Neuroprotection by alpha 2-adrenergic agonists in cerebral ischemia

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

Neuroprotective actions of norepinephrine in neurological diseases

Precise control of norepinephrine (NE) levels and NE-receptor interaction is crucial for proper function of the brain. Much evidence for this view comes from experimental studies that indicate an important role for NE in the pathophysiology and treatment of various conditions, including cognitive dysfunction, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and sleep disorders. NE provides neuroprotection against several types of insults in multiple ways. It abrogates oxidative stress, attenuates neuroinflammatory responses in neurons and glial cells, reduces neuronal and glial cell activity, promotes autophagy, and ameliorates apoptotic responses to a variety of insults. It is beneficial for the treatment of neurodegenerative diseases because it improves the generation of neurotrophic factors, promotes neuronal survival, and plays an important role in the regulation of adult neurogenesis. This review aims to present the evidence supporting a principal role for NE in neuroprotection, and molecular mechanisms of neuroprotection.

Stress hyperglycemia exacerbates inflammatory brain injury after stroke

Post-stroke hyperglycemia occurs in 30% - 60% of ischemic stroke patients as part of the systemic stress response, but neither clinical evidence nor pre-clinical studies indicate whether post-stroke hyperglycemia affects stroke outcome. Here we investigated this issue using a mouse model of permanent ischemia. Mice were maintained either normoglycemic or hyperglycemic during the interval of 17 - 48 hours after ischemia onset. Post-stroke hyperglycemia was found to increase infarct volume, blood-brain barrier disruption, and hemorrhage formation, and to impair motor recovery. Post-stroke hyperglycemia also increased superoxide formation by peri-infarct microglia/macrophages. In contrast, post-stroke hyperglycemia did not increase superoxide formation or exacerbate motor impairment in p47 phox-/- mice, which cannot form an active superoxide-producing NADPH oxidase-2 complex. These results suggest that hyperglycemia occurring hours-to-days after ischemia can increase oxidative stress in peri-infarct tissues by fueling NADPH oxidase activity in reactive microglia/macrophages, and by this mechanism contribute to worsened functional outcome.

Autophagy and anti-inflammation ameliorate diabetic neuropathy with Rilmenidine

PURPOSE

To evaluate the neuroprotective effects of Rilmenidine on diabetic peripheral neuropathy (DPN) in a rat model of diabetes induced by streptozotocin (STZ).

METHODS

STZ (60 mg/kg) was administered to adult Sprague-Dawley rats to induce diabetes. On the 30th day after STZ administration, electromyography (EMG) and motor function tests confirmed the presence of DPN. Group 1: Control (n = 10), Group 2: DM + 0.1 mg/kg Rilmenidine (n = 10), and Group 3: DM + 0.2 mg/kg Rilmenidine (n = 10) were administered via oral lavage for four weeks. EMG, motor function test, biochemical analysis, and histological and immunohistochemical analysis of sciatic nerves were then performed.

RESULTS

The administration of Rilmenidine to diabetic rats substantially reduced sciatic nerve inflammation and fibrosis and prevented electrophysiological alterations. Immunohistochemistry of sciatic nerves from saline-treated rats revealed increased perineural thickness, HMGB-1, tumor necrosis factor-α, and a decrease in nerve growth factor (NGF), LC-3. In contrast, Rilmendine significantly inhibited inflammation markers and prevented the reduction in NGF expression. In addition, Rilmenidine significantly decreased malondialdehyde and increased diabetic rats' total antioxidative capacity.

CONCLUSIONS

The findings of this study suggest that Rilmenidine may have therapeutic effects on DNP by modulating antioxidant and autophagic pathways.

Prevention of alcohol withdrawal syndrome in the surgical ICU: an American Association for the Surgery of Trauma Critical Care Committee Clinical Consensus Document

Alcohol withdrawal syndrome is a common and challenging clinical entity present in trauma and surgical intensive care unit (ICU) patients. The screening tools, assessment strategies, and pharmacological methods for preventing alcohol withdrawal have significantly changed during the past 20 years. This Clinical Consensus Document created by the American Association for the Surgery of Trauma Critical Care Committee reviews the best practices for screening, monitoring, and prophylactic treatment of alcohol withdrawal in the surgical ICU.

Guanabenz mitigates the neuropathological alterations and cell death in Alzheimer's disease

Alzheimer's disease (AD) pathology is characterized by cognitive impairment, increased acetylcholinesterase (AChE) activity, and impaired neuronal communication. Clinically, AChE inhibitors are being used to treat AD patients; however, these remain unable to prevent the disease progression. Therefore, further development of new therapeutic molecules is required having broad spectrum effects on AD-related various neurodegenerative events. Since repurposing is a quick mode to search the therapeutic molecules; henceforth, this study was conducted to evaluate the anti-Alzheimer activity of drug guanabenz which is already in use for the management of high blood pressure in clinics. The study was performed employing both cellular and rat models of AD along with donepezil as reference drug. Guanabenz treatment in both the experimental models showed significant protection against AD-specific behavioral and pathological indicators like AChE activity, tau phosphorylation, amyloid precursor protein, and memory retention. In conjunction, guanabenz also attenuated the AD-related oxidative stress, impaired mitochondrial functionality (MMP, cytochrome-c translocation, ATP level, and mitochondrial complex I activity), endoplasmic reticulum stress (GRP78, GADD153, cleaved caspase-12), neuronal apoptosis (Bcl-2, Bax, cleaved caspase-3), and DNA fragmentation. In conclusion, findings suggested the panoptic protective effect of guanabenz on disease-related multiple degenerative markers and signaling. Furthermore, clinical trial may shed light and expedite the availability of new therapeutic anti-Alzheimer's molecule for the wellbeing of AD patients.

Autonomic control of cerebral blood flow: fundamental comparisons between peripheral and cerebrovascular circulations in humans

Understanding the contribution of the autonomic nervous system to cerebral blood flow (CBF) control is challenging, and interpretations are unclear. The identification of calcium channels and adrenoreceptors within cerebral vessels has led to common misconceptions that the function of these receptors and actions mirror those of the peripheral vasculature. This review outlines the fundamental differences and complex actions of cerebral autonomic activation compared with the peripheral circulation. Anatomical differences, including the closed nature of the cerebrovasculature, and differential adrenoreceptor subtypes, density, distribution and sensitivity, provide evidence that measures on peripheral sympathetic nerve activity cannot be extrapolated to the cerebrovasculature. Cerebral sympathetic nerve activity seems to act opposingly to the peripheral circulation, mediated at least in part by changes in intracranial pressure and cerebral blood volume. Additionally, heterogeneity in cerebral adrenoreceptor distribution highlights region-specific autonomic regulation of CBF. Compensatory chemo- and autoregulatory responses throughout the cerebral circulation, and interactions with parasympathetic nerve activity are unique features to the cerebral circulation. This crosstalk between sympathetic and parasympathetic reflexes acts to ensure adequate perfusion of CBF to rising and falling perfusion pressures, optimizing delivery of oxygen and nutrients to the brain, while attempting to maintain blood volume and intracranial pressure. Herein, we highlight the distinct similarities and differences between autonomic control of cerebral and peripheral blood flow, and the regional specificity of sympathetic and parasympathetic regulation within the cerebrovasculature. Future research directions are outlined with the goal to further our understanding of autonomic control of CBF in humans.

Comparative effects of dexmedetomidine and propofol on brain and lung damage in experimental acute ischemic stroke

Acute ischemic stroke is associated with pulmonary complications, and often dexmedetomidine and propofol are used to decrease cerebral metabolic rate. However, it is unknown the immunomodulatory actions of dexmedetomidine and propofol on brain and lungs during acute ischemic stroke. The effects of dexmedetomidine and propofol were compared on perilesional brain tissue and lung damage after acute ischemic stroke in rats. Further, the mean amount of both sedatives was directly evaluated on alveolar macrophages and lung endothelial cells primarily extracted 24-h after acute ischemic stroke. In twenty-five Wistar rats, ischemic stroke was induced and after 24-h treated with sodium thiopental (STROKE), dexmedetomidine and propofol. Dexmedetomidine, compared to STROKE, reduced diffuse alveolar damage score [median(interquartile range); 12(7.8–15.3) vs. 19.5(18–24), p = 0.007)], bronchoconstriction index [2.28(2.08–2.36) vs. 2.64(2.53–2.77), p = 0.006], and TNF-α expression (p = 0.0003), while propofol increased VCAM-1 expression compared to STROKE (p = 0.0004). In perilesional brain tissue, dexmedetomidine, compared to STROKE, decreased TNF-α (p = 0.010), while propofol increased VCAM-1 compared to STROKE (p = 0.024). In alveolar macrophages and endothelial cells, dexmedetomidine decreased IL-6 and IL-1β compared to STROKE (p = 0.002, and p = 0.040, respectively), and reduced IL-1β compared to propofol (p = 0.014). Dexmedetomidine, but not propofol, induced brain and lung protection in experimental acute ischemic stroke.

Neuroprotective Agents for Neonates with Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) remains a significant source of long-term neurodevelopmental impairment despite overall improvements in survival without disability in neonates who undergo therapeutic hypothermia. Each phase in the evolution of hypoxic-ischemic injury presents potential pharmacologic targets for neuroprotective agents. Melatonin is a promising emerging therapy for early phases of ischemic injury, but utility is currently limited by the lack of pharmaceutical-grade products. Magnesium has been extensively studied for its neuroprotective effects in the preterm population. Studies in neonates with HIE have produced mixed outcomes. Erythropoietin use in HIE with or without therapeutic hypothermia appears to be safe and may provide additional benefit. Dexmedetomidine, N-acetylcysteine, xenon, and topiramate all have promising animal data, but need additional human trials to elucidate what role they may play in HIE. Frequent review of existing literature is required to ensure provision of evidence-based pharmacologic agents for neuroprotection following HIE.

Central sympathetic nerve activation in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a life-threatening condition, and although its two main complications-cerebral vasospasm (CVS)/delayed cerebral ischemia (DCI) and early brain injury (EBI)-have been widely studied, prognosis has not improved over time. The sympathetic nerve (SN) system is important for the regulation of cardiovascular function and is closely associated with cerebral vessels and the regulation of cerebral blood flow and cerebrovascular function; thus, excessive SN activation leads to a rapid breakdown of homeostasis in the brain. In the hyperacute phase, patients with SAH can experience possibly lethal conditions that are thought to be associated with SN activation (catecholamine surge)-related arrhythmia, neurogenic pulmonary edema, and irreversible injury to the hypothalamus and brainstem. Although the role of the SN system in SAH has long been investigated and considerable evidence has been collected, the exact pathophysiology remains undetermined, mainly because the relationships between the SN system and SAH are complicated, and many SN-modulating factors are involved. Thus, research concerning these relationships needs to explore novel findings that correlate with the relevant concepts based on past reliable evidence. Here, we explore the role of the central SN (CSN) system in SAH pathophysiology and provide a comprehensive review of the functional CSN network; brain injury in hyperacute phase involving the CSN system; pathophysiological overlap between the CSN system and the two major SAH complications, CVS/DCI and EBI; CSN-modulating factors; and SAH-related extracerebral organ injury. Further studies are warranted to determine the specific roles of the CSN system in the brain injuries associated with SAH.

The Current Role of Dexmedetomidine as Neuroprotective Agent: An Updated Review

Dexmedetomidine, selective α2-adrenergic agonist dexmedetomidine, has been widely used clinically for sedation and anesthesia. The role of dexmedetomidine has been an interesting topic of neonatological and anesthetic research since a series of advantages of dexmedetomidine, such as enhancing recovery from surgery, reducing opioid prescription, decreasing sympathetic tone, inhibiting inflammatory reactions, and protecting organs, were reported. Particularly, an increasing number of animal studies have demonstrated that dexmedetomidine ameliorates the neurological outcomes associated with various brain and spinal cord injuries. In addition, a growing number of clinical trials have reported the efficacy of dexmedetomidine for decreasing the rates of postoperative neurological dysfunction, such as delirium and stroke, which strongly highlights the possibility of dexmedetomidine functioning as a neuroprotective agent for future clinical use. Mechanism studies have linked dexmedetomidine’s neuroprotective properties with its modulation of neuroinflammation, apoptosis, oxidative stress, and synaptic plasticity via the α2-adrenergic receptor, dependently or independently. By reviewing recent advances and preclinical and clinical evidence on the neuroprotective effects of dexmedetomidine, we hope to provide a complete understanding of the above mechanism and provide insights into the potential efficacy of this agent in clinical use for patients.

The role of α adrenergic receptors in mediating the inhibitory effect of electrical brain stimulation on epileptiform activity in rat hippocampal slices

The Inhibitory effect of electrical low-frequency stimulation (LFS) on neuronal excitability and seizure occurrence has been indicated in experimental models, but the precise mechanism has not established. This investigation was intended to figure out the role of α₁ and α₂ adrenergic receptors in LFS' inhibitory effect on neuronal excitability. Epileptiform activity induced in an in vitro rat hippocampal slice preparation by high K⁺ ACSF and LFS (900 square wave pulses at 1 Hz) was administered at the beginning of epileptiform activity to the Schaffer collaterals. In CA1 pyramidal neurons, the electrophysiological properties were measured at the baseline, before high K⁺ ACSF washout, and at 15 min after high K⁺ ACSF washout using whole-cell, patch-clamp recording. Results indicated that after high K⁺ ACSF washout, prazosine (10 µM; α₁ adrenergic receptor antagonist) and yohimbine (5 µM; α₂ adrenergic receptor antagonist) suppressed the LFS' effect of reducing rheobase current and utilization time following depolarizing ramp current, the latency to the first spike following a depolarizing current and latency to the first rebound action potential following hyperpolarizing current pulses. Thus, it may be proposed that LFS' inhibitory action on the neuronal hyperexcitability, in some way, is mediated by α₁ and α₂ adrenergic receptors.

Dexmedetomidine inhibits the PSD95-NMDA receptor interaction to promote functional recovery following traumatic brain injury

The present study examined the effects of dexmedetomidine (Dex) on cognitive and motor recovery in mice following traumatic brain injury (TBI). TBI induces synaptic damage, which leads to motor dysfunction and cognitive decline. Although Dex is known to induce neuroprotection, its role following TBI remains unknown. In the present study, male C57BL/6 mice (8 weeks old; n=72) were subjected to cortical impact injury to generate a TBI mice model. Mice were divided into four groups: TBI, sham, TBI + vehicle, and TBI + Dex. Mice in the TBI + vehicle and TBI + Dex groups received intraperitoneal injections of saline (n=18) and 100 µg/kg Dex (n=18), respectively, at 1 and 12 h following surgery. At 24 h post-injury, 10 animals from each group were sacrificed, and brain tissue was isolated for Fluoro-Jade B staining and RNA and protein extraction. At 72 h post-TBI, motor function was evaluated. Furthermore, cognitive impairment was assessed between day 14 and 19 using the Morris water maze. The results demonstrated that the mRNA and protein expression of post-synaptic density 95 (PSD95) was reduced post-TBI. In addition, neuronal degeneration was evaluated using FJB staining, where PSD95 formed a complex with the N-methyl-D-aspartic acid (NMDA) receptor subunit (NR2B) and neuronal nitric oxide synthase (nNOS) inducing neuronal death post-TBI. Treatment with Dex efficiently decreased the PSD95-NR2B-nNOS interaction, which reduced the TBI-induced neuronal death. Furthermore, Dex treatment contributed to the enhanced cognitive and motor recovery following TBI. The results from the present study reported a potential mechanistic action of Dex treatment post-TBI, which may be associated with the inhibition of PSD95-NMDA interaction.

Mechanisms of ammonium-induced neurotoxicity. Neuroprotective effect of alpha-2 adrenergic agonists

Here we report the effects of ammonium on the main biophysical features of neurons and astrocytes during the first minutes of exposure. We found that ammonium causes the depolarization of neurons, which leads to the generation of high-frequency action potentials (APs). The initial alkalization and subsequent acidification of the intracellular medium in neurons occur along with the generation of calcium oscillations. Moreover, although the kinetics of calcium response of neurons and astrocytes is different, the dynamics of changes in the intracellular pH (pH_i) is similar. The rate of superoxide production and mitochondrial membrane potential do not change in most neurons and astrocytes during ammonium exposure. At the same time, we observed an increased superoxide production and a decrease in the mitochondrial potential in some neurons in response to ammonium application. However, in both cases, the amplitude of the calcium response in these neurons is significantly higher compared to other neurons. Application of UK 14,304, an agonist of alpha-2 adrenergic receptors (A-2ARs), decreased the frequency of APs upon ammonium-induced high-frequency spike activity. Moreover, we also observed periods of hyperpolarization occurred in individual neurons. We suppose that this hyperpolarization contributes to the suppression of activity and can be mediated by astrocytic GABA release, which is stimulated upon activation of A-2ARs. Thus, our findings reveal a new possible mechanism of the protective action of alpha-2 adrenergic agonists against ammonium-induced hyperexcitation and demonstrate the correlation between intracellular calcium concentration, mitochondrial membrane potential, pH_i, the intensity of superoxide production in hippocampal cells under acute hyperammonemia.

Synthesis and biological evaluation of imidazoline derivatives as potential CNS and CVS agents

A series of substituted imidazoline derivatives were synthesized and characterized. Compounds were tested in-vivo for their antihypertensive, analgesic, antiaggressive, depressant, antidepressant, and ALD₅₀ activities. The compounds 3a, 3c, 4c, 5a, and 6c showed cardiovascular as well as central nervous system activities and are potential candidate as drug among all fifteen compounds tested. All these compounds have shown better activity for antihypertensive, analgesic, antiaggressive, and depressant-antidepressant, properties than reference compounds clonidine, morphine, diazepam, and imipramine respectively. Most of the compounds have shown ALD₅₀ > 500 mg/kg with maximum in 4a and 5a (>1000 mg/kg).

Antioxidant effects of dexmedetomidine against hydrogen peroxide-induced DNA damage in vitro by alkaline Comet assay

Background/aim

Dexmedetomidine (DEX) is an alpha-2 adrenergic agonist that is commonly used as a sedative and anesthetic. The protective effects of DEX against oxidative damage under both in vitro and in vivo conditions have been demonstrated. It was aimed to evaluate and compare the protective effects of DEX and vitamin C (Vit C) on DNA against H₂O₂-induced DNA damage in human lymphocyte cell cultures in vitro by alkaline Comet assay.

Materials and methods

Lymphocyte cell cultures were divided into 5 groups, as the negative control, solvent control, positive control, hydrogen peroxide (H₂O₂; 150 μM) + DEX (1 μM; 2.5 μM; 5 μM), and H₂O₂ (150 μM) + Vit C (1 μM; 2.5 μM; 5 μM), and incubated at 37 °C for 1 h. Cell viability was measured using the Trypan blue test. DNA damage was measured using the Alkali Comet Technique and the % percent tail intensity was evaluated. Statistical analysis was performed using 1-way ANOVA and the Tukey multiple comparison test.

Results

It was observed that H₂O₂ significantly induced DNA damage in the lymphocytes and this damage was decreased significantly with Vit C and DEX. It was observed that Vit C at doses of 1 μM and 2.5 μM had a significantly stronger antioxidant effect, but there was no significant difference between the antioxidant effects of Vit C and DEX with a dose of 5 μM. The dose of 5 μM DEX was found to be the most effective in reducing oxidative DNA damage.

Conclusion

There is limited data on the protective effects of DEX against oxidative DNA damage. The primary effect might be cytoprotection. The results herein showed that DEX was protective against H₂O₂-induced in vitro oxidative DNA damage in lymphocyte cell cultures in a dose-dependent manner. DEX might have a potential therapeutic value in the prevention of oxidative DNA damage in patients.

A nurse-driven analgesia and sedation protocol reduces length of PICU stay and cumulative dose of benzodiazepines after corrective surgery for tetralogy of Fallot

PURPOSE

Analgesia and sedation protocols are reported to reduce the requirement of sedative and analgesic agents, duration of mechanical ventilation, and length of pediatric intensive care unit (PICU) stay. However, these studies often were conducted based on inhomogeneous cohorts. The aim of this study was the evaluation of a nurse-driven analgesia and sedation protocol in a homogenous population of infants following corrective surgery for tetralogy of Fallot (TOF).

DESIGN AND METHODS

This retrospective analysis was conducted in a cardiac PICU of a tertiary referral center. Two cohorts of patients who underwent corrective surgery for TOF below the age of 7 months, were retrospectively evaluated before and after implementation of a nurse-driven analgesia and sedation protocol. We compared peak and cumulative doses of midazolam, morphine, and clonidine, length of PICU stay and time on mechanical ventilation.

RESULTS

A total of 33 patients were included in the preimplementation period and 32 during the postimplementation period. Implementation of the nurse-driven analgesia and sedation protocol had no effect on time on mechanical ventilation (72 hr [24-141] vs. 49 hr [24-98]), but significantly on length of PICU stay (7 days [5-14] vs. 5 days [4-7]). Cumulative doses of midazolam (7.37 mg/kg [4.70-17.65] vs. 5.0 mg/kg [2.70-9.12]) as well as peak doses of midazolam (0.22 mg·kg^-1 ·hr^-1 [0.20-0.33] vs. 0.15 mg·kg^-1 ·hr^-1 [0.13-0.20]) and morphine (50.0 µg·kg^-1 ·hr^-1 [39.7-79.9] vs. 42.5 µg·kg^-1 ·hr^-1 [29.7-51.8]) were significantly reduced. The postimplemantation group showed no increase in postoperative complications and adverse events.

PRACTICE IMPLICATIONS

The implementation of a nurse-driven analgesia and sedation protocol is safe in infants following corrective surgery for TOF. It reduces significantly the length of PICU stay, cumulative and peak doses of midazolam and peak doses of morphine.

Evaluation of an updated sedation protocol to reduce benzodiazepines in a pediatric intensive care unit

Aim: Midazolam like other benzodiazepines is supposed to be neurotoxic in small children and to represent a risk factor for the development of delirium. The aim of this study was to evaluate whether a modified analgesia and sedation protocol is feasible and effective to reduce the requirement of midazolam in neonates and young infants after cardiac surgery.Methods: Patients aged 6 months or younger who underwent surgery for congenital heart disease with cardiopulmonary bypass were enrolled and divided into a pre-modification group (January-December 2016) and after adjusting our sedation protocol into a post-modification group (January-December 2018). We assessed the doses of midazolam, morphine and clonidine as well as sedation scores according to our nurse-driven sedation protocol every 8 h until 120 h after cardiac surgery. During weaning from analgesia and sedation, children were monitored regarding withdrawal symptoms and pediatric delirium.Results: Sixty-five patients were included (33 patients in the pre-modification group, 32 patients in the post-modification group). The number of patients receiving midazolam and the cumulative dose of midazolam could be successfully reduced. The sedation scores were still within the desired target range for adequate sedation without any negative side effects.Conclusions: It is feasible and safe to reduce the use of midazolam in infants after cardiac surgery maintaining sedation goals based on a modified nurse-driven analgesia and sedation protocol.

Effects of precondition α2-adrenoceptor agents on memory- and anxiety-related processes in the transient cerebral ischemic rats

Neurological evidence for the neuroprotective function of α₂-adrenoceptors in the cerebral ischemia is inconsistent. It is not examined how pretreatment with a single dose of α₂-adrenoceptor agents can affect motor function and anxiety- and memory-related responses in the cerebral ischemic animals. The transient forebrain ischemia model was provided, using a bilateral common carotid arterial occlusion (two-vessel occlusion, 2VO) in male Wistar rats. The 2VO rats impaired motor functions in the Rota-rod and wire grip tests and also decreased the step-through latency and the percentage of time spent on the open arms (%OAT), the percentage of entries into the open arms (%OAE) as well as locomotion in the elevated plus maze (EPM), indicating a memory deficit and anxiety-like behavior. Intraperitoneal single administration of yohimbine (0, 0.001, 0.01, and 0.1 mg/kg) before the 2VO did not alter these parameters while the higher and middle doses of clonidine (0.01 and 0.1 mg/kg) prevented the memory deficit and hypo-locomotion and its middle dose abrogated Rota-rod dysfunction and anxiety-like response. Meanwhile, both drugs did not influence on the measured behaviors in the sham groups by themselves. Moreover, yohimbine (0.001 mg/kg) abolished the beneficial effects of clonidine (0.01 and 0.1 mg/kg) on motor function in the Rota-rod and memory retention and also at its middle dose on the %OAT and locomotion in the 2VO rats. Our findings show a neuroprotective role for clonidine in motor function and memory- and anxiety-related behaviors of 2VO rats and the importance of α₂-adrenoceptors in these processes.

Dexmedetomidine modulates neuroinflammation and improves outcome via alpha2-adrenergic receptor signaling after rat spinal cord injury

BACKGROUND

Spinal cord injury induces inflammatory responses that include the release of cytokines and the recruitment and activation of macrophages and microglia. Neuroinflammation at the lesion site contributes to secondary tissue injury and permanent locomotor dysfunction. Dexmedetomidine (DEX), a highly selective α2-adrenergic receptor agonist, is anti-inflammatory and neuroprotective in both preclinical and clinical trials. We investigated the effect of DEX on the microglial response, and histological and neurological outcomes in a rat model of cervical spinal cord injury.

METHODS

Anaesthetised rats underwent unilateral (right) C5 spinal cord contusion (75 kdyne) using an impactor device. The locomotor function, injury size, and inflammatory responses were assessed. The effect of DEX was also studied in a microglial cell culture model.

RESULTS

DEX significantly improved the ipsilateral upper-limb motor dysfunction (grooming and paw placement; P<0.0001 and P=0.0012), decreased the injury size (P<0.05), spared white matter (P<0.05), and reduced the number of activated macrophages (P<0.05) at the injury site 4 weeks post-SCI. In DEX-treated rats after injury, tissue RNA expression indicated a significant downregulation of pro-inflammatory markers (e.g. interleukin [IL]-1β, tumour necrosis factor-α, interleukin (IL)-6, and CD11b) and an upregulation of anti-inflammatory and pro-resolving M2 responses (e.g. IL-4, arginase-1, and CD206) (P<0.05). In lipopolysaccharide-stimulated cultured microglia, DEX produced a similar inflammation-modulatory effect as was seen in spinal cord injury. The benefits of DEX on these outcomes were mostly reversed by an α2-adrenergic receptor antagonist.

CONCLUSIONS

DEX significantly improves neurological outcomes and decreases tissue damage after spinal cord injury, which is associated with modulation of neuroinflammation and is partially mediated via α2-adrenergic receptor signaling.

Dexmedetomidine protects hippocampal neurons against hypoxia/reoxygenation-induced apoptosis through activation HIF-1α/p53 signaling

PURPOSE

To observe the effect of dexmedetomidine (DEX) on mitochondrial apoptosis of hippocampal neurons in hypoxia/reoxygenation (H/R) brain injury in developing rats, and to investigate its regulatory mechanism on HIF-1α/p53 signaling pathway.

METHODS

Hypoxia/reoxygenation model was used in this study. TUNEL assay was performed to detect cell apoptosis. Immunohistochemical analysis and Western-blotting analysis were conducted to detect Cytochrome-C (Cyt-c), APAF-1, Caspase-3, Neuroglobin (Ngb), HIF-1α and p53 expression. After 28 days, Morris water maze (MWM) was performed.

RESULTS

50 μg/kg DEX improved H/R-induced brain injury and inhibited mitochondrial apoptosis in rats. Western-blotting and Immunohistochemical results demonstrated that DEX could up-regulate Ngb through α₂ receptor to inhibit H/R-induced mitochondrial apoptosis. In addition, by adding inhibitors yohimbine and 2-methoxyestradiol (2ME2), we found that DEX could activate HIF-1α/p53 signaling pathway. MWM test showed that DEX could enhance long-term learning and memory of H/R brain injury rats.

CONCLUSION

DEX alleviates H/R-induced brain injury and mitochondrial apoptosis in developing rats through α₂ receptor, which may be related to activation of HIF-1α/p53 signaling pathway to up-regulate the expression of Ngb.

Atomoxetine, a selective norepinephrine reuptake inhibitor, improves short-term histological outcomes after hypoxic-ischemic brain injury in the neonatal male rat

BACKGROUND

Despite the recent progress of perinatal medicine, perinatal hypoxic-ischemic (HI) insult remains an important cause of brain injury in neonates, and is pathologically characterized by neuronal loss and the presence of microglia. Neurotransmitters, such as norepinephrine (NE) and glutamate, are involved in the pathogenesis of hypoxic-ischemic encephalopathy via the interaction between neurons and microglia. Although it is well known that the monoamine neurotransmitter NE acts as an anti-inflammatory agent in the brain under pathological conditions, its effects on perinatal HI insult remains elusive. Atomoxetine, a selective NE reuptake inhibitor, has been used clinically for the treatment of attention-deficit hyperactivity disorder in children. Here, we investigated whether the enhancement of endogenous NE by administration of atomoxetine could protect neonates against HI insult by using the neonatal male rat model. We also examined the involvement of microglia in this process.

METHODS

Unilateral HI brain injury was induced by the combination of left carotid artery dissection followed by ligation and hypoxia (8% O₂, 2 h) in postnatal day 7 (P7) male rat pups. The pups were randomized into three groups: the atomoxetine treatment immediately after HI insult, the atomoxetine treatment at 3 h after HI insult, or the vehicle treatment group. The pups were euthanized on P8 and P14, and the brain regions including the cortex, striatum, hippocampus, and thalamus were evaluated by immunohistochemistry.

RESULTS

HI insult resulted in severe brain damage in the ipsilateral hemisphere at P14. Atomoxetine treatment immediately after HI insult significantly increased NE levels in the ipsilateral hemisphere at 1 h after HI insult and reduced the neuronal damage via the increased phosphorylation of cAMP response element-binding protein (pCREB) in all brain regions examined. In addition, the number of microglia was maintained under atomoxetine treatment compared with that of the vehicle treatment group. To determine the involvement of microglia in the process of neuronal loss by HI insult, we further examined the influence of hypoxia on rat primary cultured microglia by the quantitative real-time polymerase chain reaction. Hypoxia did not cause the upregulation of interleukin-1beta (IL-1β) mRNA expression, but decreased the microglial intrinsic nitric oxide synthase (iNOS)/arginase1 mRNA expression ratio. NE treatment further decreased the microglial iNOS/arginase1 mRNA expression ratio. In contrast, no significant neuroprotective effect was observed at P14 when atomoxetine was administered at 3 h after HI insult.

CONCLUSIONS

These findings suggested that the enhancement of intrinsic neurotransmitter NE signaling by a selective NE reuptake inhibitor, atomoxetine, reduced the perinatal HI insult brain injury. In addition, atomoxetine treatment was associated with changes of TUNEL, pCREB, and BDNF expression levels, and microglial numbers, morphology, and responses.

Dexmedetomidine as an Anesthetic Adjuvant in Cardiac Surgery: a Cohort Study

OBJECTIVE:

α-₂-agonists cause sympathetic inhibition combined with parasympathetic activation and have other properties that could be beneficial during cardiac anesthesia. We evaluated the effects of dexmedetomidine as an anesthetic adjuvant compared to a control group during cardiac surgery.

METHODS:

We performed a retrospective analysis of prospectively collected data from all adult patients (> 18 years old) undergoing cardiac surgery. Patients were divided into two groups, regarding the use of dexmedetomidine as an adjuvant intraoperatively (DEX group) and a control group who did not receive α-₂-agonist (CON group).

RESULTS:

A total of 1302 patients who underwent cardiac surgery, either coronary artery bypass graft or valve surgery, were included; 796 in the DEX group and 506 in the CON group. Need for reoperation (2% vs. 2.8%, P=0.001), type 1 neurological injury (2% vs. 4.7%, P=0.005) and prolonged hospitalization (3.1% vs. 7.3%, P=0.001) were significantly less frequent in the DEX group than in the CON group. Thirty-day mortality rates were 3.4% in the DEX group and 9.7% in the CON group (P<0.001). Using multivariable Cox regression analysis with in hospital death as the dependent variable, dexmedetomidine was independently associated with a lower risk of 30-day mortality (odds ratio [OR]=0.39, 95% confidence interval [CI]: 0.24-0.65, P≤0.001). The Logistic EuroSCORE (OR=1.05, 95% CI: 1.02-1.10, P=0.004) and age (OR=1.03, 95% CI: 1.01-1.06, P=0.003) were independently associated with a higher risk of 30-day mortality.

CONCLUSION:

Dexmedetomidine used as an anesthetic adjuvant was associated with better outcomes in patients undergoing coronary artery bypass graft and valve surgery. Randomized prospective controlled trials are warranted to confirm our results.

Clonidine preconditioning improved cerebral ischemia-induced learning and memory deficits in rats via ERK1/2-CREB/ NF-κB-NR2B pathway

Clonidine, a classical α-2 adrenergic agonists, has been shown to antagonize brain damage caused by hypoxia, cerebral ischemia and excitotoxicity and reduce cerebral infarction volume in recent studies. We herein investigate the regulatory effect and possible underlying mechanism of clonidine on learning and memory in rats with cerebral ischemia. The cerebral ischemia rat model was established by right middle cerebral artery occlusion for 2h and reperfusion for 28 days. Drugs were administrated to the rats for consecutive 7 days intraperitoneally and once again on the day of surgery. The learning and memory in rats was assayed by Morris water maze. Moreover, protein expression levels of NMDAR2B (NR2B)/ phosphor - NR2B, ERK1/2/phosphor- ERK1/2, CREB/phosphor-CREB and NF-κB/phosphor-NF-κB in the cortex and hippocampus of the rats were assayed by western blotting. Our results demonstrated that clonidine treatment significantly abrogated the negative effect induced by cerebral ischemia on the learning and memory in the rats. In the Western blotting assay, clonidine treatment led to significant up-regulation of the expression level of NR2B and Phospho-NR2B in the hippocampus of the rats when compared with the cerebral ischemia group. Furthermore, clonidine also significantly decreased the protein expression levels of ERK1/2, Phospho-ERK1/2, CREB, Phospho-CREB and Phospho-NF-κB in the hippocampus of the rats when compared with the cerebral ischemia group. In conclusion, clonidine could improve the learning and memory ability of rats with cerebral ischemia, and NR2B, ERK1/2, CREB, NF-κB were involved in this effect.

Critical Evaluation of the Lund Concept for Treatment of Severe Traumatic Head Injury, 25 Years after Its Introduction

When introduced in 1992, the Lund concept (LC) was the first complete guideline for treatment of severe traumatic brain injury (s-TBI). It was a theoretical approach, based mainly on general physiological principles-i.e., of brain volume control and optimization of brain perfusion and oxygenation of the penumbra zone. The concept gave relatively strict outlines for cerebral perfusion pressure, fluid therapy, ventilation, sedation, nutrition, the use of vasopressors, and osmotherapy. The LC strives for treatment of the pathophysiological mechanisms behind symptoms rather than just treating the symptoms. The treatment is standardized, with less need for individualization. Alternative guidelines published a few years later (e.g., the Brain Trauma Foundation guidelines and European guidelines) were mainly based on meta-analytic approaches from clinical outcome studies and to some extent from systematic reviews. When introduced, they differed extensively from the LC. We still lack any large randomized outcome study comparing the whole concept of BTF guidelines with other guidelines including the LC. From that point of view, there is limited clinical evidence favoring any of the s-TBI guidelines used today. In principle, the LC has not been changed since its introduction. Some components of the alternative guidelines have approached those in the LC. In this review, I discuss some important principles of brain hemodynamics that have been lodestars during formulation of the LC. Aspects of ventilation, nutrition, and temperature control are also discussed. I critically evaluate the most important components of the LC 25 years after its introduction, based on hemodynamic principles and on the results of own an others experimental and human studies that have been published since then.

Comparison of Calcium Dynamics and Specific Features for G Protein-Coupled Receptor-Targeting Drugs Using Live Cell Imaging and Automated Analysis

G protein-coupled receptors (GPCRs) are targets for designing a large fraction of the drugs in the pharmaceutical industry. For GPCR-targeting drug screening using cell-based assays, measurement of cytosolic calcium has been widely used to obtain dose-response profiles. However, it remains challenging to obtain drug-specific features due to cell-to-cell heterogeneity in drug-cell responses obtained from live cell imaging. Here, we present a framework combining live cell imaging of a cell population and a feature extraction method for classification of responses of drugs targeting GPCRs CXCR4 and α2AR. We measured the calcium dynamics using confocal microscopy and compared the responses for SDF-1α and norepinephrine. The results clearly show that the clustering patterns of responses for the two GPCRs are significantly different. Additionally, we show that different drugs targeting the same GPCR induce different calcium response signatures. We also implemented principal component analysis and k means for feature extraction and used nondominated (ND) sorting for ranking a group of drugs at various doses. The presented approach can be used to model a cell population as a mixture of subpopulations. It also offers specific advantages, such as higher spatial resolution, classification of responses, and ranking of drugs, potentially providing a platform for high-content drug screening.

Low Dose Dexmedetomidine Attenuates Hemodynamic Response to Skull Pin Holder Application

Background:

The application of skull pin holder elicits an adverse hemodynamic response that can be deleterious; there are many drugs that have been used to attenuate this response. We have conducted this study to evaluate the efficacy of intravenous (i.v.) dexmedetomidine on attenuation of hemodynamic responses to skull pin head holder application and to compare the effectiveness of two doses of i.v. dexmedetomidine (1 μg/kg and 0.5 μg/kg bolus).

Materials and Methods:

Ninety American Society of Anesthesiologists physical Status I–III patients undergoing craniotomy were randomized into three groups of thirty each. After intubation, patients in Group A received 1 μg/kg of i.v. dexmedetomidine, Group B received 0.5 μg/kg of i.v. dexmedetomidine, whereas Group C received an equivalent quantity of normal saline. Hemodynamic parameters were monitored regularly after skull pin insertion.

Results:

There was no significant difference in the monitored hemodynamic parameters among the three groups from baseline until intubation. Heart rate (HR) and mean arterial pressure (MAP) increased significantly at skull pin insertion and subsequent points in Group C, whereas the values decreased in Groups A and B (P < 0.05). Patients in Group A showed a higher and sustained attenuation of MAP. Patients in Group C had a higher incidence of tachycardia and hypertension requiring additional measures to attenuate the response.

Conclusions:

Dexmedetomidine in either dosage (1 μg/kg or 0.5 μg/kg) was effective in attenuating hemodynamic response to skull pin insertion. Dexmedetomidine in doses of 0.5 μg/kg was as effective in attenuating the HR and MAP response to skull pin insertion as compared to a dose of 1 μg/kg.

Dexmedetomidine alleviates cerebral ischemia-induced short-term memory impairment by inhibiting the expression of apoptosis-related molecules in the hippocampus of gerbils

Cerebral ischemia results from cerebrovascular occlusion, which leads to neuronal cell death and eventually causes neurological impairments. Dexmedetomidine is a potent and highly selective α₂-adrenoreceptor agonist with actions such as sedation, anxiolysis, analgesia and anesthetic-sparing effects. We investigated the effect of dexmedetomidine on apoptosis in the hippocampus after transient global ischemia in gerbils. Transient global ischemia was induced by ligation of both common carotid arteries. Dexmedetomidine was administrated intraperitoneally at three respective doses (0.1, 1 and 10 µg/kg) once per day for 14 consecutive days beginning a day after surgery. Short-term memory was assessed by use of a step-down avoidance task. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assay, immunohistochemistry for caspase-3, and western blot analysis of Bcl-2-associated X protein, B-cell lymphoma 2, Bid, cytochrome c, apoptotic protease activating factor-1 and caspase-9 in the hippocampus. Induction of global ischemia deteriorated short-term memory by enhancing the expression of apoptosis-related molecules in the hippocampus. Treatment with dexmedetomidine suppressed the expression of apoptosis-related molecules under ischemic conditions, resulting in short-term memory improvement. Under normal conditions, dexmedetomidine exerted no significant effect on apoptosis in the hippocampus. The present results suggest that the α₂-adrenoceptor agonist dexmedetomidine may be a useful therapeutic agent for the treatment of ischemic brain diseases.

Clonidine preconditioning alleviated focal cerebral ischemic insult in rats via up-regulating p-NMDAR1 and down-regulating NMDAR2A / p-NMDAR2B

A brain ischemia rat model was established by middle cerebral artery occlusion (MCAO) for 2h and reperfusion for 4h to investigate the underlying mechanism of the neuroprotection action of clonidine, a classical alpha-2 adrenergic agonist, on cerebral ischemia. Clonidine and yohimbine were intraperitoneally given to the rats each day for a week before ischemia. Neurological deficits evaluations were carried out at 6h after operation. TTC staining method was used to measure the volume of brain infarction. Expression levels of NMDAR1, NMDAR2A, NMDAR2B were assayed by western blotting. Our data demonstrated that clonidine pretreatment significantly improved the neurological deficit scores and reduced the brain infarct volumes of the rats. Furthermore, protein expression level of p-NMDAR2B in cortex was significantly up-regulated whereas that of p-NMDAR1 was decreased when compared with the sham-operated rats. Remarkably, clonidine treatment led to significant down-regulation of p-NMDAR2B and NMDAR2A in addition to enhancement of the expression level of p-NMDAR1 in cortex. This is the first report illustrating the neuroprotective role of clonidine may be mediated through modulation of the expression levels of p-NMDAR2B, NMDAR2A and p-NMDAR1 during cerebral ischemia.

Dexmedetomidine promotes the recovery of the field excitatory postsynaptic potentials (fEPSPs) in rat hippocampal slices exposed to oxygen-glucose deprivation

Dexmedetomidine (DEX), a selective α2 adrenergic agonist, is an anesthetic and sedative agent, and is reported to exert neuroprotective effects after hypoxic ischemia. However, there are few studies on the electrophysiological effect of DEX in hippocampal slices under ischemic conditions. The effects of DEX on field potential in hippocampal slices exposed to oxygen-glucose deprivation (OGD) were evaluated. Hippocampal slices were prepared from rats, and the evoked field excitatory postsynaptic potentials (fEPSPs) were recorded using the MED 64 system. Hypoxic-ischemia was induced by perfusion with glucose-free artificial cerebrospinal fluid (aCSF) bubbled with 95% N2 and 5% CO2, and hippocampal slices were perfused with DEX-added aCSF before, during, and after OGD induction. In the normal hippocampal slices, perfusion with 1 and 10μM DEX did not significantly decrease the normalized fEPSP amplitude, but 100μM DEX significantly reduced the fEPSP amplitude compared with its baseline control. The induction of OGD remarkably decreased the fEPSP amplitude, whereas the pre-, co-, and post-treatment of 10μM DEX gradually promoted recovery after washing out, and consequently the amplitude of fEPSP in DEX pre-, co-, and post-treated OGD slices were significantly higher than that in the untreated OGD slices at 10min and 60min after washing out. In particular, co-treatment with DEX conspicuously promoted the recovery of the fEPSP amplitude at the beginning of washing out. These results suggest the possibility of DEX as a therapeutic agent to prevent hypoxic-ischemic brain damage and promote functional recovery after ischemia.

Autonomic dysfunction in acute ischemic stroke: an underexplored therapeutic area?

Impaired autonomic function, characterized by a predominance of sympathetic activity, is common in patients with acute ischemic stroke. This review describes methods to measure autonomic dysfunction in stroke patients. It summarizes a potential relationship between ischemic stroke-associated autonomic dysfunction and factors that have been associated with worse outcome, including cardiac complications, blood pressure variability changes, hyperglycemia, immune depression, sleep disordered breathing, thrombotic effects, and malignant edema. Involvement of the insular cortex has been suspected to play an important role in causing sympathovagal imbalance, but its exact role and that of other brain regions remain unclear. Although sympathetic overactivity in patients with ischemic stroke appears to be a negative prognostic factor, it remains to be seen whether therapeutic strategies that reduce sympathetic activity or increase parasympathetic activity might improve outcome.

Spinal cord protection via alpha-2 agonist-mediated increase in glial cell-line-derived neurotrophic factor

OBJECTIVES

Delayed paraplegia secondary to ischemia-reperfusion injury is a devastating complication of thoracoabdominal aortic surgery. Alpha-2 agonists have been shown to attenuate ischemia-reperfusion injury, but the mechanism for protection has yet to be elucidated. A growing body of evidence suggests that astrocytes play a critical role in neuroprotection by release of neurotrophins. We hypothesize that alpha-2 agonism with dexmedetomidine increases glial cell-line-derived neurotrophic factor in spinal cord astrocytes to provide spinal cord protection.

METHODS

Spinal cords were isolated en bloc from C57BL/6 mice, and primary spinal cord astrocytes and neurons were selected for and grown separately in culture. Astrocytes were treated with dexmedetomidine, and glial cell-line-derived neurotrophic factor was tested for by enzyme-linked immunosorbent assay. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess neuronal viability.

RESULTS

Spinal cord primary astrocytes treated with dexmedetomidine at 1 μmol/L and 10 μmol/L had significantly increased glial cell-line-derived neurotrophic factor production compared with control (P < .05). Neurons subjected to oxygen glucose deprivation had significant preservation (P < .05) of viability with use of dexmedetomidine-treated astrocyte media. Glial cell-line-derived neurotrophic factor neutralizing antibody eliminated the protective effects of the dexmedetomidine-treated astrocyte media (P < .05).

CONCLUSIONS

Astrocytes have been shown to preserve neuronal viability via release of neurotrophic factors. Dexmedetomidine increases glial cell-derived neurotrophic factor from spinal cord astrocytes via the alpha-2 receptor. Treatment with alpha-2 agonist dexmedetomidine may be a clinical tool for use in spinal cord protection in aortic surgery.

Dexmedetomidine suppresses interleukin-1β-induced interleukin-6 synthesis in rat glial cells

Dexmedetomidine, an α2-adrenoceptor agonist, is used as a sedative medication for criticalyl ill patients and is known to exert neuroprotective effects by direct action on neurons and indirect action on neurons through astrocytes. Interleukin (IL)-6 plays a key role in neuroinflammation, which accompanies infection, traumatic brain injury, ischemia, neurodegenerative disorders, as both a pro-inflammatory cytokine and an anti-inflammatory cytokine. Dexmedetomidine suppresses immune function. However, the effects of dexmedetomidine on cytokine synthesis in the central nervous system (CNS) remain elusive. We previously reported that IL-1β stimulates IL-6 synthesis in the rat C6 glioma cell line through the phosphorylation of p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK) and IκB. In the present study, we investigated the effects of dexmedetomidine on the IL-1β-induced IL-6 synthesis in C6 cells. Dexmedetomidine inhibited the IL-1β-stimulated IL-6 release and mRNA expression in C6 cells. 8-Bromo-adenosine-3',5'-cyclic monophosphate, but not 8-bromo-guanosine 3',5'-cyclic monophosphate, significantly enhanced the IL-1β-induced IL-6 release and mRNA expression. However, dexmedetomidine failed to affect cAMP accumulation in the cells treated with IL-1β or forskolin, an activator of adenylyl cyclase. Yohimbine, an α2-adrenoceptor antagonist, did not reverse the suppressive effects of dexmedetomidine on the IL-1β-induced IL-6 release. Dexmedetomidine did not affect the IL-1β-induced phosphorylation of p38 MAP kinase, SAPK/JNK, IκB, nuclear factor (NF)-κB or c-Jun. Our findings strongly suggest that dexmedetomidine inhibits the IL-1β-induced IL-6 synthesis independently of the adenylyl cyclase-cAMP pathway through α2-adrenoceptors in C6 glioma cells. It is possible that dexmedetomidine may affect the immune system in the CNS by regulating the production of IL-6.

Guanfacine is an effective countermeasure for hypobaric hypoxia-induced cognitive decline

Hypobaric hypoxia (HH), an environmental stress resulting from ascent to high altitude, affects perception, memory, judgment, and attention, resulting in degradation of many aspects of normal functioning. Alpha 2A adrenergic agonist, guanfacine proved to be beneficial in the amelioration of neurological outcomes of many neuropsychiatric disorders involving adrenergic imbalance and neurodegeneration. Adrenergic dysregulation and neuronal damage have been implicated in hypoxia-induced cognitive deficits, however, efficacy of guanfacine as a countermeasure for HH-induced cognitive decline remains to be evaluated. We, therefore, have studied the effect of this drug on the HH-induced cognitive deficits, adrenergic dysfunction and neuronal damage. Rats were exposed to HH at a simulated altitude of 25,000 feet for 7days and received an IM injection of either saline or guanfacine at a dose of 1mg/kg. Adrenergic transmission was evaluated by biomarkers i.e. norepinephrine (NE), dopamine (DA) and tyrosine hydroxylase (TH) in medial prefrontal cortex (PFC) by biochemical and immunohistochemical assays. Spine and dendritic morphology of pyramidal neurons in layer II of medial PFC was studied using Golgi-Cox staining and Neurolucida neuronal tracing. The cognitive performance was assessed by Delayed Alternation Task using a T-Maze. There was a significant reduction in HH-induced increases in NE, DA and TH levels with guanfacine treatment. Guanfacine rescued HH-induced dendritic atrophy and mushroom type spine loss. The spatial working memory deficits induced by HH were significantly ameliorated with guanfacine treatment. Furthermore, the cognitive performance showed a positive correlation with dendritic arbors and spine numbers. These results showed that the HH-induced cognitive decline is associated with adrenergic dysregulation and neuronal damage in layer II of medial PFC, and that guanfacine treatment during HH ameliorated these functional and morphological deficits. The study suggests a potential role of the alpha-2A adrenergic agonist, guanfacine, in amelioration of PFC dysfunction caused by high altitude exposure.

Neuroprotective Effects of Dexmedetomidine against Glutamate Agonist-induced Neuronal Cell Death Are Related to Increased Astrocyte Brain-derived Neurotrophic Factor Expression

Background:

Brain-derived neurotrophic factor (BDNF) plays a prominent role in neuroprotection against perinatal brain injury. Dexmedetomidine, a selective agonist of α2-adrenergic receptors, also provides neuroprotection against glutamate-induced damage. Because adrenergic receptor agonists can modulate BDNF expression, our goal was to examine whether dexmedetomidine’s neuroprotective effects are mediated by BDNF modulation in mouse perinatal brain injury.

Methods:

The protective effects against glutamate-induced injury of BDNF and dexmedetomidine alone or in combination with either a neutralizing BDNF antibody or an inhibitor of the extracellular signal-regulated kinase pathway (PD098059) were compared in perinatal ibotenate-induced cortical lesions (n = 10–20 pups/groups) and in mouse neuronal cultures (300 μm of ibotenate for 6 h). The effect of dexmedetomidine on BDNF expression was examined in vivo and in vitro with cortical neuronal and astrocyte isolated cultures.

Results:

Both BDNF and dexmedetomidine produced a significant neuroprotective effect in vivo and in vitro. Dexmedetomidine enhanced Bdnf4 and Bdnf5 transcription and BDNF protein cortical expression in vivo. Dexmedetomidine also enhanced Bdnf4 and Bdnf5 transcription and increased BDNF media concentration in isolated astrocyte cultures but not in neuronal cultures. Dexmedetomidine’s protective effect was inhibited with BDNF antibody (mean lesion size ± SD: 577 ± 148 μm vs. 1028 ± 213 μm, n = 14–20, P &lt; 0.001) and PD098059 in vivo but not in isolated neuron cultures. Finally, PD098059 inhibited the increased release of BDNF induced by dexmedetomidine in astrocyte cultures.

Conclusion:

These results suggest that dexmedetomidine increased astrocyte expression of BDNF through an extracellular signal-regulated kinase-dependent pathway, inducing subsequent neuroprotective effects.

Dexmedetomidine protects against oxygen–glucose deprivation-induced injury through the I2 imidazoline receptor-PI3K/AKT pathway in rat C6 glioma cells

Objectives

To explore the protection and the mechanism of dexmedetomidine on the oxygen–glucose deprivation (OGD) insults in rat C6 glioma cells.

Methods

Cells were subjected to OGD then assessed by viability studies. After dexmedetomidine treatment, p-AKT, hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF) and RTP801 expression were measured.

Key findings

Three hours of OGD decreased cell viability to 48.8%, which was reversed to 67.4% by 1 µm dexmedetomidine. Hoechst 33342 and propidium iodide double stains showed that the protection of dexmedetomidine was mainly by an anti-apoptosis effect, which was also strengthened by decreasing caspase-3 expression. Dexmedetomidine protection was mainly blocked by the I2 imidazoline receptor antagonist idazoxan and BU 224, but not by the α1-adrenoceptor antagonist prazosin, the α2-adrenoceptor antagonist yohimbine and RX 821002, or the I1 imidazoline receptor antagonist efaroxan. On the other hand, dexmedetomidine enhanced AKT phosphorylation. Furthermore, the protection of dexmedetomidine was blocked by the PI3K/AKT inhibitor wortmannin. The proteins of HIF-1α, VEGF and RTP801 were significantly increased by dexmedetomidine treatment.

Conclusions

Dexmedetomidine activated the I2 imidazoline receptor-PI3K/AKT pathway, and up-regulated HIF-1α, VEGF and RTP801 expression to protect against OGD-induced injury in rat C6 cells.