Glycine transporter I inhibitor, N-methylglycine (sarcosine), added to antipsychotics for the treatment of schizophrenia.

BACKGROUND: Hypofunction of N-methyl-D-aspartate glutamate receptor had been implicated in the pathophysiology of schizophrenia. Treatment with D-serine or glycine, endogenous full agonists of the glycine site of N-methyl-D-aspartate receptor, or D-cycloserine, a partial agonist, improve the symptoms of schizophrenia. N-methylglycine (sarcosine) is an endogenous antagonist of glycine transporter-1, which potentiates glycine's action on N-methyl-D-aspartate glycine site and can have beneficial effects on schizophrenia. METHODS: Thirty-eight schizophrenic patients were enrolled in a 6-week double-blind, placebo-controlled trial of sarcosine (2 g/d), which was added to their stable antipsychotic regimens. Twenty of them received risperidone. Measures of clinical efficacy and side effects were determined every other week. RESULTS: Patient who received sarcosine treatment revealed significant improvements in their positive, negative, cognitive, and general psychiatric symptoms. Similar therapeutic effects were observed when only risperidone-treated patients were analyzed. Sarcosine was well-tolerated, and no significant side effect was noted. CONCLUSIONS: Sarcosine treatment can benefit schizophrenic patients treated by antipsychotics including risperidone. The significant improvement with the sarcosine further supports the hypothesis of N-methyl-D-aspartate receptor hypofunction in schizophrenia. Glycine transporter-1 is a novel target for the pharmacotherapy to enhance N-methyl-D-aspartate function.     

Extracellular adenosine,formed during low level NMDA receptor activation,provides an inhibitory threshold against further NMDA receptor-midiated neurotransmission in the cortex

In the cortex only a few of the available NMDA receptors must be activated to evoke maximal release of adenosine. In fact, maximal adenosine release occurs at 30 μM NMDA, a concentration at which noradrenaline release is only 20% maximal. NMDA-evoked noradrenaline release appears to require the generation of propagated action potentials, while adenosine release does not. Noncompetitive block of NMDA-evoked release of adenosine, but not noradrenaline, can be overcome by increasing NMDA concentrations. The above findings are consistent with the possibility that there are spare receptors for NMDA-evoked adenosine release, but not for nor-adrenaline release. These spare receptors are not due to elevated levels of glycine in the vicinity of those NMDA receptors mediating adenosine release. Functionally, it appears that low level NMDA receptor activation provides a purinergic inhibitory threshold against higher level NMDA receptor mediated processes. This could provide inhibitory tone and selectivity for critical functions, such as learning, memory, and synaptic plasticity in the cortex. © 1993 Wiley-Liss, Inc.     

Autoradiographic localization of dopamine uptake sites in the rat brain with3H-GBR 12935

Summary The firing rate and terminal excitability of identified nigrostriatal dopamine (DA) neurons was determined before, and over a 10–15 min period following, direct intrastriatal administration of the glutamate (GLU) agonist NMDA, or saline. NMDA (0.025 and 0.075 mol) produced a short latency increase in DA cell firing rate. In 7/8 cases, this increase in firing rate was accompanied by a profound reduction in terminal excitability. The decrease in excitability usually outlasted the increase in firing rate (sometimes by more than 8 min), and was superseded at a later stage by a marked increase in excitability. None of these effects were seen with saline (n=5), and they could all be blocked by preadministration of the competitive NMDA antagonist AP-7 (0.025 mol; n=6). The sequence of events leading to the observed results is argued to be as follows; NMDA initially excites striatal efferents to the DA cell, which through disinhibition and direct stimulation increase DA cell firing rate. Increased firing rate leads to enhanced striatal DA release. Dopamine's inhibitory influence pre-empts any effect NMDA itself may have on the terminals of nigrostriatal neurons, and counteracts NMDA's stimulatory effect on striatal output cells. Furthermore, the marked reduction in terminal excitability suggests that DA becomes the dominant influence in the striatum for a time. Hence, the net outcome of the injection is augmented striatal DA tone. Later, the effect of residual NMDA becomes predominant once more.     

Effect of N-phthalamoyl-L-glutamic acid,a selective NMDA receptor agonist,on binding of3H-L-glutamate with hippocampal synaptic membranes

Institute of Experimental Medicine, Russian Academy of Medical Sciences, St. Petersburg. (Presented by Academician of the Russian Academy of Medical Sciences A. N. Klimov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 113, No. 6, pp. 563–565, June, 1992.     

Cerebral protection by AMPA- and NMDA-receptor antagonists administered after severe insulin-induced hypoglycemia

Summary Excitatory amino acids are implicated in the development of neuronal cell damage following periods of reversible cerebral ischemia or insulin-induced hypoglycemic coma. To explore the importance of glutamate receptor activation in the posthypoglycemic phase, we exposed rats to 20 min of insulin-induced severe hypoglycemia. The rats were treated immediately after the hypoglycemic insult with four regimes of glutamate receptor antagonists: (1) the AMPA (-amino-3-hydroxy-5-methyl-4-isoxazole propriate)-receptor antagonist NBQX [2.3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxaline] given as a bolus dose of 30 mg · kg^-1 i.p., followed by an i.v. infusion of 225 g · kg^-1 · min^-1 for 6 h; (2) the non-competitive NMDA-receptor antagonist, dizocilpine (MK-801) 1 mg · kg^-1 given i.v.; (3) a combined NBQX treatment, (a bolus dose of 10 mg · kg^-1 i.p., followed by an i.v. infusion of 225 g · kg^-1 · min^-1 for 6 h), with dizocilpine 0.33 mg · kg^-1 given twice i.p. at 0 and 15 min after recovery and (4) the competitive NMDA-receptor blocker CGP 40116 [D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid] 10 mg · kg^-1 given i.p.. In the striatum, all glutamate receptor blockers significantly decreased neuronal damage by approximately 30%. An approximately 50% decrease in neuronal damage was demonstrated in neocortex and hippocampus following the combined treatment with NBQX and dizocilpine, while protection was variable following the treatment with a single glutamate-receptor antagonist. We conclude that neuronal damage continues to develop in the striatum and in cortical brain regions in the posthypoglycemic period and that both NMDA- and AMPA-receptors contribute to this process, possibly by a change in the cellular response to both AMPA- and NMDA-receptor stimulation.     

镇痛药研究进展

镇痛药研究引入了细胞及分子生物学的最新研究手段和方法，并从神经激肽类阻滞剂、N-甲基-D-天门冬氨酸(N—methyl—D—aspartate，NMDA)受体阻滞剂、腺苷激酶抑制剂、脑啡肽分解酶抑制剂、降钙素基因相关肽(Calcitonin gene—related peptide，CGRP)受体阻滞剂、镇痛复合制剂等方面拓宽了镇痛药研究的思路。新建立的研究模型包括培养脊髓背根神经节神经元模型及吞咽反应模型。     

二苯乙烯苷对脑缺血再灌注沙土鼠学习记忆功能及NMDA受体亲合力的影响

目的:研究2,3,5,4'-四羟基二苯乙烯-2-O-β-D-葡萄糖苷(2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside,简称二苯乙烯苷)对脑缺血再灌注沙土鼠学习记忆功能和对N-甲基-D-天冬氨酸(NMDA)受体亲合力的影响.方法:夹闭沙土鼠双侧颈总动脉10min,然后撤去动脉夹实现再灌注,7d后通过水迷宫测定学习记忆功能的改变,随后处死,测定前脑组织NMDA受体与[3H]MK801的亲合力.结果:Morris水迷宫实验显示,模型组游出时间和游泳距离比假手术组明显延长,二苯乙烯苷治疗组的游出时间和游泳距离均比模型组缩短.受体亲合情况测定结果显示,模型组的NMDA受体与[3H]MK801的亲和力比假手术组明显升高,而二苯乙烯苷治疗组可以降低模型动物的NMDA受体亲合力.结论:二苯乙烯苷能够改善缺血再灌注所导致的学习记忆功能障碍,降低NMDA受体与[3H]MK801亲合力,可能具有脑保护作用.     

Effects of intrathecal NMDA and AMPA receptors agonists or antagonists on antinociception of propofol

AIM: To study the effects of intrathecal (it) agonists and antagonists of N-methyl-D-aspartate (NMDA) and alpha amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors and NMDAR1 antisense oligodeoxynucleotides (AS ODN) on the antinociception of propofol. METHODS: Hot-plate test (HPPT) and acetic acid-induced writhing test were used to measure the nociceptive thresholds in mice. The effects of intrathecal NMDA,     

氯胺酮对大鼠吗啡戒断症状的影响及其作用机理

目的　研究氯胺酮对大鼠吗啡戒断症状的影响及其可能的机理。方法　建立大鼠吗啡依赖模型 ,在用纳洛酮催瘾前 2min给予不同剂量的氯胺酮 ,观察其戒断症状的改变 ;用分光光度法测定戒断时大鼠一氧化氮 (NO)含量、一氧化氮合酶 (NOS)活性 ,用放射免疫法测定环鸟苷酸 (cGMP)含量。结果　 3个剂量的氯胺酮 (5、10和 2 0mg·kg- 1)均可缓解吗啡戒断时探究、扭体、湿狗样抖动、跳跃等运动反应 ,减少活动次数 ,抑制植物神经系统症状。10、2 0mg·kg- 1氯胺酮可显著减轻吗啡戒断所致的体重下降 ,小剂量氯胺酮 (5mg·kg- 1)可抑制吗啡依赖大鼠前额叶皮质、小脑的NOS活性和NO、cGMP含量的增高。结论　氯胺酮可缓解大鼠吗啡戒断症状 ,其作用机理可能与减弱大鼠吗啡戒断时NMDA NO cGMP通路效应有关。     

N-甲基-D-天门冬氨酸受体亚型NR1、NR2A在大鼠视网膜缺血再灌注损伤模型中的表达

目的:研究N-甲基-D-天门冬氨酸受体(N-methyl-D-aspartate receptor,NMDAR)功能亚单位NMDAR1、NM-DAR2A在Wister大鼠视网膜缺血再灌注模型中的表达情况。方法:18只健康成年Wister大鼠分成6组,每组3只,都取其右眼行视神经周围血管结扎手术制备视网膜缺血再灌注模型,左眼作为对照组不行手术。60分钟后去除结扎缝线恢复血流,分别于再灌注后即刻、3、12、24、72、168小时处死大鼠,摘除眼球,做冰冻切片。用免疫组织化学方法观察NR1、NR2A在视网膜缺血再灌注后不同时刻的变化并进行图象分析及统计学处理。结果:(1)各实验组和对照组间及各实验组间NMDAR1的表达无统计学意义。(2)除即刻组外各实验组和对照组间及各实验组间NMDAR2A的表达均有统计学意义,从再灌注后3小时至168小时NMDR2A表达缓慢上升。结论:(1)NMDAR1与视网膜缺血再灌注损伤无关,不参与谷氨酸的兴奋性毒性作用。(2)NMDAR2A与视网膜缺血再灌注损伤有关,参与谷氨酸兴奋性毒性作用。