Low Concentrations Of Dopamine Research Articles

Effect of polydopamine deposition conditions on polysulfone ultrafiltration membrane properties and threshold flux during oil/water emulsion filtration

Surface modification of porous membranes for water filtration has been extensively reported in the literature to improve fouling resistance. However, surface modification can significantly change the membrane filtration properties, sometimes resulting in more severe fouling than with the original, unmodified membrane. This study focused on demonstrating surface modification strategies and membrane comparison strategies to better understand the complex, competing phenomena occurring when membranes are surface modified. Polysulfone ultrafiltration membranes were modified with polydopamine (PDA) at different initial dopamine concentrations and deposition times. Membrane properties, including surface hydrophilicity, roughness, and zeta potential, were characterized. PDA coatings significantly increased surface hydrophilicity, but they did not markedly change the surface roughness or zeta potential. The threshold flux during oil/water emulsion filtration was determined and used as a fouling parameter for membranes modified with PDA at various modification conditions. The threshold flux increased when PDA was deposited at low initial dopamine concentrations or short coating times. However, PDA deposition at high initial dopamine concentrations or long coating times decreased the threshold flux, suggesting that a tradeoff exists between increased hydrophilicity and reduced pore size due to surface modification. An increase in membrane surface hydrophilicity was observed at all PDA deposition conditions, which tends to reduce foulant adhesion and increase threshold flux. However, extensive PDA coating significantly decreased membrane pure water permeance, suggesting that some membrane pores may have been narrowed or blocked, increasing local permeate flux through the remaining pores in the PDA-modified membranes. This higher local flux would exacerbate fouling and decrease threshold flux. Comparing unmodified and PDA-modified membranes having similar pure water permeance values, the PDA-modified membranes had higher threshold fluxes than the unmodified membranes.

Nanostructure Modified Microelectrode for Electrochemical Detection of Dopamine with Ascorbic Acid and Uric Acid.

Dopamine (DA) is one kind of neurotransmitter in central nervous system which is indicator of neural disease. For this reason, determination of DA concentration in central nervous system is very important for early diagnosis of neural disease. In this study, we designed micro electrode array and fabricated by MEMS technology. Furthermore, we fabricated 3-D conducting nanostructure on electrode surface for enhanced sensitivity and selectivity due to increased surface area. Compared with macro and normal micro electrode, the 3-D nanostructure modified micro electrode shows better electrical performance. These surface modified pin type electrode was applied to detect low concentration of DA and successfully detect various concentration of DA from 100 μM to 1 μM with linear relationship in the presence of ascorbic acid and uric acid. From these results, our newly designed electrode shows possibility to be applied as brain biosensor for neural disease diagnosis such as Parkinson's diseases.

Mussel-inspired fabrication of novel superhydrophobic and superoleophilic sponge modified using a high density of nanoaggregates at low concentration of dopamine

A superhydrophobic/superoleophilic sponge with outstanding adsorbency and flame-retardancy was fabricated by modification using a high density of polydopamine-nanoaggregates at low concentration of dopamine.

Dopamine regulation of striatal inhibitory transmission and plasticity: dopamine, low or high?

Basal ganglia are known for their involvement in motor control. This function is accomplished via the modulatory actions of different signalling molecules; one of these is dopamine (DA), which, besides regulating cognition and reward mechanisms, participates in the organization of motor programmes by filtering and selecting cortical commands on striatal synapses (Bromberg-Martin et al., 2010). Modulatory actions of DA in the striatum are very well described in relation to corticostriatal inputs and glutamatergic release on GABAergic medium spiny neurons (MSNs), the projection cells of the nucleus (Cepeda et al., 1993). However, the nigrostriatal pathway's DA also ends at the striatal local GABAergic circuits made by synaptic inputs on MSNs, which come from axonal collaterals of other MSNs, as well as from GABAergic interneurons (Koos et al., 2004). These inhibitory influences shape MSNs activity, both of which DA modulates (Guzman et al., 2003). We recently reported that DA decreases the effect of inhibitory synapses between GABAergic interneurons on MSNs (Nieto-Mendoza and Hernandez-Echeagaray, 2015); however, DA's effects on long-term synaptic plasticity induced in these synapses (GABAergic interneurons-MSNs) depend on the DA concentration and DA receptor subtype activation. High frequency stimulation at low DA concentrations produced mostly long-term depression (LTD), which was also favored in the presence of a D2 agonist, whereas a high concentration of DA favored the generation of long-term potentiation (LTP), which was associated with D1 receptor activation. DA neurons normally display a tonic and slow-firing frequency that is correlated to low rates of DA release; however, high frequency firing of nigrostriatal cells is associated with increases in DA release in the striatum (Cachope and Cheer, 2014). Alterations in striatal DA physiological levels are associated with some neurodegenerative diseases. Low DA levels lead to motor impairments, such as tremors, stiffness or slowing of movement characteristics of Parkinson's disease (PD). On the other hand, increased DA levels have been observed in Huntington's disease (HD), which, besides movement alterations, is also associated with cognitive and psychiatric disorders (Cepeda et al., 2014). We evaluated how the synaptic plasticity between GABAergic interneurons and MSNs was modified in mice treated with non-toxic doses of the mitochondrial inhibitor 3-nitropropionic acid (3-NP), a toxin used as a pharmacological model of striatal degeneration because it mimics some of the features of early stages of HD. The plasticity produced in slices from 3-NP-treated mice in vivo was similar to the LTP triggered under high levels of DA in healthy tissue slices. The D2 antagonist did not affect the LTP, but in the presence of the PKA inhibitor, it prevented LTP induction and generated LTD, suggesting that in a damaged striatum, D1/PKA signalling pathway play a preponderant role in the generation of LTP. Sustained elevation of DA in the striatum causes motor dysfunction, as well as the selective degeneration of MSN (Cyr et al., 2002; Chen et al., 2013). It is known that 3-NP treatment increases DA levels in the striatum (Johnson et al., 2000), and therefore, LTP produced in the inhibitory synapses on MSN, which express D1 receptors, may result from an increase of DA levels in the striatum, modulating inputs of interneurons that largely project to the perisomatic area of MSNs. This occurs because 3-NP treatment reduces the number of spines and the thickness of the dendrites (Mendoza et al., 2014). The interneurons responsible for inhibition in the perisomatic area of MSNs are known to have a synaptic impact, mainly on MSNs expressing D1 receptors (Gustafson et al., 2006). This inhibition is important because GABAergic LTP in MSNs that express D1 receptors may protect them from excitatory inputs from the cortex, and perhaps this is one of the reasons why these neurons are less damaged than are D2 expressing cells in the early stages of striatal degeneration. What can we learn from this? Similar to with excitatory synaptic plasticity in the striatum, DA modulates inhibitory long-term synaptic plasticity. In addition, activation of D1 or D2 DA receptors favors LTP or LTD expression, respectively, while low DA concentration favors LTD through D2 receptor activation. Likewise, increments of DA levels or striatal degeneration promote LTP associated with D1 receptor activation. LTP in the inhibitory synapses on MSN expressing D1 receptors may prevent exacerbated activity of the direct pathway (D1), and perhaps, may also prevent uncontrolled movement in the early stages of striatal degeneration, while LTD in the inhibitory synapses will also disinhibit the indirect pathway (D2), promoting movement. This work was supported by Consejo Nacional de Ciencia y Tecnologia, CONACYT-81062.

A Colorimetric Probe for Dopamine Based on Gold Nanoparticles-electrospun Nanofibre Composite

An easily prepared solid state colorimetric probe for detecting the neurotransmitter dopamine (DA) was developed. The probe, in the form of an electrospun Nylon−6 (N6) nanofibre with embedded un−functionalized gold nanoparticles (UF−AuNPs) produces a clear colour change in the presence of a DA that is detectable by the naked eye. Characterisation of the nanofibre using UV/vis spectroscopy and electron microscopy (TEM) confirmed the formation of the AuNPs in the polymer solution, and that the AuNPs were completely encapsulated within the composite nanofibres before exposure to the analytes. The probe exhibited very high sensitivity towards DA resulting in colour change of the composite fibres from purple to navy blue/black even under low concentrations of DA. The probe was also selective to DA since the colour remained unchanged in the presence of commonly encountered interfering species such as ascorbic acid, uric acid, catechol, epinephrine and norepinephrine. Moreover, the colour change was observed rapid, occurring either immediately on contact with higher concentrations (5 x10−4 M) or within about 3−5min for the lower concentrations (e.g. 5 x10−7 M). Since this probe does not require the use of any instruments, and is both rapid and stable over time, it can be applied in the field by an inexperienced person.

A novel mussel-inspired strategy toward superhydrophobic surfaces for self-driven crude oil spill cleanup

A superhydrophobic fabric was first fabricated by a novel mussel-inspired strategy with the aid of folic acid and a low concentration of dopamine without any additional nanoparticle incorporation. A mini boat of this fabric can automatically recycle oil spills while floating freely on water.

Metabolism of amino acids differs in the brains of Djungarian hamster (P. sungorus) and Roborovskii hamster (P. roborovskii).

Djungarian hamster (P. sungorus) and Roborovskii hamster (P. roborovskii) belong to the same genus of phodopus. Roborovskii hamster shows high locomotor activity and low level of dopamine (DA) in the brain. Administration of L-tyrosine, a precursor of DA, decreases locomotor activity in Roborovskii hamsters. However, the amino acid metabolism in relation to the hyperactivity is not yet well known. In the present study, L- and D-amino acid concentrations in the brain, liver, and plasma in Djungarian and Roborovskii hamsters were investigated during day and night times to explain the possible difference in hyperactivity between them. Most of the examined amino acids were higher in the night time when hamsters are active compared to those in day time. L- and D-tyrosine concentrations were higher in the liver of Roborovskii hamsters than in Djungarian hamsters. Furthermore, brain concentration of D-tyrosine was higher in the Roborovskii than in Djungarian hamsters, but no significant difference was observed for L-tyrosine concentrations between the two species. These results suggest that the conversion of L-tyrosine to D-tyrosine in the brain of Roborovskii hamster may be higher than in Djungarian hamster, which may cause low DA concentration and hyperactivity in Roborovskii hamster. On the other hand, L- and D-serine, which are known as sedative factors, were lower in Roborovskii hamsters than Djungarian hamster. These results suggest that species-specific regulation in amino acid metabolism may contribute to hyperactivity in Roborovskii hamsters.

Comparison and Reappraisal of Carbon Electrodes for the Voltammetric Detection of Dopamine

The electro-oxidation of dopamine (DA) is investigated on the unmodified surfaces of five different classes of carbon electrodes: glassy carbon (GC), oxygen-terminated polycrystalline boron-doped diamond (pBDD), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and the basal surface of highly oriented pyrolytic graphite (HOPG), encompassing five distinct grades with step edge density and coverage varying by more than 2 orders of magnitude. Surfaces were prepared carefully and characterized by a range of techniques, including atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. Although pBDD was found to be the least susceptible to surface fouling (even at relatively high DA concentrations), the reaction showed sluggish kinetics on this electrode. In contrast, DA electro-oxidation at pristine basal plane HOPG at concentrations ≤100 μM in 0.15 M PBS, pH 7.2, showed fast kinetics and only minor susceptibility toward surface fouling from DA byproducts, although the extent of HOPG surface contamination by oxidation products increased substantially at higher concentrations (with the response similar on all grades, irrespective of step edge coverage). EPPG also showed a fast response, with little indication of passivation with repeated voltammetric cycling but a relatively high background signal due to the high capacitance of this graphite surface termination. Of all five carbon electrode types, freshly cleaved basal plane HOPG showed the clearest signal (distinct from the background) at low concentrations of DA (<10 μM) as a consequence of the low capacitance. Studies of the electrochemical oxidation of DA in the presence of the common interferents ascorbic acid (AA) and serotonin (5-HT), of relevance to neurochemical analysis, showed that the signals for DA were still clearly and easily resolved at basal plane HOPG surfaces. In the presence of AA, repetitive voltammetry caused products of AA electro-oxidation to adsorb onto the HOPG surface, forming a permselective film that allowed the electrochemical oxidation of DA to proceed unimpeded, while greatly inhibiting the electrochemical response of AA itself. The studies presented provide conclusive evidence that the pristine surface of basal plane HOPG is highly active for the detection of DA, irrespective of the step edge density and method of cleavage, and adds to a growing body of evidence that the basal plane of HOPG is a much more active electrode for many classes of electrode reactions than previously believed.

Supersensitive presynaptic dopamine D2 receptor inhibition of the striatopallidal projection in nigrostriatal dopamine-deficient mice

The dopamine (DA) D2 receptor (D2R)-expressing medium spiny neurons (D2-MSNs) in the striatum project to and inhibit the GABAergic neurons in the globus pallidus (GP), forming an important link in the indirect pathway of the basal ganglia movement control circuit. These striatopallidal axon terminals express presynaptic D2Rs that inhibit GABA release and thus regulate basal ganglion function. Here we show that in transcription factor Pitx3 gene mutant mice with a severe DA loss in the dorsal striatum mimicking the DA denervation in Parkinson's disease (PD), the striatopallidal GABAergic synaptic transmission displayed a heightened sensitivity to presynaptic D2R-mediated inhibition with the dose-response curve shifted to the left, although the maximal inhibition was not changed. Functionally, low concentrations of DA were able to more efficaciously reduce the striatopallidal inhibition-induced pauses of GP neuron activity in DA-deficient Pitx3 mutant mice than in wild-type mice. These results demonstrate that presynaptic D2R inhibition of the striatopallidal synapse becomes supersensitized after DA loss. These supersensitive D2Rs may compensate for the lost DA in PD and also induce a strong disinhibition of GP neuron activity that may contribute to the motor-stimulating effects of dopaminergic treatments in PD.

Mesocortical dopamine system modulates mechanical nociceptive responses recorded in the rat prefrontal cortex

BackgroundPsychological conditions affect pain responses in the human anterior cingulate cortex (ACC) according to brain imaging analysis. The rodent prefrontal cortex (PFC) including cingulate areas is also related to the affective dimension of pain. We previously reported PFC nociceptive responses inhibited by inputs from the amygdala, such as with dopamine (DA) D2 receptor (D2R) blockers, to show decreased effect on amygdala projections. In this study, we examined whether direct projections from the ventral tegmental area (VTA) to the PFC affect nociceptive responses in the PFC.ResultsHigh frequency stimulation (HFS, 50 Hz, 30 s) delivered to the VTA produced long-lasting suppression (LLS) of nociceptive responses in the rat PFC including cingulate and prelimbic areas. Nociceptive responses evoked by mechanical pressure stimulation (2 s duration at 500 g constant force) applied to the tails of urethane-anesthetized rats were recorded using extracellular unit recording methods in the PFC. HFS delivered to the VTA, which has been reported to increase DA concentrations in the PFC, significantly suppressed nociceptive responses. The LLS of nociceptive responses persisted for about 30 minutes and recovered to the control level within 60 min after HFS. We also demonstrated local microinjection of a selective D2 agonist of DA receptors to induce LLS of mechanical nociceptive responses, while a D2 but not a D1 antagonist impaired the LLS evoked by HFS. In contrast, DA depletion by a 6-hydroxydopamine injection or a low concentration of DA induced by a κ-opiate receptor agonist injected into the VTA had minimal effect on nociceptive responses in the PFC.ConclusionHFS delivered to VTA inhibited nociceptive responses for a long period in PFC. DA D2R activation mediated by local D2 agonist injection also induced LLS of mechanical nociceptive responses. The mesocortical DA system may modify PFC nociceptive responses via D2 activity.

Psychopathological and peripheral levels of neurobiological correlates of obsessive–compulsive symptoms in patients with epilepsy: A hospital-based study

ObjectivesObsessive–compulsive symptoms (OCSs) and disorder (OCD) are often underdiagnosed in the out-patient epilepsy clinic. This work aimed at determining the risks and comorbidities (psychopathological and neurobiological correlates) of OCSs in treated adults with idiopathic epilepsy recruited from a university hospital. MethodsPsychiatric evaluation was done using DSM-IV (The Diagnostic and Statistical Manual of Mental Health Disorders). Obsessive–compulsive disorder was identified using the Mini International Neuropsychiatric Interview (MINI). The Beck Depression Inventory (BDI-II), Hamilton Anxiety Rating Scale (HAM-A), and Yale-Brown Obsessive Compulsive Scale (Y-BOCS) were used to determine the severity of the related psychiatric symptoms. ResultsOut of 474 patients screened, included in this study were 107 with no psychiatric symptoms and 188 with OCSs [classified as those with at least OCSs=93; mild OCSs=36; moderate, severe, and extreme OCSs=59]. A hundred healthy subjects were included as controls. Blood concentrations of serotonin, adrenaline, noradrenaline, and dopamine were measured. Compared with controls, patients with OCSs had higher frequencies of depression and anxiety. Low concentrations of serotonin, adrenaline, noradrenaline, and dopamine were reported regardless of the presence or the absence of psychiatric symptoms, OCS severities, and antiepileptic drug (AED)-related variables (dose and serum drug level). Significant correlations were identified between Y-BOCS, BDI-II, and HAM-A scores, age, age at onset, and concentrations of noradrenaline. ConclusionThis study indicates that a) OCSs are common in patients with epilepsy. Male sex, age, duration of illness, seizure focus, lateralization, and intractability to AEDs are its main risks; b) depression and anxiety are comorbid psychopathologies; and c) serotonin, catecholamines, and dopamine are linked to epilepsy-related variables and its comorbid psychopathies but not to its medications.

Effect of polymer matrix on the sensitivity of microfibrous fluorescent chemosensor containing dendritic porphyrin for the detection of dopamine

To use as a fluorescent chemosensor for detecting dopamine, dendritic porphyrin (Den-Por(Zn))-incorporated electrospun microfibrous membranes, polycaprolactone (PCL)-Por(Zn), poly(vinyl acetate) (PVAc)-Por(Zn), and poly(4-vinylpyridine) (P4VP)-Por(Zn), were fabricated. The resulting fibers exhibited a fully interconnected pore structure with narrow pore size distribution. Energy dispersive X-ray spectroscopy and attenuated total reflectance–Fourier transform infrared (ATR–FTIR) results clearly revealed the introduction of dendritic porphyrin on the surface of electrospun membranes. Among the electrospun membranes, P4VP-Por(Zn) exhibited highest sensitivity to dopamine. P4VP-Por(Zn) showed more hydrophilic property than other fibers, and the strong intermolecular interaction between P4VP and dopamine was observed. Therefore, the significant decline of fluorescence intensity even after the reaction with low concentrations of dopamine was measured, in which dopamine probably acted as a quencher. This is attributed to the complex formation between dopamine and Zn of Den-Por(Zn) introduced into the P4VP-Por(Zn) via the chelation.

Electrodeposition for preparation of efficient surface-enhanced Raman scattering-active silver nanoparticle substrates for neurotransmitter detection

A stable and efficient surface-enhanced Raman scattering (SERS) substrate for neurotransmitter and cholinergic neurotransmission precursor detection was obtained by silver nanoparticle (AgNP) electrodeposition onto tin-doped indium oxide (ITO) using cyclic voltammetry. The size and surface coverage of the deposited AgNPs were controlled by changing the scan rate and the number of scans. The SERS performance of these substrates was analyzed by studying its reproducibility, repeatability and signal enhancement measured from p-aminothiophenol (p-ATP) covalently bonded to the substrate. We compared the SERS performance for samples with different Ag particle coverage and particle sizes. The performance was also compared with a commercial substrate. Our substrates exhibited a SERS enhancement factor of around 107 for p-ATP which is three orders of magnitude larger than for the commercial substrate. Apart from this high enhancement effect the substrate also shows extremely good reproducibility. The average spectral correlation coefficient (Γ) is 0.96. This is larger than for the commercial substrate (0.85) exhibiting a much lower SERS signal intensity. Finally, the application of our substrates as SERS bio-sensors was demonstrated with the detection of the neurotransmitters acetylcholine, dopamine, epinephrine and choline, the precursor for acetylcholine. The intensive SERS spectra observed for low concentrations of choline (2×10−6M), acetylcholine (4×10−6M), dopamine (1×10−7M) and epinephrine (7×10−4M) demonstrated the high sensitivity of our substrate. The high sensitivity and fast data acquisition make our substrates suitable for testing physiological samples.

Neuromodulator-evoked synaptic metaplasticity within a central pattern generator network.

Synapses show short-term activity-dependent dynamics that alter the strength of neuronal interactions. This synaptic plasticity can be tuned by neuromodulation as a form of metaplasticity. We examined neuromodulator-induced metaplasticity at a graded chemical synapse in a model central pattern generator (CPG), the pyloric network of the spiny lobster stomatogastric ganglion. Dopamine, serotonin, and octopamine each produce a unique motor pattern from the pyloric network, partially through their modulation of synaptic strength in the network. We characterized synaptic depression and its amine modulation at the graded synapse from the pyloric dilator neuron to the lateral pyloric neuron (PD→LP synapse), driving the PD neuron with both long square pulses and trains of realistic waveforms over a range of presynaptic voltages. We found that the three amines can differentially affect the amplitude of graded synaptic transmission independently of the synaptic dynamics. Low concentrations of dopamine had weak and variable effects on the strength of the graded inhibitory postsynaptic potentials (gIPSPs) but reliably accelerated the onset of synaptic depression and recovery from depression independently of gIPSP amplitude. Octopamine enhanced gIPSP amplitude but decreased the amount of synaptic depression; it slowed the onset of depression and accelerated its recovery during square pulse stimulation. Serotonin reduced gIPSP amplitude but increased the amount of synaptic depression and accelerated the onset of depression. These results suggest that amine-induced metaplasticity at graded chemical synapses can alter the parameters of synaptic dynamics in multiple and independent ways.

Electrochemical behavior of dopamine and ascorbic acid at dendritic Au rod surfaces: Selective detection of dopamine in the presence of high concentration of ascorbic acid

Electrochemical behavior of dopamine (DA) and ascorbic acid (AA) at dendritic Au rod (DAR) surfaces prepared by a simple and fast electrodeposition from sulfite-based Au(I) electrolytes was investigated. The unique DAR structures with sharp edge Au sites differentiated the anodic waves between DA and AA, and the electrooxidation of DA at DAR surfaces was significantly enhanced at lower DA concentration ranges. The DAR surfaces enabled the differential pulse voltammetric determination of DA in the presence of 0.1mM of AA, and the modification of the DAR with Nafion layers enhanced the sensitivity and selectivity against AA. Electrochemical deposition would offer an efficient route for fabricating nanostructured surfaces for electrochemical determination of biologically important species.

Ambient illuminance, retinal dopamine release and refractive development in chicks

Form deprivation and low illuminance of ambient light are known to induce myopia in chicks. Low concentrations of retinal dopamine, a light-driven neurohormone, was previously shown to be associated with form deprivation myopia. In the present study we examined the dependence of retinal dopamine release in chicks on illuminance during light–dark cycles and in continuous light, and the role of retinal dopamine release in illuminance dependent refractive development. Newly hatched chicks (n = 166) were divided into two experimental groups, a dopamine (n = 88) and a refraction group (n = 78). Both groups were further divided into six illumination groups for exposure of chicks to illuminances of 50, 500 or 10,000 lux of incandescent illumination (referred to throughout as low, medium, and high illuminance, respectively), either under a light–dark cycle with lights on between 7 AM and 7 PM or under continuous illumination. For the dopamine experiment, chicks were euthanized and vitreous was extracted on day 14 post-hatching at 7, 8 AM and 1 PM. Vitreal dihydroxyphenylacetic acid (DOPAC) and dopamine concentrations were quantified by high-performance liquid chromatography coupled to electrochemical detection. For the refraction experiment, chicks underwent refraction, keratometry and A-scan ultrasonography on days 30, 60 and 90 post-hatching, and each of those measurements was correlated with vitreal DOPAC concentration measured at 1 PM (representing the index of retinal dopamine release). The results showed that under light–dark cycles, vitreal DOPAC concentration was strongly correlated with log illuminance, and was significantly correlated with the developing refraction, corneal radius of curvature, and axial length values. On day 90, low vitreal DOPAC concentrations were associated with myopia (−2.41 ± 1.23 D), flat cornea, deep anterior and vitreous chambers, and thin lens. Under continuous light, vitreal DOPAC concentrations measured at 1 PM in the low, medium, and high illuminance groups did not differ from the concentrations measured at 8 AM. On day 90, low DOPAC concentrations were associated with emmetropia (+0.63 ± 3.61), steep cornea, and shallow vitreous chamber. We concluded that ambient light over a log illuminance range of 1.69–4 is linearly related to vitreal DOPAC concentration. Under both light–dark cycles and continuous light, the intensity of ambient light regulates the release of retinal dopamine. Refractive development is associated with illuminance dependent dopamine release.

Poly(Rhodamine B) modified carbon paste electrode for the selective detection of dopamine

An electrochemical sensor for the selective detection of dopamine was developed by the electropolymerization of Rhodamine B dye at a carbon paste electrode. Under physiological conditions, the modified electrode was able to resolve the voltammetric peak of dopamine from all interfering species whose concentrations were thousand folds more than that of dopamine. A wide linear dynamic range of 6–1000μM and a detection limit of 3.99×10−6M were observed for dopamine. The main advantage of the modified electrode using differential pulse voltammetric technique is its inability to sense the presence of micro-molar levels of ascorbic acid and uric acid while it can detect dopamine at the micro-molar level. This unique property of the modified electrode eliminates the possible interferences of low concentrations of ascorbic acid while also making it more sensitive and convenient to use as a sensor for the detection of low concentrations of dopamine in real samples. Satisfactory results were obtained while the modified electrode was employed for determination of dopamine in human blood serum and dopamine hydrochloride injection. The electrode showed excellent reproducibility, selectivity and antifouling effects.

Dopaminergic modulation of low-Mg2+-induced epileptiform activity in the intact hippocampus of the newborn mouse in vitro

To investigate whether epileptiform activity in the immature brain is modulated by dopamine, we examined the effects of dopaminergic agonists and antagonists in an intact in vitro preparation of the isolated corticohippocampal formation of immature (postnatal days 3 and 4) C57/Bl6 mice using field potential recordings from CA3. Epileptiform discharges were induced by a reduction of the extracellular Mg(2+) concentration to 0.2 mM. These experiments revealed that low concentrations of dopamine (<0.3 μM) attenuated epileptiform activity, whereas >3 μM dopamine enhanced epileptiform activity. The D1-agonist SKF38393 (10 μM) had a strong proconvulsive effect, and the D2-like agonist quinpirole (10 μM) mediated a weak anticonvulsive effect. The proconvulsive effect of 10 μM dopamine was completely abolished by the D1-like receptor antagonist SCH39166 (2 μM) or the D2-like antagonist sulpiride (10 μM), whereas the D2 antagonist L-741626 (50 nM) and the D3 antagonist SB-277011-A (0.1 μM) were without effect. The anticonvulsive effect of 0.1 μM dopamine could be suppressed by D1-like, D2, or D3 receptor antagonists. A proconvulsive effect of 10 μM dopamine was also observed when AMPA, NMDA, or GABA(A) receptors were blocked. In summary, these results suggest that 1) dopamine influences epileptiform activity already at early developmental stages; 2) dopamine can bidirectionally influence the excitability; 3) D1-like receptors mediate the proconvulsive effect of high dopamine concentrations, although the pharmacology of the anticonvulsive effect is less clear; and 4) dopamine-induced alterations in GABAergic and glutamatergic systems may contribute to this effect.

HIV‐1 protein Tat inhibits vesicular monoamine transporter‐2 activity in rat striatum

HIV‐1 protein Tat inhibits vesicular monoamine transporter‐2 activity in rat striatum

Reversal of Dopamine Inhibition of Dopaminergic Neurons of the Ventral Tegmental Area is Mediated by Protein Kinase C

Adaptation of putative dopaminergic (pDA) neurons in the ventral tegmental area (VTA) to drugs of abuse may alter information processing related to reward and reinforcement and is an important factor in the development of addiction. We have demonstrated that prolonged increases in the concentration of dopamine (DA) result in a time-dependent decrease in sensitivity of pDA neurons to DA, which we termed DA inhibition reversal (DIR). In this study, we used extracellular recordings to examine factors mediating DIR. A 40 min administration of DA (2.5-10 μM), but not the DA D2 receptor agonist quinpirole (50-200 nM), resulted in inhibition of neuronal firing followed by DIR. In the presence of 100 nM cocaine, inhibition followed by DIR was seen with much lower DA concentrations. Reversal of quinpirole inhibition could be induced by an activator of protein kinase C, but not of protein kinase A. Inhibitors of protein kinase C or phospholipase C blocked the development of DIR. Disruption of intracellular calcium release also prevented DIR. Reduction of extracellular calcium or inhibition of store-operated calcium entry blocked DIR, but the L-type calcium channel blocker nifedipine did not. DIR was age-dependent and not seen in pDA VTA neurons from rat pups younger than 15 days postnatally. Our data indicate that DIR is mediated by protein kinase C, and implicate a conventional protein kinase C. This characterization of DIR gives insight into the regulation of autoinhibition of pDA VTA neurons, and the resulting long-term alteration in information processing related to reward and reinforcement.