Baicalin protects neonatal rat brains against hypoxicischemic injury by upregulating glutamate transporter 1 via the phosphoinositide 3-kinase/protein kinase B signaling pathway

Baicalin is a flavonoid compound extracted from Scutellaria baicalensis root.Recent evidence indicates that baicalin is neuroprotective in models of ischemic stroke.Here,we investigate the neuroprotective effect of baicalin in a neonatal rat model of hypoxic-ischemic encephalopathy.Seven-day-old pups underwent left common carotid artery ligation followed by hypoxia（8% oxygen at 37°C） for 2 hours,before being injected with baicalin（120 mg/kg intraperitoneally） and examined 24 hours later.Baicalin effectively reduced cerebral infarct volume and neuronal loss,inhibited apoptosis,and upregulated the expression of p-Akt and glutamate transporter 1.Intracerebroventricular injection of the phosphoinositide 3-kinase/protein kinase B（PI3 K/Akt） inhibitor LY294002 30 minutes before injury blocked the effect of baicalin on p-Akt and glutamate transporter 1,and weakened the associated neuroprotective effect.Our findings provide the first evidence,to our knowledge that baicalin can protect neonatal rat brains against hypoxic-ischemic injury by upregulating glutamate transporter 1 via the PI3 K/Akt signaling pathway.

Neuroprotective effects of cromakalim on cerebral ischemia-reperfusion injury in rats Correlation with hippocampal metabotropic glutamate receptor 1 alpha and glutamate transporter 1

BACKGROUND：Studies have reported that potassium channel openers exhibit a protective effect on cerebral ischemia-reperfusion injury and inhibit glutamate excitotoxicity in rats.However,the effects of the glutamate receptor 1α and glutamate transporter 1 remain poorly understood.OBJECTIVE：To investigate the prophylactic use of the adenosine triphosphate-sensitive potassium channel opener cromakalim on neurological function and cerebral infarct size,as well as glutamate receptor 1α and glutamate transporter 1 expression,in rats with cerebral ischemia-reperfusion injury,and to explore action mechanisms underlying reduced glutamate excitotoxicity and neuroprotection in rats.DESIGN,TIME AND SETTING：Randomized,controlled,animal experiment was performed at the Brain Institute,Qingdao University Medical College,Between July 2008 and April 2009.MATERIALS：Cromakalim was purchased from Sigma,USA; rabbit anti-glutamate receptor 1α polyclonal antibody was offered by Wuhan Boster,China; rabbit anti-glutamate transporter 1 polyclonal antibody was offered by Santa Cruz Biotechnology,USA.METHODS：Sixty male,Wistar rats,aged 6 months,were randomly assigned to three groups （n =20）：sham-surgery,model,and cromakalim.Intraluminal thread methods were used to establish middle cerebral artery occlusion in rats from the model and cromakalim groups.Rats from the sham-surgery group were subjected to exposed common carotid artery,external carotid artery,and internal carotid artery,without occlusion.Cromakalim （10 mg/kg） was administered 30 minutes prior to middle cerebral artery occlusion,but there was no intervention in the model and sham-surgery groups.MAIN OUTCOME MEASURES：At 24 hours post-surgery,neurological behavioral functions were evaluated using Bederson＇s test,cerebral infarction volume was determined following tetrazolium chloride staining,and glutamate receptor 1a and glutamate transporter 1 expressions were detected using immunohistochemistry.RESULTS：Following cerebral ischemia-reperfusion injury,neurological behavioral malfunctions were obvious in all mice.Focal cerebral infarction was detected in ischemic hemispheres,glutamate receptor 1α expression increased,and glutamate transporter 1 expression decreased in the ischemic hemisphere （P〈 0.05）.Compared with the model group,neurological behavioral functions significantly improved,cerebral infarction volume was significantly reduced （P〈 0.05）,glutamate receptor 1α expression was significantly decreased,and glutamate transporter 1 expression was increased in the cromakalim group （P 〈 0.05）.CONCLUSION：Improved neurological function and reduced cerebral infarction volume in rats through the preventive use of cromakalim could be related to decreased glutamate receptor 1α expression and enhanced glutamate transporter 1 expression.

Glutamate Transporter 1-mediated Antidepressant-like Effect in a Rat Model of Chronic Unpredictable Stress

In recent years, more attention has been paid to the role of the glutamate transporter 1 （GLT-1, EAAT2） in major depressive disorder （MDD）. However, experimental data on brain GLT-1 levels are, to some extent, inconsistent in human postmortem and animal studies, These discrepancies imply that the role of GLT-1 in the pathophysiology of MDD and the action of antidepressants remain obscure. This work was designed to study the impact of chronic unpredictable stress （CUS） for 2 ses- sions per day for 35 days and four weeks of fluoxetine （FLX） on depressive-like behaviors in rats, as well as the concomitant expression of the GLT-1 protein in the hippocampus. Behavioral changes were assessed by the sucrose preference and open field tests. GLT-1 levels were detected by immunohisto- chemistry and Western blot analysis. Our study demonstrated that the animals exposed to CUS showed depressive-like behaviors and exhibited a significant decrease in GLT-1 expression in the hippocampus. Chronic FLX treatment reversed the behavioral deficits and the CUS-induced decrease in GLT-1 levels. Taken together, our results support the reduction of GLT-1 in human postmortem studies in MDD and suggest that GLT-1 may be involved in the antidepressant activity of FLX. Our studies further support the notion that GLT-1 is an attractive candidate molecule associated with the fundamental processes of MDD and may be a potential, and novel pharmacological target for the treatment of MDD.

Expression of multiple glutamate transporter splice variants in the rodent testis

Glutamate is a regulated molecule in the mammalian testis. Extracellular regulation of glutamate in the body is determined largely by the expression of plasmalemmal glutamate transporters. We have examined by PCR, western blotting and immunocytochemistry the expression of a panel of sodium-dependent plasmalemmal glutamate transporters in the rat testis. Proteins examined included： glutamate aspartate transporter （GLAST）, glutamate transporter 1 （GLT1）, excitatory amino acid carrier 1 （EAAC1）, excitatory amino acid transporter 4 （EAAT4） and EAAT5. We demonstrate that many of the glutamate transporters in the testis are alternately spliced. GLAST is present as exon-3- and exon-9-skipping forms. GLT1 was similarly present as the alternately spliced forms GLT1 b and GLTlc, whereas the abundant brain form （GLTla） was detectable only at the mRNA level. EAAT5 was also strongly expressed, whereas EAAC1 and EAAT4 were absent. These patterns of expression were compared with the patterns of endogenous glutamate localization and with patterns of D-aspartate accumulation, as assessed by immunocytochemistry. The presence of multiple glutamate transporters in the testis, including unusually spliced forms, suggests that glutamate homeostasis may be critical in this organ. The apparent presence of many of these transporters in the testis and sperm may indicate a need for glutamate transport by such cells.

Electroacupuncture Alleviates Motor Symptoms and Up-Regulates Vesicular Glutamatergic Transporter 1 Expression in the Subthalamic Nucleus in a Unilateral 6-Hydroxydopamine-Lesioned Hemi-Parkinsonian Rat Model

Previous studies have shown that electroacupuncture（EA） promotes recovery of motor function in Parkinson＇s disease（PD）. However the mechanisms are not completely understood. Clinically, the subthalamic nucleus（STN） is a critical target for deep brain stimulation treatment of PD, and vesicular glutamate transporter 1（VGlu T1） plays an important role in the modulation of glutamate in the STN derived from the cortex. In this study,a 6-hydroxydopamine（6-OHDA）-lesioned rat model of PD was treated with 100 Hz EA for 4 weeks. Immunohistochemical analysis of tyrosine hydroxylase（TH） showed that EA treatment had no effect on TH expression in the ipsilateral striatum or substantia nigra pars compacta,though it alleviated several of the parkinsonian motor symptoms. Compared with the hemi-parkinsonian rats without EA treatment, the 100 Hz EA treatment significantly decreased apomorphine-induced rotation and increased the latency in the Rotarod test. Notably, the EA treatment reversed the 6-OHDA-induced down-regulation of VGlu T1 in the STN. The results demonstrated that EA alleviated motor symptoms and up-regulated VGlu T1 in the ipsilateral STN of hemi-parkinsonian rats, suggesting that up-regulation of VGlu T1 in the STN may be related to the effects of EA on parkinsonian motor symptoms via restoration of function in the cortico-STN pathway.

Combined action of MK-801 and ceftriaxone impairs the acquisition and reinstatement of morphine-induced conditioned place preference,and delays morphine extinction in rats

Objective It is well established that glutamate and its receptors, particularly the N-methyl-D-aspartate receptor （NMDAR）, play a significant role in addiction and that the inhibition of glutamatergic hyperfunction reduces addictive behaviors in experimental animals. Specifically, NMDAR antagonists such as MK-801, and an inducer of the expression of glutamate transporter subtype-1 （GLT-1） （ceftriaxone） are known to inhibit addictive behavior. The purpose of this study was to determine whether the combined action of a low dose of MK-801 and a low dose of ceftriaxone provides better inhibition of the acquisition, extinction, and reinstatement of morphine-induced conditioned place preference （CPP） than either compound alone. Methods A morphine-paired CPP experiment was used to study the effects of low doses of MK-801, ceftriaxone and a combination of both on reward-related memory （acquisition, extinction, and reinstatement of morphine preference） in rats. Results A low dose of neither MK-801 （0.05 mg/kg, i.p.） nor ceftriaxone （25 mg/kg, i.p.） alone effectively impaired CPP behaviors. However, when applied in combination, they reduced the acquisition of morphine-induced CPP and completely prevented morphine reinstatement. Their combination also notably impaired the extinction of morphine-induced CPP. Conclusion The combined action of a low dose of an NMDAR antagonist （MK-801） and GLT-1 activation by ceftriaxone effectively changed different phases of CPP behavior.