Application Of Dopamine Research Articles

Exogenous dopamine mitigates the effects of salinity stress in tomato seedlings by alleviating the oxidative stress and regulating phytohormones

Salt stress is a worldwide major threat to agricultural production. The aim was to investigate the effects of exogenous dopamine (DA) treatments on physiological, morphological and biochemical characteristics of tomato seedlings under salinity stress. Salt stress was created using a 100 mM NaCl solution. Dopamine solutions (0, 50, 100 and 200 µM) were applied with 7-day intervals. Salt stress significantly suppressed plant growth and DA treatments alleviated the negative effects of salt stress on the growth of tomato seedlings. 100 µM DA treatment increased plant and root dry weights, plant stem diameter, plant height and, leaf area by 286.84%, 150.00%, 108.37%, 160.89%, and 158.28%, respectively, compared to the control. Under salinity LRWC, SPAD, chl-a, chl-b, and total chlorophyll contents decreased; membrane permeability (MP), H2O2, MDA, proline and sucrose contents, CAT, POD and SOD activities increased. Under salt stress, when 100 µM DA was applied, LRWC, SPAD, chl-a, chl-b, and total chlorophyll contents of plants increased by 13.64%, 18.62%, 43.08%, 64.90%, and 50.00%, while MP reduced by 21.08% compared to the control. When 200 µM DA was applied under salt stress, H2O2, MDA, proline and sucrose contents, and CAT, POD and SOD activities were reduced by 31.86%, 18.66%, 56.00%, 38.24%, 11.16%, 17.81% and 10.80%, respectively, compared to non-DA-treated plants. Exogenous application of DA increased IAA content, decreased ABA content and increased ratio of K+/Na+ and Ca2+/Na+ under salt stress as well. In conclusion, exogenous dopamine treatments effectively prevent cellular damage in tomato seedlings and improve plant tolerance to salt stress.

Effect of Dopamine on Growth, Some Biochemical Attributes, and the Yield of Crisphead Lettuce under Nitrogen Deficiency

Nitrogen (N) represents the most important nutrient for plant growth and productivity, but extreme and ineffective usage of N fertilizer results in boosted plant production expenditures and environmental contamination. For the world’s sustainable food production and environmental profits, there has been increased research interest in reducing the use of N fertilization along with improving plant N deficiency (ND) tolerance. Dopamine (DA), a potential antioxidant, mediates several physio-biochemical processes in plants under normal or stressful conditions. However, their roles in increasing ND tolerance in crisphead lettuce are not well-documented. We investigate the role of DA concentration (0.50 and 100 µM) on the growth and yield of crisphead lettuce plants under ND. Under normal conditions (100% recommended N fertilizer dose), DA (50 and 100 μM) application significantly enhanced growth, chlorophyll concentration, N%, antioxidant enzymes activity, as well as yield and its components, decreased nitrate accumulation and oxidative biomarkers compared to untreated plants (0 μM DA). ND significantly decreased plant growth and yield attributes as well as evoked oxidative impairment and nitrate accumulation as compared to 100% recommended N fertilizer dose in the absence of DA. However, within ND conditions, the application of DA concentrations significantly mitigated ND-induced oxidative burst and improved plant growth, chlorophyll concentration, N%, nitrate concentration, peroxidase, catalase, superoxide dismutase, total soluble solid, vitamin C, dry matter %, and total sugars, over 0 μM DA treated plants. Current findings highlighted that exogenous application of 100 μM DA could reinforce the crisphead lettuce plant’s resilience to ND by minimizing reactive oxygen species accumulation and promoting enzymatic antioxidants alongside growth, yield, and quality improvement. The beneficial effects of DA in lessening ND’s drastic impacts on crisphead lettuce resulted from upregulating antioxidant enzyme activity, impairment of oxidative biomarkers, and maintaining chlorophyll levels. The current findings open pioneering prospects to reduce nitrogen fertilization by DA application without any drastic effect on plant productivity. But further research is needed to fully understand DA effects and their mechanisms in inducing ND tolerance in different plant species, including crisphead lettuce.

New Insight into the Function of Dopamine (DA) during Cd Stress in Duckweed (Lemna turionifera 5511).

Dopamine (DA), a kind of neurotransmitter in animals, has been proven to cause a positive influence on plants during abiotic stress. In the present study, the function of DA on plants under cadmium (Cd) stress was revealed. The yellowing of duckweed leaves under Cd stress could be alleviated by an exogenous DA (10/20/50/100/200 μM) supplement, and 50 μM was the optimal concentration to resist Cd stress by reducing root breakage, restoring photosynthesis and chlorophyll content. In addition, 24 h DA treatment increased Cd content by 1.3 times in duckweed under Cd stress through promoting the influx of Cd2+. Furthermore, the gene expression changes study showed that photosynthesis-related genes were up-regulated by DA addition under Cd stress. Additionally, the mechanisms of DA-induced Cd detoxification and accumulation were also investigated; some critical genes, such as vacuolar iron transporter 1 (VIT1), multidrug resistance-associated protein (MRP) and Rubisco, were significantly up-regulated with DA addition under Cd stress. An increase in intracellular Ca2+ content and a decrease in Ca2+ efflux induced by DA under Cd stress were observed, as well as synchrony with changes in the expression of cyclic nucleotide-gated ion channel 2 (CNGC2), predicting that, in plants, CNGC2 may be an upstream target for DA action and trigger the change of intracellular Ca2+ signal. Our results demonstrate that DA supplementation can improve Cd resistance by enhancing duckweed photosynthesis, changing intracellular Ca2+ signaling, and enhancing Cd detoxification and accumulation. Interestingly, we found that exposure to Cd reduced endogenous DA content, which is the result of a blocked shikimate acid pathway and decreased expression of the tyrosine aminotransferase (TAT) gene. The function of DA in Cd stress offers a new insight into the application and study of DA to Cd phytoremediation in aquatic systems.

Nicotine-mediated dopamine regulates short neuropeptide F to inhibit brown planthopper feeding behavior in tobacco-rice rotation cropping.

The tobacco-rice rotation cropping (TRRC) is an ecologically friendly system that can both alleviate soil nicotine pollution and decrease the brown planthopper (BPH, Nilaparvata lugens Stål) fitness on rice. However, few studies on this green and effective rotational cropping system have been reported. In particular, the underlying mechanisms of TRRC on the significant reduction of field pest population at the molecular level is still unknown. Field investigation showed that BPH population decreased significantly in TRRC than in rice-rice successive cropping (RRSC) field. In addition, the short neuropeptide F (NlsNPF) and its receptor NlA7 of BPH had half-times lower levels in the TRRC field. Behavioral bioassay indicated a 1.93-fold increase in the number of salivary flanges of the dsNlsNPF group, while BPH fitness parameters, such as honeydew, weight gain, and mortality decreased significantly. Dopamine (DA) content in BPH decreased by ~11.1% under the influence of nicotine, and its presence increased the expression levels of NlsNPF and NlA7. Exogenous DA application eliminated the inhibitory effects of nicotine on BPH feeding and restored the fitness levels of its parameters. Independent application of either a mixture of dsNlsNPF with a nanocarrier or nicotine to the normal rice field revealed that the latter could produce better effects in combination with dsRNA. These findings confirmed that DA regulated NlsNPF to inhibit the BPH feeding behavior in TRRC. The results not only provided novel findings on the mechanism of pest-host interactions, but also presented new method for integrated pest management. © 2023 Society of Chemical Industry.

Altered dopaminergic pathways and therapeutic effects of intranasal dopamine in two distinct mouse models of autism

The dopamine (DA) system has a profound impact on reward-motivated behavior and is critically involved in neurodevelopmental disorders, such as autism spectrum disorder (ASD). Although DA defects are found in autistic patients, it is not well defined how the DA pathways are altered in ASD and whether DA can be utilized as a potential therapeutic agent for ASD. To this end, we employed a phenotypic and a genetic ASD model, i.e., Black and Tan BRachyury T+Itpr3tf/J (BTBR) mice and Fragile X Mental Retardation 1 knockout (Fmr1-KO) mice, respectively. Immunostaining of tyrosine hydroxylase (TH) to mark dopaminergic neurons revealed an overall reduction in the TH expression in the substantia nigra, ventral tegmental area and dorsal striatum of BTBR mice, as compared to C57BL/6 J wild-type ones. In contrast, Fmr1-KO animals did not show such an alteration but displayed abnormal morphology of TH-positive axons in the striatum with higher “complexity” and lower “texture”. Both strains exhibited decreased expression of striatal dopamine transporter (DAT) and increased spatial coupling between vesicular glutamate transporter 1 (VGLUT1, a label for glutamatergic terminals) and TH signals, while GABAergic neurons quantified by glutamic acid decarboxylase 67 (GAD67) remained intact. Intranasal administration of DA rescued the deficits in non-selective attention, object-based attention and social approaching of BTBR mice, likely by enhancing the level of TH in the striatum. Application of intranasal DA to Fmr1-KO animals alleviated their impairment of social novelty, in association with reduced striatal TH protein. These results suggest that although the DA system is modified differently in the two ASD models, intranasal treatment with DA effectively rectifies their behavioral phenotypes, which may present a promising therapy for diverse types of ASD.

Exogenous Dopamine Application Promotes Alkali Tolerance of Apple Seedlings.

Arid and semiarid apple producing areas suffer from severe alkalinity of soil, which strongly affects the yield and quality of apples. Dopamine (DA) is involved in metabolic activities in response to abiotic stress in plants. To detect the effects of exogenous DA application on the adaption of apple (Malus hupehensis) seedlings to alkali stress and as a protection from oxidative stress, 0.1 mM DA was identified as the most suitable concentration by hydroponic culture. Further experimentation showed that the growth and photosynthesis of apple seedlings were significantly inhibited under alkali stress, and more reactive oxygen species accumulated, compared with control. However, exogenous DA application suppressed the loss of the plant height, root length, chlorophyll levels, and photosynthetic capacity of apple seedlings that were caused by alkali stress. In the leaves of alkali stressed seedlings, the catalase, superoxide dismutase, and peroxidase activities were lower and hydrogen peroxide and malondialdehyde levels were higher than in the untreated plants. The presence of DA significantly alleviated such effects of alkali stress. In addition, exogenous DA application increased the antioxidant capacity of apple seedlings under alkali stress by increasing the level of chlorogenic acid. These results are significant for improving the alkali tolerance of apple in apple-producing areas with alkalized soil.

Corticostriatal synaptic plasticity alterations in the R6/1 transgenic mouse model of Huntington's disease.

Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal dopamine (DA)-glutamate interactions, severe alterations in motor control, and reduced behavioral flexibility. Experimental models of disease show that during symptomatic phases, HD shares with other hyperkinetic disorders the loss of synaptic depotentiation in the striatal spiny projection neurons (SPNs). Here we test the hypothesis that corticostriatal long-term depression (LTD), a well-conserved synaptic scaling down response to environmental stimuli, is also altered in symptomatic male R6/1 mice, a HD model with gradual development of symptoms. In vitro patch-clamp and intracellular recordings of corticostriatal slices from R6/1 mice confirm that, similar to other models characterized by hyperkinesia and striatal DA D1 receptor pathway dysregulation, once long-term potentiation (LTP) is induced, synaptic depotentiation is lost. Our new observations show that activity-dependent LTD was abolished in SPNs of mutant mice. In an experimental condition in which N-methyl-d-aspartate (NMDA) receptors are normally not recruited, in vitro bath application of DA revealed an abnormal response of D1 receptors that caused a shift in synaptic plasticity direction resulting in an NMDA-dependent LTP. Our results demonstrate that corticostriatal LTD is lost in R6/1 mouse model and confirm the role of aberrant DA-glutamate interactions in the alterations of synaptic scaling down associated with HD symptoms.

Effect of microinjections of dopamine into the nucleus accumbens shell on emission of 50 kHz USV: Comparison with effects of d-amphetamine

Systemic pharmacological manipulation of dopamine (DA) signaling has been central to many investigations of 50 kHz ultrasonic vocalizations (USVs) in the rat. In particular, the indirect DA releaser d-amphetamine (AMPH) has been used extensively in many such investigations. The possible unique character of the native transmitter relative to DA-stimulating drugs such as AMPH in inducing and modulating emission of 50 kHz USVs has not been investigated. Adult male Long Evans rats were tested with intracerebral application of DA into the nucleus accumbens shell at several doses (3.75 μg–120 μg) to determine its capacity to induce 50 kHz USV emission. Additionally, the call profile characteristics of intracerebral DA injections were compared with those of intracerebral application of AMPH. Results indicated that local increases in DA signaling within the nucleus accumbens shell are sufficient to increase 50 kHz call rate, reduce latency to call, and increase the degree of frequency modulation of emitted USVs. However, our results found that microinjections of DA were not as efficacious in either inducing 50 kHz USVs or increasing frequency modulation without antagonism of the dopamine reuptake transporter when compared with AMPH. In summary, these results support the notion that the native transmitter DA is driving the increase in frequency modulation seen after administration of DA stimulating drugs. These results also suggest that drugs affecting dopamine may be altering the 50 kHz call profile in a distinct manner from the native transmitter and thus caution should be used in interpreting their effects.

Dopamine acting at D1-like, D2-like and α1-adrenergic receptors differentially modulates theta and gamma oscillatory activity in primary motor cortex.

The loss of dopamine (DA) in Parkinson’s is accompanied by the emergence of exaggerated theta and beta frequency neuronal oscillatory activity in the primary motor cortex (M1) and basal ganglia. DA replacement therapy or deep brain stimulation reduces the power of these oscillations and this is coincident with an improvement in motor performance implying a causal relationship. Here we provide in vitro evidence for the differential modulation of theta and gamma activity in M1 by DA acting at receptors exhibiting conventional and non-conventional DA pharmacology. Recording local field potentials in deep layer V of rat M1, co-application of carbachol (CCh, 5 μM) and kainic acid (KA, 150 nM) elicited simultaneous oscillations at a frequency of 6.49 ± 0.18 Hz (theta, n = 84) and 34.97 ± 0.39 Hz (gamma, n = 84). Bath application of DA resulted in a decrease in gamma power with no change in theta power. However, application of either the D1-like receptor agonist SKF38393 or the D2-like agonist quinpirole increased the power of both theta and gamma suggesting that the DA-mediated inhibition of oscillatory power is by action at other sites other than classical DA receptors. Application of amphetamine, which promotes endogenous amine neurotransmitter release, or the adrenergic α1-selective agonist phenylephrine mimicked the action of DA and reduced gamma power, a result unaffected by prior co-application of D1 and D2 receptor antagonists SCH23390 and sulpiride. Finally, application of the α1-adrenergic receptor antagonist prazosin blocked the action of DA on gamma power suggestive of interaction between α1 and DA receptors. These results show that DA mediates complex actions acting at dopamine D1-like and D2-like receptors, α1 adrenergic receptors and possibly DA/α1 heteromultimeric receptors to differentially modulate theta and gamma activity in M1.

Vagally mediated effects of brain stem dopamine on gastric tone and phasic contractions of the rat

Dopamine (DA)-containing fibers and neurons are embedded within the brain stem dorsal vagal complex (DVC); we have shown previously that DA modulates the membrane properties of neurons of the dorsal motor nucleus of the vagus (DMV) via DA1 and DA2 receptors. The vagally dependent modulation of gastric tone and phasic contractions, i.e., motility, by DA, however, has not been characterized. With the use of microinjections of DA in the DVC while recording gastric tone and motility, the aims of the present study were 1) assess the gastric effects of brain stem DA application, 2) identify the DA receptor subtype, and, 3) identify the postganglionic pathway(s) activated. Dopamine microinjection in the DVC decreased gastric tone and motility in both corpus and antrum in 29 of 34 rats, and the effects were abolished by ipsilateral vagotomy and fourth ventricular treatment with the selective DA2 receptor antagonist L741,626 but not by application of the selective DA1 receptor antagonist SCH 23390. Systemic administration of the cholinergic antagonist atropine attenuated the inhibition of corpus and antrum tone in response to DA microinjection in the DVC. Conversely, systemic administration of the nitric oxide synthase inhibitor nitro-l-arginine methyl ester did not alter the DA-induced decrease in gastric tone and motility. Our data provide evidence of a dopaminergic modulation of a brain stem vagal neurocircuit that controls gastric tone and motility.NEW & NOTEWORTHY Dopamine administration in the brain stem decreases gastric tone and phasic contractions. The gastric effects of dopamine are mediated via dopamine 2 receptors on neurons of the dorsal motor nucleus of the vagus. The inhibitory effects of dopamine are mediated via inhibition of the postganglionic cholinergic pathway.

Dopaminergic Control of Locomotor Patterning during Development: A Tail for the Ages.

Dopamine (DA) directly modulates motor circuits in the brain and spinal cord. While the somata of all dopaminergic (DAergic) neurons in zebrafish and mammals are supraspinal, some of these, termed diencephalospinal neurons (DDNs), send long-distance descending projections into the spinal cord (Figure ​(Figure1A)1A) and have recently been implicated in spinal network (Reimer et al., 2013) and locomotor development (Lambert et al., 2012) in zebrafish. After many years of seminal research on the morphology and genetic specification of zebrafish DDNs and the DAergic diencephalospinal tract (DDT) (Schweitzer and Driever, 2009), our recent study was the first to explicitly investigate DDN function (Lambert et al., 2012). We combined pharmacological DAergic perturbations, demarcated transections, and selective chemogenetic ablation of orthopedia (otp) neurons to demonstrate that conserved DAergic otp neurons–a subset of which are DDNs (Fujimoto et al., 2011; Figure 1A2)—provide the impetus for endogenous DA receptor 4 (D4R) signaling to initiate and maintain a developmental switch, between 80 and 96 h post fertilization (hpf), to the mature episodic locomotor pattern of zebrafish. Interestingly, Reimer et al. (2013) also demonstrated that DAergic otp neurons drive endogenous D4R signaling, confirmed both pharmacologically and genetically, but for an even earlier developmental function- to influence the differentiation of spinal motor progenitor cells between 24 and 48 hpf. Both studies used additional experimental approaches to demonstrate that D4R signaling directly in the spinal cord was sufficient to emulate the developmental processes under question: localized spinal application of DA or D4R agonists was shown to influence progenitor pools, when applied for many hours (Reimer et al., 2013), or to modulate the duration of locomotor episodes, when applied for just 5–10 min (Lambert et al., 2012). Collectively, these studies unveil that DDNs may drive endogenous spinal D4R signaling, via the DDT, for two temporally distinct roles in locomotor development: (1) a transient early role that acts directly on progenitor pools but not neurons, with long lasting consequences (Figure ​(Figure1B,1B, left), and (2) a late role that likely acts through ongoing spinal neuronal signaling, for maintenance of episodic locomotor patterns (Figure ​(Figure1B,1B, right). This commentary considers the extent to which an understanding of each of these developmental roles integrates with or is modified by the most recent DDN-related findings of Jay et al.

Dopaminergic Modulation of Excitatory Transmission in the Anterior Cingulate Cortex of Adult Mice.

Dopamine (DA) possesses potent neuromodulatory properties in the central nervous system. In the anterior cingulate cortex, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAR) are key ion channels in mediating nerve injury induced long-term potentiation (LTP) and chronic pain phenotype. In the present study, we reported the effects of DA on glutamate mediated excitatory post-synaptic currents (EPSCs) in pyramidal neurons of layer II/III of the ACC in adult mice. Bath application of DA (50 μM) caused a significant, rapid and reversible inhibition of evoked EPSCs (eEPSC). This inhibitory effect is dose-related and was absent in lower concentration of DA (5 μM). Furthermore, selective postsynaptic application of GDP-β-S (1.6 mM) in the internal solution completely abolished the inhibitory effects of DA (50 μM). We also investigated modulation of spontaneous EPSCs (sEPSCs) and TTX sensitive, miniature EPSCs (mEPSCs) by DA. Our results indicated mixed effects of potentiation and inhibition of frequency and amplitude for sEPSCs and mEPSCs. Furthermore, high doses of SCH23390 (100 μM) and sulpiride (100 μM) revealed that, inhibition of eEPSCs is mediated by postsynaptic D2-receptors (D2R). Our finding posits a pre- and postsynaptic mode of pyramidal neuron EPSC modulation in mice ACC by DA.

Midbrain dopamine neurons bidirectionally regulate CA3-CA1 synaptic drive.

Dopamine (DA) is required for hippocampal-dependent memory and long-term potentiation (LTP) at CA1 Schaffer collateral (SC) synapses. It is therefore surprising that exogenously applied DA has little effect on SC synapses, but suppresses CA1 perforant path (PP) inputs. To examine DA actions under more physiological conditions, we used optogenetics to release DA from ventral tegmental area inputs to hippocampus. Unlike exogenous DA application, optogenetic release of DA caused a bidirectional, activity-dependent modulation of SC synapses, with no effect on PP inputs. Low levels of DA release, simulating tonic DA neuron firing, depressed the SC response through a D4 receptor-dependent enhancement of feedforward inhibition mediated by parvalbumin-expressing interneurons. Higher levels of DA release, simulating phasic firing, increased SC responses through a D1 receptor-dependent enhancement of excitatory transmission. Thus, tonic-phasic transitions in DA neuron firing in response to motivational demands may cause a modulatory switch from inhibition to enhancement of hippocampal information flow.

Brainstem Dopamine Controls Gastric Tone And Motility

Gastrointestinal (GI) dysfunctions, such as gastroparesis, are prodromic to Parkinson's disease (PD). Upper GI functions are modulated by neurons in the dorsal vagal complex (DVC); recently, we reported a monosynaptic dopaminergic connection between the substantia nigra pars compacta (SNpc) and the DVC, activation of which modulates gastric tone and motility via dopamine (DA)1 receptors. The effects of DVC application of DA on gastric tone and motility, however, have not been characterized.Gastric tone & motility were recorded in rats using strain gauges sewn onto the anterior gastric wall. DA (0.1pmoles‐10nmoles/60nL; N=10‐16) microinjected in the left DVC decreased tone & motility in both the corpus (at 1nmole, tone: ‐152±21mg; motility: ‐57±6% of baseline) and in the antrum (at 1nmole, tone: ‐222±22 mg; motility: ‐41±6% of baseline, respectively; P<0.05 for all).Equivalent doses of DA induced a larger decrease in antrum compared to corpus tone, while motility was affected similarly. The effects of DA were blocked by ipsilateral vagotomy (N=4) and by application of DA2 (L741626), but not DA1 (SCH23390), antagonists (both at 45nM, N=7).DVC application of the dopamine uptake inhibitor, benztropine (100nmoles, N=2‐6), decreased tone (‐76±24 and ‐245±85mg) but increased motility (23±7 and 41±18% of baseline) in corpus and antrum, respectively.Our data indicate that the dopaminergic innervation of the DVC modulates gastric tone and motility differentially: when exogenous DA is applied, the effects are mediated mainly via DA2 receptors, which are also tonically active in setting gastric tone; conversely, a tonic DA1 input modulates gastric motility. We would like to suggest that this latter pathway is involved in the reduced gastric motility observed in PD.

Dopamine-Induced Dissociation of BOLD and Neural Activity in Macaque Visual Cortex

Neuromodulators determine how neural circuits process information during cognitive states such as wakefulness, attention, learning, and memory. fMRI can provide insight into their function and dynamics, but their exact effect on BOLD responses remains unclear, limiting our ability to interpret the effects of changes in behavioral state using fMRI. Here, we investigated the effects of dopamine (DA) injections on neural responses and haemodynamic signals in macaque primary visual cortex (V1) using fMRI (7T) and intracortical electrophysiology. Aside from DA's involvement in diseases such as Parkinson's and schizophrenia, it also plays a role in visual perception. We mimicked DAergic neuromodulation by systemic injection of L-DOPA and Carbidopa (LDC) or by local application of DA in V1 and found that systemic application of LDC increased the signal-to-noise ratio (SNR) and amplitude of the visually evoked neural responses in V1. However, visually induced BOLD responses decreased, whereas cerebral blood flow (CBF) responses increased. This dissociation of BOLD and CBF suggests that dopamine increases energy metabolism by a disproportionate amount relative to the CBF response, causing the reduced BOLD response. Local application of DA in V1 had no effect on neural activity, suggesting that the dopaminergic effects are mediated by long-range interactions. The combination of BOLD-based and CBF-based fMRI can provide a signature of dopaminergic neuromodulation, indicating that the application of multimodal methods can improve our ability to distinguish sensory processing from neuromodulatory effects.

Simultaneous Determination of Dopamine in Presence of Ascorbic Acid with Fe-Ag CTAB Nanoparticles Carbon Paste Electrode

A novel electro-chemical method was designed to develop a simple, inexpensive, selective and sensitive electrochemical sensor by modifying carbon paste electrode for the simultaneous determination of dopamine (DA) without the interference of ascorbic acid (AA). Chemically modified carbon paste electrode was prepared by the incorporation of iron-silver bimetallic nanoparticles (Fe-AgNps/Fe-AgCTABMCPE) in presence of cationic surfactant Cetyltrimethyl ammonium Bromide (CTAB) was used for the surface modification and the properties of the modified electrode was studied by using the analytical techniques like cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscope (SEM) image. The modified electrode showed a couple of distinct and well-defined redox peaks for DA and AA mixture, which was not observed with bare carbon paste electrode in 0.1 M phosphate buffer solution (PBS) of pH 7.0 with a scan rate of 50 mVs -1 . There was a good enhancement in redox peak current for DA by 3 folds when compared to bare carbon paste electrode. The anodic peak current vs. scan rate was found to be linear with a correlation coefficient of 0.9951 indicating that the reaction is a diffusion controlled process. The anodic peak current (Ipa) showed a linear relation with concentration of DA with a correlation coefficient of 0.9986 and the detection limit was found to be 3.52×10 -5 M. The detection limit of DA is 0.01 μM with a correlation coefficient of 0.9953 and AA is 0.4 μM with a correlation coefficient of 0.9952 respectively. Hence this chemically modified electrochemical sensor showed a reliable result for the voltammetric determination of AA in the presence of DA and it can be ideal for the practical application of DA in human blood serum and dopamine hydro chloride injection.

Effects of dopamine on response properties of ON-OFF RGCs in encoding stimulus durations

Single retinal ganglion cell's (RGCs) response properties, such as spike count and response latency, are known to encode some features of visual stimuli. On the other hand, neuronal response can be modulated by dopamine (DA), an important endogenous neuromodulator in the retina. In the present study, we investigated the effects of DA on the spike count and the response latency of bullfrog ON-OFF RGCs during exposure to different stimulus durations. We found that neuronal spike count and response latency were both changed with stimulus durations, and exogenous DA (10 μM) obviously attenuated the stimulus-duration-dependent response latency change. Information analysis showed that the information about light ON duration was mainly carried by the OFF response and vice versa, and the stimulation information was carried by both spike count and response latency. However, during DA application, the information carried by the response latency was greatly decreased, which suggests that dopaminergic pathway is involved in modulating the role of response latency in encoding the information about stimulus durations.

Dopaminergic tone persistently regulates voltage-gated ion current densities through the D1R-PKA axis, RNA polymerase II transcription, RNAi, mTORC1, and translation

Long-term intrinsic and synaptic plasticity must be coordinated to ensure stability and flexibility in neuronal circuits. Coordination might be achieved through shared transduction components. Dopamine (DA) is a well-established participant in many forms of long-term synaptic plasticity. Recent work indicates that DA is also involved in both activity-dependent and -independent forms of long-term intrinsic plasticity. We previously examined DA-enabled long-term intrinsic plasticity in a single identified neuron. The lateral pyloric (LP) neuron is a component of the pyloric network in the crustacean stomatogastric nervous system (STNS). LP expresses type 1 DA receptors (D1Rs). A 1 h bath application of 5 nM DA followed by washout produced a significant increase in the maximal conductance (Gmax) of the LP transient potassium current (IA) that peaked ~4 h after the start of DA application; furthermore, if a change in neuronal activity accompanied the DA application, then a persistent increase in the LP hyperpolarization activated current (Ih) was also observed. Here, we repeated these experiments with pharmacological and peptide inhibitors to determine the cellular processes and signaling proteins involved. We discovered that the persistent, DA-induced activity-independent (IA) and activity-dependent (Ih) changes in ionic conductances depended upon many of the same elements that enable long-term synaptic plasticity, including: the D1R-protein kinase A (PKA) axis, RNA polymerase II transcription, RNA interference (RNAi), and mechanistic target of rapamycin (mTOR)-dependent translation. We interpret the data to mean that increasing the tonic DA concentration enhances expression of a microRNA(s) (miRs), resulting in increased cap-dependent translation of an unidentified protein(s).

Dopaminergic Modulation of GABAergic Transmission in the Entorhinal Cortex: Concerted Roles of 1 Adrenoreceptors, Inward Rectifier K+, and T-Type Ca2+ Channels

Whereas the entorhinal cortex (EC) receives profuse dopaminergic innervations from the midbrain, the effects of dopamine (DA) on γ-Aminobutyric acid (GABA)ergic interneurons in this brain region have not been determined. We probed the actions of DA on GABAA receptor-mediated synaptic transmission in the EC. Application of DA increased the frequency, not the amplitude, of spontaneous IPSCs (sIPSCs) and miniature IPSCs (mIPSCs) recorded from entorhinal principal neurons, but slightly reduced the amplitude of the evoked IPSCs. The effects of DA were unexpectedly found to be mediated by α1 adrenoreceptors, but not by DA receptors. DA endogenously released by the application of amphetamine also increased the frequency of sIPSCs. Ca(2+) influx via T-type Ca(2+) channels was required for DA-induced facilitation of sIPSCs and mIPSCs. DA depolarized and enhanced the firing frequency of action potentials of interneurons. DA-induced depolarization was independent of extracellular Na(+) and Ca(2+) and did not require the functions of hyperpolarization-activated (Ih) channels and T-type Ca(2+) channels. DA-generated currents showed a reversal potential close to the K(+) reversal potential and inward rectification, suggesting that DA inhibits the inward rectifier K(+) channels (Kirs). Our results demonstrate that DA facilitates GABA release by activating α1 adrenoreceptors to inhibit Kirs, which further depolarize interneurons resulting in secondary Ca(2+) influx via T-type Ca(+) channels.

Gap junction permeability modulated by dopamine exerts effects on spatial and temporal correlation of retinal ganglion cells’ firing activities

Synchronized activities among retinal ganglion cells (RGCs) via gap junctions can be increased by exogenous dopamine (DA). During DA application, single neurons' firing activities become more synchronized with its adjacent neighbors. One intriguing question is how the enhanced spatial synchronization alters the temporal firing structure of single neurons. In the present study, firing activities of bullfrog's dimming detectors in response to binary pseudo-random checker-board flickering were recorded via a multi-channel recording system. DA was applied in the retina to modulate synchronized activities between RGCs, and the effect of DA on firing activities of single neurons was examined. It was found that, during application of DA, synchronized activities between single neuron and its neighboring neurons was enhanced. At the meantime, the temporal structures of single neuron spike train changed significantly, and the temporal correlation in single neuron's response decreased. The pharmacological study results indicated that the activation of D1 receptor might have effects on gap junction permeability between RGCs. Our results suggested that the dopaminergic pathway participated in the modulation of spatial and temporal correlation of RGCs' firing activities, and may exert critical effects on visual information processing in the retina.