Dopamine responsiveness is regulated by targeted sorting of D2 receptors

Abstract Aberrant dopaminergic signaling is a critical determinant in multiple psychiatric disorders, and in many disease states, dopamine receptor number is altered. Here we identify a molecular mechanism that selectively targets D2 receptors for degradation after their activation by dopamine. The degradative fate of D2 receptors is determined by an interaction with G protein coupled receptor-associated sorting protein (GASP). As a consequence of this GASP interaction, D2 responses in rat brain fail to resensitize after agonist treatment. Disruption of the D2-GASP interaction facilitates recovery of D2 responses, suggesting that modulation of the D2-GASP interaction is important for the functional down-regulation of D2 receptors.

Temporal expression of G-protein-coupled receptor 54 (GPR54), gonadotropin-releasing hormones (GnRH), and dopamine receptor D2 (drd2) in pubertal female grey mullet, Mugil cephalus.

The G-protein-coupled receptor 54 (muGPR54) cDNA was cloned from the brain of the grey mullet, and its expression level, as well as those of the gonadotropin-releasing hormones (GnRH1, GnRH2, GnRH3) and dopamine receptor D2 (drd2), in the brain, pituitary and ovary of pubertal fish (early, intermediate, advanced) were determined by real-time quantitative RT-PCR (QPCR). The muGPR54 cDNA has an open reading frame of 1140 bp with a predicted 380 amino acid peptide, containing seven putative transmembrane domains and putative N-glycosylation and protein kinase C phosphorylation sites. QPCR results showed that the early stage of puberty in grey mullet is characterized by significantly high levels of expression of GPR54, GnRH and drd2 in the brain relative to the intermediate and advanced stages, except for GnRH1 that increased at the advanced stage of puberty. In the pituitary, drd2 expression declined significantly at the advanced stage relative to levels at the intermediate stage. Ovarian expression of GPR54 significantly increased from the intermediate stage of puberty relative to the early stage while that of GnRH1 acutely increased at the advanced stage of puberty. The ovarian expression of drd2 decreased as puberty progressed, but the changes were not significant. The results suggest the possible role of GPR54 and GnRH in positively regulating pubertal development in grey mullet and the dopaminergic inhibition of reproductive function mediated by drd2.

Electron Beam Surface Remelting of AISI D2 Cold-Worked Die Steel

Electron beam surface remelting has been carried out on AISI D2 cold-worked die steel. The microstructure and hardening behavior of the electron beam surface remelted AISI D2 cold-worked die steel have been studied by means of optical microscopy and Vickers hardness testing. It was found that AISI D2 steel can be successfully surface hardened by electron beam surface remelting. This surface hardening effect can be attributed to microstructural refinement following electron beam surface remelting. (C) 2002 Elsevier Science B.V. All rights reserved.

光系统II反应中心D1/D2/Cyt b559复合物的光谱特性及其光破坏作用的研究

采用柱层析法从菠菜叶绿体中分离纯化得到高等植物光系统Ⅱ(PSⅡ)反应中心色素蛋白复合体Dl/D2/Cyt b559，并对其性质，特别是光破坏作用的分子机理进行了研究。主要结果如下： 1、PSⅡ反应中心复合物所含的色素比大约为Chla／2 Pheo a=6.0。其四阶导数光谱在红区有两个峰，表明该反应中心至少存在两种结合状态的Chla。 2、Dl/D2/Cyt b559复合物的荧光相对产率及发射光谱的谱带位置与样品的浓度直接相关。只有当样品的浓度达到足够稀的程度(Chla和Pheo a总浓度小于1μg／ml)，才能得到较真实的荧光光谱，其峰位在681nm处。 3、Dl/D2/Cyt b559复合物的CD光谱在红区（Qy带）有一对反向谱带，正蜂为680nm,负峰为660nm，而在β-胡萝卜素的吸收区没有明显的CD信号。当该反应中心复合物受光破坏后，CD信号明显下降，而且当正峰完全消失后，负峰仍然存在，说明负峰不仅包含P680 的信号，也包含其它色素分子的信号，很可能有部分来源于Pheo a。 4、Dl/D2/Cyt b559复合物在488nm处激发的共振拉曼光谱显示四个主要谱带，其峰位分别在1532(ν1)、1165(ν2)、1010(ν3)和970cm-1（ν4）处，表明PSⅡ反应中心结合的B-胡萝卜素分子是全反式构型。Dl/D2/Cyt b559复合物的色素抽提液的拉曼光谱也显示四个主要的拉曼峰，其中ν4谱带的强度急剧下降，说明PSⅡ反应中心内部结合的β-胡萝卜素分子与抽提液中自由的β-胡萝卜素分子的构象不同，而与光合细菌反应中心内部的类胡萝卜素分子的构象相似，其共轭多烯链的平面也处于扭曲状态。 5、光照使PSⅡ反应中心的原初电子供体P680受到破坏，在光照后的暗放置过程中P680分子继续受到破坏，表明在光照过程中很可能有一个相对稳定的反应中间体产生，以至于光照后暗放置过程中Dl/D2/Cyt b559复合物的光谱特性继续发生变化。也就是说，PSⅡ反应中心Dl/D2/Cyt b559复合物的光破坏不是一步反应，而是一个多步反应或多条途径。 6、光照使Dl/D2/Cyt b559复合物中的组氨酸(His)残基受到很大程度的破坏，甲硫氨酸(Met）残基的含量也略有下降，而其它氨基酸的含量基本保持不变。His残基的破坏很可能与光照后暗放置过程中Dl/D2/Cyt b559复合物的光谱特性变化相关。我们认为His残基的光照破坏很可能是Dl/D2/Cyt b559复合物受光照破坏的另一分子机理。 7、人工电子受体癸基质体醌(DPQ)可以与Dl/D2/Cyt b559复合物进行重组。Dl/D2/Cyt b559复合物的荧光衰减分析表明，在DPQ重组之后，两个长寿命荧光组分（24ns和73ns）的寿命减小，而且占整个荧光的分数也下降，表明这两个长寿命荧光衰减组分均来源于电荷重组过程。同时，β-胡萝卜素分子在DPQ重组之后更易于被光照破坏，这个过程可能与β-胡萝卜素分子的生理功能相关。 8、在没有外加人工电子受体的情况下，光照使DDl/D2/Cyt b559 复合物的多肽组成发生一定变化。SDS-PAGE图谱中出现一个约40KDa的新谱带，同时Dl与D2多肽的表观分子量增加，谱带染色强度下降。 9、本文根据以上实验结果，着重对Dl/D2/Cyt b559复合物光破坏的分子机理进行了分析和讨论，并在D1蛋白裂解的两种可能途经中又增加了一个新的可能导致Dl蛋白裂解的途径，即：His残基的光照破坏可以作为Dl/D2/Cyt b559复合物光破坏及Dl蛋白裂解的又一分子机理，这为深入研究PSⅡ反应中心的光破坏提供了新的线索，也为今后研究活体内光抑制现象的分子机制打下了良好的基础

Extremely low-frequency electromagnetic field exposure during chronic morphine treatment strengthens downregulation of dopamine D2 receptors in rat dorsal hippocampus after morphine withdrawal

The aim of this study was to investigate the effect of extremely low-frequency electromagnetic field (ELF-EMF) exposure during morphine treatment on dopamine D2 receptor (D2R) density in the rat dorsal hippocampus following withdrawal. Rats were exposed t

DOPAMINE D2 RECEPTOR MECHANISMS CONTRIBUTE TO AGE-RELATED COGNITIVE DECLINE - THE EFFECTS OF QUINPIROLE ON MEMORY AND MOTOR-PERFORMANCE IN MONKEYS

The D2 dopamine (DA) receptor agonist, quinpirole, was characterized in young adult monkeys, young reserpine-treated monkeys and aged monkeys to assess the contribution of DA to age-related loss of prefrontal cortical (PFC) cognitive function, Monkeys were tested on a delayed response memory task that depends on the PFC, and a fine motor task that taps the functions of the motor cortex, In young adult monkeys, low quinpirole doses impaired performance of the PFC and fine motor tasks, while higher doses improved memory performance and induced dyskinesias and ''hallucinatory-like'' behaviors. The pattern of the quinpirole response in reserpine-treated monkeys suggested that the impairments in delayed response and fine motor performance resulted from drug actions at D2 autoreceptors, while the improvement in delayed response performance, dyskinesias and ''hallucinatory-like'' behaviors resulted from actions at postsynaptic receptors. In aged monkeys, low doses of quinpirole continued to impair fine motor performance, but lost their ability to impair delayed response performance. The magnitude of cognitive improvement and the incidence of ''hallucinatory-like'' behaviors were also reduced in the aged animals, suggesting some loss of postsynaptic D2 receptor function, The pattern of results is consistent with the greater loss of DA from the PFC than from motor areas in aged monkey brain (Goldman-Rakic and Brown, 1981; Wenk et al., 1989), and indicates that DA depletion contributes significantly to age-related cognitive decline.

D2-4放线菌的筛选及其抗生物质研究

利用有益微生物及其代谢产物来防治植物病害，已成为一个十分活跃并具有巨大应用前景的领域。本论文采用土壤预处理等特殊方法，从长白山不同高度的土壤中筛选出1068株放线菌。通过对峙培养法和杯碟法，筛选出D1-1等10株对蔬菜病害菌具有抑制作用的菌株。离体叶片实验中发现D2-4发酵液对黄瓜、辣椒、番茄等蔬菜真菌病害具有一定的防治效果。以水和常用化学农药作为空白和药物对照，对D2-4发酵液进行了盆栽实验，结果对番茄灰霉、辣椒根腐和黄瓜枯萎病的防治效果分别为70.65％、63.27％、65.04％，初步显示出良好的防治效果。通过单因素和均匀设计实验，优化了DZ-4菌发酵培养基的组成，考察了培养时间、接种量、菌龄等对抑菌活性的影响。确定了最佳发酵培养基成分：黄豆饼粉1.10％、葡萄糖2.71％、蔗糖1.00％、NaCl0.10％、酵母膏0.10％、发酵培养基初始pH为6.61。最佳发酵时间为96h左右，培养20～24h的种子液以7％的接种量转接有利于提高抑菌活性。经发酵培养基和发酵条件的优化，发酵液抑菌活性达到了6588 u／ml，比原始发酵培养基（3678 u／ml）活性提高了79.12％。经发酵液的预处理、离子交换层析、吸附柱层析、高效液相色谱纯化等步骤，对D2-4抗生素进行了分离纯化研究。通过纸层析、纸电泳等试验最后确定该农用抗生素为弱碱性水溶性抗生素。对D2-4抗生素纯品进行了红外吸收光谱、紫外吸收光谱等理化性质的研究。

D2-4放线菌抗真菌病害活性成分研究

从长白山森林土壤中分离的放线菌D2 4产生的抗生素对蕃茄灰霉病等蔬菜及经济作物的某些真菌病害有很好的防治效果。通过离子交换和吸附层析对抗生素进行了分离纯化。此抗生素为一种弱碱性水溶性抗生素 ,在酸性和中性条件下稳定 ,在碱性条件下不稳定 ,温度耐受性较强 ,在适宜pH条件下 ,1 0 0℃处理0 .5h ,其活性基本不变。