多巴胺诱导PC12细胞凋亡的免疫组织化学及超微结构分析

目的 研究帕金森病（PD）多巴胺能神经元的死亡机制,方法在免疫组织化学基础上,采用流式细胞仪,电泳及电镜技术观察不同浓度多巴胺（DA）诱导大鼠嗜铬细胞瘤PC12细胞凋亡的超微结构及生化改变。结果 适当浓度DA可诱导PC12细胞凋亡,早期表现为线粒体结构及功能的改变并有抗凋亡蛋白bcl-2的达,后期电镜下可见亡特征性核结构改变及典型的DNA阶梯状电泳带,结论 细胞凋亡参与了PD的病变过程,线粒体在早期细胞凋亡中起着重要的调节作用。     

多巴胺D2受体基因启动子A-241G多态性在精神分裂症家系中的连锁不平衡传递

目的:探讨多巴胺D2受体基因(dopamine D2 receptor,DRD2)启动子A-241G多态性与精神分裂症的关系.方法:采集101个家系,每家有2名或2名以上符合ICD-10精神分裂症诊断标准患病同胞且父母存活.对DRD2启动子的A-241G多态性进行检测.结果:(1)DRD2启动子的A-241G等位基因频度和基因型频度在父母组、非患病同胞组和患病同胞组之间差异无显著性,在3组不同性别之间以及在精神分裂症不同亚型之间基因型频度和等位基因频度的分布差异亦无显著性;(2) 传递不平衡检验发现在患病同胞(χ2 =0.94,P>0.05,OR=0.83,95%可信区间0.57～1.21)中未表现传递不平衡性,而在非患病同胞(χ2 =6.76,P<0.01,OR=3.17,95%可信区间0.41～24.71)中存在传递不平衡性,其中-241A等位基因在非患病同胞中传递较多;(3) 基因型与妄想总分、幻觉总分、思维形式障碍、情感障碍、精神性失语及症状持续时间等临床特征相关.结论:DRD2启动子的A-241G多态性对精神分裂症的发病和临床表现具有一定影响.     

缺氧缺血性新生大鼠脑组织内多巴胺含量的动态变化

目的　观察缺氧缺血性脑损伤 (Hypoxic-ischemicbraindamage ,HIBD)后不同时间大脑皮层、纹状体、脑干内多巴胺 (Dopamine,DA)含量的动态变化 ,探讨DA在HIBD中的变化规律。方法　 7日龄SD大鼠 99只 ,采用阻断左侧颈总动脉后置于含 8%O2 的低氧环境中 ,建立HIBD动物模型。用高效液相-电化学检测法 (HPLC -ECD)测定脑损伤后 0h、0 .5h、1h、3h、6h、9h、12h、2 4h、48h不同时间皮层、纹状体和脑干内多巴胺DA含量的动态变化。结果　动物缺氧缺血 (Hypoxic -ischemic,HI)后多巴胺在 0 .5h即有明显上升 ,6h时纹状体内DA含量达到高峰 ;9h大脑皮层和脑干达峰值 ,之后缓慢下降。结论　新生鼠缺氧缺血后脑细胞内多巴胺含量变化有一定的规律 ,各脑区变化情况有差别。     

肝素钠软膏对多巴胺诱发兔静脉及其周围组织损伤治疗的实验研究

目的：笔者观察了肝素钠软膏、５０％硫酸镁、透明质酸酶对多巴胺诱发兔静脉及其周围组织损伤的治疗作用。方法：兔耳静脉连续注身大剂量的多巴胺和静脉周围组织注射多巴胺诱发静脉炎。结果：５０％硫酸镁加肝素钠软膏对多巴胺诱发的静脉炎治疗效果最好,其次为肝素钠软膏和５０％硫酸镁,透明质酸酶无治疗作用。     

Catecholamine modulatory effects of nepicastat (RS-25560-197), a novel,potent and selective inhibitor of dopamine-β-hydroxylase

1. Inhibitory modulation of sympathetic nerve function may have a favourable impact on the progression of congestive heart failure. Nepicastat is a novel inhibitor of dopamine-β-hydroxylase, the enzyme which catalyses the conversion of dopamine to noradrenaline in sympathetic nerves. The in vitro pharmacology and in vivo catecholamine modulatory effects of nepicastat were investigated in the present study.
2. Nepicastat produced concentration-dependent inhibition of bovine (IC₅₀=8.5±0.8 nM) and human (IC₅₀=9.0±0.8  nM)dopamine-β-hydroxylase. The corresponding R-enantiomer (RS-25560-198) was approximately 2–3 fold less potent than nepicastat. Nepicastat had negligible affinity (>10 μM) for twelve other enzymes and thirteen neurotransmitter receptors.
3. Administration of nepicastat to spontaneously hypertensive rats (SHRs) (three consecutive doses of either 3, 10, 30 or 100 mg kg⁻¹, p.o.; 12 h apart) or beagle dogs (0.05, 0.5, 1.5 or 5 mg kg⁻¹, p.o.; b.i.d., for 5 days) produced dose-dependent decreases in noradrenaline content, increases in dopamine content and increases in dopamine/noradrenaline ratio in the artery (mesenteric or renal), left ventricle and cerebral cortex. At the highest dose studied, the decreases in tissue noradrenaline were 47%, 35% and 42% (in SHRs) and 88%, 91% and 96% (in dogs) in the artery, left ventricle and cerebral cortex, respectively. When tested at 30 mg kg⁻¹, p.o., in SHRs, nepicastat produced significantly greater changes in noradrenaline and dopamine content, as compared to the R-enantiomer (RS-25560-198), in the mesenteric artery and left ventricle.
4. Administration of nepicastat (2 mg kg⁻¹, b.i.d, p.o.) to beagle dogs for 15 days produced significant decreases in plasma concentrations of noradrenaline and increases in plasma concentrations of dopamine and dopamine/noradrenaline ratio. The peak reduction (52%) in plasma concentration of noradrenaline and the peak increase (646%) in plasma concentration of dopamine were observed on day-6 and day-7 of dosing, respectively.
5. The findings of this study suggest that nepicastat is a potent, selective and orally active inhibitor of dopamine-β-hydroxylase which produces gradual modulation of the sympathetic nervous system by inhibiting the biosynthesis of noradrenaline. This drug may, therefore, be of value in the treatment of cardiovascular disorders associated with over-activation of the sympathetic nervous system, such as congestive heart failure.

     

Inhibition of gastrointestinal motility by MPTP via adrenergic and dopaminergic mechanisms

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was injected intraperitoneally in mice and caused an acute inhibition (of over 60%) of gastrointestinal motility, which was measured by the transit of charcoal. This inhibition was not related to conversion of MPTP to MPP⁺. Administration of the -adrenergic blocker propranolol significantly reduced, but did not completely block, the effect of MPTP. The dopaminergic blocker haloperidol also partly reversed the effects of MPTP. When these blockers were administered together, the action of MPTP was fully blocked. The results indicate that the toxin acted by releasing catecholamines (presumably norepinephrine and dopamine), thereby inhibiting motility.Supported by a grant from the Joint Research Fund of the Hebrew University and Hadassah.     

Behavioral significance of phasic changes in mesolimbic dopamine-dependent electrochemical signal associated with heroin self-injections

Summary High-speed chronoamperometry with monoamine-selective carbon fiber electrodes was used in rats to monitor, during 5–6 consecutive daily sessions, changes in DA-dependent electrochemical signal in the nucleus accumbens (NAcc) during intravenous heroin (0.1 mg/kg) self-administration (SA) behavior and passive repeated drug injections performed with a temporal scheme similar to that in the SA experiment. In trained animals, biphasic signal fluctuations time-locked to the individual lever-presses were found to accompany all but the first daily SAs. The signal gradually increased by 30–40 nM for the 10 minutes preceding the SA, reached a peak at the moment of lever-press and decreased abruptly by 40 nM for 3–4 min after heroin SA. The cycle then repeated, reaching a new peak at the moment of the next lever-press. Rapid bi-directional fluctuations in signal associated with individual heroin SAs were superimposed on substantial tonic increase in signal baseline (400–500 nM). This increase quickly developed after presentation of heroin-related light cue and the first SA, was relatively stable during all subsequent SAs and decreased towards the baseline after the last SA of a session. Changes in signal baseline induced by repeated heroin SAs depended strongly upon the signal's basal level (r=– 0.787); that signal preferentially increased when its basal values were low (0–300 nM), and decreased when signal was tonically elevated (> 600 nM). Repeated passive heroin injections also induced biphasic signal fluctuations and a similar tonic increase in signal baseline. Although a transient signal decrease (25 nM for 2–4 minutes) followed by a prolonged signal increase occurred after each but not the first passive injection, the gradual pre-injection signal acceleration was absent.Although DOPAC, a principal DA metabolite, may significantly contribute to the tonic increase in electrochemical signal seen during SA session, the changes in extracellular DA may be the main contributor to both the rapid signal increases preceding drug-taking and the transient signal decreases following heroin SA. If so, the present findings suggest that activation of mesolimbic DA cells and increase in DA transmission may be involved in the mediation of motivational and/or activational components of drug-seeking and drug-taking behavior. An acute termination of previous drug- and behavior-associated DA activation with a transient inhibition of DA release, immediately following heroin SA may correlate with the drug's rewarding action, representing a part of a mechanism regulating drug-taking behavior.     

Renal response to amino acid infusion in rats: effect of dopamine receptor antagonists and benserazide

Previously, we have found that feeding is a dominant factor controlling urinary dopamine excretion (U_DA) in conscious rats (Mühlbauer and Osswald 1992). Since the renal response to feeding is also characterized by an increase in glomerular filtration rate (GFR), we wanted to investigate in a first step whether the feeding-induced elevations of GFR and U_DA could be causally related phenomena. Therefore, we studied the influence of dopamine synthesis and dopamine receptor blockade on the renal response to amino acid infusion (AA) in thiopental anesthetized rats. AA infusion (n = 7) increased GFR by 33±7% (P<0.001) and U_DA by 87±19% (P<0.001). In the presence of benserazide (BZD, n = 5), an inhibitor of dopamine synthesis, infused i.v. at a dose of 30 g/min/kg, U_DA was suppressed to values below detection limit and the AA-induced GFR increase was abolished. Continuous intravenous infusion of the DA₁ receptor antagonist SCH 23390 (SCH, n = 7) in a dose of 4.0 g/kg/min did not prevent the AA-induced increase in GFR (33±3%, P<0.001) and U_DA (97±12%, P< 0.001). In contrast, S-sulpiride (SUL), a specific DA₂ receptor antagonist, infused continuously i.v. in a dose of 5 g/kg/min, completely abolished the AA-induced GFR increase, while U_DA was increased 1.6-fold (P<0.01). Like BZD, both dopamine receptor antagonists did not affect renal sodium excretion substantially.Our results suggest, that endogenous dopamine could act as a mediator in the renal response to amino acid infusion in the rat, most likely by activation of DA₂ receptors. Correspondence to:B. Mühlbauer at the above address     

Lasting reduction in mesolimbic dopamine neuronal activity after morphine withdrawal

The activity of mesolimbic dopaminergic neurons was investigated in rats at various times after a chronic regimen of morphine, which produced, upon suspension, a marked somatic withdrawal syndrome. Single-cell extracellular recording techniques, coupled with antidromic identification from the nucleus accumbens, were used to monitor neuronal activity while behavioural observations allowed quantification of the somatic signs of morphine withdrawal. Temporal correlation of electrophysiological indices, such as firing rate and burst firing, with scores obtained through behavioural assessments proved negative, in that somatic signs were pronounced at 24 h after suspension of treatment and then subsided to control values at 72 h after the last morphine injection. In contrast, the firing rate and burst firing of mesolimbic dopaminergic neurons were found to be reduced at 1, 3 and 7 days after morphine withdrawal. After 14 drug-free days, electrophysiological analysis revealed an apparent normalization of various parameters. However, at this time, intravenous administration of morphine produced an increment of electrical activity which was significantly higher than that obtained in control (saline treated) rats. Further, administration of the opiate antagonist naltrexone, administered without prior morphine, at 3, 7 and 14 days after the last morphine administration, failed to alter dopaminergic neuronal activity. The results indicate: (i) that the activity of mesolimbic dopaminergic neurons remains reduced well after somatic signs of withdrawal have disappeared; (ii) after 14 days of withdrawal, the augmented magnitude of the electrophysiological response to exogenous morphine suggests an increased sensitivity of opiate receptors; and (iii) the lack of relationship between dopaminergic activity and somatic signs of withdrawal corroborates the notion that dopaminergic activity in the mesolimbic system does not participate in the neurobiological mechanisms responsible for somatic withdrawal. The present results may be relevant to the phenomenon of drug addiction in humans and consequent relapse after drug-free periods.     

Pergolide potentiates L-DOPA-induced dopamine release in rat striatum after lesioning with 6-hydroxydopamine

Summary. We used intrastriatal microdialysis to study the effect of pergolide, a D₁/D₂ dopamine (DA) receptor agonist on biotransformation of exogenous L-DOPA in hemi-Parkinsonian rats. DA and metabolites were assayed by microbore liquid chromatography. Pergolide (50 μg/kg, i.p) caused a 67% and 87% decrease in striatal EC levels of DA in intact and denervated striatum respectively. In intact striatum but not in denervated striatum, pergolide decreased EC levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) (53% and 42% decrease, respectively). L-DOPA (100 mg/kg, i.p.) produced significant increase in EC levels of DA, DOPAC and HVA in intact and denervated striatum with and without local perfusion of 10⁻⁴ M pergolide. In denervated striatum, L-DOPA-induced DA increase was significantly higher in rats with pergolide. Our results suggest that, in an animal model of Parkinson's disease, pergolide in association with L-DOPA favors the restoration of striatal EC DA levels. Received April 24, 1998; accepted July 23, 1998