Initial investigations on dopamine D4 receptors generated much interest in the role of this receptor in schizophrenia and other aspects of human behavior, as well as new opportunities for novel therapeutics.However, attempts to treat patients suffering from schizophrenia with dopamine D4 agents have failed to yield satisfactory results so far.An examination of the dopamine D4 literature shows that contrasting and conflicting data seemed to be the norm in this field of research.This paper reviews the literature on the dopamine D4 receptor and discusses many of the associated methodological problems that might have contributed to the paradoxical findings.
Inositol 1, 4, 5−trisphosphate(IP3)−mediated Ca2+ signalling regulates many important cell functions, and the spatio−temporal dynamics of the Ca2+ signalling is a crucial factor for its versatility.The molecular mechanisms that control Ca2+ signalling are now being investigated, and I here describe the subtypes of IP3 receptors that have distinct functional properties and contribute to the diversity of Ca2+ signalling patterns.I also discuss the spatio−temporal dynamics of intracellular IP3 concentration, describing recent methodological advances in monitoring intracellular IP3 concentration.These findings highlight the potential importance of the spatio−temporal information of any signalling molecule.
3−Amino−5−methyl−2(2−methyl−3−thienyl)−imidazo[1, 2−a]thieno[3, 2−c]pyridine, SPI−447, is a potent gastric H+, K+−ATPase inhibitor, but a detailed mechanism of the inhibition is unknown.This study was designed to investigate the mechanism by which SPI−447 inhibits gastric H+, K+−ATPase.For this purpose, the inhibitory action of SPI−447 on gastric H+, K+−ATPase from porcine gastric mucosa was compared with that of omeprazole(an irreversible inhibitor)and SCH28080(a reversible inhibitor).All compounds produced dose−dependent inhibition of gastric H+, K+−ATPase, and the inhibitory intensities were increased under acidic conditions.The anti−H+, K+−ATPase actions of SPI−447 and SCH28080 were attenuated by dilution, but not influenced by glutathione pretreatment.In contrast, that of omeprazole was not influenced by dilution, but was suppressed by glutathione pretreatment.KCl addition reversed the inhibition of H+, K+−ATPase−mediated H+−transport by SPI−447 and SCH28080, but had no effect on that by omeprazole.The anti−gastric H+, K+−ATPase action of SPI−447 was additive with that of SCH28080.SPI−447 and SCH28080 had no effect on Na+, K+−ATPase activity.These findings indicated that the inhibitory mechanism of SPI−447 on gastric H+, K+−ATPase was similar to that of SCH28080, but different from that of omeprazole;i.e., 1)reversible, 2)SH−group independent, 3)K+−competitive, and 4)highly specific against gastric H+, K+−ATPase.
We investigated the anti−allergic effect of mao−bushi−saishin−to(MBS)on the type I allergy model in mice.When MBS was administered orally at a dose of 0.5 or 1.0g/kg, edema of the footpad, the amount of plasma IgE and the ratio of eosinophilic leukocytes in peritoneal exudate cells were all dose−relatedly suppressed.Moreover to investigate the anti−type I allergic mechanisms of MBS, enzyme−linked immunosorbent assay was performed to determine the interleukin(IL)−4, IL−5 and interferon(IFN)−gamma production from splenocytes that were stimulated by pokeweed mitogen for 48 h.In addition, we assayed IgE production from splenic B cells stimulated with the lipopolysaccharide and IL−4 for 7 days.MBS inhibited the IL−4 and IFN−gamma production, but IL−5 and IgE production were not affected.Thus possibly, the inhibition of IL−4 production may partially be involved in the expression of the anti−type I allergic effects of MBS.
Chronic administration of morphine is known to decrease the levels of neurofilaments(NFs)in the ventral tegmental area.We ligated a promoter region of the mouse 68−KDa neurofilament(NF−68)gene to the pGL3−enhancer vector containing a luciferase gene, transfected it into SK−N−SH cells and then analyzed transcriptional activity in the cells treated with agonists or antagonists of opiate receptors.The activity of the NF−68 promoter was suppressed by naloxone about 55% at 10-5 M and 30% at 10-7 M at 48h, but suppressed not by morphine.Naltrexone at 10-5 M suppressed the promoter activity about 20%, but levallorphan, DAMGO, DPDPE and U50488 did not.The inhibition by naloxone was dose−dependent and not reversed by morphine.The inhibitory effect of naloxone was not observed in N18TG−2 cells and PC12 cells.Experiments with various deletion mutants revealed that a region responsible for naloxone suppression spans from −328 to − 101 in the gene.These results suggest that naloxone has the ability to suppress transcriptional activity in some neurons.
We explored L−DOPA esters with chemically bulky structures to find a potent stable competitive antagonist against L−DOPA, compared to DOPA methyl ester(DOPA ME).In anesthetized rats, DOPA cyclohexyl ester(DOPA CHE), DOPA cyclopentyl ester(DOPA CPE)and DOPA cyclopentyldimethyl ester(DOPA CPDME)at 1μg microinjected into depressor sites of the nucleus tractus solitarii elicited or tended to elicit more marked antagonism against depressor responses to 60 ng L−DOPA, compard to DOPA ME.At 100 ng, DOPA CHE elicited the most potent antagonism.At 1μg, duration of the antagonistic activity of DOPA CHE was approximately three times longer than that of DOPA ME.During microdialysis of the nucleus accumbens, conversion from DOPA CHE at 1μM perfused via probes to extracellular L−DOPA was the lowest among these compounds and less than one half of that from DOPA ME.Binding studies showed that the recognition site for L−DOPA differs from ionotropic glutamatergic, dopaminergic D1 and D2 receptors.We recently found that L−DOPA evoked by transient ischemia may act as a DOPA CHE−sensitive causal factor for glutamate release and resultant neuronal cell death.DOPA CHE is the most potent, relatively stable competitive antagonist against L−DOPA and is a useful mother compound to develop neuroprotective drugs.
The effects of GABAmimetic drugs on inhibition of amygdaloid kindled seizures induced by clobenpropit were investigated to clarify the relationship between histaminergic and GABAergic systems in seizures.I.p.injection of clobenpropit caused dose−dependent inhibition of amygdaloid kindled seizures.GABAmimetic drugs such as diazepam, sodium valproate and muscimol also inhibited amygdaloid kindled seizures in a dose−dependent manner.Diazepam at doses of 0.2 and 0.5 mg/kg, which showed no significant effect on amygdaloid kindled seizures when used separately, significantly potentiated the effect of clobenpropit.Similar findings were observed with sodium valproate and muscimol at doses of 100 mg/kg and 5 ng, respectively, although neither showed any significant effects when administered separately.Bicuculline caused significant antagonism of the inhibition of amygdaloid kindled seizures induced by clobenpropit, while the effect of diazepam was not antagonized by diphenhydramine.These results suggested that inhibition of amygdaloid kindled seizures induced by histamine is closely associated with the actions of GABA.
Fructooligosaccharides(FOS)have been shown to stimulate the absorption of several minerals in the intestine.In the present study, the effects of FOS on osteopenia induced by total gastrectomy were examined.Twenty eight male Sprague Dawley rats were divided into 2 groups:sham−operated(SH)and gastrectomized(GX).After a one−week adaptation period following surgery, the rats were fed synthetic diets with or without 7.5% FOS for 5 weeks.The right femur was then examined by soft X−ray, and the bone mineral density(BMD)was measured.Based on the soft X−ray findings, both cancellous and cortical bone were markedly decreased in GX rats, but not in GX+FOS rats.GX rats showed a 30% lower BMD in the metaphysis and a 20% lower BMD in the diaphysis, compared with SH rats(P<0.01).As assessed by morphometry, significant decreases were observed in cortical bone in the diaphysis and trabecular bone in the distal metaphysis(P<0.01).On the other hand, dietary FOS completely prevented these changes following gastrectomy.These findings indicate that dietary FOS might contribute to the prevention of bone diseases following gastrectomy.
Previously, we reported that(R)−(−)−1−(benzo[b]thiophen−5−yl)−2−[2−(N, N−diethylamino)ethoxy]ethanol hydrochloride(T−588), a novel putative cognitive enhancer, stimulated noradrenaline(NA)release from rat cerebral cortical slices.In this study, we investigated the effects of T−588 compared to other secretagogues on NA release from PC12 cells.Addition of as little as 10 μM T−588 stimulated [3H]NA release in a dose−dependent and an extracellular Ca2+−independent manner from PC12 cells.Ten micromolar ionomycin−, 300 μM adenosine−5′−O−(γ−thiotriphosphate)− and 10 μM forskolin−induced extracellular Ca2+−dependent [3H]−NA release was further enhanced by 30 μM T−588.Cytosolic synaptophysin and 25−kDa synaptosome−associated protein immunoreactivity was increased by addition of T−588 in a dose−dependent manner.Interestingly, increases in synaptic vesicle−related proteins triggered by T−588 had a 4−min lag time and were completely dependent on extracellular CaCl2.These findings suggest that T−588 stimulates NA release from PC12 cells in a Ca2+−independent manner.T−588 also induced the translocation of synaptic vesicles in a Ca2+−dependent manner.
The periarterial electrical nerve stimulation readily induced a double−peaked vasoconstriction in the isolated, perfused canine splenic artery.P2X−Purinoceptors have previously been shown to be involved mainly in the 1st−phase response and α1−adrenoceptors, mostly in the 2nd−one.The dose used of neuropeptide Y(NPY)(0.01−0.1μM)given into the preparation caused a slight but insignificant vasoconstriction.The treatment with NPY at concentrations of 0.01−0.1μM produced a parallel inhibition on the 1st− and 2nd−phase responses following nerve stimulation at the frequencies used(1−10 Hz)in a dose−dependent manner.The vasoconstrictor responses to administered ATP(0.01−1μmol)or noradrenaline(0.03−3 nmol)were slightly but not significantly potentiated by 0.1μM NPY.The results indicate that NPY predominantly exerts a prejunctionally inhibitory modulation on the purinergic and adrenergic transmission in peripheral sympathetic nerves innervating the canine splenic artery.
We tried to induce selective perivascular purinergic nerve stimulation in isolated canine splenic arterial preparations, using the cannula insertion method.Under the conditions of periarterial electrical stimulation(ES), i.e., trains of 1, 3 and 10 pulses, 1−ms pulse duration and 10−V amplitude at 1 Hz, monophasic vasoconstriction was consistently induced.The ES−induced vasoconstriction was not influenced by prazosin in doses that completely inhibited noradrenaline−induced vasoconstrictions, but it was suppressed by α, β−methylene ATP, a P2X purinoceptor desensitizer.Thus, it is indicated that a selective purinergic transmitter release is readily obtained in the isolated splenic arterial preparation.
Activation of protease−activated receptor(PAR)−1 or PAR−2 elicits inflammation most probably via mast cell degranulation in vivo.The present study aimed at characterizing PARs in rat peritoneal mast cells(PMC).Messenger RNA for PAR−1, but not for PAR−2, was detected in PMC.Thrombin, the PAR−1 agonist SFLLR−NH2 or the PAR−2 agonist SLIGRL−NH2 failed to induce histamine release from PMC.Surprisingly, the PAR−2−inactive control peptide LSIGRL−NH2 triggered histamine release from PMC.Thus, PAR−1, but not PAR−2, are expressed in PMC, whereas neither PAR−1 nor PAR−2 are considered to be involved in degranulation of PMC.LSIGRL−NH2 does not appear to be appropriate as a control peptide for PAR−2 in inflammation studies.
Cigarette smoking is a well−known risk factor for atherosclerosis, but the mechanism of the adverse biological effect of smoking remains to be established.Cigarette smoke contains high concentrations of free radicals and oxidants.We show here that cigarette smoke extracts(CSE), prepared by bubbling the gas phase of smoke into phosphate−buffered saline, could convert tyrosine to 3−nitrotyrosine.The tyrosine nitration terminated 6 h after incubating tyrosine with CSE at 37°C.These results indicate that the active oxidants in CSE are peroxynitrite−generating species like 3−morpholinosydnonimine(SIN−1), suggesting that they modify plasma lipoproteins and contribute to the pathogenesis of atherosclerosis.
The effects of phenytoin and its major metabolite, 5−(4−hydroxyphenyl)−5−phenylhydantoin(HPPH), on bone resorption of neonatal mouse calvaria were examined in vitro.Both phenytoin and HPPH induced significant bone resorption as compared to the controls after 72 h in culture.This effect may be the cause of phenytoin−induced bone loss in vivo.