The associative brain at work: Evidence from paired associative stimulation studies in humans

The original protocol of Paired Associative Stimulation (PAS) in humans implies repetitive cortical and peripheral nerve stimuli, delivered at specific inter-stimulus intervals, able to elicit non-invasively long-term potentiation (LTP)- and long-term depression (LTD)-like plasticity in the human motor cortex. PAS has been designed to drive cortical LTP/LTD according to the Hebbian rule of associative plasticity. Over the last two decades, a growing number of researchers have increasingly used the PAS technique to assess cortical associative plasticity in healthy humans and in patients with movement disorders and other neuropsychiatric diseases. The present review covers the physiology, pharmacology, pathology and motor effects of PAS. Further sections of the review focus on new protocols of “modified PAS” and possible future application of PAS in neuromorphic circuits designed for brain-computer interface.     

The NMDA receptor antagonist dizocilpine differentially affects environment-dependent and environment-independent ethanol tolerance

Antagonists of theN-methyl-D-aspartate subtype of glutamate receptor have been reported to block the development of tolerance to various effects of ethanol and opiates, using paradigms in which tolerance is believed to be governed by learning. There is considerable evidence to implicate theN-methyl-D-aspartate receptor in learning processes, and therefore the ability of the antagonists to block tolerance has been attributed to their effects on learning. To evaluate this hypothesis, we compared, in C57BL/6 mice, the effect of the uncompetitiveN-methyl-D-aspartate receptor antagonist, dizocilpine, on environment-dependent (associative) tolerance to ethanol, which is governed by learning, and on environment-independent (nonassociative) ethanol tolerance, in which learning plays a minimal role. Environment-dependent tolerance was induced by repeated ethanol injections, and dizocilpine blocked the development of this type of tolerance to the hypothermic and incoordinating effects of ethanol. In contrast, when environment-independent ethanol tolerance was induced by feeding the mice an ethanol-containing liquid diet, dizocilpine treatment had no effect on the development of tolerance to the hypothermic, incoordinating or hypnotic effects of ethanol. The results support the hypothesis that the effect of N-methyl-D-aspartate receptor antagonists on ethanol tolerance reflects the more general role of this receptor in processes involving learning and memory.     

Effects of L-trans-pyrrolidine-2,4-dicarboxylate, a glutamate uptake inhibitor, on NMDA receptor-mediated calcium influx and extracellular glutamate accumulation in cultured cerebellar granule neurons

Glutamate uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylate (PDC, 20 μM) elevated basal and N-methyl-D-aspartate (NMDA, 100 μM)-induced extracellular glutamate accumulation, while it did not augment kainate (100 μM)-induced glutamate accumulation in cultured cerebellar granule neurons. However, pretreatment with PDC for 1 h significantly reduced NMDA-induced glutamate accumulation, but did not affect kainate-induced response. Pretreatment with glutamate (5 μM) for 1 h also reduced NMDA-induced glutamate accumulation, but did not kainate-induced response. Upon a brief application (3–10 min), PDC did neither induce elevation of intracellular calcium concentration ([Ca²⁺]_i) nor modulate NMDA-induced [Ca²⁺]_i elevation. Pretreatment with PDC for 1 h reduced NMDA-induced [Ca²⁺]_i elevation, but it did not reduce kainate-induced [Ca²⁺]_i elevation. These results suggest that glutamate concentration in synaptic clefts of neuronal cells is increased by prolonged exposure (1 h) of the cells to PDC, and the accumulated glutamate subsequently induces selective desensitization of NMDA receptor.     

帕金森病运动并发症发生机制中G蛋白偶联受体激酶6与N-甲基-D-天冬氨酸受体关系的研究

目的 研究G蛋白偶联受体激酶6(GRK6)在帕金森病(PD)运动并发症发生机制中与N-甲基-D-天冬氨酸(NMDA)受体的关系.方法 建立PD运动并发症大鼠模型,25只大鼠分为3组.异动症(LID)组10只,腹腔注射左旋多巴甲酯23 d;MK-801处理组10只,第23天左旋多巴甲酯注射前腹腔注射MK-801;PD组5只,腹腔注射0.2%维生素C液.另设假手术组5只为对照组.观察MK-801处理左旋多巴诱导的运动并发症模型大鼠的行为变化,并用免疫组织化学方法和Western印迹方法检测大鼠纹状体区GRK6蛋白的表达情况.结果 PD组大鼠长期使用左旋多巴后出现明显的异常不自主运动,与人类LID具有相似特征.免疫组化结果显示.PD组损伤侧纹状体区GRK6阳性细胞指数减少至(4.81±1.31)×103(P＜0.05),LID组损伤侧GRK6阳性细胞指数进一步减少至(3.23±0.41)×103(P＜0.01).MK-801组LID大鼠异常不自主运动评分减少,药效期延长,同时损伤侧纹状体区GRK6阳性细胞指数增多至(4.64±1.39)×103(P＜0.05).Western印迹法检测结果同免疫组化基本相符,PD组损毁侧/未损毁侧纹状体区GRK6含量比值为(83.7±2.1)%,LID组GRK6值降低为(76.8±2.2)%,而MK-801组GRK6值升高至(91.1±2.7)%(P＜0.01).结论 NMDA受体拮抗剂能逆转大鼠运动并发症的发生,其机制可能与GRK6增多,抑制了谷氨酸受体的过度活化有关.

Abstract：

Objective To investigate the relationship between G protein-coupled receptor kinase 6 (GRK6) and N-methyl-D-aspartate (NMDA) receptor in the mechanism study underlying motor complications in Parkinson's disease (PD).Methods The rat models (n= 25) of Parkinsonism related motor complications were established and were randomly divided into levodopa-induced dyskinesia (LID) group (n= 10,intraperitoneal injection of levodopa for 23 d),MK-801 treatment group (n= 10,intraperitoneal injection of MK-801 at day23 after intraperitoneal injection with levodopa for 22 days) and PD group (n= 5,intraperitoneal injection of vitamin C).Another 5 rats were served as controls (sham-operation group).The behavior changes of rats in MK-801 treatment group were observed,and the expression of GRK6 in the striate of rats was detected by immunohistochemistry and Western blot.Results After the chronic treatment with levodopa methyl ester,PD rats displayed abnormal involuntary movements,which was similar to levodopainduced dyskinesia in PD patients.Immunohistochemistry showed that GRK6-positive cells of lesion side were decreased in LID rats as compared with PD rats [(3.23±0.41 ) × 103 vs.(4.81 ± 1.31 ) ×103,P＜0.01].Rats in MK-801 treatment group displayed the decreased AIM scores and increased peak rotation,and the increased GRK6-positive cells of lesion side as compared with LID rats (P＜0.05).Western blot showed that the levels of GRK6 was 83.7% ±2.1% in PD group (presented as lesion side/unlesion side),76.8% ± 2.2% in LID group and 91.1% ± 2.7% in MK-801 treatment group (intergroups comparison:all P＜0.05).These results were in accordance with the results of immunohistochemistry.Conclusions Antagonist of NMDA receptor can be used to reduce the motor complications in rats.It may be due to increased GRK6 which inhibits the overactivation of glutamic acid receptors.     

低频电针对海洛因依赖小鼠海马N-甲基-D-天冬氨酸受体NR1、NR2A、NR2B亚型蛋白表达的影响

摘要 目的：通过观察低频电针对海洛因心理依赖小鼠海马N-甲基-D-天冬氨酸(NMDA)的亚型NMDAR1(NR1)、NMDAR-2A(NR2A)、NMDAR-2B(NR2B)表达的影响,探讨低频电针对海洛因成瘾记忆干预作用的可能中枢机制。 方法：筛选无天然位置偏爱的雄性小鼠45只,随机分为对照组、海洛因心理依赖模型组（模型组）、模型电针组（模针组）,每组15只。海洛因剂量递增注射结合条件性位置偏爱（conditioned place preference, CPP）训练制作海洛因心理依赖模型,2Hz低频电针“内关”、“三阴交”,点刺“四神聪”穴。采用白箱CPP值变化评价低频电针治疗效应,免疫组化方法检测海马NMDA受体亚型（NR1、NR2A、NR2B）的表达。 结果：①模针组白箱CPP值较模型组明显降低(P＜0.05)。②模针组小鼠NR1、NR2B阳性表达较模型组增强(P＜0.05)。③模针组小鼠NR2A阳性表达较模型组降低(P＜0.05)。 结论：低频电针疗法能增强海洛因心理依赖小鼠海马NR1、NR2B,降低NR2A的阳性表达。这种改变可能与低频电针调节海洛因依赖的机制有关。     

Effects of adrenal steroid manipulations and repeated restraint stress on dynorphin mRNA levels and excitatory amino acid receptor binding in hippocampus

Adrenal steroid and stress effects were determined in hippocampus on levels of dynorphin (DYN) mRNA, expressed in dentate gyrus, and excitatory amino acid receptors, measured in Ammon's horn and dentate gyrus. Adrenalectomy (ADX) decreased DYN mRNA levels in dentate gyrus and replacement with aldosterone (ALDO), a specific type I adrenal steroid receptor agonist, prevented the decrease. Ru28362, a specific type II receptor agonist, had no effect. Likewise, kainate receptor binding to the stratum lucidum and hilus region of dorsal hippocampus was decreased after ADX and this decrease was prevented by ALDO but not by Ru28362 treatment. Similar though smaller effects were found for CNQX binding to AMPA receptors but only in the dentate gyrus molecular or infra- and supragranular layers. Although corticosterone (CORT) treatment of intact rats (40 mg/kg for 3 weeks) elevated DYN mRNA levels in dentate gyrus, up to 14 days of daily restraint stress (1 or 6 h/day) had no significant effect. Neither CORT treatment nor repeated restraint stress altered NMDA and non-NMDA glutamate receptors in hippocampus. The results of this study showing ADX-induced decreases of DYN mRNA and CNQX binding in dentate gyrus and decreased kainate binding in mossy fiber terminal regions are consistent with morphological evidence showing that adrenal steroids maintain normal integrity and structure of dentate gyrus neurons and do so via type I adrenal steroid receptors. These same parameters are apparently not sensitive to chronic restraint stress although the effects of other stressors must be examined.     

N-甲基-D-天门冬氨酸诱导Wistar乳鼠癫痫发作West综合征动物模型的初步探讨

目的:探讨NMDA诱发Wistar乳鼠惊厥发作的表现及皮质脑电图特点和建立West综合征动物模型的可能性。方法:选用12日龄Wistar乳鼠系统地进行腹腔注射NMDA诱导癫痫发作,对其痫性发作的类型、潜伏期、发病率及行为改变和皮质脑电图变化作以相应记录。结果:12~13日龄的Wistar乳鼠引出甩尾等自动症及前弓反张发作,14～25日龄的Wistar乳鼠只有自动症而没有前弓反张发作。对照组皮质脑电图无明显癫痫性波形发放,仅可见偶发棘波,NMDA处理组则在自动症及惊厥发作期间出现某些特征性改变。对照组及NMDA处理组在组织形态学方面未见明显异常改变。结论:NMDA可以诱导Wistar乳鼠产生一种独特的、年龄依赖性癫痫发作,虽未满足West综合征动物模型的全部标准,但发作表现和脑电图改变与儿童时期West综合征有相似之处。     

Amygdala lesions block the amnestic effects of diazepam

This experiment examined the effects of pre-training systemic injections of the benzodiazepine (BZ) diazepam (DZP) on learning and retention of an inhibitory avoidance response in rats with bilateral lesions of the amygdaloid complex (AC) induced by intra-amygdala injections of the excitotoxin N-methyl-D-aspartic acid (NMDA). Unoperated, sham-operated and AC-lesioned rats received i.p. injections of DZP (1.0 or 2.0 mg/kg) or vehicle 30 min prior to training in a continuous multiple-trial inhibitory avoidance task. Retention was tested 48 h later. The acquisition and retention of the AC-lesioned rats were impaired, relative to that of the unoperated and sham controls. In the unoperated and sham controls, DZP impaired retention but did not affect acquisition. In contrast, in animals with AC lesions, DZP did not affect either acquisition or retention. These findings suggest that the amnestic effects of DZP are mediated, at least in part, through influences involving the AC.     

帕金森病运动并发症发生机制中G蛋白偶联受体激酶6与N-甲基-D-天冬氨酸受体关系的研究

Objective To investigate the relationship between G protein-coupled receptor kinase 6 (GRK6) and N-methyl-D-aspartate (NMDA) receptor in the mechanism study underlying motor complications in Parkinson's disease (PD).Methods The rat models (n= 25) of Parkinsonism related motor complications were established and were randomly divided into levodopa-induced dyskinesia (LID) group (n= 10,intraperitoneal injection of levodopa for 23 d),MK-801 treatment group (n= 10,intraperitoneal injection of MK-801 at day23 after intraperitoneal injection with levodopa for 22 days) and PD group (n= 5,intraperitoneal injection of vitamin C).Another 5 rats were served as controls (sham-operation group).The behavior changes of rats in MK-801 treatment group were observed,and the expression of GRK6 in the striate of rats was detected by immunohistochemistry and Western blot.Results After the chronic treatment with levodopa methyl ester,PD rats displayed abnormal involuntary movements,which was similar to levodopainduced dyskinesia in PD patients.Immunohistochemistry showed that GRK6-positive cells of lesion side were decreased in LID rats as compared with PD rats [(3.23±0.41 ) × 103 vs.(4.81 ± 1.31 ) ×103,P＜0.01].Rats in MK-801 treatment group displayed the decreased AIM scores and increased peak rotation,and the increased GRK6-positive cells of lesion side as compared with LID rats (P＜0.05).Western blot showed that the levels of GRK6 was 83.7% ±2.1% in PD group (presented as lesion side/unlesion side),76.8% ± 2.2% in LID group and 91.1% ± 2.7% in MK-801 treatment group (intergroups comparison:all P＜0.05).These results were in accordance with the results of immunohistochemistry.Conclusions Antagonist of NMDA receptor can be used to reduce the motor complications in rats.It may be due to increased GRK6 which inhibits the overactivation of glutamic acid receptors.     

Effect of CGS 19755, a competitive N-methyl-D-aspartate antagonist, on general anesthetic potency

CGS 19755 is a competitive N-methyl-D-aspartate (NMDA) receptor antagonist which penetrates the blood-brain barrier. The effect of pretreatment with subanesthetic doses of CGS 19755 on general anesthetic potency was determined in mice. Mice were pretreated with saline or CGS 19755 by intraperitoneal (IP) administration 30 min before IP administration of an anesthetic dose of ethanol or pentobarbital or measurement of the volatile anesthetic minimum alveolar concentration (MAC). CGS 19755 increased the duration of ethanol- and pentobarbital-induced loss of righting reflex in a dose-dependent manner. The highest dose of CGS 19755 tested, 50 mg/kg, increased duration of loss of righting reflex by about four- and twofold for ethanol and pentobarbital, respectively. CGS 19755 also decreased the MAC for halothane. However, CGS 19755 pretreatment had no effect on the MAC for diethyl ether. These results suggest that the potency of certain general anesthetic agents can be increased by antagonism of brain NMDA receptors.