Study Dopamine Release Research Articles

Trifunctional fluorescent manganese ferrite nanoparticles for hyperthermia therapy, cell probing and drug delivery

Here we have reported a new protocol for drug delivery from hollow sphere manganese ferrite nanoparticles (HMF NPs). The crystalline structure of HMF NPs is obtained from XRD measurement and the morphological and elemental analysis are obtained from FESEM & TEM measurements. Here the HMF NPs are properly designed for delivery of dopamine (DA) as anticancer drug to cancer site. The DA polymerizes to a giant molecule polydopamine (PDA) inside hollow HMF in presence of TRIS buffer at pH (8.5) and a composite, HMF-PDA is formed. Being giant molecule polydopamine remain stable inside the hollow particles, but when these HMF-PDA come in contact of low pH i.e. pH 5 (cancer cells pH), free DA starts to be released. At hyperthermic temperature (45 °C) release enhances compare to physiological temperature (37 °C). The DA release studies are monitored by UV-visible absorption spectroscopy with progress of time at different temperatures and pH. It has been observed that HMF-PDA has fluorescent property whereas DA has no such effects. So, incorporation of PDA inside HMF and tagging of HMF-PDA with cancer cells can also be monitored by fluorescence imaging. Hence, we have successfully synthesized trifunctional HMF-PDA composite which can serve three purposes like cancer cell probing by fluorescence imaging, hyperthermia therapy and drug delivery by magnetic field and pH trigger method.

43.4 THE ROLE OF MOLECULAR IMAGING IN GUIDING DRUG DEVELOPMENT

BackgroundMolecular imaging with Positron Emission Tomography (PET) has the unique capability of examining molecules in the brains of human subjects in real time. This has been well exploited in the study of dopaminergic transmission in schizophrenia. The results have on one hand confirmed some predictions, and on the other hand they have brought up unexpected findings, that have the potential to affect drug development in a major way.MethodsPET studies of dopamine release, synthesis, storage, receptors and transporters across labs and different experiments will be reviewed to extract findings that differ from preconceived notions. These have the capability of re-focusing drug development based on new evidence.ResultsExpected findings that PET studies have confirmed are those of striatal dopaminergic excess, measured as enhanced presynaptic release capacity and presynaptic enzymatic synthesis capacity. Also expected was hypodopaminergic transmission in the dorso-lateral prefrontal cortex.The unexpected findings from PET have been as follows: 1) the striatal excess is most predominant in the associative striatum, rather than the limbic striatum. 2) hypodopaminergia is generalized to all extrastriatal areas of the brainThese observations of opposite presynaptic dopaminergic dysfunction between striatal and extrastriatal regions suggest that the striatal excess may not be driven by activity levels of midbrain DA cells but may result from abnormal striatal local regulation of presynaptic DA release, affecting specifically the associative striatum, region which shows largest magnitude of excess DA. Furthermore alterations in dopaminergic signaling in opposing directions may have a dual effect on learning across functional domains by weakening learning from salient or relevant signals and reinforcing stimulus independent signals, thus explaining different symptom domains.DiscussionMore work is needed to understand the cellular mechanisms of dopaminergic dysfunction in schizophrenia. The evidence presented here, while limited, highlights the challenges of drug development in the absence of real in vivo information from patients, and the need for multidisciplinary cross talk to address these challenges.

Evaluation of dopamine D2/3specific binding in the cerebellum for the positron emission tomography radiotracer [11C]FLB 457: Implications for measuring cortical dopamine release

AbstractIn a recent positron emission tomography (PET) study, we demonstrated the ability to measure amphetamine‐induced dopamine (DA) release in the human cortex with the DA D2/3 radioligand [11C]FLB 457. As previous studies in animals have shown that a relatively high fraction of the [11C]FLB 457 signal in the cerebellum represents specific binding to D2/3 receptors, there was concern that the use of the cerebellum as a measure of nonspecific binding (i.e., reference region) to derive [11C]FLB 457 binding potential (BP) (BPND) would bias cortical DA release measurements. Thus, we evaluated the fractional contribution of specific binding to D2/3 receptors in the human cerebellum for [11C]FLB 457. Six healthy human subjects (5M/1F) were studied twice with [11C]FLB 457, once at baseline and again following a single oral dose of 15 mg of aripiprazole, a D2/3 partial agonist. [11C]FLB 457 distribution volume (VT) was estimated using kinetic analysis in the cortical regions of interest and potential reference regions. The change in [11C]FLB 457 VT following aripiprazole ranged from −33 to −42% in the cortical regions of interest (ROIs). The aripiprazole‐induced change in [11C]FLB 457 VT in three potential reference regions suggests significant specific binding the cerebellum (CER, –17 ± 12%), but not pons (PON, –10 ± 10%) and centrum semiovale (CESVL, –3 ± 12%). Nevertheless, a reanalysis of the published [11C]FLB 457 test–retest and amphetamine studies suggests that the use of the PON VT and CESVL VT as an estimate of nonspecific binding to derive [11C]FLB 457 BPND in DA release studies is unlikely to be successful because it leads to less reproducible outcome measures, which in turn diminishes the ability to measure DA release in the cortex. D2/3 blocking studies with aripiprazole and [11C]FLB 457 suggest specific binding to D2/3 receptors in the cerebellum. These data also suggest that the contribution of specific binding to D2/3 receptors in the cerebellum is lower than that in the cortical ROIs and that CER VT is mostly representative of nonspecific binding. Nevertheless, caution is advised when using reference tissue methods that rely solely on the cerebellum signal as an input function to quantify [11C]FLB 457 BPND. Synapse, 2011. © 2011 Wiley‐Liss, Inc.

Amphetamine-induced striatal dopamine release in major depressive disorder

Introduction: Although reduced dopaminergic neurotransmission in the ventral striatum (VST), a region involved in reward processing and motivated behavior, has been hypothesized to contribute to the depressive symptoms of anhedonia and psychomotor retardation, no studies of dopamine release in striatal subregions in major depression are available. Thus we assessed dopamine D2-like (D2) receptor availability andamphetamine-induceddopamine release in striatal subregionsof patientswithmajordepressive disorder (MDD) andofmatched healthy controls using positron emission tomography (PET), and examined the relations between dopaminergic parameters and depressive symptoms.

Heterogeneous population of dopaminergic neurons derived from mouse embryonic stem cells: preliminary phenotyping based on receptor expression and function

The possibility exists that directed differentiation of mouse embryonic stem (mES) cells is capable of yielding enriched populations of dopaminergic neurons, but at present there is little understanding of the pharmacological properties of these cells; or whether such cells represent a pharmacologically, phenotypically similar population. In this study we used a simple culture protocol to generate dopaminergic neurons and offer a preliminary pharmacological investigation of these cells using Ca2+ imaging and [3H]-dopamine release studies. In fluo-4 AM loaded cells, 13-17 days postplating, and after the addition of tetrodotoxin some of the population of mouse embryonic stem cell-derived neurons responded to adenosine triphosphate (ATP), noradrenaline (NA), acetylcholine (ACh) and L-glutamate (L-glut) with elevations of Ca2+ influx. Within the microtubule-associated protein and tyrosine hydroxylase (TH)-positive cell population adenosine triphosphate, noradrenaline, acetylcholine and L-glutamate elicited positive elevations of Ca2+ in 74, 66, 58 and 67% of the population; cells could be further subdivided into three major pharmacologically distinct populations based on the combinations of agonist they responded to. Acetylcholine (30 microM) and noradrenaline (30 microM) were the only agonists to elicit significant tritium overflow from [3H]-dopamine loaded cells. The acetylcholine effect was blocked by atropine (1 microM) and tetrodotoxin (1 microM) and elevated by haloperidol (100 nM). The noradrenaline effects were reduced by cocaine (10 microM), but not by tetrodotoxin (100 nM). These data indicate that the dopaminergic neurons derived from mouse embryonic stem cells represent a heterogeneous population possessing combinations of purinergic, adrenergic, cholinergic and glutamatergic receptors located on the cell soma.

Alterations in Dopamine Release But Not Dopamine Autoreceptor Function in Dopamine D3Receptor Mutant Mice

Dopamine (DA) autoreceptors expressed along the somatodendritic extent of midbrain DA neurons modulate impulse activity, whereas those expressed at DA nerve terminals regulate both DA synthesis and release. Considerable evidence has indicated that these DA autoreceptors are of the D2 subtype of DA receptors. However, many pharmacological studies have suggested an autoreceptor role for the DA D3 receptor. This possibility was tested with mice lacking the D3 receptor as a result of gene targeting. The basal firing rates of DA neurons within both the substantia nigra and ventral tegmental area were not different in D3 receptor mutant and wild-type mice. The putative D3 receptor-selective agonist R(+)-trans-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-(1)benzopyrano(4,3-b)-1,4-oxazin+ ++-9-ol (PD 128907) was equipotent at inhibiting the activity of both populations of midbrain DA neurons in the two groups of mice. In the gamma-butyrolactone (GBL) model of DA autoreceptor function, mutant and wild-type mice were identical with respect to striatal DA synthesis and its suppression by PD 128907. In vivo microdialysis studies of DA release in ventral striatum revealed higher basal levels of extracellular DA in mutant mice but similar inhibitory effects of PD 128907 in mutant and wild-type mice. These results suggest that the effects of PD 128907 on dopamine cell function reflect stimulation of D2 as opposed to D3 receptors. Although D3 receptors do not seem to be significantly involved in DA autoreceptor function, they may participate in postsynaptically activated short-loop feedback modulation of DA release.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. basis for 5-HT-DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

Site and mechanism of behavioral tolerance to cocaine: a study of dopamine release in Wistar-Kyoto and spontaneously hypertensive rats.

Wistar-Kyoto and spontaneously hypertensive rats received i.v. infusions of cocaine hydrochloride (60 mg/kg per day) for 3, 7, and 14 days, or saline for 7 days. Acute cocaine challenge (40 mg/kg, s.c.) was given to treated and control rats 24 hr after the termination of each infusion period. There were no strain differences in brain levels of cocaine during cocaine infusion, nor after cocaine challenges. There were no strain differences in resting levels of [3H]dopamine release. Release of [3H]dopamine decreased in nuclei accumbens of 7- and 14-day cocaine-infused animals. Release of [3H]dopamine was maximal in both brain regions 2 hr after acute cocaine challenge. After 14 days of cocaine infusion, cocaine challenge in both strains reduced [3H]dopamine release in the nucleus accumbens, but not in the striatum; the reduction being greater in Wistar-Kyoto rats. The behavioral tolerance which accompanies similar cocaine infusion regimens may be related to striatal "tolerance" to cocaine-induced dopamine release.

Effects of enantiomers of MDA, MDMA and related analogues on [ 3H]serotonin and [ 3H]dopamine release from superfused rat brain slices

The primary amines 3,4-methylenedioxyamphetamine (MDA), and 1-(1,3-benzodioxol-5-yl)-2-butanamine (BDB) were measured for efficacy in release of [ 3H]serotonin (5-HT) from rat hippocampal slices, and release of [ 3H]dopamine (DA) from rat caudate nucleus slices. The N-methyl derivatives of MDA and BDB, MDMA and MBDB, respectively, and the optical antipodes of these four agents were compared in this paradigm. All of the test compounds demonstrated a similar efficacy of [ 3H]5-HT release in the micromolar concentration range. No significant stereoselectivity was seen in measurements of 5-HT release. However, striking differences were found between the test compounds when [ 3H]DA release was studied. N-methylation of racemic MDA resulted in a decreased ability to release DA, while side chain extension from α-ethyl completely abolished this activity. Stereoselectivity for the S-(+)-isomers of MDA and MDMA was also demonstrated in the DA release studies. Correlation of these biochemical findings with human subjective reports indicates that serotonin release may play a more important role in the mechanism of action than does dopamine release.