In vivo evaluation of the dopaminergic neurotransmission system using [123I]FP‐CIT SPECT in 6‐OHDA lesioned rats

The 6‐hydroxydopamine (6‐OHDA) rodent model of Parkinson's disease (PD) has been used to evaluate the nigrostriatal pathway. The aim of this work was to explore the relationship between the degree of 6‐OHDA‐induced dopaminergic degeneration and [¹²³I]FP‐CIT binding using single photon emission computed tomography (SPECT). Fourteen rats received a 6‐OHDA injection (4 or 8 µg) into the left medial forebrain bundle. After 3 weeks, magnetic resonance imaging and scans with a small‐animal SPECT system were performed. Finally, the nigrostriatal lesion was assessed by immunohistochemical analysis. Immunohistochemical analysis confirmed two levels of dopaminergic degeneration. Lesions induced by 6‐OHDA diminished the ipsilateral [¹²³I]FP‐CIT binding by 61 and 76%, respectively. The decrease in tracer uptake between control and lesioned animals was statistically significant, as was the difference between the two 6‐OHDA lesioned groups. Results concluded that [¹²³I]FP‐CIT SPECT is a useful technique to discriminate the degree of dopaminergic degeneration in a rat model of PD. Copyright © 2014 John Wiley & Sons, Ltd.     

烟草成份保护多巴胺神经元作用的研究

目的：探讨烟草成份保护多巴胺神经元对抗6－羟基多巴胺（6－OHDA）的神经毒性作用。方法：采用大鼠脑内立体注射6－OHDA建立帕金森病模型，连续观察术前4周开始分别给予被动吸烟和腹腔注射尼古丁（每次0.1mg/kg或0.4mg/kg,bid，持续6周）对阿朴吗啡诱发的旋转行为，纹状体多巴胺（dopamine,DA)的含量和黑质酪氨酸羟化酶（Tyrosine Hydroxylase,TH）阳性神经细胞数目的影响。结果：被动吸烟和腹腔注射尼古丁的大鼠旋转行为明显减少，受损侧纹状体DA含量和黑质TH阳性神经元的数目较对照组增高（P＜0．01），高剂量尼古丁作为更为显著。结论：烟草成份可减轻6－OHDA对黑质DA神经元的损伤。     

Pharmacological blockade of TRPV1 receptors modulates the effects of 6‐OHDA on motor and cognitive functions in a rat model of Parkinson's disease

TRPV1 receptors and cannabinoid system are considered as important modulators of basal ganglia functions, and their pharmacologic manipulation represents a promising therapy to alleviate Parkinson‐induced hypokinesia. Recent evidence suggests that the blockade of cannabinoid receptors might be beneficial to alleviate motor deficits observed in Parkinson's disease. In the present study, we have evaluated the effects of AMG₉₈₁₀, a selective antagonist of TRPV1 receptors, on the motor and cognitive functions in a rat model of Parkinson's disease generated by an intracerebroventricular injection of 6‐ hydroxydopamine (6‐OHDA) (200 μg per animal). The injection of 10 nmol of AMG₉₈₁₀ for a single dose (AMG1) and for 2 weeks (AMG14) partially attenuated the hypokinesia shown by these animals in motor function evaluation tests, whereas chronic administration of AMG had destructive effects on learning and memory in 6‐OHDA‐treated rats. Animals in the AMG 1 and AMG 14 groups showed an increased latency to fall in rotarod and grasping tests in each trials compared with 6‐OHDA‐treated rats (P < 0.01) and DMSO 1 and 14 groups (P < 0.05). Our data indicate that pharmacological blockade of TRPV1 receptors by AMG ₉₈₁₀ attenuates the hypokinetic effects of 6‐OHDA and that TRPV1 receptors play an important role in 6‐OHDA‐induced hypokinesia, athough elucidation of the neurochemical substrate involved in this process remains a major challenge for the future.     

6-羟基多巴胺诱发大鼠黑质细胞凋亡的实验研究

目的：为了解证实细胞凋亡参与了帕金森病（Parkinson disease,PD)的发病和黑质细胞凋亡的调控因素。方法：通过脑立体定位注射6－羟基多巴胺（6－OHDA）建立大鼠PD模型。采用TUNEL法、原位杂交技术、电镜观察等，选择6－DHDA注射术后1、3、5、7、14及21d为研究时点，观察大鼠PD模型形成过程中黑质细胞凋亡的数量及超微结构变化情况，并检测黑质细胞Bcl-2 mRNA、P53 mRNA表达情况及铁的浓度。结果：用TUNEL法发现黑质细胞存在细胞凋亡，与对照组比较差异有显著性（P＜0．05），7d 细胞凋亡数为最高，21d最低；电镜观察在此过程中黑质细胞存在典型的细胞凋良，并逐渐加重;Bcl-2和铁随时间增加而升高，P53则在1d为最高，其后很快下降，但都高于对照组（P＜0．05）。结论：6－OHDA能诱发大鼠黑质细胞凋亡，细胞凋亡参与了PD发病，并受到Bcl-2、P53和铁的影响。     

KA‐bridged transplantation of mesencephalic tissue and olfactory ensheathing cells in a Parkinsonian rat model

The pathology of Parkinson's disease (PD) results mainly from nigrostriatal pathway damage. Unfortunately, commonly used PD therapies do not repair the disconnected circuitry. It has been reported that using kainic acid (KA, an excitatory amino acid) in bridging transplantation may be useful to generate an artificial tract and reconstruct the nigrostriatal pathway in 6‐hydroxydopamine (6‐OHDA) lesioned rats. In this study, we used KA bridging and a co‐graft of rat olfactory ensheathing cells (OECs) and rat E14 embryonic ventral mesencephalic (VM) tissue to restore the nigrostriatal pathway of the PD model rats. The methamphetamine‐induced rotational behaviour, 4‐[¹⁸F]–ADAM (a selectively serotonin transporter radioligand)/micro‐PET imaging, and immunohistochemistry were used to assess the effects of the transplantation. At 9 weeks post‐grafting in PD model rats, the results showed that the PD rats undergoing VM tissue and OECs co‐grafts (VM–OECs) exhibited better motor recovery compared to the rats receiving VM tissue transplantation only. The striatal uptake of 4‐[¹⁸F]–ADAM and tyrosine hydroxylase immunoreactivity (TH‐ir) of the grafted area in the VM–OECs group were also more improved than those of the VM alone group. These results suggested that OECs may enhance the survival of the grafted VM tissue and facilitate the recovery of motor function after VM transplantation. Moreover, OECs possibly promote the elongation of dopaminergic and serotonergic axon in the bridging graft. Copyright © 2015 John Wiley & Sons, Ltd.     

Delayed Dominant-Negative TNF Gene Therapy Halts Progressive Loss of Nigral Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Parkinson''s disease (PD) is a progressive neurodegenerative disorder typified by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Recent evidence indicates that neuroinflammation may play a critical role in the pathogenesis of PD, particularly tumor necrosis factor (TNF). We have previously shown that soluble TNF (solTNF) is required to mediate robust degeneration induced by 6-hydroxydopamine (6-OHDA) or lipopolysaccharide. What remains unknown is whether TNF inhibition can attenuate the delayed and progressive phase of neurodegeneration. To test this, rats were injected in the SNpc with lentivirus encoding dominant-negative TNF (lenti-DN-TNF) 2 weeks after receiving a 6-OHDA lesion. Remarkably, when examined 5 weeks after the initial 6-OHDA lesion, no further loss of nigral DA neurons was observed. Lenti-DN-TNF also attenuated microglial activation. Together, these data suggest that TNF is likely a critical mediator of nigral DA neuron death during the delayed and progressive phase of neurodegeneration, and that microglia may be the principal cell type involved. These promising findings provide compelling reasons to perform DN-TNF gene transfer studies in nonhuman primates with the long-term goal of using it in the clinic to prevent the delayed and progressive degeneration of DA neurons that gives rise to motor symptoms in PD.     

Mechanism of specific dopaminergic neuronal death in Parkinson's disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic (DAergic) neurons of the nigrostriatal system, with resulting reduction in striatal dopamine (DA) concentration. Various mechanisms have been implicated in the pathogenesis and progression of PD. Among them, mitochondrial dysfunction, inflammation and oxidative stress had been accepted as the most plausible mechanism of disease progression. The free radicals/oxidative stress produced by MPTP, 6-hydroxydopamine, rotenone, activated microglias, and disturbances in mitochondrial respiratory enzymes provide a common pathway for the progression of all kinds of neurons. On the other hand, numerous studies on DA-induced neurotoxicity have been reported recently, and DA itself exerts cytotoxicity in DAergic neurons mainly due to the generation of highly reactive DA -quinones which are DAergic neuron-specific cytotoxic molecules. DA quinones may irreversibly alter protein function through the formation 5-cysteinyl-dopamine on the protein. For example, the formation of DA quinone-alpha-synuclein complex consequently increases cytotoxic protofibrils and covalent modification of functional enzymes. Thus, DA quinones play an important role in 'specific' DAergic neuro-degeneration of PD.     

Embryonic stem cells as a cell source for treating Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterised by a loss of midbrain dopaminergic (DA) neurons. Transplantation of DA neurons represents a promising treatment for PD, and embryonic stem (ES) cells are a good candidate source for DA neurons. However, although recent reports have demonstrated that DA neurons can be efficiently induced from ES cells and function therapeutically in an animal model of PD, many problems remain to be solved in order for ES cells to be used for clinical applications. This review will describe the current status of this field and the obstacles yet to be overcome, and will outline future research approaches from the clinical perspective.     

颈动脉体球细胞块移植治疗帕金森病大鼠行为学的实验研究

探讨帕金森病（ＰＤ）大鼠颈动脉体球细胞块移植后其行为学的变化。采用６－羟多巴胺（６－ＯＨＤＡ）损毁大鼠一侧黑质细胞制成ＰＤ样大鼠模型。在右侧纹状体内分别移植入胚胎黑质和自、异体颈动脉体球细胞块。在移植后２、４、８和１２周记录阿朴吗啡诱发大鼠的旋转行为,同步分析存活酪氨酸羟化酶（ＴＨ）阳性细胞数目。结果：在１２周时与胚胎中脑组织移植相比较,自、异体颈动脉体球细胞移植组大鼠旋转行为改善更为明显。存活ＴＨ＾＋细胞显著增多（分别Ｐ〈０．０５）,但自、异体颈动脉体球细胞移植组间比较差异无显著性,提示：颈动脉体球细胞块移植后ＰＤ大鼠行为学显著改善。效果优于胚胎中脑组织块的移植。     

ES cell therapy for Parkinson's disease

Neural transplantation, as a treatment for advanced Parkinson's disease (PD), has been studied for more than a decade due to the potential replacement of degenerated dopaminergic (DA) neurons. Several open-label studies on implantation of fetal nigral neurons revealed improvement in motor functions. However, the benefits were incomplete in double-blind trials. Progressive neural or embryonic stem (ES) cell research has raised hopes of creating novel cell replacement therapies for PD. DA neurons have been efficiently produced from primate ES cells in astrocyte-conditioned medium. Transplantation of neuronal stem cells derived from primate ES cells into a primate model of PD restored striatal DA function, suggesting ES cells are suitable donor cells.     

Protective effect of sulforaphane against dopaminergic cell death

Parkinson's disease (PD) is a progressive neurodegenerative disorder with a selective loss of dopaminergic neurons in the substantia nigra. Evidence suggests oxidation of dopamine (DA) to DA quinone and consequent oxidative stress as a major factor contributing to this vulnerability. We have previously observed that exposure to or induction of NAD(P)H:quinone reductase (QR1), the enzyme that catalyzes the reduction of quinone, effectively protects DA cells. Sulforaphane (SF) is a drug identified as a potent inducer of QR1 in various non-neuronal cells. In the present study, we show that SF protects against compounds known to induce DA quinone production (6-hydroxydopamine and tetrahydrobiopterin) in DAergic cell lines CATH.a and SK-N-BE(2)C as well as in mesencephalic DAergic neurons. SF leads to attenuation of the increase in protein-bound quinone in tetrahydrobiopterin-treated cells, but this does not occur in cells that have been depleted of DA, suggesting involvement of DA quinone. SF pretreatment prevents membrane damage, DNA fragmentation, and accumulation of reactive oxygen species. SF causes increases in mRNA levels and enzymatic activity of QR1 in a dose-dependent manner. Taken together, these results indicate that SF causes induction of QR1 gene expression, removal of intracellular DA quinone, and protection against toxicity in DAergic cells. Thus, this major isothiocyanate found in cruciferous vegetables may serve as a potential candidate for development of treatment and/or prevention of PD.     

Transplantation of porcine umbilical cord matrix mesenchymal stem cells in a mouse model of Parkinson's disease

The present study compared mesenchymal stem cells derived from umbilical cord matrix (UCM‐MSCs) with bone marrow (BM‐MSCs) of miniature pigs on their phenotypic profiles and ability to differentiate in vitro into osteocytes, adipocytes and neuron‐like cells. This study further evaluated the therapeutic potential of UCM‐MSCs in a mouse Parkinson's disease (PD) model. Differences in expression of some cell surface and cytoplasm specific markers were evident between UCM‐MSCs and BM‐MSCs. However, the expression profile indicated the primitive nature of UCM‐MSCs, along with their less or non‐immunogenic features, compared with BM‐MSCs. In vitro differentiation results showed that BM‐MSCs had a higher tendency to form osteocytes and adipocytes, whereas UCM‐MSCs possessed an increased potential to transform into immature or mature neuron‐like cells. Based on these findings, UCM‐MSCs were transplanted into the right substantia nigra (SN) of a mouse PD model. Transplantation of UCM‐MSCs partially recovered the mouse PD model by showing an improvement in basic motor behaviour, as assessed by rotarod and bridge tests. These observations were further supported by the expression of markers, including nestin, tyrosine hydroxylase (TH), neuronal growth factor (NGF), vascular endothelial growth factor (VEGF) and interleukin‐6 (IL‐6), at the site of cell transplantation. Our findings of xenotransplantation have collectively suggested the potential utility of UCM‐MSCs in developing viable therapeutic strategies for PD. Copyright © 2011 John Wiley & Sons, Ltd.     

Neurotoxin-induced ER stress in mouse dopaminergic neurons involves downregulation of TRPC1 and inhibition of AKT/mTOR signaling

Individuals with Parkinson’s disease (PD) experience a progressive decline in motor function as a result of selective loss of dopaminergic (DA) neurons in the substantia nigra. The mechanism(s) underlying the loss of DA neurons is not known. Here, we show that a neurotoxin that causes a disease that mimics PD upon administration to mice, because it induces the selective loss of DA neurons in the substantia nigra, alters Ca²⁺ homeostasis and induces ER stress. In a human neuroblastoma cell line, we found that endogenous store-operated Ca²⁺ entry (SOCE), which is critical for maintaining ER Ca²⁺ levels, is dependent on transient receptor potential channel 1 (TRPC1) activity. Neurotoxin treatment decreased TRPC1 expression, TRPC1 interaction with the SOCE modulator stromal interaction molecule 1 (STIM1), and Ca²⁺ entry into the cells. Overexpression of functional TRPC1 protected against neurotoxin-induced loss of SOCE, the associated decrease in ER Ca²⁺ levels, and the resultant unfolded protein response (UPR). In contrast, silencing of TRPC1 or STIM1 increased the UPR. Furthermore, Ca²⁺ entry via TRPC1 activated the AKT pathway, which has a known role in neuroprotection. Consistent with these in vitro data, Trpc1^–/– mice had an increased UPR and a reduced number of DA neurons. Brain lysates of patients with PD also showed an increased UPR and decreased TRPC1 levels. Importantly, overexpression of TRPC1 in mice restored AKT/mTOR signaling and increased DA neuron survival following neurotoxin administration. Overall, these results suggest that TRPC1 is involved in regulating Ca²⁺ homeostasis and inhibiting the UPR and thus contributes to neuronal survival.     

The lipopolysaccharide Parkinson's disease animal model: mechanistic studies and drug discovery

Research in the last two decades has unveiled an important role for neuroinflammation in the degeneration of the nigrostriatal dopaminergic (DA) pathway that constitutes the pathological basis of the prevailing movement disorder, Parkinson's disease (PD). Neuroinflammation is characterized by the activation of brain glial cells, primarily microglia and astrocytes that release various soluble factors that include free radicals (reactive oxygen and nitrogen species), cytokines, and lipid metabolites. The majority of these glia-derived factors are proinflammatory and neurotoxic and are particularly deleterious to oxidative damage-vulnerable nigral DA neurons. As a proof of concept, various immunologic stimuli have been employed to directly induce glial activation to model DA neurodegeneration in PD. The bacterial endotoxin, lipopolysaccharide (LPS), has been the most extensively utilized glial activator for the induction of inflammatory DA neurodegeneration. In this review, we will summarize the various in vitro and in vivo LPS PD models. Furthermore, we will highlight the contribution of the LPS PD models to the mechanistic studies of PD pathogenesis and the search for neuroprotective agents for the treatment of PD.     

Pharmacological characterization of PD 118717, a putative piperazinyl benzopyranone dopamine autoreceptor agonist.

PD 118717 (7-[3-[4-(2-pyrimidinyl)-1-piperazinyl]-propoxy]-2H-1- benzopyran-2-one sulfate) proved to be a dopamine (DA) D-2 autoreceptor agonist in biochemical and electrophysiological studies in rats and to exhibit an antipsychotic-like profile in behavioral tests in rodents and monkeys. In vitro binding studies indicated that PD 118717 bound selectively to DA D-2 vs. D-1 receptors and exhibited agonist binding properties (biphasic inhibitory curves and GTP shift) similar to DA. It also had significant affinity for serotonin-(5-HT)1A but not 5-HT1B and 5-HT2 receptors. PD 118717 was active in antagonizing the tau-butyrolactone-induced accumulation of dopa in rat striatum and mesolimbic regions. PD 118717 also depressed the firing of DA neurons in substantia nigra pars compacta of rats. In both of the latter tests the effects of PD 118717 were reversed by haloperidol. PD 118717 decreased brain DA metabolism, decreased DA utilization, decreased accumulation of dopa after inhibition of L-aromatic amino acid decarboxylase, stimulated serum corticosterone and inhibited stimulated serum prolactin levels. PD 118717 did not alter striatal acetylcholine levels; nor did it induce locomotor stimulation or stereotypy in normal animals, suggesting a lack of postsynaptic DA stimulation of normosensitive DA receptors. In tests designed to reveal even weak postsynaptic DA agonist effects, PD 118717 stimulated locomotor activity in 6-hydroxydopamine-lesioned animals and relatively higher doses induced a low degree of stereotyped behavior when combined with the DA D-1 agonist SKF 38393. PD 118717 decreased the accumulation of 5-hydroxytryptophan in brain, an effect probably due to an agonist action at 5-HT1A receptors. PD 118717 decreased spontaneous locomotor activity in rodents, antagonized amphetamine-stimulated hyperactivity in mice and inhibited Sidman avoidance in monkeys, effects seen with antipsychotic agents. Unlike DA antagonist antipsychotics, PD 118717 did not induce extrapyramidal dysfunction in monkeys. PD 118717 displayed behavioral activity after p.o. dosing and its effects did not show tolerance on repeated dosing. In conclusion, PD 118717 has the profile of a DA autoreceptor agonist in neurochemical and neurophysiological tests and produces effects suggestive of antipsychotic efficacy without neurological side effect liability in preclinical behavioral tests.     

热休克蛋白70在大鼠黑质多巴胺神经元损伤中的表达

目的 :探讨热休克蛋白 70 (HSP70 )在大鼠黑质多巴胺 (DA)神经元损伤中的表达以及在帕金森病 (PD)诊断中的意义。方法 :将 48只大鼠随机分为黑质DA神经元损毁组 (PD组 )和对照组各 2 4只。PD组注射 6 羟多巴胺 (6 OHDA)损毁大鼠黑质DA神经元 ,对照组仅注射 6 OHDA溶媒。于注射后 1、7、14及 2 1d采用免疫组织化学、尼氏染色、电镜手段动态观察HSP70在损毁的DA神经元中的表达以及DA神经元形态学变化。结果 :在 6 O HDA损毁黑质 1～ 2 1d ,对照组黑质HSP70表达和尼氏细胞计数差异无显著性 (P >0 .0 5 )。PD组HSP70表达在 1d最高 ,7d锐减 ,14和 2 1d则逐渐减少 ,分别为 2 5 %、74%、87%及 88% ;尼氏细胞计数在 4个时间点分别减少1%、13%、35 %及 48% ;超微结构损伤程度呈进行性加重。结论 :PD渐进性发病具有其形态学基础 ,HSP70可作为DA神经元存活的指标和早期诊断PD的指标。     

Behavioral recovery in a primate model of Parkinson's disease by triple transduction of striatal cells with adeno-associated viral vectors expressing dopamine-synthesizing enzymes

One potential strategy for gene therapy of Parkinson's disease (PD) is the local production of dopamine (DA) in the striatum induced by restoring DA-synthesizing enzymes. In addition to tyrosine hydroxylase (TH) and aromatic-L-amino-acid decarboxylase (AADC), GTP cyclohydrolase I (GCH) is necessary for efficient DA production. Using adeno-associated virus (AAV) vectors, we previously demonstrated that expression of these three enzymes in the striatum resulted in long-term behavioral recovery in rat models of PD. We here extend the preclinical exploration to primate models of PD. Mixtures of three separate AAV vectors expressing TH, AADC, and GCH, respectively, were stereotaxically injected into the unilateral putamen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys. Coexpression of the enzymes in the unilateral putamen resulted in remarkable improvement in manual dexterity on the contralateral to the AAV-TH/-AADC/-GCH-injected side. Behavioral recovery persisted during the observation period (four monkeys: 48 days, 65 days, 50 days, and >10 months, each). TH-immunoreactive (TH-IR), AADC-IR, and GCH-IR cells were present in a large region of the putamen. Microdialysis demonstrated that concentrations of DA in the AAV-TH/-AADC/-GCH-injected putamen were increased compared with the control side. Our results show that AAV vectors efficiently introduce DA-synthesizing enzyme genes into the striatum of primates with restoration of motor functions. This triple transduction method may offer a potential therapeutic strategy for PD.     

Endothelin (ET)-1-induced inhibition of ATP release from PC-12 cells is mediated by the ETB receptor: differential response to ET-1 on ATP, neuropeptide Y, and dopamine levels

During sympathetic neurotransmitter release, there is evidence for differential modulation of cotransmitter release by endothelin (ET)-1. Using nerve growth factor (NGF)-differentiated PC12 cells, the effects of ET-1 on K(+)-stimulated release of ATP, dopamine (DA), and neuropeptide Y (NPY) were quantified using high-pressure liquid chromatography or radioimmunoassay. ET-1, in a concentration-dependent manner, inhibited the release of ATP, but not DA and NPY. Preincubation with the ET(A/B) antagonist, PD 142893 (N-acetyl-beta-phenyl-D-Phe-Leu-Asp-Ile-Ile-Trp), reversed the inhibitory effect of ET-1 on ATP release, which remained unaffected in the presence of the ET(A)-specific antagonist BQ123 [cyclo(D-Asp-Pro-D-Val-Leu-D-Trp)]. The ET(B) agonists, sarafotoxin 6c (Cys-Thr-Cys-Asn-Asp-Met-Thr-Asp-Glu-Glu-Cys-Leu-Asn-Phe-Cys-His-Gln-Asp-Val-Ile-Trp), BQ 3020 (N-acetyl-[Ala(11,15)]-endothelin 1 fragment 6-21Ac-Leu-Met-Asp-Lys-Glu-Ala-Val-Tyr-Phe-Ala-His-Leu-Asp-IIe-IIe-Trp), and IRL 1620 (N-succinyl-[Glu(9), Ala(11,15)]-endothelin 1 fragment 8-21Suc-Asp-Glu-Glu-Ala-Val-Tyr-Phe-Ala-His-Leu-Asp-Ile-Ile-Trp), decreased K(+)-stimulated release of ATP in a dose-dependent manner, and this effect was reversed by the ET(B) antagonists RES 701-1 [cyclic (Gly1-Asp9) (Gly-Asn-Trp-His-Gly-Thr-Ala-Pro-Asp-Trp-Phe-Phe-Asn-Tyr-Tyr-Trp)] and BQ 788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-l-leucyl]-1-(methoxycarbonyl)-D-tryptophyl]-D-norleucine sodium salt). Preincubation of PC12 cells with pertussis toxin reversed the ET-1-induced inhibition of the K(+)-evoked ATP release. Real-time intracellular calcium level recordings were performed on PC-12 cell suspensions, and ET-1 induced a dose-dependent decrease in the K(+)-evoked calcium levels. Nifedipine, the L-type voltage-dependent Ca(2+) channel antagonist, caused inhibition of the K(+)-stimulated ATP release, but the N-type Ca(2+) channel antagonist, omega-conotoxin GVIA, did not reverse the effect on ATP release. These data suggest that ET-1 modulates the release of ATP via the ET(B) receptor and its associated G(i/o) G-protein through attenuation of the influx of extracellular Ca(2+) through L-type channels.     

Effect of (R)-salsolinol and N-methyl-(R)-salsolinol on the balance impairment between dopamine and acetylcholine in rat brain: involvement in pathogenesis of Parkinson disease

BACKGROUND: Parkinson disease (PD), a progressive neurodegenerative disease, affects at least 1% of population above the age of 65. Although the specific etiology of PD remains unclear, recently the endogenous neurotoxins such as (R)-salsolinol [(R)-Sal] and N-methyl-(R)-salsolinol [(R)-NMSal] have been thought to play a major role in PD. Much interest is focused on the degeneration of dopamine neurons induced by these neurotoxins. However, little literature is available on the impact of endogenous neurotoxins on the balance between dopamine (DA) and acetylcholine (ACh). METHODS: After injection of (R)-Sal or (R)-NMSal into the rat brain striatum, the concentrations of DA and its metabolites were detected by HPLC with electrochemical detection. We assessed the influence of neurotoxins on acetylcholinesterase (AChE) activity and developed a microdialysis-electrochemical device to measure ACh concentrations with enzyme-modified electrodes. RESULTS: (R)-Sal and (R)-NMSal led to concentration-dependent decreases in the activity of AChE. ACh concentrations in striatum treated with (R)-Sal or (R)-NMSal were increased to 131.7% and 239.8% of control, respectively. As to the dopaminergic system, (R)-NMSal caused a significant decrease in DA concentrations and (R)-Sal reduced the concentrations of DA metabolites in the striatum. CONCLUSIONS: (R)-Sal and (R)-NMSal exerted a considerable effect on the balance between DA and ACh by impairing the cholinergic system as well as the dopaminergic system. It is likely that the disruption of balance between DA and ACh plays a critical role in the pathogenesis of neurotoxin-induced PD.