaluated with a 2-way analysis of variance. Statistical significance was set at p < .05. Overall, PaO2 increased in all groups; however no significant difference was found between recumbencies (dorsal, right and left lateral) and RT versus H in changes over time for PaO2 (p = .064 and p = .070, respectively), Cdyn (p = .721 and p = .672, respectively), F-shunt (p = .055 and p = .054, respectively), or VD/VT (p = .616 and p = .064, respectively). In healthy anesthetized horses, 5-degree RT did not affect changes in PaO2 as compared to H position.

Dexmedetomidine attenuates sepsis-associated inflammation and encephalopathy via central α2A adrenoceptor

Sepsis-associated encephalopathy (SAE) is a significant clinical issue that is associated with increased mortality and cost of health care. Dexmedetomidine, an α2 adrenoceptor agonist that is used to provide sedation, has been shown to induce neuroprotection under various conditions. This study was designed to determine whether dexmedetomidine protects against SAE and whether α2 adrenoceptor plays a role in this protection. Six- to eight-week old CD-1 male mice were subjected to cecal ligation and puncture (CLP). They were treated with intraperitoneal injection of dexmedetomidine in the presence or absence of α2 adrenoceptor antagonists, atipamezole or yohimbine, or an α2A adrenoceptor antagonist, BRL-44408. Hippocampus and blood were harvested for measuring cytokines. Mice were subjected to Barnes maze and fear conditioning 14 days after CLP to evaluate their learning and memory. CLP significantly increased the proinflammatory cytokines including tumor necrosis factor α, interleukin (IL)-6 and IL-1β in the blood and hippocampus. CLP also increased the permeability of blood-brain barrier (BBB) and impaired learning and memory. These CLP detrimental effects were attenuated by dexmedetomidine. Intracerebroventricular application of atipamezole, yohimbine or BRL-44408 blocked the protection of dexmedetomidine on the brain but not on the systemic inflammation. Astrocytes but not microglia expressed α2A adrenoceptors. Microglial depletion did not abolish the protective effects of dexmedetomidine. These results suggest that dexmedetomidine reduces systemic inflammation, neuroinflammation, injury of BBB and cognitive dysfunction in septic mice. The protective effects of dexmedetomidine on the brain may be mediated by α2A adrenoceptors in the astrocytes.

Efficacy of caudal vs intravenous administration of α2 adrenoceptor agonists to prolong analgesia in pediatric caudal block: A systematic review and meta-analysis.

α2 adrenoceptor agonists have been proposed as adjuncts to prolong analgesia in pediatric caudal block. The aim of this meta-analysis was to compare the analgesic efficacy of caudal vs intravenous α2 adrenoceptor agonists during pediatric caudal block. A systematic search, data extraction, bias risk assessment, and pooled data analysis were performed following the PRISMA guidelines. All randomized controlled trials comparing caudal with intravenous α2 adrenoceptor agonists in pediatric caudal block were included. Relative risk and weighted mean differences (the corresponding 95% confidence intervals) were calculated for dichotomous and continuous data, respectively. Trial sequential analyses were performed to evaluate the credibility of the meta-analysis. A total of 244 patients in five trials were identified. Compared with the intravenous group (9.56±4.23hours), the time to the first rescue analgesia was prolonged in the caudal α2 adrenoceptor agonists group (12.72±5.99hours) by a weighted mean difference of 2.98hours [95% confidence interval: 0.59-5.36hours; P=.01]. The number of children requiring rescue analgesia in the caudal group (64, 66.67%) was lower than that in the intravenous group (80, 81.63%) [relative risk=0.82; 95% confidence interval: 0.69-0.97; P=.02]. These findings were also verified by trial sequential analysis. There were no significant differences in the side effects. Caudal α2 adrenoceptor agonists as adjuncts to local anesthetic during pediatric caudal block are more effective than intravenous injection. However, the results were affected by small sample size and significant heterogeneity.

Upregulation of μ-Opioid Receptor in the Rat Spinal Cord Contributes to the α2-Adrenoceptor Agonist Dexmedetomidine-Induced Attenuation of Chronic Morphine Tolerance in Cancer Pain.

BackgroundSustained morphine treatment for cancer pain has been limited due to analgesic tolerance. Opioid receptor internalization and desensitization mediated by downregulation of mu-opioid receptor (MOR) expression have been confirmed as one of the mechanisms of chronic morphine tolerance. In addition to the opiate system, the α2-adrenergic system is involved in the development of morphine tolerance. Several studies reported that co-administration of α2-adrenoceptor agonist dexmedetomidine inhibits morphine tolerance in normal or neuropathic pain animals. However, the effect of dexmedetomidine on morphine tolerance has not been studied in cancer pain. Therefore, we investigated the effect of intrathecal injection of dexmedetomidine on the development of morphine tolerance in cancer pain and on the expression of MOR in the spinal cord of morphine-tolerant cancer pain rats.MethodsThe model was established using a rat’s right hind paw injection of Walker 256 cancer cells. Subcutaneous morphine (10mg/kg) was administrated twice daily for 7 days; meanwhile, the rats received intrathecal α2-adrenoceptor agonist dexmedetomidine (10μ/kg) or antagonist MK-467 (0.25mg/kg) in test groups. Rats receiving drug vehicle served as the control group. Antinociception was detected by von Frey filaments and hot-plate tests. The expression of MOR in the spinal cord was examined through real-time reverse transcription polymerase chain reaction and Western blotting. The data were analyzed via analysis of variance followed by Student t-test with Bonferroni correction.ResultsSeven-day chronic morphine administration elicited notable analgesic tolerance in the rats with cancer pain. Co-administration of α2-adrenoceptor agonist dexmedetomidine enhanced morphine analgesia and attenuated morphine tolerance, which could be blocked by α2-adrenoceptor antagonist MK-467. Furthermore, pre-treatment of dexmedetomidine significantly upregulated MOR protein expression without a notable change in MOR mRNA expression in the spinal cord.ConclusionOur findings suggest that intrathecal injection of dexmedetomidine enhanced morphine analgesia and attenuated morphine tolerance in cancer pain, potentially by upregulating MOR expression in the spinal cord. The α2-adrenoceptor agonist may provide a more versatile analgesia option for morphine treatment for cancer pain.

Dexmedetomidine suppresses bupivacaine-induced parthanatos in human SH-SY5Y cells via the miR-7-5p/PARP1 axis-mediated ROS

This study aims to explore the regulatory mechanisms of dexmedetomidine in parthanatos. MTT assay was applied to reveal cell viability; JC-1 staining assay was utilized to reveal mitochondrial membrane potential. Reactive oxygen species (ROS) probe, DCFH-DA, was used to detect intracellular ROS production. Luciferase activity assay was applied to measure the binding between miR-7-5p and PARP1. We first identified that bupivacaine inhibited the viability and induced the parthanatos of human neuroblastoma SH-SY5Y cells. In addition, dexmedetomidine, a potent α2-adrenoceptor agonist, reversed the regulatory effect of bupivacaine on parthanatos of SH-SY5Y. More importantly, dexmedetomidine counteracted bupivacaine-induced changes of mitochondrial membrane potential and ROS production in SH-SY5Y cells. Hyper-activation of PARP1 plays a vital role in parthanatos. Further exploration of our study identified that bupivacaine triggered overexpression of PARP1 in SH-SY5Y cells. Bioinformatics analysis revealed that miR-7-5p targeted the 3' untranslated region (3' UTR) of PARP1 to inhibit PARP1 expression. In addition, dexmedetomidine recovered the suppressive effects of bupivacaine on miR-7-5p expression. Dexmedetomidine suppressed bupivacaine-induced parthanatos in SH-SY5Y cells via the miR-7-5p/PARP1 axis, which may shed a new insight into parthanatos-dependent neuronal injury.

The indirect γ-aminobutyric acid (GABA) receptor agonist gabaculine-induced loss of the righting reflex may inhibit the descending analgesic pathway

In the spinal cord, γ-aminobutyric acid (GABA) interneurons play an essential role in antinociception. However, not all actions of GABA favor antinociception at the supraspinal level. We previously reported that gabaculine, which increases endogenous GABA in the synaptic clefts, induces loss of the righting reflex (LORR) that is one indicator of hypnosis, but not immobility in response to noxious stimulus. A slow pain is transmitted to the spinal cord via C fibers and evokes substance P (SP) release from their terminals. However, the antinociceptive effects of gabaculine are still unknown. Our study examined whether the analgesic effects of the opioid morphine or the α2-adrenoceptor agonist dexmedetomidine, whose actions are mediated through facilitation of the descending analgesic pathway, are affected by gabaculine-induced LORR. We also explored the effects of GABA receptor agonists on SP release from cultured dorsal root ganglion (DRG) neurons. All drugs were administered systemically to mice. To assess antinociception, loss of nociceptive response (analgesia) and immobility were evaluated. DRG cells were dissected from rats. Gabaculine produced no analgesia. Either morphine or dexmedetomidine in combination with gabaculine induced immobility; however, the doses of each drug required to induce immobility were much higher than those required to induce analgesia. Capsaicin significantly increased SP release from DRG cells, but a high concentration (1 mM) of the GABA receptor agonist muscimol, propofol, gaboxadol, or baclofen did not inhibit the capsaicin-induced SP release, suggesting that their antinociceptive effects were not through this mechanism. Thus, the gabaculine-induced LORR may inhibit the descending analgesic pathway.

Both α1B- and α1A-adrenoceptor subtypes are involved in contractions of rat spleen.

The spleen is a reservoir for circulating blood cells, and can contract to expel them. We have investigated the adrenoceptors involved in isometric contractions of rat spleen produced by noradrenaline (NA) and the α1-adrenoceptor agonist phenylephrine (Phe). Contractions to NA were antagonized by both the α1-adrenoceptor antagonist prazosin (10-8M) and the α2-adrenoceptor antagonist yohimbine (10-6M), and the combination produced further shifts in NA potency. Contractions to Phe were antagonized by prazosin (10-8M) which caused a marked parallel shift in the concentration-response curve. High non-selective concentrations of the α1D-adrenoceptor antagonist BMY7378 (10-6M), the α1A-adrenoceptor antagonist RS100329 ((3×10-8M), and the putative α1B-adrenoceptor antagonist cyclazosin (10-8M) also produced parallel shifts in the Phe concentration-response curve. BMY7378 at the selective concentration of 3×10-8M had no effect on responses to Phe, but RS100329 in the selective concentration of 3×10-9M produced a marked shift in the effects of high concentrations of Phe. Hence, antagonists in concentrations that block both α1A- and α1B-adrenoceptors produce approximately parallel shifts in Phe potency. Contractions of rat spleen to adrenergic agonists involve α2- and α1B-adrenoceptors, with a lesser role for α1A-adrenoceptors. This confirms the suggestion that smooth muscle contractions commonly involve multiple subtypes.

Endothelial Nitric Oxide Suppresses Action-Potential-Like Transient Spikes and Vasospasm in Small Resistance Arteries.

Endothelial dysfunction in small arteries is a ubiquitous, early feature of cardiovascular disease, including hypertension. Dysfunction reflects reduced bioavailability of endothelium-derived nitric oxide (NO) and depressed endothelium-dependent hyperpolarization that enhances vasoreactivity. We measured smooth muscle membrane potential and tension, smooth muscle calcium, and used real-time quantitative polymerase chain reaction in small arteries and isolated tubes of endothelium to investigate how dysfunction enhances vasoreactivity. Rat nonmyogenic mesenteric resistance arteries developed vasomotion to micromolar phenylephrine (α1-adrenoceptor agonist); symmetrical vasoconstrictor oscillations mediated by L-type voltage-gated Ca2+ channels (VGCCs). Inhibiting NO synthesis abolished vasomotion so nanomolar phenylephrine now stimulated rapid, transient depolarizing spikes in the smooth muscle associated with chaotic vasomotion/vasospasm. Endothelium-dependent hyperpolarization block also enabled phenylephrine-vasospasm but without spikes or chaotic vasomotion. Depolarizing spikes were Ca2+-based and abolished by either T-type or L-type VGCCs blockers with depressed vasoconstriction. Removing NO also enabled transient spikes/vasoconstriction to Bay K-8644 (L-type VGCC activator). However, these were abolished by the L-type VGCC blocker nifedipine but not T-type VGCC block. Phenylephrine also initiated T-type VGCC-transient spikes and enhanced vasoconstriction after NO loss in nonmyogenic arteries from spontaneously hypertensive rats. In contrast to mesenteric arteries, myogenic coronary arteries displayed transient spikes and further vasoconstriction spontaneously on loss of NO. T-type VGCC block abolished these spikes and additional vasoconstriction but not myogenic tone. Therefore, in myogenic and nonmyogenic small arteries, reduced NO bioavailability engages T-type VGCCs, triggering transient depolarizing spikes in normally quiescent vascular smooth muscle to cause vasospasm. T-type block may offer a means to suppress vasospasm without inhibiting myogenic tone mediated by L-type VGCCs.

Pharmacological Characterization of a Novel Mouse Model of Cholestatic Pruritus.

Patients with cholestatic liver diseases, such as primary biliary cirrhosis, usually suffer from pruritus. However, the pathogenesis of cholestatic pruritus is unclear, and there is no current effective treatment for it. In order to find a treatment for the condition, an appropriate mouse model should be developed. Therefore, here, we established a surgically-induced mouse model of cholestatic pruritus. The bile duct was ligated in order to block bile secretion from the anterior, right, and left lobes, with the exception of the caudate lobe. Serum levels of total bile acid increased after bile duct ligation (BDL). The spontaneous hind paw scratching was also increased in BDL mice. Spontaneous scratching was reduced in BDL mice by naloxone (µ-opioid receptor antagonist), U-50,488H (κ-opioid receptor agonist), and clonidine (α2-adrenoceptor agonist). Azelastine (H1 receptor antagonist with membrane-stabilizing activity) slightly reduced scratching. However, terfenadine (H1 receptor antagonist), methysergide (serotonin (5-HT)2 receptor antagonist), ondansetron (5-HT3 receptor antagonist), proteinase-activated receptor 2-neutralizing antibody, fluvoxamine (selective serotonin reuptake inhibitor), milnacipran (serotonin-noradrenalin reuptake inhibitor), and cyproheptadine (H1 and 5-HT2 receptor antagonist) did not affect scratching. These results suggested that partial obstruction of bile secretion in mice induced anti-histamine-resistant itching and that central opioid system is involved in cholestatic itching.

Dysfunctional bladder neurophysiology in urofacial syndrome Hpse2 mutant mice.

Urofacial syndrome (UFS) is an autosomal recessive disease characterized by detrusor contraction against an incompletely dilated outflow tract. This dyssynergia causes dribbling incontinence and incomplete voiding. Around half of individuals with UFS have biallelic mutations of HPSE2 that encodes heparanase 2, a protein found in pelvic ganglia and bladder nerves. Homozygous Hpse2 mutant mice have abnormal patterns of nerves in the bladder body and outflow tract, and also have dysfunctional urinary voiding. We hypothesized that bladder neurophysiology is abnormal Hpse2 mutant mice. Myography was used to study bladder bodies and outflow tracts isolated from juvenile mice. Myogenic function was analyzed after chemical stimulation or blockade of key receptors. Neurogenic function was assessed by electrical field stimulation (EFS). Muscarinic receptor expression was semi-quantified by Western blot analysis. Nitrergic nerve-mediated relaxation of precontracted mutant outflow tracts was significantly decreased vs littermate controls. The contractile ability of mutant outflow tracts was normal as assessed by KCl and the α1-adrenoceptor agonist phenylephrine. EFS of mutant bladder bodies induced significantly weaker contractions than controls. Conversely, the muscarinic agonist carbachol induced significantly stronger contractions of bladder body than controls. The Hpse2 model of UFS features aberrant bladder neuromuscular physiology. Further work is required to determine whether similar aberrations occur in patients with UFS.

Chronic diabetes and hypertension impair the in vivo functional response to phenylephrine independent of α1-adrenoceptor expression

Diabetes and hypertension can coexist and exacerbate each other. In the early stages of diabetes, there is a decreased vascular response of the sympathetic nervous system (SNS), probably due to lower expression of α1-adrenoceptors; however, it is unclear how diabetes in advanced stages changes the functionality of the SNS, especially the expression of α1-adrenoceptors. Thus, the aim of this work was to analyse the functional response to phenylephrine, a selective α1-adrenoceptor agonist, and the expression of α1-adrenoceptors in chronic diabetes and hypertension. Male SHR and WKY rats aged 10–12 weeks were administered either streptozotocin (60 mg/kg i.p.) or a vehicle (control group). Eight weeks after administration, dose-response curves to phenylephrine were generated and the gene and protein expression of α1-adrenoceptor subtypes (α1A-, α1B- and α1D-adrenoceptors) in the heart and aorta were measured. The response to phenylephrine was diminished in hypertensive rats and in normotensive diabetic rats. The coexistence of both diabetes and hypertension produced an even smaller response to phenylephrine than that observed for each condition separately. In the heart and aorta of diabetic rats, no changes in α1A-, α1B- or α1D-adrenoceptor mRNA expression were observed; however, protein expression was increased, mainly for the α1D-adrenoceptor. Hypertension increased mRNA and protein expression of α1-adrenoceptors in a tissue-dependent manner. The coexistence of both diabetes and hypertension produced differences in the regulation of mRNA and protein expression (increase or decrease) in both the heart and aorta. In conclusion, diabetes, hypertension and the coexistence of both pathologies impairs the in vivo response to phenylephrine. However, the differences in α1A-, α1B- and α1D-adrenoceptor expression cannot explain the reduced response to the agonist. This should be further explored in future experiments.

Dexmedetomidine exerts neuroprotective effects during high glucose-induced neural injury by inhibiting miR-125b.

Diabetic neuropathy (DNP) is the most common complication of diabetes mellitus affecting approximately 50% of diabetes patients. Studying the effect of potential drugs with antioxidant properties and minimal toxicities on neural cells may lead to the development of new and safe pharmacotherapy. Dexmedetomidine (DEX), a highly selective α2-adrenoceptor agonist, is a clinically used sedative also known to have neural protection effect. In the present study, we aimed to investigate the protective role of DEX in high glucose (HG)-induced neural injury and its potential miRNA-related mechanisms. Our results showed that DEX exerted neuroprotective effects during high glucose-induced damage to PC12 cells in a dose-dependent manner. DEX restored cell viability and repressed LDH, Caspase-3 activity, ROS production, and cell apoptosis in HG-treated PC12 cells. MiR-125b-5p was significantly up-regulated in PC12 cells upon HG treatment and it was demonstrated as an target for DEX. The neuroprotective effects of DEX on HG-induced cellular injury were reversed through miR-125b-5p overexpression, and vitamin D receptor (VDR) is a direct targeted of the miR-125b-5p. Together, our results indicate that DEX displays neuroprotective effects on PC-12 cells under high glucose through regulating miR-125b-5p/VDR axis. Our findings might raise the possibility of potential therapeutic application of DEX for managing diabetic neuropathy neural injuries.

Effects of intramuscular vatinoxan (MK-467), co-administered with medetomidine and butorphanol, on cardiopulmonary and anaesthetic effects of intravenous ketamine in dogs

ObjectiveTo investigate the impact of intramuscular (IM) co-administration of the peripheral α2-adrenoceptor agonist vatinoxan (MK-467) with medetomidine and butorphanol prior to intravenous (IV) ketamine on the cardiopulmonary and anaesthetic effects in dogs, followed by atipamezole reversal. Study designRandomized, masked crossover study. AnimalsA total of eight purpose-bred Beagle dogs aged 3 years. MethodsEach dog was instrumented and administered two treatments 2 weeks apart: medetomidine (20 μg kg–1) and butorphanol (100 μg kg–1) premedication with vatinoxan (500 μg kg–1; treatment MVB) or without vatinoxan (treatment MB) IM 20 minutes before IV ketamine (4 mg kg–1). Atipamezole (100 μg kg–1) was administered IM 60 minutes after ketamine. Heart rate (HR), mean arterial (MAP) and central venous (CVP) pressures and cardiac output (CO) were measured; cardiac (CI) and systemic vascular resistance (SVRI) indices were calculated before and 10 minutes after MVB or MB, and 10, 25, 40, 55, 70 and 100 minutes after ketamine. Data were analysed with repeated measures analysis of covariance models. A p-value <0.05 was considered statistically significant. Sedation, induction, intubation and recovery scores were assessed. ResultsAt most time points, HR and CI were significantly higher, and SVRI and CVP significantly lower with MVB than with MB. With both treatments, SVRI and MAP decreased after ketamine, whereas HR and CI increased. MAP was significantly lower with MVB than with MB; mild hypotension (57–59 mmHg) was recorded in two dogs with MVB prior to atipamezole administration. Sedation, induction, intubation and recovery scores were not different between treatments, but intolerance to the endotracheal tube was observed earlier with MVB. Conclusions and clinical relevanceHaemodynamic performance was improved by vatinoxan co-administration with medetomidine–butorphanol, before and after ketamine administration. However, vatinoxan was associated with mild hypotension after ketamine with the dose used in this study. Vatinoxan shortened the duration of anaesthesia.

Evaluation of the potential toxicity of haloperidol, clozapine and a new putative antipsychotic molecule, PT-31, in an alternative toxicity model, C. elegans

Schizophrenia is a disabling mental illness that affects approximately 1% of the world population. The treatment of this disorder is based on two generations of substances, typical antipsychotics, such as haloperidol, and atypical antipsychotics, such as clozapine, which can cause severe adverse effects. Therefore, the development of novel molecules that are safe and efficacious to treat the disease is crucial. PT-31 is a putative α2-adrenoceptor agonist effective against schizophrenia positive and cognitive symptoms in mice. C. elegans is an alternative model that has been successfully used to investigate the toxicity of a variety of substances. The present study aimed to evaluate the potential toxicity of the new molecule PT-31 and the antipsychotics haloperidol and clozapine in C. elegans. The evaluation was carried out based on toxicity endpoint tests, survival, developmental and behavioral assays. The antipsychotics haloperidol and clozapine decreased nematode survival by 30 and 40%, respectively, exposing the potential toxicity of these substances whereas PT-31 was safer based on this parameter. Similar results were obtained in the nematode developmental assay: haloperidol and clozapine significantly reduced nematode body length and area, whereas PT-31 preserved the normal development of the nematodes. The behavioral assessment was based on the frequency of body bends; none of the antipsychotics affected the locomotion rate of the nematodes, and PT-31 also did not compromise this parameter, demonstrating the safety of this new compound and reinforcing the recognized toxicity of antipsychotics.

State-dependent modulation of sympathetic firing by α1-adrenoceptors requires constitutive PKC activity in the neonatal rat spinal cord.

The central adrenergic and noradrenergic neurotransmitter systems diffusively affect the operation of the spinal neural network and dynamically gauge central sympathetic outflow. Using in vitro splanchnic nerve-thoracic spinal cord preparations as an experimental model, this study examined the intraspinal α1-adrenoceptor-meidated modulation of sympathetic firing behaviors. Several sympathetic single-fiber activities were simultaneously recorded. Application of phenylephrine (Phe, an α1-adrenoceptor agonist) increased, decreased or did not affect spontaneous firing. A log-log plot of the change ratios of the average firing rates (AFR) versus their basal AFR displays a linear data distribution. Thus, the heterogeneity in α1-adrenoceptor-mediated responses is well described by a power law function. Phe-induced power-law firing modulation (plFM) was sensitive to prazosin (Prz, an α1-adrenoceptor antagonist). Heparin (Hep, a competitive IP3 receptor blocker) and chelerythrine (Che, a protein kinase C inhibitor) also caused plFM. Phe-induced plFM persisted in the presence of Hep; however, it was occluded by Che pretreatment. Pair-wise analysis of single-fiber activities revealed synchronous sympathetic discharges. Application of Phe, Hep or Che suppressed synchronous discharges in fiber pairs with apparent correlated firing (ACF) and induced or potentiated synchronous discharges in those without or with minimal ACF. Thus, the basal activities of the sympathetic preganglionic neurons participate in determining the responses mediated by the activation of α1-adrenoceptors. This deterministic factor, which is intrinsic to spinal neural networks, helps the supraspinal adrenergic and noradrenergic systems differentially control their widely distributed neural targets.

Dexmedetomidine‑mediated regulation of miR‑17‑3p in H9C2 cells after hypoxia/reoxygenation injury

Patients with heart disease often suffer from ischemia, which can be treated by reperfusion. However, this treatment can lead to the development of ischemia/reperfusion (I/R) injury, an inflammatory condition that can cause further heart damage. Dexmedetomidine (Dex), an α2-adrenoceptor agonist, and the microRNA (miR)-17-3p, have both been suggested to alleviate I/R injury and cardiac tissue inflammation. The aim of the present study was to investigate whether Dex and miR-17-3p could act together to prevent I/R injury. H9C2 cells, a myoblast cell line used as a model of rat cardiomyocytes, were cultured in a hypoxic environment for 3 h, and then reoxygenated for 3 h. This hypoxia/reoxygenation (H/R) was used to model I/R. Cell Counting kit-8 was used to determine cell viability and an annexin V-FITC/propidium iodide apoptosis kit used to analyze cell apoptosis. A dual luciferase reporter assay was used to determine the interaction between miR-17-3p and toll-like receptor 4 (TLR4). Western blotting and reverse transcription-quantitative PCR were used to determine protein levels and mRNA expression of TLR4 and galectin-3. A concentration of 0.1-10 µmol/l Dex attenuated H/R injury, which was accompanied by increased miR-17-3p levels. Additionally, the inhibition of miR-17-3p exacerbated H/R injury and reduced the effect of Dex on H/R injury. H/R led to an increased galectin-3 level compared with that in control cells, and Dex or miR-17-3p inhibitor did not markedly affect the level of galectin-3, indicating that Dex alleviated the effects of I/R injury through other pathways. Inhibition of miR-17-3p in Dex-induced H9C2 cells during H/R increased the expression of inflammatory mediators including tumor necrosis factor-α, interleukin (IL)-6, IL-1β and phosphorylated NFκB subunit p65, while Dex reduced the H/R-induced expression of these inflammatory mediators. Inhibition of TLR4 also attenuated H/R injury. In summary, the findings of the present study indicated that Dex reduced H/R injury in H9C2 cell via the modulation of inflammatory signaling pathways, and these inflammatory factors could be regulated by miR-17-3p.