The Relationship Between the Stimulation of Dopamine Synthesis and Release Produced by Amphetamine and High Potassium in Striatal Slices

The effects of amphetamine (amph) and high K+ on the synthesis and release of dopamine (DA) were compared in striatal slices. Both agents stimulated DA synthesis as well as release. For both agents, Ca2+ was required for the initiation of synthesis stimulation as well as for the maintenance of this stimulation. The addition of EGTA to medium containing slices that were already stimulated by 1.0 microM-amph or 55 mM-K+ markedly reduced the stimulation of DA synthesis. Although it has been reported that high K+ activates soluble tyrosine hydroxylase (TH), neither high K+ nor amph appeared to increase the affinity of the synthetic cofactor, 6-MPH4, or decrease the affinity of the catechol, DA, for TH. This finding was supported by the observation that the inhibitory effect of L-DOPA on DA synthesis in slices, in which synthesis was stimulated by either agent, was not decreased. Although both 1.0 microM-amph and 55 mM-K+ stimulated the release of [3H]DA from striatal slices, the release produced by K+ was Ca2+-dependent, whereas release produced by amph did not occur at any concentration tested. Studies on pH requirements for both synthesis and release also confirmed a similarity between amph and K+ in stimulating synthesis but not in stimulating release. These results suggest that depolarizing agents, such as high K+, couple synthesis and release of DA by a Ca2+-dependent mechanism. In contrast, the simultaneous stimulation of synthesis and release by amph is not regulated by Ca2+.     

Characterization of the Human Dopamine Transporter Heterologously Expressed in BHK-21 Cells

1. cDNA of the human dopamine transporter (hDAT) was cloned into a cloning vector based on the Semliki Forest virus. Electroporation of in vitro transcribed mRNA from this plasmid into BHK-21 cells resulted in production of the transporter as measured by [³H]dopamine uptake (K _m = 2.0 ± 0.4 M), which was specifically inhibited in the presence of cocaine.2. The recombinant transporter protein exhibited an apparent molecular mass of 56 kDa, which was reduced to 50 kDa after tunicamycin treatment of the producing BHK-21 cells. Tunicamycin treatment of the electroporated cells also resulted in a decrease in transport activity with no change in the K _m value (2.1 ± 0.4 M).3. The localization of the heterologously produced transporter in the BHK cells either with or without tunicamycin treatment was studied by electron microscopic immunogold staining. The glycosylated transporter was found to be localized at the plasma membrane, whereas in the case of the unglycosylated transporter, transport to the plasma membrane was blocked.     

Relationships Between the Catechol Substrate Binding Site and Amphetamine, Cocaine, and Mazindol Binding Sites in a Kinetic Model of the Striatal Transporter of Dopamine In Vitro

Abstract: Experiments were conducted to determine how (−)-cocaine and S (+)-amphetamine binding sites relate to each other and to the catechol substrate site on the striatal dopamine transporter (sDAT). In controls, m -tyramine and S (+)-amphetamine caused release of dopamine from intracellular stores at concentrations ≥12-fold those observed to inhibit inwardly directed sDAT activity for dopamine. In preparations from animals pretreated with reserpine, m -tyramine and S (+)-amphetamine caused release of preloaded dopamine at concentrations similar to those that inhibit inwardly directed sDAT activity. S (+)-Amphetamine and m -tyramine inhibited sDAT activity for dopamine by competing for a common binding site with dopamine and each other, suggesting that phenethylamines are substrate analogues at the plasmalemmal sDAT. (−)-Cocaine inhibited sDAT at a site separate from that for substrate analogues. This site is mutually interactive with the substrate site ( K _int = 583 n M ). Mazindol competitively inhibited sDAT at the substrate analogue binding site. The results with (−)-cocaine suggest that the (−)-cocaine binding site on sDAT is distinct from that of hydroxyphenethylamine substrates, reinforcing the notion that an antagonist for (−)-cocaine binding may be developed to block (−)-cocaine binding with minimal effects on dopamine transporter activity. However, a strategy of how to antagonize drugs of abuse acting as substrate analogues is still elusive.     

Differential Interactions of Desipramine with Amphetamine and Methamphetamine: Evidence that Amphetamine Releases Dopamine from Noradrenergic Neurons in the Medial Prefrontal Cortex

Amphetamine is more effective than methamphetamine at raising dopamine levels in the prefrontal cortex. The current study tested the hypothesis that norepinephrine transporters are involved in this difference. Using microdialysis, dopamine, norepinephrine, and serotonin were measured in the rat prefrontal cortex after administration of methamphetamine or amphetamine, with and without perfusion of desipramine. Amphetamine raised norepinephrine levels more than methamphetamine did. Desipramine raised dopamine and serotonin levels but did not alter metabolite levels. Desipramine attenuated the increase in dopamine by amphetamine while increasing the dopamine released by methamphetamine. These data suggest that methamphetamine and amphetamine differ in altering prefrontal cortical dopamine levels and in interacting with norepinephrine transporters. It is proposed that amphetamine releases dopamine in the prefrontal cortex primarily through norepinephrine transporters, whereas methamphetamine interacts minimally with norepinephrine transporters.     

Syntaxin 1A and Receptor for Activated C Kinase Interact with the N-Terminal Region of Human Dopamine Transporter

The dopamine transporter (DAT) regulates the extent and duration of dopamine receptor activation through sodium-dependant reuptake of dopamine into presynaptic neurons, resulting in termination of dopaminergic neurotransmission. Using the yeast two-hybrid system, we have identified novel interactions between DAT, the SNARE protein syntaxin 1A, and the receptor for activated C kinases (RACK1). This association involves the intracellular N-terminal domain of human DAT (hDAT). Our data suggest that hDAT may exist as dimers or oligomers and that its protein-protein interactions with syntaxin 1A and RACK1 form functional regulatory complexes that may mediate DAT trafficking through modulation of hDAT phosphorylation by PKC.     

Inhibition of the Endogenous Volume-regulated Anion Channel (VRAC) in HEK293 Cells by Acidic Di-Aryl-Ureas

The endogenous volume-regulated anion channel (VRAC) from HEK293 cells was pharmacologically characterized using the whole-cell patch-clamp technique. Under isotonic conditions a small (1.3 nS), Ca²⁺-independent Cl conductance was measured. However, swelling at 75% tonicity activated a VRAC identified as an outward-rectifying anion current (P _l > P _Cl > P _gluconate), which was ATP-dependent and showed inactivation at positive potentials. Activation of this current followed a sigmoid time course, reaching a plateau conductance of 42.6 nS after 12–15 min (t _1/2 = 7 min). The pharmacology of this VRAC was investigated using standard Cl^–-channel blockers (NPPB, DIDS, and tamoxifen) as well as a new group (acidic di-aryl ureas) of Cl^–-channel blockers (NS1652, NS3623, NS3749, and NS3728). The acidic di-aryl ureas were originally synthezised for inhibition of the human erythrocyte Cl^– conductance in vivo. NS3728 was the most potent VRAC blocker in this series (IC ₅₀ = 0.40 µM) and even more potent than tamoxifen (2.2 µM). NS3728 accelerated channel inactivation at positive potentials. These results show that acidic di-aryl ureas constitute a promising starting point for the synthesis of potent inhibitors of VRAC.     

High Yield Expression of Recombinant Human Proteins with the Transient Transfection of HEK293 Cells in Suspension

The art of producing recombinant proteins with complex post-translational modifications represents a major challenge for studies of structure and function. The rapid establishment and high recovery from transiently-transfected mammalian cell lines addresses this barrier and is an effective means of expressing proteins that are naturally channeled through the ER and Golgi-mediated secretory pathway. Here is one protocol for protein expression using the human HEK293F and HEK293S cell lines transfected with a mammalian expression vector designed for high protein yields. The applicability of this system is demonstrated using three representative glycoproteins that expressed with yields between 95-120 mg of purified protein recovered per liter of culture. These proteins are the human FcγRIIIa and the rat α2-6 sialyltransferase, ST6GalI, both expressed with an N-terminal GFP fusion, as well as the unmodified human immunoglobulin G1 Fc. This robust system utilizes a serum-free medium that is adaptable for expression of isotopically enriched proteins and carbohydrates for structural studies using mass spectrometry and nuclear magnetic resonance spectroscopy. Furthermore, the composition of the N-glycan can be tuned by adding a small molecule to prevent certain glycan modifications in a manner that does not reduce yield.     

Voltammetric Studies on Mechanisms of Dopamine Efflux in the Presence of Substrates and Cocaine from Cells Expressing Human Norepinephrine Transporter

Abstract: The effects of substrates m -tyramine and β-phenethylamine, as well as cocaine, on the DA efflux from a cell line stably expressing the human norepinephrine transporter (hNET) were investigated by using rotating disk electrode voltammetry. Both the substrates and cocaine induced apparent DA efflux in a concentration-dependent manner. Their EC₅₀ values for inducing DA efflux were similar to their IC₅₀ values for inhibiting DA uptake. The substrate-induced DA efflux was inhibited by various NET blockers, enhanced by raising the internal [Na⁺] with Na⁺,K⁺-ATPase inhibition, but was insensitive to membrane potential-altering agents valinomycin, veratridine, and high [K⁺]. The initial rate of m -tyramine-induced DA efflux was related to preloaded [DA] in a manner defined by a Michaelis-Menten expression. In contrast, DA efflux in the presence of cocaine displayed a much slower efflux rate, lower efficacy, was not stimulated by elevated internal [Na⁺], and was nonsaturable with preloaded [DA]. Single exponential kinetic analysis of the entire time course of the DA efflux showed that the apparent first-order rate constant for m -tyramine-induced DA efflux declined with increased preloaded [DA], whereas that for the DA efflux in the presence of cocaine was unchanged with varying preloaded [DA]. These results suggest that the substrates stimulate the NET-dependent DA efflux by increasing the accessibility of the NET to internal DA, whereas cocaine "uncovers" NET-independent DA efflux by reducing the accessibility of diffused/leaked external DA to the NET.     

Human serum albumin interaction,in silico and anticancer evaluation of Pine-Gold nanoparticles

Unique characteristics displayed by phytoconstituent conjugated nanoparticles and their crucial interactions with proteins serve to develop nanoparticle-bio-interface platform. Gold nanoparticles of 16 nm in size were generated using aqueous extracts of pine bark and further conjugated to human serum albumin. The gold nanoparticles-protein complex was characterized by surface plasmon resonance, UV–vis and emission spectroscopy techniques. Further, it was characterized for surface morphology and elemental composition, crystallographic quality, nanoparticles size, shape, stability, structural determination and the identification of capping agent. Moreover, the interaction of gold nanoparticles with human serum albumin was investigated using conventional spectroscopy techniques. Fluorescence quenching and absorption studies demonstrated an effective binding of human serum albumin with oleamide capped gold nanoparticles. The molecular docking study showed a binding affinity of -6.1 kcal/mol whereas the molecular dynamics simulation indicated that the binding of oleamide to human serum albumin. A biological evaluation of pine bark extract-gold nanoparticles showed cytotoxicity with increased cell mortality in lung cancer cells and minimal toxicity on non-cancerous human embryonic kidney cells, respectively.     

Presence and Characterization of the Dopamine Transporter in Human Resting Lymphocytes

The paucity of information on the presence of the dopamine transporter (DAT) in blood cells, prompted us to explore it in human resting lymphocytes by means of the binding of ³H-WIN 35,428, a compound which is currently considered the most selective ligand for labelling this protein, and by means of the specific reuptake of ³H-dopamine (³H-DA). Lymphocytes were obtained by 15 healthy subjects. The results showed the presence of a specific and saturable binding of ³H-WIN 35,428, which labelled one site only. A specific ³H-DA reuptake was also measured. The pharmacological characterization of both binding and reuptake was overlapping. These findings would indicate that human resting lymphocytes carry the DAT, whose functions in periphery are still unknown.     

Differential Internalization Rates and Postendocytic Sorting of the Norepinephrine and Dopamine Transporters Are Controlled by Structural Elements in the N Termini

The norepinephrine transporter (NET) mediates reuptake of synaptically released norepinephrine in central and peripheral noradrenergic neurons. The molecular processes governing availability of NET in the plasma membrane are poorly understood. Here we use the fluorescent cocaine analogue JHC 1-64, as well as several other approaches, to investigate the trafficking itinerary of NET in live noradrenergic neurons. Confocal imaging revealed extensive constitutive internalization of JHC 1-64-labeled NET in the neuronal somata, proximal extensions and presynaptic boutons. Phorbol 12-myristate 13-acetate increased intracellular accumulation of JHC 1-64-labeled NET and caused a parallel reduction in uptake capacity. Internalized NET strongly colocalized with the “long loop” recycling marker Rab11, whereas less overlap was seen with the “short loop” recycling marker Rab4 and the late endosomal marker Rab7. Moreover, mitigating Rab11 function by overexpression of dominant negative Rab11 impaired NET function. Sorting of NET to the Rab11 recycling compartment was further supported by confocal imaging and reversible biotinylation experiments in transfected differentiated CATH.a cells. In contrast to NET, the dopamine transporter displayed markedly less constitutive internalization and limited sorting to the Rab11 recycling compartment in the differentiated CATH.a cells. Exchange of domains between the two homologous transporters revealed that this difference was determined by non-conserved structural elements in the intracellular N terminus. We conclude that NET displays a distinct trafficking itinerary characterized by continuous shuffling between the plasma membrane and the Rab11 recycling compartment and that the functional integrity of the Rab11 compartment is critical for maintaining proper presynaptic NET function.     

Investigation of Dopamine Content, Synthesis, and Release in the Rabbit Retina In Vitro: I. Effects of Dopamine Precursors, Reserpine, Amphetamine, and l-DOPA Decarboxylase and Monoamine Oxidase Inhibitors

The basal catecholamine content of rabbit retina was determined by liquid chromatography with electrochemical detection (LC-EC) and 3,4-dihydroxyphenylethylamine (dopamine, DA) found to be the major catecholamine. The immediate DA precursor, 3,4-dihydroxyphenylalanine (L-DOPA), and the metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were also detected at about 2.8% and 17% of DA levels, respectively. When added exogenously, L-tyrosine did not increase the rate of DA synthesis over the basal level. In contrast, exogenous L-DOPA led to a 3.5-fold increase in DA, and to a 20-fold increase in DOPAC content. The monoamine oxidase inhibitors pargyline and (-)-deprenyl differentially affected the degradation of DA, since 100 microM pargyline was apparently more effective than 100 microM (-)-deprenyl. Reserpine and (+/-)-amphetamine each induced a Ca2+-independent decrease of DA stores. The separate actions of reserpine and (+/-)-amphetamine in lowering tissue DA levels were additive, suggesting two separate pools of DA available for release from presynaptic stores. The present study demonstrates that the LC-EC technique may be used to investigate the modulation of the synthesis and release of retinal DA in vitro, without the prior uptake of radiolabelled transmitter.     

Evoked Acetylcholine Release by Immortalized Brain Endothelial Cells Genetically Modified to Express Choline Acetyltransferase and/or the Vesicular Acetylcholine Transporter

Immortalized rat brain endothelial RBE4 cells do not express choline acetyltransferase (ChAT), but they do express an endogenous machinery that enables them to release specifically acetylcholine (ACh) on calcium entry when they have been passively loaded with the neurotransmitter. Indeed, we have previously reported that these cells do not release glutamate or GABA after loading with these transmitters. The present study was set up to engineer stable cell lines producing ACh by transfecting them with an expression vector construct containing the rat ChAT. ChAT transfectants expressed a high level of ChAT activity and accumulated endogenous ACh. We examined evoked ACh release from RBE4 cells using two parallel approaches. First, Ca2+-dependent ACh release induced by a calcium ionophore was followed with a chemiluminescent procedure. We showed that ChAT-transfected cells released the transmitter they had synthesized and accumulated in the presence of an esterase inhibitor. Second, ACh released on an electrical depolarization was detected in real time by a whole-cell voltage-clamped Xenopus myocyte in contact with the cell. Whether cells synthesized ACh or whether they were passively loaded with ACh, electrical stimulation elicited the release of ACh quanta detected as inward synaptic-like currents in the myocyte. Repetitive stimulation elicited a continuous train of responses of decreasing amplitudes, with rare failures. Amplitude analysis showed that the currents peaked at preferential levels, as if they were multiples of an elementary component. Furthermore, we selected an RBE4 transgenic clone exhibiting a high level of ChAT activity to introduce the Torpedo vesicular ACh transporter (VAChT) gene. However, as the expression of ChAT was inactivated in stable VAChT transfectants, the potential influence of VAChT on evoked ACh release could only be studied on cells passively loaded with ACh. VAChT expression modified the pattern of ACh delivery on repetitive electrical stimulation. Stimulation trains evoked several groups of responses interrupted by many failures. The total amount of released ACh and the mean quantal size were not modified. As brain endothelial cells are known as suitable cellular vectors for delivering gene products to the brain, the present results suggest that RBE4 cells genetically modified to produce ACh and intrinsically able to support evoked ACh release may provide a useful tool for improving altered cholinergic function in the CNS.     

Cyclic AMP Modulates Differentially the Release of Dopamine Induced by Hypoxia and Other Stimuli and Increases Dopamine Synthesis in the Rabbit Carotid Body

We have investigated the effects of different treatments that increase cyclic AMP levels on the in vitro synthesis and release of catecholamines in the rabbit carotid body. We also measured the rate of 45Ca2+ efflux from previously loaded carotid bodies under different conditions. Forskolin produced a dose-dependent increase in the release of [3H]dopamine elicited by a hypoxic stimulus of medium intensity (PO2 = 33 mm Hg) without altering basal [3H]dopamine release (100% O2-equilibrated medium). At a concentration of 5 x 10(-6) M, forskolin increased the release of [3H]dopamine induced by hypoxic stimuli of different intensities; the increase was maximal (498%) at the lowest intensity of hypoxic stimuli (PO2 = 66 mm Hg), averaged 260% for hypoxic stimuli of intermediate intensity and 2 x 10(-4) M cyanide, and was 150% under anoxia. Dibutyryl cyclic AMP (2 mM) and 3-isobutyl-1-methylxanthine (0.5 mM) mimicked forskolin effects under hypoxic stimulation. Forskolin (5 x 10(-6) M) also increased (180%) the release of [3H]dopamine induced by 20% CO2/pH 6.6, 2.5 x 10(-4) M dinitrophenol, and 3 x 10(-5) M ionomycin. Forskolin and 3-isobutyl-1-methylxanthine were without effect on the release of [3H]dopamine elicited by 30 mM extracellular K+. Forskolin (5 x 10(-6) M) augmented significantly the rate of 45Ca2+ efflux induced by hypoxic stimuli (PO2 of 33 and 66 mm Hg) and 2 x 10(-4) M cyanide and showed a tendency to increase (20%) the 45Ca2+ efflux induced by dinitrophenol and low pH and to decrease (21%) the efflux induced by 30 mM K+ without altering the rate of efflux under basal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Salviae Miltiorrhizae BGE Radix Increases Rat Striatal K+-Stimulated Dopamine Release and Activates the Dopamine Release with Protection Against Hydrogen Peroxide-Induced Injury in Rat Pheochromocytoma PC12 Cells

The present study investigated the effect of the medicinal plant Salviae miltiorrhizae radix (SMR) on dopaminergic neurotransmission in comparison with amphetamine. The effect of SM (0.1 g/ml) on K⁺ (20 mM)-stimulated dopamine (DA) release from rat striatal slices was compared with amphetamine (10⁻⁴ M). Amphetamine and SMR significantly increased K⁺-stimulated DA release (P<0.001) from rat striatal slices when compared with K⁺-stimulated alone. On the other hand, to examine whether in vitro SMR treatment induces DA release in PC12 cells, the role of protein kinases has been investigated in the induction of the SMR-mediated events by using inhibitors of protein kinase C (PKC), mitogen activated protein kinase (MAP kinase) or protein kinase A (PKA). PKC inhibitors chelerythrine (50 and 100 nM), Ro31-8220 (100 nM) and the MAP kinase inhibitor, PD98059 (20 μM) inhibited the ability of SMR to elicit the SMR-stimulated DA release. The direct-acting PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA, 100 nM) mimicked the ability of SMR to elicit DA release. On the contrary, a selective PKA inhibitor, 50 μM Rp-8-Br-cAMP, blocked the development of SMR-stimulated DA release. The results demonstrated that SMR may stimulate DA release and that SMR-induced increases in MAP kinase and PKC are important for induction of the enhancement in transporter-mediated DA release and PKA was also required for the enhancement in SMR-stimulated DA release. SMR treatment (0.1–10 μg/ml) to the hydrogen peroxide (H₂O₂)-treated PC12 cells activated the enzyme activities such as catalase, superoxide dismutase and glutathione peroxidase, and decreased the malondialdehyde level, indicating that SMR has also protective effects against free radical-induced cell toxicity. Therefore, the mechanism by which SMR induces the enhancement in SMR-stimulated DA release is apparent. It remains to be determined whether the effect of SMR on DA function is important in its therapeutic use in the treatment of drug addiction.     

Allosteric Interaction Between the Site Labeled by [3H]Imipramine and the Serotonin Transporter in Human Platelets

The nature of interaction between the site labeled by [3H]imipramine (IMI) and the 5-hydroxytryptamine (5-HT, serotonin) transporter in human platelets was examined. The sulfhydryl characterizing agent N-ethylmaleimide (NEM) differentially affected [3H]5-HT uptake and [3H]IMI binding in human platelet preparations. Concentrations of NEM that completely abolished [3H]5-HT uptake only minimally reduced [3H]IMI binding. Examining the effect of IMI on the kinetics of human platelet [3H]5-HT uptake revealed significant reductions in maximal velocity (Vmax) without altering affinity (Km). IC50 values for selected uptake blockers on [3H]IMI binding and [3H]5-HT uptake were determined. IC50 values of these compounds for uptake and binding revealed that agents such as IMI, chlorpromazine, amitriptyline, and nisoxetine were preferential inhibitors of [3H]IMI binding whereas fluoxetine, CL 216, 303, pyrilamine, and bicifadine were preferential [3H]5-HT uptake blockers. 5-HT was a weak displacer of [3H]IMI binding (IC25 = 3.0 microM) and exhibited a rather low Hill coefficient (nH app = 0.46). Results reported herein support the notion of an allosteric interaction between the [3H]IMI binding site and the 5-HT transporter complex in human platelets.     

Cations Affect [3H]Mazindol and [3H]WIN 35,428 Binding to the Human Dopamine Transporter in a Similar Fashion

Abstract: The present study addresses the possibility that there are different cocaine-related and mazindol-related binding domains on the dopamine transporter (DAT) that show differential sensitivity to cations. The effects of Zn²⁺, Mg²⁺, Hg²⁺, Li⁺, K⁺, and Na⁺ were assessed on the binding of [³H]mazindol and [³H]WIN 35,428 to the human (h) DAT expressed in C6 glioma cells under identical conditions for intact cell and membrane assays. The latter were performed at both 0 and 21°C. Zn²⁺ (30–100 µ M ) stimulated binding of both radioligands to membranes, with a relatively smaller effect for [³H]mazindol; Mg²⁺ (0.1–100 µ M ) had no effect; Hg²⁺ at ∼3 µ M stimulated binding to membranes, with a relatively smaller effect for [³H]mazindol than [³H]WIN 35,428 at 0°C, and at 30–100 µ M inhibited both intact cell and membrane binding; Li⁺ and K⁺ substitution (30–100 m M ) inhibited binding to membranes more severely than to intact cells; and Na⁺ substitution was strongly stimulatory. With only a few exceptions, the patterns of ion effects were remarkably similar for both radioligands at both 0 and 21°C, suggesting the involvement of common binding domains on the hDAT impacted similarly by cations. Therefore, if there are different binding domains for WIN 35,428 and mazindol, these are not affected differentially by the cations studied in the present experiments, except for the stimulatory effect of Zn²⁺ at 0 and 21°C and Hg²⁺ at 0°C.     

Salviae miltiorrhizae Radix Inhibits Superoxide Generation by Activated Rat Microglias and Mimics the Action of Amphetamine on in vitro Rat Striatal Dopamine Release

Salviae miltiorrhizae Radix (SMR), an eminent herb in the treatment of cardiovascular disorder (called blood stasis in traditional Chinese medicine), is widely used in China, Japan, Taiwan and Korea. SMR is also herbal medicines used in the treatment of drug addiction without scientific support for their mechanism of action. We evaluated the effect of SMR on superoxide production by rat microglias using a 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one-dependent chemiluminescence assay. SMR dose-dependently inhibited superoxide production by microglias stimulated with phorbol myristate acetate or opsonized zymosan, while it had no effect on superoxide production by a hypoxanthinexanthine oxidase system. These results indicate that SMR does not have a scavenging effect, but has an inhibitory effect on superoxide generation by microglias. Although SMR is commonly used for treating chronic cerebral infarction, it may also have a protective effect on progression of Parkinson's disease or Alzheimer's disease. On the other hand, the present study investigated the effect of the medicinal plant on dopaminergic neurotransmission in comparison with amphetamine. The effect of crude water extracts (0.1 g/ml) of SMR on K+ (20 mM)-stimulated dopamine release from rat striatal slices was compared with amphetamine (10(-4) M) using high-performance liquid chromatography with electrochemical detection to measure endogenous dopamine. Amphetamine and SMR significantly increased K+-stimulated dopamine release (P<0.001) from rat striatal slices when compared with K+-stimulated alone. SMR potentiated the effect of amphetamine on K+-stimulated dopamine release (P<0.001) when compared with amphetamine alone. The results indicate that SMR may stimulate dopamine release in the same manner as amphetamine. It remains to be determined whether the effect of this extract on dopamine function is important in its therapeutic use in the treatment of drug addiction.     

Antioxidants Inhibit the Human Cortical Neuron Apoptosis Induced by Hydrogen Peroxide,Tumor Necrosis Factor Alpha,Dopamine and Beta-amyloid Peptide 1-42

Several substances related to the neurodegenerative diseases of Alzheimer and Parkinson, such as hydrogen peroxide, tumor necrosis factor alpha, dopamine and beta-amyloid peptide 1-42, have been shown to induce apoptosis in tumoral cell lines and rat neurons but not in human neurons. Moreover, the role of mitochondria (membrane potential) during neuronal apoptosis is still a matter of debate. We present here, for the first time, in cultured human cortical neurons that the DNA fragmentation induced by these substances was preceded by a decrease of the mitochondrial membrane potential. We have also examined the antiapoptotic effect of the antioxidants glutathione, N -acetyl-cysteine and ascorbic acid. All these antioxidants inhibited the apoptosis induced by hydrogen peroxide, tumor necrosis factor alpha, dopamine and beta-amyloid peptide 1-42, since they were able to inhibit completely the mitochondrial membrane potential depolarization and the DNA fragmentation.