兴奋性氨基酸介导脊髓伤害性信息传递

ＮＭＤＡ和非ＮＭＤＡ受体广泛存在于猫脊髓背角神经元上,并参与介导伤害性信息传递;ＮＭＤＡ受体主要介导皮肤的伤害性传入,非ＮＭＤＡ受体则主要介导肌肉和内脏的伤害性传入;皮肤和肌肉的伤害性传入分别诱发释放更多的门冬氨酸和谷氨酸可能是这种差别的主要原因之一;ＮＭＤＡ受体的不同调节位点在伤害性信息传递中有密切的协同作用;兴奋性氨基酸和Ｐ物质及其受体在介导和调制伤害性信息传递中的相互作用可以分别发生在神经元     

NMDA受体与中枢神经系统发育

中枢神经系统兴奋性氨基酸离子型受体－ＮＭＤＡ受体,是由ＮＭＤＡＲ１和ＮＭＤＡＲ２两个亚单位共同构成的受体通道复合体。ＮＭＤＡ受本激活后可引起神经元细胞对Ｎａ＾＋,Ｋ＾＋和Ｃａ＾２＋通透性增强,产生兴奋性突触后电位,在中枢神经发育的过程中,ＮＭＤＡ受体通过不同亚型的选择性表达,改变自身的结构和功能,进而影响ＮＭＤＡ受体介导的Ｃａ＾２＋内流,调节神经元内Ｃａ＾２＋依赖的第二信使系统,最终实现对中枢神经     

微透析测试刺激皮肤和肌肉神经引起的天门冬氨酸和谷氨酸在脊髓的释放

为分析ＮＭＤＡ和非ＮＭＤＡ受体在介导脊髓不同性质疼痛的机能分化,应用微透析技术,测量刺激皮肤和肌肉神经引起的天门冬氨酸（Ａｓｐ）和谷氨酸（Ｇｌｕ）在脊髓背角的释放。电刺激皮肤神经兴奋Ｃ纤维诱发的Ａｓｐ和Ｇｌｕ的释放分别是基础值的（３２３±５５）％（Ｐ＜００１）和（１６９±１６）％（Ｐ＜００５）;电刺激肌肉神经兴奋Ｃ纤维诱发的Ａｓｐ和Ｇｌｕ的释放分别是基础值的（１５０±１６）％（Ｐ＜００１）和（２１８±４２）％（Ｐ＜００５）。兴奋皮肤传入引起的Ａｓｐ释放明显高于Ｇｌｕ的释放（约３倍）;而兴奋肌肉传入引起的Ｇｌｕ释放明显高于Ａｓｐ的释放（约２倍）。从而提示,皮肤伤害性传入主要引起Ａｓｐ的释放增加,而肌肉的伤害性传入则主要引起Ｇｌｕ的释放增加,它们分别主要作用于ＮＭＤＡ和非ＮＭＤＡ受体而介导不同的痛传入信息。     

竞争性NMDA受体拮抗剂

ＭＮＤＡ受体拮抗剂主要分为二大类,即竞争性拮抗剂和非竞争性拮抗剂,本文综述了竞争性ＮＭＤＡ受体拮抗剂的研究进展。     

谷氨酸NMDA受体与惊厥

本文介绍了近几年对谷氨酸ＮＭＤＡ受体的研究进展,并就中枢神经系统中,ＮＭＤＡ受体发育,分布特点及其受体激动剂与拮挤在惊厥中的作用等方面探讨了该受体与惊厥产生,发展和扩散的关系,同时也概述了惊厥发生机制中ＮＭＤＡ受体可能起的作用。     

大脑皮层神经元NMDA受体的单通道特性

本文用膜片箝技术对机械分离培养的大鼠大脑皮层神经元胞体上的ＮＭＤＡ受体的单通道特性进行了研究,实验用细胞贴附和内面向外两种形式记录单离子通道的活动。电极液内含有ＮＭＤＡ或Ｌ－门冬氨酸时,在皮层神经元上常见电导为３５ｐＳ的离子通道。通道对Ｎａ＋,Ｋ＋非选择性通透,对Ｃｌ－不通透,其平均开放时间和开放概率随超极化程度增大而降低。开放、关闭时间及ｂｕｒｓｔ时程的分布直方图均需双指数拟合。Ｍｇ２＋以电压和浓度依赖性的方式减小通道开放时间,ＡＰＶ能阻断通道活动,温度降低使通道开放时间延长及电流幅度减小。本文结果表明大脑皮层神经元上ＮＭＤＡ受体通道活动自身具有电压依赖性,因此提示ＮＭＤＡ受体通道的正常功能活动可能依赖于某些细胞内调控过程的存在。     

NMDA受体拮抗剂对阿片类药物耐受和依赖的阻断作用

本文综述阻断ＮＭＤＡ受体离子通道复合药物对阿惩耐受和成瘾发生的影响。行为药理学研究显示,非竞争性ＮＭＤＡ受体拮抗剂、竞争性ＮＭＤＡ受体拮抗剂和甘氨酸受占拮抗剂能抑制阿片耐受和戒断反应,其药理学特性明显不同于其他类型抗阿片耐受和成瘾的药物,阐述了ＮＭＤＡ受体拮抗剂治疗阿片类芗耐受和领事的系列化机制。并指出ＮＭＤＡ受体拮抗剂具有神经毒性。     

氯氨酮和L-NAME抑制模拟高原低氧大鼠下丘脑NOS和生长抑素mRNA的表达

用高原低氧模型及原位杂交、ＮＡＤＰＨ－ｄ组织化学法,探讨氯氨酮和Ｌ－ＮＡＭＥ对急性高原低氧大鼠下丘脑一氧化氮合酶（ＮＯＳ）和生长抑素ｍＲＮＡ（ＳＳ ｍＲＮＡ）表达的影响。结果表明,急性高原低氧引起下丘脑ＮＯＳ和ＳＳ ｍＲＮＡ过度表达,如先用ＮＭＤＡ受体拮抗剂氯氨酮和ＮＯＳ抑制剂Ｌ－ＮＡＭＥ预处理,ＮＯＳ和ＳＳ ｍＲＮＡ的表达均明显被抑制。结果提示,ＮＭＤＡ受体参与了急生高原低氧引起的下丘脑ＮＯＳ和     

小鼠大脑皮质N—甲基—D—天冬氨酸受体的鉴定及其的衰老时的变化

以放射性配基结合分析法对正常成年小鼠大脑皮中Ｎ－甲基－Ｄ－天冬氨酸（ＮＭＤＡ）受体作了鉴定;观察了衰老小鼠ＮＭＤＡ受体、空间辨别能力、海马突触传递长时程增强的变化及补肾中药复方对这些变化的影响。结果表明：小鼠大脑皮质含有丰富的、高亲和力的ＮＭＤＡ受体;衰老过程中小鼠ＮＭＤＡ受体的最大结合容量Ｂｍａｘ）呈渐进性降低,空间辨别能力下降,ＬＴＰ的振幅和斜率明显降低;补肾中药复方具有提高衰才小鼠ＮＭＤＡ受     

AMPA和KA受体通道的分子结构及功能特性

近期的克隆研究证实,尽管α－氨基－３－羧基－５－甲基异恶唑－４－丙酸（ＡＭＰＡ）和红藻氨酸（ＫＡ）受体能被相同的激动剂激活,但它们是不同的相互独立的受体复合体。同时,已经证明非Ｎ－甲基－门冬氨酸（ＮＭＤＡ）受体的某些亚型具有Ｃａ＾２＋通透性,这种特性以前认为只有ＮＭＤＡ受体才具有。     

GABAergic disinhibition facilitates polysynaptic excitatory transmission in rat anterior cingulate cortex

Various studies implicate the anterior cingulate cortex (ACC) in processing pain. Combining whole-cell patch clamp recordings in rat ACC slices and a formalin-induced conditioned place avoidance (F-CPA) behavioral model, the present study was to address the effect of GABA(A) receptors on excitatory transmission to ACC layer V neurons and its possible functional significance related to pain. Removal of GABA(A) inhibition by bicuculline (10 microM) induced a novel long-lasting response in layer V neurons, which could be blocked by high divalent extracellular solution and was sensitive to relatively higher rate stimuli. Co-application of NMDA receptor antagonist APV (50 microM) and non-NMDA receptor antagonist DNQX (10 microM) completely blocked the responses. Enhancement of inhibition by intra-ACC microinjection of muscimol abolished the acquisition of F-CPA without affecting formalin-induced acute nociceptive responses. These results suggest that GABA(A) inhibition may be involved in pain-related aversion by modulating glutamate-mediated excitatory transmission in the ACC.     

Direct Evidence That Excitotoxicity in Cultured Neurons Is Mediated via N-Methyl-D-Aspartate (NMDA) as well as Non-NMDA Receptors

Cultured GABAergic cerebral cortex neurons were exposed to the excitatory amino acid (EAA) L-glutamate, kainate (KA), N-methyl-D-aspartate (NMDA), or RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionate (AMPA). To ensure a constant glutamate concentration in the culture media during the exposure periods, the glutamate uptake inhibitor L-aspartic acid beta-hydroxamate was added at 500 microM to the cultures that were exposed to glutamate. Each of these EAAs was able to induce neurotoxicity. It was not possible to reduce or prevent glutamate-induced cytotoxicity by blocking only one of the glutamate receptor subtypes with either the NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoate (APV) or with one of the specific non-NMDA antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX). However, if the cultures were exposed simultaneously to glutamate and the antagonists in combination, i.e., APV plus CNQX or APV plus DNQX, the toxicity was completely prevented. Furthermore, CNQX and DNQX were shown to be selective blockers of cytotoxic phenomena induced by non-NMDA glutamate agonists with no effect on NMDA-induced cell death. Likewise, APV prevented NMDA-induced cell death without affecting the KA- or AMPA-induced neurotoxicity. It is concluded that EAA-dependent neurotoxicity is induced by NMDA as well as non-NMDA receptors.     

Role of the medullary lateral tegmental field in reflex-mediated sympathoexcitation in cats

We tested the hypothesis that blockade of N-methyl-D-aspartate (NMDA) and non-NMDA receptors on medullary lateral tegmental field (LTF) neurons would reduce the sympathoexcitatory responses elicited by electrical stimulation of vagal, trigeminal, and sciatic afferents, posterior hypothalamus, and midbrain periaqueductal gray as well as by activation of arterial chemoreceptors with intravenous NaCN. Bilateral microinjection of a non-NMDA receptor antagonist into LTF of urethane-anesthetized cats significantly decreased vagal afferent-evoked excitatory responses in inferior cardiac and vertebral nerves to 29 +/- 8 and 24 +/- 6% of control (n = 7), respectively. Likewise, blockade of non-NMDA receptors significantly reduced chemoreceptor reflex-induced increases in inferior cardiac (from 210 +/- 22 to 129 +/- 13% of control; n = 4) and vertebral nerves (from 253 +/- 41 to 154 +/- 20% of control; n = 7) and mean arterial pressure (from 39 +/- 7 to 21 +/- 5 mmHg; n = 8). Microinjection of muscimol, but not an NMDA receptor antagonist, caused similar attenuation of these excitatory responses. Sympathoexcitatory responses to the other stimuli were not attenuated by microinjection of a non-NMDA receptor antagonist or muscimol into LTF. In fact, excitatory responses elicited by stimulation of trigeminal, and in some cases sciatic, afferents were enhanced. These data reveal two new roles for the LTF in control of sympathetic nerve activity in cats. One, LTF neurons are involved in mediating sympathoexcitation elicited by activation of vagal afferents and arterial chemoreceptors, primarily via activation of non-NMDA receptors. Two, non-NMDA receptor-mediated activation of other LTF neurons tonically suppresses transmission in trigeminal-sympathetic and sciatic-sympathetic reflex pathways.     

Formation and maintenance of ventilatory long-term facilitation require NMDA but not non-NMDA receptors in awake rats

N-methyl-d-aspartate (NMDA) receptor antagonism in the phrenic motonucleus area eliminates phrenic long-term facilitation (pLTF; a persistent augmentation of phrenic nerve activity after episodic hypoxia) in anesthetized rats. However, whether NMDA antagonism can eliminate ventilatory LTF (vLTF) in awake rats is unclear. The role of non-NMDA receptors in LTF is also unknown. Serotonin receptor antagonism before, but not after, episodic hypoxia eliminates pLTF, suggesting that serotonin receptors are required for induction, but not maintenance, of pLTF. However, because NMDA and non-NMDA ionotropic glutamate receptors are directly involved in mediating the inspiratory drive to phrenic, hypoglossal, and intercostal motoneurons, we hypothesized that these receptors are required for both formation and maintenance of vLTF. vLTF, induced by five episodes of 5-min poikilocapnic hypoxia (10% O(2)) with 5-min normoxia intervals, was measured with plethysmography in conscious adult male Sprague-Dawley rats. Either (+/-)-2-amino-5-phosphonovaleric acid (APV; NMDA antagonist, 1.5 mg/kg) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; non-NMDA antagonist, 10 mg/kg) was systemically (ip) injected approximately 30 min before hypoxia. APV was also injected immediately after or 20 min after episodic hypoxia in additional groups. As control, vehicle was similarly injected in each rat 1-2 days before. Regardless of being injected before or after episodic hypoxia, vehicle did not alter vLTF ( approximately 23%), whereas APV eliminated vLTF while having little effect on baseline ventilation or hypoxic ventilatory response. In contrast, CNQX enhanced vLTF ( approximately 34%) while decreasing baseline ventilation. Collectively, these results suggest that activation of NMDA but not non-NMDA receptors is necessary for formation and maintenance of vLTF in awake rats.     

NMDA as well as non-NMDA receptor antagonists can prevent the phase-shifting effects of light on the circadian system of the golden hamster.

The present experiments were designed to evaluate whether the intraventricular administration of excitatory amino acid (EAA) receptor antagonists would prevent light-induced phase shifts of the circadian rhythm of wheel-running activity in the hamster. Administration of the non-N-methyl-D-aspartate (non-NMDA) antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) blocked light-induced phase advances and delays. Similarly, administration of the competitive NMDA receptor antagonist, 3(2-carboxypiperazin-4-yl)-propyl-l-phosphonic acid (CPP), prevented light-induced phase advances and delays. Neither drug by itself caused any consistent effect on the phase of the rhythm. These data provide further evidence that EAA receptors mediate the effects of light on the circadian system, and suggest that both NMDA and non-NMDA receptor types may be involved.     

NMDA and non-NMDA receptors mediate responses in the primary gustatory nucleus in goldfish

Primary gustatory afferents from the oropharynx of the goldfish, Carassius auratus, terminate in the vagal lobe, a laminated structure in the dorsal medulla comparable to the gustatory portion of the nucleus of the solitary tract in mammals. We utilized an in vitro brain slice preparation to test the role of different ionotropic glutamate receptor subtypes in synaptic transmission of gustatory information by recording changes in field potentials after application of various glutamate receptor antagonists. Electrical stimulation of the vagus nerve (NX) evokes two short-latency postsynaptic field potentials from sensory layers of the vagal lobe. 6,7-Dinitroquinoxaline-2,3-dione and 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione, two non-N-methyl-D-aspartate (NMDA) ionotropic receptor antagonists, blocked these short-latency potentials. Slower potentials that were revealed under Mg2+ -free conditions, were abolished by the NMDA receptor antagonist, D(-)-2-amino-5-phosphonovaleric acid (APV). Repetitive stimulation produced short-term facilitation, which was attenuated by application of APV. These results indicate that the synaptic responses in the vagal lobe produced by stimulation of the gustatory roots of the NX involve both NMDA and non-NMDA receptors. An NMDA receptor-mediated facilitation may serve to amplify incoming bursts of primary afferent activity.     

Excitatory synaptic currents in Purkinje cells

The N-methyl-D-aspartate (NMDA) and non-NMDA classes of glutamate receptor combine in many regions of the central nervous system to form a dual-component excitatory postsynaptic current. Non-NMDA receptors mediate synaptic transmission at the resting potential, whereas NMDA receptors contribute during periods of postsynaptic depolarization and play a role in the generation of long-term synaptic potentiation. To investigate the receptor types underlying excitatory synaptic transmission in the cerebellum, we have recorded excitatory postsynaptic currents (EPSCS), by using whole-cell techniques, from Purkinje cells in adult rat cerebellar slices. Stimulation in the white matter or granule-cell layer resulted in an all-or-none synaptic current as a result of climbing-fibre activation. Stimulation in the molecular layer caused a graded synaptic current, as expected for activation of parallel fibres. When the parallel fibres were stimulated twice at an interval of 40 ms, the second EPSC was facilitated; similar paired-pulse stimulation of the climbing fibre resulted in a depression of the second EPSC. Both parallel-fibre and climbing-fibre responses exhibited linear current-voltage relations. At a holding potential of -40 mV or in the nominal absence of Mg2+ these synaptic responses were unaffected by the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV), but were blocked by the non-NMDA receptor antagonist 6-cyano-2,3-dihydro-7-nitroquinoxalinedione (CNQX). NMDA applied to the bath failed to evoke an inward current, whereas aspartate or glutamate induced a substantial current; this current was, however, largely reduced by CNQX, indicating that non-NMDA receptors mediate this response. These results indicate that both types of excitatory input to adult Purkinje cells are mediated exclusively by glutamate receptors of the non-NMDA type, and that these cells entirely lack NMDA receptors.     

Neurotransmission of autonomic components of aortic baroreceptor afferents in the NTS of awake rats

The effect of sequential blockade of N-methyl-D-aspartic acid (NMDA) receptors with DL-2-amino-5-phosphonopentanoic acid (AP-5) and non-NMDA receptors with 6,7-dinitroquinoxaline-2,3 dione (DNQX) in the nucleus tractus solitarii (NTS) on the cardiovascular responses to electrical stimulation (ES) of the aortic depressor nerve (ADN) was evaluated in awake rats. Two protocols were used. In protocol 1, bilateral microinjection of AP-5 into the NTS (n = 7) reduced the hypotensive response to ES of the ADN; subsequent microinjection of DNQX produced additional reduction in this response. AP-5 reduced the bradycardic response, and DNQX almost abolished this response. In protocol 2, bilateral microinjection of DNQX into the NTS (n = 6) reduced the hypotensive response, and subsequent microinjection of AP-5 significantly reduced this response. DNQX produced a significant reduction in bradycardic response, and AP-5 abolished this response. The data indicate that processing of the parasympathetic component of the NTS aortic baroreceptor afferents is mediated by both NMDA and non-NMDA receptors, whereas processing of the sympathoinhibitory component seems to be only partially mediated by ionotropic receptors.     

Somatostatin stimulates striatal acetylcholine release by glutamatergic receptors: an in vivo microdialysis study

The modulation of striatal cholinergic neurons by somatostatin (SOM) was studied by measuring the release of acetylcholine (ACh) in the striatum of freely moving rats. The samples were collected via a transversal microdialysis probe. ACh level in the dialysate was measured by the high performance liquid chromatography method with an electrochemical detector. Local administration of SOM (0.1, 0.5 and 1 microM) produced a long-lasting and concentration-dependent increase in the basal striatal ACh output. The stimulant effect of SOM was antagonized by the SOM receptor antagonist cyclo(7-aminopentanoyl-Phe-D-Trp-Lys-Thr[BZL]) (1 microM). In a series of experiments, we studied the effect of 6,7-dinitroquinoxaline-2, 3-dione (DNQX), a selective non-NMDA (N-methyl-D-aspartate) glutamatergic antagonist, on the basal and SOM-induced ACh release from the striatum. DNQX, 2 microM, perfused through the striatum had no effect on the basal ACh output but inhibited the SOM (1 microM)-induced ACh release. The non-NMDA glutamatergic receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3- benzodiazepine (GYKI-52466), 10 microM, antagonized the SOM (1 microM)-induced release of ACh in the striatum. Local administration of the NMDA glutamatergic receptor antagonist, 2-amino-5-phosphonopentanoic acid (APV), 100 microM, blocked SOM (1 microM)-evoked ACh release. Local infusion of tetrodotoxin (1 microM) decreased the basal release of ACh and abolished the 1 microM SOM-induced increase in ACh output suggesting that the stimulated release of ACh depends on neuronal firing. The present results are the first to demonstrate a neuromodulatory role of SOM in the regulation of cholinergic neuronal activity of the striatum of freely moving rats. The potentiating effect of SOM on ACh release in the striatum is mediated (i) by SOM receptor located on glutamatergic nerve terminals, and (ii) by NMDA and non-NMDA glutamatergic receptors located on dendrites of cholinergic interneurones of the striatum.     

AMPA and NMDA glutamate receptors are found in both peptidergic and non-peptidergic primary afferent neurons in the rat

Two distinct classes of nociceptive primary afferents, peptidergic and non-peptidergic, respond similarly to acute noxious stimulation; however the peptidergic afferents are more likely to play a role in inflammatory pain, while the non-peptidergic afferents may be more characteristically involved in neuropathic pain. Using multiple immunofluorescence, we determined the proportions of neurons in the rat L4 dorsal root ganglion (DRG) that co-express AMPA or NMDA glutamate receptors and markers for the peptidergic and non-peptidergic classes of primary afferents, substance P and P2X(3), respectively. The fraction of DRG neurons immunostained for the NR1 subunit of the NMDA receptor (40%) was significantly higher than that of DRG neurons immunostained for the GluR2/3 (27%) or the GluR4 (34%) subunits of the AMPA receptor. Of all DRG neurons double-immunostained for glutamate receptor subunits and either marker for peptidergic and non-peptidergic afferents, a significantly larger proportion expressed GluR4 than GluR2/3 or NR1 and in a significantly larger proportion of P2X(3)- than SP-positive DRG neurons. These observations support the idea that nociceptors, involved primarily in the mediation of neuropathic pain, may be presynaptically modulated by GluR4-containing AMPA receptors.