Differential roles of NMDA and non-NMDA receptor activation in induction and maintenance of thermal hyperalgesia in rats with painful peripheral mononeuropathy

Central activation of excitatory amino acid receptors has been implicated in neuropathic pain following nerve injury. In a rat model of painful peripheral mononeuropathy, we compared the effects of non-competitive NMDA receptor antagonists (MK 801 and HA966) and a non-NMDA receptor antagonist (CNQX) on induction and maintenance of thermal hyperalgesia induced by chronic constrictive injury (CCI) of the rat common sciatic nerve. Thermal hyperalgesia to radiant heat was assessed by using a foot-withdrawal test and NMDA/non-NMDA receptor antagonists were administered intrathecally onto the lumbar spinal cord before and after nerve injury. Four daily single treatments with 20 nmol HA966 or CNQX beginning 15 min prior to nerve ligation (pre-injury treatment), reliably reduced thermal hyperalgesia in CCI rats on days 3, 5, 7 and 10 after nerve ligation. Thermal hyperalgesia was also reduced in CCI rats receiving a single post-injury treatment with HA966 (20 or 80 nmol) or MK 801 (5 or 20 nmol) on day 3 after nerve ligation when thermal hyperalgesia was well developed. In contrast, a single post-injury CNQX (20 or 80 nmol) treatment failed to reduce thermal hyperalgesia or to potentiate effects of HA966 or MK 801 (5 or 20 nmol) on thermal hyperalgesia in CCI rats. Moreover, multiple post-injury CNQX treatments utilizing the same dose regime as employed for the pre-injury treatment attenuated thermal hyperalgesia but only when the treatment began 1 or 24 h (but not 72 h) after nerve ligation.(ABSTRACT TRUNCATED AT 250 WORDS)     

NMDA receptor mediated dendritic plasticity in cortical cultures after oxygen-glucose deprivation

Dendrites and spines undergo dynamic changes in physiological and pathological conditions. Dendritic outgrowth has been observed in surviving neurons months after ischemia, which is associated with the functional compensation. It remains unclear how dendrites in surviving neurons are altered shortly after ischemia, which might reveal the mechanisms underlying neuronal survival. Using primary cortical cultures, we monitored the dendritic changes in individual neurons after oxygen-glucose deprivation (OGD). Two to four hours of OGD induced approximately 30–50% cell death in 24 h. However, the total dendritic length in surviving neurons was significantly increased after OGD with a peak at 6 h after re-oxygenation. The increase of dendritic length after OGD was mainly due to the sprouting rather than the extension of the dendrites. The dendritic outgrowth after 2 h of OGD was greater than that after 4 h of OGD. Application of NMDA receptor blocker MK-801 abolished OGD-induced dendritic outgrowth, whereas application of AMPA receptor antagonist CNQX had no significant effects. These results demonstrate a NMDA receptor-dependent dendritic plasticity shortly after OGD, which provides insights into the early response of surviving neurons after ischemia.     

非NMDA受体拮抗剂对大鼠牙髓伤害性刺激诱导的延髓Fos表达

目的 研究兴奋性氨基酸非ＮＭＤＡ受体在牙髓伤害性信息传递中的作用,为揭示牙痛的产生机制打下基础。方法 将实验动物随机分为４组。第１组单纯给予机械穿髓刺激;第２组预先侧脑室注射非ＮＭＤＡ受体拮抗剂ＣＮＱＸ,再给予相同的穿髓刺激;第３组只行ＣＮＱＸ侧脑室注射,不予穿髓刺激;第４组为正常对照组。动物存活相同时间后取延髓做Ｆｏｓ蛋白免疫组化反应。观察３组动物Ｆｏｓ免疫反应阳性细胞的数量与第１组比较没有显著     

Activation of medial prefrontal cortex neurons by phencyclidine is mediated via AMPA/kainate glutamate receptors in anesthetized rats

Phencyclidine (PCP) is a psychotomimetic drug that elicits schizophrenia-like symptoms in healthy individuals, and animals administered PCP are now considered a reliable pharmacological model of schizophrenia. Recent studies have shown that systemically administered PCP produces long-lasting activation of medial prefrontal cortex (mPFC) neurons, and that hyperactivation of mPFC neurons plays a critically important role in the development of PCP-induced behavioral abnormalities. However, the receptors mediating this mPFC activation have not been clearly determined. Here, we examined the effects of local application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an AMPA/kainate glutamate receptor antagonist, scopolamine, a muscarinic acetylcholine receptor antagonist, and mecamylamine, a nicotinic acetylcholine receptor antagonist, on the increase in firing rate of mPFC neurons induced by systemic PCP in anesthetized rats. After tonic activation of mPFC neurons by PCP had been established, CNQX, scopolamine, or mecamylamine was iontophoretically applied or pressure-ejected on the recorded neuron. CNQX suppressed PCP-induced elevation of firing rate to baseline level, though scopolamine and mecamylamine each induced little change in firing rate. These findings suggest that PCP-induced activation of mPFC neurons is mediated primarily via AMPA/kainate glutamate receptors.     

Glutamatergic systems in the bed nucleus of the stria terminalis,effects on cardiovascular system

The bed nucleus of the stria terminalis (BST) is a part of the limbic system. Two studies have shown that microinjection of l-glutamate in the BST elicited cardiovascular depressive and bradycardic responses, but in one study, both pressor and depressor responses were observed in the chemical stimulation of BST by glutamate in the urethane-anesthetized rats. Also, the roles of glutamate receptor subtypes have not been investigated yet. The aim of this study was to find the effects of glutamate and its receptors on the blood pressure and heart rate in the BST of urethane-anesthetized rats. The drugs (50 nl) were microinjected into the BST of anaesthetized rats. The blood pressure and heart rate were recorded throughout each experiment. The average changes in the mean arterial pressure and heart rate at different intervals were compared both within each case group and between the case and the control groups, using repeated measures ANOVA. Microinjection of l-glutamate (0.25 M) into the BST resulted in the decrease of the mean arterial pressure (−18.85 ± 3.84 mmHg) and heart rate (−18 ± 4 beats/min). Injection of AP5, antagonist of glutamate NMDA receptor (2.5 , 5 mM) and CNQX, antagonist of glutamate AMPA receptor (0.5, 1 mM) had no significant effect on the mean arterial pressure and heart rate. Either Ap5 or CNQX, when co-injected with glutamate, abolished the depressor and bradycardic effects of glutamate, suggesting that simultaneous activation of both glutamate receptors is necessary for the effect of glutamate system to emerge.     

CNQX对伤害性刺激隐神经诱发大鼠脊髓Fos蛋白表达的影响

目的 探讨伤害性刺激隐神经（SN）能否诱发脊髓神经元Fos蛋白表达及发生机制.方法 应用免疫组化方法观察伤害性刺激SN和尾静脉注射谷氨酸非NMDA受体拮抗剂（CNQX）后诱发脊髓神经元Fos蛋白表达的变化.结果 伤害性刺激SN后,诱导脊髓神经元Fos蛋白表达显著增强,CNQX拮抗了Fos蛋白表达的显著增强.结论 以伤害性刺激SN模拟躯体痛后,CNQX拮抗了伤害性刺激SN引起的脊髓神经元Fos蛋白表达的显著增加,表明非NMDA受体在躯体痛的调控中起到了重要的作用.     

CNQX对乙醇、乙醛调控大脑皮质神经元神经甾体水平的影响

目的 研究乙醇、乙醛对原代培养大鼠大脑皮质神经元神经甾体水平的影响以及与AMPA受体调控的相关性. 方法 应用AMPA受体拮抗剂CNQX阻断AMPA受体,用50mmol/L乙醇或25 mmol/L乙醛处理神经元,收集细胞培养上清,采用高效液相色谱质谱法分离测定游离型神经甾体孕烯醇酮(PREG)、脱氢表雄酮(DHEA)、别孕烯醇酮(AP)及结合型神经甾体脱氢表雄酮硫酸酯(DHEAS)、孕烯醇酮硫酸酯(PREGS)的含量,观察CNQX对乙醇、乙醛调控原代培养神经元神经甾体水平的影响. 结果乙醇可明显升高神经元PREG、AP和PREGS的水平,与PBS对照组比较差异有统计学意义(P＜0.05);乙醛可明显升高神经元PREG、DHEA、PREGS和DHEAS的水平,与PBS对照组比较差异有统计学意义(P＜0.05).CNQX反转了乙醇升高PREG、PREGS水平的作用以及乙醛升高PREG、DHEAS水平的作用,却使AP水平明显升高,组间比较差异有统计学意义(P＜0.05). 结论 乙醇、乙醛对大脑皮质神经元神经甾体PREG、DHEA、AP、PREGS和DHEAS的影响各不相同,CNQX反转了乙醇上调PREG、PREGS水平的作用以及乙醛上调PREG、DHEAS水平的作用.     

Differential effects of NMDA and AMPA/kainate receptor antagonists on superoxide production and MnSOD activity in rat brain following intrahippocampal injection

The involvement of NMDA and AMPA/kainate receptors in the induction of superoxide radical production in the rat brain was examined after injection of kainate, non-NMDA receptor agonist, kainate plus 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), selective AMPA/kainate receptor antagonist, or kainate plus 2-amino-5-phosphonopentanoic acid (APV), selective NMDA receptor antagonist. Competitive glutamate receptor antagonists were injected with kainate unilaterally into the CA3 region of the rat hippocampus. We investigated superoxide production and mitochondrial MnSOD activity after injection. The measurements took place at different times (5, 15 min, 2, 48 h and 7 days) in the ipsi- and contralateral hippocampus, forebrain cortex, striatum, and cerebellum homogenates. Used glutamate antagonists APV and CNQX both expressed sufficient neuroprotection in sense of decreasing superoxide production and increasing MnSOD levels, but with differential effect in mechanisms and time dynamics. Our findings suggest that NMDA and AMPA/kainate receptors are differentially involved in superoxide production. Following intrahippocampal antagonists injection they, also, interpose different neuroprotection effect on the induction of MnSOD activity in distinct brain regions affected by the injury, which are functionally connected via afferents and efferents. It suggests that MnSOD protects the cells in these regions from superoxide-induced damage and therefore may limit the retrograde and anterograde spread of neurotoxicity.     

Comparative analysis of the pharmacology of GluR1 in complex with transmembrane AMPA receptor regulatory proteins gamma2, gamma3, gamma4, and gamma8

AMPA receptors (AMPARs) mediate the majority of fast synaptic transmission in the CNS of vertebrates. They are believed to be associated with members of the transmembrane AMPA receptor regulatory protein (TARP) family. TARPs mediate the delivery of AMPA receptors to the plasma membrane and mediate their synaptic trafficking. Moreover, TARPs modulate essential electrophysiological properties of AMPA receptors. Here, we compare the influence of rat TARPs (gamma2, gamma3, gamma4, and gamma8) on pharmacological properties of rat GluR1(Q)flip. We show that agonist potencies are increased by all TARPs, but to individually different extents. On the other hand, all TARPs increase agonist potencies at the virtually non-desensitizing mutant GluR1-L479Y almost identically. Comparison of the influence of individual TARPs on relative agonist efficacies confirmed that the TARPs can be functionally subdivided into two subgroups, one consisting of gamma2 and gamma3 and one consisting of gamma4 and gamma8. Surprisingly, we found that TARPs convert certain AMPA receptor antagonists to agonists. The potency of one of these converted antagonists is dependent on the particular TARP. Moreover, TARPs (except gamma4) reduce the ion channel block by the synthetic Joro spider toxin analog 1-naphthylacetyl spermine (NASP). In addition, TARPs increase the permeability of the receptor to calcium, indicating that TARPs directly modulate important ion pore properties. In summary, the data presented herein will illustrate and help to understand the previously unexpected complexities of modulation of AMPA receptor pharmacological properties by TARPs.     

NBQX, an improved non-NMDA antagonist studied in retinal ganglion cells

The quinoxaline derivative, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo (F) quinoxaline (NBQX), significantly reduced the currents evoked by exogenous application of quisqualate (QQ), kainate (KA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) when applied to ganglion cells, using whole-cell recording in a slice preparation of the tiger salamander retina. A comparison between NBQX and CNQX indicates that NBQX is more effective in blocking AMPA receptors. Also, at up to 10 μM, NBQX has no effect on NMDA-induced currents. Thus at this concentration, NBQX shows no affinity for the glycine binding site of NMDA receptors. For this reason, NBQX is preferred over CNQX for a more effective and selective antagonism toward non-NMDA receptors.