• Molecules and Cells
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• v.25 no.2
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• pp.149-157
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• 2008

Dopamine is a major neurotransmitter in the mammalian central nervous system (CNS) that regulates neuroendocrine functions, locomotor activity, cognition and emotion. The dopamine system has been extensively studied because dysfunction of this system is linked to various pathological conditions including Parkinson's disease, schizophrenia, Tourette's syndrome, and drug addiction. Accordingly, intense efforts to delineate the full complement of signaling pathways mediated by individual receptor subtypes have been pursued. Dopamine D1-like receptors are of particular interest because they are the most abundant dopamine receptors in CNS. Recent work suggests that dopamine signaling could be regulated via dopamine receptor interacting proteins (DRIPs). Unraveling these DRIPs involved in the dopamine system may provide a better understanding of the mechanisms underlying CNS disorders related to dopamine system dysfunction and may help identify novel therapeutic targets.

• Toxicological Research
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• v.6 no.1
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• pp.75-88
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• 1990

The characteristics of dopamine uptake, D-1 and D-2 receptors after acute and subacute cocaine administration were determind in striatum from WKY and SHR. Cocaine was administered either acutely (40 mg/kg, s.c.) or twice daily (20 mg/kg, s.c.) for 3 and 7 days in 9-wk old WKY and SHR. Rats were sacrificed 30 min, 2 or 24 h after the single injection and 18 h after the last administration to the subacutely treated group. The changes in dopamine uptake, dopamine uptake sites, D-1 and D-2 receptors were determined using $(^3H)$dopamine, $(^3H)$-GBR-12935, $(^3H)$SCH-23390 and $(^3H)$sulpiride, respectively. In acutely treated rats, significant increases in $V_{max}$of dopamine uptake were observed 30 min after the cocanine injection in both strains without changes in $K_m$ values. The in vitro $IC_{50}$for cocaine was significantly decreased 30 min in WKY and 2 h in SHR. However, that for in vitro GBR-12909 was significantly increased 30 min and 2 h in both strains. Also densities of $(^3H)$-GBR-12935 binding sites were significantly increased 30 min and 2 h without changes in their $K_d$. Significant increases in D-2 receptor density were observed 30 min, 2 or 24 h after acute injection in both strains without changes in their affinities. The density of D-1 receptor was significantly decreased 30 min after the injection in WKY, but not in SHR. In subacutely treated rats, a significant increase in $K_m$ of dopamine uptake was observed in 7-day treated SHR. The in vitro $IC_{50}$fot GBR-12909 was significantly increased in 3-day treated WKY. The density of D-1 receptors was significantly increased in 3- and 7-day treated WKY, but not in SHR. The affinity of both binding sites remained unchanged. The results suggest that cocanine administration alters dopamine uptake, characteristics of dopamine uptake sites and dopamine receptor binding characteristics in rat brain. Furthermore, D-1 and D-2 dopamine receptors appear to be differently regulated.

• BMB Reports
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• v.28 no.3
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• pp.221-226
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• 1995

Dopamine mediates inhibitory responses in Helix aspersa neurons from the right parietal lobe ("F-lobe") of the circumoesophageal ganglia. The effects appeared as a dose-dependent hyperpolarization of the plasma membrane and a decrease in the occurrence of spontaneous action potentials. The average hyperpolarization with 5 ${\mu}m$ dopamine was -12 mV (${\pm}1.5$mV, S.D., n=12). Dopamine also modulated the currents 'responsible for shaping the action potentials in these neurons. When dopamine was added and action potentials were triggered by an injection of current, the initial depolarization was slowed, the amplitude and the duration of action potentials were decreased, and the after-hyperpolarization was more pronounced. The amplitude and the duration of action potential were reduced about 15 mV and about 13% by 5 ${\mu}m$ dopamine, respectively. The effects of dopamine on the resting membrane potentials and the action potentials of Helix neurons were dose-dependent in the concentration range 0.1 ${\mu}m$ to 50 ${\mu}m$. In order to show 1) that the effects of dopamine were mediated by dopamine receptors rather than by direct action on ionic channels and 2) which type of dopamine receptor might be responsible for the various effects, we assayed the ability of mammalian dopamine receptor antagonists, SCH-23390 (antagonist of D1 receptor) and spiperone (antagonist of D2 receptor), to block the dopamine-dependent changes. The D1 and D2 antagonists partially inhibited the dopamine-dependent hyperpolarization and the decrease in action potential amplitude. They both completely blocked the decrease in action potential duration and the increase in action potential after-hyperpolarization. The dopamine-induced slowdown of the depolarization in the initial phase of the action potentials was less effected by SCH-23390 and spiperone. From the results we suggest 1) that Helix F-lobe neurons may have a single type of dopamine receptor that binds both SCH-23390 and spiperone and 2) that the dopamine receptor of Helix F-lobe neurons may be homologous with and primitive to the family of mammalian dopamine receptors.

• Animal cells and systems
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• v.3 no.2
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• pp.103-113
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• 1999

Many in-depth reviews related to regulations of prolactin secretion are available. We will, therefore, focus on controversial aspects using personal opinion in this review. The neuroendocrine control of prolactin secretion from the anterior pituitary gland involves multiple factors including prolactin-release inhibiting factor (PIF) and prolactin releasing factor (PRF). The PIF exerts a tonic inhibitory control in the physiological conditions. The PIF should be able to effectively inhibit prolactin release or a lifetime, but the inhibitory action of dopamine cannot be sustained for a long period of time. Perifusion of a high concentration of dopamine (l ,000 nM) could not sustain inhibitory action on prolactin release but when a small amount of ascorbic acid (0.1 mM) is added in a low concentration of dopamine (3 nM) solution, prolactin release was inhibited for a long period. Ascorbate is essential for dopamine action to inhibit prolactin release. We have, therefore, concluded that the PIF is dopamine plus ascorbate. The major transduction system for dopamine to inhibit prolactin release is the adenylyl cyclase system. Dopamine decreases cyclic AMP concentration by inhibiting adenylyl cyclase, and cyclic AMP stimulates prolactin release. However, the inhibitory mechanism of dopamine on prolactin release is much more complex than simple inhibition of CAMP production. The dopamine not only inhibits cyclic AMP synthesis but also inhibits prolactin release by acting on a link(s) after the CAMP event in a chain reaction for inhibiting prolactin release. Low concentrations of dopamine stimulate prolactin release. Lactotropes are made of several different subtypes of cells and several different dopamine receptors are found in pituitary. The inhibitory and stimulatory actions induced by dopamine can be generated by different subtype of receptors. The GH$_4$ZR$_7$ cells express only the short isoform (D$_{2s}$) of the dopamine receptor, as a result of transfecting the D$_{2s}$ receptors into GH$_4$C$_1$ cells which do not express any dopamine receptors. When dopamine stimulates or inhibits prolactin release in GH$_4$ZR$_7$ cells, it is clear that the dopamine should act on dopamine D$_{2s}$ receptors since there is no other dopamine receptor in the GH$_4$ZR$_7$. Dopamine is able to stimulate prolactin release in a relatively low concentration while it inhibits in a high concentration in GH$_4$ZR$_7$. These observations indicate that the dopamine D$_2$ receptor can activate stimulatory and/or inhibitory transduction system depending upon dopamine concentrations.

• Journal of Gastric Cancer
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• v.6 no.3
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• pp.132-138
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• 2006

Purpose: Dopamine is a neurotransmitter, but in the GIT, the roles of dopamine are a regulator of epithelial cell proliferation, an endogenous protective factor, and a regulator of stomach cancer cell proliferation. By using two different gastric-cancer cell lines, we assessed the effects of dopamine and dopamine receptors on the proliferation of human gastric-cancer cells. Materials and Methods: To assess the effects of dopamine and dopamine receptors on the proliferation of human gastric-cancer cells, we investigated cell proliferation and the expression of D1, D2L, and D2S receptor in two gastric-cancer cell lines, SNU 601 and KCU-C2. The effects of dopamine and dopamine receptors on the level of the cell proliferation were determined by staining with an A/H/E (acridine orange, hoechst and ethidium bromide) mixture. Results: After dopamine treatment, the cell viability was significantly decreased in SNU 601 cells (P<0.05) where the D2L receptor was absent, but not in KCU-C2 cells. After treatment with raclopride, a D2 receptor antagonist, dopamine-dose-dependent inhibition of cell proliferation was observed in SNU 601 cells (P<0.05). After treatment with SCH 23390, a D1 receptor antagonist, dopamine significantly increased ceil proliferation in KCU-C2 cells (P<0.05), but inhibited ceil proliferation in SNU 601 cells (no D2L receptor). Conclusion: The dopamine signal via the D1 or the D2S receptor inhibited proliferation of gastric-cancer cells, but that via the D2L receptor increased proliferation. These results suggest that the regulatory effects of dopamine in the gastric-cancer cell proliferation may be controlled by using dopamine receptors.

• Archives of Pharmacal Research
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• v.19 no.4
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• pp.275-279
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• 1996

To study the functional roles of dopamine receptors, we decided to raise antibodies against these proteins. To make antigen, we expressed the whole 3rd cytoplasmic loop of dopamine receptors in a fusion protein with glutathione-S-transferase (GST). $For D_2\; and\; D_3$ receptors, it was successful to express and purify fusion proteins for the whole 3rd cytoplasmic loops. However, we could not express the fusion protein for the whole 3rd cytoplasmic loop of $D_4$ dopamine receptor in the bacteria. To study the causes that prevent the bacterial expression of the GST-fusion protein of the 3rd cytoplasmic loop of $D_4$ dopamine receptor, we conducted more detailed studies on $D_4$ dopamine receptor. To locate the region which prevents bacterial expression, we made sequential constructs in the 3rd cytoplasmic loop decreasing the size step by step, and confirmed their expressions in the SDS PAGE. It was found that certain regions of 3rd cytoplasmic loop of $D_4$ dopamine receptor, located in N-terminal side of the 3rd cytoplasmic loop of $D_4$ dopamine receptor suppress the bacterial expression of fusion protein.

• The Korean Journal of Nuclear Medicine
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• v.34 no.3
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• pp.159-168
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• 2000

In the 1980s, techniques to image the human subjects in a three-dimensional direction were developed. Two major techniques are SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography) which allow the detector to detect a single photon or annihilation photons emitted from the subjects injected with radiopharmaceuticals. Since the latter two techniques can measure the density of receptors, enzymes and transporters in living human, it may be very important project to develop selective methods of labeling with radionuclides and to develop new radiopharmaceuticals. There has been a considerable interest in developing new compounds which specifically bind to dopamine and serotonin receptor and transporters, and it will be thus very useful to label those compounds with radionuclides in order to gain a better understanding in biochemical and pharmacological interactions in living human. This review mentions the characteristics of radioligands for the imaging of dopamine and serotonin receptors and transporters. Although significant progress has been achieved in the development of new PET and SPECT ligands for in vivo imaging of those receptors and transporters, there are continuous needs of new diagnostic radioligands.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1995.04a
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• pp.100-100
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• 1995

Several behavioral studies have suggested that ginseng total saponin (GTS) antagonizes morphine actions. Based on these observations, we conducted biochemical studies to elucidate the cellular mechanism of GTS actions. morphine hydrochloride (10mg/kg, sc) and/or on (400mg/kg, oral ) were administered to mice for 14 consecutive days. Ligand binding studies were conducted from striatal membranes. For opioid receptors, morphine increased the affinity but decreased the maximal binding sites for $^3$H naloxone. GTS partially recovered it. In case of dopamine receptors, morphine increased affinity and maximal binding sites for 3H spiperone. and GTS partially blocked it. These results suggest that morphine affects cellular events by modulating opioid receptors and that opioid receptors interact with dopamine receptors to change the mental status. GTS could be helpful for the treatment of morphine- induced mental disorders.

• Archives of Pharmacal Research
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• v.17 no.6
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• pp.398-404
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• 1994

The behavioral response, depamine metabolism, and characteristics of dopamine subtypes after developing the hyperlycemia were studied in the striata of rats. In animals developed hyperglycemia, the on-set duration of cataleptic behavior responded to SCH 23390 injection was delayed abd shortened, respectively. However, the cataleptic response to spiperone occurred significantly earlier in on-set and prolonged in duration. Dopamine metabolites, dihydroxyphenylacetic acid (DDPAC) and homovanillic acid (HVA), were significantly reduced in teh striata of hyeprglycemic rats. However, level of DA was significantly increased. It is noted that the ratios of DOPAC and HVA to DA were decreased, suggesting decreased tumover of DA. The affinity of striatal D-1 receptors was significantly increased without changes in the number of binding sites, while the maximum binding number of D-2 recptors was significantly increased without affecting its affinity in the diabetic rats. These results indicate that the dopaminergic activity in striatia was altered in hyperglycemic rats. Furthermore, it suggests that the upregulation of dopamine receptors might be due to the decreased dopamine matabolism.

• Biomolecules & Therapeutics
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• v.2 no.1
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• pp.16-22
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• 1994

Using 2 to 4 day-old postnatal rats, primary brain cell cultures were made from various brain regions (substantia nigra, hippocampus, striatum, and nucleus accumbens). Whole-cell patch clamp technique was used for electrophysiological studies. Neurons cultured from substantia nigra were characterized more in detail to test whether these cultured neurons were appropriate for physiological studies. Immunocytochemical and electrophysiological properties of these cultured neurons agreed with those from other in vivo or in vitro studies suggesting that cultured neurons maintained normal cytological and physiological conditions. Modulation of ionic channels through dopamine receptors were studied from brain areas where dopamine plays important roles on brain functions. When neurons were clamped near resting membrane potential (-74mV), R(+), R(+)-SKF 38393, a specific D$_1$receptor agonist, activated cultured striatal neurons, and dopamine itself produced biphasic responses. Responses of cultured hippocampal neurons to dopamine agonists were kinds of mirror images to those from striatal neurons; D$_1$receptor agonists inhibited hippocampal neurons but quinpirole, a D$_2$receptor agonist, activated them. Neurons cultured from nucleus accumbens were inhibited by dopamine.