帕金森病大鼠模型纹状体中谷氨酸、γ-氨基丁酸与多巴胺之间的关系

目的:了解帕金森病大鼠模型纹状体内谷氨酸(glutamate,Glu)、γ-氨基丁酸(gama-aminobutyric acid,GABA)和多巴胺(dopamine,DA)之间的关系,从而进一步探讨帕金森病的发病机制。方法:动物分为溶剂对照组、假手术组和帕金森模型组。大脑右侧黑质致密部和前脑内侧束两点注射6-羟基多巴胺(6-hydroxydopamine,6-OHDA)建立帕金森病大鼠模型,溶剂对照组注入生理盐水,假手术组不注射任何药物,采用脑微透析术于建模后第3,4,5,6周连续动态透析大鼠毁损侧纹状体,结合高效液相色谱(HPLC)动态监测各组谷氨酸、GABA和多巴胺的变化。结果:(1)PD组纹状体内多巴胺含量到第5周仅为溶剂对照组和假手术组的1/5;(2)谷氨酸含量随建模时间逐渐升高,到第6周PD组是溶剂对照组和假手术组的1倍以上;(3)GABA含量呈下降趋势,到第6周约降至溶剂对照组、假手术组的1/2。结论:帕金森病大鼠模型纹状体内谷氨酸的变化与多巴胺分泌可能存在某种联系;GABA含量随建模时间的增加而下降。     

In vivo variation in metabotropic glutamate receptor subtype 5 binding using positron emission tomography and [11C]ABP688

The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in the pathophysiology of mood and anxiety disorders. Recently, a positron emission tomography (PET) tracer exhibiting high selectivity and specificity for mGluR5, 3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-¹¹C-methyl-oxime ([¹¹C]ABP688), was developed. In this work, eight healthy adult male humans were imaged twice to assess within-subject [¹¹C]ABP688 binding variability using PET. In seven of the eight subjects, significantly higher binding was observed during the second (retest) scan. This binding increase could not be definitively explained by differences in ligand injected mass or dose, or changes in metabolism between scans. In addition, this type of systematic binding increase was not observed in a [¹¹C]ABP688 test–retest study performed by our group on anaesthetized baboons. It is therefore possible that the increased binding was because of physiological changes occurring between scans, such as changes in endogenous glutamate levels. If PET imaging with [¹¹C]ABP688 could detect such differences, as preliminary evidence suggests, it could be used to help uncover the role of glutamate in the pathophysiology of brain disorders. However, regardless of its ability to detect endogenous glutamate differences, [¹¹C]ABP688 binding variability could make accurate assessments of drug occupancy or group differences using this ligand difficult.     

Knockout of GAD65 has major impact on synaptic GABA synthesized from astrocyte-derived glutamine

γ-Aminobutyric acid (GABA) synthesis from glutamate is catalyzed by glutamate decarboxylase (GAD) of which two isoforms, GAD65 and GAD67, have been identified. The GAD65 has repeatedly been shown to be important during intensified synaptic activity. To specifically elucidate the significance of GAD65 for maintenance of the highly compartmentalized intracellular and intercellular GABA homeostasis, GAD65 knockout and corresponding wild-type mice were injected with [1-¹³C]glucose and the astrocyte-specific substrate [1,2-¹³C]acetate. Synthesis of GABA from glutamine in the GABAergic synapses was further investigated in GAD65 knockout and wild-type mice using [1,2-¹³C]acetate and in some cases γ-vinylGABA (GVG, Vigabatrin), an inhibitor of GABA degradation. A detailed metabolic mapping was obtained by nuclear magnetic resonance (NMR) spectroscopic analysis of tissue extracts of cerebral cortex and hippocampus. The GABA content in both brain regions was reduced by ∼20%. Moreover, it was revealed that GAD65 is crucial for maintenance of biosynthesis of synaptic GABA particularly by direct synthesis from astrocytic glutamine via glutamate. The GAD67 was found to be important for synthesis of GABA from glutamine both via direct synthesis and via a pathway involving mitochondrial metabolism. Furthermore, a severe neuronal hypometabolism, involving glycolysis and tricarboxylic acid (TCA) cycle activity, was observed in cerebral cortex of GAD65 knockout mice.     

Cocaine causes deficits in radial migration and alters the distribution of glutamate and GABA neurons in the developing rat cerebral cortex

Prenatal cocaine exposure induces cytoarchitectural changes in the embryonic neocortex; however, the biological mechanisms and type of cortical neurons involved in these changes are not known. Previously, we found that neural progenitor proliferation in the neocortical ventricular zone (VZ) is inhibited by cocaine; here, we examine the changes in cortical neurogenesis and migration of glutamate and GABA neurons induced by prenatal cocaine exposure. Pregnant rats received 20 mg/kg of cocaine intraperitoneally twice at an interval of 12 h during three periods of neocortical neurogenesis. Neocortical area and distribution of developing neurons were examined by counting Tuj1+, glutamate+, or GABA+ cells in different areas of the cerebral cortex. Cocaine decreased neocortical area by reducing the size of the Tuj1+ layer, but only when administered during early periods of neocortical neurogenesis. The number of glutamatergic neurons was increased in the VZ but was decreased in the outer cortical laminae. Although the number of GABA+ neurons in the VZ of both the neocortex and ganglionic eminences was unchanged, GABA+ cells decreased in all other neocortical laminae. Tangential migration of GABA+ cells was also disrupted by cocaine. These findings suggest that in utero cocaine exposure disturbs radial migration of neocortical neurons, possibly because of decreased radial glia guiding support through enhanced differentiation of neocortical VZ progenitors. Cocaine interrupts radial migration of both glutamatergic and GABAergic neurons within the neocortex, in addition to the tangential migration of GABAergic neurons from the subcortical telecephalon. This may result in abnormal neocortical cytoarchitecture and concomitant adverse functional effects. Synapse 65:21–34, 2011. © 2010 Wiley‐Liss, Inc.     

Effects of acute cocaine or dopamine receptor agonists on AMPA receptor distribution in the rat nucleus accumbens

Changes in α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate receptor (AMPAR) surface expression in the rodent nucleus accumbens (NAc) are produced by cocaine exposure and implicated in addiction‐related behaviors. The direction of change depends on the animal's prior drug history. However, little is known about the effect of a single exposure to cocaine on AMPAR distribution in the NAc of untreated rats. This is essential information for interpreting the literature on AMPAR trafficking after repeated cocaine exposure. In this study, we used a protein crosslinking assay to determine the effect of a single cocaine injection on surface and intracellular AMPAR subunit levels in the rat NAc. We found increased AMPAR surface expression in the NAc 24 h, but not 30 min or 2 h, after cocaine injection. A major effect of cocaine is to increase extracellular dopamine (DA) levels, leading to DA receptor activation. Therefore, we also evaluated the effects of directly acting DA receptor agonists. In contrast to the effects of cocaine, AMPAR surface expression was significantly decreased 24 h after injection of the D2‐class agonist quinpirole, whereas no significant effects were produced by the D1‐class agonist SKF 81297 or the mixed DA agonist apomorphine. Our results show that the effects of a single cocaine exposure in drug‐ and injection‐naïve rats are distinct from those previously reported after repeated cocaine administration. They further suggest that cocaine exerts these effects by influencing neuronal circuits rather than simply stimulating NAc DA transmission. Synapse 65:54–63, 2011. © 2010 Wiley‐Liss, Inc.     

Synthesis,characterization, and monkey PET studies of [18F]MK‐1312, a PET tracer for quantification of mGluR1 receptor occupancy by MK‐5435

Two moderately lipophilic, high affinity ligands for metabotropic glutamate receptor subtype 1 (mGluR1) were radiolabeled with a positron‐emitting radioisotope and evaluated in rhesus monkey as potential PET tracers. Both ligands were radiolabeled with fluorine‐18 via nucleophilic displacement of the corresponding 2‐chloropyridine precursor with [¹⁸F]potassium fluoride. [¹⁸F] MK‐1312 was found to have a suitable signal for quantification of mGluR1 receptors in nonhuman primates and was more thoroughly characterized. In vitro autoradiographic studies with [¹⁸F] MK‐1312 in rhesus monkey and human brain tissue slices revealed an uptake distribution consistent with the known distribution of mGluR1, with the highest uptake in the cerebellum, moderate uptake in the hippocampus, thalamus, and cortical regions, and lowest uptake in the caudate and putamen. In vitro saturation binding studies in rhesus monkey and human cerebellum homogenates confirmed that [¹⁸F] MK‐1312 binds to a single site with a B_max/K_d ratio of 132 and 98, respectively. PET studies in rhesus monkey with [¹⁸F] MK‐1312 showed high brain uptake and a regional distribution consistent with in vitro autoradiography results. Blockade of [¹⁸F] MK‐1312 uptake with mGluR1 allosteric antagonist MK‐5435 dose‐dependently reduced tracer uptake in all regions of gray matter to a similarly low level of tracer uptake. This revealed a large specific signal useful for determination of mGluR1 receptor occupancy in rhesus monkey. Taken together, these results are promising for clinical PET studies with [¹⁸F] MK‐1312 to determine mGluR1 occupancy of MK‐5435. Synapse 2011. © 2010 Wiley‐Liss, Inc.     

微透析技术监测大鼠脑损伤

目的:探讨微透析技术在脑损伤后局部生化物质监测中的运用.方法:自由落体硬膜外撞击方法制作轻度和重度大鼠脑损伤模型,应用微透析技术收集损伤前后局部的细胞外液,观测损伤后透析液的谷氨酸含量(Glu)的动态变化,脑组织的病理改变和伤侧脑组织的含水量.结果:①损伤组谷氨酸基础水平与对照组基本相同,伤后迅速升高,30min达高峰...     

Evaluation of corpus geniculatum laterale and vitreous fluid by magnetic resonance spectroscopy in patients with glaucoma; a preliminary study

PurposeTo determine whether metabolite changes at cellular level occur in vitreous and lateral geniculate body (LGB) in patients with glaucoma by magnetic resonance spectroscopy (MRS).MethodsA total of 29 eyes of 29 patients with glaucoma, no existing ocular pathology and systemic disease (group 1), and 13 eyes of 13 healthy individuals whose routine ophthalmological examinations were normal (group 2) were included in the study. Single-voxel MRS examination was performed by placing region of interest in vitreous and LGB. Glutamate-glutamine (Glx)/creatin (Cr) ratios and lactate peaks in the vitreous, and the Glx/Cr, N-acetyl aspartate (NAA)/Cr, choline (Cho)/Cr ratios in the ipsilateral area of LGB were evaluated.ResultsA statistically significant difference was found between the two groups for the Glx/Cr ratio in both the vitreous and LGB (P=0.0001). There was no statistically significant difference between the two groups for the NAA/Cr, and Cho/Cr ratios in the LGB (P=0.108). A lactate peak was established in the vitreous of 11 glaucoma patients.ConclusionDetermining increased Glx/Cr ratios in both the vitreous and LGB of glaucoma patients, supports the theory of apoptosis in the etiopathogenesis of glaucoma. The MRS method, which can measure biochemical structures and metabolites of tissues, and also shows on a single spectrum, may be a new and non-invasive method for confirming the diagnosis of glaucoma and the role of apoptosis in the etiopathogenesis of glaucoma.