Electrophysiological evidences for the contribution of NMDA receptors to the inhibition of clonidine on the RVLM presympathetic neurons

The main objective of this study is to test the hypothesis that N-methyl-D-aspartate(NMDA) receptors within the rostral ventrolateral medulla(RVLM) are involved in the inhibition of clonidine on the RVLM presympathetic neurons. Totally,22 presympathetic neurons were recorded in anesthetized and paralyzed rats. The majority of these neurons(n=16 of 22) were significantly inhibited by iontophoretic(30 nA) clonidine,the other 6 neurons were insensitive to clonidine. In seven clonidine-sensitive neurons,iontophoretic clonidine(30 nA) antagonized the neuronal excitation of iontophoretic NMDA receptor agonist NMDA(20 nA). In remaining nine clonidine-sensitive neurons,iontophoretic NMDA receptor antagonist MK801 (60 nA) significantly attenuated the neuronal inhibition of iontophoretic(30 nA) clonidine. In conclusion,these results suggest that NMDA receptors contribute to the inhibition of clonidine on the RVLM presympathetic neurons.     

Effect of clonidine added to ropivacaine for epidural anesthesia

Objective To evaluate the effect of clonidine added to ropivacaine for epidural anesthesia. Methods Sixty ASA Ⅰ - Ⅱ patients aged 24 - 62 yr, weighing 50 - 76 kg, scheduled for elective gynecological surgery under epidural anesthesia were randomly assigned to one of four equal groups of 15 patients each, according to the dose of clonidine added to ropivacaine solution: group 1 (R) received no clonidine and served as control;group 2 - 4 in which clonidine 50,100 or 150 μg was added to 0. 75% ropivacaine 25 ml (R - C 50, R - C 100, R - C 150). Epidural anesthesia was performed at L2-3. Epidural catheter was inserted into epidural space and advanced in cephalad direction for 3 : 5 cm. Ropivacaine solution was prepared and provided by a specially designated person. A test dose of 5 ml of ropivacaine was given. 5 min later when epidural placement of catheter was confirmed, the rest 20 ml of ropivacaine was given in fractions of 5 ml every 2-3 min. At the beginning of operation midazolam 2.5-3.5 mg was giv     

Effect of Xingnaojing Injection (醒脑静注射液) on Hippocampal N-methyl-D-aspartic Acid Receptors of Focal Cerebral Ischemia in Rats

Objective: To observe and elucidate the neuroprotective effect of Xingnaojing (XNJ) injection on hippocampal N-methyl-D-aspartic acid (NMDA) receptors of focal cerebral ischemia in rats. Methods: Cerebral ischemia was established by occluding the middle cerebral artery with an intraluminal suture technique in rats. Neurological deficit score, infarct volume and quantity of NMDA receptors were estimated in all groups and compared. Results: After being treated with XNJ, the score decreased in the initial 6 hours and infarct volume decreased in 24 hours. And within 24 hours, the quantity of NMDA receptors obviously decreased compared with the model group (P<0. 01) It indicated that XNJ could ameliorate neurological behavior of middle cerebral artery occlusion rats and down-regulate the expression of hippocampal NMDA receptors. Conclusion: The neuroprotective effect of XNJ on focal cerebral ischemia is possibly related to down-regulating the expression of NMDA receptors in rats.     

单次联合注射可乐定与氯胺酮在缓解慢性炎症痛中的协同作用

Objective: To observe the interactive analgesia on inflammatory pain between ketamineand clonidine. Methods: Using half dose method to design experiment, namely to obseve the analgesiceffect by given subcutaneous(s. c. ) injection simultaneously of half dose of ketamine (the dose is fixed)and half dose of clonidine (doses are changing) Scores of pain was tested by dorsal flexion of anklejoint. Results: (1) s. c. injection of ketamine (10 mg· kg-1 ) or clonidine (20 μg· kg-1 ) alone produceno significant analgesia. While s. c. injection of other doses of clonidine alone (40, 80, 160μg·kg-1)produced slight analgesia; (2)when the dose of each drug was reduced by one-half and given (dose ofketamine was 5 mg·kg - 1,clonidine dose was 40μg· kg-1 or 80 ig·kg-1 ) simultaneous, the scores ofpain reduced significant lower than that produced by either drug alone. Conclusion: The resultssuggested that combined using of some proportions of ketamine and clonidine could produce synergisticanalgesia.     

Ketamine Promotes Inflammation through Increasing TLR4 Expression in RAW264.7 Cells

Summery: Ketamine(KTM), a N-methyl-D-aspartate(NMDA) receptor antagonist, was found to has an anti-inflammatory effect, but some patients suffered from exacerbated pro-inflammatory reactions after anesthesia with KTM. The present study was aimed to examine the underlying mechanism of pro-inflammatory effects of KTM. In this study, RAW264.7 cells were exposed to KTM and NMDA alone or combined for 30 min before lipopolysaccharide(LPS) stimulation. The expression levels of IL-6 and TNF-α were detected by RT-PCR and ELISA, and those of NMDA receptors by RT-PCR in RAW264.7 cells. Additionally, the TLR4 expression was determined by RT-PCR and flow cytometry, respectively. The results showed that in RAW264.7 cells, KTM alone promoted the TLR4 expression, but did not increase the expression of IL-6 or TNF-α. In the presence of LPS, KTM caused a significantly higher expression of IL-6 and TNF-α than LPS alone. NMDA could neither alter the IL-6 and TNF-α m RNA expression, nor reverse the enhanced expression of IL-6 and TNF-α m RNA by KTM in LPS-challenged cells. After TLR4-si RNA transfection, RAW264.7 cells pretreated with KTM no longer promoted the IL-6 and TNF-α expression in the presence of LPS. In conclusion, KTM accelerated LPS-induced inflammation in RAW264.7 cells by promoting TLR4 expression, independent of NMDA receptor.     

Influences of NR2B-containing NMDA receptors knockdown on neural activity in hippocampal newborn neurons

Adult-born neurons undergo a transient period of plasticity during their integration into the neural circuit.This transient plasticity may involve NMDA receptors containing NR2B,the major subunit expressed at early developmental stages.The main objective of the present study was to investigate the effects of NR2B gene knockdown on the functional integration of the adult-born granule cells generated from the subgranule zone (SGZ) in the hippocampus.The small interfering RNA (siRNA) was used to knock down the NR2B gene in the adult-born hippocampal neurons.In the functional integration test,the mice were exposed to a novel environment (open field arena),and the expression of c-fos was immunohistochemically detected in the hippocampus.After exposure to the novel environment,siRNA-NR2B mice were significantly different from control mice in either the number of squares or the number of rears they crossed,showing decreased horizontal and vertical activity (P<0.05).Moreover,the c-fos expression was increased in both control and siRNA-NR2B mice after open field test.But,it was significantly lower in siRNA-NR2B neurons than in control neurons.It was concluded that the neural activity of newborn neurons is regulated by their own NR2B-containing NMDA glutamate receptors during a short,critical period after neuronal birth.     

Lead Can Inhibit NMDA-,K~ -,QA/KA-Induced Increases in Intracellular Free Ca~(2 ) in Cultured Rat Hippocampal Neurons

Objective To examine the effects of Pb2 on N-methyl-D-aspartate (NMDA)-, K - and quisqualate(QA)/kainite(KA)-induced increases in intracellular free calcium concentration ([Ca2 ],) in cultured fetal rat hippocampal neurons in order to explain the cognitive and learning deficits produced by this heavy metal. Methods Laser scanning confocal microscopy was used. Results The results clearly demonstrated that adding Pb2 before or after NMDA/glycine stimulation selectively inhibited the stimulated increases in [Ca2 ], in a concentration-dependent manner. In contrast, Pb2 treatment did not markedly affect increases in [Ca2 ], induced by an admixture of QA and KA. The minimal inhibitory effect of Pb2 occurred at 1μmol/L, and more than seventy percent abolition of the NMDA-stimulated increase in [Ca2 ], was observed at 100 μmol/L Pb2 . Evaluation of Pb2 -induced increase in [Ca2 ], response to elevating extracellular concentrations of NMDA, glycine or calcium revealed that Pb2 was a noncompetitive antagon     

Recent development in NMDA receptors

Purpose To identify the structure and the function of NMDA receptors, to understand the modulatory mechanism of some endogenous and exogenous compounds on NMDA receptors, and to provide theoretical basis for developing new drugs that modulate NMDA receptors. Data sources A total of 24 originally identified articles were selected.Study selection A total of 24 articles were selected from several hundred original articles or reviews. The content of selected articles are in accordance with our purpose and the authors are authorized scientists in the study on NMDA receptors.Data extraction After careful review of the selected papers, the meaningful results and conclusions were extracted using scientific criteria and our experience in the research of NMDA receptors.Results NMDA receptor contains at least five subunits. They were designated as the NR1 (ζ1), NR2A (ε1), NR2B (ε2), NR2C (ε3), and NR2D (ε4). A unique feature of NMDA receptor is the requirement for both glutamate and the co-agnist glycine for the efficient gating. NMDA receptor is modulated by a number of endogenous and exogenous compounds. Mg(2+) not only blocks the NMDA channel in a voltage-dependent manner but also potentiates NMDA-induced responses at positive membrane potentials. Na(+), K(+) and Ca(2+) not only pass through the NMDA receptor channel but also modulate the activity of NMDA receptors. Zn(2+) blocks the NMDA current in a noncompetitive and a voltage-independent manner. It has been demonstrated that polyamines do not directly activate NMDA receptors, but instead act to potentiate or inhibit glutamate-mediated responses. The activity of NMDA receptors is also strikingly sensitive to the changes in H(+) concentration, and partially inhibited by the ambient concentration of H(+) under physiological conditions.Conclusions NMDA receptors are glutamate-regulated by ion channels that are permeable to Ca(2+), Na(+), K(+) and are sensitive to voltage-dependent Mg(2+) block. This channel complex contributes to excitatory synaptic transmission at sites throughout the brain and the spinal cord,and is modulated by a number of endogenous and exogenous compounds. NMDA receptors play a key role in wide range of physiologic and pathologic processes. Five NMDA receptor subunits have now been characterized in both rat and mouse brain.     

Lead Can Inhibit NMDA^—,K^＋—,QA／KA—Induced Increases in Intracellular Free Ca^2＋ in Cultured at Hippocampal Neurons

Objective To examine the effects of Pb2+ on N-methyl-D-aspartate (NMDA)-, K+- and quisqualate(QA)/kainite(KA)-induced increases in intracellular free calcium concentration ([Ca2+]i) in cultured fetal rat hippocampal neurons in order to explain the cognitive and learning deficits produced by this heavy metal. Methods Laser scanning confocal microscopy was used. Results The results clearly demonstrated that adding Pb2+ before or after NMDA/glycine stimulation selectively inhibited the stimulated increases in [Ca2+]i in a concentration-dependent manner. In contrast, Pb2+ treatment did not markedly affect increases in [Ca2+]i induced by an admixture of QA and KA. The minimal inhibitory effect of Pb2+ occurred at 1 μ mol/L, and more than seventy percent abolition of the NMDA-stimulated increase in [Ca2+]iwas observed at 100 μmol/L Pb2+. Evaluation of pb2+-induced increase in [Ca2+]i response to elevating extracellular concentrations of NMDA, glycine or calcium revealed that Pb2+ was a noncompetitive antagonist of both NMDA and glycine, and a competitive antagonist of Ca2+ at NMDA receptor channels. In addition, Pb2+ inhibited depolarization-evoked increases in [Ca2+]i mediated by K+ stimulation (30 μmol/L), indicating that Pb2+ also depressed the voltage-dependent calcium channels. Also, the results showed that Pb2+ appeared to be able to elevate the resting levels of [Ca2+]i in cultured neurons, implying a reason for pb2+-enhanced spontaneous release of several neurotransmitters reported in several previous studies. Conclusion Lead can inhibit NMDA-, K+-, QA/KA-inducod increases in intracellular [Ca2+]i in cultured hippocampal neurons.